diff --git a/.cargo/config b/.cargo/config.toml similarity index 100% rename from .cargo/config rename to .cargo/config.toml diff --git a/.git-blame-ignore-revs b/.git-blame-ignore-revs new file mode 100644 index 0000000000..3c71ce4186 --- /dev/null +++ b/.git-blame-ignore-revs @@ -0,0 +1,2 @@ +# Ran dprint fmt on the repo +3a30e4c1fbe641afc066b3af9eb01dcdf5ed8b24 diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml index 65574a070e..8bcb4297c0 100644 --- a/.github/workflows/main.yml +++ b/.github/workflows/main.yml @@ -1,6 +1,9 @@ name: CI on: [push, pull_request] +env: + MDBOOK_VERSION: 0.5.1 + jobs: test: name: Run tests @@ -12,20 +15,50 @@ jobs: - name: Install Rust run: | rustup set profile minimal - rustup toolchain install 1.67 -c rust-docs - rustup default 1.67 + rustup toolchain install 1.90 -c rust-docs + rustup default 1.90 - name: Install mdbook run: | mkdir bin - curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.4.21/mdbook-v0.4.21-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin - echo "$(pwd)/bin" >> ${GITHUB_PATH} + curl -sSL https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin + echo "$(pwd)/bin" >> "${GITHUB_PATH}" - name: Report versions run: | rustup --version rustc -Vv mdbook --version + + # mdBook does not currently have particularly good support for “external” + # crates. To make the test suite work correctly with `trpl`, we must first + # build `trpl` itself (`mdbook` will not do it), and then explicitly pass + # its `deps` path as a library search path for `mdbook test`. That will make + # sure all the crates can be resolved when running the tests. + - name: Build `trpl` crate + run: | + cd packages/trpl + cargo build - name: Run tests - run: mdbook test + run: + mdbook test --library-path packages/trpl/target/debug/deps + package_tests: + name: Run package tests + runs-on: ubuntu-latest + steps: + - uses: actions/checkout@master + - name: Update rustup + run: rustup self update + - name: Install Rust + run: | + rustup set profile minimal + rustup toolchain install 1.90 -c rust-docs + rustup default 1.90 + - name: Run `tools` package tests + run: | + cargo test + - name: Run `mdbook-trpl` package tests + working-directory: packages/mdbook-trpl + run: | + cargo test lint: name: Run lints runs-on: ubuntu-latest @@ -41,8 +74,8 @@ jobs: - name: Install mdbook run: | mkdir bin - curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.4.21/mdbook-v0.4.21-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin - echo "$(pwd)/bin" >> ${GITHUB_PATH} + curl -sSL https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin + echo "$(pwd)/bin" >> "${GITHUB_PATH}" - name: Install aspell run: sudo apt-get install aspell - name: Install shellcheck @@ -55,7 +88,7 @@ jobs: aspell --version shellcheck --version - name: Shellcheck - run: find . -name '*.sh' | xargs shellcheck + run: find . -name '*.sh' -print0 | xargs -0 shellcheck - name: Spellcheck run: bash ci/spellcheck.sh list - name: Lint for local file paths @@ -67,6 +100,6 @@ jobs: - name: Check for broken links run: | curl -sSLo linkcheck.sh \ - https://raw.githubusercontent.com/rust-lang/rust/master/src/tools/linkchecker/linkcheck.sh + https://raw.githubusercontent.com/rust-lang/rust/HEAD/src/tools/linkchecker/linkcheck.sh # Cannot use --all here because of the generated redirect pages aren't available. sh linkcheck.sh book diff --git a/.gitignore b/.gitignore index 4c699f440a..6bd6995e09 100644 --- a/.gitignore +++ b/.gitignore @@ -5,3 +5,6 @@ book/ target tmp +.nova +.vscode +.zed diff --git a/2018-edition/book.toml b/2018-edition/book.toml index 03b59090b4..45a3991a05 100644 --- a/2018-edition/book.toml +++ b/2018-edition/book.toml @@ -1,6 +1,6 @@ [book] title = "The Rust Programming Language" -author = "Steve Klabnik and Carol Nichols, with Contributions from the Rust Community" +authors = ["Steve Klabnik", "Carol Nichols", "Contributions from the Rust Community"] [output.html] additional-css = ["ferris.css"] diff --git a/2018-edition/src/ch17-00-oop.md b/2018-edition/src/ch17-00-oop.md index c731bbc95b..6ff4dc33e8 100644 --- a/2018-edition/src/ch17-00-oop.md +++ b/2018-edition/src/ch17-00-oop.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-00-oop.html) instead. +version of the book](../ch18-00-oop.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-00-oop.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-00-oop.html). diff --git a/2018-edition/src/ch17-01-what-is-oo.md b/2018-edition/src/ch17-01-what-is-oo.md index ed1ec4013d..28835201bf 100644 --- a/2018-edition/src/ch17-01-what-is-oo.md +++ b/2018-edition/src/ch17-01-what-is-oo.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-01-what-is-oo.html) instead. +version of the book](../ch18-01-what-is-oo.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-01-what-is-oo.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-01-what-is-oo.html). diff --git a/2018-edition/src/ch17-02-trait-objects.md b/2018-edition/src/ch17-02-trait-objects.md index 1999647aae..b83ab904ee 100644 --- a/2018-edition/src/ch17-02-trait-objects.md +++ b/2018-edition/src/ch17-02-trait-objects.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-02-trait-objects.html) instead. +version of the book](../ch18-02-trait-objects.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-02-trait-objects.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-02-trait-objects.html). diff --git a/2018-edition/src/ch17-03-oo-design-patterns.md b/2018-edition/src/ch17-03-oo-design-patterns.md index 1b74425fe2..9513538f57 100644 --- a/2018-edition/src/ch17-03-oo-design-patterns.md +++ b/2018-edition/src/ch17-03-oo-design-patterns.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-03-oo-design-patterns.html) instead. +version of the book](../ch18-03-oo-design-patterns.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-03-oo-design-patterns.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch17-03-oo-design-patterns.html). diff --git a/2018-edition/src/ch18-00-patterns.md b/2018-edition/src/ch18-00-patterns.md index f3da1f40d2..213bac305d 100644 --- a/2018-edition/src/ch18-00-patterns.md +++ b/2018-edition/src/ch18-00-patterns.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-00-patterns.html) instead. +version of the book](../ch19-00-patterns.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-00-patterns.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-00-patterns.html). diff --git a/2018-edition/src/ch18-01-all-the-places-for-patterns.md b/2018-edition/src/ch18-01-all-the-places-for-patterns.md index ccf3884069..f2dfa71a32 100644 --- a/2018-edition/src/ch18-01-all-the-places-for-patterns.md +++ b/2018-edition/src/ch18-01-all-the-places-for-patterns.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-01-all-the-places-for-patterns.html) instead. +version of the book](../ch19-01-all-the-places-for-patterns.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-01-all-the-places-for-patterns.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-01-all-the-places-for-patterns.html). diff --git a/2018-edition/src/ch18-02-refutability.md b/2018-edition/src/ch18-02-refutability.md index a3e2bcff76..3eddb4dcd5 100644 --- a/2018-edition/src/ch18-02-refutability.md +++ b/2018-edition/src/ch18-02-refutability.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-02-refutability.html) instead. +version of the book](../ch19-02-refutability.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-02-refutability.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-02-refutability.html). diff --git a/2018-edition/src/ch18-03-pattern-syntax.md b/2018-edition/src/ch18-03-pattern-syntax.md index 0e0929e7b8..44c73500e1 100644 --- a/2018-edition/src/ch18-03-pattern-syntax.md +++ b/2018-edition/src/ch18-03-pattern-syntax.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-03-pattern-syntax.html) instead. +version of the book](../ch19-03-pattern-syntax.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-03-pattern-syntax.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch18-03-pattern-syntax.html). diff --git a/2018-edition/src/ch19-00-advanced-features.md b/2018-edition/src/ch19-00-advanced-features.md index b34d6b9b67..16c72a906a 100644 --- a/2018-edition/src/ch19-00-advanced-features.md +++ b/2018-edition/src/ch19-00-advanced-features.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-00-advanced-features.html) instead. +version of the book](../ch20-00-advanced-features.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-00-advanced-features.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-00-advanced-features.html). diff --git a/2018-edition/src/ch19-01-unsafe-rust.md b/2018-edition/src/ch19-01-unsafe-rust.md index 34b569fee6..7316eb44a9 100644 --- a/2018-edition/src/ch19-01-unsafe-rust.md +++ b/2018-edition/src/ch19-01-unsafe-rust.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-01-unsafe-rust.html) instead. +version of the book](../ch20-01-unsafe-rust.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-01-unsafe-rust.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-01-unsafe-rust.html). diff --git a/2018-edition/src/ch19-03-advanced-traits.md b/2018-edition/src/ch19-03-advanced-traits.md index 4219b208b9..94f578ae28 100644 --- a/2018-edition/src/ch19-03-advanced-traits.md +++ b/2018-edition/src/ch19-03-advanced-traits.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-03-advanced-traits.html) instead. +version of the book](../ch20-02-advanced-traits.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-03-advanced-traits.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-03-advanced-traits.html). diff --git a/2018-edition/src/ch19-04-advanced-types.md b/2018-edition/src/ch19-04-advanced-types.md index fecbd52dc8..7628f68b42 100644 --- a/2018-edition/src/ch19-04-advanced-types.md +++ b/2018-edition/src/ch19-04-advanced-types.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-04-advanced-types.html) instead. +version of the book](../ch20-03-advanced-types.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-04-advanced-types.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-04-advanced-types.html). diff --git a/2018-edition/src/ch19-05-advanced-functions-and-closures.md b/2018-edition/src/ch19-05-advanced-functions-and-closures.md index 1bf0450904..d31f20a62f 100644 --- a/2018-edition/src/ch19-05-advanced-functions-and-closures.md +++ b/2018-edition/src/ch19-05-advanced-functions-and-closures.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-05-advanced-functions-and-closures.html) instead. +version of the book](../ch20-04-advanced-functions-and-closures.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-05-advanced-functions-and-closures.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-05-advanced-functions-and-closures.html). diff --git a/2018-edition/src/ch19-06-macros.md b/2018-edition/src/ch19-06-macros.md index bf019c5d68..cd92908bb0 100644 --- a/2018-edition/src/ch19-06-macros.md +++ b/2018-edition/src/ch19-06-macros.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-06-macros.html) instead. +version of the book](../ch20-05-macros.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-06-macros.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-06-macros.html). diff --git a/2018-edition/src/ch20-00-final-project-a-web-server.md b/2018-edition/src/ch20-00-final-project-a-web-server.md index f9b9e5c2d2..cac5584895 100644 --- a/2018-edition/src/ch20-00-final-project-a-web-server.md +++ b/2018-edition/src/ch20-00-final-project-a-web-server.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-00-final-project-a-web-server.html) instead. +version of the book](../ch21-00-final-project-a-web-server.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-00-final-project-a-web-server.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-00-final-project-a-web-server.html). diff --git a/2018-edition/src/ch20-01-single-threaded.md b/2018-edition/src/ch20-01-single-threaded.md index 30d0884adb..e1b4200be8 100644 --- a/2018-edition/src/ch20-01-single-threaded.md +++ b/2018-edition/src/ch20-01-single-threaded.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-01-single-threaded.html) instead. +version of the book](../ch21-01-single-threaded.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-01-single-threaded.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-01-single-threaded.html). diff --git a/2018-edition/src/ch20-02-multithreaded.md b/2018-edition/src/ch20-02-multithreaded.md index e8b592ad22..7d54d56bc8 100644 --- a/2018-edition/src/ch20-02-multithreaded.md +++ b/2018-edition/src/ch20-02-multithreaded.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-02-multithreaded.html) instead. +version of the book](../ch21-02-multithreaded.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-02-multithreaded.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-02-multithreaded.html). diff --git a/2018-edition/src/ch20-03-graceful-shutdown-and-cleanup.md b/2018-edition/src/ch20-03-graceful-shutdown-and-cleanup.md index 928d199bee..f4879c4ac7 100644 --- a/2018-edition/src/ch20-03-graceful-shutdown-and-cleanup.md +++ b/2018-edition/src/ch20-03-graceful-shutdown-and-cleanup.md @@ -3,8 +3,8 @@ The 2018 edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-03-graceful-shutdown-and-cleanup.html) instead. +version of the book](../ch21-03-graceful-shutdown-and-cleanup.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-03-graceful-shutdown-and-cleanup.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/2018-edition/ch20-03-graceful-shutdown-and-cleanup.html). diff --git a/ADMIN_TASKS.md b/ADMIN_TASKS.md index 2a92eefd26..d4c650d104 100644 --- a/ADMIN_TASKS.md +++ b/ADMIN_TASKS.md @@ -14,14 +14,21 @@ occasional maintenance tasks. does) - Inspect the changes (by looking at the files changed according to git) and their effects (by looking at the files in `tmp/book-before` and - `tmp/book-after`) and commit them if they look good + `tmp/book-after`) and commit them if they look good - Grep for `manual-regeneration` and follow the instructions in those places to update output that cannot be generated by a script ## Update the `edition` in all listings To update the `edition = "[year]"` metadata in all the listings' `Cargo.toml`s, -run the `./tools/update-editions.sh` script and commit the changes. +run the `./tools/update-editions.sh` script. Check the diff to make sure it +looks reasonable, and in particular check whether the updates necessitate any +changes to the text. Then commit the changes. + +## Update the `edition` in mdBook config + +Open `book.toml` and `nostarch/book.toml` and set the `edition` value in the +`[rust]` table to the new edition. ## Release a new version of the listings @@ -31,9 +38,8 @@ create a new release artifact, for example if there have been code changes due to edits or due to updating Rust and `rustfmt`, do the following: - Create a git tag for the release and push it to GitHub, or create a new tag - by going to the GitHub UI, [drafting a new - release](https://github.com/rust-lang/book/releases/new), and entering a new - tag instead of selecting an existing tag + by going to the GitHub UI, [drafting a new release](https://github.com/rust-lang/book/releases/new), and entering a new + tag instead of selecting an existing tag - Run `cargo run --bin release_listings`, which will generate `tmp/listings.tar.gz` - Upload `tmp/listings.tar.gz` in the GitHub UI for the draft release @@ -49,50 +55,50 @@ extracted into a file. To do that: - Find where the new listing should go in the `listings` directory. - There is one subdirectory for each chapter - Numbered listings should use `listing-[chapter num]-[listing num]` for - their directory names. + their directory names. - Listings without a number should start with `no-listing-` followed by a - number that indicates its position in the chapter relative to the other - listings without numbers in the chapter, then a short description that - someone could read to find the code they're looking for. + number that indicates its position in the chapter relative to the other + listings without numbers in the chapter, then a short description that + someone could read to find the code they're looking for. - Listings used only for displaying the output of the code (for example, when - we say "if we had written x instead of y, we would get this compiler - error:" but we don't actually show code x) should be named with - `output-only-` followed by a number that indicates its position in the - chapter relative to the other listings used only for output, then a short - description that authors or contributors could read to find the code - they're looking for. + we say "if we had written x instead of y, we would get this compiler + error:" but we don't actually show code x) should be named with + `output-only-` followed by a number that indicates its position in the + chapter relative to the other listings used only for output, then a short + description that authors or contributors could read to find the code + they're looking for. - **Remember to adjust surrounding listing numbers as appropriate!** - Create a full Cargo project in that directory, either by using `cargo new` or copying another listing as a starting point. - Add the code and any surrounding code needed to create a full working example. - If you only want to show part of the code in the file, use anchor comments (`// ANCHOR: some_tag` and `// ANCHOR_END: some_tag`) to mark the parts of - the file you want to show. -- For Rust code, use the `{{#rustdoc_include [fileame:some_tag]}}` directive + the file you want to show. +- For Rust code, use the `{{#rustdoc_include [filename:some_tag]}}` directive within the code blocks in the text. The `rustdoc_include` directive gives the - code that doesn't get displayed to `rustdoc` for `mdbook test` purposes. + code that doesn't get displayed to `rustdoc` for `mdbook test` purposes. - For anything else, use the `{{#include [filename:some_tag]}}` directive. - If you want to display the output of a command in the text as well, create an `output.txt` file in the listing's directory as follows: - Run the command, like `cargo run` or `cargo test`, and copy all of the - output. + output. - Create a new `output.txt` file with the first line `$ [the command you ran]`. - Paste the output you just copied. - Run `./tools/update-rustc.sh`, which should perform some normalization on - the compiler output. + the compiler output. - Include the output in the text with the `{{#include [filename]}}` directive. - Add and commit output.txt. - If you want to display output but for some reason it can't be generated by a script (say, because of user input or external events like making a web - request), keep the output inline but make a comment that contains - `manual-regeneration` and instructions for manually updating the inline - output. + request), keep the output inline but make a comment that contains + `manual-regeneration` and instructions for manually updating the inline + output. - If you don't want this example to even be attempted to be formatted by `rustfmt` (for example because the example doesn't parse on purpose), add a - `rustfmt-ignore` file in the listing's directory and the reason it's not - being formatted as the contents of that file (in case it's a rustfmt bug that - might get fixed someday). + `rustfmt-ignore` file in the listing's directory and the reason it's not + being formatted as the contents of that file (in case it's a rustfmt bug that + might get fixed someday). ## See the effect of some change on the rendered book @@ -133,3 +139,13 @@ $ dot dot/trpl04-01.dot -Tsvg > src/img/trpl04-01.svg In the generated SVG, remove the width and the height attributes from the `svg` element and set the `viewBox` attribute to `0.00 0.00 1000.00 1000.00` or other values that don't cut off the image. + +## Publish a preview to GitHub Pages + +We sometimes publish to GitHub Pages for in-progress previews. The recommended +flow for publishing is: + +- Install the `ghp-import` tool by running `pip install ghp-import` (or `pipx install ghp-import`, using [pipx][pipx]). +- In the root, run `tools/generate-preview.sh` + +[pipx]: https://pipx.pypa.io/stable/#install-pipx diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md index a20cb58501..23fea7c0a5 100644 --- a/CONTRIBUTING.md +++ b/CONTRIBUTING.md @@ -11,6 +11,35 @@ of the print version. The snapshot files reflect what has been sent or not, so they only get updated when edits are sent to No Starch. **Do not submit pull requests changing files in the `nostarch` directory, they will be closed.** +We use [`rustfmt`][rustfmt] to apply standard formatting to Rust code in the +repo and [`dprint`][dprint] to apply standard formatting to the Markdown source +and the non-Rust code in the project. + +[rustfmt]: https://github.com/rust-lang/rustfmt +[dprint]: https://dprint.dev + +You will normally have `rustfmt` installed if you have a Rust toolchain +installed; if for some reason you do not have a copy of `rustfmt`, you can add +it by running the following command: + +```sh +rustup component add rustfmt +``` + +To install `dprint`, you can run the following command: + +```sh +cargo install dprint +``` + +Or follow the [instructions][install-dprint] on the `dprint` website. + +[install-dprint]: https://dprint.dev/install/ + +To format Rust code, you can run `rustfmt `, and to format other +files, you can pass `dprint fmt `. Many text editors also have native +support or extensions for both `rustfmt` and `dprint`. + ## Checking for Fixes The book rides the Rust release trains. Therefore, if you see a problem on @@ -45,8 +74,7 @@ or pull request. [nostarch]: https://nostarch.com/rust-programming-language-2nd-edition -So far, we've been doing a larger revision to coincide with [Rust -Editions](https://doc.rust-lang.org/edition-guide/). Between those larger +So far, we've been doing a larger revision to coincide with [Rust Editions](https://doc.rust-lang.org/edition-guide/). Between those larger revisions, we will only be correcting errors. If your issue or pull request isn't strictly fixing an error, it might sit until the next time that we're working on a large revision: expect on the order of months or years. Thank you diff --git a/Cargo.lock b/Cargo.lock index d0bbf7586c..c1fd7d4b54 100644 --- a/Cargo.lock +++ b/Cargo.lock @@ -1,6 +1,6 @@ # This file is automatically @generated by Cargo. # It is not intended for manual editing. -version = 3 +version = 4 [[package]] name = "adler" @@ -10,9 +10,9 @@ checksum = "f26201604c87b1e01bd3d98f8d5d9a8fcbb815e8cedb41ffccbeb4bf593a35fe" [[package]] name = "aho-corasick" -version = "0.7.18" +version = "1.1.3" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "1e37cfd5e7657ada45f742d6e99ca5788580b5c529dc78faf11ece6dc702656f" +checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916" dependencies = [ "memchr", ] @@ -23,6 +23,12 @@ version = "1.3.2" source = "registry+https://github.com/rust-lang/crates.io-index" checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a" +[[package]] +name = "bitflags" +version = "2.5.0" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "cf4b9d6a944f767f8e5e0db018570623c85f3d925ac718db4e06d0187adb21c1" + [[package]] name = "cfg-if" version = "1.0.0" @@ -31,9 +37,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd" [[package]] name = "crc32fast" -version = "1.3.2" +version = "1.4.0" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "b540bd8bc810d3885c6ea91e2018302f68baba2129ab3e88f32389ee9370880d" +checksum = "b3855a8a784b474f333699ef2bbca9db2c4a1f6d9088a90a2d25b1eb53111eaa" dependencies = [ "cfg-if", ] @@ -50,23 +56,33 @@ dependencies = [ "strsim", ] +[[package]] +name = "errno" +version = "0.3.8" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "a258e46cdc063eb8519c00b9fc845fc47bcfca4130e2f08e88665ceda8474245" +dependencies = [ + "libc", + "windows-sys", +] + [[package]] name = "filetime" -version = "0.2.16" +version = "0.2.23" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "c0408e2626025178a6a7f7ffc05a25bc47103229f19c113755de7bf63816290c" +checksum = "1ee447700ac8aa0b2f2bd7bc4462ad686ba06baa6727ac149a2d6277f0d240fd" dependencies = [ "cfg-if", "libc", "redox_syscall", - "winapi", + "windows-sys", ] [[package]] name = "flate2" -version = "1.0.24" +version = "1.0.30" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "f82b0f4c27ad9f8bfd1f3208d882da2b09c301bc1c828fd3a00d0216d2fbbff6" +checksum = "5f54427cfd1c7829e2a139fcefea601bf088ebca651d2bf53ebc600eac295dae" dependencies = [ "crc32fast", "miniz_oxide", @@ -80,57 +96,75 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646" [[package]] name = "libc" -version = "0.2.126" +version = "0.2.153" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "9c198f91728a82281a64e1f4f9eeb25d82cb32a5de251c6bd1b5154d63a8e7bd" + +[[package]] +name = "linux-raw-sys" +version = "0.4.13" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "349d5a591cd28b49e1d1037471617a32ddcda5731b99419008085f72d5a53836" +checksum = "01cda141df6706de531b6c46c3a33ecca755538219bd484262fa09410c13539c" [[package]] name = "memchr" -version = "2.5.0" +version = "2.7.2" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d" +checksum = "6c8640c5d730cb13ebd907d8d04b52f55ac9a2eec55b440c8892f40d56c76c1d" [[package]] name = "miniz_oxide" -version = "0.5.3" +version = "0.7.2" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "6f5c75688da582b8ffc1f1799e9db273f32133c49e048f614d22ec3256773ccc" +checksum = "9d811f3e15f28568be3407c8e7fdb6514c1cda3cb30683f15b6a1a1dc4ea14a7" dependencies = [ "adler", ] [[package]] name = "proc-macro2" -version = "1.0.39" +version = "1.0.80" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "c54b25569025b7fc9651de43004ae593a75ad88543b17178aa5e1b9c4f15f56f" +checksum = "a56dea16b0a29e94408b9aa5e2940a4eedbd128a1ba20e8f7ae60fd3d465af0e" dependencies = [ "unicode-ident", ] [[package]] name = "quote" -version = "1.0.18" +version = "1.0.36" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "a1feb54ed693b93a84e14094943b84b7c4eae204c512b7ccb95ab0c66d278ad1" +checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7" dependencies = [ "proc-macro2", ] [[package]] name = "redox_syscall" -version = "0.2.13" +version = "0.4.1" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "62f25bc4c7e55e0b0b7a1d43fb893f4fa1361d0abe38b9ce4f323c2adfe6ef42" +checksum = "4722d768eff46b75989dd134e5c353f0d6296e5aaa3132e776cbdb56be7731aa" dependencies = [ - "bitflags", + "bitflags 1.3.2", ] [[package]] name = "regex" -version = "1.5.6" +version = "1.10.4" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "c117dbdfde9c8308975b6a18d71f3f385c89461f7b3fb054288ecf2a2058ba4c" +dependencies = [ + "aho-corasick", + "memchr", + "regex-automata", + "regex-syntax", +] + +[[package]] +name = "regex-automata" +version = "0.4.6" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "d83f127d94bdbcda4c8cc2e50f6f84f4b611f69c902699ca385a39c3a75f9ff1" +checksum = "86b83b8b9847f9bf95ef68afb0b8e6cdb80f498442f5179a29fad448fcc1eaea" dependencies = [ "aho-corasick", "memchr", @@ -139,12 +173,12 @@ dependencies = [ [[package]] name = "regex-syntax" -version = "0.6.26" +version = "0.8.3" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "49b3de9ec5dc0a3417da371aab17d729997c15010e7fd24ff707773a33bddb64" +checksum = "adad44e29e4c806119491a7f06f03de4d1af22c3a680dd47f1e6e179439d1f56" [[package]] -name = "rust-book" +name = "rust-book-tools" version = "0.0.1" dependencies = [ "docopt", @@ -156,6 +190,19 @@ dependencies = [ "walkdir", ] +[[package]] +name = "rustix" +version = "0.38.34" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "70dc5ec042f7a43c4a73241207cecc9873a06d45debb38b329f8541d85c2730f" +dependencies = [ + "bitflags 2.5.0", + "errno", + "libc", + "linux-raw-sys", + "windows-sys", +] + [[package]] name = "same-file" version = "1.0.6" @@ -167,18 +214,18 @@ dependencies = [ [[package]] name = "serde" -version = "1.0.137" +version = "1.0.197" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "61ea8d54c77f8315140a05f4c7237403bf38b72704d031543aa1d16abbf517d1" +checksum = "3fb1c873e1b9b056a4dc4c0c198b24c3ffa059243875552b2bd0933b1aee4ce2" dependencies = [ "serde_derive", ] [[package]] name = "serde_derive" -version = "1.0.137" +version = "1.0.197" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "1f26faba0c3959972377d3b2d306ee9f71faee9714294e41bb777f83f88578be" +checksum = "7eb0b34b42edc17f6b7cac84a52a1c5f0e1bb2227e997ca9011ea3dd34e8610b" dependencies = [ "proc-macro2", "quote", @@ -193,9 +240,9 @@ checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623" [[package]] name = "syn" -version = "1.0.96" +version = "2.0.59" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "0748dd251e24453cb8717f0354206b91557e4ec8703673a4b30208f2abaf1ebf" +checksum = "4a6531ffc7b071655e4ce2e04bd464c4830bb585a61cabb96cf808f05172615a" dependencies = [ "proc-macro2", "quote", @@ -204,9 +251,9 @@ dependencies = [ [[package]] name = "tar" -version = "0.4.38" +version = "0.4.40" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "4b55807c0344e1e6c04d7c965f5289c39a8d94ae23ed5c0b57aabac549f871c6" +checksum = "b16afcea1f22891c49a00c751c7b63b2233284064f11a200fc624137c51e2ddb" dependencies = [ "filetime", "libc", @@ -221,12 +268,11 @@ checksum = "d22af068fba1eb5edcb4aea19d382b2a3deb4c8f9d475c589b6ada9e0fd493ee" [[package]] name = "walkdir" -version = "2.3.2" +version = "2.5.0" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "808cf2735cd4b6866113f648b791c6adc5714537bc222d9347bb203386ffda56" +checksum = "29790946404f91d9c5d06f9874efddea1dc06c5efe94541a7d6863108e3a5e4b" dependencies = [ "same-file", - "winapi", "winapi-util", ] @@ -261,11 +307,86 @@ version = "0.4.0" source = "registry+https://github.com/rust-lang/crates.io-index" checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f" +[[package]] +name = "windows-sys" +version = "0.52.0" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "282be5f36a8ce781fad8c8ae18fa3f9beff57ec1b52cb3de0789201425d9a33d" +dependencies = [ + "windows-targets", +] + +[[package]] +name = "windows-targets" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "9b724f72796e036ab90c1021d4780d4d3d648aca59e491e6b98e725b84e99973" +dependencies = [ + "windows_aarch64_gnullvm", + "windows_aarch64_msvc", + "windows_i686_gnu", + "windows_i686_gnullvm", + "windows_i686_msvc", + "windows_x86_64_gnu", + "windows_x86_64_gnullvm", + "windows_x86_64_msvc", +] + +[[package]] +name = "windows_aarch64_gnullvm" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "32a4622180e7a0ec044bb555404c800bc9fd9ec262ec147edd5989ccd0c02cd3" + +[[package]] +name = "windows_aarch64_msvc" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "09ec2a7bb152e2252b53fa7803150007879548bc709c039df7627cabbd05d469" + +[[package]] +name = "windows_i686_gnu" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "8e9b5ad5ab802e97eb8e295ac6720e509ee4c243f69d781394014ebfe8bbfa0b" + +[[package]] +name = "windows_i686_gnullvm" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "0eee52d38c090b3caa76c563b86c3a4bd71ef1a819287c19d586d7334ae8ed66" + +[[package]] +name = "windows_i686_msvc" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "240948bc05c5e7c6dabba28bf89d89ffce3e303022809e73deaefe4f6ec56c66" + +[[package]] +name = "windows_x86_64_gnu" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "147a5c80aabfbf0c7d901cb5895d1de30ef2907eb21fbbab29ca94c5b08b1a78" + +[[package]] +name = "windows_x86_64_gnullvm" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "24d5b23dc417412679681396f2b49f3de8c1473deb516bd34410872eff51ed0d" + +[[package]] +name = "windows_x86_64_msvc" +version = "0.52.6" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec" + [[package]] name = "xattr" -version = "0.2.3" +version = "1.3.1" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "6d1526bbe5aaeb5eb06885f4d987bcdfa5e23187055de9b83fe00156a821fabc" +checksum = "8da84f1a25939b27f6820d92aed108f83ff920fdf11a7b19366c27c4cda81d4f" dependencies = [ "libc", + "linux-raw-sys", + "rustix", ] diff --git a/Cargo.toml b/Cargo.toml index c59425f920..73c7ba471a 100644 --- a/Cargo.toml +++ b/Cargo.toml @@ -1,42 +1,14 @@ -[package] -name = "rust-book" -version = "0.0.1" -description = "The Rust Book" -edition = "2018" - -[[bin]] -name = "concat_chapters" -path = "tools/src/bin/concat_chapters.rs" - -[[bin]] -name = "convert_quotes" -path = "tools/src/bin/convert_quotes.rs" - -[[bin]] -name = "lfp" -path = "tools/src/bin/lfp.rs" - -[[bin]] -name = "link2print" -path = "tools/src/bin/link2print.rs" - -[[bin]] -name = "release_listings" -path = "tools/src/bin/release_listings.rs" - -[[bin]] -name = "remove_hidden_lines" -path = "tools/src/bin/remove_hidden_lines.rs" - -[[bin]] -name = "remove_links" -path = "tools/src/bin/remove_links.rs" - -[[bin]] -name = "remove_markup" -path = "tools/src/bin/remove_markup.rs" - -[dependencies] +[workspace] +members = ["packages/tools"] +default-members = ["packages/tools"] +resolver = "2" +exclude = [ + "linkchecker", # linkchecker is part of the CI workflow + "listings", # these are intentionally distinct from the workspace + "tmp", # listings are built here when updating output via tools/update-rustc.sh +] + +[workspace.dependencies] walkdir = "2.3.1" docopt = "1.1.0" serde = "1.0" diff --git a/README.md b/README.md index c70c85e727..6ee459448b 100644 --- a/README.md +++ b/README.md @@ -27,10 +27,10 @@ Building the book requires [mdBook], ideally the same version that rust-lang/rust uses in [this file][rust-mdbook]. To get it: [mdBook]: https://github.com/rust-lang/mdBook -[rust-mdbook]: https://github.com/rust-lang/rust/blob/master/src/tools/rustbook/Cargo.toml +[rust-mdbook]: https://github.com/rust-lang/rust/blob/HEAD/src/tools/rustbook/Cargo.toml ```bash -$ cargo install mdbook --version +$ cargo install mdbook --locked --version ``` ## Building @@ -45,6 +45,7 @@ The output will be in the `book` subdirectory. To check it out, open it in your web browser. _Firefox:_ + ```bash $ firefox book/index.html # Linux $ open -a "Firefox" book/index.html # OS X @@ -53,6 +54,7 @@ $ start firefox.exe .\book\index.html # Windows (Cmd) ``` _Chrome:_ + ```bash $ google-chrome book/index.html # Linux $ open -a "Google Chrome" book/index.html # OS X @@ -63,7 +65,8 @@ $ start chrome.exe .\book\index.html # Windows (Cmd) To run the tests: ```bash -$ mdbook test +$ cd packages/trpl +$ mdbook test --library-path packages/trpl/target/debug/deps ``` ## Contributing @@ -78,8 +81,7 @@ to keep the online version of the book close to the print version when possible, it may take longer than you're used to for us to address your issue or pull request. -So far, we've been doing a larger revision to coincide with [Rust -Editions](https://doc.rust-lang.org/edition-guide/). Between those larger +So far, we've been doing a larger revision to coincide with [Rust Editions](https://doc.rust-lang.org/edition-guide/). Between those larger revisions, we will only be correcting errors. If your issue or pull request isn't strictly fixing an error, it might sit until the next time that we're working on a large revision: expect on the order of months or years. Thank you @@ -100,6 +102,6 @@ before we merge any in, but feel free to start! To scan source files for spelling errors, you can use the `spellcheck.sh` script available in the `ci` directory. It needs a dictionary of valid words, which is provided in `ci/dictionary.txt`. If the script produces a false -positive (say, you used word `BTreeMap` which the script considers invalid), +positive (say, you used the word `BTreeMap` which the script considers invalid), you need to add this word to `ci/dictionary.txt` (keep the sorted order for consistency). diff --git a/book.toml b/book.toml index 31419fde8d..cba4f905a2 100644 --- a/book.toml +++ b/book.toml @@ -1,8 +1,52 @@ +# Sync any changes to this *other than where explicitly specified* with the copy +# in `nostarch/book.toml`! + [book] title = "The Rust Programming Language" -authors = ["Steve Klabnik", "Carol Nichols", "Contributions from the Rust Community"] +authors = ["Steve Klabnik", "Carol Nichols", "Chris Krycho", "Contributions from the Rust Community"] [output.html] -additional-css = ["ferris.css", "theme/2018-edition.css"] +additional-css = ["ferris.css", "theme/2018-edition.css", "theme/semantic-notes.css", "theme/listing.css"] additional-js = ["ferris.js"] git-repository-url = "https://github.com/rust-lang/book" + +[output.html.search] +use-boolean-and = true + +[output.html.redirect] +"ch17-00-oop.html" = "ch18-00-oop.html" +"ch17-01-what-is-oo.html" = "ch18-01-what-is-oo.html" +"ch17-02-trait-objects.html" = "ch18-02-trait-objects.html" +"ch17-03-oo-design-patterns.html" = "ch18-03-oo-design-patterns.html" +"ch18-00-patterns.html" = "ch19-00-patterns.html" +"ch18-01-all-the-places-for-patterns.html" = "ch19-01-all-the-places-for-patterns.html" +"ch18-02-refutability.html" = "ch19-02-refutability.html" +"ch18-03-pattern-syntax.html" = "ch19-03-pattern-syntax.html" +"ch19-00-advanced-features.html" = "ch20-00-advanced-features.html" +"ch19-01-unsafe-rust.html" = "ch20-01-unsafe-rust.html" +"ch19-03-advanced-traits.html" = "ch20-02-advanced-traits.html" +"ch20-03-advanced-traits.html" = "ch20-02-advanced-traits.html" +"ch19-04-advanced-types.html" = "ch20-03-advanced-types.html" +"ch20-04-advanced-types.html" = "ch20-03-advanced-types.html" +"ch19-05-advanced-functions-and-closures.html" = "ch20-04-advanced-functions-and-closures.html" +"ch20-05-advanced-functions-and-closures.html" = "ch20-04-advanced-functions-and-closures.html" +"ch19-06-macros.html" = "ch20-05-macros.html" +"ch20-06-macros.html" = "ch20-05-macros.html" +"ch20-00-final-project-a-web-server.html" = "ch21-00-final-project-a-web-server.html" +"ch20-01-single-threaded.html" = "ch21-01-single-threaded.html" +"ch20-02-multithreaded.html" = "ch21-02-multithreaded.html" +"ch20-03-graceful-shutdown-and-cleanup.html" = "ch21-03-graceful-shutdown-and-cleanup.html" + +# Do not sync this preprocessor; it is for the HTML renderer only. +[preprocessor.trpl-note] +command = "cargo run --manifest-path packages/mdbook-trpl/Cargo.toml --bin mdbook-trpl-note" + +[preprocessor.trpl-listing] +command = "cargo run --manifest-path packages/mdbook-trpl/Cargo.toml --bin mdbook-trpl-listing" +output-mode = "default" + +[rust] +edition = "2024" + +[build] +extra-watch-dirs = ["packages/mdbook-trpl"] diff --git a/ci/dictionary.txt b/ci/dictionary.txt index a91df4a036..92cb8e5096 100644 --- a/ci/dictionary.txt +++ b/ci/dictionary.txt @@ -2,8 +2,7 @@ personal_ws-1.1 en 0 utf-8 abcabcabc abcd abcdefghijklmnopqrstuvwxyz -adaptor -adaptors +ABIs AddAssign Addr adfb @@ -35,6 +34,7 @@ backtraces BACKTRACE Backtraces Baz's +beefeb benchmarking bioinformatics bitand @@ -54,13 +54,16 @@ bool boolean Boolean Booleans +booleans Bors BorrowMutError BoxMeUp +boxt BTreeSet BufRead BufReader BuildHasher +byteorder Cacher cacher Cagain @@ -104,10 +107,12 @@ CustomSmartPointer CustomSmartPointers data's DataStruct +dbea deallocate deallocated deallocating deallocation +debounce debuginfo decl decrementing @@ -144,10 +149,13 @@ DisplayBacktrace DivAssign DraftPost DSTs +durations ebook ebooks Edsger +efdcd egular +ElementRef else's emoji encodings @@ -159,6 +167,8 @@ Enums eprintln Erlang ErrorKind +Español +ETAPS eval executables ExitCode @@ -178,6 +188,7 @@ filesystem's filesystems filmmaking Firefox +FirstAwaitPoint FnMut FnOnce formatter @@ -186,6 +197,8 @@ FrenchToast FromIterator FromResidual frontend +FuturesUnordered +GetAwaitPoint getrandom getter getters @@ -196,6 +209,8 @@ grapheme Grapheme growable gzip +handcoded +handoff hardcode hardcoded hardcoding @@ -240,7 +255,10 @@ inline instantiation internet interoperate +IntoFuture IntoIterator +intra +intratask InvalidDigit invariants ioerror @@ -255,10 +273,12 @@ isize iter iterator's JavaScript +JoinAll JoinHandle Kay's kinded Klabnik +Krycho lang LastWriteTime latin @@ -287,14 +307,20 @@ lval macOS Matsakis mathematic +mdbook memoization metadata Metadata metaprogramming +metavariable mibbit Mibbit +microcontroller +microcontrollers millis minigrep +Miri +miri mixup mkdir MockMessenger @@ -306,10 +332,12 @@ monomorphized MoveMessage Mozilla mpsc +MSRV msvc MulAssign multibyte multithreaded +multithreading mutex mutex's Mutex @@ -317,6 +345,8 @@ mutexes Mutexes MutexGuard mutext +mutextarct +MyAsyncStateMachine MyBox myprogram namespace @@ -338,6 +368,7 @@ nondeterministic nonequality nongeneric noplayground +NoStarch NotFound nsprust null's @@ -348,6 +379,7 @@ OpenGL optimizations OptionalFloatingPointNumber OptionalNumber +optiont OsStr OsString other's @@ -357,7 +389,9 @@ OurError OutlinePrint overloadable overread +PageTitleFuture PanicPayload +parallelizable param parameterize ParseIntError @@ -369,7 +403,9 @@ PendingReviewPost PlaceholderType polymorphism PoolCreationError +por portia +postfix powershell PowerShell powi @@ -395,6 +431,8 @@ RangeTo RangeFull README READMEs +ReadFinished +ReceiverStream rect recurse recv @@ -405,11 +443,13 @@ refactoring refcell RefCell refcellt +refcelltrct RefMut reformats refutability reimplement RemAssign +repost repr representable request's @@ -420,6 +460,7 @@ retweet rewordings rint ripgrep +Rumbul runnable runtime runtimes @@ -428,14 +469,17 @@ Rustaceans rUsT rustc rustdoc +RUSTFLAGS Rustonomicon rustfix rustfmt +RustLangES rustup sampleproject screenshot searchstring SecondaryColor +SecondAwaitPoint SelectBox semver SemVer @@ -452,7 +496,9 @@ sizeof SliceIndex Smalltalk snuck +SocialPost someproject +SomeType someusername SPDX spdx @@ -468,6 +514,7 @@ stdlib stdout steveklabnik's stringify +StreamExt Stroustrup Stroustrup's struct @@ -488,7 +535,9 @@ Submodules submodule’s suboptimal subpath +subslices substring +subtasks subteams subtree subtyping @@ -499,6 +548,7 @@ TcpListener TcpStream templating test's +TextAwaitPoint TextField That'd there'd @@ -511,6 +561,8 @@ tlborm tlsv TODO TokenStream +Tokio +tokio toml TOML toolchain @@ -535,6 +587,8 @@ uncomment Uncomment uncommenting unevaluated +unhandled +unicode Uninstalling uninstall unittests @@ -548,11 +602,13 @@ unsynchronized Unyank UpperCamelCase URIs +urls UsefulType username USERPROFILE usize UsState +util utils vals variable's @@ -566,9 +622,11 @@ Vlissides vscode vtable waitlist +wasi wasn weakt WeatherForecast +webpage WebSocket whitespace wildcard @@ -584,4 +642,5 @@ WriteMessage xcode xpression yyyy +zerocopy ZipImpl diff --git a/dot/trpl04-05.dot b/dot/trpl04-05.dot index ca1f7e06e9..ccdad725aa 100644 --- a/dot/trpl04-05.dot +++ b/dot/trpl04-05.dot @@ -1,32 +1,38 @@ digraph { - rankdir=LR; - overlap=false; - dpi=300.0; - node [shape="plaintext"]; - - table0[label=< - - - -
s
namevalue
ptr
>]; - table1[label=< - - - - - -
s1
namevalue
ptr
len5
capacity5
>]; - table2[label=< - - - - - - -
indexvalue
0h
1e
2l
3l
4o
>]; - - edge[tailclip="false"]; - table1:pointer:c -> table2:pointee; - table0:borrower:c -> table1:borrowee; -} - + rankdir = LR; + overlap = false; + dpi = 300.0; + node [shape = "plaintext";]; + + s [label = < + + + + + +
s
namevalue
ptr
len4
capacity4
>;]; + + subgraph cluster_heap { + peripheries = 0; + rank = "same"; + + hello [label = < + + + + + + +
indexvalue
0h
1e
2l
3l
4o
>;]; + + ahoy [label = < + + + + + +
indexvalue
0a
1h
2o
3y
>;]; + } + + s -> ahoy [tailport = "pointer:c"; headport = "pointee"; tailclip = false;]; +} \ No newline at end of file diff --git a/dot/trpl04-06.dot b/dot/trpl04-06.dot index a23f179a77..ca1f7e06e9 100644 --- a/dot/trpl04-06.dot +++ b/dot/trpl04-06.dot @@ -5,37 +5,28 @@ digraph { node [shape="plaintext"]; table0[label=< - + - - +
world
s
namevalue
ptr
len5
ptr
>]; - - table3[label=< - + table1[label=<
s
+ - - - + + +
s1
namevalue
ptr
len11
capacity11
ptr
len5
capacity5
>]; - table4[label=< + table2[label=<
- - - - - -
indexvalue
0h
1e
2l
3l
4o
5
6w
7o
8r
9l
10d
>]; - edge[tailclip="false"]; - table0:pointer2:c -> table4:pointee2; - table3:pointer:c -> table4:pointee; + table1:pointer:c -> table2:pointee; + table0:borrower:c -> table1:borrowee; } diff --git a/dot/trpl04-07.dot b/dot/trpl04-07.dot new file mode 100644 index 0000000000..a23f179a77 --- /dev/null +++ b/dot/trpl04-07.dot @@ -0,0 +1,41 @@ +digraph { + rankdir=LR; + overlap=false; + dpi=300.0; + node [shape="plaintext"]; + + table0[label=< + + + + +
world
namevalue
ptr
len5
>]; + + table3[label=< + + + + + +
s
namevalue
ptr
len11
capacity11
>]; + table4[label=< + + + + + + + + + + + + +
indexvalue
0h
1e
2l
3l
4o
5
6w
7o
8r
9l
10d
>]; + + + edge[tailclip="false"]; + table0:pointer2:c -> table4:pointee2; + table3:pointer:c -> table4:pointee; +} + diff --git a/dot/trpl17-01.dot b/dot/trpl17-01.dot new file mode 100644 index 0000000000..ed2d969f2f --- /dev/null +++ b/dot/trpl17-01.dot @@ -0,0 +1,41 @@ +digraph { + dpi = 300.0; + + rankdir = "LR"; + + // makes ordering between subgraphs work + newrank = true; + + node [shape = diamond;]; + + subgraph cluster_task_a { + label = "Task A"; + + A1; + A2; + A3; + A4; + + A1 -> A2 -> A3 -> A4 -> A0 [style = invis;]; + + // for vertical alignment purposes only + A0 [style = invis;]; + + // Makes the heights line up between the boxes. + A4 -> A0 [style = invis;]; + } + + subgraph cluster_task_b { + label = "Task B"; + + B0 [style = invis;]; + + B1; + B2; + B3; + + B0 -> B1 -> B2 -> B3 [style = invis;]; + } + + A1 -> B1 -> A2 -> B2 -> A3 -> A4 -> B3; +} \ No newline at end of file diff --git a/dot/trpl17-02.dot b/dot/trpl17-02.dot new file mode 100644 index 0000000000..3e4116a7de --- /dev/null +++ b/dot/trpl17-02.dot @@ -0,0 +1,25 @@ +digraph { + dpi = 300.0; + + rankdir = "LR"; + splines = false; + cluster = true; + + node [shape = diamond;]; + + // The graphs end up with the correct order, i.e. Task 1 *above* Task 2, when + // this is first. + subgraph cluster_ColleagueB { + label = "Task B"; + B1 -> B2 -> B3; + + B0 [style = invis;]; + B3 -> B0 [style = invis;]; + } + + subgraph cluster_ColleagueA { + newrank = true; + label = "Task A"; + A1 -> A2 -> A3 -> A4; + } +} \ No newline at end of file diff --git a/dot/trpl17-03.dot b/dot/trpl17-03.dot new file mode 100644 index 0000000000..7d5a4971cf --- /dev/null +++ b/dot/trpl17-03.dot @@ -0,0 +1,32 @@ +digraph { + dpi = 300.0; + + rankdir = "LR"; + splines = false; + cluster = true; + + node [shape = diamond;]; + + // The graphs end up with the correct order, i.e. Task 1 *above* Task 2, when + // this is first. + subgraph cluster_ColleagueB { + label = "Task A"; + A1; + A2; + A0_1 [style = invis;]; + A3; + + A1 -> A2; + A2 -> A0_1 [arrowhead = "tee"; headport = "A0_1:c"; headclip = false;]; + A0_1; + A0_1 -> A3 [dir = both; arrowtail = "tee"; tailclip = false;]; + } + + subgraph cluster_ColleagueA { + newrank = true; + label = "Task B"; + B1 -> B2 -> B3 -> B4; + } + + B3 -> A3; +} \ No newline at end of file diff --git a/dot/trpl17-04.dot b/dot/trpl17-04.dot new file mode 100644 index 0000000000..6c63b7bde4 --- /dev/null +++ b/dot/trpl17-04.dot @@ -0,0 +1,19 @@ +digraph { + rankdir = RL; + overlap = false; + dpi = 300.0; + splines = false; + cluster = true; + + node [shape = "plaintext";]; + + fut1 [label = < + + + + +
fut1
0
1
>;]; + + edge [tailclip = "false";]; + fut1:source:c -> fut1:target [dir = forward;]; +} \ No newline at end of file diff --git a/dot/trpl17-05.dot b/dot/trpl17-05.dot new file mode 100644 index 0000000000..afcf8e77a1 --- /dev/null +++ b/dot/trpl17-05.dot @@ -0,0 +1,32 @@ +digraph { + rankdir = RL; + overlap = false; + dpi = 300.0; + splines = false; + cluster = true; + + node [shape = "plaintext";]; + + // Group the two together, which results in the desired alignment. + subgraph { + // But don't show the frame! + style = "invis"; + + fut1 [label = < + + + + +
fut1
?
?
?
>;]; + + fut2 [label = < + + + + +
fut2
0
1
>;]; + + edge [tailclip = "false"; dir = forward]; + fut2:source:c -> fut1:target:e; + } +} \ No newline at end of file diff --git a/dot/trpl17-06.dot b/dot/trpl17-06.dot new file mode 100644 index 0000000000..e036a385c3 --- /dev/null +++ b/dot/trpl17-06.dot @@ -0,0 +1,42 @@ +digraph { + rankdir = LR; + dpi = 300.0; + + node [shape = "plaintext";]; + + pinned_box [label = < + + +
Pin
>;]; + + subgraph cluster_box { + label = ""; + peripheries = 0; + + subgraph cluster_box_internal { + peripheries = 1; + label = "b1"; + shape = box; + style = solid; + pin [shape = "point";]; + } + } + + subgraph cluster_deref { + style = bold; + label = "pinned"; + + box [label = < + + + + + +
fut
0
...
1
>;]; + } + + edge [tailclip = false;]; + pinned_box -> pin [tailport = "source:c"; arrowhead = "none";]; + pin -> box [headport = "target";]; + box -> box [tailport = "source:c"; headport = "internal";]; +} \ No newline at end of file diff --git a/dot/trpl17-07.dot b/dot/trpl17-07.dot new file mode 100644 index 0000000000..11b79574c4 --- /dev/null +++ b/dot/trpl17-07.dot @@ -0,0 +1,64 @@ +digraph { + rankdir = LR; + newrank = true; + dpi = 300.0; + + node [shape = "plaintext";]; + + + subgraph cluster_not_fut { + peripheries = 0; + + pin [label = < + + +
Pin
>;]; + + subgraph cluster_boxes { + peripheries = 0; + rank = same; + + subgraph cluster_box_1 { + subgraph cluster_box_2_internal { + label = "b1"; + shape = box; + style = solid; + style = filled; + peripheries = 1; + box1 [shape = "point";style = "invis";]; + } + } + + subgraph cluster_box_2 { + subgraph cluster_box_2_internal { + label = "b2"; + shape = box; + style = solid; + peripheries = 1; + box2 [shape = "point";]; + } + } + } + } + subgraph cluster_target { + style = bold; + label = "pinned"; + + fut [label = < + + + + + +
fut
0
...
1
>;]; + } + + + box1 -> box2 [rankdir = TB; style = invis;]; + + edge [tailclip = false;]; + pin -> box1 [style = "invis";]; + pin -> box2 [tailport = "source:c"; arrowhead = "none";]; + box2 -> fut [headport = "target";]; + fut -> fut [tailport = "source:c"; headport = "internal";]; +} \ No newline at end of file diff --git a/dot/trpl17-08.dot b/dot/trpl17-08.dot new file mode 100644 index 0000000000..8e9897f46d --- /dev/null +++ b/dot/trpl17-08.dot @@ -0,0 +1,39 @@ +digraph { + rankdir = LR; + overlap = false; + dpi = 300.0; + splines = false; + cluster = true; + newrank = true; + outputorder = in; + compound = true; + labelloc = "c"; + + node [shape = "plaintext";]; + + pinned_box [label = < + + +
Pin
>;]; + + + subgraph cluster_deref { + style = dashed; + label = "String"; + + pin [shape = "point";]; + + fut [label = < + + + + + + +
5usizehello
>;]; + } + + edge [tailclip = false;]; + pinned_box -> pin [tailport = "source:c"; arrowhead = "none";]; + pin -> fut [headport = "target";]; +} \ No newline at end of file diff --git a/dot/trpl17-09.dot b/dot/trpl17-09.dot new file mode 100644 index 0000000000..de73007511 --- /dev/null +++ b/dot/trpl17-09.dot @@ -0,0 +1,62 @@ +digraph { + rankdir = LR; + overlap = false; + dpi = 300.0; + splines = false; + cluster = true; + newrank = true; + outputorder = in; + compound = true; + labelloc = "c"; + + node [shape = "plaintext";]; + + pinned_box [label = < + + +
Pin
>;]; + + subgraph cluster_both { + peripheries = 0; + + + + string1 [label = < + + + + + + + + + +
s1
5usizehello
>;]; + + subgraph cluster_deref { + style = dashed; + label = "String"; + peripheries = 1; + + pin [shape = "point";]; + + string2 [label = < + + + + + + + + + + + +
s2
7usizegoodbye
>;]; + } + } + + edge [tailclip = false;]; + pinned_box -> pin [tailport = "source:c"; arrowhead = "none";]; + pin -> string2 [headport = "target";]; +} \ No newline at end of file diff --git a/dprint.jsonc b/dprint.jsonc new file mode 100644 index 0000000000..0ffe670fb0 --- /dev/null +++ b/dprint.jsonc @@ -0,0 +1,32 @@ +{ + "typescript": {}, + "json": {}, + "markdown": { + "lineWidth": 80, + "textWrap": "always" + }, + "malva": {}, + "excludes": [ + "**/node_modules", + "**/*-lock.json", + "**/target", + // We don’t to apply auto-formatting to this *yet*, at a minimum. It may be + // helpful as a way of replacing some of the manual formatting we do in both + // the nostarch script and the script for pulling data back over from docx, + // though, so we may *start* doing so in the future. + "nostarch", + // These should never change at this point + "2018-edition", + "first-edition", + "second-edition", + "redirects", + // has empty list items which look like headings to a formatter + ".github/ISSUE_TEMPLATE/bug_report.md", + ], + "plugins": [ + "https://plugins.dprint.dev/typescript-0.93.3.wasm", + "https://plugins.dprint.dev/json-0.19.4.wasm", + "https://plugins.dprint.dev/markdown-0.17.8.wasm", + "https://plugins.dprint.dev/g-plane/malva-v0.11.0.wasm", + ], +} diff --git a/ferris.css b/ferris.css index fb4a553ffb..513efa1431 100644 --- a/ferris.css +++ b/ferris.css @@ -43,3 +43,25 @@ body.ayu .not_desired_behavior { .ferris-explain { width: 100px; } + +/* + A bit of a hack to make small Ferris use the existing buttons container but + only show/hide the buttons on hover over the `pre`. Targeting `.listing` + increases the specificity of this rule. +*/ +pre > .buttons { + visibility: visible; + opacity: 1; + transition: none; +} + +pre > .buttons button { + visibility: hidden; + opacity: 0; + transition: visibility 0.1s linear, opacity 0.1s linear; +} + +pre:hover > .buttons button { + visibility: visible; + opacity: 1; +} diff --git a/ferris.js b/ferris.js index bb601a4e28..13b1ceb9a5 100644 --- a/ferris.js +++ b/ferris.js @@ -1,65 +1,102 @@ -var ferrisTypes = [ +// @ts-check + +/** + * @typedef {{ attr: string, title: string }} FerrisType + */ + +/** @type {Array} */ +const FERRIS_TYPES = [ { - attr: 'does_not_compile', - title: 'This code does not compile!' + attr: "does_not_compile", + title: "This code does not compile!", }, { - attr: 'panics', - title: 'This code panics!' + attr: "panics", + title: "This code panics!", }, { - attr: 'not_desired_behavior', - title: 'This code does not produce the desired behavior.' - } -] + attr: "not_desired_behavior", + title: "This code does not produce the desired behavior.", + }, +]; -document.addEventListener('DOMContentLoaded', () => { - for (var ferrisType of ferrisTypes) { - attachFerrises(ferrisType) +document.addEventListener("DOMContentLoaded", () => { + for (let ferrisType of FERRIS_TYPES) { + attachFerrises(ferrisType); } -}) +}); +/** + * @param {FerrisType} type + */ function attachFerrises(type) { - var elements = document.getElementsByClassName(type.attr) + let elements = document.getElementsByClassName(type.attr); + + for (let codeBlock of elements) { + // Skip SVG etc.: in principle, these should never be attached to those, but + // this means if someone happens to have a browser extension which *is* + // attaching them, it will not break the code. + if (!(codeBlock instanceof HTMLElement)) { + continue; + } + + let codeLines = codeBlock.innerText; + let extra = codeLines.endsWith("\n") ? 1 : 0; + let numLines = codeLines.split("\n").length - extra; + + /** @type {'small' | 'large'} */ + let size = numLines < 4 ? "small" : "large"; - for (var codeBlock of elements) { - var lines = codeBlock.innerText.replace(/\n$/, '').split(/\n/).length - var size = 'large' - if (lines < 4) { - size = 'small' + let container = prepareFerrisContainer(codeBlock, size == "small"); + if (!container) { + continue; } - var container = prepareFerrisContainer(codeBlock, size == 'small') - container.appendChild(createFerris(type, size)) + container.appendChild(createFerris(type, size)); } } +/** + * @param {HTMLElement} element - Code block element to attach a Ferris to. + * @param {boolean} useButtons - Whether to attach to existing buttons. + * @returns {Element | null} - The container element to use. + */ function prepareFerrisContainer(element, useButtons) { - var foundButtons = element.parentElement.querySelector('.buttons') + let foundButtons = element.parentElement?.querySelector(".buttons"); if (useButtons && foundButtons) { - return foundButtons + return foundButtons; } - var div = document.createElement('div') - div.classList.add('ferris-container') + let div = document.createElement("div"); + div.classList.add("ferris-container"); + + if (!element.parentElement) { + console.error(`Could not install Ferris on ${element}, which is missing a parent`); + return null; + } - element.parentElement.insertBefore(div, element) + element.parentElement.insertBefore(div, element); - return div + return div; } +/** + * @param {FerrisType} type + * @param {'small' | 'large'} size + * @returns {HTMLAnchorElement} - The generated anchor element. + */ function createFerris(type, size) { - var a = document.createElement('a') - a.setAttribute('href', 'ch00-00-introduction.html#ferris') - a.setAttribute('target', '_blank') + let a = document.createElement("a"); + a.setAttribute("href", "ch00-00-introduction.html#ferris"); + a.setAttribute("target", "_blank"); - var img = document.createElement('img') - img.setAttribute('src', 'img/ferris/' + type.attr + '.svg') - img.setAttribute('title', type.title) - img.classList.add('ferris') - img.classList.add('ferris-' + size) + let img = document.createElement("img"); + img.setAttribute("src", "img/ferris/" + type.attr + ".svg"); + img.setAttribute("title", type.title); + img.classList.add("ferris"); + img.classList.add("ferris-" + size); - a.appendChild(img) + a.appendChild(img); - return a + return a; } diff --git a/first-edition/book.toml b/first-edition/book.toml index 3a3189c4d7..59ee4b1e02 100644 --- a/first-edition/book.toml +++ b/first-edition/book.toml @@ -1,3 +1,3 @@ [book] title = "The Rust Programming Language" -author = "The Rust Project Developers" +authors = ["The Rust Project Developers"] diff --git a/first-edition/src/associated-types.md b/first-edition/src/associated-types.md index 626048e9e6..69340a5392 100644 --- a/first-edition/src/associated-types.md +++ b/first-edition/src/associated-types.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-03-advanced-traits.html#specifying-placeholder-types-in-trait-definitions-with-associated-types) instead. +version of the book](../ch20-02-advanced-traits.html#specifying-placeholder-types-in-trait-definitions-with-associated-types) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/const-and-static.md b/first-edition/src/const-and-static.md index aa634112b2..7e667e50c6 100644 --- a/first-edition/src/const-and-static.md +++ b/first-edition/src/const-and-static.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-01-unsafe-rust.html#accessing-or-modifying-a-mutable-static-variable) instead. +version of the book](../ch20-01-unsafe-rust.html#accessing-or-modifying-a-mutable-static-variable) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/ffi.md b/first-edition/src/ffi.md index 2adaff9d8f..a8c3f818ee 100644 --- a/first-edition/src/ffi.md +++ b/first-edition/src/ffi.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-01-unsafe-rust.html#calling-rust-functions-from-other-languages) instead. +version of the book](../ch20-01-unsafe-rust.html#calling-rust-functions-from-other-languages) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/macros.md b/first-edition/src/macros.md index 6bafdc1e43..587f0c79b1 100644 --- a/first-edition/src/macros.md +++ b/first-edition/src/macros.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-06-macros.html) instead. +version of the book](../ch20-05-macros.html) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/operators-and-overloading.md b/first-edition/src/operators-and-overloading.md index 921a2a6854..2b4eecfbd4 100644 --- a/first-edition/src/operators-and-overloading.md +++ b/first-edition/src/operators-and-overloading.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-03-advanced-traits.html#default-generic-type-parameters-and-operator-overloading) instead. +version of the book](../ch20-02-advanced-traits.html#default-generic-type-parameters-and-operator-overloading) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/patterns.md b/first-edition/src/patterns.md index d722d397e9..7bc6949b2f 100644 --- a/first-edition/src/patterns.md +++ b/first-edition/src/patterns.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-03-pattern-syntax.html) instead. +version of the book](../ch19-03-pattern-syntax.html) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/procedural-macros.md b/first-edition/src/procedural-macros.md index 9778383d80..b52a43d748 100644 --- a/first-edition/src/procedural-macros.md +++ b/first-edition/src/procedural-macros.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-06-macros.html?highlight=procedural#procedural-macros-for-generating-code-from-attributes) instead. +version of the book](../ch20-05-macros.html?highlight=procedural#procedural-macros-for-generating-code-from-attributes) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/raw-pointers.md b/first-edition/src/raw-pointers.md index c149da8681..a4cc68d474 100644 --- a/first-edition/src/raw-pointers.md +++ b/first-edition/src/raw-pointers.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-01-unsafe-rust.html#dereferencing-a-raw-pointer) instead. +version of the book](../ch20-01-unsafe-rust.html#dereferencing-a-raw-pointer) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/trait-objects.md b/first-edition/src/trait-objects.md index 871bad6140..a04d16b4b2 100644 --- a/first-edition/src/trait-objects.md +++ b/first-edition/src/trait-objects.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-02-trait-objects.html) instead. +version of the book](../ch18-02-trait-objects.html) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/type-aliases.md b/first-edition/src/type-aliases.md index 7ac51ff191..8e9bde0f11 100644 --- a/first-edition/src/type-aliases.md +++ b/first-edition/src/type-aliases.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-04-advanced-types.html#creating-type-synonyms-with-type-aliases) instead. +version of the book](../ch20-03-advanced-types.html#creating-type-synonyms-with-type-aliases) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/unsafe.md b/first-edition/src/unsafe.md index be816dfd3d..187fef52e1 100644 --- a/first-edition/src/unsafe.md +++ b/first-edition/src/unsafe.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-01-unsafe-rust.html) instead. +version of the book](../ch20-01-unsafe-rust.html) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/first-edition/src/unsized-types.md b/first-edition/src/unsized-types.md index 4ec43ecadf..cc16741f9c 100644 --- a/first-edition/src/unsized-types.md +++ b/first-edition/src/unsized-types.md @@ -3,7 +3,7 @@ The first edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait) instead. +version of the book](../ch20-03-advanced-types.html#dynamically-sized-types-and-the-sized-trait) instead. If you have an internet connection, you can [find a copy distributed with Rust diff --git a/listings/ch02-guessing-game-tutorial/listing-02-01/Cargo.toml b/listings/ch02-guessing-game-tutorial/listing-02-01/Cargo.toml index 78c94fef95..122c1bd074 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-01/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/listing-02-01/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.lock b/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.lock index edc20385bd..b3b58cc17f 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.lock +++ b/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.lock @@ -1,6 +1,12 @@ # This file is automatically @generated by Cargo. # It is not intended for manual editing. -version = 3 +version = 4 + +[[package]] +name = "byteorder" +version = "1.5.0" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "1fd0f2584146f6f2ef48085050886acf353beff7305ebd1ae69500e27c67f64b" [[package]] name = "cfg-if" @@ -10,9 +16,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd" [[package]] name = "getrandom" -version = "0.2.7" +version = "0.2.15" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "4eb1a864a501629691edf6c15a593b7a51eebaa1e8468e9ddc623de7c9b58ec6" +checksum = "c4567c8db10ae91089c99af84c68c38da3ec2f087c3f82960bcdbf3656b6f4d7" dependencies = [ "cfg-if", "libc", @@ -28,15 +34,36 @@ dependencies = [ [[package]] name = "libc" -version = "0.2.127" +version = "0.2.170" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "505e71a4706fa491e9b1b55f51b95d4037d0821ee40131190475f692b35b009b" +checksum = "875b3680cb2f8f71bdcf9a30f38d48282f5d3c95cbf9b3fa57269bb5d5c06828" [[package]] name = "ppv-lite86" -version = "0.2.16" +version = "0.2.20" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "eb9f9e6e233e5c4a35559a617bf40a4ec447db2e84c20b55a6f83167b7e57872" +checksum = "77957b295656769bb8ad2b6a6b09d897d94f05c41b069aede1fcdaa675eaea04" +dependencies = [ + "zerocopy", +] + +[[package]] +name = "proc-macro2" +version = "1.0.93" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "60946a68e5f9d28b0dc1c21bb8a97ee7d018a8b322fa57838ba31cc878e22d99" +dependencies = [ + "unicode-ident", +] + +[[package]] +name = "quote" +version = "1.0.38" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "0e4dccaaaf89514f546c693ddc140f729f958c247918a13380cccc6078391acc" +dependencies = [ + "proc-macro2", +] [[package]] name = "rand" @@ -61,15 +88,53 @@ dependencies = [ [[package]] name = "rand_core" -version = "0.6.3" +version = "0.6.4" source = "registry+https://github.com/rust-lang/crates.io-index" -checksum = "d34f1408f55294453790c48b2f1ebbb1c5b4b7563eb1f418bcfcfdbb06ebb4e7" +checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c" dependencies = [ "getrandom", ] +[[package]] +name = "syn" +version = "2.0.98" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "36147f1a48ae0ec2b5b3bc5b537d267457555a10dc06f3dbc8cb11ba3006d3b1" +dependencies = [ + "proc-macro2", + "quote", + "unicode-ident", +] + +[[package]] +name = "unicode-ident" +version = "1.0.17" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "00e2473a93778eb0bad35909dff6a10d28e63f792f16ed15e404fca9d5eeedbe" + [[package]] name = "wasi" version = "0.11.0+wasi-snapshot-preview1" source = "registry+https://github.com/rust-lang/crates.io-index" checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423" + +[[package]] +name = "zerocopy" +version = "0.7.35" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "1b9b4fd18abc82b8136838da5d50bae7bdea537c574d8dc1a34ed098d6c166f0" +dependencies = [ + "byteorder", + "zerocopy-derive", +] + +[[package]] +name = "zerocopy-derive" +version = "0.7.35" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "fa4f8080344d4671fb4e831a13ad1e68092748387dfc4f55e356242fae12ce3e" +dependencies = [ + "proc-macro2", + "quote", + "syn", +] diff --git a/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.toml b/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/listing-02-03/Cargo.toml b/listings/ch02-guessing-game-tutorial/listing-02-03/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-03/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/listing-02-03/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs b/listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs index 1ba2d4d41f..0ae11e3d41 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs +++ b/listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs @@ -1,5 +1,6 @@ // ANCHOR: all use std::io; + // ANCHOR: ch07-04 use rand::Rng; diff --git a/listings/ch02-guessing-game-tutorial/listing-02-04/Cargo.toml b/listings/ch02-guessing-game-tutorial/listing-02-04/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-04/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/listing-02-04/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/listing-02-04/output.txt b/listings/ch02-guessing-game-tutorial/listing-02-04/output.txt index 3640c06946..ba310bad26 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-04/output.txt +++ b/listings/ch02-guessing-game-tutorial/listing-02-04/output.txt @@ -8,17 +8,17 @@ $ cargo build Compiling rand v0.8.5 Compiling guessing_game v0.1.0 (file:///projects/guessing_game) error[E0308]: mismatched types - --> src/main.rs:22:21 + --> src/main.rs:23:21 | -22 | match guess.cmp(&secret_number) { - | --- ^^^^^^^^^^^^^^ expected struct `String`, found integer +23 | match guess.cmp(&secret_number) { + | --- ^^^^^^^^^^^^^^ expected `&String`, found `&{integer}` | | - | arguments to this function are incorrect + | arguments to this method are incorrect | = note: expected reference `&String` found reference `&{integer}` -note: associated function defined here - --> /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/cmp.rs:783:8 +note: method defined here + --> /rustc/1159e78c4747b02ef996e55082b704c09b970588/library/core/src/cmp.rs:979:8 For more information about this error, try `rustc --explain E0308`. -error: could not compile `guessing_game` due to previous error +error: could not compile `guessing_game` (bin "guessing_game") due to 1 previous error diff --git a/listings/ch02-guessing-game-tutorial/listing-02-04/src/main.rs b/listings/ch02-guessing-game-tutorial/listing-02-04/src/main.rs index 6e58a76455..fae3c29c6f 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-04/src/main.rs +++ b/listings/ch02-guessing-game-tutorial/listing-02-04/src/main.rs @@ -1,8 +1,9 @@ // ANCHOR: here -use rand::Rng; use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { // --snip-- // ANCHOR_END: here diff --git a/listings/ch02-guessing-game-tutorial/listing-02-05/Cargo.toml b/listings/ch02-guessing-game-tutorial/listing-02-05/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-05/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/listing-02-05/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/listing-02-05/src/main.rs b/listings/ch02-guessing-game-tutorial/listing-02-05/src/main.rs index 12f497e181..0ca4853d49 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-05/src/main.rs +++ b/listings/ch02-guessing-game-tutorial/listing-02-05/src/main.rs @@ -1,7 +1,8 @@ -use rand::Rng; use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { println!("Guess the number!"); diff --git a/listings/ch02-guessing-game-tutorial/listing-02-06/Cargo.toml b/listings/ch02-guessing-game-tutorial/listing-02-06/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-06/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/listing-02-06/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/listing-02-06/src/main.rs b/listings/ch02-guessing-game-tutorial/listing-02-06/src/main.rs index 7fcbb99fbf..bd728b4dc2 100644 --- a/listings/ch02-guessing-game-tutorial/listing-02-06/src/main.rs +++ b/listings/ch02-guessing-game-tutorial/listing-02-06/src/main.rs @@ -1,7 +1,8 @@ -use rand::Rng; use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { println!("Guess the number!"); diff --git a/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.toml b/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.toml index 78c94fef95..53e7b397ea 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.toml @@ -1,8 +1,6 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" - -# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html +edition = "2024" [dependencies] diff --git a/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/output.txt b/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/output.txt index 2724c145d3..d3ca35ca75 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/output.txt +++ b/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 1.50s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s Running `target/debug/guessing_game` Hello, world! diff --git a/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/Cargo.toml b/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/Cargo.toml index 78c94fef95..122c1bd074 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/output.txt b/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/output.txt index 9517af95f0..417d4e3cb9 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/output.txt +++ b/listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/output.txt @@ -8,6 +8,10 @@ warning: unused `Result` that must be used | = note: this `Result` may be an `Err` variant, which should be handled = note: `#[warn(unused_must_use)]` on by default +help: use `let _ = ...` to ignore the resulting value + | +10 | let _ = io::stdin().read_line(&mut guess); + | +++++++ warning: `guessing_game` (bin "guessing_game") generated 1 warning - Finished dev [unoptimized + debuginfo] target(s) in 0.59s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.59s diff --git a/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/Cargo.toml b/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/src/main.rs b/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/src/main.rs index 7f076c592d..e4ec0c9af1 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/src/main.rs +++ b/listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/src/main.rs @@ -1,7 +1,8 @@ -use rand::Rng; use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { println!("Guess the number!"); diff --git a/listings/ch02-guessing-game-tutorial/no-listing-04-looping/Cargo.toml b/listings/ch02-guessing-game-tutorial/no-listing-04-looping/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-04-looping/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/no-listing-04-looping/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/no-listing-04-looping/src/main.rs b/listings/ch02-guessing-game-tutorial/no-listing-04-looping/src/main.rs index f97d1c58ce..934be44446 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-04-looping/src/main.rs +++ b/listings/ch02-guessing-game-tutorial/no-listing-04-looping/src/main.rs @@ -1,7 +1,8 @@ -use rand::Rng; use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { println!("Guess the number!"); diff --git a/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/Cargo.toml b/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/Cargo.toml +++ b/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/src/main.rs b/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/src/main.rs index def0a0e7ee..77cbc938e8 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/src/main.rs +++ b/listings/ch02-guessing-game-tutorial/no-listing-05-quitting/src/main.rs @@ -1,7 +1,8 @@ -use rand::Rng; use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { println!("Guess the number!"); diff --git a/listings/ch03-common-programming-concepts/listing-03-01/Cargo.toml b/listings/ch03-common-programming-concepts/listing-03-01/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/listing-03-01/Cargo.toml +++ b/listings/ch03-common-programming-concepts/listing-03-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/listing-03-02/Cargo.toml b/listings/ch03-common-programming-concepts/listing-03-02/Cargo.toml index 659645556b..b12fd9760a 100644 --- a/listings/ch03-common-programming-concepts/listing-03-02/Cargo.toml +++ b/listings/ch03-common-programming-concepts/listing-03-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "branches" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/listing-03-02/output.txt b/listings/ch03-common-programming-concepts/listing-03-02/output.txt index 3eb8d102a5..3b0deaec6c 100644 --- a/listings/ch03-common-programming-concepts/listing-03-02/output.txt +++ b/listings/ch03-common-programming-concepts/listing-03-02/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.30s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.30s Running `target/debug/branches` The value of number is: 5 diff --git a/listings/ch03-common-programming-concepts/listing-03-03/Cargo.toml b/listings/ch03-common-programming-concepts/listing-03-03/Cargo.toml index 810e8bbc0a..a046a76338 100644 --- a/listings/ch03-common-programming-concepts/listing-03-03/Cargo.toml +++ b/listings/ch03-common-programming-concepts/listing-03-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "loops" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/listing-03-04/Cargo.toml b/listings/ch03-common-programming-concepts/listing-03-04/Cargo.toml index 810e8bbc0a..a046a76338 100644 --- a/listings/ch03-common-programming-concepts/listing-03-04/Cargo.toml +++ b/listings/ch03-common-programming-concepts/listing-03-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "loops" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/listing-03-04/output.txt b/listings/ch03-common-programming-concepts/listing-03-04/output.txt index 35c0f804a7..82408ac823 100644 --- a/listings/ch03-common-programming-concepts/listing-03-04/output.txt +++ b/listings/ch03-common-programming-concepts/listing-03-04/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling loops v0.1.0 (file:///projects/loops) - Finished dev [unoptimized + debuginfo] target(s) in 0.32s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.32s Running `target/debug/loops` the value is: 10 the value is: 20 diff --git a/listings/ch03-common-programming-concepts/listing-03-05/Cargo.toml b/listings/ch03-common-programming-concepts/listing-03-05/Cargo.toml index 810e8bbc0a..a046a76338 100644 --- a/listings/ch03-common-programming-concepts/listing-03-05/Cargo.toml +++ b/listings/ch03-common-programming-concepts/listing-03-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "loops" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/Cargo.toml index 4da3b81504..c093eb645c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "variables" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/output.txt b/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/output.txt index ed87cb2c87..85efb431ea 100644 --- a/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/output.txt @@ -4,13 +4,15 @@ error[E0384]: cannot assign twice to immutable variable `x` --> src/main.rs:4:5 | 2 | let x = 5; - | - - | | - | first assignment to `x` - | help: consider making this binding mutable: `mut x` + | - first assignment to `x` 3 | println!("The value of x is: {x}"); 4 | x = 6; | ^^^^^ cannot assign twice to immutable variable + | +help: consider making this binding mutable + | +2 | let mut x = 5; + | +++ For more information about this error, try `rustc --explain E0384`. -error: could not compile `variables` due to previous error +error: could not compile `variables` (bin "variables") due to 1 previous error diff --git a/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/Cargo.toml index 4da3b81504..c093eb645c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "variables" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/output.txt b/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/output.txt index 8ed6598ff1..ed0c0c3429 100644 --- a/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-02-adding-mut/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling variables v0.1.0 (file:///projects/variables) - Finished dev [unoptimized + debuginfo] target(s) in 0.30s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.30s Running `target/debug/variables` The value of x is: 5 The value of x is: 6 diff --git a/listings/ch03-common-programming-concepts/no-listing-03-shadowing/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-03-shadowing/Cargo.toml index 4da3b81504..c093eb645c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-03-shadowing/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-03-shadowing/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "variables" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-03-shadowing/output.txt b/listings/ch03-common-programming-concepts/no-listing-03-shadowing/output.txt index f310e9ffa2..6ff531b559 100644 --- a/listings/ch03-common-programming-concepts/no-listing-03-shadowing/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-03-shadowing/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling variables v0.1.0 (file:///projects/variables) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/variables` The value of x in the inner scope is: 12 The value of x is: 6 diff --git a/listings/ch03-common-programming-concepts/no-listing-04-shadowing-can-change-types/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-04-shadowing-can-change-types/Cargo.toml index 4da3b81504..c093eb645c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-04-shadowing-can-change-types/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-04-shadowing-can-change-types/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "variables" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/Cargo.toml index 4da3b81504..c093eb645c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "variables" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/output.txt b/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/output.txt index 31a07efc4b..578a1f4aa5 100644 --- a/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/output.txt @@ -9,4 +9,4 @@ error[E0308]: mismatched types | ^^^^^^^^^^^^ expected `&str`, found `usize` For more information about this error, try `rustc --explain E0308`. -error: could not compile `variables` due to previous error +error: could not compile `variables` (bin "variables") due to 1 previous error diff --git a/listings/ch03-common-programming-concepts/no-listing-06-floating-point/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-06-floating-point/Cargo.toml index 83610e7561..c293ee0a55 100644 --- a/listings/ch03-common-programming-concepts/no-listing-06-floating-point/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-06-floating-point/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "floating-point" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-07-numeric-operations/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-07-numeric-operations/Cargo.toml index b4bea55e3d..98935b4c2d 100644 --- a/listings/ch03-common-programming-concepts/no-listing-07-numeric-operations/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-07-numeric-operations/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "numeric-operations" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-08-boolean/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-08-boolean/Cargo.toml index 47e42cef8a..4a6f21a0b7 100644 --- a/listings/ch03-common-programming-concepts/no-listing-08-boolean/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-08-boolean/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "boolean" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-09-char/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-09-char/Cargo.toml index a1ef3b537c..613f326767 100644 --- a/listings/ch03-common-programming-concepts/no-listing-09-char/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-09-char/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "char" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-10-tuples/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-10-tuples/Cargo.toml index 9b0879c2c6..29036e9a35 100644 --- a/listings/ch03-common-programming-concepts/no-listing-10-tuples/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-10-tuples/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "tuples" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-11-destructuring-tuples/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-11-destructuring-tuples/Cargo.toml index 9b0879c2c6..29036e9a35 100644 --- a/listings/ch03-common-programming-concepts/no-listing-11-destructuring-tuples/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-11-destructuring-tuples/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "tuples" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-12-tuple-indexing/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-12-tuple-indexing/Cargo.toml index 9b0879c2c6..29036e9a35 100644 --- a/listings/ch03-common-programming-concepts/no-listing-12-tuple-indexing/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-12-tuple-indexing/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "tuples" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-13-arrays/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-13-arrays/Cargo.toml index 96be3e2b17..564293c98f 100644 --- a/listings/ch03-common-programming-concepts/no-listing-13-arrays/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-13-arrays/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "arrays" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-14-array-indexing/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-14-array-indexing/Cargo.toml index 96be3e2b17..564293c98f 100644 --- a/listings/ch03-common-programming-concepts/no-listing-14-array-indexing/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-14-array-indexing/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "arrays" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-15-invalid-array-access/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-15-invalid-array-access/Cargo.toml index 96be3e2b17..564293c98f 100644 --- a/listings/ch03-common-programming-concepts/no-listing-15-invalid-array-access/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-15-invalid-array-access/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "arrays" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-16-functions/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-16-functions/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-16-functions/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-16-functions/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-16-functions/output.txt b/listings/ch03-common-programming-concepts/no-listing-16-functions/output.txt index 723fad32ad..898cf5fb63 100644 --- a/listings/ch03-common-programming-concepts/no-listing-16-functions/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-16-functions/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 0.28s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.28s Running `target/debug/functions` Hello, world! Another function. diff --git a/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/output.txt b/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/output.txt index 546bbc0473..377f72886c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 1.21s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.21s Running `target/debug/functions` The value of x is: 5 diff --git a/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/output.txt b/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/output.txt index 6210234c9e..91e71c174d 100644 --- a/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/functions` The measurement is: 5h diff --git a/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/output.txt b/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/output.txt index 6ae56e09dc..504fdd6ec7 100644 --- a/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/output.txt @@ -5,22 +5,8 @@ error: expected expression, found `let` statement | 2 | let x = (let y = 6); | ^^^ - -error: expected expression, found statement (`let`) - --> src/main.rs:2:14 - | -2 | let x = (let y = 6); - | ^^^^^^^^^ - | - = note: variable declaration using `let` is a statement - -error[E0658]: `let` expressions in this position are unstable - --> src/main.rs:2:14 - | -2 | let x = (let y = 6); - | ^^^^^^^^^ | - = note: see issue #53667 for more information + = note: only supported directly in conditions of `if` and `while` expressions warning: unnecessary parentheses around assigned value --> src/main.rs:2:13 @@ -35,6 +21,5 @@ help: remove these parentheses 2 + let x = let y = 6; | -For more information about this error, try `rustc --explain E0658`. warning: `functions` (bin "functions") generated 1 warning -error: could not compile `functions` due to 3 previous errors; 1 warning emitted +error: could not compile `functions` (bin "functions") due to 1 previous error; 1 warning emitted diff --git a/listings/ch03-common-programming-concepts/no-listing-20-blocks-are-expressions/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-20-blocks-are-expressions/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-20-blocks-are-expressions/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-20-blocks-are-expressions/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/output.txt b/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/output.txt index a457e33996..e66e4b980a 100644 --- a/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-21-function-return-values/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 0.30s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.30s Running `target/debug/functions` The value of x is: 5 diff --git a/listings/ch03-common-programming-concepts/no-listing-22-function-parameter-and-return/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-22-function-parameter-and-return/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-22-function-parameter-and-return/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-22-function-parameter-and-return/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/Cargo.toml index 478b346fd5..9c392ab08b 100644 --- a/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/output.txt b/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/output.txt index d27a7fae28..18fdfd1b41 100644 --- a/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/output.txt @@ -11,4 +11,4 @@ error[E0308]: mismatched types | - help: remove this semicolon to return this value For more information about this error, try `rustc --explain E0308`. -error: could not compile `functions` due to previous error +error: could not compile `functions` (bin "functions") due to 1 previous error diff --git a/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/Cargo.toml index e0576b5dce..e4bffc604c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "comments" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/src/main.rs b/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/src/main.rs index 535f4b993b..64b55dbbf8 100644 --- a/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/src/main.rs +++ b/listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/src/main.rs @@ -1,3 +1,3 @@ fn main() { - let lucky_number = 7; // I’m feeling lucky today + let lucky_number = 7; // I'm feeling lucky today } diff --git a/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/Cargo.toml index e0576b5dce..e4bffc604c 100644 --- a/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "comments" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/src/main.rs b/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/src/main.rs index 81cd935591..2d619c2bee 100644 --- a/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/src/main.rs +++ b/listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/src/main.rs @@ -1,4 +1,4 @@ fn main() { - // I’m feeling lucky today + // I'm feeling lucky today let lucky_number = 7; } diff --git a/listings/ch03-common-programming-concepts/no-listing-26-if-true/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-26-if-true/Cargo.toml index 659645556b..b12fd9760a 100644 --- a/listings/ch03-common-programming-concepts/no-listing-26-if-true/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-26-if-true/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "branches" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-26-if-true/output.txt b/listings/ch03-common-programming-concepts/no-listing-26-if-true/output.txt index 3d8c7dc333..d39b3b5fcb 100644 --- a/listings/ch03-common-programming-concepts/no-listing-26-if-true/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-26-if-true/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/branches` condition was true diff --git a/listings/ch03-common-programming-concepts/no-listing-27-if-false/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-27-if-false/Cargo.toml index 659645556b..b12fd9760a 100644 --- a/listings/ch03-common-programming-concepts/no-listing-27-if-false/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-27-if-false/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "branches" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-27-if-false/output.txt b/listings/ch03-common-programming-concepts/no-listing-27-if-false/output.txt index e40da961c9..3aa1e1c054 100644 --- a/listings/ch03-common-programming-concepts/no-listing-27-if-false/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-27-if-false/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/branches` condition was false diff --git a/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/Cargo.toml index 659645556b..b12fd9760a 100644 --- a/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "branches" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/output.txt b/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/output.txt index 735bfe758e..c9c0b0c469 100644 --- a/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/output.txt @@ -7,4 +7,4 @@ error[E0308]: mismatched types | ^^^^^^ expected `bool`, found integer For more information about this error, try `rustc --explain E0308`. -error: could not compile `branches` due to previous error +error: could not compile `branches` (bin "branches") due to 1 previous error diff --git a/listings/ch03-common-programming-concepts/no-listing-29-if-not-equal-0/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-29-if-not-equal-0/Cargo.toml index 659645556b..b12fd9760a 100644 --- a/listings/ch03-common-programming-concepts/no-listing-29-if-not-equal-0/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-29-if-not-equal-0/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "branches" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-30-else-if/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-30-else-if/Cargo.toml index 659645556b..b12fd9760a 100644 --- a/listings/ch03-common-programming-concepts/no-listing-30-else-if/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-30-else-if/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "branches" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-30-else-if/output.txt b/listings/ch03-common-programming-concepts/no-listing-30-else-if/output.txt index b218941ad0..d5195248a9 100644 --- a/listings/ch03-common-programming-concepts/no-listing-30-else-if/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-30-else-if/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/branches` number is divisible by 3 diff --git a/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/Cargo.toml index 659645556b..b12fd9760a 100644 --- a/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "branches" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/output.txt b/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/output.txt index e922acd29c..7fb857f035 100644 --- a/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/output.txt @@ -9,4 +9,4 @@ error[E0308]: `if` and `else` have incompatible types | expected because of this For more information about this error, try `rustc --explain E0308`. -error: could not compile `branches` due to previous error +error: could not compile `branches` (bin "branches") due to 1 previous error diff --git a/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/Cargo.toml index 810e8bbc0a..a046a76338 100644 --- a/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "loops" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt b/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt index d4d322fb49..4977b2b34d 100644 --- a/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt +++ b/listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling loops v0.1.0 (file:///projects/loops) - Finished dev [unoptimized + debuginfo] target(s) in 0.58s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.58s Running `target/debug/loops` count = 0 remaining = 10 diff --git a/listings/ch03-common-programming-concepts/no-listing-32-loop/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-32-loop/Cargo.toml index 810e8bbc0a..a046a76338 100644 --- a/listings/ch03-common-programming-concepts/no-listing-32-loop/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-32-loop/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "loops" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-33-return-value-from-loop/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-33-return-value-from-loop/Cargo.toml index 810e8bbc0a..a046a76338 100644 --- a/listings/ch03-common-programming-concepts/no-listing-33-return-value-from-loop/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-33-return-value-from-loop/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "loops" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/no-listing-34-for-range/Cargo.toml b/listings/ch03-common-programming-concepts/no-listing-34-for-range/Cargo.toml index 810e8bbc0a..a046a76338 100644 --- a/listings/ch03-common-programming-concepts/no-listing-34-for-range/Cargo.toml +++ b/listings/ch03-common-programming-concepts/no-listing-34-for-range/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "loops" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/Cargo.toml b/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/Cargo.toml index 8ad4d5aa6b..05020d2765 100644 --- a/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/Cargo.toml +++ b/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "no_type_annotations" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/output.txt b/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/output.txt index 8a11cccd51..ee6a979432 100644 --- a/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/output.txt +++ b/listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/output.txt @@ -1,15 +1,16 @@ $ cargo build Compiling no_type_annotations v0.1.0 (file:///projects/no_type_annotations) -error[E0282]: type annotations needed +error[E0284]: type annotations needed --> src/main.rs:2:9 | 2 | let guess = "42".parse().expect("Not a number!"); - | ^^^^^ + | ^^^^^ ----- type must be known at this point | + = note: cannot satisfy `<_ as FromStr>::Err == _` help: consider giving `guess` an explicit type | -2 | let guess: _ = "42".parse().expect("Not a number!"); - | +++ +2 | let guess: /* Type */ = "42".parse().expect("Not a number!"); + | ++++++++++++ -For more information about this error, try `rustc --explain E0282`. -error: could not compile `no_type_annotations` due to previous error +For more information about this error, try `rustc --explain E0284`. +error: could not compile `no_type_annotations` (bin "no_type_annotations") due to 1 previous error diff --git a/listings/ch04-understanding-ownership/listing-04-01/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-01/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-01/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-01/src/main.rs b/listings/ch04-understanding-ownership/listing-04-01/src/main.rs index 148ad84c97..698137f463 100644 --- a/listings/ch04-understanding-ownership/listing-04-01/src/main.rs +++ b/listings/ch04-understanding-ownership/listing-04-01/src/main.rs @@ -1,9 +1,9 @@ fn main() { // ANCHOR: here - { // s is not valid here, it’s not yet declared + { // s is not valid here, since it's not yet declared let s = "hello"; // s is valid from this point forward // do stuff with s } // this scope is now over, and s is no longer valid // ANCHOR_END: here -} \ No newline at end of file +} diff --git a/listings/ch04-understanding-ownership/listing-04-02/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-02/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-02/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-03/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-03/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-03/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-03/src/main.rs b/listings/ch04-understanding-ownership/listing-04-03/src/main.rs index b001cc5f4a..b2524c90da 100644 --- a/listings/ch04-understanding-ownership/listing-04-03/src/main.rs +++ b/listings/ch04-understanding-ownership/listing-04-03/src/main.rs @@ -6,18 +6,18 @@ fn main() { let x = 5; // x comes into scope - makes_copy(x); // x would move into the function, - // but i32 is Copy, so it's okay to still - // use x afterward + makes_copy(x); // Because i32 implements the Copy trait, + // x does NOT move into the function, + // so it's okay to use x afterward. -} // Here, x goes out of scope, then s. But because s's value was moved, nothing - // special happens. +} // Here, x goes out of scope, then s. However, because s's value was moved, + // nothing special happens. fn takes_ownership(some_string: String) { // some_string comes into scope - println!("{}", some_string); + println!("{some_string}"); } // Here, some_string goes out of scope and `drop` is called. The backing // memory is freed. fn makes_copy(some_integer: i32) { // some_integer comes into scope - println!("{}", some_integer); + println!("{some_integer}"); } // Here, some_integer goes out of scope. Nothing special happens. diff --git a/listings/ch04-understanding-ownership/listing-04-04/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-04/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-04/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-04/src/main.rs b/listings/ch04-understanding-ownership/listing-04-04/src/main.rs index e206bec7a8..c18dc5bc90 100644 --- a/listings/ch04-understanding-ownership/listing-04-04/src/main.rs +++ b/listings/ch04-understanding-ownership/listing-04-04/src/main.rs @@ -1,29 +1,30 @@ fn main() { - let s1 = gives_ownership(); // gives_ownership moves its return - // value into s1 + let s1 = gives_ownership(); // gives_ownership moves its return + // value into s1 - let s2 = String::from("hello"); // s2 comes into scope + let s2 = String::from("hello"); // s2 comes into scope - let s3 = takes_and_gives_back(s2); // s2 is moved into - // takes_and_gives_back, which also - // moves its return value into s3 + let s3 = takes_and_gives_back(s2); // s2 is moved into + // takes_and_gives_back, which also + // moves its return value into s3 } // Here, s3 goes out of scope and is dropped. s2 was moved, so nothing // happens. s1 goes out of scope and is dropped. -fn gives_ownership() -> String { // gives_ownership will move its - // return value into the function - // that calls it +fn gives_ownership() -> String { // gives_ownership will move its + // return value into the function + // that calls it let some_string = String::from("yours"); // some_string comes into scope - some_string // some_string is returned and - // moves out to the calling - // function + some_string // some_string is returned and + // moves out to the calling + // function } -// This function takes a String and returns one -fn takes_and_gives_back(a_string: String) -> String { // a_string comes into - // scope +// This function takes a String and returns a String. +fn takes_and_gives_back(a_string: String) -> String { + // a_string comes into + // scope a_string // a_string is returned and moves out to the calling function } diff --git a/listings/ch04-understanding-ownership/listing-04-05/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-05/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-05/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-05/src/main.rs b/listings/ch04-understanding-ownership/listing-04-05/src/main.rs index 22aee1419e..2782483a77 100644 --- a/listings/ch04-understanding-ownership/listing-04-05/src/main.rs +++ b/listings/ch04-understanding-ownership/listing-04-05/src/main.rs @@ -3,7 +3,7 @@ fn main() { let (s2, len) = calculate_length(s1); - println!("The length of '{}' is {}.", s2, len); + println!("The length of '{s2}' is {len}."); } fn calculate_length(s: String) -> (String, usize) { diff --git a/listings/ch04-understanding-ownership/listing-04-06/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-06/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-06/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-06/output.txt b/listings/ch04-understanding-ownership/listing-04-06/output.txt index 1176f4e3ac..c78cd5d3de 100644 --- a/listings/ch04-understanding-ownership/listing-04-06/output.txt +++ b/listings/ch04-understanding-ownership/listing-04-06/output.txt @@ -3,10 +3,13 @@ $ cargo run error[E0596]: cannot borrow `*some_string` as mutable, as it is behind a `&` reference --> src/main.rs:8:5 | -7 | fn change(some_string: &String) { - | ------- help: consider changing this to be a mutable reference: `&mut String` 8 | some_string.push_str(", world"); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `some_string` is a `&` reference, so the data it refers to cannot be borrowed as mutable + | ^^^^^^^^^^^ `some_string` is a `&` reference, so the data it refers to cannot be borrowed as mutable + | +help: consider changing this to be a mutable reference + | +7 | fn change(some_string: &mut String) { + | +++ For more information about this error, try `rustc --explain E0596`. -error: could not compile `ownership` due to previous error +error: could not compile `ownership` (bin "ownership") due to 1 previous error diff --git a/listings/ch04-understanding-ownership/listing-04-07/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-07/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-07/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-08/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-08/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-08/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-08/src/main.rs b/listings/ch04-understanding-ownership/listing-04-08/src/main.rs index b6182fe2b7..c7b0d1354a 100644 --- a/listings/ch04-understanding-ownership/listing-04-08/src/main.rs +++ b/listings/ch04-understanding-ownership/listing-04-08/src/main.rs @@ -18,7 +18,7 @@ fn main() { s.clear(); // this empties the String, making it equal to "" - // word still has the value 5 here, but there's no more string that - // we could meaningfully use the value 5 with. word is now totally invalid! + // word still has the value 5 here, but s no longer has any content that we + // could meaningfully use with the value 5, so word is now totally invalid! } // ANCHOR_END: here diff --git a/listings/ch04-understanding-ownership/listing-04-09/Cargo.toml b/listings/ch04-understanding-ownership/listing-04-09/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/listing-04-09/Cargo.toml +++ b/listings/ch04-understanding-ownership/listing-04-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/listing-04-09/src/main.rs b/listings/ch04-understanding-ownership/listing-04-09/src/main.rs index 5a6ceaa1e4..161b388544 100644 --- a/listings/ch04-understanding-ownership/listing-04-09/src/main.rs +++ b/listings/ch04-understanding-ownership/listing-04-09/src/main.rs @@ -16,16 +16,17 @@ fn first_word(s: &str) -> &str { fn main() { let my_string = String::from("hello world"); - // `first_word` works on slices of `String`s, whether partial or whole + // `first_word` works on slices of `String`s, whether partial or whole. let word = first_word(&my_string[0..6]); let word = first_word(&my_string[..]); // `first_word` also works on references to `String`s, which are equivalent - // to whole slices of `String`s + // to whole slices of `String`s. let word = first_word(&my_string); let my_string_literal = "hello world"; - // `first_word` works on slices of string literals, whether partial or whole + // `first_word` works on slices of string literals, whether partial or + // whole. let word = first_word(&my_string_literal[0..6]); let word = first_word(&my_string_literal[..]); diff --git a/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/src/main.rs b/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/src/main.rs index b68f0f1e78..e4edd1a5d9 100644 --- a/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/src/main.rs @@ -4,6 +4,6 @@ fn main() { s.push_str(", world!"); // push_str() appends a literal to a String - println!("{}", s); // This will print `hello, world!` - // ANCHOR_END: here + println!("{s}"); // this will print `hello, world!` + // ANCHOR_END: here } diff --git a/listings/ch04-understanding-ownership/no-listing-02-string-scope/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-02-string-scope/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-02-string-scope/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-02-string-scope/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-03-string-move/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-03-string-move/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-03-string-move/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-03-string-move/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/output.txt b/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/output.txt index 4a53567018..a7c555dc48 100644 --- a/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/output.txt +++ b/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/output.txt @@ -1,15 +1,15 @@ $ cargo run Compiling ownership v0.1.0 (file:///projects/ownership) error[E0382]: borrow of moved value: `s1` - --> src/main.rs:5:28 + --> src/main.rs:5:16 | 2 | let s1 = String::from("hello"); | -- move occurs because `s1` has type `String`, which does not implement the `Copy` trait 3 | let s2 = s1; | -- value moved here 4 | -5 | println!("{}, world!", s1); - | ^^ value borrowed here after move +5 | println!("{s1}, world!"); + | ^^ value borrowed here after move | = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) help: consider cloning the value if the performance cost is acceptable @@ -18,4 +18,4 @@ help: consider cloning the value if the performance cost is acceptable | ++++++++ For more information about this error, try `rustc --explain E0382`. -error: could not compile `ownership` due to previous error +error: could not compile `ownership` (bin "ownership") due to 1 previous error diff --git a/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/src/main.rs b/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/src/main.rs index d0b9f18795..e35f6d8034 100644 --- a/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/src/main.rs @@ -3,6 +3,6 @@ fn main() { let s1 = String::from("hello"); let s2 = s1; - println!("{}, world!", s1); + println!("{s1}, world!"); // ANCHOR_END: here } diff --git a/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.lock b/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/Cargo.lock similarity index 77% rename from listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.lock rename to listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/Cargo.lock index ee5d79095f..2aa4918e5d 100644 --- a/listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.lock +++ b/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/Cargo.lock @@ -1,7 +1,6 @@ # This file is automatically @generated by Cargo. # It is not intended for manual editing. -version = 3 - [[package]] -name = "guessing_game" +name = "ownership" version = "0.1.0" + diff --git a/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/Cargo.toml new file mode 100644 index 0000000000..a4b0049f1d --- /dev/null +++ b/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "ownership" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/src/main.rs b/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/src/main.rs new file mode 100644 index 0000000000..b2d0846c11 --- /dev/null +++ b/listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/src/main.rs @@ -0,0 +1,8 @@ +fn main() { + // ANCHOR: here + let mut s = String::from("hello"); + s = String::from("ahoy"); + + println!("{s}, world!"); + // ANCHOR_END: here +} diff --git a/listings/ch04-understanding-ownership/no-listing-05-clone/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-05-clone/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-05-clone/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-05-clone/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-05-clone/src/main.rs b/listings/ch04-understanding-ownership/no-listing-05-clone/src/main.rs index 4e61cc1a16..0b65e5f611 100644 --- a/listings/ch04-understanding-ownership/no-listing-05-clone/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-05-clone/src/main.rs @@ -3,6 +3,6 @@ fn main() { let s1 = String::from("hello"); let s2 = s1.clone(); - println!("s1 = {}, s2 = {}", s1, s2); + println!("s1 = {s1}, s2 = {s2}"); // ANCHOR_END: here } diff --git a/listings/ch04-understanding-ownership/no-listing-06-copy/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-06-copy/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-06-copy/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-06-copy/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-06-copy/src/main.rs b/listings/ch04-understanding-ownership/no-listing-06-copy/src/main.rs index 63a1fae248..b6fd2445d0 100644 --- a/listings/ch04-understanding-ownership/no-listing-06-copy/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-06-copy/src/main.rs @@ -3,6 +3,6 @@ fn main() { let x = 5; let y = x; - println!("x = {}, y = {}", x, y); + println!("x = {x}, y = {y}"); // ANCHOR_END: here } diff --git a/listings/ch04-understanding-ownership/no-listing-07-reference/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-07-reference/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-07-reference/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-07-reference/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs b/listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs index fd32a5fc95..6f6d5fb239 100644 --- a/listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs @@ -6,7 +6,7 @@ fn main() { let len = calculate_length(&s1); // ANCHOR_END: here - println!("The length of '{}' is {}.", s1, len); + println!("The length of '{s1}' is {len}."); } fn calculate_length(s: &String) -> usize { diff --git a/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/src/main.rs b/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/src/main.rs index 6686a801c0..326b66e90a 100644 --- a/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/src/main.rs @@ -3,12 +3,12 @@ fn main() { let len = calculate_length(&s1); - println!("The length of '{}' is {}.", s1, len); + println!("The length of '{s1}' is {len}."); } // ANCHOR: here fn calculate_length(s: &String) -> usize { // s is a reference to a String s.len() -} // Here, s goes out of scope. But because it does not have ownership of what - // it refers to, it is not dropped. +} // Here, s goes out of scope. But because s does not have ownership of what + // it refers to, the String is not dropped. // ANCHOR_END: here diff --git a/listings/ch04-understanding-ownership/no-listing-09-fixes-listing-04-06/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-09-fixes-listing-04-06/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-09-fixes-listing-04-06/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-09-fixes-listing-04-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/output.txt b/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/output.txt index 8820d2d695..afb412bd4e 100644 --- a/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/output.txt +++ b/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/output.txt @@ -8,8 +8,8 @@ error[E0499]: cannot borrow `s` as mutable more than once at a time 5 | let r2 = &mut s; | ^^^^^^ second mutable borrow occurs here 6 | -7 | println!("{}, {}", r1, r2); - | -- first borrow later used here +7 | println!("{r1}, {r2}"); + | -- first borrow later used here For more information about this error, try `rustc --explain E0499`. -error: could not compile `ownership` due to previous error +error: could not compile `ownership` (bin "ownership") due to 1 previous error diff --git a/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/src/main.rs b/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/src/main.rs index ddbf8120f9..8fe3a567d4 100644 --- a/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/src/main.rs @@ -5,6 +5,6 @@ fn main() { let r1 = &mut s; let r2 = &mut s; - println!("{}, {}", r1, r2); + println!("{r1}, {r2}"); // ANCHOR_END: here } diff --git a/listings/ch04-understanding-ownership/no-listing-11-muts-in-separate-scopes/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-11-muts-in-separate-scopes/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-11-muts-in-separate-scopes/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-11-muts-in-separate-scopes/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/output.txt b/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/output.txt index d1e9db2c4b..151a8233e2 100644 --- a/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/output.txt +++ b/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/output.txt @@ -9,8 +9,8 @@ error[E0502]: cannot borrow `s` as mutable because it is also borrowed as immuta 6 | let r3 = &mut s; // BIG PROBLEM | ^^^^^^ mutable borrow occurs here 7 | -8 | println!("{}, {}, and {}", r1, r2, r3); - | -- immutable borrow later used here +8 | println!("{r1}, {r2}, and {r3}"); + | -- immutable borrow later used here For more information about this error, try `rustc --explain E0502`. -error: could not compile `ownership` due to previous error +error: could not compile `ownership` (bin "ownership") due to 1 previous error diff --git a/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/src/main.rs b/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/src/main.rs index 0da04c010e..f00df72d36 100644 --- a/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/src/main.rs @@ -6,6 +6,6 @@ fn main() { let r2 = &s; // no problem let r3 = &mut s; // BIG PROBLEM - println!("{}, {}, and {}", r1, r2, r3); + println!("{r1}, {r2}, and {r3}"); // ANCHOR_END: here } diff --git a/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/src/main.rs b/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/src/main.rs index 8619449669..3034e12de4 100644 --- a/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/src/main.rs @@ -4,10 +4,10 @@ fn main() { let r1 = &s; // no problem let r2 = &s; // no problem - println!("{} and {}", r1, r2); - // variables r1 and r2 will not be used after this point + println!("{r1} and {r2}"); + // Variables r1 and r2 will not be used after this point. let r3 = &mut s; // no problem - println!("{}", r3); + println!("{r3}"); // ANCHOR_END: here } diff --git a/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/output.txt b/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/output.txt index b466a3dce5..70e58af8b5 100644 --- a/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/output.txt +++ b/listings/ch04-understanding-ownership/no-listing-14-dangling-reference/output.txt @@ -7,10 +7,15 @@ error[E0106]: missing lifetime specifier | ^ expected named lifetime parameter | = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from -help: consider using the `'static` lifetime +help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static` | 5 | fn dangle() -> &'static String { | +++++++ +help: instead, you are more likely to want to return an owned value + | +5 - fn dangle() -> &String { +5 + fn dangle() -> String { + | For more information about this error, try `rustc --explain E0106`. -error: could not compile `ownership` due to previous error +error: could not compile `ownership` (bin "ownership") due to 1 previous error diff --git a/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/src/main.rs b/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/src/main.rs index 9fbb372a05..119c99fab7 100644 --- a/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/src/main.rs @@ -8,6 +8,6 @@ fn dangle() -> &String { // dangle returns a reference to a String let s = String::from("hello"); // s is a new String &s // we return a reference to the String, s -} // Here, s goes out of scope, and is dropped. Its memory goes away. +} // Here, s goes out of scope and is dropped, so its memory goes away. // Danger! -// ANCHOR_END: here + // ANCHOR_END: here diff --git a/listings/ch04-understanding-ownership/no-listing-16-no-dangle/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-16-no-dangle/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-16-no-dangle/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-16-no-dangle/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-17-slice/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-17-slice/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-17-slice/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-17-slice/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-18-first-word-slice/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-18-first-word-slice/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-18-first-word-slice/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-18-first-word-slice/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-19-slice-error/Cargo.toml b/listings/ch04-understanding-ownership/no-listing-19-slice-error/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch04-understanding-ownership/no-listing-19-slice-error/Cargo.toml +++ b/listings/ch04-understanding-ownership/no-listing-19-slice-error/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch04-understanding-ownership/no-listing-19-slice-error/output.txt b/listings/ch04-understanding-ownership/no-listing-19-slice-error/output.txt index ab0c41f4df..1bdc0e9d6c 100644 --- a/listings/ch04-understanding-ownership/no-listing-19-slice-error/output.txt +++ b/listings/ch04-understanding-ownership/no-listing-19-slice-error/output.txt @@ -9,8 +9,8 @@ error[E0502]: cannot borrow `s` as mutable because it is also borrowed as immuta 18 | s.clear(); // error! | ^^^^^^^^^ mutable borrow occurs here 19 | -20 | println!("the first word is: {}", word); - | ---- immutable borrow later used here +20 | println!("the first word is: {word}"); + | ---- immutable borrow later used here For more information about this error, try `rustc --explain E0502`. -error: could not compile `ownership` due to previous error +error: could not compile `ownership` (bin "ownership") due to 1 previous error diff --git a/listings/ch04-understanding-ownership/no-listing-19-slice-error/src/main.rs b/listings/ch04-understanding-ownership/no-listing-19-slice-error/src/main.rs index 99e04018d2..b23e45f435 100644 --- a/listings/ch04-understanding-ownership/no-listing-19-slice-error/src/main.rs +++ b/listings/ch04-understanding-ownership/no-listing-19-slice-error/src/main.rs @@ -18,6 +18,6 @@ fn main() { s.clear(); // error! - println!("the first word is: {}", word); + println!("the first word is: {word}"); } // ANCHOR_END: here diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-01/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-01/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-01/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-02/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-02/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-02/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-03/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-03/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-03/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-04/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-04/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-04/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-05/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-05/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-05/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-06/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-06/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-06/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-07/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-07/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-07/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-08/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-08/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-08/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-08/output.txt b/listings/ch05-using-structs-to-structure-related-data/listing-05-08/output.txt index c44b58238d..79b8307772 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-08/output.txt +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-08/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling rectangles v0.1.0 (file:///projects/rectangles) - Finished dev [unoptimized + debuginfo] target(s) in 0.42s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.42s Running `target/debug/rectangles` The area of the rectangle is 1500 square pixels. diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-09/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-09/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-09/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-10/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-10/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-10/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-11/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-11/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-11/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-11/output.txt b/listings/ch05-using-structs-to-structure-related-data/listing-05-11/output.txt index 7d3bfcdac4..4e50153bd0 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-11/output.txt +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-11/output.txt @@ -1,14 +1,17 @@ $ cargo run Compiling rectangles v0.1.0 (file:///projects/rectangles) error[E0277]: `Rectangle` doesn't implement `std::fmt::Display` - --> src/main.rs:12:29 + --> src/main.rs:12:25 | -12 | println!("rect1 is {}", rect1); - | ^^^^^ `Rectangle` cannot be formatted with the default formatter +12 | println!("rect1 is {rect1}"); + | -^^^^^- + | || + | |`Rectangle` cannot be formatted with the default formatter + | required by this formatting parameter | = help: the trait `std::fmt::Display` is not implemented for `Rectangle` = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) For more information about this error, try `rustc --explain E0277`. -error: could not compile `rectangles` due to previous error +error: could not compile `rectangles` (bin "rectangles") due to 1 previous error diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-11/src/main.rs b/listings/ch05-using-structs-to-structure-related-data/listing-05-11/src/main.rs index 0ff8dcc8cc..07659f1920 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-11/src/main.rs +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-11/src/main.rs @@ -9,5 +9,5 @@ fn main() { height: 50, }; - println!("rect1 is {}", rect1); + println!("rect1 is {rect1}"); } diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-12/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-12/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-12/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-12/output.txt b/listings/ch05-using-structs-to-structure-related-data/listing-05-12/output.txt index c37be6b5bf..0c810b1f44 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-12/output.txt +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-12/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling rectangles v0.1.0 (file:///projects/rectangles) - Finished dev [unoptimized + debuginfo] target(s) in 0.48s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s Running `target/debug/rectangles` rect1 is Rectangle { width: 30, height: 50 } diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-12/src/main.rs b/listings/ch05-using-structs-to-structure-related-data/listing-05-12/src/main.rs index 2ffc4b8e7b..67e0b92a47 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-12/src/main.rs +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-12/src/main.rs @@ -10,5 +10,5 @@ fn main() { height: 50, }; - println!("rect1 is {:?}", rect1); + println!("rect1 is {rect1:?}"); } diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-13/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-13/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-13/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-14/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-14/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-14/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-15/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-15/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-15/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/listing-05-16/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/listing-05-16/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/listing-05-16/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/listing-05-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-01-tuple-structs/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/no-listing-01-tuple-structs/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-01-tuple-structs/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-01-tuple-structs/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/Cargo.toml index d36dbc1d34..748f9d6dfc 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/output.txt b/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/output.txt index e28da599c7..5f9344c512 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/output.txt +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-02-reference-in-struct/output.txt @@ -28,4 +28,4 @@ help: consider introducing a named lifetime parameter | For more information about this error, try `rustc --explain E0106`. -error: could not compile `structs` due to 2 previous errors +error: could not compile `structs` (bin "structs") due to 2 previous errors diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-03-associated-functions/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/no-listing-03-associated-functions/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-03-associated-functions/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-03-associated-functions/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-04-unit-like-structs/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/no-listing-04-unit-like-structs/Cargo.toml index 3232b60653..7251aaa8de 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-04-unit-like-structs/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-04-unit-like-structs/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "structs" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/output.txt b/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/output.txt index 2685859954..1c1f07dfbc 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/output.txt +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/output.txt @@ -1,9 +1,9 @@ $ cargo run Compiling rectangles v0.1.0 (file:///projects/rectangles) - Finished dev [unoptimized + debuginfo] target(s) in 0.61s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.61s Running `target/debug/rectangles` -[src/main.rs:10] 30 * scale = 60 -[src/main.rs:14] &rect1 = Rectangle { +[src/main.rs:10:16] 30 * scale = 60 +[src/main.rs:14:5] &rect1 = Rectangle { width: 60, height: 50, } diff --git a/listings/ch05-using-structs-to-structure-related-data/no-listing-06-method-field-interaction/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/no-listing-06-method-field-interaction/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/no-listing-06-method-field-interaction/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/no-listing-06-method-field-interaction/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/output.txt b/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/output.txt index 58cb842bfa..25e0661fb3 100644 --- a/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/output.txt +++ b/listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/output.txt @@ -4,15 +4,18 @@ error[E0277]: `Rectangle` doesn't implement `Debug` --> src/main.rs:12:31 | 12 | println!("rect1 is {:?}", rect1); - | ^^^^^ `Rectangle` cannot be formatted using `{:?}` + | ---- ^^^^^ `Rectangle` cannot be formatted using `{:?}` because it doesn't implement `Debug` + | | + | required by this formatting parameter | = help: the trait `Debug` is not implemented for `Rectangle` = note: add `#[derive(Debug)]` to `Rectangle` or manually `impl Debug for Rectangle` = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) help: consider annotating `Rectangle` with `#[derive(Debug)]` | -1 | #[derive(Debug)] + 1 + #[derive(Debug)] + 2 | struct Rectangle { | For more information about this error, try `rustc --explain E0277`. -error: could not compile `rectangles` due to previous error +error: could not compile `rectangles` (bin "rectangles") due to 1 previous error diff --git a/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/Cargo.toml b/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/Cargo.toml +++ b/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/output.txt b/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/output.txt index db6deed9b7..4a6c5a9a14 100644 --- a/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/output.txt +++ b/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling rectangles v0.1.0 (file:///projects/rectangles) - Finished dev [unoptimized + debuginfo] target(s) in 0.48s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s Running `target/debug/rectangles` rect1 is Rectangle { width: 30, diff --git a/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/src/main.rs b/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/src/main.rs index 84e32aee49..f763b50d3b 100644 --- a/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/src/main.rs +++ b/listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/src/main.rs @@ -10,5 +10,5 @@ fn main() { height: 50, }; - println!("rect1 is {:#?}", rect1); + println!("rect1 is {rect1:#?}"); } diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-01/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-01/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/listing-06-01/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/listing-06-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-02/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-02/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/listing-06-02/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/listing-06-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-03/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-03/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/listing-06-03/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/listing-06-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-04/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-04/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/listing-06-04/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/listing-06-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-05/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-05/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/listing-06-05/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/listing-06-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-06/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-06/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/listing-06-06/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/listing-06-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-06/src/main.rs b/listings/ch06-enums-and-pattern-matching/listing-06-06/src/main.rs index dc2bffb911..0a037517ab 100644 --- a/listings/ch06-enums-and-pattern-matching/listing-06-06/src/main.rs +++ b/listings/ch06-enums-and-pattern-matching/listing-06-06/src/main.rs @@ -2,7 +2,7 @@ fn main() { // ANCHOR: here let config_max = Some(3u8); match config_max { - Some(max) => println!("The maximum is configured to be {}", max), + Some(max) => println!("The maximum is configured to be {max}"), _ => (), } // ANCHOR_END: here diff --git a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/Cargo.lock b/listings/ch06-enums-and-pattern-matching/listing-06-07/Cargo.lock similarity index 89% rename from listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/Cargo.lock rename to listings/ch06-enums-and-pattern-matching/listing-06-07/Cargo.lock index d37189b337..f62e8ac453 100644 --- a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/Cargo.lock +++ b/listings/ch06-enums-and-pattern-matching/listing-06-07/Cargo.lock @@ -1,6 +1,6 @@ # This file is automatically @generated by Cargo. # It is not intended for manual editing. [[package]] -name = "adder" +name = "enums" version = "0.1.0" diff --git a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/adder/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-07/Cargo.toml similarity index 57% rename from listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/adder/Cargo.toml rename to listings/ch06-enums-and-pattern-matching/listing-06-07/Cargo.toml index e61cb12e3e..d4e6b38af1 100644 --- a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/adder/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/listing-06-07/Cargo.toml @@ -1,6 +1,6 @@ [package] -name = "adder" +name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-07/src/main.rs b/listings/ch06-enums-and-pattern-matching/listing-06-07/src/main.rs new file mode 100644 index 0000000000..af7ec51179 --- /dev/null +++ b/listings/ch06-enums-and-pattern-matching/listing-06-07/src/main.rs @@ -0,0 +1,45 @@ +#[derive(Debug)] // so we can inspect the state in a minute +enum UsState { + Alabama, + Alaska, + // --snip-- +} + +// ANCHOR: state +impl UsState { + fn existed_in(&self, year: u16) -> bool { + match self { + UsState::Alabama => year >= 1819, + UsState::Alaska => year >= 1959, + // -- snip -- + } + } +} +// ANCHOR_END: state + +enum Coin { + Penny, + Nickel, + Dime, + Quarter(UsState), +} + +// ANCHOR: describe +fn describe_state_quarter(coin: Coin) -> Option { + if let Coin::Quarter(state) = coin { + if state.existed_in(1900) { + Some(format!("{state:?} is pretty old, for America!")) + } else { + Some(format!("{state:?} is relatively new.")) + } + } else { + None + } +} +// ANCHOR_END: describe + +fn main() { + if let Some(desc) = describe_state_quarter(Coin::Quarter(UsState::Alaska)) { + println!("{desc}"); + } +} diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-08/Cargo.lock b/listings/ch06-enums-and-pattern-matching/listing-06-08/Cargo.lock new file mode 100644 index 0000000000..f62e8ac453 --- /dev/null +++ b/listings/ch06-enums-and-pattern-matching/listing-06-08/Cargo.lock @@ -0,0 +1,6 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +[[package]] +name = "enums" +version = "0.1.0" + diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-08/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-08/Cargo.toml new file mode 100644 index 0000000000..d4e6b38af1 --- /dev/null +++ b/listings/ch06-enums-and-pattern-matching/listing-06-08/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "enums" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-08/src/main.rs b/listings/ch06-enums-and-pattern-matching/listing-06-08/src/main.rs new file mode 100644 index 0000000000..cde9f043d6 --- /dev/null +++ b/listings/ch06-enums-and-pattern-matching/listing-06-08/src/main.rs @@ -0,0 +1,45 @@ +#[derive(Debug)] // so we can inspect the state in a minute +enum UsState { + Alabama, + Alaska, + // --snip-- +} + +impl UsState { + fn existed_in(&self, year: u16) -> bool { + match self { + UsState::Alabama => year >= 1819, + UsState::Alaska => year >= 1959, + // -- snip -- + } + } +} + +enum Coin { + Penny, + Nickel, + Dime, + Quarter(UsState), +} + +// ANCHOR: describe +fn describe_state_quarter(coin: Coin) -> Option { + let state = if let Coin::Quarter(state) = coin { + state + } else { + return None; + }; + + if state.existed_in(1900) { + Some(format!("{state:?} is pretty old, for America!")) + } else { + Some(format!("{state:?} is relatively new.")) + } +} +// ANCHOR_END: describe + +fn main() { + if let Some(desc) = describe_state_quarter(Coin::Quarter(UsState::Alaska)) { + println!("{desc}"); + } +} diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-09/Cargo.lock b/listings/ch06-enums-and-pattern-matching/listing-06-09/Cargo.lock new file mode 100644 index 0000000000..f62e8ac453 --- /dev/null +++ b/listings/ch06-enums-and-pattern-matching/listing-06-09/Cargo.lock @@ -0,0 +1,6 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +[[package]] +name = "enums" +version = "0.1.0" + diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-09/Cargo.toml b/listings/ch06-enums-and-pattern-matching/listing-06-09/Cargo.toml new file mode 100644 index 0000000000..d4e6b38af1 --- /dev/null +++ b/listings/ch06-enums-and-pattern-matching/listing-06-09/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "enums" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/listing-06-09/src/main.rs b/listings/ch06-enums-and-pattern-matching/listing-06-09/src/main.rs new file mode 100644 index 0000000000..cffa151901 --- /dev/null +++ b/listings/ch06-enums-and-pattern-matching/listing-06-09/src/main.rs @@ -0,0 +1,43 @@ +#[derive(Debug)] // so we can inspect the state in a minute +enum UsState { + Alabama, + Alaska, + // --snip-- +} + +impl UsState { + fn existed_in(&self, year: u16) -> bool { + match self { + UsState::Alabama => year >= 1819, + UsState::Alaska => year >= 1959, + // -- snip -- + } + } +} + +enum Coin { + Penny, + Nickel, + Dime, + Quarter(UsState), +} + +// ANCHOR: describe +fn describe_state_quarter(coin: Coin) -> Option { + let Coin::Quarter(state) = coin else { + return None; + }; + + if state.existed_in(1900) { + Some(format!("{state:?} is pretty old, for America!")) + } else { + Some(format!("{state:?} is relatively new.")) + } +} +// ANCHOR_END: describe + +fn main() { + if let Some(desc) = describe_state_quarter(Coin::Quarter(UsState::Alaska)) { + println!("{desc}"); + } +} diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-02-enum-with-data/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-02-enum-with-data/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-02-enum-with-data/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-02-enum-with-data/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-03-variants-with-different-data/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-03-variants-with-different-data/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-03-variants-with-different-data/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-03-variants-with-different-data/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/src/main.rs b/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/src/main.rs index df451be8b6..fb3ff249ac 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/src/main.rs +++ b/listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/src/main.rs @@ -6,6 +6,6 @@ struct MoveMessage { } struct WriteMessage(String); // tuple struct struct ChangeColorMessage(i32, i32, i32); // tuple struct - // ANCHOR_END: here +// ANCHOR_END: here fn main() {} diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-05-methods-on-enums/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-05-methods-on-enums/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-05-methods-on-enums/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-05-methods-on-enums/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-06-option-examples/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-06-option-examples/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-06-option-examples/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-06-option-examples/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/output.txt b/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/output.txt index a16dc01807..78e064d990 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/output.txt +++ b/listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/output.txt @@ -8,10 +8,10 @@ error[E0277]: cannot add `Option` to `i8` | = help: the trait `Add>` is not implemented for `i8` = help: the following other types implement trait `Add`: - <&'a i8 as Add> - <&i8 as Add<&i8>> - > - + `&i8` implements `Add` + `&i8` implements `Add` + `i8` implements `Add<&i8>` + `i8` implements `Add` For more information about this error, try `rustc --explain E0277`. -error: could not compile `enums` due to previous error +error: could not compile `enums` (bin "enums") due to 1 previous error diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-08-match-arm-multiple-lines/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-08-match-arm-multiple-lines/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-08-match-arm-multiple-lines/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-08-match-arm-multiple-lines/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/src/main.rs b/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/src/main.rs index a4d500c11c..298215d405 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/src/main.rs +++ b/listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/src/main.rs @@ -19,7 +19,7 @@ fn value_in_cents(coin: Coin) -> u8 { Coin::Nickel => 5, Coin::Dime => 10, Coin::Quarter(state) => { - println!("State quarter from {:?}!", state); + println!("State quarter from {state:?}!"); 25 } } diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/output.txt b/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/output.txt index 75d056f843..3d06cff218 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/output.txt +++ b/listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/output.txt @@ -7,10 +7,10 @@ error[E0004]: non-exhaustive patterns: `None` not covered | ^ pattern `None` not covered | note: `Option` defined here - --> /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/option.rs:518:1 + --> /rustc/1159e78c4747b02ef996e55082b704c09b970588/library/core/src/option.rs:593:1 + ::: /rustc/1159e78c4747b02ef996e55082b704c09b970588/library/core/src/option.rs:597:5 | - = note: -/rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/option.rs:522:5: not covered + = note: not covered = note: the matched value is of type `Option` help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown | @@ -19,4 +19,4 @@ help: ensure that all possible cases are being handled by adding a match arm wit | For more information about this error, try `rustc --explain E0004`. -error: could not compile `enums` due to previous error +error: could not compile `enums` (bin "enums") due to 1 previous error diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/src/main.rs b/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/src/main.rs index 735086d4ed..7d7254ea0f 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/src/main.rs +++ b/listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/src/main.rs @@ -2,7 +2,7 @@ fn main() { // ANCHOR: here let config_max = Some(3u8); if let Some(max) = config_max { - println!("The maximum is configured to be {}", max); + println!("The maximum is configured to be {max}"); } // ANCHOR_END: here } diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/src/main.rs b/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/src/main.rs index 12c4c0fec1..d0d7d80271 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/src/main.rs +++ b/listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/src/main.rs @@ -17,7 +17,7 @@ fn main() { // ANCHOR: here let mut count = 0; match coin { - Coin::Quarter(state) => println!("State quarter from {:?}!", state), + Coin::Quarter(state) => println!("State quarter from {state:?}!"), _ => count += 1, } // ANCHOR_END: here diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/src/main.rs b/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/src/main.rs index ba7eda27b4..3bb3630350 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/src/main.rs +++ b/listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/src/main.rs @@ -17,7 +17,7 @@ fn main() { // ANCHOR: here let mut count = 0; if let Coin::Quarter(state) = coin { - println!("State quarter from {:?}!", state); + println!("State quarter from {state:?}!"); } else { count += 1; } diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-15-binding-catchall/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-15-binding-catchall/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-15-binding-catchall/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-15-binding-catchall/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-16-underscore-catchall/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-16-underscore-catchall/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-16-underscore-catchall/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-16-underscore-catchall/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch06-enums-and-pattern-matching/no-listing-17-underscore-unit/Cargo.toml b/listings/ch06-enums-and-pattern-matching/no-listing-17-underscore-unit/Cargo.toml index e959295f91..d4e6b38af1 100644 --- a/listings/ch06-enums-and-pattern-matching/no-listing-17-underscore-unit/Cargo.toml +++ b/listings/ch06-enums-and-pattern-matching/no-listing-17-underscore-unit/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "enums" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-01/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-01/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-01/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-03/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-03/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-03/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-03/output.txt b/listings/ch07-managing-growing-projects/listing-07-03/output.txt index 481dcb3f74..aeaf0e6991 100644 --- a/listings/ch07-managing-growing-projects/listing-07-03/output.txt +++ b/listings/ch07-managing-growing-projects/listing-07-03/output.txt @@ -4,7 +4,9 @@ error[E0603]: module `hosting` is private --> src/lib.rs:9:28 | 9 | crate::front_of_house::hosting::add_to_waitlist(); - | ^^^^^^^ private module + | ^^^^^^^ --------------- function `add_to_waitlist` is not publicly re-exported + | | + | private module | note: the module `hosting` is defined here --> src/lib.rs:2:5 @@ -16,13 +18,15 @@ error[E0603]: module `hosting` is private --> src/lib.rs:12:21 | 12 | front_of_house::hosting::add_to_waitlist(); - | ^^^^^^^ private module + | ^^^^^^^ --------------- function `add_to_waitlist` is not publicly re-exported + | | + | private module | note: the module `hosting` is defined here --> src/lib.rs:2:5 | -2 | mod hosting { + 2 | mod hosting { | ^^^^^^^^^^^ For more information about this error, try `rustc --explain E0603`. -error: could not compile `restaurant` due to 2 previous errors +error: could not compile `restaurant` (lib) due to 2 previous errors diff --git a/listings/ch07-managing-growing-projects/listing-07-05/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-05/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-05/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-05/output.txt b/listings/ch07-managing-growing-projects/listing-07-05/output.txt index 63eb89a146..1283eb5398 100644 --- a/listings/ch07-managing-growing-projects/listing-07-05/output.txt +++ b/listings/ch07-managing-growing-projects/listing-07-05/output.txt @@ -1,28 +1,28 @@ $ cargo build Compiling restaurant v0.1.0 (file:///projects/restaurant) error[E0603]: function `add_to_waitlist` is private - --> src/lib.rs:9:37 - | -9 | crate::front_of_house::hosting::add_to_waitlist(); - | ^^^^^^^^^^^^^^^ private function - | + --> src/lib.rs:10:37 + | +10 | crate::front_of_house::hosting::add_to_waitlist(); + | ^^^^^^^^^^^^^^^ private function + | note: the function `add_to_waitlist` is defined here - --> src/lib.rs:3:9 - | -3 | fn add_to_waitlist() {} - | ^^^^^^^^^^^^^^^^^^^^ + --> src/lib.rs:3:9 + | + 3 | fn add_to_waitlist() {} + | ^^^^^^^^^^^^^^^^^^^^ error[E0603]: function `add_to_waitlist` is private - --> src/lib.rs:12:30 + --> src/lib.rs:13:30 | -12 | front_of_house::hosting::add_to_waitlist(); +13 | front_of_house::hosting::add_to_waitlist(); | ^^^^^^^^^^^^^^^ private function | note: the function `add_to_waitlist` is defined here --> src/lib.rs:3:9 | -3 | fn add_to_waitlist() {} + 3 | fn add_to_waitlist() {} | ^^^^^^^^^^^^^^^^^^^^ For more information about this error, try `rustc --explain E0603`. -error: could not compile `restaurant` due to 2 previous errors +error: could not compile `restaurant` (lib) due to 2 previous errors diff --git a/listings/ch07-managing-growing-projects/listing-07-05/src/lib.rs b/listings/ch07-managing-growing-projects/listing-07-05/src/lib.rs index 05372dbe5e..a6808159df 100644 --- a/listings/ch07-managing-growing-projects/listing-07-05/src/lib.rs +++ b/listings/ch07-managing-growing-projects/listing-07-05/src/lib.rs @@ -1,9 +1,12 @@ +// ANCHOR: here mod front_of_house { pub mod hosting { fn add_to_waitlist() {} } } +// -- snip -- +// ANCHOR_END: here pub fn eat_at_restaurant() { // Absolute path crate::front_of_house::hosting::add_to_waitlist(); diff --git a/listings/ch07-managing-growing-projects/listing-07-07/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-07/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-07/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-07/src/lib.rs b/listings/ch07-managing-growing-projects/listing-07-07/src/lib.rs index 7b89ee7cd2..af5ae77f5f 100644 --- a/listings/ch07-managing-growing-projects/listing-07-07/src/lib.rs +++ b/listings/ch07-managing-growing-projects/listing-07-07/src/lib.rs @@ -1,9 +1,12 @@ +// ANCHOR: here mod front_of_house { pub mod hosting { pub fn add_to_waitlist() {} } } +// -- snip -- +// ANCHOR_END: here pub fn eat_at_restaurant() { // Absolute path crate::front_of_house::hosting::add_to_waitlist(); diff --git a/listings/ch07-managing-growing-projects/listing-07-08/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-08/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-08/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-09/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-09/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-09/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-09/src/lib.rs b/listings/ch07-managing-growing-projects/listing-07-09/src/lib.rs index 92c4695d50..48eb996a8b 100644 --- a/listings/ch07-managing-growing-projects/listing-07-09/src/lib.rs +++ b/listings/ch07-managing-growing-projects/listing-07-09/src/lib.rs @@ -15,13 +15,13 @@ mod back_of_house { } pub fn eat_at_restaurant() { - // Order a breakfast in the summer with Rye toast + // Order a breakfast in the summer with Rye toast. let mut meal = back_of_house::Breakfast::summer("Rye"); - // Change our mind about what bread we'd like + // Change our mind about what bread we'd like. meal.toast = String::from("Wheat"); println!("I'd like {} toast please", meal.toast); // The next line won't compile if we uncomment it; we're not allowed - // to see or modify the seasonal fruit that comes with the meal + // to see or modify the seasonal fruit that comes with the meal. // meal.seasonal_fruit = String::from("blueberries"); } diff --git a/listings/ch07-managing-growing-projects/listing-07-10/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-10/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-10/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-11/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-11/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-11/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-12/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-12/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-12/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-12/output.txt b/listings/ch07-managing-growing-projects/listing-07-12/output.txt index 1bc89bf322..e094fc8d03 100644 --- a/listings/ch07-managing-growing-projects/listing-07-12/output.txt +++ b/listings/ch07-managing-growing-projects/listing-07-12/output.txt @@ -1,5 +1,17 @@ $ cargo build Compiling restaurant v0.1.0 (file:///projects/restaurant) +error[E0433]: failed to resolve: use of unresolved module or unlinked crate `hosting` + --> src/lib.rs:11:9 + | +11 | hosting::add_to_waitlist(); + | ^^^^^^^ use of unresolved module or unlinked crate `hosting` + | + = help: if you wanted to use a crate named `hosting`, use `cargo add hosting` to add it to your `Cargo.toml` +help: consider importing this module through its public re-export + | +10 + use crate::hosting; + | + warning: unused import: `crate::front_of_house::hosting` --> src/lib.rs:7:5 | @@ -8,12 +20,6 @@ warning: unused import: `crate::front_of_house::hosting` | = note: `#[warn(unused_imports)]` on by default -error[E0433]: failed to resolve: use of undeclared crate or module `hosting` - --> src/lib.rs:11:9 - | -11 | hosting::add_to_waitlist(); - | ^^^^^^^ use of undeclared crate or module `hosting` - For more information about this error, try `rustc --explain E0433`. warning: `restaurant` (lib) generated 1 warning -error: could not compile `restaurant` due to previous error; 1 warning emitted +error: could not compile `restaurant` (lib) due to 1 previous error; 1 warning emitted diff --git a/listings/ch07-managing-growing-projects/listing-07-13/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-13/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-13/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-14/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-14/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-14/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-15/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-15/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-15/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-16/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-16/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-16/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-17/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-17/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-17/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-17/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-18/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-18/Cargo.toml index d508e9578d..9f9c4acb96 100644 --- a/listings/ch07-managing-growing-projects/listing-07-18/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-18/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] rand = "0.8.5" diff --git a/listings/ch07-managing-growing-projects/listing-07-19/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-19/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-19/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-19/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-20/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-20/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-20/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-20/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/listing-07-21-and-22/Cargo.toml b/listings/ch07-managing-growing-projects/listing-07-21-and-22/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/listing-07-21-and-22/Cargo.toml +++ b/listings/ch07-managing-growing-projects/listing-07-21-and-22/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/no-listing-01-use-std-unnested/Cargo.toml b/listings/ch07-managing-growing-projects/no-listing-01-use-std-unnested/Cargo.toml index 7eda67aeaf..eba27a883c 100644 --- a/listings/ch07-managing-growing-projects/no-listing-01-use-std-unnested/Cargo.toml +++ b/listings/ch07-managing-growing-projects/no-listing-01-use-std-unnested/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/Cargo.toml b/listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/Cargo.toml index 60cec7cb01..8e47b7abe8 100644 --- a/listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/Cargo.toml +++ b/listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "restaurant" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/quick-reference-example/Cargo.toml b/listings/ch07-managing-growing-projects/quick-reference-example/Cargo.toml index 6e904abbe7..49be9c5947 100644 --- a/listings/ch07-managing-growing-projects/quick-reference-example/Cargo.toml +++ b/listings/ch07-managing-growing-projects/quick-reference-example/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "backyard" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch07-managing-growing-projects/quick-reference-example/output.txt b/listings/ch07-managing-growing-projects/quick-reference-example/output.txt index e36a45eb0d..04ac6f6c03 100644 --- a/listings/ch07-managing-growing-projects/quick-reference-example/output.txt +++ b/listings/ch07-managing-growing-projects/quick-reference-example/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling backyard v0.1.0 (file:///projects/backyard) - Finished dev [unoptimized + debuginfo] target(s) in 0.36s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.36s Running `target/debug/backyard` I'm growing Asparagus! diff --git a/listings/ch07-managing-growing-projects/quick-reference-example/src/main.rs b/listings/ch07-managing-growing-projects/quick-reference-example/src/main.rs index 7a024a9a0d..0d9a0ca92f 100644 --- a/listings/ch07-managing-growing-projects/quick-reference-example/src/main.rs +++ b/listings/ch07-managing-growing-projects/quick-reference-example/src/main.rs @@ -4,5 +4,5 @@ pub mod garden; fn main() { let plant = Asparagus {}; - println!("I'm growing {:?}!", plant); + println!("I'm growing {plant:?}!"); } diff --git a/listings/ch08-common-collections/listing-08-01/Cargo.toml b/listings/ch08-common-collections/listing-08-01/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-01/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-02/Cargo.toml b/listings/ch08-common-collections/listing-08-02/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-02/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-03/Cargo.toml b/listings/ch08-common-collections/listing-08-03/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-03/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-04/Cargo.toml b/listings/ch08-common-collections/listing-08-04/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-04/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-05/Cargo.toml b/listings/ch08-common-collections/listing-08-05/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-05/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-06/Cargo.toml b/listings/ch08-common-collections/listing-08-06/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-06/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-06/output.txt b/listings/ch08-common-collections/listing-08-06/output.txt index 3104205f30..e3b14759a8 100644 --- a/listings/ch08-common-collections/listing-08-06/output.txt +++ b/listings/ch08-common-collections/listing-08-06/output.txt @@ -13,4 +13,4 @@ error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immuta | ----- immutable borrow later used here For more information about this error, try `rustc --explain E0502`. -error: could not compile `collections` due to previous error +error: could not compile `collections` (bin "collections") due to 1 previous error diff --git a/listings/ch08-common-collections/listing-08-07/Cargo.toml b/listings/ch08-common-collections/listing-08-07/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-07/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-08/Cargo.toml b/listings/ch08-common-collections/listing-08-08/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-08/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-09/Cargo.toml b/listings/ch08-common-collections/listing-08-09/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-09/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-10/Cargo.toml b/listings/ch08-common-collections/listing-08-10/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-10/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-10/src/main.rs b/listings/ch08-common-collections/listing-08-10/src/main.rs index abda2db660..a7d2dfa569 100644 --- a/listings/ch08-common-collections/listing-08-10/src/main.rs +++ b/listings/ch08-common-collections/listing-08-10/src/main.rs @@ -5,5 +5,5 @@ fn main() { // do stuff with v } // <- v goes out of scope and is freed here - // ANCHOR_END: here + // ANCHOR_END: here } diff --git a/listings/ch08-common-collections/listing-08-11/Cargo.toml b/listings/ch08-common-collections/listing-08-11/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-11/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-12/Cargo.toml b/listings/ch08-common-collections/listing-08-12/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-12/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-12/src/main.rs b/listings/ch08-common-collections/listing-08-12/src/main.rs index d9e5e768ab..48f00ef3cb 100644 --- a/listings/ch08-common-collections/listing-08-12/src/main.rs +++ b/listings/ch08-common-collections/listing-08-12/src/main.rs @@ -4,7 +4,7 @@ fn main() { let s = data.to_string(); - // the method also works on a literal directly: + // The method also works on a literal directly: let s = "initial contents".to_string(); // ANCHOR_END: here } diff --git a/listings/ch08-common-collections/listing-08-13/Cargo.toml b/listings/ch08-common-collections/listing-08-13/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-13/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-14/Cargo.toml b/listings/ch08-common-collections/listing-08-14/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-14/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-14/src/main.rs b/listings/ch08-common-collections/listing-08-14/src/main.rs index f701fd578b..bf737ab446 100644 --- a/listings/ch08-common-collections/listing-08-14/src/main.rs +++ b/listings/ch08-common-collections/listing-08-14/src/main.rs @@ -3,7 +3,7 @@ fn main() { let hello = String::from("السلام عليكم"); let hello = String::from("Dobrý den"); let hello = String::from("Hello"); - let hello = String::from("שָׁלוֹם"); + let hello = String::from("שלום"); let hello = String::from("नमस्ते"); let hello = String::from("こんにちは"); let hello = String::from("안녕하세요"); diff --git a/listings/ch08-common-collections/listing-08-15/Cargo.toml b/listings/ch08-common-collections/listing-08-15/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-15/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-16/Cargo.toml b/listings/ch08-common-collections/listing-08-16/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-16/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-17/Cargo.toml b/listings/ch08-common-collections/listing-08-17/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-17/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-17/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-18/Cargo.toml b/listings/ch08-common-collections/listing-08-18/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-18/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-18/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-18/src/main.rs b/listings/ch08-common-collections/listing-08-18/src/main.rs index 93939a69fb..8e55dc5116 100644 --- a/listings/ch08-common-collections/listing-08-18/src/main.rs +++ b/listings/ch08-common-collections/listing-08-18/src/main.rs @@ -3,5 +3,5 @@ fn main() { let s1 = String::from("Hello, "); let s2 = String::from("world!"); let s3 = s1 + &s2; // note s1 has been moved here and can no longer be used - // ANCHOR_END: here + // ANCHOR_END: here } diff --git a/listings/ch08-common-collections/listing-08-19/Cargo.toml b/listings/ch08-common-collections/listing-08-19/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-19/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-19/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-19/output.txt b/listings/ch08-common-collections/listing-08-19/output.txt index 3a682457c6..3aa92ad5d3 100644 --- a/listings/ch08-common-collections/listing-08-19/output.txt +++ b/listings/ch08-common-collections/listing-08-19/output.txt @@ -1,19 +1,18 @@ $ cargo run Compiling collections v0.1.0 (file:///projects/collections) -error[E0277]: the type `String` cannot be indexed by `{integer}` - --> src/main.rs:3:13 +error[E0277]: the type `str` cannot be indexed by `{integer}` + --> src/main.rs:3:16 | 3 | let h = s1[0]; - | ^^^^^ `String` cannot be indexed by `{integer}` + | ^ string indices are ranges of `usize` | - = help: the trait `Index<{integer}>` is not implemented for `String` - = help: the following other types implement trait `Index`: - >> - > - >> - >> - >> - >> + = help: the trait `SliceIndex` is not implemented for `{integer}` + = note: you can use `.chars().nth()` or `.bytes().nth()` + for more information, see chapter 8 in The Book: + = help: the following other types implement trait `SliceIndex`: + `usize` implements `SliceIndex` + `usize` implements `SliceIndex<[T]>` + = note: required for `String` to implement `Index<{integer}>` For more information about this error, try `rustc --explain E0277`. -error: could not compile `collections` due to previous error +error: could not compile `collections` (bin "collections") due to 1 previous error diff --git a/listings/ch08-common-collections/listing-08-19/src/main.rs b/listings/ch08-common-collections/listing-08-19/src/main.rs index fc08e9ceaa..44b3b5bb9a 100644 --- a/listings/ch08-common-collections/listing-08-19/src/main.rs +++ b/listings/ch08-common-collections/listing-08-19/src/main.rs @@ -1,6 +1,6 @@ fn main() { // ANCHOR: here - let s1 = String::from("hello"); + let s1 = String::from("hi"); let h = s1[0]; // ANCHOR_END: here } diff --git a/listings/ch08-common-collections/listing-08-20/Cargo.toml b/listings/ch08-common-collections/listing-08-20/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-20/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-20/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-21/Cargo.toml b/listings/ch08-common-collections/listing-08-21/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-21/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-21/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-22/Cargo.toml b/listings/ch08-common-collections/listing-08-22/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-22/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-22/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-23/Cargo.toml b/listings/ch08-common-collections/listing-08-23/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-23/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-23/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-23/src/main.rs b/listings/ch08-common-collections/listing-08-23/src/main.rs index e8684cf2b6..29025b4177 100644 --- a/listings/ch08-common-collections/listing-08-23/src/main.rs +++ b/listings/ch08-common-collections/listing-08-23/src/main.rs @@ -7,6 +7,6 @@ fn main() { scores.insert(String::from("Blue"), 10); scores.insert(String::from("Blue"), 25); - println!("{:?}", scores); + println!("{scores:?}"); // ANCHOR_END: here } diff --git a/listings/ch08-common-collections/listing-08-24/Cargo.toml b/listings/ch08-common-collections/listing-08-24/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-24/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-24/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-24/src/main.rs b/listings/ch08-common-collections/listing-08-24/src/main.rs index 3ad97b57af..013895632e 100644 --- a/listings/ch08-common-collections/listing-08-24/src/main.rs +++ b/listings/ch08-common-collections/listing-08-24/src/main.rs @@ -8,6 +8,6 @@ fn main() { scores.entry(String::from("Yellow")).or_insert(50); scores.entry(String::from("Blue")).or_insert(50); - println!("{:?}", scores); + println!("{scores:?}"); // ANCHOR_END: here } diff --git a/listings/ch08-common-collections/listing-08-25/Cargo.toml b/listings/ch08-common-collections/listing-08-25/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/listing-08-25/Cargo.toml +++ b/listings/ch08-common-collections/listing-08-25/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/listing-08-25/src/main.rs b/listings/ch08-common-collections/listing-08-25/src/main.rs index f3f6aa166d..84dd1cd4ba 100644 --- a/listings/ch08-common-collections/listing-08-25/src/main.rs +++ b/listings/ch08-common-collections/listing-08-25/src/main.rs @@ -11,6 +11,6 @@ fn main() { *count += 1; } - println!("{:?}", map); + println!("{map:?}"); // ANCHOR_END: here } diff --git a/listings/ch08-common-collections/no-listing-01-concat-multiple-strings/Cargo.toml b/listings/ch08-common-collections/no-listing-01-concat-multiple-strings/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/no-listing-01-concat-multiple-strings/Cargo.toml +++ b/listings/ch08-common-collections/no-listing-01-concat-multiple-strings/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/no-listing-02-format/Cargo.toml b/listings/ch08-common-collections/no-listing-02-format/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/no-listing-02-format/Cargo.toml +++ b/listings/ch08-common-collections/no-listing-02-format/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/no-listing-03-iterate-over-hashmap/Cargo.toml b/listings/ch08-common-collections/no-listing-03-iterate-over-hashmap/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/no-listing-03-iterate-over-hashmap/Cargo.toml +++ b/listings/ch08-common-collections/no-listing-03-iterate-over-hashmap/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/output-only-01-not-char-boundary/Cargo.toml b/listings/ch08-common-collections/output-only-01-not-char-boundary/Cargo.toml index fe49598234..fd854232dc 100644 --- a/listings/ch08-common-collections/output-only-01-not-char-boundary/Cargo.toml +++ b/listings/ch08-common-collections/output-only-01-not-char-boundary/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "collections" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch08-common-collections/output-only-01-not-char-boundary/output.txt b/listings/ch08-common-collections/output-only-01-not-char-boundary/output.txt index 35db879c9b..c66cccca9f 100644 --- a/listings/ch08-common-collections/output-only-01-not-char-boundary/output.txt +++ b/listings/ch08-common-collections/output-only-01-not-char-boundary/output.txt @@ -1,6 +1,8 @@ $ cargo run Compiling collections v0.1.0 (file:///projects/collections) - Finished dev [unoptimized + debuginfo] target(s) in 0.43s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.43s Running `target/debug/collections` -thread 'main' panicked at 'byte index 1 is not a char boundary; it is inside 'З' (bytes 0..2) of `Здравствуйте`', src/main.rs:4:14 + +thread 'main' panicked at src/main.rs:4:19: +byte index 1 is not a char boundary; it is inside 'З' (bytes 0..2) of `Здравствуйте` note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch09-error-handling/listing-09-01/Cargo.toml b/listings/ch09-error-handling/listing-09-01/Cargo.toml index 660e2c819d..94b8cffcb7 100644 --- a/listings/ch09-error-handling/listing-09-01/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "panic" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-01/output.txt b/listings/ch09-error-handling/listing-09-01/output.txt index 89aebb952f..2c92e13851 100644 --- a/listings/ch09-error-handling/listing-09-01/output.txt +++ b/listings/ch09-error-handling/listing-09-01/output.txt @@ -1,6 +1,8 @@ $ cargo run Compiling panic v0.1.0 (file:///projects/panic) - Finished dev [unoptimized + debuginfo] target(s) in 0.27s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.27s Running `target/debug/panic` -thread 'main' panicked at 'index out of bounds: the len is 3 but the index is 99', src/main.rs:4:5 + +thread 'main' panicked at src/main.rs:4:6: +index out of bounds: the len is 3 but the index is 99 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch09-error-handling/listing-09-03/Cargo.toml b/listings/ch09-error-handling/listing-09-03/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-03/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-04/Cargo.toml b/listings/ch09-error-handling/listing-09-04/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-04/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-04/output.txt b/listings/ch09-error-handling/listing-09-04/output.txt index f776a591ce..3ecc9c0dc9 100644 --- a/listings/ch09-error-handling/listing-09-04/output.txt +++ b/listings/ch09-error-handling/listing-09-04/output.txt @@ -1,6 +1,8 @@ $ cargo run Compiling error-handling v0.1.0 (file:///projects/error-handling) - Finished dev [unoptimized + debuginfo] target(s) in 0.73s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.73s Running `target/debug/error-handling` -thread 'main' panicked at 'Problem opening the file: Os { code: 2, kind: NotFound, message: "No such file or directory" }', src/main.rs:8:23 + +thread 'main' panicked at src/main.rs:8:23: +Problem opening the file: Os { code: 2, kind: NotFound, message: "No such file or directory" } note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch09-error-handling/listing-09-04/src/main.rs b/listings/ch09-error-handling/listing-09-04/src/main.rs index 69da109fe4..832f57f0e6 100644 --- a/listings/ch09-error-handling/listing-09-04/src/main.rs +++ b/listings/ch09-error-handling/listing-09-04/src/main.rs @@ -5,6 +5,6 @@ fn main() { let greeting_file = match greeting_file_result { Ok(file) => file, - Err(error) => panic!("Problem opening the file: {:?}", error), + Err(error) => panic!("Problem opening the file: {error:?}"), }; } diff --git a/listings/ch09-error-handling/listing-09-05/Cargo.toml b/listings/ch09-error-handling/listing-09-05/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-05/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-05/src/main.rs b/listings/ch09-error-handling/listing-09-05/src/main.rs index 83ea01044f..20f470ba20 100644 --- a/listings/ch09-error-handling/listing-09-05/src/main.rs +++ b/listings/ch09-error-handling/listing-09-05/src/main.rs @@ -9,10 +9,10 @@ fn main() { Err(error) => match error.kind() { ErrorKind::NotFound => match File::create("hello.txt") { Ok(fc) => fc, - Err(e) => panic!("Problem creating the file: {:?}", e), + Err(e) => panic!("Problem creating the file: {e:?}"), }, - other_error => { - panic!("Problem opening the file: {:?}", other_error); + _ => { + panic!("Problem opening the file: {error:?}"); } }, }; diff --git a/listings/ch09-error-handling/listing-09-06/Cargo.toml b/listings/ch09-error-handling/listing-09-06/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-06/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-07/Cargo.toml b/listings/ch09-error-handling/listing-09-07/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-07/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-08/Cargo.toml b/listings/ch09-error-handling/listing-09-08/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-08/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-09/Cargo.toml b/listings/ch09-error-handling/listing-09-09/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-09/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-10/Cargo.toml b/listings/ch09-error-handling/listing-09-10/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-10/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-10/output.txt b/listings/ch09-error-handling/listing-09-10/output.txt index 75b9cf2e33..a8c707e40a 100644 --- a/listings/ch09-error-handling/listing-09-10/output.txt +++ b/listings/ch09-error-handling/listing-09-10/output.txt @@ -8,7 +8,12 @@ error[E0277]: the `?` operator can only be used in a function that returns `Resu 4 | let greeting_file = File::open("hello.txt")?; | ^ cannot use the `?` operator in a function that returns `()` | - = help: the trait `FromResidual>` is not implemented for `()` +help: consider adding return type + | +3 ~ fn main() -> Result<(), Box> { +4 | let greeting_file = File::open("hello.txt")?; +5 + Ok(()) + | For more information about this error, try `rustc --explain E0277`. -error: could not compile `error-handling` due to previous error +error: could not compile `error-handling` (bin "error-handling") due to 1 previous error diff --git a/listings/ch09-error-handling/listing-09-11/Cargo.toml b/listings/ch09-error-handling/listing-09-11/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-11/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-12/Cargo.toml b/listings/ch09-error-handling/listing-09-12/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/listing-09-12/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/listing-09-13/Cargo.toml b/listings/ch09-error-handling/listing-09-13/Cargo.toml index d508e9578d..9f9c4acb96 100644 --- a/listings/ch09-error-handling/listing-09-13/Cargo.toml +++ b/listings/ch09-error-handling/listing-09-13/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] rand = "0.8.5" diff --git a/listings/ch09-error-handling/listing-09-13/src/guessing_game.rs b/listings/ch09-error-handling/listing-09-13/src/guessing_game.rs new file mode 100644 index 0000000000..d093831100 --- /dev/null +++ b/listings/ch09-error-handling/listing-09-13/src/guessing_game.rs @@ -0,0 +1,17 @@ +pub struct Guess { + value: i32, +} + +impl Guess { + pub fn new(value: i32) -> Guess { + if value < 1 || value > 100 { + panic!("Guess value must be between 1 and 100, got {value}."); + } + + Guess { value } + } + + pub fn value(&self) -> i32 { + self.value + } +} diff --git a/listings/ch09-error-handling/listing-09-13/src/main.rs b/listings/ch09-error-handling/listing-09-13/src/main.rs index 9e07c1ee25..6c3e963450 100644 --- a/listings/ch09-error-handling/listing-09-13/src/main.rs +++ b/listings/ch09-error-handling/listing-09-13/src/main.rs @@ -1,26 +1,9 @@ +use guessing_game::Guess; use rand::Rng; use std::cmp::Ordering; use std::io; -// ANCHOR: here -pub struct Guess { - value: i32, -} - -impl Guess { - pub fn new(value: i32) -> Guess { - if value < 1 || value > 100 { - panic!("Guess value must be between 1 and 100, got {}.", value); - } - - Guess { value } - } - - pub fn value(&self) -> i32 { - self.value - } -} -// ANCHOR_END: here +mod guessing_game; fn main() { println!("Guess the number!"); diff --git a/listings/ch09-error-handling/no-listing-01-panic/Cargo.toml b/listings/ch09-error-handling/no-listing-01-panic/Cargo.toml index 660e2c819d..94b8cffcb7 100644 --- a/listings/ch09-error-handling/no-listing-01-panic/Cargo.toml +++ b/listings/ch09-error-handling/no-listing-01-panic/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "panic" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/no-listing-01-panic/output.txt b/listings/ch09-error-handling/no-listing-01-panic/output.txt index b25ed85d7c..4268ef1d51 100644 --- a/listings/ch09-error-handling/no-listing-01-panic/output.txt +++ b/listings/ch09-error-handling/no-listing-01-panic/output.txt @@ -1,6 +1,8 @@ $ cargo run Compiling panic v0.1.0 (file:///projects/panic) - Finished dev [unoptimized + debuginfo] target(s) in 0.25s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.25s Running `target/debug/panic` -thread 'main' panicked at 'crash and burn', src/main.rs:2:5 + +thread 'main' panicked at src/main.rs:2:5: +crash and burn note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch09-error-handling/no-listing-04-unwrap/Cargo.toml b/listings/ch09-error-handling/no-listing-04-unwrap/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/no-listing-04-unwrap/Cargo.toml +++ b/listings/ch09-error-handling/no-listing-04-unwrap/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/no-listing-05-expect/Cargo.toml b/listings/ch09-error-handling/no-listing-05-expect/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/no-listing-05-expect/Cargo.toml +++ b/listings/ch09-error-handling/no-listing-05-expect/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/no-listing-08-unwrap-that-cant-fail/Cargo.toml b/listings/ch09-error-handling/no-listing-08-unwrap-that-cant-fail/Cargo.toml index c496db7834..225a1e058f 100644 --- a/listings/ch09-error-handling/no-listing-08-unwrap-that-cant-fail/Cargo.toml +++ b/listings/ch09-error-handling/no-listing-08-unwrap-that-cant-fail/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "error-handling" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch09-error-handling/no-listing-09-guess-out-of-range/Cargo.toml b/listings/ch09-error-handling/no-listing-09-guess-out-of-range/Cargo.toml index d508e9578d..9f9c4acb96 100644 --- a/listings/ch09-error-handling/no-listing-09-guess-out-of-range/Cargo.toml +++ b/listings/ch09-error-handling/no-listing-09-guess-out-of-range/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] rand = "0.8.5" diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/src/main.rs index a4dba7ed43..c9e9bbbd21 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/src/main.rs @@ -10,7 +10,7 @@ fn main() { } } - println!("The largest number is {}", largest); + println!("The largest number is {largest}"); // ANCHOR_END: here assert_eq!(*largest, 100); // ANCHOR: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/src/main.rs index 8c523a8be3..fd43154a94 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/src/main.rs @@ -9,7 +9,7 @@ fn main() { } } - println!("The largest number is {}", largest); + println!("The largest number is {largest}"); let number_list = vec![102, 34, 6000, 89, 54, 2, 43, 8]; @@ -21,5 +21,5 @@ fn main() { } } - println!("The largest number is {}", largest); + println!("The largest number is {largest}"); } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/src/main.rs index 899222909c..1878f5aacc 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/src/main.rs @@ -15,7 +15,7 @@ fn main() { let number_list = vec![34, 50, 25, 100, 65]; let result = largest(&number_list); - println!("The largest number is {}", result); + println!("The largest number is {result}"); // ANCHOR_END: here assert_eq!(*result, 100); // ANCHOR: here @@ -23,7 +23,7 @@ fn main() { let number_list = vec![102, 34, 6000, 89, 54, 2, 43, 8]; let result = largest(&number_list); - println!("The largest number is {}", result); + println!("The largest number is {result}"); // ANCHOR_END: here assert_eq!(*result, 6000); // ANCHOR: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/src/main.rs index a47e3f232c..ac3b1f7c1e 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/src/main.rs @@ -27,7 +27,7 @@ fn main() { let number_list = vec![34, 50, 25, 100, 65]; let result = largest_i32(&number_list); - println!("The largest number is {}", result); + println!("The largest number is {result}"); // ANCHOR_END: here assert_eq!(*result, 100); // ANCHOR: here @@ -35,7 +35,7 @@ fn main() { let char_list = vec!['y', 'm', 'a', 'q']; let result = largest_char(&char_list); - println!("The largest char is {}", result); + println!("The largest char is {result}"); // ANCHOR_END: here assert_eq!(*result, 'y'); // ANCHOR: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/output.txt b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/output.txt index 1a705ed570..54a8c6285b 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/output.txt +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/output.txt @@ -8,10 +8,10 @@ error[E0369]: binary operation `>` cannot be applied to type `&T` | | | &T | -help: consider restricting type parameter `T` +help: consider restricting type parameter `T` with trait `PartialOrd` | 1 | fn largest(list: &[T]) -> &T { | ++++++++++++++++++++++ For more information about this error, try `rustc --explain E0369`. -error: could not compile `chapter10` due to previous error +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/src/main.rs index df33743f78..094eb416a7 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/src/main.rs @@ -14,10 +14,10 @@ fn main() { let number_list = vec![34, 50, 25, 100, 65]; let result = largest(&number_list); - println!("The largest number is {}", result); + println!("The largest number is {result}"); let char_list = vec!['y', 'm', 'a', 'q']; let result = largest(&char_list); - println!("The largest char is {}", result); + println!("The largest char is {result}"); } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-06/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-06/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-06/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/output.txt b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/output.txt index 2482c38432..5f6c3f4657 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/output.txt +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/output.txt @@ -7,4 +7,4 @@ error[E0308]: mismatched types | ^^^ expected integer, found floating-point number For more information about this error, try `rustc --explain E0308`. -error: could not compile `chapter10` due to previous error +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-08/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-08/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-08/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-09/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-09/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-09/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-10/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-10/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-10/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-11/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-11/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-11/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-12/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-12/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-12/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/src/lib.rs index c4c83329ef..cbf66ab27a 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/src/lib.rs @@ -16,14 +16,14 @@ impl Summary for NewsArticle { } } -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/src/lib.rs index fb59b84fb1..d64ea00729 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/src/lib.rs @@ -15,14 +15,14 @@ pub struct NewsArticle { impl Summary for NewsArticle {} -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-15/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-15/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-15/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/output.txt b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/output.txt index ad73272099..29cf2f392f 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/output.txt +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/output.txt @@ -3,13 +3,15 @@ $ cargo run error[E0597]: `x` does not live long enough --> src/main.rs:6:13 | +5 | let x = 5; + | - binding `x` declared here 6 | r = &x; | ^^ borrowed value does not live long enough 7 | } | - `x` dropped here while still borrowed 8 | -9 | println!("r: {}", r); - | - borrow later used here +9 | println!("r: {r}"); + | - borrow later used here For more information about this error, try `rustc --explain E0597`. -error: could not compile `chapter10` due to previous error +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/src/main.rs index d71134ea09..773340eabc 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/src/main.rs @@ -6,5 +6,5 @@ fn main() { r = &x; } - println!("r: {}", r); + println!("r: {r}"); } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/src/main.rs index e8ca92328a..6679bcf31e 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/src/main.rs @@ -6,5 +6,5 @@ fn main() { r = &x; // | | } // -+ | // | - println!("r: {}", r); // | + println!("r: {r}"); // | } // ---------+ diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/src/main.rs index 09ae3919cd..634ff9391a 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/src/main.rs @@ -3,6 +3,6 @@ fn main() { // | let r = &x; // --+-- 'a | // | | - println!("r: {}", r); // | | + println!("r: {r}"); // | | // --+ | } // ----------+ diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/src/main.rs index 0f076a71db..8b64cd0008 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/src/main.rs @@ -3,5 +3,5 @@ fn main() { let string2 = "xyz"; let result = longest(string1.as_str(), string2); - println!("The longest string is {}", result); + println!("The longest string is {result}"); } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/output.txt b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/output.txt index 534a984a63..a6783b2ccd 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/output.txt +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/output.txt @@ -13,4 +13,4 @@ help: consider introducing a named lifetime parameter | ++++ ++ ++ ++ For more information about this error, try `rustc --explain E0106`. -error: could not compile `chapter10` due to previous error +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/src/main.rs index 6af8c9f0da..c80cf87a6d 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/src/main.rs @@ -3,15 +3,11 @@ fn main() { let string2 = "xyz"; let result = longest(string1.as_str(), string2); - println!("The longest string is {}", result); + println!("The longest string is {result}"); } // ANCHOR: here fn longest(x: &str, y: &str) -> &str { - if x.len() > y.len() { - x - } else { - y - } + if x.len() > y.len() { x } else { y } } // ANCHOR_END: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/src/main.rs index 09c3a0daaa..c7b92f7ba9 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/src/main.rs @@ -3,15 +3,11 @@ fn main() { let string2 = "xyz"; let result = longest(string1.as_str(), string2); - println!("The longest string is {}", result); + println!("The longest string is {result}"); } // ANCHOR: here fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { - if x.len() > y.len() { - x - } else { - y - } + if x.len() > y.len() { x } else { y } } // ANCHOR_END: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/src/main.rs index 836ec72959..b1a24a4086 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/src/main.rs @@ -5,15 +5,11 @@ fn main() { { let string2 = String::from("xyz"); let result = longest(string1.as_str(), string2.as_str()); - println!("The longest string is {}", result); + println!("The longest string is {result}"); } } // ANCHOR_END: here fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { - if x.len() > y.len() { - x - } else { - y - } + if x.len() > y.len() { x } else { y } } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/output.txt b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/output.txt index 7f31ce02c4..63d1668cae 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/output.txt +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/output.txt @@ -3,12 +3,14 @@ $ cargo run error[E0597]: `string2` does not live long enough --> src/main.rs:6:44 | +5 | let string2 = String::from("xyz"); + | ------- binding `string2` declared here 6 | result = longest(string1.as_str(), string2.as_str()); - | ^^^^^^^^^^^^^^^^ borrowed value does not live long enough + | ^^^^^^^ borrowed value does not live long enough 7 | } | - `string2` dropped here while still borrowed -8 | println!("The longest string is {}", result); - | ------ borrow later used here +8 | println!("The longest string is {result}"); + | ------ borrow later used here For more information about this error, try `rustc --explain E0597`. -error: could not compile `chapter10` due to previous error +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/src/main.rs index 2a6fa5898f..a8bc4ef496 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/src/main.rs @@ -6,14 +6,10 @@ fn main() { let string2 = String::from("xyz"); result = longest(string1.as_str(), string2.as_str()); } - println!("The longest string is {}", result); + println!("The longest string is {result}"); } // ANCHOR_END: here fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { - if x.len() > y.len() { - x - } else { - y - } + if x.len() > y.len() { x } else { y } } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/src/main.rs index 2937b194ca..ca3cf86d21 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/src/main.rs @@ -4,7 +4,7 @@ struct ImportantExcerpt<'a> { fn main() { let novel = String::from("Call me Ishmael. Some years ago..."); - let first_sentence = novel.split('.').next().expect("Could not find a '.'"); + let first_sentence = novel.split('.').next().unwrap(); let i = ImportantExcerpt { part: first_sentence, }; diff --git a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-25/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-25/Cargo.toml index e8847526dc..a4b0049f1d 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/listing-10-25/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/listing-10-25/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "ownership" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/lib.rs index fa644ca4fb..1036ff9016 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/lib.rs @@ -15,14 +15,14 @@ impl Summary for NewsArticle { } } -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/main.rs index 0b51121d94..d94ed0a463 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/main.rs @@ -1,14 +1,14 @@ -use aggregator::{Summary, Tweet}; +use aggregator::{SocialPost, Summary}; fn main() { - let tweet = Tweet { + let post = SocialPost { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, - retweet: false, + repost: false, }; - println!("1 new tweet: {}", tweet.summarize()); + println!("1 new post: {}", post.summarize()); } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/src/lib.rs index b6f93a68f7..d0abd43f04 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/src/lib.rs @@ -13,14 +13,14 @@ pub struct NewsArticle { impl Summary for NewsArticle {} -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/lib.rs index 643906f691..dac17fc144 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/lib.rs @@ -8,15 +8,15 @@ pub trait Summary { } // ANCHOR_END: here -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } // ANCHOR: impl -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize_author(&self) -> String { format!("@{}", self.username) } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/main.rs index e05e8e1c67..35b0eea09a 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/main.rs @@ -1,16 +1,16 @@ -use aggregator::{self, Summary, Tweet}; +use aggregator::{self, SocialPost, Summary}; fn main() { // ANCHOR: here - let tweet = Tweet { + let post = SocialPost { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, - retweet: false, + repost: false, }; - println!("1 new tweet: {}", tweet.summarize()); + println!("1 new post: {}", post.summarize()); // ANCHOR_END: here } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/src/lib.rs index 2619943515..18a8ddbfd2 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/src/lib.rs @@ -15,14 +15,14 @@ impl Summary for NewsArticle { } } -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/src/lib.rs index a611fce38e..a596c893d3 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/src/lib.rs @@ -15,14 +15,14 @@ impl Summary for NewsArticle { } } -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } @@ -30,13 +30,13 @@ impl Summary for Tweet { // ANCHOR: here fn returns_summarizable() -> impl Summary { - Tweet { + SocialPost { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, - retweet: false, + repost: false, } } // ANCHOR_END: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/Cargo.toml index 46f46a7f44..789790bdd8 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "aggregator" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/src/lib.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/src/lib.rs index 7cd81d4c32..a9ffbcdc79 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/src/lib.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/src/lib.rs @@ -15,14 +15,14 @@ impl Summary for NewsArticle { } } -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } @@ -43,13 +43,13 @@ fn returns_summarizable(switch: bool) -> impl Summary { ), } } else { - Tweet { + SocialPost { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, - retweet: false, + repost: false, } } } diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-07-where-clause/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-07-where-clause/Cargo.toml index 4dbde90901..44949be6d3 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-07-where-clause/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-07-where-clause/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/src/main.rs index d144305cb0..4c35d90e3a 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/src/main.rs @@ -3,7 +3,7 @@ fn main() { let string2 = "efghijklmnopqrstuvwxyz"; let result = longest(string1.as_str(), string2); - println!("The longest string is {}", result); + println!("The longest string is {result}"); } // ANCHOR: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/output.txt b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/output.txt index 0c628b6977..9b9ef2338c 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/output.txt +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/output.txt @@ -1,10 +1,13 @@ $ cargo run Compiling chapter10 v0.1.0 (file:///projects/chapter10) -error[E0515]: cannot return reference to local variable `result` +error[E0515]: cannot return value referencing local variable `result` --> src/main.rs:11:5 | 11 | result.as_str() - | ^^^^^^^^^^^^^^^ returns a reference to data owned by the current function + | ------^^^^^^^^^ + | | + | returns a value referencing data owned by the current function + | `result` is borrowed here For more information about this error, try `rustc --explain E0515`. -error: could not compile `chapter10` due to previous error +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/src/main.rs index aca4be0a78..4d596ec434 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/src/main.rs @@ -3,7 +3,7 @@ fn main() { let string2 = "xyz"; let result = longest(string1.as_str(), string2); - println!("The longest string is {}", result); + println!("The longest string is {result}"); } // ANCHOR: here diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/src/main.rs index 32ad530b51..c04ec38236 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/src/main.rs @@ -13,7 +13,7 @@ impl<'a> ImportantExcerpt<'a> { // ANCHOR: 3rd impl<'a> ImportantExcerpt<'a> { fn announce_and_return_part(&self, announcement: &str) -> &str { - println!("Attention please: {}", announcement); + println!("Attention please: {announcement}"); self.part } } @@ -21,7 +21,7 @@ impl<'a> ImportantExcerpt<'a> { fn main() { let novel = String::from("Call me Ishmael. Some years ago..."); - let first_sentence = novel.split('.').next().expect("Could not find a '.'"); + let first_sentence = novel.split('.').next().unwrap(); let i = ImportantExcerpt { part: first_sentence, }; diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/Cargo.toml b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/Cargo.toml index 489f809672..a13293a336 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/Cargo.toml +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "chapter10" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/src/main.rs b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/src/main.rs index cfafa9a6d3..de3703f907 100644 --- a/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/src/main.rs +++ b/listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/src/main.rs @@ -7,7 +7,7 @@ fn main() { string2, "Today is someone's birthday!", ); - println!("The longest string is {}", result); + println!("The longest string is {result}"); } // ANCHOR: here @@ -21,11 +21,7 @@ fn longest_with_an_announcement<'a, T>( where T: Display, { - println!("Announcement! {}", ann); - if x.len() > y.len() { - x - } else { - y - } + println!("Announcement! {ann}"); + if x.len() > y.len() { x } else { y } } // ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/listing-11-01/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-01/Cargo.toml index b7d36d44cb..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/listing-11-01/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-01/Cargo.toml @@ -1,8 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" - -# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-01/output.txt b/listings/ch11-writing-automated-tests/listing-11-01/output.txt index c3e812ed80..76e144c47e 100644 --- a/listings/ch11-writing-automated-tests/listing-11-01/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-01/output.txt @@ -1,7 +1,7 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.57s - Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.57s + Running unittests src/lib.rs (target/debug/deps/adder-01ad14159ff659ab) running 1 test test tests::it_works ... ok diff --git a/listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs index 1b4a90c938..b93cf3ffd9 100644 --- a/listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs @@ -1,8 +1,14 @@ +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { + use super::*; + #[test] fn it_works() { - let result = 2 + 2; + let result = add(2, 2); assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/listing-11-03/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-03/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/listing-11-03/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-03/output.txt b/listings/ch11-writing-automated-tests/listing-11-03/output.txt index e8c31e79ec..830213172f 100644 --- a/listings/ch11-writing-automated-tests/listing-11-03/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-03/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.72s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.72s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 2 tests @@ -10,7 +10,9 @@ test tests::exploration ... ok failures: ---- tests::another stdout ---- -thread 'tests::another' panicked at 'Make this test fail', src/lib.rs:10:9 + +thread 'tests::another' panicked at src/lib.rs:17:9: +Make this test fail note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs index a9ec008919..336ea081a1 100644 --- a/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs @@ -1,9 +1,15 @@ -// ANCHOR: here +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { + use super::*; + #[test] fn exploration() { - assert_eq!(2 + 2, 4); + let result = add(2, 2); + assert_eq!(result, 4); } #[test] @@ -11,4 +17,3 @@ mod tests { panic!("Make this test fail"); } } -// ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/listing-11-05/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-05/Cargo.toml index 2447c67f51..7693d91073 100644 --- a/listings/ch11-writing-automated-tests/listing-11-05/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangle" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-05/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-05/src/lib.rs index 0f1bc4e084..0a03a2b447 100644 --- a/listings/ch11-writing-automated-tests/listing-11-05/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-05/src/lib.rs @@ -1,4 +1,3 @@ -// ANCHOR: here #[derive(Debug)] struct Rectangle { width: u32, @@ -10,4 +9,3 @@ impl Rectangle { self.width > other.width && self.height > other.height } } -// ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/listing-11-06/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-06/Cargo.toml index 2447c67f51..7693d91073 100644 --- a/listings/ch11-writing-automated-tests/listing-11-06/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangle" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-06/output.txt b/listings/ch11-writing-automated-tests/listing-11-06/output.txt index dad02b460f..e03add2290 100644 --- a/listings/ch11-writing-automated-tests/listing-11-06/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-06/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling rectangle v0.1.0 (file:///projects/rectangle) - Finished test [unoptimized + debuginfo] target(s) in 0.66s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s Running unittests src/lib.rs (target/debug/deps/rectangle-6584c4561e48942e) running 1 test diff --git a/listings/ch11-writing-automated-tests/listing-11-07/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-07/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/listing-11-07/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-07/output.txt b/listings/ch11-writing-automated-tests/listing-11-07/output.txt index fa02835bdc..908ed572c6 100644 --- a/listings/ch11-writing-automated-tests/listing-11-07/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-07/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.58s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.58s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test diff --git a/listings/ch11-writing-automated-tests/listing-11-07/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-07/src/lib.rs index 3e5d66bfaf..24790eb3a0 100644 --- a/listings/ch11-writing-automated-tests/listing-11-07/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-07/src/lib.rs @@ -1,4 +1,4 @@ -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { a + 2 } @@ -8,6 +8,7 @@ mod tests { #[test] fn it_adds_two() { - assert_eq!(4, add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/listing-11-08/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-08/Cargo.toml index 4e348c8d26..53e7b397ea 100644 --- a/listings/ch11-writing-automated-tests/listing-11-08/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-08/output.txt b/listings/ch11-writing-automated-tests/listing-11-08/output.txt index caca1542f8..a5a764377d 100644 --- a/listings/ch11-writing-automated-tests/listing-11-08/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-08/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished test [unoptimized + debuginfo] target(s) in 0.58s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.58s Running unittests src/lib.rs (target/debug/deps/guessing_game-57d70c3acb738f4d) running 1 test diff --git a/listings/ch11-writing-automated-tests/listing-11-08/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-08/src/lib.rs index 9391be5b1f..54e447bb93 100644 --- a/listings/ch11-writing-automated-tests/listing-11-08/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-08/src/lib.rs @@ -5,7 +5,7 @@ pub struct Guess { impl Guess { pub fn new(value: i32) -> Guess { if value < 1 || value > 100 { - panic!("Guess value must be between 1 and 100, got {}.", value); + panic!("Guess value must be between 1 and 100, got {value}."); } Guess { value } diff --git a/listings/ch11-writing-automated-tests/listing-11-09/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-09/Cargo.toml index 4e348c8d26..53e7b397ea 100644 --- a/listings/ch11-writing-automated-tests/listing-11-09/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-09/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-09/src/lib.rs index cc1c5c35d0..1bb464137b 100644 --- a/listings/ch11-writing-automated-tests/listing-11-09/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-09/src/lib.rs @@ -9,13 +9,11 @@ impl Guess { pub fn new(value: i32) -> Guess { if value < 1 { panic!( - "Guess value must be greater than or equal to 1, got {}.", - value + "Guess value must be greater than or equal to 1, got {value}." ); } else if value > 100 { panic!( - "Guess value must be less than or equal to 100, got {}.", - value + "Guess value must be less than or equal to 100, got {value}." ); } diff --git a/listings/ch11-writing-automated-tests/listing-11-10/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-10/Cargo.toml index f751864dec..84052beff0 100644 --- a/listings/ch11-writing-automated-tests/listing-11-10/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "silly-function" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-10/output.txt b/listings/ch11-writing-automated-tests/listing-11-10/output.txt index b0d10deaa8..6dc3371537 100644 --- a/listings/ch11-writing-automated-tests/listing-11-10/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-10/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling silly-function v0.1.0 (file:///projects/silly-function) - Finished test [unoptimized + debuginfo] target(s) in 0.58s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.58s Running unittests src/lib.rs (target/debug/deps/silly_function-160869f38cff9166) running 2 tests @@ -11,9 +11,11 @@ failures: ---- tests::this_test_will_fail stdout ---- I got the value 8 -thread 'tests::this_test_will_fail' panicked at 'assertion failed: `(left == right)` - left: `5`, - right: `10`', src/lib.rs:19:9 + +thread 'tests::this_test_will_fail' panicked at src/lib.rs:19:9: +assertion `left == right` failed + left: 10 + right: 5 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch11-writing-automated-tests/listing-11-10/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-10/src/lib.rs index 6fd76ce006..3fbde2a1ed 100644 --- a/listings/ch11-writing-automated-tests/listing-11-10/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-10/src/lib.rs @@ -1,5 +1,5 @@ fn prints_and_returns_10(a: i32) -> i32 { - println!("I got the value {}", a); + println!("I got the value {a}"); 10 } @@ -10,12 +10,12 @@ mod tests { #[test] fn this_test_will_pass() { let value = prints_and_returns_10(4); - assert_eq!(10, value); + assert_eq!(value, 10); } #[test] fn this_test_will_fail() { let value = prints_and_returns_10(8); - assert_eq!(5, value); + assert_eq!(value, 5); } } diff --git a/listings/ch11-writing-automated-tests/listing-11-11/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-11/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/listing-11-11/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-11/output.txt b/listings/ch11-writing-automated-tests/listing-11-11/output.txt index fe19c83c4b..a0fe55df11 100644 --- a/listings/ch11-writing-automated-tests/listing-11-11/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-11/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.62s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.62s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 3 tests diff --git a/listings/ch11-writing-automated-tests/listing-11-11/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-11/src/lib.rs index f56715263e..aec014381f 100644 --- a/listings/ch11-writing-automated-tests/listing-11-11/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-11/src/lib.rs @@ -1,4 +1,4 @@ -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { a + 2 } @@ -8,16 +8,19 @@ mod tests { #[test] fn add_two_and_two() { - assert_eq!(4, add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } #[test] fn add_three_and_two() { - assert_eq!(5, add_two(3)); + let result = add_two(3); + assert_eq!(result, 5); } #[test] fn one_hundred() { - assert_eq!(102, add_two(100)); + let result = add_two(100); + assert_eq!(result, 102); } } diff --git a/listings/ch11-writing-automated-tests/listing-11-12/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-12/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/listing-11-12/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-12/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-12/src/lib.rs index c3961b1f62..375466a1c2 100644 --- a/listings/ch11-writing-automated-tests/listing-11-12/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-12/src/lib.rs @@ -1,9 +1,9 @@ -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { internal_adder(a, 2) } -fn internal_adder(a: i32, b: i32) -> i32 { - a + b +fn internal_adder(left: u64, right: u64) -> u64 { + left + right } #[cfg(test)] @@ -12,6 +12,7 @@ mod tests { #[test] fn internal() { - assert_eq!(4, internal_adder(2, 2)); + let result = internal_adder(2, 2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/listing-11-13/Cargo.toml b/listings/ch11-writing-automated-tests/listing-11-13/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/listing-11-13/Cargo.toml +++ b/listings/ch11-writing-automated-tests/listing-11-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/listing-11-13/output.txt b/listings/ch11-writing-automated-tests/listing-11-13/output.txt index 22970e9e16..84344add72 100644 --- a/listings/ch11-writing-automated-tests/listing-11-13/output.txt +++ b/listings/ch11-writing-automated-tests/listing-11-13/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 1.31s + Finished `test` profile [unoptimized + debuginfo] target(s) in 1.31s Running unittests src/lib.rs (target/debug/deps/adder-1082c4b063a8fbe6) running 1 test diff --git a/listings/ch11-writing-automated-tests/listing-11-13/src/lib.rs b/listings/ch11-writing-automated-tests/listing-11-13/src/lib.rs index c3961b1f62..9ba15d8b22 100644 --- a/listings/ch11-writing-automated-tests/listing-11-13/src/lib.rs +++ b/listings/ch11-writing-automated-tests/listing-11-13/src/lib.rs @@ -1,9 +1,9 @@ -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: usize) -> usize { internal_adder(a, 2) } -fn internal_adder(a: i32, b: i32) -> i32 { - a + b +fn internal_adder(left: usize, right: usize) -> usize { + left + right } #[cfg(test)] @@ -12,6 +12,7 @@ mod tests { #[test] fn internal() { - assert_eq!(4, internal_adder(2, 2)); + let result = internal_adder(2, 2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/listing-11-13/tests/integration_test.rs b/listings/ch11-writing-automated-tests/listing-11-13/tests/integration_test.rs index e26fa71096..d6b88a7505 100644 --- a/listings/ch11-writing-automated-tests/listing-11-13/tests/integration_test.rs +++ b/listings/ch11-writing-automated-tests/listing-11-13/tests/integration_test.rs @@ -1,6 +1,7 @@ -use adder; +use adder::add_two; #[test] fn it_adds_two() { - assert_eq!(4, adder::add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } diff --git a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/output.txt b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/output.txt index 8a3330844b..79d3ae25ce 100644 --- a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.59s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.59s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test diff --git a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs index 330bddf6ac..5014a76f2b 100644 --- a/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs @@ -1,7 +1,14 @@ +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { + use super::*; + #[test] fn exploration() { - assert_eq!(2 + 2, 4); + let result = add(2, 2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/Cargo.toml index 2447c67f51..7693d91073 100644 --- a/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangle" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/output.txt b/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/output.txt index 30e45e5259..63044036d1 100644 --- a/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling rectangle v0.1.0 (file:///projects/rectangle) - Finished test [unoptimized + debuginfo] target(s) in 0.66s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s Running unittests src/lib.rs (target/debug/deps/rectangle-6584c4561e48942e) running 2 tests diff --git a/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/Cargo.toml index 2447c67f51..7693d91073 100644 --- a/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangle" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/output.txt b/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/output.txt index 6fbb5e4966..cd0d11a05b 100644 --- a/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling rectangle v0.1.0 (file:///projects/rectangle) - Finished test [unoptimized + debuginfo] target(s) in 0.66s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s Running unittests src/lib.rs (target/debug/deps/rectangle-6584c4561e48942e) running 2 tests @@ -10,7 +10,9 @@ test tests::smaller_cannot_hold_larger ... ok failures: ---- tests::larger_can_hold_smaller stdout ---- -thread 'tests::larger_can_hold_smaller' panicked at 'assertion failed: larger.can_hold(&smaller)', src/lib.rs:28:9 + +thread 'tests::larger_can_hold_smaller' panicked at src/lib.rs:28:9: +assertion failed: larger.can_hold(&smaller) note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/output.txt b/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/output.txt index 00bf63fff6..ca853f54cd 100644 --- a/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.61s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.61s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test @@ -9,9 +9,11 @@ test tests::it_adds_two ... FAILED failures: ---- tests::it_adds_two stdout ---- -thread 'tests::it_adds_two' panicked at 'assertion failed: `(left == right)` - left: `4`, - right: `5`', src/lib.rs:11:9 + +thread 'tests::it_adds_two' panicked at src/lib.rs:12:9: +assertion `left == right` failed + left: 5 + right: 4 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/src/lib.rs index f186625261..6ec4986c59 100644 --- a/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/src/lib.rs @@ -1,5 +1,5 @@ // ANCHOR: here -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { a + 3 } // ANCHOR_END: here @@ -10,6 +10,7 @@ mod tests { #[test] fn it_adds_two() { - assert_eq!(4, add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/no-listing-05-greeter/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-05-greeter/Cargo.toml index 90a826cf43..e1d72850f1 100644 --- a/listings/ch11-writing-automated-tests/no-listing-05-greeter/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-05-greeter/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "greeter" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-05-greeter/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-05-greeter/src/lib.rs index 3ba3d8819e..433cf148ea 100644 --- a/listings/ch11-writing-automated-tests/no-listing-05-greeter/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-05-greeter/src/lib.rs @@ -1,5 +1,5 @@ pub fn greeting(name: &str) -> String { - format!("Hello {}!", name) + format!("Hello {name}!") } #[cfg(test)] diff --git a/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/Cargo.toml index 90a826cf43..e1d72850f1 100644 --- a/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "greeter" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/output.txt b/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/output.txt index 68d724f118..4aad2212f6 100644 --- a/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling greeter v0.1.0 (file:///projects/greeter) - Finished test [unoptimized + debuginfo] target(s) in 0.91s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.91s Running unittests src/lib.rs (target/debug/deps/greeter-170b942eb5bf5e3a) running 1 test @@ -9,7 +9,9 @@ test tests::greeting_contains_name ... FAILED failures: ---- tests::greeting_contains_name stdout ---- -thread 'tests::greeting_contains_name' panicked at 'assertion failed: result.contains(\"Carol\")', src/lib.rs:12:9 + +thread 'tests::greeting_contains_name' panicked at src/lib.rs:12:9: +assertion failed: result.contains("Carol") note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/Cargo.toml index 90a826cf43..e1d72850f1 100644 --- a/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "greeter" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/output.txt b/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/output.txt index 03d6ad7f13..ac3044d20e 100644 --- a/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling greeter v0.1.0 (file:///projects/greeter) - Finished test [unoptimized + debuginfo] target(s) in 0.93s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.93s Running unittests src/lib.rs (target/debug/deps/greeter-170b942eb5bf5e3a) running 1 test @@ -9,7 +9,9 @@ test tests::greeting_contains_name ... FAILED failures: ---- tests::greeting_contains_name stdout ---- -thread 'tests::greeting_contains_name' panicked at 'Greeting did not contain name, value was `Hello!`', src/lib.rs:12:9 + +thread 'tests::greeting_contains_name' panicked at src/lib.rs:12:9: +Greeting did not contain name, value was `Hello!` note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/src/lib.rs index 519c7a4c6f..8bbaca53fd 100644 --- a/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/src/lib.rs @@ -12,8 +12,7 @@ mod tests { let result = greeting("Carol"); assert!( result.contains("Carol"), - "Greeting did not contain name, value was `{}`", - result + "Greeting did not contain name, value was `{result}`" ); } // ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/Cargo.toml index 4e348c8d26..53e7b397ea 100644 --- a/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/output.txt b/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/output.txt index 9318d4ce0d..2936e3a065 100644 --- a/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished test [unoptimized + debuginfo] target(s) in 0.62s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.62s Running unittests src/lib.rs (target/debug/deps/guessing_game-57d70c3acb738f4d) running 1 test @@ -9,7 +9,7 @@ test tests::greater_than_100 - should panic ... FAILED failures: ---- tests::greater_than_100 stdout ---- -note: test did not panic as expected +note: test did not panic as expected at src/lib.rs:21:8 failures: tests::greater_than_100 diff --git a/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/src/lib.rs index 32540ba83c..0f962fcd79 100644 --- a/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/src/lib.rs @@ -7,7 +7,7 @@ pub struct Guess { impl Guess { pub fn new(value: i32) -> Guess { if value < 1 { - panic!("Guess value must be between 1 and 100, got {}.", value); + panic!("Guess value must be between 1 and 100, got {value}."); } Guess { value } diff --git a/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/Cargo.toml index 4e348c8d26..53e7b397ea 100644 --- a/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/output.txt b/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/output.txt index 0b045e8be9..fc8d13fab2 100644 --- a/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished test [unoptimized + debuginfo] target(s) in 0.66s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s Running unittests src/lib.rs (target/debug/deps/guessing_game-57d70c3acb738f4d) running 1 test @@ -9,11 +9,13 @@ test tests::greater_than_100 - should panic ... FAILED failures: ---- tests::greater_than_100 stdout ---- -thread 'tests::greater_than_100' panicked at 'Guess value must be greater than or equal to 1, got 200.', src/lib.rs:13:13 + +thread 'tests::greater_than_100' panicked at src/lib.rs:12:13: +Guess value must be greater than or equal to 1, got 200. note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace note: panic did not contain expected string - panic message: `"Guess value must be greater than or equal to 1, got 200."`, - expected substring: `"less than or equal to 100"` + panic message: "Guess value must be greater than or equal to 1, got 200." + expected substring: "less than or equal to 100" failures: tests::greater_than_100 diff --git a/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/src/lib.rs index 7703dd75ae..fb5fc0e77b 100644 --- a/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/src/lib.rs @@ -7,13 +7,11 @@ impl Guess { // ANCHOR: here if value < 1 { panic!( - "Guess value must be less than or equal to 100, got {}.", - value + "Guess value must be less than or equal to 100, got {value}." ); } else if value > 100 { panic!( - "Guess value must be greater than or equal to 1, got {}.", - value + "Guess value must be greater than or equal to 1, got {value}." ); } // ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs index 6284f4f291..87db05b619 100644 --- a/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs @@ -1,11 +1,21 @@ +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + +// ANCHOR: here #[cfg(test)] mod tests { + use super::*; + #[test] fn it_works() -> Result<(), String> { - if 2 + 2 == 4 { + let result = add(2, 2); + + if result == 4 { Ok(()) } else { Err(String::from("two plus two does not equal four")) } } } +// ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/output.txt b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/output.txt index c559de8d00..bc40c96eb8 100644 --- a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/output.txt @@ -1,11 +1,11 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.60s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.60s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 2 tests -test expensive_test ... ignored -test it_works ... ok +test tests::expensive_test ... ignored +test tests::it_works ... ok test result: ok. 1 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out; finished in 0.00s diff --git a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs index d54a6095d7..05fbe1af0a 100644 --- a/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs @@ -1,10 +1,22 @@ -#[test] -fn it_works() { - assert_eq!(2 + 2, 4); +pub fn add(left: u64, right: u64) -> u64 { + left + right } -#[test] -#[ignore] -fn expensive_test() { - // code that takes an hour to run +// ANCHOR: here +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn it_works() { + let result = add(2, 2); + assert_eq!(result, 4); + } + + #[test] + #[ignore] + fn expensive_test() { + // code that takes an hour to run + } } +// ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/output.txt b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/output.txt index 324d566abd..e258394593 100644 --- a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/output.txt +++ b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.89s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.89s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test diff --git a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/src/lib.rs index c3961b1f62..9ba15d8b22 100644 --- a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/src/lib.rs @@ -1,9 +1,9 @@ -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: usize) -> usize { internal_adder(a, 2) } -fn internal_adder(a: i32, b: i32) -> i32 { - a + b +fn internal_adder(left: usize, right: usize) -> usize { + left + right } #[cfg(test)] @@ -12,6 +12,7 @@ mod tests { #[test] fn internal() { - assert_eq!(4, internal_adder(2, 2)); + let result = internal_adder(2, 2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/tests/integration_test.rs b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/tests/integration_test.rs index e26fa71096..d6b88a7505 100644 --- a/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/tests/integration_test.rs +++ b/listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/tests/integration_test.rs @@ -1,6 +1,7 @@ -use adder; +use adder::add_two; #[test] fn it_adds_two() { - assert_eq!(4, adder::add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } diff --git a/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/Cargo.toml b/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/Cargo.toml +++ b/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/src/lib.rs b/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/src/lib.rs index c3961b1f62..9ba15d8b22 100644 --- a/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/src/lib.rs +++ b/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/src/lib.rs @@ -1,9 +1,9 @@ -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: usize) -> usize { internal_adder(a, 2) } -fn internal_adder(a: i32, b: i32) -> i32 { - a + b +fn internal_adder(left: usize, right: usize) -> usize { + left + right } #[cfg(test)] @@ -12,6 +12,7 @@ mod tests { #[test] fn internal() { - assert_eq!(4, internal_adder(2, 2)); + let result = internal_adder(2, 2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/tests/integration_test.rs b/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/tests/integration_test.rs index 58b8b7b89b..d18b5b689b 100644 --- a/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/tests/integration_test.rs +++ b/listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/tests/integration_test.rs @@ -1,9 +1,11 @@ -use adder; +use adder::add_two; mod common; #[test] fn it_adds_two() { common::setup(); - assert_eq!(4, adder::add_two(2)); + + let result = add_two(2); + assert_eq!(result, 4); } diff --git a/listings/ch11-writing-automated-tests/output-only-01-show-output/Cargo.toml b/listings/ch11-writing-automated-tests/output-only-01-show-output/Cargo.toml index f751864dec..84052beff0 100644 --- a/listings/ch11-writing-automated-tests/output-only-01-show-output/Cargo.toml +++ b/listings/ch11-writing-automated-tests/output-only-01-show-output/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "silly-function" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/output-only-01-show-output/output.txt b/listings/ch11-writing-automated-tests/output-only-01-show-output/output.txt index bc03145a18..b541a0dd73 100644 --- a/listings/ch11-writing-automated-tests/output-only-01-show-output/output.txt +++ b/listings/ch11-writing-automated-tests/output-only-01-show-output/output.txt @@ -1,6 +1,6 @@ $ cargo test -- --show-output Compiling silly-function v0.1.0 (file:///projects/silly-function) - Finished test [unoptimized + debuginfo] target(s) in 0.60s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.60s Running unittests src/lib.rs (target/debug/deps/silly_function-160869f38cff9166) running 2 tests @@ -20,9 +20,11 @@ failures: ---- tests::this_test_will_fail stdout ---- I got the value 8 -thread 'tests::this_test_will_fail' panicked at 'assertion failed: `(left == right)` - left: `5`, - right: `10`', src/lib.rs:19:9 + +thread 'tests::this_test_will_fail' panicked at src/lib.rs:19:9: +assertion `left == right` failed + left: 10 + right: 5 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch11-writing-automated-tests/output-only-01-show-output/src/lib.rs b/listings/ch11-writing-automated-tests/output-only-01-show-output/src/lib.rs index 43c4c92f9a..141d51ee6e 100644 --- a/listings/ch11-writing-automated-tests/output-only-01-show-output/src/lib.rs +++ b/listings/ch11-writing-automated-tests/output-only-01-show-output/src/lib.rs @@ -1,5 +1,5 @@ pub fn prints_and_returns_10(a: i32) -> i32 { - println!("I got the value {}", a); + println!("I got the value {a}"); 10 } @@ -10,12 +10,12 @@ mod tests { #[test] fn this_test_will_pass() { let value = prints_and_returns_10(4); - assert_eq!(10, value); + assert_eq!(value, 10); } #[test] fn this_test_will_fail() { let value = prints_and_returns_10(8); - assert_eq!(5, value); + assert_eq!(value, 5); } } diff --git a/listings/ch11-writing-automated-tests/output-only-02-single-test/Cargo.toml b/listings/ch11-writing-automated-tests/output-only-02-single-test/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/output-only-02-single-test/Cargo.toml +++ b/listings/ch11-writing-automated-tests/output-only-02-single-test/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/output-only-02-single-test/output.txt b/listings/ch11-writing-automated-tests/output-only-02-single-test/output.txt index f2da984427..47e2a478e6 100644 --- a/listings/ch11-writing-automated-tests/output-only-02-single-test/output.txt +++ b/listings/ch11-writing-automated-tests/output-only-02-single-test/output.txt @@ -1,6 +1,6 @@ $ cargo test one_hundred Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.69s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.69s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test diff --git a/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/Cargo.toml b/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/Cargo.toml +++ b/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/output.txt b/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/output.txt index 255a051b51..d08940aeed 100644 --- a/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/output.txt +++ b/listings/ch11-writing-automated-tests/output-only-03-multiple-tests/output.txt @@ -1,6 +1,6 @@ $ cargo test add Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.61s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.61s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 2 tests diff --git a/listings/ch11-writing-automated-tests/output-only-04-running-ignored/Cargo.toml b/listings/ch11-writing-automated-tests/output-only-04-running-ignored/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/output-only-04-running-ignored/Cargo.toml +++ b/listings/ch11-writing-automated-tests/output-only-04-running-ignored/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/output-only-04-running-ignored/output.txt b/listings/ch11-writing-automated-tests/output-only-04-running-ignored/output.txt index b37868d3db..8f0d7dfe52 100644 --- a/listings/ch11-writing-automated-tests/output-only-04-running-ignored/output.txt +++ b/listings/ch11-writing-automated-tests/output-only-04-running-ignored/output.txt @@ -1,10 +1,10 @@ $ cargo test -- --ignored Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.61s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.61s Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test -test expensive_test ... ok +test tests::expensive_test ... ok test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s diff --git a/listings/ch11-writing-automated-tests/output-only-04-running-ignored/src/lib.rs b/listings/ch11-writing-automated-tests/output-only-04-running-ignored/src/lib.rs index 2290c699d8..05fbe1af0a 100644 --- a/listings/ch11-writing-automated-tests/output-only-04-running-ignored/src/lib.rs +++ b/listings/ch11-writing-automated-tests/output-only-04-running-ignored/src/lib.rs @@ -1,12 +1,22 @@ -// ANCHOR: here -#[test] -fn it_works() { - assert_eq!(2 + 2, 4); +pub fn add(left: u64, right: u64) -> u64 { + left + right } -#[test] -#[ignore] -fn expensive_test() { - // code that takes an hour to run +// ANCHOR: here +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn it_works() { + let result = add(2, 2); + assert_eq!(result, 4); + } + + #[test] + #[ignore] + fn expensive_test() { + // code that takes an hour to run + } } // ANCHOR_END: here diff --git a/listings/ch11-writing-automated-tests/output-only-05-single-integration/Cargo.toml b/listings/ch11-writing-automated-tests/output-only-05-single-integration/Cargo.toml index e61cb12e3e..9a5826ad47 100644 --- a/listings/ch11-writing-automated-tests/output-only-05-single-integration/Cargo.toml +++ b/listings/ch11-writing-automated-tests/output-only-05-single-integration/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch11-writing-automated-tests/output-only-05-single-integration/output.txt b/listings/ch11-writing-automated-tests/output-only-05-single-integration/output.txt index 260beaa2d6..2745d0f81a 100644 --- a/listings/ch11-writing-automated-tests/output-only-05-single-integration/output.txt +++ b/listings/ch11-writing-automated-tests/output-only-05-single-integration/output.txt @@ -1,6 +1,6 @@ $ cargo test --test integration_test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.64s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.64s Running tests/integration_test.rs (target/debug/deps/integration_test-82e7799c1bc62298) running 1 test diff --git a/listings/ch11-writing-automated-tests/output-only-05-single-integration/src/lib.rs b/listings/ch11-writing-automated-tests/output-only-05-single-integration/src/lib.rs index c3961b1f62..9ba15d8b22 100644 --- a/listings/ch11-writing-automated-tests/output-only-05-single-integration/src/lib.rs +++ b/listings/ch11-writing-automated-tests/output-only-05-single-integration/src/lib.rs @@ -1,9 +1,9 @@ -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: usize) -> usize { internal_adder(a, 2) } -fn internal_adder(a: i32, b: i32) -> i32 { - a + b +fn internal_adder(left: usize, right: usize) -> usize { + left + right } #[cfg(test)] @@ -12,6 +12,7 @@ mod tests { #[test] fn internal() { - assert_eq!(4, internal_adder(2, 2)); + let result = internal_adder(2, 2); + assert_eq!(result, 4); } } diff --git a/listings/ch11-writing-automated-tests/output-only-05-single-integration/tests/integration_test.rs b/listings/ch11-writing-automated-tests/output-only-05-single-integration/tests/integration_test.rs index e26fa71096..d6b88a7505 100644 --- a/listings/ch11-writing-automated-tests/output-only-05-single-integration/tests/integration_test.rs +++ b/listings/ch11-writing-automated-tests/output-only-05-single-integration/tests/integration_test.rs @@ -1,6 +1,7 @@ -use adder; +use adder::add_two; #[test] fn it_adds_two() { - assert_eq!(4, adder::add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } diff --git a/listings/ch12-an-io-project/listing-12-01/Cargo.toml b/listings/ch12-an-io-project/listing-12-01/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-01/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-01/output.txt b/listings/ch12-an-io-project/listing-12-01/output.txt index 529115f8d4..d2abb056be 100644 --- a/listings/ch12-an-io-project/listing-12-01/output.txt +++ b/listings/ch12-an-io-project/listing-12-01/output.txt @@ -1,7 +1,7 @@ $ cargo run Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.61s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.61s Running `target/debug/minigrep` -[src/main.rs:5] args = [ +[src/main.rs:5:5] args = [ "target/debug/minigrep", ] diff --git a/listings/ch12-an-io-project/listing-12-02/Cargo.toml b/listings/ch12-an-io-project/listing-12-02/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-02/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-02/output.txt b/listings/ch12-an-io-project/listing-12-02/output.txt index 6ef87f7ce0..ad87dcf06d 100644 --- a/listings/ch12-an-io-project/listing-12-02/output.txt +++ b/listings/ch12-an-io-project/listing-12-02/output.txt @@ -1,6 +1,6 @@ $ cargo run -- test sample.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep test sample.txt` Searching for test In file sample.txt diff --git a/listings/ch12-an-io-project/listing-12-02/src/main.rs b/listings/ch12-an-io-project/listing-12-02/src/main.rs index ae2fa7bb1b..afc3c3c9f9 100644 --- a/listings/ch12-an-io-project/listing-12-02/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-02/src/main.rs @@ -6,6 +6,6 @@ fn main() { let query = &args[1]; let file_path = &args[2]; - println!("Searching for {}", query); - println!("In file {}", file_path); + println!("Searching for {query}"); + println!("In file {file_path}"); } diff --git a/listings/ch12-an-io-project/listing-12-03/Cargo.toml b/listings/ch12-an-io-project/listing-12-03/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-03/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-03/src/main.rs b/listings/ch12-an-io-project/listing-12-03/src/main.rs index ae2fa7bb1b..afc3c3c9f9 100644 --- a/listings/ch12-an-io-project/listing-12-03/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-03/src/main.rs @@ -6,6 +6,6 @@ fn main() { let query = &args[1]; let file_path = &args[2]; - println!("Searching for {}", query); - println!("In file {}", file_path); + println!("Searching for {query}"); + println!("In file {file_path}"); } diff --git a/listings/ch12-an-io-project/listing-12-04/Cargo.toml b/listings/ch12-an-io-project/listing-12-04/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-04/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-04/output.txt b/listings/ch12-an-io-project/listing-12-04/output.txt index 6582ca1693..d8cfe392df 100644 --- a/listings/ch12-an-io-project/listing-12-04/output.txt +++ b/listings/ch12-an-io-project/listing-12-04/output.txt @@ -1,6 +1,6 @@ $ cargo run -- the poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep the poem.txt` Searching for the In file poem.txt diff --git a/listings/ch12-an-io-project/listing-12-04/src/main.rs b/listings/ch12-an-io-project/listing-12-04/src/main.rs index 944e4300ec..f343249797 100644 --- a/listings/ch12-an-io-project/listing-12-04/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-04/src/main.rs @@ -10,9 +10,9 @@ fn main() { let query = &args[1]; let file_path = &args[2]; - println!("Searching for {}", query); + println!("Searching for {query}"); // ANCHOR: here - println!("In file {}", file_path); + println!("In file {file_path}"); let contents = fs::read_to_string(file_path) .expect("Should have been able to read the file"); diff --git a/listings/ch12-an-io-project/listing-12-05/Cargo.toml b/listings/ch12-an-io-project/listing-12-05/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-05/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-05/src/main.rs b/listings/ch12-an-io-project/listing-12-05/src/main.rs index 0615918338..838cacf39a 100644 --- a/listings/ch12-an-io-project/listing-12-05/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-05/src/main.rs @@ -10,8 +10,8 @@ fn main() { // --snip-- // ANCHOR_END: here - println!("Searching for {}", query); - println!("In file {}", file_path); + println!("Searching for {query}"); + println!("In file {file_path}"); let contents = fs::read_to_string(file_path) .expect("Should have been able to read the file"); diff --git a/listings/ch12-an-io-project/listing-12-06/Cargo.toml b/listings/ch12-an-io-project/listing-12-06/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-06/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-07/Cargo.toml b/listings/ch12-an-io-project/listing-12-07/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-07/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-07/output.txt b/listings/ch12-an-io-project/listing-12-07/output.txt index d3fa7777d5..03ce35173d 100644 --- a/listings/ch12-an-io-project/listing-12-07/output.txt +++ b/listings/ch12-an-io-project/listing-12-07/output.txt @@ -1,6 +1,8 @@ $ cargo run Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep` -thread 'main' panicked at 'index out of bounds: the len is 1 but the index is 1', src/main.rs:27:21 + +thread 'main' panicked at src/main.rs:27:21: +index out of bounds: the len is 1 but the index is 1 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch12-an-io-project/listing-12-08/Cargo.toml b/listings/ch12-an-io-project/listing-12-08/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-08/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-08/output.txt b/listings/ch12-an-io-project/listing-12-08/output.txt index de2abd1afc..86174205d5 100644 --- a/listings/ch12-an-io-project/listing-12-08/output.txt +++ b/listings/ch12-an-io-project/listing-12-08/output.txt @@ -1,6 +1,8 @@ $ cargo run Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep` -thread 'main' panicked at 'not enough arguments', src/main.rs:26:13 + +thread 'main' panicked at src/main.rs:26:13: +not enough arguments note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch12-an-io-project/listing-12-09/Cargo.toml b/listings/ch12-an-io-project/listing-12-09/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-09/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-10/Cargo.toml b/listings/ch12-an-io-project/listing-12-10/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-10/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-10/output.txt b/listings/ch12-an-io-project/listing-12-10/output.txt index 7aad57f52d..c5e085b45e 100644 --- a/listings/ch12-an-io-project/listing-12-10/output.txt +++ b/listings/ch12-an-io-project/listing-12-10/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.48s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s Running `target/debug/minigrep` Problem parsing arguments: not enough arguments diff --git a/listings/ch12-an-io-project/listing-12-11/Cargo.toml b/listings/ch12-an-io-project/listing-12-11/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-11/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-12/Cargo.toml b/listings/ch12-an-io-project/listing-12-12/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-12/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-12/output.txt b/listings/ch12-an-io-project/listing-12-12/output.txt index 9870b21255..6c5e67ba45 100644 --- a/listings/ch12-an-io-project/listing-12-12/output.txt +++ b/listings/ch12-an-io-project/listing-12-12/output.txt @@ -1,4 +1,4 @@ -$ cargo run the poem.txt +$ cargo run -- the poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) warning: unused `Result` that must be used --> src/main.rs:19:5 @@ -8,9 +8,13 @@ warning: unused `Result` that must be used | = note: this `Result` may be an `Err` variant, which should be handled = note: `#[warn(unused_must_use)]` on by default +help: use `let _ = ...` to ignore the resulting value + | +19 | let _ = run(config); + | +++++++ warning: `minigrep` (bin "minigrep") generated 1 warning - Finished dev [unoptimized + debuginfo] target(s) in 0.71s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.71s Running `target/debug/minigrep the poem.txt` Searching for the In file poem.txt diff --git a/listings/ch12-an-io-project/listing-12-13/Cargo.toml b/listings/ch12-an-io-project/listing-12-13/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-13/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-13/src/lib.rs b/listings/ch12-an-io-project/listing-12-13/src/lib.rs index 1a3c480893..f039accd26 100644 --- a/listings/ch12-an-io-project/listing-12-13/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-13/src/lib.rs @@ -1,36 +1,3 @@ -// ANCHOR: here -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { + unimplemented!(); } - -impl Config { - pub fn build(args: &[String]) -> Result { - // --snip-- - // ANCHOR_END: here - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - // ANCHOR: here - } -} - -pub fn run(config: Config) -> Result<(), Box> { - // --snip-- - // ANCHOR_END: here - let contents = fs::read_to_string(config.file_path)?; - - println!("With text:\n{contents}"); - - Ok(()) - // ANCHOR: here -} -// ANCHOR_END: here diff --git a/listings/ch12-an-io-project/listing-12-13/src/main.rs b/listings/ch12-an-io-project/listing-12-13/src/main.rs index 09756ca3f0..dfdca75bc9 100644 --- a/listings/ch12-an-io-project/listing-12-13/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-13/src/main.rs @@ -1,4 +1,6 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; fn main() { @@ -17,3 +19,29 @@ fn main() { process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + println!("With text:\n{contents}"); + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-14/Cargo.toml b/listings/ch12-an-io-project/listing-12-14/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-14/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-14/src/lib.rs b/listings/ch12-an-io-project/listing-12-14/src/lib.rs index 4f3a4e865b..f039accd26 100644 --- a/listings/ch12-an-io-project/listing-12-14/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-14/src/lib.rs @@ -1,28 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - println!("With text:\n{contents}"); - - Ok(()) +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { + unimplemented!(); } diff --git a/listings/ch12-an-io-project/listing-12-14/src/main.rs b/listings/ch12-an-io-project/listing-12-14/src/main.rs index 3b76009b50..77148ce232 100644 --- a/listings/ch12-an-io-project/listing-12-14/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-14/src/main.rs @@ -1,8 +1,11 @@ -// ANCHOR: here use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +// ANCHOR: here +// --snip-- +use minigrep::search; fn main() { // --snip-- @@ -14,16 +17,43 @@ fn main() { process::exit(1); }); - println!("Searching for {}", config.query); - println!("In file {}", config.file_path); - - // ANCHOR: here - if let Err(e) = minigrep::run(config) { - // --snip-- - // ANCHOR_END: here + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); - // ANCHOR: here } + // ANCHOR: here +} + +// --snip-- + +// ANCHOR_END: here + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +// ANCHOR: here +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) } // ANCHOR_END: here diff --git a/listings/ch12-an-io-project/listing-12-15/Cargo.toml b/listings/ch12-an-io-project/listing-12-15/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-15/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-15/src/lib.rs b/listings/ch12-an-io-project/listing-12-15/src/lib.rs index 20c4a782b9..fcac0a659b 100644 --- a/listings/ch12-an-io-project/listing-12-15/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-15/src/lib.rs @@ -1,31 +1,10 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - Ok(()) +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { + unimplemented!(); } // ANCHOR: here +// --snip-- + #[cfg(test)] mod tests { use super::*; diff --git a/listings/ch12-an-io-project/listing-12-15/src/main.rs b/listings/ch12-an-io-project/listing-12-15/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/listing-12-15/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-15/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-16/Cargo.toml b/listings/ch12-an-io-project/listing-12-16/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-16/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-16/output.txt b/listings/ch12-an-io-project/listing-12-16/output.txt index be4a97eea2..69f41a6c9c 100644 --- a/listings/ch12-an-io-project/listing-12-16/output.txt +++ b/listings/ch12-an-io-project/listing-12-16/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished test [unoptimized + debuginfo] target(s) in 0.97s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.97s Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) running 1 test @@ -9,9 +9,11 @@ test tests::one_result ... FAILED failures: ---- tests::one_result stdout ---- -thread 'tests::one_result' panicked at 'assertion failed: `(left == right)` - left: `["safe, fast, productive."]`, - right: `[]`', src/lib.rs:44:9 + +thread 'tests::one_result' panicked at src/lib.rs:17:9: +assertion `left == right` failed + left: ["safe, fast, productive."] + right: [] note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch12-an-io-project/listing-12-16/src/lib.rs b/listings/ch12-an-io-project/listing-12-16/src/lib.rs index f5e593484a..fa9680436c 100644 --- a/listings/ch12-an-io-project/listing-12-16/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-16/src/lib.rs @@ -1,30 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - Ok(()) -} - // ANCHOR: here pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { vec![] diff --git a/listings/ch12-an-io-project/listing-12-16/src/main.rs b/listings/ch12-an-io-project/listing-12-16/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/listing-12-16/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-16/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-17/Cargo.toml b/listings/ch12-an-io-project/listing-12-17/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-17/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-17/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-17/src/lib.rs b/listings/ch12-an-io-project/listing-12-17/src/lib.rs index cb9fab4016..8b381b320e 100644 --- a/listings/ch12-an-io-project/listing-12-17/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-17/src/lib.rs @@ -1,30 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - Ok(()) -} - // ANCHOR: here pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { for line in contents.lines() { diff --git a/listings/ch12-an-io-project/listing-12-17/src/main.rs b/listings/ch12-an-io-project/listing-12-17/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/listing-12-17/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-17/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-18/Cargo.toml b/listings/ch12-an-io-project/listing-12-18/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-18/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-18/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-18/src/lib.rs b/listings/ch12-an-io-project/listing-12-18/src/lib.rs index a05d046d7d..256d6b527a 100644 --- a/listings/ch12-an-io-project/listing-12-18/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-18/src/lib.rs @@ -1,30 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - Ok(()) -} - // ANCHOR: here pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { for line in contents.lines() { diff --git a/listings/ch12-an-io-project/listing-12-18/src/main.rs b/listings/ch12-an-io-project/listing-12-18/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/listing-12-18/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-18/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-19/Cargo.toml b/listings/ch12-an-io-project/listing-12-19/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-19/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-19/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-19/output.txt b/listings/ch12-an-io-project/listing-12-19/output.txt index 9b2078cb82..ed87e4f582 100644 --- a/listings/ch12-an-io-project/listing-12-19/output.txt +++ b/listings/ch12-an-io-project/listing-12-19/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished test [unoptimized + debuginfo] target(s) in 1.22s + Finished `test` profile [unoptimized + debuginfo] target(s) in 1.22s Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) running 1 test diff --git a/listings/ch12-an-io-project/listing-12-19/src/lib.rs b/listings/ch12-an-io-project/listing-12-19/src/lib.rs index f5d3ffa9f6..a169012b9e 100644 --- a/listings/ch12-an-io-project/listing-12-19/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-19/src/lib.rs @@ -1,30 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - Ok(()) -} - // ANCHOR: here // ANCHOR: ch13 pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { diff --git a/listings/ch12-an-io-project/listing-12-19/src/main.rs b/listings/ch12-an-io-project/listing-12-19/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/listing-12-19/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-19/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-20/Cargo.toml b/listings/ch12-an-io-project/listing-12-20/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-20/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-20/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-20/src/lib.rs b/listings/ch12-an-io-project/listing-12-20/src/lib.rs index a757f7f550..333d7513e5 100644 --- a/listings/ch12-an-io-project/listing-12-20/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-20/src/lib.rs @@ -1,34 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - for line in search(&config.query, &contents) { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch12-an-io-project/listing-12-20/src/main.rs b/listings/ch12-an-io-project/listing-12-20/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/listing-12-20/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-20/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-21/Cargo.toml b/listings/ch12-an-io-project/listing-12-21/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-21/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-21/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-21/output.txt b/listings/ch12-an-io-project/listing-12-21/output.txt index dafeb7862c..945df3fd52 100644 --- a/listings/ch12-an-io-project/listing-12-21/output.txt +++ b/listings/ch12-an-io-project/listing-12-21/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished test [unoptimized + debuginfo] target(s) in 1.33s + Finished `test` profile [unoptimized + debuginfo] target(s) in 1.33s Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) running 2 tests diff --git a/listings/ch12-an-io-project/listing-12-21/src/lib.rs b/listings/ch12-an-io-project/listing-12-21/src/lib.rs index 3aaa04082c..b534d03cc3 100644 --- a/listings/ch12-an-io-project/listing-12-21/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-21/src/lib.rs @@ -1,34 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - for line in search(&config.query, &contents) { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch12-an-io-project/listing-12-21/src/main.rs b/listings/ch12-an-io-project/listing-12-21/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/listing-12-21/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-21/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-22/Cargo.toml b/listings/ch12-an-io-project/listing-12-22/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-22/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-22/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-22/src/lib.rs b/listings/ch12-an-io-project/listing-12-22/src/lib.rs index c3f4723f10..b534d03cc3 100644 --- a/listings/ch12-an-io-project/listing-12-22/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-22/src/lib.rs @@ -1,45 +1,3 @@ -use std::error::Error; -use std::fs; - -// ANCHOR: here -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} -// ANCHOR_END: here - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -// ANCHOR: there -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} -// ANCHOR_END: there - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); @@ -52,6 +10,7 @@ pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { results } +// ANCHOR: here pub fn search_case_insensitive<'a>( query: &str, contents: &'a str, @@ -67,6 +26,7 @@ pub fn search_case_insensitive<'a>( results } +// ANCHOR_END: here #[cfg(test)] mod tests { diff --git a/listings/ch12-an-io-project/listing-12-22/src/main.rs b/listings/ch12-an-io-project/listing-12-22/src/main.rs index a4f8a74114..16b509d6b1 100644 --- a/listings/ch12-an-io-project/listing-12-22/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-22/src/main.rs @@ -1,7 +1,14 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +// ANCHOR: there +use minigrep::{search, search_case_insensitive}; + +// --snip-- + +// ANCHOR_END: there fn main() { let args: Vec = env::args().collect(); @@ -11,8 +18,47 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +// ANCHOR: here +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} +// ANCHOR_END: here + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +// ANCHOR: there +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} +// ANCHOR_END: there diff --git a/listings/ch12-an-io-project/listing-12-23/Cargo.toml b/listings/ch12-an-io-project/listing-12-23/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-23/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-23/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-23/output.txt b/listings/ch12-an-io-project/listing-12-23/output.txt index eaffc2f24d..5c6fc0c53b 100644 --- a/listings/ch12-an-io-project/listing-12-23/output.txt +++ b/listings/ch12-an-io-project/listing-12-23/output.txt @@ -1,6 +1,6 @@ $ cargo run -- to poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep to poem.txt` Are you nobody, too? How dreary to be somebody! diff --git a/listings/ch12-an-io-project/listing-12-23/src/lib.rs b/listings/ch12-an-io-project/listing-12-23/src/lib.rs index 20eda21975..0c48286ded 100644 --- a/listings/ch12-an-io-project/listing-12-23/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-23/src/lib.rs @@ -1,54 +1,3 @@ -// ANCHOR: here -use std::env; -// --snip-- - -// ANCHOR_END: here -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -// ANCHOR: here -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} -// ANCHOR_END: here - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch12-an-io-project/listing-12-23/src/main.rs b/listings/ch12-an-io-project/listing-12-23/src/main.rs index a4f8a74114..0579b5e2fb 100644 --- a/listings/ch12-an-io-project/listing-12-23/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-23/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::{search, search_case_insensitive}; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,51 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} + +// ANCHOR: here +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + let ignore_case = env::var("IGNORE_CASE").is_ok(); + + Ok(Config { + query, + file_path, + ignore_case, + }) + } +} +// ANCHOR_END: here + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/listing-12-24/Cargo.toml b/listings/ch12-an-io-project/listing-12-24/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/listing-12-24/Cargo.toml +++ b/listings/ch12-an-io-project/listing-12-24/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/listing-12-24/src/lib.rs b/listings/ch12-an-io-project/listing-12-24/src/lib.rs index 292b097897..0c48286ded 100644 --- a/listings/ch12-an-io-project/listing-12-24/src/lib.rs +++ b/listings/ch12-an-io-project/listing-12-24/src/lib.rs @@ -1,48 +1,3 @@ -use std::env; -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch12-an-io-project/listing-12-24/src/main.rs b/listings/ch12-an-io-project/listing-12-24/src/main.rs index 1278a6c174..eb49fae032 100644 --- a/listings/ch12-an-io-project/listing-12-24/src/main.rs +++ b/listings/ch12-an-io-project/listing-12-24/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::{search, search_case_insensitive}; // ANCHOR: here fn main() { @@ -12,9 +14,50 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { eprintln!("Application error: {e}"); process::exit(1); } } // ANCHOR_END: here + +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + let ignore_case = env::var("IGNORE_CASE").is_ok(); + + Ok(Config { + query, + file_path, + ignore_case, + }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/no-listing-01-handling-errors-in-main/Cargo.toml b/listings/ch12-an-io-project/no-listing-01-handling-errors-in-main/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/no-listing-01-handling-errors-in-main/Cargo.toml +++ b/listings/ch12-an-io-project/no-listing-01-handling-errors-in-main/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/no-listing-02-using-search-in-run/Cargo.toml b/listings/ch12-an-io-project/no-listing-02-using-search-in-run/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/no-listing-02-using-search-in-run/Cargo.toml +++ b/listings/ch12-an-io-project/no-listing-02-using-search-in-run/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/no-listing-02-using-search-in-run/output.txt b/listings/ch12-an-io-project/no-listing-02-using-search-in-run/output.txt index a5a4ef8c2b..44b203620b 100644 --- a/listings/ch12-an-io-project/no-listing-02-using-search-in-run/output.txt +++ b/listings/ch12-an-io-project/no-listing-02-using-search-in-run/output.txt @@ -1,5 +1,5 @@ $ cargo run -- frog poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.38s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.38s Running `target/debug/minigrep frog poem.txt` How public, like a frog diff --git a/listings/ch12-an-io-project/output-only-01-with-args/Cargo.toml b/listings/ch12-an-io-project/output-only-01-with-args/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/output-only-01-with-args/Cargo.toml +++ b/listings/ch12-an-io-project/output-only-01-with-args/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/output-only-01-with-args/output.txt b/listings/ch12-an-io-project/output-only-01-with-args/output.txt index b48bb0e108..5f733a7dd6 100644 --- a/listings/ch12-an-io-project/output-only-01-with-args/output.txt +++ b/listings/ch12-an-io-project/output-only-01-with-args/output.txt @@ -1,8 +1,8 @@ $ cargo run -- needle haystack Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 1.57s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.57s Running `target/debug/minigrep needle haystack` -[src/main.rs:5] args = [ +[src/main.rs:5:5] args = [ "target/debug/minigrep", "needle", "haystack", diff --git a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/Cargo.toml b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/Cargo.toml +++ b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/output.txt b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/output.txt index 93116dd5ed..cc3e3e5f11 100644 --- a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/output.txt +++ b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/output.txt @@ -1,16 +1,16 @@ $ cargo build Compiling minigrep v0.1.0 (file:///projects/minigrep) error[E0106]: missing lifetime specifier - --> src/lib.rs:28:51 - | -28 | pub fn search(query: &str, contents: &str) -> Vec<&str> { - | ---- ---- ^ expected named lifetime parameter - | - = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `query` or `contents` + --> src/lib.rs:1:51 + | +1 | pub fn search(query: &str, contents: &str) -> Vec<&str> { + | ---- ---- ^ expected named lifetime parameter + | + = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `query` or `contents` help: consider introducing a named lifetime parameter - | -28 | pub fn search<'a>(query: &'a str, contents: &'a str) -> Vec<&'a str> { - | ++++ ++ ++ ++ + | +1 | pub fn search<'a>(query: &'a str, contents: &'a str) -> Vec<&'a str> { + | ++++ ++ ++ ++ For more information about this error, try `rustc --explain E0106`. -error: could not compile `minigrep` due to previous error +error: could not compile `minigrep` (lib) due to 1 previous error diff --git a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/lib.rs b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/lib.rs index df623bdeaa..fd1b4b91f1 100644 --- a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/lib.rs +++ b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/lib.rs @@ -1,31 +1,3 @@ -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - Ok(Config { query, file_path }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - Ok(()) -} - -// ANCHOR: here pub fn search(query: &str, contents: &str) -> Vec<&str> { vec![] } diff --git a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/main.rs b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/main.rs index a4f8a74114..e169d7aa43 100644 --- a/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/main.rs +++ b/listings/ch12-an-io-project/output-only-02-missing-lifetimes/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,36 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch12-an-io-project/output-only-03-multiple-matches/Cargo.toml b/listings/ch12-an-io-project/output-only-03-multiple-matches/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/output-only-03-multiple-matches/Cargo.toml +++ b/listings/ch12-an-io-project/output-only-03-multiple-matches/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/output-only-03-multiple-matches/output.txt b/listings/ch12-an-io-project/output-only-03-multiple-matches/output.txt index b468357665..704df25909 100644 --- a/listings/ch12-an-io-project/output-only-03-multiple-matches/output.txt +++ b/listings/ch12-an-io-project/output-only-03-multiple-matches/output.txt @@ -1,6 +1,6 @@ $ cargo run -- body poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep body poem.txt` I'm nobody! Who are you? Are you nobody, too? diff --git a/listings/ch12-an-io-project/output-only-04-no-matches/Cargo.toml b/listings/ch12-an-io-project/output-only-04-no-matches/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch12-an-io-project/output-only-04-no-matches/Cargo.toml +++ b/listings/ch12-an-io-project/output-only-04-no-matches/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch12-an-io-project/output-only-04-no-matches/output.txt b/listings/ch12-an-io-project/output-only-04-no-matches/output.txt index a53624f836..57f3a617c4 100644 --- a/listings/ch12-an-io-project/output-only-04-no-matches/output.txt +++ b/listings/ch12-an-io-project/output-only-04-no-matches/output.txt @@ -1,4 +1,4 @@ $ cargo run -- monomorphization poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep monomorphization poem.txt` diff --git a/listings/ch13-functional-features/listing-12-23-reproduced/Cargo.toml b/listings/ch13-functional-features/listing-12-23-reproduced/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch13-functional-features/listing-12-23-reproduced/Cargo.toml +++ b/listings/ch13-functional-features/listing-12-23-reproduced/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-12-23-reproduced/src/lib.rs b/listings/ch13-functional-features/listing-12-23-reproduced/src/lib.rs index e54343d242..0c48286ded 100644 --- a/listings/ch13-functional-features/listing-12-23-reproduced/src/lib.rs +++ b/listings/ch13-functional-features/listing-12-23-reproduced/src/lib.rs @@ -1,50 +1,3 @@ -use std::env; -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -// ANCHOR: ch13 -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} -// ANCHOR_END: ch13 - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch13-functional-features/listing-12-23-reproduced/src/main.rs b/listings/ch13-functional-features/listing-12-23-reproduced/src/main.rs index a4f8a74114..a0a31803d5 100644 --- a/listings/ch13-functional-features/listing-12-23-reproduced/src/main.rs +++ b/listings/ch13-functional-features/listing-12-23-reproduced/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::{search, search_case_insensitive}; fn main() { let args: Vec = env::args().collect(); @@ -11,8 +13,51 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { println!("Application error: {e}"); process::exit(1); } } + +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} + +// ANCHOR: ch13 +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + let ignore_case = env::var("IGNORE_CASE").is_ok(); + + Ok(Config { + query, + file_path, + ignore_case, + }) + } +} +// ANCHOR_END: ch13 + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch13-functional-features/listing-12-24-reproduced/Cargo.toml b/listings/ch13-functional-features/listing-12-24-reproduced/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch13-functional-features/listing-12-24-reproduced/Cargo.toml +++ b/listings/ch13-functional-features/listing-12-24-reproduced/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-12-24-reproduced/src/lib.rs b/listings/ch13-functional-features/listing-12-24-reproduced/src/lib.rs index 292b097897..0c48286ded 100644 --- a/listings/ch13-functional-features/listing-12-24-reproduced/src/lib.rs +++ b/listings/ch13-functional-features/listing-12-24-reproduced/src/lib.rs @@ -1,48 +1,3 @@ -use std::env; -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch13-functional-features/listing-12-24-reproduced/src/main.rs b/listings/ch13-functional-features/listing-12-24-reproduced/src/main.rs index f9d179c8ce..27c5d772b0 100644 --- a/listings/ch13-functional-features/listing-12-24-reproduced/src/main.rs +++ b/listings/ch13-functional-features/listing-12-24-reproduced/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::{search, search_case_insensitive}; // ANCHOR: ch13 fn main() { @@ -15,10 +17,51 @@ fn main() { // --snip-- // ANCHOR_END: ch13 - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { eprintln!("Application error: {e}"); process::exit(1); } // ANCHOR: ch13 } // ANCHOR_END: ch13 + +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + let ignore_case = env::var("IGNORE_CASE").is_ok(); + + Ok(Config { + query, + file_path, + ignore_case, + }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch13-functional-features/listing-13-01/Cargo.toml b/listings/ch13-functional-features/listing-13-01/Cargo.toml index 1eb392dfaf..4f2229130d 100644 --- a/listings/ch13-functional-features/listing-13-01/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "shirt-company" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-01/output.txt b/listings/ch13-functional-features/listing-13-01/output.txt index b64a4d8dc4..28c829f4e9 100644 --- a/listings/ch13-functional-features/listing-13-01/output.txt +++ b/listings/ch13-functional-features/listing-13-01/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling shirt-company v0.1.0 (file:///projects/shirt-company) - Finished dev [unoptimized + debuginfo] target(s) in 0.27s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.27s Running `target/debug/shirt-company` The user with preference Some(Red) gets Red The user with preference None gets Blue diff --git a/listings/ch13-functional-features/listing-13-02/Cargo.toml b/listings/ch13-functional-features/listing-13-02/Cargo.toml index f09a737d4d..af49cfa92f 100644 --- a/listings/ch13-functional-features/listing-13-02/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "workout-app" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-03/Cargo.toml b/listings/ch13-functional-features/listing-13-03/Cargo.toml index 914c4cfaa8..d2a312ba07 100644 --- a/listings/ch13-functional-features/listing-13-03/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "closure-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-03/output.txt b/listings/ch13-functional-features/listing-13-03/output.txt index 68838deff0..8d3bebc97e 100644 --- a/listings/ch13-functional-features/listing-13-03/output.txt +++ b/listings/ch13-functional-features/listing-13-03/output.txt @@ -4,16 +4,26 @@ error[E0308]: mismatched types --> src/main.rs:5:29 | 5 | let n = example_closure(5); - | --------------- ^- help: try using a conversion method: `.to_string()` - | | | - | | expected struct `String`, found integer + | --------------- ^ expected `String`, found integer + | | | arguments to this function are incorrect | +note: expected because the closure was earlier called with an argument of type `String` + --> src/main.rs:4:29 + | +4 | let s = example_closure(String::from("hello")); + | --------------- ^^^^^^^^^^^^^^^^^^^^^ expected because this argument is of type `String` + | | + | in this closure call note: closure parameter defined here --> src/main.rs:2:28 | 2 | let example_closure = |x| x; | ^ +help: try using a conversion method + | +5 | let n = example_closure(5.to_string()); + | ++++++++++++ For more information about this error, try `rustc --explain E0308`. -error: could not compile `closure-example` due to previous error +error: could not compile `closure-example` (bin "closure-example") due to 1 previous error diff --git a/listings/ch13-functional-features/listing-13-04/Cargo.toml b/listings/ch13-functional-features/listing-13-04/Cargo.toml index 914c4cfaa8..d2a312ba07 100644 --- a/listings/ch13-functional-features/listing-13-04/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "closure-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-04/output.txt b/listings/ch13-functional-features/listing-13-04/output.txt index 64d763b511..fd33cb71fe 100644 --- a/listings/ch13-functional-features/listing-13-04/output.txt +++ b/listings/ch13-functional-features/listing-13-04/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling closure-example v0.1.0 (file:///projects/closure-example) - Finished dev [unoptimized + debuginfo] target(s) in 0.43s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.43s Running `target/debug/closure-example` Before defining closure: [1, 2, 3] Before calling closure: [1, 2, 3] diff --git a/listings/ch13-functional-features/listing-13-04/src/main.rs b/listings/ch13-functional-features/listing-13-04/src/main.rs index 43b91bb30e..19f51a6f71 100644 --- a/listings/ch13-functional-features/listing-13-04/src/main.rs +++ b/listings/ch13-functional-features/listing-13-04/src/main.rs @@ -1,10 +1,10 @@ fn main() { let list = vec![1, 2, 3]; - println!("Before defining closure: {:?}", list); + println!("Before defining closure: {list:?}"); - let only_borrows = || println!("From closure: {:?}", list); + let only_borrows = || println!("From closure: {list:?}"); - println!("Before calling closure: {:?}", list); + println!("Before calling closure: {list:?}"); only_borrows(); - println!("After calling closure: {:?}", list); + println!("After calling closure: {list:?}"); } diff --git a/listings/ch13-functional-features/listing-13-05/Cargo.toml b/listings/ch13-functional-features/listing-13-05/Cargo.toml index 914c4cfaa8..d2a312ba07 100644 --- a/listings/ch13-functional-features/listing-13-05/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "closure-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-05/output.txt b/listings/ch13-functional-features/listing-13-05/output.txt index ce0ad5e37f..af22182a18 100644 --- a/listings/ch13-functional-features/listing-13-05/output.txt +++ b/listings/ch13-functional-features/listing-13-05/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling closure-example v0.1.0 (file:///projects/closure-example) - Finished dev [unoptimized + debuginfo] target(s) in 0.43s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.43s Running `target/debug/closure-example` Before defining closure: [1, 2, 3] After calling closure: [1, 2, 3, 7] diff --git a/listings/ch13-functional-features/listing-13-05/src/main.rs b/listings/ch13-functional-features/listing-13-05/src/main.rs index 37f8130e2c..f6c2a53de6 100644 --- a/listings/ch13-functional-features/listing-13-05/src/main.rs +++ b/listings/ch13-functional-features/listing-13-05/src/main.rs @@ -1,9 +1,9 @@ fn main() { let mut list = vec![1, 2, 3]; - println!("Before defining closure: {:?}", list); + println!("Before defining closure: {list:?}"); let mut borrows_mutably = || list.push(7); borrows_mutably(); - println!("After calling closure: {:?}", list); + println!("After calling closure: {list:?}"); } diff --git a/listings/ch13-functional-features/listing-13-06/Cargo.toml b/listings/ch13-functional-features/listing-13-06/Cargo.toml index 8085ade0f5..e8f11bd4b5 100644 --- a/listings/ch13-functional-features/listing-13-06/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-06/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "closure-example" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch13-functional-features/listing-13-06/src/main.rs b/listings/ch13-functional-features/listing-13-06/src/main.rs index 2c8e18c9fd..ee9ca04570 100644 --- a/listings/ch13-functional-features/listing-13-06/src/main.rs +++ b/listings/ch13-functional-features/listing-13-06/src/main.rs @@ -2,9 +2,9 @@ use std::thread; fn main() { let list = vec![1, 2, 3]; - println!("Before defining closure: {:?}", list); + println!("Before defining closure: {list:?}"); - thread::spawn(move || println!("From thread: {:?}", list)) + thread::spawn(move || println!("From thread: {list:?}")) .join() .unwrap(); } diff --git a/listings/ch13-functional-features/listing-13-07/Cargo.toml b/listings/ch13-functional-features/listing-13-07/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch13-functional-features/listing-13-07/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-07/output.txt b/listings/ch13-functional-features/listing-13-07/output.txt index f18fce46ed..8c11d84dc6 100644 --- a/listings/ch13-functional-features/listing-13-07/output.txt +++ b/listings/ch13-functional-features/listing-13-07/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling rectangles v0.1.0 (file:///projects/rectangles) - Finished dev [unoptimized + debuginfo] target(s) in 0.41s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.41s Running `target/debug/rectangles` [ Rectangle { diff --git a/listings/ch13-functional-features/listing-13-07/src/main.rs b/listings/ch13-functional-features/listing-13-07/src/main.rs index 73a25e5f91..e7ab8d3402 100644 --- a/listings/ch13-functional-features/listing-13-07/src/main.rs +++ b/listings/ch13-functional-features/listing-13-07/src/main.rs @@ -12,5 +12,5 @@ fn main() { ]; list.sort_by_key(|r| r.width); - println!("{:#?}", list); + println!("{list:#?}"); } diff --git a/listings/ch13-functional-features/listing-13-08/Cargo.toml b/listings/ch13-functional-features/listing-13-08/Cargo.toml index 703c9d9778..2331b52c65 100644 --- a/listings/ch13-functional-features/listing-13-08/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-08/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch13-functional-features/listing-13-08/output.txt b/listings/ch13-functional-features/listing-13-08/output.txt index a910537667..000f7f9e76 100644 --- a/listings/ch13-functional-features/listing-13-08/output.txt +++ b/listings/ch13-functional-features/listing-13-08/output.txt @@ -3,13 +3,20 @@ $ cargo run error[E0507]: cannot move out of `value`, a captured variable in an `FnMut` closure --> src/main.rs:18:30 | -15 | let value = String::from("by key called"); - | ----- captured outer variable +15 | let value = String::from("closure called"); + | ----- ------------------------------ move occurs because `value` has type `String`, which does not implement the `Copy` trait + | | + | captured outer variable 16 | 17 | list.sort_by_key(|r| { | --- captured by this `FnMut` closure 18 | sort_operations.push(value); - | ^^^^^ move occurs because `value` has type `String`, which does not implement the `Copy` trait + | ^^^^^ `value` is moved here + | +help: consider cloning the value if the performance cost is acceptable + | +18 | sort_operations.push(value.clone()); + | ++++++++ For more information about this error, try `rustc --explain E0507`. -error: could not compile `rectangles` due to previous error +error: could not compile `rectangles` (bin "rectangles") due to 1 previous error diff --git a/listings/ch13-functional-features/listing-13-08/src/main.rs b/listings/ch13-functional-features/listing-13-08/src/main.rs index 3b9c9cbdfd..e00fec70fc 100644 --- a/listings/ch13-functional-features/listing-13-08/src/main.rs +++ b/listings/ch13-functional-features/listing-13-08/src/main.rs @@ -12,11 +12,11 @@ fn main() { ]; let mut sort_operations = vec![]; - let value = String::from("by key called"); + let value = String::from("closure called"); list.sort_by_key(|r| { sort_operations.push(value); r.width }); - println!("{:#?}", list); + println!("{list:#?}"); } diff --git a/listings/ch13-functional-features/listing-13-09/Cargo.toml b/listings/ch13-functional-features/listing-13-09/Cargo.toml index 4a279a450d..bd5e247b57 100644 --- a/listings/ch13-functional-features/listing-13-09/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "rectangles" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-09/src/main.rs b/listings/ch13-functional-features/listing-13-09/src/main.rs index a60d6fd3fc..f007e3c04d 100644 --- a/listings/ch13-functional-features/listing-13-09/src/main.rs +++ b/listings/ch13-functional-features/listing-13-09/src/main.rs @@ -16,5 +16,5 @@ fn main() { num_sort_operations += 1; r.width }); - println!("{:#?}, sorted in {num_sort_operations} operations", list); + println!("{list:#?}, sorted in {num_sort_operations} operations"); } diff --git a/listings/ch13-functional-features/listing-13-10/Cargo.toml b/listings/ch13-functional-features/listing-13-10/Cargo.toml index 2652a8a1a4..4db0b0f6f1 100644 --- a/listings/ch13-functional-features/listing-13-10/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "iterators" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-11/Cargo.toml b/listings/ch13-functional-features/listing-13-11/Cargo.toml index 2652a8a1a4..4db0b0f6f1 100644 --- a/listings/ch13-functional-features/listing-13-11/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "iterators" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-11/src/main.rs b/listings/ch13-functional-features/listing-13-11/src/main.rs index 712aff4085..b4e85169ab 100644 --- a/listings/ch13-functional-features/listing-13-11/src/main.rs +++ b/listings/ch13-functional-features/listing-13-11/src/main.rs @@ -5,7 +5,7 @@ fn main() { let v1_iter = v1.iter(); for val in v1_iter { - println!("Got: {}", val); + println!("Got: {val}"); } // ANCHOR_END: here } diff --git a/listings/ch13-functional-features/listing-13-12/Cargo.toml b/listings/ch13-functional-features/listing-13-12/Cargo.toml index 2652a8a1a4..4db0b0f6f1 100644 --- a/listings/ch13-functional-features/listing-13-12/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "iterators" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-13/Cargo.toml b/listings/ch13-functional-features/listing-13-13/Cargo.toml index 2652a8a1a4..4db0b0f6f1 100644 --- a/listings/ch13-functional-features/listing-13-13/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "iterators" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-14/Cargo.toml b/listings/ch13-functional-features/listing-13-14/Cargo.toml index 2652a8a1a4..4db0b0f6f1 100644 --- a/listings/ch13-functional-features/listing-13-14/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "iterators" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-14/output.txt b/listings/ch13-functional-features/listing-13-14/output.txt index 9930379910..d46dd5c421 100644 --- a/listings/ch13-functional-features/listing-13-14/output.txt +++ b/listings/ch13-functional-features/listing-13-14/output.txt @@ -8,7 +8,11 @@ warning: unused `Map` that must be used | = note: iterators are lazy and do nothing unless consumed = note: `#[warn(unused_must_use)]` on by default +help: use `let _ = ...` to ignore the resulting value + | +4 | let _ = v1.iter().map(|x| x + 1); + | +++++++ warning: `iterators` (bin "iterators") generated 1 warning - Finished dev [unoptimized + debuginfo] target(s) in 0.47s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.47s Running `target/debug/iterators` diff --git a/listings/ch13-functional-features/listing-13-15/Cargo.toml b/listings/ch13-functional-features/listing-13-15/Cargo.toml index 2652a8a1a4..4db0b0f6f1 100644 --- a/listings/ch13-functional-features/listing-13-15/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "iterators" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-16/Cargo.toml b/listings/ch13-functional-features/listing-13-16/Cargo.toml index cc803776b6..a6b4567302 100644 --- a/listings/ch13-functional-features/listing-13-16/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "shoe_size" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-18/Cargo.toml b/listings/ch13-functional-features/listing-13-18/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch13-functional-features/listing-13-18/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-18/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-18/src/lib.rs b/listings/ch13-functional-features/listing-13-18/src/lib.rs index 292b097897..0c48286ded 100644 --- a/listings/ch13-functional-features/listing-13-18/src/lib.rs +++ b/listings/ch13-functional-features/listing-13-18/src/lib.rs @@ -1,48 +1,3 @@ -use std::env; -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -impl Config { - pub fn build(args: &[String]) -> Result { - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch13-functional-features/listing-13-18/src/main.rs b/listings/ch13-functional-features/listing-13-18/src/main.rs index 40109ef638..84e52dde31 100644 --- a/listings/ch13-functional-features/listing-13-18/src/main.rs +++ b/listings/ch13-functional-features/listing-13-18/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::{search, search_case_insensitive}; // ANCHOR: here fn main() { @@ -13,10 +15,51 @@ fn main() { // --snip-- // ANCHOR_END: here - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { eprintln!("Application error: {e}"); process::exit(1); } // ANCHOR: here } // ANCHOR_END: here + +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + let ignore_case = env::var("IGNORE_CASE").is_ok(); + + Ok(Config { + query, + file_path, + ignore_case, + }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch13-functional-features/listing-13-19/Cargo.toml b/listings/ch13-functional-features/listing-13-19/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch13-functional-features/listing-13-19/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-19/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-19/src/lib.rs b/listings/ch13-functional-features/listing-13-19/src/lib.rs index 79ae2b8f6c..0c48286ded 100644 --- a/listings/ch13-functional-features/listing-13-19/src/lib.rs +++ b/listings/ch13-functional-features/listing-13-19/src/lib.rs @@ -1,53 +1,3 @@ -use std::env; -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -// ANCHOR: here -impl Config { - pub fn build( - mut args: impl Iterator, - ) -> Result { - // --snip-- - // ANCHOR_END: here - if args.len() < 3 { - return Err("not enough arguments"); - } - - let query = args[1].clone(); - let file_path = args[2].clone(); - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch13-functional-features/listing-13-19/src/main.rs b/listings/ch13-functional-features/listing-13-19/src/main.rs index 9ac0225455..ff907d050b 100644 --- a/listings/ch13-functional-features/listing-13-19/src/main.rs +++ b/listings/ch13-functional-features/listing-13-19/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::{search, search_case_insensitive}; fn main() { let config = Config::build(env::args()).unwrap_or_else(|err| { @@ -9,8 +11,54 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { eprintln!("Application error: {e}"); process::exit(1); } } + +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} + +// ANCHOR: here +impl Config { + fn build( + mut args: impl Iterator, + ) -> Result { + // --snip-- + // ANCHOR_END: here + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + let ignore_case = env::var("IGNORE_CASE").is_ok(); + + Ok(Config { + query, + file_path, + ignore_case, + }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch13-functional-features/listing-13-20/Cargo.toml b/listings/ch13-functional-features/listing-13-20/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch13-functional-features/listing-13-20/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-20/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-20/src/lib.rs b/listings/ch13-functional-features/listing-13-20/src/lib.rs index 4410964a7d..0c48286ded 100644 --- a/listings/ch13-functional-features/listing-13-20/src/lib.rs +++ b/listings/ch13-functional-features/listing-13-20/src/lib.rs @@ -1,57 +1,3 @@ -use std::env; -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -// ANCHOR: here -impl Config { - pub fn build( - mut args: impl Iterator, - ) -> Result { - args.next(); - - let query = match args.next() { - Some(arg) => arg, - None => return Err("Didn't get a query string"), - }; - - let file_path = match args.next() { - Some(arg) => arg, - None => return Err("Didn't get a file path"), - }; - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} -// ANCHOR_END: here - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); diff --git a/listings/ch13-functional-features/listing-13-20/src/main.rs b/listings/ch13-functional-features/listing-13-20/src/main.rs index 9ac0225455..5b18c2a643 100644 --- a/listings/ch13-functional-features/listing-13-20/src/main.rs +++ b/listings/ch13-functional-features/listing-13-20/src/main.rs @@ -1,7 +1,9 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::{search, search_case_insensitive}; fn main() { let config = Config::build(env::args()).unwrap_or_else(|err| { @@ -9,8 +11,58 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { eprintln!("Application error: {e}"); process::exit(1); } } + +pub struct Config { + pub query: String, + pub file_path: String, + pub ignore_case: bool, +} + +// ANCHOR: here +impl Config { + fn build( + mut args: impl Iterator, + ) -> Result { + args.next(); + + let query = match args.next() { + Some(arg) => arg, + None => return Err("Didn't get a query string"), + }; + + let file_path = match args.next() { + Some(arg) => arg, + None => return Err("Didn't get a file path"), + }; + + let ignore_case = env::var("IGNORE_CASE").is_ok(); + + Ok(Config { + query, + file_path, + ignore_case, + }) + } +} +// ANCHOR_END: here + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + let results = if config.ignore_case { + search_case_insensitive(&config.query, &contents) + } else { + search(&config.query, &contents) + }; + + for line in results { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch13-functional-features/listing-13-22/Cargo.toml b/listings/ch13-functional-features/listing-13-22/Cargo.toml index 64c2a3f520..b8302aef85 100644 --- a/listings/ch13-functional-features/listing-13-22/Cargo.toml +++ b/listings/ch13-functional-features/listing-13-22/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "minigrep" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch13-functional-features/listing-13-22/src/lib.rs b/listings/ch13-functional-features/listing-13-22/src/lib.rs index d694669b45..28af29e727 100644 --- a/listings/ch13-functional-features/listing-13-22/src/lib.rs +++ b/listings/ch13-functional-features/listing-13-22/src/lib.rs @@ -1,55 +1,3 @@ -use std::env; -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, - pub ignore_case: bool, -} - -impl Config { - pub fn build( - mut args: impl Iterator, - ) -> Result { - args.next(); - - let query = match args.next() { - Some(arg) => arg, - None => return Err("Didn't get a query string"), - }; - - let file_path = match args.next() { - Some(arg) => arg, - None => return Err("Didn't get a file path"), - }; - - let ignore_case = env::var("IGNORE_CASE").is_ok(); - - Ok(Config { - query, - file_path, - ignore_case, - }) - } -} - -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; - - let results = if config.ignore_case { - search_case_insensitive(&config.query, &contents) - } else { - search(&config.query, &contents) - }; - - for line in results { - println!("{line}"); - } - - Ok(()) -} - // ANCHOR: here pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { contents diff --git a/listings/ch13-functional-features/listing-13-22/src/main.rs b/listings/ch13-functional-features/listing-13-22/src/main.rs index 9ac0225455..e169d7aa43 100644 --- a/listings/ch13-functional-features/listing-13-22/src/main.rs +++ b/listings/ch13-functional-features/listing-13-22/src/main.rs @@ -1,16 +1,48 @@ use std::env; +use std::error::Error; +use std::fs; use std::process; -use minigrep::Config; +use minigrep::search; fn main() { - let config = Config::build(env::args()).unwrap_or_else(|err| { - eprintln!("Problem parsing arguments: {err}"); + let args: Vec = env::args().collect(); + + let config = Config::build(&args).unwrap_or_else(|err| { + println!("Problem parsing arguments: {err}"); process::exit(1); }); - if let Err(e) = minigrep::run(config) { - eprintln!("Application error: {e}"); + if let Err(e) = run(config) { + println!("Application error: {e}"); process::exit(1); } } + +struct Config { + query: String, + file_path: String, +} + +impl Config { + fn build(args: &[String]) -> Result { + if args.len() < 3 { + return Err("not enough arguments"); + } + + let query = args[1].clone(); + let file_path = args[2].clone(); + + Ok(Config { query, file_path }) + } +} + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); + } + + Ok(()) +} diff --git a/listings/ch14-more-about-cargo/listing-14-01/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-01/Cargo.toml index c52da04129..60664c6887 100644 --- a/listings/ch14-more-about-cargo/listing-14-01/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "my_crate" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-02/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-02/Cargo.toml index c52da04129..60664c6887 100644 --- a/listings/ch14-more-about-cargo/listing-14-02/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "my_crate" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-03/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-03/Cargo.toml index 66ef4b532d..f16924bc67 100644 --- a/listings/ch14-more-about-cargo/listing-14-03/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "art" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-04/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-04/Cargo.toml index 66ef4b532d..f16924bc67 100644 --- a/listings/ch14-more-about-cargo/listing-14-04/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "art" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-05/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-05/Cargo.toml index 66ef4b532d..f16924bc67 100644 --- a/listings/ch14-more-about-cargo/listing-14-05/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "art" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-06/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-06/Cargo.toml index 66ef4b532d..f16924bc67 100644 --- a/listings/ch14-more-about-cargo/listing-14-06/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "art" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-06/src/main.rs b/listings/ch14-more-about-cargo/listing-14-06/src/main.rs index 51f3b761db..4b6e112afe 100644 --- a/listings/ch14-more-about-cargo/listing-14-06/src/main.rs +++ b/listings/ch14-more-about-cargo/listing-14-06/src/main.rs @@ -1,6 +1,6 @@ // ANCHOR: here -use art::mix; use art::PrimaryColor; +use art::mix; fn main() { // --snip-- diff --git a/listings/ch14-more-about-cargo/listing-14-07/add/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-07/add/Cargo.toml index 1448801d5b..2bc25b73d2 100644 --- a/listings/ch14-more-about-cargo/listing-14-07/add/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-07/add/Cargo.toml @@ -1,6 +1,3 @@ [workspace] - -members = [ - "adder", - "add_one", -] +resolver = "3" +members = ["adder", "add_one"] diff --git a/listings/ch14-more-about-cargo/listing-14-07/add/add_one/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-07/add/add_one/Cargo.toml index 8af4ab8166..dcfb7f9046 100644 --- a/listings/ch14-more-about-cargo/listing-14-07/add/add_one/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-07/add/add_one/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "add_one" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-07/add/adder/Cargo.toml b/listings/ch14-more-about-cargo/listing-14-07/add/adder/Cargo.toml index feb3d956ea..980d5bfc95 100644 --- a/listings/ch14-more-about-cargo/listing-14-07/add/adder/Cargo.toml +++ b/listings/ch14-more-about-cargo/listing-14-07/add/adder/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/listing-14-07/add/adder/src/main.rs b/listings/ch14-more-about-cargo/listing-14-07/add/adder/src/main.rs index 1316294909..ead4e1dd83 100644 --- a/listings/ch14-more-about-cargo/listing-14-07/add/adder/src/main.rs +++ b/listings/ch14-more-about-cargo/listing-14-07/add/adder/src/main.rs @@ -1,5 +1,3 @@ -use add_one; - fn main() { let num = 10; println!("Hello, world! {num} plus one is {}!", add_one::add_one(num)); diff --git a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/Cargo.toml deleted file mode 100644 index c5ea8e510b..0000000000 --- a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/Cargo.toml +++ /dev/null @@ -1,5 +0,0 @@ -[workspace] - -members = [ - "adder", -] diff --git a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/adder/src/main.rs b/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/adder/src/main.rs deleted file mode 100644 index e7a11a969c..0000000000 --- a/listings/ch14-more-about-cargo/no-listing-01-workspace-with-adder-crate/add/adder/src/main.rs +++ /dev/null @@ -1,3 +0,0 @@ -fn main() { - println!("Hello, world!"); -} diff --git a/listings/ch14-more-about-cargo/no-listing-01-workspace/add/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-01-workspace/add/Cargo.toml new file mode 100644 index 0000000000..daa8c449cc --- /dev/null +++ b/listings/ch14-more-about-cargo/no-listing-01-workspace/add/Cargo.toml @@ -0,0 +1,2 @@ +[workspace] +resolver = "3" diff --git a/listings/ch14-more-about-cargo/no-listing-01-workspace/add/rustfmt-ignore b/listings/ch14-more-about-cargo/no-listing-01-workspace/add/rustfmt-ignore new file mode 100644 index 0000000000..cff2dcf3e4 --- /dev/null +++ b/listings/ch14-more-about-cargo/no-listing-01-workspace/add/rustfmt-ignore @@ -0,0 +1 @@ +There's no Rust code in here; just us Cargo.tomls. \ No newline at end of file diff --git a/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/Cargo.toml index 1448801d5b..2bc25b73d2 100644 --- a/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/Cargo.toml @@ -1,6 +1,3 @@ [workspace] - -members = [ - "adder", - "add_one", -] +resolver = "3" +members = ["adder", "add_one"] diff --git a/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/add_one/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/add_one/Cargo.toml index 8af4ab8166..dcfb7f9046 100644 --- a/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/add_one/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/add_one/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "add_one" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/adder/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/adder/Cargo.toml index 55c02036c4..5f4a489077 100644 --- a/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/adder/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/adder/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] add_one = { path = "../add_one" } diff --git a/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/Cargo.toml index 1448801d5b..2bc25b73d2 100644 --- a/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/Cargo.toml @@ -1,6 +1,3 @@ [workspace] - -members = [ - "adder", - "add_one", -] +resolver = "3" +members = ["adder", "add_one"] diff --git a/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/add_one/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/add_one/Cargo.toml index bc758bd883..d399d96e7b 100644 --- a/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/add_one/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/add_one/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "add_one" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] rand = "0.8.5" diff --git a/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/adder/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/adder/Cargo.toml index feb3d956ea..980d5bfc95 100644 --- a/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/adder/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/adder/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/Cargo.toml index 1448801d5b..2bc25b73d2 100644 --- a/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/Cargo.toml @@ -1,6 +1,3 @@ [workspace] - -members = [ - "adder", - "add_one", -] +resolver = "3" +members = ["adder", "add_one"] diff --git a/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/add_one/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/add_one/Cargo.toml index 8af4ab8166..dcfb7f9046 100644 --- a/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/add_one/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/add_one/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "add_one" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/adder/Cargo.toml b/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/adder/Cargo.toml index feb3d956ea..980d5bfc95 100644 --- a/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/adder/Cargo.toml +++ b/listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/adder/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/output-only-01-adder-crate/add/Cargo.toml b/listings/ch14-more-about-cargo/output-only-01-adder-crate/add/Cargo.toml index c5ea8e510b..448a0383ab 100644 --- a/listings/ch14-more-about-cargo/output-only-01-adder-crate/add/Cargo.toml +++ b/listings/ch14-more-about-cargo/output-only-01-adder-crate/add/Cargo.toml @@ -1,5 +1,3 @@ [workspace] - -members = [ - "adder", -] +resolver = "3" +members = ["adder"] diff --git a/listings/ch14-more-about-cargo/output-only-02-add-one/add/Cargo.toml b/listings/ch14-more-about-cargo/output-only-02-add-one/add/Cargo.toml index 1448801d5b..28af3b3b70 100644 --- a/listings/ch14-more-about-cargo/output-only-02-add-one/add/Cargo.toml +++ b/listings/ch14-more-about-cargo/output-only-02-add-one/add/Cargo.toml @@ -1,6 +1,3 @@ [workspace] - -members = [ - "adder", - "add_one", -] +resolver = "3" +members = ["add_one", "adder"] diff --git a/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/Cargo.toml b/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/Cargo.toml index 9000184707..dcfb7f9046 100644 --- a/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/Cargo.toml +++ b/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/Cargo.toml @@ -1,8 +1,6 @@ [package] name = "add_one" version = "0.1.0" -edition = "2021" - -# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/src/lib.rs b/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/src/lib.rs index 1b4a90c938..b93cf3ffd9 100644 --- a/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/src/lib.rs +++ b/listings/ch14-more-about-cargo/output-only-02-add-one/add/add_one/src/lib.rs @@ -1,8 +1,14 @@ +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { + use super::*; + #[test] fn it_works() { - let result = 2 + 2; + let result = add(2, 2); assert_eq!(result, 4); } } diff --git a/listings/ch14-more-about-cargo/output-only-02-add-one/add/adder/Cargo.toml b/listings/ch14-more-about-cargo/output-only-02-add-one/add/adder/Cargo.toml index feb3d956ea..980d5bfc95 100644 --- a/listings/ch14-more-about-cargo/output-only-02-add-one/add/adder/Cargo.toml +++ b/listings/ch14-more-about-cargo/output-only-02-add-one/add/adder/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch14-more-about-cargo/output-only-03-use-rand/add/Cargo.toml b/listings/ch14-more-about-cargo/output-only-03-use-rand/add/Cargo.toml index 1448801d5b..2bc25b73d2 100644 --- a/listings/ch14-more-about-cargo/output-only-03-use-rand/add/Cargo.toml +++ b/listings/ch14-more-about-cargo/output-only-03-use-rand/add/Cargo.toml @@ -1,6 +1,3 @@ [workspace] - -members = [ - "adder", - "add_one", -] +resolver = "3" +members = ["adder", "add_one"] diff --git a/listings/ch14-more-about-cargo/output-only-03-use-rand/add/add_one/Cargo.toml b/listings/ch14-more-about-cargo/output-only-03-use-rand/add/add_one/Cargo.toml index bc758bd883..d399d96e7b 100644 --- a/listings/ch14-more-about-cargo/output-only-03-use-rand/add/add_one/Cargo.toml +++ b/listings/ch14-more-about-cargo/output-only-03-use-rand/add/add_one/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "add_one" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] rand = "0.8.5" diff --git a/listings/ch14-more-about-cargo/output-only-03-use-rand/add/adder/Cargo.toml b/listings/ch14-more-about-cargo/output-only-03-use-rand/add/adder/Cargo.toml index feb3d956ea..980d5bfc95 100644 --- a/listings/ch14-more-about-cargo/output-only-03-use-rand/add/adder/Cargo.toml +++ b/listings/ch14-more-about-cargo/output-only-03-use-rand/add/adder/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "adder" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-01/Cargo.toml b/listings/ch15-smart-pointers/listing-15-01/Cargo.toml index 690385c7a4..f645b871de 100644 --- a/listings/ch15-smart-pointers/listing-15-01/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "box-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-01/src/main.rs b/listings/ch15-smart-pointers/listing-15-01/src/main.rs index 8da1d905d6..97f04f3858 100644 --- a/listings/ch15-smart-pointers/listing-15-01/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-01/src/main.rs @@ -1,4 +1,4 @@ fn main() { let b = Box::new(5); - println!("b = {}", b); + println!("b = {b}"); } diff --git a/listings/ch15-smart-pointers/listing-15-02/Cargo.toml b/listings/ch15-smart-pointers/listing-15-02/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-02/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-03/Cargo.toml b/listings/ch15-smart-pointers/listing-15-03/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-03/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-03/output.txt b/listings/ch15-smart-pointers/listing-15-03/output.txt index 04b6976fed..2563fb6472 100644 --- a/listings/ch15-smart-pointers/listing-15-03/output.txt +++ b/listings/ch15-smart-pointers/listing-15-03/output.txt @@ -13,5 +13,16 @@ help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle 2 | Cons(i32, Box), | ++++ + -For more information about this error, try `rustc --explain E0072`. -error: could not compile `cons-list` due to previous error +error[E0391]: cycle detected when computing when `List` needs drop + --> src/main.rs:1:1 + | +1 | enum List { + | ^^^^^^^^^ + | + = note: ...which immediately requires computing when `List` needs drop again + = note: cycle used when computing whether `List` needs drop + = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information + +Some errors have detailed explanations: E0072, E0391. +For more information about an error, try `rustc --explain E0072`. +error: could not compile `cons-list` (bin "cons-list") due to 2 previous errors diff --git a/listings/ch15-smart-pointers/listing-15-03/src/main.rs b/listings/ch15-smart-pointers/listing-15-03/src/main.rs index a96f3d7b18..991f690985 100644 --- a/listings/ch15-smart-pointers/listing-15-03/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-03/src/main.rs @@ -4,6 +4,8 @@ enum List { } // ANCHOR: here +// --snip-- + use crate::List::{Cons, Nil}; fn main() { diff --git a/listings/ch15-smart-pointers/listing-15-05/Cargo.toml b/listings/ch15-smart-pointers/listing-15-05/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-05/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-06/Cargo.toml b/listings/ch15-smart-pointers/listing-15-06/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-06/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-07/Cargo.toml b/listings/ch15-smart-pointers/listing-15-07/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-07/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-08/Cargo.toml b/listings/ch15-smart-pointers/listing-15-08/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-08/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-09/Cargo.toml b/listings/ch15-smart-pointers/listing-15-09/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-09/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-09/output.txt b/listings/ch15-smart-pointers/listing-15-09/output.txt index 75e5f1c8c4..eb4cdd12fe 100644 --- a/listings/ch15-smart-pointers/listing-15-09/output.txt +++ b/listings/ch15-smart-pointers/listing-15-09/output.txt @@ -4,7 +4,7 @@ error[E0614]: type `MyBox<{integer}>` cannot be dereferenced --> src/main.rs:14:19 | 14 | assert_eq!(5, *y); - | ^^ + | ^^ can't be dereferenced For more information about this error, try `rustc --explain E0614`. -error: could not compile `deref-example` due to previous error +error: could not compile `deref-example` (bin "deref-example") due to 1 previous error diff --git a/listings/ch15-smart-pointers/listing-15-10/Cargo.toml b/listings/ch15-smart-pointers/listing-15-10/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-10/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-11/Cargo.toml b/listings/ch15-smart-pointers/listing-15-11/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-11/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-12/Cargo.toml b/listings/ch15-smart-pointers/listing-15-12/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-12/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-13/Cargo.toml b/listings/ch15-smart-pointers/listing-15-13/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/listing-15-13/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-14/Cargo.toml b/listings/ch15-smart-pointers/listing-15-14/Cargo.toml index 1e4c994815..9b930b59b8 100644 --- a/listings/ch15-smart-pointers/listing-15-14/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "drop-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-14/output.txt b/listings/ch15-smart-pointers/listing-15-14/output.txt index 4e795949a0..939bc7f458 100644 --- a/listings/ch15-smart-pointers/listing-15-14/output.txt +++ b/listings/ch15-smart-pointers/listing-15-14/output.txt @@ -1,7 +1,7 @@ $ cargo run Compiling drop-example v0.1.0 (file:///projects/drop-example) - Finished dev [unoptimized + debuginfo] target(s) in 0.60s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.60s Running `target/debug/drop-example` -CustomSmartPointers created. +CustomSmartPointers created Dropping CustomSmartPointer with data `other stuff`! Dropping CustomSmartPointer with data `my stuff`! diff --git a/listings/ch15-smart-pointers/listing-15-14/src/main.rs b/listings/ch15-smart-pointers/listing-15-14/src/main.rs index 231612ae62..bcf95160f6 100644 --- a/listings/ch15-smart-pointers/listing-15-14/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-14/src/main.rs @@ -15,5 +15,5 @@ fn main() { let d = CustomSmartPointer { data: String::from("other stuff"), }; - println!("CustomSmartPointers created."); + println!("CustomSmartPointers created"); } diff --git a/listings/ch15-smart-pointers/listing-15-15/Cargo.toml b/listings/ch15-smart-pointers/listing-15-15/Cargo.toml index 1e4c994815..9b930b59b8 100644 --- a/listings/ch15-smart-pointers/listing-15-15/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "drop-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-15/output.txt b/listings/ch15-smart-pointers/listing-15-15/output.txt index a38c9ccb76..d7811605c5 100644 --- a/listings/ch15-smart-pointers/listing-15-15/output.txt +++ b/listings/ch15-smart-pointers/listing-15-15/output.txt @@ -4,10 +4,13 @@ error[E0040]: explicit use of destructor method --> src/main.rs:16:7 | 16 | c.drop(); - | --^^^^-- - | | | - | | explicit destructor calls not allowed - | help: consider using `drop` function: `drop(c)` + | ^^^^ explicit destructor calls not allowed + | +help: consider using `drop` function + | +16 - c.drop(); +16 + drop(c); + | For more information about this error, try `rustc --explain E0040`. -error: could not compile `drop-example` due to previous error +error: could not compile `drop-example` (bin "drop-example") due to 1 previous error diff --git a/listings/ch15-smart-pointers/listing-15-15/src/main.rs b/listings/ch15-smart-pointers/listing-15-15/src/main.rs index ff3b391a91..5fddbac967 100644 --- a/listings/ch15-smart-pointers/listing-15-15/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-15/src/main.rs @@ -13,8 +13,8 @@ fn main() { let c = CustomSmartPointer { data: String::from("some data"), }; - println!("CustomSmartPointer created."); + println!("CustomSmartPointer created"); c.drop(); - println!("CustomSmartPointer dropped before the end of main."); + println!("CustomSmartPointer dropped before the end of main"); } // ANCHOR_END: here diff --git a/listings/ch15-smart-pointers/listing-15-16/Cargo.toml b/listings/ch15-smart-pointers/listing-15-16/Cargo.toml index 1e4c994815..9b930b59b8 100644 --- a/listings/ch15-smart-pointers/listing-15-16/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "drop-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-16/output.txt b/listings/ch15-smart-pointers/listing-15-16/output.txt index e960cd89a2..ae2ed04d08 100644 --- a/listings/ch15-smart-pointers/listing-15-16/output.txt +++ b/listings/ch15-smart-pointers/listing-15-16/output.txt @@ -1,7 +1,7 @@ $ cargo run Compiling drop-example v0.1.0 (file:///projects/drop-example) - Finished dev [unoptimized + debuginfo] target(s) in 0.73s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.73s Running `target/debug/drop-example` -CustomSmartPointer created. +CustomSmartPointer created Dropping CustomSmartPointer with data `some data`! -CustomSmartPointer dropped before the end of main. +CustomSmartPointer dropped before the end of main diff --git a/listings/ch15-smart-pointers/listing-15-16/src/main.rs b/listings/ch15-smart-pointers/listing-15-16/src/main.rs index f11715c45e..af62879976 100644 --- a/listings/ch15-smart-pointers/listing-15-16/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-16/src/main.rs @@ -13,8 +13,8 @@ fn main() { let c = CustomSmartPointer { data: String::from("some data"), }; - println!("CustomSmartPointer created."); + println!("CustomSmartPointer created"); drop(c); - println!("CustomSmartPointer dropped before the end of main."); + println!("CustomSmartPointer dropped before the end of main"); } // ANCHOR_END: here diff --git a/listings/ch15-smart-pointers/listing-15-17/Cargo.toml b/listings/ch15-smart-pointers/listing-15-17/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-17/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-17/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-17/output.txt b/listings/ch15-smart-pointers/listing-15-17/output.txt index ab314d8837..13bc178479 100644 --- a/listings/ch15-smart-pointers/listing-15-17/output.txt +++ b/listings/ch15-smart-pointers/listing-15-17/output.txt @@ -3,12 +3,21 @@ $ cargo run error[E0382]: use of moved value: `a` --> src/main.rs:11:30 | -9 | let a = Cons(5, Box::new(Cons(10, Box::new(Nil)))); + 9 | let a = Cons(5, Box::new(Cons(10, Box::new(Nil)))); | - move occurs because `a` has type `List`, which does not implement the `Copy` trait 10 | let b = Cons(3, Box::new(a)); | - value moved here 11 | let c = Cons(4, Box::new(a)); | ^ value used here after move + | +note: if `List` implemented `Clone`, you could clone the value + --> src/main.rs:1:1 + | + 1 | enum List { + | ^^^^^^^^^ consider implementing `Clone` for this type +... +10 | let b = Cons(3, Box::new(a)); + | - you could clone this value For more information about this error, try `rustc --explain E0382`. -error: could not compile `cons-list` due to previous error +error: could not compile `cons-list` (bin "cons-list") due to 1 previous error diff --git a/listings/ch15-smart-pointers/listing-15-18/Cargo.toml b/listings/ch15-smart-pointers/listing-15-18/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-18/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-18/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-19/Cargo.toml b/listings/ch15-smart-pointers/listing-15-19/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-19/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-19/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-19/output.txt b/listings/ch15-smart-pointers/listing-15-19/output.txt index 6a8cc8efe1..252ccae893 100644 --- a/listings/ch15-smart-pointers/listing-15-19/output.txt +++ b/listings/ch15-smart-pointers/listing-15-19/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling cons-list v0.1.0 (file:///projects/cons-list) - Finished dev [unoptimized + debuginfo] target(s) in 0.45s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.45s Running `target/debug/cons-list` count after creating a = 1 count after creating b = 2 diff --git a/listings/ch15-smart-pointers/listing-15-19/src/main.rs b/listings/ch15-smart-pointers/listing-15-19/src/main.rs index 1bd7bc533a..06a25ebb40 100644 --- a/listings/ch15-smart-pointers/listing-15-19/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-19/src/main.rs @@ -7,6 +7,8 @@ use crate::List::{Cons, Nil}; use std::rc::Rc; // ANCHOR: here +// --snip-- + fn main() { let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil))))); println!("count after creating a = {}", Rc::strong_count(&a)); diff --git a/listings/ch15-smart-pointers/listing-15-20/Cargo.toml b/listings/ch15-smart-pointers/listing-15-20/Cargo.toml index 98c3f537c6..f5e2eb12c0 100644 --- a/listings/ch15-smart-pointers/listing-15-20/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-20/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "limit-tracker" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-21/Cargo.toml b/listings/ch15-smart-pointers/listing-15-21/Cargo.toml index 98c3f537c6..f5e2eb12c0 100644 --- a/listings/ch15-smart-pointers/listing-15-21/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-21/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "limit-tracker" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-21/output.txt b/listings/ch15-smart-pointers/listing-15-21/output.txt index 6b07b66ea2..2af4167527 100644 --- a/listings/ch15-smart-pointers/listing-15-21/output.txt +++ b/listings/ch15-smart-pointers/listing-15-21/output.txt @@ -3,12 +3,17 @@ $ cargo test error[E0596]: cannot borrow `self.sent_messages` as mutable, as it is behind a `&` reference --> src/lib.rs:58:13 | -2 | fn send(&self, msg: &str); - | ----- help: consider changing that to be a mutable reference: `&mut self` -... 58 | self.sent_messages.push(String::from(message)); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `self` is a `&` reference, so the data it refers to cannot be borrowed as mutable + | ^^^^^^^^^^^^^^^^^^ `self` is a `&` reference, so the data it refers to cannot be borrowed as mutable + | +help: consider changing this to be a mutable reference in the `impl` method and the `trait` definition + | + 2 ~ fn send(&mut self, msg: &str); + 3 | } +... +56 | impl Messenger for MockMessenger { +57 ~ fn send(&mut self, message: &str) { + | For more information about this error, try `rustc --explain E0596`. -error: could not compile `limit-tracker` due to previous error -warning: build failed, waiting for other jobs to finish... +error: could not compile `limit-tracker` (lib test) due to 1 previous error diff --git a/listings/ch15-smart-pointers/listing-15-22/Cargo.toml b/listings/ch15-smart-pointers/listing-15-22/Cargo.toml index 98c3f537c6..f5e2eb12c0 100644 --- a/listings/ch15-smart-pointers/listing-15-22/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-22/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "limit-tracker" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-23/Cargo.toml b/listings/ch15-smart-pointers/listing-15-23/Cargo.toml index 98c3f537c6..f5e2eb12c0 100644 --- a/listings/ch15-smart-pointers/listing-15-23/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-23/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "limit-tracker" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-23/output.txt b/listings/ch15-smart-pointers/listing-15-23/output.txt index 0ffabf7650..2f01484b07 100644 --- a/listings/ch15-smart-pointers/listing-15-23/output.txt +++ b/listings/ch15-smart-pointers/listing-15-23/output.txt @@ -1,6 +1,6 @@ $ cargo test Compiling limit-tracker v0.1.0 (file:///projects/limit-tracker) - Finished test [unoptimized + debuginfo] target(s) in 0.91s + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.91s Running unittests src/lib.rs (target/debug/deps/limit_tracker-e599811fa246dbde) running 1 test @@ -9,7 +9,9 @@ test tests::it_sends_an_over_75_percent_warning_message ... FAILED failures: ---- tests::it_sends_an_over_75_percent_warning_message stdout ---- -thread 'tests::it_sends_an_over_75_percent_warning_message' panicked at 'already borrowed: BorrowMutError', src/lib.rs:60:53 + +thread 'tests::it_sends_an_over_75_percent_warning_message' panicked at src/lib.rs:60:53: +RefCell already borrowed note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace diff --git a/listings/ch15-smart-pointers/listing-15-24/Cargo.toml b/listings/ch15-smart-pointers/listing-15-24/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-24/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-24/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-24/output.txt b/listings/ch15-smart-pointers/listing-15-24/output.txt index 21b3530d95..bbdc588c6e 100644 --- a/listings/ch15-smart-pointers/listing-15-24/output.txt +++ b/listings/ch15-smart-pointers/listing-15-24/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling cons-list v0.1.0 (file:///projects/cons-list) - Finished dev [unoptimized + debuginfo] target(s) in 0.63s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.63s Running `target/debug/cons-list` a after = Cons(RefCell { value: 15 }, Nil) b after = Cons(RefCell { value: 3 }, Cons(RefCell { value: 15 }, Nil)) diff --git a/listings/ch15-smart-pointers/listing-15-24/src/main.rs b/listings/ch15-smart-pointers/listing-15-24/src/main.rs index e225bd8620..e3dda1a196 100644 --- a/listings/ch15-smart-pointers/listing-15-24/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-24/src/main.rs @@ -18,7 +18,7 @@ fn main() { *value.borrow_mut() += 10; - println!("a after = {:?}", a); - println!("b after = {:?}", b); - println!("c after = {:?}", c); + println!("a after = {a:?}"); + println!("b after = {b:?}"); + println!("c after = {c:?}"); } diff --git a/listings/ch15-smart-pointers/listing-15-25/Cargo.toml b/listings/ch15-smart-pointers/listing-15-25/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-25/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-25/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-25/src/main.rs b/listings/ch15-smart-pointers/listing-15-25/src/main.rs index f36c7fd06d..6051014de7 100644 --- a/listings/ch15-smart-pointers/listing-15-25/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-25/src/main.rs @@ -1,3 +1,4 @@ +// ANCHOR: here use crate::List::{Cons, Nil}; use std::cell::RefCell; use std::rc::Rc; @@ -16,5 +17,6 @@ impl List { } } } +// ANCHOR_END: here fn main() {} diff --git a/listings/ch15-smart-pointers/listing-15-26/Cargo.toml b/listings/ch15-smart-pointers/listing-15-26/Cargo.toml index dce1515c3e..d3f10bdeb4 100644 --- a/listings/ch15-smart-pointers/listing-15-26/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-26/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "cons-list" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-26/output.txt b/listings/ch15-smart-pointers/listing-15-26/output.txt index 8b8eb40b60..b8e70e47dc 100644 --- a/listings/ch15-smart-pointers/listing-15-26/output.txt +++ b/listings/ch15-smart-pointers/listing-15-26/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling cons-list v0.1.0 (file:///projects/cons-list) - Finished dev [unoptimized + debuginfo] target(s) in 0.53s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.53s Running `target/debug/cons-list` a initial rc count = 1 a next item = Some(RefCell { value: Nil }) diff --git a/listings/ch15-smart-pointers/listing-15-26/src/main.rs b/listings/ch15-smart-pointers/listing-15-26/src/main.rs index 08963aaa51..1c811968fb 100644 --- a/listings/ch15-smart-pointers/listing-15-26/src/main.rs +++ b/listings/ch15-smart-pointers/listing-15-26/src/main.rs @@ -38,7 +38,7 @@ fn main() { println!("a rc count after changing a = {}", Rc::strong_count(&a)); // Uncomment the next line to see that we have a cycle; - // it will overflow the stack + // it will overflow the stack. // println!("a next item = {:?}", a.tail()); } // ANCHOR_END: here diff --git a/listings/ch15-smart-pointers/listing-15-27/Cargo.toml b/listings/ch15-smart-pointers/listing-15-27/Cargo.toml index 0bbf897d08..72a0e7ceab 100644 --- a/listings/ch15-smart-pointers/listing-15-27/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-27/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "tree" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-28/Cargo.toml b/listings/ch15-smart-pointers/listing-15-28/Cargo.toml index 0bbf897d08..72a0e7ceab 100644 --- a/listings/ch15-smart-pointers/listing-15-28/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-28/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "tree" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/listing-15-29/Cargo.toml b/listings/ch15-smart-pointers/listing-15-29/Cargo.toml index 0bbf897d08..72a0e7ceab 100644 --- a/listings/ch15-smart-pointers/listing-15-29/Cargo.toml +++ b/listings/ch15-smart-pointers/listing-15-29/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "tree" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/Cargo.toml b/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/Cargo.toml index 16f92447f6..c172b538f4 100644 --- a/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/Cargo.toml +++ b/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "borrowing" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/output.txt b/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/output.txt index 8e84746eec..95b9b68a82 100644 --- a/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/output.txt +++ b/listings/ch15-smart-pointers/no-listing-01-cant-borrow-immutable-as-mutable/output.txt @@ -3,10 +3,13 @@ $ cargo run error[E0596]: cannot borrow `x` as mutable, as it is not declared as mutable --> src/main.rs:3:13 | -2 | let x = 5; - | - help: consider changing this to be mutable: `mut x` 3 | let y = &mut x; | ^^^^^^ cannot borrow as mutable + | +help: consider changing this to be mutable + | +2 | let mut x = 5; + | +++ For more information about this error, try `rustc --explain E0596`. -error: could not compile `borrowing` due to previous error +error: could not compile `borrowing` (bin "borrowing") due to 1 previous error diff --git a/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/Cargo.toml b/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/Cargo.toml index 67ec198f74..bfefa23ee1 100644 --- a/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/Cargo.toml +++ b/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "deref-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/output.txt b/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/output.txt index a03cc34e2e..d1eccd2b22 100644 --- a/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/output.txt +++ b/listings/ch15-smart-pointers/output-only-01-comparing-to-reference/output.txt @@ -7,17 +7,7 @@ error[E0277]: can't compare `{integer}` with `&{integer}` | ^^^^^^^^^^^^^^^^ no implementation for `{integer} == &{integer}` | = help: the trait `PartialEq<&{integer}>` is not implemented for `{integer}` - = help: the following other types implement trait `PartialEq`: - f32 - f64 - i128 - i16 - i32 - i64 - i8 - isize - and 6 others = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info) For more information about this error, try `rustc --explain E0277`. -error: could not compile `deref-example` due to previous error +error: could not compile `deref-example` (bin "deref-example") due to 1 previous error diff --git a/listings/ch16-fearless-concurrency/listing-16-01/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-01/Cargo.toml index bd4edf7626..f210198185 100644 --- a/listings/ch16-fearless-concurrency/listing-16-01/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "threads" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-01/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-01/src/main.rs index 6305a98e3d..ea10ba282a 100644 --- a/listings/ch16-fearless-concurrency/listing-16-01/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-01/src/main.rs @@ -4,13 +4,13 @@ use std::time::Duration; fn main() { thread::spawn(|| { for i in 1..10 { - println!("hi number {} from the spawned thread!", i); + println!("hi number {i} from the spawned thread!"); thread::sleep(Duration::from_millis(1)); } }); for i in 1..5 { - println!("hi number {} from the main thread!", i); + println!("hi number {i} from the main thread!"); thread::sleep(Duration::from_millis(1)); } } diff --git a/listings/ch16-fearless-concurrency/listing-16-02/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-02/Cargo.toml index bd4edf7626..f210198185 100644 --- a/listings/ch16-fearless-concurrency/listing-16-02/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "threads" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-02/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-02/src/main.rs index e37607f1d6..33bf53f400 100644 --- a/listings/ch16-fearless-concurrency/listing-16-02/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-02/src/main.rs @@ -4,13 +4,13 @@ use std::time::Duration; fn main() { let handle = thread::spawn(|| { for i in 1..10 { - println!("hi number {} from the spawned thread!", i); + println!("hi number {i} from the spawned thread!"); thread::sleep(Duration::from_millis(1)); } }); for i in 1..5 { - println!("hi number {} from the main thread!", i); + println!("hi number {i} from the main thread!"); thread::sleep(Duration::from_millis(1)); } diff --git a/listings/ch16-fearless-concurrency/listing-16-03/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-03/Cargo.toml index bd4edf7626..f210198185 100644 --- a/listings/ch16-fearless-concurrency/listing-16-03/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "threads" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-03/output.txt b/listings/ch16-fearless-concurrency/listing-16-03/output.txt index 321bf59d70..3de4d4d3f2 100644 --- a/listings/ch16-fearless-concurrency/listing-16-03/output.txt +++ b/listings/ch16-fearless-concurrency/listing-16-03/output.txt @@ -5,15 +5,15 @@ error[E0373]: closure may outlive the current function, but it borrows `v`, whic | 6 | let handle = thread::spawn(|| { | ^^ may outlive borrowed value `v` -7 | println!("Here's a vector: {:?}", v); - | - `v` is borrowed here +7 | println!("Here's a vector: {v:?}"); + | - `v` is borrowed here | note: function requires argument type to outlive `'static` --> src/main.rs:6:18 | 6 | let handle = thread::spawn(|| { | __________________^ -7 | | println!("Here's a vector: {:?}", v); +7 | | println!("Here's a vector: {v:?}"); 8 | | }); | |______^ help: to force the closure to take ownership of `v` (and any other referenced variables), use the `move` keyword @@ -22,4 +22,4 @@ help: to force the closure to take ownership of `v` (and any other referenced va | ++++ For more information about this error, try `rustc --explain E0373`. -error: could not compile `threads` due to previous error +error: could not compile `threads` (bin "threads") due to 1 previous error diff --git a/listings/ch16-fearless-concurrency/listing-16-03/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-03/src/main.rs index defc876482..b2231c5b86 100644 --- a/listings/ch16-fearless-concurrency/listing-16-03/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-03/src/main.rs @@ -4,7 +4,7 @@ fn main() { let v = vec![1, 2, 3]; let handle = thread::spawn(|| { - println!("Here's a vector: {:?}", v); + println!("Here's a vector: {v:?}"); }); handle.join().unwrap(); diff --git a/listings/ch16-fearless-concurrency/listing-16-04/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-04/Cargo.toml index bd4edf7626..f210198185 100644 --- a/listings/ch16-fearless-concurrency/listing-16-04/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "threads" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-04/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-04/src/main.rs index 0bccc5f56f..f0a9058a1c 100644 --- a/listings/ch16-fearless-concurrency/listing-16-04/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-04/src/main.rs @@ -4,7 +4,7 @@ fn main() { let v = vec![1, 2, 3]; let handle = thread::spawn(|| { - println!("Here's a vector: {:?}", v); + println!("Here's a vector: {v:?}"); }); drop(v); // oh no! diff --git a/listings/ch16-fearless-concurrency/listing-16-05/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-05/Cargo.toml index bd4edf7626..f210198185 100644 --- a/listings/ch16-fearless-concurrency/listing-16-05/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "threads" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-05/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-05/src/main.rs index a6547dc4c1..76783e6149 100644 --- a/listings/ch16-fearless-concurrency/listing-16-05/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-05/src/main.rs @@ -4,7 +4,7 @@ fn main() { let v = vec![1, 2, 3]; let handle = thread::spawn(move || { - println!("Here's a vector: {:?}", v); + println!("Here's a vector: {v:?}"); }); handle.join().unwrap(); diff --git a/listings/ch16-fearless-concurrency/listing-16-06/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-06/Cargo.toml index 24bd2ee7b4..4bf22a497f 100644 --- a/listings/ch16-fearless-concurrency/listing-16-06/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "message-passing" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-07/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-07/Cargo.toml index 24bd2ee7b4..4bf22a497f 100644 --- a/listings/ch16-fearless-concurrency/listing-16-07/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-07/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "message-passing" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-08/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-08/Cargo.toml index 24bd2ee7b4..4bf22a497f 100644 --- a/listings/ch16-fearless-concurrency/listing-16-08/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-08/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "message-passing" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-08/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-08/src/main.rs index fbba9167d4..e7ac452dcd 100644 --- a/listings/ch16-fearless-concurrency/listing-16-08/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-08/src/main.rs @@ -10,5 +10,5 @@ fn main() { }); let received = rx.recv().unwrap(); - println!("Got: {}", received); + println!("Got: {received}"); } diff --git a/listings/ch16-fearless-concurrency/listing-16-09/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-09/Cargo.toml index 24bd2ee7b4..4bf22a497f 100644 --- a/listings/ch16-fearless-concurrency/listing-16-09/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-09/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "message-passing" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-09/output.txt b/listings/ch16-fearless-concurrency/listing-16-09/output.txt index db85185372..f6d3ee7d6e 100644 --- a/listings/ch16-fearless-concurrency/listing-16-09/output.txt +++ b/listings/ch16-fearless-concurrency/listing-16-09/output.txt @@ -1,16 +1,16 @@ $ cargo run Compiling message-passing v0.1.0 (file:///projects/message-passing) error[E0382]: borrow of moved value: `val` - --> src/main.rs:10:31 + --> src/main.rs:10:27 | -8 | let val = String::from("hi"); + 8 | let val = String::from("hi"); | --- move occurs because `val` has type `String`, which does not implement the `Copy` trait -9 | tx.send(val).unwrap(); + 9 | tx.send(val).unwrap(); | --- value moved here -10 | println!("val is {}", val); - | ^^^ value borrowed here after move +10 | println!("val is {val}"); + | ^^^ value borrowed here after move | = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) For more information about this error, try `rustc --explain E0382`. -error: could not compile `message-passing` due to previous error +error: could not compile `message-passing` (bin "message-passing") due to 1 previous error diff --git a/listings/ch16-fearless-concurrency/listing-16-09/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-09/src/main.rs index 98a8129ab3..fe20d3474a 100644 --- a/listings/ch16-fearless-concurrency/listing-16-09/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-09/src/main.rs @@ -7,9 +7,9 @@ fn main() { thread::spawn(move || { let val = String::from("hi"); tx.send(val).unwrap(); - println!("val is {}", val); + println!("val is {val}"); }); let received = rx.recv().unwrap(); - println!("Got: {}", received); + println!("Got: {received}"); } diff --git a/listings/ch16-fearless-concurrency/listing-16-10/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-10/Cargo.toml index 24bd2ee7b4..4bf22a497f 100644 --- a/listings/ch16-fearless-concurrency/listing-16-10/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-10/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "message-passing" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-10/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-10/src/main.rs index 82b220de45..c9702bd858 100644 --- a/listings/ch16-fearless-concurrency/listing-16-10/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-10/src/main.rs @@ -20,6 +20,6 @@ fn main() { }); for received in rx { - println!("Got: {}", received); + println!("Got: {received}"); } } diff --git a/listings/ch16-fearless-concurrency/listing-16-11/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-11/Cargo.toml index 24bd2ee7b4..4bf22a497f 100644 --- a/listings/ch16-fearless-concurrency/listing-16-11/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "message-passing" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-11/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-11/src/main.rs index d92deab5cb..174a5d14bb 100644 --- a/listings/ch16-fearless-concurrency/listing-16-11/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-11/src/main.rs @@ -38,7 +38,7 @@ fn main() { }); for received in rx { - println!("Got: {}", received); + println!("Got: {received}"); } // --snip-- diff --git a/listings/ch16-fearless-concurrency/listing-16-12/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-12/Cargo.toml index da297eaba1..e77784295e 100644 --- a/listings/ch16-fearless-concurrency/listing-16-12/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "shared-state" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-12/src/main.rs b/listings/ch16-fearless-concurrency/listing-16-12/src/main.rs index 0c0d6767ad..99ba5b489a 100644 --- a/listings/ch16-fearless-concurrency/listing-16-12/src/main.rs +++ b/listings/ch16-fearless-concurrency/listing-16-12/src/main.rs @@ -8,5 +8,5 @@ fn main() { *num = 6; } - println!("m = {:?}", m); + println!("m = {m:?}"); } diff --git a/listings/ch16-fearless-concurrency/listing-16-13/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-13/Cargo.toml index da297eaba1..e77784295e 100644 --- a/listings/ch16-fearless-concurrency/listing-16-13/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "shared-state" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-13/output.txt b/listings/ch16-fearless-concurrency/listing-16-13/output.txt index ea6963903d..598e0ad7c4 100644 --- a/listings/ch16-fearless-concurrency/listing-16-13/output.txt +++ b/listings/ch16-fearless-concurrency/listing-16-13/output.txt @@ -1,15 +1,26 @@ $ cargo run Compiling shared-state v0.1.0 (file:///projects/shared-state) -error[E0382]: use of moved value: `counter` - --> src/main.rs:9:36 +error[E0382]: borrow of moved value: `counter` + --> src/main.rs:21:29 | -5 | let counter = Mutex::new(0); - | ------- move occurs because `counter` has type `Mutex`, which does not implement the `Copy` trait + 5 | let counter = Mutex::new(0); + | ------- move occurs because `counter` has type `std::sync::Mutex`, which does not implement the `Copy` trait ... -9 | let handle = thread::spawn(move || { - | ^^^^^^^ value moved into closure here, in previous iteration of loop -10 | let mut num = counter.lock().unwrap(); - | ------- use occurs due to use in closure + 8 | for _ in 0..10 { + | -------------- inside of this loop + 9 | let handle = thread::spawn(move || { + | ------- value moved into closure here, in previous iteration of loop +... +21 | println!("Result: {}", *counter.lock().unwrap()); + | ^^^^^^^ value borrowed here after move + | +help: consider moving the expression out of the loop so it is only moved once + | + 8 ~ let mut value = counter.lock(); + 9 ~ for _ in 0..10 { +10 | let handle = thread::spawn(move || { +11 ~ let mut num = value.unwrap(); + | For more information about this error, try `rustc --explain E0382`. -error: could not compile `shared-state` due to previous error +error: could not compile `shared-state` (bin "shared-state") due to 1 previous error diff --git a/listings/ch16-fearless-concurrency/listing-16-14/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-14/Cargo.toml index da297eaba1..e77784295e 100644 --- a/listings/ch16-fearless-concurrency/listing-16-14/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "shared-state" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/listing-16-14/output.txt b/listings/ch16-fearless-concurrency/listing-16-14/output.txt index e8cf21a736..7b856e2e84 100644 --- a/listings/ch16-fearless-concurrency/listing-16-14/output.txt +++ b/listings/ch16-fearless-concurrency/listing-16-14/output.txt @@ -1,30 +1,28 @@ $ cargo run Compiling shared-state v0.1.0 (file:///projects/shared-state) -error[E0277]: `Rc>` cannot be sent between threads safely +error[E0277]: `Rc>` cannot be sent between threads safely --> src/main.rs:11:36 | 11 | let handle = thread::spawn(move || { | ------------- ^------ | | | - | ______________________|_____________within this `[closure@src/main.rs:11:36: 11:43]` + | ______________________|_____________within this `{closure@src/main.rs:11:36: 11:43}` | | | | | required by a bound introduced by this call 12 | | let mut num = counter.lock().unwrap(); 13 | | 14 | | *num += 1; 15 | | }); - | |_________^ `Rc>` cannot be sent between threads safely + | |_________^ `Rc>` cannot be sent between threads safely | - = help: within `[closure@src/main.rs:11:36: 11:43]`, the trait `Send` is not implemented for `Rc>` + = help: within `{closure@src/main.rs:11:36: 11:43}`, the trait `Send` is not implemented for `Rc>` note: required because it's used within this closure --> src/main.rs:11:36 | 11 | let handle = thread::spawn(move || { | ^^^^^^^ note: required by a bound in `spawn` - --> /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/std/src/thread/mod.rs:704:8 - | - = note: required by this bound in `spawn` + --> /rustc/1159e78c4747b02ef996e55082b704c09b970588/library/std/src/thread/mod.rs:723:1 For more information about this error, try `rustc --explain E0277`. -error: could not compile `shared-state` due to previous error +error: could not compile `shared-state` (bin "shared-state") due to 1 previous error diff --git a/listings/ch16-fearless-concurrency/listing-16-15/Cargo.toml b/listings/ch16-fearless-concurrency/listing-16-15/Cargo.toml index da297eaba1..e77784295e 100644 --- a/listings/ch16-fearless-concurrency/listing-16-15/Cargo.toml +++ b/listings/ch16-fearless-concurrency/listing-16-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "shared-state" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/Cargo.toml b/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/Cargo.toml index bd4edf7626..f210198185 100644 --- a/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/Cargo.toml +++ b/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "threads" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/src/main.rs b/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/src/main.rs index 6205e57d33..7023a90f64 100644 --- a/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/src/main.rs +++ b/listings/ch16-fearless-concurrency/no-listing-01-join-too-early/src/main.rs @@ -4,7 +4,7 @@ use std::time::Duration; fn main() { let handle = thread::spawn(|| { for i in 1..10 { - println!("hi number {} from the spawned thread!", i); + println!("hi number {i} from the spawned thread!"); thread::sleep(Duration::from_millis(1)); } }); @@ -12,7 +12,7 @@ fn main() { handle.join().unwrap(); for i in 1..5 { - println!("hi number {} from the main thread!", i); + println!("hi number {i} from the main thread!"); thread::sleep(Duration::from_millis(1)); } } diff --git a/listings/ch16-fearless-concurrency/no-listing-02-no-loop-to-understand-error/Cargo.toml b/listings/ch16-fearless-concurrency/no-listing-02-no-loop-to-understand-error/Cargo.toml index da297eaba1..e77784295e 100644 --- a/listings/ch16-fearless-concurrency/no-listing-02-no-loop-to-understand-error/Cargo.toml +++ b/listings/ch16-fearless-concurrency/no-listing-02-no-loop-to-understand-error/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "shared-state" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/output-only-01-move-drop/Cargo.toml b/listings/ch16-fearless-concurrency/output-only-01-move-drop/Cargo.toml index bd4edf7626..f210198185 100644 --- a/listings/ch16-fearless-concurrency/output-only-01-move-drop/Cargo.toml +++ b/listings/ch16-fearless-concurrency/output-only-01-move-drop/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "threads" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch16-fearless-concurrency/output-only-01-move-drop/output.txt b/listings/ch16-fearless-concurrency/output-only-01-move-drop/output.txt index 301a9a44a4..6a8d57f84d 100644 --- a/listings/ch16-fearless-concurrency/output-only-01-move-drop/output.txt +++ b/listings/ch16-fearless-concurrency/output-only-01-move-drop/output.txt @@ -3,16 +3,23 @@ $ cargo run error[E0382]: use of moved value: `v` --> src/main.rs:10:10 | -4 | let v = vec![1, 2, 3]; + 4 | let v = vec![1, 2, 3]; | - move occurs because `v` has type `Vec`, which does not implement the `Copy` trait -5 | -6 | let handle = thread::spawn(move || { + 5 | + 6 | let handle = thread::spawn(move || { | ------- value moved into closure here -7 | println!("Here's a vector: {:?}", v); - | - variable moved due to use in closure + 7 | println!("Here's a vector: {v:?}"); + | - variable moved due to use in closure ... 10 | drop(v); // oh no! | ^ value used here after move + | +help: consider cloning the value before moving it into the closure + | + 6 ~ let value = v.clone(); + 7 ~ let handle = thread::spawn(move || { + 8 ~ println!("Here's a vector: {value:?}"); + | For more information about this error, try `rustc --explain E0382`. -error: could not compile `threads` due to previous error +error: could not compile `threads` (bin "threads") due to 1 previous error diff --git a/listings/ch16-fearless-concurrency/output-only-01-move-drop/src/main.rs b/listings/ch16-fearless-concurrency/output-only-01-move-drop/src/main.rs index 70f659c5f6..cc71cbab0b 100644 --- a/listings/ch16-fearless-concurrency/output-only-01-move-drop/src/main.rs +++ b/listings/ch16-fearless-concurrency/output-only-01-move-drop/src/main.rs @@ -4,7 +4,7 @@ fn 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https://doc.rust-lang.org/cargo/reference/manifest.html + +[dependencies] +trpl = { path = "../../../packages/trpl" } diff --git a/listings/ch17-async-await/listing-17-06/src/main.rs b/listings/ch17-async-await/listing-17-06/src/main.rs new file mode 100644 index 0000000000..2fe6a5f29d --- /dev/null +++ b/listings/ch17-async-await/listing-17-06/src/main.rs @@ -0,0 +1,21 @@ +extern crate trpl; // required for mdbook test + +// ANCHOR: all +use std::time::Duration; + +fn main() { + trpl::block_on(async { + trpl::spawn_task(async { + for i in 1..10 { + println!("hi number {i} from the first task!"); + trpl::sleep(Duration::from_millis(500)).await; + } + }); + + for i in 1..5 { + println!("hi number {i} from the second task!"); + trpl::sleep(Duration::from_millis(500)).await; + } + }); +} +// ANCHOR_END: all diff --git a/listings/ch17-async-await/listing-17-07/Cargo.lock b/listings/ch17-async-await/listing-17-07/Cargo.lock new file mode 100644 index 0000000000..7efd72f633 --- /dev/null +++ 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ANCHOR: here + let (tx, mut rx) = trpl::channel(); + + let tx1 = tx.clone(); + let tx1_fut = async move { + let vals = vec![ + String::from("hi"), + String::from("from"), + String::from("the"), + String::from("future"), + ]; + + for val in vals { + tx1.send(val).unwrap(); + trpl::sleep(Duration::from_millis(500)).await; + } + }; + + let rx_fut = async { + while let Some(value) = rx.recv().await { + println!("received '{value}'"); + } + }; + + let tx_fut = async move { + let vals = vec![ + String::from("more"), + String::from("messages"), + String::from("for"), + String::from("you"), + ]; + + for val in vals { + tx.send(val).unwrap(); + trpl::sleep(Duration::from_millis(1500)).await; + } + }; + + trpl::join!(tx1_fut, tx_fut, rx_fut); + // ANCHOR_END: here + }); +} diff --git a/listings/ch17-async-await/listing-17-14/Cargo.lock b/listings/ch17-async-await/listing-17-14/Cargo.lock new file mode 100644 index 0000000000..7efd72f633 --- /dev/null +++ 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https://doc.rust-lang.org/cargo/reference/manifest.html + +[dependencies] +trpl = { path = "../../../packages/trpl" } diff --git a/listings/ch17-async-await/listing-17-17/src/main.rs b/listings/ch17-async-await/listing-17-17/src/main.rs new file mode 100644 index 0000000000..07c13c0b1a --- /dev/null +++ b/listings/ch17-async-await/listing-17-17/src/main.rs @@ -0,0 +1,40 @@ +extern crate trpl; // required for mdbook test + +use std::{thread, time::Duration}; + +fn main() { + trpl::block_on(async { + // ANCHOR: yields + let a = async { + println!("'a' started."); + slow("a", 30); + trpl::yield_now().await; + slow("a", 10); + trpl::yield_now().await; + slow("a", 20); + trpl::yield_now().await; + println!("'a' finished."); + }; + + let b = async { + println!("'b' started."); + slow("b", 75); + trpl::yield_now().await; + slow("b", 10); + trpl::yield_now().await; + slow("b", 15); + trpl::yield_now().await; + slow("b", 350); + trpl::yield_now().await; + println!("'b' finished."); + }; + // 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their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html +[dependencies] +trpl = { path = "../../../packages/trpl" } diff --git a/listings/ch17-async-await/listing-17-21/src/main.rs b/listings/ch17-async-await/listing-17-21/src/main.rs new file mode 100644 index 0000000000..7900b39ce4 --- /dev/null +++ b/listings/ch17-async-await/listing-17-21/src/main.rs @@ -0,0 +1,15 @@ +extern crate trpl; // required for mdbook test + +fn main() { + trpl::block_on(async { + // ANCHOR: stream + let values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; + let iter = values.iter().map(|n| n * 2); + let mut stream = trpl::stream_from_iter(iter); + + while let Some(value) = stream.next().await { + println!("The value was: {value}"); + } + // ANCHOR_END: stream + }); +} diff --git a/listings/ch17-async-await/listing-17-22/Cargo.lock b/listings/ch17-async-await/listing-17-22/Cargo.lock new file mode 100644 index 0000000000..1a59804c89 --- /dev/null +++ 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ANCHOR_END: here +use std::time::Duration; + +fn main() { + trpl::block_on(async { + let (tx, mut rx) = trpl::channel(); + + let tx1 = tx.clone(); + // ANCHOR: here + let tx1_fut = pin!(async move { + // --snip-- + // ANCHOR_END: here + let vals = vec![ + String::from("hi"), + String::from("from"), + String::from("the"), + String::from("future"), + ]; + + for val in vals { + tx1.send(val).unwrap(); + trpl::sleep(Duration::from_secs(1)).await; + } + // ANCHOR: here + }); + + // ANCHOR_END: here + // ANCHOR: here + let rx_fut = pin!(async { + // --snip-- + // ANCHOR_END: here + while let Some(value) = rx.recv().await { + println!("received '{value}'"); + } + // ANCHOR: here + }); + + let tx_fut = pin!(async move { + // --snip-- + // ANCHOR_END: here + let vals = vec![ + String::from("more"), + String::from("messages"), + String::from("for"), + String::from("you"), + ]; + + for val in vals { + tx.send(val).unwrap(); + trpl::sleep(Duration::from_secs(1)).await; + } + // ANCHOR: here + }); 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mode 100644 index 0000000000..e5c8a84843 --- /dev/null +++ b/listings/ch17-async-await/no-listing-state-machine/Cargo.toml @@ -0,0 +1,8 @@ +[package] +name = "async_await" +version = "0.1.0" +edition = "2024" + +# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html +[dependencies] +trpl = { path = "../../../packages/trpl" } diff --git a/listings/ch17-async-await/no-listing-state-machine/output.txt b/listings/ch17-async-await/no-listing-state-machine/output.txt new file mode 100644 index 0000000000..10a18bc488 --- /dev/null +++ b/listings/ch17-async-await/no-listing-state-machine/output.txt @@ -0,0 +1,2 @@ +$ cargo run +error: a bin target must be available for `cargo run` diff --git a/listings/ch17-async-await/no-listing-state-machine/src/lib.rs b/listings/ch17-async-await/no-listing-state-machine/src/lib.rs new file mode 100644 index 0000000000..1273283140 --- /dev/null +++ b/listings/ch17-async-await/no-listing-state-machine/src/lib.rs @@ -0,0 +1,9 @@ +extern crate trpl; // required for mdbook test + +// ANCHOR: enum +enum PageTitleFuture<'a> { + Initial { url: &'a str }, + GetAwaitPoint { url: &'a str }, + TextAwaitPoint { response: trpl::Response }, +} +// ANCHOR_END: enum diff --git a/listings/ch11-writing-automated-tests/listing-11-01/Cargo.lock b/listings/ch17-async-await/no-listing-stream-ext/Cargo.lock similarity index 86% rename from listings/ch11-writing-automated-tests/listing-11-01/Cargo.lock rename to listings/ch17-async-await/no-listing-stream-ext/Cargo.lock index 8b8c69d33a..d30b928a6c 100644 --- a/listings/ch11-writing-automated-tests/listing-11-01/Cargo.lock +++ b/listings/ch17-async-await/no-listing-stream-ext/Cargo.lock @@ -3,5 +3,5 @@ version = 3 [[package]] -name = "adder" +name = "async_await" version = "0.1.0" diff --git a/listings/ch17-async-await/no-listing-stream-ext/Cargo.toml b/listings/ch17-async-await/no-listing-stream-ext/Cargo.toml new file mode 100644 index 0000000000..12171e3621 --- /dev/null +++ b/listings/ch17-async-await/no-listing-stream-ext/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "async_await" +version = "0.1.0" +edition = "2024" + +# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html diff --git a/listings/ch17-async-await/no-listing-stream-ext/output.txt b/listings/ch17-async-await/no-listing-stream-ext/output.txt new file mode 100644 index 0000000000..10a18bc488 --- /dev/null +++ b/listings/ch17-async-await/no-listing-stream-ext/output.txt @@ -0,0 +1,2 @@ +$ cargo run +error: a bin target must be available for `cargo run` diff --git a/listings/ch17-async-await/no-listing-stream-ext/src/lib.rs b/listings/ch17-async-await/no-listing-stream-ext/src/lib.rs new file mode 100644 index 0000000000..09a980c04d --- /dev/null +++ b/listings/ch17-async-await/no-listing-stream-ext/src/lib.rs @@ -0,0 +1,20 @@ +use std::pin::Pin; +use std::task::{Context, Poll}; + +trait Stream { + type Item; + fn poll_next( + self: Pin<&mut Self>, + cx: &mut Context<'_>, + ) -> Poll>; +} + +// ANCHOR: here +trait StreamExt: Stream { + async fn next(&mut self) -> Option + where + Self: Unpin; + + // other methods... +} +// ANCHOR_END: here diff --git a/listings/ch17-oop/listing-17-07/Cargo.toml b/listings/ch17-oop/listing-17-07/Cargo.toml deleted file mode 100644 index 9b816e7661..0000000000 --- a/listings/ch17-oop/listing-17-07/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "gui" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-08/Cargo.toml b/listings/ch17-oop/listing-17-08/Cargo.toml deleted file mode 100644 index 9b816e7661..0000000000 --- a/listings/ch17-oop/listing-17-08/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "gui" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-09/Cargo.toml b/listings/ch17-oop/listing-17-09/Cargo.toml deleted file mode 100644 index 9b816e7661..0000000000 --- a/listings/ch17-oop/listing-17-09/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "gui" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-10/Cargo.toml b/listings/ch17-oop/listing-17-10/Cargo.toml deleted file mode 100644 index 9b816e7661..0000000000 --- a/listings/ch17-oop/listing-17-10/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "gui" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-15/Cargo.toml b/listings/ch17-oop/listing-17-15/Cargo.toml deleted file mode 100644 index 1619af5c64..0000000000 --- a/listings/ch17-oop/listing-17-15/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "blog" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-16/Cargo.toml b/listings/ch17-oop/listing-17-16/Cargo.toml deleted file mode 100644 index 1619af5c64..0000000000 --- a/listings/ch17-oop/listing-17-16/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "blog" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-17/Cargo.toml b/listings/ch17-oop/listing-17-17/Cargo.toml deleted file mode 100644 index 1619af5c64..0000000000 --- a/listings/ch17-oop/listing-17-17/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "blog" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-18/Cargo.toml b/listings/ch17-oop/listing-17-18/Cargo.toml deleted file mode 100644 index 1619af5c64..0000000000 --- a/listings/ch17-oop/listing-17-18/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "blog" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-19/Cargo.toml b/listings/ch17-oop/listing-17-19/Cargo.toml deleted file mode 100644 index 1619af5c64..0000000000 --- a/listings/ch17-oop/listing-17-19/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "blog" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-20/Cargo.toml b/listings/ch17-oop/listing-17-20/Cargo.toml deleted file mode 100644 index 1619af5c64..0000000000 --- a/listings/ch17-oop/listing-17-20/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "blog" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-21/Cargo.toml b/listings/ch17-oop/listing-17-21/Cargo.toml deleted file mode 100644 index 1619af5c64..0000000000 --- a/listings/ch17-oop/listing-17-21/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "blog" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch17-oop/listing-17-01/Cargo.lock b/listings/ch18-oop/listing-18-01/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-01/Cargo.lock rename to listings/ch18-oop/listing-18-01/Cargo.lock diff --git a/listings/ch17-oop/listing-17-01/Cargo.toml b/listings/ch18-oop/listing-18-01/Cargo.toml similarity index 81% rename from listings/ch17-oop/listing-17-01/Cargo.toml rename to listings/ch18-oop/listing-18-01/Cargo.toml index aed614e939..af2ec971d9 100644 --- a/listings/ch17-oop/listing-17-01/Cargo.toml +++ b/listings/ch18-oop/listing-18-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "averaged-collection" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-01/src/lib.rs b/listings/ch18-oop/listing-18-01/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-01/src/lib.rs rename to listings/ch18-oop/listing-18-01/src/lib.rs diff --git a/listings/ch17-oop/listing-17-02/Cargo.lock b/listings/ch18-oop/listing-18-02/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-02/Cargo.lock rename to listings/ch18-oop/listing-18-02/Cargo.lock diff --git a/listings/ch17-oop/listing-17-02/Cargo.toml b/listings/ch18-oop/listing-18-02/Cargo.toml similarity index 81% rename from listings/ch17-oop/listing-17-02/Cargo.toml rename to listings/ch18-oop/listing-18-02/Cargo.toml index aed614e939..af2ec971d9 100644 --- a/listings/ch17-oop/listing-17-02/Cargo.toml +++ b/listings/ch18-oop/listing-18-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "averaged-collection" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-02/src/lib.rs b/listings/ch18-oop/listing-18-02/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-02/src/lib.rs rename to listings/ch18-oop/listing-18-02/src/lib.rs diff --git a/listings/ch17-oop/listing-17-03/Cargo.lock b/listings/ch18-oop/listing-18-03/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-03/Cargo.lock rename to listings/ch18-oop/listing-18-03/Cargo.lock diff --git a/listings/ch17-oop/listing-17-06/Cargo.toml b/listings/ch18-oop/listing-18-03/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-06/Cargo.toml rename to listings/ch18-oop/listing-18-03/Cargo.toml index 9b816e7661..ac8282d685 100644 --- a/listings/ch17-oop/listing-17-06/Cargo.toml +++ b/listings/ch18-oop/listing-18-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "gui" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-03/src/lib.rs b/listings/ch18-oop/listing-18-03/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-03/src/lib.rs rename to listings/ch18-oop/listing-18-03/src/lib.rs diff --git a/listings/ch17-oop/listing-17-04/Cargo.lock b/listings/ch18-oop/listing-18-04/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-04/Cargo.lock rename to listings/ch18-oop/listing-18-04/Cargo.lock diff --git a/listings/ch17-oop/listing-17-04/Cargo.toml b/listings/ch18-oop/listing-18-04/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-04/Cargo.toml rename to listings/ch18-oop/listing-18-04/Cargo.toml index 9b816e7661..ac8282d685 100644 --- a/listings/ch17-oop/listing-17-04/Cargo.toml +++ b/listings/ch18-oop/listing-18-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "gui" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-04/src/lib.rs b/listings/ch18-oop/listing-18-04/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-04/src/lib.rs rename to listings/ch18-oop/listing-18-04/src/lib.rs diff --git a/listings/ch17-oop/listing-17-05/Cargo.lock b/listings/ch18-oop/listing-18-05/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-05/Cargo.lock rename to listings/ch18-oop/listing-18-05/Cargo.lock diff --git a/listings/ch17-oop/listing-17-03/Cargo.toml b/listings/ch18-oop/listing-18-05/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-03/Cargo.toml rename to listings/ch18-oop/listing-18-05/Cargo.toml index 9b816e7661..ac8282d685 100644 --- a/listings/ch17-oop/listing-17-03/Cargo.toml +++ b/listings/ch18-oop/listing-18-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "gui" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-05/src/lib.rs b/listings/ch18-oop/listing-18-05/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-05/src/lib.rs rename to listings/ch18-oop/listing-18-05/src/lib.rs diff --git a/listings/ch17-oop/listing-17-06/Cargo.lock b/listings/ch18-oop/listing-18-06/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-06/Cargo.lock rename to listings/ch18-oop/listing-18-06/Cargo.lock diff --git a/listings/ch17-oop/listing-17-05/Cargo.toml b/listings/ch18-oop/listing-18-06/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-05/Cargo.toml rename to listings/ch18-oop/listing-18-06/Cargo.toml index 9b816e7661..ac8282d685 100644 --- a/listings/ch17-oop/listing-17-05/Cargo.toml +++ b/listings/ch18-oop/listing-18-06/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "gui" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-06/src/lib.rs b/listings/ch18-oop/listing-18-06/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-06/src/lib.rs rename to listings/ch18-oop/listing-18-06/src/lib.rs diff --git a/listings/ch17-oop/listing-17-07/Cargo.lock b/listings/ch18-oop/listing-18-07/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-07/Cargo.lock rename to listings/ch18-oop/listing-18-07/Cargo.lock diff --git a/listings/ch18-oop/listing-18-07/Cargo.toml b/listings/ch18-oop/listing-18-07/Cargo.toml new file mode 100644 index 0000000000..ac8282d685 --- /dev/null +++ b/listings/ch18-oop/listing-18-07/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "gui" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-07/src/lib.rs b/listings/ch18-oop/listing-18-07/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-07/src/lib.rs rename to listings/ch18-oop/listing-18-07/src/lib.rs diff --git a/listings/ch17-oop/listing-17-08/Cargo.lock b/listings/ch18-oop/listing-18-08/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-08/Cargo.lock rename to listings/ch18-oop/listing-18-08/Cargo.lock diff --git a/listings/ch18-oop/listing-18-08/Cargo.toml b/listings/ch18-oop/listing-18-08/Cargo.toml new file mode 100644 index 0000000000..ac8282d685 --- /dev/null +++ b/listings/ch18-oop/listing-18-08/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "gui" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-08/src/lib.rs b/listings/ch18-oop/listing-18-08/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-08/src/lib.rs rename to listings/ch18-oop/listing-18-08/src/lib.rs diff --git a/listings/ch17-oop/listing-17-08/src/main.rs b/listings/ch18-oop/listing-18-08/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-08/src/main.rs rename to listings/ch18-oop/listing-18-08/src/main.rs diff --git a/listings/ch17-oop/listing-17-09/Cargo.lock b/listings/ch18-oop/listing-18-09/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-09/Cargo.lock rename to listings/ch18-oop/listing-18-09/Cargo.lock diff --git a/listings/ch18-oop/listing-18-09/Cargo.toml b/listings/ch18-oop/listing-18-09/Cargo.toml new file mode 100644 index 0000000000..ac8282d685 --- /dev/null +++ b/listings/ch18-oop/listing-18-09/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "gui" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-09/src/lib.rs b/listings/ch18-oop/listing-18-09/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-09/src/lib.rs rename to listings/ch18-oop/listing-18-09/src/lib.rs diff --git a/listings/ch17-oop/listing-17-09/src/main.rs b/listings/ch18-oop/listing-18-09/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-09/src/main.rs rename to listings/ch18-oop/listing-18-09/src/main.rs diff --git a/listings/ch17-oop/listing-17-10/Cargo.lock b/listings/ch18-oop/listing-18-10/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-10/Cargo.lock rename to listings/ch18-oop/listing-18-10/Cargo.lock diff --git a/listings/ch18-oop/listing-18-10/Cargo.toml b/listings/ch18-oop/listing-18-10/Cargo.toml new file mode 100644 index 0000000000..ac8282d685 --- /dev/null +++ b/listings/ch18-oop/listing-18-10/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "gui" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-10/output.txt b/listings/ch18-oop/listing-18-10/output.txt similarity index 76% rename from listings/ch17-oop/listing-17-10/output.txt rename to listings/ch18-oop/listing-18-10/output.txt index e0a455f3b4..78d7c39a32 100644 --- a/listings/ch17-oop/listing-17-10/output.txt +++ b/listings/ch18-oop/listing-18-10/output.txt @@ -7,7 +7,7 @@ error[E0277]: the trait bound `String: Draw` is not satisfied | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Draw` is not implemented for `String` | = help: the trait `Draw` is implemented for `Button` - = note: required for the cast from `String` to the object type `dyn Draw` + = note: required for the cast from `Box` to `Box` For more information about this error, try `rustc --explain E0277`. -error: could not compile `gui` due to previous error +error: could not compile `gui` (bin "gui") due to 1 previous error diff --git a/listings/ch17-oop/listing-17-10/src/lib.rs b/listings/ch18-oop/listing-18-10/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-10/src/lib.rs rename to listings/ch18-oop/listing-18-10/src/lib.rs diff --git a/listings/ch17-oop/listing-17-10/src/main.rs b/listings/ch18-oop/listing-18-10/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-10/src/main.rs rename to listings/ch18-oop/listing-18-10/src/main.rs diff --git a/listings/ch17-oop/listing-17-11/Cargo.lock b/listings/ch18-oop/listing-18-11/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-11/Cargo.lock rename to listings/ch18-oop/listing-18-11/Cargo.lock diff --git a/listings/ch17-oop/listing-17-11/Cargo.toml b/listings/ch18-oop/listing-18-11/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-11/Cargo.toml rename to listings/ch18-oop/listing-18-11/Cargo.toml index 1619af5c64..790832e0a9 100644 --- a/listings/ch17-oop/listing-17-11/Cargo.toml +++ b/listings/ch18-oop/listing-18-11/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "blog" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-11/src/main.rs b/listings/ch18-oop/listing-18-11/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-11/src/main.rs rename to listings/ch18-oop/listing-18-11/src/main.rs diff --git a/listings/ch17-oop/listing-17-12/Cargo.lock b/listings/ch18-oop/listing-18-12/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-12/Cargo.lock rename to listings/ch18-oop/listing-18-12/Cargo.lock diff --git a/listings/ch17-oop/listing-17-12/Cargo.toml b/listings/ch18-oop/listing-18-12/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-12/Cargo.toml rename to listings/ch18-oop/listing-18-12/Cargo.toml index 1619af5c64..790832e0a9 100644 --- a/listings/ch17-oop/listing-17-12/Cargo.toml +++ b/listings/ch18-oop/listing-18-12/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "blog" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-12/src/lib.rs b/listings/ch18-oop/listing-18-12/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-12/src/lib.rs rename to listings/ch18-oop/listing-18-12/src/lib.rs diff --git a/listings/ch17-oop/listing-17-12/src/main.rs b/listings/ch18-oop/listing-18-12/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-12/src/main.rs rename to listings/ch18-oop/listing-18-12/src/main.rs diff --git a/listings/ch17-oop/listing-17-13/Cargo.lock b/listings/ch18-oop/listing-18-13/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-13/Cargo.lock rename to listings/ch18-oop/listing-18-13/Cargo.lock diff --git a/listings/ch17-oop/listing-17-13/Cargo.toml b/listings/ch18-oop/listing-18-13/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-13/Cargo.toml rename to listings/ch18-oop/listing-18-13/Cargo.toml index 1619af5c64..790832e0a9 100644 --- a/listings/ch17-oop/listing-17-13/Cargo.toml +++ b/listings/ch18-oop/listing-18-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "blog" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-13/src/lib.rs b/listings/ch18-oop/listing-18-13/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-13/src/lib.rs rename to listings/ch18-oop/listing-18-13/src/lib.rs diff --git a/listings/ch17-oop/listing-17-13/src/main.rs b/listings/ch18-oop/listing-18-13/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-13/src/main.rs rename to listings/ch18-oop/listing-18-13/src/main.rs diff --git a/listings/ch17-oop/listing-17-14/Cargo.lock b/listings/ch18-oop/listing-18-14/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-14/Cargo.lock rename to listings/ch18-oop/listing-18-14/Cargo.lock diff --git a/listings/ch17-oop/listing-17-14/Cargo.toml b/listings/ch18-oop/listing-18-14/Cargo.toml similarity index 77% rename from listings/ch17-oop/listing-17-14/Cargo.toml rename to listings/ch18-oop/listing-18-14/Cargo.toml index 1619af5c64..790832e0a9 100644 --- a/listings/ch17-oop/listing-17-14/Cargo.toml +++ b/listings/ch18-oop/listing-18-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "blog" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch17-oop/listing-17-14/src/lib.rs b/listings/ch18-oop/listing-18-14/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-14/src/lib.rs rename to listings/ch18-oop/listing-18-14/src/lib.rs diff --git a/listings/ch17-oop/listing-17-14/src/main.rs b/listings/ch18-oop/listing-18-14/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-14/src/main.rs rename to listings/ch18-oop/listing-18-14/src/main.rs diff --git a/listings/ch17-oop/listing-17-15/Cargo.lock b/listings/ch18-oop/listing-18-15/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-15/Cargo.lock rename to listings/ch18-oop/listing-18-15/Cargo.lock diff --git a/listings/ch18-oop/listing-18-15/Cargo.toml b/listings/ch18-oop/listing-18-15/Cargo.toml new file mode 100644 index 0000000000..790832e0a9 --- /dev/null +++ b/listings/ch18-oop/listing-18-15/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "blog" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-15/src/lib.rs b/listings/ch18-oop/listing-18-15/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-15/src/lib.rs rename to listings/ch18-oop/listing-18-15/src/lib.rs diff --git a/listings/ch17-oop/listing-17-15/src/main.rs b/listings/ch18-oop/listing-18-15/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-15/src/main.rs rename to listings/ch18-oop/listing-18-15/src/main.rs diff --git a/listings/ch17-oop/listing-17-16/Cargo.lock b/listings/ch18-oop/listing-18-16/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-16/Cargo.lock rename to listings/ch18-oop/listing-18-16/Cargo.lock diff --git a/listings/ch18-oop/listing-18-16/Cargo.toml b/listings/ch18-oop/listing-18-16/Cargo.toml new file mode 100644 index 0000000000..790832e0a9 --- /dev/null +++ b/listings/ch18-oop/listing-18-16/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "blog" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-16/src/lib.rs b/listings/ch18-oop/listing-18-16/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-16/src/lib.rs rename to listings/ch18-oop/listing-18-16/src/lib.rs diff --git a/listings/ch17-oop/listing-17-16/src/main.rs b/listings/ch18-oop/listing-18-16/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-16/src/main.rs rename to listings/ch18-oop/listing-18-16/src/main.rs diff --git a/listings/ch17-oop/listing-17-17/Cargo.lock b/listings/ch18-oop/listing-18-17/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-17/Cargo.lock rename to listings/ch18-oop/listing-18-17/Cargo.lock diff --git a/listings/ch18-oop/listing-18-17/Cargo.toml b/listings/ch18-oop/listing-18-17/Cargo.toml new file mode 100644 index 0000000000..790832e0a9 --- /dev/null +++ b/listings/ch18-oop/listing-18-17/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "blog" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-17/src/lib.rs b/listings/ch18-oop/listing-18-17/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-17/src/lib.rs rename to listings/ch18-oop/listing-18-17/src/lib.rs diff --git a/listings/ch17-oop/listing-17-17/src/main.rs b/listings/ch18-oop/listing-18-17/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-17/src/main.rs rename to listings/ch18-oop/listing-18-17/src/main.rs diff --git a/listings/ch17-oop/listing-17-18/Cargo.lock b/listings/ch18-oop/listing-18-18/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-18/Cargo.lock rename to listings/ch18-oop/listing-18-18/Cargo.lock diff --git a/listings/ch18-oop/listing-18-18/Cargo.toml b/listings/ch18-oop/listing-18-18/Cargo.toml new file mode 100644 index 0000000000..790832e0a9 --- /dev/null +++ b/listings/ch18-oop/listing-18-18/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "blog" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-18/src/lib.rs b/listings/ch18-oop/listing-18-18/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-18/src/lib.rs rename to listings/ch18-oop/listing-18-18/src/lib.rs diff --git a/listings/ch17-oop/listing-17-18/src/main.rs b/listings/ch18-oop/listing-18-18/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-18/src/main.rs rename to listings/ch18-oop/listing-18-18/src/main.rs diff --git a/listings/ch17-oop/listing-17-19/Cargo.lock b/listings/ch18-oop/listing-18-19/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-19/Cargo.lock rename to listings/ch18-oop/listing-18-19/Cargo.lock diff --git a/listings/ch18-oop/listing-18-19/Cargo.toml b/listings/ch18-oop/listing-18-19/Cargo.toml new file mode 100644 index 0000000000..790832e0a9 --- /dev/null +++ b/listings/ch18-oop/listing-18-19/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "blog" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-19/src/lib.rs b/listings/ch18-oop/listing-18-19/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-19/src/lib.rs rename to listings/ch18-oop/listing-18-19/src/lib.rs diff --git a/listings/ch17-oop/listing-17-20/Cargo.lock b/listings/ch18-oop/listing-18-20/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-20/Cargo.lock rename to listings/ch18-oop/listing-18-20/Cargo.lock diff --git a/listings/ch18-oop/listing-18-20/Cargo.toml b/listings/ch18-oop/listing-18-20/Cargo.toml new file mode 100644 index 0000000000..790832e0a9 --- /dev/null +++ b/listings/ch18-oop/listing-18-20/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "blog" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-20/src/lib.rs b/listings/ch18-oop/listing-18-20/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-20/src/lib.rs rename to listings/ch18-oop/listing-18-20/src/lib.rs diff --git a/listings/ch17-oop/listing-17-21/Cargo.lock b/listings/ch18-oop/listing-18-21/Cargo.lock similarity index 100% rename from listings/ch17-oop/listing-17-21/Cargo.lock rename to listings/ch18-oop/listing-18-21/Cargo.lock diff --git a/listings/ch18-oop/listing-18-21/Cargo.toml b/listings/ch18-oop/listing-18-21/Cargo.toml new file mode 100644 index 0000000000..790832e0a9 --- /dev/null +++ b/listings/ch18-oop/listing-18-21/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "blog" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch17-oop/listing-17-21/src/lib.rs b/listings/ch18-oop/listing-18-21/src/lib.rs similarity index 100% rename from listings/ch17-oop/listing-17-21/src/lib.rs rename to listings/ch18-oop/listing-18-21/src/lib.rs diff --git a/listings/ch17-oop/listing-17-21/src/main.rs b/listings/ch18-oop/listing-18-21/src/main.rs similarity index 100% rename from listings/ch17-oop/listing-17-21/src/main.rs rename to listings/ch18-oop/listing-18-21/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-02/src/main.rs b/listings/ch18-patterns-and-matching/listing-18-02/src/main.rs deleted file mode 100644 index 5f75a4f2db..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-02/src/main.rs +++ /dev/null @@ -1,13 +0,0 @@ -fn main() { - // ANCHOR: here - let mut stack = Vec::new(); - - stack.push(1); - stack.push(2); - stack.push(3); - - while let Some(top) = stack.pop() { - println!("{}", top); - } - // ANCHOR_END: here -} diff --git a/listings/ch18-patterns-and-matching/listing-18-05/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-05/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-05/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-06/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-06/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-06/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-07/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-07/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-07/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-08/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-08/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-08/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-08/output.txt b/listings/ch18-patterns-and-matching/listing-18-08/output.txt deleted file mode 100644 index 52efabb5c1..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-08/output.txt +++ /dev/null @@ -1,27 +0,0 @@ -$ cargo run - Compiling patterns v0.1.0 (file:///projects/patterns) -error[E0005]: refutable pattern in local binding: `None` not covered - --> src/main.rs:3:9 - | -3 | let Some(x) = some_option_value; - | ^^^^^^^ pattern `None` not covered - | - = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant - = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html -note: `Option` defined here - --> /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/option.rs:518:1 - | - = note: -/rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/core/src/option.rs:522:5: not covered - = note: the matched value is of type `Option` -help: you might want to use `if let` to ignore the variant that isn't matched - | -3 | let x = if let Some(x) = some_option_value { x } else { todo!() }; - | ++++++++++ ++++++++++++++++++++++ -help: alternatively, you might want to use let else to handle the variant that isn't matched - | -3 | let Some(x) = some_option_value else { todo!() }; - | ++++++++++++++++ - -For more information about this error, try `rustc --explain E0005`. -error: could not compile `patterns` due to previous error diff --git a/listings/ch18-patterns-and-matching/listing-18-09/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-09/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-09/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-10/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-10/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-10/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-10/output.txt b/listings/ch18-patterns-and-matching/listing-18-10/output.txt deleted file mode 100644 index 6488fb29ca..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-10/output.txt +++ /dev/null @@ -1,16 +0,0 @@ -$ cargo run - Compiling patterns v0.1.0 (file:///projects/patterns) -warning: irrefutable `if let` pattern - --> src/main.rs:2:8 - | -2 | if let x = 5 { - | ^^^^^^^^^ - | - = note: this pattern will always match, so the `if let` is useless - = help: consider replacing the `if let` with a `let` - = note: `#[warn(irrefutable_let_patterns)]` on by default - -warning: `patterns` (bin "patterns") generated 1 warning - Finished dev [unoptimized + debuginfo] target(s) in 0.39s - Running `target/debug/patterns` -5 diff --git a/listings/ch18-patterns-and-matching/listing-18-11/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-11/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-11/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-12/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-12/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-12/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-13/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-13/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-13/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-14/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-14/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-14/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-15/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-15/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-15/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-16/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-16/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-16/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-17/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-17/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-17/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-17/src/main.rs b/listings/ch18-patterns-and-matching/listing-18-17/src/main.rs deleted file mode 100644 index cf1fbe0721..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-17/src/main.rs +++ /dev/null @@ -1,7 +0,0 @@ -fn foo(_: i32, y: i32) { - println!("This code only uses the y parameter: {}", y); -} - -fn main() { - foo(3, 4); -} diff --git a/listings/ch18-patterns-and-matching/listing-18-18/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-18/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-18/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-19/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-19/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-19/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-20/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-20/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-20/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-21/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-21/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-21/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-22/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-22/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-22/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-23/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-23/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-23/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-24/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-24/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-24/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-25/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-25/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-25/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-26/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-26/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-26/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-26/src/main.rs b/listings/ch18-patterns-and-matching/listing-18-26/src/main.rs deleted file mode 100644 index 41fce97950..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-26/src/main.rs +++ /dev/null @@ -1,11 +0,0 @@ -fn main() { - // ANCHOR: here - let num = Some(4); - - match num { - Some(x) if x % 2 == 0 => println!("The number {} is even", x), - Some(x) => println!("The number {} is odd", x), - None => (), - } - // ANCHOR_END: here -} diff --git a/listings/ch18-patterns-and-matching/listing-18-27/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-27/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-27/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-28/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-28/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-28/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-29/Cargo.toml b/listings/ch18-patterns-and-matching/listing-18-29/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/listing-18-29/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-01-literals/Cargo.toml b/listings/ch18-patterns-and-matching/no-listing-01-literals/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/no-listing-01-literals/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.toml b/listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-03-ranges/Cargo.toml b/listings/ch18-patterns-and-matching/no-listing-03-ranges/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/no-listing-03-ranges/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.toml b/listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.toml b/listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.toml deleted file mode 100644 index 82fe057bbc..0000000000 --- a/listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "patterns" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-05/Cargo.toml b/listings/ch19-advanced-features/listing-19-05/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/listing-19-05/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-06/Cargo.toml b/listings/ch19-advanced-features/listing-19-06/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/listing-19-06/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-07/Cargo.toml b/listings/ch19-advanced-features/listing-19-07/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/listing-19-07/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-08/Cargo.toml b/listings/ch19-advanced-features/listing-19-08/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/listing-19-08/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-09/Cargo.toml b/listings/ch19-advanced-features/listing-19-09/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/listing-19-09/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-10/Cargo.toml b/listings/ch19-advanced-features/listing-19-10/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/listing-19-10/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-10/src/main.rs b/listings/ch19-advanced-features/listing-19-10/src/main.rs deleted file mode 100644 index e8dab68e0d..0000000000 --- a/listings/ch19-advanced-features/listing-19-10/src/main.rs +++ /dev/null @@ -1,15 +0,0 @@ -static mut COUNTER: u32 = 0; - -fn add_to_count(inc: u32) { - unsafe { - COUNTER += inc; - } -} - -fn main() { - add_to_count(3); - - unsafe { - println!("COUNTER: {}", COUNTER); - } -} diff --git a/listings/ch19-advanced-features/listing-19-11/Cargo.toml b/listings/ch19-advanced-features/listing-19-11/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/listing-19-11/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-16/Cargo.toml b/listings/ch19-advanced-features/listing-19-16/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-16/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-17/Cargo.toml b/listings/ch19-advanced-features/listing-19-17/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-17/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-18/Cargo.toml b/listings/ch19-advanced-features/listing-19-18/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-18/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-19/Cargo.toml b/listings/ch19-advanced-features/listing-19-19/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-19/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-20/Cargo.toml b/listings/ch19-advanced-features/listing-19-20/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-20/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-21/Cargo.toml b/listings/ch19-advanced-features/listing-19-21/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-21/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-22/Cargo.toml b/listings/ch19-advanced-features/listing-19-22/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-22/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-23/Cargo.toml b/listings/ch19-advanced-features/listing-19-23/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/listing-19-23/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/Cargo.lock b/listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/Cargo.lock deleted file mode 100644 index 9a38c8ac26..0000000000 --- a/listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/Cargo.lock +++ /dev/null @@ -1,46 +0,0 @@ -# This file is automatically @generated by Cargo. -# It is not intended for manual editing. -[[package]] -name = "hello_macro_derive" -version = "0.1.0" -dependencies = [ - "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)", - "syn 1.0.14 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "proc-macro2" -version = "1.0.8" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "quote" -version = "1.0.2" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "proc-macro2 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "syn" -version = "1.0.14" -source = 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"826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c" diff --git a/listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/Cargo.lock b/listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/Cargo.lock deleted file mode 100644 index 9a38c8ac26..0000000000 --- a/listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/Cargo.lock +++ /dev/null @@ -1,46 +0,0 @@ -# This file is automatically @generated by Cargo. -# It is not intended for manual editing. -[[package]] -name = "hello_macro_derive" -version = "0.1.0" -dependencies = [ - "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)", - "syn 1.0.14 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "proc-macro2" -version = "1.0.8" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name 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"053a8c8bcc71fcce321828dc897a98ab9760bef03a4fc36693c231e5b3216cfe" -"checksum syn 1.0.14 (registry+https://github.com/rust-lang/crates.io-index)" = "af6f3550d8dff9ef7dc34d384ac6f107e5d31c8f57d9f28e0081503f547ac8f5" -"checksum unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c" diff --git a/listings/ch19-advanced-features/no-listing-01-unsafe-fn/Cargo.toml b/listings/ch19-advanced-features/no-listing-01-unsafe-fn/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/no-listing-01-unsafe-fn/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.toml b/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt b/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt deleted file mode 100644 index 0991f10faa..0000000000 --- a/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt +++ /dev/null @@ -1,18 +0,0 @@ -$ cargo run - Compiling traits-example v0.1.0 (file:///projects/traits-example) -error[E0277]: `Point` doesn't implement `std::fmt::Display` - --> src/main.rs:20:6 - | -20 | impl OutlinePrint for Point {} - | ^^^^^^^^^^^^ `Point` cannot be formatted with the default formatter - | - = help: the trait `std::fmt::Display` is not implemented for `Point` - = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead -note: required by a bound in `OutlinePrint` - --> src/main.rs:3:21 - | -3 | trait OutlinePrint: fmt::Display { - | ^^^^^^^^^^^^ required by this bound in `OutlinePrint` - -For more information about this error, try `rustc --explain E0277`. -error: could not compile `traits-example` due to previous error diff --git a/listings/ch19-advanced-features/no-listing-03-impl-display-for-point/Cargo.toml b/listings/ch19-advanced-features/no-listing-03-impl-display-for-point/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/no-listing-03-impl-display-for-point/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-05-write-trait/Cargo.toml b/listings/ch19-advanced-features/no-listing-05-write-trait/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/no-listing-05-write-trait/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-06-result-alias/Cargo.toml b/listings/ch19-advanced-features/no-listing-06-result-alias/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/no-listing-06-result-alias/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-07-never-type/Cargo.toml b/listings/ch19-advanced-features/no-listing-07-never-type/Cargo.toml deleted file mode 100644 index 52395a5873..0000000000 --- a/listings/ch19-advanced-features/no-listing-07-never-type/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "traits-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-09-unwrap-definition/Cargo.toml b/listings/ch19-advanced-features/no-listing-09-unwrap-definition/Cargo.toml deleted file mode 100644 index a2ae20c77c..0000000000 --- a/listings/ch19-advanced-features/no-listing-09-unwrap-definition/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "types-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-10-loop-returns-never/Cargo.toml b/listings/ch19-advanced-features/no-listing-10-loop-returns-never/Cargo.toml deleted file mode 100644 index a2ae20c77c..0000000000 --- a/listings/ch19-advanced-features/no-listing-10-loop-returns-never/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "types-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-11-cant-create-str/Cargo.toml b/listings/ch19-advanced-features/no-listing-11-cant-create-str/Cargo.toml deleted file mode 100644 index a2ae20c77c..0000000000 --- a/listings/ch19-advanced-features/no-listing-11-cant-create-str/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "types-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-12-generic-fn-definition/Cargo.toml b/listings/ch19-advanced-features/no-listing-12-generic-fn-definition/Cargo.toml deleted file mode 100644 index a2ae20c77c..0000000000 --- a/listings/ch19-advanced-features/no-listing-12-generic-fn-definition/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "types-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.toml b/listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.toml deleted file mode 100644 index a2ae20c77c..0000000000 --- a/listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "types-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/Cargo.toml b/listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/Cargo.toml deleted file mode 100644 index a2ae20c77c..0000000000 --- a/listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "types-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-18-returns-closure/Cargo.toml b/listings/ch19-advanced-features/no-listing-18-returns-closure/Cargo.toml deleted file mode 100644 index b196f35b55..0000000000 --- a/listings/ch19-advanced-features/no-listing-18-returns-closure/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "functions-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-18-returns-closure/output.txt b/listings/ch19-advanced-features/no-listing-18-returns-closure/output.txt deleted file mode 100644 index 104f2cf0fe..0000000000 --- a/listings/ch19-advanced-features/no-listing-18-returns-closure/output.txt +++ /dev/null @@ -1,16 +0,0 @@ -$ cargo build - Compiling functions-example v0.1.0 (file:///projects/functions-example) -error[E0746]: return type cannot have an unboxed trait object - --> src/lib.rs:1:25 - | -1 | fn returns_closure() -> dyn Fn(i32) -> i32 { - | ^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time - | - = note: for information on `impl Trait`, see -help: use `impl Fn(i32) -> i32` as the return type, as all return paths are of type `[closure@src/lib.rs:2:5: 2:8]`, which implements `Fn(i32) -> i32` - | -1 | fn returns_closure() -> impl Fn(i32) -> i32 { - | ~~~~~~~~~~~~~~~~~~~ - -For more information about this error, try `rustc --explain E0746`. -error: could not compile `functions-example` due to previous error diff --git a/listings/ch19-advanced-features/no-listing-18-returns-closure/src/lib.rs b/listings/ch19-advanced-features/no-listing-18-returns-closure/src/lib.rs deleted file mode 100644 index d699ac34eb..0000000000 --- a/listings/ch19-advanced-features/no-listing-18-returns-closure/src/lib.rs +++ /dev/null @@ -1,3 +0,0 @@ -fn returns_closure() -> dyn Fn(i32) -> i32 { - |x| x + 1 -} diff --git a/listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/Cargo.toml b/listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/Cargo.toml deleted file mode 100644 index b196f35b55..0000000000 --- a/listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "functions-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/src/lib.rs b/listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/src/lib.rs deleted file mode 100644 index b114077472..0000000000 --- a/listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/src/lib.rs +++ /dev/null @@ -1,3 +0,0 @@ -fn returns_closure() -> Box i32> { - Box::new(|x| x + 1) -} diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.toml b/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.toml deleted file mode 100644 index c6fb920877..0000000000 --- a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello_macro" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.lock b/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.lock deleted file mode 100644 index 9a38c8ac26..0000000000 --- a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.lock +++ /dev/null @@ -1,46 +0,0 @@ -# This file is automatically @generated by Cargo. -# It is not intended for manual editing. -[[package]] -name = "hello_macro_derive" -version = "0.1.0" -dependencies = [ - "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)", - "syn 1.0.14 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "proc-macro2" -version = "1.0.8" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "quote" -version = "1.0.2" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "proc-macro2 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "syn" -version = "1.0.14" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "proc-macro2 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)", - "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)", - "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "unicode-xid" -version = "0.2.0" -source = "registry+https://github.com/rust-lang/crates.io-index" - -[metadata] -"checksum proc-macro2 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)" = "3acb317c6ff86a4e579dfa00fc5e6cca91ecbb4e7eb2df0468805b674eb88548" -"checksum quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "053a8c8bcc71fcce321828dc897a98ab9760bef03a4fc36693c231e5b3216cfe" -"checksum syn 1.0.14 (registry+https://github.com/rust-lang/crates.io-index)" = "af6f3550d8dff9ef7dc34d384ac6f107e5d31c8f57d9f28e0081503f547ac8f5" -"checksum unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c" diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/Cargo.lock b/listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/Cargo.lock deleted file mode 100644 index dee23ecf96..0000000000 --- a/listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/Cargo.lock +++ /dev/null @@ -1,58 +0,0 @@ -# This file is automatically @generated by Cargo. -# It is not intended for manual editing. -[[package]] -name = "hello_macro" -version = "0.1.0" - -[[package]] -name = "hello_macro_derive" -version = "0.1.0" -dependencies = [ - "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)", - "syn 1.0.14 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "pancakes" -version = "0.1.0" -dependencies = [ - "hello_macro 0.1.0", - "hello_macro_derive 0.1.0", -] - -[[package]] -name = "proc-macro2" -version = "1.0.8" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "quote" -version = "1.0.2" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "proc-macro2 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "syn" -version = "1.0.14" -source = "registry+https://github.com/rust-lang/crates.io-index" -dependencies = [ - "proc-macro2 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)", - "quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)", - "unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)", -] - -[[package]] -name = "unicode-xid" -version = "0.2.0" -source = "registry+https://github.com/rust-lang/crates.io-index" - -[metadata] -"checksum proc-macro2 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)" = "3acb317c6ff86a4e579dfa00fc5e6cca91ecbb4e7eb2df0468805b674eb88548" -"checksum quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "053a8c8bcc71fcce321828dc897a98ab9760bef03a4fc36693c231e5b3216cfe" -"checksum syn 1.0.14 (registry+https://github.com/rust-lang/crates.io-index)" = "af6f3550d8dff9ef7dc34d384ac6f107e5d31c8f57d9f28e0081503f547ac8f5" -"checksum unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c" diff --git a/listings/ch19-advanced-features/output-only-01-missing-unsafe/Cargo.toml b/listings/ch19-advanced-features/output-only-01-missing-unsafe/Cargo.toml deleted file mode 100644 index 3e8a292013..0000000000 --- a/listings/ch19-advanced-features/output-only-01-missing-unsafe/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "unsafe-example" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-01/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-01/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-01/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-01/Cargo.lock diff --git a/listings/ch18-patterns-and-matching/listing-18-01/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-01/Cargo.toml similarity index 78% rename from listings/ch18-patterns-and-matching/listing-18-01/Cargo.toml rename to listings/ch19-patterns-and-matching/listing-19-01/Cargo.toml index 82fe057bbc..7e3247669f 100644 --- a/listings/ch18-patterns-and-matching/listing-18-01/Cargo.toml +++ b/listings/ch19-patterns-and-matching/listing-19-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "patterns" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-04/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-01/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-04/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-01/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-02/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-02/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-02/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-02/Cargo.lock diff --git a/listings/ch18-patterns-and-matching/listing-18-02/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-02/Cargo.toml similarity index 78% rename from listings/ch18-patterns-and-matching/listing-18-02/Cargo.toml rename to listings/ch19-patterns-and-matching/listing-19-02/Cargo.toml index 82fe057bbc..7e3247669f 100644 --- a/listings/ch18-patterns-and-matching/listing-18-02/Cargo.toml +++ b/listings/ch19-patterns-and-matching/listing-19-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "patterns" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-05/output.txt b/listings/ch19-patterns-and-matching/listing-19-02/output.txt similarity index 86% rename from listings/ch18-patterns-and-matching/listing-18-05/output.txt rename to listings/ch19-patterns-and-matching/listing-19-02/output.txt index 57916a1f15..8002272a72 100644 --- a/listings/ch18-patterns-and-matching/listing-18-05/output.txt +++ b/listings/ch19-patterns-and-matching/listing-19-02/output.txt @@ -12,4 +12,4 @@ error[E0308]: mismatched types found tuple `(_, _)` For more information about this error, try `rustc --explain E0308`. -error: could not compile `patterns` due to previous error +error: could not compile `patterns` (bin "patterns") due to 1 previous error diff --git a/listings/ch18-patterns-and-matching/listing-18-05/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-02/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-05/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-02/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-03/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-03/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-03/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-03/Cargo.lock diff --git a/listings/ch18-patterns-and-matching/listing-18-03/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-03/Cargo.toml similarity index 78% rename from listings/ch18-patterns-and-matching/listing-18-03/Cargo.toml rename to listings/ch19-patterns-and-matching/listing-19-03/Cargo.toml index 82fe057bbc..7e3247669f 100644 --- a/listings/ch18-patterns-and-matching/listing-18-03/Cargo.toml +++ b/listings/ch19-patterns-and-matching/listing-19-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "patterns" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-01/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-03/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-01/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-03/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-04/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-04/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-04/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-04/Cargo.lock diff --git a/listings/ch18-patterns-and-matching/listing-18-04/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-04/Cargo.toml similarity index 78% rename from listings/ch18-patterns-and-matching/listing-18-04/Cargo.toml rename to listings/ch19-patterns-and-matching/listing-19-04/Cargo.toml index 82fe057bbc..7e3247669f 100644 --- a/listings/ch18-patterns-and-matching/listing-18-04/Cargo.toml +++ b/listings/ch19-patterns-and-matching/listing-19-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "patterns" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-patterns-and-matching/listing-19-04/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-04/src/main.rs new file mode 100644 index 0000000000..4605557f0b --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-04/src/main.rs @@ -0,0 +1,14 @@ +fn main() { + // ANCHOR: here + let (tx, rx) = std::sync::mpsc::channel(); + std::thread::spawn(move || { + for val in [1, 2, 3] { + tx.send(val).unwrap(); + } + }); + + while let Ok(value) = rx.recv() { + println!("{value}"); + } + // ANCHOR_END: here +} diff --git a/listings/ch18-patterns-and-matching/listing-18-05/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-05/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-05/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-05/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-05/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-05/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-05/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-03/output.txt b/listings/ch19-patterns-and-matching/listing-19-05/output.txt similarity index 68% rename from listings/ch18-patterns-and-matching/listing-18-03/output.txt rename to listings/ch19-patterns-and-matching/listing-19-05/output.txt index 02fdecbf5c..9add287fa4 100644 --- a/listings/ch18-patterns-and-matching/listing-18-03/output.txt +++ b/listings/ch19-patterns-and-matching/listing-19-05/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling patterns v0.1.0 (file:///projects/patterns) - Finished dev [unoptimized + debuginfo] target(s) in 0.52s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.52s Running `target/debug/patterns` a is at index 0 b is at index 1 diff --git a/listings/ch18-patterns-and-matching/listing-18-03/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-05/src/main.rs similarity index 73% rename from listings/ch18-patterns-and-matching/listing-18-03/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-05/src/main.rs index eb922d62cd..218c180635 100644 --- a/listings/ch18-patterns-and-matching/listing-18-03/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-05/src/main.rs @@ -3,7 +3,7 @@ fn main() { let v = vec!['a', 'b', 'c']; for (index, value) in v.iter().enumerate() { - println!("{} is at index {}", value, index); + println!("{value} is at index {index}"); } // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-06/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-06/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-06/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-06/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-06/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-06/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-06/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-06/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-06/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-06/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-06/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-07/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-07/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-07/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-07/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-07/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-07/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-07/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-07/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-07/src/main.rs similarity index 70% rename from listings/ch18-patterns-and-matching/listing-18-07/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-07/src/main.rs index 4eccb8088c..70069424c6 100644 --- a/listings/ch18-patterns-and-matching/listing-18-07/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-07/src/main.rs @@ -1,5 +1,5 @@ fn print_coordinates(&(x, y): &(i32, i32)) { - println!("Current location: ({}, {})", x, y); + println!("Current location: ({x}, {y})"); } fn main() { diff --git a/listings/ch18-patterns-and-matching/listing-18-08/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-08/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-08/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-08/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-08/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-08/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-08/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-patterns-and-matching/listing-19-08/output.txt b/listings/ch19-patterns-and-matching/listing-19-08/output.txt new file mode 100644 index 0000000000..0ed34b7164 --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-08/output.txt @@ -0,0 +1,18 @@ +$ cargo run + Compiling patterns v0.1.0 (file:///projects/patterns) +error[E0005]: refutable pattern in local binding + --> src/main.rs:3:9 + | +3 | let Some(x) = some_option_value; + | ^^^^^^^ pattern `None` not covered + | + = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant + = note: for more information, visit https://doc.rust-lang.org/book/ch19-02-refutability.html + = note: the matched value is of type `Option` +help: you might want to use `let else` to handle the variant that isn't matched + | +3 | let Some(x) = some_option_value else { todo!() }; + | ++++++++++++++++ + +For more information about this error, try `rustc --explain E0005`. +error: could not compile `patterns` (bin "patterns") due to 1 previous error diff --git a/listings/ch18-patterns-and-matching/listing-18-08/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-08/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-08/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-08/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-09/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-09/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-09/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-09/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-09/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-09/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-09/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-09/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-09/src/main.rs similarity index 58% rename from listings/ch18-patterns-and-matching/listing-18-09/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-09/src/main.rs index d6274fc0e1..e974935eb5 100644 --- a/listings/ch18-patterns-and-matching/listing-18-09/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-09/src/main.rs @@ -1,8 +1,8 @@ fn main() { let some_option_value: Option = None; // ANCHOR: here - if let Some(x) = some_option_value { - println!("{}", x); - } + let Some(x) = some_option_value else { + return; + }; // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-10/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-10/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-10/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-10/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-10/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-10/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-10/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-patterns-and-matching/listing-19-10/output.txt b/listings/ch19-patterns-and-matching/listing-19-10/output.txt new file mode 100644 index 0000000000..7f825dcca1 --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-10/output.txt @@ -0,0 +1,15 @@ +$ cargo run + Compiling patterns v0.1.0 (file:///projects/patterns) +warning: irrefutable `let...else` pattern + --> src/main.rs:2:5 + | +2 | let x = 5 else { + | ^^^^^^^^^ + | + = note: this pattern will always match, so the `else` clause is useless + = help: consider removing the `else` clause + = note: `#[warn(irrefutable_let_patterns)]` on by default + +warning: `patterns` (bin "patterns") generated 1 warning + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.39s + Running `target/debug/patterns` diff --git a/listings/ch18-patterns-and-matching/listing-18-10/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-10/src/main.rs similarity index 58% rename from listings/ch18-patterns-and-matching/listing-18-10/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-10/src/main.rs index cb81772e0c..6186890be2 100644 --- a/listings/ch18-patterns-and-matching/listing-18-10/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-10/src/main.rs @@ -1,7 +1,7 @@ fn main() { // ANCHOR: here - if let x = 5 { - println!("{}", x); + let x = 5 else { + return; }; // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-11/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-11/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-11/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-11/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-11/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-11/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-11/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-11/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-11/src/main.rs similarity index 66% rename from listings/ch18-patterns-and-matching/listing-18-11/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-11/src/main.rs index db942b7ac7..0552128036 100644 --- a/listings/ch18-patterns-and-matching/listing-18-11/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-11/src/main.rs @@ -6,9 +6,9 @@ fn main() { match x { Some(50) => println!("Got 50"), Some(y) => println!("Matched, y = {y}"), - _ => println!("Default case, x = {:?}", x), + _ => println!("Default case, x = {x:?}"), } - println!("at the end: x = {:?}, y = {y}", x); + println!("at the end: x = {x:?}, y = {y}"); // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-12/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-12/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-12/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-12/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-12/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-12/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-12/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-12/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-12/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-12/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-12/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-13/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-13/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-13/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-13/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-13/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-13/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-13/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-13/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-13/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-13/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-13/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-14/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-14/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-14/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-14/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-14/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-14/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-14/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-14/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-14/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-14/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-14/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-15/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-15/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-15/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-15/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-15/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-15/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-15/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-15/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-15/src/main.rs similarity index 87% rename from listings/ch18-patterns-and-matching/listing-18-15/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-15/src/main.rs index a3138b2277..65ff116504 100644 --- a/listings/ch18-patterns-and-matching/listing-18-15/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-15/src/main.rs @@ -19,7 +19,7 @@ fn main() { println!("Text message: {text}"); } Message::ChangeColor(r, g, b) => { - println!("Change the color to red {r}, green {g}, and blue {b}",) + println!("Change color to red {r}, green {g}, and blue {b}"); } } } diff --git a/listings/ch18-patterns-and-matching/listing-18-16/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-16/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-16/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-16/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-16/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-16/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-16/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-16/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-16/src/main.rs similarity index 97% rename from listings/ch18-patterns-and-matching/listing-18-16/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-16/src/main.rs index 1e7ad5f193..a31eeffb97 100644 --- a/listings/ch18-patterns-and-matching/listing-18-16/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-16/src/main.rs @@ -18,7 +18,7 @@ fn main() { println!("Change color to red {r}, green {g}, and blue {b}"); } Message::ChangeColor(Color::Hsv(h, s, v)) => { - println!("Change color to hue {h}, saturation {s}, value {v}") + println!("Change color to hue {h}, saturation {s}, value {v}"); } _ => (), } diff --git a/listings/ch18-patterns-and-matching/listing-18-17/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-17/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-17/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-17/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-17/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-17/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-17/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-patterns-and-matching/listing-19-17/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-17/src/main.rs new file mode 100644 index 0000000000..7053860348 --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-17/src/main.rs @@ -0,0 +1,7 @@ +fn foo(_: i32, y: i32) { + println!("This code only uses the y parameter: {y}"); +} + +fn main() { + foo(3, 4); +} diff --git a/listings/ch18-patterns-and-matching/listing-18-18/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-18/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-18/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-18/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-18/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-18/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-18/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-18/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-18/src/main.rs similarity index 88% rename from listings/ch18-patterns-and-matching/listing-18-18/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-18/src/main.rs index b776c64c42..2b8877620a 100644 --- a/listings/ch18-patterns-and-matching/listing-18-18/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-18/src/main.rs @@ -12,6 +12,6 @@ fn main() { } } - println!("setting is {:?}", setting_value); + println!("setting is {setting_value:?}"); // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-19/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-19/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-19/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-19/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-19/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-19/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-19/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-19/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-19/src/main.rs similarity index 72% rename from listings/ch18-patterns-and-matching/listing-18-19/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-19/src/main.rs index e28dab111c..43220b8243 100644 --- a/listings/ch18-patterns-and-matching/listing-18-19/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-19/src/main.rs @@ -4,7 +4,7 @@ fn main() { match numbers { (first, _, third, _, fifth) => { - println!("Some numbers: {first}, {third}, {fifth}") + println!("Some numbers: {first}, {third}, {fifth}"); } } // ANCHOR_END: here diff --git a/listings/ch18-patterns-and-matching/listing-18-20/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-20/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-20/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-20/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-20/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-20/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-20/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-20/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-20/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-20/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-20/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-21/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-21/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-21/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-21/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-21/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-21/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-21/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-21/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-21/src/main.rs similarity index 87% rename from listings/ch18-patterns-and-matching/listing-18-21/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-21/src/main.rs index 980610503f..320db62f5f 100644 --- a/listings/ch18-patterns-and-matching/listing-18-21/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-21/src/main.rs @@ -6,6 +6,6 @@ fn main() { println!("found a string"); } - println!("{:?}", s); + println!("{s:?}"); // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-22/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-22/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-22/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-22/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-22/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-22/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-22/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-22/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-22/src/main.rs similarity index 87% rename from listings/ch18-patterns-and-matching/listing-18-22/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-22/src/main.rs index e2faa345bc..9df1492b29 100644 --- a/listings/ch18-patterns-and-matching/listing-18-22/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-22/src/main.rs @@ -6,6 +6,6 @@ fn main() { println!("found a string"); } - println!("{:?}", s); + println!("{s:?}"); // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-23/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-23/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-23/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-23/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-23/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-23/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-23/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-23/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-23/src/main.rs similarity index 79% rename from listings/ch18-patterns-and-matching/listing-18-23/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-23/src/main.rs index 7a9d9bb36f..491d6c53f8 100644 --- a/listings/ch18-patterns-and-matching/listing-18-23/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-23/src/main.rs @@ -9,7 +9,7 @@ fn main() { let origin = Point { x: 0, y: 0, z: 0 }; match origin { - Point { x, .. } => println!("x is {}", x), + Point { x, .. } => println!("x is {x}"), } // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/listing-18-24/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-24/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-24/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-24/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-24/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-24/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-24/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-24/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-24/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-24/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-24/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-25/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-25/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-25/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-25/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-25/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-25/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-25/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-25/output.txt b/listings/ch19-patterns-and-matching/listing-19-25/output.txt similarity index 79% rename from listings/ch18-patterns-and-matching/listing-18-25/output.txt rename to listings/ch19-patterns-and-matching/listing-19-25/output.txt index 7e0357eac2..bd5e0f9d7b 100644 --- a/listings/ch18-patterns-and-matching/listing-18-25/output.txt +++ b/listings/ch19-patterns-and-matching/listing-19-25/output.txt @@ -8,4 +8,4 @@ error: `..` can only be used once per tuple pattern | | | previously used here -error: could not compile `patterns` due to previous error +error: could not compile `patterns` (bin "patterns") due to 1 previous error diff --git a/listings/ch18-patterns-and-matching/listing-18-25/rustfmt-ignore b/listings/ch19-patterns-and-matching/listing-19-25/rustfmt-ignore similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-25/rustfmt-ignore rename to listings/ch19-patterns-and-matching/listing-19-25/rustfmt-ignore diff --git a/listings/ch18-patterns-and-matching/listing-18-25/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-25/src/main.rs similarity index 70% rename from listings/ch18-patterns-and-matching/listing-18-25/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-25/src/main.rs index b90884eb9c..6c3b24b7db 100644 --- a/listings/ch18-patterns-and-matching/listing-18-25/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-25/src/main.rs @@ -3,7 +3,7 @@ fn main() { match numbers { (.., second, ..) => { - println!("Some numbers: {}", second) + println!("Some numbers: {second}") }, } } diff --git a/listings/ch18-patterns-and-matching/listing-18-26/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-26/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-26/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-26/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-26/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-26/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-26/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-patterns-and-matching/listing-19-26/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-26/src/main.rs new file mode 100644 index 0000000000..2566169a7d --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-26/src/main.rs @@ -0,0 +1,11 @@ +fn main() { + // ANCHOR: here + let num = Some(4); + + match num { + Some(x) if x % 2 == 0 => println!("The number {x} is even"), + Some(x) => println!("The number {x} is odd"), + None => (), + } + // ANCHOR_END: here +} diff --git a/listings/ch18-patterns-and-matching/listing-18-27/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-27/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-27/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-27/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-27/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-27/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-27/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-27/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-27/src/main.rs similarity index 62% rename from listings/ch18-patterns-and-matching/listing-18-27/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-27/src/main.rs index 8386a0ab8f..06fd949964 100644 --- a/listings/ch18-patterns-and-matching/listing-18-27/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-27/src/main.rs @@ -5,8 +5,8 @@ fn main() { match x { Some(50) => println!("Got 50"), Some(n) if n == y => println!("Matched, n = {n}"), - _ => println!("Default case, x = {:?}", x), + _ => println!("Default case, x = {x:?}"), } - println!("at the end: x = {:?}, y = {y}", x); + println!("at the end: x = {x:?}, y = {y}"); } diff --git a/listings/ch18-patterns-and-matching/listing-18-28/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-28/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-28/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-28/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-28/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-28/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-28/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-28/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-28/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-28/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-28/src/main.rs diff --git a/listings/ch18-patterns-and-matching/listing-18-29/Cargo.lock b/listings/ch19-patterns-and-matching/listing-19-29/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/listing-18-29/Cargo.lock rename to listings/ch19-patterns-and-matching/listing-19-29/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/listing-19-29/Cargo.toml b/listings/ch19-patterns-and-matching/listing-19-29/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/listing-19-29/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/listing-18-29/src/main.rs b/listings/ch19-patterns-and-matching/listing-19-29/src/main.rs similarity index 71% rename from listings/ch18-patterns-and-matching/listing-18-29/src/main.rs rename to listings/ch19-patterns-and-matching/listing-19-29/src/main.rs index 3514deb636..325af3057a 100644 --- a/listings/ch18-patterns-and-matching/listing-18-29/src/main.rs +++ b/listings/ch19-patterns-and-matching/listing-19-29/src/main.rs @@ -7,13 +7,13 @@ fn main() { let msg = Message::Hello { id: 5 }; match msg { - Message::Hello { - id: id_variable @ 3..=7, - } => println!("Found an id in range: {}", id_variable), + Message::Hello { id: id @ 3..=7 } => { + println!("Found an id in range: {id}") + } Message::Hello { id: 10..=12 } => { println!("Found an id in another range") } - Message::Hello { id } => println!("Found some other id: {}", id), + Message::Hello { id } => println!("Found some other id: {id}"), } // ANCHOR_END: here } diff --git a/listings/ch18-patterns-and-matching/no-listing-01-literals/Cargo.lock b/listings/ch19-patterns-and-matching/no-listing-01-literals/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-01-literals/Cargo.lock rename to listings/ch19-patterns-and-matching/no-listing-01-literals/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/no-listing-01-literals/Cargo.toml b/listings/ch19-patterns-and-matching/no-listing-01-literals/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/no-listing-01-literals/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-01-literals/src/main.rs b/listings/ch19-patterns-and-matching/no-listing-01-literals/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-01-literals/src/main.rs rename to listings/ch19-patterns-and-matching/no-listing-01-literals/src/main.rs diff --git a/listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.lock b/listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.lock rename to listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.toml b/listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/src/main.rs b/listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/src/main.rs rename to listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/src/main.rs diff --git a/listings/ch18-patterns-and-matching/no-listing-03-ranges/Cargo.lock b/listings/ch19-patterns-and-matching/no-listing-03-ranges/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-03-ranges/Cargo.lock rename to listings/ch19-patterns-and-matching/no-listing-03-ranges/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/no-listing-03-ranges/Cargo.toml b/listings/ch19-patterns-and-matching/no-listing-03-ranges/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/no-listing-03-ranges/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-03-ranges/src/main.rs b/listings/ch19-patterns-and-matching/no-listing-03-ranges/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-03-ranges/src/main.rs rename to listings/ch19-patterns-and-matching/no-listing-03-ranges/src/main.rs diff --git a/listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.lock b/listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.lock rename to listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.toml b/listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/src/main.rs b/listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/src/main.rs rename to listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/src/main.rs diff --git a/listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.lock b/listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.lock similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.lock rename to listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.lock diff --git a/listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.toml b/listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.toml new file mode 100644 index 0000000000..7e3247669f --- /dev/null +++ b/listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "patterns" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/src/main.rs b/listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/src/main.rs similarity index 100% rename from listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/src/main.rs rename to listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-01/Cargo.lock b/listings/ch20-advanced-features/listing-20-01/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-01/Cargo.lock rename to listings/ch20-advanced-features/listing-20-01/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-01/Cargo.toml b/listings/ch20-advanced-features/listing-20-01/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-01/Cargo.toml rename to listings/ch20-advanced-features/listing-20-01/Cargo.toml index 3e8a292013..690cfbdd4d 100644 --- a/listings/ch19-advanced-features/listing-19-01/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "unsafe-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-01/src/main.rs b/listings/ch20-advanced-features/listing-20-01/src/main.rs similarity index 54% rename from listings/ch19-advanced-features/listing-19-01/src/main.rs rename to listings/ch20-advanced-features/listing-20-01/src/main.rs index 893f578905..492b43ba3b 100644 --- a/listings/ch19-advanced-features/listing-19-01/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-01/src/main.rs @@ -2,7 +2,7 @@ fn main() { // ANCHOR: here let mut num = 5; - let r1 = &num as *const i32; - let r2 = &mut num as *mut i32; + let r1 = &raw const num; + let r2 = &raw mut num; // ANCHOR_END: here } diff --git a/listings/ch19-advanced-features/listing-19-02/Cargo.lock b/listings/ch20-advanced-features/listing-20-02/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-02/Cargo.lock rename to listings/ch20-advanced-features/listing-20-02/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-02/Cargo.toml b/listings/ch20-advanced-features/listing-20-02/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-02/Cargo.toml rename to listings/ch20-advanced-features/listing-20-02/Cargo.toml index 3e8a292013..690cfbdd4d 100644 --- a/listings/ch19-advanced-features/listing-19-02/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "unsafe-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-02/src/main.rs b/listings/ch20-advanced-features/listing-20-02/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-02/src/main.rs rename to listings/ch20-advanced-features/listing-20-02/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-03/Cargo.lock b/listings/ch20-advanced-features/listing-20-03/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-03/Cargo.lock rename to listings/ch20-advanced-features/listing-20-03/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-03/Cargo.toml b/listings/ch20-advanced-features/listing-20-03/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-03/Cargo.toml rename to listings/ch20-advanced-features/listing-20-03/Cargo.toml index 3e8a292013..690cfbdd4d 100644 --- a/listings/ch19-advanced-features/listing-19-03/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "unsafe-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-03/src/main.rs b/listings/ch20-advanced-features/listing-20-03/src/main.rs similarity index 71% rename from listings/ch19-advanced-features/listing-19-03/src/main.rs rename to listings/ch20-advanced-features/listing-20-03/src/main.rs index 02a0be6b0e..6ed8ca2afc 100644 --- a/listings/ch19-advanced-features/listing-19-03/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-03/src/main.rs @@ -2,8 +2,8 @@ fn main() { // ANCHOR: here let mut num = 5; - let r1 = &num as *const i32; - let r2 = &mut num as *mut i32; + let r1 = &raw const num; + let r2 = &raw mut num; unsafe { println!("r1 is: {}", *r1); diff --git a/listings/ch19-advanced-features/listing-19-04/Cargo.lock b/listings/ch20-advanced-features/listing-20-04/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-04/Cargo.lock rename to listings/ch20-advanced-features/listing-20-04/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-04/Cargo.toml b/listings/ch20-advanced-features/listing-20-04/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-04/Cargo.toml rename to listings/ch20-advanced-features/listing-20-04/Cargo.toml index 3e8a292013..690cfbdd4d 100644 --- a/listings/ch19-advanced-features/listing-19-04/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-04/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "unsafe-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-04/src/main.rs b/listings/ch20-advanced-features/listing-20-04/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-04/src/main.rs rename to listings/ch20-advanced-features/listing-20-04/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-05/Cargo.lock b/listings/ch20-advanced-features/listing-20-05/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-05/Cargo.lock rename to listings/ch20-advanced-features/listing-20-05/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-05/Cargo.toml b/listings/ch20-advanced-features/listing-20-05/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-05/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-05/output.txt b/listings/ch20-advanced-features/listing-20-05/output.txt similarity index 80% rename from listings/ch19-advanced-features/listing-19-05/output.txt rename to listings/ch20-advanced-features/listing-20-05/output.txt index f4b7582acc..514e25331c 100644 --- a/listings/ch19-advanced-features/listing-19-05/output.txt +++ b/listings/ch20-advanced-features/listing-20-05/output.txt @@ -12,6 +12,8 @@ error[E0499]: cannot borrow `*values` as mutable more than once at a time | | | second mutable borrow occurs here | | first mutable borrow occurs here | returning this value requires that `*values` is borrowed for `'1` + | + = help: use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices For more information about this error, try `rustc --explain E0499`. -error: could not compile `unsafe-example` due to previous error +error: could not compile `unsafe-example` (bin "unsafe-example") due to 1 previous error diff --git a/listings/ch19-advanced-features/listing-19-05/src/main.rs b/listings/ch20-advanced-features/listing-20-05/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-05/src/main.rs rename to listings/ch20-advanced-features/listing-20-05/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-06/Cargo.lock b/listings/ch20-advanced-features/listing-20-06/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-06/Cargo.lock rename to listings/ch20-advanced-features/listing-20-06/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-06/Cargo.toml b/listings/ch20-advanced-features/listing-20-06/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-06/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-06/src/main.rs b/listings/ch20-advanced-features/listing-20-06/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-06/src/main.rs rename to listings/ch20-advanced-features/listing-20-06/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-07/Cargo.lock b/listings/ch20-advanced-features/listing-20-07/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-07/Cargo.lock rename to listings/ch20-advanced-features/listing-20-07/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-07/Cargo.toml b/listings/ch20-advanced-features/listing-20-07/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-07/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/listing-20-07/output.txt b/listings/ch20-advanced-features/listing-20-07/output.txt new file mode 100644 index 0000000000..ef123ce651 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-07/output.txt @@ -0,0 +1,33 @@ +$ cargo +nightly miri run + Compiling unsafe-example v0.1.0 (file:///projects/unsafe-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s + Running `file:///home/.rustup/toolchains/nightly/bin/cargo-miri runner target/miri/debug/unsafe-example` +warning: integer-to-pointer cast + --> src/main.rs:5:13 + | +5 | let r = address as *mut i32; + | ^^^^^^^^^^^^^^^^^^^ integer-to-pointer cast + | + = help: this program is using integer-to-pointer casts or (equivalently) `ptr::with_exposed_provenance`, which means that Miri might miss pointer bugs in this program + = help: see https://doc.rust-lang.org/nightly/std/ptr/fn.with_exposed_provenance.html for more details on that operation + = help: to ensure that Miri does not miss bugs in your program, use Strict Provenance APIs (https://doc.rust-lang.org/nightly/std/ptr/index.html#strict-provenance, https://crates.io/crates/sptr) instead + = help: you can then set `MIRIFLAGS=-Zmiri-strict-provenance` to ensure you are not relying on `with_exposed_provenance` semantics + = help: alternatively, `MIRIFLAGS=-Zmiri-permissive-provenance` disables this warning + = note: BACKTRACE: + = note: inside `main` at src/main.rs:5:13: 5:32 + +error: Undefined Behavior: pointer not dereferenceable: pointer must be dereferenceable for 40000 bytes, but got 0x1234[noalloc] which is a dangling pointer (it has no provenance) + --> src/main.rs:7:35 + | +7 | let values: &[i32] = unsafe { slice::from_raw_parts_mut(r, 10000) }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here + | + = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior + = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information + = note: BACKTRACE: + = note: inside `main` at src/main.rs:7:35: 7:70 + +note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace + +error: aborting due to 1 previous error; 1 warning emitted + diff --git a/listings/ch19-advanced-features/listing-19-07/src/main.rs b/listings/ch20-advanced-features/listing-20-07/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-07/src/main.rs rename to listings/ch20-advanced-features/listing-20-07/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-08/Cargo.lock b/listings/ch20-advanced-features/listing-20-08/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-08/Cargo.lock rename to listings/ch20-advanced-features/listing-20-08/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-08/Cargo.toml b/listings/ch20-advanced-features/listing-20-08/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-08/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-08/src/main.rs b/listings/ch20-advanced-features/listing-20-08/src/main.rs similarity index 87% rename from listings/ch19-advanced-features/listing-19-08/src/main.rs rename to listings/ch20-advanced-features/listing-20-08/src/main.rs index 8b56630c95..90c183adec 100644 --- a/listings/ch19-advanced-features/listing-19-08/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-08/src/main.rs @@ -1,4 +1,4 @@ -extern "C" { +unsafe extern "C" { fn abs(input: i32) -> i32; } diff --git a/listings/ch19-advanced-features/listing-19-09/Cargo.lock b/listings/ch20-advanced-features/listing-20-09/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-09/Cargo.lock rename to listings/ch20-advanced-features/listing-20-09/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-09/Cargo.toml b/listings/ch20-advanced-features/listing-20-09/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-09/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/listing-20-09/src/main.rs b/listings/ch20-advanced-features/listing-20-09/src/main.rs new file mode 100644 index 0000000000..7d77d51e4f --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-09/src/main.rs @@ -0,0 +1,7 @@ +unsafe extern "C" { + safe fn abs(input: i32) -> i32; +} + +fn main() { + println!("Absolute value of -3 according to C: {}", abs(-3)); +} diff --git a/listings/ch19-advanced-features/listing-19-10/Cargo.lock b/listings/ch20-advanced-features/listing-20-10/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-10/Cargo.lock rename to listings/ch20-advanced-features/listing-20-10/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-10/Cargo.toml b/listings/ch20-advanced-features/listing-20-10/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-10/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-09/src/main.rs b/listings/ch20-advanced-features/listing-20-10/src/main.rs similarity index 58% rename from listings/ch19-advanced-features/listing-19-09/src/main.rs rename to listings/ch20-advanced-features/listing-20-10/src/main.rs index 82a4b4219f..b757e36323 100644 --- a/listings/ch19-advanced-features/listing-19-09/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-10/src/main.rs @@ -1,5 +1,5 @@ static HELLO_WORLD: &str = "Hello, world!"; fn main() { - println!("name is: {}", HELLO_WORLD); + println!("value is: {HELLO_WORLD}"); } diff --git a/listings/ch19-advanced-features/listing-19-11/Cargo.lock b/listings/ch20-advanced-features/listing-20-11/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-11/Cargo.lock rename to listings/ch20-advanced-features/listing-20-11/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-11/Cargo.toml b/listings/ch20-advanced-features/listing-20-11/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-11/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/listing-20-11/src/main.rs b/listings/ch20-advanced-features/listing-20-11/src/main.rs new file mode 100644 index 0000000000..4e292b18bf --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-11/src/main.rs @@ -0,0 +1,18 @@ +static mut COUNTER: u32 = 0; + +/// SAFETY: Calling this from more than a single thread at a time is undefined +/// behavior, so you *must* guarantee you only call it from a single thread at +/// a time. +unsafe fn add_to_count(inc: u32) { + unsafe { + COUNTER += inc; + } +} + +fn main() { + unsafe { + // SAFETY: This is only called from a single thread in `main`. + add_to_count(3); + println!("COUNTER: {}", *(&raw const COUNTER)); + } +} diff --git a/listings/ch19-advanced-features/no-listing-01-unsafe-fn/Cargo.lock b/listings/ch20-advanced-features/listing-20-12/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-01-unsafe-fn/Cargo.lock rename to listings/ch20-advanced-features/listing-20-12/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-12/Cargo.toml b/listings/ch20-advanced-features/listing-20-12/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-12/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-11/src/main.rs b/listings/ch20-advanced-features/listing-20-12/src/main.rs similarity index 77% rename from listings/ch19-advanced-features/listing-19-11/src/main.rs rename to listings/ch20-advanced-features/listing-20-12/src/main.rs index 885c1aa1d8..2301b0cac6 100644 --- a/listings/ch19-advanced-features/listing-19-11/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-12/src/main.rs @@ -1,3 +1,4 @@ +// ANCHOR: here unsafe trait Foo { // methods go here } @@ -5,5 +6,6 @@ unsafe trait Foo { unsafe impl Foo for i32 { // method implementations go here } +// ANCHOR_END: here fn main() {} diff --git a/listings/ch19-advanced-features/listing-19-12/Cargo.lock b/listings/ch20-advanced-features/listing-20-13/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-12/Cargo.lock rename to listings/ch20-advanced-features/listing-20-13/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-12/Cargo.toml b/listings/ch20-advanced-features/listing-20-13/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-12/Cargo.toml rename to listings/ch20-advanced-features/listing-20-13/Cargo.toml index 52395a5873..9c48a44e57 100644 --- a/listings/ch19-advanced-features/listing-19-12/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-13/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "traits-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-12/src/lib.rs b/listings/ch20-advanced-features/listing-20-13/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-12/src/lib.rs rename to listings/ch20-advanced-features/listing-20-13/src/lib.rs diff --git a/listings/ch19-advanced-features/listing-19-13/Cargo.lock b/listings/ch20-advanced-features/listing-20-14/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-13/Cargo.lock rename to listings/ch20-advanced-features/listing-20-14/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-13/Cargo.toml b/listings/ch20-advanced-features/listing-20-14/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-13/Cargo.toml rename to listings/ch20-advanced-features/listing-20-14/Cargo.toml index 52395a5873..9c48a44e57 100644 --- a/listings/ch19-advanced-features/listing-19-13/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-14/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "traits-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-13/src/lib.rs b/listings/ch20-advanced-features/listing-20-14/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-13/src/lib.rs rename to listings/ch20-advanced-features/listing-20-14/src/lib.rs diff --git a/listings/ch19-advanced-features/listing-19-14/Cargo.lock b/listings/ch20-advanced-features/listing-20-15/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-14/Cargo.lock rename to listings/ch20-advanced-features/listing-20-15/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-14/Cargo.toml b/listings/ch20-advanced-features/listing-20-15/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-14/Cargo.toml rename to listings/ch20-advanced-features/listing-20-15/Cargo.toml index 52395a5873..9c48a44e57 100644 --- a/listings/ch19-advanced-features/listing-19-14/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-15/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "traits-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-14/src/main.rs b/listings/ch20-advanced-features/listing-20-15/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-14/src/main.rs rename to listings/ch20-advanced-features/listing-20-15/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-15/Cargo.lock b/listings/ch20-advanced-features/listing-20-16/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-15/Cargo.lock rename to listings/ch20-advanced-features/listing-20-16/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-15/Cargo.toml b/listings/ch20-advanced-features/listing-20-16/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-15/Cargo.toml rename to listings/ch20-advanced-features/listing-20-16/Cargo.toml index 52395a5873..9c48a44e57 100644 --- a/listings/ch19-advanced-features/listing-19-15/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-16/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "traits-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-15/src/lib.rs b/listings/ch20-advanced-features/listing-20-16/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-15/src/lib.rs rename to listings/ch20-advanced-features/listing-20-16/src/lib.rs diff --git a/listings/ch19-advanced-features/listing-19-16/Cargo.lock b/listings/ch20-advanced-features/listing-20-17/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-16/Cargo.lock rename to listings/ch20-advanced-features/listing-20-17/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-17/Cargo.toml b/listings/ch20-advanced-features/listing-20-17/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-17/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-16/src/main.rs b/listings/ch20-advanced-features/listing-20-17/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-16/src/main.rs rename to listings/ch20-advanced-features/listing-20-17/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-17/Cargo.lock b/listings/ch20-advanced-features/listing-20-18/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-17/Cargo.lock rename to listings/ch20-advanced-features/listing-20-18/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-18/Cargo.toml b/listings/ch20-advanced-features/listing-20-18/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-18/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-17/src/main.rs b/listings/ch20-advanced-features/listing-20-18/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-17/src/main.rs rename to listings/ch20-advanced-features/listing-20-18/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-18/Cargo.lock b/listings/ch20-advanced-features/listing-20-19/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-18/Cargo.lock rename to listings/ch20-advanced-features/listing-20-19/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-19/Cargo.toml b/listings/ch20-advanced-features/listing-20-19/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-19/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-18/output.txt b/listings/ch20-advanced-features/listing-20-19/output.txt similarity index 71% rename from listings/ch19-advanced-features/listing-19-18/output.txt rename to listings/ch20-advanced-features/listing-20-19/output.txt index 2e9da17d65..d7e315bfab 100644 --- a/listings/ch19-advanced-features/listing-19-18/output.txt +++ b/listings/ch20-advanced-features/listing-20-19/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling traits-example v0.1.0 (file:///projects/traits-example) - Finished dev [unoptimized + debuginfo] target(s) in 0.46s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.46s Running `target/debug/traits-example` This is your captain speaking. Up! diff --git a/listings/ch19-advanced-features/listing-19-18/src/main.rs b/listings/ch20-advanced-features/listing-20-19/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-18/src/main.rs rename to listings/ch20-advanced-features/listing-20-19/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-19/Cargo.lock b/listings/ch20-advanced-features/listing-20-20/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-19/Cargo.lock rename to listings/ch20-advanced-features/listing-20-20/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-20/Cargo.toml b/listings/ch20-advanced-features/listing-20-20/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-20/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-19/output.txt b/listings/ch20-advanced-features/listing-20-20/output.txt similarity index 67% rename from listings/ch19-advanced-features/listing-19-19/output.txt rename to listings/ch20-advanced-features/listing-20-20/output.txt index 087e802b1a..b6e283f202 100644 --- a/listings/ch19-advanced-features/listing-19-19/output.txt +++ b/listings/ch20-advanced-features/listing-20-20/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling traits-example v0.1.0 (file:///projects/traits-example) - Finished dev [unoptimized + debuginfo] target(s) in 0.54s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.54s Running `target/debug/traits-example` A baby dog is called a Spot diff --git a/listings/ch19-advanced-features/listing-19-19/src/main.rs b/listings/ch20-advanced-features/listing-20-20/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-19/src/main.rs rename to listings/ch20-advanced-features/listing-20-20/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-20/Cargo.lock b/listings/ch20-advanced-features/listing-20-21/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-20/Cargo.lock rename to listings/ch20-advanced-features/listing-20-21/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-21/Cargo.toml b/listings/ch20-advanced-features/listing-20-21/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-21/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-20/output.txt b/listings/ch20-advanced-features/listing-20-21/output.txt similarity index 80% rename from listings/ch19-advanced-features/listing-19-20/output.txt rename to listings/ch20-advanced-features/listing-20-21/output.txt index 5942876044..b62a1fc9c5 100644 --- a/listings/ch19-advanced-features/listing-19-20/output.txt +++ b/listings/ch20-advanced-features/listing-20-21/output.txt @@ -3,11 +3,11 @@ $ cargo run error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type --> src/main.rs:20:43 | -2 | fn baby_name() -> String; + 2 | fn baby_name() -> String; | ------------------------- `Animal::baby_name` defined here ... 20 | println!("A baby dog is called a {}", Animal::baby_name()); - | ^^^^^^^^^^^^^^^^^ cannot call associated function of trait + | ^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait | help: use the fully-qualified path to the only available implementation | @@ -15,4 +15,4 @@ help: use the fully-qualified path to the only available implementation | +++++++ + For more information about this error, try `rustc --explain E0790`. -error: could not compile `traits-example` due to previous error +error: could not compile `traits-example` (bin "traits-example") due to 1 previous error diff --git a/listings/ch19-advanced-features/listing-19-20/src/main.rs b/listings/ch20-advanced-features/listing-20-21/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-20/src/main.rs rename to listings/ch20-advanced-features/listing-20-21/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-21/Cargo.lock b/listings/ch20-advanced-features/listing-20-22/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-21/Cargo.lock rename to listings/ch20-advanced-features/listing-20-22/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-22/Cargo.toml b/listings/ch20-advanced-features/listing-20-22/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-22/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-21/output.txt b/listings/ch20-advanced-features/listing-20-22/output.txt similarity index 68% rename from listings/ch19-advanced-features/listing-19-21/output.txt rename to listings/ch20-advanced-features/listing-20-22/output.txt index 4d1ee5ab48..f59d0bc27d 100644 --- a/listings/ch19-advanced-features/listing-19-21/output.txt +++ b/listings/ch20-advanced-features/listing-20-22/output.txt @@ -1,5 +1,5 @@ $ cargo run Compiling traits-example v0.1.0 (file:///projects/traits-example) - Finished dev [unoptimized + debuginfo] target(s) in 0.48s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s Running `target/debug/traits-example` A baby dog is called a puppy diff --git a/listings/ch19-advanced-features/listing-19-21/src/main.rs b/listings/ch20-advanced-features/listing-20-22/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-21/src/main.rs rename to listings/ch20-advanced-features/listing-20-22/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-22/Cargo.lock b/listings/ch20-advanced-features/listing-20-23/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-22/Cargo.lock rename to listings/ch20-advanced-features/listing-20-23/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-23/Cargo.toml b/listings/ch20-advanced-features/listing-20-23/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-23/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-22/src/main.rs b/listings/ch20-advanced-features/listing-20-23/src/main.rs similarity index 91% rename from listings/ch19-advanced-features/listing-19-22/src/main.rs rename to listings/ch20-advanced-features/listing-20-23/src/main.rs index febe58b0c5..7069fef179 100644 --- a/listings/ch19-advanced-features/listing-19-22/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-23/src/main.rs @@ -7,7 +7,7 @@ trait OutlinePrint: fmt::Display { let len = output.len(); println!("{}", "*".repeat(len + 4)); println!("*{}*", " ".repeat(len + 2)); - println!("* {} *", output); + println!("* {output} *"); println!("*{}*", " ".repeat(len + 2)); println!("{}", "*".repeat(len + 4)); } diff --git a/listings/ch19-advanced-features/listing-19-23/Cargo.lock b/listings/ch20-advanced-features/listing-20-24/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-23/Cargo.lock rename to listings/ch20-advanced-features/listing-20-24/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-24/Cargo.toml b/listings/ch20-advanced-features/listing-20-24/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-24/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/listing-19-23/src/main.rs b/listings/ch20-advanced-features/listing-20-24/src/main.rs similarity index 91% rename from listings/ch19-advanced-features/listing-19-23/src/main.rs rename to listings/ch20-advanced-features/listing-20-24/src/main.rs index eae46c92f3..f8c8366b4c 100644 --- a/listings/ch19-advanced-features/listing-19-23/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-24/src/main.rs @@ -10,5 +10,5 @@ impl fmt::Display for Wrapper { fn main() { let w = Wrapper(vec![String::from("hello"), String::from("world")]); - println!("w = {}", w); + println!("w = {w}"); } diff --git a/listings/ch19-advanced-features/listing-19-24/Cargo.lock b/listings/ch20-advanced-features/listing-20-25/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-24/Cargo.lock rename to listings/ch20-advanced-features/listing-20-25/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-24/Cargo.toml b/listings/ch20-advanced-features/listing-20-25/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/listing-19-24/Cargo.toml rename to listings/ch20-advanced-features/listing-20-25/Cargo.toml index a2ae20c77c..9884d38311 100644 --- a/listings/ch19-advanced-features/listing-19-24/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-25/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "types-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-24/src/main.rs b/listings/ch20-advanced-features/listing-20-25/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-24/src/main.rs rename to listings/ch20-advanced-features/listing-20-25/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-25/Cargo.lock b/listings/ch20-advanced-features/listing-20-26/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-25/Cargo.lock rename to listings/ch20-advanced-features/listing-20-26/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-25/Cargo.toml b/listings/ch20-advanced-features/listing-20-26/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/listing-19-25/Cargo.toml rename to listings/ch20-advanced-features/listing-20-26/Cargo.toml index a2ae20c77c..9884d38311 100644 --- a/listings/ch19-advanced-features/listing-19-25/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-26/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "types-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-25/src/main.rs b/listings/ch20-advanced-features/listing-20-26/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-25/src/main.rs rename to listings/ch20-advanced-features/listing-20-26/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-27/Cargo.lock b/listings/ch20-advanced-features/listing-20-28/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-27/Cargo.lock rename to listings/ch20-advanced-features/listing-20-28/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-27/Cargo.toml b/listings/ch20-advanced-features/listing-20-28/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-27/Cargo.toml rename to listings/ch20-advanced-features/listing-20-28/Cargo.toml index b196f35b55..3644460993 100644 --- a/listings/ch19-advanced-features/listing-19-27/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-28/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-27/src/main.rs b/listings/ch20-advanced-features/listing-20-28/src/main.rs similarity index 79% rename from listings/ch19-advanced-features/listing-19-27/src/main.rs rename to listings/ch20-advanced-features/listing-20-28/src/main.rs index 91b2cf04bf..312df2412f 100644 --- a/listings/ch19-advanced-features/listing-19-27/src/main.rs +++ b/listings/ch20-advanced-features/listing-20-28/src/main.rs @@ -9,5 +9,5 @@ fn do_twice(f: fn(i32) -> i32, arg: i32) -> i32 { fn main() { let answer = do_twice(add_one, 5); - println!("The answer is: {}", answer); + println!("The answer is: {answer}"); } diff --git a/listings/ch19-advanced-features/no-listing-15-map-closure/Cargo.lock b/listings/ch20-advanced-features/listing-20-29/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-15-map-closure/Cargo.lock rename to listings/ch20-advanced-features/listing-20-29/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-15-map-closure/Cargo.toml b/listings/ch20-advanced-features/listing-20-29/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/no-listing-15-map-closure/Cargo.toml rename to listings/ch20-advanced-features/listing-20-29/Cargo.toml index b196f35b55..3644460993 100644 --- a/listings/ch19-advanced-features/no-listing-15-map-closure/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-29/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/no-listing-15-map-closure/src/main.rs b/listings/ch20-advanced-features/listing-20-29/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-15-map-closure/src/main.rs rename to listings/ch20-advanced-features/listing-20-29/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-16-map-function/Cargo.lock b/listings/ch20-advanced-features/listing-20-30/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-16-map-function/Cargo.lock rename to listings/ch20-advanced-features/listing-20-30/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-16-map-function/Cargo.toml b/listings/ch20-advanced-features/listing-20-30/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/no-listing-16-map-function/Cargo.toml rename to listings/ch20-advanced-features/listing-20-30/Cargo.toml index b196f35b55..3644460993 100644 --- a/listings/ch19-advanced-features/no-listing-16-map-function/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-30/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/no-listing-16-map-function/src/main.rs b/listings/ch20-advanced-features/listing-20-30/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-16-map-function/src/main.rs rename to listings/ch20-advanced-features/listing-20-30/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-17-map-initializer/Cargo.lock b/listings/ch20-advanced-features/listing-20-31/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-17-map-initializer/Cargo.lock rename to listings/ch20-advanced-features/listing-20-31/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-17-map-initializer/Cargo.toml b/listings/ch20-advanced-features/listing-20-31/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/no-listing-17-map-initializer/Cargo.toml rename to listings/ch20-advanced-features/listing-20-31/Cargo.toml index b196f35b55..3644460993 100644 --- a/listings/ch19-advanced-features/no-listing-17-map-initializer/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-31/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "functions-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/no-listing-17-map-initializer/src/main.rs b/listings/ch20-advanced-features/listing-20-31/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-17-map-initializer/src/main.rs rename to listings/ch20-advanced-features/listing-20-31/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-18-returns-closure/Cargo.lock b/listings/ch20-advanced-features/listing-20-32/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-18-returns-closure/Cargo.lock rename to listings/ch20-advanced-features/listing-20-32/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-32/Cargo.toml b/listings/ch20-advanced-features/listing-20-32/Cargo.toml new file mode 100644 index 0000000000..3644460993 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-32/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "functions-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/listing-20-32/src/lib.rs b/listings/ch20-advanced-features/listing-20-32/src/lib.rs new file mode 100644 index 0000000000..7679cc7c0a --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-32/src/lib.rs @@ -0,0 +1,3 @@ +fn returns_closure() -> impl Fn(i32) -> i32 { + |x| x + 1 +} diff --git a/listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/Cargo.lock b/listings/ch20-advanced-features/listing-20-33/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/Cargo.lock rename to listings/ch20-advanced-features/listing-20-33/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-33/Cargo.toml b/listings/ch20-advanced-features/listing-20-33/Cargo.toml new file mode 100644 index 0000000000..3644460993 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-33/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "functions-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/listing-20-33/output.txt b/listings/ch20-advanced-features/listing-20-33/output.txt new file mode 100644 index 0000000000..2673661280 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-33/output.txt @@ -0,0 +1,20 @@ +$ cargo build + Compiling functions-example v0.1.0 (file:///projects/functions-example) +error[E0308]: mismatched types + --> src/main.rs:2:44 + | + 2 | let handlers = vec![returns_closure(), returns_initialized_closure(123)]; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected opaque type, found a different opaque type +... + 9 | fn returns_closure() -> impl Fn(i32) -> i32 { + | ------------------- the expected opaque type +... +13 | fn returns_initialized_closure(init: i32) -> impl Fn(i32) -> i32 { + | ------------------- the found opaque type + | + = note: expected opaque type `impl Fn(i32) -> i32` + found opaque type `impl Fn(i32) -> i32` + = note: distinct uses of `impl Trait` result in different opaque types + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `functions-example` (bin "functions-example") due to 1 previous error diff --git a/listings/ch20-advanced-features/listing-20-33/src/main.rs b/listings/ch20-advanced-features/listing-20-33/src/main.rs new file mode 100644 index 0000000000..d7db7a0b47 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-33/src/main.rs @@ -0,0 +1,15 @@ +fn main() { + let handlers = vec![returns_closure(), returns_initialized_closure(123)]; + for handler in handlers { + let output = handler(5); + println!("{output}"); + } +} + +fn returns_closure() -> impl Fn(i32) -> i32 { + |x| x + 1 +} + +fn returns_initialized_closure(init: i32) -> impl Fn(i32) -> i32 { + move |x| x + init +} diff --git a/listings/ch20-advanced-features/listing-20-34/Cargo.lock b/listings/ch20-advanced-features/listing-20-34/Cargo.lock new file mode 100644 index 0000000000..b2327c755a --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-34/Cargo.lock @@ -0,0 +1,6 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +[[package]] +name = "functions-example" +version = "0.1.0" + diff --git a/listings/ch20-advanced-features/listing-20-34/Cargo.toml b/listings/ch20-advanced-features/listing-20-34/Cargo.toml new file mode 100644 index 0000000000..3644460993 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-34/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "functions-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/listing-20-34/src/main.rs b/listings/ch20-advanced-features/listing-20-34/src/main.rs new file mode 100644 index 0000000000..975a7f54b8 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-34/src/main.rs @@ -0,0 +1,17 @@ +fn main() { + let handlers = vec![returns_closure(), returns_initialized_closure(123)]; + for handler in handlers { + let output = handler(5); + println!("{output}"); + } +} + +// ANCHOR: here +fn returns_closure() -> Box i32> { + Box::new(|x| x + 1) +} + +fn returns_initialized_closure(init: i32) -> Box i32> { + Box::new(move |x| x + init) +} +// ANCHOR_END: here diff --git a/listings/ch19-advanced-features/listing-19-28/Cargo.lock b/listings/ch20-advanced-features/listing-20-35/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-28/Cargo.lock rename to listings/ch20-advanced-features/listing-20-35/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-28/Cargo.toml b/listings/ch20-advanced-features/listing-20-35/Cargo.toml similarity index 80% rename from listings/ch19-advanced-features/listing-19-28/Cargo.toml rename to listings/ch20-advanced-features/listing-20-35/Cargo.toml index 9218091c89..76689ec01b 100644 --- a/listings/ch19-advanced-features/listing-19-28/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-35/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "macros-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-28/src/lib.rs b/listings/ch20-advanced-features/listing-20-35/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-28/src/lib.rs rename to listings/ch20-advanced-features/listing-20-35/src/lib.rs diff --git a/listings/ch19-advanced-features/listing-19-30/Cargo.lock b/listings/ch20-advanced-features/listing-20-37/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-30/Cargo.lock rename to listings/ch20-advanced-features/listing-20-37/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-30/Cargo.toml b/listings/ch20-advanced-features/listing-20-37/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/listing-19-30/Cargo.toml rename to listings/ch20-advanced-features/listing-20-37/Cargo.toml index c6fb920877..aaaf3bf827 100644 --- a/listings/ch19-advanced-features/listing-19-30/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-37/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello_macro" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-30/src/main.rs b/listings/ch20-advanced-features/listing-20-37/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-30/src/main.rs rename to listings/ch20-advanced-features/listing-20-37/src/main.rs diff --git a/listings/ch19-advanced-features/listing-19-31/hello_macro/Cargo.lock b/listings/ch20-advanced-features/listing-20-38/hello_macro/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-31/hello_macro/Cargo.lock rename to listings/ch20-advanced-features/listing-20-38/hello_macro/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-31/hello_macro/Cargo.toml b/listings/ch20-advanced-features/listing-20-38/hello_macro/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/listing-19-31/hello_macro/Cargo.toml rename to listings/ch20-advanced-features/listing-20-38/hello_macro/Cargo.toml index c6fb920877..aaaf3bf827 100644 --- a/listings/ch19-advanced-features/listing-19-31/hello_macro/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-38/hello_macro/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello_macro" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-31/hello_macro/src/lib.rs b/listings/ch20-advanced-features/listing-20-38/hello_macro/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-31/hello_macro/src/lib.rs rename to listings/ch20-advanced-features/listing-20-38/hello_macro/src/lib.rs diff --git a/listings/ch19-advanced-features/listing-19-33/hello_macro/Cargo.lock b/listings/ch20-advanced-features/listing-20-39/hello_macro/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/listing-19-33/hello_macro/Cargo.lock rename to listings/ch20-advanced-features/listing-20-39/hello_macro/Cargo.lock diff --git a/listings/ch19-advanced-features/listing-19-33/hello_macro/Cargo.toml b/listings/ch20-advanced-features/listing-20-39/hello_macro/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/listing-19-33/hello_macro/Cargo.toml rename to listings/ch20-advanced-features/listing-20-39/hello_macro/Cargo.toml index c6fb920877..aaaf3bf827 100644 --- a/listings/ch19-advanced-features/listing-19-33/hello_macro/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-39/hello_macro/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello_macro" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/listing-19-33/hello_macro/src/lib.rs b/listings/ch20-advanced-features/listing-20-39/hello_macro/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-33/hello_macro/src/lib.rs rename to listings/ch20-advanced-features/listing-20-39/hello_macro/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/Cargo.lock b/listings/ch20-advanced-features/listing-20-39/pancakes/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/Cargo.lock rename to listings/ch20-advanced-features/listing-20-39/pancakes/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/Cargo.toml b/listings/ch20-advanced-features/listing-20-39/pancakes/Cargo.toml similarity index 85% rename from listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/Cargo.toml rename to listings/ch20-advanced-features/listing-20-39/pancakes/Cargo.toml index 3ad910862a..faee67fcde 100644 --- a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-39/pancakes/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "pancakes" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] hello_macro = { path = "../hello_macro" } \ No newline at end of file diff --git a/listings/ch19-advanced-features/listing-19-31/hello_macro/src/main.rs b/listings/ch20-advanced-features/listing-20-39/pancakes/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-31/hello_macro/src/main.rs rename to listings/ch20-advanced-features/listing-20-39/pancakes/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/Cargo.lock b/listings/ch20-advanced-features/listing-20-40/hello_macro/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/Cargo.lock rename to listings/ch20-advanced-features/listing-20-40/hello_macro/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/Cargo.toml b/listings/ch20-advanced-features/listing-20-40/hello_macro/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/Cargo.toml rename to listings/ch20-advanced-features/listing-20-40/hello_macro/Cargo.toml index c6fb920877..aaaf3bf827 100644 --- a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-40/hello_macro/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello_macro" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/Cargo.lock b/listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/Cargo.lock new file mode 100644 index 0000000000..6be987b21b --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/Cargo.lock @@ -0,0 +1,46 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +version = 3 + +[[package]] +name = "hello_macro_derive" +version = "0.1.0" +dependencies = [ + "quote", + "syn", +] + +[[package]] +name = "proc-macro2" +version = "1.0.80" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "a56dea16b0a29e94408b9aa5e2940a4eedbd128a1ba20e8f7ae60fd3d465af0e" +dependencies = [ + "unicode-ident", +] + +[[package]] +name = "quote" +version = "1.0.36" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7" +dependencies = [ + "proc-macro2", +] + +[[package]] +name = "syn" +version = "2.0.59" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "4a6531ffc7b071655e4ce2e04bd464c4830bb585a61cabb96cf808f05172615a" +dependencies = [ + "proc-macro2", + "quote", + "unicode-ident", +] + +[[package]] +name = "unicode-ident" +version = "1.0.12" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b" diff --git a/listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/Cargo.toml b/listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/Cargo.toml rename to listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/Cargo.toml index aa076ac48b..8e54d81ade 100644 --- a/listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/Cargo.toml @@ -1,11 +1,11 @@ [package] name = "hello_macro_derive" version = "0.1.0" -edition = "2021" +edition = "2024" [lib] proc-macro = true [dependencies] -syn = "1.0" +syn = "2.0" quote = "1.0" diff --git a/listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/src/lib.rs b/listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/src/lib.rs similarity index 78% rename from listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/src/lib.rs rename to listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/src/lib.rs index 11643a8d62..7ae9e55df3 100644 --- a/listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/src/lib.rs +++ b/listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/src/lib.rs @@ -1,13 +1,12 @@ use proc_macro::TokenStream; use quote::quote; -use syn; #[proc_macro_derive(HelloMacro)] pub fn hello_macro_derive(input: TokenStream) -> TokenStream { // Construct a representation of Rust code as a syntax tree - // that we can manipulate + // that we can manipulate. let ast = syn::parse(input).unwrap(); - // Build the trait implementation + // Build the trait implementation. impl_hello_macro(&ast) } diff --git a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/src/lib.rs b/listings/ch20-advanced-features/listing-20-40/hello_macro/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/src/lib.rs rename to listings/ch20-advanced-features/listing-20-40/hello_macro/src/lib.rs diff --git a/listings/ch19-advanced-features/listing-19-33/hello_macro/src/main.rs b/listings/ch20-advanced-features/listing-20-40/hello_macro/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/listing-19-33/hello_macro/src/main.rs rename to listings/ch20-advanced-features/listing-20-40/hello_macro/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.lock b/listings/ch20-advanced-features/listing-20-42/hello_macro/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.lock rename to listings/ch20-advanced-features/listing-20-42/hello_macro/Cargo.lock diff --git a/listings/ch20-advanced-features/listing-20-42/hello_macro/Cargo.toml b/listings/ch20-advanced-features/listing-20-42/hello_macro/Cargo.toml new file mode 100644 index 0000000000..aaaf3bf827 --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-42/hello_macro/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello_macro" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/Cargo.lock b/listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/Cargo.lock new file mode 100644 index 0000000000..6be987b21b --- /dev/null +++ b/listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/Cargo.lock @@ -0,0 +1,46 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +version = 3 + +[[package]] +name = "hello_macro_derive" +version = "0.1.0" +dependencies = [ + "quote", + "syn", +] + +[[package]] +name = "proc-macro2" +version = "1.0.80" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "a56dea16b0a29e94408b9aa5e2940a4eedbd128a1ba20e8f7ae60fd3d465af0e" +dependencies = [ + "unicode-ident", +] + +[[package]] +name = "quote" +version = "1.0.36" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7" +dependencies = [ + "proc-macro2", +] + +[[package]] +name = "syn" +version = "2.0.59" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "4a6531ffc7b071655e4ce2e04bd464c4830bb585a61cabb96cf808f05172615a" +dependencies = [ + "proc-macro2", + "quote", + "unicode-ident", +] + +[[package]] +name = "unicode-ident" +version = "1.0.12" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b" diff --git a/listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/Cargo.toml b/listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/Cargo.toml rename to listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/Cargo.toml index aa076ac48b..8e54d81ade 100644 --- a/listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/Cargo.toml +++ b/listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/Cargo.toml @@ -1,11 +1,11 @@ [package] name = "hello_macro_derive" version = "0.1.0" -edition = "2021" +edition = "2024" [lib] proc-macro = true [dependencies] -syn = "1.0" +syn = "2.0" quote = "1.0" diff --git a/listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/src/lib.rs b/listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/src/lib.rs similarity index 92% rename from listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/src/lib.rs rename to listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/src/lib.rs index dac6c98f66..bba8ffba47 100644 --- a/listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/src/lib.rs +++ b/listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/src/lib.rs @@ -1,6 +1,5 @@ use proc_macro::TokenStream; use quote::quote; -use syn; #[proc_macro_derive(HelloMacro)] pub fn hello_macro_derive(input: TokenStream) -> TokenStream { @@ -15,13 +14,13 @@ pub fn hello_macro_derive(input: TokenStream) -> TokenStream { // ANCHOR: here fn impl_hello_macro(ast: &syn::DeriveInput) -> TokenStream { let name = &ast.ident; - let gen = quote! { + let generated = quote! { impl HelloMacro for #name { fn hello_macro() { println!("Hello, Macro! My name is {}!", stringify!(#name)); } } }; - gen.into() + generated.into() } // ANCHOR_END: here diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/src/lib.rs b/listings/ch20-advanced-features/listing-20-42/hello_macro/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/src/lib.rs rename to listings/ch20-advanced-features/listing-20-42/hello_macro/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/src/main.rs b/listings/ch20-advanced-features/listing-20-42/hello_macro/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/src/main.rs rename to listings/ch20-advanced-features/listing-20-42/hello_macro/src/main.rs diff --git a/listings/ch19-advanced-features/output-only-01-missing-unsafe/Cargo.lock b/listings/ch20-advanced-features/no-listing-01-unsafe-fn/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/output-only-01-missing-unsafe/Cargo.lock rename to listings/ch20-advanced-features/no-listing-01-unsafe-fn/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-01-unsafe-fn/Cargo.toml b/listings/ch20-advanced-features/no-listing-01-unsafe-fn/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-01-unsafe-fn/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-01-unsafe-fn/src/main.rs b/listings/ch20-advanced-features/no-listing-01-unsafe-fn/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-01-unsafe-fn/src/main.rs rename to listings/ch20-advanced-features/no-listing-01-unsafe-fn/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.lock b/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.lock rename to listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.toml b/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt b/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt new file mode 100644 index 0000000000..2d45a218b2 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt @@ -0,0 +1,30 @@ +$ cargo run + Compiling traits-example v0.1.0 (file:///projects/traits-example) +error[E0277]: `Point` doesn't implement `std::fmt::Display` + --> src/main.rs:20:23 + | +20 | impl OutlinePrint for Point {} + | ^^^^^ the trait `std::fmt::Display` is not implemented for `Point` + | +note: required by a bound in `OutlinePrint` + --> src/main.rs:3:21 + | + 3 | trait OutlinePrint: fmt::Display { + | ^^^^^^^^^^^^ required by this bound in `OutlinePrint` + +error[E0277]: `Point` doesn't implement `std::fmt::Display` + --> src/main.rs:24:7 + | +24 | p.outline_print(); + | ^^^^^^^^^^^^^ the trait `std::fmt::Display` is not implemented for `Point` + | +note: required by a bound in `OutlinePrint::outline_print` + --> src/main.rs:3:21 + | + 3 | trait OutlinePrint: fmt::Display { + | ^^^^^^^^^^^^ required by this bound in `OutlinePrint::outline_print` + 4 | fn outline_print(&self) { + | ------------- required by a bound in this associated function + +For more information about this error, try `rustc --explain E0277`. +error: could not compile `traits-example` (bin "traits-example") due to 2 previous errors diff --git a/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs b/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs similarity index 93% rename from listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs rename to listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs index a1e2fe4c46..0e45f3c283 100644 --- a/listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs +++ b/listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs @@ -6,7 +6,7 @@ trait OutlinePrint: fmt::Display { let len = output.len(); println!("{}", "*".repeat(len + 4)); println!("*{}*", " ".repeat(len + 2)); - println!("* {} *", output); + println!("* {output} *"); println!("*{}*", " ".repeat(len + 2)); println!("{}", "*".repeat(len + 4)); } diff --git a/listings/ch19-advanced-features/no-listing-03-impl-display-for-point/Cargo.lock b/listings/ch20-advanced-features/no-listing-03-impl-display-for-point/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-03-impl-display-for-point/Cargo.lock rename to listings/ch20-advanced-features/no-listing-03-impl-display-for-point/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-03-impl-display-for-point/Cargo.toml b/listings/ch20-advanced-features/no-listing-03-impl-display-for-point/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-03-impl-display-for-point/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-03-impl-display-for-point/src/main.rs b/listings/ch20-advanced-features/no-listing-03-impl-display-for-point/src/main.rs similarity index 94% rename from listings/ch19-advanced-features/no-listing-03-impl-display-for-point/src/main.rs rename to listings/ch20-advanced-features/no-listing-03-impl-display-for-point/src/main.rs index c7bbb6a708..fa5be1c7cf 100644 --- a/listings/ch19-advanced-features/no-listing-03-impl-display-for-point/src/main.rs +++ b/listings/ch20-advanced-features/no-listing-03-impl-display-for-point/src/main.rs @@ -4,7 +4,7 @@ trait OutlinePrint: fmt::Display { let len = output.len(); println!("{}", "*".repeat(len + 4)); println!("*{}*", " ".repeat(len + 2)); - println!("* {} *", output); + println!("* {output} *"); println!("*{}*", " ".repeat(len + 2)); println!("{}", "*".repeat(len + 4)); } diff --git a/listings/ch19-advanced-features/no-listing-04-kilometers-alias/Cargo.lock b/listings/ch20-advanced-features/no-listing-04-kilometers-alias/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-04-kilometers-alias/Cargo.lock rename to listings/ch20-advanced-features/no-listing-04-kilometers-alias/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-04-kilometers-alias/Cargo.toml b/listings/ch20-advanced-features/no-listing-04-kilometers-alias/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/no-listing-04-kilometers-alias/Cargo.toml rename to listings/ch20-advanced-features/no-listing-04-kilometers-alias/Cargo.toml index a2ae20c77c..9884d38311 100644 --- a/listings/ch19-advanced-features/no-listing-04-kilometers-alias/Cargo.toml +++ b/listings/ch20-advanced-features/no-listing-04-kilometers-alias/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "types-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/no-listing-04-kilometers-alias/src/main.rs b/listings/ch20-advanced-features/no-listing-04-kilometers-alias/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-04-kilometers-alias/src/main.rs rename to listings/ch20-advanced-features/no-listing-04-kilometers-alias/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-05-write-trait/Cargo.lock b/listings/ch20-advanced-features/no-listing-05-write-trait/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-05-write-trait/Cargo.lock rename to listings/ch20-advanced-features/no-listing-05-write-trait/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-05-write-trait/Cargo.toml b/listings/ch20-advanced-features/no-listing-05-write-trait/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-05-write-trait/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-05-write-trait/src/lib.rs b/listings/ch20-advanced-features/no-listing-05-write-trait/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-05-write-trait/src/lib.rs rename to listings/ch20-advanced-features/no-listing-05-write-trait/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-06-result-alias/Cargo.lock b/listings/ch20-advanced-features/no-listing-06-result-alias/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-06-result-alias/Cargo.lock rename to listings/ch20-advanced-features/no-listing-06-result-alias/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-06-result-alias/Cargo.toml b/listings/ch20-advanced-features/no-listing-06-result-alias/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-06-result-alias/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-06-result-alias/src/lib.rs b/listings/ch20-advanced-features/no-listing-06-result-alias/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-06-result-alias/src/lib.rs rename to listings/ch20-advanced-features/no-listing-06-result-alias/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-07-never-type/Cargo.lock b/listings/ch20-advanced-features/no-listing-07-never-type/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-07-never-type/Cargo.lock rename to listings/ch20-advanced-features/no-listing-07-never-type/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-07-never-type/Cargo.toml b/listings/ch20-advanced-features/no-listing-07-never-type/Cargo.toml new file mode 100644 index 0000000000..9c48a44e57 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-07-never-type/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "traits-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-07-never-type/src/lib.rs b/listings/ch20-advanced-features/no-listing-07-never-type/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-07-never-type/src/lib.rs rename to listings/ch20-advanced-features/no-listing-07-never-type/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-08-match-arms-different-types/Cargo.lock b/listings/ch20-advanced-features/no-listing-08-match-arms-different-types/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-08-match-arms-different-types/Cargo.lock rename to listings/ch20-advanced-features/no-listing-08-match-arms-different-types/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-08-match-arms-different-types/Cargo.toml b/listings/ch20-advanced-features/no-listing-08-match-arms-different-types/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/no-listing-08-match-arms-different-types/Cargo.toml rename to listings/ch20-advanced-features/no-listing-08-match-arms-different-types/Cargo.toml index a2ae20c77c..9884d38311 100644 --- a/listings/ch19-advanced-features/no-listing-08-match-arms-different-types/Cargo.toml +++ b/listings/ch20-advanced-features/no-listing-08-match-arms-different-types/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "types-example" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/no-listing-08-match-arms-different-types/src/main.rs b/listings/ch20-advanced-features/no-listing-08-match-arms-different-types/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-08-match-arms-different-types/src/main.rs rename to listings/ch20-advanced-features/no-listing-08-match-arms-different-types/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-09-unwrap-definition/Cargo.lock b/listings/ch20-advanced-features/no-listing-09-unwrap-definition/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-09-unwrap-definition/Cargo.lock rename to listings/ch20-advanced-features/no-listing-09-unwrap-definition/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-09-unwrap-definition/Cargo.toml b/listings/ch20-advanced-features/no-listing-09-unwrap-definition/Cargo.toml new file mode 100644 index 0000000000..9884d38311 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-09-unwrap-definition/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "types-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-09-unwrap-definition/src/lib.rs b/listings/ch20-advanced-features/no-listing-09-unwrap-definition/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-09-unwrap-definition/src/lib.rs rename to listings/ch20-advanced-features/no-listing-09-unwrap-definition/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-10-loop-returns-never/Cargo.lock b/listings/ch20-advanced-features/no-listing-10-loop-returns-never/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-10-loop-returns-never/Cargo.lock rename to listings/ch20-advanced-features/no-listing-10-loop-returns-never/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-10-loop-returns-never/Cargo.toml b/listings/ch20-advanced-features/no-listing-10-loop-returns-never/Cargo.toml new file mode 100644 index 0000000000..9884d38311 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-10-loop-returns-never/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "types-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-10-loop-returns-never/src/main.rs b/listings/ch20-advanced-features/no-listing-10-loop-returns-never/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-10-loop-returns-never/src/main.rs rename to listings/ch20-advanced-features/no-listing-10-loop-returns-never/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-11-cant-create-str/Cargo.lock b/listings/ch20-advanced-features/no-listing-11-cant-create-str/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-11-cant-create-str/Cargo.lock rename to listings/ch20-advanced-features/no-listing-11-cant-create-str/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-11-cant-create-str/Cargo.toml b/listings/ch20-advanced-features/no-listing-11-cant-create-str/Cargo.toml new file mode 100644 index 0000000000..9884d38311 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-11-cant-create-str/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "types-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-11-cant-create-str/src/main.rs b/listings/ch20-advanced-features/no-listing-11-cant-create-str/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-11-cant-create-str/src/main.rs rename to listings/ch20-advanced-features/no-listing-11-cant-create-str/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-12-generic-fn-definition/Cargo.lock b/listings/ch20-advanced-features/no-listing-12-generic-fn-definition/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-12-generic-fn-definition/Cargo.lock rename to listings/ch20-advanced-features/no-listing-12-generic-fn-definition/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-12-generic-fn-definition/Cargo.toml b/listings/ch20-advanced-features/no-listing-12-generic-fn-definition/Cargo.toml new file mode 100644 index 0000000000..9884d38311 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-12-generic-fn-definition/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "types-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-12-generic-fn-definition/src/lib.rs b/listings/ch20-advanced-features/no-listing-12-generic-fn-definition/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-12-generic-fn-definition/src/lib.rs rename to listings/ch20-advanced-features/no-listing-12-generic-fn-definition/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.lock b/listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.lock rename to listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.toml b/listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.toml new file mode 100644 index 0000000000..9884d38311 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "types-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/src/lib.rs b/listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/src/lib.rs rename to listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/src/lib.rs diff --git a/listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/Cargo.lock b/listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/Cargo.lock rename to listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/Cargo.lock diff --git a/listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/Cargo.toml b/listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/Cargo.toml new file mode 100644 index 0000000000..9884d38311 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "types-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/src/lib.rs b/listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/src/lib.rs rename to listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/src/lib.rs diff --git a/listings/ch20-advanced-features/no-listing-18-returns-closure/Cargo.lock b/listings/ch20-advanced-features/no-listing-18-returns-closure/Cargo.lock new file mode 100644 index 0000000000..b2327c755a --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-18-returns-closure/Cargo.lock @@ -0,0 +1,6 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +[[package]] +name = "functions-example" +version = "0.1.0" + diff --git a/listings/ch20-advanced-features/no-listing-18-returns-closure/Cargo.toml b/listings/ch20-advanced-features/no-listing-18-returns-closure/Cargo.toml new file mode 100644 index 0000000000..3644460993 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-18-returns-closure/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "functions-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/no-listing-18-returns-closure/src/lib.rs b/listings/ch20-advanced-features/no-listing-18-returns-closure/src/lib.rs new file mode 100644 index 0000000000..20fb4bc0c2 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-18-returns-closure/src/lib.rs @@ -0,0 +1,3 @@ +fn returns_closure(init: i32) -> impl Fn(i32) -> i32 { + move |x| x + init +} diff --git a/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.lock b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.lock new file mode 100644 index 0000000000..39afcf282f --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.lock @@ -0,0 +1,6 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +[[package]] +name = "hello_macro" +version = "0.1.0" + diff --git a/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.toml b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.toml new file mode 100644 index 0000000000..aaaf3bf827 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello_macro" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.lock b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.lock new file mode 100644 index 0000000000..6be987b21b --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.lock @@ -0,0 +1,46 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +version = 3 + +[[package]] +name = "hello_macro_derive" +version = "0.1.0" +dependencies = [ + "quote", + "syn", +] + +[[package]] +name = "proc-macro2" +version = "1.0.80" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "a56dea16b0a29e94408b9aa5e2940a4eedbd128a1ba20e8f7ae60fd3d465af0e" +dependencies = [ + "unicode-ident", +] + +[[package]] +name = "quote" +version = "1.0.36" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7" +dependencies = [ + "proc-macro2", +] + +[[package]] +name = "syn" +version = "2.0.59" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "4a6531ffc7b071655e4ce2e04bd464c4830bb585a61cabb96cf808f05172615a" +dependencies = [ + "proc-macro2", + "quote", + "unicode-ident", +] + +[[package]] +name = "unicode-ident" +version = "1.0.12" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b" diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.toml b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.toml similarity index 79% rename from listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.toml rename to listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.toml index aa076ac48b..8e54d81ade 100644 --- a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.toml +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/Cargo.toml @@ -1,11 +1,11 @@ [package] name = "hello_macro_derive" version = "0.1.0" -edition = "2021" +edition = "2024" [lib] proc-macro = true [dependencies] -syn = "1.0" +syn = "2.0" quote = "1.0" diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/src/lib.rs b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/src/lib.rs similarity index 92% rename from listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/src/lib.rs rename to listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/src/lib.rs index 5e0b96c277..fd38085464 100644 --- a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/src/lib.rs +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/hello_macro_derive/src/lib.rs @@ -1,6 +1,5 @@ use proc_macro::TokenStream; use quote::quote; -use syn; #[proc_macro_derive(HelloMacro)] pub fn hello_macro_derive(input: TokenStream) -> TokenStream { @@ -14,12 +13,12 @@ pub fn hello_macro_derive(input: TokenStream) -> TokenStream { fn impl_hello_macro(ast: &syn::DeriveInput) -> TokenStream { let name = &ast.ident; - let gen = quote! { + let generated = quote! { impl HelloMacro for #name { fn hello_macro() { println!("Hello, Macro! My name is {}!", stringify!(#name)); } } }; - gen.into() + generated.into() } diff --git a/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/src/lib.rs b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/src/lib.rs new file mode 100644 index 0000000000..e74793184b --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/src/lib.rs @@ -0,0 +1,3 @@ +pub trait HelloMacro { + fn hello_macro(); +} diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/src/main.rs b/listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-21-pancakes/hello_macro/src/main.rs rename to listings/ch20-advanced-features/no-listing-21-pancakes/hello_macro/src/main.rs diff --git a/listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/Cargo.lock b/listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/Cargo.lock new file mode 100644 index 0000000000..3849f15217 --- /dev/null +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/Cargo.lock @@ -0,0 +1,58 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +version = 3 + +[[package]] +name = "hello_macro" +version = "0.1.0" + +[[package]] +name = "hello_macro_derive" +version = "0.1.0" +dependencies = [ + "quote", + "syn", +] + +[[package]] +name = "pancakes" +version = "0.1.0" +dependencies = [ + "hello_macro", + "hello_macro_derive", +] + +[[package]] +name = "proc-macro2" +version = "1.0.80" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "a56dea16b0a29e94408b9aa5e2940a4eedbd128a1ba20e8f7ae60fd3d465af0e" +dependencies = [ + "unicode-ident", +] + +[[package]] +name = "quote" +version = "1.0.36" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "0fa76aaf39101c457836aec0ce2316dbdc3ab723cdda1c6bd4e6ad4208acaca7" +dependencies = [ + "proc-macro2", +] + +[[package]] +name = "syn" +version = "2.0.59" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "4a6531ffc7b071655e4ce2e04bd464c4830bb585a61cabb96cf808f05172615a" +dependencies = [ + "proc-macro2", + "quote", + "unicode-ident", +] + +[[package]] +name = "unicode-ident" +version = "1.0.12" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b" diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml b/listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml similarity index 91% rename from listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml rename to listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml index cb3a98c3a8..2b1b36cd28 100644 --- a/listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml +++ b/listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml @@ -1,7 +1,7 @@ [package] name = "pancakes" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] hello_macro = { path = "../hello_macro" } diff --git a/listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/src/main.rs b/listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/src/main.rs rename to listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/src/main.rs diff --git a/listings/ch19-advanced-features/no-listing-22-iterator-on-counter/Cargo.lock b/listings/ch20-advanced-features/no-listing-22-iterator-on-counter/Cargo.lock similarity index 100% rename from listings/ch19-advanced-features/no-listing-22-iterator-on-counter/Cargo.lock rename to listings/ch20-advanced-features/no-listing-22-iterator-on-counter/Cargo.lock diff --git a/listings/ch19-advanced-features/no-listing-22-iterator-on-counter/Cargo.toml b/listings/ch20-advanced-features/no-listing-22-iterator-on-counter/Cargo.toml similarity index 78% rename from listings/ch19-advanced-features/no-listing-22-iterator-on-counter/Cargo.toml rename to listings/ch20-advanced-features/no-listing-22-iterator-on-counter/Cargo.toml index 9e103f3eb3..2096415b85 100644 --- a/listings/ch19-advanced-features/no-listing-22-iterator-on-counter/Cargo.toml +++ b/listings/ch20-advanced-features/no-listing-22-iterator-on-counter/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "counter" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch19-advanced-features/no-listing-22-iterator-on-counter/src/lib.rs b/listings/ch20-advanced-features/no-listing-22-iterator-on-counter/src/lib.rs similarity index 100% rename from listings/ch19-advanced-features/no-listing-22-iterator-on-counter/src/lib.rs rename to listings/ch20-advanced-features/no-listing-22-iterator-on-counter/src/lib.rs diff --git a/listings/ch20-advanced-features/output-only-01-missing-unsafe/Cargo.lock b/listings/ch20-advanced-features/output-only-01-missing-unsafe/Cargo.lock new file mode 100644 index 0000000000..497817bf27 --- /dev/null +++ b/listings/ch20-advanced-features/output-only-01-missing-unsafe/Cargo.lock @@ -0,0 +1,6 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +[[package]] +name = "unsafe-example" +version = "0.1.0" + diff --git a/listings/ch20-advanced-features/output-only-01-missing-unsafe/Cargo.toml b/listings/ch20-advanced-features/output-only-01-missing-unsafe/Cargo.toml new file mode 100644 index 0000000000..690cfbdd4d --- /dev/null +++ b/listings/ch20-advanced-features/output-only-01-missing-unsafe/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "unsafe-example" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch19-advanced-features/output-only-01-missing-unsafe/output.txt b/listings/ch20-advanced-features/output-only-01-missing-unsafe/output.txt similarity index 66% rename from listings/ch19-advanced-features/output-only-01-missing-unsafe/output.txt rename to listings/ch20-advanced-features/output-only-01-missing-unsafe/output.txt index 5886bc6307..f85a4d3c1f 100644 --- a/listings/ch19-advanced-features/output-only-01-missing-unsafe/output.txt +++ b/listings/ch20-advanced-features/output-only-01-missing-unsafe/output.txt @@ -1,6 +1,6 @@ $ cargo run Compiling unsafe-example v0.1.0 (file:///projects/unsafe-example) -error[E0133]: call to unsafe function is unsafe and requires unsafe function or block +error[E0133]: call to unsafe function `dangerous` is unsafe and requires unsafe block --> src/main.rs:4:5 | 4 | dangerous(); @@ -9,4 +9,4 @@ error[E0133]: call to unsafe function is unsafe and requires unsafe function or = note: consult the function's documentation for information on how to avoid undefined behavior For more information about this error, try `rustc --explain E0133`. -error: could not compile `unsafe-example` due to previous error +error: could not compile `unsafe-example` (bin "unsafe-example") due to 1 previous error diff --git a/listings/ch19-advanced-features/output-only-01-missing-unsafe/src/main.rs b/listings/ch20-advanced-features/output-only-01-missing-unsafe/src/main.rs similarity index 100% rename from listings/ch19-advanced-features/output-only-01-missing-unsafe/src/main.rs rename to listings/ch20-advanced-features/output-only-01-missing-unsafe/src/main.rs diff --git a/listings/ch20-web-server/listing-20-06/Cargo.toml b/listings/ch20-web-server/listing-20-06/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-06/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-07/Cargo.toml b/listings/ch20-web-server/listing-20-07/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-07/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-09/Cargo.toml b/listings/ch20-web-server/listing-20-09/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-09/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-10/Cargo.toml b/listings/ch20-web-server/listing-20-10/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-10/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-11/Cargo.toml b/listings/ch20-web-server/listing-20-11/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-11/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-12/Cargo.toml b/listings/ch20-web-server/listing-20-12/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-12/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-13/Cargo.toml b/listings/ch20-web-server/listing-20-13/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-13/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-14/Cargo.toml b/listings/ch20-web-server/listing-20-14/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-14/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-15/Cargo.toml b/listings/ch20-web-server/listing-20-15/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-15/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-16/Cargo.toml b/listings/ch20-web-server/listing-20-16/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-16/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-17/Cargo.toml b/listings/ch20-web-server/listing-20-17/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-17/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-17/output.txt b/listings/ch20-web-server/listing-20-17/output.txt deleted file mode 100644 index 8bedfecfd4..0000000000 --- a/listings/ch20-web-server/listing-20-17/output.txt +++ /dev/null @@ -1,13 +0,0 @@ -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) -error[E0382]: use of moved value: `receiver` - --> src/lib.rs:26:42 - | -21 | let (sender, receiver) = mpsc::channel(); - | -------- move occurs because `receiver` has type `std::sync::mpsc::Receiver`, which does not implement the `Copy` trait -... -26 | workers.push(Worker::new(id, receiver)); - | ^^^^^^^^ value moved here, in previous iteration of loop - -For more information about this error, try `rustc --explain E0382`. -error: could not compile `hello` due to previous error diff --git a/listings/ch20-web-server/listing-20-17/src/main.rs b/listings/ch20-web-server/listing-20-17/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/listing-20-17/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/listing-20-18/Cargo.toml b/listings/ch20-web-server/listing-20-18/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-18/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-18/src/main.rs b/listings/ch20-web-server/listing-20-18/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/listing-20-18/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/listing-20-19/Cargo.toml b/listings/ch20-web-server/listing-20-19/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-19/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-19/src/main.rs b/listings/ch20-web-server/listing-20-19/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/listing-20-19/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/listing-20-20/Cargo.toml b/listings/ch20-web-server/listing-20-20/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-20/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-20/src/main.rs b/listings/ch20-web-server/listing-20-20/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/listing-20-20/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/listing-20-21/Cargo.toml b/listings/ch20-web-server/listing-20-21/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-21/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-21/src/main.rs b/listings/ch20-web-server/listing-20-21/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/listing-20-21/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/listing-20-22/Cargo.toml b/listings/ch20-web-server/listing-20-22/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-22/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-22/src/main.rs b/listings/ch20-web-server/listing-20-22/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/listing-20-22/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/listing-20-23/Cargo.toml b/listings/ch20-web-server/listing-20-23/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-23/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-24/Cargo.toml b/listings/ch20-web-server/listing-20-24/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-24/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-25/Cargo.toml b/listings/ch20-web-server/listing-20-25/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/listing-20-25/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/listing-20-25/src/main.rs b/listings/ch20-web-server/listing-20-25/src/main.rs deleted file mode 100644 index a649ff1031..0000000000 --- a/listings/ch20-web-server/listing-20-25/src/main.rs +++ /dev/null @@ -1,53 +0,0 @@ -use hello::ThreadPool; -use std::fs; -use std::io::prelude::*; -use std::net::TcpListener; -use std::net::TcpStream; -use std::thread; -use std::time::Duration; - -// ANCHOR: here -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming().take(2) { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } - - println!("Shutting down."); -} -// ANCHOR_END: here - -fn handle_connection(mut stream: TcpStream) { - let mut buffer = [0; 1024]; - stream.read(&mut buffer).unwrap(); - - let get = b"GET / HTTP/1.1\r\n"; - let sleep = b"GET /sleep HTTP/1.1\r\n"; - - let (status_line, filename) = if buffer.starts_with(get) { - ("HTTP/1.1 200 OK", "hello.html") - } else if buffer.starts_with(sleep) { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } else { - ("HTTP/1.1 404 NOT FOUND", "404.html") - }; - - let contents = fs::read_to_string(filename).unwrap(); - - let response = format!( - "{}\r\nContent-Length: {}\r\n\r\n{}", - status_line, - contents.len(), - contents - ); - - stream.write_all(response.as_bytes()).unwrap(); - stream.flush().unwrap(); -} diff --git a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/Cargo.toml b/listings/ch20-web-server/no-listing-01-define-threadpool-struct/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/Cargo.toml b/listings/ch20-web-server/no-listing-02-impl-threadpool-new/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/src/main.rs b/listings/ch20-web-server/no-listing-02-impl-threadpool-new/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/no-listing-03-define-execute/Cargo.toml b/listings/ch20-web-server/no-listing-03-define-execute/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/no-listing-03-define-execute/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/no-listing-03-define-execute/output.txt b/listings/ch20-web-server/no-listing-03-define-execute/output.txt deleted file mode 100644 index dc76c43d6f..0000000000 --- a/listings/ch20-web-server/no-listing-03-define-execute/output.txt +++ /dev/null @@ -1,3 +0,0 @@ -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) - Finished dev [unoptimized + debuginfo] target(s) in 0.24s diff --git a/listings/ch20-web-server/no-listing-03-define-execute/src/main.rs b/listings/ch20-web-server/no-listing-03-define-execute/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/no-listing-03-define-execute/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/no-listing-04-update-worker-definition/Cargo.toml b/listings/ch20-web-server/no-listing-04-update-worker-definition/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/no-listing-04-update-worker-definition/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/no-listing-04-update-worker-definition/output.txt b/listings/ch20-web-server/no-listing-04-update-worker-definition/output.txt deleted file mode 100644 index fec2377dc2..0000000000 --- a/listings/ch20-web-server/no-listing-04-update-worker-definition/output.txt +++ /dev/null @@ -1,31 +0,0 @@ -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) -error[E0599]: no method named `join` found for enum `Option` in the current scope - --> src/lib.rs:52:27 - | -52 | worker.thread.join().unwrap(); - | ^^^^ method not found in `Option>` - | -note: the method `join` exists on the type `JoinHandle<()>` - --> /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/std/src/thread/mod.rs:1581:5 -help: consider using `Option::expect` to unwrap the `JoinHandle<()>` value, panicking if the value is an `Option::None` - | -52 | worker.thread.expect("REASON").join().unwrap(); - | +++++++++++++++++ - -error[E0308]: mismatched types - --> src/lib.rs:72:22 - | -72 | Worker { id, thread } - | ^^^^^^ expected enum `Option`, found struct `JoinHandle` - | - = note: expected enum `Option>` - found struct `JoinHandle<_>` -help: try wrapping the expression in `Some` - | -72 | Worker { id, thread: Some(thread) } - | +++++++++++++ + - -Some errors have detailed explanations: E0308, E0599. -For more information about an error, try `rustc --explain E0308`. -error: could not compile `hello` due to 2 previous errors diff --git a/listings/ch20-web-server/no-listing-04-update-worker-definition/src/main.rs b/listings/ch20-web-server/no-listing-04-update-worker-definition/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/no-listing-04-update-worker-definition/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/no-listing-05-fix-worker-new/Cargo.toml b/listings/ch20-web-server/no-listing-05-fix-worker-new/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/no-listing-05-fix-worker-new/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/no-listing-05-fix-worker-new/src/main.rs b/listings/ch20-web-server/no-listing-05-fix-worker-new/src/main.rs deleted file mode 100644 index 79efb28a2a..0000000000 --- a/listings/ch20-web-server/no-listing-05-fix-worker-new/src/main.rs +++ /dev/null @@ -1,43 +0,0 @@ -use hello::ThreadPool; -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming() { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } -} - -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let request_line = buf_reader.lines().next().unwrap().unwrap(); - - let (status_line, filename) = match &request_line[..] { - "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } - _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; - - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); - - let response = - format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); - - stream.write_all(response.as_bytes()).unwrap(); -} diff --git a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/Cargo.toml b/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/no-listing-07-final-code/Cargo.toml b/listings/ch20-web-server/no-listing-07-final-code/Cargo.toml deleted file mode 100644 index fe619478a6..0000000000 --- a/listings/ch20-web-server/no-listing-07-final-code/Cargo.toml +++ /dev/null @@ -1,6 +0,0 @@ -[package] -name = "hello" -version = "0.1.0" -edition = "2021" - -[dependencies] diff --git a/listings/ch20-web-server/no-listing-07-final-code/src/main.rs b/listings/ch20-web-server/no-listing-07-final-code/src/main.rs deleted file mode 100644 index 3161c2ee5c..0000000000 --- a/listings/ch20-web-server/no-listing-07-final-code/src/main.rs +++ /dev/null @@ -1,51 +0,0 @@ -use hello::ThreadPool; -use std::fs; -use std::io::prelude::*; -use std::net::TcpListener; -use std::net::TcpStream; -use std::thread; -use std::time::Duration; - -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); - - for stream in listener.incoming().take(2) { - let stream = stream.unwrap(); - - pool.execute(|| { - handle_connection(stream); - }); - } - - println!("Shutting down."); -} - -fn handle_connection(mut stream: TcpStream) { - let mut buffer = [0; 1024]; - stream.read(&mut buffer).unwrap(); - - let get = b"GET / HTTP/1.1\r\n"; - let sleep = b"GET /sleep HTTP/1.1\r\n"; - - let (status_line, filename) = if buffer.starts_with(get) { - ("HTTP/1.1 200 OK", "hello.html") - } else if buffer.starts_with(sleep) { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") - } else { - ("HTTP/1.1 404 NOT FOUND", "404.html") - }; - - let contents = fs::read_to_string(filename).unwrap(); - - let response = format!( - "{}\r\nContent-Length: {}\r\n\r\n{}", - status_line, - contents.len(), - contents - ); - - stream.write_all(response.as_bytes()).unwrap(); - stream.flush().unwrap(); -} diff --git a/listings/ch20-web-server/listing-20-01/Cargo.lock b/listings/ch21-web-server/listing-21-01/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-01/Cargo.lock rename to listings/ch21-web-server/listing-21-01/Cargo.lock diff --git a/listings/ch20-web-server/listing-20-01/Cargo.toml b/listings/ch21-web-server/listing-21-01/Cargo.toml similarity index 77% rename from listings/ch20-web-server/listing-20-01/Cargo.toml rename to listings/ch21-web-server/listing-21-01/Cargo.toml index fe619478a6..f6f3649e20 100644 --- a/listings/ch20-web-server/listing-20-01/Cargo.toml +++ b/listings/ch21-web-server/listing-21-01/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch20-web-server/listing-20-01/src/main.rs b/listings/ch21-web-server/listing-21-01/src/main.rs similarity index 100% rename from listings/ch20-web-server/listing-20-01/src/main.rs rename to listings/ch21-web-server/listing-21-01/src/main.rs diff --git a/listings/ch20-web-server/listing-20-02/Cargo.lock b/listings/ch21-web-server/listing-21-02/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-02/Cargo.lock rename to listings/ch21-web-server/listing-21-02/Cargo.lock diff --git a/listings/ch20-web-server/listing-20-02/Cargo.toml b/listings/ch21-web-server/listing-21-02/Cargo.toml similarity index 77% rename from listings/ch20-web-server/listing-20-02/Cargo.toml rename to listings/ch21-web-server/listing-21-02/Cargo.toml index fe619478a6..f6f3649e20 100644 --- a/listings/ch20-web-server/listing-20-02/Cargo.toml +++ b/listings/ch21-web-server/listing-21-02/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch20-web-server/listing-20-02/src/main.rs b/listings/ch21-web-server/listing-21-02/src/main.rs similarity index 78% rename from listings/ch20-web-server/listing-20-02/src/main.rs rename to listings/ch21-web-server/listing-21-02/src/main.rs index 7240c73c7f..fe31142615 100644 --- a/listings/ch20-web-server/listing-20-02/src/main.rs +++ b/listings/ch21-web-server/listing-21-02/src/main.rs @@ -1,5 +1,5 @@ use std::{ - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, }; @@ -14,12 +14,12 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let http_request: Vec<_> = buf_reader .lines() .map(|result| result.unwrap()) .take_while(|line| !line.is_empty()) .collect(); - println!("Request: {:#?}", http_request); + println!("Request: {http_request:#?}"); } diff --git a/listings/ch20-web-server/listing-20-03/Cargo.lock b/listings/ch21-web-server/listing-21-03/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-03/Cargo.lock rename to listings/ch21-web-server/listing-21-03/Cargo.lock diff --git a/listings/ch20-web-server/listing-20-03/Cargo.toml b/listings/ch21-web-server/listing-21-03/Cargo.toml similarity index 77% rename from listings/ch20-web-server/listing-20-03/Cargo.toml rename to listings/ch21-web-server/listing-21-03/Cargo.toml index fe619478a6..f6f3649e20 100644 --- a/listings/ch20-web-server/listing-20-03/Cargo.toml +++ b/listings/ch21-web-server/listing-21-03/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch20-web-server/listing-20-03/src/main.rs b/listings/ch21-web-server/listing-21-03/src/main.rs similarity index 87% rename from listings/ch20-web-server/listing-20-03/src/main.rs rename to listings/ch21-web-server/listing-21-03/src/main.rs index c72d4a9c67..52e586ac64 100644 --- a/listings/ch20-web-server/listing-20-03/src/main.rs +++ b/listings/ch21-web-server/listing-21-03/src/main.rs @@ -1,5 +1,5 @@ use std::{ - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, }; @@ -15,7 +15,7 @@ fn main() { // ANCHOR: here fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let http_request: Vec<_> = buf_reader .lines() .map(|result| result.unwrap()) diff --git a/listings/ch20-web-server/listing-20-05/Cargo.lock b/listings/ch21-web-server/listing-21-05/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-05/Cargo.lock rename to listings/ch21-web-server/listing-21-05/Cargo.lock diff --git a/listings/ch20-web-server/listing-20-05/Cargo.toml b/listings/ch21-web-server/listing-21-05/Cargo.toml similarity index 77% rename from listings/ch20-web-server/listing-20-05/Cargo.toml rename to listings/ch21-web-server/listing-21-05/Cargo.toml index fe619478a6..f6f3649e20 100644 --- a/listings/ch20-web-server/listing-20-05/Cargo.toml +++ b/listings/ch21-web-server/listing-21-05/Cargo.toml @@ -1,6 +1,6 @@ [package] name = "hello" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] diff --git a/listings/ch20-web-server/listing-20-05/hello.html b/listings/ch21-web-server/listing-21-05/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-05/hello.html rename to listings/ch21-web-server/listing-21-05/hello.html diff --git a/listings/ch20-web-server/listing-20-05/src/main.rs b/listings/ch21-web-server/listing-21-05/src/main.rs similarity index 91% rename from listings/ch20-web-server/listing-20-05/src/main.rs rename to listings/ch21-web-server/listing-21-05/src/main.rs index d4b78b640e..25fc312d54 100644 --- a/listings/ch20-web-server/listing-20-05/src/main.rs +++ b/listings/ch21-web-server/listing-21-05/src/main.rs @@ -1,7 +1,7 @@ // ANCHOR: here use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, }; // --snip-- @@ -19,7 +19,7 @@ fn main() { // ANCHOR: here fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let http_request: Vec<_> = buf_reader .lines() .map(|result| result.unwrap()) diff --git a/listings/ch20-web-server/listing-20-06/Cargo.lock b/listings/ch21-web-server/listing-21-06/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-06/Cargo.lock rename to listings/ch21-web-server/listing-21-06/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-06/Cargo.toml b/listings/ch21-web-server/listing-21-06/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-06/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-06/hello.html b/listings/ch21-web-server/listing-21-06/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-06/hello.html rename to listings/ch21-web-server/listing-21-06/hello.html diff --git a/listings/ch20-web-server/listing-20-06/src/main.rs b/listings/ch21-web-server/listing-21-06/src/main.rs similarity index 90% rename from listings/ch20-web-server/listing-20-06/src/main.rs rename to listings/ch21-web-server/listing-21-06/src/main.rs index 5523a42d7c..2b26aef4e5 100644 --- a/listings/ch20-web-server/listing-20-06/src/main.rs +++ b/listings/ch21-web-server/listing-21-06/src/main.rs @@ -1,6 +1,6 @@ use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, }; @@ -17,7 +17,7 @@ fn main() { // --snip-- fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); if request_line == "GET / HTTP/1.1" { diff --git a/listings/ch20-web-server/listing-20-07/404.html b/listings/ch21-web-server/listing-21-07/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-07/404.html rename to listings/ch21-web-server/listing-21-07/404.html diff --git a/listings/ch20-web-server/listing-20-07/Cargo.lock b/listings/ch21-web-server/listing-21-07/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-07/Cargo.lock rename to listings/ch21-web-server/listing-21-07/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-07/Cargo.toml b/listings/ch21-web-server/listing-21-07/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-07/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-07/hello.html b/listings/ch21-web-server/listing-21-07/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-07/hello.html rename to listings/ch21-web-server/listing-21-07/hello.html diff --git a/listings/ch20-web-server/listing-20-07/src/main.rs b/listings/ch21-web-server/listing-21-07/src/main.rs similarity index 93% rename from listings/ch20-web-server/listing-20-07/src/main.rs rename to listings/ch21-web-server/listing-21-07/src/main.rs index a14b7d538c..137ecd9eaf 100644 --- a/listings/ch20-web-server/listing-20-07/src/main.rs +++ b/listings/ch21-web-server/listing-21-07/src/main.rs @@ -1,6 +1,6 @@ use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, }; @@ -15,7 +15,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); if request_line == "GET / HTTP/1.1" { diff --git a/listings/ch20-web-server/listing-20-09/404.html b/listings/ch21-web-server/listing-21-09/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-09/404.html rename to listings/ch21-web-server/listing-21-09/404.html diff --git a/listings/ch20-web-server/listing-20-09/Cargo.lock b/listings/ch21-web-server/listing-21-09/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-09/Cargo.lock rename to listings/ch21-web-server/listing-21-09/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-09/Cargo.toml b/listings/ch21-web-server/listing-21-09/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-09/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-09/hello.html b/listings/ch21-web-server/listing-21-09/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-09/hello.html rename to listings/ch21-web-server/listing-21-09/hello.html diff --git a/listings/ch20-web-server/listing-20-09/src/main.rs b/listings/ch21-web-server/listing-21-09/src/main.rs similarity index 91% rename from listings/ch20-web-server/listing-20-09/src/main.rs rename to listings/ch21-web-server/listing-21-09/src/main.rs index ffc51e803e..001491de6f 100644 --- a/listings/ch20-web-server/listing-20-09/src/main.rs +++ b/listings/ch21-web-server/listing-21-09/src/main.rs @@ -1,6 +1,6 @@ use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, }; @@ -19,7 +19,7 @@ fn main() { fn handle_connection(mut stream: TcpStream) { // --snip-- // ANCHOR_END: here - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); // ANCHOR: here diff --git a/listings/ch20-web-server/listing-20-10/404.html b/listings/ch21-web-server/listing-21-10/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-10/404.html rename to listings/ch21-web-server/listing-21-10/404.html diff --git a/listings/ch20-web-server/listing-20-10/Cargo.lock b/listings/ch21-web-server/listing-21-10/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-10/Cargo.lock rename to listings/ch21-web-server/listing-21-10/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-10/Cargo.toml b/listings/ch21-web-server/listing-21-10/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-10/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-10/hello.html b/listings/ch21-web-server/listing-21-10/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-10/hello.html rename to listings/ch21-web-server/listing-21-10/hello.html diff --git a/listings/ch20-web-server/listing-20-10/src/main.rs b/listings/ch21-web-server/listing-21-10/src/main.rs similarity index 93% rename from listings/ch20-web-server/listing-20-10/src/main.rs rename to listings/ch21-web-server/listing-21-10/src/main.rs index 5a18b45c02..81b36562af 100644 --- a/listings/ch20-web-server/listing-20-10/src/main.rs +++ b/listings/ch21-web-server/listing-21-10/src/main.rs @@ -1,7 +1,7 @@ // ANCHOR: here use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -24,7 +24,7 @@ fn handle_connection(mut stream: TcpStream) { // --snip-- // ANCHOR_END: here - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); // ANCHOR: here diff --git a/listings/ch20-web-server/listing-20-11/404.html b/listings/ch21-web-server/listing-21-11/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-11/404.html rename to listings/ch21-web-server/listing-21-11/404.html diff --git a/listings/ch20-web-server/listing-20-11/Cargo.lock b/listings/ch21-web-server/listing-21-11/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-11/Cargo.lock rename to listings/ch21-web-server/listing-21-11/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-11/Cargo.toml b/listings/ch21-web-server/listing-21-11/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-11/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-11/hello.html b/listings/ch21-web-server/listing-21-11/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-11/hello.html rename to listings/ch21-web-server/listing-21-11/hello.html diff --git a/listings/ch20-web-server/listing-20-11/src/main.rs b/listings/ch21-web-server/listing-21-11/src/main.rs similarity index 92% rename from listings/ch20-web-server/listing-20-11/src/main.rs rename to listings/ch21-web-server/listing-21-11/src/main.rs index 1181357b0e..dd3c52b3fd 100644 --- a/listings/ch20-web-server/listing-20-11/src/main.rs +++ b/listings/ch21-web-server/listing-21-11/src/main.rs @@ -1,6 +1,6 @@ use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -21,7 +21,7 @@ fn main() { // ANCHOR_END: here fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-12/404.html b/listings/ch21-web-server/listing-21-12/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-12/404.html rename to listings/ch21-web-server/listing-21-12/404.html diff --git a/listings/ch20-web-server/listing-20-12/Cargo.lock b/listings/ch21-web-server/listing-21-12/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-12/Cargo.lock rename to listings/ch21-web-server/listing-21-12/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-12/Cargo.toml b/listings/ch21-web-server/listing-21-12/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-12/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-12/hello.html b/listings/ch21-web-server/listing-21-12/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-12/hello.html rename to listings/ch21-web-server/listing-21-12/hello.html diff --git a/listings/ch20-web-server/listing-20-12/output.txt b/listings/ch21-web-server/listing-21-12/output.txt similarity index 82% rename from listings/ch20-web-server/listing-20-12/output.txt rename to listings/ch21-web-server/listing-21-12/output.txt index 57a58b960e..0faae99204 100644 --- a/listings/ch20-web-server/listing-20-12/output.txt +++ b/listings/ch21-web-server/listing-21-12/output.txt @@ -7,4 +7,4 @@ error[E0433]: failed to resolve: use of undeclared type `ThreadPool` | ^^^^^^^^^^ use of undeclared type `ThreadPool` For more information about this error, try `rustc --explain E0433`. -error: could not compile `hello` due to previous error +error: could not compile `hello` (bin "hello") due to 1 previous error diff --git a/listings/ch20-web-server/listing-20-12/src/main.rs b/listings/ch21-web-server/listing-21-12/src/main.rs similarity index 92% rename from listings/ch20-web-server/listing-20-12/src/main.rs rename to listings/ch21-web-server/listing-21-12/src/main.rs index 21b9a80f10..fb0678f032 100644 --- a/listings/ch20-web-server/listing-20-12/src/main.rs +++ b/listings/ch21-web-server/listing-21-12/src/main.rs @@ -1,6 +1,6 @@ use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -22,7 +22,7 @@ fn main() { // ANCHOR_END: here fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-13/404.html b/listings/ch21-web-server/listing-21-13/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-13/404.html rename to listings/ch21-web-server/listing-21-13/404.html diff --git a/listings/ch20-web-server/listing-20-13/Cargo.lock b/listings/ch21-web-server/listing-21-13/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-13/Cargo.lock rename to listings/ch21-web-server/listing-21-13/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-13/Cargo.toml b/listings/ch21-web-server/listing-21-13/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-13/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-13/hello.html b/listings/ch21-web-server/listing-21-13/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-13/hello.html rename to listings/ch21-web-server/listing-21-13/hello.html diff --git a/listings/ch20-web-server/listing-20-13/src/lib.rs b/listings/ch21-web-server/listing-21-13/src/lib.rs similarity index 100% rename from listings/ch20-web-server/listing-20-13/src/lib.rs rename to listings/ch21-web-server/listing-21-13/src/lib.rs diff --git a/listings/ch20-web-server/listing-20-16/src/main.rs b/listings/ch21-web-server/listing-21-13/src/main.rs similarity index 92% rename from listings/ch20-web-server/listing-20-16/src/main.rs rename to listings/ch21-web-server/listing-21-13/src/main.rs index 79efb28a2a..ca3608da70 100644 --- a/listings/ch20-web-server/listing-20-16/src/main.rs +++ b/listings/ch21-web-server/listing-21-13/src/main.rs @@ -1,7 +1,7 @@ use hello::ThreadPool; use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -21,7 +21,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-14/404.html b/listings/ch21-web-server/listing-21-14/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-14/404.html rename to listings/ch21-web-server/listing-21-14/404.html diff --git a/listings/ch20-web-server/listing-20-14/Cargo.lock b/listings/ch21-web-server/listing-21-14/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-14/Cargo.lock rename to listings/ch21-web-server/listing-21-14/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-14/Cargo.toml b/listings/ch21-web-server/listing-21-14/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-14/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-14/hello.html b/listings/ch21-web-server/listing-21-14/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-14/hello.html rename to listings/ch21-web-server/listing-21-14/hello.html diff --git a/listings/ch20-web-server/listing-20-14/src/lib.rs b/listings/ch21-web-server/listing-21-14/src/lib.rs similarity index 100% rename from listings/ch20-web-server/listing-20-14/src/lib.rs rename to listings/ch21-web-server/listing-21-14/src/lib.rs diff --git a/listings/ch20-web-server/listing-20-15/src/main.rs b/listings/ch21-web-server/listing-21-14/src/main.rs similarity index 92% rename from listings/ch20-web-server/listing-20-15/src/main.rs rename to listings/ch21-web-server/listing-21-14/src/main.rs index 79efb28a2a..ca3608da70 100644 --- a/listings/ch20-web-server/listing-20-15/src/main.rs +++ b/listings/ch21-web-server/listing-21-14/src/main.rs @@ -1,7 +1,7 @@ use hello::ThreadPool; use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -21,7 +21,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-15/404.html b/listings/ch21-web-server/listing-21-15/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-15/404.html rename to listings/ch21-web-server/listing-21-15/404.html diff --git a/listings/ch20-web-server/listing-20-15/Cargo.lock b/listings/ch21-web-server/listing-21-15/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-15/Cargo.lock rename to listings/ch21-web-server/listing-21-15/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-15/Cargo.toml b/listings/ch21-web-server/listing-21-15/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-15/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-15/hello.html b/listings/ch21-web-server/listing-21-15/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-15/hello.html rename to listings/ch21-web-server/listing-21-15/hello.html diff --git a/listings/ch20-web-server/listing-20-15/src/lib.rs b/listings/ch21-web-server/listing-21-15/src/lib.rs similarity index 100% rename from listings/ch20-web-server/listing-20-15/src/lib.rs rename to listings/ch21-web-server/listing-21-15/src/lib.rs diff --git a/listings/ch20-web-server/listing-20-14/src/main.rs b/listings/ch21-web-server/listing-21-15/src/main.rs similarity index 92% rename from listings/ch20-web-server/listing-20-14/src/main.rs rename to listings/ch21-web-server/listing-21-15/src/main.rs index 79efb28a2a..ca3608da70 100644 --- a/listings/ch20-web-server/listing-20-14/src/main.rs +++ b/listings/ch21-web-server/listing-21-15/src/main.rs @@ -1,7 +1,7 @@ use hello::ThreadPool; use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -21,7 +21,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-16/404.html b/listings/ch21-web-server/listing-21-16/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-16/404.html rename to listings/ch21-web-server/listing-21-16/404.html diff --git a/listings/ch20-web-server/listing-20-16/Cargo.lock b/listings/ch21-web-server/listing-21-16/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-16/Cargo.lock rename to listings/ch21-web-server/listing-21-16/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-16/Cargo.toml b/listings/ch21-web-server/listing-21-16/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-16/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-16/hello.html b/listings/ch21-web-server/listing-21-16/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-16/hello.html rename to listings/ch21-web-server/listing-21-16/hello.html diff --git a/listings/ch20-web-server/listing-20-16/src/lib.rs b/listings/ch21-web-server/listing-21-16/src/lib.rs similarity index 100% rename from listings/ch20-web-server/listing-20-16/src/lib.rs rename to listings/ch21-web-server/listing-21-16/src/lib.rs diff --git a/listings/ch20-web-server/listing-20-13/src/main.rs b/listings/ch21-web-server/listing-21-16/src/main.rs similarity index 92% rename from listings/ch20-web-server/listing-20-13/src/main.rs rename to listings/ch21-web-server/listing-21-16/src/main.rs index 79efb28a2a..ca3608da70 100644 --- a/listings/ch20-web-server/listing-20-13/src/main.rs +++ b/listings/ch21-web-server/listing-21-16/src/main.rs @@ -1,7 +1,7 @@ use hello::ThreadPool; use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -21,7 +21,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-17/404.html b/listings/ch21-web-server/listing-21-17/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-17/404.html rename to listings/ch21-web-server/listing-21-17/404.html diff --git a/listings/ch20-web-server/listing-20-17/Cargo.lock b/listings/ch21-web-server/listing-21-17/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-17/Cargo.lock rename to listings/ch21-web-server/listing-21-17/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-17/Cargo.toml b/listings/ch21-web-server/listing-21-17/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-17/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-17/hello.html b/listings/ch21-web-server/listing-21-17/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-17/hello.html rename to listings/ch21-web-server/listing-21-17/hello.html diff --git a/listings/ch21-web-server/listing-21-17/output.txt b/listings/ch21-web-server/listing-21-17/output.txt new file mode 100644 index 0000000000..2768265514 --- /dev/null +++ b/listings/ch21-web-server/listing-21-17/output.txt @@ -0,0 +1,27 @@ +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) +error[E0382]: use of moved value: `receiver` + --> src/lib.rs:26:42 + | +21 | let (sender, receiver) = mpsc::channel(); + | -------- move occurs because `receiver` has type `std::sync::mpsc::Receiver`, which does not implement the `Copy` trait +... +25 | for id in 0..size { + | ----------------- inside of this loop +26 | workers.push(Worker::new(id, receiver)); + | ^^^^^^^^ value moved here, in previous iteration of loop + | +note: consider changing this parameter type in method `new` to borrow instead if owning the value isn't necessary + --> src/lib.rs:47:33 + | +47 | fn new(id: usize, receiver: mpsc::Receiver) -> Worker { + | --- in this method ^^^^^^^^^^^^^^^^^^^ this parameter takes ownership of the value +help: consider moving the expression out of the loop so it is only moved once + | +25 ~ let mut value = Worker::new(id, receiver); +26 ~ for id in 0..size { +27 ~ workers.push(value); + | + +For more information about this error, try `rustc --explain E0382`. +error: could not compile `hello` (lib) due to 1 previous error diff --git a/listings/ch20-web-server/listing-20-17/src/lib.rs b/listings/ch21-web-server/listing-21-17/src/lib.rs similarity index 100% rename from listings/ch20-web-server/listing-20-17/src/lib.rs rename to listings/ch21-web-server/listing-21-17/src/lib.rs diff --git a/listings/ch21-web-server/listing-21-17/src/main.rs b/listings/ch21-web-server/listing-21-17/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/listing-21-17/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/listing-20-18/404.html b/listings/ch21-web-server/listing-21-18/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-18/404.html rename to listings/ch21-web-server/listing-21-18/404.html diff --git a/listings/ch20-web-server/listing-20-18/Cargo.lock b/listings/ch21-web-server/listing-21-18/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-18/Cargo.lock rename to listings/ch21-web-server/listing-21-18/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-18/Cargo.toml b/listings/ch21-web-server/listing-21-18/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-18/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-18/hello.html b/listings/ch21-web-server/listing-21-18/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-18/hello.html rename to listings/ch21-web-server/listing-21-18/hello.html diff --git a/listings/ch20-web-server/listing-20-18/src/lib.rs b/listings/ch21-web-server/listing-21-18/src/lib.rs similarity index 97% rename from listings/ch20-web-server/listing-20-18/src/lib.rs rename to listings/ch21-web-server/listing-21-18/src/lib.rs index 4bff8acada..7df8ed35a5 100644 --- a/listings/ch20-web-server/listing-20-18/src/lib.rs +++ b/listings/ch21-web-server/listing-21-18/src/lib.rs @@ -1,6 +1,6 @@ // ANCHOR: here use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; // --snip-- diff --git a/listings/ch21-web-server/listing-21-18/src/main.rs b/listings/ch21-web-server/listing-21-18/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/listing-21-18/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/listing-20-19/404.html b/listings/ch21-web-server/listing-21-19/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-19/404.html rename to listings/ch21-web-server/listing-21-19/404.html diff --git a/listings/ch20-web-server/listing-20-19/Cargo.lock b/listings/ch21-web-server/listing-21-19/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-19/Cargo.lock rename to listings/ch21-web-server/listing-21-19/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-19/Cargo.toml b/listings/ch21-web-server/listing-21-19/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-19/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-19/hello.html b/listings/ch21-web-server/listing-21-19/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-19/hello.html rename to listings/ch21-web-server/listing-21-19/hello.html diff --git a/listings/ch20-web-server/listing-20-19/src/lib.rs b/listings/ch21-web-server/listing-21-19/src/lib.rs similarity index 97% rename from listings/ch20-web-server/listing-20-19/src/lib.rs rename to listings/ch21-web-server/listing-21-19/src/lib.rs index aeb1facd64..c240becf15 100644 --- a/listings/ch20-web-server/listing-20-19/src/lib.rs +++ b/listings/ch21-web-server/listing-21-19/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; diff --git a/listings/ch21-web-server/listing-21-19/src/main.rs b/listings/ch21-web-server/listing-21-19/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/listing-21-19/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/listing-20-20/404.html b/listings/ch21-web-server/listing-21-20/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-20/404.html rename to listings/ch21-web-server/listing-21-20/404.html diff --git a/listings/ch20-web-server/listing-20-20/Cargo.lock b/listings/ch21-web-server/listing-21-20/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-20/Cargo.lock rename to listings/ch21-web-server/listing-21-20/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-20/Cargo.toml b/listings/ch21-web-server/listing-21-20/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-20/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-20/hello.html b/listings/ch21-web-server/listing-21-20/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-20/hello.html rename to listings/ch21-web-server/listing-21-20/hello.html diff --git a/listings/ch20-web-server/listing-20-20/src/lib.rs b/listings/ch21-web-server/listing-21-20/src/lib.rs similarity index 81% rename from listings/ch20-web-server/listing-20-20/src/lib.rs rename to listings/ch21-web-server/listing-21-20/src/lib.rs index 86157c9e71..17540e7bea 100644 --- a/listings/ch20-web-server/listing-20-20/src/lib.rs +++ b/listings/ch21-web-server/listing-21-20/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -54,12 +54,14 @@ struct Worker { impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let job = receiver.lock().unwrap().recv().unwrap(); + let thread = thread::spawn(move || { + loop { + let job = receiver.lock().unwrap().recv().unwrap(); - println!("Worker {id} got a job; executing."); + println!("Worker {id} got a job; executing."); - job(); + job(); + } }); Worker { id, thread } diff --git a/listings/ch21-web-server/listing-21-20/src/main.rs b/listings/ch21-web-server/listing-21-20/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/listing-21-20/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/listing-20-21/404.html b/listings/ch21-web-server/listing-21-21/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-21/404.html rename to listings/ch21-web-server/listing-21-21/404.html diff --git a/listings/ch20-web-server/listing-20-21/Cargo.lock b/listings/ch21-web-server/listing-21-21/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-21/Cargo.lock rename to listings/ch21-web-server/listing-21-21/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-21/Cargo.toml b/listings/ch21-web-server/listing-21-21/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-21/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-21/hello.html b/listings/ch21-web-server/listing-21-21/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-21/hello.html rename to listings/ch21-web-server/listing-21-21/hello.html diff --git a/listings/ch20-web-server/listing-20-21/src/lib.rs b/listings/ch21-web-server/listing-21-21/src/lib.rs similarity index 97% rename from listings/ch20-web-server/listing-20-21/src/lib.rs rename to listings/ch21-web-server/listing-21-21/src/lib.rs index 17b37e77be..be899feec1 100644 --- a/listings/ch20-web-server/listing-20-21/src/lib.rs +++ b/listings/ch21-web-server/listing-21-21/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; diff --git a/listings/ch21-web-server/listing-21-21/src/main.rs b/listings/ch21-web-server/listing-21-21/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/listing-21-21/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/listing-20-22/404.html b/listings/ch21-web-server/listing-21-22/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-22/404.html rename to listings/ch21-web-server/listing-21-22/404.html diff --git a/listings/ch20-web-server/listing-20-22/Cargo.lock b/listings/ch21-web-server/listing-21-22/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-22/Cargo.lock rename to listings/ch21-web-server/listing-21-22/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-22/Cargo.toml b/listings/ch21-web-server/listing-21-22/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-22/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-22/hello.html b/listings/ch21-web-server/listing-21-22/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-22/hello.html rename to listings/ch21-web-server/listing-21-22/hello.html diff --git a/listings/ch20-web-server/listing-20-22/output.txt b/listings/ch21-web-server/listing-21-22/output.txt similarity index 67% rename from listings/ch20-web-server/listing-20-22/output.txt rename to listings/ch21-web-server/listing-21-22/output.txt index 342bf9a16d..6e6b2e639b 100644 --- a/listings/ch20-web-server/listing-20-22/output.txt +++ b/listings/ch21-web-server/listing-21-22/output.txt @@ -8,8 +8,8 @@ error[E0507]: cannot move out of `worker.thread` which is behind a mutable refer | | | move occurs because `worker.thread` has type `JoinHandle<()>`, which does not implement the `Copy` trait | -note: this function takes ownership of the receiver `self`, which moves `worker.thread` - --> /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library/std/src/thread/mod.rs:1581:17 +note: `JoinHandle::::join` takes ownership of the receiver `self`, which moves `worker.thread` + --> /rustc/1159e78c4747b02ef996e55082b704c09b970588/library/std/src/thread/mod.rs:1921:17 For more information about this error, try `rustc --explain E0507`. -error: could not compile `hello` due to previous error +error: could not compile `hello` (lib) due to 1 previous error diff --git a/listings/ch20-web-server/listing-20-22/src/lib.rs b/listings/ch21-web-server/listing-21-22/src/lib.rs similarity index 84% rename from listings/ch20-web-server/listing-20-22/src/lib.rs rename to listings/ch21-web-server/listing-21-22/src/lib.rs index 72a8c48088..7c7eb6e14a 100644 --- a/listings/ch20-web-server/listing-20-22/src/lib.rs +++ b/listings/ch21-web-server/listing-21-22/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -63,12 +63,14 @@ struct Worker { impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let job = receiver.lock().unwrap().recv().unwrap(); + let thread = thread::spawn(move || { + loop { + let job = receiver.lock().unwrap().recv().unwrap(); - println!("Worker {id} got a job; executing."); + println!("Worker {id} got a job; executing."); - job(); + job(); + } }); Worker { id, thread } diff --git a/listings/ch21-web-server/listing-21-22/src/main.rs b/listings/ch21-web-server/listing-21-22/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/listing-21-22/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/listing-20-23/404.html b/listings/ch21-web-server/listing-21-23/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-23/404.html rename to listings/ch21-web-server/listing-21-23/404.html diff --git a/listings/ch20-web-server/listing-20-23/Cargo.lock b/listings/ch21-web-server/listing-21-23/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-23/Cargo.lock rename to listings/ch21-web-server/listing-21-23/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-23/Cargo.toml b/listings/ch21-web-server/listing-21-23/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-23/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-23/hello.html b/listings/ch21-web-server/listing-21-23/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-23/hello.html rename to listings/ch21-web-server/listing-21-23/hello.html diff --git a/listings/ch20-web-server/listing-20-23/src/lib.rs b/listings/ch21-web-server/listing-21-23/src/lib.rs similarity index 75% rename from listings/ch20-web-server/listing-20-23/src/lib.rs rename to listings/ch21-web-server/listing-21-23/src/lib.rs index eea339b027..a767864339 100644 --- a/listings/ch20-web-server/listing-20-23/src/lib.rs +++ b/listings/ch21-web-server/listing-21-23/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -61,12 +61,10 @@ impl Drop for ThreadPool { fn drop(&mut self) { drop(self.sender.take()); - for worker in &mut self.workers { + for worker in self.workers.drain(..) { println!("Shutting down worker {}", worker.id); - if let Some(thread) = worker.thread.take() { - thread.join().unwrap(); - } + worker.thread.join().unwrap(); } } } @@ -74,22 +72,21 @@ impl Drop for ThreadPool { struct Worker { id: usize, - thread: Option>, + thread: thread::JoinHandle<()>, } impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let job = receiver.lock().unwrap().recv().unwrap(); + let thread = thread::spawn(move || { + loop { + let job = receiver.lock().unwrap().recv().unwrap(); - println!("Worker {id} got a job; executing."); + println!("Worker {id} got a job; executing."); - job(); + job(); + } }); - Worker { - id, - thread: Some(thread), - } + Worker { id, thread } } } diff --git a/listings/ch20-web-server/listing-20-23/src/main.rs b/listings/ch21-web-server/listing-21-23/src/main.rs similarity index 93% rename from listings/ch20-web-server/listing-20-23/src/main.rs rename to listings/ch21-web-server/listing-21-23/src/main.rs index b6aa046d1b..f68c11e0b2 100644 --- a/listings/ch20-web-server/listing-20-23/src/main.rs +++ b/listings/ch21-web-server/listing-21-23/src/main.rs @@ -1,7 +1,7 @@ use hello::ThreadPool; use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -23,7 +23,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-24/404.html b/listings/ch21-web-server/listing-21-24/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-24/404.html rename to listings/ch21-web-server/listing-21-24/404.html diff --git a/listings/ch20-web-server/listing-20-24/Cargo.lock b/listings/ch21-web-server/listing-21-24/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-24/Cargo.lock rename to listings/ch21-web-server/listing-21-24/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-24/Cargo.toml b/listings/ch21-web-server/listing-21-24/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-24/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-24/hello.html b/listings/ch21-web-server/listing-21-24/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-24/hello.html rename to listings/ch21-web-server/listing-21-24/hello.html diff --git a/listings/ch20-web-server/listing-20-24/src/lib.rs b/listings/ch21-web-server/listing-21-24/src/lib.rs similarity index 65% rename from listings/ch20-web-server/listing-20-24/src/lib.rs rename to listings/ch21-web-server/listing-21-24/src/lib.rs index 28c0dea262..cef880db14 100644 --- a/listings/ch20-web-server/listing-20-24/src/lib.rs +++ b/listings/ch21-web-server/listing-21-24/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -51,44 +51,41 @@ impl Drop for ThreadPool { fn drop(&mut self) { drop(self.sender.take()); - for worker in &mut self.workers { + for worker in self.workers.drain(..) { println!("Shutting down worker {}", worker.id); - if let Some(thread) = worker.thread.take() { - thread.join().unwrap(); - } + worker.thread.join().unwrap(); } } } struct Worker { id: usize, - thread: Option>, + thread: thread::JoinHandle<()>, } // ANCHOR: here impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let message = receiver.lock().unwrap().recv(); - - match message { - Ok(job) => { - println!("Worker {id} got a job; executing."); - - job(); - } - Err(_) => { - println!("Worker {id} disconnected; shutting down."); - break; + let thread = thread::spawn(move || { + loop { + let message = receiver.lock().unwrap().recv(); + + match message { + Ok(job) => { + println!("Worker {id} got a job; executing."); + + job(); + } + Err(_) => { + println!("Worker {id} disconnected; shutting down."); + break; + } } } }); - Worker { - id, - thread: Some(thread), - } + Worker { id, thread } } } // ANCHOR_END: here diff --git a/listings/ch20-web-server/listing-20-24/src/main.rs b/listings/ch21-web-server/listing-21-24/src/main.rs similarity index 93% rename from listings/ch20-web-server/listing-20-24/src/main.rs rename to listings/ch21-web-server/listing-21-24/src/main.rs index b6aa046d1b..f68c11e0b2 100644 --- a/listings/ch20-web-server/listing-20-24/src/main.rs +++ b/listings/ch21-web-server/listing-21-24/src/main.rs @@ -1,7 +1,7 @@ use hello::ThreadPool; use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -23,7 +23,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/listing-20-25/404.html b/listings/ch21-web-server/listing-21-25/404.html similarity index 100% rename from listings/ch20-web-server/listing-20-25/404.html rename to listings/ch21-web-server/listing-21-25/404.html diff --git a/listings/ch20-web-server/listing-20-25/Cargo.lock b/listings/ch21-web-server/listing-21-25/Cargo.lock similarity index 100% rename from listings/ch20-web-server/listing-20-25/Cargo.lock rename to listings/ch21-web-server/listing-21-25/Cargo.lock diff --git a/listings/ch21-web-server/listing-21-25/Cargo.toml b/listings/ch21-web-server/listing-21-25/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/listing-21-25/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/listing-20-25/hello.html b/listings/ch21-web-server/listing-21-25/hello.html similarity index 100% rename from listings/ch20-web-server/listing-20-25/hello.html rename to listings/ch21-web-server/listing-21-25/hello.html diff --git a/listings/ch20-web-server/listing-20-25/src/lib.rs b/listings/ch21-web-server/listing-21-25/src/lib.rs similarity index 65% rename from listings/ch20-web-server/listing-20-25/src/lib.rs rename to listings/ch21-web-server/listing-21-25/src/lib.rs index 54c0489abf..8db88f20ed 100644 --- a/listings/ch20-web-server/listing-20-25/src/lib.rs +++ b/listings/ch21-web-server/listing-21-25/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -51,42 +51,39 @@ impl Drop for ThreadPool { fn drop(&mut self) { drop(self.sender.take()); - for worker in &mut self.workers { + for worker in self.workers.drain(..) { println!("Shutting down worker {}", worker.id); - if let Some(thread) = worker.thread.take() { - thread.join().unwrap(); - } + worker.thread.join().unwrap(); } } } struct Worker { id: usize, - thread: Option>, + thread: thread::JoinHandle<()>, } impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let message = receiver.lock().unwrap().recv(); - - match message { - Ok(job) => { - println!("Worker {id} got a job; executing."); - - job(); - } - Err(_) => { - println!("Worker {id} disconnected; shutting down."); - break; + let thread = thread::spawn(move || { + loop { + let message = receiver.lock().unwrap().recv(); + + match message { + Ok(job) => { + println!("Worker {id} got a job; executing."); + + job(); + } + Err(_) => { + println!("Worker {id} disconnected; shutting down."); + break; + } } } }); - Worker { - id, - thread: Some(thread), - } + Worker { id, thread } } } diff --git a/listings/ch21-web-server/listing-21-25/src/main.rs b/listings/ch21-web-server/listing-21-25/src/main.rs new file mode 100644 index 0000000000..dabf2e474c --- /dev/null +++ b/listings/ch21-web-server/listing-21-25/src/main.rs @@ -0,0 +1,47 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +// ANCHOR: here +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming().take(2) { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } + + println!("Shutting down."); +} +// ANCHOR_END: here + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/404.html b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/404.html similarity index 100% rename from listings/ch20-web-server/no-listing-01-define-threadpool-struct/404.html rename to listings/ch21-web-server/no-listing-01-define-threadpool-struct/404.html diff --git a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/Cargo.lock b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/Cargo.lock similarity index 100% rename from listings/ch20-web-server/no-listing-01-define-threadpool-struct/Cargo.lock rename to listings/ch21-web-server/no-listing-01-define-threadpool-struct/Cargo.lock diff --git a/listings/ch21-web-server/no-listing-01-define-threadpool-struct/Cargo.toml b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/hello.html b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/hello.html similarity index 100% rename from listings/ch20-web-server/no-listing-01-define-threadpool-struct/hello.html rename to listings/ch21-web-server/no-listing-01-define-threadpool-struct/hello.html diff --git a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/output.txt b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/output.txt similarity index 84% rename from listings/ch20-web-server/no-listing-01-define-threadpool-struct/output.txt rename to listings/ch21-web-server/no-listing-01-define-threadpool-struct/output.txt index fa337b8a80..85ebfb8138 100644 --- a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/output.txt +++ b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/output.txt @@ -7,4 +7,4 @@ error[E0599]: no function or associated item named `new` found for struct `Threa | ^^^ function or associated item not found in `ThreadPool` For more information about this error, try `rustc --explain E0599`. -error: could not compile `hello` due to previous error +error: could not compile `hello` (bin "hello") due to 1 previous error diff --git a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/src/lib.rs b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/src/lib.rs similarity index 100% rename from listings/ch20-web-server/no-listing-01-define-threadpool-struct/src/lib.rs rename to listings/ch21-web-server/no-listing-01-define-threadpool-struct/src/lib.rs diff --git a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/src/main.rs b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/src/main.rs similarity index 93% rename from listings/ch20-web-server/no-listing-01-define-threadpool-struct/src/main.rs rename to listings/ch21-web-server/no-listing-01-define-threadpool-struct/src/main.rs index f7b42167f9..e3c522caef 100644 --- a/listings/ch20-web-server/no-listing-01-define-threadpool-struct/src/main.rs +++ b/listings/ch21-web-server/no-listing-01-define-threadpool-struct/src/main.rs @@ -3,7 +3,7 @@ use hello::ThreadPool; // ANCHOR_END: here use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -23,7 +23,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/404.html b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/404.html similarity index 100% rename from listings/ch20-web-server/no-listing-02-impl-threadpool-new/404.html rename to listings/ch21-web-server/no-listing-02-impl-threadpool-new/404.html diff --git a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/Cargo.lock b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/Cargo.lock similarity index 100% rename from listings/ch20-web-server/no-listing-02-impl-threadpool-new/Cargo.lock rename to listings/ch21-web-server/no-listing-02-impl-threadpool-new/Cargo.lock diff --git a/listings/ch21-web-server/no-listing-02-impl-threadpool-new/Cargo.toml b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/hello.html b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/hello.html similarity index 100% rename from listings/ch20-web-server/no-listing-02-impl-threadpool-new/hello.html rename to listings/ch21-web-server/no-listing-02-impl-threadpool-new/hello.html diff --git a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/output.txt b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/output.txt similarity index 68% rename from listings/ch20-web-server/no-listing-02-impl-threadpool-new/output.txt rename to listings/ch21-web-server/no-listing-02-impl-threadpool-new/output.txt index 44c8f3953b..667041862d 100644 --- a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/output.txt +++ b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/output.txt @@ -4,7 +4,7 @@ error[E0599]: no method named `execute` found for struct `ThreadPool` in the cur --> src/main.rs:17:14 | 17 | pool.execute(|| { - | ^^^^^^^ method not found in `ThreadPool` + | -----^^^^^^^ method not found in `ThreadPool` For more information about this error, try `rustc --explain E0599`. -error: could not compile `hello` due to previous error +error: could not compile `hello` (bin "hello") due to 1 previous error diff --git a/listings/ch20-web-server/no-listing-02-impl-threadpool-new/src/lib.rs b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/src/lib.rs similarity index 100% rename from listings/ch20-web-server/no-listing-02-impl-threadpool-new/src/lib.rs rename to listings/ch21-web-server/no-listing-02-impl-threadpool-new/src/lib.rs diff --git a/listings/ch21-web-server/no-listing-02-impl-threadpool-new/src/main.rs b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/no-listing-02-impl-threadpool-new/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/no-listing-03-define-execute/404.html b/listings/ch21-web-server/no-listing-03-define-execute/404.html similarity index 100% rename from listings/ch20-web-server/no-listing-03-define-execute/404.html rename to listings/ch21-web-server/no-listing-03-define-execute/404.html diff --git a/listings/ch20-web-server/no-listing-03-define-execute/Cargo.lock b/listings/ch21-web-server/no-listing-03-define-execute/Cargo.lock similarity index 100% rename from listings/ch20-web-server/no-listing-03-define-execute/Cargo.lock rename to listings/ch21-web-server/no-listing-03-define-execute/Cargo.lock diff --git a/listings/ch21-web-server/no-listing-03-define-execute/Cargo.toml b/listings/ch21-web-server/no-listing-03-define-execute/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/no-listing-03-define-execute/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/no-listing-03-define-execute/hello.html b/listings/ch21-web-server/no-listing-03-define-execute/hello.html similarity index 100% rename from listings/ch20-web-server/no-listing-03-define-execute/hello.html rename to listings/ch21-web-server/no-listing-03-define-execute/hello.html diff --git a/listings/ch21-web-server/no-listing-03-define-execute/output.txt b/listings/ch21-web-server/no-listing-03-define-execute/output.txt new file mode 100644 index 0000000000..10d212672a --- /dev/null +++ b/listings/ch21-web-server/no-listing-03-define-execute/output.txt @@ -0,0 +1,3 @@ +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.24s diff --git a/listings/ch20-web-server/no-listing-03-define-execute/src/lib.rs b/listings/ch21-web-server/no-listing-03-define-execute/src/lib.rs similarity index 100% rename from listings/ch20-web-server/no-listing-03-define-execute/src/lib.rs rename to listings/ch21-web-server/no-listing-03-define-execute/src/lib.rs diff --git a/listings/ch21-web-server/no-listing-03-define-execute/src/main.rs b/listings/ch21-web-server/no-listing-03-define-execute/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/no-listing-03-define-execute/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/no-listing-04-update-worker-definition/404.html b/listings/ch21-web-server/no-listing-04-update-drop-definition/404.html similarity index 100% rename from listings/ch20-web-server/no-listing-04-update-worker-definition/404.html rename to listings/ch21-web-server/no-listing-04-update-drop-definition/404.html diff --git a/listings/ch20-web-server/no-listing-04-update-worker-definition/Cargo.lock b/listings/ch21-web-server/no-listing-04-update-drop-definition/Cargo.lock similarity index 100% rename from listings/ch20-web-server/no-listing-04-update-worker-definition/Cargo.lock rename to listings/ch21-web-server/no-listing-04-update-drop-definition/Cargo.lock diff --git a/listings/ch21-web-server/no-listing-04-update-drop-definition/Cargo.toml b/listings/ch21-web-server/no-listing-04-update-drop-definition/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/no-listing-04-update-drop-definition/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/no-listing-04-update-worker-definition/hello.html b/listings/ch21-web-server/no-listing-04-update-drop-definition/hello.html similarity index 100% rename from listings/ch20-web-server/no-listing-04-update-worker-definition/hello.html rename to listings/ch21-web-server/no-listing-04-update-drop-definition/hello.html diff --git a/listings/ch21-web-server/no-listing-04-update-drop-definition/output.txt b/listings/ch21-web-server/no-listing-04-update-drop-definition/output.txt new file mode 100644 index 0000000000..a59b08bcdd --- /dev/null +++ b/listings/ch21-web-server/no-listing-04-update-drop-definition/output.txt @@ -0,0 +1,3 @@ +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.07s diff --git a/listings/ch20-web-server/no-listing-04-update-worker-definition/src/lib.rs b/listings/ch21-web-server/no-listing-04-update-drop-definition/src/lib.rs similarity index 79% rename from listings/ch20-web-server/no-listing-04-update-worker-definition/src/lib.rs rename to listings/ch21-web-server/no-listing-04-update-drop-definition/src/lib.rs index 6ef710a26b..d9fda0f256 100644 --- a/listings/ch20-web-server/no-listing-04-update-worker-definition/src/lib.rs +++ b/listings/ch21-web-server/no-listing-04-update-drop-definition/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -44,31 +44,33 @@ impl ThreadPool { } } +// ANCHOR: here impl Drop for ThreadPool { fn drop(&mut self) { - for worker in &mut self.workers { + for worker in self.workers.drain(..) { println!("Shutting down worker {}", worker.id); worker.thread.join().unwrap(); } } } +// ANCHOR_END: here -// ANCHOR: here struct Worker { id: usize, - thread: Option>, + thread: thread::JoinHandle<()>, } -// ANCHOR_END: here impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let job = receiver.lock().unwrap().recv().unwrap(); + let thread = thread::spawn(move || { + loop { + let job = receiver.lock().unwrap().recv().unwrap(); - println!("Worker {id} got a job; executing."); + println!("Worker {id} got a job; executing."); - job(); + job(); + } }); Worker { id, thread } diff --git a/listings/ch21-web-server/no-listing-04-update-drop-definition/src/main.rs b/listings/ch21-web-server/no-listing-04-update-drop-definition/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/no-listing-04-update-drop-definition/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/no-listing-05-fix-worker-new/404.html b/listings/ch21-web-server/no-listing-05-fix-worker-new/404.html similarity index 100% rename from listings/ch20-web-server/no-listing-05-fix-worker-new/404.html rename to listings/ch21-web-server/no-listing-05-fix-worker-new/404.html diff --git a/listings/ch20-web-server/no-listing-05-fix-worker-new/Cargo.lock b/listings/ch21-web-server/no-listing-05-fix-worker-new/Cargo.lock similarity index 100% rename from listings/ch20-web-server/no-listing-05-fix-worker-new/Cargo.lock rename to listings/ch21-web-server/no-listing-05-fix-worker-new/Cargo.lock diff --git a/listings/ch21-web-server/no-listing-05-fix-worker-new/Cargo.toml b/listings/ch21-web-server/no-listing-05-fix-worker-new/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/no-listing-05-fix-worker-new/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/no-listing-05-fix-worker-new/hello.html b/listings/ch21-web-server/no-listing-05-fix-worker-new/hello.html similarity index 100% rename from listings/ch20-web-server/no-listing-05-fix-worker-new/hello.html rename to listings/ch21-web-server/no-listing-05-fix-worker-new/hello.html diff --git a/listings/ch20-web-server/no-listing-05-fix-worker-new/src/lib.rs b/listings/ch21-web-server/no-listing-05-fix-worker-new/src/lib.rs similarity index 85% rename from listings/ch20-web-server/no-listing-05-fix-worker-new/src/lib.rs rename to listings/ch21-web-server/no-listing-05-fix-worker-new/src/lib.rs index ede3750a17..31237a61a6 100644 --- a/listings/ch20-web-server/no-listing-05-fix-worker-new/src/lib.rs +++ b/listings/ch21-web-server/no-listing-05-fix-worker-new/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -65,12 +65,14 @@ impl Worker { // --snip-- // ANCHOR_END: here - let thread = thread::spawn(move || loop { - let job = receiver.lock().unwrap().recv().unwrap(); + let thread = thread::spawn(move || { + loop { + let job = receiver.lock().unwrap().recv().unwrap(); - println!("Worker {id} got a job; executing."); + println!("Worker {id} got a job; executing."); - job(); + job(); + } }); // ANCHOR: here diff --git a/listings/ch21-web-server/no-listing-05-fix-worker-new/src/main.rs b/listings/ch21-web-server/no-listing-05-fix-worker-new/src/main.rs new file mode 100644 index 0000000000..ca3608da70 --- /dev/null +++ b/listings/ch21-web-server/no-listing-05-fix-worker-new/src/main.rs @@ -0,0 +1,43 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/404.html b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/404.html similarity index 100% rename from listings/ch20-web-server/no-listing-06-fix-threadpool-drop/404.html rename to listings/ch21-web-server/no-listing-06-fix-threadpool-drop/404.html diff --git a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/Cargo.lock b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/Cargo.lock similarity index 100% rename from listings/ch20-web-server/no-listing-06-fix-threadpool-drop/Cargo.lock rename to listings/ch21-web-server/no-listing-06-fix-threadpool-drop/Cargo.lock diff --git a/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/Cargo.toml b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/hello.html b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/hello.html similarity index 100% rename from listings/ch20-web-server/no-listing-06-fix-threadpool-drop/hello.html rename to listings/ch21-web-server/no-listing-06-fix-threadpool-drop/hello.html diff --git a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/src/lib.rs b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/src/lib.rs similarity index 85% rename from listings/ch20-web-server/no-listing-06-fix-threadpool-drop/src/lib.rs rename to listings/ch21-web-server/no-listing-06-fix-threadpool-drop/src/lib.rs index b795ea53b0..9fb67e0186 100644 --- a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/src/lib.rs +++ b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -65,12 +65,14 @@ struct Worker { impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let job = receiver.lock().unwrap().recv().unwrap(); + let thread = thread::spawn(move || { + loop { + let job = receiver.lock().unwrap().recv().unwrap(); - println!("Worker {id} got a job; executing."); + println!("Worker {id} got a job; executing."); - job(); + job(); + } }); Worker { diff --git a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/src/main.rs b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/src/main.rs similarity index 93% rename from listings/ch20-web-server/no-listing-06-fix-threadpool-drop/src/main.rs rename to listings/ch21-web-server/no-listing-06-fix-threadpool-drop/src/main.rs index b6aa046d1b..f68c11e0b2 100644 --- a/listings/ch20-web-server/no-listing-06-fix-threadpool-drop/src/main.rs +++ b/listings/ch21-web-server/no-listing-06-fix-threadpool-drop/src/main.rs @@ -1,7 +1,7 @@ use hello::ThreadPool; use std::{ fs, - io::{prelude::*, BufReader}, + io::{BufReader, prelude::*}, net::{TcpListener, TcpStream}, thread, time::Duration, @@ -23,7 +23,7 @@ fn main() { } fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); + let buf_reader = BufReader::new(&stream); let request_line = buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) = match &request_line[..] { diff --git a/listings/ch20-web-server/no-listing-07-final-code/404.html b/listings/ch21-web-server/no-listing-07-final-code/404.html similarity index 100% rename from listings/ch20-web-server/no-listing-07-final-code/404.html rename to listings/ch21-web-server/no-listing-07-final-code/404.html diff --git a/listings/ch20-web-server/no-listing-07-final-code/Cargo.lock b/listings/ch21-web-server/no-listing-07-final-code/Cargo.lock similarity index 100% rename from listings/ch20-web-server/no-listing-07-final-code/Cargo.lock rename to listings/ch21-web-server/no-listing-07-final-code/Cargo.lock diff --git a/listings/ch21-web-server/no-listing-07-final-code/Cargo.toml b/listings/ch21-web-server/no-listing-07-final-code/Cargo.toml new file mode 100644 index 0000000000..f6f3649e20 --- /dev/null +++ b/listings/ch21-web-server/no-listing-07-final-code/Cargo.toml @@ -0,0 +1,6 @@ +[package] +name = "hello" +version = "0.1.0" +edition = "2024" + +[dependencies] diff --git a/listings/ch20-web-server/no-listing-07-final-code/hello.html b/listings/ch21-web-server/no-listing-07-final-code/hello.html similarity index 100% rename from listings/ch20-web-server/no-listing-07-final-code/hello.html rename to listings/ch21-web-server/no-listing-07-final-code/hello.html diff --git a/listings/ch20-web-server/no-listing-07-final-code/src/lib.rs b/listings/ch21-web-server/no-listing-07-final-code/src/lib.rs similarity index 76% rename from listings/ch20-web-server/no-listing-07-final-code/src/lib.rs rename to listings/ch21-web-server/no-listing-07-final-code/src/lib.rs index 54c0489abf..e8decb0cc2 100644 --- a/listings/ch20-web-server/no-listing-07-final-code/src/lib.rs +++ b/listings/ch21-web-server/no-listing-07-final-code/src/lib.rs @@ -1,5 +1,5 @@ use std::{ - sync::{mpsc, Arc, Mutex}, + sync::{Arc, Mutex, mpsc}, thread, }; @@ -68,18 +68,20 @@ struct Worker { impl Worker { fn new(id: usize, receiver: Arc>>) -> Worker { - let thread = thread::spawn(move || loop { - let message = receiver.lock().unwrap().recv(); - - match message { - Ok(job) => { - println!("Worker {id} got a job; executing."); - - job(); - } - Err(_) => { - println!("Worker {id} disconnected; shutting down."); - break; + let thread = thread::spawn(move || { + loop { + let message = receiver.lock().unwrap().recv(); + + match message { + Ok(job) => { + println!("Worker {id} got a job; executing."); + + job(); + } + Err(_) => { + println!("Worker {id} disconnected; shutting down."); + break; + } } } }); diff --git a/listings/ch21-web-server/no-listing-07-final-code/src/main.rs b/listings/ch21-web-server/no-listing-07-final-code/src/main.rs new file mode 100644 index 0000000000..f68c11e0b2 --- /dev/null +++ b/listings/ch21-web-server/no-listing-07-final-code/src/main.rs @@ -0,0 +1,45 @@ +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming().take(2) { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } + + println!("Shutting down."); +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} diff --git a/nostarch/acknowledgments.md b/nostarch/acknowledgments.md deleted file mode 100644 index c29cb712ab..0000000000 --- a/nostarch/acknowledgments.md +++ /dev/null @@ -1,17 +0,0 @@ -# Acknowledgments - -We would like to thank everyone who has worked on the Rust language for -creating an amazing language worth writing a book about. We’re grateful to -everyone in the Rust community for being welcoming and creating an environment -worth welcoming more folks into. - -We’re especially thankful for everyone who read early versions of this book -online and provided feedback, bug reports, and pull requests. Special thanks to -Eduard-Mihai Burtescu, Alex Crichton, and JT for providing technical review and -Karen Rustad Tölva for the cover art. Thank you to our team at No Starch, -including Bill Pollock, Liz Chadwick, and Janelle Ludowise, for improving this -book and bringing it to print. - -Carol is grateful for the opportunity to work on this book. She thanks her -family for their constant love and support, especially her husband Jake -Goulding and her daughter Vivian. diff --git a/nostarch/appendix.md b/nostarch/appendix.md index 98432a1dac..7a68652b70 100644 --- a/nostarch/appendix.md +++ b/nostarch/appendix.md @@ -6,66 +6,71 @@ directory, so all fixes need to be made in `/src/`. [TOC] +# Appendix + +The following sections contain reference material you may find useful in your +Rust journey. + ## Appendix A: Keywords The following lists contain keywords that are reserved for current or future use by the Rust language. As such, they cannot be used as identifiers (except -as raw identifiers, as we’ll discuss in “Raw Identifiers” on page XX). -*Identifiers* are names of functions, variables, parameters, struct fields, -modules, crates, constants, macros, static values, attributes, types, traits, -or lifetimes. +as raw identifiers, as we discuss in the “Raw +Identifiers” section). *Identifiers* are names +of functions, variables, parameters, struct fields, modules, crates, constants, +macros, static values, attributes, types, traits, or lifetimes. -## Keywords Currently in Use +### Keywords Currently in Use The following is a list of keywords currently in use, with their functionality described. -* **`as` **: perform primitive casting, disambiguate the specific trait -containing an item, or rename items in `use` statements -* **`async` **: return a `Future` instead of blocking the current thread -* **`await` **: suspend execution until the result of a `Future` is ready -* **`break` **: exit a loop immediately -* **`const` **: define constant items or constant raw pointers -* **`continue` **: continue to the next loop iteration -* **`crate` **: in a module path, refers to the crate root -* **`dyn` **: dynamic dispatch to a trait object -* **`else` **: fallback for `if` and `if let` control flow constructs -* **`enum` **: define an enumeration -* **`extern` **: link an external function or variable -* **`false` **: Boolean false literal -* **`fn` **: define a function or the function pointer type -* **`for` **: loop over items from an iterator, implement a trait, or specify a -higher-ranked lifetime -* **`if` **: branch based on the result of a conditional expression -* **`impl` **: implement inherent or trait functionality -* **`in` **: part of `for` loop syntax -* **`let` **: bind a variable -* **`loop` **: loop unconditionally -* **`match` **: match a value to patterns -* **`mod` **: define a module -* **`move` **: make a closure take ownership of all its captures -* **`mut` **: denote mutability in references, raw pointers, or pattern bindings -* **`pub` **: denote public visibility in struct fields, `impl` blocks, or -modules -* **`ref` **: bind by reference -* **`return` **: return from function -* **`Self` **: a type alias for the type we are defining or implementing -* **`self` **: method subject or current module -* **`static` **: global variable or lifetime lasting the entire program -execution -* **`struct` **: define a structure -* **`super` **: parent module of the current module -* **`trait` **: define a trait -* **`true` **: Boolean true literal -* **`type` **: define a type alias or associated type -* **`union` **: define a union; is a keyword only when used in a union -declaration -* **`unsafe` **: denote unsafe code, functions, traits, or implementations -* **`use` **: bring symbols into scope -* **`where` **: denote clauses that constrain a type -* **`while` **: loop conditionally based on the result of an expression - -## Keywords Reserved for Future Use +* **`as`**: Perform primitive casting, disambiguate the specific trait + containing an item, or rename items in `use` statements. +* **`async`**: Return a `Future` instead of blocking the current thread. +* **`await`**: Suspend execution until the result of a `Future` is ready. +* **`break`**: Exit a loop immediately. +* **`const`**: Define constant items or constant raw pointers. +* **`continue`**: Continue to the next loop iteration. +* **`crate`**: In a module path, refers to the crate root. +* **`dyn`**: Dynamic dispatch to a trait object. +* **`else`**: Fallback for `if` and `if let` control flow constructs. +* **`enum`**: Define an enumeration. +* **`extern`**: Link an external function or variable. +* **`false`**: Boolean false literal. +* **`fn`**: Define a function or the function pointer type. +* **`for`**: Loop over items from an iterator, implement a trait, or specify a + higher ranked lifetime. +* **`if`**: Branch based on the result of a conditional expression. +* **`impl`**: Implement inherent or trait functionality. +* **`in`**: Part of `for` loop syntax. +* **`let`**: Bind a variable. +* **`loop`**: Loop unconditionally. +* **`match`**: Match a value to patterns. +* **`mod`**: Define a module. +* **`move`**: Make a closure take ownership of all its captures. +* **`mut`**: Denote mutability in references, raw pointers, or pattern bindings. +* **`pub`**: Denote public visibility in struct fields, `impl` blocks, or + modules. +* **`ref`**: Bind by reference. +* **`return`**: Return from function. +* **`Self`**: A type alias for the type we are defining or implementing. +* **`self`**: Method subject or current module. +* **`static`**: Global variable or lifetime lasting the entire program + execution. +* **`struct`**: Define a structure. +* **`super`**: Parent module of the current module. +* **`trait`**: Define a trait. +* **`true`**: Boolean true literal. +* **`type`**: Define a type alias or associated type. +* **`union`**: Define a union; is a keyword only when + used in a union declaration. +* **`unsafe`**: Denote unsafe code, functions, traits, or implementations. +* **`use`**: Bring symbols into scope. +* **`where`**: Denote clauses that constrain a type. +* **`while`**: Loop conditionally based on the result of an expression. + +### Keywords Reserved for Future Use The following keywords do not yet have any functionality but are reserved by Rust for potential future use: @@ -75,6 +80,7 @@ Rust for potential future use: * `box` * `do` * `final` +* `gen` * `macro` * `override` * `priv` @@ -84,7 +90,7 @@ Rust for potential future use: * `virtual` * `yield` -## Raw Identifiers +### Raw Identifiers *Raw identifiers* are the syntax that lets you use keywords where they wouldn’t normally be allowed. You use a raw identifier by prefixing a keyword with `r#`. @@ -130,15 +136,15 @@ This code will compile without any errors. Note the `r#` prefix on the function name in its definition as well as where the function is called in `main`. Raw identifiers allow you to use any word you choose as an identifier, even if -that word happens to be a reserved keyword. This gives us more freedom to -choose identifier names, as well as lets us integrate with programs written in -a language where these words aren’t keywords. In addition, raw identifiers -allow you to use libraries written in a different Rust edition than your crate -uses. For example, `try` isn’t a keyword in the 2015 edition but is in the 2018 -and 2021 editions. If you depend on a library that is written using the 2015 +that word happens to be a reserved keyword. This gives us more freedom to choose +identifier names, as well as lets us integrate with programs written in a +language where these words aren’t keywords. In addition, raw identifiers allow +you to use libraries written in a different Rust edition than your crate uses. +For example, `try` isn’t a keyword in the 2015 edition but is in the 2018, 2021, +and 2024 editions. If you depend on a library that is written using the 2015 edition and has a `try` function, you’ll need to use the raw identifier syntax, -`r#try` in this case, to call that function from your 2021 edition code. See -Appendix E for more information on editions. +`r#try` in this case, to call that function from your code on later editions. +See Appendix E for more information on editions. ## Appendix B: Operators and Symbols @@ -146,7 +152,7 @@ This appendix contains a glossary of Rust’s syntax, including operators and other symbols that appear by themselves or in the context of paths, generics, trait bounds, macros, attributes, comments, tuples, and brackets. -## Operators +### Operators Table B-1 contains the operators in Rust, an example of how the operator would appear in context, a short explanation, and whether that operator is @@ -155,70 +161,66 @@ overload that operator is listed. Table B-1: Operators -| Operator | Example | Explanation | Overloadable? | -|---|---|---|---| -| `!` | `ident!(...)`, `ident!{...}`, `ident![...]` | Macro expansion | | -| `!` | `!expr` | Bitwise or logical complement | `Not` | -| `!=` | `expr != expr` | Nonequality comparison | `PartialEq` | -| `% | `expr % expr` | Arithmetic remainder | `Rem` | -| `%=` | `var %= expr` | Arithmetic remainder and assignment | `RemAssign` | -| `& | `&expr`, `&mut expr` | Borrow | | -| `&` | `&type`, `&mut type`, `&'a type`, `&'a mut type` | Borrowed pointer -type | | -| `&` | `expr & expr` | Bitwise AND | `BitAnd` | -| `&=` | `var &= expr` | Bitwise AND and assignment | `BitAndAssign` | -| `&&` | `expr && expr` | Short-circuiting logical AND | | -| `* | `expr * expr` | Arithmetic multiplication | `Mul` | -| `*=` | `var *= expr` | Arithmetic multiplication and assignment | `MulAssign` -| -| `*` | `*expr` | Dereference | `Deref` | -| `*` | `*const type`, `*mut type | Raw pointer | | -| `+ | `trait + trait`, `'a + trait` | Compound type constraint | | -| `+ | `expr + expr` | Arithmetic addition | `Add` | -| `+=` | `var += expr` | Arithmetic addition and assignment | `AddAssign` | -| `,` | `expr, expr` | Argument and element separator | | -| `- | `- expr` | Arithmetic negation | `Neg` | -| `- | `expr - expr` | Arithmetic subtraction | `Sub` | -| `-=` | `var -= expr` | Arithmetic subtraction and assignment | `SubAssign` | -| `-> | `fn(...) -> type`, `|…| -> type` | Function and closure return type | | -| `. | `expr.ident` | Member access | | -| `..` | `..`, `expr..`, `..expr`, `expr..expr` | Right-exclusive range literal -| `PartialOrd` | -| `..=` | `..=expr`, `expr..=expr` | Right-inclusive range literal | -`PartialOrd` | -| `..` | `..expr` | Struct literal update syntax | | -| `..` | `variant(x, ..)`, `struct_type { x, .. }` | “And the rest” pattern -binding | | -| `...` | `expr...expr` | (Deprecated, use `..=` instead) In a pattern: -inclusive range pattern | | -| `/ | `expr / expr` | Arithmetic division | `Div` | -| `/=` | `var /= expr` | Arithmetic division and assignment | `DivAssign` | -| `: | `pat: type`, `ident: type` | Constraints | | -| `:` | `ident: expr` | Struct field initializer | | -| `:` | `'a: loop {...}` | Loop label | | -| `; | `expr;` | Statement and item terminator | | -| `;` | `[...; len]` | Part of fixed-size array syntax | | -| `<<` | `expr << expr` | Left-shift | `Shl` | -| `<<=` | `var <<= expr` | Left-shift and assignment | `ShlAssign` | -| `<` | `expr < expr` | Less than comparison | `PartialOrd` | -| `<=` | `expr <= expr` | Less than or equal to comparison | `PartialOrd` | -| `=` | `var = expr`, `ident = type` | Assignment/equivalence | | -| `==` | `expr == expr` | Equality comparison | `PartialEq` | -| `=>` | `pat => expr` | Part of match arm syntax | | -| `>` | `expr > expr` | Greater than comparison | `PartialOrd` | -| `>=` | `expr >= expr` | Greater than or equal to comparison | `PartialOrd` | -| `>>` | `expr >> expr` | Right-shift | `Shr` | -| `>>=` | `var >>= expr` | Right-shift and assignment | `ShrAssign` | -| `@ | `ident @ pat` | Pattern binding | | -| `^` | `expr ^ expr` | Bitwise exclusive OR | `BitXor` | -| `^=` | `var ^= expr` | Bitwise exclusive OR and assignment | `BitXorAssign` | -| `| | `pat | pat` | Pattern alternatives | | -| `|` | `expr | expr` | Bitwise OR | `BitOr` | -| `|=` | `var |= expr` | Bitwise OR and assignment | `BitOrAssign` | -| `||` | `expr || expr` | Short-circuiting logical OR | | -| `? | `expr?` | Error propagation | | - -## Non-operator Symbols +|Operator|Example|Explanation|Overloadable?| +|--------|-------|-----------|-------------| +|`!`|`ident!(...)`, `ident!{...}`, `ident![...]`|Macro expansion|| +|`!`|`!expr`|Bitwise or logical complement|`Not`| +|`!=`|`expr != expr`|Nonequality comparison|`PartialEq`| +|`%`|`expr % expr`|Arithmetic remainder|`Rem`| +|`%=`|`var %= expr`|Arithmetic remainder and assignment|`RemAssign`| +|`&`|`&expr`, `&mut expr`|Borrow|| +|`&`|`&type`, `&mut type`, `&'a type`, `&'a mut type`|Borrowed pointer type|| +|`&`|`expr & expr`|Bitwise AND|`BitAnd`| +|`&=`|`var &= expr`|Bitwise AND and assignment|`BitAndAssign`| +|`&&`|`expr && expr`|Short-circuiting logical AND|| +|`*`|`expr * expr`|Arithmetic multiplication|`Mul`| +|`*=`|`var *= expr`|Arithmetic multiplication and assignment|`MulAssign`| +|`*`|`*expr`|Dereference|`Deref`| +|`*`|`*const type`, `*mut type`|Raw pointer|| +|`+`|`trait + trait`, `'a + trait`|Compound type constraint|| +|`+`|`expr + expr`|Arithmetic addition|`Add`| +|`+=`|`var += expr`|Arithmetic addition and assignment|`AddAssign`| +|`,`|`expr, expr`|Argument and element separator|| +|`-`|`- expr`|Arithmetic negation|`Neg`| +|`-`|`expr - expr`|Arithmetic subtraction|`Sub`| +|`-=`|`var -= expr`|Arithmetic subtraction and assignment|`SubAssign`| +|`->`|`fn(...) -> type`, \|…\| -> type|Function and closure return type|| +|`.`|`expr.ident`|Field access|| +|`.`|`expr.ident(expr, ...)`|Method call|| +|`.`|`expr.0`, `expr.1`, and so on|Tuple indexing|| +|`..`|`..`, `expr..`, `..expr`, `expr..expr`|Right-exclusive range literal|`PartialOrd`| +|`..=`|`..=expr`, `expr..=expr`|Right-inclusive range literal|`PartialOrd`| +|`..`|`..expr`|Struct literal update syntax|| +|`..`|`variant(x, ..)`, `struct_type { x, .. }`|“And the rest” pattern binding|| +|`...`|`expr...expr`|(Deprecated, use `..=` instead) In a pattern: inclusive range pattern|| +|`/`|`expr / expr`|Arithmetic division|`Div`| +|`/=`|`var /= expr`|Arithmetic division and assignment|`DivAssign`| +|`:`|`pat: type`, `ident: type`|Constraints|| +|`:`|`ident: expr`|Struct field initializer|| +|`:`|`'a: loop {...}`|Loop label|| +|`;`|`expr;`|Statement and item terminator|| +|`;`|`[...; len]`|Part of fixed-size array syntax|| +|`<<`|`expr << expr`|Left-shift|`Shl`| +|`<<=`|`var <<= expr`|Left-shift and assignment|`ShlAssign`| +|`<`|`expr < expr`|Less than comparison|`PartialOrd`| +|`<=`|`expr <= expr`|Less than or equal to comparison|`PartialOrd`| +|`=`|`var = expr`, `ident = type`|Assignment/equivalence|| +|`==`|`expr == expr`|Equality comparison|`PartialEq`| +|`=>`|`pat => expr`|Part of match arm syntax|| +|`>`|`expr > expr`|Greater than comparison|`PartialOrd`| +|`>=`|`expr >= expr`|Greater than or equal to comparison|`PartialOrd`| +|`>>`|`expr >> expr`|Right-shift|`Shr`| +|`>>=`|`var >>= expr`|Right-shift and assignment|`ShrAssign`| +|`@`|`ident @ pat`|Pattern binding|| +|`^`|`expr ^ expr`|Bitwise exclusive OR|`BitXor`| +|`^=`|`var ^= expr`|Bitwise exclusive OR and assignment|`BitXorAssign`| +|\||pat \| pat|Pattern alternatives|| +|\||expr \| expr|Bitwise OR|`BitOr`| +|\|=|var \|= expr|Bitwise OR and assignment|`BitOrAssign`| +|\|\||expr \|\| expr|Short-circuiting logical OR|| +|`?`|`expr?`|Error propagation|| + +### Non-operator Symbols The following tables contain all symbols that don’t function as operators; that is, they don’t behave like a function or method call. @@ -226,151 +228,130 @@ is, they don’t behave like a function or method call. Table B-2 shows symbols that appear on their own and are valid in a variety of locations. -Table B-2: Stand-Alone Syntax - -| Symbol | Explanation | -|---|---| -| `'ident | Named lifetime or loop label | -| `...u8`, `...i32`, `...f64`, `...usize`, and so on | Numeric literal of -specific type | -| `"..." | String literal | -| `r"..."`, `r#"..."#`, `r##"..."##`, and so on | Raw string literal; escape -characters not processed | -| `b"..."` | Byte string literal; constructs an array of bytes instead of a -string | -| `br"..."`, `br#"..."#`, `br##"..."##`, and so on | Raw byte string literal; -combination of raw and byte string literal | -| `'...' | Character literal | -| `b'...' | ASCII byte literal | -| `|…| expr | Closure | -| `! | Always-empty bottom type for diverging functions | -| `_ | “Ignored” pattern binding; also used to make integer literals readable | +Table B-2: Stand-alone Syntax + +|Symbol|Explanation| +|------|-----------| +|`'ident`|Named lifetime or loop label| +|Digits immediately followed by `u8`, `i32`, `f64`, `usize`, and so on|Numeric literal of specific type| +|`"..."`|String literal| +|`r"..."`, `r#"..."#`, `r##"..."##`, and so on|Raw string literal; escape characters not processed| +|`b"..."`|Byte string literal; constructs an array of bytes instead of a string| +|`br"..."`, `br#"..."#`, `br##"..."##`, and so on|Raw byte string literal; combination of raw and byte string literal| +|`'...'`|Character literal| +|`b'...'`|ASCII byte literal| +|\|…\| expr|Closure| +|`!`|Always-empty bottom type for diverging functions| +|`_`|“Ignored” pattern binding; also used to make integer literals readable| Table B-3 shows symbols that appear in the context of a path through the module hierarchy to an item. Table B-3: Path-Related Syntax -| Symbol | Explanation | -|---|---| -| `ident::ident | Namespace path | -| `::path` | Path relative to the crate root (that is, an explicitly absolute -path) | -| `self::path` | Path relative to the current module (that is, an explicitly -relative path) | -| `super::path` | Path relative to the parent of the current module | -| `type::ident`, `::ident | Associated constants, functions, and -types | -| `::...` | Associated item for a type that cannot be directly named (for -example, `<&T>::...`, `<[T]>::...`, and so on) | -| `trait::method(...)` | Disambiguating a method call by naming the trait that -defines it | -| `type::method(...)` | Disambiguating a method call by naming the type for -which it’s defined | -| `::method(...)` | Disambiguating a method call by naming the -trait and type | +|Symbol|Explanation| +|------|-----------| +|`ident::ident`|Namespace path| +|`::path`|Path relative to the crate root (that is, an explicitly absolute path)| +|`self::path`|Path relative to the current module (that is, an explicitly relative path)| +|`super::path`|Path relative to the parent of the current module| +|`type::ident`, `::ident`|Associated constants, functions, and types| +|`::...`|Associated item for a type that cannot be directly named (for example, `<&T>::...`, `<[T]>::...`, and so on)| +|`trait::method(...)`|Disambiguating a method call by naming the trait that defines it| +|`type::method(...)`|Disambiguating a method call by naming the type for which it’s defined| +|`::method(...)`|Disambiguating a method call by naming the trait and type| Table B-4 shows symbols that appear in the context of using generic type parameters. Table B-4: Generics -| Symbol | Explanation | -|---|---| -| `path<...>` | Specifies parameters to a generic type in a type (for example, -`Vec`) | -| `path::<...>, method::<...>` | Specifies parameters to a generic type, -function, or method in an expression; often referred to as turbofish (for -example, `"42".parse::()`) | -| `fn ident<...> ...` | Define generic function | -| `struct ident<...> ...` | Define generic structure | -| `enum ident<...> ...` | Define generic enumeration | -| `impl<...> ...` | Define generic implementation | -| `for<...> type` | Higher-ranked lifetime bounds | -| `type` | A generic type where one or more associated types have -specific assignments (for example, `Iterator`) | +|Symbol|Explanation| +|------|-----------| +|`path<...>`|Specifies parameters to a generic type in a type (for example, `Vec`)| +|`path::<...>`, `method::<...>`|Specifies parameters to a generic type, function, or method in an expression; often referred to as *turbofish* (for example, `"42".parse::()`)| +|`fn ident<...> ...`|Define generic function| +|`struct ident<...> ...`|Define generic structure| +|`enum ident<...> ...`|Define generic enumeration| +|`impl<...> ...`|Define generic implementation| +|`for<...> type`|Higher ranked lifetime bounds| +|`type`|A generic type where one or more associated types have specific assignments (for example, `Iterator`)| Table B-5 shows symbols that appear in the context of constraining generic type parameters with trait bounds. Table B-5: Trait Bound Constraints -| Symbol | Explanation | -|---|---| -| T: U` | Generic parameter `T` constrained to types that implement `U` | -| `T: 'a` | Generic type `T` must outlive lifetime `'a` (meaning the type -cannot transitively contain any references with lifetimes shorter than `'a`) | -| `T: 'static` | Generic type `T` contains no borrowed references other than -`'static` ones | -| `'b: 'a` | Generic lifetime `'b` must outlive lifetime `'a` | -| `T: ?Sized` | Allow generic type parameter to be a dynamically sized type | -| `'a + trait`, `trait + trait` | Compound type constraint | +|Symbol|Explanation| +|------|-----------| +|`T: U`|Generic parameter `T` constrained to types that implement `U`| +|`T: 'a`|Generic type `T` must outlive lifetime `'a` (meaning the type cannot transitively contain any references with lifetimes shorter than `'a`)| +|`T: 'static`|Generic type `T` contains no borrowed references other than `'static` ones| +|`'b: 'a`|Generic lifetime `'b` must outlive lifetime `'a`| +|`T: ?Sized`|Allow generic type parameter to be a dynamically sized type| +|`'a + trait`, `trait + trait`|Compound type constraint| Table B-6 shows symbols that appear in the context of calling or defining macros and specifying attributes on an item. Table B-6: Macros and Attributes -| Symbol | Explanation | -|---|---| -| `#[meta]` | Outer attribute | -| `#![meta]` | Inner attribute | -| `$ident` | Macro substitution | -| `$ident:kind` | Macro capture | -| `$(…)…` | Macro repetition | -| `ident!(...)`, `ident!{...}`, `ident![...]` | Macro invocation | +|Symbol|Explanation| +|------|-----------| +|`#[meta]`|Outer attribute| +|`#![meta]`|Inner attribute| +|`$ident`|Macro substitution| +|`$ident:kind`|Macro metavariable| +|`$(...)...`|Macro repetition| +|`ident!(...)`, `ident!{...}`, `ident![...]`|Macro invocation| Table B-7 shows symbols that create comments. Table B-7: Comments -| Symbol | Explanation | -|---|---| -| `//` | Line comment | -| `//!` | Inner line doc comment | -| `///` | Outer line doc comment | -| `/*...*/` | Block comment | -| `/*!...*/` | Inner block doc comment | -| `/**...*/` | Outer block doc comment | - -Table B-8 shows symbols that appear in the context of using tuples. - -Table B-8: Tuples - -| Symbol | Explanation | -|---|---| -| `() | Empty tuple (aka unit), both literal and type | -| `(expr)` | Parenthesized expression | -| `(expr,)` | Single-element tuple expression | -| `(type,)` | Single-element tuple type | -| `(expr, ...)` | Tuple expression | -| `(type, ...)` | Tuple type | -| `expr(expr, ...)` | Function call expression; also used to initialize tuple -`struct`s and tuple `enum` variants | -| `expr.0`, `expr.1`, and so on | Tuple indexing | +|Symbol|Explanation| +|------|-----------| +|`//`|Line comment| +|`//!`|Inner line doc comment| +|`///`|Outer line doc comment| +|`/*...*/`|Block comment| +|`/*!...*/`|Inner block doc comment| +|`/**...*/`|Outer block doc comment| + +Table B-8 shows the contexts in which parentheses are used. + +Table B-8: Parentheses + +|Symbol|Explanation| +|------|-----------| +|`()`|Empty tuple (aka unit), both literal and type| +|`(expr)`|Parenthesized expression| +|`(expr,)`|Single-element tuple expression| +|`(type,)`|Single-element tuple type| +|`(expr, ...)`|Tuple expression| +|`(type, ...)`|Tuple type| +|`expr(expr, ...)`|Function call expression; also used to initialize tuple `struct`s and tuple `enum` variants| Table B-9 shows the contexts in which curly brackets are used. Table B-9: Curly Brackets -| Context | Explanation | -|---|---| -| `{...}` | Block expression | -| `Type {...}` | `struct` literal | +|Context|Explanation| +|-------|-----------| +|`{...}`|Block expression| +|`Type {...}`|Struct literal| Table B-10 shows the contexts in which square brackets are used. Table B-10: Square Brackets -| Context | Explanation | -|---|---| -| `[...]` | Array literal | -| `[expr; len]` | Array literal containing `len` copies of `expr` | -| `[type; len]` | Array type containing `len` instances of `type` | -| `expr[expr]` | Collection indexing; overloadable (`Index`, `IndexMut`) | -| `expr[..]`, `expr[a..]`, `expr[..b]`, `expr[a..b]` | Collection indexing -pretending to be collection slicing, using `Range`, `RangeFrom`, `RangeTo`, or -`RangeFull` as the “index” | +|Context|Explanation| +|-------|-----------| +|`[...]`|Array literal| +|`[expr; len]`|Array literal containing `len` copies of `expr`| +|`[type; len]`|Array type containing `len` instances of `type`| +|`expr[expr]`|Collection indexing; overloadable (`Index`, `IndexMut`)| +|`expr[..]`, `expr[a..]`, `expr[..b]`, `expr[a..b]`|Collection indexing pretending to be collection slicing, using `Range`, `RangeFrom`, `RangeTo`, or `RangeFull` as the “index”| ## Appendix C: Derivable Traits @@ -389,8 +370,8 @@ library that you can use with `derive`. Each section covers: * Examples of operations that require the trait If you want different behavior from that provided by the `derive` attribute, -consult the standard library documentation for each trait for details on how to -manually implement them. +consult the standard library documentation +for each trait for details on how to manually implement them. The traits listed here are the only ones defined by the standard library that can be implemented on your types using `derive`. Other traits defined in the @@ -405,11 +386,12 @@ would be most relevant to them? The Rust compiler doesn’t have this insight, s it can’t provide appropriate default behavior for you. The list of derivable traits provided in this appendix is not comprehensive: -libraries can implement `derive` for their own traits, making the list of +Libraries can implement `derive` for their own traits, making the list of traits you can use `derive` with truly open ended. Implementing `derive` -involves using a procedural macro, which is covered in “Macros” on page XX. +involves using a procedural macro, which is covered in the “Custom `derive` +Macros” section in Chapter 20. -## Debug for Programmer Output +### Debug for Programmer Output The `Debug` trait enables debug formatting in format strings, which you indicate by adding `:?` within `{}` placeholders. @@ -420,17 +402,17 @@ at a particular point in a program’s execution. The `Debug` trait is required, for example, in the use of the `assert_eq!` macro. This macro prints the values of instances given as arguments if the -equality assertion fails so programmers can see why the two instances weren’t -equal. +equality assertion fails so that programmers can see why the two instances +weren’t equal. -## PartialEq and Eq for Equality Comparisons +### PartialEq and Eq for Equality Comparisons The `PartialEq` trait allows you to compare instances of a type to check for equality and enables use of the `==` and `!=` operators. Deriving `PartialEq` implements the `eq` method. When `PartialEq` is derived on structs, two instances are equal only if *all* fields are equal, and the -instances are not equal if any fields are not equal. When derived on enums, +instances are not equal if *any* fields are not equal. When derived on enums, each variant is equal to itself and not equal to the other variants. The `PartialEq` trait is required, for example, with the use of the @@ -441,13 +423,13 @@ The `Eq` trait has no methods. Its purpose is to signal that for every value of the annotated type, the value is equal to itself. The `Eq` trait can only be applied to types that also implement `PartialEq`, although not all types that implement `PartialEq` can implement `Eq`. One example of this is floating-point -number types: the implementation of floating-point numbers states that two +number types: The implementation of floating-point numbers states that two instances of the not-a-number (`NaN`) value are not equal to each other. An example of when `Eq` is required is for keys in a `HashMap` so that the `HashMap` can tell whether two keys are the same. -## PartialOrd and Ord for Ordering Comparisons +### PartialOrd and Ord for Ordering Comparisons The `PartialOrd` trait allows you to compare instances of a type for sorting purposes. A type that implements `PartialOrd` can be used with the `<`, `>`, @@ -457,8 +439,8 @@ that also implement `PartialEq`. Deriving `PartialOrd` implements the `partial_cmp` method, which returns an `Option` that will be `None` when the values given don’t produce an ordering. An example of a value that doesn’t produce an ordering, even though -most values of that type can be compared, is the not-a-number (`NaN`) floating -point value. Calling `partial_cmp` with any floating-point number and the `NaN` +most values of that type can be compared, is the `NaN` floating point value. +Calling `partial_cmp` with any floating-point number and the `NaN` floating-point value will return `None`. When derived on structs, `PartialOrd` compares two instances by comparing the @@ -481,12 +463,13 @@ implementation for `partial_cmp` does with `PartialOrd`. An example of when `Ord` is required is when storing values in a `BTreeSet`, a data structure that stores data based on the sort order of the values. -## Clone and Copy for Duplicating Values +### Clone and Copy for Duplicating Values The `Clone` trait allows you to explicitly create a deep copy of a value, and the duplication process might involve running arbitrary code and copying heap -data. See “Variables and Data Interacting with Clone” on page XX for more -information on `Clone`. +data. See the “Variables and Data Interacting with +Clone” section in +Chapter 4 for more information on `Clone`. Deriving `Clone` implements the `clone` method, which when implemented for the whole type, calls `clone` on each of the parts of the type. This means all the @@ -495,11 +478,12 @@ fields or values in the type must also implement `Clone` to derive `Clone`. An example of when `Clone` is required is when calling the `to_vec` method on a slice. The slice doesn’t own the type instances it contains, but the vector returned from `to_vec` will need to own its instances, so `to_vec` calls -`clone` on each item. Thus the type stored in the slice must implement `Clone`. +`clone` on each item. Thus, the type stored in the slice must implement `Clone`. The `Copy` trait allows you to duplicate a value by only copying bits stored on -the stack; no arbitrary code is necessary. See “Stack-Only Data: Copy” on page -XX for more information on `Copy`. +the stack; no arbitrary code is necessary. See the “Stack-Only Data: +Copy” section in Chapter 4 for more +information on `Copy`. The `Copy` trait doesn’t define any methods to prevent programmers from overloading those methods and violating the assumption that no arbitrary code @@ -518,7 +502,7 @@ the code more concise. Everything possible with `Copy` you can also accomplish with `Clone`, but the code might be slower or have to use `clone` in places. -## Hash for Mapping a Value to a Value of Fixed Size +### Hash for Mapping a Value to a Value of Fixed Size The `Hash` trait allows you to take an instance of a type of arbitrary size and map that instance to a value of fixed size using a hash function. Deriving @@ -529,7 +513,7 @@ meaning all fields or values must also implement `Hash` to derive `Hash`. An example of when `Hash` is required is in storing keys in a `HashMap` to store data efficiently. -## Default for Default Values +### Default for Default Values The `Default` trait allows you to create a default value for a type. Deriving `Default` implements the `default` function. The derived implementation of the @@ -538,9 +522,10 @@ meaning all fields or values in the type must also implement `Default` to derive `Default`. The `Default::default` function is commonly used in combination with the struct -update syntax discussed in “Creating Instances from Other Instances with Struct -Update Syntax” on page XX. You can customize a few fields of a struct and then -set and use a default value for the rest of the fields by using +update syntax discussed in the “Creating Instances from Other Instances with +Struct Update +Syntax” section in Chapter 5. You can customize a few fields of a struct and +then set and use a default value for the rest of the fields by using `..Default::default()`. The `Default` trait is required when you use the method `unwrap_or_default` on @@ -554,15 +539,15 @@ In this appendix, we talk about some useful development tools that the Rust project provides. We’ll look at automatic formatting, quick ways to apply warning fixes, a linter, and integrating with IDEs. -## Automatic Formatting with rustfmt +### Automatic Formatting with rustfmt The `rustfmt` tool reformats your code according to the community code style. Many collaborative projects use `rustfmt` to prevent arguments about which -style to use when writing Rust: everyone formats their code using the tool. +style to use when writing Rust: Everyone formats their code using the tool. Rust installations include `rustfmt` by default, so you should already have the programs `rustfmt` and `cargo-fmt` on your system. These two commands are -analagous to `rustc` and `cargo` in that `rustfmt` allows finer-grained control +analogous to `rustc` and `cargo` in that `rustfmt` allows finer grained control and `cargo-fmt` understands conventions of a project that uses Cargo. To format any Cargo project, enter the following: @@ -574,7 +559,7 @@ Running this command reformats all the Rust code in the current crate. This should only change the code style, not the code semantics. For more information on `rustfmt`, see its documentation at *https://github.com/rust-lang/rustfmt*. -## Fix Your Code with rustfix +### Fix Your Code with rustfix The `rustfix` tool is included with Rust installations and can automatically fix compiler warnings that have a clear way to correct the problem that’s @@ -584,36 +569,31 @@ example, consider this code: Filename: src/main.rs ``` -fn do_something() {} - fn main() { - for i in 0..100 { - do_something(); - } + let mut x = 42; + println!("{x}"); } ``` -Here, we’re calling the `do_something` function 100 times, but we never use the -variable `i` in the body of the `for` loop. Rust warns us about that: +Here, we’re defining the variable `x` as mutable, but we never actually mutate +it. Rust warns us about that: ``` $ cargo build Compiling myprogram v0.1.0 (file:///projects/myprogram) -warning: unused variable: `i` - --> src/main.rs:4:9 +warning: variable does not need to be mutable + --> src/main.rs:2:9 | -4 | for i in 0..100 { - | ^ help: consider using `_i` instead +2 | let mut x = 0; + | ----^ + | | + | help: remove this `mut` | - = note: #[warn(unused_variables)] on by default - - Finished dev [unoptimized + debuginfo] target(s) in 0.50s + = note: `#[warn(unused_mut)]` on by default ``` -The warning suggests that we use `_i` as a name instead: the underscore -indicates that we intend for this variable to be unused. We can automatically -apply that suggestion using the `rustfix` tool by running the command `cargo -fix`: +The warning suggests that we remove the `mut` keyword. We can automatically +apply that suggestion using the `rustfix` tool by running the command `cargo fix`: ``` $ cargo fix @@ -628,25 +608,22 @@ code: Filename: src/main.rs ``` -fn do_something() {} - fn main() { - for _i in 0..100 { - do_something(); - } + let x = 42; + println!("{x}"); } ``` -The `for` loop variable is now named `_i`, and the warning no longer appears. +The variable `x` is now immutable, and the warning no longer appears. You can also use the `cargo fix` command to transition your code between different Rust editions. Editions are covered in Appendix E. -## More Lints with Clippy +### More Lints with Clippy -The Clippy tool is a collection of lints to analyze your code so you can catch -common mistakes and improve your Rust code. Clippy is included with standard -Rust installations. +The Clippy tool is a collection of lints to analyze your code so that you can +catch common mistakes and improve your Rust code. Clippy is included with +standard Rust installations. To run Clippy’s lints on any Cargo project, enter the following: @@ -657,7 +634,7 @@ $ cargo clippy For example, say you write a program that uses an approximation of a mathematical constant, such as pi, as this program does: -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -667,6 +644,8 @@ fn main() { } ``` + + Running `cargo clippy` on this project results in this error: ``` @@ -678,8 +657,7 @@ error: approximate value of `f{32, 64}::consts::PI` found | = note: `#[deny(clippy::approx_constant)]` on by default = help: consider using the constant directly - = help: for further information visit https://rust-lang.github.io/rust- -clippy/master/index.html#approx_constant + = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#approx_constant ``` This error lets you know that Rust already has a more precise `PI` constant @@ -688,7 +666,7 @@ instead. You would then change your code to use the `PI` constant. The following code doesn’t result in any errors or warnings from Clippy: -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -698,22 +676,22 @@ fn main() { } ``` -For more information on Clippy, see its documentation at -*https://github.com/rust-lang/rust-clippy**.* -## IDE Integration Using rust-analyzer + +For more information on Clippy, see its documentation at *https://github.com/rust-lang/rust-clippy*. + +### IDE Integration Using rust-analyzer To help with IDE integration, the Rust community recommends using -`rust-analyzer`. This tool is a set of compiler-centric utilities that speak -Language Server Protocol, which is a specification for IDEs and programming -languages to communicate with each other. Different clients can use -`rust-analyzer`, such as the Rust analyzer plug-in for Visual Studio Code at -*https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer*. +`rust-analyzer`. This tool is a set of +compiler-centric utilities that speak Language Server Protocol, which is a specification for IDEs and programming languages to +communicate with each other. Different clients can use `rust-analyzer`, such as +the Rust analyzer plug-in for Visual Studio Code at *https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer*. -Visit the `rust-analyzer` project’s home page at -*https://rust-analyzer.github.io* for installation instructions, then install -the language server support in your particular IDE. Your IDE will gain -capabilities such as autocompletion, jump to definition, and inline errors +Visit the `rust-analyzer` project’s home page +for installation instructions, then install the language server support in your +particular IDE. Your IDE will gain capabilities such as autocompletion, jump to +definition, and inline errors. ## Appendix E: Editions @@ -727,7 +705,7 @@ while, all of these tiny changes add up. But from release to release, it can be difficult to look back and say, “Wow, between Rust 1.10 and Rust 1.31, Rust has changed a lot!” -Every two or three years, the Rust team produces a new Rust *edition*. Each +Every three years or so, the Rust team produces a new Rust *edition*. Each edition brings together the features that have landed into a clear package with fully updated documentation and tooling. New editions ship as part of the usual six-week release process. @@ -735,14 +713,15 @@ six-week release process. Editions serve different purposes for different people: * For active Rust users, a new edition brings together incremental changes into -an easy-to-understand package. + an easy-to-understand package. * For non-users, a new edition signals that some major advancements have -landed, which might make Rust worth another look. + landed, which might make Rust worth another look. * For those developing Rust, a new edition provides a rallying point for the -project as a whole. + project as a whole. -At the time of this writing, three Rust editions are available: Rust 2015, Rust -2018, and Rust 2021. This book is written using Rust 2021 edition idioms. +At the time of this writing, four Rust editions are available: Rust 2015, Rust +2018, Rust 2021, and Rust 2024. This book is written using Rust 2024 edition +idioms. The `edition` key in *Cargo.toml* indicates which edition the compiler should use for your code. If the key doesn’t exist, Rust uses `2015` as the edition @@ -762,14 +741,250 @@ Rust 2018, your project will compile and be able to use that dependency. The opposite situation, where your project uses Rust 2018 and a dependency uses Rust 2015, works as well. -To be clear: most features will be available on all editions. Developers using +To be clear: Most features will be available on all editions. Developers using any Rust edition will continue to see improvements as new stable releases are made. However, in some cases, mainly when new keywords are added, some new features might only be available in later editions. You will need to switch editions if you want to take advantage of such features. -For more details, *The* *Edition Guide* at -*https://doc.rust-lang.org/stable/edition-guide* is a complete book about -editions that enumerates the differences between editions and explains how to -automatically upgrade your code to a new edition via `cargo fix`. +For more details, see *The Rust Edition Guide* at *https://doc.rust-lang.org/stable/edition-guide*. This is a +complete book that enumerates the differences between editions and explains how +to automatically upgrade your code to a new edition via `cargo fix`. + +## Appendix F: Translations of the Book + +For resources in languages other than English. Most are still in progress; see +the Translations label at *https://github.com/rust-lang/book/issues?q=is%3Aopen+is%3Aissue+label%3ATranslations* to help or let us know about a new translation! + +* Português at *https://github.com/rust-br/rust-book-pt-br* (BR) +* Português at *https://github.com/nunojesus/rust-book-pt-pt* (PT) +* 简体中文: KaiserY/trpl-zh-cn at *https://github.com/KaiserY/trpl-zh-cn*, gnu4cn/rust-lang-Zh_CN at *https://github.com/gnu4cn/rust-lang-Zh_CN* +* 正體中文 at *https://github.com/rust-tw/book-tw* +* Українська at *https://rust-lang-ua.github.io/rustbook_ukrainian* +* Español at *https://github.com/thecodix/book*, alternate at *https://github.com/ManRR/rust-book-es*, Español por RustLangES at *https://github.com/RustLangES/rust-book-es* +* Русский at *https://github.com/rust-lang-ru/book* +* 한국어 at *https://github.com/rust-kr/doc.rust-kr.org* +* 日本語 at *https://github.com/rust-lang-ja/book-ja* +* Français at *https://github.com/Jimskapt/rust-book-fr* +* Polski at *https://github.com/paytchoo/book-pl* +* Cebuano at *https://github.com/agentzero1/book* +* Tagalog at *https://github.com/josephace135/book* +* Esperanto at *https://github.com/psychoslave/Rust-libro* +* ελληνική at *https://github.com/TChatzigiannakis/rust-book-greek* +* Svenska at *https://github.com/sebras/book* +* Farsi at *https://github.com/RustFarsi/book*, Persian (FA) at *https://github.com/persian-rust/book* +* Deutsch at *https://github.com/rust-lang-de/rustbook-de* +* हिंदी at *https://github.com/venkatarun95/rust-book-hindi* +* ไทย at *https://github.com/rust-lang-th/book-th* +* Danske at *https://github.com/DanKHansen/book-dk* +* O’zbek at *https://github.com/rust-lang-uz/book* +* Tiếng Việt at *https://github.com/tuanemdev/rust-book-vn* +* Italiano at *https://nixxo.github.io/rust-lang-book-it/* +* বাংলা at *https://github.com/IsmailHosenIsmailJames/rust-book-bn* + +## Appendix G - How Rust is Made and “Nightly Rust” + +This appendix is about how Rust is made and how that affects you as a Rust +developer. + +### Stability Without Stagnation + +As a language, Rust cares a *lot* about the stability of your code. We want +Rust to be a rock-solid foundation you can build on, and if things were +constantly changing, that would be impossible. At the same time, if we can’t +experiment with new features, we may not find out important flaws until after +their release, when we can no longer change things. + +Our solution to this problem is what we call “stability without stagnation”, +and our guiding principle is this: you should never have to fear upgrading to a +new version of stable Rust. Each upgrade should be painless, but should also +bring you new features, fewer bugs, and faster compile times. + +### Choo, Choo! Release Channels and Riding the Trains + +Rust development operates on a *train schedule*. That is, all development is +done in the main branch of the Rust repository. Releases follow a software +release train model, which has been used by Cisco IOS and other software +projects. There are three *release channels* for Rust: + +* Nightly +* Beta +* Stable + +Most Rust developers primarily use the stable channel, but those who want to +try out experimental new features may use nightly or beta. + +Here’s an example of how the development and release process works: let’s +assume that the Rust team is working on the release of Rust 1.5. That release +happened in December of 2015, but it will provide us with realistic version +numbers. A new feature is added to Rust: a new commit lands on the main +branch. Each night, a new nightly version of Rust is produced. Every day is a +release day, and these releases are created by our release infrastructure +automatically. So as time passes, our releases look like this, once a night: + +``` +nightly: * - - * - - * +``` + +Every six weeks, it’s time to prepare a new release! The `beta` branch of the +Rust repository branches off from the main branch used by nightly. Now, +there are two releases: + +``` +nightly: * - - * - - * + | +beta: * +``` + +Most Rust users do not use beta releases actively, but test against beta in +their CI system to help Rust discover possible regressions. In the meantime, +there’s still a nightly release every night: + +``` +nightly: * - - * - - * - - * - - * + | +beta: * +``` + +Let’s say a regression is found. Good thing we had some time to test the beta +release before the regression snuck into a stable release! The fix is applied +to the main branch, so that nightly is fixed, and then the fix is backported to +the `beta` branch, and a new release of beta is produced: + +``` +nightly: * - - * - - * - - * - - * - - * + | +beta: * - - - - - - - - * +``` + +Six weeks after the first beta was created, it’s time for a stable release! The +`stable` branch is produced from the `beta` branch: + +``` +nightly: * - - * - - * - - * - - * - - * - * - * + | +beta: * - - - - - - - - * + | +stable: * +``` + +Hooray! Rust 1.5 is done! However, we’ve forgotten one thing: because the six +weeks have gone by, we also need a new beta of the *next* version of Rust, 1.6. +So after `stable` branches off of `beta`, the next version of `beta` branches +off of `nightly` again: + +``` +nightly: * - - * - - * - - * - - * - - * - * - * + | | +beta: * - - - - - - - - * * + | +stable: * +``` + +This is called the “train model” because every six weeks, a release “leaves the +station”, but still has to take a journey through the beta channel before it +arrives as a stable release. + +Rust releases every six weeks, like clockwork. If you know the date of one Rust +release, you can know the date of the next one: it’s six weeks later. A nice +aspect of having releases scheduled every six weeks is that the next train is +coming soon. If a feature happens to miss a particular release, there’s no need +to worry: another one is happening in a short time! This helps reduce pressure +to sneak possibly unpolished features in close to the release deadline. + +Thanks to this process, you can always check out the next build of Rust and +verify for yourself that it’s easy to upgrade to: if a beta release doesn’t +work as expected, you can report it to the team and get it fixed before the +next stable release happens! Breakage in a beta release is relatively rare, but +`rustc` is still a piece of software, and bugs do exist. + +### Maintenance time + +The Rust project supports the most recent stable version. When a new stable +version is released, the old version reaches its end of life (EOL). This means +each version is supported for six weeks. + +### Unstable Features + +There’s one more catch with this release model: unstable features. Rust uses a +technique called “feature flags” to determine what features are enabled in a +given release. If a new feature is under active development, it lands on the +main branch, and therefore, in nightly, but behind a *feature flag*. If you, as +a user, wish to try out the work-in-progress feature, you can, but you must be +using a nightly release of Rust and annotate your source code with the +appropriate flag to opt in. + +If you’re using a beta or stable release of Rust, you can’t use any feature +flags. This is the key that allows us to get practical use with new features +before we declare them stable forever. Those who wish to opt into the bleeding +edge can do so, and those who want a rock-solid experience can stick with +stable and know that their code won’t break. Stability without stagnation. + +This book only contains information about stable features, as in-progress +features are still changing, and surely they’ll be different between when this +book was written and when they get enabled in stable builds. You can find +documentation for nightly-only features online. + +### Rustup and the Role of Rust Nightly + +Rustup makes it easy to change between different release channels of Rust, on a +global or per-project basis. By default, you’ll have stable Rust installed. To +install nightly, for example: + +``` +$ rustup toolchain install nightly +``` + +You can see all of the *toolchains* (releases of Rust and associated +components) you have installed with `rustup` as well. Here’s an example on one +of your authors’ Windows computer: + +``` +> rustup toolchain list +stable-x86_64-pc-windows-msvc (default) +beta-x86_64-pc-windows-msvc +nightly-x86_64-pc-windows-msvc +``` + +As you can see, the stable toolchain is the default. Most Rust users use stable +most of the time. You might want to use stable most of the time, but use +nightly on a specific project, because you care about a cutting-edge feature. +To do so, you can use `rustup override` in that project’s directory to set the +nightly toolchain as the one `rustup` should use when you’re in that directory: + +``` +$ cd ~/projects/needs-nightly +$ rustup override set nightly +``` +Now, every time you call `rustc` or `cargo` inside of +*~/projects/needs-nightly*, `rustup` will make sure that you are using nightly +Rust, rather than your default of stable Rust. This comes in handy when you +have a lot of Rust projects! + +### The RFC Process and Teams + +So how do you learn about these new features? Rust’s development model follows +a *Request For Comments (RFC) process*. If you’d like an improvement in Rust, +you can write up a proposal, called an RFC. + +Anyone can write RFCs to improve Rust, and the proposals are reviewed and +discussed by the Rust team, which is comprised of many topic subteams. There’s +a full list of the teams on Rust’s website at *https://www.rust-lang.org/governance*, which includes teams for +each area of the project: language design, compiler implementation, +infrastructure, documentation, and more. The appropriate team reads the +proposal and the comments, writes some comments of their own, and eventually, +there’s consensus to accept or reject the feature. + +If the feature is accepted, an issue is opened on the Rust repository, and +someone can implement it. The person who implements it very well may not be the +person who proposed the feature in the first place! When the implementation is +ready, it lands on the main branch behind a feature gate, as we discussed in +the “Unstable Features” section. + +After some time, once Rust developers who use nightly releases have been able +to try out the new feature, team members will discuss the feature, how it’s +worked out on nightly, and decide if it should make it into stable Rust or not. +If the decision is to move forward, the feature gate is removed, and the +feature is now considered stable! It rides the trains into a new stable release +of Rust. diff --git a/nostarch/appendix_a.md b/nostarch/appendix_a.md index ca3883be48..92b3c83393 100644 --- a/nostarch/appendix_a.md +++ b/nostarch/appendix_a.md @@ -10,62 +10,62 @@ directory, so all fixes need to be made in `/src/`. The following lists contain keywords that are reserved for current or future use by the Rust language. As such, they cannot be used as identifiers (except -as raw identifiers, as we’ll discuss in “Raw Identifiers” on page XX). -*Identifiers* are names of functions, variables, parameters, struct fields, -modules, crates, constants, macros, static values, attributes, types, traits, -or lifetimes. +as raw identifiers, as we discuss in the “Raw +Identifiers” section). *Identifiers* are names +of functions, variables, parameters, struct fields, modules, crates, constants, +macros, static values, attributes, types, traits, or lifetimes. -## Keywords Currently in Use +### Keywords Currently in Use The following is a list of keywords currently in use, with their functionality described. -* **`as` **: perform primitive casting, disambiguate the specific trait -containing an item, or rename items in `use` statements -* **`async` **: return a `Future` instead of blocking the current thread -* **`await` **: suspend execution until the result of a `Future` is ready -* **`break` **: exit a loop immediately -* **`const` **: define constant items or constant raw pointers -* **`continue` **: continue to the next loop iteration -* **`crate` **: in a module path, refers to the crate root -* **`dyn` **: dynamic dispatch to a trait object -* **`else` **: fallback for `if` and `if let` control flow constructs -* **`enum` **: define an enumeration -* **`extern` **: link an external function or variable -* **`false` **: Boolean false literal -* **`fn` **: define a function or the function pointer type -* **`for` **: loop over items from an iterator, implement a trait, or specify a -higher-ranked lifetime -* **`if` **: branch based on the result of a conditional expression -* **`impl` **: implement inherent or trait functionality -* **`in` **: part of `for` loop syntax -* **`let` **: bind a variable -* **`loop` **: loop unconditionally -* **`match` **: match a value to patterns -* **`mod` **: define a module -* **`move` **: make a closure take ownership of all its captures -* **`mut` **: denote mutability in references, raw pointers, or pattern bindings -* **`pub` **: denote public visibility in struct fields, `impl` blocks, or -modules -* **`ref` **: bind by reference -* **`return` **: return from function -* **`Self` **: a type alias for the type we are defining or implementing -* **`self` **: method subject or current module -* **`static` **: global variable or lifetime lasting the entire program -execution -* **`struct` **: define a structure -* **`super` **: parent module of the current module -* **`trait` **: define a trait -* **`true` **: Boolean true literal -* **`type` **: define a type alias or associated type -* **`union` **: define a union; is a keyword only when used in a union -declaration -* **`unsafe` **: denote unsafe code, functions, traits, or implementations -* **`use` **: bring symbols into scope -* **`where` **: denote clauses that constrain a type -* **`while` **: loop conditionally based on the result of an expression - -## Keywords Reserved for Future Use +* **`as`**: Perform primitive casting, disambiguate the specific trait + containing an item, or rename items in `use` statements. +* **`async`**: Return a `Future` instead of blocking the current thread. +* **`await`**: Suspend execution until the result of a `Future` is ready. +* **`break`**: Exit a loop immediately. +* **`const`**: Define constant items or constant raw pointers. +* **`continue`**: Continue to the next loop iteration. +* **`crate`**: In a module path, refers to the crate root. +* **`dyn`**: Dynamic dispatch to a trait object. +* **`else`**: Fallback for `if` and `if let` control flow constructs. +* **`enum`**: Define an enumeration. +* **`extern`**: Link an external function or variable. +* **`false`**: Boolean false literal. +* **`fn`**: Define a function or the function pointer type. +* **`for`**: Loop over items from an iterator, implement a trait, or specify a + higher ranked lifetime. +* **`if`**: Branch based on the result of a conditional expression. +* **`impl`**: Implement inherent or trait functionality. +* **`in`**: Part of `for` loop syntax. +* **`let`**: Bind a variable. +* **`loop`**: Loop unconditionally. +* **`match`**: Match a value to patterns. +* **`mod`**: Define a module. +* **`move`**: Make a closure take ownership of all its captures. +* **`mut`**: Denote mutability in references, raw pointers, or pattern bindings. +* **`pub`**: Denote public visibility in struct fields, `impl` blocks, or + modules. +* **`ref`**: Bind by reference. +* **`return`**: Return from function. +* **`Self`**: A type alias for the type we are defining or implementing. +* **`self`**: Method subject or current module. +* **`static`**: Global variable or lifetime lasting the entire program + execution. +* **`struct`**: Define a structure. +* **`super`**: Parent module of the current module. +* **`trait`**: Define a trait. +* **`true`**: Boolean true literal. +* **`type`**: Define a type alias or associated type. +* **`union`**: Define a union; is a keyword only when + used in a union declaration. +* **`unsafe`**: Denote unsafe code, functions, traits, or implementations. +* **`use`**: Bring symbols into scope. +* **`where`**: Denote clauses that constrain a type. +* **`while`**: Loop conditionally based on the result of an expression. + +### Keywords Reserved for Future Use The following keywords do not yet have any functionality but are reserved by Rust for potential future use: @@ -75,6 +75,7 @@ Rust for potential future use: * `box` * `do` * `final` +* `gen` * `macro` * `override` * `priv` @@ -84,7 +85,7 @@ Rust for potential future use: * `virtual` * `yield` -## Raw Identifiers +### Raw Identifiers *Raw identifiers* are the syntax that lets you use keywords where they wouldn’t normally be allowed. You use a raw identifier by prefixing a keyword with `r#`. @@ -130,13 +131,12 @@ This code will compile without any errors. Note the `r#` prefix on the function name in its definition as well as where the function is called in `main`. Raw identifiers allow you to use any word you choose as an identifier, even if -that word happens to be a reserved keyword. This gives us more freedom to -choose identifier names, as well as lets us integrate with programs written in -a language where these words aren’t keywords. In addition, raw identifiers -allow you to use libraries written in a different Rust edition than your crate -uses. For example, `try` isn’t a keyword in the 2015 edition but is in the 2018 -and 2021 editions. If you depend on a library that is written using the 2015 +that word happens to be a reserved keyword. This gives us more freedom to choose +identifier names, as well as lets us integrate with programs written in a +language where these words aren’t keywords. In addition, raw identifiers allow +you to use libraries written in a different Rust edition than your crate uses. +For example, `try` isn’t a keyword in the 2015 edition but is in the 2018, 2021, +and 2024 editions. If you depend on a library that is written using the 2015 edition and has a `try` function, you’ll need to use the raw identifier syntax, -`r#try` in this case, to call that function from your 2021 edition code. See -Appendix E for more information on editions. - +`r#try` in this case, to call that function from your code on later editions. +See Appendix E for more information on editions. diff --git a/nostarch/appendix_b.md b/nostarch/appendix_b.md index 236608b6d2..4d894dd51e 100644 --- a/nostarch/appendix_b.md +++ b/nostarch/appendix_b.md @@ -46,9 +46,10 @@ type | | | `-` | `- expr` | Arithmetic negation | `Neg` | | `-` | `expr - expr` | Arithmetic subtraction | `Sub` | | `-=` | `var -= expr` | Arithmetic subtraction and assignment | `SubAssign` | -| `->` | `fn(...) -> type`, `|…| -> type` | Function and closure return type | -| -| `. | `expr.ident` | Member access | | +| `->` | `fn(...) -> type`, `|...| -> type` | Function and closure return type | | +| `.` | `expr.ident` | Field access | | +| `.` | `expr.ident(expr, ...)` | Method call | | +| `.` | `expr.0`, `expr.1`, and so on | Tuple indexing | | | `..` | `..`, `expr..`, `..expr`, `expr..expr` | Right-exclusive range literal | `PartialOrd` | | `..=` | `..=expr`, `expr..=expr` | Right-inclusive range literal | @@ -60,7 +61,7 @@ binding | | inclusive range pattern | | | `/` | `expr / expr` | Arithmetic division | `Div` | | `/=` | `var /= expr` | Arithmetic division and assignment | `DivAssign` | -| `: | `pat: type`, `ident: type` | Constraints | | +| `:` | `pat: type`, `ident: type` | Constraints | | | `:` | `ident: expr` | Struct field initializer | | | `:` | `'a: loop {...}` | Loop label | | | `;` | `expr;` | Statement and item terminator | | @@ -93,13 +94,13 @@ is, they don’t behave like a function or method call. Table B-2 shows symbols that appear on their own and are valid in a variety of locations. -Table B-2: Stand-Alone Syntax +Table B-2: Stand-alone Syntax | Symbol | Explanation | |---|---| | `'ident` | Named lifetime or loop label | -| `...u8`, `...i32`, `...f64`, `...usize`, and so on | Numeric literal of -specific type | +| Digits immediately followed by `u8`, `i32`, `f64`, `usize`, and so on | +Numeric literal of specific type | | `"..."` | String literal | | `r"..."`, `r#"..."#`, `r##"..."##`, and so on | Raw string literal; escape characters not processed | @@ -109,7 +110,7 @@ string | combination of raw and byte string literal | | `'...'` | Character literal | | `b'...'` | ASCII byte literal | -| `|…| expr` | Closure | +| `|...| expr` | Closure | | `!` | Always-empty bottom type for diverging functions | | `_` | “Ignored” pattern binding; also used to make integer literals readable | @@ -146,14 +147,14 @@ Table B-4: Generics |---|---| | `path<...>` | Specifies parameters to a generic type in a type (for example, `Vec`) | -| `path::<...>, method::<...>` | Specifies parameters to a generic type, -function, or method in an expression; often referred to as turbofish (for +| `path::<...>`, `method::<...>` | Specifies parameters to a generic type, +function, or method in an expression; often referred to as *turbofish* (for example, `"42".parse::()`) | | `fn ident<...> ...` | Define generic function | | `struct ident<...> ...` | Define generic structure | | `enum ident<...> ...` | Define generic enumeration | | `impl<...> ...` | Define generic implementation | -| `for<...> type` | Higher-ranked lifetime bounds | +| `for<...> type` | Higher ranked lifetime bounds | | `type` | A generic type where one or more associated types have specific assignments (for example, `Iterator`) | @@ -164,7 +165,7 @@ Table B-5: Trait Bound Constraints | Symbol | Explanation | |---|---| -| T: U` | Generic parameter `T` constrained to types that implement `U` | +| `T: U` | Generic parameter `T` constrained to types that implement `U` | | `T: 'a` | Generic type `T` must outlive lifetime `'a` (meaning the type cannot transitively contain any references with lifetimes shorter than `'a`) | | `T: 'static` | Generic type `T` contains no borrowed references other than @@ -183,8 +184,8 @@ Table B-6: Macros and Attributes | `#[meta]` | Outer attribute | | `#![meta]` | Inner attribute | | `$ident` | Macro substitution | -| `$ident:kind` | Macro capture | -| `$(…)…` | Macro repetition | +| `$ident:kind` | Macro metavariable | +| `$(...)...` | Macro repetition | | `ident!(...)`, `ident!{...}`, `ident![...]` | Macro invocation | Table B-7 shows symbols that create comments. @@ -200,9 +201,9 @@ Table B-7: Comments | `/*!...*/` | Inner block doc comment | | `/**...*/` | Outer block doc comment | -Table B-8 shows symbols that appear in the context of using tuples. +Table B-8 shows the contexts in which parentheses are used. -Table B-8: Tuples +Table B-8: Parentheses | Symbol | Explanation | |---|---| @@ -214,7 +215,6 @@ Table B-8: Tuples | `(type, ...)` | Tuple type | | `expr(expr, ...)` | Function call expression; also used to initialize tuple `struct`s and tuple `enum` variants | -| `expr.0`, `expr.1`, and so on | Tuple indexing | Table B-9 shows the contexts in which curly brackets are used. @@ -223,7 +223,7 @@ Table B-9: Curly Brackets | Context | Explanation | |---|---| | `{...}` | Block expression | -| `Type {...}` | `struct` literal | +| `Type {...}` | Struct literal | Table B-10 shows the contexts in which square brackets are used. diff --git a/nostarch/appendix_c.md b/nostarch/appendix_c.md index 53131eb5fa..4023b12fa7 100644 --- a/nostarch/appendix_c.md +++ b/nostarch/appendix_c.md @@ -39,9 +39,10 @@ would be most relevant to them? The Rust compiler doesn’t have this insight, s it can’t provide appropriate default behavior for you. The list of derivable traits provided in this appendix is not comprehensive: -libraries can implement `derive` for their own traits, making the list of +Libraries can implement `derive` for their own traits, making the list of traits you can use `derive` with truly open ended. Implementing `derive` -involves using a procedural macro, which is covered in “Macros” on page XX. +involves using a procedural macro, which is covered in the “Custom `derive` +Macros” section in Chapter 20. ## Debug for Programmer Output @@ -54,8 +55,8 @@ at a particular point in a program’s execution. The `Debug` trait is required, for example, in the use of the `assert_eq!` macro. This macro prints the values of instances given as arguments if the -equality assertion fails so programmers can see why the two instances weren’t -equal. +equality assertion fails so that programmers can see why the two instances +weren’t equal. ## PartialEq and Eq for Equality Comparisons @@ -64,7 +65,7 @@ equality and enables use of the `==` and `!=` operators. Deriving `PartialEq` implements the `eq` method. When `PartialEq` is derived on structs, two instances are equal only if *all* fields are equal, and the -instances are not equal if any fields are not equal. When derived on enums, +instances are not equal if *any* fields are not equal. When derived on enums, each variant is equal to itself and not equal to the other variants. The `PartialEq` trait is required, for example, with the use of the @@ -75,7 +76,7 @@ The `Eq` trait has no methods. Its purpose is to signal that for every value of the annotated type, the value is equal to itself. The `Eq` trait can only be applied to types that also implement `PartialEq`, although not all types that implement `PartialEq` can implement `Eq`. One example of this is floating-point -number types: the implementation of floating-point numbers states that two +number types: The implementation of floating-point numbers states that two instances of the not-a-number (`NaN`) value are not equal to each other. An example of when `Eq` is required is for keys in a `HashMap` so that @@ -91,8 +92,8 @@ that also implement `PartialEq`. Deriving `PartialOrd` implements the `partial_cmp` method, which returns an `Option` that will be `None` when the values given don’t produce an ordering. An example of a value that doesn’t produce an ordering, even though -most values of that type can be compared, is the not-a-number (`NaN`) floating -point value. Calling `partial_cmp` with any floating-point number and the `NaN` +most values of that type can be compared, is the `NaN` floating point value. +Calling `partial_cmp` with any floating-point number and the `NaN` floating-point value will return `None`. When derived on structs, `PartialOrd` compares two instances by comparing the @@ -119,8 +120,8 @@ a data structure that stores data based on the sort order of the values. The `Clone` trait allows you to explicitly create a deep copy of a value, and the duplication process might involve running arbitrary code and copying heap -data. See “Variables and Data Interacting with Clone” on page XX for more -information on `Clone`. +data. See the “Variables and Data Interacting with Clone” section in Chapter 4 +for more information on `Clone`. Deriving `Clone` implements the `clone` method, which when implemented for the whole type, calls `clone` on each of the parts of the type. This means all the @@ -129,11 +130,11 @@ fields or values in the type must also implement `Clone` to derive `Clone`. An example of when `Clone` is required is when calling the `to_vec` method on a slice. The slice doesn’t own the type instances it contains, but the vector returned from `to_vec` will need to own its instances, so `to_vec` calls -`clone` on each item. Thus the type stored in the slice must implement `Clone`. +`clone` on each item. Thus, the type stored in the slice must implement `Clone`. The `Copy` trait allows you to duplicate a value by only copying bits stored on -the stack; no arbitrary code is necessary. See “Stack-Only Data: Copy” on page -XX for more information on `Copy`. +the stack; no arbitrary code is necessary. See the “Stack-Only Data: Copy” +section in Chapter 4 for more information on `Copy`. The `Copy` trait doesn’t define any methods to prevent programmers from overloading those methods and violating the assumption that no arbitrary code @@ -172,9 +173,9 @@ meaning all fields or values in the type must also implement `Default` to derive `Default`. The `Default::default` function is commonly used in combination with the struct -update syntax discussed in “Creating Instances from Other Instances with Struct -Update Syntax” on page XX. You can customize a few fields of a struct and then -set and use a default value for the rest of the fields by using +update syntax discussed in the “Creating Instances with Struct Update Syntax” +section in Chapter 5. You can customize a few fields of a struct and then set +and use a default value for the rest of the fields by using `..Default::default()`. The `Default` trait is required when you use the method `unwrap_or_default` on diff --git a/nostarch/appendix_d.md b/nostarch/appendix_d.md index 96b73e9544..48a5fa33d0 100644 --- a/nostarch/appendix_d.md +++ b/nostarch/appendix_d.md @@ -16,11 +16,11 @@ warning fixes, a linter, and integrating with IDEs. The `rustfmt` tool reformats your code according to the community code style. Many collaborative projects use `rustfmt` to prevent arguments about which -style to use when writing Rust: everyone formats their code using the tool. +style to use when writing Rust: Everyone formats their code using the tool. Rust installations include `rustfmt` by default, so you should already have the programs `rustfmt` and `cargo-fmt` on your system. These two commands are -analagous to `rustc` and `cargo` in that `rustfmt` allows finer-grained control +analogous to `rustc` and `cargo` in that `rustfmt` allows finer grained control and `cargo-fmt` understands conventions of a project that uses Cargo. To format any Cargo project, enter the following: @@ -42,34 +42,30 @@ example, consider this code: Filename: src/main.rs ``` -fn do_something() {} - fn main() { - for i in 0..100 { - do_something(); - } + let mut x = 42; + println!("{x}"); } ``` -Here, we’re calling the `do_something` function 100 times, but we never use the -variable `i` in the body of the `for` loop. Rust warns us about that: +Here, we’re defining the variable `x` as mutable, but we never actually mutate +it. Rust warns us about that: ``` $ cargo build Compiling myprogram v0.1.0 (file:///projects/myprogram) -warning: unused variable: `i` - --> src/main.rs:4:9 +warning: variable does not need to be mutable + --> src/main.rs:2:9 | -4 | for i in 0..100 { - | ^ help: consider using `_i` instead +2 | let mut x = 0; + | ----^ + | | + | help: remove this `mut` | - = note: #[warn(unused_variables)] on by default - - Finished dev [unoptimized + debuginfo] target(s) in 0.50s + = note: `#[warn(unused_mut)]` on by default ``` -The warning suggests that we use `_i` as a name instead: the underscore -indicates that we intend for this variable to be unused. We can automatically +The warning suggests that we remove the `mut` keyword. We can automatically apply that suggestion using the `rustfix` tool by running the command `cargo fix`: @@ -86,25 +82,22 @@ code: Filename: src/main.rs ``` -fn do_something() {} - fn main() { - for _i in 0..100 { - do_something(); - } + let x = 42; + println!("{x}"); } ``` -The `for` loop variable is now named `_i`, and the warning no longer appears. +The variable `x` is now immutable, and the warning no longer appears. You can also use the `cargo fix` command to transition your code between different Rust editions. Editions are covered in Appendix E. ## More Lints with Clippy -The Clippy tool is a collection of lints to analyze your code so you can catch -common mistakes and improve your Rust code. Clippy is included with standard -Rust installations. +The Clippy tool is a collection of lints to analyze your code so that you can +catch common mistakes and improve your Rust code. Clippy is included with +standard Rust installations. To run Clippy’s lints on any Cargo project, enter the following: @@ -157,7 +150,7 @@ fn main() { ``` For more information on Clippy, see its documentation at -*https://github.com/rust-lang/rust-clippy**.* +*https://github.com/rust-lang/rust-clippy*. ## IDE Integration Using rust-analyzer @@ -171,5 +164,5 @@ languages to communicate with each other. Different clients can use Visit the `rust-analyzer` project’s home page at *https://rust-analyzer.github.io* for installation instructions, then install the language server support in your particular IDE. Your IDE will gain -capabilities such as autocompletion, jump to definition, and inline errors +capabilities such as autocompletion, jump to definition, and inline errors. diff --git a/nostarch/appendix_e.md b/nostarch/appendix_e.md index ddb12b782b..f7244328cf 100644 --- a/nostarch/appendix_e.md +++ b/nostarch/appendix_e.md @@ -18,7 +18,7 @@ while, all of these tiny changes add up. But from release to release, it can be difficult to look back and say, “Wow, between Rust 1.10 and Rust 1.31, Rust has changed a lot!” -Every two or three years, the Rust team produces a new Rust *edition*. Each +Every three years or so, the Rust team produces a new Rust *edition*. Each edition brings together the features that have landed into a clear package with fully updated documentation and tooling. New editions ship as part of the usual six-week release process. @@ -32,8 +32,9 @@ landed, which might make Rust worth another look. * For those developing Rust, a new edition provides a rallying point for the project as a whole. -At the time of this writing, three Rust editions are available: Rust 2015, Rust -2018, and Rust 2021. This book is written using Rust 2021 edition idioms. +At the time of this writing, four Rust editions are available: Rust 2015, Rust +2018, Rust 2021, and Rust 2024. This book is written using Rust 2024 edition +idioms. The `edition` key in *Cargo.toml* indicates which edition the compiler should use for your code. If the key doesn’t exist, Rust uses `2015` as the edition @@ -53,14 +54,14 @@ Rust 2018, your project will compile and be able to use that dependency. The opposite situation, where your project uses Rust 2018 and a dependency uses Rust 2015, works as well. -To be clear: most features will be available on all editions. Developers using +To be clear: Most features will be available on all editions. Developers using any Rust edition will continue to see improvements as new stable releases are made. However, in some cases, mainly when new keywords are added, some new features might only be available in later editions. You will need to switch editions if you want to take advantage of such features. -For more details, *The* *Edition Guide* at -*https://doc.rust-lang.org/stable/edition-guide* is a complete book about -editions that enumerates the differences between editions and explains how to -automatically upgrade your code to a new edition via `cargo fix`. +For more details, see *The Rust Edition Guide* at +*https://doc.rust-lang.org/stable/edition-guide*. This is a complete book that +enumerates the differences between editions and explains how to automatically +upgrade your code to a new edition via `cargo fix`. diff --git a/nostarch/book.toml b/nostarch/book.toml new file mode 100644 index 0000000000..d80cfe2cbb --- /dev/null +++ b/nostarch/book.toml @@ -0,0 +1,29 @@ +[book] +title = "The Rust Programming Language" +authors = ["Steve Klabnik", "Carol Nichols", "Chris Krycho", "Contributions from the Rust Community"] +src = "../src" # needs to be explicit (it is implicit in `/book.toml`). + +[output.html] +additional-css = ["../ferris.css", "../theme/2018-edition.css", "../theme/semantic-notes.css"] +additional-js = ["../ferris.js"] +git-repository-url = "https://github.com/rust-lang/book" + +[build] +build-dir = "../tmp" + +[preprocessor.trpl-listing] +command = "cargo run --manifest-path ../packages/mdbook-trpl/Cargo.toml --bin mdbook-trpl-listing" +output-mode = "simple" + +# Only used in this version, *not* in the root `book.toml`, because its job is +# to remove `
` and `
` markup from the version we send them. +[preprocessor.trpl-figure] +command = "cargo run --manifest-path ../packages/mdbook-trpl/Cargo.toml --bin mdbook-trpl-figure" +output-mode = "simple" + +[preprocessor.trpl-heading] +command = "cargo run --manifest-path ../packages/mdbook-trpl/Cargo.toml --bin mdbook-trpl-heading" +output-mode = "simple" + +[rust] +edition = "2024" diff --git a/nostarch/chapter00.md b/nostarch/chapter00.md new file mode 100644 index 0000000000..5be07f2473 --- /dev/null +++ b/nostarch/chapter00.md @@ -0,0 +1,204 @@ + + +[TOC] + +# Introduction + +> Note: This edition of the book is the same as The Rust Programming +> Language at *https://nostarch.com/rust-programming-language-3rd-edition* available in print and ebook format from No Starch +> Press at *https://nostarch.com/*. + +Welcome to *The Rust Programming Language*, an introductory book about Rust. +The Rust programming language helps you write faster, more reliable software. +High-level ergonomics and low-level control are often at odds in programming +language design; Rust challenges that conflict. Through balancing powerful +technical capacity and a great developer experience, Rust gives you the option +to control low-level details (such as memory usage) without all the hassle +traditionally associated with such control. + +## Who Rust Is For + +Rust is ideal for many people for a variety of reasons. Let’s look at a few of +the most important groups. + +### Teams of Developers + +Rust is proving to be a productive tool for collaborating among large teams of +developers with varying levels of systems programming knowledge. Low-level code +is prone to various subtle bugs, which in most other languages can only be +caught through extensive testing and careful code review by experienced +developers. In Rust, the compiler plays a gatekeeper role by refusing to +compile code with these elusive bugs, including concurrency bugs. By working +alongside the compiler, the team can spend its time focusing on the program’s +logic rather than chasing down bugs. + +Rust also brings contemporary developer tools to the systems programming world: + +* Cargo, the included dependency manager and build tool, makes adding, + compiling, and managing dependencies painless and consistent across the Rust + ecosystem. +* The `rustfmt` formatting tool ensures a consistent coding style across + developers. +* The Rust Language Server powers integrated development environment (IDE) + integration for code completion and inline error messages. + +By using these and other tools in the Rust ecosystem, developers can be +productive while writing systems-level code. + +### Students + +Rust is for students and those who are interested in learning about systems +concepts. Using Rust, many people have learned about topics like operating +systems development. The community is very welcoming and happy to answer +students’ questions. Through efforts such as this book, the Rust teams want to +make systems concepts more accessible to more people, especially those new to +programming. + +### Companies + +Hundreds of companies, large and small, use Rust in production for a variety of +tasks, including command line tools, web services, DevOps tooling, embedded +devices, audio and video analysis and transcoding, cryptocurrencies, +bioinformatics, search engines, Internet of Things applications, machine +learning, and even major parts of the Firefox web browser. + +### Open Source Developers + +Rust is for people who want to build the Rust programming language, community, +developer tools, and libraries. We’d love to have you contribute to the Rust +language. + +### People Who Value Speed and Stability + +Rust is for people who crave speed and stability in a language. By speed, we +mean both how quickly Rust code can run and the speed at which Rust lets you +write programs. The Rust compiler’s checks ensure stability through feature +additions and refactoring. This is in contrast to the brittle legacy code in +languages without these checks, which developers are often afraid to modify. By +striving for zero-cost abstractions—higher-level features that compile to +lower-level code as fast as code written manually—Rust endeavors to make safe +code be fast code as well. + +The Rust language hopes to support many other users as well; those mentioned +here are merely some of the biggest stakeholders. Overall, Rust’s greatest +ambition is to eliminate the trade-offs that programmers have accepted for +decades by providing safety *and* productivity, speed *and* ergonomics. Give +Rust a try, and see if its choices work for you. + +## Who This Book Is For + +This book assumes that you’ve written code in another programming language, but +it doesn’t make any assumptions about which one. We’ve tried to make the +material broadly accessible to those from a wide variety of programming +backgrounds. We don’t spend a lot of time talking about what programming *is* +or how to think about it. If you’re entirely new to programming, you would be +better served by reading a book that specifically provides an introduction to +programming. + +## How to Use This Book + +In general, this book assumes that you’re reading it in sequence from front to +back. Later chapters build on concepts in earlier chapters, and earlier +chapters might not delve into details on a particular topic but will revisit +the topic in a later chapter. + +You’ll find two kinds of chapters in this book: concept chapters and project +chapters. In concept chapters, you’ll learn about an aspect of Rust. In project +chapters, we’ll build small programs together, applying what you’ve learned so +far. Chapter 2, Chapter 12, and Chapter 21 are project chapters; the rest are +concept chapters. + +**Chapter 1** explains how to install Rust, how to write a “Hello, world!” +program, and how to use Cargo, Rust’s package manager and build tool. **Chapter +2** is a hands-on introduction to writing a program in Rust, having you build +up a number-guessing game. Here, we cover concepts at a high level, and later +chapters will provide additional detail. If you want to get your hands dirty +right away, Chapter 2 is the place for that. If you’re a particularly +meticulous learner who prefers to learn every detail before moving on to the +next, you might want to skip Chapter 2 and go straight to **Chapter 3**, which +covers Rust features that are similar to those of other programming languages; +then, you can return to Chapter 2 when you’d like to work on a project applying +the details you’ve learned. + +In **Chapter 4**, you’ll learn about Rust’s ownership system. **Chapter 5** +discusses structs and methods. **Chapter 6** covers enums, `match` expressions, +and the `if let` and `let...else` control flow constructs. You’ll use structs +and enums to make custom types. + +In **Chapter 7**, you’ll learn about Rust’s module system and about privacy +rules for organizing your code and its public application programming interface +(API). **Chapter 8** discusses some common collection data structures that the +standard library provides: vectors, strings, and hash maps. **Chapter 9** +explores Rust’s error-handling philosophy and techniques. + +**Chapter 10** digs into generics, traits, and lifetimes, which give you the +power to define code that applies to multiple types. **Chapter 11** is all +about testing, which even with Rust’s safety guarantees is necessary to ensure +that your program’s logic is correct. In **Chapter 12**, we’ll build our own +implementation of a subset of functionality from the `grep` command line tool +that searches for text within files. For this, we’ll use many of the concepts +we discussed in the previous chapters. + +**Chapter 13** explores closures and iterators: features of Rust that come from +functional programming languages. In **Chapter 14**, we’ll examine Cargo in +more depth and talk about best practices for sharing your libraries with +others. **Chapter 15** discusses smart pointers that the standard library +provides and the traits that enable their functionality. + +In **Chapter 16**, we’ll walk through different models of concurrent +programming and talk about how Rust helps you program in multiple threads +fearlessly. In **Chapter 17**, we build on that by exploring Rust’s async and +await syntax, along with tasks, futures, and streams, and the lightweight +concurrency model they enable. + +**Chapter 18** looks at how Rust idioms compare to object-oriented programming +principles you might be familiar with. **Chapter 19** is a reference on +patterns and pattern matching, which are powerful ways of expressing ideas +throughout Rust programs. **Chapter 20** contains a smorgasbord of advanced +topics of interest, including unsafe Rust, macros, and more about lifetimes, +traits, types, functions, and closures. + +In **Chapter 21**, we’ll complete a project in which we’ll implement a +low-level multithreaded web server! + +Finally, some appendixes contain useful information about the language in a +more reference-like format. **Appendix A** covers Rust’s keywords, **Appendix +B** covers Rust’s operators and symbols, **Appendix C** covers derivable traits +provided by the standard library, **Appendix D** covers some useful development +tools, and **Appendix E** explains Rust editions. In **Appendix F**, you can +find translations of the book, and in **Appendix G** we’ll cover how Rust is +made and what nightly Rust is. + +There is no wrong way to read this book: If you want to skip ahead, go for it! +You might have to jump back to earlier chapters if you experience any +confusion. But do whatever works for you. + + + +An important part of the process of learning Rust is learning how to read the +error messages the compiler displays: These will guide you toward working code. +As such, we’ll provide many examples that don’t compile along with the error +message the compiler will show you in each situation. Know that if you enter +and run a random example, it may not compile! Make sure you read the +surrounding text to see whether the example you’re trying to run is meant to +error. In most situations, we’ll lead you to the correct version of any code +that doesn’t compile. Ferris will also help you distinguish code that isn’t +meant to work: + +|Ferris|Meaning| +|------|-------| +|Ferris with a question mark|This code does not compile!| +|Ferris throwing up their hands|This code panics!| +|Ferris with one claw up, shrugging|This code does not produce the desired behavior.| + +In most situations, we’ll lead you to the correct version of any code that +doesn’t compile. + +## Source Code + +The source files from which this book is generated can be found on +GitHub at *https://github.com/rust-lang/book/tree/main/src*. diff --git a/nostarch/chapter01.md b/nostarch/chapter01.md index 3379b14f22..df138f6202 100644 --- a/nostarch/chapter01.md +++ b/nostarch/chapter01.md @@ -21,10 +21,8 @@ The first step is to install Rust. We’ll download Rust through `rustup`, a command line tool for managing Rust versions and associated tools. You’ll need an internet connection for the download. -> Note: If you prefer not to use `rustup` for some reason, please see the Other -Rust Installation Methods page at -*https://forge.rust-lang.org/infra/other-installation-methods.html* for more -options. +> Note: If you prefer not to use `rustup` for some reason, please see the +> Other Rust Installation Methods page at *https://forge.rust-lang.org/infra/other-installation-methods.html* for more options. The following steps install the latest stable version of the Rust compiler. Rust’s stability guarantees ensure that all the examples in the book that @@ -34,20 +32,20 @@ warnings. In other words, any newer, stable version of Rust you install using these steps should work as expected with the content of this book. > ### Command Line Notation -> +> > In this chapter and throughout the book, we’ll show some commands used in the -terminal. Lines that you should enter in a terminal all start with `$`. You -don’t need to type the `$` character; it’s the command line prompt shown to -indicate the start of each command. Lines that don’t start with `$` typically -show the output of the previous command. Additionally, PowerShell-specific -examples will use `>` rather than `$`. +> terminal. Lines that you should enter in a terminal all start with `$`. You +> don’t need to type the `$` character; it’s the command line prompt shown to +> indicate the start of each command. Lines that don’t start with `$` typically +> show the output of the previous command. Additionally, PowerShell-specific +> examples will use `>` rather than `$`. ### Installing rustup on Linux or macOS If you’re using Linux or macOS, open a terminal and enter the following command: ``` -$ curl --proto '=https' --tlsv1.3 https://sh.rustup.rs -sSf | sh +$ curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf | sh ``` The command downloads a script and starts the installation of the `rustup` @@ -76,19 +74,11 @@ the `build-essential` package. ### Installing rustup on Windows -On Windows, go to *https://www.rust-lang.org/tools/install* and follow the -instructions for installing Rust. At some point in the installation, you’ll -receive a message explaining that you’ll also need the MSVC build tools for -Visual Studio 2013 or later. - -To acquire the build tools, you’ll need to install Visual Studio 2022 from -*https://visualstudio.microsoft.com/downloads*. When asked which workloads to -install, include: - -* “Desktop Development with C++” -* The Windows 10 or 11 SDK -* The English language pack component, along with any other language pack of -your choosing +On Windows, go to https://www.rust-lang.org/tools/install and follow the instructions for installing Rust. At some point in the +installation, you’ll be prompted to install Visual Studio. This provides a +linker and the native libraries needed to compile programs. If you need more +help with this step, see +https://rust-lang.github.io/rustup/installation/windows-msvc.html. The rest of this book uses commands that work in both *cmd.exe* and PowerShell. If there are specific differences, we’ll explain which to use. @@ -133,8 +123,7 @@ $ echo $PATH If that’s all correct and Rust still isn’t working, there are a number of places you can get help. Find out how to get in touch with other Rustaceans (a -silly nickname we call ourselves) on the community page at -*https://www.rust-lang.org/community*. +silly nickname we call ourselves) on the community page at *https://www.rust-lang.org/community*. ### Updating and Uninstalling @@ -152,7 +141,11 @@ shell: $ rustup self uninstall ``` -### Local Documentation + + + + +### Reading the Local Documentation The installation of Rust also includes a local copy of the documentation so that you can read it offline. Run `rustup doc` to open the local documentation @@ -162,6 +155,38 @@ Any time a type or function is provided by the standard library and you’re not sure what it does or how to use it, use the application programming interface (API) documentation to find out! + + + + +### Using Text Editors and IDEs + +This book makes no assumptions about what tools you use to author Rust code. +Just about any text editor will get the job done! However, many text editors and +integrated development environments (IDEs) have built-in support for Rust. You +can always find a fairly current list of many editors and IDEs on the tools +page at *https://www.rust-lang.org/tools* on the Rust website. + +### Working Offline with This Book + +In several examples, we will use Rust packages beyond the standard library. To +work through those examples, you will either need to have an internet connection +or to have downloaded those dependencies ahead of time. To download the +dependencies ahead of time, you can run the following commands. (We’ll explain +what `cargo` is and what each of these commands does in detail later.) + +``` +$ cargo new get-dependencies +$ cd get-dependencies +$ cargo add rand@0.8.5 trpl@0.2.0 +``` + +This will cache the downloads for these packages so you will not need to +download them later. Once you have run this command, you do not need to keep the +`get-dependencies` folder. If you have run this command, you can use the +`--offline` flag with all `cargo` commands in the rest of the book to use these +cached versions instead of attempting to use the network. + ## Hello, World! Now that you’ve installed Rust, it’s time to write your first Rust program. @@ -169,14 +194,18 @@ It’s traditional when learning a new language to write a little program that prints the text `Hello, world!` to the screen, so we’ll do the same here! > Note: This book assumes basic familiarity with the command line. Rust makes -no specific demands about your editing or tooling or where your code lives, so -if you prefer to use an integrated development environment (IDE) instead of the -command line, feel free to use your favorite IDE. Many IDEs now have some -degree of Rust support; check the IDE’s documentation for details. The Rust -team has been focusing on enabling great IDE support via `rust-analyzer`. See -Appendix D for more details. +> no specific demands about your editing or tooling or where your code lives, so +> if you prefer to use an IDE instead of the command line, feel free to use your +> favorite IDE. Many IDEs now have some degree of Rust support; check the IDE’s +> documentation for details. The Rust team has been focusing on enabling great +> IDE support via `rust-analyzer`. See Appendix D +> for more details. -### Creating a Project Directory + + + + +### Project Directory Setup You’ll start by making a directory to store your Rust code. It doesn’t matter to Rust where your code lives, but for the exercises and projects in this book, @@ -204,7 +233,11 @@ For Windows CMD, enter this: > cd hello_world ``` -### Writing and Running a Rust Program + + + + +### Rust Program Basics Next, make a new source file and call it *main.rs*. Rust files always end with the *.rs* extension. If you’re using more than one word in your filename, the @@ -213,7 +246,7 @@ convention is to use an underscore to separate them. For example, use Now open the *main.rs* file you just created and enter the code in Listing 1-1. -Filename: main.rs +main.rs ``` fn main() { @@ -233,22 +266,27 @@ $ ./main Hello, world! ``` -On Windows, enter the command `.\main.exe` instead of `./main`: +On Windows, enter the command `.\main` instead of `./main`: ``` > rustc main.rs -> .\main.exe +> .\main Hello, world! ``` Regardless of your operating system, the string `Hello, world!` should print to -the terminal. If you don’t see this output, refer back to “Troubleshooting” on -page XX for ways to get help. +the terminal. If you don’t see this output, refer back to the +“Troubleshooting” part of the Installation +section for ways to get help. If `Hello, world!` did print, congratulations! You’ve officially written a Rust program. That makes you a Rust programmer—welcome! -### Anatomy of a Rust Program + + + + +### The Anatomy of a Rust Program Let’s review this “Hello, world!” program in detail. Here’s the first piece of the puzzle: @@ -259,46 +297,50 @@ fn main() { } ``` -These lines define a function named `main`. The `main` function is special: it +These lines define a function named `main`. The `main` function is special: It is always the first code that runs in every executable Rust program. Here, the first line declares a function named `main` that has no parameters and returns -nothing. If there were parameters, they would go inside the parentheses `()`. +nothing. If there were parameters, they would go inside the parentheses (`()`). The function body is wrapped in `{}`. Rust requires curly brackets around all function bodies. It’s good style to place the opening curly bracket on the same line as the function declaration, adding one space in between. > Note: If you want to stick to a standard style across Rust projects, you can -use an automatic formatter tool called `rustfmt` to format your code in a -particular style (more on `rustfmt` in Appendix D). The Rust team has included -this tool with the standard Rust distribution, as `rustc` is, so it should -already be installed on your computer! +> use an automatic formatter tool called `rustfmt` to format your code in a +> particular style (more on `rustfmt` in +> Appendix D). The Rust team has included this tool +> with the standard Rust distribution, as `rustc` is, so it should already be +> installed on your computer! The body of the `main` function holds the following code: ``` - println!("Hello, world!"); +println!("Hello, world!"); ``` -This line does all the work in this little program: it prints text to the -screen. There are four important details to notice here. - -First, Rust style is to indent with four spaces, not a tab. +This line does all the work in this little program: It prints text to the +screen. There are three important details to notice here. -Second, `println!` calls a Rust macro. If it had called a function instead, it -would be entered as `println` (without the `!`). We’ll discuss Rust macros in -more detail in Chapter 19. For now, you just need to know that using a `!` -means that you’re calling a macro instead of a normal function and that macros -don’t always follow the same rules as functions. +First, `println!` calls a Rust macro. If it had called a function instead, it +would be entered as `println` (without the `!`). Rust macros are a way to write +code that generates code to extend Rust syntax, and we’ll discuss them in more +detail in Chapter 20. For now, you just need to +know that using a `!` means that you’re calling a macro instead of a normal +function and that macros don’t always follow the same rules as functions. -Third, you see the `"Hello, world!"` string. We pass this string as an argument +Second, you see the `"Hello, world!"` string. We pass this string as an argument to `println!`, and the string is printed to the screen. -Fourth, we end the line with a semicolon (`;`), which indicates that this -expression is over and the next one is ready to begin. Most lines of Rust code +Third, we end the line with a semicolon (`;`), which indicates that this +expression is over, and the next one is ready to begin. Most lines of Rust code end with a semicolon. -### Compiling and Running Are Separate Steps + + + + +### Compilation and Execution You’ve just run a newly created program, so let’s examine each step in the process. @@ -339,11 +381,10 @@ Windows, a file containing debugging information with the *.pdb* extension. From here, you run the *main* or *main.exe* file, like this: ``` -$ ./main # or .\main.exe on Windows +$ ./main # or .\main on Windows ``` -If your *main.rs* is your “Hello, world!” program, this line prints `Hello, -world!` to your terminal. +If your *main.rs* is your “Hello, world!” program, this line prints `Hello, world!` to your terminal. If you’re more familiar with a dynamic language, such as Ruby, Python, or JavaScript, you might not be used to compiling and running a program as @@ -375,16 +416,16 @@ using Cargo, adding dependencies will be much easier to do. Because the vast majority of Rust projects use Cargo, the rest of this book assumes that you’re using Cargo too. Cargo comes installed with Rust if you -used the official installers discussed in “Installation” on page XX. If you -installed Rust through some other means, check whether Cargo is installed by -entering the following in your terminal: +used the official installers discussed in the +“Installation” section. If you installed Rust +through some other means, check whether Cargo is installed by entering the +following in your terminal: ``` $ cargo --version ``` -If you see a version number, you have it! If you see an error, such as `command -not found`, look at the documentation for your method of installation to +If you see a version number, you have it! If you see an error, such as `command not found`, look at the documentation for your method of installation to determine how to install Cargo separately. ### Creating a Project with Cargo @@ -412,27 +453,27 @@ Git files won’t be generated if you run `cargo new` within an existing Git repository; you can override this behavior by using `cargo new --vcs=git`. > Note: Git is a common version control system. You can change `cargo new` to -use a different version control system or no version control system by using -the `--vcs` flag. Run `cargo new --help` to see the available options. +> use a different version control system or no version control system by using +> the `--vcs` flag. Run `cargo new --help` to see the available options. Open *Cargo.toml* in your text editor of choice. It should look similar to the code in Listing 1-2. -Filename: Cargo.toml +Cargo.toml ``` [package] name = "hello_cargo" version = "0.1.0" -edition = "2021" +edition = "2024" [dependencies] ``` Listing 1-2: Contents of *Cargo.toml* generated by `cargo new` -This file is in the *TOML* (*Tom’s Obvious, Minimal Language*) format, which is -Cargo’s configuration format. +This file is in the *TOML* (*Tom’s Obvious, Minimal +Language*) format, which is Cargo’s configuration format. The first line, `[package]`, is a section heading that indicates that the following statements are configuring a package. As we add more information to @@ -459,7 +500,7 @@ fn main() { Cargo has generated a “Hello, world!” program for you, just like the one we wrote in Listing 1-1! So far, the differences between our project and the -project Cargo generated are that Cargo placed the code in the *src* directory +project Cargo generated are that Cargo placed the code in the *src* directory, and we have a *Cargo.toml* configuration file in the top directory. Cargo expects your source files to live inside the *src* directory. The @@ -471,7 +512,8 @@ everything is in its place. If you started a project that doesn’t use Cargo, as we did with the “Hello, world!” project, you can convert it to a project that does use Cargo. Move the project code into the *src* directory and create an appropriate *Cargo.toml* -file. +file. One easy way to get that *Cargo.toml* file is to run `cargo init`, which +will create it for you automatically. ### Building and Running a Cargo Project @@ -495,8 +537,7 @@ $ ./target/debug/hello_cargo # or .\target\debug\hello_cargo.exe on Windows Hello, world! ``` -If all goes well, `Hello, world!` should print to the terminal. Running `cargo -build` for the first time also causes Cargo to create a new file at the top +If all goes well, `Hello, world!` should print to the terminal. Running `cargo build` for the first time also causes Cargo to create a new file at the top level: *Cargo.lock*. This file keeps track of the exact versions of dependencies in your project. This project doesn’t have dependencies, so the file is a bit sparse. You won’t ever need to change this file manually; Cargo @@ -513,9 +554,7 @@ $ cargo run Hello, world! ``` -Using `cargo run` is more convenient than having to remember to run `cargo -build` and then use the whole path to the binary, so most developers use `cargo -run`. +Using `cargo run` is more convenient than having to remember to run `cargo build` and then use the whole path to the binary, so most developers use `cargo run`. Notice that this time we didn’t see output indicating that Cargo was compiling `hello_cargo`. Cargo figured out that the files hadn’t changed, so it didn’t @@ -545,7 +584,7 @@ Why would you not want an executable? Often, `cargo check` is much faster than continually checking your work while writing the code, using `cargo check` will speed up the process of letting you know if your project is still compiling! As such, many Rustaceans run `cargo check` periodically as they write their -program to make sure it compiles. Then they run `cargo build` when they’re +program to make sure it compiles. Then, they run `cargo build` when they’re ready to use the executable. Let’s recap what we’ve learned so far about Cargo: @@ -554,9 +593,9 @@ Let’s recap what we’ve learned so far about Cargo: * We can build a project using `cargo build`. * We can build and run a project in one step using `cargo run`. * We can build a project without producing a binary to check for errors using -`cargo check`. + `cargo check`. * Instead of saving the result of the build in the same directory as our code, -Cargo stores it in the *target/debug* directory. + Cargo stores it in the *target/debug* directory. An additional advantage of using Cargo is that the commands are the same no matter which operating system you’re working on. So, at this point, we’ll no @@ -564,8 +603,7 @@ longer provide specific instructions for Linux and macOS versus Windows. ### Building for Release -When your project is finally ready for release, you can use `cargo build ---release` to compile it with optimizations. This command will create an +When your project is finally ready for release, you can use `cargo build --release` to compile it with optimizations. This command will create an executable in *target/release* instead of *target/debug*. The optimizations make your Rust code run faster, but turning them on lengthens the time it takes for your program to compile. This is why there are two different profiles: one @@ -575,7 +613,11 @@ repeatedly and that will run as fast as possible. If you’re benchmarking your code’s running time, be sure to run `cargo build --release` and benchmark with the executable in *target/release*. -### Cargo as Convention + + + + +### Leveraging Cargo’s Conventions With simple projects, Cargo doesn’t provide a lot of value over just using `rustc`, but it will prove its worth as your programs become more intricate. @@ -593,22 +635,20 @@ $ cd someproject $ cargo build ``` -For more information about Cargo, check out its documentation at -*https://doc.rust-lang.org/cargo*. +For more information about Cargo, check out its documentation at *https://doc.rust-lang.org/cargo/*. ## Summary -You’re already off to a great start on your Rust journey! In this chapter, -you’ve learned how to: +You’re already off to a great start on your Rust journey! In this chapter, you +learned how to: -* Install the latest stable version of Rust using `rustup` -* Update to a newer Rust version -* Open locally installed documentation -* Write and run a “Hello, world!” program using `rustc` directly -* Create and run a new project using the conventions of Cargo +* Install the latest stable version of Rust using `rustup`. +* Update to a newer Rust version. +* Open locally installed documentation. +* Write and run a “Hello, world!” program using `rustc` directly. +* Create and run a new project using the conventions of Cargo. This is a great time to build a more substantial program to get used to reading and writing Rust code. So, in Chapter 2, we’ll build a guessing game program. If you would rather start by learning how common programming concepts work in Rust, see Chapter 3 and then return to Chapter 2. - diff --git a/nostarch/chapter02.md b/nostarch/chapter02.md index b01770dc5c..471649b36f 100644 --- a/nostarch/chapter02.md +++ b/nostarch/chapter02.md @@ -16,7 +16,7 @@ these ideas in more detail. In this chapter, you’ll just practice the fundamentals. We’ll implement a classic beginner programming problem: a guessing game. Here’s -how it works: the program will generate a random integer between 1 and 100. It +how it works: The program will generate a random integer between 1 and 100. It will then prompt the player to enter a guess. After a guess is entered, the program will indicate whether the guess is too low or too high. If the guess is correct, the game will print a congratulatory message and exit. @@ -37,16 +37,22 @@ directory. Look at the generated *Cargo.toml* file: + + Filename: Cargo.toml ``` [package] name = "guessing_game" version = "0.1.0" -edition = "2021" - -# See more keys and their definitions at -https://doc.rust-lang.org/cargo/reference/manifest.html +edition = "2024" [dependencies] ``` @@ -68,7 +74,7 @@ using the `cargo run` command: ``` $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 1.50s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s Running `target/debug/guessing_game` Hello, world! ``` @@ -86,7 +92,7 @@ that input, and check that the input is in the expected form. To start, we’ll allow the player to input a guess. Enter the code in Listing 2-1 into *src/main.rs*. -Filename: src/main.rs +src/main.rs ``` use std::io; @@ -119,8 +125,7 @@ use std::io; By default, Rust has a set of items defined in the standard library that it brings into the scope of every program. This set is called the *prelude*, and -you can see everything in it at -*https://doc.rust-lang.org/std/prelude/index.html*. +you can see everything in it in the standard library documentation at *../std/prelude/index.html*. If a type you want to use isn’t in the prelude, you have to bring that type into scope explicitly with a `use` statement. Using the `std::io` library @@ -141,9 +146,9 @@ As you also learned in Chapter 1, `println!` is a macro that prints a string to the screen: ``` -println!("Guess the number!"); + println!("Guess the number!"); -println!("Please input your guess."); + println!("Please input your guess."); ``` This code is printing a prompt stating what the game is and requesting input @@ -154,7 +159,7 @@ from the user. Next, we’ll create a *variable* to store the user input, like this: ``` -let mut guess = String::new(); + let mut guess = String::new(); ``` Now the program is getting interesting! There’s a lot going on in this little @@ -164,11 +169,12 @@ line. We use the `let` statement to create the variable. Here’s another exampl let apples = 5; ``` -This line creates a new variable named `apples` and binds it to the value 5. In -Rust, variables are immutable by default, meaning once we give the variable a -value, the value won’t change. We’ll be discussing this concept in detail in -“Variables and Mutability” on page XX. To make a variable mutable, we add `mut` -before the variable name: +This line creates a new variable named `apples` and binds it to the value `5`. +In Rust, variables are immutable by default, meaning once we give the variable +a value, the value won’t change. We’ll be discussing this concept in detail in +the “Variables and Mutability” +section in Chapter 3. To make a variable mutable, we add `mut` before the +variable name: ``` let apples = 5; // immutable @@ -176,16 +182,16 @@ let mut bananas = 5; // mutable ``` > Note: The `//` syntax starts a comment that continues until the end of the -line. Rust ignores everything in comments. We’ll discuss comments in more -detail in Chapter 3. +> line. Rust ignores everything in comments. We’ll discuss comments in more +> detail in Chapter 3. Returning to the guessing game program, you now know that `let mut guess` will introduce a mutable variable named `guess`. The equal sign (`=`) tells Rust we want to bind something to the variable now. On the right of the equal sign is the value that `guess` is bound to, which is the result of calling -`String::new`, a function that returns a new instance of a `String`. `String` -is a string type provided by the standard library that is a growable, UTF-8 -encoded bit of text. +`String::new`, a function that returns a new instance of a `String`. +`String` is a string type provided by the standard +library that is a growable, UTF-8 encoded bit of text. The `::` syntax in the `::new` line indicates that `new` is an associated function of the `String` type. An *associated function* is a function that’s @@ -204,23 +210,23 @@ the `stdin` function from the `io` module, which will allow us to handle user input: ``` -io::stdin() - .read_line(&mut guess) + io::stdin() + .read_line(&mut guess) ``` -If we hadn’t imported the `io` library with `use std::io;` at the beginning of +If we hadn’t imported the `io` module with `use std::io;` at the beginning of the program, we could still use the function by writing this function call as -`std::io::stdin`. The `stdin` function returns an instance of `std::io::Stdin`, -which is a type that represents a handle to the standard input for your -terminal. - -Next, the line `.read_line(&mut guess)` calls the `read_line` method on the -standard input handle to get input from the user. We’re also passing `&mut -guess` as the argument to `read_line` to tell it what string to store the user -input in. The full job of `read_line` is to take whatever the user types into -standard input and append that into a string (without overwriting its -contents), so we therefore pass that string as an argument. The string argument -needs to be mutable so the method can change the string’s content. +`std::io::stdin`. The `stdin` function returns an instance of +`std::io::Stdin`, which is a type that represents a +handle to the standard input for your terminal. + +Next, the line `.read_line(&mut guess)` calls the `read_line` method on the standard input handle to get input from the user. +We’re also passing `&mut guess` as the argument to `read_line` to tell it what +string to store the user input in. The full job of `read_line` is to take +whatever the user types into standard input and append that into a string +(without overwriting its contents), so we therefore pass that string as an +argument. The string argument needs to be mutable so that the method can change +the string’s content. The `&` indicates that this argument is a *reference*, which gives you a way to let multiple parts of your code access one piece of data without needing to @@ -232,6 +238,10 @@ immutable by default. Hence, you need to write `&mut guess` rather than `&guess` to make it mutable. (Chapter 4 will explain references more thoroughly.) + + + + ### Handling Potential Failure with Result We’re still working on this line of code. We’re now discussing a third line of @@ -239,7 +249,7 @@ text, but note that it’s still part of a single logical line of code. The next part is this method: ``` -.expect("Failed to read line"); + .expect("Failed to read line"); ``` We could have written this code as: @@ -254,27 +264,27 @@ lines when you call a method with the `.method_name()` syntax. Now let’s discuss what this line does. As mentioned earlier, `read_line` puts whatever the user enters into the string -we pass to it, but it also returns a `Result` value. `Result` is an -*enumeration*, often called an *enum*, which is a type that can be in one of -multiple possible states. We call each possible state a *variant*. +we pass to it, but it also returns a `Result` value. `Result` is an *enumeration*, often called an *enum*, +which is a type that can be in one of multiple possible states. We call each +possible state a *variant*. -Chapter 6 will cover enums in more detail. The purpose of these `Result` types -is to encode error-handling information. +Chapter 6 will cover enums in more detail. The purpose +of these `Result` types is to encode error-handling information. `Result`’s variants are `Ok` and `Err`. The `Ok` variant indicates the -operation was successful, and inside `Ok` is the successfully generated value. -The `Err` variant means the operation failed, and `Err` contains information +operation was successful, and it contains the successfully generated value. +The `Err` variant means the operation failed, and it contains information about how or why the operation failed. Values of the `Result` type, like values of any type, have methods defined on -them. An instance of `Result` has an `expect` method that you can call. If this -instance of `Result` is an `Err` value, `expect` will cause the program to -crash and display the message that you passed as an argument to `expect`. If -the `read_line` method returns an `Err`, it would likely be the result of an -error coming from the underlying operating system. If this instance of `Result` -is an `Ok` value, `expect` will take the return value that `Ok` is holding and -return just that value to you so you can use it. In this case, that value is -the number of bytes in the user’s input. +them. An instance of `Result` has an `expect` method +that you can call. If this instance of `Result` is an `Err` value, `expect` +will cause the program to crash and display the message that you passed as an +argument to `expect`. If the `read_line` method returns an `Err`, it would +likely be the result of an error coming from the underlying operating system. +If this instance of `Result` is an `Ok` value, `expect` will take the return +value that `Ok` is holding and return just that value to you so that you can +use it. In this case, that value is the number of bytes in the user’s input. If you don’t call `expect`, the program will compile, but you’ll get a warning: @@ -285,13 +295,17 @@ warning: unused `Result` that must be used --> src/main.rs:10:5 | 10 | io::stdin().read_line(&mut guess); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | - = note: `#[warn(unused_must_use)]` on by default = note: this `Result` may be an `Err` variant, which should be handled + = note: `#[warn(unused_must_use)]` on by default +help: use `let _ = ...` to ignore the resulting value + | +10 | let _ = io::stdin().read_line(&mut guess); + | +++++++ warning: `guessing_game` (bin "guessing_game") generated 1 warning - Finished dev [unoptimized + debuginfo] target(s) in 0.59s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.59s ``` Rust warns that you haven’t used the `Result` value returned from `read_line`, @@ -299,7 +313,8 @@ indicating that the program hasn’t handled a possible error. The right way to suppress the warning is to actually write error-handling code, but in our case we just want to crash this program when a problem occurs, so we -can use `expect`. You’ll learn about recovering from errors in Chapter 9. +can use `expect`. You’ll learn about recovering from errors in Chapter +9. ### Printing Values with println! Placeholders @@ -307,11 +322,11 @@ Aside from the closing curly bracket, there’s only one more line to discuss in the code so far: ``` -println!("You guessed: {guess}"); + println!("You guessed: {guess}"); ``` This line prints the string that now contains the user’s input. The `{}` set of -curly brackets is a placeholder: think of `{}` as little crab pincers that hold +curly brackets is a placeholder: Think of `{}` as little crab pincers that hold a value in place. When printing the value of a variable, the variable name can go inside the curly brackets. When printing the result of evaluating an expression, place empty curly brackets in the format string, then follow the @@ -326,16 +341,22 @@ let y = 10; println!("x = {x} and y + 2 = {}", y + 2); ``` -This code would print `x = 5 and y = 12`. +This code would print `x = 5 and y + 2 = 12`. ### Testing the First Part Let’s test the first part of the guessing game. Run it using `cargo run`: + + ``` $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 6.44s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 6.44s Running `target/debug/guessing_game` Guess the number! Please input your guess. @@ -343,24 +364,28 @@ Please input your guess. You guessed: 6 ``` -At this point, the first part of the game is done: we’re getting input from the +At this point, the first part of the game is done: We’re getting input from the keyboard and then printing it. ## Generating a Secret Number Next, we need to generate a secret number that the user will try to guess. The -secret number should be different every time so the game is fun to play more -than once. We’ll use a random number between 1 and 100 so the game isn’t too -difficult. Rust doesn’t yet include random number functionality in its standard -library. However, the Rust team does provide a `rand` crate at -*https://crates.io/crates/rand* with said functionality. +secret number should be different every time so that the game is fun to play +more than once. We’ll use a random number between 1 and 100 so that the game +isn’t too difficult. Rust doesn’t yet include random number functionality in +its standard library. However, the Rust team does provide a `rand` +crate at *https://crates.io/crates/rand* with said functionality. + + -### Using a Crate to Get More Functionality + + +### Increasing Functionality with a Crate Remember that a crate is a collection of Rust source code files. The project -we’ve been building is a *binary crate*, which is an executable. The `rand` -crate is a *library crate*, which contains code that is intended to be used in -other programs and can’t be executed on its own. +we’ve been building is a binary crate, which is an executable. The `rand` crate +is a library crate, which contains code that is intended to be used in other +programs and can’t be executed on its own. Cargo’s coordination of external crates is where Cargo really shines. Before we can write code that uses `rand`, we need to modify the *Cargo.toml* file to @@ -369,6 +394,12 @@ following line to the bottom, beneath the `[dependencies]` section header that Cargo created for you. Be sure to specify `rand` exactly as we have here, with this version number, or the code examples in this tutorial may not work: + + Filename: Cargo.toml ``` @@ -377,45 +408,55 @@ rand = "0.8.5" ``` In the *Cargo.toml* file, everything that follows a header is part of that -section that continues until another section starts. In `[dependencies]` you +section that continues until another section starts. In `[dependencies]`, you tell Cargo which external crates your project depends on and which versions of those crates you require. In this case, we specify the `rand` crate with the -semantic version specifier `0.8.5`. Cargo understands Semantic Versioning -(sometimes called *SemVer*), which is a standard for writing version numbers. -The specifier `0.8.5` is actually shorthand for `^0.8.5`, which means any -version that is at least 0.8.5 but below 0.9.0. +semantic version specifier `0.8.5`. Cargo understands Semantic +Versioning (sometimes called *SemVer*), which is a +standard for writing version numbers. The specifier `0.8.5` is actually +shorthand for `^0.8.5`, which means any version that is at least 0.8.5 but +below 0.9.0. Cargo considers these versions to have public APIs compatible with version -0.8.5, and this specification ensures you’ll get the latest patch release that -will still compile with the code in this chapter. Any version 0.9.0 or greater -is not guaranteed to have the same API as what the following examples use. +0.8.5, and this specification ensures that you’ll get the latest patch release +that will still compile with the code in this chapter. Any version 0.9.0 or +greater is not guaranteed to have the same API as what the following examples +use. Now, without changing any of the code, let’s build the project, as shown in Listing 2-2. + + + ``` $ cargo build - Updating crates.io index - Downloaded rand v0.8.5 - Downloaded libc v0.2.127 - Downloaded getrandom v0.2.7 - Downloaded cfg-if v1.0.0 - Downloaded ppv-lite86 v0.2.16 - Downloaded rand_chacha v0.3.1 - Downloaded rand_core v0.6.3 - Compiling rand_core v0.6.3 - Compiling libc v0.2.127 - Compiling getrandom v0.2.7 - Compiling cfg-if v1.0.0 - Compiling ppv-lite86 v0.2.16 - Compiling rand_chacha v0.3.1 - Compiling rand v0.8.5 - Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 2.53s -``` - -Listing 2-2: The output from running `cargo build` after adding the `rand` -crate as a dependency + Updating crates.io index + Locking 15 packages to latest Rust 1.85.0 compatible versions + Adding rand v0.8.5 (available: v0.9.0) + Compiling proc-macro2 v1.0.93 + Compiling unicode-ident v1.0.17 + Compiling libc v0.2.170 + Compiling cfg-if v1.0.0 + Compiling byteorder v1.5.0 + Compiling getrandom v0.2.15 + Compiling rand_core v0.6.4 + Compiling quote v1.0.38 + Compiling syn v2.0.98 + Compiling zerocopy-derive v0.7.35 + Compiling zerocopy v0.7.35 + Compiling ppv-lite86 v0.2.20 + Compiling rand_chacha v0.3.1 + Compiling rand v0.8.5 + Compiling guessing_game v0.1.0 (file:///projects/guessing_game) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.48s +``` + +Listing 2-2: The output from running `cargo build` after adding the `rand` crate as a dependency You may see different version numbers (but they will all be compatible with the code, thanks to SemVer!) and different lines (depending on the operating @@ -423,8 +464,8 @@ system), and the lines may be in a different order. When we include an external dependency, Cargo fetches the latest versions of everything that dependency needs from the *registry*, which is a copy of data -from Crates.io at *https://crates.io*. Crates.io is where people in the Rust -ecosystem post their open source Rust projects for others to use. +from Crates.io at *https://crates.io/*. Crates.io is where people in the Rust ecosystem +post their open source Rust projects for others to use. After updating the registry, Cargo checks the `[dependencies]` section and downloads any crates listed that aren’t already downloaded. In this case, @@ -442,22 +483,31 @@ do, it simply exits. If you open the *src/main.rs* file, make a trivial change, and then save it and build again, you’ll only see two lines of output: + + ``` $ cargo build Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 2.53 secs + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.13s ``` These lines show that Cargo only updates the build with your tiny change to the *src/main.rs* file. Your dependencies haven’t changed, so Cargo knows it can reuse what it has already downloaded and compiled for those. -#### Ensuring Reproducible Builds with the Cargo.lock File + + + + +#### Ensuring Reproducible Builds -Cargo has a mechanism that ensures you can rebuild the same artifact every time -you or anyone else builds your code: Cargo will use only the versions of the -dependencies you specified until you indicate otherwise. For example, say that -next week version 0.8.6 of the `rand` crate comes out, and that version +Cargo has a mechanism that ensures that you can rebuild the same artifact every +time you or anyone else builds your code: Cargo will use only the versions of +the dependencies you specified until you indicate otherwise. For example, say +that next week version 0.8.6 of the `rand` crate comes out, and that version contains an important bug fix, but it also contains a regression that will break your code. To handle this, Rust creates the *Cargo.lock* file the first time you run `cargo build`, so we now have this in the *guessing_game* @@ -483,10 +533,17 @@ for versions greater than 0.8.5 and less than 0.9.0. If the `rand` crate has released the two new versions 0.8.6 and 0.9.0, you would see the following if you ran `cargo update`: + + ``` $ cargo update Updating crates.io index - Updating rand v0.8.5 -> v0.8.6 + Locking 1 package to latest Rust 1.85.0 compatible version + Updating rand v0.8.5 -> v0.8.6 (available: v0.9.0) ``` Cargo ignores the 0.9.0 release. At this point, you would also notice a change @@ -503,28 +560,30 @@ The next time you run `cargo build`, Cargo will update the registry of crates available and reevaluate your `rand` requirements according to the new version you have specified. -There’s a lot more to say about Cargo and its ecosystem, which we’ll discuss in -Chapter 14, but for now, that’s all you need to know. Cargo makes it very easy -to reuse libraries, so Rustaceans are able to write smaller projects that are -assembled from a number of packages. +There’s a lot more to say about Cargo and its +ecosystem, which we’ll discuss in Chapter 14, but +for now, that’s all you need to know. Cargo makes it very easy to reuse +libraries, so Rustaceans are able to write smaller projects that are assembled +from a number of packages. ### Generating a Random Number Let’s start using `rand` to generate a number to guess. The next step is to update *src/main.rs*, as shown in Listing 2-3. -Filename: src/main.rs +src/main.rs ``` use std::io; -1 use rand::Rng; + +use rand::Rng; fn main() { println!("Guess the number!"); - 2 let secret_number = rand::thread_rng().gen_range(1..=100); + let secret_number = rand::thread_rng().gen_range(1..=100); - 3 println!("The secret number is: {secret_number}"); + println!("The secret number is: {secret_number}"); println!("Please input your guess."); @@ -540,14 +599,14 @@ fn main() { Listing 2-3: Adding code to generate a random number -First we add the line `use rand::Rng;` [1]. The `Rng` trait defines methods -that random number generators implement, and this trait must be in scope for us -to use those methods. Chapter 10 will cover traits in detail. +First, we add the line `use rand::Rng;`. The `Rng` trait defines methods that +random number generators implement, and this trait must be in scope for us to +use those methods. Chapter 10 will cover traits in detail. -Next, we’re adding two lines in the middle. In the first line [2], we call the +Next, we’re adding two lines in the middle. In the first line, we call the `rand::thread_rng` function that gives us the particular random number generator we’re going to use: one that is local to the current thread of -execution and is seeded by the operating system. Then we call the `gen_range` +execution and is seeded by the operating system. Then, we call the `gen_range` method on the random number generator. This method is defined by the `Rng` trait that we brought into scope with the `use rand::Rng;` statement. The `gen_range` method takes a range expression as an argument and generates a @@ -556,24 +615,31 @@ the form `start..=end` and is inclusive on the lower and upper bounds, so we need to specify `1..=100` to request a number between 1 and 100. > Note: You won’t just know which traits to use and which methods and functions -to call from a crate, so each crate has documentation with instructions for -using it. Another neat feature of Cargo is that running the `cargo doc --open` -command will build documentation provided by all your dependencies locally and -open it in your browser. If you’re interested in other functionality in the -`rand` crate, for example, run `cargo doc --open` and click `rand` in the -sidebar on the left. - -The second new line [3] prints the secret number. This is useful while we’re +> to call from a crate, so each crate has documentation with instructions for +> using it. Another neat feature of Cargo is that running the `cargo doc --open` command will build documentation provided by all your dependencies +> locally and open it in your browser. If you’re interested in other +> functionality in the `rand` crate, for example, run `cargo doc --open` and +> click `rand` in the sidebar on the left. + +The second new line prints the secret number. This is useful while we’re developing the program to be able to test it, but we’ll delete it from the final version. It’s not much of a game if the program prints the answer as soon as it starts! Try running the program a few times: + + ``` $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 2.53s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s Running `target/debug/guessing_game` Guess the number! The secret number is: 7 @@ -582,7 +648,7 @@ Please input your guess. You guessed: 4 $ cargo run - Finished dev [unoptimized + debuginfo] target(s) in 0.02s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s Running `target/debug/guessing_game` Guess the number! The secret number is: 83 @@ -600,19 +666,20 @@ Now that we have user input and a random number, we can compare them. That step is shown in Listing 2-4. Note that this code won’t compile just yet, as we will explain. -Filename: src/main.rs +src/main.rs ``` -use rand::Rng; -1 use std::cmp::Ordering; +use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { - --snip-- + // --snip-- println!("You guessed: {guess}"); - 2 match guess.3 cmp(&secret_number) { + match guess.cmp(&secret_number) { Ordering::Less => println!("Too small!"), Ordering::Greater => println!("Too big!"), Ordering::Equal => println!("You win!"), @@ -622,27 +689,27 @@ fn main() { Listing 2-4: Handling the possible return values of comparing two numbers -First we add another `use` statement [1], bringing a type called +First, we add another `use` statement, bringing a type called `std::cmp::Ordering` into scope from the standard library. The `Ordering` type is another enum and has the variants `Less`, `Greater`, and `Equal`. These are the three outcomes that are possible when you compare two values. -Then we add five new lines at the bottom that use the `Ordering` type. The -`cmp` method [3] compares two values and can be called on anything that can be -compared. It takes a reference to whatever you want to compare with: here it’s -comparing `guess` to `secret_number`. Then it returns a variant of the +Then, we add five new lines at the bottom that use the `Ordering` type. The +`cmp` method compares two values and can be called on anything that can be +compared. It takes a reference to whatever you want to compare with: Here, it’s +comparing `guess` to `secret_number`. Then, it returns a variant of the `Ordering` enum we brought into scope with the `use` statement. We use a -`match` expression [2] to decide what to do next based on which variant of -`Ordering` was returned from the call to `cmp` with the values in `guess` and -`secret_number`. +`match` expression to decide what to do next based on +which variant of `Ordering` was returned from the call to `cmp` with the values +in `guess` and `secret_number`. A `match` expression is made up of *arms*. An arm consists of a *pattern* to match against, and the code that should be run if the value given to `match` fits that arm’s pattern. Rust takes the value given to `match` and looks through each arm’s pattern in turn. Patterns and the `match` construct are -powerful Rust features: they let you express a variety of situations your code -might encounter and they make sure you handle them all. These features will be -covered in detail in Chapter 6 and Chapter 18, respectively. +powerful Rust features: They let you express a variety of situations your code +might encounter, and they make sure you handle them all. These features will be +covered in detail in Chapter 6 and Chapter 19, respectively. Let’s walk through an example with the `match` expression we use here. Say that the user has guessed 50 and the randomly generated secret number this time is @@ -661,17 +728,36 @@ arm in this scenario. However, the code in Listing 2-4 won’t compile yet. Let’s try it: + + ``` $ cargo build + Compiling libc v0.2.86 + Compiling getrandom v0.2.2 + Compiling cfg-if v1.0.0 + Compiling ppv-lite86 v0.2.10 + Compiling rand_core v0.6.2 + Compiling rand_chacha v0.3.0 + Compiling rand v0.8.5 Compiling guessing_game v0.1.0 (file:///projects/guessing_game) error[E0308]: mismatched types - --> src/main.rs:22:21 + --> src/main.rs:23:21 | -22 | match guess.cmp(&secret_number) { - | ^^^^^^^^^^^^^^ expected struct `String`, found integer +23 | match guess.cmp(&secret_number) { + | --- ^^^^^^^^^^^^^^ expected `&String`, found `&{integer}` + | | + | arguments to this method are incorrect | = note: expected reference `&String` found reference `&{integer}` +note: method defined here + --> /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/cmp.rs:964:8 + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `guessing_game` (bin "guessing_game") due to 1 previous error ``` The core of the error states that there are *mismatched types*. Rust has a @@ -686,32 +772,35 @@ elsewhere that would cause Rust to infer a different numerical type. The reason for the error is that Rust cannot compare a string and a number type. Ultimately, we want to convert the `String` the program reads as input into a -real number type so we can compare it numerically to the secret number. We do +number type so that we can compare it numerically to the secret number. We do so by adding this line to the `main` function body: Filename: src/main.rs ``` ---snip-- + // --snip-- -let mut guess = String::new(); + let mut guess = String::new(); -io::stdin() - .read_line(&mut guess) - .expect("Failed to read line"); + io::stdin() + .read_line(&mut guess) + .expect("Failed to read line"); -let guess: u32 = guess - .trim() - .parse() - .expect("Please type a number!"); + let guess: u32 = guess.trim().parse().expect("Please type a number!"); -println!("You guessed: {guess}"); + println!("You guessed: {guess}"); -match guess.cmp(&secret_number) { - Ordering::Less => println!("Too small!"), - Ordering::Greater => println!("Too big!"), - Ordering::Equal => println!("You win!"), -} + match guess.cmp(&secret_number) { + Ordering::Less => println!("Too small!"), + Ordering::Greater => println!("Too big!"), + Ordering::Equal => println!("You win!"), + } +``` + +The line is: + +``` +let guess: u32 = guess.trim().parse().expect("Please type a number!"); ``` We create a variable named `guess`. But wait, doesn’t the program already have @@ -719,50 +808,60 @@ a variable named `guess`? It does, but helpfully Rust allows us to shadow the previous value of `guess` with a new one. *Shadowing* lets us reuse the `guess` variable name rather than forcing us to create two unique variables, such as `guess_str` and `guess`, for example. We’ll cover this in more detail in -Chapter 3, but for now, know that this feature is often used when you want to -convert a value from one type to another type. +Chapter 3, but for now, know that this feature is +often used when you want to convert a value from one type to another type. We bind this new variable to the expression `guess.trim().parse()`. The `guess` in the expression refers to the original `guess` variable that contained the input as a string. The `trim` method on a `String` instance will eliminate any -whitespace at the beginning and end, which we must do to be able to compare the -string to the `u32`, which can only contain numerical data. The user must press -enter to satisfy `read_line` and input their guess, which adds a newline -character to the string. For example, if the user types `5` and presses enter, -`guess` looks like this: `5\n`. The `\n` represents “newline.” (On Windows, -pressing enter results in a carriage return and a newline, `\r\n`.) The `trim` -method eliminates `\n` or `\r\n`, resulting in just `5`. - -The `parse` method on strings converts a string to another type. Here, we use -it to convert from a string to a number. We need to tell Rust the exact number -type we want by using `let guess: u32`. The colon (`:`) after `guess` tells -Rust we’ll annotate the variable’s type. Rust has a few built-in number types; -the `u32` seen here is an unsigned, 32-bit integer. It’s a good default choice -for a small positive number. You’ll learn about other number types in Chapter 3. +whitespace at the beginning and end, which we must do before we can convert the +string to a `u32`, which can only contain numerical data. The user must press +enter to satisfy `read_line` and input their guess, which adds a +newline character to the string. For example, if the user types 5 and +presses enter, `guess` looks like this: `5\n`. The `\n` represents +“newline.” (On Windows, pressing enter results in a carriage return +and a newline, `\r\n`.) The `trim` method eliminates `\n` or `\r\n`, resulting +in just `5`. + +The `parse` method on strings converts a string to +another type. Here, we use it to convert from a string to a number. We need to +tell Rust the exact number type we want by using `let guess: u32`. The colon +(`:`) after `guess` tells Rust we’ll annotate the variable’s type. Rust has a +few built-in number types; the `u32` seen here is an unsigned, 32-bit integer. +It’s a good default choice for a small positive number. You’ll learn about +other number types in Chapter 3. Additionally, the `u32` annotation in this example program and the comparison with `secret_number` means Rust will infer that `secret_number` should be a -`u32` as well. So now the comparison will be between two values of the same +`u32` as well. So, now the comparison will be between two values of the same type! The `parse` method will only work on characters that can logically be converted into numbers and so can easily cause errors. If, for example, the string -contained `A`👍`%`, there would be no way to convert that to a number. Because -it might fail, the `parse` method returns a `Result` type, much as the -`read_line` method does (discussed earlier in “Handling Potential Failure with -Result” on page XX). We’ll treat this `Result` the same way by using the -`expect` method again. If `parse` returns an `Err` `Result` variant because it -couldn’t create a number from the string, the `expect` call will crash the game -and print the message we give it. If `parse` can successfully convert the -string to a number, it will return the `Ok` variant of `Result`, and `expect` -will return the number that we want from the `Ok` value. +contained `A👍%`, there would be no way to convert that to a number. Because it +might fail, the `parse` method returns a `Result` type, much as the `read_line` +method does (discussed earlier in “Handling Potential Failure with +`Result`”). We’ll treat +this `Result` the same way by using the `expect` method again. If `parse` +returns an `Err` `Result` variant because it couldn’t create a number from the +string, the `expect` call will crash the game and print the message we give it. +If `parse` can successfully convert the string to a number, it will return the +`Ok` variant of `Result`, and `expect` will return the number that we want from +the `Ok` value. Let’s run the program now: + + ``` $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 0.43s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s Running `target/debug/guessing_game` Guess the number! The secret number is: 58 @@ -774,7 +873,7 @@ Too big! Nice! Even though spaces were added before the guess, the program still figured out that the user guessed 76. Run the program a few times to verify the -different behavior with different kinds of input: guess the number correctly, +different behavior with different kinds of input: Guess the number correctly, guess a number that is too high, and guess a number that is too low. We have most of the game working now, but the user can make only one guess. @@ -788,19 +887,20 @@ more chances at guessing the number: Filename: src/main.rs ``` ---snip-- + // --snip-- -println!("The secret number is: {secret_number}"); + println!("The secret number is: {secret_number}"); -loop { - println!("Please input your guess."); + loop { + println!("Please input your guess."); - --snip-- + // --snip-- - match guess.cmp(&secret_number) { - Ordering::Less => println!("Too small!"), - Ordering::Greater => println!("Too big!"), - Ordering::Equal => println!("You win!"), + match guess.cmp(&secret_number) { + Ordering::Less => println!("Too small!"), + Ordering::Greater => println!("Too big!"), + Ordering::Equal => println!("You win!"), + } } } ``` @@ -811,15 +911,26 @@ and run the program again. The program will now ask for another guess forever, which actually introduces a new problem. It doesn’t seem like the user can quit! The user could always interrupt the program by using the keyboard shortcut -ctrl-C. But there’s another way to escape this insatiable monster, as mentioned -in the `parse` discussion in “Comparing the Guess to the Secret Number” on page -XX: if the user enters a non-number answer, the program will crash. We can take +ctrl-C. But there’s another way to escape this insatiable +monster, as mentioned in the `parse` discussion in “Comparing the Guess to the +Secret Number”: If +the user enters a non-number answer, the program will crash. We can take advantage of that to allow the user to quit, as shown here: + + ``` $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 1.50s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s Running `target/debug/guessing_game` Guess the number! The secret number is: 59 @@ -837,8 +948,9 @@ You guessed: 59 You win! Please input your guess. quit -thread 'main' panicked at 'Please type a number!: ParseIntError -{ kind: InvalidDigit }', src/main.rs:28:47 + +thread 'main' panicked at src/main.rs:28:47: +Please type a number!: ParseIntError { kind: InvalidDigit } note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` @@ -853,14 +965,16 @@ Let’s program the game to quit when the user wins by adding a `break` statemen Filename: src/main.rs ``` ---snip-- + // --snip-- -match guess.cmp(&secret_number) { - Ordering::Less => println!("Too small!"), - Ordering::Greater => println!("Too big!"), - Ordering::Equal => { - println!("You win!"); - break; + match guess.cmp(&secret_number) { + Ordering::Less => println!("Too small!"), + Ordering::Greater => println!("Too big!"), + Ordering::Equal => { + println!("You win!"); + break; + } + } } } ``` @@ -872,31 +986,30 @@ exiting the program, because the loop is the last part of `main`. ### Handling Invalid Input To further refine the game’s behavior, rather than crashing the program when -the user inputs a non-number, let’s make the game ignore a non-number so the -user can continue guessing. We can do that by altering the line where `guess` -is converted from a `String` to a `u32`, as shown in Listing 2-5. +the user inputs a non-number, let’s make the game ignore a non-number so that +the user can continue guessing. We can do that by altering the line where +`guess` is converted from a `String` to a `u32`, as shown in Listing 2-5. -Filename: src/main.rs +src/main.rs ``` ---snip-- + // --snip-- -io::stdin() - .read_line(&mut guess) - .expect("Failed to read line"); + io::stdin() + .read_line(&mut guess) + .expect("Failed to read line"); -let guess: u32 = match guess.trim().parse() { - Ok(num) => num, - Err(_) => continue, -}; + let guess: u32 = match guess.trim().parse() { + Ok(num) => num, + Err(_) => continue, + }; -println!("You guessed: {guess}"); + println!("You guessed: {guess}"); ---snip-- + // --snip-- ``` -Listing 2-5: Ignoring a non-number guess and asking for another guess instead -of crashing the program +Listing 2-5: Ignoring a non-number guess and asking for another guess instead of crashing the program We switch from an `expect` call to a `match` expression to move from crashing on an error to handling the error. Remember that `parse` returns a `Result` @@ -914,18 +1027,27 @@ If `parse` is *not* able to turn the string into a number, it will return an `Err` value that contains more information about the error. The `Err` value does not match the `Ok(num)` pattern in the first `match` arm, but it does match the `Err(_)` pattern in the second arm. The underscore, `_`, is a -catchall value; in this example, we’re saying we want to match all `Err` -values, no matter what information they have inside them. So the program will +catch-all value; in this example, we’re saying we want to match all `Err` +values, no matter what information they have inside them. So, the program will execute the second arm’s code, `continue`, which tells the program to go to the next iteration of the `loop` and ask for another guess. So, effectively, the program ignores all errors that `parse` might encounter! Now everything in the program should work as expected. Let’s try it: + + ``` $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 4.45s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.13s Running `target/debug/guessing_game` Guess the number! The secret number is: 61 @@ -950,13 +1072,14 @@ that the program is still printing the secret number. That worked well for testing, but it ruins the game. Let’s delete the `println!` that outputs the secret number. Listing 2-6 shows the final code. -Filename: src/main.rs +src/main.rs ``` -use rand::Rng; use std::cmp::Ordering; use std::io; +use rand::Rng; + fn main() { println!("Guess the number!"); @@ -1003,4 +1126,3 @@ covers concepts that most programming languages have, such as variables, data types, and functions, and shows how to use them in Rust. Chapter 4 explores ownership, a feature that makes Rust different from other languages. Chapter 5 discusses structs and method syntax, and Chapter 6 explains how enums work. - diff --git a/nostarch/chapter03.md b/nostarch/chapter03.md index 249032fd79..2b53775fd3 100644 --- a/nostarch/chapter03.md +++ b/nostarch/chapter03.md @@ -12,25 +12,26 @@ This chapter covers concepts that appear in almost every programming language and how they work in Rust. Many programming languages have much in common at their core. None of the concepts presented in this chapter are unique to Rust, but we’ll discuss them in the context of Rust and explain the conventions -around using these concepts. +around using them. Specifically, you’ll learn about variables, basic types, functions, comments, and control flow. These foundations will be in every Rust program, and learning them early will give you a strong core to start from. -> ### Keywords -> +> #### Keywords +> > The Rust language has a set of *keywords* that are reserved for use by the -language only, much as in other languages. Keep in mind that you cannot use -these words as names of variables or functions. Most of the keywords have -special meanings, and you’ll be using them to do various tasks in your Rust -programs; a few have no current functionality associated with them but have -been reserved for functionality that might be added to Rust in the future. You -can find a list of the keywords in Appendix A. +> language only, much as in other languages. Keep in mind that you cannot use +> these words as names of variables or functions. Most of the keywords have +> special meanings, and you’ll be using them to do various tasks in your Rust +> programs; a few have no current functionality associated with them but have +> been reserved for functionality that might be added to Rust in the future. You +> can find the list of the keywords in Appendix A. ## Variables and Mutability -As mentioned in “Storing Values with Variables” on page XX, by default, +As mentioned in the “Storing Values with +Variables” section, by default, variables are immutable. This is one of many nudges Rust gives you to write your code in a way that takes advantage of the safety and easy concurrency that Rust offers. However, you still have the option to make your variables mutable. @@ -65,13 +66,18 @@ error[E0384]: cannot assign twice to immutable variable `x` --> src/main.rs:4:5 | 2 | let x = 5; - | - - | | - | first assignment to `x` - | help: consider making this binding mutable: `mut x` + | - first assignment to `x` 3 | println!("The value of x is: {x}"); 4 | x = 6; | ^^^^^ cannot assign twice to immutable variable + | +help: consider making this binding mutable + | +2 | let mut x = 5; + | +++ + +For more information about this error, try `rustc --explain E0384`. +error: could not compile `variables` (bin "variables") due to 1 previous error ``` This example shows how the compiler helps you find errors in your programs. @@ -79,11 +85,10 @@ Compiler errors can be frustrating, but really they only mean your program isn’t safely doing what you want it to do yet; they do *not* mean that you’re not a good programmer! Experienced Rustaceans still get compiler errors. -You received the error message `cannot assign twice to immutable variable `x`` -because you tried to assign a second value to the immutable `x` variable. +You received the error message `` cannot assign twice to immutable variable `x` `` because you tried to assign a second value to the immutable `x` variable. It’s important that we get compile-time errors when we attempt to change a -value that’s designated as immutable because this very situation can lead to +value that’s designated as immutable, because this very situation can lead to bugs. If one part of our code operates on the assumption that a value will never change and another part of our code changes that value, it’s possible that the first part of the code won’t do what it was designed to do. The cause @@ -93,11 +98,12 @@ compiler guarantees that when you state that a value won’t change, it really won’t change, so you don’t have to keep track of it yourself. Your code is thus easier to reason through. -But mutability can be very useful, and can make code more convenient to write. +But mutability can be very useful and can make code more convenient to write. Although variables are immutable by default, you can make them mutable by -adding `mut` in front of the variable name as you did in Chapter 2. Adding -`mut` also conveys intent to future readers of the code by indicating that -other parts of the code will be changing this variable’s value. +adding `mut` in front of the variable name as you did in Chapter +2. Adding `mut` also conveys +intent to future readers of the code by indicating that other parts of the code +will be changing this variable’s value. For example, let’s change *src/main.rs* to the following: @@ -117,7 +123,7 @@ When we run the program now, we get this: ``` $ cargo run Compiling variables v0.1.0 (file:///projects/variables) - Finished dev [unoptimized + debuginfo] target(s) in 0.30s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.30s Running `target/debug/variables` The value of x is: 5 The value of x is: 6 @@ -127,7 +133,11 @@ We’re allowed to change the value bound to `x` from `5` to `6` when `mut` is used. Ultimately, deciding whether to use mutability or not is up to you and depends on what you think is clearest in that particular situation. -### Constants + + + + +### Declaring Constants Like immutable variables, *constants* are values that are bound to a name and are not allowed to change, but there are a few differences between constants @@ -136,9 +146,9 @@ and variables. First, you aren’t allowed to use `mut` with constants. Constants aren’t just immutable by default—they’re always immutable. You declare constants using the `const` keyword instead of the `let` keyword, and the type of the value *must* -be annotated. We’ll cover types and type annotations in “Data Types” on page -XX, so don’t worry about the details right now. Just know that you must always -annotate the type. +be annotated. We’ll cover types and type annotations in the next section, +“Data Types”, so don’t worry about the details +right now. Just know that you must always annotate the type. Constants can be declared in any scope, including the global scope, which makes them useful for values that many parts of code need to know about. @@ -152,16 +162,16 @@ Here’s an example of a constant declaration: const THREE_HOURS_IN_SECONDS: u32 = 60 * 60 * 3; ``` -The constant’s name is `THREE_HOURS_IN_SECONDS` and its value is set to the +The constant’s name is `THREE_HOURS_IN_SECONDS`, and its value is set to the result of multiplying 60 (the number of seconds in a minute) by 60 (the number of minutes in an hour) by 3 (the number of hours we want to count in this program). Rust’s naming convention for constants is to use all uppercase with underscores between words. The compiler is able to evaluate a limited set of operations at compile time, which lets us choose to write out this value in a way that’s easier to understand and verify, rather than setting this constant -to the value `10,800`. See the Rust Reference’s section on constant evaluation -at *https://doc.rust-lang.org/reference/const_eval.html* for more information -on what operations can be used when declaring constants. +to the value 10,800. See the Rust Reference’s section on constant +evaluation at *../reference/const_eval.html* for more information on what operations can be used +when declaring constants. Constants are valid for the entire time a program runs, within the scope in which they were declared. This property makes constants useful for values in @@ -171,13 +181,14 @@ earn, or the speed of light. Naming hardcoded values used throughout your program as constants is useful in conveying the meaning of that value to future maintainers of the code. It also -helps to have only one place in your code you would need to change if the +helps to have only one place in your code that you would need to change if the hardcoded value needed to be updated in the future. ### Shadowing -As you saw in the guessing game tutorial in Chapter 2, you can declare a new -variable with the same name as a previous variable. Rustaceans say that the +As you saw in the guessing game tutorial in Chapter +2, you can declare a +new variable with the same name as a previous variable. Rustaceans say that the first variable is *shadowed* by the second, which means that the second variable is what the compiler will see when you use the name of the variable. In effect, the second variable overshadows the first, taking any uses of the @@ -202,9 +213,9 @@ fn main() { } ``` -This program first binds `x` to a value of `5`. Then it creates a new variable -`x` by repeating `let x =`, taking the original value and adding `1` so the -value of `x` is then `6`. Then, within an inner scope created with the curly +This program first binds `x` to a value of `5`. Then, it creates a new variable +`x` by repeating `let x =`, taking the original value and adding `1` so that +the value of `x` is `6`. Then, within an inner scope created with the curly brackets, the third `let` statement also shadows `x` and creates a new variable, multiplying the previous value by `2` to give `x` a value of `12`. When that scope is over, the inner shadowing ends and `x` returns to being `6`. @@ -213,7 +224,7 @@ When we run this program, it will output the following: ``` $ cargo run Compiling variables v0.1.0 (file:///projects/variables) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/variables` The value of x in the inner scope is: 12 The value of x is: 6 @@ -223,7 +234,7 @@ Shadowing is different from marking a variable as `mut` because we’ll get a compile-time error if we accidentally try to reassign to this variable without using the `let` keyword. By using `let`, we can perform a few transformations on a value but have the variable be immutable after those transformations have -been completed. +completed. The other difference between `mut` and shadowing is that because we’re effectively creating a new variable when we use the `let` keyword again, we can @@ -232,19 +243,19 @@ program asks a user to show how many spaces they want between some text by inputting space characters, and then we want to store that input as a number: ``` -let spaces = " "; -let spaces = spaces.len(); + let spaces = " "; + let spaces = spaces.len(); ``` -The first `spaces` variable is a string type and the second `spaces` variable +The first `spaces` variable is a string type, and the second `spaces` variable is a number type. Shadowing thus spares us from having to come up with different names, such as `spaces_str` and `spaces_num`; instead, we can reuse the simpler `spaces` name. However, if we try to use `mut` for this, as shown here, we’ll get a compile-time error: ``` -let mut spaces = " "; -spaces = spaces.len(); + let mut spaces = " "; + spaces = spaces.len(); ``` The error says we’re not allowed to mutate a variable’s type: @@ -259,6 +270,9 @@ error[E0308]: mismatched types | ----- expected due to this value 3 | spaces = spaces.len(); | ^^^^^^^^^^^^ expected `&str`, found `usize` + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `variables` (bin "variables") due to 1 previous error ``` Now that we’ve explored how variables work, let’s look at more data types they @@ -267,15 +281,16 @@ can have. ## Data Types Every value in Rust is of a certain *data type*, which tells Rust what kind of -data is being specified so it knows how to work with that data. We’ll look at -two data type subsets: scalar and compound. +data is being specified so that it knows how to work with that data. We’ll look +at two data type subsets: scalar and compound. Keep in mind that Rust is a *statically typed* language, which means that it must know the types of all variables at compile time. The compiler can usually infer what type we want to use based on the value and how we use it. In cases when many types are possible, such as when we converted a `String` to a numeric -type using `parse` in “Comparing the Guess to the Secret Number” on page XX, we -must add a type annotation, like this: +type using `parse` in the “Comparing the Guess to the Secret +Number” section in +Chapter 2, we must add a type annotation, like this: ``` let guess: u32 = "42".parse().expect("Not a number!"); @@ -288,11 +303,20 @@ information from us to know which type we want to use: ``` $ cargo build Compiling no_type_annotations v0.1.0 (file:///projects/no_type_annotations) -error[E0282]: type annotations needed +error[E0284]: type annotations needed --> src/main.rs:2:9 | 2 | let guess = "42".parse().expect("Not a number!"); - | ^^^^^ consider giving `guess` a type + | ^^^^^ ----- type must be known at this point + | + = note: cannot satisfy `<_ as FromStr>::Err == _` +help: consider giving `guess` an explicit type + | +2 | let guess: /* Type */ = "42".parse().expect("Not a number!"); + | ++++++++++++ + +For more information about this error, try `rustc --explain E0284`. +error: could not compile `no_type_annotations` (bin "no_type_annotations") due to 1 previous error ``` You’ll see different type annotations for other data types. @@ -314,34 +338,33 @@ the type of an integer value. Table 3-1: Integer Types in Rust -| Length | Signed | Unsigned | -|---|---|---| -| 8-bit | `i8` | `u8` | -| 16-bit | `i16` | `u16` | -| 32-bit | `i32` | `u32` | -| 64-bit | `i64` | `u64` | -| 128-bit | `i128` | `u128` | -| arch | `isize` | `usize` | +|Length|Signed|Unsigned| +|------|------|--------| +|8-bit|`i8`|`u8`| +|16-bit|`i16`|`u16`| +|32-bit|`i32`|`u32`| +|64-bit|`i64`|`u64`| +|128-bit|`i128`|`u128`| +|Architecture-dependent|`isize`|`usize`| Each variant can be either signed or unsigned and has an explicit size. *Signed* and *unsigned* refer to whether it’s possible for the number to be negative—in other words, whether the number needs to have a sign with it (signed) or whether it will only ever be positive and can therefore be -represented without a sign (unsigned). It’s like writing numbers on paper: when +represented without a sign (unsigned). It’s like writing numbers on paper: When the sign matters, a number is shown with a plus sign or a minus sign; however, when it’s safe to assume the number is positive, it’s shown with no sign. Signed numbers are stored using two’s complement representation. -Each signed variant can store numbers from -(2n - 1) to 2n - -1 - 1 inclusive, where *n* is the number of bits that variant uses. So an -`i8` can store numbers from -(27) to 27 - 1, which equals --128 to 127. Unsigned variants can store numbers from 0 to 2n - 1, -so a `u8` can store numbers from 0 to 28 - 1, which equals 0 to 255. +Each signed variant can store numbers from −(2n − 1) to 2n − +1 − 1 inclusive, where *n* is the number of bits that variant uses. So, an +`i8` can store numbers from −(27) to 27 − 1, which equals +−128 to 127. Unsigned variants can store numbers from 0 to 2n − 1, +so a `u8` can store numbers from 0 to 28 − 1, which equals 0 to 255. Additionally, the `isize` and `usize` types depend on the architecture of the -computer your program is running on, which is denoted in the table as “arch”: -64 bits if you’re on a 64-bit architecture and 32 bits if you’re on a 32-bit -architecture. +computer your program is running on: 64 bits if you’re on a 64-bit architecture +and 32 bits if you’re on a 32-bit architecture. You can write integer literals in any of the forms shown in Table 3-2. Note that number literals that can be multiple numeric types allow a type suffix, @@ -351,47 +374,49 @@ have the same value as if you had specified `1000`. Table 3-2: Integer Literals in Rust -| Number literals | Example | -|---|---| -| Decimal | `98_222` | -| Hex | `0xff` | -| Octal | `0o77` | -| Binary | `0b1111_0000` | -| Byte (`u8` only) | `b'A'` | +|Number literals|Example| +|---------------|-------| +|Decimal|`98_222`| +|Hex|`0xff`| +|Octal|`0o77`| +|Binary|`0b1111_0000`| +|Byte (`u8` only)|`b'A'`| So how do you know which type of integer to use? If you’re unsure, Rust’s -defaults are generally good places to start: integer types default to `i32`. +defaults are generally good places to start: Integer types default to `i32`. The primary situation in which you’d use `isize` or `usize` is when indexing some sort of collection. -> ### Integer Overflow -> +> ##### Integer Overflow +> > Let’s say you have a variable of type `u8` that can hold values between 0 and -255. If you try to change the variable to a value outside that range, such as -256, *integer overflow* will occur, which can result in one of two behaviors. -When you’re compiling in debug mode, Rust includes checks for integer overflow -that cause your program to *panic* at runtime if this behavior occurs. Rust -uses the term *panicking* when a program exits with an error; we’ll discuss -panics in more depth in “Unrecoverable Errors with panic!” on page XX. -> +> 255. If you try to change the variable to a value outside that range, such as +> 256, *integer overflow* will occur, which can result in one of two behaviors. +> When you’re compiling in debug mode, Rust includes checks for integer overflow +> that cause your program to *panic* at runtime if this behavior occurs. Rust +> uses the term *panicking* when a program exits with an error; we’ll discuss +> panics in more depth in the “Unrecoverable Errors with +> `panic!`” section in Chapter +> 9. +> > When you’re compiling in release mode with the `--release` flag, Rust does -*not* include checks for integer overflow that cause panics. Instead, if -overflow occurs, Rust performs *two’s complement wrapping*. In short, values -greater than the maximum value the type can hold “wrap around” to the minimum -of the values the type can hold. In the case of a `u8`, the value 256 becomes -0, the value 257 becomes 1, and so on. The program won’t panic, but the -variable will have a value that probably isn’t what you were expecting it to -have. Relying on integer overflow’s wrapping behavior is considered an error. -> +> *not* include checks for integer overflow that cause panics. Instead, if +> overflow occurs, Rust performs *two’s complement wrapping*. In short, values +> greater than the maximum value the type can hold “wrap around” to the minimum +> of the values the type can hold. In the case of a `u8`, the value 256 becomes +> 0, the value 257 becomes 1, and so on. The program won’t panic, but the +> variable will have a value that probably isn’t what you were expecting it to +> have. Relying on integer overflow’s wrapping behavior is considered an error. +> > To explicitly handle the possibility of overflow, you can use these families -of methods provided by the standard library for primitive numeric types: -> +> of methods provided by the standard library for primitive numeric types: +> > * Wrap in all modes with the `wrapping_*` methods, such as `wrapping_add`. > * Return the `None` value if there is overflow with the `checked_*` methods. -> * Return the value and a boolean indicating whether there was overflow with -the `overflowing_*` methods. +> * Return the value and a Boolean indicating whether there was overflow with +> the `overflowing_*` methods. > * Saturate at the value’s minimum or maximum values with the `saturating_*` -methods. +> methods. #### Floating-Point Types @@ -413,8 +438,7 @@ fn main() { } ``` -Floating-point numbers are represented according to the IEEE-754 standard. The -`f32` type is a single-precision float, and `f64` has double precision. +Floating-point numbers are represented according to the IEEE-754 standard. #### Numeric Operations @@ -446,8 +470,9 @@ fn main() { ``` Each expression in these statements uses a mathematical operator and evaluates -to a single value, which is then bound to a variable. Appendix B contains a -list of all operators that Rust provides. +to a single value, which is then bound to a variable. Appendix +B contains a list of all operators that Rust +provides. #### The Boolean Type @@ -466,8 +491,8 @@ fn main() { ``` The main way to use Boolean values is through conditionals, such as an `if` -expression. We’ll cover how `if` expressions work in Rust in “Control Flow” on -page XX. +expression. We’ll cover how `if` expressions work in Rust in the “Control +Flow” section. #### The Character Type @@ -484,16 +509,16 @@ fn main() { } ``` -Note that we specify `char` literals with single quotes, as opposed to string -literals, which use double quotes. Rust’s `char` type is four bytes in size and -represents a Unicode Scalar Value, which means it can represent a lot more than -just ASCII. Accented letters; Chinese, Japanese, and Korean characters; emoji; -and zero-width spaces are all valid `char` values in Rust. Unicode Scalar -Values range from `U+0000` to `U+D7FF` and `U+E000` to `U+10FFFF` inclusive. -However, a “character” isn’t really a concept in Unicode, so your human -intuition for what a “character” is may not match up with what a `char` is in -Rust. We’ll discuss this topic in detail in “Storing UTF-8 Encoded Text with -Strings” on page XX. +Note that we specify `char` literals with single quotation marks, as opposed to +string literals, which use double quotation marks. Rust’s `char` type is 4 +bytes in size and represents a Unicode scalar value, which means it can +represent a lot more than just ASCII. Accented letters; Chinese, Japanese, and +Korean characters; emojis; and zero-width spaces are all valid `char` values in +Rust. Unicode scalar values range from `U+0000` to `U+D7FF` and `U+E000` to +`U+10FFFF` inclusive. However, a “character” isn’t really a concept in Unicode, +so your human intuition for what a “character” is may not match up with what a +`char` is in Rust. We’ll discuss this topic in detail in “Storing UTF-8 +Encoded Text with Strings” in Chapter 8. ### Compound Types @@ -503,7 +528,7 @@ primitive compound types: tuples and arrays. #### The Tuple Type A *tuple* is a general way of grouping together a number of values with a -variety of types into one compound type. Tuples have a fixed length: once +variety of types into one compound type. Tuples have a fixed length: Once declared, they cannot grow or shrink in size. We create a tuple by writing a comma-separated list of values inside @@ -584,13 +609,15 @@ fn main() { } ``` -Arrays are useful when you want your data allocated on the stack rather than -the heap (we will discuss the stack and the heap more in Chapter 4) or when you -want to ensure you always have a fixed number of elements. An array isn’t as -flexible as the vector type, though. A *vector* is a similar collection type -provided by the standard library that *is* allowed to grow or shrink in size. -If you’re unsure whether to use an array or a vector, chances are you should -use a vector. Chapter 8 discusses vectors in more detail. +Arrays are useful when you want your data allocated on the stack, the same as +the other types we have seen so far, rather than the heap (we will discuss the +stack and the heap more in Chapter 4) or when +you want to ensure that you always have a fixed number of elements. An array +isn’t as flexible as the vector type, though. A vector is a similar collection +type provided by the standard library that *is* allowed to grow or shrink in +size because its contents live on the heap. If you’re unsure whether to use an +array or a vector, chances are you should use a vector. Chapter +8 discusses vectors in more detail. However, arrays are more useful when you know the number of elements will not need to change. For example, if you were using the names of the month in a @@ -624,7 +651,11 @@ The array named `a` will contain `5` elements that will all be set to the value `3` initially. This is the same as writing `let a = [3, 3, 3, 3, 3];` but in a more concise way. -#### Accessing Array Elements + + + + +#### Array Element Access An array is a single chunk of memory of a known, fixed size that can be allocated on the stack. You can access elements of an array using indexing, @@ -674,9 +705,7 @@ fn main() { let element = a[index]; - println!( - "The value of the element at index {index} is: {element}" - ); + println!("The value of the element at index {index} is: {element}"); } ``` @@ -685,13 +714,19 @@ enter `0`, `1`, `2`, `3`, or `4`, the program will print out the corresponding value at that index in the array. If you instead enter a number past the end of the array, such as `10`, you’ll see output like this: + + ``` -thread 'main' panicked at 'index out of bounds: the len is 5 but the index is -10', src/main.rs:19:19 +thread 'main' panicked at src/main.rs:19:19: +index out of bounds: the len is 5 but the index is 10 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` -The program resulted in a *runtime* error at the point of using an invalid +The program resulted in a runtime error at the point of using an invalid value in the indexing operation. The program exited with an error message and didn’t execute the final `println!` statement. When you attempt to access an element using indexing, Rust will check that the index you’ve specified is less @@ -750,7 +785,7 @@ should see the following output: ``` $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 0.28s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.28s Running `target/debug/functions` Hello, world! Another function. @@ -789,7 +824,7 @@ Try running this program; you should get the following output: ``` $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 1.21s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.21s Running `target/debug/functions` The value of x is: 5 ``` @@ -800,10 +835,10 @@ The declaration of `another_function` has one parameter named `x`. The type of in the format string. In function signatures, you *must* declare the type of each parameter. This is -a deliberate decision in Rust’s design: requiring type annotations in function +a deliberate decision in Rust’s design: Requiring type annotations in function definitions means the compiler almost never needs you to use them elsewhere in the code to figure out what type you mean. The compiler is also able to give -more helpful error messages if it knows what types the function expects. +more-helpful error messages if it knows what types the function expects. When defining multiple parameters, separate the parameter declarations with commas, like this: @@ -826,13 +861,12 @@ named `unit_label` and is type `char`. The function then prints text containing both the `value` and the `unit_label`. Let’s try running this code. Replace the program currently in your *functions* -project’s *src/main.rs* file with the preceding example and run it using `cargo -run`: +project’s *src/main.rs* file with the preceding example and run it using `cargo run`: ``` $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/functions` The measurement is: 5h ``` @@ -850,15 +884,17 @@ understand. Other languages don’t have the same distinctions, so let’s look what statements and expressions are and how their differences affect the bodies of functions. -* **Statements **: are instructions that perform some action and do not return -a value. -* **Expressions **: evaluate to a resultant value. Let’s look at some examples. +* *Statements* are instructions that perform some action and do not return + a value. +* *Expressions* evaluate to a resultant value. + +Let’s look at some examples. We’ve actually already used statements and expressions. Creating a variable and assigning a value to it with the `let` keyword is a statement. In Listing 3-1, `let y = 6;` is a statement. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -869,7 +905,8 @@ fn main() { Listing 3-1: A `main` function declaration containing one statement Function definitions are also statements; the entire preceding example is a -statement in itself. +statement in itself. (As we’ll see shortly, calling a function is not a +statement, though.) Statements do not return values. Therefore, you can’t assign a `let` statement to another variable, as the following code tries to do; you’ll get an error: @@ -887,22 +924,29 @@ When you run this program, the error you’ll get looks like this: ``` $ cargo run Compiling functions v0.1.0 (file:///projects/functions) -error: expected expression, found statement (`let`) +error: expected expression, found `let` statement --> src/main.rs:2:14 | 2 | let x = (let y = 6); - | ^^^^^^^^^ + | ^^^ | - = note: variable declaration using `let` is a statement + = note: only supported directly in conditions of `if` and `while` expressions -error[E0658]: `let` expressions in this position are unstable - --> src/main.rs:2:14 +warning: unnecessary parentheses around assigned value + --> src/main.rs:2:13 | 2 | let x = (let y = 6); - | ^^^^^^^^^ + | ^ ^ | - = note: see issue #53667 for -more information + = note: `#[warn(unused_parens)]` on by default +help: remove these parentheses + | +2 - let x = (let y = 6); +2 + let x = let y = 6; + | + +warning: `functions` (bin "functions") generated 1 warning +error: could not compile `functions` (bin "functions") due to 1 previous error; 1 warning emitted ``` The `let y = 6` statement does not return a value, so there isn’t anything for @@ -914,7 +958,7 @@ languages, you can write `x = y = 6` and have both `x` and `y` have the value Expressions evaluate to a value and make up most of the rest of the code that you’ll write in Rust. Consider a math operation, such as `5 + 6`, which is an expression that evaluates to the value `11`. Expressions can be part of -statements: in Listing 3-1, the `6` in the statement `let y = 6;` is an +statements: In Listing 3-1, the `6` in the statement `let y = 6;` is an expression that evaluates to the value `6`. Calling a function is an expression. Calling a macro is an expression. A new scope block created with curly brackets is an expression, for example: @@ -923,22 +967,30 @@ Filename: src/main.rs ``` fn main() { - 1 let y = {2 + let y = { let x = 3; - 3 x + 1 + x + 1 }; println!("The value of y is: {y}"); } ``` -The expression [2] is a block that, in this case, evaluates to `4`. That value -gets bound to `y` as part of the `let` statement [1]. Note the line without a -semicolon at the end [3], which is unlike most of the lines you’ve seen so far. -Expressions do not include ending semicolons. If you add a semicolon to the end -of an expression, you turn it into a statement, and it will then not return a -value. Keep this in mind as you explore function return values and expressions -next. +This expression: + +``` +{ + let x = 3; + x + 1 +} +``` + +is a block that, in this case, evaluates to `4`. That value gets bound to `y` +as part of the `let` statement. Note the `x + 1` line without a semicolon at +the end, which is unlike most of the lines you’ve seen so far. Expressions do +not include ending semicolons. If you add a semicolon to the end of an +expression, you turn it into a statement, and it will then not return a value. +Keep this in mind as you explore function return values and expressions next. ### Functions with Return Values @@ -972,14 +1024,14 @@ running this code; the output should look like this: ``` $ cargo run Compiling functions v0.1.0 (file:///projects/functions) - Finished dev [unoptimized + debuginfo] target(s) in 0.30s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.30s Running `target/debug/functions` The value of x is: 5 ``` The `5` in `five` is the function’s return value, which is why the return type is `i32`. Let’s examine this in more detail. There are two important bits: -first, the line `let x = five();` shows that we’re using the return value of a +First, the line `let x = five();` shows that we’re using the return value of a function to initialize a variable. Because the function `five` returns a `5`, that line is the same as the following: @@ -1007,9 +1059,9 @@ fn plus_one(x: i32) -> i32 { } ``` -Running this code will print `The value of x is: 6`. But if we place a -semicolon at the end of the line containing `x + 1`, changing it from an -expression to a statement, we’ll get an error: +Running this code will print `The value of x is: 6`. But what happens if we +place a semicolon at the end of the line containing `x + 1`, changing it from +an expression to a statement? Filename: src/main.rs @@ -1025,7 +1077,7 @@ fn plus_one(x: i32) -> i32 { } ``` -Compiling this code produces an error, as follows: +Compiling this code will produce an error, as follows: ``` $ cargo run @@ -1038,7 +1090,10 @@ error[E0308]: mismatched types | | | implicitly returns `()` as its body has no tail or `return` expression 8 | x + 1; - | - help: remove this semicolon + | - help: remove this semicolon to return this value + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `functions` (bin "functions") due to 1 previous error ``` The main error message, `mismatched types`, reveals the core issue with this @@ -1046,15 +1101,15 @@ code. The definition of the function `plus_one` says that it will return an `i32`, but statements don’t evaluate to a value, which is expressed by `()`, the unit type. Therefore, nothing is returned, which contradicts the function definition and results in an error. In this output, Rust provides a message to -possibly help rectify this issue: it suggests removing the semicolon, which +possibly help rectify this issue: It suggests removing the semicolon, which would fix the error. ## Comments All programmers strive to make their code easy to understand, but sometimes extra explanation is warranted. In these cases, programmers leave *comments* in -their source code that the compiler will ignore but people reading the source -code may find useful. +their source code that the compiler will ignore but that people reading the +source code may find useful. Here’s a simple comment: @@ -1067,9 +1122,9 @@ comment continues until the end of the line. For comments that extend beyond a single line, you’ll need to include `//` on each line, like this: ``` -// So we’re doing something complicated here, long enough that we need +// So we're doing something complicated here, long enough that we need // multiple lines of comments to do it! Whew! Hopefully, this comment will -// explain what’s going on. +// explain what's going on. ``` Comments can also be placed at the end of lines containing code: @@ -1078,7 +1133,7 @@ Filename: src/main.rs ``` fn main() { - let lucky_number = 7; // I’m feeling lucky today + let lucky_number = 7; // I'm feeling lucky today } ``` @@ -1089,20 +1144,22 @@ Filename: src/main.rs ``` fn main() { - // I’m feeling lucky today + // I'm feeling lucky today let lucky_number = 7; } ``` Rust also has another kind of comment, documentation comments, which we’ll -discuss in “Publishing a Crate to Crates.io” on page XX. +discuss in the “Publishing a Crate to Crates.io” +section of Chapter 14. ## Control Flow -The ability to run some code depending on whether a condition is `true` and to -run some code repeatedly while a condition is `true` are basic building blocks -in most programming languages. The most common constructs that let you control -the flow of execution of Rust code are `if` expressions and loops. +The ability to run some code depending on whether a condition is `true` and the +ability to run some code repeatedly while a condition is `true` are basic +building blocks in most programming languages. The most common constructs that +let you control the flow of execution of Rust code are `if` expressions and +loops. ### if Expressions @@ -1132,8 +1189,8 @@ this case, the condition checks whether or not the variable `number` has a value less than 5. We place the block of code to execute if the condition is `true` immediately after the condition inside curly brackets. Blocks of code associated with the conditions in `if` expressions are sometimes called *arms*, -just like the arms in `match` expressions that we discussed in “Comparing the -Guess to the Secret Number” on page XX. +just like the arms in `match` expressions that we discussed in the “Comparing +the Guess to the Secret Number” section of Chapter 2. Optionally, we can also include an `else` expression, which we chose to do here, to give the program an alternative block of code to execute should the @@ -1146,7 +1203,7 @@ Try running this code; you should see the following output: ``` $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/branches` condition was true ``` @@ -1163,7 +1220,7 @@ Run the program again, and look at the output: ``` $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/branches` condition was false ``` @@ -1195,6 +1252,9 @@ error[E0308]: mismatched types | 4 | if number { | ^^^^^^ expected `bool`, found integer + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `branches` (bin "branches") due to 1 previous error ``` The error indicates that Rust expected a `bool` but got an integer. Unlike @@ -1247,7 +1307,7 @@ see the following output: ``` $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.31s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.31s Running `target/debug/branches` number is divisible by 3 ``` @@ -1268,7 +1328,7 @@ Rust branching construct called `match` for these cases. Because `if` is an expression, we can use it on the right side of a `let` statement to assign the outcome to a variable, as in Listing 3-2. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1287,7 +1347,7 @@ expression. Run this code to see what happens: ``` $ cargo run Compiling branches v0.1.0 (file:///projects/branches) - Finished dev [unoptimized + debuginfo] target(s) in 0.30s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.30s Running `target/debug/branches` The value of number is: 5 ``` @@ -1323,20 +1383,22 @@ error[E0308]: `if` and `else` have incompatible types --> src/main.rs:4:44 | 4 | let number = if condition { 5 } else { "six" }; - | - ^^^^^ expected integer, found -`&str` + | - ^^^^^ expected integer, found `&str` | | | expected because of this + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `branches` (bin "branches") due to 1 previous error ``` The expression in the `if` block evaluates to an integer, and the expression in -the `else` block evaluates to a string. This won’t work because variables must -have a single type, and Rust needs to know at compile time what type the -`number` variable is, definitively. Knowing the type of `number` lets the -compiler verify the type is valid everywhere we use `number`. Rust wouldn’t be -able to do that if the type of `number` was only determined at runtime; the -compiler would be more complex and would make fewer guarantees about the code -if it had to keep track of multiple hypothetical types for any variable. +the `else` block evaluates to a string. This won’t work, because variables must +have a single type, and Rust needs to know definitively at compile time what +type the `number` variable is. Knowing the type of `number` lets the compiler +verify the type is valid everywhere we use `number`. Rust wouldn’t be able to +do that if the type of `number` was only determined at runtime; the compiler +would be more complex and would make fewer guarantees about the code if it had +to keep track of multiple hypothetical types for any variable. ### Repetition with Loops @@ -1350,7 +1412,7 @@ Rust has three kinds of loops: `loop`, `while`, and `for`. Let’s try each one. #### Repeating Code with loop The `loop` keyword tells Rust to execute a block of code over and over again -forever or until you explicitly tell it to stop. +either forever or until you explicitly tell it to stop. As an example, change the *src/main.rs* file in your *loops* directory to look like this: @@ -1366,14 +1428,20 @@ fn main() { ``` When we run this program, we’ll see `again!` printed over and over continuously -until we stop the program manually. Most terminals support the keyboard -shortcut ctrl-C to interrupt a program that is stuck in a continual loop. Give -it a try: +until we stop the program manually. Most terminals support the keyboard shortcut +ctrl-C to interrupt a program that is stuck in a continual +loop. Give it a try: + + ``` $ cargo run Compiling loops v0.1.0 (file:///projects/loops) - Finished dev [unoptimized + debuginfo] target(s) in 0.29s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s Running `target/debug/loops` again! again! @@ -1382,15 +1450,16 @@ again! ^Cagain! ``` -The symbol `^C` represents where you pressed ctrl-C. You may or may not see the -word `again!` printed after the `^C`, depending on where the code was in the -loop when it received the interrupt signal. +The symbol `^C` represents where you pressed ctrl-C. + +You may or may not see the word `again!` printed after the `^C`, depending on +where the code was in the loop when it received the interrupt signal. Fortunately, Rust also provides a way to break out of a loop using code. You can place the `break` keyword within the loop to tell the program when to stop -executing the loop. Recall that we did this in the guessing game in “Quitting -After a Correct Guess” on page XX to exit the program when the user won the -game by guessing the correct number. +executing the loop. Recall that we did this in the guessing game in the +“Quitting After a Correct Guess” section of Chapter 2 to exit the program when the user won the game by +guessing the correct number. We also used `continue` in the guessing game, which in a loop tells the program to skip over any remaining code in this iteration of the loop and go to the @@ -1402,8 +1471,8 @@ One of the uses of a `loop` is to retry an operation you know might fail, such as checking whether a thread has completed its job. You might also need to pass the result of that operation out of the loop to the rest of your code. To do this, you can add the value you want returned after the `break` expression you -use to stop the loop; that value will be returned out of the loop so you can -use it, as shown here: +use to stop the loop; that value will be returned out of the loop so that you +can use it, as shown here: ``` fn main() { @@ -1422,14 +1491,21 @@ fn main() { ``` Before the loop, we declare a variable named `counter` and initialize it to -`0`. Then we declare a variable named `result` to hold the value returned from +`0`. Then, we declare a variable named `result` to hold the value returned from the loop. On every iteration of the loop, we add `1` to the `counter` variable, and then check whether the `counter` is equal to `10`. When it is, we use the `break` keyword with the value `counter * 2`. After the loop, we use a semicolon to end the statement that assigns the value to `result`. Finally, we print the value in `result`, which in this case is `20`. -#### Loop Labels to Disambiguate Between Multiple Loops +You can also `return` from inside a loop. While `break` only exits the current +loop, `return` always exits the current function. + + + + + +#### Disambiguating with Loop Labels If you have loops within loops, `break` and `continue` apply to the innermost loop at that point. You can optionally specify a *loop label* on a loop that @@ -1463,12 +1539,12 @@ fn main() { The outer loop has the label `'counting_up`, and it will count up from 0 to 2. The inner loop without a label counts down from 10 to 9. The first `break` that -doesn’t specify a label will exit the inner loop only. The `break -'counting_up;` statement will exit the outer loop. This code prints: +doesn’t specify a label will exit the inner loop only. The `break 'counting_up;` statement will exit the outer loop. This code prints: ``` +$ cargo run Compiling loops v0.1.0 (file:///projects/loops) - Finished dev [unoptimized + debuginfo] target(s) in 0.58s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.58s Running `target/debug/loops` count = 0 remaining = 10 @@ -1481,7 +1557,11 @@ remaining = 10 End count = 2 ``` -#### Conditional Loops with while + + + + +#### Streamlining Conditional Loops with while A program will often need to evaluate a condition within a loop. While the condition is `true`, the loop runs. When the condition ceases to be `true`, the @@ -1490,9 +1570,9 @@ like this using a combination of `loop`, `if`, `else`, and `break`; you could try that now in a program, if you’d like. However, this pattern is so common that Rust has a built-in language construct for it, called a `while` loop. In Listing 3-3, we use `while` to loop the program three times, counting down each -time, and then, after the loop, print a message and exit. +time, and then, after the loop, to print a message and exit. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1508,8 +1588,7 @@ fn main() { } ``` -Listing 3-3: Using a `while` loop to run code while a condition evaluates to -`true` +Listing 3-3: Using a `while` loop to run code while a condition evaluates to `true` This construct eliminates a lot of nesting that would be necessary if you used `loop`, `if`, `else`, and `break`, and it’s clearer. While a condition @@ -1521,7 +1600,7 @@ You can choose to use the `while` construct to loop over the elements of a collection, such as an array. For example, the loop in Listing 3-4 prints each element in the array `a`. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1539,14 +1618,14 @@ fn main() { Listing 3-4: Looping through each element of a collection using a `while` loop Here, the code counts up through the elements in the array. It starts at index -`0`, and then loops until it reaches the final index in the array (that is, +`0` and then loops until it reaches the final index in the array (that is, when `index < 5` is no longer `true`). Running this code will print every element in the array: ``` $ cargo run Compiling loops v0.1.0 (file:///projects/loops) - Finished dev [unoptimized + debuginfo] target(s) in 0.32s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.32s Running `target/debug/loops` the value is: 10 the value is: 20 @@ -1559,7 +1638,7 @@ All five array values appear in the terminal, as expected. Even though `index` will reach a value of `5` at some point, the loop stops executing before trying to fetch a sixth value from the array. -However, this approach is error prone; we could cause the program to panic if +However, this approach is error-prone; we could cause the program to panic if the index value or test condition is incorrect. For example, if you changed the definition of the `a` array to have four elements but forgot to update the condition to `while index < 4`, the code would panic. It’s also slow, because @@ -1569,7 +1648,7 @@ index is within the bounds of the array on every iteration through the loop. As a more concise alternative, you can use a `for` loop and execute some code for each item in a collection. A `for` loop looks like the code in Listing 3-5. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1586,7 +1665,9 @@ Listing 3-5: Looping through each element of a collection using a `for` loop When we run this code, we’ll see the same output as in Listing 3-4. More importantly, we’ve now increased the safety of the code and eliminated the chance of bugs that might result from going beyond the end of the array or not -going far enough and missing some items. +going far enough and missing some items. Machine code generated from `for` +loops can be more efficient as well because the index doesn’t need to be +compared to the length of the array at every iteration. Using the `for` loop, you wouldn’t need to remember to change any other code if you changed the number of values in the array, as you would with the method @@ -1618,7 +1699,7 @@ This code is a bit nicer, isn’t it? ## Summary -You made it! This was a sizable chapter: you learned about variables, scalar +You made it! This was a sizable chapter: You learned about variables, scalar and compound data types, functions, comments, `if` expressions, and loops! To practice with the concepts discussed in this chapter, try building programs to do the following: @@ -1626,8 +1707,7 @@ do the following: * Convert temperatures between Fahrenheit and Celsius. * Generate the *n*th Fibonacci number. * Print the lyrics to the Christmas carol “The Twelve Days of Christmas,” -taking advantage of the repetition in the song. + taking advantage of the repetition in the song. When you’re ready to move on, we’ll talk about a concept in Rust that *doesn’t* commonly exist in other programming languages: ownership. - diff --git a/nostarch/chapter04.md b/nostarch/chapter04.md index 11f7f4944b..c968309c54 100644 --- a/nostarch/chapter04.md +++ b/nostarch/chapter04.md @@ -20,7 +20,7 @@ features: borrowing, slices, and how Rust lays data out in memory. All programs have to manage the way they use a computer’s memory while running. Some languages have garbage collection that regularly looks for no-longer-used memory as the program runs; in other languages, the programmer must explicitly -allocate and free the memory. Rust uses a third approach: memory is managed +allocate and free the memory. Rust uses a third approach: Memory is managed through a system of ownership with a set of rules that the compiler checks. If any of the rules are violated, the program won’t compile. None of the features of ownership will slow down your program while it’s running. @@ -36,65 +36,69 @@ working through some examples that focus on a very common data structure: strings. > ### The Stack and the Heap -> +> > Many programming languages don’t require you to think about the stack and the -heap very often. But in a systems programming language like Rust, whether a -value is on the stack or the heap affects how the language behaves and why you -have to make certain decisions. Parts of ownership will be described in -relation to the stack and the heap later in this chapter, so here is a brief -explanation in preparation. -> +> heap very often. But in a systems programming language like Rust, whether a +> value is on the stack or the heap affects how the language behaves and why +> you have to make certain decisions. Parts of ownership will be described in +> relation to the stack and the heap later in this chapter, so here is a brief +> explanation in preparation. +> > Both the stack and the heap are parts of memory available to your code to use -at runtime, but they are structured in different ways. The stack stores values -in the order it gets them and removes the values in the opposite order. This is -referred to as *last in, first out*. Think of a stack of plates: when you add -more plates, you put them on top of the pile, and when you need a plate, you -take one off the top. Adding or removing plates from the middle or bottom -wouldn’t work as well! Adding data is called *pushing onto the stack*, and -removing data is called *popping off the stack*. All data stored on the stack -must have a known, fixed size. Data with an unknown size at compile time or a -size that might change must be stored on the heap instead. -> -> The heap is less organized: when you put data on the heap, you request a -certain amount of space. The memory allocator finds an empty spot in the heap -that is big enough, marks it as being in use, and returns a *pointer*, which is -the address of that location. This process is called *allocating on the heap* -and is sometimes abbreviated as just *allocating* (pushing values onto the -stack is not considered allocating). Because the pointer to the heap is a -known, fixed size, you can store the pointer on the stack, but when you want -the actual data, you must follow the pointer. Think of being seated at a -restaurant. When you enter, you state the number of people in your group, and -the host finds an empty table that fits everyone and leads you there. If -someone in your group comes late, they can ask where you’ve been seated to find -you. -> +> at runtime, but they are structured in different ways. The stack stores +> values in the order it gets them and removes the values in the opposite +> order. This is referred to as *last in, first out (LIFO)*. Think of a stack of +> plates: When you add more plates, you put them on top of the pile, and when +> you need a plate, you take one off the top. Adding or removing plates from +> the middle or bottom wouldn’t work as well! Adding data is called *pushing +> onto the stack*, and removing data is called *popping off the stack*. All +> data stored on the stack must have a known, fixed size. Data with an unknown +> size at compile time or a size that might change must be stored on the heap +> instead. +> +> The heap is less organized: When you put data on the heap, you request a +> certain amount of space. The memory allocator finds an empty spot in the heap +> that is big enough, marks it as being in use, and returns a *pointer*, which +> is the address of that location. This process is called *allocating on the +> heap* and is sometimes abbreviated as just *allocating* (pushing values onto +> the stack is not considered allocating). Because the pointer to the heap is a +> known, fixed size, you can store the pointer on the stack, but when you want +> the actual data, you must follow the pointer. Think of being seated at a +> restaurant. When you enter, you state the number of people in your group, and +> the host finds an empty table that fits everyone and leads you there. If +> someone in your group comes late, they can ask where you’ve been seated to +> find you. +> > Pushing to the stack is faster than allocating on the heap because the -allocator never has to search for a place to store new data; that location is -always at the top of the stack. Comparatively, allocating space on the heap -requires more work because the allocator must first find a big enough space to -hold the data and then perform bookkeeping to prepare for the next allocation. -> -> Accessing data in the heap is slower than accessing data on the stack because -you have to follow a pointer to get there. Contemporary processors are faster -if they jump around less in memory. Continuing the analogy, consider a server -at a restaurant taking orders from many tables. It’s most efficient to get all -the orders at one table before moving on to the next table. Taking an order -from table A, then an order from table B, then one from A again, and then one -from B again would be a much slower process. By the same token, a processor can -do its job better if it works on data that’s close to other data (as it is on -the stack) rather than farther away (as it can be on the heap). -> +> allocator never has to search for a place to store new data; that location is +> always at the top of the stack. Comparatively, allocating space on the heap +> requires more work because the allocator must first find a big enough space +> to hold the data and then perform bookkeeping to prepare for the next +> allocation. +> +> Accessing data in the heap is generally slower than accessing data on the +> stack because you have to follow a pointer to get there. Contemporary +> processors are faster if they jump around less in memory. Continuing the +> analogy, consider a server at a restaurant taking orders from many tables. +> It’s most efficient to get all the orders at one table before moving on to +> the next table. Taking an order from table A, then an order from table B, +> then one from A again, and then one from B again would be a much slower +> process. By the same token, a processor can usually do its job better if it +> works on data that’s close to other data (as it is on the stack) rather than +> farther away (as it can be on the heap). +> > When your code calls a function, the values passed into the function -(including, potentially, pointers to data on the heap) and the function’s local -variables get pushed onto the stack. When the function is over, those values -get popped off the stack. -> +> (including, potentially, pointers to data on the heap) and the function’s +> local variables get pushed onto the stack. When the function is over, those +> values get popped off the stack. +> > Keeping track of what parts of code are using what data on the heap, -minimizing the amount of duplicate data on the heap, and cleaning up unused -data on the heap so you don’t run out of space are all problems that ownership -addresses. Once you understand ownership, you won’t need to think about the -stack and the heap very often, but knowing that the main purpose of ownership -is to manage heap data can help explain why it works the way it does. +> minimizing the amount of duplicate data on the heap, and cleaning up unused +> data on the heap so that you don’t run out of space are all problems that +> ownership addresses. Once you understand ownership, you won’t need to think +> about the stack and the heap very often. But knowing that the main purpose of +> ownership is to manage heap data can help explain why it works the way it +> does. ### Ownership Rules @@ -108,13 +112,13 @@ work through the examples that illustrate them: ### Variable Scope Now that we’re past basic Rust syntax, we won’t include all the `fn main() {` -code in examples, so if you’re following along, make sure to put the following -examples inside a `main` function manually. As a result, our examples will be a -bit more concise, letting us focus on the actual details rather than +code in the examples, so if you’re following along, make sure to put the +following examples inside a `main` function manually. As a result, our examples +will be a bit more concise, letting us focus on the actual details rather than boilerplate code. -As a first example of ownership, we’ll look at the *scope* of some variables. A -scope is the range within a program for which an item is valid. Take the +As a first example of ownership, we’ll look at the scope of some variables. A +*scope* is the range within a program for which an item is valid. Take the following variable: ``` @@ -123,15 +127,16 @@ let s = "hello"; The variable `s` refers to a string literal, where the value of the string is hardcoded into the text of our program. The variable is valid from the point at -which it’s declared until the end of the current *scope*. Listing 4-1 shows a +which it’s declared until the end of the current scope. Listing 4-1 shows a program with comments annotating where the variable `s` would be valid. + ``` -{ // s is not valid here, since it's not yet declared - let s = "hello"; // s is valid from this point forward + { // s is not valid here, since it's not yet declared + let s = "hello"; // s is valid from this point forward - // do stuff with s -} // this scope is now over, and s is no longer valid + // do stuff with s + } // this scope is now over, and s is no longer valid ``` Listing 4-1: A variable and the scope in which it is valid @@ -148,25 +153,25 @@ understanding by introducing the `String` type. ### The String Type To illustrate the rules of ownership, we need a data type that is more complex -than those we covered in “Data Types” on page XX. The types covered previously -are of a known size, can be stored on the stack and popped off the stack when -their scope is over, and can be quickly and trivially copied to make a new, -independent instance if another part of code needs to use the same value in a -different scope. But we want to look at data that is stored on the heap and -explore how Rust knows when to clean up that data, and the `String` type is a -great example. +than those we covered in the “Data Types” section +of Chapter 3. The types covered previously are of a known size, can be stored +on the stack and popped off the stack when their scope is over, and can be +quickly and trivially copied to make a new, independent instance if another +part of code needs to use the same value in a different scope. But we want to +look at data that is stored on the heap and explore how Rust knows when to +clean up that data, and the `String` type is a great example. We’ll concentrate on the parts of `String` that relate to ownership. These aspects also apply to other complex data types, whether they are provided by -the standard library or created by you. We’ll discuss `String` in more depth in -Chapter 8. +the standard library or created by you. We’ll discuss non-ownership aspects of +`String` in Chapter 8. We’ve already seen string literals, where a string value is hardcoded into our program. String literals are convenient, but they aren’t suitable for every situation in which we may want to use text. One reason is that they’re immutable. Another is that not every string value can be known when we write -our code: for example, what if we want to take user input and store it? For -these situations, Rust has a second string type, `String`. This type manages +our code: For example, what if we want to take user input and store it? It is +for these situations that Rust has the `String` type. This type manages data allocated on the heap and as such is able to store an amount of text that is unknown to us at compile time. You can create a `String` from a string literal using the `from` function, like so: @@ -177,18 +182,18 @@ let s = String::from("hello"); The double colon `::` operator allows us to namespace this particular `from` function under the `String` type rather than using some sort of name like -`string_from`. We’ll discuss this syntax more in “Method Syntax” on page XX, -and when we talk about namespacing with modules in “Paths for Referring to an -Item in the Module Tree” on page XX. +`string_from`. We’ll discuss this syntax more in the “Methods” section of Chapter 5, and when we talk about namespacing with +modules in “Paths for Referring to an Item in the Module +Tree” in Chapter 7. This kind of string *can* be mutated: ``` -let mut s = String::from("hello"); + let mut s = String::from("hello"); -s.push_str(", world!"); // push_str() appends a literal to a String + s.push_str(", world!"); // push_str() appends a literal to a String -println!("{s}"); // This will print `hello, world!` + println!("{s}"); // this will print `hello, world!` ``` So, what’s the difference here? Why can `String` be mutated but literals @@ -209,9 +214,9 @@ to hold the contents. This means: * The memory must be requested from the memory allocator at runtime. * We need a way of returning this memory to the allocator when we’re done with -our `String`. + our `String`. -That first part is done by us: when we call `String::from`, its implementation +That first part is done by us: When we call `String::from`, its implementation requests the memory it needs. This is pretty much universal in programming languages. @@ -225,48 +230,54 @@ we’ll waste memory. If we do it too early, we’ll have an invalid variable. I we do it twice, that’s a bug too. We need to pair exactly one `allocate` with exactly one `free`. -Rust takes a different path: the memory is automatically returned once the +Rust takes a different path: The memory is automatically returned once the variable that owns it goes out of scope. Here’s a version of our scope example from Listing 4-1 using a `String` instead of a string literal: ``` -{ - let s = String::from("hello"); // s is valid from this point forward + { + let s = String::from("hello"); // s is valid from this point forward - // do stuff with s -} // this scope is now over, and s is no - // longer valid + // do stuff with s + } // this scope is now over, and s is no + // longer valid ``` There is a natural point at which we can return the memory our `String` needs to the allocator: when `s` goes out of scope. When a variable goes out of -scope, Rust calls a special function for us. This function is called `drop`, -and it’s where the author of `String` can put the code to return the memory. -Rust calls `drop` automatically at the closing curly bracket. +scope, Rust calls a special function for us. This function is called +`drop`, and it’s where the author of `String` can put +the code to return the memory. Rust calls `drop` automatically at the closing +curly bracket. > Note: In C++, this pattern of deallocating resources at the end of an item’s -lifetime is sometimes called *Resource Acquisition Is Initialization* *(RAII)*. -The `drop` function in Rust will be familiar to you if you’ve used RAII -patterns. +> lifetime is sometimes called *Resource Acquisition Is Initialization (RAII)*. +> The `drop` function in Rust will be familiar to you if you’ve used RAII +> patterns. This pattern has a profound impact on the way Rust code is written. It may seem simple right now, but the behavior of code can be unexpected in more complicated situations when we want to have multiple variables use the data we’ve allocated on the heap. Let’s explore some of those situations now. + + + + #### Variables and Data Interacting with Move Multiple variables can interact with the same data in different ways in Rust. -Let’s look at an example using an integer in Listing 4-2. +Listing 4-2 shows an example using an integer. + ``` -let x = 5; -let y = x; + let x = 5; + let y = x; ``` Listing 4-2: Assigning the integer value of variable `x` to `y` -We can probably guess what this is doing: “bind the value `5` to `x`; then make +We can probably guess what this is doing: “Bind the value `5` to `x`; then, make a copy of the value in `x` and bind it to `y`.” We now have two variables, `x` and `y`, and both equal `5`. This is indeed what is happening, because integers are simple values with a known, fixed size, and these two `5` values are pushed @@ -275,12 +286,12 @@ onto the stack. Now let’s look at the `String` version: ``` -let s1 = String::from("hello"); -let s2 = s1; + let s1 = String::from("hello"); + let s2 = s1; ``` This looks very similar, so we might assume that the way it works would be the -same: that is, the second line would make a copy of the value in `s1` and bind +same: That is, the second line would make a copy of the value in `s1` and bind it to `s2`. But this isn’t quite what happens. Take a look at Figure 4-1 to see what is happening to `String` under the @@ -289,8 +300,14 @@ the memory that holds the contents of the string, a length, and a capacity. This group of data is stored on the stack. On the right is the memory on the heap that holds the contents. -Figure 4-1: Representation in memory of a `String` holding the value `"hello"` -bound to `s1` +Two tables: the first table contains the representation of s1 on the +stack, consisting of its length (5), capacity (5), and a pointer to the first +value in the second table. The second table contains the representation of the +string data on the heap, byte by byte. + +Figure 4-1: The representation in memory of a `String` +holding the value `"hello"` bound to `s1` The length is how much memory, in bytes, the contents of the `String` are currently using. The capacity is the total amount of memory, in bytes, that the @@ -303,21 +320,29 @@ pointer, the length, and the capacity that are on the stack. We do not copy the data on the heap that the pointer refers to. In other words, the data representation in memory looks like Figure 4-2. -Figure 4-2: Representation in memory of the variable `s2` that has a copy of -the pointer, length, and capacity of `s1` +Three tables: tables s1 and s2 representing those strings on the +stack, respectively, and both pointing to the same string data on the heap. + +Figure 4-2: The representation in memory of the variable +`s2` that has a copy of the pointer, length, and capacity of `s1` The representation does *not* look like Figure 4-3, which is what memory would look like if Rust instead copied the heap data as well. If Rust did this, the operation `s2 = s1` could be very expensive in terms of runtime performance if the data on the heap were large. -Figure 4-3: Another possibility for what `s2 = s1` might do if Rust copied the -heap data as well +Four tables: two tables representing the stack data for s1 and s2, +and each points to its own copy of string data on the heap. + +Figure 4-3: Another possibility for what `s2 = s1` might +do if Rust copied the heap data as well Earlier, we said that when a variable goes out of scope, Rust automatically calls the `drop` function and cleans up the heap memory for that variable. But Figure 4-2 shows both data pointers pointing to the same location. This is a -problem: when `s2` and `s1` go out of scope, they will both try to free the +problem: When `s2` and `s1` go out of scope, they will both try to free the same memory. This is known as a *double free* error and is one of the memory safety bugs we mentioned previously. Freeing memory twice can lead to memory corruption, which can potentially lead to security vulnerabilities. @@ -328,27 +353,37 @@ out of scope. Check out what happens when you try to use `s1` after `s2` is created; it won’t work: ``` -let s1 = String::from("hello"); -let s2 = s1; + let s1 = String::from("hello"); + let s2 = s1; -println!("{s1}, world!"); + println!("{s1}, world!"); ``` You’ll get an error like this because Rust prevents you from using the invalidated reference: ``` +$ cargo run + Compiling ownership v0.1.0 (file:///projects/ownership) error[E0382]: borrow of moved value: `s1` - --> src/main.rs:5:28 + --> src/main.rs:5:15 | 2 | let s1 = String::from("hello"); - | -- move occurs because `s1` has type `String`, which - does not implement the `Copy` trait + | -- move occurs because `s1` has type `String`, which does not implement the `Copy` trait 3 | let s2 = s1; | -- value moved here 4 | 5 | println!("{s1}, world!"); - | ^^ value borrowed here after move + | ^^^^ value borrowed here after move + | + = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) +help: consider cloning the value if the performance cost is acceptable + | +3 | let s2 = s1.clone(); + | ++++++++ + +For more information about this error, try `rustc --explain E0382`. +error: could not compile `ownership` (bin "ownership") due to 1 previous error ``` If you’ve heard the terms *shallow copy* and *deep copy* while working with @@ -358,7 +393,14 @@ because Rust also invalidates the first variable, instead of being called a shallow copy, it’s known as a *move*. In this example, we would say that `s1` was *moved* into `s2`. So, what actually happens is shown in Figure 4-4. -Figure 4-4: Representation in memory after `s1` has been invalidated +Three tables: tables s1 and s2 representing those strings on the +stack, respectively, and both pointing to the same string data on the heap. +Table s1 is grayed out because s1 is no longer valid; only s2 can be used to +access the heap data. + +Figure 4-4: The representation in memory after `s1` has +been invalidated That solves our problem! With only `s2` valid, when it goes out of scope it alone will free the memory, and we’re done. @@ -367,6 +409,41 @@ In addition, there’s a design choice that’s implied by this: Rust will never automatically create “deep” copies of your data. Therefore, any *automatic* copying can be assumed to be inexpensive in terms of runtime performance. +#### Scope and Assignment + +The inverse of this is true for the relationship between scoping, ownership, and +memory being freed via the `drop` function as well. When you assign a completely +new value to an existing variable, Rust will call `drop` and free the original +value’s memory immediately. Consider this code, for example: + +``` + let mut s = String::from("hello"); + s = String::from("ahoy"); + + println!("{s}, world!"); +``` + +We initially declare a variable `s` and bind it to a `String` with the value +`"hello"`. Then, we immediately create a new `String` with the value `"ahoy"` +and assign it to `s`. At this point, nothing is referring to the original value +on the heap at all. Figure 4-5 illustrates the stack and heap data now: + +One table representing the string value on the stack, pointing to +the second piece of string data (ahoy) on the heap, with the original string +data (hello) grayed out because it cannot be accessed anymore. + +Figure 4-5: The representation in memory after the initial +value has been replaced in its entirety + +The original string thus immediately goes out of scope. Rust will run the `drop` +function on it and its memory will be freed right away. When we print the value +at the end, it will be `"ahoy, world!"`. + + + + + #### Variables and Data Interacting with Clone If we *do* want to deeply copy the heap data of the `String`, not just the @@ -377,10 +454,10 @@ programming languages, you’ve probably seen them before. Here’s an example of the `clone` method in action: ``` -let s1 = String::from("hello"); -let s2 = s1.clone(); + let s1 = String::from("hello"); + let s2 = s1.clone(); -println!("s1 = {s1}, s2 = {s2}"); + println!("s1 = {s1}, s2 = {s2}"); ``` This works just fine and explicitly produces the behavior shown in Figure 4-3, @@ -396,13 +473,13 @@ There’s another wrinkle we haven’t talked about yet. This code using integers—part of which was shown in Listing 4-2—works and is valid: ``` -let x = 5; -let y = x; + let x = 5; + let y = x; -println!("x = {x}, y = {y}"); + println!("x = {x}, y = {y}"); ``` -But this code seems to contradict what we just learned: we don’t have a call to +But this code seems to contradict what we just learned: We don’t have a call to `clone`, but `x` is still valid and wasn’t moved into `y`. The reason is that types such as integers that have a known size at compile @@ -414,15 +491,16 @@ different from the usual shallow copying, and we can leave it out. Rust has a special annotation called the `Copy` trait that we can place on types that are stored on the stack, as integers are (we’ll talk more about -traits in Chapter 10). If a type implements the `Copy` trait, variables that -use it do not move, but rather are trivially copied, making them still valid -after assignment to another variable. +traits in Chapter 10). If a type implements the `Copy` +trait, variables that use it do not move, but rather are trivially copied, +making them still valid after assignment to another variable. Rust won’t let us annotate a type with `Copy` if the type, or any of its parts, has implemented the `Drop` trait. If the type needs something special to happen when the value goes out of scope and we add the `Copy` annotation to that type, we’ll get a compile-time error. To learn about how to add the `Copy` annotation -to your type to implement the trait, see “Derivable Traits” on page XX. +to your type to implement the trait, see “Derivable +Traits” in Appendix C. So, what types implement the `Copy` trait? You can check the documentation for the given type to be sure, but as a general rule, any group of simple scalar @@ -435,7 +513,7 @@ implement `Copy`: * All the floating-point types, such as `f64`. * The character type, `char`. * Tuples, if they only contain types that also implement `Copy`. For example, -`(i32, i32)` implements `Copy`, but `(i32, String)` does not. + `(i32, i32)` implements `Copy`, but `(i32, String)` does not. ### Ownership and Functions @@ -444,8 +522,9 @@ assigning a value to a variable. Passing a variable to a function will move or copy, just as assignment does. Listing 4-3 has an example with some annotations showing where variables go into and out of scope. +src/main.rs + ``` -// src/main.rs fn main() { let s = String::from("hello"); // s comes into scope @@ -454,21 +533,21 @@ fn main() { let x = 5; // x comes into scope - makes_copy(x); // x would move into the function, - // but i32 is Copy, so it's okay to still - // use x afterward + makes_copy(x); // Because i32 implements the Copy trait, + // x does NOT move into the function, + // so it's okay to use x afterward. } // Here, x goes out of scope, then s. However, because s's value was moved, - // nothing special happens + // nothing special happens. fn takes_ownership(some_string: String) { // some_string comes into scope println!("{some_string}"); } // Here, some_string goes out of scope and `drop` is called. The backing - // memory is freed + // memory is freed. fn makes_copy(some_integer: i32) { // some_integer comes into scope println!("{some_integer}"); -} // Here, some_integer goes out of scope. Nothing special happens +} // Here, some_integer goes out of scope. Nothing special happens. ``` Listing 4-3: Functions with ownership and scope annotated @@ -484,34 +563,36 @@ Returning values can also transfer ownership. Listing 4-4 shows an example of a function that returns some value, with similar annotations as those in Listing 4-3. +src/main.rs + ``` -// src/main.rs fn main() { - let s1 = gives_ownership(); // gives_ownership moves its return - // value into s1 + let s1 = gives_ownership(); // gives_ownership moves its return + // value into s1 - let s2 = String::from("hello"); // s2 comes into scope + let s2 = String::from("hello"); // s2 comes into scope - let s3 = takes_and_gives_back(s2); // s2 is moved into - // takes_and_gives_back, which also - // moves its return value into s3 + let s3 = takes_and_gives_back(s2); // s2 is moved into + // takes_and_gives_back, which also + // moves its return value into s3 } // Here, s3 goes out of scope and is dropped. s2 was moved, so nothing - // happens. s1 goes out of scope and is dropped + // happens. s1 goes out of scope and is dropped. -fn gives_ownership() -> String { // gives_ownership will move its - // return value into the function - // that calls it +fn gives_ownership() -> String { // gives_ownership will move its + // return value into the function + // that calls it let some_string = String::from("yours"); // some_string comes into scope - some_string // some_string is returned and - // moves out to the calling - // function + some_string // some_string is returned and + // moves out to the calling + // function } -// This function takes a String and returns a String -fn takes_and_gives_back(a_string: String) -> String { // a_string comes into - // scope +// This function takes a String and returns a String. +fn takes_and_gives_back(a_string: String) -> String { + // a_string comes into + // scope a_string // a_string is returned and moves out to the calling function } @@ -519,7 +600,7 @@ fn takes_and_gives_back(a_string: String) -> String { // a_string comes into Listing 4-4: Transferring ownership of return values -The ownership of a variable follows the same pattern every time: assigning a +The ownership of a variable follows the same pattern every time: Assigning a value to another variable moves it. When a variable that includes data on the heap goes out of scope, the value will be cleaned up by `drop` unless ownership of the data has been moved to another variable. @@ -532,7 +613,7 @@ from the body of the function that we might want to return as well. Rust does let us return multiple values using a tuple, as shown in Listing 4-5. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -554,15 +635,15 @@ Listing 4-5: Returning ownership of parameters But this is too much ceremony and a lot of work for a concept that should be common. Luckily for us, Rust has a feature for using a value without -transferring ownership, called *references*. +transferring ownership: references. ## References and Borrowing The issue with the tuple code in Listing 4-5 is that we have to return the -`String` to the calling function so we can still use the `String` after the -call to `calculate_length`, because the `String` was moved into +`String` to the calling function so that we can still use the `String` after +the call to `calculate_length`, because the `String` was moved into `calculate_length`. Instead, we can provide a reference to the `String` value. -A *reference* is like a pointer in that it’s an address we can follow to access +A reference is like a pointer in that it’s an address we can follow to access the data stored at that address; that data is owned by some other variable. Unlike a pointer, a reference is guaranteed to point to a valid value of a particular type for the life of that reference. @@ -570,7 +651,7 @@ particular type for the life of that reference. Here is how you would define and use a `calculate_length` function that has a reference to an object as a parameter instead of taking ownership of the value: -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -586,30 +667,37 @@ fn calculate_length(s: &String) -> usize { } ``` + + First, notice that all the tuple code in the variable declaration and the function return value is gone. Second, note that we pass `&s1` into `calculate_length` and, in its definition, we take `&String` rather than -`String`. These ampersands represent *references*, and they allow you to refer -to some value without taking ownership of it. Figure 4-5 depicts this concept. +`String`. These ampersands represent references, and they allow you to refer to +some value without taking ownership of it. Figure 4-6 depicts this concept. -Figure 4-5: A diagram of `&String s` pointing at `String s1` +Three tables: the table for s contains only a pointer to the table +for s1. The table for s1 contains the stack data for s1 and points to the +string data on the heap. + +Figure 4-6: A diagram of `&String` `s` pointing at +`String` `s1` > Note: The opposite of referencing by using `&` is *dereferencing*, which is -accomplished with the dereference operator, `*`. We’ll see some uses of the -dereference operator in Chapter 8 and discuss details of dereferencing in -Chapter 15. +> accomplished with the dereference operator, `*`. We’ll see some uses of the +> dereference operator in Chapter 8 and discuss details of dereferencing in +> Chapter 15. Let’s take a closer look at the function call here: ``` -let s1 = String::from("hello"); + let s1 = String::from("hello"); -let len = calculate_length(&s1); + let len = calculate_length(&s1); ``` The `&s1` syntax lets us create a reference that *refers* to the value of `s1` -but does not own it. Because it does not own it, the value it points to will -not be dropped when the reference stops being used. +but does not own it. Because the reference does not own it, the value it points +to will not be dropped when the reference stops being used. Likewise, the signature of the function uses `&` to indicate that the type of the parameter `s` is a reference. Let’s add some explanatory annotations: @@ -617,8 +705,8 @@ the parameter `s` is a reference. Let’s add some explanatory annotations: ``` fn calculate_length(s: &String) -> usize { // s is a reference to a String s.len() -} // Here, s goes out of scope. But because it does not have ownership of what - // it refers to, the String is not dropped +} // Here, s goes out of scope. But because s does not have ownership of what + // it refers to, the String is not dropped. ``` The scope in which the variable `s` is valid is the same as any function @@ -633,9 +721,9 @@ person owns something, you can borrow it from them. When you’re done, you have to give it back. You don’t own it. So, what happens if we try to modify something we’re borrowing? Try the code in -Listing 4-6. Spoiler alert: it doesn’t work! +Listing 4-6. Spoiler alert: It doesn’t work! -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -654,16 +742,21 @@ Listing 4-6: Attempting to modify a borrowed value Here’s the error: ``` -error[E0596]: cannot borrow `*some_string` as mutable, as it is behind a `&` -reference +$ cargo run + Compiling ownership v0.1.0 (file:///projects/ownership) +error[E0596]: cannot borrow `*some_string` as mutable, as it is behind a `&` reference --> src/main.rs:8:5 | -7 | fn change(some_string: &String) { - | ------- help: consider changing this to be a mutable -reference: `&mut String` 8 | some_string.push_str(", world"); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `some_string` is a `&` reference, so -the data it refers to cannot be borrowed as mutable + | ^^^^^^^^^^^ `some_string` is a `&` reference, so the data it refers to cannot be borrowed as mutable + | +help: consider changing this to be a mutable reference + | +7 | fn change(some_string: &mut String) { + | +++ + +For more information about this error, try `rustc --explain E0596`. +error: could not compile `ownership` (bin "ownership") due to 1 previous error ``` Just as variables are immutable by default, so are references. We’re not @@ -674,7 +767,7 @@ allowed to modify something we have a reference to. We can fix the code from Listing 4-6 to allow us to modify a borrowed value with just a few small tweaks that use, instead, a *mutable reference*: -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -688,29 +781,35 @@ fn change(some_string: &mut String) { } ``` -First we change `s` to be `mut`. Then we create a mutable reference with `&mut -s` where we call the `change` function, and update the function signature to -accept a mutable reference with `some_string: &mut String`. This makes it very -clear that the `change` function will mutate the value it borrows. -Mutable references have one big restriction: if you have a mutable reference to + +First, we change `s` to be `mut`. Then, we create a mutable reference with +`&mut s` where we call the `change` function and update the function signature +to accept a mutable reference with `some_string: &mut String`. This makes it +very clear that the `change` function will mutate the value it borrows. + +Mutable references have one big restriction: If you have a mutable reference to a value, you can have no other references to that value. This code that attempts to create two mutable references to `s` will fail: -Filename: src/main.rs +src/main.rs ``` -let mut s = String::from("hello"); + let mut s = String::from("hello"); -let r1 = &mut s; -let r2 = &mut s; + let r1 = &mut s; + let r2 = &mut s; -println!("{r1}, {r2}"); + println!("{r1}, {r2}"); ``` + + Here’s the error: ``` +$ cargo run + Compiling ownership v0.1.0 (file:///projects/ownership) error[E0499]: cannot borrow `s` as mutable more than once at a time --> src/main.rs:5:14 | @@ -720,7 +819,10 @@ error[E0499]: cannot borrow `s` as mutable more than once at a time | ^^^^^^ second mutable borrow occurs here 6 | 7 | println!("{r1}, {r2}"); - | -- first borrow later used here + | ---- first borrow later used here + +For more information about this error, try `rustc --explain E0499`. +error: could not compile `ownership` (bin "ownership") due to 1 previous error ``` This error says that this code is invalid because we cannot borrow `s` as @@ -748,33 +850,34 @@ As always, we can use curly brackets to create a new scope, allowing for multiple mutable references, just not *simultaneous* ones: ``` -let mut s = String::from("hello"); + let mut s = String::from("hello"); -{ - let r1 = &mut s; -} // r1 goes out of scope here, so we can make a new reference with no problems + { + let r1 = &mut s; + } // r1 goes out of scope here, so we can make a new reference with no problems. -let r2 = &mut s; + let r2 = &mut s; ``` Rust enforces a similar rule for combining mutable and immutable references. This code results in an error: ``` -let mut s = String::from("hello"); + let mut s = String::from("hello"); -let r1 = &s; // no problem -let r2 = &s; // no problem -let r3 = &mut s; // BIG PROBLEM + let r1 = &s; // no problem + let r2 = &s; // no problem + let r3 = &mut s; // BIG PROBLEM -println!("{r1}, {r2}, and {r3}"); + println!("{r1}, {r2}, and {r3}"); ``` Here’s the error: ``` -error[E0502]: cannot borrow `s` as mutable because it is also borrowed as -immutable +$ cargo run + Compiling ownership v0.1.0 (file:///projects/ownership) +error[E0502]: cannot borrow `s` as mutable because it is also borrowed as immutable --> src/main.rs:6:14 | 4 | let r1 = &s; // no problem @@ -784,7 +887,10 @@ immutable | ^^^^^^ mutable borrow occurs here 7 | 8 | println!("{r1}, {r2}, and {r3}"); - | -- immutable borrow later used here + | ---- immutable borrow later used here + +For more information about this error, try `rustc --explain E0502`. +error: could not compile `ownership` (bin "ownership") due to 1 previous error ``` Whew! We *also* cannot have a mutable reference while we have an immutable one @@ -797,30 +903,30 @@ reading of the data. Note that a reference’s scope starts from where it is introduced and continues through the last time that reference is used. For instance, this code will -compile because the last usage of the immutable references, the `println!`, -occurs before the mutable reference is introduced: +compile because the last usage of the immutable references is in the `println!`, +before the mutable reference is introduced: ``` -let mut s = String::from("hello"); + let mut s = String::from("hello"); -let r1 = &s; // no problem -let r2 = &s; // no problem -println!("{r1} and {r2}"); -// variables r1 and r2 will not be used after this point + let r1 = &s; // no problem + let r2 = &s; // no problem + println!("{r1} and {r2}"); + // Variables r1 and r2 will not be used after this point. -let r3 = &mut s; // no problem -println!("{r3}"); + let r3 = &mut s; // no problem + println!("{r3}"); ``` The scopes of the immutable references `r1` and `r2` end after the `println!` where they are last used, which is before the mutable reference `r3` is -created. These scopes don’t overlap, so this code is allowed: the compiler can +created. These scopes don’t overlap, so this code is allowed: The compiler can tell that the reference is no longer being used at a point before the end of the scope. Even though borrowing errors may be frustrating at times, remember that it’s the Rust compiler pointing out a potential bug early (at compile time rather -than at runtime) and showing you exactly where the problem is. Then you don’t +than at runtime) and showing you exactly where the problem is. Then, you don’t have to track down why your data isn’t what you thought it was. ### Dangling References @@ -829,14 +935,14 @@ In languages with pointers, it’s easy to erroneously create a *dangling pointer*—a pointer that references a location in memory that may have been given to someone else—by freeing some memory while preserving a pointer to that memory. In Rust, by contrast, the compiler guarantees that references will -never be dangling references: if you have a reference to some data, the +never be dangling references: If you have a reference to some data, the compiler will ensure that the data will not go out of scope before the reference to the data does. Let’s try to create a dangling reference to see how Rust prevents them with a compile-time error: -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -850,21 +956,39 @@ fn dangle() -> &String { } ``` + + Here’s the error: ``` +$ cargo run + Compiling ownership v0.1.0 (file:///projects/ownership) error[E0106]: missing lifetime specifier --> src/main.rs:5:16 | 5 | fn dangle() -> &String { | ^ expected named lifetime parameter | - = help: this function's return type contains a borrowed value, -but there is no value for it to be borrowed from -help: consider using the `'static` lifetime + = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from +help: consider using the `'static` lifetime, but this is uncommon unless you're returning a borrowed value from a `const` or a `static` | 5 | fn dangle() -> &'static String { - | ~~~~~~~~ + | +++++++ +help: instead, you are more likely to want to return an owned value + | +5 - fn dangle() -> &String { +5 + fn dangle() -> String { + | + +error[E0515]: cannot return reference to local variable `s` + --> src/main.rs:8:5 + | +8 | &s + | ^^ returns a reference to data owned by the current function + +Some errors have detailed explanations: E0106, E0515. +For more information about an error, try `rustc --explain E0106`. +error: could not compile `ownership` (bin "ownership") due to 2 previous errors ``` This error message refers to a feature we haven’t covered yet: lifetimes. We’ll @@ -872,24 +996,27 @@ discuss lifetimes in detail in Chapter 10. But, if you disregard the parts about lifetimes, the message does contain the key to why this code is a problem: ``` -this function's return type contains a borrowed value, but there -is no value for it to be borrowed from +this function's return type contains a borrowed value, but there is no value +for it to be borrowed from ``` Let’s take a closer look at exactly what’s happening at each stage of our `dangle` code: +src/main.rs + ``` -// src/main.rs fn dangle() -> &String { // dangle returns a reference to a String let s = String::from("hello"); // s is a new String &s // we return a reference to the String, s -} // Here, s goes out of scope and is dropped, so its memory goes away +} // Here, s goes out of scope and is dropped, so its memory goes away. // Danger! ``` + + Because `s` is created inside `dangle`, when the code of `dangle` is finished, `s` will be deallocated. But we tried to return a reference to it. That means this reference would be pointing to an invalid `String`. That’s no good! Rust @@ -913,22 +1040,27 @@ deallocated. Let’s recap what we’ve discussed about references: * At any given time, you can have *either* one mutable reference *or* any -number of immutable references. + number of immutable references. * References must always be valid. Next, we’ll look at a different kind of reference: slices. ## The Slice Type -*Slices* let you reference a contiguous sequence of elements in a collection -rather than the whole collection. A slice is a kind of reference, so it does -not have ownership. +*Slices* let you reference a contiguous sequence of elements in a +collection. A slice is a kind +of reference, so it does not have ownership. -Here’s a small programming problem: write a function that takes a string of +Here’s a small programming problem: Write a function that takes a string of words separated by spaces and returns the first word it finds in that string. If the function doesn’t find a space in the string, the whole string must be one word, so the entire string should be returned. +> Note: For the purposes of introducing slices, we are assuming ASCII only in +> this section; a more thorough discussion of UTF-8 handling is in the +> “Storing UTF-8 Encoded Text with Strings” section +> of Chapter 8. + Let’s work through how we’d write the signature of this function without using slices, to understand the problem that slices will solve: @@ -936,51 +1068,71 @@ slices, to understand the problem that slices will solve: fn first_word(s: &String) -> ? ``` -The `first_word` function has a `&String` as a parameter. We don’t want -ownership, so this is fine. But what should we return? We don’t really have a -way to talk about *part* of a string. However, we could return the index of the -end of the word, indicated by a space. Let’s try that, as shown in Listing 4-7. +The `first_word` function has a parameter of type `&String`. We don’t need +ownership, so this is fine. (In idiomatic Rust, functions do not take ownership +of their arguments unless they need to, and the reasons for that will become +clear as we keep going.) But what should we return? We don’t really have a way +to talk about *part* of a string. However, we could return the index of the end +of the word, indicated by a space. Let’s try that, as shown in Listing 4-7. -Filename: src/main.rs +src/main.rs ``` fn first_word(s: &String) -> usize { - 1 let bytes = s.as_bytes(); + let bytes = s.as_bytes(); - for (2 i, &item) in 3 bytes.iter().enumerate() { - 4 if item == b' ' { + for (i, &item) in bytes.iter().enumerate() { + if item == b' ' { return i; } } - 5 s.len() + s.len() } ``` -Listing 4-7: The `first_word` function that returns a byte index value into the -`String` parameter +Listing 4-7: The `first_word` function that returns a byte index value into the `String` parameter Because we need to go through the `String` element by element and check whether a value is a space, we’ll convert our `String` to an array of bytes using the -`as_bytes` method [1]. +`as_bytes` method. + +``` + let bytes = s.as_bytes(); +``` + +Next, we create an iterator over the array of bytes using the `iter` method: + +``` + for (i, &item) in bytes.iter().enumerate() { +``` -Next, we create an iterator over the array of bytes using the `iter` method -[3]. We’ll discuss iterators in more detail in Chapter 13. For now, know that -`iter` is a method that returns each element in a collection and that -`enumerate` wraps the result of `iter` and returns each element as part of a -tuple instead. The first element of the tuple returned from `enumerate` is the -index, and the second element is a reference to the element. This is a bit more -convenient than calculating the index ourselves. +We’ll discuss iterators in more detail in Chapter 13. +For now, know that `iter` is a method that returns each element in a collection +and that `enumerate` wraps the result of `iter` and returns each element as +part of a tuple instead. The first element of the tuple returned from +`enumerate` is the index, and the second element is a reference to the element. +This is a bit more convenient than calculating the index ourselves. Because the `enumerate` method returns a tuple, we can use patterns to -destructure that tuple. We’ll be discussing patterns more in Chapter 6. In the -`for` loop, we specify a pattern that has `i` for the index in the tuple and -`&item` for the single byte in the tuple [2]. Because we get a reference to the -element from `.iter().enumerate()`, we use `&` in the pattern. +destructure that tuple. We’ll be discussing patterns more in Chapter +6. In the `for` loop, we specify a pattern that has `i` +for the index in the tuple and `&item` for the single byte in the tuple. +Because we get a reference to the element from `.iter().enumerate()`, we use +`&` in the pattern. Inside the `for` loop, we search for the byte that represents the space by -using the byte literal syntax [4]. If we find a space, we return the position. -Otherwise, we return the length of the string by using `s.len()` [5]. +using the byte literal syntax. If we find a space, we return the position. +Otherwise, we return the length of the string by using `s.len()`. + +``` + if item == b' ' { + return i; + } + } + + s.len() +``` We now have a way to find out the index of the end of the first word in the string, but there’s a problem. We’re returning a `usize` on its own, but it’s @@ -989,8 +1141,9 @@ because it’s a separate value from the `String`, there’s no guarantee that i will still be valid in the future. Consider the program in Listing 4-8 that uses the `first_word` function from Listing 4-7. +src/main.rs + ``` -// src/main.rs fn main() { let mut s = String::from("hello world"); @@ -998,13 +1151,12 @@ fn main() { s.clear(); // this empties the String, making it equal to "" - // word still has the value 5 here, but there's no more string that - // we could meaningfully use the value 5 with. word is now totally invalid! + // word still has the value 5 here, but s no longer has any content that we + // could meaningfully use with the value 5, so word is now totally invalid! } ``` -Listing 4-8: Storing the result from calling the `first_word` function and then -changing the `String` contents +Listing 4-8: Storing the result from calling the `first_word` function and then changing the `String` contents This program compiles without any errors and would also do so if we used `word` after calling `s.clear()`. Because `word` isn’t connected to the state of `s` @@ -1013,7 +1165,7 @@ the variable `s` to try to extract the first word out, but this would be a bug because the contents of `s` have changed since we saved `5` in `word`. Having to worry about the index in `word` getting out of sync with the data in -`s` is tedious and error prone! Managing these indices is even more brittle if +`s` is tedious and error-prone! Managing these indices is even more brittle if we write a `second_word` function. Its signature would have to look like this: ``` @@ -1029,28 +1181,37 @@ Luckily, Rust has a solution to this problem: string slices. ### String Slices -A *string slice* is a reference to part of a `String`, and it looks like this: +A *string slice* is a reference to a contiguous sequence of the elements of a +`String`, and it looks like this: ``` -let s = String::from("hello world"); + let s = String::from("hello world"); -let hello = &s[0..5]; -let world = &s[6..11]; + let hello = &s[0..5]; + let world = &s[6..11]; ``` Rather than a reference to the entire `String`, `hello` is a reference to a portion of the `String`, specified in the extra `[0..5]` bit. We create slices -using a range within brackets by specifying `[starting_index..ending_index]`, -where `starting_index` is the first position in the slice and `ending_index` is -one more than the last position in the slice. Internally, the slice data -structure stores the starting position and the length of the slice, which -corresponds to `ending_index` minus `starting_index`. So, in the case of `let -world = &s[6..11];`, `world` would be a slice that contains a pointer to the -byte at index 6 of `s` with a length value of `5`. - -Figure 4-6 shows this in a diagram. - -Figure 4-6: String slice referring to part of a `String` +using a range within square brackets by specifying +`[starting_index..ending_index]`, where *`starting_index`* is the first +position in the slice and *`ending_index`* is one more than the last position +in the slice. Internally, the slice data structure stores the starting position +and the length of the slice, which corresponds to *`ending_index`* minus +*`starting_index`*. So, in the case of `let world = &s[6..11];`, `world` would +be a slice that contains a pointer to the byte at index 6 of `s` with a length +value of `5`. + +Figure 4-7 shows this in a diagram. + +Three tables: a table representing the stack data of s, which points +to the byte at index 0 in a table of the string data "hello world" on +the heap. The third table represents the stack data of the slice world, which +has a length value of 5 and points to byte 6 of the heap data table. + +Figure 4-7: A string slice referring to part of a +`String` With Rust’s `..` range syntax, if you want to start at index 0, you can drop the value before the two periods. In other words, these are equal: @@ -1074,7 +1235,7 @@ let slice = &s[3..len]; let slice = &s[3..]; ``` -You can also drop both values to take a slice of the entire string. So these +You can also drop both values to take a slice of the entire string. So, these are equal: ``` @@ -1087,16 +1248,13 @@ let slice = &s[..]; ``` > Note: String slice range indices must occur at valid UTF-8 character -boundaries. If you attempt to create a string slice in the middle of a -multibyte character, your program will exit with an error. For the purposes of -introducing string slices, we are assuming ASCII only in this section; a more -thorough discussion of UTF-8 handling is in “Storing UTF-8 Encoded Text with -Strings” on page XX. +> boundaries. If you attempt to create a string slice in the middle of a +> multibyte character, your program will exit with an error. With all this information in mind, let’s rewrite `first_word` to return a slice. The type that signifies “string slice” is written as `&str`: -Filename: src/main.rs +src/main.rs ``` fn first_word(s: &String) -> &str { @@ -1112,6 +1270,8 @@ fn first_word(s: &String) -> &str { } ``` + + We get the index for the end of the word the same way we did in Listing 4-7, by looking for the first occurrence of a space. When we find a space, we return a string slice using the start of the string and the index of the space as the @@ -1128,16 +1288,16 @@ fn second_word(s: &String) -> &str { ``` We now have a straightforward API that’s much harder to mess up because the -compiler will ensure the references into the `String` remain valid. Remember -the bug in the program in Listing 4-8, when we got the index to the end of the -first word but then cleared the string so our index was invalid? That code was -logically incorrect but didn’t show any immediate errors. The problems would -show up later if we kept trying to use the first word index with an emptied -string. Slices make this bug impossible and let us know we have a problem with -our code much sooner. Using the slice version of `first_word` will throw a -compile-time error: +compiler will ensure that the references into the `String` remain valid. +Remember the bug in the program in Listing 4-8, when we got the index to the +end of the first word but then cleared the string so our index was invalid? +That code was logically incorrect but didn’t show any immediate errors. The +problems would show up later if we kept trying to use the first word index with +an emptied string. Slices make this bug impossible and let us know much sooner +that we have a problem with our code. Using the slice version of `first_word` +will throw a compile-time error: -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1151,11 +1311,14 @@ fn main() { } ``` + + Here’s the compiler error: ``` -error[E0502]: cannot borrow `s` as mutable because it is also borrowed as -immutable +$ cargo run + Compiling ownership v0.1.0 (file:///projects/ownership) +error[E0502]: cannot borrow `s` as mutable because it is also borrowed as immutable --> src/main.rs:18:5 | 16 | let word = first_word(&s); @@ -1165,7 +1328,10 @@ immutable | ^^^^^^^^^ mutable borrow occurs here 19 | 20 | println!("the first word is: {word}"); - | ---- immutable borrow later used here + | ------ immutable borrow later used here + +For more information about this error, try `rustc --explain E0502`. +error: could not compile `ownership` (bin "ownership") due to 1 previous error ``` Recall from the borrowing rules that if we have an immutable reference to @@ -1177,6 +1343,10 @@ reference in `clear` and the immutable reference in `word` from existing at the same time, and compilation fails. Not only has Rust made our API easier to use, but it has also eliminated an entire class of errors at compile time! + + + + #### String Literals as Slices Recall that we talked about string literals being stored inside the binary. Now @@ -1186,7 +1356,7 @@ that we know about slices, we can properly understand string literals: let s = "Hello, world!"; ``` -The type of `s` here is `&str`: it’s a slice pointing to that specific point of +The type of `s` here is `&str`: It’s a slice pointing to that specific point of the binary. This is also why string literals are immutable; `&str` is an immutable reference. @@ -1203,39 +1373,38 @@ A more experienced Rustacean would write the signature shown in Listing 4-9 instead because it allows us to use the same function on both `&String` values and `&str` values. + ``` fn first_word(s: &str) -> &str { ``` -Listing 4-9: Improving the `first_word` function by using a string slice for -the type of the `s` parameter +Listing 4-9: Improving the `first_word` function by using a string slice for the type of the `s` parameter If we have a string slice, we can pass that directly. If we have a `String`, we can pass a slice of the `String` or a reference to the `String`. This -flexibility takes advantage of *deref coercions*, a feature we will cover in -“Implicit Deref Coercions with Functions and Methods” on page XX. +flexibility takes advantage of deref coercions, a feature we will cover in +the “Using Deref Coercions in Functions and Methods” section of Chapter 15. Defining a function to take a string slice instead of a reference to a `String` makes our API more general and useful without losing any functionality: -Filename: src/main.rs +src/main.rs ``` fn main() { let my_string = String::from("hello world"); - // `first_word` works on slices of `String`s, whether partial - // or whole + // `first_word` works on slices of `String`s, whether partial or whole. let word = first_word(&my_string[0..6]); let word = first_word(&my_string[..]); - // `first_word` also works on references to `String`s, which - // are equivalent to whole slices of `String`s + // `first_word` also works on references to `String`s, which are equivalent + // to whole slices of `String`s. let word = first_word(&my_string); let my_string_literal = "hello world"; - // `first_word` works on slices of string literals, - // whether partial or whole + // `first_word` works on slices of string literals, whether partial or + // whole. let word = first_word(&my_string_literal[0..6]); let word = first_word(&my_string_literal[..]); @@ -1245,6 +1414,8 @@ fn main() { } ``` + + ### Other Slices String slices, as you might imagine, are specific to strings. But there’s a @@ -1274,11 +1445,10 @@ detail when we talk about vectors in Chapter 8. The concepts of ownership, borrowing, and slices ensure memory safety in Rust programs at compile time. The Rust language gives you control over your memory -usage in the same way as other systems programming languages, but having the +usage in the same way as other systems programming languages. But having the owner of data automatically clean up that data when the owner goes out of scope means you don’t have to write and debug extra code to get this control. Ownership affects how lots of other parts of Rust work, so we’ll talk about these concepts further throughout the rest of the book. Let’s move on to Chapter 5 and look at grouping pieces of data together in a `struct`. - diff --git a/nostarch/chapter05.md b/nostarch/chapter05.md index 9881a3b748..db516ed005 100644 --- a/nostarch/chapter05.md +++ b/nostarch/chapter05.md @@ -10,10 +10,10 @@ directory, so all fixes need to be made in `/src/`. A *struct*, or *structure*, is a custom data type that lets you package together and name multiple related values that make up a meaningful group. If -you’re familiar with an object-oriented language, a *struct* is like an -object’s data attributes. In this chapter, we’ll compare and contrast tuples -with structs to build on what you already know and demonstrate when structs are -a better way to group data. +you’re familiar with an object-oriented language, a struct is like an object’s +data attributes. In this chapter, we’ll compare and contrast tuples with +structs to build on what you already know and demonstrate when structs are a +better way to group data. We’ll demonstrate how to define and instantiate structs. We’ll discuss how to define associated functions, especially the kind of associated functions called @@ -23,12 +23,11 @@ program’s domain to take full advantage of Rust’s compile-time type checking ## Defining and Instantiating Structs -Structs are similar to tuples, discussed in “The Tuple Type” on page XX, in -that both hold multiple related values. Like tuples, the pieces of a struct can -be different types. Unlike with tuples, in a struct you’ll name each piece of -data so it’s clear what the values mean. Adding these names means that structs -are more flexible than tuples: you don’t have to rely on the order of the data -to specify or access the values of an instance. +Structs are similar to tuples, discussed in “The Tuple Type” section, in that both hold multiple related values. Like tuples, the +pieces of a struct can be different types. Unlike with tuples, in a struct +you’ll name each piece of data so it’s clear what the values mean. Adding these +names means that structs are more flexible than tuples: You don’t have to rely +on the order of the data to specify or access the values of an instance. To define a struct, we enter the keyword `struct` and name the entire struct. A struct’s name should describe the significance of the pieces of data being @@ -36,7 +35,7 @@ grouped together. Then, inside curly brackets, we define the names and types of the pieces of data, which we call *fields*. For example, Listing 5-1 shows a struct that stores information about a user account. -Filename: src/main.rs +src/main.rs ``` struct User { @@ -51,15 +50,14 @@ Listing 5-1: A `User` struct definition To use a struct after we’ve defined it, we create an *instance* of that struct by specifying concrete values for each of the fields. We create an instance by -stating the name of the struct and then add curly brackets containing key: -value pairs, where the keys are the names of the fields and the values are the +stating the name of the struct and then add curly brackets containing *`key: value`* pairs, where the keys are the names of the fields and the values are the data we want to store in those fields. We don’t have to specify the fields in the same order in which we declared them in the struct. In other words, the struct definition is like a general template for the type, and instances fill in that template with particular data to create values of the type. For example, we can declare a particular user as shown in Listing 5-2. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -80,7 +78,7 @@ mutable, we can change a value by using the dot notation and assigning into a particular field. Listing 5-3 shows how to change the value in the `email` field of a mutable `User` instance. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -103,8 +101,10 @@ instance of the struct as the last expression in the function body to implicitly return that new instance. Listing 5-4 shows a `build_user` function that returns a `User` instance with -the given email and username. The `active` field gets the value of `true`, and -the `sign_in_count` gets a value of `1`. +the given email and username. The `active` field gets the value `true`, and the +`sign_in_count` gets a value of `1`. + +src/main.rs ``` fn build_user(email: String, username: String) -> User { @@ -117,20 +117,25 @@ fn build_user(email: String, username: String) -> User { } ``` -Listing 5-4: A `build_user` function that takes an email and username and -returns a `User` instance +Listing 5-4: A `build_user` function that takes an email and username and returns a `User` instance It makes sense to name the function parameters with the same name as the struct fields, but having to repeat the `email` and `username` field names and variables is a bit tedious. If the struct had more fields, repeating each name would get even more annoying. Luckily, there’s a convenient shorthand! + + + + ### Using the Field Init Shorthand Because the parameter names and the struct field names are exactly the same in Listing 5-4, we can use the *field init shorthand* syntax to rewrite -`build_user` so it behaves exactly the same but doesn’t have the repetition of -`username` and `email`, as shown in Listing 5-5. +`build_user` so that it behaves exactly the same but doesn’t have the +repetition of `username` and `email`, as shown in Listing 5-5. + +src/main.rs ``` fn build_user(email: String, username: String) -> User { @@ -143,8 +148,7 @@ fn build_user(email: String, username: String) -> User { } ``` -Listing 5-5: A `build_user` function that uses field init shorthand because the -`username` and `email` parameters have the same name as struct fields +Listing 5-5: A `build_user` function that uses field init shorthand because the `username` and `email` parameters have the same name as struct fields Here, we’re creating a new instance of the `User` struct, which has a field named `email`. We want to set the `email` field’s value to the value in the @@ -152,21 +156,25 @@ named `email`. We want to set the `email` field’s value to the value in the the `email` parameter have the same name, we only need to write `email` rather than `email: email`. -### Creating Instances from Other Instances with Struct Update Syntax + + + + +### Creating Instances with Struct Update Syntax It’s often useful to create a new instance of a struct that includes most of -the values from another instance, but changes some. You can do this using -*struct update syntax*. +the values from another instance of the same type, but changes some of them. +You can do this using struct update syntax. -First, in Listing 5-6 we show how to create a new `User` instance in `user2` -regularly, without the update syntax. We set a new value for `email` but +First, in Listing 5-6 we show how to create a new `User` instance in `user2` in +the regular way, without the update syntax. We set a new value for `email` but otherwise use the same values from `user1` that we created in Listing 5-2. -Filename: src/main.rs +src/main.rs ``` fn main() { - --snip-- + // --snip-- let user2 = User { active: user1.active, @@ -177,18 +185,17 @@ fn main() { } ``` -Listing 5-6: Creating a new `User` instance using one of the values from `user1` +Listing 5-6: Creating a new `User` instance using all but one of the values from `user1` Using struct update syntax, we can achieve the same effect with less code, as shown in Listing 5-7. The syntax `..` specifies that the remaining fields not explicitly set should have the same value as the fields in the given instance. -Filename: src/main.rs +src/main.rs ``` fn main() { - --snip-- - + // --snip-- let user2 = User { email: String::from("another@example.com"), @@ -197,8 +204,7 @@ fn main() { } ``` -Listing 5-7: Using struct update syntax to set a new `email` value for a `User` -instance but to use the rest of the values from `user1` +Listing 5-7: Using struct update syntax to set a new `email` value for a `User` instance but to use the rest of the values from `user1` The code in Listing 5-7 also creates an instance in `user2` that has a different value for `email` but has the same values for the `username`, @@ -209,16 +215,22 @@ many fields as we want in any order, regardless of the order of the fields in the struct’s definition. Note that the struct update syntax uses `=` like an assignment; this is because -it moves the data, just as we saw in “Variables and Data Interacting with Move” -on page XX. In this example, we can no longer use `user1` after creating -`user2` because the `String` in the `username` field of `user1` was moved into -`user2`. If we had given `user2` new `String` values for both `email` and -`username`, and thus only used the `active` and `sign_in_count` values from -`user1`, then `user1` would still be valid after creating `user2`. Both -`active` and `sign_in_count` are types that implement the `Copy` trait, so the -behavior we discussed in “Stack-Only Data: Copy” on page XX would apply. +it moves the data, just as we saw in the “Variables and Data Interacting with +Move” section. In this example, we can no longer use +`user1` after creating `user2` because the `String` in the `username` field of +`user1` was moved into `user2`. If we had given `user2` new `String` values for +both `email` and `username`, and thus only used the `active` and `sign_in_count` +values from `user1`, then `user1` would still be valid after creating `user2`. +Both `active` and `sign_in_count` are types that implement the `Copy` trait, so +the behavior we discussed in the “Stack-Only Data: Copy” +section would apply. We can also still use `user1.email` in this example, +because its value was not moved out of `user1`. -### Using Tuple Structs Without Named Fields to Create Different Types + + + + +### Creating Different Types with Tuple Structs Rust also supports structs that look similar to tuples, called *tuple structs*. Tuple structs have the added meaning the struct name provides but don’t have @@ -231,7 +243,7 @@ To define a tuple struct, start with the `struct` keyword and the struct name followed by the types in the tuple. For example, here we define and use two tuple structs named `Color` and `Point`: -Filename: src/main.rs +src/main.rs ``` struct Color(i32, i32, i32); @@ -243,6 +255,8 @@ fn main() { } ``` + + Note that the `black` and `origin` values are different types because they’re instances of different tuple structs. Each struct you define is its own type, even though the fields within the struct might have the same types. For @@ -250,19 +264,26 @@ example, a function that takes a parameter of type `Color` cannot take a `Point` as an argument, even though both types are made up of three `i32` values. Otherwise, tuple struct instances are similar to tuples in that you can destructure them into their individual pieces, and you can use a `.` followed -by the index to access an individual value. +by the index to access an individual value. Unlike tuples, tuple structs +require you to name the type of the struct when you destructure them. For +example, we would write `let Point(x, y, z) = origin;` to destructure the +values in the `origin` point into variables named `x`, `y`, and `z`. + + -### Unit-Like Structs Without Any Fields + + +### Defining Unit-Like Structs You can also define structs that don’t have any fields! These are called *unit-like structs* because they behave similarly to `()`, the unit type that -we mentioned in “The Tuple Type” on page XX. Unit-like structs can be useful -when you need to implement a trait on some type but don’t have any data that -you want to store in the type itself. We’ll discuss traits in Chapter 10. -Here’s an example of declaring and instantiating a unit struct named -`AlwaysEqual`: +we mentioned in “The Tuple Type” section. Unit-like +structs can be useful when you need to implement a trait on some type but don’t +have any data that you want to store in the type itself. We’ll discuss traits +in Chapter 10. Here’s an example of declaring and instantiating a unit struct +named `AlwaysEqual`: -Filename: src/main.rs +src/main.rs ``` struct AlwaysEqual; @@ -272,38 +293,44 @@ fn main() { } ``` + + To define `AlwaysEqual`, we use the `struct` keyword, the name we want, and -then a semicolon. No need for curly brackets or parentheses! Then we can get an -instance of `AlwaysEqual` in the `subject` variable in a similar way: using the -name we defined, without any curly brackets or parentheses. Imagine that later -we’ll implement behavior for this type such that every instance of +then a semicolon. No need for curly brackets or parentheses! Then, we can get +an instance of `AlwaysEqual` in the `subject` variable in a similar way: using +the name we defined, without any curly brackets or parentheses. Imagine that +later we’ll implement behavior for this type such that every instance of `AlwaysEqual` is always equal to every instance of any other type, perhaps to have a known result for testing purposes. We wouldn’t need any data to implement that behavior! You’ll see in Chapter 10 how to define traits and implement them on any type, including unit-like structs. > ### Ownership of Struct Data -> +> > In the `User` struct definition in Listing 5-1, we used the owned `String` -type rather than the `&str` string slice type. This is a deliberate choice -because we want each instance of this struct to own all of its data and for -that data to be valid for as long as the entire struct is valid. -> +> type rather than the `&str` string slice type. This is a deliberate choice +> because we want each instance of this struct to own all of its data and for +> that data to be valid for as long as the entire struct is valid. +> > It’s also possible for structs to store references to data owned by something -else, but to do so requires the use of *lifetimes*, a Rust feature that we’ll -discuss in Chapter 10. Lifetimes ensure that the data referenced by a struct is -valid for as long as the struct is. Let’s say you try to store a reference in a -struct without specifying lifetimes, like the following in *src/main.rs*; this -won’t work: -> -> ``` +> else, but to do so requires the use of *lifetimes*, a Rust feature that we’ll +> discuss in Chapter 10. Lifetimes ensure that the data referenced by a struct +> is valid for as long as the struct is. Let’s say you try to store a reference +> in a struct without specifying lifetimes, like the following in +> *src/main.rs*; this won’t work: +> +> +> +> +> +> ````rust,ignore,does_not_compile > struct User { > active: bool, > username: &str, > email: &str, > sign_in_count: u64, > } -> +> > fn main() { > let user1 = User { > active: true, @@ -312,12 +339,14 @@ won’t work: > sign_in_count: 1, > }; > } -> ``` -> +> ```` +> +> +> > The compiler will complain that it needs lifetime specifiers: -> -> ``` -> $ `cargo run` +> +> ````console +> $ cargo run > Compiling structs v0.1.0 (file:///projects/structs) > error[E0106]: missing lifetime specifier > --> src/main.rs:3:15 @@ -331,7 +360,7 @@ won’t work: > 2 | active: bool, > 3 ~ username: &'a str, > | -> +> > error[E0106]: missing lifetime specifier > --> src/main.rs:4:12 > | @@ -345,16 +374,26 @@ won’t work: > 3 | username: &str, > 4 ~ email: &'a str, > | -> ``` -> -> In Chapter 10, we’ll discuss how to fix these errors so you can store -references in structs, but for now, we’ll fix errors like these using owned -types like `String` instead of references like `&str`. +> +> For more information about this error, try `rustc --explain E0106`. +> error: could not compile `structs` (bin "structs") due to 2 previous errors +> ```` +> +> In Chapter 10, we’ll discuss how to fix these errors so that you can store +> references in structs, but for now, we’ll fix errors like these using owned +> types like `String` instead of references like `&str`. + + ## An Example Program Using Structs To understand when we might want to use structs, let’s write a program that -calculates the area of a rectangle. We’ll start by using single variables, and +calculates the area of a rectangle. We’ll start by using single variables and then refactor the program until we’re using structs instead. Let’s make a new binary project with Cargo called *rectangles* that will take @@ -362,7 +401,7 @@ the width and height of a rectangle specified in pixels and calculate the area of the rectangle. Listing 5-8 shows a short program with one way of doing exactly that in our project’s *src/main.rs*. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -380,12 +419,15 @@ fn area(width: u32, height: u32) -> u32 { } ``` -Listing 5-8: Calculating the area of a rectangle specified by separate width -and height variables +Listing 5-8: Calculating the area of a rectangle specified by separate width and height variables Now, run this program using `cargo run`: ``` +$ cargo run + Compiling rectangles v0.1.0 (file:///projects/rectangles) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.42s + Running `target/debug/rectangles` The area of the rectangle is 1500 square pixels. ``` @@ -403,13 +445,14 @@ The `area` function is supposed to calculate the area of one rectangle, but the function we wrote has two parameters, and it’s not clear anywhere in our program that the parameters are related. It would be more readable and more manageable to group width and height together. We’ve already discussed one way -we might do that in “The Tuple Type” on page XX: by using tuples. +we might do that in “The Tuple Type” section +of Chapter 3: by using tuples. ### Refactoring with Tuples Listing 5-9 shows another version of our program that uses tuples. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -417,21 +460,21 @@ fn main() { println!( "The area of the rectangle is {} square pixels.", - 1 area(rect1) + area(rect1) ); } fn area(dimensions: (u32, u32)) -> u32 { - 2 dimensions.0 * dimensions.1 + dimensions.0 * dimensions.1 } ``` Listing 5-9: Specifying the width and height of the rectangle with a tuple In one way, this program is better. Tuples let us add a bit of structure, and -we’re now passing just one argument [1]. But in another way, this version is -less clear: tuples don’t name their elements, so we have to index into the -parts of the tuple [2], making our calculation less obvious. +we’re now passing just one argument. But in another way, this version is less +clear: Tuples don’t name their elements, so we have to index into the parts of +the tuple, making our calculation less obvious. Mixing up the width and height wouldn’t matter for the area calculation, but if we want to draw the rectangle on the screen, it would matter! We would have to @@ -440,22 +483,26 @@ index `1`. This would be even harder for someone else to figure out and keep in mind if they were to use our code. Because we haven’t conveyed the meaning of our data in our code, it’s now easier to introduce errors. -### Refactoring with Structs: Adding More Meaning + + + + +### Refactoring with Structs We use structs to add meaning by labeling the data. We can transform the tuple we’re using into a struct with a name for the whole as well as names for the parts, as shown in Listing 5-10. -Filename: src/main.rs +src/main.rs ``` -1 struct Rectangle { - 2 width: u32, +struct Rectangle { + width: u32, height: u32, } fn main() { - 3 let rect1 = Rectangle { + let rect1 = Rectangle { width: 30, height: 50, }; @@ -466,42 +513,46 @@ fn main() { ); } -4 fn area(rectangle: &Rectangle) -> u32 { - 5 rectangle.width * rectangle.height +fn area(rectangle: &Rectangle) -> u32 { + rectangle.width * rectangle.height } ``` Listing 5-10: Defining a `Rectangle` struct -Here, we’ve defined a struct and named it `Rectangle` [1]. Inside the curly +Here, we’ve defined a struct and named it `Rectangle`. Inside the curly brackets, we defined the fields as `width` and `height`, both of which have -type `u32` [2]. Then, in `main`, we created a particular instance of -`Rectangle` that has a width of `30` and a height of `50` [3]. +type `u32`. Then, in `main`, we created a particular instance of `Rectangle` +that has a width of `30` and a height of `50`. Our `area` function is now defined with one parameter, which we’ve named -`rectangle`, whose type is an immutable borrow of a struct `Rectangle` instance -[4]. As mentioned in Chapter 4, we want to borrow the struct rather than take -ownership of it. This way, `main` retains its ownership and can continue using -`rect1`, which is the reason we use the `&` in the function signature and where -we call the function. +`rectangle`, whose type is an immutable borrow of a struct `Rectangle` +instance. As mentioned in Chapter 4, we want to borrow the struct rather than +take ownership of it. This way, `main` retains its ownership and can continue +using `rect1`, which is the reason we use the `&` in the function signature and +where we call the function. The `area` function accesses the `width` and `height` fields of the `Rectangle` -instance [5] (note that accessing fields of a borrowed struct instance does not +instance (note that accessing fields of a borrowed struct instance does not move the field values, which is why you often see borrows of structs). Our -function signature for `area` now says exactly what we mean: calculate the area +function signature for `area` now says exactly what we mean: Calculate the area of `Rectangle`, using its `width` and `height` fields. This conveys that the width and height are related to each other, and it gives descriptive names to the values rather than using the tuple index values of `0` and `1`. This is a win for clarity. -### Adding Useful Functionality with Derived Traits + + + + +### Adding Functionality with Derived Traits It’d be useful to be able to print an instance of `Rectangle` while we’re debugging our program and see the values for all its fields. Listing 5-11 tries -using the `println!` macro as we have used in previous chapters. This won’t -work, however. +using the `println!` macro as we have used in +previous chapters. This won’t work, however. -Filename: src/main.rs +src/main.rs ``` struct Rectangle { @@ -515,7 +566,7 @@ fn main() { height: 50, }; - println!("rect1 is {}", rect1); + println!("rect1 is {rect1}"); } ``` @@ -541,16 +592,14 @@ implementation of `Display` to use with `println!` and the `{}` placeholder. If we continue reading the errors, we’ll find this helpful note: ``` -= help: the trait `std::fmt::Display` is not implemented for `Rectangle` -= note: in format strings you may be able to use `{:?}` (or {:#?} for -pretty-print) instead + = help: the trait `std::fmt::Display` is not implemented for `Rectangle` + = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead ``` -Let’s try it! The `println!` macro call will now look like `println!("rect1 is -{:?}", rect1);`. Putting the specifier `:?` inside the curly brackets tells +Let’s try it! The `println!` macro call will now look like `println!("rect1 is {rect1:?}");`. Putting the specifier `:?` inside the curly brackets tells `println!` we want to use an output format called `Debug`. The `Debug` trait -enables us to print our struct in a way that is useful for developers so we can -see its value while we’re debugging our code. +enables us to print our struct in a way that is useful for developers so that +we can see its value while we’re debugging our code. Compile the code with this change. Drat! We still get an error: @@ -561,8 +610,8 @@ error[E0277]: `Rectangle` doesn't implement `Debug` But again, the compiler gives us a helpful note: ``` -= help: the trait `Debug` is not implemented for `Rectangle` -= note: add `#[derive(Debug)]` or manually implement `Debug` + = help: the trait `Debug` is not implemented for `Rectangle` + = note: add `#[derive(Debug)]` to `Rectangle` or manually `impl Debug for Rectangle` ``` Rust *does* include functionality to print out debugging information, but we @@ -570,7 +619,7 @@ have to explicitly opt in to make that functionality available for our struct. To do that, we add the outer attribute `#[derive(Debug)]` just before the struct definition, as shown in Listing 5-12. -Filename: src/main.rs +src/main.rs ``` #[derive(Debug)] @@ -585,17 +634,20 @@ fn main() { height: 50, }; - println!("rect1 is {:?}", rect1); + println!("rect1 is {rect1:?}"); } ``` -Listing 5-12: Adding the attribute to derive the `Debug` trait and printing the -`Rectangle` instance using debug formatting +Listing 5-12: Adding the attribute to derive the `Debug` trait and printing the `Rectangle` instance using debug formatting Now when we run the program, we won’t get any errors, and we’ll see the following output: ``` +$ cargo run + Compiling rectangles v0.1.0 (file:///projects/rectangles) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s + Running `target/debug/rectangles` rect1 is Rectangle { width: 30, height: 50 } ``` @@ -606,6 +658,10 @@ those cases, we can use `{:#?}` instead of `{:?}` in the `println!` string. In this example, using the `{:#?}` style will output the following: ``` +$ cargo run + Compiling rectangles v0.1.0 (file:///projects/rectangles) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s + Running `target/debug/rectangles` rect1 is Rectangle { width: 30, height: 50, @@ -613,22 +669,20 @@ rect1 is Rectangle { ``` Another way to print out a value using the `Debug` format is to use the `dbg!` -macro, which takes ownership of an expression (as opposed to `println!`, which -takes a reference), prints the file and line number of where that `dbg!` macro -call occurs in your code along with the resultant value of that expression, and -returns ownership of the value. +macro, which takes ownership of an expression (as opposed +to `println!`, which takes a reference), prints the file and line number of +where that `dbg!` macro call occurs in your code along with the resultant value +of that expression, and returns ownership of the value. > Note: Calling the `dbg!` macro prints to the standard error console stream -(`stderr`), as opposed to `println!`, which prints to the standard output -console stream (`stdout`). We’ll talk more about `stderr` and `stdout` in -“Writing Error Messages to Standard Error Instead of Standard Output” on page -XX. +> (`stderr`), as opposed to `println!`, which prints to the standard output +> console stream (`stdout`). We’ll talk more about `stderr` and `stdout` in the +> “Redirecting Errors to Standard Error” section in Chapter +> 12. Here’s an example where we’re interested in the value that gets assigned to the `width` field, as well as the value of the whole struct in `rect1`: -Filename: src/main.rs - ``` #[derive(Debug)] struct Rectangle { @@ -639,67 +693,75 @@ struct Rectangle { fn main() { let scale = 2; let rect1 = Rectangle { - 1 width: dbg!(30 * scale), + width: dbg!(30 * scale), height: 50, }; - 2 dbg!(&rect1); + dbg!(&rect1); } ``` -We can put `dbg!` around the expression `30 * scale` [1] and, because `dbg!` +We can put `dbg!` around the expression `30 * scale` and, because `dbg!` returns ownership of the expression’s value, the `width` field will get the same value as if we didn’t have the `dbg!` call there. We don’t want `dbg!` to -take ownership of `rect1`, so we use a reference to `rect1` in the next call -[2]. Here’s what the output of this example looks like: +take ownership of `rect1`, so we use a reference to `rect1` in the next call. +Here’s what the output of this example looks like: ``` -[src/main.rs:10] 30 * scale = 60 -[src/main.rs:14] &rect1 = Rectangle { +$ cargo run + Compiling rectangles v0.1.0 (file:///projects/rectangles) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.61s + Running `target/debug/rectangles` +[src/main.rs:10:16] 30 * scale = 60 +[src/main.rs:14:5] &rect1 = Rectangle { width: 60, height: 50, } ``` -We can see the first bit of output came from [1] where we’re debugging the -expression `30 * scale`, and its resultant value is `60` (the `Debug` -formatting implemented for integers is to print only their value). The `dbg!` -call at [2] outputs the value of `&rect1`, which is the `Rectangle` struct. -This output uses the pretty `Debug` formatting of the `Rectangle` type. The -`dbg!` macro can be really helpful when you’re trying to figure out what your -code is doing! +We can see the first bit of output came from *src/main.rs* line 10 where we’re +debugging the expression `30 * scale`, and its resultant value is `60` (the +`Debug` formatting implemented for integers is to print only their value). The +`dbg!` call on line 14 of *src/main.rs* outputs the value of `&rect1`, which is +the `Rectangle` struct. This output uses the pretty `Debug` formatting of the +`Rectangle` type. The `dbg!` macro can be really helpful when you’re trying to +figure out what your code is doing! In addition to the `Debug` trait, Rust has provided a number of traits for us to use with the `derive` attribute that can add useful behavior to our custom -types. Those traits and their behaviors are listed in Appendix C. We’ll cover -how to implement these traits with custom behavior as well as how to create -your own traits in Chapter 10. There are also many attributes other than -`derive`; for more information, see the “Attributes” section of the Rust -Reference at *https://doc.rust-lang.org/reference/attributes.html*. +types. Those traits and their behaviors are listed in Appendix C. We’ll cover how to implement these traits with custom behavior as +well as how to create your own traits in Chapter 10. There are also many +attributes other than `derive`; for more information, see the “Attributes” +section of the Rust Reference at *../reference/attributes.html*. -Our `area` function is very specific: it only computes the area of rectangles. +Our `area` function is very specific: It only computes the area of rectangles. It would be helpful to tie this behavior more closely to our `Rectangle` struct because it won’t work with any other type. Let’s look at how we can continue to -refactor this code by turning the `area` function into an `area` *method* +refactor this code by turning the `area` function into an `area` method defined on our `Rectangle` type. -## Method Syntax +## Methods -*Methods* are similar to functions: we declare them with the `fn` keyword and a +Methods are similar to functions: We declare them with the `fn` keyword and a name, they can have parameters and a return value, and they contain some code that’s run when the method is called from somewhere else. Unlike functions, methods are defined within the context of a struct (or an enum or a trait -object, which we cover in Chapter 6 and Chapter 17, respectively), and their -first parameter is always `self`, which represents the instance of the struct -the method is being called on. +object, which we cover in Chapter 6 and Chapter +18, respectively), and their first parameter is +always `self`, which represents the instance of the struct the method is being +called on. -### Defining Methods + + + + +### Method Syntax Let’s change the `area` function that has a `Rectangle` instance as a parameter and instead make an `area` method defined on the `Rectangle` struct, as shown in Listing 5-13. -Filename: src/main.rs +src/main.rs ``` #[derive(Debug)] @@ -708,8 +770,8 @@ struct Rectangle { height: u32, } -1 impl Rectangle { - 2 fn area(&self) -> u32 { +impl Rectangle { + fn area(&self) -> u32 { self.width * self.height } } @@ -722,7 +784,7 @@ fn main() { println!( "The area of the rectangle is {} square pixels.", - 3 rect1.area() + rect1.area() ); } ``` @@ -730,14 +792,14 @@ fn main() { Listing 5-13: Defining an `area` method on the `Rectangle` struct To define the function within the context of `Rectangle`, we start an `impl` -(implementation) block for `Rectangle` [1]. Everything within this `impl` block -will be associated with the `Rectangle` type. Then we move the `area` function -within the `impl` curly brackets [2] and change the first (and in this case, -only) parameter to be `self` in the signature and everywhere within the body. -In `main`, where we called the `area` function and passed `rect1` as an -argument, we can instead use *method syntax* to call the `area` method on our -`Rectangle` instance [3]. The method syntax goes after an instance: we add a -dot followed by the method name, parentheses, and any arguments. +(implementation) block for `Rectangle`. Everything within this `impl` block +will be associated with the `Rectangle` type. Then, we move the `area` function +within the `impl` curly brackets and change the first (and in this case, only) +parameter to be `self` in the signature and everywhere within the body. In +`main`, where we called the `area` function and passed `rect1` as an argument, +we can instead use *method syntax* to call the `area` method on our `Rectangle` +instance. The method syntax goes after an instance: We add a dot followed by +the method name, parentheses, and any arguments. In the signature for `area`, we use `&self` instead of `rectangle: &Rectangle`. The `&self` is actually short for `self: &Self`. Within an `impl` block, the @@ -751,7 +813,7 @@ immutably, as we’ve done here, or borrow `self` mutably, just as they can any other parameter. We chose `&self` here for the same reason we used `&Rectangle` in the function -version: we don’t want to take ownership, and we just want to read the data in +version: We don’t want to take ownership, and we just want to read the data in the struct, not write to it. If we wanted to change the instance that we’ve called the method on as part of what the method does, we’d use `&mut self` as the first parameter. Having a method that takes ownership of the instance by @@ -770,7 +832,7 @@ Note that we can choose to give a method the same name as one of the struct’s fields. For example, we can define a method on `Rectangle` that is also named `width`: -Filename: src/main.rs +src/main.rs ``` impl Rectangle { @@ -786,57 +848,74 @@ fn main() { }; if rect1.width() { - println!( - "The rectangle has a nonzero width; it is {}", - rect1.width - ); + println!("The rectangle has a nonzero width; it is {}", rect1.width); } } ``` + + Here, we’re choosing to make the `width` method return `true` if the value in the instance’s `width` field is greater than `0` and `false` if the value is -`0`: we can use a field within a method of the same name for any purpose. In +`0`: We can use a field within a method of the same name for any purpose. In `main`, when we follow `rect1.width` with parentheses, Rust knows we mean the method `width`. When we don’t use parentheses, Rust knows we mean the field `width`. -Often, but not always, when we give methods with the same name as a field we -want it to only return the value in the field and do nothing else. Methods like -this are called *getters*, and Rust does not implement them automatically for -struct fields as some other languages do. Getters are useful because you can -make the field private but the method public, and thus enable read-only access -to that field as part of the type’s public API. We will discuss what public and -private are and how to designate a field or method as public or private in -Chapter 7. +Often, but not always, when we give a method the same name as a field we want +it to only return the value in the field and do nothing else. Methods like this +are called *getters*, and Rust does not implement them automatically for struct +fields as some other languages do. Getters are useful because you can make the +field private but the method public and thus enable read-only access to that +field as part of the type’s public API. We will discuss what public and private +are and how to designate a field or method as public or private in Chapter +7. > ### Where’s the -> Operator? -> -> In C and C++, two different operators are used for calling methods: you use -`.` if you’re calling a method on the object directly and `->` if you’re -calling the method on a pointer to the object and need to dereference the -pointer first. In other words, if `object` is a pointer, -`object->`something`()` is similar to `(*object).`something`()`. -> +> +> In C and C++, two different operators are used for calling methods: You use +> `.` if you’re calling a method on the object directly and `->` if you’re +> calling the method on a pointer to the object and need to dereference the +> pointer first. In other words, if `object` is a pointer, +> `object->something()` is similar to `(*object).something()`. +> > Rust doesn’t have an equivalent to the `->` operator; instead, Rust has a -feature called *automatic referencing and dereferencing*. Calling methods is -one of the few places in Rust that has this behavior. -> -> Here’s how it works: when you call a method with `object.`something`()`, Rust -automatically adds in `&`, `&mut`, or `*` so `object` matches the signature of -the method. In other words, the following are the same: -> -> ``` +> feature called *automatic referencing and dereferencing*. Calling methods is +> one of the few places in Rust with this behavior. +> +> Here’s how it works: When you call a method with `object.something()`, Rust +> automatically adds in `&`, `&mut`, or `*` so that `object` matches the +> signature of the method. In other words, the following are the same: +> +> +> +> ````rust +> # #[derive(Debug,Copy,Clone)] +> # struct Point { +> # x: f64, +> # y: f64, +> # } +> # +> # impl Point { +> # fn distance(&self, other: &Point) -> f64 { +> # let x_squared = f64::powi(other.x - self.x, 2); +> # let y_squared = f64::powi(other.y - self.y, 2); +> # +> # f64::sqrt(x_squared + y_squared) +> # } +> # } +> # let p1 = Point { x: 0.0, y: 0.0 }; +> # let p2 = Point { x: 5.0, y: 6.5 }; > p1.distance(&p2); > (&p1).distance(&p2); -> ``` -> +> ```` +> > The first one looks much cleaner. This automatic referencing behavior works -because methods have a clear receiver—the type of `self`. Given the receiver -and name of a method, Rust can figure out definitively whether the method is -reading (`&self`), mutating (`&mut self`), or consuming (`self`). The fact that -Rust makes borrowing implicit for method receivers is a big part of making -ownership ergonomic in practice. +> because methods have a clear receiver—the type of `self`. Given the receiver +> and name of a method, Rust can figure out definitively whether the method is +> reading (`&self`), mutating (`&mut self`), or consuming (`self`). The fact +> that Rust makes borrowing implicit for method receivers is a big part of +> making ownership ergonomic in practice. ### Methods with More Parameters @@ -847,7 +926,7 @@ within `self` (the first `Rectangle`); otherwise, it should return `false`. That is, once we’ve defined the `can_hold` method, we want to be able to write the program shown in Listing 5-14. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -887,14 +966,14 @@ parameter will be by looking at the code that calls the method: `rect1.can_hold(&rect2)` passes in `&rect2`, which is an immutable borrow to `rect2`, an instance of `Rectangle`. This makes sense because we only need to read `rect2` (rather than write, which would mean we’d need a mutable borrow), -and we want `main` to retain ownership of `rect2` so we can use it again after -calling the `can_hold` method. The return value of `can_hold` will be a +and we want `main` to retain ownership of `rect2` so that we can use it again +after calling the `can_hold` method. The return value of `can_hold` will be a Boolean, and the implementation will check whether the width and height of `self` are greater than the width and height of the other `Rectangle`, respectively. Let’s add the new `can_hold` method to the `impl` block from Listing 5-13, shown in Listing 5-15. -Filename: src/main.rs +src/main.rs ``` impl Rectangle { @@ -908,8 +987,7 @@ impl Rectangle { } ``` -Listing 5-15: Implementing the `can_hold` method on `Rectangle` that takes -another `Rectangle` instance as a parameter +Listing 5-15: Implementing the `can_hold` method on `Rectangle` that takes another `Rectangle` instance as a parameter When we run this code with the `main` function in Listing 5-14, we’ll get our desired output. Methods can take multiple parameters that we add to the @@ -937,8 +1015,8 @@ Filename: src/main.rs ``` impl Rectangle { - fn square(size: u32) -> 1 Self { - 2 Self { + fn square(size: u32) -> Self { + Self { width: size, height: size, } @@ -946,14 +1024,15 @@ impl Rectangle { } ``` -The `Self` keywords in the return type [1] and in the body of the function [2] -are aliases for the type that appears after the `impl` keyword, which in this -case is `Rectangle`. +The `Self` keywords in the return type and in the body of the function are +aliases for the type that appears after the `impl` keyword, which in this case +is `Rectangle`. To call this associated function, we use the `::` syntax with the struct name; `let sq = Rectangle::square(3);` is an example. This function is namespaced by -the struct: the `::` syntax is used for both associated functions and -namespaces created by modules. We’ll discuss modules in Chapter 7. +the struct: The `::` syntax is used for both associated functions and +namespaces created by modules. We’ll discuss modules in Chapter +7. ### Multiple impl Blocks @@ -961,6 +1040,7 @@ Each struct is allowed to have multiple `impl` blocks. For example, Listing 5-15 is equivalent to the code shown in Listing 5-16, which has each method in its own `impl` block. + ``` impl Rectangle { fn area(&self) -> u32 { @@ -990,6 +1070,5 @@ functions that are associated with your type, and methods are a kind of associated function that let you specify the behavior that instances of your structs have. -But structs aren’t the only way you can create custom types: let’s turn to +But structs aren’t the only way you can create custom types: Let’s turn to Rust’s enum feature to add another tool to your toolbox. - diff --git a/nostarch/chapter06.md b/nostarch/chapter06.md index ea4328bea8..ef22bebc25 100644 --- a/nostarch/chapter06.md +++ b/nostarch/chapter06.md @@ -8,11 +8,11 @@ directory, so all fixes need to be made in `/src/`. # Enums and Pattern Matching -In this chapter, we’ll look at *enumerations*, also referred to as *enums*. -Enums allow you to define a type by enumerating its possible *variants*. First +In this chapter, we’ll look at enumerations, also referred to as *enums*. +Enums allow you to define a type by enumerating its possible variants. First we’ll define and use an enum to show how an enum can encode meaning along with data. Next, we’ll explore a particularly useful enum, called `Option`, which -expresses that a value can be either something or nothing. Then we’ll look at +expresses that a value can be either something or nothing. Then, we’ll look at how pattern matching in the `match` expression makes it easy to run different code for different values of an enum. Finally, we’ll cover how the `if let` construct is another convenient and concise idiom available to handle enums in @@ -58,8 +58,8 @@ enum IpAddrKind { We can create instances of each of the two variants of `IpAddrKind` like this: ``` -let four = IpAddrKind::V4; -let six = IpAddrKind::V6; + let four = IpAddrKind::V4; + let six = IpAddrKind::V6; ``` Note that the variants of the enum are namespaced under its identifier, and we @@ -74,8 +74,8 @@ fn route(ip_kind: IpAddrKind) {} And we can call this function with either variant: ``` -route(IpAddrKind::V4); -route(IpAddrKind::V6); + route(IpAddrKind::V4); + route(IpAddrKind::V6); ``` Using enums has even more advantages. Thinking more about our IP address type, @@ -84,65 +84,65 @@ only know what *kind* it is. Given that you just learned about structs in Chapter 5, you might be tempted to tackle this problem with structs as shown in Listing 6-1. + ``` -1 enum IpAddrKind { - V4, - V6, -} + enum IpAddrKind { + V4, + V6, + } -2 struct IpAddr { - 3 kind: IpAddrKind, - 4 address: String, -} + struct IpAddr { + kind: IpAddrKind, + address: String, + } -5 let home = IpAddr { - kind: IpAddrKind::V4, - address: String::from("127.0.0.1"), -}; + let home = IpAddr { + kind: IpAddrKind::V4, + address: String::from("127.0.0.1"), + }; -6 let loopback = IpAddr { - kind: IpAddrKind::V6, - address: String::from("::1"), -}; + let loopback = IpAddr { + kind: IpAddrKind::V6, + address: String::from("::1"), + }; ``` -Listing 6-1: Storing the data and `IpAddrKind` variant of an IP address using a -`struct` +Listing 6-1: Storing the data and `IpAddrKind` variant of an IP address using a `struct` -Here, we’ve defined a struct `IpAddr` [2] that has two fields: a `kind` field -[3] that is of type `IpAddrKind` (the enum we defined previously [1]) and an -`address` field [4] of type `String`. We have two instances of this struct. The -first is `home` [5], and it has the value `IpAddrKind::V4` as its `kind` with -associated address data of `127.0.0.1`. The second instance is `loopback` [6]. -It has the other variant of `IpAddrKind` as its `kind` value, `V6`, and has -address `::1` associated with it. We’ve used a struct to bundle the `kind` and -`address` values together, so now the variant is associated with the value. +Here, we’ve defined a struct `IpAddr` that has two fields: a `kind` field that +is of type `IpAddrKind` (the enum we defined previously) and an `address` field +of type `String`. We have two instances of this struct. The first is `home`, +and it has the value `IpAddrKind::V4` as its `kind` with associated address +data of `127.0.0.1`. The second instance is `loopback`. It has the other +variant of `IpAddrKind` as its `kind` value, `V6`, and has address `::1` +associated with it. We’ve used a struct to bundle the `kind` and `address` +values together, so now the variant is associated with the value. However, representing the same concept using just an enum is more concise: -rather than an enum inside a struct, we can put data directly into each enum +Rather than an enum inside a struct, we can put data directly into each enum variant. This new definition of the `IpAddr` enum says that both `V4` and `V6` variants will have associated `String` values: ``` -enum IpAddr { - V4(String), - V6(String), -} + enum IpAddr { + V4(String), + V6(String), + } -let home = IpAddr::V4(String::from("127.0.0.1")); + let home = IpAddr::V4(String::from("127.0.0.1")); -let loopback = IpAddr::V6(String::from("::1")); + let loopback = IpAddr::V6(String::from("::1")); ``` We attach data to each variant of the enum directly, so there is no need for an extra struct. Here, it’s also easier to see another detail of how enums work: -the name of each enum variant that we define also becomes a function that +The name of each enum variant that we define also becomes a function that constructs an instance of the enum. That is, `IpAddr::V4()` is a function call that takes a `String` argument and returns an instance of the `IpAddr` type. We automatically get this constructor function defined as a result of defining the enum. -There’s another advantage to using an enum rather than a struct: each variant +There’s another advantage to using an enum rather than a struct: Each variant can have different types and amounts of associated data. Version four IP addresses will always have four numeric components that will have values between 0 and 255. If we wanted to store `V4` addresses as four `u8` values but @@ -150,31 +150,32 @@ still express `V6` addresses as one `String` value, we wouldn’t be able to wit a struct. Enums handle this case with ease: ``` -enum IpAddr { - V4(u8, u8, u8, u8), - V6(String), -} + enum IpAddr { + V4(u8, u8, u8, u8), + V6(String), + } -let home = IpAddr::V4(127, 0, 0, 1); + let home = IpAddr::V4(127, 0, 0, 1); -let loopback = IpAddr::V6(String::from("::1")); + let loopback = IpAddr::V6(String::from("::1")); ``` We’ve shown several different ways to define data structures to store version four and version six IP addresses. However, as it turns out, wanting to store IP addresses and encode which kind they are is so common that the standard -library has a definition we can use! Let’s look at how the standard library -defines `IpAddr`: it has the exact enum and variants that we’ve defined and -used, but it embeds the address data inside the variants in the form of two -different structs, which are defined differently for each variant: +library has a definition we can use! Let’s look at how +the standard library defines `IpAddr`. It has the exact enum and variants that +we’ve defined and used, but it embeds the address data inside the variants in +the form of two different structs, which are defined differently for each +variant: ``` struct Ipv4Addr { - --snip-- + // --snip-- } struct Ipv6Addr { - --snip-- + // --snip-- } enum IpAddr { @@ -193,9 +194,10 @@ we can still create and use our own definition without conflict because we haven’t brought the standard library’s definition into our scope. We’ll talk more about bringing types into scope in Chapter 7. -Let’s look at another example of an enum in Listing 6-2: this one has a wide +Let’s look at another example of an enum in Listing 6-2: This one has a wide variety of types embedded in its variants. + ``` enum Message { Quit, @@ -205,15 +207,14 @@ enum Message { } ``` -Listing 6-2: A `Message` enum whose variants each store different amounts and -types of values +Listing 6-2: A `Message` enum whose variants each store different amounts and types of values This enum has four variants with different types: -* `Quit` has no data associated with it at all. -* `Move` has named fields, like a struct does. -* `Write` includes a single `String`. -* `ChangeColor` includes three `i32` values. +* `Quit`: Has no data associated with it at all +* `Move`: Has named fields, like a struct does +* `Write`: Includes a single `String` +* `ChangeColor`: Includes three `i32` values Defining an enum with variants such as the ones in Listing 6-2 is similar to defining different kinds of struct definitions, except the enum doesn’t use the @@ -235,41 +236,45 @@ But if we used the different structs, each of which has its own type, we couldn’t as easily define a function to take any of these kinds of messages as we could with the `Message` enum defined in Listing 6-2, which is a single type. -There is one more similarity between enums and structs: just as we’re able to +There is one more similarity between enums and structs: Just as we’re able to define methods on structs using `impl`, we’re also able to define methods on enums. Here’s a method named `call` that we could define on our `Message` enum: ``` -impl Message { - fn call(&self) { - 1 // method body would be defined here + impl Message { + fn call(&self) { + // method body would be defined here + } } -} -2 let m = Message::Write(String::from("hello")); -m.call(); + let m = Message::Write(String::from("hello")); + m.call(); ``` The body of the method would use `self` to get the value that we called the -method on. In this example, we’ve created a variable `m` [2] that has the value +method on. In this example, we’ve created a variable `m` that has the value `Message::Write(String::from("hello"))`, and that is what `self` will be in the -body of the `call` method [1] when `m.call()` runs. +body of the `call` method when `m.call()` runs. Let’s look at another enum in the standard library that is very common and useful: `Option`. -### The Option Enum and Its Advantages Over Null Values + + + + +### The Option Enum This section explores a case study of `Option`, which is another enum defined by the standard library. The `Option` type encodes the very common scenario in -which a value could be something or it could be nothing. +which a value could be something, or it could be nothing. -For example, if you request the first item in a list containing multiple items, -you would get a value. If you request the first item in an empty list, you -would get nothing. Expressing this concept in terms of the type system means -the compiler can check whether you’ve handled all the cases you should be -handling; this functionality can prevent bugs that are extremely common in -other programming languages. +For example, if you request the first item in a non-empty list, you would get +a value. If you request the first item in an empty list, you would get nothing. +Expressing this concept in terms of the type system means the compiler can +check whether you’ve handled all the cases you should be handling; this +functionality can prevent bugs that are extremely common in other programming +languages. Programming language design is often thought of in terms of which features you include, but the features you exclude are important too. Rust doesn’t have the @@ -278,27 +283,29 @@ is no value there. In languages with null, variables can always be in one of two states: null or not-null. In his 2009 presentation “Null References: The Billion Dollar Mistake,” Tony -Hoare, the inventor of null, has this to say: +Hoare, the inventor of null, had this to say: > I call it my billion-dollar mistake. At that time, I was designing the first -comprehensive type system for references in an object-oriented language. My -goal was to ensure that all use of references should be absolutely safe, with -checking performed automatically by the compiler. But I couldn’t resist the -temptation to put in a null reference, simply because it was so easy to -implement. This has led to innumerable errors, vulnerabilities, and system -crashes, which have probably caused a billion dollars of pain and damage in the -last forty years.The problem with null values is that if you try to use a null -value as a not-null value, you’ll get an error of some kind. Because this null -or not-null property is pervasive, it’s extremely easy to make this kind of -error. - -However, the concept that null is trying to express is still a useful one: a +> comprehensive type system for references in an object-oriented language. My +> goal was to ensure that all use of references should be absolutely safe, with +> checking performed automatically by the compiler. But I couldn’t resist the +> temptation to put in a null reference, simply because it was so easy to +> implement. This has led to innumerable errors, vulnerabilities, and system +> crashes, which have probably caused a billion dollars of pain and damage in +> the last forty years. + +The problem with null values is that if you try to use a null value as a +not-null value, you’ll get an error of some kind. Because this null or not-null +property is pervasive, it’s extremely easy to make this kind of error. + +However, the concept that null is trying to express is still a useful one: A null is a value that is currently invalid or absent for some reason. The problem isn’t really with the concept but with the particular implementation. As such, Rust does not have nulls, but it does have an enum that can encode the concept of a value being present or absent. This enum is -`Option`, and it is defined by the standard library as follows: +`Option`, and it is defined by the standard library +as follows: ``` enum Option { @@ -309,7 +316,7 @@ enum Option { The `Option` enum is so useful that it’s even included in the prelude; you don’t need to bring it into scope explicitly. Its variants are also included in -the prelude: you can use `Some` and `None` directly without the `Option::` +the prelude: You can use `Some` and `None` directly without the `Option::` prefix. The `Option` enum is still just a regular enum, and `Some(T)` and `None` are still variants of type `Option`. @@ -319,26 +326,26 @@ For now, all you need to know is that `` means that the `Some` variant of the `Option` enum can hold one piece of data of any type, and that each concrete type that gets used in place of `T` makes the overall `Option` type a different type. Here are some examples of using `Option` values to hold -number types and string types: +number types and char types: ``` -let some_number = Some(5); -let some_char = Some('e'); + let some_number = Some(5); + let some_char = Some('e'); -let absent_number: Option = None; + let absent_number: Option = None; ``` The type of `some_number` is `Option`. The type of `some_char` is `Option`, which is a different type. Rust can infer these types because we’ve specified a value inside the `Some` variant. For `absent_number`, Rust -requires us to annotate the overall `Option` type: the compiler can’t infer the +requires us to annotate the overall `Option` type: The compiler can’t infer the type that the corresponding `Some` variant will hold by looking only at a `None` value. Here, we tell Rust that we mean for `absent_number` to be of type `Option`. -When we have a `Some` value, we know that a value is present and the value is +When we have a `Some` value, we know that a value is present, and the value is held within the `Some`. When we have a `None` value, in some sense it means the -same thing as null: we don’t have a valid value. So why is having `Option` +same thing as null: We don’t have a valid value. So, why is having `Option` any better than having null? In short, because `Option` and `T` (where `T` can be any type) are different @@ -347,15 +354,17 @@ definitely a valid value. For example, this code won’t compile, because it’s trying to add an `i8` to an `Option`: ``` -let x: i8 = 5; -let y: Option = Some(5); + let x: i8 = 5; + let y: Option = Some(5); -let sum = x + y; + let sum = x + y; ``` If we run this code, we get an error message like this one: ``` +$ cargo run + Compiling enums v0.1.0 (file:///projects/enums) error[E0277]: cannot add `Option` to `i8` --> src/main.rs:5:17 | @@ -363,6 +372,14 @@ error[E0277]: cannot add `Option` to `i8` | ^ no implementation for `i8 + Option` | = help: the trait `Add>` is not implemented for `i8` + = help: the following other types implement trait `Add`: + `&i8` implements `Add` + `&i8` implements `Add` + `i8` implements `Add<&i8>` + `i8` implements `Add` + +For more information about this error, try `rustc --explain E0277`. +error: could not compile `enums` (bin "enums") due to 1 previous error ``` Intense! In effect, this error message means that Rust doesn’t understand how @@ -378,41 +395,47 @@ In other words, you have to convert an `Option` to a `T` before you can perform `T` operations with it. Generally, this helps catch one of the most common issues with null: assuming that something isn’t null when it actually is. -Eliminating the risk of incorrectly assuming a not-null value helps you to be -more confident in your code. In order to have a value that can possibly be -null, you must explicitly opt in by making the type of that value `Option`. -Then, when you use that value, you are required to explicitly handle the case -when the value is null. Everywhere that a value has a type that isn’t an -`Option`, you *can* safely assume that the value isn’t null. This was a -deliberate design decision for Rust to limit null’s pervasiveness and increase -the safety of Rust code. +Eliminating the risk of incorrectly assuming a not-null value helps you be more +confident in your code. In order to have a value that can possibly be null, you +must explicitly opt in by making the type of that value `Option`. Then, when +you use that value, you are required to explicitly handle the case when the +value is null. Everywhere that a value has a type that isn’t an `Option`, +you *can* safely assume that the value isn’t null. This was a deliberate design +decision for Rust to limit null’s pervasiveness and increase the safety of Rust +code. So how do you get the `T` value out of a `Some` variant when you have a value of type `Option` so that you can use that value? The `Option` enum has a large number of methods that are useful in a variety of situations; you can -check them out in its documentation. Becoming familiar with the methods on -`Option` will be extremely useful in your journey with Rust. +check them out in its documentation. Becoming familiar +with the methods on `Option` will be extremely useful in your journey with +Rust. In general, in order to use an `Option` value, you want to have code that will handle each variant. You want some code that will run only when you have a `Some(T)` value, and this code is allowed to use the inner `T`. You want some other code to run only if you have a `None` value, and that code doesn’t have a `T` value available. The `match` expression is a control flow construct that -does just this when used with enums: it will run different code depending on +does just this when used with enums: It will run different code depending on which variant of the enum it has, and that code can use the data inside the matching value. + + + + ## The match Control Flow Construct Rust has an extremely powerful control flow construct called `match` that allows you to compare a value against a series of patterns and then execute code based on which pattern matches. Patterns can be made up of literal values, -variable names, wildcards, and many other things; Chapter 18 covers all the -different kinds of patterns and what they do. The power of `match` comes from -the expressiveness of the patterns and the fact that the compiler confirms that -all possible cases are handled. +variable names, wildcards, and many other things; Chapter +19 covers all the different kinds of patterns +and what they do. The power of `match` comes from the expressiveness of the +patterns and the fact that the compiler confirms that all possible cases are +handled. -Think of a `match` expression as being like a coin-sorting machine: coins slide +Think of a `match` expression as being like a coin-sorting machine: Coins slide down a track with variously sized holes along it, and each coin falls through the first hole it encounters that it fits into. In the same way, values go through each pattern in a `match`, and at the first pattern the value “fits,” @@ -423,8 +446,9 @@ function that takes an unknown US coin and, in a similar way as the counting machine, determines which coin it is and returns its value in cents, as shown in Listing 6-3. + ``` -1 enum Coin { +enum Coin { Penny, Nickel, Dime, @@ -432,8 +456,8 @@ in Listing 6-3. } fn value_in_cents(coin: Coin) -> u8 { - 2 match coin { - 3 Coin::Penny => 1, + match coin { + Coin::Penny => 1, Coin::Nickel => 5, Coin::Dime => 10, Coin::Quarter => 25, @@ -441,26 +465,25 @@ fn value_in_cents(coin: Coin) -> u8 { } ``` -Listing 6-3: An enum and a `match` expression that has the variants of the enum -as its patterns +Listing 6-3: An enum and a `match` expression that has the variants of the enum as its patterns -Let’s break down the `match` in the `value_in_cents` function. First we list +Let’s break down the `match` in the `value_in_cents` function. First, we list the `match` keyword followed by an expression, which in this case is the value -`coin` [2]. This seems very similar to an expression used with `if`, but -there’s a big difference: with `if`, the expression needs to return a Boolean -value, but here it can return any type. The type of `coin` in this example is -the `Coin` enum that we defined at [1]. +`coin`. This seems very similar to a conditional expression used with `if`, but +there’s a big difference: With `if`, the condition needs to evaluate to a +Boolean value, but here it can be any type. The type of `coin` in this example +is the `Coin` enum that we defined on the first line. Next are the `match` arms. An arm has two parts: a pattern and some code. The first arm here has a pattern that is the value `Coin::Penny` and then the `=>` -operator that separates the pattern and the code to run [3]. The code in this -case is just the value `1`. Each arm is separated from the next with a comma. +operator that separates the pattern and the code to run. The code in this case +is just the value `1`. Each arm is separated from the next with a comma. When the `match` expression executes, it compares the resultant value against the pattern of each arm, in order. If a pattern matches the value, the code associated with that pattern is executed. If that pattern doesn’t match the value, execution continues to the next arm, much as in a coin-sorting machine. -We can have as many arms as we need: in Listing 6-3, our `match` has four arms. +We can have as many arms as we need: In Listing 6-3, our `match` has four arms. The code associated with each arm is an expression, and the resultant value of the expression in the matching arm is the value that gets returned for the @@ -470,8 +493,8 @@ We don’t typically use curly brackets if the match arm code is short, as it is in Listing 6-3 where each arm just returns a value. If you want to run multiple lines of code in a match arm, you must use curly brackets, and the comma following the arm is then optional. For example, the following code prints -“Lucky penny!” every time the method is called with a `Coin::Penny`, but still -returns the last value of the block, `1`: +“Lucky penny!” every time the method is called with a `Coin::Penny`, but it +still returns the last value of the block, `1`: ``` fn value_in_cents(coin: Coin) -> u8 { @@ -500,12 +523,13 @@ designs, so only quarters have this extra value. We can add this information to our `enum` by changing the `Quarter` variant to include a `UsState` value stored inside it, which we’ve done in Listing 6-4. + ``` #[derive(Debug)] // so we can inspect the state in a minute enum UsState { Alabama, Alaska, - --snip-- + // --snip-- } enum Coin { @@ -516,8 +540,7 @@ enum Coin { } ``` -Listing 6-4: A `Coin` enum in which the `Quarter` variant also holds a -`UsState` value +Listing 6-4: A `Coin` enum in which the `Quarter` variant also holds a `UsState` value Let’s imagine that a friend is trying to collect all 50 state quarters. While we sort our loose change by coin type, we’ll also call out the name of the @@ -527,7 +550,7 @@ they can add it to their collection. In the match expression for this code, we add a variable called `state` to the pattern that matches values of the variant `Coin::Quarter`. When a `Coin::Quarter` matches, the `state` variable will bind to the value of that -quarter’s state. Then we can use `state` in the code for that arm, like so: +quarter’s state. Then, we can use `state` in the code for that arm, like so: ``` fn value_in_cents(coin: Coin) -> u8 { @@ -536,7 +559,7 @@ fn value_in_cents(coin: Coin) -> u8 { Coin::Nickel => 5, Coin::Dime => 10, Coin::Quarter(state) => { - println!("State quarter from {:?}!", state); + println!("State quarter from {state:?}!"); 25 } } @@ -550,7 +573,11 @@ that point, the binding for `state` will be the value `UsState::Alaska`. We can then use that binding in the `println!` expression, thus getting the inner state value out of the `Coin` enum variant for `Quarter`. -### Matching with Option + + + + +### The Option match Pattern In the previous section, we wanted to get the inner `T` value out of the `Some` case when using `Option`; we can also handle `Option` using `match`, as @@ -566,43 +593,48 @@ operations. This function is very easy to write, thanks to `match`, and will look like Listing 6-5. + ``` -fn plus_one(x: Option) -> Option { - match x { - 1 None => None, - 2 Some(i) => Some(i + 1), + fn plus_one(x: Option) -> Option { + match x { + None => None, + Some(i) => Some(i + 1), + } } -} -let five = Some(5); -let six = plus_one(five); 3 -let none = plus_one(None); 4 + let five = Some(5); + let six = plus_one(five); + let none = plus_one(None); ``` Listing 6-5: A function that uses a `match` expression on an `Option` Let’s examine the first execution of `plus_one` in more detail. When we call -`plus_one(five)` [3], the variable `x` in the body of `plus_one` will have the +`plus_one(five)`, the variable `x` in the body of `plus_one` will have the value `Some(5)`. We then compare that against each match arm: ``` -None => None, + None => None, ``` -The `Some(5)` value doesn’t match the pattern `None` [1], so we continue to the +The `Some(5)` value doesn’t match the pattern `None`, so we continue to the next arm: ``` -Some(i) => Some(i + 1), + Some(i) => Some(i + 1), ``` -Does `Some(5)` match `Some(i)` [2]? Why yes, it does! We have the same variant. -The `i` binds to the value contained in `Some`, so `i` takes the value `5`. The -code in the match arm is then executed, so we add 1 to the value of `i` and -create a new `Some` value with our total `6` inside. +Does `Some(5)` match `Some(i)`? It does! We have the same variant. The `i` +binds to the value contained in `Some`, so `i` takes the value `5`. The code in +the match arm is then executed, so we add 1 to the value of `i` and create a +new `Some` value with our total `6` inside. Now let’s consider the second call of `plus_one` in Listing 6-5, where `x` is -`None` [4]. We enter the `match` and compare to the first arm [1]. +`None`. We enter the `match` and compare to the first arm: + +``` + None => None, +``` It matches! There’s no value to add to, so the program stops and returns the `None` value on the right side of `=>`. Because the first arm matched, no other @@ -616,16 +648,16 @@ consistently a user favorite. ### Matches Are Exhaustive -There’s one other aspect of `match` we need to discuss: the arms’ patterns must +There’s one other aspect of `match` we need to discuss: The arms’ patterns must cover all possibilities. Consider this version of our `plus_one` function, which has a bug and won’t compile: ``` -fn plus_one(x: Option) -> Option { - match x { - Some(i) => Some(i + 1), + fn plus_one(x: Option) -> Option { + match x { + Some(i) => Some(i + 1), + } } -} ``` We didn’t handle the `None` case, so this code will cause a bug. Luckily, it’s @@ -633,36 +665,43 @@ a bug Rust knows how to catch. If we try to compile this code, we’ll get this error: ``` +$ cargo run + Compiling enums v0.1.0 (file:///projects/enums) error[E0004]: non-exhaustive patterns: `None` not covered --> src/main.rs:3:15 | 3 | match x { | ^ pattern `None` not covered | - note: `Option` defined here - = note: the matched value is of type `Option` -help: ensure that all possible cases are being handled by adding -a match arm with a wildcard pattern or an explicit pattern as -shown - | -4 ~ Some(i) => Some(i + 1), -5 ~ None => todo!(), - | -``` - -Rust knows that we didn’t cover every possible case, and even knows which -pattern we forgot! Matches in Rust are *exhaustive*: we must exhaust every last +note: `Option` defined here + --> /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/option.rs:572:1 + ::: /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/core/src/option.rs:576:5 + | + = note: not covered + = note: the matched value is of type `Option` +help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown + | +4 ~ Some(i) => Some(i + 1), +5 ~ None => todo!(), + | + +For more information about this error, try `rustc --explain E0004`. +error: could not compile `enums` (bin "enums") due to 1 previous error +``` + +Rust knows that we didn’t cover every possible case and even knows which +pattern we forgot! Matches in Rust are *exhaustive*: We must exhaust every last possibility in order for the code to be valid. Especially in the case of `Option`, when Rust prevents us from forgetting to explicitly handle the `None` case, it protects us from assuming that we have a value when we might have null, thus making the billion-dollar mistake discussed earlier impossible. -### Catch-all Patterns and the _ Placeholder +### Catch-All Patterns and the \_ Placeholder Using enums, we can also take special actions for a few particular values, but for all other values take one default action. Imagine we’re implementing a game -where, if you roll a 3 on a dice roll, your player doesn’t move, but instead -gets a new fancy hat. If you roll a 7, your player loses a fancy hat. For all +where, if you roll a 3 on a dice roll, your player doesn’t move but instead +gets a fancy new hat. If you roll a 7, your player loses a fancy hat. For all other values, your player moves that number of spaces on the game board. Here’s a `match` that implements that logic, with the result of the dice roll hardcoded rather than a random value, and all other logic represented by @@ -670,50 +709,51 @@ functions without bodies because actually implementing them is out of scope for this example: ``` -let dice_roll = 9; -match dice_roll { - 3 => add_fancy_hat(), - 7 => remove_fancy_hat(), - 1 other => move_player(other), -} + let dice_roll = 9; + match dice_roll { + 3 => add_fancy_hat(), + 7 => remove_fancy_hat(), + other => move_player(other), + } -fn add_fancy_hat() {} -fn remove_fancy_hat() {} -fn move_player(num_spaces: u8) {} + fn add_fancy_hat() {} + fn remove_fancy_hat() {} + fn move_player(num_spaces: u8) {} ``` For the first two arms, the patterns are the literal values `3` and `7`. For the last arm that covers every other possible value, the pattern is the -variable we’ve chosen to name `other` [1]. The code that runs for the `other` -arm uses the variable by passing it to the `move_player` function. +variable we’ve chosen to name `other`. The code that runs for the `other` arm +uses the variable by passing it to the `move_player` function. This code compiles, even though we haven’t listed all the possible values a `u8` can have, because the last pattern will match all values not specifically listed. This catch-all pattern meets the requirement that `match` must be exhaustive. Note that we have to put the catch-all arm last because the -patterns are evaluated in order. If we put the catch-all arm earlier, the other -arms would never run, so Rust will warn us if we add arms after a catch-all! +patterns are evaluated in order. If we had put the catch-all arm earlier, the +other arms would never run, so Rust will warn us if we add arms after a +catch-all! Rust also has a pattern we can use when we want a catch-all but don’t want to *use* the value in the catch-all pattern: `_` is a special pattern that matches any value and does not bind to that value. This tells Rust we aren’t going to use the value, so Rust won’t warn us about an unused variable. -Let’s change the rules of the game: now, if you roll anything other than a 3 or +Let’s change the rules of the game: Now, if you roll anything other than a 3 or a 7, you must roll again. We no longer need to use the catch-all value, so we can change our code to use `_` instead of the variable named `other`: ``` -let dice_roll = 9; -match dice_roll { - 3 => add_fancy_hat(), - 7 => remove_fancy_hat(), - _ => reroll(), -} + let dice_roll = 9; + match dice_roll { + 3 => add_fancy_hat(), + 7 => remove_fancy_hat(), + _ => reroll(), + } -fn add_fancy_hat() {} -fn remove_fancy_hat() {} -fn reroll() {} + fn add_fancy_hat() {} + fn remove_fancy_hat() {} + fn reroll() {} ``` This example also meets the exhaustiveness requirement because we’re explicitly @@ -722,29 +762,30 @@ ignoring all other values in the last arm; we haven’t forgotten anything. Finally, we’ll change the rules of the game one more time so that nothing else happens on your turn if you roll anything other than a 3 or a 7. We can express that by using the unit value (the empty tuple type we mentioned in “The Tuple -Type” on page XX) as the code that goes with the `_` arm: +Type” section) as the code that goes with the `_` arm: ``` -let dice_roll = 9; -match dice_roll { - 3 => add_fancy_hat(), - 7 => remove_fancy_hat(), - _ => (), -} + let dice_roll = 9; + match dice_roll { + 3 => add_fancy_hat(), + 7 => remove_fancy_hat(), + _ => (), + } -fn add_fancy_hat() {} -fn remove_fancy_hat() {} + fn add_fancy_hat() {} + fn remove_fancy_hat() {} ``` Here, we’re telling Rust explicitly that we aren’t going to use any other value that doesn’t match a pattern in an earlier arm, and we don’t want to run any code in this case. -There’s more about patterns and matching that we’ll cover in Chapter 18. For -now, we’re going to move on to the `if let` syntax, which can be useful in -situations where the `match` expression is a bit wordy. +There’s more about patterns and matching that we’ll cover in Chapter +19. For now, we’re going to move on to the +`if let` syntax, which can be useful in situations where the `match` expression +is a bit wordy. -## Concise Control Flow with if let +## Concise Control Flow with if let and let else The `if let` syntax lets you combine `if` and `let` into a less verbose way to handle values that match one pattern while ignoring the rest. Consider the @@ -752,31 +793,30 @@ program in Listing 6-6 that matches on an `Option` value in the `config_max` variable but only wants to execute code if the value is the `Some` variant. + ``` -let config_max = Some(3u8); -match config_max { - Some(max) => println!("The maximum is configured to be {max}"), - _ => (), -} + let config_max = Some(3u8); + match config_max { + Some(max) => println!("The maximum is configured to be {max}"), + _ => (), + } ``` -Listing 6-6: A `match` that only cares about executing code when the value is -`Some` +Listing 6-6: A `match` that only cares about executing code when the value is `Some` If the value is `Some`, we print out the value in the `Some` variant by binding the value to the variable `max` in the pattern. We don’t want to do anything -with the `None` value. To satisfy the `match` expression, we have to add `_ => -()` after processing just one variant, which is annoying boilerplate code to +with the `None` value. To satisfy the `match` expression, we have to add `_ => ()` after processing just one variant, which is annoying boilerplate code to add. Instead, we could write this in a shorter way using `if let`. The following code behaves the same as the `match` in Listing 6-6: ``` -let config_max = Some(3u8); -if let Some(max) = config_max { - println!("The maximum is configured to be {max}"); -} + let config_max = Some(3u8); + if let Some(max) = config_max { + println!("The maximum is configured to be {max}"); + } ``` The syntax `if let` takes a pattern and an expression separated by an equal @@ -784,14 +824,13 @@ sign. It works the same way as a `match`, where the expression is given to the `match` and the pattern is its first arm. In this case, the pattern is `Some(max)`, and the `max` binds to the value inside the `Some`. We can then use `max` in the body of the `if let` block in the same way we used `max` in -the corresponding `match` arm. The code in the `if let` block isn’t run if the -value doesn’t match the pattern. +the corresponding `match` arm. The code in the `if let` block only runs if the +value matches the pattern. Using `if let` means less typing, less indentation, and less boilerplate code. -However, you lose the exhaustive checking that `match` enforces. Choosing -between `match` and `if let` depends on what you’re doing in your particular -situation and whether gaining conciseness is an appropriate trade-off for -losing exhaustive checking. +However, you lose the exhaustive checking `match` enforces that ensures that +you aren’t forgetting to handle any cases. Choosing between `match` and `if let` depends on what you’re doing in your particular situation and whether +gaining conciseness is an appropriate trade-off for losing exhaustive checking. In other words, you can think of `if let` as syntax sugar for a `match` that runs code when the value matches one pattern and then ignores all other values. @@ -805,26 +844,125 @@ announcing the state of the quarters, we could do that with a `match` expression, like this: ``` -let mut count = 0; -match coin { - Coin::Quarter(state) => println!("State quarter from {:?}!", state), - _ => count += 1, -} + let mut count = 0; + match coin { + Coin::Quarter(state) => println!("State quarter from {state:?}!"), + _ => count += 1, + } ``` Or we could use an `if let` and `else` expression, like this: ``` -let mut count = 0; -if let Coin::Quarter(state) = coin { - println!("State quarter from {:?}!", state); -} else { - count += 1; + let mut count = 0; + if let Coin::Quarter(state) = coin { + println!("State quarter from {state:?}!"); + } else { + count += 1; + } +``` + +## Staying on the “Happy Path” with let...else + +The common pattern is to perform some computation when a value is present and +return a default value otherwise. Continuing with our example of coins with a +`UsState` value, if we wanted to say something funny depending on how old the +state on the quarter was, we might introduce a method on `UsState` to check the +age of a state, like so: + +``` +impl UsState { + fn existed_in(&self, year: u16) -> bool { + match self { + UsState::Alabama => year >= 1819, + UsState::Alaska => year >= 1959, + // -- snip -- + } + } +} +``` + +Then, we might use `if let` to match on the type of coin, introducing a `state` +variable within the body of the condition, as in Listing 6-7. + + +``` +fn describe_state_quarter(coin: Coin) -> Option { + if let Coin::Quarter(state) = coin { + if state.existed_in(1900) { + Some(format!("{state:?} is pretty old, for America!")) + } else { + Some(format!("{state:?} is relatively new.")) + } + } else { + None + } } ``` +Listing 6-7: Checking whether a state existed in 1900 by using conditionals nested inside an `if let` + +That gets the job done, but it has pushed the work into the body of the `if let` statement, and if the work to be done is more complicated, it might be +hard to follow exactly how the top-level branches relate. We could also take +advantage of the fact that expressions produce a value either to produce the +`state` from the `if let` or to return early, as in Listing 6-8. (You could do +something similar with a `match`, too.) + + +``` +fn describe_state_quarter(coin: Coin) -> Option { + let state = if let Coin::Quarter(state) = coin { + state + } else { + return None; + }; + + if state.existed_in(1900) { + Some(format!("{state:?} is pretty old, for America!")) + } else { + Some(format!("{state:?} is relatively new.")) + } +} +``` + +Listing 6-8: Using `if let` to produce a value or return early + +This is a bit annoying to follow in its own way, though! One branch of the `if let` produces a value, and the other one returns from the function entirely. + +To make this common pattern nicer to express, Rust has `let...else`. The +`let...else` syntax takes a pattern on the left side and an expression on the +right, very similar to `if let`, but it does not have an `if` branch, only an +`else` branch. If the pattern matches, it will bind the value from the pattern +in the outer scope. If the pattern does *not* match, the program will flow into +the `else` arm, which must return from the function. + +In Listing 6-9, you can see how Listing 6-8 looks when using `let...else` in +place of `if let`. + + +``` +fn describe_state_quarter(coin: Coin) -> Option { + let Coin::Quarter(state) = coin else { + return None; + }; + + if state.existed_in(1900) { + Some(format!("{state:?} is pretty old, for America!")) + } else { + Some(format!("{state:?} is relatively new.")) + } +} +``` + +Listing 6-9: Using `let...else` to clarify the flow through the function + +Notice that it stays on the “happy path” in the main body of the function this +way, without having significantly different control flow for two branches the +way the `if let` did. + If you have a situation in which your program has logic that is too verbose to -express using a `match`, remember that `if let` is in your Rust toolbox as well. +express using a `match`, remember that `if let` and `let...else` are in your +Rust toolbox as well. ## Summary @@ -835,11 +973,10 @@ data inside them, you can use `match` or `if let` to extract and use those values, depending on how many cases you need to handle. Your Rust programs can now express concepts in your domain using structs and -enums. Creating custom types to use in your API ensures type safety: the +enums. Creating custom types to use in your API ensures type safety: The compiler will make certain your functions only get values of the type each function expects. In order to provide a well-organized API to your users that is straightforward to use and only exposes exactly what your users will need, let’s now turn to Rust’s modules. - diff --git a/nostarch/chapter07.md b/nostarch/chapter07.md index 8b2dce7776..f5ee14212b 100644 --- a/nostarch/chapter07.md +++ b/nostarch/chapter07.md @@ -6,7 +6,11 @@ directory, so all fixes need to be made in `/src/`. [TOC] -# Managing Growing Projects with Packages, Crates, and Modules + + + + +# Packages, Crates, and Modules As you write large programs, organizing your code will become increasingly important. By grouping related functionality and separating code with distinct @@ -19,18 +23,18 @@ and then multiple files. A package can contain multiple binary crates and optionally one library crate. As a package grows, you can extract parts into separate crates that become external dependencies. This chapter covers all these techniques. For very large projects comprising a set of interrelated -packages that evolve together, Cargo provides *workspaces*, which we’ll cover -in “Cargo Workspaces” on page XX. +packages that evolve together, Cargo provides workspaces, which we’ll cover in +“Cargo Workspaces” in Chapter 14. We’ll also discuss encapsulating implementation details, which lets you reuse -code at a higher level: once you’ve implemented an operation, other code can +code at a higher level: Once you’ve implemented an operation, other code can call your code via its public interface without having to know how the implementation works. The way you write code defines which parts are public for other code to use and which parts are private implementation details that you reserve the right to change. This is another way to limit the amount of detail you have to keep in your head. -A related concept is scope: the nested context in which code is written has a +A related concept is scope: The nested context in which code is written has a set of names that are defined as “in scope.” When reading, writing, and compiling code, programmers and compilers need to know whether a particular name at a particular spot refers to a variable, function, struct, enum, module, @@ -43,11 +47,11 @@ organization, including which details are exposed, which details are private, and what names are in each scope in your programs. These features, sometimes collectively referred to as the *module system*, include: -* **Packages **: A Cargo feature that lets you build, test, and share crates +* **Packages**: A Cargo feature that lets you build, test, and share crates * **Crates**: A tree of modules that produces a library or executable * **Modules and use**: Let you control the organization, scope, and privacy of -paths -* **Paths **: A way of naming an item, such as a struct, function, or module + paths +* **Paths**: A way of naming an item, such as a struct, function, or module In this chapter, we’ll cover all these features, discuss how they interact, and explain how to use them to manage scope. By the end, you should have a solid @@ -59,10 +63,9 @@ The first parts of the module system we’ll cover are packages and crates. A *crate* is the smallest amount of code that the Rust compiler considers at a time. Even if you run `rustc` rather than `cargo` and pass a single source code -file (as we did all the way back in “Writing and Running a Rust Program” on -page XX), the compiler considers that file to be a crate. Crates can contain -modules, and the modules may be defined in other files that get compiled with -the crate, as we’ll see in the coming sections. +file (as we did all the way back in “Rust Program Basics” in Chapter 1), the compiler considers that file to be a crate. Crates can +contain modules, and the modules may be defined in other files that get +compiled with the crate, as we’ll see in the coming sections. A crate can come in one of two forms: a binary crate or a library crate. *Binary crates* are programs you can compile to an executable that you can run, @@ -72,14 +75,14 @@ created so far have been binary crates. *Library crates* don’t have a `main` function, and they don’t compile to an executable. Instead, they define functionality intended to be shared with -multiple projects. For example, the `rand` crate we used in Chapter 2 provides -functionality that generates random numbers. Most of the time when Rustaceans -say “crate,” they mean library crate, and they use “crate” interchangeably with -the general programming concept of a “library.” +multiple projects. For example, the `rand` crate we used in Chapter +2 provides functionality that generates random numbers. +Most of the time when Rustaceans say “crate,” they mean library crate, and they +use “crate” interchangeably with the general programming concept of a “library.” The *crate root* is a source file that the Rust compiler starts from and makes -up the root module of your crate (we’ll explain modules in depth in “Defining -Modules to Control Scope and Privacy” on page XX). +up the root module of your crate (we’ll explain modules in depth in “Control +Scope and Privacy with Modules”). A *package* is a bundle of one or more crates that provides a set of functionality. A package contains a *Cargo.toml* file that describes how to @@ -89,12 +92,11 @@ package also contains a library crate that the binary crate depends on. Other projects can depend on the Cargo library crate to use the same logic the Cargo command line tool uses. -A crate can come in one of two forms: a binary crate or a library crate. A -package can contain as many binary crates as you like, but at most only one +A package can contain as many binary crates as you like, but at most only one library crate. A package must contain at least one crate, whether that’s a library or binary crate. -Let’s walk through what happens when we create a package. First we enter the +Let’s walk through what happens when we create a package. First, we enter the command `cargo new my-project`: ``` @@ -108,115 +110,125 @@ main.rs ``` After we run `cargo new my-project`, we use `ls` to see what Cargo creates. In -the project directory, there’s a *Cargo.toml* file, giving us a package. +the *my-project* directory, there’s a *Cargo.toml* file, giving us a package. There’s also a *src* directory that contains *main.rs*. Open *Cargo.toml* in -your text editor, and note there’s no mention of *src/main.rs*. Cargo follows a -convention that *src/main.rs* is the crate root of a binary crate with the same -name as the package. Likewise, Cargo knows that if the package directory -contains *src/lib.rs*, the package contains a library crate with the same name -as the package, and *src/lib.rs* is its crate root. Cargo passes the crate root -files to `rustc` to build the library or binary. +your text editor and note that there’s no mention of *src/main.rs*. Cargo +follows a convention that *src/main.rs* is the crate root of a binary crate +with the same name as the package. Likewise, Cargo knows that if the package +directory contains *src/lib.rs*, the package contains a library crate with the +same name as the package, and *src/lib.rs* is its crate root. Cargo passes the +crate root files to `rustc` to build the library or binary. Here, we have a package that only contains *src/main.rs*, meaning it only contains a binary crate named `my-project`. If a package contains *src/main.rs* and *src/lib.rs*, it has two crates: a binary and a library, both with the same name as the package. A package can have multiple binary crates by placing files -in the *src/bin* directory: each file will be a separate binary crate. +in the *src/bin* directory: Each file will be a separate binary crate. + + + + + +## Control Scope and Privacy with Modules + +In this section, we’ll talk about modules and other parts of the module system, +namely *paths*, which allow you to name items; the `use` keyword that brings a +path into scope; and the `pub` keyword to make items public. We’ll also discuss +the `as` keyword, external packages, and the glob operator. -> ### Modules Cheat Sheet -> -> Before we get to the details of modules and paths, here we provide a quick +### Modules Cheat Sheet + +Before we get to the details of modules and paths, here we provide a quick reference on how modules, paths, the `use` keyword, and the `pub` keyword work in the compiler, and how most developers organize their code. We’ll be going through examples of each of these rules throughout this chapter, but this is a great place to refer to as a reminder of how modules work. -> -> * **Start from the crate root**: When compiling a crate, the compiler first -looks in the crate root file (usually *src/lib.rs* for a library crate or -*src/main.rs* for a binary crate) for code to compile. -> * **Declaring modules**: In the crate root file, you can declare new modules; -say you declare a “garden” module with `mod garden;`. The compiler will look -for the module’s code in these places: -> -> * Inline, within curly brackets that replace the semicolon following `mod -garden` -> * In the file *src/garden.rs.* -> * In the file *src/garden/mod.rs* -> * **Declaring submodules**: In any file other than the crate root, you can -declare submodules. For example, you might declare `mod vegetables;` in -*src/garden.rs*. The compiler will look for the submodule’s code within the -directory named for the parent module in these places: -> -> * Inline, directly following `mod vegetables`, within curly brackets instead -of the semicolon -> * In the file *src/garden/vegetables.rs* -> * In the file *src/garden/vegetables/mod.rs* -> * **Paths to code in modules**: Once a module is part of your crate, you can -refer to code in that module from anywhere else in that same crate, as long as -the privacy rules allow, using the path to the code. For example, an -`Asparagus` type in the garden vegetables module would be found at -`crate::garden::vegetables::Asparagus`. -> * **Private vs. public**: Code within a module is private from its parent -modules by default. To make a module public, declare it with `pub mod` instead -of `mod`. To make items within a public module public as well, use `pub` before -their declarations. -> * **The use keyword**: Within a scope, the `use` keyword creates shortcuts to -items to reduce repetition of long paths. In any scope that can refer to -`crate::garden::vegetables::Asparagus`, you can create a shortcut with `use -crate::garden::vegetables::Asparagus;` and from then on you only need to write -`Asparagus` to make use of that type in the scope. -> -> Here, we create a binary crate named `backyard` that illustrates these rules. -The crate’s directory, also named `backyard`, contains these files and + +* **Start from the crate root**: When compiling a crate, the compiler first + looks in the crate root file (usually *src/lib.rs* for a library crate and + *src/main.rs* for a binary crate) for code to compile. +* **Declaring modules**: In the crate root file, you can declare new modules; + say you declare a “garden” module with `mod garden;`. The compiler will look + for the module’s code in these places: + * Inline, within curly brackets that replace the semicolon following `mod garden` + * In the file *src/garden.rs* + * In the file *src/garden/mod.rs* +* **Declaring submodules**: In any file other than the crate root, you can + declare submodules. For example, you might declare `mod vegetables;` in + *src/garden.rs*. The compiler will look for the submodule’s code within the + directory named for the parent module in these places: + * Inline, directly following `mod vegetables`, within curly brackets instead + of the semicolon + * In the file *src/garden/vegetables.rs* + * In the file *src/garden/vegetables/mod.rs* +* **Paths to code in modules**: Once a module is part of your crate, you can + refer to code in that module from anywhere else in that same crate, as long + as the privacy rules allow, using the path to the code. For example, an + `Asparagus` type in the garden vegetables module would be found at + `crate::garden::vegetables::Asparagus`. +* **Private vs. public**: Code within a module is private from its parent + modules by default. To make a module public, declare it with `pub mod` + instead of `mod`. To make items within a public module public as well, use + `pub` before their declarations. +* **The `use` keyword**: Within a scope, the `use` keyword creates shortcuts to + items to reduce repetition of long paths. In any scope that can refer to + `crate::garden::vegetables::Asparagus`, you can create a shortcut with `use crate::garden::vegetables::Asparagus;`, and from then on you only need to + write `Asparagus` to make use of that type in the scope. + +Here, we create a binary crate named `backyard` that illustrates these rules. +The crate’s directory, also named *backyard*, contains these files and directories: -> -> ``` -> backyard -> ├── Cargo.lock -> ├── Cargo.toml -> └── src -> ├── garden -> │ └── vegetables.rs -> ├── garden.rs -> └── main.rs -> ``` -> -> The crate root file in this case is *src/main.rs*, and it contains: -> -> ``` -> use crate::garden::vegetables::Asparagus; -> -> pub mod garden; -> -> fn main() { -> let plant = Asparagus {}; -> println!("I'm growing {:?}!", plant); -> } -> ``` -> -> The `pub mod garden;` line tells the compiler to include the code it finds in + +``` +backyard +├── Cargo.lock +├── Cargo.toml +└── src + ├── garden + │   └── vegetables.rs + ├── garden.rs + └── main.rs +``` + +The crate root file in this case is *src/main.rs*, and it contains: + +src/main.rs + +``` +use crate::garden::vegetables::Asparagus; + +pub mod garden; + +fn main() { + let plant = Asparagus {}; + println!("I'm growing {plant:?}!"); +} +``` + + + +The `pub mod garden;` line tells the compiler to include the code it finds in *src/garden.rs*, which is: -> -> ``` -> pub mod vegetables; -> ``` -> -> Here, `pub mod vegetables;` means the code in *src/garden/vegetables.rs* is + +src/garden.rs + +``` +pub mod vegetables; +``` + + + +Here, `pub mod vegetables;` means the code in *src/garden/vegetables.rs* is included too. That code is: -> -> ``` -> #[derive(Debug)] -> pub struct Asparagus {} -> ``` -> -> Now let’s get into the details of these rules and demonstrate them in action! -## Defining Modules to Control Scope and Privacy +``` +#[derive(Debug)] +pub struct Asparagus {} +``` -In this section, we’ll talk about modules and other parts of the module system, -namely *paths*, which allow you to name items; the `use` keyword that brings a -path into scope; and the `pub` keyword to make items public. We’ll also discuss -the `as` keyword, external packages, and the glob operator. +Now let’s get into the details of these rules and demonstrate them in action! + +### Grouping Related Code in Modules *Modules* let us organize code within a crate for readability and easy reuse. Modules also allow us to control the *privacy* of items because code within a @@ -230,20 +242,19 @@ restaurant. We’ll define the signatures of functions but leave their bodies empty to concentrate on the organization of the code rather than the implementation of a restaurant. -In the restaurant industry, some parts of a restaurant are referred to as -*front of house* and others as *back of house*. Front of house is where -customers are; this encompasses where the hosts seat customers, servers take -orders and payment, and bartenders make drinks. Back of house is where the -chefs and cooks work in the kitchen, dishwashers clean up, and managers do -administrative work. +In the restaurant industry, some parts of a restaurant are referred to as front +of house and others as back of house. *Front of house* is where customers are; +this encompasses where the hosts seat customers, servers take orders and +payment, and bartenders make drinks. *Back of house* is where the chefs and +cooks work in the kitchen, dishwashers clean up, and managers do administrative +work. To structure our crate in this way, we can organize its functions into nested -modules. Create a new library named `restaurant` by running `cargo new -restaurant --lib`. Then enter the code in Listing 7-1 into *src/lib.rs* to +modules. Create a new library named `restaurant` by running `cargo new restaurant --lib`. Then, enter the code in Listing 7-1 into *src/lib.rs* to define some modules and function signatures; this code is the front of house section. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -263,15 +274,14 @@ mod front_of_house { } ``` -Listing 7-1: A `front_of_house` module containing other modules that then -contain functions +Listing 7-1: A `front_of_house` module containing other modules that then contain functions We define a module with the `mod` keyword followed by the name of the module (in this case, `front_of_house`). The body of the module then goes inside curly brackets. Inside modules, we can place other modules, as in this case with the modules `hosting` and `serving`. Modules can also hold definitions for other -items, such as structs, enums, constants, traits, and—as in Listing -7-1—functions. +items, such as structs, enums, constants, traits, and as in Listing 7-1, +functions. By using modules, we can group related definitions together and name why they’re related. Programmers using this code can navigate the code based on the @@ -279,13 +289,14 @@ groups rather than having to read through all the definitions, making it easier to find the definitions relevant to them. Programmers adding new functionality to this code would know where to place the code to keep the program organized. -Earlier, we mentioned that *src/main.rs* and *src/lib.rs* are called crate -roots. The reason for their name is that the contents of either of these two +Earlier, we mentioned that *src/main.rs* and *src/lib.rs* are called *crate +roots*\_. The reason for their name is that the contents of either of these two files form a module named `crate` at the root of the crate’s module structure, known as the *module tree*. Listing 7-2 shows the module tree for the structure in Listing 7-1. + ``` crate └── front_of_house @@ -321,17 +332,17 @@ know its path. A path can take two forms: -* An *absolute path* is the full path starting from a crate root; for code from -an external crate, the absolute path begins with the crate name, and for code -from the current crate, it starts with the literal `crate`. +* An *absolute path* is the full path starting from a crate root; for code + from an external crate, the absolute path begins with the crate name, and for + code from the current crate, it starts with the literal `crate`. * A *relative path* starts from the current module and uses `self`, `super`, or -an identifier in the current module. + an identifier in the current module. Both absolute and relative paths are followed by one or more identifiers separated by double colons (`::`). Returning to Listing 7-1, say we want to call the `add_to_waitlist` function. -This is the same as asking: what’s the path of the `add_to_waitlist` function? +This is the same as asking: What’s the path of the `add_to_waitlist` function? Listing 7-3 contains Listing 7-1 with some of the modules and functions removed. We’ll show two ways to call the `add_to_waitlist` function from a new function, @@ -340,10 +351,10 @@ there’s another problem remaining that will prevent this example from compilin as is. We’ll explain why in a bit. The `eat_at_restaurant` function is part of our library crate’s public API, so -we mark it with the `pub` keyword. In “Exposing Paths with the pub Keyword” on -page XX, we’ll go into more detail about `pub`. +we mark it with the `pub` keyword. In the “Exposing Paths with the `pub` +Keyword” section, we’ll go into more detail about `pub`. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -361,15 +372,14 @@ pub fn eat_at_restaurant() { } ``` -Listing 7-3: Calling the `add_to_waitlist` function using absolute and relative -paths +Listing 7-3: Calling the `add_to_waitlist` function using absolute and relative paths The first time we call the `add_to_waitlist` function in `eat_at_restaurant`, we use an absolute path. The `add_to_waitlist` function is defined in the same crate as `eat_at_restaurant`, which means we can use the `crate` keyword to start an absolute path. We then include each of the successive modules until we make our way to `add_to_waitlist`. You can imagine a filesystem with the same -structure: we’d specify the path `/front_of_house/hosting/add_to_waitlist` to +structure: We’d specify the path `/front_of_house/hosting/add_to_waitlist` to run the `add_to_waitlist` program; using the `crate` name to start from the crate root is like using `/` to start from the filesystem root in your shell. @@ -396,6 +406,7 @@ each other. Let’s try to compile Listing 7-3 and find out why it won’t compile yet! The errors we get are shown in Listing 7-4. + ``` $ cargo build Compiling restaurant v0.1.0 (file:///projects/restaurant) @@ -403,7 +414,9 @@ error[E0603]: module `hosting` is private --> src/lib.rs:9:28 | 9 | crate::front_of_house::hosting::add_to_waitlist(); - | ^^^^^^^ private module + | ^^^^^^^ --------------- function `add_to_waitlist` is not publicly re-exported + | | + | private module | note: the module `hosting` is defined here --> src/lib.rs:2:5 @@ -415,13 +428,18 @@ error[E0603]: module `hosting` is private --> src/lib.rs:12:21 | 12 | front_of_house::hosting::add_to_waitlist(); - | ^^^^^^^ private module + | ^^^^^^^ --------------- function `add_to_waitlist` is not publicly re-exported + | | + | private module | note: the module `hosting` is defined here --> src/lib.rs:2:5 | 2 | mod hosting { | ^^^^^^^^^^^ + +For more information about this error, try `rustc --explain E0603`. +error: could not compile `restaurant` (lib) due to 2 previous errors ``` Listing 7-4: Compiler errors from building the code in Listing 7-3 @@ -438,14 +456,14 @@ items in child modules can use the items in their ancestor modules. This is because child modules wrap and hide their implementation details, but the child modules can see the context in which they’re defined. To continue with our metaphor, think of the privacy rules as being like the back office of a -restaurant: what goes on in there is private to restaurant customers, but +restaurant: What goes on in there is private to restaurant customers, but office managers can see and do everything in the restaurant they operate. Rust chose to have the module system function this way so that hiding inner implementation details is the default. That way, you know which parts of the -inner code you can change without breaking outer code. However, Rust does give -you the option to expose inner parts of child modules’ code to outer ancestor -modules by using the `pub` keyword to make an item public. +inner code you can change without breaking the outer code. However, Rust does +give you the option to expose inner parts of child modules’ code to outer +ancestor modules by using the `pub` keyword to make an item public. ### Exposing Paths with the pub Keyword @@ -454,7 +472,7 @@ private. We want the `eat_at_restaurant` function in the parent module to have access to the `add_to_waitlist` function in the child module, so we mark the `hosting` module with the `pub` keyword, as shown in Listing 7-5. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -463,34 +481,34 @@ mod front_of_house { } } ---snip-- +// -- snip -- ``` -Listing 7-5: Declaring the `hosting` module as `pub` to use it from -`eat_at_restaurant` +Listing 7-5: Declaring the `hosting` module as `pub` to use it from `eat_at_restaurant` Unfortunately, the code in Listing 7-5 still results in compiler errors, as shown in Listing 7-6. + ``` $ cargo build Compiling restaurant v0.1.0 (file:///projects/restaurant) error[E0603]: function `add_to_waitlist` is private - --> src/lib.rs:9:37 - | -9 | crate::front_of_house::hosting::add_to_waitlist(); - | ^^^^^^^^^^^^^^^ private function - | + --> src/lib.rs:10:37 + | +10 | crate::front_of_house::hosting::add_to_waitlist(); + | ^^^^^^^^^^^^^^^ private function + | note: the function `add_to_waitlist` is defined here - --> src/lib.rs:3:9 - | -3 | fn add_to_waitlist() {} - | ^^^^^^^^^^^^^^^^^^^^ + --> src/lib.rs:3:9 + | +3 | fn add_to_waitlist() {} + | ^^^^^^^^^^^^^^^^^^^^ error[E0603]: function `add_to_waitlist` is private - --> src/lib.rs:12:30 + --> src/lib.rs:13:30 | -12 | front_of_house::hosting::add_to_waitlist(); +13 | front_of_house::hosting::add_to_waitlist(); | ^^^^^^^^^^^^^^^ private function | note: the function `add_to_waitlist` is defined here @@ -498,6 +516,9 @@ note: the function `add_to_waitlist` is defined here | 3 | fn add_to_waitlist() {} | ^^^^^^^^^^^^^^^^^^^^ + +For more information about this error, try `rustc --explain E0603`. +error: could not compile `restaurant` (lib) due to 2 previous errors ``` Listing 7-6: Compiler errors from building the code in Listing 7-5 @@ -518,7 +539,7 @@ modules. Let’s also make the `add_to_waitlist` function public by adding the `pub` keyword before its definition, as in Listing 7-7. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -527,15 +548,14 @@ mod front_of_house { } } ---snip-- +// -- snip -- ``` -Listing 7-7: Adding the `pub` keyword to `mod hosting` and `fn add_to_waitlist` -lets us call the function from `eat_at_restaurant`. +Listing 7-7: Adding the `pub` keyword to `mod hosting` and `fn add_to_waitlist` lets us call the function from `eat_at_restaurant`. Now the code will compile! To see why adding the `pub` keyword lets us use -these paths in `add_to_waitlist` with respect to the privacy rules, let’s look -at the absolute and the relative paths. +these paths in `eat_at_restaurant` with respect to the privacy rules, let’s +look at the absolute and the relative paths. In the absolute path, we start with `crate`, the root of our crate’s module tree. The `front_of_house` module is defined in the crate root. While @@ -544,54 +564,54 @@ defined in the same module as `front_of_house` (that is, `eat_at_restaurant` and `front_of_house` are siblings), we can refer to `front_of_house` from `eat_at_restaurant`. Next is the `hosting` module marked with `pub`. We can access the parent module of `hosting`, so we can access `hosting`. Finally, the -`add_to_waitlist` function is marked with `pub` and we can access its parent +`add_to_waitlist` function is marked with `pub`, and we can access its parent module, so this function call works! In the relative path, the logic is the same as the absolute path except for the -first step: rather than starting from the crate root, the path starts from +first step: Rather than starting from the crate root, the path starts from `front_of_house`. The `front_of_house` module is defined within the same module as `eat_at_restaurant`, so the relative path starting from the module in which `eat_at_restaurant` is defined works. Then, because `hosting` and `add_to_waitlist` are marked with `pub`, the rest of the path works, and this function call is valid! -If you plan on sharing your library crate so other projects can use your code, -your public API is your contract with users of your crate that determines how -they can interact with your code. There are many considerations around managing -changes to your public API to make it easier for people to depend on your -crate. These considerations are beyond the scope of this book; if you’re -interested in this topic, see the Rust API Guidelines at -*https://rust-lang.github.io/api-guidelines*. +If you plan to share your library crate so that other projects can use your +code, your public API is your contract with users of your crate that determines +how they can interact with your code. There are many considerations around +managing changes to your public API to make it easier for people to depend on +your crate. These considerations are beyond the scope of this book; if you’re +interested in this topic, see the Rust API Guidelines at *https://rust-lang.github.io/api-guidelines/*. -> ### Best Practices for Packages with a Binary and a Library -> +> #### Best Practices for Packages with a Binary and a Library +> > We mentioned that a package can contain both a *src/main.rs* binary crate -root as well as a *src/lib.rs* library crate root, and both crates will have -the package name by default. Typically, packages with this pattern of -containing both a library and a binary crate will have just enough code in the -binary crate to start an executable that calls code with the library crate. -This lets other projects benefit from the most functionality that the package -provides because the library crate’s code can be shared. -> +> root as well as a *src/lib.rs* library crate root, and both crates will have +> the package name by default. Typically, packages with this pattern of +> containing both a library and a binary crate will have just enough code in the +> binary crate to start an executable that calls code defined in the library +> crate. This lets other projects benefit from the most functionality that the +> package provides because the library crate’s code can be shared. +> > The module tree should be defined in *src/lib.rs*. Then, any public items can -be used in the binary crate by starting paths with the name of the package. The -binary crate becomes a user of the library crate just like a completely -external crate would use the library crate: it can only use the public API. -This helps you design a good API; not only are you the author, you’re also a -client! -> -> In Chapter 12, we’ll demonstrate this organizational practice with a command -line program that will contain both a binary crate and a library crate. +> be used in the binary crate by starting paths with the name of the package. +> The binary crate becomes a user of the library crate just like a completely +> external crate would use the library crate: It can only use the public API. +> This helps you design a good API; not only are you the author, but you’re +> also a client! +> +> In Chapter 12, we’ll demonstrate this organizational +> practice with a command line program that will contain both a binary crate +> and a library crate. ### Starting Relative Paths with super We can construct relative paths that begin in the parent module, rather than the current module or the crate root, by using `super` at the start of the -path. This is like starting a filesystem path with the `..` syntax. Using -`super` allows us to reference an item that we know is in the parent module, -which can make rearranging the module tree easier when the module is closely -related to the parent but the parent might be moved elsewhere in the module -tree someday. +path. This is like starting a filesystem path with the `..` syntax that means +to go to the parent directory. Using `super` allows us to reference an item +that we know is in the parent module, which can make rearranging the module +tree easier when the module is closely related to the parent but the parent +might be moved elsewhere in the module tree someday. Consider the code in Listing 7-8 that models the situation in which a chef fixes an incorrect order and personally brings it out to the customer. The @@ -599,7 +619,7 @@ function `fix_incorrect_order` defined in the `back_of_house` module calls the function `deliver_order` defined in the parent module by specifying the path to `deliver_order`, starting with `super`. -Filename: src/lib.rs +src/lib.rs ``` fn deliver_order() {} @@ -622,8 +642,8 @@ is `crate`, the root. From there, we look for `deliver_order` and find it. Success! We think the `back_of_house` module and the `deliver_order` function are likely to stay in the same relationship to each other and get moved together should we decide to reorganize the crate’s module tree. Therefore, we -used `super` so we’ll have fewer places to update code in the future if this -code gets moved to a different module. +used `super` so that we’ll have fewer places to update code in the future if +this code gets moved to a different module. ### Making Structs and Enums Public @@ -638,7 +658,7 @@ comes with a meal, but the chef decides which fruit accompanies the meal based on what’s in season and in stock. The available fruit changes quickly, so customers can’t choose the fruit or even see which fruit they’ll get. -Filename: src/lib.rs +src/lib.rs ``` mod back_of_house { @@ -658,15 +678,14 @@ mod back_of_house { } pub fn eat_at_restaurant() { - // Order a breakfast in the summer with Rye toast + // Order a breakfast in the summer with Rye toast. let mut meal = back_of_house::Breakfast::summer("Rye"); - // Change our mind about what bread we'd like + // Change our mind about what bread we'd like. meal.toast = String::from("Wheat"); println!("I'd like {} toast please", meal.toast); - // The next line won't compile if we uncomment it; we're not - // allowed to see or modify the seasonal fruit that comes - // with the meal + // The next line won't compile if we uncomment it; we're not allowed + // to see or modify the seasonal fruit that comes with the meal. // meal.seasonal_fruit = String::from("blueberries"); } ``` @@ -683,13 +702,13 @@ Also, note that because `back_of_house::Breakfast` has a private field, the struct needs to provide a public associated function that constructs an instance of `Breakfast` (we’ve named it `summer` here). If `Breakfast` didn’t have such a function, we couldn’t create an instance of `Breakfast` in -`eat_at_restaurant` because we couldn’t set the value of the private +`eat_at_restaurant`, because we couldn’t set the value of the private `seasonal_fruit` field in `eat_at_restaurant`. In contrast, if we make an enum public, all of its variants are then public. We only need the `pub` before the `enum` keyword, as shown in Listing 7-10. -Filename: src/lib.rs +src/lib.rs ``` mod back_of_house { @@ -726,15 +745,15 @@ Having to write out the paths to call functions can feel inconvenient and repetitive. In Listing 7-7, whether we chose the absolute or relative path to the `add_to_waitlist` function, every time we wanted to call `add_to_waitlist` we had to specify `front_of_house` and `hosting` too. Fortunately, there’s a -way to simplify this process: we can create a shortcut to a path with the `use` -keyword once, and then use the shorter name everywhere else in the scope. +way to simplify this process: We can create a shortcut to a path with the `use` +keyword once and then use the shorter name everywhere else in the scope. In Listing 7-11, we bring the `crate::front_of_house::hosting` module into the -scope of the `eat_at_restaurant` function so we only have to specify +scope of the `eat_at_restaurant` function so that we only have to specify `hosting::add_to_waitlist` to call the `add_to_waitlist` function in `eat_at_restaurant`. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -763,7 +782,7 @@ Note that `use` only creates the shortcut for the particular scope in which the child module named `customer`, which is then a different scope than the `use` statement, so the function body won’t compile. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -787,11 +806,18 @@ The compiler error shows that the shortcut no longer applies within the `customer` module: ``` +$ cargo build + Compiling restaurant v0.1.0 (file:///projects/restaurant) error[E0433]: failed to resolve: use of undeclared crate or module `hosting` --> src/lib.rs:11:9 | 11 | hosting::add_to_waitlist(); | ^^^^^^^ use of undeclared crate or module `hosting` + | +help: consider importing this module through its public re-export + | +10 + use crate::hosting; + | warning: unused import: `crate::front_of_house::hosting` --> src/lib.rs:7:5 @@ -800,6 +826,10 @@ warning: unused import: `crate::front_of_house::hosting` | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: `#[warn(unused_imports)]` on by default + +For more information about this error, try `rustc --explain E0433`. +warning: `restaurant` (lib) generated 1 warning +error: could not compile `restaurant` (lib) due to 1 previous error; 1 warning emitted ``` Notice there’s also a warning that the `use` is no longer used in its scope! To @@ -809,12 +839,11 @@ the shortcut in the parent module with `super::hosting` within the child ### Creating Idiomatic use Paths -In Listing 7-11, you might have wondered why we specified `use -crate::front_of_house::hosting` and then called `hosting::add_to_waitlist` in +In Listing 7-11, you might have wondered why we specified `use crate::front_of_house::hosting` and then called `hosting::add_to_waitlist` in `eat_at_restaurant`, rather than specifying the `use` path all the way out to the `add_to_waitlist` function to achieve the same result, as in Listing 7-13. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -830,8 +859,7 @@ pub fn eat_at_restaurant() { } ``` -Listing 7-13: Bringing the `add_to_waitlist` function into scope with `use`, -which is unidiomatic +Listing 7-13: Bringing the `add_to_waitlist` function into scope with `use`, which is unidiomatic Although both Listing 7-11 and Listing 7-13 accomplish the same task, Listing 7-11 is the idiomatic way to bring a function into scope with `use`. Bringing @@ -846,7 +874,7 @@ it’s idiomatic to specify the full path. Listing 7-14 shows the idiomatic way to bring the standard library’s `HashMap` struct into the scope of a binary crate. -Filename: src/main.rs +src/main.rs ``` use std::collections::HashMap; @@ -859,7 +887,7 @@ fn main() { Listing 7-14: Bringing `HashMap` into scope in an idiomatic way -There’s no strong reason behind this idiom: it’s just the convention that has +There’s no strong reason behind this idiom: It’s just the convention that has emerged, and folks have gotten used to reading and writing Rust code this way. The exception to this idiom is if we’re bringing two items with the same name @@ -867,23 +895,22 @@ into scope with `use` statements, because Rust doesn’t allow that. Listing 7-1 shows how to bring two `Result` types into scope that have the same name but different parent modules, and how to refer to them. -Filename: src/lib.rs +src/lib.rs ``` use std::fmt; use std::io; fn function1() -> fmt::Result { - --snip-- + // --snip-- } fn function2() -> io::Result<()> { - --snip-- + // --snip-- } ``` -Listing 7-15: Bringing two types with the same name into the same scope -requires using their parent modules. +Listing 7-15: Bringing two types with the same name into the same scope requires using their parent modules. As you can see, using the parent modules distinguishes the two `Result` types. If instead we specified `use std::fmt::Result` and `use std::io::Result`, we’d @@ -893,22 +920,22 @@ meant when we used `Result`. ### Providing New Names with the as Keyword There’s another solution to the problem of bringing two types of the same name -into the same scope with `use`: after the path, we can specify `as` and a new +into the same scope with `use`: After the path, we can specify `as` and a new local name, or *alias*, for the type. Listing 7-16 shows another way to write the code in Listing 7-15 by renaming one of the two `Result` types using `as`. -Filename: src/lib.rs +src/lib.rs ``` use std::fmt::Result; use std::io::Result as IoResult; fn function1() -> Result { - --snip-- + // --snip-- } fn function2() -> IoResult<()> { - --snip-- + // --snip-- } ``` @@ -921,17 +948,17 @@ considered idiomatic, so the choice is up to you! ### Re-exporting Names with pub use -When we bring a name into scope with the `use` keyword, the name available in -the new scope is private. To enable the code that calls our code to refer to -that name as if it had been defined in that code’s scope, we can combine `pub` -and `use`. This technique is called *re-exporting* because we’re bringing an -item into scope but also making that item available for others to bring into -their scope. +When we bring a name into scope with the `use` keyword, the name is private to +the scope into which we imported it. To enable code outside that scope to refer +to that name as if it had been defined in that scope, we can combine `pub` and +`use`. This technique is called *re-exporting* because we’re bringing an item +into scope but also making that item available for others to bring into their +scope. Listing 7-17 shows the code in Listing 7-11 with `use` in the root module changed to `pub use`. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house { @@ -947,25 +974,23 @@ pub fn eat_at_restaurant() { } ``` -Listing 7-17: Making a name available for any code to use from a new scope with -`pub use` +Listing 7-17: Making a name available for any code to use from a new scope with `pub use` Before this change, external code would have to call the `add_to_waitlist` function by using the path -`restaurant::front_of_house::hosting::add_to_waitlist()`. Now that this `pub -use` has re-exported the `hosting` module from the root module, external code +`restaurant::front_of_house::hosting::add_to_waitlist()`, which also would have +required the `front_of_house` module to be marked as `pub`. Now that this `pub use` has re-exported the `hosting` module from the root module, external code can use the path `restaurant::hosting::add_to_waitlist()` instead. Re-exporting is useful when the internal structure of your code is different from how programmers calling your code would think about the domain. For example, in this restaurant metaphor, the people running the restaurant think about “front of house” and “back of house.” But customers visiting a restaurant -probably won’t think about the parts of the restaurant in those terms. With -`pub use`, we can write our code with one structure but expose a different -structure. Doing so makes our library well organized for programmers working on -the library and programmers calling the library. We’ll look at another example -of `pub use` and how it affects your crate’s documentation in “Exporting a -Convenient Public API with pub use” on page XX. +probably won’t think about the parts of the restaurant in those terms. With `pub use`, we can write our code with one structure but expose a different structure. +Doing so makes our library well organized for programmers working on the library +and programmers calling the library. We’ll look at another example of `pub use` +and how it affects your crate’s documentation in “Exporting a Convenient Public +API” in Chapter 14. ### Using External Packages @@ -973,21 +998,29 @@ In Chapter 2, we programmed a guessing game project that used an external package called `rand` to get random numbers. To use `rand` in our project, we added this line to *Cargo.toml*: -Filename: Cargo.toml + + +Cargo.toml ``` rand = "0.8.5" ``` + + Adding `rand` as a dependency in *Cargo.toml* tells Cargo to download the -`rand` package and any dependencies from *https://crates.io*, and make `rand` -available to our project. +`rand` package and any dependencies from crates.io at *https://crates.io/* and +make `rand` available to our project. Then, to bring `rand` definitions into the scope of our package, we added a `use` line starting with the name of the crate, `rand`, and listed the items we -wanted to bring into scope. Recall that in “Generating a Random Number” on page -XX, we brought the `Rng` trait into scope and called the `rand::thread_rng` -function: +wanted to bring into scope. Recall that in “Generating a Random +Number” in Chapter 2, we brought the `Rng` trait into +scope and called the `rand::thread_rng` function: ``` use rand::Rng; @@ -998,9 +1031,9 @@ fn main() { ``` Members of the Rust community have made many packages available at -*https://crates.io*, and pulling any of them into your package involves these -same steps: listing them in your package’s *Cargo.toml* file and using `use` to -bring items from their crates into scope. +crates.io at *https://crates.io/*, and pulling any of them into your package +involves these same steps: listing them in your package’s *Cargo.toml* file and +using `use` to bring items from their crates into scope. Note that the standard `std` library is also a crate that’s external to our package. Because the standard library is shipped with the Rust language, we @@ -1015,37 +1048,42 @@ use std::collections::HashMap; This is an absolute path starting with `std`, the name of the standard library crate. -### Using Nested Paths to Clean Up Large use Lists + + + + +### Using Nested Paths to Clean Up use Lists If we’re using multiple items defined in the same crate or same module, listing each item on its own line can take up a lot of vertical space in our files. For example, these two `use` statements we had in the guessing game in Listing 2-4 bring items from `std` into scope: -Filename: src/main.rs +src/main.rs ``` ---snip-- +// --snip-- use std::cmp::Ordering; use std::io; ---snip-- +// --snip-- ``` + + Instead, we can use nested paths to bring the same items into scope in one line. We do this by specifying the common part of the path, followed by two colons, and then curly brackets around a list of the parts of the paths that differ, as shown in Listing 7-18. -Filename: src/main.rs +src/main.rs ``` ---snip-- +// --snip-- use std::{cmp::Ordering, io}; ---snip-- +// --snip-- ``` -Listing 7-18: Specifying a nested path to bring multiple items with the same -prefix into scope +Listing 7-18: Specifying a nested path to bring multiple items with the same prefix into scope In bigger programs, bringing many items into scope from the same crate or module using nested paths can reduce the number of separate `use` statements @@ -1056,7 +1094,7 @@ two `use` statements that share a subpath. For example, Listing 7-19 shows two `use` statements: one that brings `std::io` into scope and one that brings `std::io::Write` into scope. -Filename: src/lib.rs +src/lib.rs ``` use std::io; @@ -1069,7 +1107,7 @@ The common part of these two paths is `std::io`, and that’s the complete first path. To merge these two paths into one `use` statement, we can use `self` in the nested path, as shown in Listing 7-20. -Filename: src/lib.rs +src/lib.rs ``` use std::io::{self, Write}; @@ -1079,7 +1117,11 @@ Listing 7-20: Combining the paths in Listing 7-19 into one `use` statement This line brings `std::io` and `std::io::Write` into scope. -### The Glob Operator + + + + +### Importing Items with the Glob Operator If we want to bring *all* public items defined in a path into scope, we can specify that path followed by the `*` glob operator: @@ -1091,12 +1133,17 @@ use std::collections::*; This `use` statement brings all public items defined in `std::collections` into the current scope. Be careful when using the glob operator! Glob can make it harder to tell what names are in scope and where a name used in your program -was defined. - -The glob operator is often used when testing to bring everything under test -into the `tests` module; we’ll talk about that in “How to Write Tests” on page -XX. The glob operator is also sometimes used as part of the prelude pattern: -see the standard library documentation for more information on that pattern. +was defined. Additionally, if the dependency changes its definitions, what +you’ve imported changes as well, which may lead to compiler errors when you +upgrade the dependency if the dependency adds a definition with the same name +as a definition of yours in the same scope, for example. + +The glob operator is often used when testing to bring everything under test into +the `tests` module; we’ll talk about that in “How to Write +Tests” in Chapter 11. The glob operator is also +sometimes used as part of the prelude pattern: See the standard library +documentation for more +information on that pattern. ## Separating Modules into Different Files @@ -1110,13 +1157,13 @@ modules defined in the crate root file. In this case, the crate root file is *src/lib.rs*, but this procedure also works with binary crates whose crate root file is *src/main.rs*. -First we’ll extract the `front_of_house` module to its own file. Remove the +First, we’ll extract the `front_of_house` module to its own file. Remove the code inside the curly brackets for the `front_of_house` module, leaving only the `mod front_of_house;` declaration, so that *src/lib.rs* contains the code shown in Listing 7-21. Note that this won’t compile until we create the *src/front_of_house.rs* file in Listing 7-22. -Filename: src/lib.rs +src/lib.rs ``` mod front_of_house; @@ -1128,15 +1175,14 @@ pub fn eat_at_restaurant() { } ``` -Listing 7-21: Declaring the `front_of_house` module whose body will be in -*src/front_of_house.rs* +Listing 7-21: Declaring the `front_of_house` module whose body will be in *src/front_of_house.rs* Next, place the code that was in the curly brackets into a new file named *src/front_of_house.rs*, as shown in Listing 7-22. The compiler knows to look in this file because it came across the module declaration in the crate root with the name `front_of_house`. -Filename: src/front_of_house.rs +src/front_of_house.rs ``` pub mod hosting { @@ -1144,16 +1190,16 @@ pub mod hosting { } ``` -Listing 7-22: Definitions inside the `front_of_house` module in -*src/front_of_house.rs* +Listing 7-22: Definitions inside the `front_of_house` module in *src/front_of_house.rs* Note that you only need to load a file using a `mod` declaration *once* in your module tree. Once the compiler knows the file is part of the project (and knows where in the module tree the code resides because of where you’ve put the `mod` statement), other files in your project should refer to the loaded file’s code -using a path to where it was declared, as covered in “Paths for Referring to an -Item in the Module Tree” on page XX. In other words, `mod` is *not* an -“include” operation that you may have seen in other programming languages. +using a path to where it was declared, as covered in the “Paths for Referring +to an Item in the Module Tree” section. In other words, +`mod` is *not* an “include” operation that you may have seen in other +programming languages. Next, we’ll extract the `hosting` module to its own file. The process is a bit different because `hosting` is a child module of `front_of_house`, not of the @@ -1163,50 +1209,54 @@ named for its ancestors in the module tree, in this case *src/front_of_house*. To start moving `hosting`, we change *src/front_of_house.rs* to contain only the declaration of the `hosting` module: -Filename: src/front_of_house.rs +src/front_of_house.rs ``` pub mod hosting; ``` -Then we create a *src/front_of_house* directory and a *hosting.rs* file to + + +Then, we create a *src/front_of_house* directory and a *hosting.rs* file to contain the definitions made in the `hosting` module: -Filename: src/front_of_house/hosting.rs +src/front_of_house/hosting.rs ``` pub fn add_to_waitlist() {} ``` + + If we instead put *hosting.rs* in the *src* directory, the compiler would expect the *hosting.rs* code to be in a `hosting` module declared in the crate -root, and not declared as a child of the `front_of_house` module. The +root and not declared as a child of the `front_of_house` module. The compiler’s rules for which files to check for which modules’ code mean the directories and files more closely match the module tree. > ### Alternate File Paths -> +> > So far we’ve covered the most idiomatic file paths the Rust compiler uses, -but Rust also supports an older style of file path. For a module named -`front_of_house` declared in the crate root, the compiler will look for the -module’s code in: -> +> but Rust also supports an older style of file path. For a module named +> `front_of_house` declared in the crate root, the compiler will look for the +> module’s code in: +> > * *src/front_of_house.rs* (what we covered) > * *src/front_of_house/mod.rs* (older style, still supported path) -> +> > For a module named `hosting` that is a submodule of `front_of_house`, the -compiler will look for the module’s code in: -> +> compiler will look for the module’s code in: +> > * *src/front_of_house/hosting.rs* (what we covered) > * *src/front_of_house/hosting/mod.rs* (older style, still supported path) -> +> > If you use both styles for the same module, you’ll get a compiler error. -Using a mix of both styles for different modules in the same project is -allowed, but might be confusing for people navigating your project. -> +> Using a mix of both styles for different modules in the same project is +> allowed but might be confusing for people navigating your project. +> > The main downside to the style that uses files named *mod.rs* is that your -project can end up with many files named *mod.rs*, which can get confusing when -you have them open in your editor at the same time. +> project can end up with many files named *mod.rs*, which can get confusing +> when you have them open in your editor at the same time. We’ve moved each module’s code to a separate file, and the module tree remains the same. The function calls in `eat_at_restaurant` will work without any @@ -1222,12 +1272,11 @@ that module. ## Summary Rust lets you split a package into multiple crates and a crate into modules so -you can refer to items defined in one module from another module. You can do -this by specifying absolute or relative paths. These paths can be brought into -scope with a `use` statement so you can use a shorter path for multiple uses of -the item in that scope. Module code is private by default, but you can make -definitions public by adding the `pub` keyword. +that you can refer to items defined in one module from another module. You can +do this by specifying absolute or relative paths. These paths can be brought +into scope with a `use` statement so that you can use a shorter path for +multiple uses of the item in that scope. Module code is private by default, but +you can make definitions public by adding the `pub` keyword. In the next chapter, we’ll look at some collection data structures in the standard library that you can use in your neatly organized code. - diff --git a/nostarch/chapter08.md b/nostarch/chapter08.md index c44ebd8f7b..250da12e49 100644 --- a/nostarch/chapter08.md +++ b/nostarch/chapter08.md @@ -11,28 +11,28 @@ directory, so all fixes need to be made in `/src/`. Rust’s standard library includes a number of very useful data structures called *collections*. Most other data types represent one specific value, but collections can contain multiple values. Unlike the built-in array and tuple -types, the data these collections point to is stored on the heap, which means -the amount of data does not need to be known at compile time and can grow or -shrink as the program runs. Each kind of collection has different capabilities -and costs, and choosing an appropriate one for your current situation is a -skill you’ll develop over time. In this chapter, we’ll discuss three -collections that are used very often in Rust programs: +types, the data that these collections point to is stored on the heap, which +means the amount of data does not need to be known at compile time and can grow +or shrink as the program runs. Each kind of collection has different +capabilities and costs, and choosing an appropriate one for your current +situation is a skill you’ll develop over time. In this chapter, we’ll discuss +three collections that are used very often in Rust programs: * A *vector* allows you to store a variable number of values next to each other. * A *string* is a collection of characters. We’ve mentioned the `String` type -previously, but in this chapter we’ll talk about it in depth. + previously, but in this chapter, we’ll talk about it in depth. * A *hash map* allows you to associate a value with a specific key. It’s a -particular implementation of the more general data structure called a *map*. + particular implementation of the more general data structure called a *map*. To learn about the other kinds of collections provided by the standard library, -see the documentation at *https://doc.rust-lang.org/std/collections/index.html*. +see the documentation at *../std/collections/index.html*. We’ll discuss how to create and update vectors, strings, and hash maps, as well as what makes each special. ## Storing Lists of Values with Vectors -The first collection type we’ll look at is `Vec`, also known as a *vector*. +The first collection type we’ll look at is `Vec`, also known as a vector. Vectors allow you to store more than one value in a single data structure that puts all the values next to each other in memory. Vectors can only store values of the same type. They are useful when you have a list of items, such as the @@ -40,11 +40,12 @@ lines of text in a file or the prices of items in a shopping cart. ### Creating a New Vector -To create a new empty vector, we call the `Vec::new` function, as shown in +To create a new, empty vector, we call the `Vec::new` function, as shown in Listing 8-1. + ``` -let v: Vec = Vec::new(); + let v: Vec = Vec::new(); ``` Listing 8-1: Creating a new, empty vector to hold values of type `i32` @@ -58,16 +59,17 @@ When we create a vector to hold a specific type, we can specify the type within angle brackets. In Listing 8-1, we’ve told Rust that the `Vec` in `v` will hold elements of the `i32` type. -More often, you’ll create a `Vec` with initial values and Rust will infer +More often, you’ll create a `Vec` with initial values, and Rust will infer the type of value you want to store, so you rarely need to do this type annotation. Rust conveniently provides the `vec!` macro, which will create a new vector that holds the values you give it. Listing 8-2 creates a new `Vec` that holds the values `1`, `2`, and `3`. The integer type is `i32` -because that’s the default integer type, as we discussed in “Data Types” on -page XX. +because that’s the default integer type, as we discussed in the “Data +Types” section of Chapter 3. + ``` -let v = vec![1, 2, 3]; + let v = vec![1, 2, 3]; ``` Listing 8-2: Creating a new vector containing values @@ -81,13 +83,14 @@ to modify a vector. To create a vector and then add elements to it, we can use the `push` method, as shown in Listing 8-3. + ``` -let mut v = Vec::new(); + let mut v = Vec::new(); -v.push(5); -v.push(6); -v.push(7); -v.push(8); + v.push(5); + v.push(6); + v.push(7); + v.push(8); ``` Listing 8-3: Using the `push` method to add values to a vector @@ -106,43 +109,43 @@ the values that are returned from these functions for extra clarity. Listing 8-4 shows both methods of accessing a value in a vector, with indexing syntax and the `get` method. + ``` -let v = vec![1, 2, 3, 4, 5]; + let v = vec![1, 2, 3, 4, 5]; -1 let third: &i32 = &v[2]; -println!("The third element is {third}"); + let third: &i32 = &v[2]; + println!("The third element is {third}"); -2 let third: Option<&i32> = v.get(2); -match third { - Some(third) => println!("The third element is {third}"), - None => println!("There is no third element."), -} + let third: Option<&i32> = v.get(2); + match third { + Some(third) => println!("The third element is {third}"), + None => println!("There is no third element."), + } ``` -Listing 8-4: Using indexing syntax and using the `get` method to access an item -in a vector +Listing 8-4: Using indexing syntax and using the `get` method to access an item in a vector Note a few details here. We use the index value of `2` to get the third element -[1] because vectors are indexed by number, starting at zero. Using `&` and `[]` +because vectors are indexed by number, starting at zero. Using `&` and `[]` gives us a reference to the element at the index value. When we use the `get` -method with the index passed as an argument [2], we get an `Option<&T>` that we -can use with `match`. +method with the index passed as an argument, we get an `Option<&T>` that we can +use with `match`. -Rust provides these two ways to reference an element so you can choose how the -program behaves when you try to use an index value outside the range of +Rust provides these two ways to reference an element so that you can choose how +the program behaves when you try to use an index value outside the range of existing elements. As an example, let’s see what happens when we have a vector of five elements and then we try to access an element at index 100 with each technique, as shown in Listing 8-5. + ``` -let v = vec![1, 2, 3, 4, 5]; + let v = vec![1, 2, 3, 4, 5]; -let does_not_exist = &v[100]; -let does_not_exist = v.get(100); + let does_not_exist = &v[100]; + let does_not_exist = v.get(100); ``` -Listing 8-5: Attempting to access the element at index 100 in a vector -containing five elements +Listing 8-5: Attempting to access the element at index 100 in a vector containing five elements When we run this code, the first `[]` method will cause the program to panic because it references a nonexistent element. This method is best used when you @@ -161,32 +164,33 @@ enter a valid value. That would be more user-friendly than crashing the program due to a typo! When the program has a valid reference, the borrow checker enforces the -ownership and borrowing rules (covered in Chapter 4) to ensure this reference -and any other references to the contents of the vector remain valid. Recall the -rule that states you can’t have mutable and immutable references in the same -scope. That rule applies in Listing 8-6, where we hold an immutable reference -to the first element in a vector and try to add an element to the end. This -program won’t work if we also try to refer to that element later in the -function. +ownership and borrowing rules (covered in Chapter 4) to ensure that this +reference and any other references to the contents of the vector remain valid. +Recall the rule that states you can’t have mutable and immutable references in +the same scope. That rule applies in Listing 8-6, where we hold an immutable +reference to the first element in a vector and try to add an element to the +end. This program won’t work if we also try to refer to that element later in +the function. + ``` -let mut v = vec![1, 2, 3, 4, 5]; + let mut v = vec![1, 2, 3, 4, 5]; -let first = &v[0]; + let first = &v[0]; -v.push(6); + v.push(6); -println!("The first element is: {first}"); + println!("The first element is: {first}"); ``` -Listing 8-6: Attempting to add an element to a vector while holding a reference -to an item +Listing 8-6: Attempting to add an element to a vector while holding a reference to an item Compiling this code will result in this error: ``` -error[E0502]: cannot borrow `v` as mutable because it is also borrowed as -immutable +$ cargo run + Compiling collections v0.1.0 (file:///projects/collections) +error[E0502]: cannot borrow `v` as mutable because it is also borrowed as immutable --> src/main.rs:6:5 | 4 | let first = &v[0]; @@ -196,12 +200,15 @@ immutable | ^^^^^^^^^ mutable borrow occurs here 7 | 8 | println!("The first element is: {first}"); - | ----- immutable borrow later used here + | ------- immutable borrow later used here + +For more information about this error, try `rustc --explain E0502`. +error: could not compile `collections` (bin "collections") due to 1 previous error ``` -The code in Listing 8-6 might look like it should work: why should a reference +The code in Listing 8-6 might look like it should work: Why should a reference to the first element care about changes at the end of the vector? This error is -due to the way vectors work: because vectors put the values next to each other +due to the way vectors work: Because vectors put the values next to each other in memory, adding a new element onto the end of the vector might require allocating new memory and copying the old elements to the new space, if there isn’t enough room to put all the elements next to each other where the vector @@ -210,7 +217,7 @@ pointing to deallocated memory. The borrowing rules prevent programs from ending up in that situation. > Note: For more on the implementation details of the `Vec` type, see “The -Rustonomicon” at *https://doc.rust-lang.org/nomicon/vec/vec.html*. +> Rustonomicon” at *../nomicon/vec/vec.html*. ### Iterating Over the Values in a Vector @@ -219,33 +226,34 @@ elements rather than use indices to access one at a time. Listing 8-7 shows how to use a `for` loop to get immutable references to each element in a vector of `i32` values and print them. + ``` -let v = vec![100, 32, 57]; -for i in &v { - println!("{i}"); -} + let v = vec![100, 32, 57]; + for i in &v { + println!("{i}"); + } ``` -Listing 8-7: Printing each element in a vector by iterating over the elements -using a `for` loop +Listing 8-7: Printing each element in a vector by iterating over the elements using a `for` loop We can also iterate over mutable references to each element in a mutable vector in order to make changes to all the elements. The `for` loop in Listing 8-8 will add `50` to each element. + ``` -let mut v = vec![100, 32, 57]; -for i in &mut v { - *i += 50; -} + let mut v = vec![100, 32, 57]; + for i in &mut v { + *i += 50; + } ``` Listing 8-8: Iterating over mutable references to elements in a vector To change the value that the mutable reference refers to, we have to use the `*` dereference operator to get to the value in `i` before we can use the `+=` -operator. We’ll talk more about the dereference operator in “Following the -Pointer to the Value” on page XX. +operator. We’ll talk more about the dereference operator in the “Following the +Reference to the Value” section of Chapter 15. Iterating over a vector, whether immutably or mutably, is safe because of the borrow checker’s rules. If we attempted to insert or remove items in the `for` @@ -266,28 +274,29 @@ For example, say we want to get values from a row in a spreadsheet in which some of the columns in the row contain integers, some floating-point numbers, and some strings. We can define an enum whose variants will hold the different value types, and all the enum variants will be considered the same type: that -of the enum. Then we can create a vector to hold that enum and so, ultimately, -holds different types. We’ve demonstrated this in Listing 8-9. +of the enum. Then, we can create a vector to hold that enum and so, ultimately, +hold different types. We’ve demonstrated this in Listing 8-9. + ``` -enum SpreadsheetCell { - Int(i32), - Float(f64), - Text(String), -} + enum SpreadsheetCell { + Int(i32), + Float(f64), + Text(String), + } -let row = vec![ - SpreadsheetCell::Int(3), - SpreadsheetCell::Text(String::from("blue")), - SpreadsheetCell::Float(10.12), -]; + let row = vec![ + SpreadsheetCell::Int(3), + SpreadsheetCell::Text(String::from("blue")), + SpreadsheetCell::Float(10.12), + ]; ``` -Listing 8-9: Defining an `enum` to store values of different types in one vector +Listing 8-9: Defining an enum to store values of different types in one vector -Rust needs to know what types will be in the vector at compile time so it knows -exactly how much memory on the heap will be needed to store each element. We -must also be explicit about what types are allowed in this vector. If Rust +Rust needs to know what types will be in the vector at compile time so that it +knows exactly how much memory on the heap will be needed to store each element. +We must also be explicit about what types are allowed in this vector. If Rust allowed a vector to hold any type, there would be a chance that one or more of the types would cause errors with the operations performed on the elements of the vector. Using an enum plus a `match` expression means that Rust will ensure @@ -295,24 +304,25 @@ at compile time that every possible case is handled, as discussed in Chapter 6. If you don’t know the exhaustive set of types a program will get at runtime to store in a vector, the enum technique won’t work. Instead, you can use a trait -object, which we’ll cover in Chapter 17. +object, which we’ll cover in Chapter 18. Now that we’ve discussed some of the most common ways to use vectors, be sure -to review the API documentation for all of the many useful methods defined on -`Vec` by the standard library. For example, in addition to `push`, a `pop` -method removes and returns the last element. +to review the API documentation for all of the many +useful methods defined on `Vec` by the standard library. For example, in +addition to `push`, a `pop` method removes and returns the last element. ### Dropping a Vector Drops Its Elements Like any other `struct`, a vector is freed when it goes out of scope, as annotated in Listing 8-10. + ``` -{ - let v = vec![1, 2, 3, 4]; + { + let v = vec![1, 2, 3, 4]; - // do stuff with v -} // <- v goes out of scope and is freed here + // do stuff with v + } // <- v goes out of scope and is freed here ``` Listing 8-10: Showing where the vector and its elements are dropped @@ -338,15 +348,19 @@ implemented as a collection of bytes, plus some methods to provide useful functionality when those bytes are interpreted as text. In this section, we’ll talk about the operations on `String` that every collection type has, such as creating, updating, and reading. We’ll also discuss the ways in which `String` -is different from the other collections, namely how indexing into a `String` is +is different from the other collections, namely, how indexing into a `String` is complicated by the differences between how people and computers interpret `String` data. -### What Is a String? + + + + +### Defining Strings We’ll first define what we mean by the term *string*. Rust has only one string type in the core language, which is the string slice `str` that is usually seen -in its borrowed form `&str`. In Chapter 4, we talked about *string slices*, +in its borrowed form, `&str`. In Chapter 4, we talked about string slices, which are references to some UTF-8 encoded string data stored elsewhere. String literals, for example, are stored in the program’s binary and are therefore string slices. @@ -367,8 +381,9 @@ of bytes with some extra guarantees, restrictions, and capabilities. An example of a function that works the same way with `Vec` and `String` is the `new` function to create an instance, shown in Listing 8-11. + ``` -let mut s = String::new(); + let mut s = String::new(); ``` Listing 8-11: Creating a new, empty `String` @@ -379,17 +394,17 @@ string. For that, we use the `to_string` method, which is available on any type that implements the `Display` trait, as string literals do. Listing 8-12 shows two examples. + ``` -let data = "initial contents"; + let data = "initial contents"; -let s = data.to_string(); + let s = data.to_string(); -// the method also works on a literal directly: -let s = "initial contents".to_string(); + // The method also works on a literal directly: + let s = "initial contents".to_string(); ``` -Listing 8-12: Using the `to_string` method to create a `String` from a string -literal +Listing 8-12: Using the `to_string` method to create a `String` from a string literal This code creates a string containing `initial contents`. @@ -397,12 +412,12 @@ We can also use the function `String::from` to create a `String` from a string literal. The code in Listing 8-13 is equivalent to the code in Listing 8-12 that uses `to_string`. + ``` -let s = String::from("initial contents"); + let s = String::from("initial contents"); ``` -Listing 8-13: Using the `String::from` function to create a `String` from a -string literal +Listing 8-13: Using the `String::from` function to create a `String` from a string literal Because strings are used for so many things, we can use many different generic APIs for strings, providing us with a lot of options. Some of them can seem @@ -413,18 +428,19 @@ readability. Remember that strings are UTF-8 encoded, so we can include any properly encoded data in them, as shown in Listing 8-14. + ``` -let hello = String::from("السلام عليكم"); -let hello = String::from("Dobrý den"); -let hello = String::from("Hello"); -let hello = String::from("שָׁלוֹם"); -let hello = String::from("नमस्ते"); -let hello = String::from("こんにちは"); -let hello = String::from("안녕하세요"); -let hello = String::from("你好"); -let hello = String::from("Olá"); -let hello = String::from("Здравствуйте"); -let hello = String::from("Hola"); + let hello = String::from("السلام عليكم"); + let hello = String::from("Dobrý den"); + let hello = String::from("Hello"); + let hello = String::from("שלום"); + let hello = String::from("नमस्ते"); + let hello = String::from("こんにちは"); + let hello = String::from("안녕하세요"); + let hello = String::from("你好"); + let hello = String::from("Olá"); + let hello = String::from("Здравствуйте"); + let hello = String::from("Hola"); ``` Listing 8-14: Storing greetings in different languages in strings @@ -437,14 +453,19 @@ A `String` can grow in size and its contents can change, just like the contents of a `Vec`, if you push more data into it. In addition, you can conveniently use the `+` operator or the `format!` macro to concatenate `String` values. -#### Appending to a String with push_str and push + + + + +#### Appending with push_str or push We can grow a `String` by using the `push_str` method to append a string slice, as shown in Listing 8-15. + ``` -let mut s = String::from("foo"); -s.push_str("bar"); + let mut s = String::from("foo"); + s.push_str("bar"); ``` Listing 8-15: Appending a string slice to a `String` using the `push_str` method @@ -454,11 +475,12 @@ string slice because we don’t necessarily want to take ownership of the parameter. For example, in the code in Listing 8-16, we want to be able to use `s2` after appending its contents to `s1`. + ``` -let mut s1 = String::from("foo"); -let s2 = "bar"; -s1.push_str(s2); -println!("s2 is {s2}"); + let mut s1 = String::from("foo"); + let s2 = "bar"; + s1.push_str(s2); + println!("s2 is {s2}"); ``` Listing 8-16: Using a string slice after appending its contents to a `String` @@ -470,28 +492,33 @@ The `push` method takes a single character as a parameter and adds it to the `String`. Listing 8-17 adds the letter *l* to a `String` using the `push` method. + ``` -let mut s = String::from("lo"); -s.push('l'); + let mut s = String::from("lo"); + s.push('l'); ``` Listing 8-17: Adding one character to a `String` value using `push` As a result, `s` will contain `lol`. -#### Concatenation with the + Operator or the format! Macro + + + + +#### Concatenating with + or format! Often, you’ll want to combine two existing strings. One way to do so is to use the `+` operator, as shown in Listing 8-18. + ``` -let s1 = String::from("Hello, "); -let s2 = String::from("world!"); -let s3 = s1 + &s2; // note s1 has been moved here and can no longer be used + let s1 = String::from("Hello, "); + let s2 = String::from("world!"); + let s3 = s1 + &s2; // note s1 has been moved here and can no longer be used ``` -Listing 8-18: Using the `+` operator to combine two `String` values into a new -`String` value +Listing 8-18: Using the `+` operator to combine two `String` values into a new `String` value The string `s3` will contain `Hello, world!`. The reason `s1` is no longer valid after the addition, and the reason we used a reference to `s2`, has to do @@ -509,18 +536,19 @@ call this method with `String` values. We’ll discuss generics in Chapter 10. This signature gives us the clues we need in order to understand the tricky bits of the `+` operator. -First, `s2` has an `&`, meaning that we’re adding a *reference* of the second +First, `s2` has an `&`, meaning that we’re adding a reference of the second string to the first string. This is because of the `s` parameter in the `add` -function: we can only add a `&str` to a `String`; we can’t add two `String` -values together. But wait—the type of `&s2` is `&String`, not `&str`, as -specified in the second parameter to `add`. So why does Listing 8-18 compile? +function: We can only add a string slice to a `String`; we can’t add two +`String` values together. But wait—the type of `&s2` is `&String`, not `&str`, +as specified in the second parameter to `add`. So, why does Listing 8-18 +compile? The reason we’re able to use `&s2` in the call to `add` is that the compiler -can *coerce* the `&String` argument into a `&str`. When we call the `add` -method, Rust uses a *deref coercion*, which here turns `&s2` into `&s2[..]`. -We’ll discuss deref coercion in more depth in Chapter 15. Because `add` does -not take ownership of the `s` parameter, `s2` will still be a valid `String` -after this operation. +can coerce the `&String` argument into a `&str`. When we call the `add` method, +Rust uses a deref coercion, which here turns `&s2` into `&s2[..]`. We’ll +discuss deref coercion in more depth in Chapter 15. Because `add` does not take +ownership of the `s` parameter, `s2` will still be a valid `String` after this +operation. Second, we can see in the signature that `add` takes ownership of `self` because `self` does *not* have an `&`. This means `s1` in Listing 8-18 will be @@ -535,11 +563,11 @@ If we need to concatenate multiple strings, the behavior of the `+` operator gets unwieldy: ``` -let s1 = String::from("tic"); -let s2 = String::from("tac"); -let s3 = String::from("toe"); + let s1 = String::from("tic"); + let s2 = String::from("tac"); + let s3 = String::from("toe"); -let s = s1 + "-" + &s2 + "-" + &s3; + let s = s1 + "-" + &s2 + "-" + &s3; ``` At this point, `s` will be `tic-tac-toe`. With all of the `+` and `"` @@ -547,11 +575,11 @@ characters, it’s difficult to see what’s going on. For combining strings in more complicated ways, we can instead use the `format!` macro: ``` -let s1 = String::from("tic"); -let s2 = String::from("tac"); -let s3 = String::from("toe"); + let s1 = String::from("tic"); + let s2 = String::from("tac"); + let s3 = String::from("toe"); -let s = format!("{s1}-{s2}-{s3}"); + let s = format!("{s1}-{s2}-{s3}"); ``` This code also sets `s` to `tic-tac-toe`. The `format!` macro works like @@ -567,9 +595,10 @@ string by referencing them by index is a valid and common operation. However, if you try to access parts of a `String` using indexing syntax in Rust, you’ll get an error. Consider the invalid code in Listing 8-19. + ``` -let s1 = String::from("hello"); -let h = s1[0]; + let s1 = String::from("hi"); + let h = s1[0]; ``` Listing 8-19: Attempting to use indexing syntax with a `String` @@ -577,19 +606,27 @@ Listing 8-19: Attempting to use indexing syntax with a `String` This code will result in the following error: ``` -error[E0277]: the type `String` cannot be indexed by `{integer}` - --> src/main.rs:3:13 +$ cargo run + Compiling collections v0.1.0 (file:///projects/collections) +error[E0277]: the type `str` cannot be indexed by `{integer}` + --> src/main.rs:3:16 | 3 | let h = s1[0]; - | ^^^^^ `String` cannot be indexed by `{integer}` + | ^ string indices are ranges of `usize` | - = help: the trait `Index<{integer}>` is not implemented for -`String` + = note: you can use `.chars().nth()` or `.bytes().nth()` + for more information, see chapter 8 in The Book: + = help: the trait `SliceIndex` is not implemented for `{integer}` + but trait `SliceIndex<[_]>` is implemented for `usize` + = help: for that trait implementation, expected `[_]`, found `str` + = note: required for `String` to implement `Index<{integer}>` + +For more information about this error, try `rustc --explain E0277`. +error: could not compile `collections` (bin "collections") due to 1 previous error ``` -The error and the note tell the story: Rust strings don’t support indexing. But -why not? To answer that question, we need to discuss how Rust stores strings in -memory. +The error tells the story: Rust strings don’t support indexing. But why not? To +answer that question, we need to discuss how Rust stores strings in memory. #### Internal Representation @@ -597,20 +634,20 @@ A `String` is a wrapper over a `Vec`. Let’s look at some of our properly encoded UTF-8 example strings from Listing 8-14. First, this one: ``` -let hello = String::from("Hola"); + let hello = String::from("Hola"); ``` In this case, `len` will be `4`, which means the vector storing the string -`"Hola"` is 4 bytes long. Each of these letters takes one byte when encoded in +`"Hola"` is 4 bytes long. Each of these letters takes 1 byte when encoded in UTF-8. The following line, however, may surprise you (note that this string -begins with the capital Cyrillic letter *Ze*, not the Arabic number 3): +begins with the capital Cyrillic letter *Ze*, not the number 3): ``` -let hello = String::from("Здравствуйте"); + let hello = String::from("Здравствуйте"); ``` If you were asked how long the string is, you might say 12. In fact, Rust’s -answer is 24: that’s the number of bytes it takes to encode “Здравствуйте” in +answer is 24: That’s the number of bytes it takes to encode “Здравствуйте” in UTF-8, because each Unicode scalar value in that string takes 2 bytes of storage. Therefore, an index into the string’s bytes will not always correlate to a valid Unicode scalar value. To demonstrate, consider this invalid Rust @@ -627,14 +664,18 @@ seem that `answer` should in fact be `208`, but `208` is not a valid character on its own. Returning `208` is likely not what a user would want if they asked for the first letter of this string; however, that’s the only data that Rust has at byte index 0. Users generally don’t want the byte value returned, even -if the string contains only Latin letters: if `&"hello"[0]` were valid code -that returned the byte value, it would return `104`, not `h`. +if the string contains only Latin letters: If `&"hi"[0]` were valid code that +returned the byte value, it would return `104`, not `h`. The answer, then, is that to avoid returning an unexpected value and causing bugs that might not be discovered immediately, Rust doesn’t compile this code at all and prevents misunderstandings early in the development process. -#### Bytes and Scalar Values and Grapheme Clusters! Oh My! + + + + +#### Bytes, Scalar Values, and Grapheme Clusters Another point about UTF-8 is that there are actually three relevant ways to look at strings from Rust’s perspective: as bytes, scalar values, and grapheme @@ -644,8 +685,8 @@ If we look at the Hindi word “नमस्ते” written in the Devanagari stored as a vector of `u8` values that looks like this: ``` -[224, 164, 168, 224, 164, 174, 224, 164, 184, 224, 165, 141, 224, -164, 164, 224, 165, 135] +[224, 164, 168, 224, 164, 174, 224, 164, 184, 224, 165, 141, 224, 164, 164, +224, 165, 135] ``` That’s 18 bytes and is how computers ultimately store this data. If we look at @@ -657,7 +698,7 @@ bytes look like this: ``` There are six `char` values here, but the fourth and sixth are not letters: -they’re diacritics that don’t make sense on their own. Finally, if we look at +They’re diacritics that don’t make sense on their own. Finally, if we look at them as grapheme clusters, we’d get what a person would call the four letters that make up the Hindi word: @@ -691,8 +732,8 @@ let hello = "Здравствуйте"; let s = &hello[0..4]; ``` -Here, `s` will be a `&str` that contains the first four bytes of the string. -Earlier, we mentioned that each of these characters was two bytes, which means +Here, `s` will be a `&str` that contains the first 4 bytes of the string. +Earlier, we mentioned that each of these characters was 2 bytes, which means `s` will be `Зд`. If we were to try to slice only part of a character’s bytes with something like @@ -700,14 +741,24 @@ If we were to try to slice only part of a character’s bytes with something lik index were accessed in a vector: ``` -thread 'main' panicked at 'byte index 1 is not a char boundary; -it is inside 'З' (bytes 0..2) of `Здравствуйте`', src/main.rs:4:14 +$ cargo run + Compiling collections v0.1.0 (file:///projects/collections) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.43s + Running `target/debug/collections` + +thread 'main' panicked at src/main.rs:4:19: +byte index 1 is not a char boundary; it is inside 'З' (bytes 0..2) of `Здравствуйте` +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` You should use caution when creating string slices with ranges, because doing so can crash your program. -### Methods for Iterating Over Strings + + + + +### Iterating Over Strings The best way to operate on pieces of strings is to be explicit about whether you want characters or bytes. For individual Unicode scalar values, use the @@ -736,7 +787,7 @@ for b in "Зд".bytes() { } ``` -This code will print the four bytes that make up this string: +This code will print the 4 bytes that make up this string: ``` 208 @@ -746,13 +797,18 @@ This code will print the four bytes that make up this string: ``` But be sure to remember that valid Unicode scalar values may be made up of more -than one byte. +than 1 byte. Getting grapheme clusters from strings, as with the Devanagari script, is complex, so this functionality is not provided by the standard library. Crates -are available at *https://crates.io* if this is the functionality you need. +are available on crates.io if this is the +functionality you need. -### Strings Are Not So Simple + + + + +### Handling the Complexities of Strings To summarize, strings are complicated. Different programming languages make different choices about how to present this complexity to the programmer. Rust @@ -773,7 +829,7 @@ Let’s switch to something a bit less complex: hash maps! ## Storing Keys with Associated Values in Hash Maps -The last of our common collections is the *hash map*. The type `HashMap` +The last of our common collections is the hash map. The type `HashMap` stores a mapping of keys of type `K` to values of type `V` using a *hashing function*, which determines how it places these keys and values into memory. Many programming languages support this kind of data structure, but they often @@ -797,13 +853,14 @@ One way to create an empty hash map is to use `new` and to add elements with names are *Blue* and *Yellow*. The Blue team starts with 10 points, and the Yellow team starts with 50. + ``` -use std::collections::HashMap; + use std::collections::HashMap; -let mut scores = HashMap::new(); + let mut scores = HashMap::new(); -scores.insert(String::from("Blue"), 10); -scores.insert(String::from("Yellow"), 50); + scores.insert(String::from("Blue"), 10); + scores.insert(String::from("Yellow"), 50); ``` Listing 8-20: Creating a new hash map and inserting some keys and values @@ -816,7 +873,7 @@ standard library; there’s no built-in macro to construct them, for example. Just like vectors, hash maps store their data on the heap. This `HashMap` has keys of type `String` and values of type `i32`. Like vectors, hash maps are -homogeneous: all of the keys must have the same type, and all of the values +homogeneous: All of the keys must have the same type, and all of the values must have the same type. ### Accessing Values in a Hash Map @@ -824,16 +881,17 @@ must have the same type. We can get a value out of the hash map by providing its key to the `get` method, as shown in Listing 8-21. + ``` -use std::collections::HashMap; + use std::collections::HashMap; -let mut scores = HashMap::new(); + let mut scores = HashMap::new(); -scores.insert(String::from("Blue"), 10); -scores.insert(String::from("Yellow"), 50); + scores.insert(String::from("Blue"), 10); + scores.insert(String::from("Yellow"), 50); -let team_name = String::from("Blue"); -let score = scores.get(&team_name).copied().unwrap_or(0); + let team_name = String::from("Blue"); + let score = scores.get(&team_name).copied().unwrap_or(0); ``` Listing 8-21: Accessing the score for the Blue team stored in the hash map @@ -845,20 +903,20 @@ handles the `Option` by calling `copied` to get an `Option` rather than an `Option<&i32>`, then `unwrap_or` to set `score` to zero if `scores` doesn’t have an entry for the key. -We can iterate over each key–value pair in a hash map in a similar manner as we +We can iterate over each key-value pair in a hash map in a similar manner as we do with vectors, using a `for` loop: ``` -use std::collections::HashMap; + use std::collections::HashMap; -let mut scores = HashMap::new(); + let mut scores = HashMap::new(); -scores.insert(String::from("Blue"), 10); -scores.insert(String::from("Yellow"), 50); + scores.insert(String::from("Blue"), 10); + scores.insert(String::from("Yellow"), 50); -for (key, value) in &scores { - println!("{key}: {value}"); -} + for (key, value) in &scores { + println!("{key}: {value}"); + } ``` This code will print each pair in an arbitrary order: @@ -868,26 +926,30 @@ Yellow: 50 Blue: 10 ``` -### Hash Maps and Ownership + + + + +### Managing Ownership in Hash Maps For types that implement the `Copy` trait, like `i32`, the values are copied into the hash map. For owned values like `String`, the values will be moved and the hash map will be the owner of those values, as demonstrated in Listing 8-22. + ``` -use std::collections::HashMap; + use std::collections::HashMap; -let field_name = String::from("Favorite color"); -let field_value = String::from("Blue"); + let field_name = String::from("Favorite color"); + let field_value = String::from("Blue"); -let mut map = HashMap::new(); -map.insert(field_name, field_value); -// field_name and field_value are invalid at this point, try -// using them and see what compiler error you get! + let mut map = HashMap::new(); + map.insert(field_name, field_value); + // field_name and field_value are invalid at this point, try using them and + // see what compiler error you get! ``` -Listing 8-22: Showing that keys and values are owned by the hash map once -they’re inserted +Listing 8-22: Showing that keys and values are owned by the hash map once they’re inserted We aren’t able to use the variables `field_name` and `field_value` after they’ve been moved into the hash map with the call to `insert`. @@ -895,12 +957,13 @@ they’ve been moved into the hash map with the call to `insert`. If we insert references to values into the hash map, the values won’t be moved into the hash map. The values that the references point to must be valid for at least as long as the hash map is valid. We’ll talk more about these issues in -“Validating References with Lifetimes” on page XX. +“Validating References with +Lifetimes” in Chapter 10. ### Updating a Hash Map Although the number of key and value pairs is growable, each unique key can -only have one value associated with it at a time (but not vice versa: for +only have one value associated with it at a time (but not vice versa: For example, both the Blue team and the Yellow team could have the value `10` stored in the `scores` hash map). @@ -916,18 +979,19 @@ new value. Let’s look at how to do each of these! If we insert a key and a value into a hash map and then insert that same key with a different value, the value associated with that key will be replaced. Even though the code in Listing 8-23 calls `insert` twice, the hash map will -only contain one key–value pair because we’re inserting the value for the Blue +only contain one key-value pair because we’re inserting the value for the Blue team’s key both times. + ``` -use std::collections::HashMap; + use std::collections::HashMap; -let mut scores = HashMap::new(); + let mut scores = HashMap::new(); -scores.insert(String::from("Blue"), 10); -scores.insert(String::from("Blue"), 25); + scores.insert(String::from("Blue"), 10); + scores.insert(String::from("Blue"), 25); -println!("{:?}", scores); + println!("{scores:?}"); ``` Listing 8-23: Replacing a value stored with a particular key @@ -935,10 +999,14 @@ Listing 8-23: Replacing a value stored with a particular key This code will print `{"Blue": 25}`. The original value of `10` has been overwritten. + + + + #### Adding a Key and Value Only If a Key Isn’t Present It’s common to check whether a particular key already exists in the hash map -with a value and then to take the following actions: if the key does exist in +with a value and then to take the following actions: If the key does exist in the hash map, the existing value should remain the way it is; if the key doesn’t exist, insert it and a value for it. @@ -949,20 +1017,20 @@ we want to check whether the key for the Yellow team has a value associated with it. If it doesn’t, we want to insert the value `50`, and the same for the Blue team. Using the `entry` API, the code looks like Listing 8-24. + ``` -use std::collections::HashMap; + use std::collections::HashMap; -let mut scores = HashMap::new(); -scores.insert(String::from("Blue"), 10); + let mut scores = HashMap::new(); + scores.insert(String::from("Blue"), 10); -scores.entry(String::from("Yellow")).or_insert(50); -scores.entry(String::from("Blue")).or_insert(50); + scores.entry(String::from("Yellow")).or_insert(50); + scores.entry(String::from("Blue")).or_insert(50); -println!("{:?}", scores); + println!("{scores:?}"); ``` -Listing 8-24: Using the `entry` method to only insert if the key does not -already have a value +Listing 8-24: Using the `entry` method to only insert if the key does not already have a value The `or_insert` method on `Entry` is defined to return a mutable reference to the value for the corresponding `Entry` key if that key exists, and if not, it @@ -973,7 +1041,7 @@ logic ourselves and, in addition, plays more nicely with the borrow checker. Running the code in Listing 8-24 will print `{"Yellow": 50, "Blue": 10}`. The first call to `entry` will insert the key for the Yellow team with the value `50` because the Yellow team doesn’t have a value already. The second call to -`entry` will not change the hash map because the Blue team already has the +`entry` will not change the hash map, because the Blue team already has the value `10`. #### Updating a Value Based on the Old Value @@ -985,28 +1053,28 @@ the words as keys and increment the value to keep track of how many times we’v seen that word. If it’s the first time we’ve seen a word, we’ll first insert the value `0`. + ``` -use std::collections::HashMap; + use std::collections::HashMap; -let text = "hello world wonderful world"; + let text = "hello world wonderful world"; -let mut map = HashMap::new(); + let mut map = HashMap::new(); -for word in text.split_whitespace() { - let count = map.entry(word).or_insert(0); - *count += 1; -} + for word in text.split_whitespace() { + let count = map.entry(word).or_insert(0); + *count += 1; + } -println!("{:?}", map); + println!("{map:?}"); ``` -Listing 8-25: Counting occurrences of words using a hash map that stores words -and counts +Listing 8-25: Counting occurrences of words using a hash map that stores words and counts This code will print `{"world": 2, "hello": 1, "wonderful": 1}`. You might see -the same key–value pairs printed in a different order: recall from “Accessing -Values in a Hash Map” on page XX that iterating over a hash map happens in an -arbitrary order. +the same key-value pairs printed in a different order: Recall from “Accessing +Values in a Hash Map” that iterating over a hash map +happens in an arbitrary order. The `split_whitespace` method returns an iterator over subslices, separated by whitespace, of the value in `text`. The `or_insert` method returns a mutable @@ -1019,16 +1087,18 @@ changes are safe and allowed by the borrowing rules. ### Hashing Functions By default, `HashMap` uses a hashing function called *SipHash* that can provide -resistance to denial-of-service (DoS) attacks involving hash tables. This is -not the fastest hashing algorithm available, but the trade-off for better -security that comes with the drop in performance is worth it. If you profile -your code and find that the default hash function is too slow for your -purposes, you can switch to another function by specifying a different hasher. -A *hasher* is a type that implements the `BuildHasher` trait. We’ll talk about -traits and how to implement them in Chapter 10. You don’t necessarily have to -implement your own hasher from scratch; *https://crates.io* has libraries -shared by other Rust users that provide hashers implementing many common -hashing algorithms. +resistance to denial-of-service (DoS) attacks involving hash +tables[^siphash]. This is not the fastest hashing algorithm +available, but the trade-off for better security that comes with the drop in +performance is worth it. If you profile your code and find that the default +hash function is too slow for your purposes, you can switch to another function +by specifying a different hasher. A *hasher* is a type that implements the +`BuildHasher` trait. We’ll talk about traits and how to implement them in +Chapter 10. You don’t necessarily have to implement +your own hasher from scratch; crates.io +has libraries shared by other Rust users that provide hashers implementing many +common hashing algorithms. + ## Summary @@ -1037,21 +1107,20 @@ necessary in programs when you need to store, access, and modify data. Here are some exercises you should now be equipped to solve: 1. Given a list of integers, use a vector and return the median (when sorted, -the value in the middle position) and mode (the value that occurs most often; a -hash map will be helpful here) of the list. -1. Convert strings to pig latin. The first consonant of each word is moved to -the end of the word and *ay* is added, so *first* becomes *irst-fay*. Words -that start with a vowel have *hay* added to the end instead (*apple* becomes -*apple-hay*). Keep in mind the details about UTF-8 encoding! + the value in the middle position) and mode (the value that occurs most + often; a hash map will be helpful here) of the list. +1. Convert strings to Pig Latin. The first consonant of each word is moved to + the end of the word and *ay* is added, so *first* becomes *irst-fay*. Words + that start with a vowel have *hay* added to the end instead (*apple* becomes + *apple-hay*). Keep in mind the details about UTF-8 encoding! 1. Using a hash map and vectors, create a text interface to allow a user to add -employee names to a department in a company; for example, “Add Sally to -Engineering” or “Add Amir to Sales.” Then let the user retrieve a list of all -people in a department or all people in the company by department, sorted -alphabetically. + employee names to a department in a company; for example, “Add Sally to + Engineering” or “Add Amir to Sales.” Then, let the user retrieve a list of + all people in a department or all people in the company by department, sorted + alphabetically. The standard library API documentation describes methods that vectors, strings, and hash maps have that will be helpful for these exercises! We’re getting into more complex programs in which operations can fail, so it’s a perfect time to discuss error handling. We’ll do that next! - diff --git a/nostarch/chapter09.md b/nostarch/chapter09.md index 4aa81123fb..2356f063a7 100644 --- a/nostarch/chapter09.md +++ b/nostarch/chapter09.md @@ -12,13 +12,13 @@ Errors are a fact of life in software, so Rust has a number of features for handling situations in which something goes wrong. In many cases, Rust requires you to acknowledge the possibility of an error and take some action before your code will compile. This requirement makes your program more robust by ensuring -that you’ll discover errors and handle them appropriately before you’ve -deployed your code to production! +that you’ll discover errors and handle them appropriately before deploying your +code to production! -Rust groups errors into two major categories: *recoverable* and *unrecoverable* -errors. For a recoverable error, such as a *file not found* error, we most +Rust groups errors into two major categories: recoverable and unrecoverable +errors. For a *recoverable error*, such as a *file not found* error, we most likely just want to report the problem to the user and retry the operation. -Unrecoverable errors are always symptoms of bugs, such as trying to access a +*Unrecoverable errors* are always symptoms of bugs, such as trying to access a location beyond the end of an array, and so we want to immediately stop the program. @@ -43,28 +43,28 @@ environment variable, you can also have Rust display the call stack when a panic occurs to make it easier to track down the source of the panic. > ### Unwinding the Stack or Aborting in Response to a Panic -> -> By default, when a panic occurs the program starts *unwinding*, which means -Rust walks back up the stack and cleans up the data from each function it -encounters. However, walking back and cleaning up is a lot of work. Rust, -therefore, allows you to choose the alternative of immediately *aborting*, -which ends the program without cleaning up. -> +> +> By default, when a panic occurs, the program starts *unwinding*, which means +> Rust walks back up the stack and cleans up the data from each function it +> encounters. However, walking back and cleaning up is a lot of work. Rust +> therefore allows you to choose the alternative of immediately *aborting*, +> which ends the program without cleaning up. +> > Memory that the program was using will then need to be cleaned up by the -operating system. If in your project you need to make the resultant binary as -small as possible, you can switch from unwinding to aborting upon a panic by -adding `panic = 'abort'` to the appropriate `[profile]` sections in your -*Cargo.toml* file. For example, if you want to abort on panic in release mode, -add this: -> -> ``` +> operating system. If in your project you need to make the resultant binary as +> small as possible, you can switch from unwinding to aborting upon a panic by +> adding `panic = 'abort'` to the appropriate `[profile]` sections in your +> *Cargo.toml* file. For example, if you want to abort on panic in release mode, +> add this: +> +> ````toml > [profile.release] > panic = 'abort' -> ``` +> ```` Let’s try calling `panic!` in a simple program: -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -72,12 +72,19 @@ fn main() { } ``` + + When you run the program, you’ll see something like this: ``` -thread 'main' panicked at 'crash and burn', src/main.rs:2:5 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace +$ cargo run + Compiling panic v0.1.0 (file:///projects/panic) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.25s + Running `target/debug/panic` + +thread 'main' panicked at src/main.rs:2:5: +crash and burn +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` The call to `panic!` causes the error message contained in the last two lines. @@ -91,6 +98,10 @@ be in code that our code calls, and the filename and line number reported by the error message will be someone else’s code where the `panic!` macro is called, not the line of our code that eventually led to the `panic!` call. + + + + We can use the backtrace of the functions the `panic!` call came from to figure out the part of our code that is causing the problem. To understand how to use a `panic!` backtrace, let’s look at another example and see what it’s like when @@ -98,7 +109,7 @@ a `panic!` call comes from a library because of a bug in our code instead of from our code calling the macro directly. Listing 9-1 has some code that attempts to access an index in a vector beyond the range of valid indexes. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -108,8 +119,7 @@ fn main() { } ``` -Listing 9-1: Attempting to access an element beyond the end of a vector, which -will cause a call to `panic!` +Listing 9-1: Attempting to access an element beyond the end of a vector, which will cause a call to `panic!` Here, we’re attempting to access the 100th element of our vector (which is at index 99 because indexing starts at zero), but the vector has only three @@ -130,59 +140,64 @@ element at an index that doesn’t exist, Rust will stop execution and refuse to continue. Let’s try it and see: ``` -thread 'main' panicked at 'index out of bounds: the len is 3 but the index is -99', src/main.rs:4:5 +$ cargo run + Compiling panic v0.1.0 (file:///projects/panic) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.27s + Running `target/debug/panic` + +thread 'main' panicked at src/main.rs:4:6: +index out of bounds: the len is 3 but the index is 99 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` -This error points at line 4 of our *main.rs* where we attempt to access `index`. +This error points at line 4 of our *main.rs* where we attempt to access index +99 of the vector in `v`. The `note:` line tells us that we can set the `RUST_BACKTRACE` environment variable to get a backtrace of exactly what happened to cause the error. A *backtrace* is a list of all the functions that have been called to get to this -point. Backtraces in Rust work as they do in other languages: the key to +point. Backtraces in Rust work as they do in other languages: The key to reading the backtrace is to start from the top and read until you see files you wrote. That’s the spot where the problem originated. The lines above that spot are code that your code has called; the lines below are code that called your code. These before-and-after lines might include core Rust code, standard -library code, or crates that you’re using. Let’s try getting a backtrace by +library code, or crates that you’re using. Let’s try to get a backtrace by setting the `RUST_BACKTRACE` environment variable to any value except `0`. Listing 9-2 shows output similar to what you’ll see. + + + ``` $ RUST_BACKTRACE=1 cargo run -thread 'main' panicked at 'index out of bounds: the len is 3 but the index is -99', src/main.rs:4:5 +thread 'main' panicked at src/main.rs:4:6: +index out of bounds: the len is 3 but the index is 99 stack backtrace: 0: rust_begin_unwind - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/std -/src/panicking.rs:584:5 + at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/std/src/panicking.rs:692:5 1: core::panicking::panic_fmt - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core -/src/panicking.rs:142:14 + at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:75:14 2: core::panicking::panic_bounds_check - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core -/src/panicking.rs:84:5 + at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:273:5 3: >::index - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core -/src/slice/index.rs:242:10 + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/slice/index.rs:274:10 4: core::slice::index:: for [T]>::index - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core -/src/slice/index.rs:18:9 + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/slice/index.rs:16:9 5: as core::ops::index::Index>::index - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/alloc -/src/vec/mod.rs:2591:9 + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:3361:9 6: panic::main - at ./src/main.rs:4:5 + at ./src/main.rs:4:6 7: core::ops::function::FnOnce::call_once - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core -/src/ops/function.rs:248:5 -note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose -backtrace. + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5 +note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. ``` -Listing 9-2: The backtrace generated by a call to `panic!` displayed when the -environment variable `RUST_BACKTRACE` is set +Listing 9-2: The backtrace generated by a call to `panic!` displayed when the environment variable `RUST_BACKTRACE` is set That’s a lot of output! The exact output you see might be different depending on your operating system and Rust version. In order to get backtraces with this @@ -200,19 +215,20 @@ panics in the future, you’ll need to figure out what action the code is taking with what values to cause the panic and what the code should do instead. We’ll come back to `panic!` and when we should and should not use `panic!` to -handle error conditions in “To panic! or Not to panic!” on page XX. Next, we’ll -look at how to recover from an error using `Result`. +handle error conditions in the “To `panic!` or Not to +`panic!`” section later in this +chapter. Next, we’ll look at how to recover from an error using `Result`. ## Recoverable Errors with Result Most errors aren’t serious enough to require the program to stop entirely. -Sometimes when a function fails it’s for a reason that you can easily interpret +Sometimes when a function fails, it’s for a reason that you can easily interpret and respond to. For example, if you try to open a file and that operation fails because the file doesn’t exist, you might want to create the file instead of terminating the process. -Recall from “Handling Potential Failure with Result” on page XX that the -`Result` enum is defined as having two variants, `Ok` and `Err`, as follows: +Recall from “Handling Potential Failure with `Result`” in Chapter 2 that the `Result` enum is defined as having two +variants, `Ok` and `Err`, as follows: ``` enum Result { @@ -221,7 +237,7 @@ enum Result { } ``` -The `T` and `E` are generic type parameters: we’ll discuss generics in more +The `T` and `E` are generic type parameters: We’ll discuss generics in more detail in Chapter 10. What you need to know right now is that `T` represents the type of the value that will be returned in a success case within the `Ok` variant, and `E` represents the type of the error that will be returned in a @@ -231,9 +247,9 @@ many different situations where the success value and error value we want to return may differ. Let’s call a function that returns a `Result` value because the function could -fail. In Listing 9-3 we try to open a file. +fail. In Listing 9-3, we try to open a file. -Filename: src/main.rs +src/main.rs ``` use std::fs::File; @@ -250,7 +266,7 @@ has been filled in by the implementation of `File::open` with the type of the success value, `std::fs::File`, which is a file handle. The type of `E` used in the error value is `std::io::Error`. This return type means the call to `File::open` might succeed and return a file handle that we can read from or -write to. The function call also might fail: for example, the file might not +write to. The function call also might fail: For example, the file might not exist, or we might not have permission to access the file. The `File::open` function needs to have a way to tell us whether it succeeded or failed and at the same time give us either the file handle or error information. This @@ -267,7 +283,7 @@ on the value `File::open` returns. Listing 9-4 shows one way to handle the `Result` using a basic tool, the `match` expression that we discussed in Chapter 6. -Filename: src/main.rs +src/main.rs ``` use std::fs::File; @@ -277,15 +293,12 @@ fn main() { let greeting_file = match greeting_file_result { Ok(file) => file, - Err(error) => { - panic!("Problem opening the file: {:?}", error); - } + Err(error) => panic!("Problem opening the file: {error:?}"), }; } ``` -Listing 9-4: Using a `match` expression to handle the `Result` variants that -might be returned +Listing 9-4: Using a `match` expression to handle the `Result` variants that might be returned Note that, like the `Option` enum, the `Result` enum and its variants have been brought into scope by the prelude, so we don’t need to specify `Result::` @@ -302,9 +315,14 @@ there’s no file named *hello.txt* in our current directory and we run this code, we’ll see the following output from the `panic!` macro: ``` -thread 'main' panicked at 'Problem opening the file: Os { code: - 2, kind: NotFound, message: "No such file or directory" }', -src/main.rs:8:23 +$ cargo run + Compiling error-handling v0.1.0 (file:///projects/error-handling) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.73s + Running `target/debug/error-handling` + +thread 'main' panicked at src/main.rs:8:23: +Problem opening the file: Os { code: 2, kind: NotFound, message: "No such file or directory" } +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` As usual, this output tells us exactly what has gone wrong. @@ -319,7 +337,10 @@ reason—for example, because we didn’t have permission to open the file—we want the code to `panic!` in the same way it did in Listing 9-4. For this, we add an inner `match` expression, shown in Listing 9-5. -Filename: src/main.rs +src/main.rs + + ``` use std::fs::File; @@ -331,20 +352,12 @@ fn main() { let greeting_file = match greeting_file_result { Ok(file) => file, Err(error) => match error.kind() { - ErrorKind::NotFound => { - match File::create("hello.txt") { - Ok(fc) => fc, - Err(e) => panic!( - "Problem creating the file: {:?}", - e - ), - } - } - other_error => { - panic!( - "Problem opening the file: {:?}", - other_error - ); + ErrorKind::NotFound => match File::create("hello.txt") { + Ok(fc) => fc, + Err(e) => panic!("Problem creating the file: {e:?}"), + }, + _ => { + panic!("Problem opening the file: {error:?}"); } }, }; @@ -355,11 +368,11 @@ Listing 9-5: Handling different kinds of errors in different ways The type of the value that `File::open` returns inside the `Err` variant is `io::Error`, which is a struct provided by the standard library. This struct -has a method `kind` that we can call to get an `io::ErrorKind` value. The enum -`io::ErrorKind` is provided by the standard library and has variants +has a method, `kind`, that we can call to get an `io::ErrorKind` value. The +enum `io::ErrorKind` is provided by the standard library and has variants representing the different kinds of errors that might result from an `io` operation. The variant we want to use is `ErrorKind::NotFound`, which indicates -the file we’re trying to open doesn’t exist yet. So we match on +the file we’re trying to open doesn’t exist yet. So, we match on `greeting_file_result`, but we also have an inner match on `error.kind()`. The condition we want to check in the inner match is whether the value returned @@ -370,41 +383,46 @@ file can’t be created, a different error message is printed. The second arm of the outer `match` stays the same, so the program panics on any error besides the missing file error. -#### Alternatives to Using match with Result - -That’s a lot of `match`! The `match` expression is very useful but also very -much a primitive. In Chapter 13, you’ll learn about closures, which are used -with many of the methods defined on `Result`. These methods can be more -concise than using `match` when handling `Result` values in your code. - -For example, here’s another way to write the same logic as shown in Listing -9-5, this time using closures and the `unwrap_or_else` method: - -``` -// src/main.rs -use std::fs::File; -use std::io::ErrorKind; - -fn main() { - let greeting_file = File::open("hello.txt").unwrap_or_else(|error| { - if error.kind() == ErrorKind::NotFound { - File::create("hello.txt").unwrap_or_else(|error| { - panic!("Problem creating the file: {:?}", error); - }) - } else { - panic!("Problem opening the file: {:?}", error); - } - }); -} -``` - -Although this code has the same behavior as Listing 9-5, it doesn’t contain any -`match` expressions and is cleaner to read. Come back to this example after -you’ve read Chapter 13, and look up the `unwrap_or_else` method in the standard -library documentation. Many more of these methods can clean up huge nested -`match` expressions when you’re dealing with errors. - -#### Shortcuts for Panic on Error: unwrap and expect +> #### Alternatives to Using match with Result +> +> That’s a lot of `match`! The `match` expression is very useful but also very +> much a primitive. In Chapter 13, you’ll learn about closures, which are used +> with many of the methods defined on `Result`. These methods can be more +> concise than using `match` when handling `Result` values in your code. +> +> For example, here’s another way to write the same logic as shown in Listing +> 9-5, this time using closures and the `unwrap_or_else` method: +> +> +> +> ````rust,ignore +> use std::fs::File; +> use std::io::ErrorKind; +> +> fn main() { +> let greeting_file = File::open("hello.txt").unwrap_or_else(|error| { +> if error.kind() == ErrorKind::NotFound { +> File::create("hello.txt").unwrap_or_else(|error| { +> panic!("Problem creating the file: {error:?}"); +> }) +> } else { +> panic!("Problem opening the file: {error:?}"); +> } +> }); +> } +> ```` +> +> Although this code has the same behavior as Listing 9-5, it doesn’t contain +> any `match` expressions and is cleaner to read. Come back to this example +> after you’ve read Chapter 13 and look up the `unwrap_or_else` method in the +> standard library documentation. Many more of these methods can clean up huge, +> nested `match` expressions when you’re dealing with errors. + + + + + +#### Shortcuts for Panic on Error Using `match` works well enough, but it can be a bit verbose and doesn’t always communicate intent well. The `Result` type has many helper methods @@ -414,7 +432,7 @@ Listing 9-4. If the `Result` value is the `Ok` variant, `unwrap` will return the value inside the `Ok`. If the `Result` is the `Err` variant, `unwrap` will call the `panic!` macro for us. Here is an example of `unwrap` in action: -Filename: src/main.rs +src/main.rs ``` use std::fs::File; @@ -424,13 +442,20 @@ fn main() { } ``` + + If we run this code without a *hello.txt* file, we’ll see an error message from the `panic!` call that the `unwrap` method makes: + + ``` -thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os { -code: 2, kind: NotFound, message: "No such file or directory" }', -src/main.rs:4:49 +thread 'main' panicked at src/main.rs:4:49: +called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" } ``` Similarly, the `expect` method lets us also choose the `panic!` error message. @@ -438,7 +463,7 @@ Using `expect` instead of `unwrap` and providing good error messages can convey your intent and make tracking down the source of a panic easier. The syntax of `expect` looks like this: -Filename: src/main.rs +src/main.rs ``` use std::fs::File; @@ -449,15 +474,22 @@ fn main() { } ``` + + We use `expect` in the same way as `unwrap`: to return the file handle or call the `panic!` macro. The error message used by `expect` in its call to `panic!` will be the parameter that we pass to `expect`, rather than the default `panic!` message that `unwrap` uses. Here’s what it looks like: + + ``` -thread 'main' panicked at 'hello.txt should be included in this project: Os { -code: 2, kind: NotFound, message: "No such file or directory" }', -src/main.rs:5:10 +thread 'main' panicked at src/main.rs:5:10: +hello.txt should be included in this project: Os { code: 2, kind: NotFound, message: "No such file or directory" } ``` In production-quality code, most Rustaceans choose `expect` rather than @@ -468,7 +500,7 @@ information to use in debugging. ### Propagating Errors When a function’s implementation calls something that might fail, instead of -handling the error within the function itself you can return the error to the +handling the error within the function itself, you can return the error to the calling code so that it can decide what to do. This is known as *propagating* the error and gives more control to the calling code, where there might be more information or logic that dictates how the error should be handled than what @@ -478,25 +510,29 @@ For example, Listing 9-6 shows a function that reads a username from a file. If the file doesn’t exist or can’t be read, this function will return those errors to the code that called the function. -Filename: src/main.rs +src/main.rs + + ``` use std::fs::File; use std::io::{self, Read}; -1 fn read_username_from_file() -> Result { - 2 let username_file_result = File::open("hello.txt"); +fn read_username_from_file() -> Result { + let username_file_result = File::open("hello.txt"); - 3 let mut username_file = match username_file_result { - 4 Ok(file) => file, - 5 Err(e) => return Err(e), + let mut username_file = match username_file_result { + Ok(file) => file, + Err(e) => return Err(e), }; - 6 let mut username = String::new(); + let mut username = String::new(); - 7 match username_file.read_to_string(&mut username) { - 8 Ok(_) => Ok(username), - 9 Err(e) => Err(e), + match username_file.read_to_string(&mut username) { + Ok(_) => Ok(username), + Err(e) => Err(e), } } ``` @@ -506,41 +542,41 @@ Listing 9-6: A function that returns errors to the calling code using `match` This function can be written in a much shorter way, but we’re going to start by doing a lot of it manually in order to explore error handling; at the end, we’ll show the shorter way. Let’s look at the return type of the function -first: `Result` [1]. This means the function is returning a +first: `Result`. This means the function is returning a value of the type `Result`, where the generic parameter `T` has been filled in with the concrete type `String` and the generic type `E` has been filled in with the concrete type `io::Error`. If this function succeeds without any problems, the code that calls this function will receive an `Ok` value that holds a `String`—the `username` that -this function read from the file [8]. If this function encounters any problems, -the calling code will receive an `Err` value that holds an instance of -`io::Error` that contains more information about what the problems were. We -chose `io::Error` as the return type of this function because that happens to -be the type of the error value returned from both of the operations we’re -calling in this function’s body that might fail: the `File::open` function [2] -and the `read_to_string` method [7]. - -The body of the function starts by calling the `File::open` function [2]. Then -we handle the `Result` value with a `match` similar to the `match` in Listing -9-4. If `File::open` succeeds, the file handle in the pattern variable `file` -[4] becomes the value in the mutable variable `username_file` [3] and the -function continues. In the `Err` case, instead of calling `panic!`, we use the -`return` keyword to return early out of the function entirely and pass the -error value from `File::open`, now in the pattern variable `e`, back to the -calling code as this function’s error value [5]. +this function read from the file. If this function encounters any problems, the +calling code will receive an `Err` value that holds an instance of `io::Error` +that contains more information about what the problems were. We chose +`io::Error` as the return type of this function because that happens to be the +type of the error value returned from both of the operations we’re calling in +this function’s body that might fail: the `File::open` function and the +`read_to_string` method. + +The body of the function starts by calling the `File::open` function. Then, we +handle the `Result` value with a `match` similar to the `match` in Listing 9-4. +If `File::open` succeeds, the file handle in the pattern variable `file` +becomes the value in the mutable variable `username_file` and the function +continues. In the `Err` case, instead of calling `panic!`, we use the `return` +keyword to return early out of the function entirely and pass the error value +from `File::open`, now in the pattern variable `e`, back to the calling code as +this function’s error value. So, if we have a file handle in `username_file`, the function then creates a -new `String` in variable `username` [6] and calls the `read_to_string` method -on the file handle in `username_file` to read the contents of the file into -`username` [7]. The `read_to_string` method also returns a `Result` because it -might fail, even though `File::open` succeeded. So we need another `match` to -handle that `Result`: if `read_to_string` succeeds, then our function has +new `String` in variable `username` and calls the `read_to_string` method on +the file handle in `username_file` to read the contents of the file into +`username`. The `read_to_string` method also returns a `Result` because it +might fail, even though `File::open` succeeded. So, we need another `match` to +handle that `Result`: If `read_to_string` succeeds, then our function has succeeded, and we return the username from the file that’s now in `username` wrapped in an `Ok`. If `read_to_string` fails, we return the error value in the same way that we returned the error value in the `match` that handled the return value of `File::open`. However, we don’t need to explicitly say -`return`, because this is the last expression in the function [9]. +`return`, because this is the last expression in the function. The code that calls this code will then handle getting either an `Ok` value that contains a username or an `Err` value that contains an `io::Error`. It’s @@ -554,13 +590,21 @@ it to handle appropriately. This pattern of propagating errors is so common in Rust that Rust provides the question mark operator `?` to make this easier. -#### A Shortcut for Propagating Errors: The ? Operator + + + + +#### The ? Operator Shortcut Listing 9-7 shows an implementation of `read_username_from_file` that has the same functionality as in Listing 9-6, but this implementation uses the `?` operator. -Filename: src/main.rs +src/main.rs + + ``` use std::fs::File; @@ -574,19 +618,18 @@ fn read_username_from_file() -> Result { } ``` -Listing 9-7: A function that returns errors to the calling code using the `?` -operator +Listing 9-7: A function that returns errors to the calling code using the `?` operator The `?` placed after a `Result` value is defined to work in almost the same way -as the `match` expressions we defined to handle the `Result` values in Listing -9-6. If the value of the `Result` is an `Ok`, the value inside the `Ok` will -get returned from this expression, and the program will continue. If the value -is an `Err`, the `Err` will be returned from the whole function as if we had -used the `return` keyword so the error value gets propagated to the calling -code. +as the `match` expressions that we defined to handle the `Result` values in +Listing 9-6. If the value of the `Result` is an `Ok`, the value inside the `Ok` +will get returned from this expression, and the program will continue. If the +value is an `Err`, the `Err` will be returned from the whole function as if we +had used the `return` keyword so that the error value gets propagated to the +calling code. There is a difference between what the `match` expression from Listing 9-6 does -and what the `?` operator does: error values that have the `?` operator called +and what the `?` operator does: Error values that have the `?` operator called on them go through the `from` function, defined in the `From` trait in the standard library, which is used to convert values from one type into another. When the `?` operator calls the `from` function, the error type received is @@ -612,7 +655,11 @@ The `?` operator eliminates a lot of boilerplate and makes this function’s implementation simpler. We could even shorten this code further by chaining method calls immediately after the `?`, as shown in Listing 9-8. -Filename: src/main.rs +src/main.rs + + ``` use std::fs::File; @@ -640,7 +687,11 @@ this is just a different, more ergonomic way to write it. Listing 9-9 shows a way to make this even shorter using `fs::read_to_string`. -Filename: src/main.rs +src/main.rs + + ``` use std::fs; @@ -651,8 +702,7 @@ fn read_username_from_file() -> Result { } ``` -Listing 9-9: Using `fs::read_to_string` instead of opening and then reading the -file +Listing 9-9: Using `fs::read_to_string` instead of opening and then reading the file Reading a file into a string is a fairly common operation, so the standard library provides the convenient `fs::read_to_string` function that opens the @@ -661,7 +711,11 @@ into that `String`, and returns it. Of course, using `fs::read_to_string` doesn’t give us the opportunity to explain all the error handling, so we did it the longer way first. -#### Where the ? Operator Can Be Used + + + + +#### Where to Use the ? Operator The `?` operator can only be used in functions whose return type is compatible with the value the `?` is used on. This is because the `?` operator is defined @@ -675,7 +729,7 @@ In Listing 9-10, let’s look at the error we’ll get if we use the `?` operato in a `main` function with a return type that is incompatible with the type of the value we use `?` on. -Filename: src/main.rs +src/main.rs ``` use std::fs::File; @@ -685,8 +739,7 @@ fn main() { } ``` -Listing 9-10: Attempting to use the `?` in the `main` function that returns -`()` won’t compile. +Listing 9-10: Attempting to use the `?` in the `main` function that returns `()` won’t compile. This code opens a file, which might fail. The `?` operator follows the `Result` value returned by `File::open`, but this `main` function has the return type of @@ -694,19 +747,26 @@ value returned by `File::open`, but this `main` function has the return type of message: ``` -error[E0277]: the `?` operator can only be used in a function that returns -`Result` or `Option` (or another type that implements `FromResidual`) +$ cargo run + Compiling error-handling v0.1.0 (file:///projects/error-handling) +error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`) --> src/main.rs:4:48 | -3 | / fn main() { -4 | | let greeting_file = File::open("hello.txt")?; - | | ^ cannot use the `?` -operator in a function that returns `()` -5 | | } - | |_- this function should return `Result` or `Option` to accept `?` +3 | fn main() { + | --------- this function should return `Result` or `Option` to accept `?` +4 | let greeting_file = File::open("hello.txt")?; + | ^ cannot use the `?` operator in a function that returns `()` + | + = help: the trait `FromResidual>` is not implemented for `()` +help: consider adding return type | - = help: the trait `FromResidual>` is not -implemented for `()` +3 ~ fn main() -> Result<(), Box> { +4 | let greeting_file = File::open("hello.txt")?; +5 + Ok(()) + | + +For more information about this error, try `rustc --explain E0277`. +error: could not compile `error-handling` (bin "error-handling") due to 1 previous error ``` This error points out that we’re only allowed to use the `?` operator in a @@ -723,12 +783,13 @@ The error message also mentioned that `?` can be used with `Option` values as well. As with using `?` on `Result`, you can only use `?` on `Option` in a function that returns an `Option`. The behavior of the `?` operator when called on an `Option` is similar to its behavior when called on a `Result`: -if the value is `None`, the `None` will be returned early from the function at +If the value is `None`, the `None` will be returned early from the function at that point. If the value is `Some`, the value inside the `Some` is the resultant value of the expression, and the function continues. Listing 9-11 has an example of a function that finds the last character of the first line in the given text. + ``` fn last_char_of_first_line(text: &str) -> Option { text.lines().next()?.chars().last() @@ -775,7 +836,7 @@ from Listing 9-10, but we’ve changed the return type of `main` to be `Result<(), Box>` and added a return value `Ok(())` to the end. This code will now compile. -Filename: src/main.rs +src/main.rs ``` use std::error::Error; @@ -788,30 +849,30 @@ fn main() -> Result<(), Box> { } ``` -Listing 9-12: Changing `main` to return `Result<(), E>` allows the use of the -`?` operator on `Result` values. +Listing 9-12: Changing `main` to return `Result<(), E>` allows the use of the `?` operator on `Result` values. -The `Box` type is a *trait object*, which we’ll talk about in “Using -Trait Objects That Allow for Values of Different Types” on page XX. For now, -you can read `Box` to mean “any kind of error.” Using `?` on a -`Result` value in a `main` function with the error type `Box` is -allowed because it allows any `Err` value to be returned early. Even though the -body of this `main` function will only ever return errors of type -`std::io::Error`, by specifying `Box`, this signature will continue -to be correct even if more code that returns other errors is added to the body -of `main`. +The `Box` type is a trait object, which we’ll talk about in “Using +Trait Objects to Abstract over Shared Behavior” +in Chapter 18. For now, you can read `Box` to mean “any kind of +error.” Using `?` on a `Result` value in a `main` function with the error type +`Box` is allowed because it allows any `Err` value to be returned +early. Even though the body of this `main` function will only ever return +errors of type `std::io::Error`, by specifying `Box`, this signature +will continue to be correct even if more code that returns other errors is +added to the body of `main`. When a `main` function returns a `Result<(), E>`, the executable will exit with a value of `0` if `main` returns `Ok(())` and will exit with a nonzero value if `main` returns an `Err` value. Executables written in C return integers when -they exit: programs that exit successfully return the integer `0`, and programs +they exit: Programs that exit successfully return the integer `0`, and programs that error return some integer other than `0`. Rust also returns integers from executables to be compatible with this convention. The `main` function may return any types that implement the -`std::process::Termination` trait, which contains a function `report` that -returns an `ExitCode`. Consult the standard library documentation for more -information on implementing the `Termination` trait for your own types. +`std::process::Termination` trait, which contains +a function `report` that returns an `ExitCode`. Consult the standard library +documentation for more information on implementing the `Termination` trait for +your own types. Now that we’ve discussed the details of calling `panic!` or returning `Result`, let’s return to the topic of how to decide which is appropriate to use in which @@ -819,7 +880,7 @@ cases. ## To panic! or Not to panic! -So how do you decide when you should call `panic!` and when you should return +So, how do you decide when you should call `panic!` and when you should return `Result`? When code panics, there’s no way to recover. You could call `panic!` for any error situation, whether there’s a possible way to recover or not, but then you’re making the decision that a situation is unrecoverable on behalf of @@ -844,39 +905,44 @@ understood that a call to a method like `unwrap` that could panic is meant as a placeholder for the way you’d want your application to handle errors, which can differ based on what the rest of your code is doing. -Similarly, the `unwrap` and `expect` methods are very handy when prototyping, -before you’re ready to decide how to handle errors. They leave clear markers in -your code for when you’re ready to make your program more robust. +Similarly, the `unwrap` and `expect` methods are very handy when you’re +prototyping and you’re not yet ready to decide how to handle errors. They leave +clear markers in your code for when you’re ready to make your program more +robust. If a method call fails in a test, you’d want the whole test to fail, even if that method isn’t the functionality under test. Because `panic!` is how a test is marked as a failure, calling `unwrap` or `expect` is exactly what should happen. -### Cases in Which You Have More Information Than the Compiler + + + -It would also be appropriate to call `unwrap` or `expect` when you have some -other logic that ensures the `Result` will have an `Ok` value, but the logic -isn’t something the compiler understands. You’ll still have a `Result` value -that you need to handle: whatever operation you’re calling still has the -possibility of failing in general, even though it’s logically impossible in -your particular situation. If you can ensure by manually inspecting the code -that you’ll never have an `Err` variant, it’s perfectly acceptable to call -`unwrap`, and even better to document the reason you think you’ll never have an -`Err` variant in the `expect` text. Here’s an example: +### When You Have More Information Than the Compiler + +It would also be appropriate to call `expect` when you have some other logic +that ensures that the `Result` will have an `Ok` value, but the logic isn’t +something the compiler understands. You’ll still have a `Result` value that you +need to handle: Whatever operation you’re calling still has the possibility of +failing in general, even though it’s logically impossible in your particular +situation. If you can ensure by manually inspecting the code that you’ll never +have an `Err` variant, it’s perfectly acceptable to call `expect` and document +the reason you think you’ll never have an `Err` variant in the argument text. +Here’s an example: ``` -use std::net::IpAddr; + use std::net::IpAddr; -let home: IpAddr = "127.0.0.1" - .parse() - .expect("Hardcoded IP address should be valid"); + let home: IpAddr = "127.0.0.1" + .parse() + .expect("Hardcoded IP address should be valid"); ``` We’re creating an `IpAddr` instance by parsing a hardcoded string. We can see that `127.0.0.1` is a valid IP address, so it’s acceptable to use `expect` here. However, having a hardcoded, valid string doesn’t change the return type -of the `parse` method: we still get a `Result` value, and the compiler will +of the `parse` method: We still get a `Result` value, and the compiler will still make us handle the `Result` as if the `Err` variant is a possibility because the compiler isn’t smart enough to see that this string is always a valid IP address. If the IP address string came from a user rather than being @@ -895,21 +961,22 @@ contradictory values, or missing values are passed to your code—plus one or more of the following: * The bad state is something that is unexpected, as opposed to something that -will likely happen occasionally, like a user entering data in the wrong format. + will likely happen occasionally, like a user entering data in the wrong + format. * Your code after this point needs to rely on not being in this bad state, -rather than checking for the problem at every step. + rather than checking for the problem at every step. * There’s not a good way to encode this information in the types you use. We’ll -work through an example of what we mean in “Encoding States and Behavior as -Types” on page XX. + work through an example of what we mean in “Encoding States and Behavior as + Types” in Chapter 18. If someone calls your code and passes in values that don’t make sense, it’s -best to return an error if you can so the user of the library can decide what -they want to do in that case. However, in cases where continuing could be +best to return an error if you can so that the user of the library can decide +what they want to do in that case. However, in cases where continuing could be insecure or harmful, the best choice might be to call `panic!` and alert the -person using your library to the bug in their code so they can fix it during -development. Similarly, `panic!` is often appropriate if you’re calling -external code that is out of your control and it returns an invalid state that -you have no way of fixing. +person using your library to the bug in their code so that they can fix it +during development. Similarly, `panic!` is often appropriate if you’re calling +external code that is out of your control and returns an invalid state that you +have no way of fixing. However, when failure is expected, it’s more appropriate to return a `Result` than to make a `panic!` call. Examples include a parser being given malformed @@ -920,11 +987,11 @@ expected possibility that the calling code must decide how to handle. When your code performs an operation that could put a user at risk if it’s called using invalid values, your code should verify the values are valid first and panic if the values aren’t valid. This is mostly for safety reasons: -attempting to operate on invalid data can expose your code to vulnerabilities. +Attempting to operate on invalid data can expose your code to vulnerabilities. This is the main reason the standard library will call `panic!` if you attempt -an out-of-bounds memory access: trying to access memory that doesn’t belong to +an out-of-bounds memory access: Trying to access memory that doesn’t belong to the current data structure is a common security problem. Functions often have -*contracts*: their behavior is only guaranteed if the inputs meet particular +*contracts*: Their behavior is only guaranteed if the inputs meet particular requirements. Panicking when the contract is violated makes sense because a contract violation always indicates a caller-side bug, and it’s not a kind of error you want the calling code to have to explicitly handle. In fact, there’s @@ -936,125 +1003,131 @@ However, having lots of error checks in all of your functions would be verbose and annoying. Fortunately, you can use Rust’s type system (and thus the type checking done by the compiler) to do many of the checks for you. If your function has a particular type as a parameter, you can proceed with your code’s -logic knowing that the compiler has already ensured you have a valid value. For -example, if you have a type rather than an `Option`, your program expects to -have *something* rather than *nothing*. Your code then doesn’t have to handle -two cases for the `Some` and `None` variants: it will only have one case for -definitely having a value. Code trying to pass nothing to your function won’t -even compile, so your function doesn’t have to check for that case at runtime. -Another example is using an unsigned integer type such as `u32`, which ensures -the parameter is never negative. - -### Creating Custom Types for Validation - -Let’s take the idea of using Rust’s type system to ensure we have a valid value -one step further and look at creating a custom type for validation. Recall the -guessing game in Chapter 2 in which our code asked the user to guess a number -between 1 and 100. We never validated that the user’s guess was between those -numbers before checking it against our secret number; we only validated that -the guess was positive. In this case, the consequences were not very dire: our -output of “Too high” or “Too low” would still be correct. But it would be a -useful enhancement to guide the user toward valid guesses and have different -behavior when the user guesses a number that’s out of range versus when the -user types, for example, letters instead. +logic knowing that the compiler has already ensured that you have a valid +value. For example, if you have a type rather than an `Option`, your program +expects to have *something* rather than *nothing*. Your code then doesn’t have +to handle two cases for the `Some` and `None` variants: It will only have one +case for definitely having a value. Code trying to pass nothing to your +function won’t even compile, so your function doesn’t have to check for that +case at runtime. Another example is using an unsigned integer type such as +`u32`, which ensures that the parameter is never negative. + + + + + +### Custom Types for Validation + +Let’s take the idea of using Rust’s type system to ensure that we have a valid +value one step further and look at creating a custom type for validation. +Recall the guessing game in Chapter 2 in which our code asked the user to guess +a number between 1 and 100. We never validated that the user’s guess was +between those numbers before checking it against our secret number; we only +validated that the guess was positive. In this case, the consequences were not +very dire: Our output of “Too high” or “Too low” would still be correct. But it +would be a useful enhancement to guide the user toward valid guesses and have +different behavior when the user guesses a number that’s out of range versus +when the user types, for example, letters instead. One way to do this would be to parse the guess as an `i32` instead of only a `u32` to allow potentially negative numbers, and then add a check for the number being in range, like so: -Filename: src/main.rs +src/main.rs ``` -loop { - --snip-- + loop { + // --snip-- - let guess: i32 = match guess.trim().parse() { - Ok(num) => num, - Err(_) => continue, - }; + let guess: i32 = match guess.trim().parse() { + Ok(num) => num, + Err(_) => continue, + }; - if guess < 1 || guess > 100 { - println!("The secret number will be between 1 and 100."); - continue; - } + if guess < 1 || guess > 100 { + println!("The secret number will be between 1 and 100."); + continue; + } - match guess.cmp(&secret_number) { - --snip-- -} + match guess.cmp(&secret_number) { + // --snip-- + } ``` + + The `if` expression checks whether our value is out of range, tells the user about the problem, and calls `continue` to start the next iteration of the loop and ask for another guess. After the `if` expression, we can proceed with the comparisons between `guess` and the secret number knowing that `guess` is between 1 and 100. -However, this is not an ideal solution: if it were absolutely critical that the +However, this is not an ideal solution: If it were absolutely critical that the program only operated on values between 1 and 100, and it had many functions with this requirement, having a check like this in every function would be tedious (and might impact performance). -Instead, we can make a new type and put the validations in a function to create -an instance of the type rather than repeating the validations everywhere. That -way, it’s safe for functions to use the new type in their signatures and -confidently use the values they receive. Listing 9-13 shows one way to define a -`Guess` type that will only create an instance of `Guess` if the `new` function -receives a value between 1 and 100. +Instead, we can make a new type in a dedicated module and put the validations +in a function to create an instance of the type rather than repeating the +validations everywhere. That way, it’s safe for functions to use the new type +in their signatures and confidently use the values they receive. Listing 9-13 +shows one way to define a `Guess` type that will only create an instance of +`Guess` if the `new` function receives a value between 1 and 100. -Filename: src/lib.rs +src/guessing_game.rs ``` -1 pub struct Guess { +pub struct Guess { value: i32, } impl Guess { - 2 pub fn new(value: i32) -> Guess { - 3 if value < 1 || value > 100 { - 4 panic!( - "Guess value must be between 1 and 100, got {}.", - value - ); + pub fn new(value: i32) -> Guess { + if value < 1 || value > 100 { + panic!("Guess value must be between 1 and 100, got {value}."); } - 5 Guess { value } + Guess { value } } - 6 pub fn value(&self) -> i32 { + pub fn value(&self) -> i32 { self.value } } ``` -Listing 9-13: A `Guess` type that will only continue with values between 1 and -100 +Listing 9-13: A `Guess` type that will only continue with values between 1 and 100 -First we define a struct named `Guess` that has a field named `value` that -holds an `i32` [1]. This is where the number will be stored. +Note that this code in *src/guessing_game.rs* depends on adding a module +declaration `mod guessing_game;` in *src/lib.rs* that we haven’t shown here. +Within this new module’s file, we define a struct named `Guess` that has a +field named `value` that holds an `i32`. This is where the number will be +stored. -Then we implement an associated function named `new` on `Guess` that creates -instances of `Guess` values [2]. The `new` function is defined to have one +Then, we implement an associated function named `new` on `Guess` that creates +instances of `Guess` values. The `new` function is defined to have one parameter named `value` of type `i32` and to return a `Guess`. The code in the -body of the `new` function tests `value` to make sure it’s between 1 and 100 -[3]. If `value` doesn’t pass this test, we make a `panic!` call [4], which will -alert the programmer who is writing the calling code that they have a bug they -need to fix, because creating a `Guess` with a `value` outside this range would +body of the `new` function tests `value` to make sure it’s between 1 and 100. +If `value` doesn’t pass this test, we make a `panic!` call, which will alert +the programmer who is writing the calling code that they have a bug they need +to fix, because creating a `Guess` with a `value` outside this range would violate the contract that `Guess::new` is relying on. The conditions in which `Guess::new` might panic should be discussed in its public-facing API documentation; we’ll cover documentation conventions indicating the possibility of a `panic!` in the API documentation that you create in Chapter 14. If `value` does pass the test, we create a new `Guess` with its `value` field set -to the `value` parameter and return the `Guess` [5]. +to the `value` parameter and return the `Guess`. Next, we implement a method named `value` that borrows `self`, doesn’t have any -other parameters, and returns an `i32` [6]. This kind of method is sometimes -called a *getter* because its purpose is to get some data from its fields and -return it. This public method is necessary because the `value` field of the -`Guess` struct is private. It’s important that the `value` field be private so -code using the `Guess` struct is not allowed to set `value` directly: code -outside the module *must* use the `Guess::new` function to create an instance -of `Guess`, thereby ensuring there’s no way for a `Guess` to have a `value` -that hasn’t been checked by the conditions in the `Guess::new` function. +other parameters, and returns an `i32`. This kind of method is sometimes called +a *getter* because its purpose is to get some data from its fields and return +it. This public method is necessary because the `value` field of the `Guess` +struct is private. It’s important that the `value` field be private so that +code using the `Guess` struct is not allowed to set `value` directly: Code +outside the `guessing_game` module *must* use the `Guess::new` function to +create an instance of `Guess`, thereby ensuring that there’s no way for a +`Guess` to have a `value` that hasn’t been checked by the conditions in the +`Guess::new` function. A function that has a parameter or returns only numbers between 1 and 100 could then declare in its signature that it takes or returns a `Guess` rather than an @@ -1074,4 +1147,3 @@ situations will make your code more reliable in the face of inevitable problems. Now that you’ve seen useful ways that the standard library uses generics with the `Option` and `Result` enums, we’ll talk about how generics work and how you can use them in your code. - diff --git a/nostarch/chapter10.md b/nostarch/chapter10.md index bb8919d790..29860d9148 100644 --- a/nostarch/chapter10.md +++ b/nostarch/chapter10.md @@ -16,25 +16,25 @@ when compiling and running the code. Functions can take parameters of some generic type, instead of a concrete type like `i32` or `String`, in the same way they take parameters with unknown -values to run the same code on multiple concrete values. In fact, we’ve already +values to run the same code on multiple concrete values. In fact, we already used generics in Chapter 6 with `Option`, in Chapter 8 with `Vec` and `HashMap`, and in Chapter 9 with `Result`. In this chapter, you’ll explore how to define your own types, functions, and methods with generics! -First we’ll review how to extract a function to reduce code duplication. We’ll +First, we’ll review how to extract a function to reduce code duplication. We’ll then use the same technique to make a generic function from two functions that differ only in the types of their parameters. We’ll also explain how to use generic types in struct and enum definitions. -Then you’ll learn how to use *traits* to define behavior in a generic way. You +Then, you’ll learn how to use traits to define behavior in a generic way. You can combine traits with generic types to constrain a generic type to accept only those types that have a particular behavior, as opposed to just any type. Finally, we’ll discuss *lifetimes*: a variety of generics that give the compiler information about how references relate to each other. Lifetimes allow us to give the compiler enough information about borrowed values so that it can -ensure references will be valid in more situations than it could without our -help. +ensure that references will be valid in more situations than it could without +our help. ## Removing Duplication by Extracting a Function @@ -42,7 +42,7 @@ Generics allow us to replace specific types with a placeholder that represents multiple types to remove code duplication. Before diving into generics syntax, let’s first look at how to remove duplication in a way that doesn’t involve generic types by extracting a function that replaces specific values with a -placeholder that represents multiple values. Then we’ll apply the same +placeholder that represents multiple values. Then, we’ll apply the same technique to extract a generic function! By looking at how to recognize duplicated code you can extract into a function, you’ll start to recognize duplicated code that can use generics. @@ -50,17 +50,17 @@ duplicated code that can use generics. We’ll begin with the short program in Listing 10-1 that finds the largest number in a list. -Filename: src/main.rs +src/main.rs ``` fn main() { - 1 let number_list = vec![34, 50, 25, 100, 65]; + let number_list = vec![34, 50, 25, 100, 65]; - 2 let mut largest = &number_list[0]; + let mut largest = &number_list[0]; - 3 for number in &number_list { - 4 if number > largest { - 5 largest = number; + for number in &number_list { + if number > largest { + largest = number; } } @@ -70,20 +70,20 @@ fn main() { Listing 10-1: Finding the largest number in a list of numbers -We store a list of integers in the variable `number_list` [1] and place a -reference to the first number in the list in a variable named `largest` [2]. We -then iterate through all the numbers in the list [3], and if the current number -is greater than the number stored in `largest` [4], we replace the reference in -that variable [5]. However, if the current number is less than or equal to the -largest number seen so far, the variable doesn’t change, and the code moves on -to the next number in the list. After considering all the numbers in the list, -`largest` should refer to the largest number, which in this case is 100. +We store a list of integers in the variable `number_list` and place a reference +to the first number in the list in a variable named `largest`. We then iterate +through all the numbers in the list, and if the current number is greater than +the number stored in `largest`, we replace the reference in that variable. +However, if the current number is less than or equal to the largest number seen +so far, the variable doesn’t change, and the code moves on to the next number +in the list. After considering all the numbers in the list, `largest` should +refer to the largest number, which in this case is 100. We’ve now been tasked with finding the largest number in two different lists of numbers. To do so, we can choose to duplicate the code in Listing 10-1 and use the same logic at two different places in the program, as shown in Listing 10-2. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -115,21 +115,21 @@ fn main() { Listing 10-2: Code to find the largest number in *two* lists of numbers -Although this code works, duplicating code is tedious and error prone. We also +Although this code works, duplicating code is tedious and error-prone. We also have to remember to update the code in multiple places when we want to change it. To eliminate this duplication, we’ll create an abstraction by defining a -function that operates on any list of integers passed in a parameter. This +function that operates on any list of integers passed in as a parameter. This solution makes our code clearer and lets us express the concept of finding the largest number in a list abstractly. In Listing 10-3, we extract the code that finds the largest number into a -function named `largest`. Then we call the function to find the largest number +function named `largest`. Then, we call the function to find the largest number in the two lists from Listing 10-2. We could also use the function on any other list of `i32` values we might have in the future. -Filename: src/main.rs +src/main.rs ``` fn largest(list: &[i32]) -> &i32 { @@ -161,14 +161,15 @@ Listing 10-3: Abstracted code to find the largest number in two lists The `largest` function has a parameter called `list`, which represents any concrete slice of `i32` values we might pass into the function. As a result, -when we call the function, the code runs on the specific values that we pass in. +when we call the function, the code runs on the specific values that we pass +in. In summary, here are the steps we took to change the code from Listing 10-2 to Listing 10-3: 1. Identify duplicate code. 1. Extract the duplicate code into the body of the function, and specify the -inputs and return values of that code in the function signature. + inputs and return values of that code in the function signature. 1. Update the two instances of duplicated code to call the function instead. Next, we’ll use these same steps with generics to reduce code duplication. In @@ -184,7 +185,7 @@ values. How would we eliminate that duplication? Let’s find out! We use generics to create definitions for items like function signatures or structs, which we can then use with many different concrete data types. Let’s first look at how to define functions, structs, enums, and methods using -generics. Then we’ll discuss how generics affect code performance. +generics. Then, we’ll discuss how generics affect code performance. ### In Function Definitions @@ -197,7 +198,7 @@ Continuing with our `largest` function, Listing 10-4 shows two functions that both find the largest value in a slice. We’ll then combine these into a single function that uses generics. -Filename: src/main.rs +src/main.rs ``` fn largest_i32(list: &[i32]) -> &i32 { @@ -237,8 +238,7 @@ fn main() { } ``` -Listing 10-4: Two functions that differ only in their names and in the types in -their signatures +Listing 10-4: Two functions that differ only in their names and in the types in their signatures The `largest_i32` function is the one we extracted in Listing 10-3 that finds the largest `i32` in a slice. The `largest_char` function finds the largest @@ -249,13 +249,13 @@ To parameterize the types in a new single function, we need to name the type parameter, just as we do for the value parameters to a function. You can use any identifier as a type parameter name. But we’ll use `T` because, by convention, type parameter names in Rust are short, often just one letter, and -Rust’s type-naming convention is CamelCase. Short for *type*, `T` is the +Rust’s type-naming convention is UpperCamelCase. Short for *type*, `T` is the default choice of most Rust programmers. When we use a parameter in the body of the function, we have to declare the -parameter name in the signature so the compiler knows what that name means. -Similarly, when we use a type parameter name in a function signature, we have -to declare the type parameter name before we use it. To define the generic +parameter name in the signature so that the compiler knows what that name +means. Similarly, when we use a type parameter name in a function signature, we +have to declare the type parameter name before we use it. To define the generic `largest` function, we place type name declarations inside angle brackets, `<>`, between the name of the function and the parameter list, like this: @@ -263,17 +263,17 @@ to declare the type parameter name before we use it. To define the generic fn largest(list: &[T]) -> &T { ``` -We read this definition as: the function `largest` is generic over some type -`T`. This function has one parameter named `list`, which is a slice of values +We read this definition as “The function `largest` is generic over some type +`T`.” This function has one parameter named `list`, which is a slice of values of type `T`. The `largest` function will return a reference to a value of the same type `T`. Listing 10-5 shows the combined `largest` function definition using the generic data type in its signature. The listing also shows how we can call the function with either a slice of `i32` values or `char` values. Note that this code won’t -compile yet, but we’ll fix it later in this chapter. +compile yet. -Filename: src/main.rs +src/main.rs ``` fn largest(list: &[T]) -> &T { @@ -301,12 +301,13 @@ fn main() { } ``` -Listing 10-5: The `largest` function using generic type parameters; this -doesn’t compile yet +Listing 10-5: The `largest` function using generic type parameters; this doesn’t compile yet If we compile this code right now, we’ll get this error: ``` +$ cargo run + Compiling chapter10 v0.1.0 (file:///projects/chapter10) error[E0369]: binary operation `>` cannot be applied to type `&T` --> src/main.rs:5:17 | @@ -315,22 +316,25 @@ error[E0369]: binary operation `>` cannot be applied to type `&T` | | | &T | -help: consider restricting type parameter `T` +help: consider restricting type parameter `T` with trait `PartialOrd` | 1 | fn largest(list: &[T]) -> &T { | ++++++++++++++++++++++ + +For more information about this error, try `rustc --explain E0369`. +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error ``` -The help text mentions `std::cmp::PartialOrd`, which is a *trait*, and we’re +The help text mentions `std::cmp::PartialOrd`, which is a trait, and we’re going to talk about traits in the next section. For now, know that this error states that the body of `largest` won’t work for all possible types that `T` could be. Because we want to compare values of type `T` in the body, we can only use types whose values can be ordered. To enable comparisons, the standard library has the `std::cmp::PartialOrd` trait that you can implement on types -(see Appendix C for more on this trait). By following the help text’s -suggestion, we restrict the types valid for `T` to only those that implement -`PartialOrd` and this example will compile, because the standard library -implements `PartialOrd` on both `i32` and `char`. +(see Appendix C for more on this trait). To fix Listing 10-5, we can follow the +help text’s suggestion and restrict the types valid for `T` to only those that +implement `PartialOrd`. The listing will then compile, because the standard +library implements `PartialOrd` on both `i32` and `char`. ### In Struct Definitions @@ -338,12 +342,12 @@ We can also define structs to use a generic type parameter in one or more fields using the `<>` syntax. Listing 10-6 defines a `Point` struct to hold `x` and `y` coordinate values of any type. -Filename: src/main.rs +src/main.rs ``` -1 struct Point { - 2 x: T, - 3 y: T, +struct Point { + x: T, + y: T, } fn main() { @@ -355,10 +359,9 @@ fn main() { Listing 10-6: A `Point` struct that holds `x` and `y` values of type `T` The syntax for using generics in struct definitions is similar to that used in -function definitions. First we declare the name of the type parameter inside -angle brackets just after the name of the struct [1]. Then we use the generic -type in the struct definition where we would otherwise specify concrete data -types [23]. +function definitions. First, we declare the name of the type parameter inside +angle brackets just after the name of the struct. Then, we use the generic type +in the struct definition where we would otherwise specify concrete data types. Note that because we’ve used only one generic type to define `Point`, this definition says that the `Point` struct is generic over some type `T`, and @@ -366,7 +369,7 @@ the fields `x` and `y` are *both* that same type, whatever that type may be. If we create an instance of a `Point` that has values of different types, as in Listing 10-7, our code won’t compile. -Filename: src/main.rs +src/main.rs ``` struct Point { @@ -379,21 +382,24 @@ fn main() { } ``` -Listing 10-7: The fields `x` and `y` must be the same type because both have -the same generic data type `T`. +Listing 10-7: The fields `x` and `y` must be the same type because both have the same generic data type `T`. In this example, when we assign the integer value `5` to `x`, we let the compiler know that the generic type `T` will be an integer for this instance of -`Point`. Then when we specify `4.0` for `y`, which we’ve defined to have the -same type as `x`, we’ll get a type mismatch error like this: +`Point`. Then, when we specify `4.0` for `y`, which we’ve defined to have +the same type as `x`, we’ll get a type mismatch error like this: ``` +$ cargo run + Compiling chapter10 v0.1.0 (file:///projects/chapter10) error[E0308]: mismatched types --> src/main.rs:7:38 | 7 | let wont_work = Point { x: 5, y: 4.0 }; - | ^^^ expected integer, found floating- -point number + | ^^^ expected integer, found floating-point number + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error ``` To define a `Point` struct where `x` and `y` are both generics but could have @@ -401,7 +407,7 @@ different types, we can use multiple generic type parameters. For example, in Listing 10-8, we change the definition of `Point` to be generic over types `T` and `U` where `x` is of type `T` and `y` is of type `U`. -Filename: src/main.rs +src/main.rs ``` struct Point { @@ -416,8 +422,7 @@ fn main() { } ``` -Listing 10-8: A `Point` generic over two types so that `x` and `y` can be -values of different types +Listing 10-8: A `Point` generic over two types so that `x` and `y` can be values of different types Now all the instances of `Point` shown are allowed! You can use as many generic type parameters in a definition as you want, but using more than a few makes @@ -474,7 +479,7 @@ We can implement methods on structs and enums (as we did in Chapter 5) and use generic types in their definitions too. Listing 10-9 shows the `Point` struct we defined in Listing 10-6 with a method named `x` implemented on it. -Filename: src/main.rs +src/main.rs ``` struct Point { @@ -495,28 +500,27 @@ fn main() { } ``` -Listing 10-9: Implementing a method named `x` on the `Point` struct that -will return a reference to the `x` field of type `T` +Listing 10-9: Implementing a method named `x` on the `Point` struct that will return a reference to the `x` field of type `T` Here, we’ve defined a method named `x` on `Point` that returns a reference to the data in the field `x`. -Note that we have to declare `T` just after `impl` so we can use `T` to specify -that we’re implementing methods on the type `Point`. By declaring `T` as a -generic type after `impl`, Rust can identify that the type in the angle -brackets in `Point` is a generic type rather than a concrete type. We could -have chosen a different name for this generic parameter than the generic +Note that we have to declare `T` just after `impl` so that we can use `T` to +specify that we’re implementing methods on the type `Point`. By declaring +`T` as a generic type after `impl`, Rust can identify that the type in the +angle brackets in `Point` is a generic type rather than a concrete type. We +could have chosen a different name for this generic parameter than the generic parameter declared in the struct definition, but using the same name is -conventional. Methods written within an `impl` that declares the generic type -will be defined on any instance of the type, no matter what concrete type ends -up substituting for the generic type. +conventional. If you write a method within an `impl` that declares a generic +type, that method will be defined on any instance of the type, no matter what +concrete type ends up substituting for the generic type. We can also specify constraints on generic types when defining methods on the type. We could, for example, implement methods only on `Point` instances -rather than on `Point` instances with any generic type. In Listing 10-10 we +rather than on `Point` instances with any generic type. In Listing 10-10, we use the concrete type `f32`, meaning we don’t declare any types after `impl`. -Filename: src/main.rs +src/main.rs ``` impl Point { @@ -526,8 +530,7 @@ impl Point { } ``` -Listing 10-10: An `impl` block that only applies to a struct with a particular -concrete type for the generic type parameter `T` +Listing 10-10: An `impl` block that only applies to a struct with a particular concrete type for the generic type parameter `T` This code means the type `Point` will have a `distance_from_origin` method; other instances of `Point` where `T` is not of type `f32` will not @@ -537,12 +540,12 @@ available only for floating-point types. Generic type parameters in a struct definition aren’t always the same as those you use in that same struct’s method signatures. Listing 10-11 uses the generic -types `X1` and `Y1` for the `Point` struct and `X2` `Y2` for the `mixup` method -signature to make the example clearer. The method creates a new `Point` +types `X1` and `Y1` for the `Point` struct and `X2` and `Y2` for the `mixup` +method signature to make the example clearer. The method creates a new `Point` instance with the `x` value from the `self` `Point` (of type `X1`) and the `y` value from the passed-in `Point` (of type `Y2`). -Filename: src/main.rs +src/main.rs ``` struct Point { @@ -550,11 +553,8 @@ struct Point { y: Y1, } -1 impl Point { - 2 fn mixup( - self, - other: Point, - ) -> Point { +impl Point { + fn mixup(self, other: Point) -> Point { Point { x: self.x, y: other.y, @@ -563,32 +563,31 @@ struct Point { } fn main() { - 3 let p1 = Point { x: 5, y: 10.4 }; - 4 let p2 = Point { x: "Hello", y: 'c' }; + let p1 = Point { x: 5, y: 10.4 }; + let p2 = Point { x: "Hello", y: 'c' }; - 5 let p3 = p1.mixup(p2); + let p3 = p1.mixup(p2); - 6 println!("p3.x = {}, p3.y = {}", p3.x, p3.y); + println!("p3.x = {}, p3.y = {}", p3.x, p3.y); } ``` -Listing 10-11: A method that uses generic types different from its struct’s -definition +Listing 10-11: A method that uses generic types that are different from its struct’s definition In `main`, we’ve defined a `Point` that has an `i32` for `x` (with value `5`) -and an `f64` for `y` (with value `10.4` [3]). The `p2` variable is a `Point` -struct that has a string slice for `x` (with value `"Hello"`) and a `char` for -`y` (with value `c` [4]). Calling `mixup` on `p1` with the argument `p2` gives -us `p3` [5], which will have an `i32` for `x` because `x` came from `p1`. The -`p3` variable will have a `char` for `y` because `y` came from `p2`. The -`println!` macro call [6] will print `p3.x = 5, p3.y = c`. +and an `f64` for `y` (with value `10.4`). The `p2` variable is a `Point` struct +that has a string slice for `x` (with value `"Hello"`) and a `char` for `y` +(with value `c`). Calling `mixup` on `p1` with the argument `p2` gives us `p3`, +which will have an `i32` for `x` because `x` came from `p1`. The `p3` variable +will have a `char` for `y` because `y` came from `p2`. The `println!` macro +call will print `p3.x = 5, p3.y = c`. The purpose of this example is to demonstrate a situation in which some generic parameters are declared with `impl` and some are declared with the method definition. Here, the generic parameters `X1` and `Y1` are declared after -`impl` [1] because they go with the struct definition. The generic parameters -`X2` and `Y2` are declared after `fn mixup` [2] because they’re only relevant -to the method. +`impl` because they go with the struct definition. The generic parameters `X2` +and `Y2` are declared after `fn mixup` because they’re only relevant to the +method. ### Performance of Code Using Generics @@ -600,7 +599,7 @@ Rust accomplishes this by performing monomorphization of the code using generics at compile time. *Monomorphization* is the process of turning generic code into specific code by filling in the concrete types that are used when compiled. In this process, the compiler does the opposite of the steps we used -to create the generic function in Listing 10-5: the compiler looks at all the +to create the generic function in Listing 10-5: The compiler looks at all the places where generic code is called and generates code for the concrete types the generic code is called with. @@ -614,7 +613,7 @@ let float = Some(5.0); When Rust compiles this code, it performs monomorphization. During that process, the compiler reads the values that have been used in `Option` -instances and identifies two kinds of `Option`: one is `i32` and the other +instances and identifies two kinds of `Option`: One is `i32` and the other is `f64`. As such, it expands the generic definition of `Option` into two definitions specialized to `i32` and `f64`, thereby replacing the generic definition with the specific ones. @@ -622,7 +621,7 @@ definition with the specific ones. The monomorphized version of the code looks similar to the following (the compiler uses different names than what we’re using here for illustration): -Filename: src/main.rs +src/main.rs ``` enum Option_i32 { @@ -641,6 +640,8 @@ fn main() { } ``` + + The generic `Option` is replaced with the specific definitions created by the compiler. Because Rust compiles generic code into code that specifies the type in each instance, we pay no runtime cost for using generics. When the code @@ -648,7 +649,11 @@ runs, it performs just as it would if we had duplicated each definition by hand. The process of monomorphization makes Rust’s generics extremely efficient at runtime. -## Traits: Defining Shared Behavior + + + + +## Defining Shared Behavior with Traits A *trait* defines the functionality a particular type has and can share with other types. We can use traits to define shared behavior in an abstract way. We @@ -656,7 +661,7 @@ can use *trait bounds* to specify that a generic type can be any type that has certain behavior. > Note: Traits are similar to a feature often called *interfaces* in other -languages, although with some differences. +> languages, although with some differences. ### Defining a Trait @@ -667,17 +672,18 @@ define a set of behaviors necessary to accomplish some purpose. For example, let’s say we have multiple structs that hold various kinds and amounts of text: a `NewsArticle` struct that holds a news story filed in a -particular location and a `Tweet` that can have, at most, 280 characters along -with metadata that indicates whether it was a new tweet, a retweet, or a reply -to another tweet. +particular location and a `SocialPost` that can have, at most, 280 characters +along with metadata that indicates whether it was a new post, a repost, or a +reply to another post. We want to make a media aggregator library crate named `aggregator` that can -display summaries of data that might be stored in a `NewsArticle` or `Tweet` -instance. To do this, we need a summary from each type, and we’ll request that -summary by calling a `summarize` method on an instance. Listing 10-12 shows the -definition of a public `Summary` trait that expresses this behavior. +display summaries of data that might be stored in a `NewsArticle` or +`SocialPost` instance. To do this, we need a summary from each type, and we’ll +request that summary by calling a `summarize` method on an instance. Listing +10-12 shows the definition of a public `Summary` trait that expresses this +behavior. -Filename: src/lib.rs +src/lib.rs ``` pub trait Summary { @@ -685,8 +691,7 @@ pub trait Summary { } ``` -Listing 10-12: A `Summary` trait that consists of the behavior provided by a -`summarize` method +Listing 10-12: A `Summary` trait that consists of the behavior provided by a `summarize` method Here, we declare a trait using the `trait` keyword and then the trait’s name, which is `Summary` in this case. We also declare the trait as `pub` so that @@ -701,7 +706,7 @@ its own custom behavior for the body of the method. The compiler will enforce that any type that has the `Summary` trait will have the method `summarize` defined with this signature exactly. -A trait can have multiple methods in its body: the method signatures are listed +A trait can have multiple methods in its body: The method signatures are listed one per line, and each line ends in a semicolon. ### Implementing a Trait on a Type @@ -710,11 +715,11 @@ Now that we’ve defined the desired signatures of the `Summary` trait’s metho we can implement it on the types in our media aggregator. Listing 10-13 shows an implementation of the `Summary` trait on the `NewsArticle` struct that uses the headline, the author, and the location to create the return value of -`summarize`. For the `Tweet` struct, we define `summarize` as the username -followed by the entire text of the tweet, assuming that the tweet content is +`summarize`. For the `SocialPost` struct, we define `summarize` as the username +followed by the entire text of the post, assuming that the post content is already limited to 280 characters. -Filename: src/lib.rs +src/lib.rs ``` pub struct NewsArticle { @@ -726,31 +731,25 @@ pub struct NewsArticle { impl Summary for NewsArticle { fn summarize(&self) -> String { - format!( - "{}, by {} ({})", - self.headline, - self.author, - self.location - ) + format!("{}, by {} ({})", self.headline, self.author, self.location) } } -pub struct Tweet { +pub struct SocialPost { pub username: String, pub content: String, pub reply: bool, - pub retweet: bool, + pub repost: bool, } -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize(&self) -> String { format!("{}: {}", self.username, self.content) } } ``` -Listing 10-13: Implementing the `Summary` trait on the `NewsArticle` and -`Tweet` types +Listing 10-13: Implementing the `Summary` trait on the `NewsArticle` and `SocialPost` types Implementing a trait on a type is similar to implementing regular methods. The difference is that after `impl`, we put the trait name we want to implement, @@ -761,53 +760,56 @@ signature, we use curly brackets and fill in the method body with the specific behavior that we want the methods of the trait to have for the particular type. Now that the library has implemented the `Summary` trait on `NewsArticle` and -`Tweet`, users of the crate can call the trait methods on instances of -`NewsArticle` and `Tweet` in the same way we call regular methods. The only +`SocialPost`, users of the crate can call the trait methods on instances of +`NewsArticle` and `SocialPost` in the same way we call regular methods. The only difference is that the user must bring the trait into scope as well as the types. Here’s an example of how a binary crate could use our `aggregator` library crate: ``` -use aggregator::{Summary, Tweet}; +use aggregator::{SocialPost, Summary}; fn main() { - let tweet = Tweet { + let post = SocialPost { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, - retweet: false, + repost: false, }; - println!("1 new tweet: {}", tweet.summarize()); + println!("1 new post: {}", post.summarize()); } ``` -This code prints `1 new tweet: horse_ebooks: of course, as you probably already -know, people`. +This code prints `1 new post: horse_ebooks: of course, as you probably already know, people`. Other crates that depend on the `aggregator` crate can also bring the `Summary` trait into scope to implement `Summary` on their own types. One restriction to note is that we can implement a trait on a type only if either the trait or the type, or both, are local to our crate. For example, we can implement standard -library traits like `Display` on a custom type like `Tweet` as part of our -`aggregator` crate functionality because the type `Tweet` is local to our +library traits like `Display` on a custom type like `SocialPost` as part of our +`aggregator` crate functionality because the type `SocialPost` is local to our `aggregator` crate. We can also implement `Summary` on `Vec` in our `aggregator` crate because the trait `Summary` is local to our `aggregator` crate. But we can’t implement external traits on external types. For example, we can’t -implement the `Display` trait on `Vec` within our `aggregator` crate because -`Display` and `Vec` are both defined in the standard library and aren’t -local to our `aggregator` crate. This restriction is part of a property called -*coherence*, and more specifically the *orphan rule*, so named because the -parent type is not present. This rule ensures that other people’s code can’t -break your code and vice versa. Without the rule, two crates could implement -the same trait for the same type, and Rust wouldn’t know which implementation -to use. +implement the `Display` trait on `Vec` within our `aggregator` crate, +because `Display` and `Vec` are both defined in the standard library and +aren’t local to our `aggregator` crate. This restriction is part of a property +called *coherence*, and more specifically the *orphan rule*, so named because +the parent type is not present. This rule ensures that other people’s code +can’t break your code and vice versa. Without the rule, two crates could +implement the same trait for the same type, and Rust wouldn’t know which +implementation to use. + + + + -### Default Implementations +### Using Default Implementations Sometimes it’s useful to have default behavior for some or all of the methods in a trait instead of requiring implementations for all methods on every type. @@ -818,7 +820,7 @@ In Listing 10-14, we specify a default string for the `summarize` method of the `Summary` trait instead of only defining the method signature, as we did in Listing 10-12. -Filename: src/lib.rs +src/lib.rs ``` pub trait Summary { @@ -828,8 +830,7 @@ pub trait Summary { } ``` -Listing 10-14: Defining a `Summary` trait with a default implementation of the -`summarize` method +Listing 10-14: Defining a `Summary` trait with a default implementation of the `summarize` method To use a default implementation to summarize instances of `NewsArticle`, we specify an empty `impl` block with `impl Summary for NewsArticle {}`. @@ -840,27 +841,26 @@ directly, we’ve provided a default implementation and specified that the `summarize` method on an instance of `NewsArticle`, like this: ``` -let article = NewsArticle { - headline: String::from( - "Penguins win the Stanley Cup Championship!" - ), - location: String::from("Pittsburgh, PA, USA"), - author: String::from("Iceburgh"), - content: String::from( - "The Pittsburgh Penguins once again are the best \ - hockey team in the NHL.", - ), -}; + let article = NewsArticle { + headline: String::from("Penguins win the Stanley Cup Championship!"), + location: String::from("Pittsburgh, PA, USA"), + author: String::from("Iceburgh"), + content: String::from( + "The Pittsburgh Penguins once again are the best \ + hockey team in the NHL.", + ), + }; -println!("New article available! {}", article.summarize()); + println!("New article available! {}", article.summarize()); ``` This code prints `New article available! (Read more...)`. Creating a default implementation doesn’t require us to change anything about -the implementation of `Summary` on `Tweet` in Listing 10-13. The reason is that -the syntax for overriding a default implementation is the same as the syntax -for implementing a trait method that doesn’t have a default implementation. +the implementation of `Summary` on `SocialPost` in Listing 10-13. The reason is +that the syntax for overriding a default implementation is the same as the +syntax for implementing a trait method that doesn’t have a default +implementation. Default implementations can call other methods in the same trait, even if those other methods don’t have a default implementation. In this way, a trait can @@ -875,10 +875,7 @@ pub trait Summary { fn summarize_author(&self) -> String; fn summarize(&self) -> String { - format!( - "(Read more from {}...)", - self.summarize_author() - ) + format!("(Read more from {}...)", self.summarize_author()) } } ``` @@ -887,7 +884,7 @@ To use this version of `Summary`, we only need to define `summarize_author` when we implement the trait on a type: ``` -impl Summary for Tweet { +impl Summary for SocialPost { fn summarize_author(&self) -> String { format!("@{}", self.username) } @@ -895,35 +892,39 @@ impl Summary for Tweet { ``` After we define `summarize_author`, we can call `summarize` on instances of the -`Tweet` struct, and the default implementation of `summarize` will call the +`SocialPost` struct, and the default implementation of `summarize` will call the definition of `summarize_author` that we’ve provided. Because we’ve implemented `summarize_author`, the `Summary` trait has given us the behavior of the `summarize` method without requiring us to write any more code. Here’s what that looks like: ``` -let tweet = Tweet { - username: String::from("horse_ebooks"), - content: String::from( - "of course, as you probably already know, people", - ), - reply: false, - retweet: false, -}; + let post = SocialPost { + username: String::from("horse_ebooks"), + content: String::from( + "of course, as you probably already know, people", + ), + reply: false, + repost: false, + }; -println!("1 new tweet: {}", tweet.summarize()); + println!("1 new post: {}", post.summarize()); ``` -This code prints `1 new tweet: (Read more from @horse_ebooks...)`. +This code prints `1 new post: (Read more from @horse_ebooks...)`. Note that it isn’t possible to call the default implementation from an overriding implementation of that same method. -### Traits as Parameters + + + + +### Using Traits as Parameters Now that you know how to define and implement traits, we can explore how to use traits to define functions that accept many different types. We’ll use the -`Summary` trait we implemented on the `NewsArticle` and `Tweet` types in +`Summary` trait we implemented on the `NewsArticle` and `SocialPost` types in Listing 10-13 to define a `notify` function that calls the `summarize` method on its `item` parameter, which is of some type that implements the `Summary` trait. To do this, we use the `impl Trait` syntax, like this: @@ -938,10 +939,14 @@ Instead of a concrete type for the `item` parameter, we specify the `impl` keyword and the trait name. This parameter accepts any type that implements the specified trait. In the body of `notify`, we can call any methods on `item` that come from the `Summary` trait, such as `summarize`. We can call `notify` -and pass in any instance of `NewsArticle` or `Tweet`. Code that calls the -function with any other type, such as a `String` or an `i32`, won’t compile +and pass in any instance of `NewsArticle` or `SocialPost`. Code that calls the +function with any other type, such as a `String` or an `i32`, won’t compile, because those types don’t implement `Summary`. + + + + #### Trait Bound Syntax The `impl Trait` syntax works for straightforward cases but is actually syntax @@ -979,10 +984,14 @@ The generic type `T` specified as the type of the `item1` and `item2` parameters constrains the function such that the concrete type of the value passed as an argument for `item1` and `item2` must be the same. -#### Specifying Multiple Trait Bounds with the + Syntax + + + + +#### Multiple Trait Bounds with the + Syntax We can also specify more than one trait bound. Say we wanted `notify` to use -display formatting as well as `summarize` on `item`: we specify in the `notify` +display formatting as well as `summarize` on `item`: We specify in the `notify` definition that `item` must implement both `Display` and `Summary`. We can do so using the `+` syntax: @@ -1022,7 +1031,7 @@ where { ``` -This function’s signature is less cluttered: the function name, parameter list, +This function’s signature is less cluttered: The function name, parameter list, and return type are close together, similar to a function without lots of trait bounds. @@ -1033,13 +1042,13 @@ value of some type that implements a trait, as shown here: ``` fn returns_summarizable() -> impl Summary { - Tweet { + SocialPost { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, - retweet: false, + repost: false, } } ``` @@ -1047,7 +1056,8 @@ fn returns_summarizable() -> impl Summary { By using `impl Summary` for the return type, we specify that the `returns_summarizable` function returns some type that implements the `Summary` trait without naming the concrete type. In this case, `returns_summarizable` -returns a `Tweet`, but the code calling this function doesn’t need to know that. +returns a `SocialPost`, but the code calling this function doesn’t need to know +that. The ability to specify a return type only by the trait it implements is especially useful in the context of closures and iterators, which we cover in @@ -1057,8 +1067,8 @@ specify that a function returns some type that implements the `Iterator` trait without needing to write out a very long type. However, you can only use `impl Trait` if you’re returning a single type. For -example, this code that returns either a `NewsArticle` or a `Tweet` with the -return type specified as `impl Summary` wouldn’t work: +example, this code that returns either a `NewsArticle` or a `SocialPost` with +the return type specified as `impl Summary` wouldn’t work: ``` fn returns_summarizable(switch: bool) -> impl Summary { @@ -1075,36 +1085,37 @@ fn returns_summarizable(switch: bool) -> impl Summary { ), } } else { - Tweet { + SocialPost { username: String::from("horse_ebooks"), content: String::from( "of course, as you probably already know, people", ), reply: false, - retweet: false, + repost: false, } } } ``` -Returning either a `NewsArticle` or a `Tweet` isn’t allowed due to restrictions -around how the `impl Trait` syntax is implemented in the compiler. We’ll cover -how to write a function with this behavior in “Using Trait Objects That Allow -for Values of Different Types” on page XX. +Returning either a `NewsArticle` or a `SocialPost` isn’t allowed due to +restrictions around how the `impl Trait` syntax is implemented in the compiler. +We’ll cover how to write a function with this behavior in the “Using Trait +Objects to Abstract over Shared Behavior” +section of Chapter 18. ### Using Trait Bounds to Conditionally Implement Methods By using a trait bound with an `impl` block that uses generic type parameters, we can implement methods conditionally for types that implement the specified traits. For example, the type `Pair` in Listing 10-15 always implements the -`new` function to return a new instance of `Pair` (recall from “Defining -Methods” on page XX that `Self` is a type alias for the type of the `impl` -block, which in this case is `Pair`). But in the next `impl` block, -`Pair` only implements the `cmp_display` method if its inner type `T` -implements the `PartialOrd` trait that enables comparison *and* the `Display` -trait that enables printing. +`new` function to return a new instance of `Pair` (recall from the “Method +Syntax” section of Chapter 5 that `Self` is a type +alias for the type of the `impl` block, which in this case is `Pair`). But +in the next `impl` block, `Pair` only implements the `cmp_display` method if +its inner type `T` implements the `PartialOrd` trait that enables comparison +*and* the `Display` trait that enables printing. -Filename: src/lib.rs +src/lib.rs ``` use std::fmt::Display; @@ -1131,8 +1142,7 @@ impl Pair { } ``` -Listing 10-15: Conditionally implementing methods on a generic type depending -on trait bounds +Listing 10-15: Conditionally implementing methods on a generic type depending on trait bounds We can also conditionally implement a trait for any type that implements another trait. Implementations of a trait on any type that satisfies the trait @@ -1143,7 +1153,7 @@ block in the standard library looks similar to this code: ``` impl ToString for T { - --snip-- + // --snip-- } ``` @@ -1164,10 +1174,10 @@ reduce duplication but also specify to the compiler that we want the generic type to have particular behavior. The compiler can then use the trait bound information to check that all the concrete types used with our code provide the correct behavior. In dynamically typed languages, we would get an error at -runtime if we called a method on a type which didn’t define the method. But -Rust moves these errors to compile time so we’re forced to fix the problems +runtime if we called a method on a type that didn’t define the method. But Rust +moves these errors to compile time so that we’re forced to fix the problems before our code is even able to run. Additionally, we don’t have to write code -that checks for behavior at runtime because we’ve already checked at compile +that checks for behavior at runtime, because we’ve already checked at compile time. Doing so improves performance without having to give up the flexibility of generics. @@ -1177,67 +1187,81 @@ Lifetimes are another kind of generic that we’ve already been using. Rather than ensuring that a type has the behavior we want, lifetimes ensure that references are valid as long as we need them to be. -One detail we didn’t discuss in “References and Borrowing” on page XX is that -every reference in Rust has a *lifetime*, which is the scope for which that -reference is valid. Most of the time, lifetimes are implicit and inferred, just -like most of the time, types are inferred. We must annotate types only when -multiple types are possible. In a similar way, we must annotate lifetimes when -the lifetimes of references could be related in a few different ways. Rust -requires us to annotate the relationships using generic lifetime parameters to -ensure the actual references used at runtime will definitely be valid. +One detail we didn’t discuss in the “References and +Borrowing” section in Chapter 4 is +that every reference in Rust has a lifetime, which is the scope for which +that reference is valid. Most of the time, lifetimes are implicit and inferred, +just like most of the time, types are inferred. We are only required to +annotate types when multiple types are possible. In a similar way, we must +annotate lifetimes when the lifetimes of references could be related in a few +different ways. Rust requires us to annotate the relationships using generic +lifetime parameters to ensure that the actual references used at runtime will +definitely be valid. Annotating lifetimes is not even a concept most other programming languages have, so this is going to feel unfamiliar. Although we won’t cover lifetimes in their entirety in this chapter, we’ll discuss common ways you might encounter -lifetime syntax so you can get comfortable with the concept. +lifetime syntax so that you can get comfortable with the concept. + + -### Preventing Dangling References with Lifetimes + + +### Dangling References + +The main aim of lifetimes is to prevent dangling references, which, if they +were allowed to exist, would cause a program to reference data other than the +data it’s intended to reference. Consider the program in Listing 10-16, which +has an outer scope and an inner scope. -The main aim of lifetimes is to prevent *dangling references*, which cause a -program to reference data other than the data it’s intended to reference. -Consider the program in Listing 10-16, which has an outer scope and an inner -scope. ``` fn main() { - 1 let r; + let r; { - 2 let x = 5; - 3 r = &x; - 4 } + let x = 5; + r = &x; + } - 5 println!("r: {r}"); + println!("r: {r}"); } ``` Listing 10-16: An attempt to use a reference whose value has gone out of scope -> Note: The examples in Listing 10-16, 10-17, and 10-23 declare variables -without giving them an initial value, so the variable name exists in the outer -scope. At first glance, this might appear to be in conflict with Rust’s having -no null values. However, if we try to use a variable before giving it a value, -we’ll get a compile-time error, which shows that Rust indeed does not allow -null values. +> Note: The examples in Listings 10-16, 10-17, and 10-23 declare variables +> without giving them an initial value, so the variable name exists in the outer +> scope. At first glance, this might appear to be in conflict with Rust having +> no null values. However, if we try to use a variable before giving it a value, +> we’ll get a compile-time error, which shows that indeed Rust does not allow +> null values. -The outer scope declares a variable named `r` with no initial value [1], and -the inner scope declares a variable named `x` with the initial value of `5` -[2]. Inside the inner scope, we attempt to set the value of `r` as a reference -to `x` [3]. Then the inner scope ends [4], and we attempt to print the value in -`r` [5]. This code won’t compile because the value that `r` is referring to has -gone out of scope before we try to use it. Here is the error message: +The outer scope declares a variable named `r` with no initial value, and the +inner scope declares a variable named `x` with the initial value of `5`. Inside +the inner scope, we attempt to set the value of `r` as a reference to `x`. +Then, the inner scope ends, and we attempt to print the value in `r`. This code +won’t compile, because the value that `r` is referring to has gone out of scope +before we try to use it. Here is the error message: ``` +$ cargo run + Compiling chapter10 v0.1.0 (file:///projects/chapter10) error[E0597]: `x` does not live long enough --> src/main.rs:6:13 | +5 | let x = 5; + | - binding `x` declared here 6 | r = &x; | ^^ borrowed value does not live long enough 7 | } | - `x` dropped here while still borrowed 8 | 9 | println!("r: {r}"); - | - borrow later used here + | --- borrow later used here + +For more information about this error, try `rustc --explain E0597`. +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error ``` The error message says that the variable `x` “does not live long enough.” The @@ -1245,7 +1269,7 @@ reason is that `x` will be out of scope when the inner scope ends on line 7. But `r` is still valid for the outer scope; because its scope is larger, we say that it “lives longer.” If Rust allowed this code to work, `r` would be referencing memory that was deallocated when `x` went out of scope, and -anything we tried to do with `r` wouldn’t work correctly. So how does Rust +anything we tried to do with `r` wouldn’t work correctly. So, how does Rust determine that this code is invalid? It uses a borrow checker. ### The Borrow Checker @@ -1254,6 +1278,7 @@ The Rust compiler has a *borrow checker* that compares scopes to determine whether all borrows are valid. Listing 10-17 shows the same code as Listing 10-16 but with annotations showing the lifetimes of the variables. + ``` fn main() { let r; // ---------+-- 'a @@ -1267,18 +1292,18 @@ fn main() { } // ---------+ ``` -Listing 10-17: Annotations of the lifetimes of `r` and `x`, named `'a` and -`'b`, respectively +Listing 10-17: Annotations of the lifetimes of `r` and `x`, named `'a` and `'b`, respectively Here, we’ve annotated the lifetime of `r` with `'a` and the lifetime of `x` with `'b`. As you can see, the inner `'b` block is much smaller than the outer `'a` lifetime block. At compile time, Rust compares the size of the two lifetimes and sees that `r` has a lifetime of `'a` but that it refers to memory with a lifetime of `'b`. The program is rejected because `'b` is shorter than -`'a`: the subject of the reference doesn’t live as long as the reference. +`'a`: The subject of the reference doesn’t live as long as the reference. + +Listing 10-18 fixes the code so that it doesn’t have a dangling reference and +it compiles without any errors. -Listing 10-18 fixes the code so it doesn’t have a dangling reference and it -compiles without any errors. ``` fn main() { @@ -1291,16 +1316,15 @@ fn main() { } // ----------+ ``` -Listing 10-18: A valid reference because the data has a longer lifetime than -the reference +Listing 10-18: A valid reference because the data has a longer lifetime than the reference Here, `x` has the lifetime `'b`, which in this case is larger than `'a`. This means `r` can reference `x` because Rust knows that the reference in `r` will always be valid while `x` is valid. Now that you know where the lifetimes of references are and how Rust analyzes -lifetimes to ensure references will always be valid, let’s explore generic -lifetimes of parameters and return values in the context of functions. +lifetimes to ensure that references will always be valid, let’s explore generic +lifetimes in function parameters and return values. ### Generic Lifetimes in Functions @@ -1309,7 +1333,7 @@ function will take two string slices and return a single string slice. After we’ve implemented the `longest` function, the code in Listing 10-19 should print `The longest string is abcd`. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1321,48 +1345,47 @@ fn main() { } ``` -Listing 10-19: A `main` function that calls the `longest` function to find the -longer of two string slices +Listing 10-19: A `main` function that calls the `longest` function to find the longer of two string slices Note that we want the function to take string slices, which are references, rather than strings, because we don’t want the `longest` function to take -ownership of its parameters. Refer to “String Slices as Parameters” on page XX -for more discussion about why the parameters we use in Listing 10-19 are the -ones we want. +ownership of its parameters. Refer to “String Slices as +Parameters” in Chapter 4 for more +discussion about why the parameters we use in Listing 10-19 are the ones we +want. If we try to implement the `longest` function as shown in Listing 10-20, it won’t compile. -Filename: src/main.rs +src/main.rs ``` fn longest(x: &str, y: &str) -> &str { - if x.len() > y.len() { - x - } else { - y - } + if x.len() > y.len() { x } else { y } } ``` -Listing 10-20: An implementation of the `longest` function that returns the -longer of two string slices but does not yet compile +Listing 10-20: An implementation of the `longest` function that returns the longer of two string slices but does not yet compile Instead, we get the following error that talks about lifetimes: ``` +$ cargo run + Compiling chapter10 v0.1.0 (file:///projects/chapter10) error[E0106]: missing lifetime specifier --> src/main.rs:9:33 | 9 | fn longest(x: &str, y: &str) -> &str { | ---- ---- ^ expected named lifetime parameter | - = help: this function's return type contains a borrowed value, -but the signature does not say whether it is borrowed from `x` or `y` + = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `x` or `y` help: consider introducing a named lifetime parameter | 9 | fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { | ++++ ++ ++ ++ + +For more information about this error, try `rustc --explain E0106`. +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error ``` The help text reveals that the return type needs a generic lifetime parameter @@ -1379,7 +1402,7 @@ Listings 10-17 and 10-18 to determine whether the reference we return will always be valid. The borrow checker can’t determine this either, because it doesn’t know how the lifetimes of `x` and `y` relate to the lifetime of the return value. To fix this error, we’ll add generic lifetime parameters that -define the relationship between the references so the borrow checker can +define the relationship between the references so that the borrow checker can perform its analysis. ### Lifetime Annotation Syntax @@ -1390,15 +1413,15 @@ other without affecting the lifetimes. Just as functions can accept any type when the signature specifies a generic type parameter, functions can accept references with any lifetime by specifying a generic lifetime parameter. -Lifetime annotations have a slightly unusual syntax: the names of lifetime +Lifetime annotations have a slightly unusual syntax: The names of lifetime parameters must start with an apostrophe (`'`) and are usually all lowercase and very short, like generic types. Most people use the name `'a` for the first lifetime annotation. We place lifetime parameter annotations after the `&` of a reference, using a space to separate the annotation from the reference’s type. -Here are some examples: a reference to an `i32` without a lifetime parameter, a +Here are some examples—a reference to an `i32` without a lifetime parameter, a reference to an `i32` that has a lifetime parameter named `'a`, and a mutable -reference to an `i32` that also has the lifetime `'a`. +reference to an `i32` that also has the lifetime `'a`: ``` &i32 // a reference @@ -1406,37 +1429,36 @@ reference to an `i32` that also has the lifetime `'a`. &'a mut i32 // a mutable reference with an explicit lifetime ``` -One lifetime annotation by itself doesn’t have much meaning because the +One lifetime annotation by itself doesn’t have much meaning, because the annotations are meant to tell Rust how generic lifetime parameters of multiple references relate to each other. Let’s examine how the lifetime annotations relate to each other in the context of the `longest` function. -### Lifetime Annotations in Function Signatures + + + + +### In Function Signatures To use lifetime annotations in function signatures, we need to declare the -generic *lifetime* parameters inside angle brackets between the function name -and the parameter list, just as we did with generic *type* parameters. +generic lifetime parameters inside angle brackets between the function name and +the parameter list, just as we did with generic type parameters. -We want the signature to express the following constraint: the returned -reference will be valid as long as both the parameters are valid. This is the -relationship between lifetimes of the parameters and the return value. We’ll -name the lifetime `'a` and then add it to each reference, as shown in Listing -10-21. +We want the signature to express the following constraint: The returned +reference will be valid as long as both of the parameters are valid. This is +the relationship between lifetimes of the parameters and the return value. +We’ll name the lifetime `'a` and then add it to each reference, as shown in +Listing 10-21. -Filename: src/main.rs +src/main.rs ``` fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { - if x.len() > y.len() { - x - } else { - y - } + if x.len() > y.len() { x } else { y } } ``` -Listing 10-21: The `longest` function definition specifying that all the -references in the signature must have the same lifetime `'a` +Listing 10-21: The `longest` function definition specifying that all the references in the signature must have the same lifetime `'a` This code should compile and produce the result we want when we use it with the `main` function in Listing 10-19. @@ -1480,7 +1502,7 @@ Let’s look at how the lifetime annotations restrict the `longest` function by passing in references that have different concrete lifetimes. Listing 10-22 is a straightforward example. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1494,24 +1516,22 @@ fn main() { } ``` -Listing 10-22: Using the `longest` function with references to `String` values -that have different concrete lifetimes +Listing 10-22: Using the `longest` function with references to `String` values that have different concrete lifetimes In this example, `string1` is valid until the end of the outer scope, `string2` is valid until the end of the inner scope, and `result` references something that is valid until the end of the inner scope. Run this code and you’ll see -that the borrow checker approves; it will compile and print `The longest string -is long string is long`. +that the borrow checker approves; it will compile and print `The longest string is long string is long`. Next, let’s try an example that shows that the lifetime of the reference in `result` must be the smaller lifetime of the two arguments. We’ll move the declaration of the `result` variable outside the inner scope but leave the assignment of the value to the `result` variable inside the scope with -`string2`. Then we’ll move the `println!` that uses `result` to outside the +`string2`. Then, we’ll move the `println!` that uses `result` to outside the inner scope, after the inner scope has ended. The code in Listing 10-23 will not compile. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1530,16 +1550,22 @@ Listing 10-23: Attempting to use `result` after `string2` has gone out of scope When we try to compile this code, we get this error: ``` +$ cargo run + Compiling chapter10 v0.1.0 (file:///projects/chapter10) error[E0597]: `string2` does not live long enough --> src/main.rs:6:44 | +5 | let string2 = String::from("xyz"); + | ------- binding `string2` declared here 6 | result = longest(string1.as_str(), string2.as_str()); - | ^^^^^^^^^^^^^^^^ borrowed value -does not live long enough + | ^^^^^^^ borrowed value does not live long enough 7 | } | - `string2` dropped here while still borrowed 8 | println!("The longest string is {result}"); - | ------ borrow later used here + | -------- borrow later used here + +For more information about this error, try `rustc --explain E0597`. +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error ``` The error shows that for `result` to be valid for the `println!` statement, @@ -1559,9 +1585,13 @@ disallows the code in Listing 10-23 as possibly having an invalid reference. Try designing more experiments that vary the values and lifetimes of the references passed in to the `longest` function and how the returned reference is used. Make hypotheses about whether or not your experiments will pass the -borrow checker before you compile; then check to see if you’re right! +borrow checker before you compile; then, check to see if you’re right! + + + + -### Thinking in Terms of Lifetimes +### Relationships The way in which you need to specify lifetime parameters depends on what your function is doing. For example, if we changed the implementation of the @@ -1569,7 +1599,7 @@ function is doing. For example, if we changed the implementation of the string slice, we wouldn’t need to specify a lifetime on the `y` parameter. The following code will compile: -Filename: src/main.rs +src/main.rs ``` fn longest<'a>(x: &'a str, y: &str) -> &'a str { @@ -1577,6 +1607,8 @@ fn longest<'a>(x: &'a str, y: &str) -> &'a str { } ``` + + We’ve specified a lifetime parameter `'a` for the parameter `x` and the return type, but not for the parameter `y`, because the lifetime of `y` does not have any relationship with the lifetime of `x` or the return value. @@ -1589,7 +1621,7 @@ reference because the value will go out of scope at the end of the function. Consider this attempted implementation of the `longest` function that won’t compile: -Filename: src/main.rs +src/main.rs ``` fn longest<'a>(x: &str, y: &str) -> &'a str { @@ -1598,18 +1630,27 @@ fn longest<'a>(x: &str, y: &str) -> &'a str { } ``` + + Here, even though we’ve specified a lifetime parameter `'a` for the return type, this implementation will fail to compile because the return value lifetime is not related to the lifetime of the parameters at all. Here is the error message we get: ``` -error[E0515]: cannot return reference to local variable `result` +$ cargo run + Compiling chapter10 v0.1.0 (file:///projects/chapter10) +error[E0515]: cannot return value referencing local variable `result` --> src/main.rs:11:5 | 11 | result.as_str() - | ^^^^^^^^^^^^^^^ returns a reference to data owned by the -current function + | ------^^^^^^^^^ + | | + | returns a value referencing data owned by the current function + | `result` is borrowed here + +For more information about this error, try `rustc --explain E0515`. +error: could not compile `chapter10` (bin "chapter10") due to 1 previous error ``` The problem is that `result` goes out of scope and gets cleaned up at the end @@ -1617,7 +1658,7 @@ of the `longest` function. We’re also trying to return a reference to `result` from the function. There is no way we can specify lifetime parameters that would change the dangling reference, and Rust won’t let us create a dangling reference. In this case, the best fix would be to return an owned data type -rather than a reference so the calling function is then responsible for +rather than a reference so that the calling function is then responsible for cleaning up the value. Ultimately, lifetime syntax is about connecting the lifetimes of various @@ -1625,29 +1666,28 @@ parameters and return values of functions. Once they’re connected, Rust has enough information to allow memory-safe operations and disallow operations that would create dangling pointers or otherwise violate memory safety. -### Lifetime Annotations in Struct Definitions + + + + +### In Struct Definitions So far, the structs we’ve defined all hold owned types. We can define structs -to hold references, but in that case we would need to add a lifetime annotation -on every reference in the struct’s definition. Listing 10-24 has a struct named -`ImportantExcerpt` that holds a string slice. +to hold references, but in that case, we would need to add a lifetime +annotation on every reference in the struct’s definition. Listing 10-24 has a +struct named `ImportantExcerpt` that holds a string slice. -Filename: src/main.rs +src/main.rs ``` -1 struct ImportantExcerpt<'a> { - 2 part: &'a str, +struct ImportantExcerpt<'a> { + part: &'a str, } fn main() { - 3 let novel = String::from( - "Call me Ishmael. Some years ago..." - ); - 4 let first_sentence = novel - .split('.') - .next() - .expect("Could not find a '.'"); - 5 let i = ImportantExcerpt { + let novel = String::from("Call me Ishmael. Some years ago..."); + let first_sentence = novel.split('.').next().unwrap(); + let i = ImportantExcerpt { part: first_sentence, }; } @@ -1656,18 +1696,18 @@ fn main() { Listing 10-24: A struct that holds a reference, requiring a lifetime annotation This struct has the single field `part` that holds a string slice, which is a -reference [2]. As with generic data types, we declare the name of the generic -lifetime parameter inside angle brackets after the name of the struct so we can -use the lifetime parameter in the body of the struct definition [1]. This +reference. As with generic data types, we declare the name of the generic +lifetime parameter inside angle brackets after the name of the struct so that +we can use the lifetime parameter in the body of the struct definition. This annotation means an instance of `ImportantExcerpt` can’t outlive the reference it holds in its `part` field. The `main` function here creates an instance of the `ImportantExcerpt` struct -[5] that holds a reference to the first sentence of the `String` [4] owned by -the variable `novel` [3]. The data in `novel` exists before the -`ImportantExcerpt` instance is created. In addition, `novel` doesn’t go out of -scope until after the `ImportantExcerpt` goes out of scope, so the reference in -the `ImportantExcerpt` instance is valid. +that holds a reference to the first sentence of the `String` owned by the +variable `novel`. The data in `novel` exists before the `ImportantExcerpt` +instance is created. In addition, `novel` doesn’t go out of scope until after +the `ImportantExcerpt` goes out of scope, so the reference in the +`ImportantExcerpt` instance is valid. ### Lifetime Elision @@ -1676,7 +1716,7 @@ lifetime parameters for functions or structs that use references. However, we had a function in Listing 4-9, shown again in Listing 10-25, that compiled without lifetime annotations. -Filename: src/lib.rs +src/lib.rs ``` fn first_word(s: &str) -> &str { @@ -1692,11 +1732,10 @@ fn first_word(s: &str) -> &str { } ``` -Listing 10-25: A function we defined in Listing 4-9 that compiled without -lifetime annotations, even though the parameter and return type are references +Listing 10-25: A function we defined in Listing 4-9 that compiled without lifetime annotations, even though the parameter and return type are references The reason this function compiles without lifetime annotations is historical: -in early versions (pre-1.0) of Rust, this code wouldn’t have compiled because +In early versions (pre-1.0) of Rust, this code wouldn’t have compiled, because every reference needed an explicit lifetime. At that time, the function signature would have been written like this: @@ -1708,8 +1747,8 @@ After writing a lot of Rust code, the Rust team found that Rust programmers were entering the same lifetime annotations over and over in particular situations. These situations were predictable and followed a few deterministic patterns. The developers programmed these patterns into the compiler’s code so -the borrow checker could infer the lifetimes in these situations and wouldn’t -need explicit annotations. +that the borrow checker could infer the lifetimes in these situations and +wouldn’t need explicit annotations. This piece of Rust history is relevant because it’s possible that more deterministic patterns will emerge and be added to the compiler. In the future, @@ -1720,11 +1759,11 @@ The patterns programmed into Rust’s analysis of references are called the a set of particular cases that the compiler will consider, and if your code fits these cases, you don’t need to write the lifetimes explicitly. -The elision rules don’t provide full inference. If Rust deterministically -applies the rules but there is still ambiguity as to what lifetimes the -references have, the compiler won’t guess what the lifetime of the remaining -references should be. Instead of guessing, the compiler will give you an error -that you can resolve by adding the lifetime annotations. +The elision rules don’t provide full inference. If there is still ambiguity +about what lifetimes the references have after Rust applies the rules, the +compiler won’t guess what the lifetime of the remaining references should be. +Instead of guessing, the compiler will give you an error that you can resolve +by adding the lifetime annotations. Lifetimes on function or method parameters are called *input lifetimes*, and lifetimes on return values are called *output lifetimes*. @@ -1739,12 +1778,10 @@ These rules apply to `fn` definitions as well as `impl` blocks. The first rule is that the compiler assigns a lifetime parameter to each parameter that’s a reference. In other words, a function with one parameter gets one lifetime parameter: `fn foo<'a>(x: &'a i32)`; a function with two -parameters gets two separate lifetime parameters: `fn foo<'a, 'b>(x: &'a i32, -y: &'b i32)`; and so on. +parameters gets two separate lifetime parameters: `fn foo<'a, 'b>(x: &'a i32, y: &'b i32)`; and so on. The second rule is that, if there is exactly one input lifetime parameter, that -lifetime is assigned to all output lifetime parameters: `fn foo<'a>(x: &'a i32) --> &'a i32`. +lifetime is assigned to all output lifetime parameters: `fn foo<'a>(x: &'a i32) -> &'a i32`. The third rule is that, if there are multiple input lifetime parameters, but one of them is `&self` or `&mut self` because this is a method, the lifetime of @@ -1760,7 +1797,7 @@ references: fn first_word(s: &str) -> &str { ``` -Then the compiler applies the first rule, which specifies that each parameter +Then, the compiler applies the first rule, which specifies that each parameter gets its own lifetime. We’ll call it `'a` as usual, so now the signature is this: @@ -1787,31 +1824,35 @@ no lifetime parameters when we started working with it in Listing 10-20: fn longest(x: &str, y: &str) -> &str { ``` -Let’s apply the first rule: each parameter gets its own lifetime. This time we +Let’s apply the first rule: Each parameter gets its own lifetime. This time we have two parameters instead of one, so we have two lifetimes: ``` fn longest<'a, 'b>(x: &'a str, y: &'b str) -> &str { ``` -You can see that the second rule doesn’t apply because there is more than one +You can see that the second rule doesn’t apply, because there is more than one input lifetime. The third rule doesn’t apply either, because `longest` is a function rather than a method, so none of the parameters are `self`. After working through all three rules, we still haven’t figured out what the return type’s lifetime is. This is why we got an error trying to compile the code in -Listing 10-20: the compiler worked through the lifetime elision rules but still +Listing 10-20: The compiler worked through the lifetime elision rules but still couldn’t figure out all the lifetimes of the references in the signature. Because the third rule really only applies in method signatures, we’ll look at lifetimes in that context next to see why the third rule means we don’t have to annotate lifetimes in method signatures very often. -### Lifetime Annotations in Method Definitions + + + + +### In Method Definitions When we implement methods on a struct with lifetimes, we use the same syntax as -that of generic type parameters shown in Listing 10-11. Where we declare and -use the lifetime parameters depends on whether they’re related to the struct -fields or the method parameters and return values. +that of generic type parameters, as shown in Listing 10-11. Where we declare +and use the lifetime parameters depends on whether they’re related to the +struct fields or the method parameters and return values. Lifetime names for struct fields always need to be declared after the `impl` keyword and then used after the struct’s name because those lifetimes are part @@ -1823,7 +1864,7 @@ addition, the lifetime elision rules often make it so that lifetime annotations aren’t necessary in method signatures. Let’s look at some examples using the struct named `ImportantExcerpt` that we defined in Listing 10-24. -First we’ll use a method named `level` whose only parameter is a reference to +First, we’ll use a method named `level` whose only parameter is a reference to `self` and whose return value is an `i32`, which is not a reference to anything: ``` @@ -1835,8 +1876,8 @@ impl<'a> ImportantExcerpt<'a> { ``` The lifetime parameter declaration after `impl` and its use after the type name -are required, but we’re not required to annotate the lifetime of the reference -to `self` because of the first elision rule. +are required, but because of the first elision rule, we’re not required to +annotate the lifetime of the reference to `self`. Here is an example where the third lifetime elision rule applies: @@ -1867,15 +1908,19 @@ let s: &'static str = "I have a static lifetime."; The text of this string is stored directly in the program’s binary, which is always available. Therefore, the lifetime of all string literals is `'static`. -You might see suggestions to use the `'static` lifetime in error messages. But +You might see suggestions in error messages to use the `'static` lifetime. But before specifying `'static` as the lifetime for a reference, think about -whether the reference you have actually lives the entire lifetime of your -program or not, and whether you want it to. Most of the time, an error message +whether or not the reference you have actually lives the entire lifetime of +your program, and whether you want it to. Most of the time, an error message suggesting the `'static` lifetime results from attempting to create a dangling reference or a mismatch of the available lifetimes. In such cases, the solution is to fix those problems, not to specify the `'static` lifetime. -## Generic Type Parameters, Trait Bounds, and Lifetimes Together + + + + +## Generic Type Parameters, Trait Bounds, and Lifetimes Let’s briefly look at the syntax of specifying generic type parameters, trait bounds, and lifetimes all in one function! @@ -1892,11 +1937,7 @@ where T: Display, { println!("Announcement! {ann}"); - if x.len() > y.len() { - x - } else { - y - } + if x.len() > y.len() { x } else { y } } ``` @@ -1921,10 +1962,8 @@ that this flexible code won’t have any dangling references. And all of this analysis happens at compile time, which doesn’t affect runtime performance! Believe it or not, there is much more to learn on the topics we discussed in -this chapter: Chapter 17 discusses trait objects, which are another way to use +this chapter: Chapter 18 discusses trait objects, which are another way to use traits. There are also more complex scenarios involving lifetime annotations that you will only need in very advanced scenarios; for those, you should read -the Rust Reference at *https://doc.rust-lang.org/reference/trait-bounds.html*. -But next, you’ll learn how to write tests in Rust so you can make sure your -code is working the way it should. - +the Rust Reference at *../reference/trait-bounds.html*. But next, you’ll learn how to write tests in +Rust so that you can make sure your code is working the way it should. diff --git a/nostarch/chapter11.md b/nostarch/chapter11.md index cf909d70c5..f90efc3fe1 100644 --- a/nostarch/chapter11.md +++ b/nostarch/chapter11.md @@ -8,16 +8,17 @@ directory, so all fixes need to be made in `/src/`. # Writing Automated Tests -In his 1972 essay “The Humble Programmer,” Edsger W. Dijkstra said that -“Program testing can be a very effective way to show the presence of bugs, but -it is hopelessly inadequate for showing their absence.” That doesn’t mean we -shouldn’t try to test as much as we can! - -Correctness in our programs is the extent to which our code does what we intend -it to do. Rust is designed with a high degree of concern about the correctness -of programs, but correctness is complex and not easy to prove. Rust’s type -system shoulders a huge part of this burden, but the type system cannot catch -everything. As such, Rust includes support for writing automated software tests. +In his 1972 essay “The Humble Programmer,” Edsger W. Dijkstra said that “program +testing can be a very effective way to show the presence of bugs, but it is +hopelessly inadequate for showing their absence.” That doesn’t mean we shouldn’t +try to test as much as we can! + +*Correctness* in our programs is the extent to which our code does what we +intend it to do. Rust is designed with a high degree of concern about the +correctness of programs, but correctness is complex and not easy to prove. +Rust’s type system shoulders a huge part of this burden, but the type system +cannot catch everything. As such, Rust includes support for writing automated +software tests. Say we write a function `add_two` that adds 2 to whatever number is passed to it. This function’s signature accepts an integer as a parameter and returns an @@ -33,7 +34,7 @@ We can write tests that assert, for example, that when we pass `3` to the we make changes to our code to make sure any existing correct behavior has not changed. -Testing is a complex skill: although we can’t cover in one chapter every detail +Testing is a complex skill: Although we can’t cover in one chapter every detail about how to write good tests, in this chapter we will discuss the mechanics of Rust’s testing facilities. We’ll talk about the annotations and macros available to you when writing your tests, the default behavior and options @@ -42,7 +43,7 @@ integration tests. ## How to Write Tests -Tests are Rust functions that verify that the non-test code is functioning in +*Tests* are Rust functions that verify that the non-test code is functioning in the expected manner. The bodies of test functions typically perform these three actions: @@ -54,7 +55,11 @@ Let’s look at the features Rust provides specifically for writing tests that take these actions, which include the `test` attribute, a few macros, and the `should_panic` attribute. -### The Anatomy of a Test Function + + + + +### Structuring Test Functions At its simplest, a test in Rust is a function that’s annotated with the `test` attribute. Attributes are metadata about pieces of Rust code; one example is @@ -66,12 +71,12 @@ fails. Whenever we make a new library project with Cargo, a test module with a test function in it is automatically generated for us. This module gives you a -template for writing your tests so you don’t have to look up the exact +template for writing your tests so that you don’t have to look up the exact structure and syntax every time you start a new project. You can add as many additional test functions and as many test modules as you want! We’ll explore some aspects of how tests work by experimenting with the template -test before we actually test any code. Then we’ll write some real-world tests +test before we actually test any code. Then, we’ll write some real-world tests that call some code that we’ve written and assert that its behavior is correct. Let’s create a new library project called `adder` that will add two numbers: @@ -85,86 +90,101 @@ $ cd adder The contents of the *src/lib.rs* file in your `adder` library should look like Listing 11-1. -Filename: src/lib.rs +src/lib.rs + + ``` +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { - 1 #[test] + use super::*; + + #[test] fn it_works() { - let result = 2 + 2; - 2 assert_eq!(result, 4); + let result = add(2, 2); + assert_eq!(result, 4); } } ``` -Listing 11-1: The test module and function generated automatically by `cargo -new` +Listing 11-1: The code generated automatically by `cargo new` + +The file starts with an example `add` function so that we have something to +test. -For now, let’s ignore the top two lines and focus on the function. Note the -`#[test]` annotation [1]: this attribute indicates this is a test function, so -the test runner knows to treat this function as a test. We might also have -non-test functions in the `tests` module to help set up common scenarios or -perform common operations, so we always need to indicate which functions are -tests. +For now, let’s focus solely on the `it_works` function. Note the `#[test]` +annotation: This attribute indicates this is a test function, so the test +runner knows to treat this function as a test. We might also have non-test +functions in the `tests` module to help set up common scenarios or perform +common operations, so we always need to indicate which functions are tests. -The example function body uses the `assert_eq!` macro [2] to assert that -`result`, which contains the result of adding 2 and 2, equals 4. This assertion -serves as an example of the format for a typical test. Let’s run it to see that -this test passes. +The example function body uses the `assert_eq!` macro to assert that `result`, +which contains the result of calling `add` with 2 and 2, equals 4. This +assertion serves as an example of the format for a typical test. Let’s run it +to see that this test passes. The `cargo test` command runs all tests in our project, as shown in Listing 11-2. + ``` $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.57s - Running unittests src/lib.rs (target/debug/deps/adder- -92948b65e88960b4) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.57s + Running unittests src/lib.rs (target/debug/deps/adder-01ad14159ff659ab) -1 running 1 test -2 test tests::it_works ... ok +running 1 test +test tests::it_works ... ok -3 test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s - 4 Doc-tests adder + Doc-tests adder running 0 tests -test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` Listing 11-2: The output from running the automatically generated test -Cargo compiled and ran the test. We see the line `running 1 test` [1]. The next -line shows the name of the generated test function, called `it_works`, and that -the result of running that test is `ok` [2]. The overall summary `test result: -ok.` [3] means that all the tests passed, and the portion that reads `1 passed; -0 failed` totals the number of tests that passed or failed. +Cargo compiled and ran the test. We see the line `running 1 test`. The next +line shows the name of the generated test function, called `tests::it_works`, +and that the result of running that test is `ok`. The overall summary `test result: ok.` means that all the tests passed, and the portion that reads `1 passed; 0 failed` totals the number of tests that passed or failed. -It’s possible to mark a test as ignored so it doesn’t run in a particular -instance; we’ll cover that in “Ignoring Some Tests Unless Specifically -Requested” on page XX. Because we haven’t done that here, the summary shows `0 -ignored`. We can also pass an argument to the `cargo test` command to run only -tests whose name matches a string; this is called *filtering* and we’ll cover -it in “Running a Subset of Tests by Name” on page XX. Here we haven’t filtered -the tests being run, so the end of the summary shows `0 filtered out`. +It’s possible to mark a test as ignored so that it doesn’t run in a particular +instance; we’ll cover that in the “Ignoring Tests Unless Specifically +Requested” section later in this chapter. Because we +haven’t done that here, the summary shows `0 ignored`. We can also pass an +argument to the `cargo test` command to run only tests whose name matches a +string; this is called *filtering*, and we’ll cover it in the “Running a +Subset of Tests by Name” section. Here, we haven’t +filtered the tests being run, so the end of the summary shows `0 filtered out`. The `0 measured` statistic is for benchmark tests that measure performance. Benchmark tests are, as of this writing, only available in nightly Rust. See -the documentation about benchmark tests at -*https://doc.rust-lang.org/unstable-book/library-features/test.html* to learn -more. +the documentation about benchmark tests at *../unstable-book/library-features/test.html* to learn more. -The next part of the test output starting at `Doc-tests adder` [4] is for the +The next part of the test output starting at `Doc-tests adder` is for the results of any documentation tests. We don’t have any documentation tests yet, but Rust can compile any code examples that appear in our API documentation. This feature helps keep your docs and your code in sync! We’ll discuss how to -write documentation tests in “Documentation Comments as Tests” on page XX. For -now, we’ll ignore the `Doc-tests` output. +write documentation tests in the “Documentation Comments as +Tests” section of Chapter 14. For now, we’ll +ignore the `Doc-tests` output. Let’s start to customize the test to our own needs. First, change the name of the `it_works` function to a different name, such as `exploration`, like so: @@ -172,25 +192,42 @@ the `it_works` function to a different name, such as `exploration`, like so: Filename: src/lib.rs ``` +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { + use super::*; + #[test] fn exploration() { - let result = 2 + 2; + let result = add(2, 2); assert_eq!(result, 4); } } ``` -Then run `cargo test` again. The output now shows `exploration` instead of +Then, run `cargo test` again. The output now shows `exploration` instead of `it_works`: ``` +$ cargo test + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.59s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) + running 1 test test tests::exploration ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests adder + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` Now we’ll add another test, but this time we’ll make a test that fails! Tests @@ -200,14 +237,21 @@ marked as failed. In Chapter 9, we talked about how the simplest way to panic is to call the `panic!` macro. Enter the new test as a function named `another`, so your *src/lib.rs* file looks like Listing 11-3. -Filename: src/lib.rs +src/lib.rs ``` +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { + use super::*; + #[test] fn exploration() { - assert_eq!(2 + 2, 4); + let result = add(2, 2); + assert_eq!(result, 4); } #[test] @@ -217,52 +261,67 @@ mod tests { } ``` -Listing 11-3: Adding a second test that will fail because we call the `panic!` -macro +Listing 11-3: Adding a second test that will fail because we call the `panic!` macro Run the tests again using `cargo test`. The output should look like Listing 11-4, which shows that our `exploration` test passed and `another` failed. + ``` +$ cargo test + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.72s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) + running 2 tests +test tests::another ... FAILED test tests::exploration ... ok -1 test tests::another ... FAILED -2 failures: +failures: ---- tests::another stdout ---- -thread 'main' panicked at 'Make this test fail', src/lib.rs:10:9 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace -3 failures: +thread 'tests::another' panicked at src/lib.rs:17:9: +Make this test fail +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace + + +failures: tests::another -4 test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s -error: test failed, to rerun pass '--lib' +error: test failed, to rerun pass `--lib` ``` Listing 11-4: Test results when one test passes and one test fails -Instead of `ok`, the line `test tests::another` shows `FAILED` [1]. Two new -sections appear between the individual results and the summary: the first [2] + + +Instead of `ok`, the line `test tests::another` shows `FAILED`. Two new +sections appear between the individual results and the summary: The first displays the detailed reason for each test failure. In this case, we get the -details that `another` failed because it `panicked at 'Make this test fail'` on -line 10 in the *src/lib.rs* file. The next section [3] lists just the names of -all the failing tests, which is useful when there are lots of tests and lots of -detailed failing test output. We can use the name of a failing test to run just -that test to more easily debug it; we’ll talk more about ways to run tests in -“Controlling How Tests Are Run” on page XX. +details that `tests::another` failed because it panicked with the message `Make this test fail` on line 17 in the *src/lib.rs* file. The next section lists +just the names of all the failing tests, which is useful when there are lots of +tests and lots of detailed failing test output. We can use the name of a +failing test to run just that test to debug it more easily; we’ll talk more +about ways to run tests in the “Controlling How Tests Are +Run” section. -The summary line displays at the end [4]: overall, our test result is `FAILED`. -We had one test pass and one test fail. +The summary line displays at the end: Overall, our test result is `FAILED`. We +had one test pass and one test fail. Now that you’ve seen what the test results look like in different scenarios, let’s look at some macros other than `panic!` that are useful in tests. -### Checking Results with the assert! Macro + + + + +### Checking Results with assert! The `assert!` macro, provided by the standard library, is useful when you want to ensure that some condition in a test evaluates to `true`. We give the @@ -271,11 +330,11 @@ to ensure that some condition in a test evaluates to `true`. We give the `assert!` macro calls `panic!` to cause the test to fail. Using the `assert!` macro helps us check that our code is functioning in the way we intend. -In Listing 5-15, we used a `Rectangle` struct and a `can_hold` method, which -are repeated here in Listing 11-5. Let’s put this code in the *src/lib.rs* -file, then write some tests for it using the `assert!` macro. +In Chapter 5, Listing 5-15, we used a `Rectangle` struct and a `can_hold` +method, which are repeated here in Listing 11-5. Let’s put this code in the +*src/lib.rs* file, then write some tests for it using the `assert!` macro. -Filename: src/lib.rs +src/lib.rs ``` #[derive(Debug)] @@ -291,8 +350,7 @@ impl Rectangle { } ``` -Listing 11-5: Using the `Rectangle` struct and its `can_hold` method from -Chapter 5 +Listing 11-5: The `Rectangle` struct and its `can_hold` method from Chapter 5 The `can_hold` method returns a Boolean, which means it’s a perfect use case for the `assert!` macro. In Listing 11-6, we write a test that exercises the @@ -300,16 +358,16 @@ for the `assert!` macro. In Listing 11-6, we write a test that exercises the a height of 7 and asserting that it can hold another `Rectangle` instance that has a width of 5 and a height of 1. -Filename: src/lib.rs +src/lib.rs ``` #[cfg(test)] mod tests { - 1 use super::*; + use super::*; #[test] - 2 fn larger_can_hold_smaller() { - 3 let larger = Rectangle { + fn larger_can_hold_smaller() { + let larger = Rectangle { width: 8, height: 7, }; @@ -318,34 +376,44 @@ mod tests { height: 1, }; - 4 assert!(larger.can_hold(&smaller)); + assert!(larger.can_hold(&smaller)); } } ``` -Listing 11-6: A test for `can_hold` that checks whether a larger rectangle can -indeed hold a smaller rectangle +Listing 11-6: A test for `can_hold` that checks whether a larger rectangle can indeed hold a smaller rectangle -Note that we’ve added a new line inside the `tests` module: `use super::*;` -[1]. The `tests` module is a regular module that follows the usual visibility -rules we covered in “Paths for Referring to an Item in the Module Tree” on page -XX. Because the `tests` module is an inner module, we need to bring the code -under test in the outer module into the scope of the inner module. We use a -glob here, so anything we define in the outer module is available to this +Note the `use super::*;` line inside the `tests` module. The `tests` module is +a regular module that follows the usual visibility rules we covered in Chapter +7 in the “Paths for Referring to an Item in the Module +Tree” +section. Because the `tests` module is an inner module, we need to bring the +code under test in the outer module into the scope of the inner module. We use +a glob here, so anything we define in the outer module is available to this `tests` module. -We’ve named our test `larger_can_hold_smaller` [2], and we’ve created the two -`Rectangle` instances that we need [3]. Then we called the `assert!` macro and -passed it the result of calling `larger.can_hold(&smaller)` [4]. This -expression is supposed to return `true`, so our test should pass. Let’s find -out! +We’ve named our test `larger_can_hold_smaller`, and we’ve created the two +`Rectangle` instances that we need. Then, we called the `assert!` macro and +passed it the result of calling `larger.can_hold(&smaller)`. This expression is +supposed to return `true`, so our test should pass. Let’s find out! ``` +$ cargo test + Compiling rectangle v0.1.0 (file:///projects/rectangle) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s + Running unittests src/lib.rs (target/debug/deps/rectangle-6584c4561e48942e) + running 1 test test tests::larger_can_hold_smaller ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests rectangle + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` It does pass! Let’s add another test, this time asserting that a smaller @@ -360,7 +428,7 @@ mod tests { #[test] fn larger_can_hold_smaller() { - --snip-- + // --snip-- } #[test] @@ -384,22 +452,32 @@ we need to negate that result before we pass it to the `assert!` macro. As a result, our test will pass if `can_hold` returns `false`: ``` +$ cargo test + Compiling rectangle v0.1.0 (file:///projects/rectangle) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s + Running unittests src/lib.rs (target/debug/deps/rectangle-6584c4561e48942e) + running 2 tests test tests::larger_can_hold_smaller ... ok test tests::smaller_cannot_hold_larger ... ok -test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests rectangle + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` Two tests that pass! Now let’s see what happens to our test results when we introduce a bug in our code. We’ll change the implementation of the `can_hold` -method by replacing the greater-than sign with a less-than sign when it -compares the widths: +method by replacing the greater-than sign (`>`) with a less-than sign (`<`) +when it compares the widths: ``` ---snip-- - +// --snip-- impl Rectangle { fn can_hold(&self, other: &Rectangle) -> bool { self.width < other.width && self.height > other.height @@ -410,31 +488,41 @@ impl Rectangle { Running the tests now produces the following: ``` +$ cargo test + Compiling rectangle v0.1.0 (file:///projects/rectangle) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s + Running unittests src/lib.rs (target/debug/deps/rectangle-6584c4561e48942e) + running 2 tests -test tests::smaller_cannot_hold_larger ... ok test tests::larger_can_hold_smaller ... FAILED +test tests::smaller_cannot_hold_larger ... ok failures: ---- tests::larger_can_hold_smaller stdout ---- -thread 'main' panicked at 'assertion failed: -larger.can_hold(&smaller)', src/lib.rs:28:9 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace + +thread 'tests::larger_can_hold_smaller' panicked at src/lib.rs:28:9: +assertion failed: larger.can_hold(&smaller) +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace failures: tests::larger_can_hold_smaller -test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` Our tests caught the bug! Because `larger.width` is `8` and `smaller.width` is `5`, the comparison of the widths in `can_hold` now returns `false`: 8 is not less than 5. -### Testing Equality with the assert_eq! and assert_ne! Macros + + + + +### Testing Equality with assert_eq! and assert_ne! A common way to verify functionality is to test for equality between the result of the code under test and the value you expect the code to return. You could @@ -448,12 +536,12 @@ fails, which makes it easier to see *why* the test failed; conversely, the expression, without printing the values that led to the `false` value. In Listing 11-7, we write a function named `add_two` that adds `2` to its -parameter, then we test this function using the `assert_eq!` macro. +parameter, and then we test this function using the `assert_eq!` macro. -Filename: src/lib.rs +src/lib.rs ``` -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { a + 2 } @@ -463,7 +551,8 @@ mod tests { #[test] fn it_adds_two() { - assert_eq!(4, add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } } ``` @@ -473,22 +562,33 @@ Listing 11-7: Testing the function `add_two` using the `assert_eq!` macro Let’s check that it passes! ``` +$ cargo test + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.58s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) + running 1 test test tests::it_adds_two ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests adder + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` -We pass `4` as the argument to `assert_eq!`, which is equal to the result of -calling `add_two(2)`. The line for this test is `test tests::it_adds_two ... -ok`, and the `ok` text indicates that our test passed! +We create a variable named `result` that holds the result of calling +`add_two(2)`. Then, we pass `result` and `4` as the arguments to the +`assert_eq!` macro. The output line for this test is `test tests::it_adds_two ... ok`, and the `ok` text indicates that our test passed! Let’s introduce a bug into our code to see what `assert_eq!` looks like when it fails. Change the implementation of the `add_two` function to instead add `3`: ``` -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { a + 3 } ``` @@ -496,30 +596,38 @@ pub fn add_two(a: i32) -> i32 { Run the tests again: ``` +$ cargo test + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.61s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) + running 1 test test tests::it_adds_two ... FAILED failures: ---- tests::it_adds_two stdout ---- -1 thread 'main' panicked at 'assertion failed: `(left == right)` -2 left: `4`, -3 right: `5`', src/lib.rs:11:9 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace + +thread 'tests::it_adds_two' panicked at src/lib.rs:12:9: +assertion `left == right` failed + left: 5 + right: 4 +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace + failures: tests::it_adds_two -test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` -Our test caught the bug! The `it_adds_two` test failed, and the message tells -us that the assertion that failed was `assertion failed: `(left == right)`` [1] -and what the `left` [2] and `right` [3] values are. This message helps us start -debugging: the `left` argument was `4` but the `right` argument, where we had -`add_two(2)`, was `5`. You can imagine that this would be especially helpful +Our test caught the bug! The `tests::it_adds_two` test failed, and the message +tells us that the assertion that failed was `left == right` and what the `left` +and `right` values are. This message helps us start debugging: The `left` +argument, where we had the result of calling `add_two(2)`, was `5`, but the +`right` argument was `4`. You can imagine that this would be especially helpful when we have a lot of tests going on. Note that in some languages and test frameworks, the parameters to equality @@ -527,15 +635,15 @@ assertion functions are called `expected` and `actual`, and the order in which we specify the arguments matters. However, in Rust, they’re called `left` and `right`, and the order in which we specify the value we expect and the value the code produces doesn’t matter. We could write the assertion in this test as -`assert_eq!(add_two(2), 4)`, which would result in the same failure message -that displays `assertion failed: `(left == right)``. +`assert_eq!(4, result)`, which would result in the same failure message that +displays ``assertion `left == right` failed``. The `assert_ne!` macro will pass if the two values we give it are not equal and -fail if they’re equal. This macro is most useful for cases when we’re not sure -what a value *will* be, but we know what the value definitely *shouldn’t* be. -For example, if we’re testing a function that is guaranteed to change its input -in some way, but the way in which the input is changed depends on the day of -the week that we run our tests, the best thing to assert might be that the +will fail if they are equal. This macro is most useful for cases when we’re not +sure what a value *will* be, but we know what the value definitely *shouldn’t* +be. For example, if we’re testing a function that is guaranteed to change its +input in some way, but the way in which the input is changed depends on the day +of the week that we run our tests, the best thing to assert might be that the output of the function is not equal to the input. Under the surface, the `assert_eq!` and `assert_ne!` macros use the operators @@ -546,20 +654,21 @@ the standard library types implement these traits. For structs and enums that you define yourself, you’ll need to implement `PartialEq` to assert equality of those types. You’ll also need to implement `Debug` to print the values when the assertion fails. Because both traits are derivable traits, as mentioned in -Listing 5-12, this is usually as straightforward as adding the +Listing 5-12 in Chapter 5, this is usually as straightforward as adding the `#[derive(PartialEq, Debug)]` annotation to your struct or enum definition. See -Appendix C for more details about these and other derivable traits. +Appendix C, “Derivable Traits,” for more +details about these and other derivable traits. ### Adding Custom Failure Messages You can also add a custom message to be printed with the failure message as optional arguments to the `assert!`, `assert_eq!`, and `assert_ne!` macros. Any arguments specified after the required arguments are passed along to the -`format!` macro (discussed in “Concatenation with the + Operator or the format! -Macro” on page XX), so you can pass a format string that contains `{}` +`format!` macro (discussed in “Concatenating with `+` or +`format!`” in Chapter 8), so you can pass a format string that contains `{}` placeholders and values to go in those placeholders. Custom messages are useful -for documenting what an assertion means; when a test fails, you’ll have a -better idea of what the problem is with the code. +for documenting what an assertion means; when a test fails, you’ll have a better +idea of what the problem is with the code. For example, let’s say we have a function that greets people by name and we want to test that the name we pass into the function appears in the output: @@ -602,20 +711,29 @@ pub fn greeting(name: &str) -> String { Running this test produces the following: ``` +$ cargo test + Compiling greeter v0.1.0 (file:///projects/greeter) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.91s + Running unittests src/lib.rs (target/debug/deps/greeter-170b942eb5bf5e3a) + running 1 test test tests::greeting_contains_name ... FAILED failures: ---- tests::greeting_contains_name stdout ---- -thread 'main' panicked at 'assertion failed: -result.contains(\"Carol\")', src/lib.rs:12:9 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace + +thread 'tests::greeting_contains_name' panicked at src/lib.rs:12:9: +assertion failed: result.contains("Carol") +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace failures: tests::greeting_contains_name + +test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` This result just indicates that the assertion failed and which line the @@ -625,24 +743,42 @@ string with a placeholder filled in with the actual value we got from the `greeting` function: ``` -#[test] -fn greeting_contains_name() { - let result = greeting("Carol"); - assert!( - result.contains("Carol"), - "Greeting did not contain name, value was `{result}`" - ); -} + #[test] + fn greeting_contains_name() { + let result = greeting("Carol"); + assert!( + result.contains("Carol"), + "Greeting did not contain name, value was `{result}`" + ); + } ``` Now when we run the test, we’ll get a more informative error message: ``` +$ cargo test + Compiling greeter v0.1.0 (file:///projects/greeter) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.93s + Running unittests src/lib.rs (target/debug/deps/greeter-170b942eb5bf5e3a) + +running 1 test +test tests::greeting_contains_name ... FAILED + +failures: + ---- tests::greeting_contains_name stdout ---- -thread 'main' panicked at 'Greeting did not contain name, value -was `Hello!`', src/lib.rs:12:9 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace + +thread 'tests::greeting_contains_name' panicked at src/lib.rs:12:9: +Greeting did not contain name, value was `Hello!` +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace + + +failures: + tests::greeting_contains_name + +test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` We can see the value we actually got in the test output, which would help us @@ -652,10 +788,10 @@ debug what happened instead of what we were expecting to happen. In addition to checking return values, it’s important to check that our code handles error conditions as we expect. For example, consider the `Guess` type -that we created in Listing 9-13. Other code that uses `Guess` depends on the -guarantee that `Guess` instances will contain only values between 1 and 100. We -can write a test that ensures that attempting to create a `Guess` instance with -a value outside that range panics. +that we created in Chapter 9, Listing 9-13. Other code that uses `Guess` +depends on the guarantee that `Guess` instances will contain only values +between 1 and 100. We can write a test that ensures that attempting to create a +`Guess` instance with a value outside that range panics. We do this by adding the attribute `should_panic` to our test function. The test passes if the code inside the function panics; the test fails if the code @@ -664,8 +800,9 @@ inside the function doesn’t panic. Listing 11-8 shows a test that checks that the error conditions of `Guess::new` happen when we expect them to. +src/lib.rs + ``` -// src/lib.rs pub struct Guess { value: i32, } @@ -673,10 +810,7 @@ pub struct Guess { impl Guess { pub fn new(value: i32) -> Guess { if value < 1 || value > 100 { - panic!( - "Guess value must be between 1 and 100, got {}.", - value - ); + panic!("Guess value must be between 1 and 100, got {value}."); } Guess { value } @@ -695,34 +829,40 @@ mod tests { } ``` -Listing 11-8: Testing that a condition will cause a panic! +Listing 11-8: Testing that a condition will cause a `panic!` We place the `#[should_panic]` attribute after the `#[test]` attribute and before the test function it applies to. Let’s look at the result when this test passes: ``` +$ cargo test + Compiling guessing_game v0.1.0 (file:///projects/guessing_game) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.58s + Running unittests src/lib.rs (target/debug/deps/guessing_game-57d70c3acb738f4d) + running 1 test test tests::greater_than_100 - should panic ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests guessing_game + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` Looks good! Now let’s introduce a bug in our code by removing the condition that the `new` function will panic if the value is greater than 100: ``` -// src/lib.rs ---snip-- - +// --snip-- impl Guess { pub fn new(value: i32) -> Guess { if value < 1 { - panic!( - "Guess value must be between 1 and 100, got {}.", - value - ); + panic!("Guess value must be between 1 and 100, got {value}."); } Guess { value } @@ -733,6 +873,11 @@ impl Guess { When we run the test in Listing 11-8, it will fail: ``` +$ cargo test + Compiling guessing_game v0.1.0 (file:///projects/guessing_game) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.62s + Running unittests src/lib.rs (target/debug/deps/guessing_game-57d70c3acb738f4d) + running 1 test test tests::greater_than_100 - should panic ... FAILED @@ -744,8 +889,9 @@ note: test did not panic as expected failures: tests::greater_than_100 -test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` We don’t get a very helpful message in this case, but when we look at the test @@ -761,21 +907,20 @@ consider the modified code for `Guess` in Listing 11-9 where the `new` function panics with different messages depending on whether the value is too small or too large. +src/lib.rs + ``` -// src/lib.rs ---snip-- +// --snip-- impl Guess { pub fn new(value: i32) -> Guess { if value < 1 { panic!( - "Guess value must be greater than or equal to 1, got {}.", - value + "Guess value must be greater than or equal to 1, got {value}." ); } else if value > 100 { panic!( - "Guess value must be less than or equal to 100, got {}.", - value + "Guess value must be less than or equal to 100, got {value}." ); } @@ -795,14 +940,12 @@ mod tests { } ``` -Listing 11-9: Testing for a `panic!` with a panic message containing a -specified substring +Listing 11-9: Testing for a `panic!` with a panic message containing a specified substring This test will pass because the value we put in the `should_panic` attribute’s `expected` parameter is a substring of the message that the `Guess::new` function panics with. We could have specified the entire panic message that we -expect, which in this case would be `Guess value must be less than or equal to -100, got 200`. What you choose to specify depends on how much of the panic +expect, which in this case would be `Guess value must be less than or equal to 100, got 200`. What you choose to specify depends on how much of the panic message is unique or dynamic and how precise you want your test to be. In this case, a substring of the panic message is enough to ensure that the code in the test function executes the `else if value > 100` case. @@ -812,66 +955,66 @@ fails, let’s again introduce a bug into our code by swapping the bodies of the `if value < 1` and the `else if value > 100` blocks: ``` -// src/lib.rs ---snip-- -if value < 1 { - panic!( - "Guess value must be less than or equal to 100, got {}.", - value - ); -} else if value > 100 { - panic!( - "Guess value must be greater than or equal to 1, got {}.", - value - ); -} ---snip-- + if value < 1 { + panic!( + "Guess value must be less than or equal to 100, got {value}." + ); + } else if value > 100 { + panic!( + "Guess value must be greater than or equal to 1, got {value}." + ); + } ``` This time when we run the `should_panic` test, it will fail: ``` +$ cargo test + Compiling guessing_game v0.1.0 (file:///projects/guessing_game) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.66s + Running unittests src/lib.rs (target/debug/deps/guessing_game-57d70c3acb738f4d) + running 1 test test tests::greater_than_100 - should panic ... FAILED failures: ---- tests::greater_than_100 stdout ---- -thread 'main' panicked at 'Guess value must be greater than or equal to 1, got -200.', src/lib.rs:13:13 + +thread 'tests::greater_than_100' panicked at src/lib.rs:12:13: +Guess value must be greater than or equal to 1, got 200. note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace note: panic did not contain expected string - panic message: `"Guess value must be greater than or equal to 1, got -200."`, + panic message: `"Guess value must be greater than or equal to 1, got 200."`, expected substring: `"less than or equal to 100"` failures: tests::greater_than_100 -test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; -finished in 0.00s +test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` The failure message indicates that this test did indeed panic as we expected, -but the panic message did not include the expected string `'Guess value must be -less than or equal to 100'`. The panic message that we did get in this case was -`Guess value must be greater than or equal to 1, got 200`. Now we can start -figuring out where our bug is! +but the panic message did not include the expected string `less than or equal to 100`. The panic message that we did get in this case was `Guess value must be greater than or equal to 1, got 200`. Now we can start figuring out where +our bug is! ### Using Result in Tests -Our tests so far all panic when they fail. We can also write tests that use -`Result`! Here’s the test from Listing 11-1, rewritten to use `Result` and return an `Err` instead of panicking: - -Filename: src/lib.rs +All of our tests so far panic when they fail. We can also write tests that use +`Result`! Here’s the test from Listing 11-1, rewritten to use `Result` and return an `Err` instead of panicking: ``` #[cfg(test)] mod tests { + use super::*; + #[test] fn it_works() -> Result<(), String> { - if 2 + 2 == 4 { + let result = add(2, 2); + + if result == 4 { Ok(()) } else { Err(String::from("two plus two does not equal four")) @@ -885,18 +1028,17 @@ body of the function, rather than calling the `assert_eq!` macro, we return `Ok(())` when the test passes and an `Err` with a `String` inside when the test fails. -Writing tests so they return a `Result` enables you to use the question -mark operator in the body of tests, which can be a convenient way to write -tests that should fail if any operation within them returns an `Err` variant. +Writing tests so that they return a `Result` enables you to use the +question mark operator in the body of tests, which can be a convenient way to +write tests that should fail if any operation within them returns an `Err` +variant. -You can’t use the `#[should_panic]` annotation on tests that use `Result`. To assert that an operation returns an `Err` variant, *don’t* use the +You can’t use the `#[should_panic]` annotation on tests that use `Result`. To assert that an operation returns an `Err` variant, *don’t* use the question mark operator on the `Result` value. Instead, use `assert!(value.is_err())`. Now that you know several ways to write tests, let’s look at what is happening -when we run our tests and explore the different options we can use with `cargo -test`. +when we run our tests and explore the different options we can use with `cargo test`. ## Controlling How Tests Are Run @@ -913,25 +1055,26 @@ binary. To separate these two types of arguments, you list the arguments that go to `cargo test` followed by the separator `--` and then the ones that go to the test binary. Running `cargo test --help` displays the options you can use with `cargo test`, and running `cargo test -- --help` displays the options you -can use after the separator. +can use after the separator. These options are also documented in the “Tests” +section of *The `rustc` Book* at *https://doc.rust-lang.org/rustc/tests/index.html*. ### Running Tests in Parallel or Consecutively When you run multiple tests, by default they run in parallel using threads, -meaning they finish running faster and you get feedback quicker. Because the -tests are running at the same time, you must make sure your tests don’t depend -on each other or on any shared state, including a shared environment, such as -the current working directory or environment variables. +meaning they finish running more quickly and you get feedback sooner. Because +the tests are running at the same time, you must make sure your tests don’t +depend on each other or on any shared state, including a shared environment, +such as the current working directory or environment variables. For example, say each of your tests runs some code that creates a file on disk -named *test-output.txt* and writes some data to that file. Then each test reads -the data in that file and asserts that the file contains a particular value, -which is different in each test. Because the tests run at the same time, one -test might overwrite the file in the time between another test writing and -reading the file. The second test will then fail, not because the code is -incorrect but because the tests have interfered with each other while running -in parallel. One solution is to make sure each test writes to a different file; -another solution is to run the tests one at a time. +named *test-output.txt* and writes some data to that file. Then, each test +reads the data in that file and asserts that the file contains a particular +value, which is different in each test. Because the tests run at the same time, +one test might overwrite the file in the time between when another test is +writing and reading the file. The second test will then fail, not because the +code is incorrect but because the tests have interfered with each other while +running in parallel. One solution is to make sure each test writes to a +different file; another solution is to run the tests one at a time. If you don’t want to run the tests in parallel or if you want more fine-grained control over the number of threads used, you can send the `--test-threads` flag @@ -958,7 +1101,7 @@ printed to standard output with the rest of the failure message. As an example, Listing 11-10 has a silly function that prints the value of its parameter and returns 10, as well as a test that passes and a test that fails. -Filename: src/lib.rs +src/lib.rs ``` fn prints_and_returns_10(a: i32) -> i32 { @@ -973,13 +1116,13 @@ mod tests { #[test] fn this_test_will_pass() { let value = prints_and_returns_10(4); - assert_eq!(10, value); + assert_eq!(value, 10); } #[test] fn this_test_will_fail() { let value = prints_and_returns_10(8); - assert_eq!(5, value); + assert_eq!(value, 5); } } ``` @@ -989,32 +1132,39 @@ Listing 11-10: Tests for a function that calls `println!` When we run these tests with `cargo test`, we’ll see the following output: ``` +$ cargo test + Compiling silly-function v0.1.0 (file:///projects/silly-function) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.58s + Running unittests src/lib.rs (target/debug/deps/silly_function-160869f38cff9166) + running 2 tests -test tests::this_test_will_pass ... ok test tests::this_test_will_fail ... FAILED +test tests::this_test_will_pass ... ok failures: ---- tests::this_test_will_fail stdout ---- -1 I got the value 8 -thread 'main' panicked at 'assertion failed: `(left == right)` - left: `5`, - right: `10`', src/lib.rs:19:9 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace +I got the value 8 + +thread 'tests::this_test_will_fail' panicked at src/lib.rs:19:9: +assertion `left == right` failed + left: 10 + right: 5 +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace + failures: tests::this_test_will_fail -test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` Note that nowhere in this output do we see `I got the value 4`, which is printed when the test that passes runs. That output has been captured. The -output from the test that failed, `I got the value 8` [1], appears in the -section of the test summary output, which also shows the cause of the test -failure. +output from the test that failed, `I got the value 8`, appears in the section +of the test summary output, which also shows the cause of the test failure. If we want to see printed values for passing tests as well, we can tell Rust to also show the output of successful tests with `--show-output`: @@ -1027,9 +1177,14 @@ When we run the tests in Listing 11-10 again with the `--show-output` flag, we see the following output: ``` +$ cargo test -- --show-output + Compiling silly-function v0.1.0 (file:///projects/silly-function) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.60s + Running unittests src/lib.rs (target/debug/deps/silly_function-160869f38cff9166) + running 2 tests -test tests::this_test_will_pass ... ok test tests::this_test_will_fail ... FAILED +test tests::this_test_will_pass ... ok successes: @@ -1044,22 +1199,25 @@ failures: ---- tests::this_test_will_fail stdout ---- I got the value 8 -thread 'main' panicked at 'assertion failed: `(left == right)` - left: `5`, - right: `10`', src/lib.rs:19:9 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace + +thread 'tests::this_test_will_fail' panicked at src/lib.rs:19:9: +assertion `left == right` failed + left: 10 + right: 5 +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace + failures: tests::this_test_will_fail -test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: FAILED. 1 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` ### Running a Subset of Tests by Name -Sometimes, running a full test suite can take a long time. If you’re working on +Running a full test suite can sometimes take a long time. If you’re working on code in a particular area, you might want to run only the tests pertaining to that code. You can choose which tests to run by passing `cargo test` the name or names of the test(s) you want to run as an argument. @@ -1067,10 +1225,10 @@ or names of the test(s) you want to run as an argument. To demonstrate how to run a subset of tests, we’ll first create three tests for our `add_two` function, as shown in Listing 11-11, and choose which ones to run. -Filename: src/lib.rs +src/lib.rs ``` -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { a + 2 } @@ -1080,17 +1238,20 @@ mod tests { #[test] fn add_two_and_two() { - assert_eq!(4, add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } #[test] fn add_three_and_two() { - assert_eq!(5, add_two(3)); + let result = add_two(3); + assert_eq!(result, 5); } #[test] fn one_hundred() { - assert_eq!(102, add_two(100)); + let result = add_two(100); + assert_eq!(result, 102); } } ``` @@ -1101,13 +1262,24 @@ If we run the tests without passing any arguments, as we saw earlier, all the tests will run in parallel: ``` +$ cargo test + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.62s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) + running 3 tests test tests::add_three_and_two ... ok test tests::add_two_and_two ... ok test tests::one_hundred ... ok -test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests adder + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` #### Running Single Tests @@ -1117,15 +1289,14 @@ We can pass the name of any test function to `cargo test` to run only that test: ``` $ cargo test one_hundred Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.69s - Running unittests src/lib.rs (target/debug/deps/adder- -92948b65e88960b4) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.69s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test test tests::one_hundred ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 2 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 2 filtered out; finished in 0.00s + ``` Only the test with the name `one_hundred` ran; the other two tests didn’t match @@ -1144,16 +1315,15 @@ run those two by running `cargo test add`: ``` $ cargo test add Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.61s - Running unittests src/lib.rs (target/debug/deps/adder- -92948b65e88960b4) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.61s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 2 tests test tests::add_three_and_two ... ok test tests::add_two_and_two ... ok -test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 1 -filtered out; finished in 0.00s +test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s + ``` This command ran all tests with `add` in the name and filtered out the test @@ -1161,7 +1331,11 @@ named `one_hundred`. Also note that the module in which a test appears becomes part of the test’s name, so we can run all the tests in a module by filtering on the module’s name. -### Ignoring Some Tests Unless Specifically Requested + + + + +### Ignoring Tests Unless Specifically Requested Sometimes a few specific tests can be very time-consuming to execute, so you might want to exclude them during most runs of `cargo test`. Rather than @@ -1172,16 +1346,21 @@ here: Filename: src/lib.rs ``` -#[test] -fn it_works() { - let result = 2 + 2; - assert_eq!(result, 4); -} +#[cfg(test)] +mod tests { + use super::*; -#[test] -#[ignore] -fn expensive_test() { - // code that takes an hour to run + #[test] + fn it_works() { + let result = add(2, 2); + assert_eq!(result, 4); + } + + #[test] + #[ignore] + fn expensive_test() { + // code that takes an hour to run + } } ``` @@ -1191,16 +1370,21 @@ Now when we run our tests, `it_works` runs, but `expensive_test` doesn’t: ``` $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.60s - Running unittests src/lib.rs (target/debug/deps/adder- -92948b65e88960b4) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.60s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 2 tests -test expensive_test ... ignored -test it_works ... ok +test tests::expensive_test ... ignored +test tests::it_works ... ok + +test result: ok. 1 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests adder + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s -test result: ok. 1 passed; 0 failed; 1 ignored; 0 measured; 0 -filtered out; finished in 0.00s ``` The `expensive_test` function is listed as `ignored`. If we want to run only @@ -1208,15 +1392,21 @@ the ignored tests, we can use `cargo test -- --ignored`: ``` $ cargo test -- --ignored - Finished test [unoptimized + debuginfo] target(s) in 0.61s - Running unittests src/lib.rs (target/debug/deps/adder- -92948b65e88960b4) + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.61s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) running 1 test -test expensive_test ... ok +test tests::expensive_test ... ok + +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s + + Doc-tests adder + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1 -filtered out; finished in 0.00s ``` By controlling which tests run, you can make sure your `cargo test` results @@ -1248,11 +1438,10 @@ code that they’re testing. The convention is to create a module named `tests` in each file to contain the test functions and to annotate the module with `cfg(test)`. -#### The Tests Module and #[cfg(test)] +#### The tests Module and \#[cfg(test)] The `#[cfg(test)]` annotation on the `tests` module tells Rust to compile and -run the test code only when you run `cargo test`, not when you run `cargo -build`. This saves compile time when you only want to build the library and +run the test code only when you run `cargo test`, not when you run `cargo build`. This saves compile time when you only want to build the library and saves space in the resultant compiled artifact because the tests are not included. You’ll see that because integration tests go in a different directory, they don’t need the `#[cfg(test)]` annotation. However, because unit @@ -1265,26 +1454,35 @@ this chapter, Cargo generated this code for us: Filename: src/lib.rs ``` +pub fn add(left: u64, right: u64) -> u64 { + left + right +} + #[cfg(test)] mod tests { + use super::*; + #[test] fn it_works() { - let result = 2 + 2; + let result = add(2, 2); assert_eq!(result, 4); } } ``` -This code is the automatically generated `tests` module. The attribute `cfg` -stands for *configuration* and tells Rust that the following item should only -be included given a certain configuration option. In this case, the -configuration option is `test`, which is provided by Rust for compiling and -running tests. By using the `cfg` attribute, Cargo compiles our test code only -if we actively run the tests with `cargo test`. This includes any helper -functions that might be within this module, in addition to the functions -annotated with `#[test]`. +On the automatically generated `tests` module, the attribute `cfg` stands for +*configuration* and tells Rust that the following item should only be included +given a certain configuration option. In this case, the configuration option is +`test`, which is provided by Rust for compiling and running tests. By using the +`cfg` attribute, Cargo compiles our test code only if we actively run the tests +with `cargo test`. This includes any helper functions that might be within this +module, in addition to the functions annotated with `#[test]`. + + -#### Testing Private Functions + + +#### Private Function Tests There’s debate within the testing community about whether or not private functions should be tested directly, and other languages make it difficult or @@ -1292,15 +1490,15 @@ impossible to test private functions. Regardless of which testing ideology you adhere to, Rust’s privacy rules do allow you to test private functions. Consider the code in Listing 11-12 with the private function `internal_adder`. -Filename: src/lib.rs +src/lib.rs ``` -pub fn add_two(a: i32) -> i32 { +pub fn add_two(a: u64) -> u64 { internal_adder(a, 2) } -fn internal_adder(a: i32, b: i32) -> i32 { - a + b +fn internal_adder(left: u64, right: u64) -> u64 { + left + right } #[cfg(test)] @@ -1309,7 +1507,8 @@ mod tests { #[test] fn internal() { - assert_eq!(4, internal_adder(2, 2)); + let result = internal_adder(2, 2); + assert_eq!(result, 4); } } ``` @@ -1318,11 +1517,12 @@ Listing 11-12: Testing a private function Note that the `internal_adder` function is not marked as `pub`. Tests are just Rust code, and the `tests` module is just another module. As we discussed in -“Paths for Referring to an Item in the Module Tree” on page XX, items in child -modules can use the items in their ancestor modules. In this test, we bring all -of the `test` module’s parent’s items into scope with `use super::*`, and then -the test can call `internal_adder`. If you don’t think private functions should -be tested, there’s nothing in Rust that will compel you to do so. +“Paths for Referring to an Item in the Module Tree”, +items in child modules can use the items in their ancestor modules. In this +test, we bring all of the items belonging to the `tests` module’s parent into +scope with `use super::*`, and then the test can call `internal_adder`. If you +don’t think private functions should be tested, there’s nothing in Rust that +will compel you to do so. ### Integration Tests @@ -1350,29 +1550,29 @@ adder ├── Cargo.lock ├── Cargo.toml ├── src -│ └── lib.rs +│   └── lib.rs └── tests └── integration_test.rs ``` Enter the code in Listing 11-13 into the *tests/integration_test.rs* file. -Filename: tests/integration_test.rs +tests/integration_test.rs ``` -use adder; +use adder::add_two; #[test] fn it_adds_two() { - assert_eq!(4, adder::add_two(2)); + let result = add_two(2); + assert_eq!(result, 4); } ``` Listing 11-13: An integration test of a function in the `adder` crate Each file in the *tests* directory is a separate crate, so we need to bring our -library into each test crate’s scope. For that reason we add `use adder;` at -the top of the code, which we didn’t need in the unit tests. +library into each test crate’s scope. For that reason, we add `use adder::add_two;` at the top of the code, which we didn’t need in the unit tests. We don’t need to annotate any code in *tests/integration_test.rs* with `#[cfg(test)]`. Cargo treats the *tests* directory specially and compiles files @@ -1381,47 +1581,42 @@ in this directory only when we run `cargo test`. Run `cargo test` now: ``` $ cargo test Compiling adder v0.1.0 (file:///projects/adder) - Finished test [unoptimized + debuginfo] target(s) in 1.31s - Running unittests src/lib.rs (target/debug/deps/adder- -1082c4b063a8fbe6) + Finished `test` profile [unoptimized + debuginfo] target(s) in 1.31s + Running unittests src/lib.rs (target/debug/deps/adder-1082c4b063a8fbe6) -1 running 1 test +running 1 test test tests::internal ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s - 2 Running tests/integration_test.rs -(target/debug/deps/integration_test-1082c4b063a8fbe6) + Running tests/integration_test.rs (target/debug/deps/integration_test-1082c4b063a8fbe6) running 1 test -3 test it_adds_two ... ok +test it_adds_two ... ok -4 test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s Doc-tests adder running 0 tests -test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` The three sections of output include the unit tests, the integration test, and the doc tests. Note that if any test in a section fails, the following sections will not be run. For example, if a unit test fails, there won’t be any output -for integration and doc tests because those tests will only be run if all unit +for integration and doc tests, because those tests will only be run if all unit tests are passing. -The first section for the unit tests [1] is the same as we’ve been seeing: one -line for each unit test (one named `internal` that we added in Listing 11-12) -and then a summary line for the unit tests. +The first section for the unit tests is the same as we’ve been seeing: one line +for each unit test (one named `internal` that we added in Listing 11-12) and +then a summary line for the unit tests. -The integration tests section starts with the line `Running -tests/integration_test.rs` [2]. Next, there is a line for each test function in -that integration test [3] and a summary line for the results of the integration -test [4] just before the `Doc-tests adder` section starts. +The integration tests section starts with the line `Running tests/integration_test.rs`. Next, there is a line for each test function in +that integration test and a summary line for the results of the integration +test just before the `Doc-tests adder` section starts. Each integration test file has its own section, so if we add more files in the *tests* directory, there will be more integration test sections. @@ -1433,15 +1628,15 @@ followed by the name of the file: ``` $ cargo test --test integration_test - Finished test [unoptimized + debuginfo] target(s) in 0.64s - Running tests/integration_test.rs -(target/debug/deps/integration_test-82e7799c1bc62298) + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.64s + Running tests/integration_test.rs (target/debug/deps/integration_test-82e7799c1bc62298) running 1 test test it_adds_two ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` This command runs only the tests in the *tests/integration_test.rs* file. @@ -1458,12 +1653,12 @@ share the same behavior as files in *src* do, as you learned in Chapter 7 regarding how to separate code into modules and files. The different behavior of *tests* directory files is most noticeable when you -have a set of helper functions to use in multiple integration test files and -you try to follow the steps in “Separating Modules into Different Files” on -page XX to extract them into a common module. For example, if we create -*tests/common.rs* and place a function named `setup` in it, we can add some -code to `setup` that we want to call from multiple test functions in multiple -test files: +have a set of helper functions to use in multiple integration test files, and +you try to follow the steps in the “Separating Modules into Different +Files” section of Chapter 7 to +extract them into a common module. For example, if we create *tests/common.rs* +and place a function named `setup` in it, we can add some code to `setup` that +we want to call from multiple test functions in multiple test files: Filename: tests/common.rs @@ -1478,35 +1673,35 @@ When we run the tests again, we’ll see a new section in the test output for th did we call the `setup` function from anywhere: ``` +$ cargo test + Compiling adder v0.1.0 (file:///projects/adder) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.89s + Running unittests src/lib.rs (target/debug/deps/adder-92948b65e88960b4) + running 1 test test tests::internal ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s - Running tests/common.rs (target/debug/deps/common- -92948b65e88960b4) + Running tests/common.rs (target/debug/deps/common-92948b65e88960b4) running 0 tests -test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s - Running tests/integration_test.rs -(target/debug/deps/integration_test-92948b65e88960b4) + Running tests/integration_test.rs (target/debug/deps/integration_test-92948b65e88960b4) running 1 test test it_adds_two ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s Doc-tests adder running 0 tests -test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` Having `common` appear in the test results with `running 0 tests` displayed for @@ -1519,20 +1714,20 @@ project directory now looks like this: ├── Cargo.lock ├── Cargo.toml ├── src -│ └── lib.rs +│   └── lib.rs └── tests ├── common - │ └── mod.rs + │   └── mod.rs └── integration_test.rs ``` -This is the older naming convention that Rust also understands that we -mentioned in “Alternate File Paths” on page XX. Naming the file this way tells -Rust not to treat the `common` module as an integration test file. When we move -the `setup` function code into *tests/common/mod.rs* and delete the -*tests/common.rs* file, the section in the test output will no longer appear. -Files in subdirectories of the *tests* directory don’t get compiled as separate -crates or have sections in the test output. +This is the older naming convention that Rust also understands that we mentioned +in “Alternate File Paths” in Chapter 7. Naming the +file this way tells Rust not to treat the `common` module as an integration test +file. When we move the `setup` function code into *tests/common/mod.rs* and +delete the *tests/common.rs* file, the section in the test output will no longer +appear. Files in subdirectories of the *tests* directory don’t get compiled as +separate crates or have sections in the test output. After we’ve created *tests/common/mod.rs*, we can use it from any of the integration test files as a module. Here’s an example of calling the `setup` @@ -1541,14 +1736,16 @@ function from the `it_adds_two` test in *tests/integration_test.rs*: Filename: tests/integration_test.rs ``` -use adder; +use adder::add_two; mod common; #[test] fn it_adds_two() { common::setup(); - assert_eq!(4, adder::add_two(2)); + + let result = add_two(2); + assert_eq!(result, 4); } ``` @@ -1574,8 +1771,8 @@ file will work as well, and that small amount of code doesn’t need to be teste ## Summary Rust’s testing features provide a way to specify how code should function to -ensure it continues to work as you expect, even as you make changes. Unit tests -exercise different parts of a library separately and can test private +ensure that it continues to work as you expect, even as you make changes. Unit +tests exercise different parts of a library separately and can test private implementation details. Integration tests check that many parts of the library work together correctly, and they use the library’s public API to test the code in the same way external code will use it. Even though Rust’s type system and @@ -1584,4 +1781,3 @@ reduce logic bugs having to do with how your code is expected to behave. Let’s combine the knowledge you learned in this chapter and in previous chapters to work on a project! - diff --git a/nostarch/chapter12.md b/nostarch/chapter12.md index 86e9861731..7b22854400 100644 --- a/nostarch/chapter12.md +++ b/nostarch/chapter12.md @@ -18,7 +18,7 @@ an ideal language for creating command line tools, so for our project, we’ll make our own version of the classic command line search tool `grep` (**g**lobally search a **r**egular **e**xpression and **p**rint). In the simplest use case, `grep` searches a specified file for a specified string. To -do so, `grep` takes as its arguments a file path and a string. Then it reads +do so, `grep` takes as its arguments a file path and a string. Then, it reads the file, finds lines in that file that contain the string argument, and prints those lines. @@ -44,13 +44,14 @@ Our `grep` project will combine a number of concepts you’ve learned so far: * Writing tests (Chapter 11) We’ll also briefly introduce closures, iterators, and trait objects, which -Chapter 13 and Chapter 17 will cover in detail. +Chapter 13 and Chapter 18 will +cover in detail. ## Accepting Command Line Arguments Let’s create a new project with, as always, `cargo new`. We’ll call our project `minigrep` to distinguish it from the `grep` tool that you might already have -on your system. +on your system: ``` $ cargo new minigrep @@ -69,25 +70,24 @@ $ cargo run -- searchstring example-filename.txt ``` Right now, the program generated by `cargo new` cannot process arguments we -give it. Some existing libraries on *https://crates.io* can help with writing a -program that accepts command line arguments, but because you’re just learning -this concept, let’s implement this capability ourselves. +give it. Some existing libraries on crates.io at *https://crates.io/* can help +with writing a program that accepts command line arguments, but because you’re +just learning this concept, let’s implement this capability ourselves. ### Reading the Argument Values To enable `minigrep` to read the values of command line arguments we pass to it, we’ll need the `std::env::args` function provided in Rust’s standard library. This function returns an iterator of the command line arguments passed -to `minigrep`. We’ll cover iterators fully in Chapter 13. For now, you only -need to know two details about iterators: iterators produce a series of values, -and we can call the `collect` method on an iterator to turn it into a -collection, such as a vector, that contains all the elements the iterator -produces. +to `minigrep`. We’ll cover iterators fully in Chapter 13. For now, you only need to know two details about iterators: Iterators +produce a series of values, and we can call the `collect` method on an iterator +to turn it into a collection, such as a vector, which contains all the elements +the iterator produces. The code in Listing 12-1 allows your `minigrep` program to read any command -line arguments passed to it, and then collect the values into a vector. +line arguments passed to it and then collect the values into a vector. -Filename: src/main.rs +src/main.rs ``` use std::env; @@ -98,27 +98,26 @@ fn main() { } ``` -Listing 12-1: Collecting the command line arguments into a vector and printing -them +Listing 12-1: Collecting the command line arguments into a vector and printing them -First we bring the `std::env` module into scope with a `use` statement so we -can use its `args` function. Notice that the `std::env::args` function is -nested in two levels of modules. As we discussed in Chapter 7, in cases where -the desired function is nested in more than one module, we’ve chosen to bring -the parent module into scope rather than the function. By doing so, we can -easily use other functions from `std::env`. It’s also less ambiguous than -adding `use std::env::args` and then calling the function with just `args`, -because `args` might easily be mistaken for a function that’s defined in the -current module. +First, we bring the `std::env` module into scope with a `use` statement so that +we can use its `args` function. Notice that the `std::env::args` function is +nested in two levels of modules. As we discussed in Chapter +7, in cases where the desired function is +nested in more than one module, we’ve chosen to bring the parent module into +scope rather than the function. By doing so, we can easily use other functions +from `std::env`. It’s also less ambiguous than adding `use std::env::args` and +then calling the function with just `args`, because `args` might easily be +mistaken for a function that’s defined in the current module. > ### The args Function and Invalid Unicode -> +> > Note that `std::env::args` will panic if any argument contains invalid -Unicode. If your program needs to accept arguments containing invalid Unicode, -use `std::env::args_os` instead. That function returns an iterator that -produces `OsString` values instead of `String` values. We’ve chosen to use -`std::env::args` here for simplicity because `OsString` values differ per -platform and are more complex to work with than `String` values. +> Unicode. If your program needs to accept arguments containing invalid +> Unicode, use `std::env::args_os` instead. That function returns an iterator +> that produces `OsString` values instead of `String` values. We’ve chosen to +> use `std::env::args` here for simplicity because `OsString` values differ per +> platform and are more complex to work with than `String` values. On the first line of `main`, we call `env::args`, and we immediately use `collect` to turn the iterator into a vector containing all the values produced @@ -133,13 +132,20 @@ first with no arguments and then with two arguments: ``` $ cargo run ---snip-- -[src/main.rs:5] args = [ + Compiling minigrep v0.1.0 (file:///projects/minigrep) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.61s + Running `target/debug/minigrep` +[src/main.rs:5:5] args = [ "target/debug/minigrep", ] +``` + +``` $ cargo run -- needle haystack ---snip-- -[src/main.rs:5] args = [ + Compiling minigrep v0.1.0 (file:///projects/minigrep) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.57s + Running `target/debug/minigrep needle haystack` +[src/main.rs:5:5] args = [ "target/debug/minigrep", "needle", "haystack", @@ -158,10 +164,10 @@ chapter, we’ll ignore it and save only the two arguments we need. The program is currently able to access the values specified as command line arguments. Now we need to save the values of the two arguments in variables so -we can use the values throughout the rest of the program. We do that in Listing -12-2. +that we can use the values throughout the rest of the program. We do that in +Listing 12-2. -Filename: src/main.rs +src/main.rs ``` use std::env; @@ -172,13 +178,12 @@ fn main() { let query = &args[1]; let file_path = &args[2]; - println!("Searching for {}", query); - println!("In file {}", file_path); + println!("Searching for {query}"); + println!("In file {file_path}"); } ``` -Listing 12-2: Creating variables to hold the query argument and file path -argument +Listing 12-2: Creating variables to hold the query argument and file path argument As we saw when we printed the vector, the program’s name takes up the first value in the vector at `args[0]`, so we’re starting arguments at index 1. The @@ -194,7 +199,7 @@ and `sample.txt`: ``` $ cargo run -- test sample.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep test sample.txt` Searching for test In file sample.txt @@ -209,13 +214,13 @@ capabilities instead. ## Reading a File Now we’ll add functionality to read the file specified in the `file_path` -argument. First we need a sample file to test it with: we’ll use a file with a +argument. First, we need a sample file to test it with: We’ll use a file with a small amount of text over multiple lines with some repeated words. Listing 12-3 has an Emily Dickinson poem that will work well! Create a file called *poem.txt* at the root level of your project, and enter the poem “I’m Nobody! Who are you?” -Filename: poem.txt +poem.txt ``` I'm nobody! Who are you? @@ -234,34 +239,35 @@ Listing 12-3: A poem by Emily Dickinson makes a good test case. With the text in place, edit *src/main.rs* and add code to read the file, as shown in Listing 12-4. -Filename: src/main.rs +src/main.rs ``` use std::env; -1 use std::fs; +use std::fs; fn main() { - --snip-- - println!("In file {}", file_path); + // --snip-- + println!("In file {file_path}"); - 2 let contents = fs::read_to_string(file_path) + let contents = fs::read_to_string(file_path) .expect("Should have been able to read the file"); - 3 println!("With text:\n{contents}"); + println!("With text:\n{contents}"); } ``` Listing 12-4: Reading the contents of the file specified by the second argument -First we bring in a relevant part of the standard library with a `use` -statement: we need `std::fs` to handle files [1]. +First, we bring in a relevant part of the standard library with a `use` +statement: We need `std::fs` to handle files. In `main`, the new statement `fs::read_to_string` takes the `file_path`, opens -that file, and returns an `std::io::Result` of the file’s contents [2]. +that file, and returns a value of type `std::io::Result` that contains +the file’s contents. After that, we again add a temporary `println!` statement that prints the value -of `contents` after the file is read, so we can check that the program is -working so far [3]. +of `contents` after the file is read so that we can check that the program is +working so far. Let’s run this code with any string as the first command line argument (because we haven’t implemented the searching part yet) and the *poem.txt* file as the @@ -270,7 +276,7 @@ second argument: ``` $ cargo run -- the poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep the poem.txt` Searching for the In file poem.txt @@ -284,11 +290,12 @@ How dreary to be somebody! How public, like a frog To tell your name the livelong day To an admiring bog! + ``` Great! The code read and then printed the contents of the file. But the code has a few flaws. At the moment, the `main` function has multiple -responsibilities: generally, functions are clearer and easier to maintain if +responsibilities: Generally, functions are clearer and easier to maintain if each function is responsible for only one idea. The other problem is that we’re not handling errors as well as we could. The program is still small, so these flaws aren’t a big problem, but as the program grows, it will be harder to fix @@ -300,14 +307,14 @@ code. We’ll do that next. To improve our program, we’ll fix four problems that have to do with the program’s structure and how it’s handling potential errors. First, our `main` -function now performs two tasks: it parses arguments and reads files. As our +function now performs two tasks: It parses arguments and reads files. As our program grows, the number of separate tasks the `main` function handles will increase. As a function gains responsibilities, it becomes more difficult to reason about, harder to test, and harder to change without breaking one of its -parts. It’s best to separate functionality so each function is responsible for -one task. +parts. It’s best to separate functionality so that each function is responsible +for one task. -This issue also ties into the second problem: although `query` and `file_path` +This issue also ties into the second problem: Although `query` and `file_path` are configuration variables to our program, variables like `contents` are used to perform the program’s logic. The longer `main` becomes, the more variables we’ll need to bring into scope; the more variables we have in scope, the harder @@ -315,36 +322,39 @@ it will be to keep track of the purpose of each. It’s best to group the configuration variables into one structure to make their purpose clear. The third problem is that we’ve used `expect` to print an error message when -reading the file fails, but the error message just prints `Should have been -able to read the file`. Reading a file can fail in a number of ways: for +reading the file fails, but the error message just prints `Should have been able to read the file`. Reading a file can fail in a number of ways: For example, the file could be missing, or we might not have permission to open it. Right now, regardless of the situation, we’d print the same error message for everything, which wouldn’t give the user any information! -Fourth, we use `expect` repeatedly to handle different errors, and if the user -runs our program without specifying enough arguments, they’ll get an `index out -of bounds` error from Rust that doesn’t clearly explain the problem. It would -be best if all the error-handling code were in one place so future maintainers -had only one place to consult the code if the error-handling logic needed to -change. Having all the error-handling code in one place will also ensure that -we’re printing messages that will be meaningful to our end users. +Fourth, we use `expect` to handle an error, and if the user runs our program +without specifying enough arguments, they’ll get an `index out of bounds` error +from Rust that doesn’t clearly explain the problem. It would be best if all the +error-handling code were in one place so that future maintainers had only one +place to consult the code if the error-handling logic needed to change. Having +all the error-handling code in one place will also ensure that we’re printing +messages that will be meaningful to our end users. Let’s address these four problems by refactoring our project. -### Separation of Concerns for Binary Projects + + + + +### Separating Concerns in Binary Projects The organizational problem of allocating responsibility for multiple tasks to -the `main` function is common to many binary projects. As a result, the Rust -community has developed guidelines for splitting the separate concerns of a -binary program when `main` starts getting large. This process has the following -steps: +the `main` function is common to many binary projects. As a result, many Rust +programmers find it useful to split up the separate concerns of a binary +program when the `main` function starts getting large. This process has the +following steps: * Split your program into a *main.rs* file and a *lib.rs* file and move your -program’s logic to *lib.rs*. + program’s logic to *lib.rs*. * As long as your command line parsing logic is small, it can remain in -*main.rs*. + the `main` function. * When the command line parsing logic starts getting complicated, extract it -from *main.rs* and move it to *lib.rs*. + from the `main` function into other functions or types. The responsibilities that remain in the `main` function after this process should be limited to the following: @@ -357,18 +367,17 @@ should be limited to the following: This pattern is about separating concerns: *main.rs* handles running the program and *lib.rs* handles all the logic of the task at hand. Because you can’t test the `main` function directly, this structure lets you test all of -your program’s logic by moving it into functions in *lib.rs*. The code that -remains in *main.rs* will be small enough to verify its correctness by reading -it. Let’s rework our program by following this process. +your program’s logic by moving it out of the `main` function. The code that +remains in the `main` function will be small enough to verify its correctness +by reading it. Let’s rework our program by following this process. #### Extracting the Argument Parser We’ll extract the functionality for parsing arguments into a function that -`main` will call to prepare for moving the command line parsing logic to -src/lib.rs*. Listing 12-5 shows the new start of `main` that calls a new -function `parse_config`, which we’ll define in *src/main.rs* for the moment. +`main` will call. Listing 12-5 shows the new start of the `main` function that +calls a new function `parse_config`, which we’ll define in *src/main.rs*. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -376,7 +385,7 @@ fn main() { let (query, file_path) = parse_config(&args); - --snip-- + // --snip-- } fn parse_config(args: &[String]) -> (&str, &str) { @@ -422,42 +431,41 @@ other and what their purpose is. Listing 12-6 shows the improvements to the `parse_config` function. -Filename: src/main.rs +src/main.rs ``` fn main() { let args: Vec = env::args().collect(); - 1 let config = parse_config(&args); + let config = parse_config(&args); - println!("Searching for {}", 2 config.query); - println!("In file {}", 3 config.file_path); + println!("Searching for {}", config.query); + println!("In file {}", config.file_path); - let contents = fs::read_to_string(4 config.file_path) + let contents = fs::read_to_string(config.file_path) .expect("Should have been able to read the file"); - --snip-- + // --snip-- } -5 struct Config { +struct Config { query: String, file_path: String, } -6 fn parse_config(args: &[String]) -> Config { - 7 let query = args[1].clone(); - 8 let file_path = args[2].clone(); +fn parse_config(args: &[String]) -> Config { + let query = args[1].clone(); + let file_path = args[2].clone(); Config { query, file_path } } ``` -Listing 12-6: Refactoring `parse_config` to return an instance of a `Config` -struct +Listing 12-6: Refactoring `parse_config` to return an instance of a `Config` struct We’ve added a struct named `Config` defined to have fields named `query` and -`file_path` [5]. The signature of `parse_config` now indicates that it returns -a `Config` value [6]. In the body of `parse_config`, where we used to return +`file_path`. The signature of `parse_config` now indicates that it returns a +`Config` value. In the body of `parse_config`, where we used to return string slices that reference `String` values in `args`, we now define `Config` to contain owned `String` values. The `args` variable in `main` is the owner of the argument values and is only letting the `parse_config` function borrow @@ -465,30 +473,30 @@ them, which means we’d violate Rust’s borrowing rules if `Config` tried to t ownership of the values in `args`. There are a number of ways we could manage the `String` data; the easiest, -though somewhat inefficient, route is to call the `clone` method on the values -[7] [8]. This will make a full copy of the data for the `Config` instance to -own, which takes more time and memory than storing a reference to the string -data. However, cloning the data also makes our code very straightforward -because we don’t have to manage the lifetimes of the references; in this -circumstance, giving up a little performance to gain simplicity is a worthwhile -trade-off. +though somewhat inefficient, route is to call the `clone` method on the values. +This will make a full copy of the data for the `Config` instance to own, which +takes more time and memory than storing a reference to the string data. +However, cloning the data also makes our code very straightforward because we +don’t have to manage the lifetimes of the references; in this circumstance, +giving up a little performance to gain simplicity is a worthwhile trade-off. > ### The Trade-Offs of Using clone -> +> > There’s a tendency among many Rustaceans to avoid using `clone` to fix -ownership problems because of its runtime cost. In Chapter 13, you’ll learn how -to use more efficient methods in this type of situation. But for now, it’s okay -to copy a few strings to continue making progress because you’ll make these -copies only once and your file path and query string are very small. It’s -better to have a working program that’s a bit inefficient than to try to -hyperoptimize code on your first pass. As you become more experienced with -Rust, it’ll be easier to start with the most efficient solution, but for now, -it’s perfectly acceptable to call `clone`. - -We’ve updated `main` so it places the instance of `Config` returned by -`parse_config` into a variable named `config` [1], and we updated the code that -previously used the separate `query` and `file_path` variables so it now uses -the fields on the `Config` struct instead [2] [3] [4]. +> ownership problems because of its runtime cost. In +> Chapter 13, you’ll learn how to use more efficient +> methods in this type of situation. But for now, it’s okay to copy a few +> strings to continue making progress because you’ll make these copies only +> once and your file path and query string are very small. It’s better to have +> a working program that’s a bit inefficient than to try to hyperoptimize code +> on your first pass. As you become more experienced with Rust, it’ll be +> easier to start with the most efficient solution, but for now, it’s +> perfectly acceptable to call `clone`. + +We’ve updated `main` so that it places the instance of `Config` returned by +`parse_config` into a variable named `config`, and we updated the code that +previously used the separate `query` and `file_path` variables so that it now +uses the fields on the `Config` struct instead. Now our code more clearly conveys that `query` and `file_path` are related and that their purpose is to configure how the program will work. Any code that @@ -501,10 +509,10 @@ So far, we’ve extracted the logic responsible for parsing the command line arguments from `main` and placed it in the `parse_config` function. Doing so helped us see that the `query` and `file_path` values were related, and that relationship should be conveyed in our code. We then added a `Config` struct to -name the related purpose of `query` and `file_path` and to be able to return -the values’ names as struct field names from the `parse_config` function. +name the related purpose of `query` and `file_path` and to be able to return the +values’ names as struct field names from the `parse_config` function. -So now that the purpose of the `parse_config` function is to create a `Config` +So, now that the purpose of the `parse_config` function is to create a `Config` instance, we can change `parse_config` from a plain function to a function named `new` that is associated with the `Config` struct. Making this change will make the code more idiomatic. We can create instances of types in the @@ -513,21 +521,21 @@ changing `parse_config` into a `new` function associated with `Config`, we’ll be able to create instances of `Config` by calling `Config::new`. Listing 12-7 shows the changes we need to make. -Filename: src/main.rs +src/main.rs ``` fn main() { let args: Vec = env::args().collect(); - 1 let config = Config::new(&args); + let config = Config::new(&args); - --snip-- + // --snip-- } ---snip-- +// --snip-- -2 impl Config { - 3 fn new(args: &[String]) -> Config { +impl Config { + fn new(args: &[String]) -> Config { let query = args[1].clone(); let file_path = args[2].clone(); @@ -539,9 +547,9 @@ fn main() { Listing 12-7: Changing `parse_config` into `Config::new` We’ve updated `main` where we were calling `parse_config` to instead call -`Config::new` [1]. We’ve changed the name of `parse_config` to `new` [3] and -moved it within an `impl` block [2], which associates the `new` function with -`Config`. Try compiling this code again to make sure it works. +`Config::new`. We’ve changed the name of `parse_config` to `new` and moved it +within an `impl` block, which associates the `new` function with `Config`. Try +compiling this code again to make sure it works. ### Fixing the Error Handling @@ -553,12 +561,12 @@ without any arguments; it will look like this: ``` $ cargo run Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep` -thread 'main' panicked at 'index out of bounds: the len is 1 but -the index is 1', src/main.rs:27:21 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace + +thread 'main' panicked at src/main.rs:27:21: +index out of bounds: the len is 1 but the index is 1 +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` The line `index out of bounds: the len is 1 but the index is 1` is an error @@ -571,26 +579,26 @@ In Listing 12-8, we add a check in the `new` function that will verify that the slice is long enough before accessing index 1 and index 2. If the slice isn’t long enough, the program panics and displays a better error message. -Filename: src/main.rs +src/main.rs ``` ---snip-- -fn new(args: &[String]) -> Config { - if args.len() < 3 { - panic!("not enough arguments"); - } - --snip-- + // --snip-- + fn new(args: &[String]) -> Config { + if args.len() < 3 { + panic!("not enough arguments"); + } + // --snip-- ``` Listing 12-8: Adding a check for the number of arguments -This code is similar to the `Guess::new` function we wrote in Listing 9-13, -where we called `panic!` when the `value` argument was out of the range of -valid values. Instead of checking for a range of values here, we’re checking -that the length of `args` is at least `3` and the rest of the function can -operate under the assumption that this condition has been met. If `args` has -fewer than three items, this condition will be `true`, and we call the `panic!` -macro to end the program immediately. +This code is similar to the `Guess::new` function we wrote in Listing +9-13, where we called `panic!` when the +`value` argument was out of the range of valid values. Instead of checking for +a range of values here, we’re checking that the length of `args` is at least +`3` and the rest of the function can operate under the assumption that this +condition has been met. If `args` has fewer than three items, this condition +will be `true`, and we call the `panic!` macro to end the program immediately. With these extra few lines of code in `new`, let’s run the program without any arguments again to see what the error looks like now: @@ -598,21 +606,25 @@ arguments again to see what the error looks like now: ``` $ cargo run Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep` -thread 'main' panicked at 'not enough arguments', -src/main.rs:26:13 -note: run with `RUST_BACKTRACE=1` environment variable to display -a backtrace + +thread 'main' panicked at src/main.rs:26:13: +not enough arguments +note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` -This output is better: we now have a reasonable error message. However, we also +This output is better: We now have a reasonable error message. However, we also have extraneous information we don’t want to give to our users. Perhaps the -technique we used in Listing 9-13 isn’t the best one to use here: a call to -`panic!` is more appropriate for a programming problem than a usage problem, as -discussed in Chapter 9. Instead, we’ll use the other technique you learned -about in Chapter 9—returning a `Result` that indicates either success or an -error. +technique we used in Listing 9-13 isn’t the best one to use here: A call to +`panic!` is more appropriate for a programming problem than a usage problem, +as discussed in Chapter 9. Instead, +we’ll use the other technique you learned about in Chapter 9—returning a +`Result` that indicates either success or an error. + + + + #### Returning a Result Instead of Calling panic! @@ -621,16 +633,15 @@ the successful case and will describe the problem in the error case. We’re als going to change the function name from `new` to `build` because many programmers expect `new` functions to never fail. When `Config::build` is communicating to `main`, we can use the `Result` type to signal there was a -problem. Then we can change `main` to convert an `Err` variant into a more -practical error for our users without the surrounding text about `thread -'main'` and `RUST_BACKTRACE` that a call to `panic!` causes. +problem. Then, we can change `main` to convert an `Err` variant into a more +practical error for our users without the surrounding text about `thread 'main'` and `RUST_BACKTRACE` that a call to `panic!` causes. Listing 12-9 shows the changes we need to make to the return value of the function we’re now calling `Config::build` and the body of the function needed to return a `Result`. Note that this won’t compile until we update `main` as well, which we’ll do in the next listing. -Filename: src/main.rs +src/main.rs ``` impl Config { @@ -650,10 +661,10 @@ impl Config { Listing 12-9: Returning a `Result` from `Config::build` Our `build` function returns a `Result` with a `Config` instance in the success -case and an `&'static str` in the error case. Our error values will always be +case and a string literal in the error case. Our error values will always be string literals that have the `'static` lifetime. -We’ve made two changes in the body of the function: instead of calling `panic!` +We’ve made two changes in the body of the function: Instead of calling `panic!` when the user doesn’t pass enough arguments, we now return an `Err` value, and we’ve wrapped the `Config` return value in an `Ok`. These changes make the function conform to its new type signature. @@ -662,6 +673,10 @@ Returning an `Err` value from `Config::build` allows the `main` function to handle the `Result` value returned from the `build` function and exit the process more cleanly in the error case. + + + + #### Calling Config::build and Handling Errors To handle the error case and print a user-friendly message, we need to update @@ -671,41 +686,41 @@ tool with a nonzero error code away from `panic!` and instead implement it by hand. A nonzero exit status is a convention to signal to the process that called our program that the program exited with an error state. -Filename: src/main.rs +src/main.rs ``` -1 use std::process; +use std::process; fn main() { let args: Vec = env::args().collect(); - 2 let config = Config::build(&args).3 unwrap_or_else(|4 err| { - 5 println!("Problem parsing arguments: {err}"); - 6 process::exit(1); + let config = Config::build(&args).unwrap_or_else(|err| { + println!("Problem parsing arguments: {err}"); + process::exit(1); }); - --snip-- + // --snip-- ``` Listing 12-10: Exiting with an error code if building a `Config` fails In this listing, we’ve used a method we haven’t covered in detail yet: -`unwrap_or_else`, which is defined on `Result` by the standard library -[2]. Using `unwrap_or_else` allows us to define some custom, non-`panic!` error +`unwrap_or_else`, which is defined on `Result` by the standard library. +Using `unwrap_or_else` allows us to define some custom, non-`panic!` error handling. If the `Result` is an `Ok` value, this method’s behavior is similar -to `unwrap`: it returns the inner value that `Ok` is wrapping. However, if the -value is an `Err` value, this method calls the code in the *closure*, which is -an anonymous function we define and pass as an argument to `unwrap_or_else` -[3]. We’ll cover closures in more detail in Chapter 13. For now, you just need -to know that `unwrap_or_else` will pass the inner value of the `Err`, which in -this case is the static string `"not enough arguments"` that we added in -Listing 12-9, to our closure in the argument `err` that appears between the -vertical pipes [4]. The code in the closure can then use the `err` value when -it runs. +to `unwrap`: It returns the inner value that `Ok` is wrapping. However, if the +value is an `Err` value, this method calls the code in the closure, which is +an anonymous function we define and pass as an argument to `unwrap_or_else`. +We’ll cover closures in more detail in Chapter 13. For +now, you just need to know that `unwrap_or_else` will pass the inner value of +the `Err`, which in this case is the static string `"not enough arguments"` +that we added in Listing 12-9, to our closure in the argument `err` that +appears between the vertical pipes. The code in the closure can then use the +`err` value when it runs. We’ve added a new `use` line to bring `process` from the standard library into -scope [1]. The code in the closure that will be run in the error case is only -two lines: we print the `err` value [5] and then call `process::exit` [6]. The +scope. The code in the closure that will be run in the error case is only two +lines: We print the `err` value and then call `process::exit`. The `process::exit` function will stop the program immediately and return the number that was passed as the exit status code. This is similar to the `panic!`-based handling we used in Listing 12-8, but we no longer get all the @@ -714,32 +729,35 @@ extra output. Let’s try it: ``` $ cargo run Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.48s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s Running `target/debug/minigrep` Problem parsing arguments: not enough arguments ``` Great! This output is much friendlier for our users. + + + + ### Extracting Logic from main Now that we’ve finished refactoring the configuration parsing, let’s turn to -the program’s logic. As we stated in “Separation of Concerns for Binary -Projects” on page XX, we’ll extract a function named `run` that will hold all -the logic currently in the `main` function that isn’t involved with setting up -configuration or handling errors. When we’re done, `main` will be concise and -easy to verify by inspection, and we’ll be able to write tests for all the -other logic. +the program’s logic. As we stated in “Separating Concerns in Binary +Projects”, we’ll +extract a function named `run` that will hold all the logic currently in the +`main` function that isn’t involved with setting up configuration or handling +errors. When we’re done, the `main` function will be concise and easy to verify +by inspection, and we’ll be able to write tests for all the other logic. -Listing 12-11 shows the extracted `run` function. For now, we’re just making -the small, incremental improvement of extracting the function. We’re still -defining the function in *src/main.rs*. +Listing 12-11 shows the small, incremental improvement of extracting a `run` +function. -Filename: src/main.rs +src/main.rs ``` fn main() { - --snip-- + // --snip-- println!("Searching for {}", config.query); println!("In file {}", config.file_path); @@ -754,17 +772,20 @@ fn run(config: Config) { println!("With text:\n{contents}"); } ---snip-- +// --snip-- ``` -Listing 12-11: Extracting a `run` function containing the rest of the program -logic +Listing 12-11: Extracting a `run` function containing the rest of the program logic The `run` function now contains all the remaining logic from `main`, starting from reading the file. The `run` function takes the `Config` instance as an argument. -#### Returning Errors from the run Function + + + + +#### Returning Errors from run With the remaining program logic separated into the `run` function, we can improve the error handling, as we did with `Config::build` in Listing 12-9. @@ -774,60 +795,84 @@ us further consolidate the logic around handling errors into `main` in a user-friendly way. Listing 12-12 shows the changes we need to make to the signature and body of `run`. -Filename: src/main.rs +src/main.rs ``` -1 use std::error::Error; +use std::error::Error; ---snip-- +// --snip-- -2 fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)3 ?; +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; println!("With text:\n{contents}"); - 4 Ok(()) + Ok(()) } ``` Listing 12-12: Changing the `run` function to return `Result` We’ve made three significant changes here. First, we changed the return type of -the `run` function to `Result<(), Box>` [2]. This function -previously returned the unit type, `()`, and we keep that as the value returned -in the `Ok` case. - -For the error type, we used the *trait object* `Box` (and we’ve -brought `std::error::Error` into scope with a `use` statement at the top [1]). -We’ll cover trait objects in Chapter 17. For now, just know that `Box` means the function will return a type that implements the `Error` -trait, but we don’t have to specify what particular type the return value will -be. This gives us flexibility to return error values that may be of different -types in different error cases. The `dyn` keyword is short for *dynamic*. - -Second, we’ve removed the call to `expect` in favor of the `?` operator [3], as -we talked about in Chapter 9. Rather than `panic!` on an error, `?` will return -the error value from the current function for the caller to handle. - -Third, the `run` function now returns an `Ok` value in the success case [4]. +the `run` function to `Result<(), Box>`. This function previously +returned the unit type, `()`, and we keep that as the value returned in the +`Ok` case. + +For the error type, we used the trait object `Box` (and we brought +`std::error::Error` into scope with a `use` statement at the top). We’ll cover +trait objects in Chapter 18. For now, just know that +`Box` means the function will return a type that implements the +`Error` trait, but we don’t have to specify what particular type the return +value will be. This gives us flexibility to return error values that may be of +different types in different error cases. The `dyn` keyword is short for +*dynamic*. + +Second, we’ve removed the call to `expect` in favor of the `?` operator, as we +talked about in Chapter 9. Rather than +`panic!` on an error, `?` will return the error value from the current function +for the caller to handle. + +Third, the `run` function now returns an `Ok` value in the success case. We’ve declared the `run` function’s success type as `()` in the signature, which means we need to wrap the unit type value in the `Ok` value. This -`Ok(())` syntax might look a bit strange at first, but using `()` like this is +`Ok(())` syntax might look a bit strange at first. But using `()` like this is the idiomatic way to indicate that we’re calling `run` for its side effects only; it doesn’t return a value we need. When you run this code, it will compile but will display a warning: ``` +$ cargo run -- the poem.txt + Compiling minigrep v0.1.0 (file:///projects/minigrep) warning: unused `Result` that must be used --> src/main.rs:19:5 | 19 | run(config); - | ^^^^^^^^^^^^ + | ^^^^^^^^^^^ | + = note: this `Result` may be an `Err` variant, which should be handled = note: `#[warn(unused_must_use)]` on by default - = note: this `Result` may be an `Err` variant, which should be -handled +help: use `let _ = ...` to ignore the resulting value + | +19 | let _ = run(config); + | +++++++ + +warning: `minigrep` (bin "minigrep") generated 1 warning + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.71s + Running `target/debug/minigrep the poem.txt` +Searching for the +In file poem.txt +With text: +I'm nobody! Who are you? +Are you nobody, too? +Then there's a pair of us - don't tell! +They'd banish us, you know. + +How dreary to be somebody! +How public, like a frog +To tell your name the livelong day +To an admiring bog! + ``` Rust tells us that our code ignored the `Result` value and the `Result` value @@ -844,7 +889,7 @@ Filename: src/main.rs ``` fn main() { - --snip-- + // --snip-- println!("Searching for {}", config.query); println!("In file {}", config.file_path); @@ -864,7 +909,7 @@ the success case, we only care about detecting an error, so we don’t need `unwrap_or_else` to return the unwrapped value, which would only be `()`. The bodies of the `if let` and the `unwrap_or_else` functions are the same in -both cases: we print the error and exit. +both cases: We print the error and exit. ### Splitting Code into a Library Crate @@ -872,103 +917,104 @@ Our `minigrep` project is looking good so far! Now we’ll split the *src/main.rs* file and put some code into the *src/lib.rs* file. That way, we can test the code and have a *src/main.rs* file with fewer responsibilities. -Let’s move all the code that isn’t in the `main` function from *src/main.rs* to -*src/lib.rs*: +Let’s define the code responsible for searching text in *src/lib.rs* rather +than in *src/main.rs*, which will let us (or anyone else using our +`minigrep` library) call the searching function from more contexts than our +`minigrep` binary. -* The `run` function definition -* The relevant `use` statements -* The definition of `Config` -* The `Config::build` function definition +First, let’s define the `search` function signature in *src/lib.rs* as shown in +Listing 12-13, with a body that calls the `unimplemented!` macro. We’ll explain +the signature in more detail when we fill in the implementation. -The contents of *src/lib.rs* should have the signatures shown in Listing 12-13 -(we’ve omitted the bodies of the functions for brevity). Note that this won’t -compile until we modify *src/main.rs* in Listing 12-14. - -Filename: src/lib.rs +src/lib.rs ``` -use std::error::Error; -use std::fs; - -pub struct Config { - pub query: String, - pub file_path: String, -} - -impl Config { - pub fn build( - args: &[String], - ) -> Result { - --snip-- - } -} - -pub fn run(config: Config) -> Result<(), Box> { - --snip-- +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { + unimplemented!(); } ``` -Listing 12-13: Moving `Config` and `run` into *src/lib.rs* +Listing 12-13: Defining the `search` function in *src/lib.rs* -We’ve made liberal use of the `pub` keyword: on `Config`, on its fields and its -`build` method, and on the `run` function. We now have a library crate that has -a public API we can test! +We’ve used the `pub` keyword on the function definition to designate `search` +as part of our library crate’s public API. We now have a library crate that we +can use from our binary crate and that we can test! -Now we need to bring the code we moved to *src/lib.rs* into the scope of the -binary crate in *src/main.rs*, as shown in Listing 12-14. +Now we need to bring the code defined in *src/lib.rs* into the scope of the +binary crate in *src/main.rs* and call it, as shown in Listing 12-14. -Filename: src/main.rs +src/main.rs ``` -use std::env; -use std::process; - -use minigrep::Config; +// --snip-- +use minigrep::search; fn main() { - --snip-- - if let Err(e) = minigrep::run(config) { - --snip-- + // --snip-- +} + +// --snip-- + +fn run(config: Config) -> Result<(), Box> { + let contents = fs::read_to_string(config.file_path)?; + + for line in search(&config.query, &contents) { + println!("{line}"); } + + Ok(()) } ``` -Listing 12-14: Using the `minigrep` library crate in *src/main.rs* +Listing 12-14: Using the `minigrep` library crate’s `search` function in *src/main.rs* -We add a `use minigrep::Config` line to bring the `Config` type from the -library crate into the binary crate’s scope, and we prefix the `run` function -with our crate name. Now all the functionality should be connected and should -work. Run the program with `cargo run` and make sure everything works correctly. +We add a `use minigrep::search` line to bring the `search` function from +the library crate into the binary crate’s scope. Then, in the `run` function, +rather than printing out the contents of the file, we call the `search` +function and pass the `config.query` value and `contents` as arguments. Then, +`run` will use a `for` loop to print each line returned from `search` that +matched the query. This is also a good time to remove the `println!` calls in +the `main` function that displayed the query and the file path so that our +program only prints the search results (if no errors occur). + +Note that the search function will be collecting all the results into a vector +it returns before any printing happens. This implementation could be slow to +display results when searching large files, because results aren’t printed as +they’re found; we’ll discuss a possible way to fix this using iterators in +Chapter 13. Whew! That was a lot of work, but we’ve set ourselves up for success in the future. Now it’s much easier to handle errors, and we’ve made the code more modular. Almost all of our work will be done in *src/lib.rs* from here on out. Let’s take advantage of this newfound modularity by doing something that would -have been difficult with the old code but is easy with the new code: we’ll +have been difficult with the old code but is easy with the new code: We’ll write some tests! -## Developing the Library’s Functionality with Test-Driven Development + + + -Now that we’ve extracted the logic into *src/lib.rs* and left the argument -collecting and error handling in *src/main.rs*, it’s much easier to write tests -for the core functionality of our code. We can call functions directly with -various arguments and check return values without having to call our binary -from the command line. +## Adding Functionality with Test-Driven Development + +Now that we have the search logic in *src/lib.rs* separate from the `main` +function, it’s much easier to write tests for the core functionality of our +code. We can call functions directly with various arguments and check return +values without having to call our binary from the command line. In this section, we’ll add the searching logic to the `minigrep` program using the test-driven development (TDD) process with the following steps: 1. Write a test that fails and run it to make sure it fails for the reason you -expect. + expect. 1. Write or modify just enough code to make the new test pass. 1. Refactor the code you just added or changed and make sure the tests continue -to pass. + to pass. 1. Repeat from step 1! Though it’s just one of many ways to write software, TDD can help drive code design. Writing the test before you write the code that makes the test pass -helps to maintain high test coverage throughout the process. +helps maintain high test coverage throughout the process. We’ll test-drive the implementation of the functionality that will actually do the searching for the query string in the file contents and produce a list of @@ -977,17 +1023,17 @@ lines that match the query. We’ll add this functionality in a function called ### Writing a Failing Test -Because we don’t need them anymore, let’s remove the `println!` statements from -*src/lib.rs* and *src/main.rs* that we used to check the program’s behavior. -Then, in *src/lib.rs*, we’ll add a `tests` module with a test function, as we -did in Chapter 11. The test function specifies the behavior we want the -`search` function to have: it will take a query and the text to search, and it -will return only the lines from the text that contain the query. Listing 12-15 -shows this test, which won’t compile yet. +In *src/lib.rs*, we’ll add a `tests` module with a test function, as we did in +Chapter 11. The test function specifies the +behavior we want the `search` function to have: It will take a query and the +text to search, and it will return only the lines from the text that contain +the query. Listing 12-15 shows this test. -Filename: src/lib.rs +src/lib.rs ``` +// --snip-- + #[cfg(test)] mod tests { use super::*; @@ -1000,15 +1046,12 @@ Rust: safe, fast, productive. Pick three."; - assert_eq!( - vec!["safe, fast, productive."], - search(query, contents) - ); + assert_eq!(vec!["safe, fast, productive."], search(query, contents)); } } ``` -Listing 12-15: Creating a failing test for the `search` function we wish we had +Listing 12-15: Creating a failing test for the `search` function for the functionality we wish we had This test searches for the string `"duct"`. The text we’re searching is three lines, only one of which contains `"duct"` (note that the backslash after the @@ -1016,34 +1059,30 @@ opening double quote tells Rust not to put a newline character at the beginning of the contents of this string literal). We assert that the value returned from the `search` function contains only the line we expect. -We aren’t yet able to run this test and watch it fail because the test doesn’t -even compile: the `search` function doesn’t exist yet! In accordance with TDD -principles, we’ll add just enough code to get the test to compile and run by -adding a definition of the `search` function that always returns an empty -vector, as shown in Listing 12-16. Then the test should compile and fail -because an empty vector doesn’t match a vector containing the line `"safe, -fast, productive."`. +If we run this test, it will currently fail because the `unimplemented!` macro +panics with the message “not implemented”. In accordance with TDD principles, +we’ll take a small step of adding just enough code to get the test to not panic +when calling the function by defining the `search` function to always return an +empty vector, as shown in Listing 12-16. Then, the test should compile and fail +because an empty vector doesn’t match a vector containing the line `"safe, fast, productive."`. -Filename: src/lib.rs +src/lib.rs ``` -pub fn search<'a>( - query: &str, - contents: &'a str, -) -> Vec<&'a str> { +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { vec![] } ``` -Listing 12-16: Defining just enough of the `search` function so our test will -compile +Listing 12-16: Defining just enough of the `search` function so that calling it won’t panic -Notice that we need to define an explicit lifetime `'a` in the signature of -`search` and use that lifetime with the `contents` argument and the return -value. Recall in Chapter 10 that the lifetime parameters specify which argument -lifetime is connected to the lifetime of the return value. In this case, we -indicate that the returned vector should contain string slices that reference -slices of the argument `contents` (rather than the argument `query`). +Now let’s discuss why we need to define an explicit lifetime `'a` in the +signature of `search` and use that lifetime with the `contents` argument and +the return value. Recall in Chapter 10 that +the lifetime parameters specify which argument lifetime is connected to the +lifetime of the return value. In this case, we indicate that the returned +vector should contain string slices that reference slices of the argument +`contents` (rather than the argument `query`). In other words, we tell Rust that the data returned by the `search` function will live as long as the data passed into the `search` function in the @@ -1056,68 +1095,37 @@ If we forget the lifetime annotations and try to compile this function, we’ll get this error: ``` +$ cargo build + Compiling minigrep v0.1.0 (file:///projects/minigrep) error[E0106]: missing lifetime specifier - --> src/lib.rs:31:10 - | -29 | query: &str, - | ---- -30 | contents: &str, - | ---- -31 | ) -> Vec<&str> { - | ^ expected named lifetime parameter - | - = help: this function's return type contains a borrowed value, but the -signature does not say whether it is borrowed from `query` or `contents` + --> src/lib.rs:1:51 + | +1 | pub fn search(query: &str, contents: &str) -> Vec<&str> { + | ---- ---- ^ expected named lifetime parameter + | + = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `query` or `contents` help: consider introducing a named lifetime parameter - | -28 ~ pub fn search<'a>( -29 ~ query: &'a str, -30 ~ contents: &'a str, -31 ~ ) -> Vec<&'a str> { - | + | +1 | pub fn search<'a>(query: &'a str, contents: &'a str) -> Vec<&'a str> { + | ++++ ++ ++ ++ + +For more information about this error, try `rustc --explain E0106`. +error: could not compile `minigrep` (lib) due to 1 previous error ``` -Rust can’t possibly know which of the two arguments we need, so we need to tell -it explicitly. Because `contents` is the argument that contains all of our text +Rust can’t know which of the two parameters we need for the output, so we need +to tell it explicitly. Note that the help text suggests specifying the same +lifetime parameter for all the parameters and the output type, which is +incorrect! Because `contents` is the parameter that contains all of our text and we want to return the parts of that text that match, we know `contents` is -the argument that should be connected to the return value using the lifetime -syntax. +the only parameter that should be connected to the return value using the +lifetime syntax. Other programming languages don’t require you to connect arguments to return values in the signature, but this practice will get easier over time. You might -want to compare this example with the examples in “Validating References with -Lifetimes” on page XX. - -Now let’s run the test: - -``` -$ cargo test - Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished test [unoptimized + debuginfo] target(s) in 0.97s - Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) - -running 1 test -test tests::one_result ... FAILED - -failures: - ----- tests::one_result stdout ---- -thread 'tests::one_result' panicked at 'assertion failed: `(left == right)` - left: `["safe, fast, productive."]`, - right: `[]`', src/lib.rs:47:9 -note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace - - -failures: - tests::one_result - -test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; -finished in 0.00s - -error: test failed, to rerun pass '--lib' -``` - -Great, the test fails, exactly as we expected. Let’s get the test to pass! +want to compare this example with the examples in the “Validating References +with Lifetimes” section +in Chapter 10. ### Writing Code to Pass the Test @@ -1138,13 +1146,10 @@ Rust has a helpful method to handle line-by-line iteration of strings, conveniently named `lines`, that works as shown in Listing 12-17. Note that this won’t compile yet. -Filename: src/lib.rs +src/lib.rs ``` -pub fn search<'a>( - query: &str, - contents: &'a str, -) -> Vec<&'a str> { +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { for line in contents.lines() { // do something with line } @@ -1154,9 +1159,9 @@ pub fn search<'a>( Listing 12-17: Iterating through each line in `contents` The `lines` method returns an iterator. We’ll talk about iterators in depth in -Chapter 13, but recall that you saw this way of using an iterator in Listing -3-5, where we used a `for` loop with an iterator to run some code on each item -in a collection. +Chapter 13. But recall that you saw this way +of using an iterator in Listing 3-5, where we used a +`for` loop with an iterator to run some code on each item in a collection. #### Searching Each Line for the Query @@ -1165,13 +1170,10 @@ Fortunately, strings have a helpful method named `contains` that does this for us! Add a call to the `contains` method in the `search` function, as shown in Listing 12-18. Note that this still won’t compile yet. -Filename: src/lib.rs +src/lib.rs ``` -pub fn search<'a>( - query: &str, - contents: &'a str, -) -> Vec<&'a str> { +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { for line in contents.lines() { if line.contains(query) { // do something with line @@ -1180,8 +1182,7 @@ pub fn search<'a>( } ``` -Listing 12-18: Adding functionality to see whether the line contains the string -in `query` +Listing 12-18: Adding functionality to see whether the line contains the string in `query` At the moment, we’re building up functionality. To get the code to compile, we need to return a value from the body as we indicated we would in the function @@ -1194,13 +1195,10 @@ to return. For that, we can make a mutable vector before the `for` loop and call the `push` method to store a `line` in the vector. After the `for` loop, we return the vector, as shown in Listing 12-19. -Filename: src/lib.rs +src/lib.rs ``` -pub fn search<'a>( - query: &str, - contents: &'a str, -) -> Vec<&'a str> { +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); for line in contents.lines() { @@ -1213,52 +1211,44 @@ pub fn search<'a>( } ``` -Listing 12-19: Storing the lines that match so we can return them +Listing 12-19: Storing the lines that match so that we can return them Now the `search` function should return only the lines that contain `query`, and our test should pass. Let’s run the test: ``` $ cargo test ---snip-- + Compiling minigrep v0.1.0 (file:///projects/minigrep) + Finished `test` profile [unoptimized + debuginfo] target(s) in 1.22s + Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) + running 1 test test tests::one_result ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s -``` +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s -Our test passed, so we know it works! - -At this point, we could consider opportunities for refactoring the -implementation of the search function while keeping the tests passing to -maintain the same functionality. The code in the search function isn’t too bad, -but it doesn’t take advantage of some useful features of iterators. We’ll -return to this example in Chapter 13, where we’ll explore iterators in detail, -and look at how to improve it. + Running unittests src/main.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) -#### Using the search Function in the run Function +running 0 tests -Now that the `search` function is working and tested, we need to call `search` -from our `run` function. We need to pass the `config.query` value and the -`contents` that `run` reads from the file to the `search` function. Then `run` -will print each line returned from `search`: +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s -Filename: src/lib.rs + Doc-tests minigrep -``` -pub fn run(config: Config) -> Result<(), Box> { - let contents = fs::read_to_string(config.file_path)?; +running 0 tests - for line in search(&config.query, &contents) { - println!("{line}"); - } +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s - Ok(()) -} ``` -We’re still using a `for` loop to return each line from `search` and print it. +Our test passed, so we know it works! + +At this point, we could consider opportunities for refactoring the +implementation of the search function while keeping the tests passing to +maintain the same functionality. The code in the search function isn’t too bad, +but it doesn’t take advantage of some useful features of iterators. We’ll +return to this example in Chapter 13, where +we’ll explore iterators in detail, and look at how to improve it. Now the entire program should work! Let’s try it out, first with a word that should return exactly one line from the Emily Dickinson poem: *frog*. @@ -1266,7 +1256,7 @@ should return exactly one line from the Emily Dickinson poem: *frog*. ``` $ cargo run -- frog poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.38s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.38s Running `target/debug/minigrep frog poem.txt` How public, like a frog ``` @@ -1275,7 +1265,8 @@ Cool! Now let’s try a word that will match multiple lines, like *body*: ``` $ cargo run -- body poem.txt - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Compiling minigrep v0.1.0 (file:///projects/minigrep) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep body poem.txt` I'm nobody! Who are you? Are you nobody, too? @@ -1287,7 +1278,8 @@ word that isn’t anywhere in the poem, such as *monomorphization*: ``` $ cargo run -- monomorphization poem.txt - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Compiling minigrep v0.1.0 (file:///projects/minigrep) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep monomorphization poem.txt` ``` @@ -1301,23 +1293,27 @@ useful when you’re writing command line programs. ## Working with Environment Variables -We’ll improve `minigrep` by adding an extra feature: an option for +We’ll improve the `minigrep` binary by adding an extra feature: an option for case-insensitive searching that the user can turn on via an environment variable. We could make this feature a command line option and require that users enter it each time they want it to apply, but by instead making it an environment variable, we allow our users to set the environment variable once and have all their searches be case insensitive in that terminal session. -### Writing a Failing Test for the Case-Insensitive search Function + -We first add a new `search_case_insensitive` function that will be called when -the environment variable has a value. We’ll continue to follow the TDD process, -so the first step is again to write a failing test. We’ll add a new test for -the new `search_case_insensitive` function and rename our old test from -`one_result` to `case_sensitive` to clarify the differences between the two -tests, as shown in Listing 12-20. + -Filename: src/lib.rs +### Writing a Failing Test for Case-Insensitive Search + +We first add a new `search_case_insensitive` function to the `minigrep` library +that will be called when the environment variable has a value. We’ll continue +to follow the TDD process, so the first step is again to write a failing test. +We’ll add a new test for the new `search_case_insensitive` function and rename +our old test from `one_result` to `case_sensitive` to clarify the differences +between the two tests, as shown in Listing 12-20. + +src/lib.rs ``` #[cfg(test)] @@ -1333,10 +1329,7 @@ safe, fast, productive. Pick three. Duct tape."; - assert_eq!( - vec!["safe, fast, productive."], - search(query, contents) - ); + assert_eq!(vec!["safe, fast, productive."], search(query, contents)); } #[test] @@ -1356,8 +1349,7 @@ Trust me."; } ``` -Listing 12-20: Adding a new failing test for the case-insensitive function -we’re about to add +Listing 12-20: Adding a new failing test for the case-insensitive function we’re about to add Note that we’ve edited the old test’s `contents` too. We’ve added a new line with the text `"Duct tape."` using a capital *D* that shouldn’t match the query @@ -1382,18 +1374,18 @@ the same as the `search` function. The only difference is that we’ll lowercase the `query` and each `line` so that whatever the case of the input arguments, they’ll be the same case when we check whether the line contains the query. -Filename: src/lib.rs +src/lib.rs ``` pub fn search_case_insensitive<'a>( query: &str, contents: &'a str, ) -> Vec<&'a str> { - 1 let query = query.to_lowercase(); + let query = query.to_lowercase(); let mut results = Vec::new(); for line in contents.lines() { - if 2 line.to_lowercase().contains(3 &query) { + if line.to_lowercase().contains(&query) { results.push(line); } } @@ -1402,48 +1394,64 @@ pub fn search_case_insensitive<'a>( } ``` -Listing 12-21: Defining the `search_case_insensitive` function to lowercase the -query and the line before comparing them +Listing 12-21: Defining the `search_case_insensitive` function to lowercase the query and the line before comparing them -First we lowercase the `query` string and store it in a shadowed variable with -the same name [1]. Calling `to_lowercase` on the query is necessary so that no -matter whether the user’s query is `"rust"`, `"RUST"`, `"Rust"`, or `"rUsT"`, -we’ll treat the query as if it were `"rust"` and be insensitive to the case. -While `to_lowercase` will handle basic Unicode, it won’t be 100% accurate. If -we were writing a real application, we’d want to do a bit more work here, but -this section is about environment variables, not Unicode, so we’ll leave it at -that here. +First, we lowercase the `query` string and store it in a new variable with the +same name, shadowing the original `query`. Calling `to_lowercase` on the query +is necessary so that no matter whether the user’s query is `"rust"`, `"RUST"`, +`"Rust"`, or `"rUsT"`, we’ll treat the query as if it were `"rust"` and be +insensitive to the case. While `to_lowercase` will handle basic Unicode, it +won’t be 100 percent accurate. If we were writing a real application, we’d want +to do a bit more work here, but this section is about environment variables, +not Unicode, so we’ll leave it at that here. Note that `query` is now a `String` rather than a string slice because calling `to_lowercase` creates new data rather than referencing existing data. Say the -query is `"rUsT"`, as an example: that string slice doesn’t contain a lowercase +query is `"rUsT"`, as an example: That string slice doesn’t contain a lowercase `u` or `t` for us to use, so we have to allocate a new `String` containing `"rust"`. When we pass `query` as an argument to the `contains` method now, we -need to add an ampersand [3] because the signature of `contains` is defined to -take a string slice. +need to add an ampersand because the signature of `contains` is defined to take +a string slice. Next, we add a call to `to_lowercase` on each `line` to lowercase all -characters [2]. Now that we’ve converted `line` and `query` to lowercase, we’ll +characters. Now that we’ve converted `line` and `query` to lowercase, we’ll find matches no matter what the case of the query is. Let’s see if this implementation passes the tests: ``` +$ cargo test + Compiling minigrep v0.1.0 (file:///projects/minigrep) + Finished `test` profile [unoptimized + debuginfo] target(s) in 1.33s + Running unittests src/lib.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) + running 2 tests test tests::case_insensitive ... ok test tests::case_sensitive ... ok -test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.00s +test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Running unittests src/main.rs (target/debug/deps/minigrep-9cd200e5fac0fc94) + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + + Doc-tests minigrep + +running 0 tests + +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + ``` -Great! They passed. Now, let’s call the new `search_case_insensitive` function -from the `run` function. First we’ll add a configuration option to the `Config` +Great! They passed. Now let’s call the new `search_case_insensitive` function +from the `run` function. First, we’ll add a configuration option to the `Config` struct to switch between case-sensitive and case-insensitive search. Adding this field will cause compiler errors because we aren’t initializing this field anywhere yet: -Filename: src/lib.rs +Filename: src/main.rs ``` pub struct Config { @@ -1458,10 +1466,14 @@ function to check the `ignore_case` field’s value and use that to decide whether to call the `search` function or the `search_case_insensitive` function, as shown in Listing 12-22. This still won’t compile yet. -Filename: src/lib.rs +src/main.rs ``` -pub fn run(config: Config) -> Result<(), Box> { +use minigrep::{search, search_case_insensitive}; + +// --snip-- + +fn run(config: Config) -> Result<(), Box> { let contents = fs::read_to_string(config.file_path)?; let results = if config.ignore_case { @@ -1478,26 +1490,19 @@ pub fn run(config: Config) -> Result<(), Box> { } ``` -Listing 12-22: Calling either `search` or `search_case_insensitive` based on -the value in `config.ignore_case` +Listing 12-22: Calling either `search` or `search_case_insensitive` based on the value in `config.ignore_case` Finally, we need to check for the environment variable. The functions for working with environment variables are in the `env` module in the standard -library, so we bring that module into scope at the top of *src/lib.rs*. Then -we’ll use the `var` function from the `env` module to check to see if any value -has been set for an environment variable named `IGNORE_CASE`, as shown in -Listing 12-23. +library, which is already in scope at the top of *src/main.rs*. We’ll use the +`var` function from the `env` module to check to see if any value has been set +for an environment variable named `IGNORE_CASE`, as shown in Listing 12-23. -Filename: src/lib.rs +src/main.rs ``` -use std::env; ---snip-- - impl Config { - pub fn build( - args: &[String] - ) -> Result { + fn build(args: &[String]) -> Result { if args.len() < 3 { return Err("not enough arguments"); } @@ -1516,8 +1521,7 @@ impl Config { } ``` -Listing 12-23: Checking for any value in an environment variable named -`IGNORE_CASE` +Listing 12-23: Checking for any value in an environment variable named `IGNORE_CASE` Here, we create a new variable, `ignore_case`. To set its value, we call the `env::var` function and pass it the name of the `IGNORE_CASE` environment @@ -1534,18 +1538,18 @@ care about the *value* of the environment variable, just whether it’s set or unset, so we’re checking `is_ok` rather than using `unwrap`, `expect`, or any of the other methods we’ve seen on `Result`. -We pass the value in the `ignore_case` variable to the `Config` instance so the -`run` function can read that value and decide whether to call +We pass the value in the `ignore_case` variable to the `Config` instance so +that the `run` function can read that value and decide whether to call `search_case_insensitive` or `search`, as we implemented in Listing 12-22. -Let’s give it a try! First we’ll run our program without the environment +Let’s give it a try! First, we’ll run our program without the environment variable set and with the query `to`, which should match any line that contains the word *to* in all lowercase: ``` $ cargo run -- to poem.txt Compiling minigrep v0.1.0 (file:///projects/minigrep) - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.0s Running `target/debug/minigrep to poem.txt` Are you nobody, too? How dreary to be somebody! @@ -1574,6 +1578,12 @@ PS> Remove-Item Env:IGNORE_CASE We should get lines that contain *to* that might have uppercase letters: + + ``` Are you nobody, too? How dreary to be somebody! @@ -1595,9 +1605,13 @@ precedence if the program is run with one set to case sensitive and one set to ignore case. The `std::env` module contains many more useful features for dealing with -environment variables: check out its documentation to see what is available. +environment variables: Check out its documentation to see what is available. -## Writing Error Messages to Standard Error Instead of Standard Output + + + + +## Redirecting Errors to Standard Error At the moment, we’re writing all of our output to the terminal using the `println!` macro. In most terminals, there are two kinds of output: *standard @@ -1611,7 +1625,7 @@ to use something else to print to standard error. ### Checking Where Errors Are Written -First let’s observe how the content printed by `minigrep` is currently being +First, let’s observe how the content printed by `minigrep` is currently being written to standard output, including any error messages we want to write to standard error instead. We’ll do that by redirecting the standard output stream to a file while intentionally causing an error. We won’t redirect the standard @@ -1619,9 +1633,10 @@ error stream, so any content sent to standard error will continue to display on the screen. Command line programs are expected to send error messages to the standard error -stream so we can still see error messages on the screen even if we redirect the -standard output stream to a file. Our program is not currently well behaved: -we’re about to see that it saves the error message output to a file instead! +stream so that we can still see error messages on the screen even if we +redirect the standard output stream to a file. Our program is not currently +well behaved: We’re about to see that it saves the error message output to a +file instead! To demonstrate this behavior, we’ll run the program with `>` and the file path, *output.txt*, that we want to redirect the standard output stream to. We won’t @@ -1641,8 +1656,8 @@ Problem parsing arguments: not enough arguments ``` Yup, our error message is being printed to standard output. It’s much more -useful for error messages like this to be printed to standard error so only -data from a successful run ends up in the file. We’ll change that. +useful for error messages like this to be printed to standard error so that +only data from a successful run ends up in the file. We’ll change that. ### Printing Errors to Standard Error @@ -1653,7 +1668,7 @@ the `eprintln!` macro that prints to the standard error stream, so let’s chang the two places we were calling `println!` to print errors to use `eprintln!` instead. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1664,15 +1679,14 @@ fn main() { process::exit(1); }); - if let Err(e) = minigrep::run(config) { + if let Err(e) = run(config) { eprintln!("Application error: {e}"); process::exit(1); } } ``` -Listing 12-24: Writing error messages to standard error instead of standard -output using `eprintln!` +Listing 12-24: Writing error messages to standard error instead of standard output using `eprintln!` Let’s now run the program again in the same way, without any arguments and redirecting standard output with `>`: @@ -1717,4 +1731,3 @@ well tested. Next, we’ll explore some Rust features that were influenced by functional languages: closures and iterators. - diff --git a/nostarch/chapter13.md b/nostarch/chapter13.md index 52c1f5f977..ca9ddf1c1a 100644 --- a/nostarch/chapter13.md +++ b/nostarch/chapter13.md @@ -23,15 +23,20 @@ More specifically, we’ll cover: * *Closures*, a function-like construct you can store in a variable * *Iterators*, a way of processing a series of elements * How to use closures and iterators to improve the I/O project in Chapter 12 -* The performance of closures and iterators (spoiler alert: they’re faster than -you might think!) +* The performance of closures and iterators (spoiler alert: They’re faster than + you might think!) We’ve already covered some other Rust features, such as pattern matching and enums, that are also influenced by the functional style. Because mastering -closures and iterators is an important part of writing idiomatic, fast Rust +closures and iterators is an important part of writing fast, idiomatic, Rust code, we’ll devote this entire chapter to them. -## Closures: Anonymous Functions That Capture Their Environment + + + + + +## Closures Rust’s closures are anonymous functions you can save in a variable or pass as arguments to other functions. You can create the closure in one place and then @@ -40,10 +45,17 @@ functions, closures can capture values from the scope in which they’re defined We’ll demonstrate how these closure features allow for code reuse and behavior customization. -### Capturing the Environment with Closures + + + + + + + +### Capturing the Environment We’ll first examine how we can use closures to capture values from the -environment they’re defined in for later use. Here’s the scenario: every so +environment they’re defined in for later use. Here’s the scenario: Every so often, our T-shirt company gives away an exclusive, limited-edition shirt to someone on our mailing list as a promotion. People on the mailing list can optionally add their favorite color to their profile. If the person chosen for @@ -57,10 +69,10 @@ number of colors available for simplicity). We represent the company’s inventory with an `Inventory` struct that has a field named `shirts` that contains a `Vec` representing the shirt colors currently in stock. The method `giveaway` defined on `Inventory` gets the optional shirt color -preference of the free-shirt winner, and returns the shirt color the person -will get. This setup is shown in Listing 13-1. +preference of the free-shirt winner, and it returns the shirt color the +person will get. This setup is shown in Listing 13-1. -Filename: src/main.rs +src/main.rs ``` #[derive(Debug, PartialEq, Copy, Clone)] @@ -74,11 +86,8 @@ struct Inventory { } impl Inventory { - fn giveaway( - &self, - user_preference: Option, - ) -> ShirtColor { - 1 user_preference.unwrap_or_else(|| self.most_stocked()) + fn giveaway(&self, user_preference: Option) -> ShirtColor { + user_preference.unwrap_or_else(|| self.most_stocked()) } fn most_stocked(&self) -> ShirtColor { @@ -101,22 +110,18 @@ impl Inventory { fn main() { let store = Inventory { - 2 shirts: vec![ - ShirtColor::Blue, - ShirtColor::Red, - ShirtColor::Blue, - ], + shirts: vec![ShirtColor::Blue, ShirtColor::Red, ShirtColor::Blue], }; let user_pref1 = Some(ShirtColor::Red); - 3 let giveaway1 = store.giveaway(user_pref1); + let giveaway1 = store.giveaway(user_pref1); println!( "The user with preference {:?} gets {:?}", user_pref1, giveaway1 ); let user_pref2 = None; - 4 let giveaway2 = store.giveaway(user_pref2); + let giveaway2 = store.giveaway(user_pref2); println!( "The user with preference {:?} gets {:?}", user_pref2, giveaway2 @@ -127,21 +132,21 @@ fn main() { Listing 13-1: Shirt company giveaway situation The `store` defined in `main` has two blue shirts and one red shirt remaining -to distribute for this limited-edition promotion [2]. We call the `giveaway` -method for a user with a preference for a red shirt [3] and a user without any -preference [4]. +to distribute for this limited-edition promotion. We call the `giveaway` method +for a user with a preference for a red shirt and a user without any preference. Again, this code could be implemented in many ways, and here, to focus on -closures, we’ve stuck to concepts you’ve already learned, except for the body -of the `giveaway` method that uses a closure. In the `giveaway` method, we get -the user preference as a parameter of type `Option` and call the -`unwrap_or_else` method on `user_preference` [1]. The `unwrap_or_else` method -on `Option` is defined by the standard library. It takes one argument: a -closure without any arguments that returns a value `T` (the same type stored in -the `Some` variant of the `Option`, in this case `ShirtColor`). If the -`Option` is the `Some` variant, `unwrap_or_else` returns the value from -within the `Some`. If the `Option` is the `None` variant, `unwrap_or_else` -calls the closure and returns the value returned by the closure. +closures, we’ve stuck to concepts you’ve already learned, except for the body of +the `giveaway` method that uses a closure. In the `giveaway` method, we get the +user preference as a parameter of type `Option` and call the +`unwrap_or_else` method on `user_preference`. The `unwrap_or_else` method on +`Option` is defined by the standard library. +It takes one argument: a closure without any arguments that returns a value `T` +(the same type stored in the `Some` variant of the `Option`, in this case +`ShirtColor`). If the `Option` is the `Some` variant, `unwrap_or_else` +returns the value from within the `Some`. If the `Option` is the `None` +variant, `unwrap_or_else` calls the closure and returns the value returned by +the closure. We specify the closure expression `|| self.most_stocked()` as the argument to `unwrap_or_else`. This is a closure that takes no parameters itself (if the @@ -153,6 +158,10 @@ later if the result is needed. Running this code prints the following: ``` +$ cargo run + Compiling shirt-company v0.1.0 (file:///projects/shirt-company) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.27s + Running `target/debug/shirt-company` The user with preference Some(Red) gets Red The user with preference None gets Blue ``` @@ -165,7 +174,11 @@ immutable reference to the `self` `Inventory` instance and passes it with the code we specify to the `unwrap_or_else` method. Functions, on the other hand, are not able to capture their environment in this way. -### Closure Type Inference and Annotation + + + + +### Inferring and Annotating Closure Types There are more differences between functions and closures. Closures don’t usually require you to annotate the types of the parameters or the return value @@ -173,8 +186,8 @@ like `fn` functions do. Type annotations are required on functions because the types are part of an explicit interface exposed to your users. Defining this interface rigidly is important for ensuring that everyone agrees on what types of values a function uses and returns. Closures, on the other hand, aren’t used -in an exposed interface like this: they’re stored in variables and used without -naming them and exposing them to users of our library. +in an exposed interface like this: They’re stored in variables, and they’re +used without naming them and exposing them to users of our library. Closures are typically short and relevant only within a narrow context rather than in any arbitrary scenario. Within these limited contexts, the compiler can @@ -189,25 +202,24 @@ shown in Listing 13-2. In this example, we’re defining a closure and storing i in a variable rather than defining the closure in the spot we pass it as an argument, as we did in Listing 13-1. -Filename: src/main.rs +src/main.rs ``` -let expensive_closure = |num: u32| -> u32 { - println!("calculating slowly..."); - thread::sleep(Duration::from_secs(2)); - num -}; + let expensive_closure = |num: u32| -> u32 { + println!("calculating slowly..."); + thread::sleep(Duration::from_secs(2)); + num + }; ``` -Listing 13-2: Adding optional type annotations of the parameter and return -value types in the closure +Listing 13-2: Adding optional type annotations of the parameter and return value types in the closure With type annotations added, the syntax of closures looks more similar to the -syntax of functions. Here, we define a function that adds 1 to its parameter -and a closure that has the same behavior, for comparison. We’ve added some -spaces to line up the relevant parts. This illustrates how closure syntax is -similar to function syntax except for the use of pipes and the amount of syntax -that is optional: +syntax of functions. Here, we define a function that adds 1 to its parameter and +a closure that has the same behavior, for comparison. We’ve added some spaces +to line up the relevant parts. This illustrates how closure syntax is similar +to function syntax except for the use of pipes and the amount of syntax that is +optional: ``` fn add_one_v1 (x: u32) -> u32 { x + 1 } @@ -218,11 +230,11 @@ let add_one_v4 = |x| x + 1 ; The first line shows a function definition and the second line shows a fully annotated closure definition. In the third line, we remove the type annotations -from the closure definition. In the fourth line, we remove the curly brackets, -which are optional because the closure body has only one expression. These are -all valid definitions that will produce the same behavior when they’re called. -The `add_one_v3` and `add_one_v4` lines require the closures to be evaluated to -be able to compile because the types will be inferred from their usage. This is +from the closure definition. In the fourth line, we remove the brackets, which +are optional because the closure body has only one expression. These are all +valid definitions that will produce the same behavior when they’re called. The +`add_one_v3` and `add_one_v4` lines require the closures to be evaluated to be +able to compile because the types will be inferred from their usage. This is similar to `let v = Vec::new();` needing either type annotations or values of some type to be inserted into the `Vec` for Rust to be able to infer the type. @@ -235,29 +247,46 @@ Because there are no type annotations, we can call the closure with any type, which we’ve done here with `String` the first time. If we then try to call `example_closure` with an integer, we’ll get an error. -Filename: src/main.rs +src/main.rs ``` -let example_closure = |x| x; + let example_closure = |x| x; -let s = example_closure(String::from("hello")); -let n = example_closure(5); + let s = example_closure(String::from("hello")); + let n = example_closure(5); ``` -Listing 13-3: Attempting to call a closure whose types are inferred with two -different types +Listing 13-3: Attempting to call a closure whose types are inferred with two different types The compiler gives us this error: ``` +$ cargo run + Compiling closure-example v0.1.0 (file:///projects/closure-example) error[E0308]: mismatched types --> src/main.rs:5:29 | 5 | let n = example_closure(5); - | ^- help: try using a conversion method: -`.to_string()` - | | - | expected struct `String`, found integer + | --------------- ^- help: try using a conversion method: `.to_string()` + | | | + | | expected `String`, found integer + | arguments to this function are incorrect + | +note: expected because the closure was earlier called with an argument of type `String` + --> src/main.rs:4:29 + | +4 | let s = example_closure(String::from("hello")); + | --------------- ^^^^^^^^^^^^^^^^^^^^^ expected because this argument is of type `String` + | | + | in this closure call +note: closure parameter defined here + --> src/main.rs:2:28 + | +2 | let example_closure = |x| x; + | ^ + +For more information about this error, try `rustc --explain E0308`. +error: could not compile `closure-example` (bin "closure-example") due to 1 previous error ``` The first time we call `example_closure` with the `String` value, the compiler @@ -277,27 +306,26 @@ In Listing 13-4, we define a closure that captures an immutable reference to the vector named `list` because it only needs an immutable reference to print the value. -Filename: src/main.rs +src/main.rs ``` fn main() { let list = vec![1, 2, 3]; - println!("Before defining closure: {:?}", list); + println!("Before defining closure: {list:?}"); - 1 let only_borrows = || println!("From closure: {:?}", list); + let only_borrows = || println!("From closure: {list:?}"); - println!("Before calling closure: {:?}", list); - 2 only_borrows(); - println!("After calling closure: {:?}", list); + println!("Before calling closure: {list:?}"); + only_borrows(); + println!("After calling closure: {list:?}"); } ``` -Listing 13-4: Defining and calling a closure that captures an immutable -reference +Listing 13-4: Defining and calling a closure that captures an immutable reference -This example also illustrates that a variable can bind to a closure definition -[1], and we can later call the closure by using the variable name and -parentheses as if the variable name were a function name [2]. +This example also illustrates that a variable can bind to a closure definition, +and we can later call the closure by using the variable name and parentheses as +if the variable name were a function name. Because we can have multiple immutable references to `list` at the same time, `list` is still accessible from the code before the closure definition, after @@ -305,6 +333,10 @@ the closure definition but before the closure is called, and after the closure is called. This code compiles, runs, and prints: ``` +$ cargo run + Compiling closure-example v0.1.0 (file:///projects/closure-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.43s + Running `target/debug/closure-example` Before defining closure: [1, 2, 3] Before calling closure: [1, 2, 3] From closure: [1, 2, 3] @@ -314,17 +346,17 @@ After calling closure: [1, 2, 3] Next, in Listing 13-5, we change the closure body so that it adds an element to the `list` vector. The closure now captures a mutable reference. -Filename: src/main.rs +src/main.rs ``` fn main() { let mut list = vec![1, 2, 3]; - println!("Before defining closure: {:?}", list); + println!("Before defining closure: {list:?}"); let mut borrows_mutably = || list.push(7); borrows_mutably(); - println!("After calling closure: {:?}", list); + println!("After calling closure: {list:?}"); } ``` @@ -333,15 +365,19 @@ Listing 13-5: Defining and calling a closure that captures a mutable reference This code compiles, runs, and prints: ``` +$ cargo run + Compiling closure-example v0.1.0 (file:///projects/closure-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.43s + Running `target/debug/closure-example` Before defining closure: [1, 2, 3] After calling closure: [1, 2, 3, 7] ``` Note that there’s no longer a `println!` between the definition and the call of -the `borrows_mutably` closure: when `borrows_mutably` is defined, it captures a +the `borrows_mutably` closure: When `borrows_mutably` is defined, it captures a mutable reference to `list`. We don’t use the closure again after the closure is called, so the mutable borrow ends. Between the closure definition and the -closure call, an immutable borrow to print isn’t allowed because no other +closure call, an immutable borrow to print isn’t allowed, because no other borrows are allowed when there’s a mutable borrow. Try adding a `println!` there to see what error message you get! @@ -356,40 +392,47 @@ concurrency, but for now, let’s briefly explore spawning a new thread using a closure that needs the `move` keyword. Listing 13-6 shows Listing 13-4 modified to print the vector in a new thread rather than in the main thread. -Filename: src/main.rs +src/main.rs ``` use std::thread; fn main() { let list = vec![1, 2, 3]; - println!("Before defining closure: {:?}", list); + println!("Before defining closure: {list:?}"); - 1 thread::spawn(move || { - 2 println!("From thread: {:?}", list) - }).join().unwrap(); + thread::spawn(move || println!("From thread: {list:?}")) + .join() + .unwrap(); } ``` -Listing 13-6: Using `move` to force the closure for the thread to take -ownership of `list` +Listing 13-6: Using `move` to force the closure for the thread to take ownership of `list` We spawn a new thread, giving the thread a closure to run as an argument. The closure body prints out the list. In Listing 13-4, the closure only captured `list` using an immutable reference because that’s the least amount of access to `list` needed to print it. In this example, even though the closure body -still only needs an immutable reference [2], we need to specify that `list` -should be moved into the closure by putting the `move` keyword [1] at the -beginning of the closure definition. The new thread might finish before the -rest of the main thread finishes, or the main thread might finish first. If the -main thread maintains ownership of `list` but ends before the new thread and -drops `list`, the immutable reference in the thread would be invalid. -Therefore, the compiler requires that `list` be moved into the closure given to -the new thread so the reference will be valid. Try removing the `move` keyword -or using `list` in the main thread after the closure is defined to see what -compiler errors you get! - -### Moving Captured Values Out of Closures and the Fn Traits +still only needs an immutable reference, we need to specify that `list` should +be moved into the closure by putting the `move` keyword at the beginning of the +closure definition. If the main thread performed more operations before calling +`join` on the new thread, the new thread might finish before the rest of the +main thread finishes, or the main thread might finish first. If the main thread +maintained ownership of `list` but ended before the new thread and drops +`list`, the immutable reference in the thread would be invalid. Therefore, the +compiler requires that `list` be moved into the closure given to the new thread +so that the reference will be valid. Try removing the `move` keyword or using +`list` in the main thread after the closure is defined to see what compiler +errors you get! + + + + + + + + +### Moving Captured Values Out of Closures Once a closure has captured a reference or captured ownership of a value from the environment where the closure is defined (thus affecting what, if anything, @@ -397,7 +440,7 @@ is moved *into* the closure), the code in the body of the closure defines what happens to the references or values when the closure is evaluated later (thus affecting what, if anything, is moved *out of* the closure). -A closure body can do any of the following: move a captured value out of the +A closure body can do any of the following: Move a captured value out of the closure, mutate the captured value, neither move nor mutate the value, or capture nothing from the environment to begin with. @@ -408,17 +451,16 @@ implement one, two, or all three of these `Fn` traits, in an additive fashion, depending on how the closure’s body handles the values: * `FnOnce` applies to closures that can be called once. All closures implement -at least this trait because all closures can be called. A closure that moves -captured values out of its body will only implement `FnOnce` and none of the -other `Fn` traits because it can only be called once. -* `FnMut` applies to closures that don’t move captured values out of their -body, but that might mutate the captured values. These closures can be called -more than once. + at least this trait because all closures can be called. A closure that moves + captured values out of its body will only implement `FnOnce` and none of the + other `Fn` traits because it can only be called once. +* `FnMut` applies to closures that don’t move captured values out of their body + but might mutate the captured values. These closures can be called more than + once. * `Fn` applies to closures that don’t move captured values out of their body -and that don’t mutate captured values, as well as closures that capture nothing -from their environment. These closures can be called more than once without -mutating their environment, which is important in cases such as calling a -closure multiple times concurrently. + and don’t mutate captured values, as well as closures that capture nothing + from their environment. These closures can be called more than once without + mutating their environment, which is important in cases such as calling a closure multiple times concurrently. Let’s look at the definition of the `unwrap_or_else` method on `Option` that we used in Listing 13-1: @@ -439,7 +481,7 @@ impl Option { Recall that `T` is the generic type representing the type of the value in the `Some` variant of an `Option`. That type `T` is also the return type of the -`unwrap_or_else` function: code that calls `unwrap_or_else` on an +`unwrap_or_else` function: Code that calls `unwrap_or_else` on an `Option`, for example, will get a `String`. Next, notice that the `unwrap_or_else` function has the additional generic type @@ -449,29 +491,30 @@ the closure we provide when calling `unwrap_or_else`. The trait bound specified on the generic type `F` is `FnOnce() -> T`, which means `F` must be able to be called once, take no arguments, and return a `T`. Using `FnOnce` in the trait bound expresses the constraint that -`unwrap_or_else` is only going to call `f` one time, at most. In the body of +`unwrap_or_else` will not call `f` more than once. In the body of `unwrap_or_else`, we can see that if the `Option` is `Some`, `f` won’t be called. If the `Option` is `None`, `f` will be called once. Because all -closures implement `FnOnce`, `unwrap_or_else` accepts the largest variety of +closures implement `FnOnce`, `unwrap_or_else` accepts all three kinds of closures and is as flexible as it can be. -> Note: Functions can implement all three of the `Fn` traits too. If what we -want to do doesn’t require capturing a value from the environment, we can use -the name of a function rather than a closure where we need something that -implements one of the `Fn` traits. For example, on an `Option>` value, -we could call `unwrap_or_else(Vec::new)` to get a new, empty vector if the -value is `None`. +> Note: If what we want to do doesn’t require capturing a value from the +> environment, we can use the name of a function rather than a closure where we +> need something that implements one of the `Fn` traits. For example, on an +> `Option>` value, we could call `unwrap_or_else(Vec::new)` to get a +> new, empty vector if the value is `None`. The compiler automatically +> implements whichever of the `Fn` traits is applicable for a function +> definition. Now let’s look at the standard library method `sort_by_key`, defined on slices, to see how that differs from `unwrap_or_else` and why `sort_by_key` uses `FnMut` instead of `FnOnce` for the trait bound. The closure gets one argument in the form of a reference to the current item in the slice being considered, -and returns a value of type `K` that can be ordered. This function is useful +and it returns a value of type `K` that can be ordered. This function is useful when you want to sort a slice by a particular attribute of each item. In -Listing 13-7, we have a list of `Rectangle` instances and we use `sort_by_key` +Listing 13-7, we have a list of `Rectangle` instances, and we use `sort_by_key` to order them by their `width` attribute from low to high. -Filename: src/main.rs +src/main.rs ``` #[derive(Debug)] @@ -488,7 +531,7 @@ fn main() { ]; list.sort_by_key(|r| r.width); - println!("{:#?}", list); + println!("{list:#?}"); } ``` @@ -497,6 +540,10 @@ Listing 13-7: Using `sort_by_key` to order rectangles by width This code prints: ``` +$ cargo run + Compiling rectangles v0.1.0 (file:///projects/rectangles) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.41s + Running `target/debug/rectangles` [ Rectangle { width: 3, @@ -514,18 +561,21 @@ This code prints: ``` The reason `sort_by_key` is defined to take an `FnMut` closure is that it calls -the closure multiple times: once for each item in the slice. The closure `|r| -r.width` doesn’t capture, mutate, or move anything out from its environment, so +the closure multiple times: once for each item in the slice. The closure `|r| r.width` doesn’t capture, mutate, or move anything out from its environment, so it meets the trait bound requirements. In contrast, Listing 13-8 shows an example of a closure that implements just the `FnOnce` trait, because it moves a value out of the environment. The compiler won’t let us use this closure with `sort_by_key`. -Filename: src/main.rs +src/main.rs ``` ---snip-- +#[derive(Debug)] +struct Rectangle { + width: u32, + height: u32, +} fn main() { let mut list = [ @@ -535,73 +585,83 @@ fn main() { ]; let mut sort_operations = vec![]; - let value = String::from("by key called"); + let value = String::from("closure called"); list.sort_by_key(|r| { sort_operations.push(value); r.width }); - println!("{:#?}", list); + println!("{list:#?}"); } ``` Listing 13-8: Attempting to use an `FnOnce` closure with `sort_by_key` -This is a contrived, convoluted way (that doesn’t work) to try and count the -number of times `sort_by_key` gets called when sorting `list`. This code +This is a contrived, convoluted way (that doesn’t work) to try to count the +number of times `sort_by_key` calls the closure when sorting `list`. This code attempts to do this counting by pushing `value`—a `String` from the closure’s environment—into the `sort_operations` vector. The closure captures `value` and then moves `value` out of the closure by transferring ownership of `value` to the `sort_operations` vector. This closure can be called once; trying to call -it a second time wouldn’t work because `value` would no longer be in the +it a second time wouldn’t work, because `value` would no longer be in the environment to be pushed into `sort_operations` again! Therefore, this closure only implements `FnOnce`. When we try to compile this code, we get this error that `value` can’t be moved out of the closure because the closure must implement `FnMut`: ``` -error[E0507]: cannot move out of `value`, a captured variable in an `FnMut` -closure +$ cargo run + Compiling rectangles v0.1.0 (file:///projects/rectangles) +error[E0507]: cannot move out of `value`, a captured variable in an `FnMut` closure --> src/main.rs:18:30 | -15 | let value = String::from("by key called"); - | ----- captured outer variable +15 | let value = String::from("closure called"); + | ----- captured outer variable 16 | -17 | list.sort_by_key(|r| { - | ______________________- -18 | | sort_operations.push(value); - | | ^^^^^ move occurs because `value` has -type `String`, which does not implement the `Copy` trait -19 | | r.width -20 | | }); - | |_____- captured by this `FnMut` closure +17 | list.sort_by_key(|r| { + | --- captured by this `FnMut` closure +18 | sort_operations.push(value); + | ^^^^^ move occurs because `value` has type `String`, which does not implement the `Copy` trait + | +help: consider cloning the value if the performance cost is acceptable + | +18 | sort_operations.push(value.clone()); + | ++++++++ + +For more information about this error, try `rustc --explain E0507`. +error: could not compile `rectangles` (bin "rectangles") due to 1 previous error ``` The error points to the line in the closure body that moves `value` out of the environment. To fix this, we need to change the closure body so that it doesn’t move values out of the environment. Keeping a counter in the environment and incrementing its value in the closure body is a more straightforward way to -count the number of times `sort_by_key` is called. The closure in Listing 13-9 -works with `sort_by_key` because it is only capturing a mutable reference to -the `num_sort_operations` counter and can therefore be called more than once. +count the number of times the closure is called. The closure in Listing 13-9 +works with `sort_by_key` because it is only capturing a mutable reference to the +`num_sort_operations` counter and can therefore be called more than once. -Filename: src/main.rs +src/main.rs ``` ---snip-- +#[derive(Debug)] +struct Rectangle { + width: u32, + height: u32, +} fn main() { - --snip-- + let mut list = [ + Rectangle { width: 10, height: 1 }, + Rectangle { width: 3, height: 5 }, + Rectangle { width: 7, height: 12 }, + ]; let mut num_sort_operations = 0; list.sort_by_key(|r| { num_sort_operations += 1; r.width }); - println!( - "{:#?}, sorted in {num_sort_operations} operations", - list - ); + println!("{list:#?}, sorted in {num_sort_operations} operations"); } ``` @@ -625,10 +685,12 @@ Listing 13-10 creates an iterator over the items in the vector `v1` by calling the `iter` method defined on `Vec`. This code by itself doesn’t do anything useful. +src/main.rs + ``` -let v1 = vec![1, 2, 3]; + let v1 = vec![1, 2, 3]; -let v1_iter = v1.iter(); + let v1_iter = v1.iter(); ``` Listing 13-10: Creating an iterator @@ -644,14 +706,16 @@ the use of the iterator in the `for` loop. When the `for` loop is called using the iterator in `v1_iter`, each element in the iterator is used in one iteration of the loop, which prints out each value. +src/main.rs + ``` -let v1 = vec![1, 2, 3]; + let v1 = vec![1, 2, 3]; -let v1_iter = v1.iter(); + let v1_iter = v1.iter(); -for val in v1_iter { - println!("Got: {val}"); -} + for val in v1_iter { + println!("Got: {val}"); + } ``` Listing 13-11: Using an iterator in a `for` loop @@ -683,8 +747,8 @@ pub trait Iterator { ``` Notice that this definition uses some new syntax: `type Item` and `Self::Item`, -which are defining an *associated type* with this trait. We’ll talk about -associated types in depth in Chapter 19. For now, all you need to know is that +which are defining an associated type with this trait. We’ll talk about +associated types in depth in Chapter 20. For now, all you need to know is that this code says implementing the `Iterator` trait requires that you also define an `Item` type, and this `Item` type is used in the return type of the `next` method. In other words, the `Item` type will be the type returned from the @@ -698,29 +762,29 @@ We can call the `next` method on iterators directly; Listing 13-12 demonstrates what values are returned from repeated calls to `next` on the iterator created from the vector. -Filename: src/lib.rs +src/lib.rs ``` -#[test] -fn iterator_demonstration() { - let v1 = vec![1, 2, 3]; + #[test] + fn iterator_demonstration() { + let v1 = vec![1, 2, 3]; - let mut v1_iter = v1.iter(); + let mut v1_iter = v1.iter(); - assert_eq!(v1_iter.next(), Some(&1)); - assert_eq!(v1_iter.next(), Some(&2)); - assert_eq!(v1_iter.next(), Some(&3)); - assert_eq!(v1_iter.next(), None); -} + assert_eq!(v1_iter.next(), Some(&1)); + assert_eq!(v1_iter.next(), Some(&2)); + assert_eq!(v1_iter.next(), Some(&3)); + assert_eq!(v1_iter.next(), None); + } ``` Listing 13-12: Calling the `next` method on an iterator -Note that we needed to make `v1_iter` mutable: calling the `next` method on an +Note that we needed to make `v1_iter` mutable: Calling the `next` method on an iterator changes internal state that the iterator uses to keep track of where it is in the sequence. In other words, this code *consumes*, or uses up, the iterator. Each call to `next` eats up an item from the iterator. We didn’t need -to make `v1_iter` mutable when we used a `for` loop because the loop took +to make `v1_iter` mutable when we used a `for` loop, because the loop took ownership of `v1_iter` and made it mutable behind the scenes. Also note that the values we get from the calls to `next` are immutable @@ -746,25 +810,24 @@ consuming the iterator. As it iterates through, it adds each item to a running total and returns the total when iteration is complete. Listing 13-13 has a test illustrating a use of the `sum` method. -Filename: src/lib.rs +src/lib.rs ``` -#[test] -fn iterator_sum() { - let v1 = vec![1, 2, 3]; + #[test] + fn iterator_sum() { + let v1 = vec![1, 2, 3]; - let v1_iter = v1.iter(); + let v1_iter = v1.iter(); - let total: i32 = v1_iter.sum(); + let total: i32 = v1_iter.sum(); - assert_eq!(total, 6); -} + assert_eq!(total, 6); + } ``` -Listing 13-13: Calling the `sum` method to get the total of all items in the -iterator +Listing 13-13: Calling the `sum` method to get the total of all items in the iterator -We aren’t allowed to use `v1_iter` after the call to `sum` because `sum` takes +We aren’t allowed to use `v1_iter` after the call to `sum`, because `sum` takes ownership of the iterator we call it on. ### Methods That Produce Other Iterators @@ -779,12 +842,12 @@ The `map` method returns a new iterator that produces the modified items. The closure here creates a new iterator in which each item from the vector will be incremented by 1. -Filename: src/main.rs +src/main.rs ``` -let v1: Vec = vec![1, 2, 3]; + let v1: Vec = vec![1, 2, 3]; -v1.iter().map(|x| x + 1); + v1.iter().map(|x| x + 1); ``` Listing 13-14: Calling the iterator adapter `map` to create a new iterator @@ -792,40 +855,49 @@ Listing 13-14: Calling the iterator adapter `map` to create a new iterator However, this code produces a warning: ``` +$ cargo run + Compiling iterators v0.1.0 (file:///projects/iterators) warning: unused `Map` that must be used --> src/main.rs:4:5 | 4 | v1.iter().map(|x| x + 1); - | ^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^ | - = note: `#[warn(unused_must_use)]` on by default = note: iterators are lazy and do nothing unless consumed + = note: `#[warn(unused_must_use)]` on by default +help: use `let _ = ...` to ignore the resulting value + | +4 | let _ = v1.iter().map(|x| x + 1); + | +++++++ + +warning: `iterators` (bin "iterators") generated 1 warning + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.47s + Running `target/debug/iterators` ``` The code in Listing 13-14 doesn’t do anything; the closure we’ve specified -never gets called. The warning reminds us why: iterator adapters are lazy, and +never gets called. The warning reminds us why: Iterator adapters are lazy, and we need to consume the iterator here. To fix this warning and consume the iterator, we’ll use the `collect` method, which we used with `env::args` in Listing 12-1. This method consumes the iterator and collects the resultant values into a collection data type. -In Listing 13-15, we collect into a vector the results of iterating over the -iterator that’s returned from the call to `map`. This vector will end up +In Listing 13-15, we collect the results of iterating over the iterator that’s +returned from the call to `map` into a vector. This vector will end up containing each item from the original vector, incremented by 1. -Filename: src/main.rs +src/main.rs ``` -let v1: Vec = vec![1, 2, 3]; + let v1: Vec = vec![1, 2, 3]; -let v2: Vec<_> = v1.iter().map(|x| x + 1).collect(); + let v2: Vec<_> = v1.iter().map(|x| x + 1).collect(); -assert_eq!(v2, vec![2, 3, 4]); + assert_eq!(v2, vec![2, 3, 4]); ``` -Listing 13-15: Calling the `map` method to create a new iterator, and then -calling the `collect` method to consume the new iterator and create a vector +Listing 13-15: Calling the `map` method to create a new iterator, and then calling the `collect` method to consume the new iterator and create a vector Because `map` takes a closure, we can specify any operation we want to perform on each item. This is a great example of how closures let you customize some @@ -836,7 +908,11 @@ You can chain multiple calls to iterator adapters to perform complex actions in a readable way. But because all iterators are lazy, you have to call one of the consuming adapter methods to get results from calls to iterator adapters. -### Using Closures That Capture Their Environment + + + + +### Closures That Capture Their Environment Many iterator adapters take closures as arguments, and commonly the closures we’ll specify as arguments to iterator adapters will be closures that capture @@ -851,7 +927,7 @@ In Listing 13-16, we use `filter` with a closure that captures the `shoe_size` variable from its environment to iterate over a collection of `Shoe` struct instances. It will return only shoes that are the specified size. -Filename: src/lib.rs +src/lib.rs ``` #[derive(PartialEq, Debug)] @@ -904,15 +980,14 @@ mod tests { } ``` -Listing 13-16: Using the `filter` method with a closure that captures -`shoe_size` +Listing 13-16: Using the `filter` method with a closure that captures `shoe_size` The `shoes_in_size` function takes ownership of a vector of shoes and a shoe size as parameters. It returns a vector containing only shoes of the specified size. In the body of `shoes_in_size`, we call `into_iter` to create an iterator that -takes ownership of the vector. Then we call `filter` to adapt that iterator +takes ownership of the vector. Then, we call `filter` to adapt that iterator into a new iterator that only contains elements for which the closure returns `true`. @@ -939,13 +1014,11 @@ values, allowing the `Config` struct to own those values. In Listing 13-17, we’ve reproduced the implementation of the `Config::build` function as it was in Listing 12-23. -Filename: src/lib.rs +src/main.rs ``` impl Config { - pub fn build( - args: &[String] - ) -> Result { + fn build(args: &[String]) -> Result { if args.len() < 3 { return Err("not enough arguments"); } @@ -972,7 +1045,8 @@ we would remove them in the future. Well, that time is now! We needed `clone` here because we have a slice with `String` elements in the parameter `args`, but the `build` function doesn’t own `args`. To return ownership of a `Config` instance, we had to clone the values from the `query` -and `filename` fields of `Config` so the `Config` instance can own its values. +and `file_path` fields of `Config` so that the `Config` instance can own its +values. With our new knowledge about iterators, we can change the `build` function to take ownership of an iterator as its argument instead of borrowing a slice. @@ -999,7 +1073,7 @@ fn main() { process::exit(1); }); - --snip-- + // --snip-- } ``` @@ -1007,17 +1081,16 @@ We’ll first change the start of the `main` function that we had in Listing 12-24 to the code in Listing 13-18, which this time uses an iterator. This won’t compile until we update `Config::build` as well. -Filename: src/main.rs +src/main.rs ``` fn main() { - let config = - Config::build(env::args()).unwrap_or_else(|err| { - eprintln!("Problem parsing arguments: {err}"); - process::exit(1); - }); + let config = Config::build(env::args()).unwrap_or_else(|err| { + eprintln!("Problem parsing arguments: {err}"); + process::exit(1); + }); - --snip-- + // --snip-- } ``` @@ -1028,19 +1101,18 @@ iterator values into a vector and then passing a slice to `Config::build`, now we’re passing ownership of the iterator returned from `env::args` to `Config::build` directly. -Next, we need to update the definition of `Config::build`. In your I/O -project’s *src/lib.rs* file, let’s change the signature of `Config::build` to -look like Listing 13-19. This still won’t compile, because we need to update -the function body. +Next, we need to update the definition of `Config::build`. Let’s change the +signature of `Config::build` to look like Listing 13-19. This still won’t +compile, because we need to update the function body. -Filename: src/lib.rs +src/main.rs ``` impl Config { - pub fn build( + fn build( mut args: impl Iterator, ) -> Result { - --snip-- + // --snip-- ``` Listing 13-19: Updating the signature of `Config::build` to expect an iterator @@ -1049,27 +1121,31 @@ The standard library documentation for the `env::args` function shows that the type of the iterator it returns is `std::env::Args`, and that type implements the `Iterator` trait and returns `String` values. -We’ve updated the signature of the `Config::build` function so the parameter -`args` has a generic type with the trait bounds `impl Iterator` -instead of `&[String]`. This usage of the `impl Trait` syntax we discussed in -“Traits as Parameters” on page XX means that `args` can be any type that -implements the `Iterator` type and returns `String` items. +We’ve updated the signature of the `Config::build` function so that the +parameter `args` has a generic type with the trait bounds `impl Iterator` instead of `&[String]`. This usage of the `impl Trait` syntax we +discussed in the “Using Traits as Parameters” +section of Chapter 10 means that `args` can be any type that implements the +`Iterator` trait and returns `String` items. Because we’re taking ownership of `args` and we’ll be mutating `args` by iterating over it, we can add the `mut` keyword into the specification of the `args` parameter to make it mutable. -#### Using Iterator Trait Methods Instead of Indexing + + + + +#### Using Iterator Trait Methods Next, we’ll fix the body of `Config::build`. Because `args` implements the `Iterator` trait, we know we can call the `next` method on it! Listing 13-20 updates the code from Listing 12-23 to use the `next` method. -Filename: src/lib.rs +src/main.rs ``` impl Config { - pub fn build( + fn build( mut args: impl Iterator, ) -> Result { args.next(); @@ -1099,24 +1175,25 @@ Listing 13-20: Changing the body of `Config::build` to use iterator methods Remember that the first value in the return value of `env::args` is the name of the program. We want to ignore that and get to the next value, so first we call -`next` and do nothing with the return value. Then we call `next` to get the +`next` and do nothing with the return value. Then, we call `next` to get the value we want to put in the `query` field of `Config`. If `next` returns `Some`, we use a `match` to extract the value. If it returns `None`, it means -not enough arguments were given and we return early with an `Err` value. We do -the same thing for the `filename` value. +not enough arguments were given, and we return early with an `Err` value. We do +the same thing for the `file_path` value. -### Making Code Clearer with Iterator Adapters + + + + +### Clarifying Code with Iterator Adapters We can also take advantage of iterators in the `search` function in our I/O project, which is reproduced here in Listing 13-21 as it was in Listing 12-19. -Filename: src/lib.rs +src/lib.rs ``` -pub fn search<'a>( - query: &str, - contents: &'a str, -) -> Vec<&'a str> { +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { let mut results = Vec::new(); for line in contents.lines() { @@ -1138,13 +1215,10 @@ make code clearer. Removing the mutable state might enable a future enhancement to make searching happen in parallel because we wouldn’t have to manage concurrent access to the `results` vector. Listing 13-22 shows this change. -Filename: src/lib.rs +src/lib.rs ``` -pub fn search<'a>( - query: &str, - contents: &'a str, -) -> Vec<&'a str> { +pub fn search<'a>(query: &str, contents: &'a str) -> Vec<&'a str> { contents .lines() .filter(|line| line.contains(query)) @@ -1152,8 +1226,7 @@ pub fn search<'a>( } ``` -Listing 13-22: Using iterator adapter methods in the implementation of the -`search` function +Listing 13-22: Using iterator adapter methods in the implementation of the `search` function Recall that the purpose of the `search` function is to return all lines in `contents` that contain the `query`. Similar to the `filter` example in Listing @@ -1162,23 +1235,41 @@ Recall that the purpose of the `search` function is to return all lines in another vector with `collect`. Much simpler! Feel free to make the same change to use iterator methods in the `search_case_insensitive` function as well. +For a further improvement, return an iterator from the `search` function by +removing the call to `collect` and changing the return type to `impl Iterator` so that the function becomes an iterator adapter. +Note that you’ll also need to update the tests! Search through a large file +using your `minigrep` tool before and after making this change to observe the +difference in behavior. Before this change, the program won’t print any results +until it has collected all of the results, but after the change, the results +will be printed as each matching line is found because the `for` loop in the +`run` function is able to take advantage of the laziness of the iterator. + + + + + ### Choosing Between Loops and Iterators The next logical question is which style you should choose in your own code and why: the original implementation in Listing 13-21 or the version using -iterators in Listing 13-22. Most Rust programmers prefer to use the iterator -style. It’s a bit tougher to get the hang of at first, but once you get a feel -for the various iterator adapters and what they do, iterators can be easier to -understand. Instead of fiddling with the various bits of looping and building -new vectors, the code focuses on the high-level objective of the loop. This -abstracts away some of the commonplace code so it’s easier to see the concepts -that are unique to this code, such as the filtering condition each element in -the iterator must pass. +iterators in Listing 13-22 (assuming we’re collecting all the results before +returning them rather than returning the iterator). Most Rust programmers +prefer to use the iterator style. It’s a bit tougher to get the hang of at +first, but once you get a feel for the various iterator adapters and what they +do, iterators can be easier to understand. Instead of fiddling with the various +bits of looping and building new vectors, the code focuses on the high-level +objective of the loop. This abstracts away some of the commonplace code so that +it’s easier to see the concepts that are unique to this code, such as the +filtering condition each element in the iterator must pass. But are the two implementations truly equivalent? The intuitive assumption might be that the lower-level loop will be faster. Let’s talk about performance. -## Comparing Performance: Loops vs. Iterators + + + + +## Performance in Loops vs. Iterators To determine whether to use loops or iterators, you need to know which implementation is faster: the version of the `search` function with an explicit @@ -1194,70 +1285,31 @@ test bench_search_for ... bench: 19,620,300 ns/iter (+/- 915,700) test bench_search_iter ... bench: 19,234,900 ns/iter (+/- 657,200) ``` -The iterator version was slightly faster! We won’t explain the benchmark code -here because the point is not to prove that the two versions are equivalent but -to get a general sense of how these two implementations compare -performance-wise. +The two implementations have similar performance! We won’t explain the +benchmark code here because the point is not to prove that the two versions +are equivalent but to get a general sense of how these two implementations +compare performance-wise. For a more comprehensive benchmark, you should check using various texts of various sizes as the `contents`, different words and words of different lengths as the `query`, and all kinds of other variations. The point is this: -iterators, although a high-level abstraction, get compiled down to roughly the +Iterators, although a high-level abstraction, get compiled down to roughly the same code as if you’d written the lower-level code yourself. Iterators are one of Rust’s *zero-cost abstractions*, by which we mean that using the abstraction imposes no additional runtime overhead. This is analogous to how Bjarne Stroustrup, the original designer and implementor of C++, defines -*zero-overhead* in “Foundations of C++” (2012): +zero-overhead in his 2012 ETAPS keynote presentation “Foundations of C++”: > In general, C++ implementations obey the zero-overhead principle: What you -don’t use, you don’t pay for. And further: What you do use, you couldn’t hand -code any better.As another example, the following code is taken from an audio -decoder. The decoding algorithm uses the linear prediction mathematical -operation to estimate future values based on a linear function of the previous -samples. This code uses an iterator chain to do some math on three variables in -scope: a `buffer` slice of data, an array of 12 `coefficients`, and an amount -by which to shift data in `qlp_shift`. We’ve declared the variables within this -example but not given them any values; although this code doesn’t have much -meaning outside of its context, it’s still a concise, real-world example of how -Rust translates high-level ideas to low-level code. - -``` -let buffer: &mut [i32]; -let coefficients: [i64; 12]; -let qlp_shift: i16; - -for i in 12..buffer.len() { - let prediction = coefficients.iter() - .zip(&buffer[i - 12..i]) - .map(|(&c, &s)| c * s as i64) - .sum::() >> qlp_shift; - let delta = buffer[i]; - buffer[i] = prediction as i32 + delta; -} -``` +> don’t use, you don’t pay for. And further: What you do use, you couldn’t hand +> code any better. -To calculate the value of `prediction`, this code iterates through each of the -12 values in `coefficients` and uses the `zip` method to pair the coefficient -values with the previous 12 values in `buffer`. Then, for each pair, it -multiplies the values together, sums all the results, and shifts the bits in -the sum `qlp_shift` bits to the right. - -Calculations in applications like audio decoders often prioritize performance -most highly. Here, we’re creating an iterator, using two adapters, and then -consuming the value. What assembly code would this Rust code compile to? Well, -as of this writing, it compiles down to the same assembly you’d write by hand. -There’s no loop at all corresponding to the iteration over the values in -`coefficients`: Rust knows that there are 12 iterations, so it “unrolls” the -loop. *Unrolling* is an optimization that removes the overhead of the loop -controlling code and instead generates repetitive code for each iteration of -the loop. - -All of the coefficients get stored in registers, which means accessing the -values is very fast. There are no bounds checks on the array access at runtime. -All of these optimizations that Rust is able to apply make the resultant code -extremely efficient. Now that you know this, you can use iterators and closures -without fear! They make code seem like it’s higher level but don’t impose a -runtime performance penalty for doing so. +In many cases, Rust code using iterators compiles to the same assembly you’d +write by hand. Optimizations such as loop unrolling and eliminating bounds +checking on array access apply and make the resultant code extremely efficient. +Now that you know this, you can use iterators and closures without fear! They +make code seem like it’s higher level but don’t impose a runtime performance +penalty for doing so. ## Summary @@ -1270,4 +1322,3 @@ Rust’s goal to strive to provide zero-cost abstractions. Now that we’ve improved the expressiveness of our I/O project, let’s look at some more features of `cargo` that will help us share the project with the world. - diff --git a/nostarch/chapter14.md b/nostarch/chapter14.md index f5f2be7196..e376fe0109 100644 --- a/nostarch/chapter14.md +++ b/nostarch/chapter14.md @@ -13,34 +13,38 @@ test our code, but it can do a lot more. In this chapter, we’ll discuss some o its other, more advanced features to show you how to do the following: * Customize your build through release profiles. -* Publish libraries on *https://crates.i**o*. +* Publish libraries on crates.io. * Organize large projects with workspaces. -* Install binaries from *https://crates.io*. +* Install binaries from crates.io. * Extend Cargo using custom commands. Cargo can do even more than the functionality we cover in this chapter, so for -a full explanation of all its features, see its documentation at -*https://doc.rust-lang.org/cargo*. +a full explanation of all its features, see its documentation at *https://doc.rust-lang.org/cargo/*. ## Customizing Builds with Release Profiles -In Rust, *release profiles* are predefined and customizable profiles with +In Rust, *release profiles* are predefined, customizable profiles with different configurations that allow a programmer to have more control over various options for compiling code. Each profile is configured independently of the others. -Cargo has two main profiles: the `dev` profile Cargo uses when you run `cargo -build`, and the `release` profile Cargo uses when you run `cargo build ---release`. The `dev` profile is defined with good defaults for development, +Cargo has two main profiles: the `dev` profile Cargo uses when you run `cargo build`, and the `release` profile Cargo uses when you run `cargo build --release`. The `dev` profile is defined with good defaults for development, and the `release` profile has good defaults for release builds. These profile names might be familiar from the output of your builds: + + ``` $ cargo build - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s $ cargo build --release - Finished release [optimized] target(s) in 0.0s + Finished `release` profile [optimized] target(s) in 0.32s ``` The `dev` and `release` are these different profiles used by the compiler. @@ -89,15 +93,15 @@ Cargo will use the defaults for the `dev` profile plus our customization to optimizations than the default, but not as many as in a release build. For the full list of configuration options and defaults for each profile, see -Cargo’s documentation at -*https://doc.rust-lang.org/cargo/reference/profiles.html*. +Cargo’s documentation at *https://doc.rust-lang.org/cargo/reference/profiles.html*. ## Publishing a Crate to Crates.io -We’ve used packages from *https://crates.io* as dependencies of our project, -but you can also share your code with other people by publishing your own -packages. The crate registry at *https://crates.io* distributes the source code -of your packages, so it primarily hosts code that is open source. +We’ve used packages from crates.io as +dependencies of our project, but you can also share your code with other people +by publishing your own packages. The crate registry at +crates.io distributes the source code of +your packages, so it primarily hosts code that is open source. Rust and Cargo have features that make your published package easier for people to find and use. We’ll talk about some of these features next and then explain @@ -119,7 +123,7 @@ Markdown notation for formatting the text. Place documentation comments just before the item they’re documenting. Listing 14-1 shows documentation comments for an `add_one` function in a crate named `my_crate`. -Filename: src/lib.rs +src/lib.rs ``` /// Adds one to the number given. @@ -152,7 +156,10 @@ crate’s dependencies) and open the result in a web browser. Navigate to the `add_one` function and you’ll see how the text in the documentation comments is rendered, as shown in Figure 14-1. -Figure 14-1: HTML documentation for the `add_one` function +Rendered HTML documentation for the `add_one` function of `my_crate` + +Figure 14-1: The HTML documentation for the `add_one` +function #### Commonly Used Sections @@ -160,16 +167,16 @@ We used the `# Examples` Markdown heading in Listing 14-1 to create a section in the HTML with the title “Examples.” Here are some other sections that crate authors commonly use in their documentation: -* **Panics**: The scenarios in which the function being documented could panic. -Callers of the function who don’t want their programs to panic should make sure -they don’t call the function in these situations. +* **Panics**: These are the scenarios in which the function being documented + could panic. Callers of the function who don’t want their programs to panic + should make sure they don’t call the function in these situations. * **Errors**: If the function returns a `Result`, describing the kinds of -errors that might occur and what conditions might cause those errors to be -returned can be helpful to callers so they can write code to handle the -different kinds of errors in different ways. + errors that might occur and what conditions might cause those errors to be + returned can be helpful to callers so that they can write code to handle the + different kinds of errors in different ways. * **Safety**: If the function is `unsafe` to call (we discuss unsafety in -Chapter 19), there should be a section explaining why the function is unsafe -and covering the invariants that the function expects callers to uphold. + Chapter 20), there should be a section explaining why the function is unsafe + and covering the invariants that the function expects callers to uphold. Most documentation comments don’t need all of these sections, but this is a good checklist to remind you of the aspects of your code users will be @@ -178,13 +185,18 @@ interested in knowing about. #### Documentation Comments as Tests Adding example code blocks in your documentation comments can help demonstrate -how to use your library, and doing so has an additional bonus: running `cargo -test` will run the code examples in your documentation as tests! Nothing is -better than documentation with examples. But nothing is worse than examples -that don’t work because the code has changed since the documentation was -written. If we run `cargo test` with the documentation for the `add_one` -function from Listing 14-1, we will see a section in the test results that -looks like this: +how to use your library and has an additional bonus: Running `cargo test` will +run the code examples in your documentation as tests! Nothing is better than +documentation with examples. But nothing is worse than examples that don’t work +because the code has changed since the documentation was written. If we run +`cargo test` with the documentation for the `add_one` function from Listing +14-1, we will see a section in the test results that looks like this: + + ``` Doc-tests my_crate @@ -192,39 +204,42 @@ looks like this: running 1 test test src/lib.rs - add_one (line 5) ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 -filtered out; finished in 0.27s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.27s ``` -Now, if we change either the function or the example so the `assert_eq!` in the -example panics and run `cargo test` again, we’ll see that the doc tests catch -that the example and the code are out of sync with each other! +Now, if we change either the function or the example so that the `assert_eq!` +in the example panics, and run `cargo test` again, we’ll see that the doc tests +catch that the example and the code are out of sync with each other! + + -#### Commenting Contained Items + -The doc comment `//!` adds documentation to the item that *contains* the -comments rather than to the items *following* the comments. We typically use -these doc comments inside the crate root file (*src/lib.rs* by convention) or -inside a module to document the crate or the module as a whole. +#### Contained Item Comments + +The style of doc comment `//!` adds documentation to the item that *contains* +the comments rather than to the items *following* the comments. We typically +use these doc comments inside the crate root file (*src/lib.rs* by convention) +or inside a module to document the crate or the module as a whole. For example, to add documentation that describes the purpose of the `my_crate` crate that contains the `add_one` function, we add documentation comments that start with `//!` to the beginning of the *src/lib.rs* file, as shown in Listing 14-2. -Filename: src/lib.rs +src/lib.rs ``` //! # My Crate //! -//! `my_crate` is a collection of utilities to make performing -//! certain calculations more convenient. +//! `my_crate` is a collection of utilities to make performing certain +//! calculations more convenient. /// Adds one to the number given. ---snip-- +// --snip-- ``` -Listing 14-2: Documentation for the `my_crate` crate as a whole +Listing 14-2: The documentation for the `my_crate` crate as a whole Notice there isn’t any code after the last line that begins with `//!`. Because we started the comments with `//!` instead of `///`, we’re documenting the item @@ -236,14 +251,20 @@ When we run `cargo doc --open`, these comments will display on the front page of the documentation for `my_crate` above the list of public items in the crate, as shown in Figure 14-2. -Figure 14-2: Rendered documentation for `my_crate`, including the comment -describing the crate as a whole - Documentation comments within items are useful for describing crates and modules especially. Use them to explain the overall purpose of the container to help your users understand the crate’s organization. -### Exporting a Convenient Public API with pub use +Rendered HTML documentation with a comment for the crate as a whole + +Figure 14-2: The rendered documentation for `my_crate`, +including the comment describing the crate as a whole + + + + + +### Exporting a Convenient Public API The structure of your public API is a major consideration when publishing a crate. People who use your crate are less familiar with the structure than you @@ -256,13 +277,11 @@ that makes sense to you while you’re developing a crate might not be very convenient for your users. You might want to organize your structs in a hierarchy containing multiple levels, but then people who want to use a type you’ve defined deep in the hierarchy might have trouble finding out that type -exists. They might also be annoyed at having to enter `use` -`my_crate::`some_module`::`another_module`::`UsefulType`;` rather than `use` -`my_crate::`UsefulType`;`. +exists. They might also be annoyed at having to enter `use my_crate::some_module::another_module::UsefulType;` rather than `use my_crate::UsefulType;`. The good news is that if the structure *isn’t* convenient for others to use from another library, you don’t have to rearrange your internal organization: -instead, you can re-export items to make a public structure that’s different +Instead, you can re-export items to make a public structure that’s different from your private structure by using `pub use`. *Re-exporting* takes a public item in one location and makes it public in another location, as if it were defined in the other location instead. @@ -272,7 +291,7 @@ Within this library are two modules: a `kinds` module containing two enums named `PrimaryColor` and `SecondaryColor` and a `utils` module containing a function named `mix`, as shown in Listing 14-3. -Filename: src/lib.rs +src/lib.rs ``` //! # Art @@ -300,23 +319,21 @@ pub mod utils { /// Combines two primary colors in equal amounts to create /// a secondary color. - pub fn mix( - c1: PrimaryColor, - c2: PrimaryColor, - ) -> SecondaryColor { - --snip-- + pub fn mix(c1: PrimaryColor, c2: PrimaryColor) -> SecondaryColor { + // --snip-- } } ``` -Listing 14-3: An `art` library with items organized into `kinds` and `utils` -modules +Listing 14-3: An `art` library with items organized into `kinds` and `utils` modules Figure 14-3 shows what the front page of the documentation for this crate generated by `cargo doc` would look like. -Figure 14-3: Front page of the documentation for `art` that lists the `kinds` -and `utils` modules +Rendered documentation for the `art` crate that lists the `kinds` and `utils` modules + +Figure 14-3: The front page of the documentation for `art` +that lists the `kinds` and `utils` modules Note that the `PrimaryColor` and `SecondaryColor` types aren’t listed on the front page, nor is the `mix` function. We have to click `kinds` and `utils` to @@ -327,7 +344,7 @@ bring the items from `art` into scope, specifying the module structure that’s currently defined. Listing 14-4 shows an example of a crate that uses the `PrimaryColor` and `mix` items from the `art` crate. -Filename: src/main.rs +src/main.rs ``` use art::kinds::PrimaryColor; @@ -340,8 +357,7 @@ fn main() { } ``` -Listing 14-4: A crate using the `art` crate’s items with its internal structure -exported +Listing 14-4: A crate using the `art` crate’s items with its internal structure exported The author of the code in Listing 14-4, which uses the `art` crate, had to figure out that `PrimaryColor` is in the `kinds` module and `mix` is in the @@ -356,7 +372,7 @@ To remove the internal organization from the public API, we can modify the `art` crate code in Listing 14-3 to add `pub use` statements to re-export the items at the top level, as shown in Listing 14-5. -Filename: src/lib.rs +src/lib.rs ``` //! # Art @@ -368,11 +384,11 @@ pub use self::kinds::SecondaryColor; pub use self::utils::mix; pub mod kinds { - --snip-- + // --snip-- } pub mod utils { - --snip-- + // --snip-- } ``` @@ -382,21 +398,23 @@ The API documentation that `cargo doc` generates for this crate will now list and link re-exports on the front page, as shown in Figure 14-4, making the `PrimaryColor` and `SecondaryColor` types and the `mix` function easier to find. -Figure 14-4: The front page of the documentation for `art` that lists the -re-exports +Rendered documentation for the `art` crate with the re-exports on the front page + +Figure 14-4: The front page of the documentation for `art` +that lists the re-exports The `art` crate users can still see and use the internal structure from Listing 14-3 as demonstrated in Listing 14-4, or they can use the more convenient structure in Listing 14-5, as shown in Listing 14-6. -Filename: src/main.rs +src/main.rs ``` -use art::mix; use art::PrimaryColor; +use art::mix; fn main() { - --snip-- + // --snip-- } ``` @@ -408,31 +426,33 @@ people who use the crate. Another common use of `pub use` is to re-export definitions of a dependency in the current crate to make that crate’s definitions part of your crate’s public API. -Creating a useful public API structure is more of an art than a science, and -you can iterate to find the API that works best for your users. Choosing `pub -use` gives you flexibility in how you structure your crate internally and -decouples that internal structure from what you present to your users. Look at -some of the code of crates you’ve installed to see if their internal structure -differs from their public API. +Creating a useful public API structure is more an art than a science, and you +can iterate to find the API that works best for your users. Choosing `pub use` +gives you flexibility in how you structure your crate internally and decouples +that internal structure from what you present to your users. Look at some of +the code of crates you’ve installed to see if their internal structure differs +from their public API. ### Setting Up a Crates.io Account Before you can publish any crates, you need to create an account on -*https://crates.io* and get an API token. To do so, visit the home page at -*https://crates.io* and log in via a GitHub account. (The GitHub account is -currently a requirement, but the site might support other ways of creating an -account in the future.) Once you’re logged in, visit your account settings at -*https://crates.io/me* and retrieve your API key. Then run the `cargo login` -command with your API key, like this: +crates.io and get an API token. To do so, +visit the home page at crates.io and log +in via a GitHub account. (The GitHub account is currently a requirement, but +the site might support other ways of creating an account in the future.) Once +you’re logged in, visit your account settings at +https://crates.io/me/ and retrieve your +API key. Then, run the `cargo login` command and paste your API key when prompted, like this: ``` -$ cargo login abcdefghijklmnopqrstuvwxyz012345 +$ cargo login +abcdefghijklmnopqrstuvwxyz012345 ``` This command will inform Cargo of your API token and store it locally in -*~/.cargo/credentials*. Note that this token is a *secret*: do not share it -with anyone else. If you do share it with anyone for any reason, you should -revoke it and generate a new token on *https://crates.io*. +*~/.cargo/credentials.toml*. Note that this token is a secret: Do not share +it with anyone else. If you do share it with anyone for any reason, you should +revoke it and generate a new token on crates.io. ### Adding Metadata to a New Crate @@ -442,12 +462,12 @@ file. Your crate will need a unique name. While you’re working on a crate locally, you can name a crate whatever you’d like. However, crate names on -*https://crates.io* are allocated on a first-come, first-served basis. Once a -crate name is taken, no one else can publish a crate with that name. Before -attempting to publish a crate, search for the name you want to use. If the name -has been used, you will need to find another name and edit the `name` field in -the *Cargo.toml* file under the `[package]` section to use the new name for -publishing, like so: +crates.io are allocated on a first-come, +first-served basis. Once a crate name is taken, no one else can publish a crate +with that name. Before attempting to publish a crate, search for the name you +want to use. If the name has been used, you will need to find another name and +edit the `name` field in the *Cargo.toml* file under the `[package]` section to +use the new name for publishing, like so: Filename: Cargo.toml @@ -459,31 +479,33 @@ name = "guessing_game" Even if you’ve chosen a unique name, when you run `cargo publish` to publish the crate at this point, you’ll get a warning and then an error: + + ``` $ cargo publish Updating crates.io index -warning: manifest has no description, license, license-file, documentation, -homepage or repository. -See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata -for more info. +warning: manifest has no description, license, license-file, documentation, homepage or repository. +See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info. --snip-- error: failed to publish to registry at https://crates.io Caused by: - the remote server responded with an error: missing or empty metadata fields: -description, license. Please see https://doc.rust- -lang.org/cargo/reference/manifest.html for how to upload metadata + the remote server responded with an error (status 400 Bad Request): missing or empty metadata fields: description, license. Please see https://doc.rust-lang.org/cargo/reference/manifest.html for more information on configuring these fields ``` -This results in an error because you’re missing some crucial information: a -description and license are required so people will know what your crate does -and under what terms they can use it. In *Cargo.toml*, add a description that’s -just a sentence or two, because it will appear with your crate in search +This results in an error because you’re missing some crucial information: A +description and license are required so that people will know what your crate +does and under what terms they can use it. In *Cargo.toml*, add a description +that’s just a sentence or two, because it will appear with your crate in search results. For the `license` field, you need to give a *license identifier -value*. The Linux Foundation’s Software Package Data Exchange (SPDX) at -*http://spdx.org/licenses* lists the identifiers you can use for this value. -For example, to specify that you’ve licensed your crate using the MIT License, -add the `MIT` identifier: +value*. The Linux Foundation’s Software Package Data Exchange (SPDX) at *https://spdx.org/licenses/* +lists the identifiers you can use for this value. For example, to specify that +you’ve licensed your crate using the MIT License, add the `MIT` identifier: Filename: Cargo.toml @@ -513,15 +535,14 @@ Filename: Cargo.toml [package] name = "guessing_game" version = "0.1.0" -edition = "2021" -description = "A fun game where you guess what number the -computer has chosen." +edition = "2024" +description = "A fun game where you guess what number the computer has chosen." license = "MIT OR Apache-2.0" [dependencies] ``` -Cargo’s documentation at *https://doc.rust-lang.org/cargo* describes other +Cargo’s documentation at *https://doc.rust-lang.org/cargo/* describes other metadata you can specify to ensure that others can discover and use your crate more easily. @@ -529,27 +550,40 @@ more easily. Now that you’ve created an account, saved your API token, chosen a name for your crate, and specified the required metadata, you’re ready to publish! -Publishing a crate uploads a specific version to *https://crates.io* for others -to use. +Publishing a crate uploads a specific version to +crates.io for others to use. Be careful, because a publish is *permanent*. The version can never be -overwritten, and the code cannot be deleted. One major goal of Crates.io is to -act as a permanent archive of code so that builds of all projects that depend -on crates from *https://crates.io* will continue to work. Allowing version -deletions would make fulfilling that goal impossible. However, there is no -limit to the number of crate versions you can publish. +overwritten, and the code cannot be deleted except in certain circumstances. +One major goal of Crates.io is to act as a permanent archive of code so that +builds of all projects that depend on crates from +crates.io will continue to work. Allowing +version deletions would make fulfilling that goal impossible. However, there is +no limit to the number of crate versions you can publish. Run the `cargo publish` command again. It should succeed now: + + ``` $ cargo publish Updating crates.io index Packaging guessing_game v0.1.0 (file:///projects/guessing_game) + Packaged 6 files, 1.2KiB (895.0B compressed) Verifying guessing_game v0.1.0 (file:///projects/guessing_game) Compiling guessing_game v0.1.0 (file:///projects/guessing_game/target/package/guessing_game-0.1.0) - Finished dev [unoptimized + debuginfo] target(s) in 0.19s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.19s Uploading guessing_game v0.1.0 (file:///projects/guessing_game) + Uploaded guessing_game v0.1.0 to registry `crates-io` +note: waiting for `guessing_game v0.1.0` to be available at registry +`crates-io`. +You may press ctrl-c to skip waiting; the crate should be available shortly. + Published guessing_game v0.1.0 at registry `crates-io` ``` Congratulations! You’ve now shared your code with the Rust community, and @@ -559,11 +593,16 @@ anyone can easily add your crate as a dependency of their project. When you’ve made changes to your crate and are ready to release a new version, you change the `version` value specified in your *Cargo.toml* file and -republish. Use the Semantic Versioning rules at *http://semver.org* to decide -what an appropriate next version number is, based on the kinds of changes -you’ve made. Then run `cargo publish` to upload the new version. +republish. Use the Semantic Versioning rules at *https://semver.org/* to decide what an +appropriate next version number is, based on the kinds of changes you’ve made. +Then, run `cargo publish` to upload the new version. + + + + + -### Deprecating Versions from Crates.io with cargo yank +### Deprecating Versions from Crates.io Although you can’t remove previous versions of a crate, you can prevent any future projects from adding them as a new dependency. This is useful when a @@ -578,8 +617,13 @@ yank means that all projects with a *Cargo.lock* will not break, and any future To yank a version of a crate, in the directory of the crate that you’ve previously published, run `cargo yank` and specify which version you want to yank. For example, if we’ve published a crate named `guessing_game` version -1.0.1 and we want to yank it, in the project directory for `guessing_game` we’d -run: +1.0.1 and we want to yank it, then we’d run the following in the project +directory for `guessing_game`: + + ``` $ cargo yank --vers 1.0.1 @@ -610,9 +654,9 @@ help manage multiple related packages that are developed in tandem. ### Creating a Workspace A *workspace* is a set of packages that share the same *Cargo.lock* and output -directory. Let’s make a project using a workspace—we’ll use trivial code so we -can concentrate on the structure of the workspace. There are multiple ways to -structure a workspace, so we’ll just show one common way. We’ll have a +directory. Let’s make a project using a workspace—we’ll use trivial code so +that we can concentrate on the structure of the workspace. There are multiple +ways to structure a workspace, so we’ll just show one common way. We’ll have a workspace containing a binary and two libraries. The binary, which will provide the main functionality, will depend on the two libraries. One library will provide an `add_one` function and the other library an `add_two` function. @@ -627,25 +671,42 @@ $ cd add Next, in the *add* directory, we create the *Cargo.toml* file that will configure the entire workspace. This file won’t have a `[package]` section. Instead, it will start with a `[workspace]` section that will allow us to add -members to the workspace by specifying the path to the package with our binary -crate; in this case, that path is *adder*: +members to the workspace. We also make a point to use the latest and greatest +version of Cargo’s resolver algorithm in our workspace by setting the +`resolver` value to `"3"`: Filename: Cargo.toml ``` [workspace] - -members = [ - "adder", -] +resolver = "3" ``` Next, we’ll create the `adder` binary crate by running `cargo new` within the *add* directory: + + ``` $ cargo new adder Created binary (application) `adder` package + Adding `adder` as member of workspace at `file:///projects/add` +``` + +Running `cargo new` inside a workspace also automatically adds the newly created +package to the `members` key in the `[workspace]` definition in the workspace +*Cargo.toml*, like this: + +``` +[workspace] +resolver = "3" +members = ["adder"] ``` At this point, we can build the workspace by running `cargo build`. The files @@ -675,25 +736,31 @@ can avoid unnecessary rebuilding. ### Creating the Second Package in the Workspace Next, let’s create another member package in the workspace and call it -`add_one`. Change the top-level *Cargo.toml* to specify the *add_one* path in -the `members` list: - -Filename: Cargo.toml +`add_one`. Generate a new library crate named `add_one`: + + ``` -[workspace] - -members = [ - "adder", - "add_one", -] +$ cargo new add_one --lib + Created library `add_one` package + Adding `add_one` as member of workspace at `file:///projects/add` ``` -Then generate a new library crate named `add_one`: +The top-level *Cargo.toml* will now include the *add_one* path in the `members` +list: + +Filename: Cargo.toml ``` -$ cargo new add_one --lib - Created library `add_one` package +[workspace] +resolver = "3" +members = ["adder", "add_one"] ``` Your *add* directory should now have these directories and files: @@ -723,8 +790,8 @@ pub fn add_one(x: i32) -> i32 { ``` Now we can have the `adder` package with our binary depend on the `add_one` -package that has our library. First we’ll need to add a path dependency on -`add_one` to *adder/Cargo.toml*: +package that has our library. First, we’ll need to add a path dependency on +`add_one` to *adder/Cargo.toml*. Filename: adder/Cargo.toml @@ -737,21 +804,15 @@ Cargo doesn’t assume that crates in a workspace will depend on each other, so we need to be explicit about the dependency relationships. Next, let’s use the `add_one` function (from the `add_one` crate) in the -`adder` crate. Open the *adder/src/main.rs* file and add a `use` line at the -top to bring the new `add_one` library crate into scope. Then change the `main` +`adder` crate. Open the *adder/src/main.rs* file and change the `main` function to call the `add_one` function, as in Listing 14-7. -Filename: adder/src/main.rs +adder/src/main.rs ``` -use add_one; - fn main() { let num = 10; - println!( - "Hello, world! {num} plus one is {}!", - add_one::add_one(num) - ); + println!("Hello, world! {num} plus one is {}!", add_one::add_one(num)); } ``` @@ -760,27 +821,43 @@ Listing 14-7: Using the `add_one` library crate from the `adder` crate Let’s build the workspace by running `cargo build` in the top-level *add* directory! + + ``` $ cargo build Compiling add_one v0.1.0 (file:///projects/add/add_one) Compiling adder v0.1.0 (file:///projects/add/adder) - Finished dev [unoptimized + debuginfo] target(s) in 0.68s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s ``` To run the binary crate from the *add* directory, we can specify which package in the workspace we want to run by using the `-p` argument and the package name with `cargo run`: + + ``` $ cargo run -p adder - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s Running `target/debug/adder` Hello, world! 10 plus one is 11! ``` This runs the code in *adder/src/main.rs*, which depends on the `add_one` crate. -#### Depending on an External Package in a Workspace + + + + +### Depending on an External Package Notice that the workspace has only one *Cargo.lock* file at the top level, rather than having a *Cargo.lock* in each crate’s directory. This ensures that @@ -790,7 +867,13 @@ resolve both of those to one version of `rand` and record that in the one *Cargo.lock*. Making all crates in the workspace use the same dependencies means the crates will always be compatible with each other. Let’s add the `rand` crate to the `[dependencies]` section in the *add_one/Cargo.toml* file -so we can use the `rand` crate in the `add_one` crate: +so that we can use the `rand` crate in the `add_one` crate: + + Filename: add_one/Cargo.toml @@ -804,6 +887,12 @@ whole workspace by running `cargo build` in the *add* directory will bring in and compile the `rand` crate. We will get one warning because we aren’t referring to the `rand` we brought into scope: + + ``` $ cargo build Updating crates.io index @@ -811,8 +900,17 @@ $ cargo build --snip-- Compiling rand v0.8.5 Compiling add_one v0.1.0 (file:///projects/add/add_one) +warning: unused import: `rand` + --> add_one/src/lib.rs:1:5 + | +1 | use rand; + | ^^^^ + | + = note: `#[warn(unused_imports)]` on by default + +warning: `add_one` (lib) generated 1 warning (run `cargo fix --lib -p add_one` to apply 1 suggestion) Compiling adder v0.1.0 (file:///projects/add/adder) - Finished dev [unoptimized + debuginfo] target(s) in 10.18s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.95s ``` The top-level *Cargo.lock* now contains information about the dependency of @@ -821,9 +919,15 @@ workspace, we can’t use it in other crates in the workspace unless we add `rand` to their *Cargo.toml* files as well. For example, if we add `use rand;` to the *adder/src/main.rs* file for the `adder` package, we’ll get an error: + + ``` $ cargo build - --snip-- + --snip-- Compiling adder v0.1.0 (file:///projects/add/adder) error[E0432]: unresolved import `rand` --> adder/src/main.rs:2:5 @@ -835,12 +939,17 @@ error[E0432]: unresolved import `rand` To fix this, edit the *Cargo.toml* file for the `adder` package and indicate that `rand` is a dependency for it as well. Building the `adder` package will add `rand` to the list of dependencies for `adder` in *Cargo.lock*, but no -additional copies of `rand` will be downloaded. Cargo has ensured that every -crate in every package in the workspace using the `rand` package will be using -the same version, saving us space and ensuring that the crates in the workspace -will be compatible with each other. +additional copies of `rand` will be downloaded. Cargo will ensure that every +crate in every package in the workspace using the `rand` package will use the +same version as long as they specify compatible versions of `rand`, saving us +space and ensuring that the crates in the workspace will be compatible with +each other. + +If crates in the workspace specify incompatible versions of the same +dependency, Cargo will resolve each of them but will still try to resolve as +few versions as possible. -#### Adding a Test to a Workspace +### Adding a Test to a Workspace For another enhancement, let’s add a test of the `add_one::add_one` function within the `add_one` crate: @@ -867,111 +976,129 @@ Now run `cargo test` in the top-level *add* directory. Running `cargo test` in a workspace structured like this one will run the tests for all the crates in the workspace: + + ``` $ cargo test Compiling add_one v0.1.0 (file:///projects/add/add_one) Compiling adder v0.1.0 (file:///projects/add/adder) - Finished test [unoptimized + debuginfo] target(s) in 0.27s - Running unittests src/lib.rs (target/debug/deps/add_one-f0253159197f7841) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.20s + Running unittests src/lib.rs (target/debug/deps/add_one-93c49ee75dc46543) running 1 test test tests::it_works ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; -finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s - Running unittests src/main.rs (target/debug/deps/adder-49979ff40686fa8e) + Running unittests src/main.rs (target/debug/deps/adder-3a47283c568d2b6a) running 0 tests -test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; -finished in 0.00s +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s Doc-tests add_one running 0 tests -test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; -finished in 0.00s +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s ``` The first section of the output shows that the `it_works` test in the `add_one` crate passed. The next section shows that zero tests were found in the `adder` -crate, and then the last section shows zero documentation tests were found in -the `add_one` crate. +crate, and then the last section shows that zero documentation tests were found +in the `add_one` crate. We can also run tests for one particular crate in a workspace from the top-level directory by using the `-p` flag and specifying the name of the crate we want to test: + + ``` $ cargo test -p add_one - Finished test [unoptimized + debuginfo] target(s) in 0.00s - Running unittests src/lib.rs (target/debug/deps/add_one-b3235fea9a156f74) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.00s + Running unittests src/lib.rs (target/debug/deps/add_one-93c49ee75dc46543) running 1 test test tests::it_works ... ok -test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; -finished in 0.00s +test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s Doc-tests add_one running 0 tests -test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; -finished in 0.00s +test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s ``` This output shows `cargo test` only ran the tests for the `add_one` crate and didn’t run the `adder` crate tests. -If you publish the crates in the workspace to *https://crates.io*, each crate -in the workspace will need to be published separately. Like `cargo test`, we -can publish a particular crate in our workspace by using the `-p` flag and -specifying the name of the crate we want to publish. +If you publish the crates in the workspace to +crates.io, each crate in the workspace +will need to be published separately. Like `cargo test`, we can publish a +particular crate in our workspace by using the `-p` flag and specifying the +name of the crate we want to publish. For additional practice, add an `add_two` crate to this workspace in a similar way as the `add_one` crate! -As your project grows, consider using a workspace: it provides -easier-to-understand, smaller, individual components than one big blob of code. +As your project grows, consider using a workspace: It enables you to work with +smaller, easier-to-understand components than one big blob of code. Furthermore, keeping the crates in a workspace can make coordination between crates easier if they are often changed at the same time. + + + + ## Installing Binaries with cargo install The `cargo install` command allows you to install and use binary crates locally. This isn’t intended to replace system packages; it’s meant to be a convenient way for Rust developers to install tools that others have shared on -*https://crates.io*. Note that you can only install packages that have binary -targets. A *binary target* is the runnable program that is created if the crate -has a *src/main.rs* file or another file specified as a binary, as opposed to a -library target that isn’t runnable on its own but is suitable for including -within other programs. Usually, crates have information in the *README* file -about whether a crate is a library, has a binary target, or both. +crates.io. Note that you can only install +packages that have binary targets. A *binary target* is the runnable program +that is created if the crate has a *src/main.rs* file or another file specified +as a binary, as opposed to a library target that isn’t runnable on its own but +is suitable for including within other programs. Usually, crates have +information in the README file about whether a crate is a library, has a +binary target, or both. All binaries installed with `cargo install` are stored in the installation root’s *bin* folder. If you installed Rust using *rustup.rs* and don’t have any custom configurations, this directory will be *$HOME/.cargo/bin*. Ensure that -directory is in your `$PATH` to be able to run programs you’ve installed with -`cargo install`. +this directory is in your `$PATH` to be able to run programs you’ve installed +with `cargo install`. For example, in Chapter 12 we mentioned that there’s a Rust implementation of the `grep` tool called `ripgrep` for searching files. To install `ripgrep`, we can run the following: + + ``` $ cargo install ripgrep Updating crates.io index - Downloaded ripgrep v13.0.0 - Downloaded 1 crate (243.3 KB) in 0.88s - Installing ripgrep v13.0.0 - --snip-- - Compiling ripgrep v13.0.0 - Finished release [optimized + debuginfo] target(s) in 3m 10s + Downloaded ripgrep v14.1.1 + Downloaded 1 crate (213.6 KB) in 0.40s + Installing ripgrep v14.1.1 +--snip-- + Compiling grep v0.3.2 + Finished `release` profile [optimized + debuginfo] target(s) in 6.73s Installing ~/.cargo/bin/rg - Installed package `ripgrep v13.0.0` (executable `rg`) + Installed package `ripgrep v14.1.1` (executable `rg`) ``` The second-to-last line of the output shows the location and the name of the @@ -981,19 +1108,17 @@ then run `rg --help` and start using a faster, Rustier tool for searching files! ## Extending Cargo with Custom Commands -Cargo is designed so you can extend it with new subcommands without having to -modify it. If a binary in your `$PATH` is named `cargo-something`, you can run -it as if it were a Cargo subcommand by running `cargo something`. Custom +Cargo is designed so that you can extend it with new subcommands without having +to modify it. If a binary in your `$PATH` is named `cargo-something`, you can +run it as if it were a Cargo subcommand by running `cargo something`. Custom commands like this are also listed when you run `cargo --list`. Being able to use `cargo install` to install extensions and then run them just like the built-in Cargo tools is a super-convenient benefit of Cargo’s design! ## Summary -Sharing code with Cargo and *https://crates.io* is part of what makes the Rust -ecosystem useful for many different tasks. Rust’s standard library is small and -stable, but crates are easy to share, use, and improve on a timeline different -from that of the language. Don’t be shy about sharing code that’s useful to you -on *https://crates.io*; it’s likely that it will be useful to someone else as -well! - +Sharing code with Cargo and crates.io is +part of what makes the Rust ecosystem useful for many different tasks. Rust’s +standard library is small and stable, but crates are easy to share, use, and +improve on a timeline different from that of the language. Don’t be shy about +sharing code that’s useful to you on crates.io; it’s likely that it will be useful to someone else as well! diff --git a/nostarch/chapter15.md b/nostarch/chapter15.md index c0e847da1c..a3e5c900a4 100644 --- a/nostarch/chapter15.md +++ b/nostarch/chapter15.md @@ -8,7 +8,7 @@ directory, so all fixes need to be made in `/src/`. # Smart Pointers -A *pointer* is a general concept for a variable that contains an address in +A pointer is a general concept for a variable that contains an address in memory. This address refers to, or “points at,” some other data. The most common kind of pointer in Rust is a reference, which you learned about in Chapter 4. References are indicated by the `&` symbol and borrow the value they @@ -17,7 +17,7 @@ data, and they have no overhead. *Smart pointers*, on the other hand, are data structures that act like a pointer but also have additional metadata and capabilities. The concept of -smart pointers isn’t unique to Rust: smart pointers originated in C++ and exist +smart pointers isn’t unique to Rust: Smart pointers originated in C++ and exist in other languages as well. Rust has a variety of smart pointers defined in the standard library that provide functionality beyond that provided by references. To explore the general concept, we’ll look at a couple of different examples of @@ -25,24 +25,17 @@ smart pointers, including a *reference counting* smart pointer type. This pointer enables you to allow data to have multiple owners by keeping track of the number of owners and, when no owners remain, cleaning up the data. -Rust, with its concept of ownership and borrowing, has an additional difference -between references and smart pointers: while references only borrow data, in -many cases smart pointers *own* the data they point to. - -Though we didn’t call them as such at the time, we’ve already encountered a few -smart pointers in this book, including `String` and `Vec` in Chapter 8. Both -of these types count as smart pointers because they own some memory and allow -you to manipulate it. They also have metadata and extra capabilities or -guarantees. `String`, for example, stores its capacity as metadata and has the -extra ability to ensure its data will always be valid UTF-8. +In Rust, with its concept of ownership and borrowing, there is an additional +difference between references and smart pointers: While references only borrow +data, in many cases smart pointers *own* the data they point to. Smart pointers are usually implemented using structs. Unlike an ordinary struct, smart pointers implement the `Deref` and `Drop` traits. The `Deref` trait allows an instance of the smart pointer struct to behave like a reference -so you can write your code to work with either references or smart pointers. -The `Drop` trait allows you to customize the code that’s run when an instance -of the smart pointer goes out of scope. In this chapter, we’ll discuss both -traits and demonstrate why they’re important to smart pointers. +so that you can write your code to work with either references or smart +pointers. The `Drop` trait allows you to customize the code that’s run when an +instance of the smart pointer goes out of scope. In this chapter, we’ll discuss +both of these traits and demonstrate why they’re important to smart pointers. Given that the smart pointer pattern is a general design pattern used frequently in Rust, this chapter won’t cover every existing smart pointer. Many @@ -52,50 +45,55 @@ cover the most common smart pointers in the standard library: * `Box`, for allocating values on the heap * `Rc`, a reference counting type that enables multiple ownership * `Ref` and `RefMut`, accessed through `RefCell`, a type that enforces -the borrowing rules at runtime instead of compile time + the borrowing rules at runtime instead of compile time In addition, we’ll cover the *interior mutability* pattern where an immutable type exposes an API for mutating an interior value. We’ll also discuss -*reference cycles*: how they can leak memory and how to prevent them. +reference cycles: how they can leak memory and how to prevent them. Let’s dive in! ## Using Box to Point to Data on the Heap -The most straightforward smart pointer is a *box*, whose type is written -`Box`. Boxes allow you to store data on the heap rather than the stack. What -remains on the stack is the pointer to the heap data. Refer to Chapter 4 to -review the difference between the stack and the heap. +The most straightforward smart pointer is a box, whose type is written +`Box`. *Boxes* allow you to store data on the heap rather than the stack. +What remains on the stack is the pointer to the heap data. Refer to Chapter 4 +to review the difference between the stack and the heap. Boxes don’t have performance overhead, other than storing their data on the heap instead of on the stack. But they don’t have many extra capabilities either. You’ll use them most often in these situations: -* When you have a type whose size can’t be known at compile time and you want -to use a value of that type in a context that requires an exact size -* When you have a large amount of data and you want to transfer ownership but -ensure the data won’t be copied when you do so -* When you want to own a value and you care only that it’s a type that -implements a particular trait rather than being of a specific type - -We’ll demonstrate the first situation in “Enabling Recursive Types with Boxes” -on page XX. In the second case, transferring ownership of a large amount of -data can take a long time because the data is copied around on the stack. To -improve performance in this situation, we can store the large amount of data on -the heap in a box. Then, only the small amount of pointer data is copied around -on the stack, while the data it references stays in one place on the heap. The -third case is known as a *trait object*, and “Using Trait Objects That Allow -for Values of Different Types” on page XX is devoted to that topic. So what you -learn here you’ll apply again in that section! - -### Using Box to Store Data on the Heap +* When you have a type whose size can’t be known at compile time, and you want + to use a value of that type in a context that requires an exact size +* When you have a large amount of data, and you want to transfer ownership but + ensure that the data won’t be copied when you do so +* When you want to own a value, and you care only that it’s a type that + implements a particular trait rather than being of a specific type + +We’ll demonstrate the first situation in “Enabling Recursive Types with +Boxes”. In the second +case, transferring ownership of a large amount of data can take a long time +because the data is copied around on the stack. To improve performance in this +situation, we can store the large amount of data on the heap in a box. Then, +only the small amount of pointer data is copied around on the stack, while the +data it references stays in one place on the heap. The third case is known as a +*trait object*, and “Using Trait Objects to Abstract over Shared +Behavior” in Chapter 18 is devoted to that +topic. So, what you learn here you’ll apply again in that section! + + + + + +### Storing Data on the Heap Before we discuss the heap storage use case for `Box`, we’ll cover the syntax and how to interact with values stored within a `Box`. Listing 15-1 shows how to use a box to store an `i32` value on the heap. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -108,7 +106,7 @@ Listing 15-1: Storing an `i32` value on the heap using a box We define the variable `b` to have the value of a `Box` that points to the value `5`, which is allocated on the heap. This program will print `b = 5`; in -this case, we can access the data in the box similar to how we would if this +this case, we can access the data in the box similarly to how we would if this data were on the stack. Just like any owned value, when a box goes out of scope, as `b` does at the end of `main`, it will be deallocated. The deallocation happens both for the box (stored on the stack) and the data it @@ -122,20 +120,24 @@ wouldn’t be allowed to define if we didn’t have boxes. ### Enabling Recursive Types with Boxes -A value of a *recursive type* can have another value of the same type as part -of itself. Recursive types pose an issue because at compile time Rust needs to -know how much space a type takes up. However, the nesting of values of -recursive types could theoretically continue infinitely, so Rust can’t know how -much space the value needs. Because boxes have a known size, we can enable -recursive types by inserting a box in the recursive type definition. - -As an example of a recursive type, let’s explore the *cons list*. This is a -data type commonly found in functional programming languages. The cons list -type we’ll define is straightforward except for the recursion; therefore, the -concepts in the example we’ll work with will be useful any time you get into +A value of a *recursive type* can have another value of the same type as part of +itself. Recursive types pose an issue because Rust needs to know at compile time +how much space a type takes up. However, the nesting of values of recursive +types could theoretically continue infinitely, so Rust can’t know how much space +the value needs. Because boxes have a known size, we can enable recursive types +by inserting a box in the recursive type definition. + +As an example of a recursive type, let’s explore the cons list. This is a data +type commonly found in functional programming languages. The cons list type +we’ll define is straightforward except for the recursion; therefore, the +concepts in the example we’ll work with will be useful anytime you get into more complex situations involving recursive types. -#### More Information About the Cons List + + + + +#### Understanding the Cons List A *cons list* is a data structure that comes from the Lisp programming language and its dialects, is made up of nested pairs, and is the Lisp version of a @@ -152,11 +154,11 @@ list `1, 2, 3` with each pair in parentheses: ``` Each item in a cons list contains two elements: the value of the current item -and the next item. The last item in the list contains only a value called `Nil` -without a next item. A cons list is produced by recursively calling the `cons` -function. The canonical name to denote the base case of the recursion is `Nil`. -Note that this is not the same as the “null” or “nil” concept in Chapter 6, -which is an invalid or absent value. +and of the next item. The last item in the list contains only a value called +`Nil` without a next item. A cons list is produced by recursively calling the +`cons` function. The canonical name to denote the base case of the recursion is +`Nil`. Note that this is not the same as the “null” or “nil” concept discussed +in Chapter 6, which is an invalid or absent value. The cons list isn’t a commonly used data structure in Rust. Most of the time when you have a list of items in Rust, `Vec` is a better choice to use. @@ -165,10 +167,10 @@ but by starting with the cons list in this chapter, we can explore how boxes let us define a recursive data type without much distraction. Listing 15-2 contains an enum definition for a cons list. Note that this code -won’t compile yet because the `List` type doesn’t have a known size, which +won’t compile yet, because the `List` type doesn’t have a known size, which we’ll demonstrate. -Filename: src/main.rs +src/main.rs ``` enum List { @@ -177,21 +179,20 @@ enum List { } ``` -Listing 15-2: The first attempt at defining an enum to represent a cons list -data structure of `i32` values +Listing 15-2: The first attempt at defining an enum to represent a cons list data structure of `i32` values > Note: We’re implementing a cons list that holds only `i32` values for the -purposes of this example. We could have implemented it using generics, as we -discussed in Chapter 10, to define a cons list type that could store values of -any type. +> purposes of this example. We could have implemented it using generics, as we +> discussed in Chapter 10, to define a cons list type that could store values of +> any type. Using the `List` type to store the list `1, 2, 3` would look like the code in Listing 15-3. -Filename: src/main.rs +src/main.rs ``` ---snip-- +// --snip-- use crate::List::{Cons, Nil}; @@ -210,28 +211,44 @@ is one more `Cons` value that holds `3` and a `List` value, which is finally If we try to compile the code in Listing 15-3, we get the error shown in Listing 15-4. + ``` +$ cargo run + Compiling cons-list v0.1.0 (file:///projects/cons-list) error[E0072]: recursive type `List` has infinite size --> src/main.rs:1:1 | 1 | enum List { - | ^^^^^^^^^ recursive type has infinite size + | ^^^^^^^^^ 2 | Cons(i32, List), | ---- recursive without indirection | -help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `List` -representable +help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle | 2 | Cons(i32, Box), | ++++ + + +error[E0391]: cycle detected when computing when `List` needs drop + --> src/main.rs:1:1 + | +1 | enum List { + | ^^^^^^^^^ + | + = note: ...which immediately requires computing when `List` needs drop again + = note: cycle used when computing whether `List` needs drop + = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information + +Some errors have detailed explanations: E0072, E0391. +For more information about an error, try `rustc --explain E0072`. +error: could not compile `cons-list` (bin "cons-list") due to 2 previous errors ``` Listing 15-4: The error we get when attempting to define a recursive enum The error shows this type “has infinite size.” The reason is that we’ve defined -`List` with a variant that is recursive: it holds another value of itself +`List` with a variant that is recursive: It holds another value of itself directly. As a result, Rust can’t figure out how much space it needs to store a -`List` value. Let’s break down why we get this error. First we’ll look at how +`List` value. Let’s break down why we get this error. First, we’ll look at how Rust decides how much space it needs to store a value of a non-recursive type. #### Computing the Size of a Non-Recursive Type @@ -264,16 +281,26 @@ type needs, the compiler looks at the variants, starting with the `Cons` variant. The `Cons` variant holds a value of type `i32` and a value of type `List`, and this process continues infinitely, as shown in Figure 15-1. -Figure 15-1: An infinite `List` consisting of infinite `Cons` variants +An infinite Cons list: a rectangle labeled 'Cons' split into two smaller rectangles. The first smaller rectangle holds the label 'i32', and the second smaller rectangle holds the label 'Cons' and a smaller version of the outer 'Cons' rectangle. The 'Cons' rectangles continue to hold smaller and smaller versions of themselves until the smallest comfortably sized rectangle holds an infinity symbol, indicating that this repetition goes on forever. + +Figure 15-1: An infinite `List` consisting of infinite +`Cons` variants + + + + -#### Using Box to Get a Recursive Type with a Known Size +#### Getting a Recursive Type with a Known Size Because Rust can’t figure out how much space to allocate for recursively defined types, the compiler gives an error with this helpful suggestion: + + ``` -help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `List` -representable +help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle | 2 | Cons(i32, Box), | ++++ + @@ -284,7 +311,7 @@ directly, we should change the data structure to store the value indirectly by storing a pointer to the value instead. Because a `Box` is a pointer, Rust always knows how much space a `Box` -needs: a pointer’s size doesn’t change based on the amount of data it’s +needs: A pointer’s size doesn’t change based on the amount of data it’s pointing to. This means we can put a `Box` inside the `Cons` variant instead of another `List` value directly. The `Box` will point to the next `List` value that will be on the heap rather than inside the `Cons` variant. @@ -295,7 +322,7 @@ rather than inside one another. We can change the definition of the `List` enum in Listing 15-2 and the usage of the `List` in Listing 15-3 to the code in Listing 15-5, which will compile. -Filename: src/main.rs +src/main.rs ``` enum List { @@ -306,38 +333,31 @@ enum List { use crate::List::{Cons, Nil}; fn main() { - let list = Cons( - 1, - Box::new(Cons( - 2, - Box::new(Cons( - 3, - Box::new(Nil) - )) - )) - ); + let list = Cons(1, Box::new(Cons(2, Box::new(Cons(3, Box::new(Nil)))))); } ``` -Listing 15-5: Definition of `List` that uses `Box` in order to have a known -size +Listing 15-5: The definition of `List` that uses `Box` in order to have a known size The `Cons` variant needs the size of an `i32` plus the space to store the box’s -pointer data. The `Nil` variant stores no values, so it needs less space than -the `Cons` variant. We now know that any `List` value will take up the size of -an `i32` plus the size of a box’s pointer data. By using a box, we’ve broken -the infinite, recursive chain, so the compiler can figure out the size it needs -to store a `List` value. Figure 15-2 shows what the `Cons` variant looks like -now. +pointer data. The `Nil` variant stores no values, so it needs less space on the +stack than the `Cons` variant. We now know that any `List` value will take up +the size of an `i32` plus the size of a box’s pointer data. By using a box, +we’ve broken the infinite, recursive chain, so the compiler can figure out the +size it needs to store a `List` value. Figure 15-2 shows what the `Cons` +variant looks like now. + +A rectangle labeled 'Cons' split into two smaller rectangles. The first smaller rectangle holds the label 'i32', and the second smaller rectangle holds the label 'Box' with one inner rectangle that contains the label 'usize', representing the finite size of the box's pointer. -Figure 15-2: A `List` that is not infinitely sized, because `Cons` holds a `Box` +Figure 15-2: A `List` that is not infinitely sized, +because `Cons` holds a `Box` Boxes provide only the indirection and heap allocation; they don’t have any other special capabilities, like those we’ll see with the other smart pointer types. They also don’t have the performance overhead that these special capabilities incur, so they can be useful in cases like the cons list where the indirection is the only feature we need. We’ll look at more use cases for boxes -in Chapter 17. +in Chapter 18. The `Box` type is a smart pointer because it implements the `Deref` trait, which allows `Box` values to be treated like references. When a `Box` @@ -347,7 +367,12 @@ even more important to the functionality provided by the other smart pointer types we’ll discuss in the rest of this chapter. Let’s explore these two traits in more detail. -## Treating Smart Pointers Like Regular References with Deref + + + + + +## Treating Smart Pointers Like Regular References Implementing the `Deref` trait allows you to customize the behavior of the *dereference operator* `*` (not to be confused with the multiplication or glob @@ -356,60 +381,63 @@ treated like a regular reference, you can write code that operates on references and use that code with smart pointers too. Let’s first look at how the dereference operator works with regular references. -Then we’ll try to define a custom type that behaves like `Box`, and see why +Then, we’ll try to define a custom type that behaves like `Box` and see why the dereference operator doesn’t work like a reference on our newly defined type. We’ll explore how implementing the `Deref` trait makes it possible for -smart pointers to work in ways similar to references. Then we’ll look at Rust’s -*deref coercion* feature and how it lets us work with either references or +smart pointers to work in ways similar to references. Then, we’ll look at +Rust’s deref coercion feature and how it lets us work with either references or smart pointers. -> Note: There’s one big difference between the `MyBox` type we’re about to -build and the real `Box`: our version will not store its data on the heap. -We are focusing this example on `Deref`, so where the data is actually stored -is less important than the pointer-like behavior. + -### Following the Pointer to the Value + + + +### Following the Reference to the Value A regular reference is a type of pointer, and one way to think of a pointer is as an arrow to a value stored somewhere else. In Listing 15-6, we create a reference to an `i32` value and then use the dereference operator to follow the reference to the value. -Filename: src/main.rs +src/main.rs ``` fn main() { - 1 let x = 5; - 2 let y = &x; + let x = 5; + let y = &x; - 3 assert_eq!(5, x); - 4 assert_eq!(5, *y); + assert_eq!(5, x); + assert_eq!(5, *y); } ``` -Listing 15-6: Using the dereference operator to follow a reference to an `i32` -value +Listing 15-6: Using the dereference operator to follow a reference to an `i32` value -The variable `x` holds an `i32` value `5` [1]. We set `y` equal to a reference -to `x` [2]. We can assert that `x` is equal to `5` [3]. However, if we want to -make an assertion about the value in `y`, we have to use `*y` to follow the -reference to the value it’s pointing to (hence *dereference*) so the compiler -can compare the actual value [4]. Once we dereference `y`, we have access to -the integer value `y` is pointing to that we can compare with `5`. +The variable `x` holds an `i32` value `5`. We set `y` equal to a reference to +`x`. We can assert that `x` is equal to `5`. However, if we want to make an +assertion about the value in `y`, we have to use `*y` to follow the reference +to the value it’s pointing to (hence, *dereference*) so that the compiler can +compare the actual value. Once we dereference `y`, we have access to the +integer value `y` is pointing to that we can compare with `5`. If we tried to write `assert_eq!(5, y);` instead, we would get this compilation error: ``` +$ cargo run + Compiling deref-example v0.1.0 (file:///projects/deref-example) error[E0277]: can't compare `{integer}` with `&{integer}` --> src/main.rs:6:5 | 6 | assert_eq!(5, y); - | ^^^^^^^^^^^^^^^^ no implementation for `{integer} == -&{integer}` + | ^^^^^^^^^^^^^^^^ no implementation for `{integer} == &{integer}` | - = help: the trait `PartialEq<&{integer}>` is not implemented -for `{integer}` + = help: the trait `PartialEq<&{integer}>` is not implemented for `{integer}` + = note: this error originates in the macro `assert_eq` (in Nightly builds, run with -Z macro-backtrace for more info) + +For more information about this error, try `rustc --explain E0277`. +error: could not compile `deref-example` (bin "deref-example") due to 1 previous error ``` Comparing a number and a reference to a number isn’t allowed because they’re @@ -423,15 +451,15 @@ reference; the dereference operator used on the `Box` in Listing 15-7 functions in the same way as the dereference operator used on the reference in Listing 15-6. -Filename: src/main.rs +src/main.rs ``` fn main() { let x = 5; - 1 let y = Box::new(x); + let y = Box::new(x); assert_eq!(5, x); - 2 assert_eq!(5, *y); + assert_eq!(5, *y); } ``` @@ -439,49 +467,52 @@ Listing 15-7: Using the dereference operator on a `Box` The main difference between Listing 15-7 and Listing 15-6 is that here we set `y` to be an instance of a box pointing to a copied value of `x` rather than a -reference pointing to the value of `x` [1]. In the last assertion [2], we can -use the dereference operator to follow the box’s pointer in the same way that -we did when `y` was a reference. Next, we’ll explore what is special about -`Box` that enables us to use the dereference operator by defining our own -box type. +reference pointing to the value of `x`. In the last assertion, we can use the +dereference operator to follow the box’s pointer in the same way that we did +when `y` was a reference. Next, we’ll explore what is special about `Box` +that enables us to use the dereference operator by defining our own box type. ### Defining Our Own Smart Pointer -Let’s build a smart pointer similar to the `Box` type provided by the -standard library to experience how smart pointers behave differently from -references by default. Then we’ll look at how to add the ability to use the +Let’s build a wrapper type similar to the `Box` type provided by the +standard library to experience how smart pointer types behave differently from +references by default. Then, we’ll look at how to add the ability to use the dereference operator. +> Note: There’s one big difference between the `MyBox` type we’re about to +> build and the real `Box`: Our version will not store its data on the heap. +> We are focusing this example on `Deref`, so where the data is actually stored +> is less important than the pointer-like behavior. + The `Box` type is ultimately defined as a tuple struct with one element, so Listing 15-8 defines a `MyBox` type in the same way. We’ll also define a `new` function to match the `new` function defined on `Box`. -Filename: src/main.rs +src/main.rs ``` - 1 struct MyBox(T); +struct MyBox(T); impl MyBox { - 2 fn new(x: T) -> MyBox { - 3 MyBox(x) + fn new(x: T) -> MyBox { + MyBox(x) } } ``` Listing 15-8: Defining a `MyBox` type -We define a struct named `MyBox` and declare a generic parameter `T` [1] -because we want our type to hold values of any type. The `MyBox` type is a -tuple struct with one element of type `T`. The `MyBox::new` function takes one -parameter of type `T` [2] and returns a `MyBox` instance that holds the value -passed in [3]. +We define a struct named `MyBox` and declare a generic parameter `T` because we +want our type to hold values of any type. The `MyBox` type is a tuple struct +with one element of type `T`. The `MyBox::new` function takes one parameter of +type `T` and returns a `MyBox` instance that holds the value passed in. Let’s try adding the `main` function in Listing 15-7 to Listing 15-8 and changing it to use the `MyBox` type we’ve defined instead of `Box`. The -code in Listing 15-9 won’t compile because Rust doesn’t know how to dereference -`MyBox`. +code in Listing 15-9 won’t compile, because Rust doesn’t know how to +dereference `MyBox`. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -493,63 +524,70 @@ fn main() { } ``` -Listing 15-9: Attempting to use `MyBox` in the same way we used references -and `Box` +Listing 15-9: Attempting to use `MyBox` in the same way we used references and `Box` Here’s the resultant compilation error: ``` +$ cargo run + Compiling deref-example v0.1.0 (file:///projects/deref-example) error[E0614]: type `MyBox<{integer}>` cannot be dereferenced --> src/main.rs:14:19 | 14 | assert_eq!(5, *y); | ^^ + +For more information about this error, try `rustc --explain E0614`. +error: could not compile `deref-example` (bin "deref-example") due to 1 previous error ``` Our `MyBox` type can’t be dereferenced because we haven’t implemented that ability on our type. To enable dereferencing with the `*` operator, we implement the `Deref` trait. + + + + ### Implementing the Deref Trait -As discussed in “Implementing a Trait on a Type” on page XX, to implement a -trait we need to provide implementations for the trait’s required methods. The -`Deref` trait, provided by the standard library, requires us to implement one -method named `deref` that borrows `self` and returns a reference to the inner -data. Listing 15-10 contains an implementation of `Deref` to add to the -definition of `MyBox```. +As discussed in “Implementing a Trait on a Type” in +Chapter 10, to implement a trait we need to provide implementations for the +trait’s required methods. The `Deref` trait, provided by the standard library, +requires us to implement one method named `deref` that borrows `self` and +returns a reference to the inner data. Listing 15-10 contains an implementation +of `Deref` to add to the definition of `MyBox`. -Filename: src/main.rs +src/main.rs ``` use std::ops::Deref; impl Deref for MyBox { - 1 type Target = T; + type Target = T; fn deref(&self) -> &Self::Target { - 2 &self.0 + &self.0 } } ``` Listing 15-10: Implementing `Deref` on `MyBox` -The `type Target = T;` syntax [1] defines an associated type for the `Deref` -trait to use. Associated types are a slightly different way of declaring a -generic parameter, but you don’t need to worry about them for now; we’ll cover -them in more detail in Chapter 19. +The `type Target = T;` syntax defines an associated type for the `Deref` trait +to use. Associated types are a slightly different way of declaring a generic +parameter, but you don’t need to worry about them for now; we’ll cover them in +more detail in Chapter 20. -We fill in the body of the `deref` method with `&self.0` so `deref` returns a -reference to the value we want to access with the `*` operator [2]; recall from -“Using Tuple Structs Without Named Fields to Create Different Types” on page XX -that `.0` accesses the first value in a tuple struct. The `main` function in -Listing 15-9 that calls `*` on the `MyBox` value now compiles, and the -assertions pass! +We fill in the body of the `deref` method with `&self.0` so that `deref` +returns a reference to the value we want to access with the `*` operator; +recall from “Creating Different Types with Tuple Structs” in Chapter 5 that `.0` accesses the first value in a tuple struct. +The `main` function in Listing 15-9 that calls `*` on the `MyBox` value now +compiles, and the assertions pass! Without the `Deref` trait, the compiler can only dereference `&` references. The `deref` method gives the compiler the ability to take a value of any type -that implements `Deref` and call the `deref` method to get a `&` reference that +that implements `Deref` and call the `deref` method to get a reference that it knows how to dereference. When we entered `*y` in Listing 15-9, behind the scenes Rust actually ran this @@ -560,8 +598,8 @@ code: ``` Rust substitutes the `*` operator with a call to the `deref` method and then a -plain dereference so we don’t have to think about whether or not we need to -call the `deref` method. This Rust feature lets us write code that functions +plain dereference so that we don’t have to think about whether or not we need +to call the `deref` method. This Rust feature lets us write code that functions identically whether we have a regular reference or a type that implements `Deref`. @@ -578,13 +616,18 @@ Because the substitution of the `*` operator does not recurse infinitely, we end up with data of type `i32`, which matches the `5` in `assert_eq!` in Listing 15-9. -### Implicit Deref Coercions with Functions and Methods + + + + + +### Using Deref Coercion in Functions and Methods *Deref coercion* converts a reference to a type that implements the `Deref` trait into a reference to another type. For example, deref coercion can convert `&String` to `&str` because `String` implements the `Deref` trait such that it returns `&str`. Deref coercion is a convenience Rust performs on arguments to -functions and methods, and works only on types that implement the `Deref` +functions and methods, and it works only on types that implement the `Deref` trait. It happens automatically when we pass a reference to a particular type’s value as an argument to a function or method that doesn’t match the parameter type in the function or method definition. A sequence of calls to the `deref` @@ -600,7 +643,7 @@ Listing 15-8 as well as the implementation of `Deref` that we added in Listing 15-10. Listing 15-11 shows the definition of a function that has a string slice parameter. -Filename: src/main.rs +src/main.rs ``` fn hello(name: &str) { @@ -614,7 +657,7 @@ We can call the `hello` function with a string slice as an argument, such as `hello("Rust");`, for example. Deref coercion makes it possible to call `hello` with a reference to a value of type `MyBox`, as shown in Listing 15-12. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -623,8 +666,7 @@ fn main() { } ``` -Listing 15-12: Calling `hello` with a reference to a `MyBox` value, -which works because of deref coercion +Listing 15-12: Calling `hello` with a reference to a `MyBox` value, which works because of deref coercion Here we’re calling the `hello` function with the argument `&m`, which is a reference to a `MyBox` value. Because we implemented the `Deref` trait @@ -638,7 +680,7 @@ If Rust didn’t implement deref coercion, we would have to write the code in Listing 15-13 instead of the code in Listing 15-12 to call `hello` with a value of type `&MyBox`. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -647,10 +689,9 @@ fn main() { } ``` -Listing 15-13: The code we would have to write if Rust didn’t have deref -coercion +Listing 15-13: The code we would have to write if Rust didn’t have deref coercion -The `(*m)` dereferences the `MyBox` into a `String`. Then the `&` and +The `(*m)` dereferences the `MyBox` into a `String`. Then, the `&` and `[..]` take a string slice of the `String` that is equal to the whole string to match the signature of `hello`. This code without deref coercions is harder to read, write, and understand with all of these symbols involved. Deref coercion @@ -662,7 +703,11 @@ match the parameter’s type. The number of times that `Deref::deref` needs to b inserted is resolved at compile time, so there is no runtime penalty for taking advantage of deref coercion! -### How Deref Coercion Interacts with Mutability + + + + +### Handling Deref Coercion with Mutable References Similar to how you use the `Deref` trait to override the `*` operator on immutable references, you can use the `DerefMut` trait to override the `*` @@ -671,9 +716,9 @@ operator on mutable references. Rust does deref coercion when it finds types and trait implementations in three cases: -* From `&T` to `&U` when `T: Deref` -* From `&mut T` to `&mut U` when `T: DerefMut` -* From `&mut T` to `&U` when `T: Deref` +1. From `&T` to `&U` when `T: Deref` +1. From `&mut T` to `&mut U` when `T: DerefMut` +1. From `&mut T` to `&U` when `T: Deref` The first two cases are the same except that the second implements mutability. The first case states that if you have a `&T`, and `T` implements `Deref` to @@ -681,7 +726,7 @@ some type `U`, you can get a `&U` transparently. The second case states that the same deref coercion happens for mutable references. The third case is trickier: Rust will also coerce a mutable reference to an -immutable one. But the reverse is *not* possible: immutable references will +immutable one. But the reverse is *not* possible: Immutable references will never coerce to mutable references. Because of the borrowing rules, if you have a mutable reference, that mutable reference must be the only reference to that data (otherwise, the program wouldn’t compile). Converting one mutable @@ -701,15 +746,15 @@ be used to release resources like files or network connections. We’re introducing `Drop` in the context of smart pointers because the functionality of the `Drop` trait is almost always used when implementing a -smart pointer. For example, when a `Box` is dropped it will deallocate the +smart pointer. For example, when a `Box` is dropped, it will deallocate the space on the heap that the box points to. In some languages, for some types, the programmer must call code to free memory or resources every time they finish using an instance of those types. Examples -include file handles, sockets, and locks. If they forget, the system might -become overloaded and crash. In Rust, you can specify that a particular bit of -code be run whenever a value goes out of scope, and the compiler will insert -this code automatically. As a result, you don’t need to be careful about +include file handles, sockets, and locks. If the programmer forgets, the system +might become overloaded and crash. In Rust, you can specify that a particular +bit of code be run whenever a value goes out of scope, and the compiler will +insert this code automatically. As a result, you don’t need to be careful about placing cleanup code everywhere in a program that an instance of a particular type is finished with—you still won’t leak resources! @@ -722,53 +767,53 @@ Listing 15-14 shows a `CustomSmartPointer` struct whose only custom functionality is that it will print `Dropping CustomSmartPointer!` when the instance goes out of scope, to show when Rust runs the `drop` method. -Filename: src/main.rs +src/main.rs ``` struct CustomSmartPointer { data: String, } -1 impl Drop for CustomSmartPointer { +impl Drop for CustomSmartPointer { fn drop(&mut self) { - 2 println!( - "Dropping CustomSmartPointer with data `{}`!", - self.data - ); + println!("Dropping CustomSmartPointer with data `{}`!", self.data); } } fn main() { - 3 let c = CustomSmartPointer { + let c = CustomSmartPointer { data: String::from("my stuff"), }; - 4 let d = CustomSmartPointer { + let d = CustomSmartPointer { data: String::from("other stuff"), }; - 5 println!("CustomSmartPointers created."); -6 } + println!("CustomSmartPointers created"); +} ``` -Listing 15-14: A `CustomSmartPointer` struct that implements the `Drop` trait -where we would put our cleanup code +Listing 15-14: A `CustomSmartPointer` struct that implements the `Drop` trait where we would put our cleanup code The `Drop` trait is included in the prelude, so we don’t need to bring it into -scope. We implement the `Drop` trait on `CustomSmartPointer` [1] and provide an -implementation for the `drop` method that calls `println!` [2]. The body of the +scope. We implement the `Drop` trait on `CustomSmartPointer` and provide an +implementation for the `drop` method that calls `println!`. The body of the `drop` method is where you would place any logic that you wanted to run when an instance of your type goes out of scope. We’re printing some text here to demonstrate visually when Rust will call `drop`. -In `main`, we create two instances of `CustomSmartPointer` at [3] and [4] and -then print `CustomSmartPointers created` [5]. At the end of `main` [6], our -instances of `CustomSmartPointer` will go out of scope, and Rust will call the -code we put in the `drop` method [2], printing our final message. Note that we -didn’t need to call the `drop` method explicitly. +In `main`, we create two instances of `CustomSmartPointer` and then print +`CustomSmartPointers created`. At the end of `main`, our instances of +`CustomSmartPointer` will go out of scope, and Rust will call the code we put +in the `drop` method, printing our final message. Note that we didn’t need to +call the `drop` method explicitly. When we run this program, we’ll see the following output: ``` -CustomSmartPointers created. +$ cargo run + Compiling drop-example v0.1.0 (file:///projects/drop-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.60s + Running `target/debug/drop-example` +CustomSmartPointers created Dropping CustomSmartPointer with data `other stuff`! Dropping CustomSmartPointer with data `my stuff`! ``` @@ -780,49 +825,56 @@ give you a visual guide to how the `drop` method works; usually you would specify the cleanup code that your type needs to run rather than a print message. + + + + Unfortunately, it’s not straightforward to disable the automatic `drop` functionality. Disabling `drop` isn’t usually necessary; the whole point of the `Drop` trait is that it’s taken care of automatically. Occasionally, however, you might want to clean up a value early. One example is when using smart -pointers that manage locks: you might want to force the `drop` method that +pointers that manage locks: You might want to force the `drop` method that releases the lock so that other code in the same scope can acquire the lock. Rust doesn’t let you call the `Drop` trait’s `drop` method manually; instead, you have to call the `std::mem::drop` function provided by the standard library if you want to force a value to be dropped before the end of its scope. -If we try to call the `Drop` trait’s `drop` method manually by modifying the -`main` function from Listing 15-14, as shown in Listing 15-15, we’ll get a -compiler error. +Trying to call the `Drop` trait’s `drop` method manually by modifying the +`main` function from Listing 15-14 won’t work, as shown in Listing 15-15. -Filename: src/main.rs +src/main.rs ``` fn main() { let c = CustomSmartPointer { data: String::from("some data"), }; - println!("CustomSmartPointer created."); + println!("CustomSmartPointer created"); c.drop(); - println!( - "CustomSmartPointer dropped before the end of main." - ); + println!("CustomSmartPointer dropped before the end of main"); } ``` -Listing 15-15: Attempting to call the `drop` method from the `Drop` trait -manually to clean up early +Listing 15-15: Attempting to call the `drop` method from the `Drop` trait manually to clean up early When we try to compile this code, we’ll get this error: ``` +$ cargo run + Compiling drop-example v0.1.0 (file:///projects/drop-example) error[E0040]: explicit use of destructor method --> src/main.rs:16:7 | 16 | c.drop(); - | --^^^^-- - | | | - | | explicit destructor calls not allowed - | help: consider using `drop` function: `drop(c)` + | ^^^^ explicit destructor calls not allowed + | +help: consider using `drop` function + | +16 | drop(c); + | +++++ ~ + +For more information about this error, try `rustc --explain E0040`. +error: could not compile `drop-example` (bin "drop-example") due to 1 previous error ``` This error message states that we’re not allowed to explicitly call `drop`. The @@ -831,10 +883,9 @@ for a function that cleans up an instance. A *destructor* is analogous to a *constructor*, which creates an instance. The `drop` function in Rust is one particular destructor. -Rust doesn’t let us call `drop` explicitly because Rust would still +Rust doesn’t let us call `drop` explicitly, because Rust would still automatically call `drop` on the value at the end of `main`. This would cause a -*double free* error because Rust would be trying to clean up the same value -twice. +double free error because Rust would be trying to clean up the same value twice. We can’t disable the automatic insertion of `drop` when a value goes out of scope, and we can’t call the `drop` method explicitly. So, if we need to force @@ -845,44 +896,44 @@ trait. We call it by passing as an argument the value we want to force-drop. The function is in the prelude, so we can modify `main` in Listing 15-15 to call the `drop` function, as shown in Listing 15-16. -Filename: src/main.rs +src/main.rs ``` fn main() { let c = CustomSmartPointer { data: String::from("some data"), }; - println!("CustomSmartPointer created."); + println!("CustomSmartPointer created"); drop(c); - println!( - "CustomSmartPointer dropped before the end of main." - ); + println!("CustomSmartPointer dropped before the end of main"); } ``` -Listing 15-16: Calling `std::mem::drop` to explicitly drop a value before it -goes out of scope +Listing 15-16: Calling `std::mem::drop` to explicitly drop a value before it goes out of scope Running this code will print the following: ``` -CustomSmartPointer created. +$ cargo run + Compiling drop-example v0.1.0 (file:///projects/drop-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.73s + Running `target/debug/drop-example` +CustomSmartPointer created Dropping CustomSmartPointer with data `some data`! -CustomSmartPointer dropped before the end of main. +CustomSmartPointer dropped before the end of main ``` -The text `Dropping CustomSmartPointer with data `some data`!` is printed -between the `CustomSmartPointer created.` and `CustomSmartPointer dropped -before the end of main.` text, showing that the `drop` method code is called to -drop `c` at that point. +The text ``Dropping CustomSmartPointer with data `some data`!`` is printed +between the `CustomSmartPointer created` and `CustomSmartPointer dropped before the end of main` text, showing that the `drop` method code is called to drop +`c` at that point. You can use code specified in a `Drop` trait implementation in many ways to -make cleanup convenient and safe: for instance, you could use it to create your +make cleanup convenient and safe: For instance, you could use it to create your own memory allocator! With the `Drop` trait and Rust’s ownership system, you -don’t have to remember to clean up because Rust does it automatically. +don’t have to remember to clean up, because Rust does it automatically. You also don’t have to worry about problems resulting from accidentally -cleaning up values still in use: the ownership system that makes sure +cleaning up values still in use: The ownership system that makes sure references are always valid also ensures that `drop` gets called only once when the value is no longer being used. @@ -890,9 +941,9 @@ Now that we’ve examined `Box` and some of the characteristics of smart pointers, let’s look at a few other smart pointers defined in the standard library. -## Rc, the Reference Counted Smart Pointer +## Rc, the Reference-Counted Smart Pointer -In the majority of cases, ownership is clear: you know exactly which variable +In the majority of cases, ownership is clear: You know exactly which variable owns a given value. However, there are cases when a single value might have multiple owners. For example, in graph data structures, multiple edges might point to the same node, and that node is conceptually owned by all of the edges @@ -921,23 +972,35 @@ Note that `Rc` is only for use in single-threaded scenarios. When we discuss concurrency in Chapter 16, we’ll cover how to do reference counting in multithreaded programs. -### Using Rc to Share Data + + + + +### Sharing Data Let’s return to our cons list example in Listing 15-5. Recall that we defined it using `Box`. This time, we’ll create two lists that both share ownership of a third list. Conceptually, this looks similar to Figure 15-3. -Figure 15-3: Two lists, `b` and `c`, sharing ownership of a third list, `a` +A linked list with the label 'a' pointing to three elements. The first element contains the integer 5 and points to the second element. Th +e second element contains the integer 10 and points to the third element. The third element contains the value 'Nil' that signifies the end of the l +ist; it does not point anywhere. A linked list with the label 'b' points to an element that contains the integer 3 and points to the first element o +f list 'a'. A linked list with the label 'c' points to an element that contains the integer 4 and also points to the first element of list 'a' so th +at the tails of lists 'b' and 'c' are both list 'a'. -We’ll create list `a` that contains `5` and then `10`. Then we’ll make two more -lists: `b` that starts with `3` and `c` that starts with `4`. Both `b` and `c` -lists will then continue on to the first `a` list containing `5` and `10`. In -other words, both lists will share the first list containing `5` and `10`. +Figure 15-3: Two lists, `b` and `c`, sharing ownership of +a third list, `a` + +We’ll create list `a` that contains `5` and then `10`. Then, we’ll make two +more lists: `b` that starts with `3` and `c` that starts with `4`. Both the `b` +and `c` lists will then continue on to the first `a` list containing `5` and +`10`. In other words, both lists will share the first list containing `5` and +`10`. Trying to implement this scenario using our definition of `List` with `Box` won’t work, as shown in Listing 15-17. -Filename: src/main.rs +src/main.rs ``` enum List { @@ -949,32 +1012,35 @@ use crate::List::{Cons, Nil}; fn main() { let a = Cons(5, Box::new(Cons(10, Box::new(Nil)))); - 1 let b = Cons(3, Box::new(a)); - 2 let c = Cons(4, Box::new(a)); + let b = Cons(3, Box::new(a)); + let c = Cons(4, Box::new(a)); } ``` -Listing 15-17: Demonstrating that we’re not allowed to have two lists using -`Box` that try to share ownership of a third list +Listing 15-17: Demonstrating that we’re not allowed to have two lists using `Box` that try to share ownership of a third list When we compile this code, we get this error: ``` +$ cargo run + Compiling cons-list v0.1.0 (file:///projects/cons-list) error[E0382]: use of moved value: `a` --> src/main.rs:11:30 | 9 | let a = Cons(5, Box::new(Cons(10, Box::new(Nil)))); - | - move occurs because `a` has type `List`, which -does not implement the `Copy` trait + | - move occurs because `a` has type `List`, which does not implement the `Copy` trait 10 | let b = Cons(3, Box::new(a)); | - value moved here 11 | let c = Cons(4, Box::new(a)); | ^ value used here after move + +For more information about this error, try `rustc --explain E0382`. +error: could not compile `cons-list` (bin "cons-list") due to 1 previous error ``` -The `Cons` variants own the data they hold, so when we create the `b` list [1], -`a` is moved into `b` and `b` owns `a`. Then, when we try to use `a` again when -creating `c` [2], we’re not allowed to because `a` has been moved. +The `Cons` variants own the data they hold, so when we create the `b` list, `a` +is moved into `b` and `b` owns `a`. Then, when we try to use `a` again when +creating `c`, we’re not allowed to because `a` has been moved. We could change the definition of `Cons` to hold references instead, but then we would have to specify lifetime parameters. By specifying lifetime @@ -993,7 +1059,7 @@ we call `Rc::clone`, the reference count to the data within the `Rc` will increase, and the data won’t be cleaned up unless there are zero references to it. -Filename: src/main.rs +src/main.rs ``` enum List { @@ -1002,22 +1068,22 @@ enum List { } use crate::List::{Cons, Nil}; -1 use std::rc::Rc; +use std::rc::Rc; fn main() { - 2 let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil))))); - 3 let b = Cons(3, Rc::clone(&a)); - 4 let c = Cons(4, Rc::clone(&a)); + let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil))))); + let b = Cons(3, Rc::clone(&a)); + let c = Cons(4, Rc::clone(&a)); } ``` Listing 15-18: A definition of `List` that uses `Rc` -We need to add a `use` statement to bring `Rc` into scope [1] because it’s -not in the prelude. In `main`, we create the list holding `5` and `10` and -store it in a new `Rc` in `a` [2]. Then, when we create `b` [3] and `c` -[4], we call the `Rc::clone` function and pass a reference to the `Rc` in -`a` as an argument. +We need to add a `use` statement to bring `Rc` into scope because it’s not +in the prelude. In `main`, we create the list holding `5` and `10` and store it +in a new `Rc` in `a`. Then, when we create `b` and `c`, we call the +`Rc::clone` function and pass a reference to the `Rc` in `a` as an +argument. We could have called `a.clone()` rather than `Rc::clone(&a)`, but Rust’s convention is to use `Rc::clone` in this case. The implementation of @@ -1030,41 +1096,35 @@ increase the reference count. When looking for performance problems in the code, we only need to consider the deep-copy clones and can disregard calls to `Rc::clone`. -### Cloning an Rc Increases the Reference Count + -Let’s change our working example in Listing 15-18 so we can see the reference -counts changing as we create and drop references to the `Rc` in `a`. + -In Listing 15-19, we’ll change `main` so it has an inner scope around list `c`; -then we can see how the reference count changes when `c` goes out of scope. +### Cloning to Increase the Reference Count -Filename: src/main.rs +Let’s change our working example in Listing 15-18 so that we can see the +reference counts changing as we create and drop references to the `Rc` in +`a`. + +In Listing 15-19, we’ll change `main` so that it has an inner scope around list +`c`; then, we can see how the reference count changes when `c` goes out of +scope. + +src/main.rs ``` ---snip-- +// --snip-- fn main() { let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil))))); - println!( - "count after creating a = {}", - Rc::strong_count(&a) - ); + println!("count after creating a = {}", Rc::strong_count(&a)); let b = Cons(3, Rc::clone(&a)); - println!( - "count after creating b = {}", - Rc::strong_count(&a) - ); + println!("count after creating b = {}", Rc::strong_count(&a)); { let c = Cons(4, Rc::clone(&a)); - println!( - "count after creating c = {}", - Rc::strong_count(&a) - ); + println!("count after creating c = {}", Rc::strong_count(&a)); } - println!( - "count after c goes out of scope = {}", - Rc::strong_count(&a) - ); + println!("count after c goes out of scope = {}", Rc::strong_count(&a)); } ``` @@ -1074,26 +1134,30 @@ At each point in the program where the reference count changes, we print the reference count, which we get by calling the `Rc::strong_count` function. This function is named `strong_count` rather than `count` because the `Rc` type also has a `weak_count`; we’ll see what `weak_count` is used for in “Preventing -Reference Cycles Using Weak” on page XX. +Reference Cycles Using `Weak`”. This code prints the following: ``` +$ cargo run + Compiling cons-list v0.1.0 (file:///projects/cons-list) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.45s + Running `target/debug/cons-list` count after creating a = 1 count after creating b = 2 count after creating c = 3 count after c goes out of scope = 2 ``` -We can see that the `Rc` in `a` has an initial reference count of 1; then -each time we call `clone`, the count goes up by 1. When `c` goes out of scope, -the count goes down by 1. We don’t have to call a function to decrease the -reference count like we have to call `Rc::clone` to increase the reference -count: the implementation of the `Drop` trait decreases the reference count +We can see that the `Rc` in `a` has an initial reference count of 1; +then, each time we call `clone`, the count goes up by 1. When `c` goes out of +scope, the count goes down by 1. We don’t have to call a function to decrease +the reference count like we have to call `Rc::clone` to increase the reference +count: The implementation of the `Drop` trait decreases the reference count automatically when an `Rc` value goes out of scope. What we can’t see in this example is that when `b` and then `a` go out of scope -at the end of `main`, the count is then 0, and the `Rc` is cleaned up +at the end of `main`, the count is 0, and the `Rc` is cleaned up completely. Using `Rc` allows a single value to have multiple owners, and the count ensures that the value remains valid as long as any of the owners still exist. @@ -1101,7 +1165,7 @@ still exist. Via immutable references, `Rc` allows you to share data between multiple parts of your program for reading only. If `Rc` allowed you to have multiple mutable references too, you might violate one of the borrowing rules discussed -in Chapter 4: multiple mutable borrows to the same place can cause data races +in Chapter 4: Multiple mutable borrows to the same place can cause data races and inconsistencies. But being able to mutate data is very useful! In the next section, we’ll discuss the interior mutability pattern and the `RefCell` type that you can use in conjunction with an `Rc` to work with this @@ -1115,7 +1179,7 @@ action is disallowed by the borrowing rules. To mutate data, the pattern uses `unsafe` code inside a data structure to bend Rust’s usual rules that govern mutation and borrowing. Unsafe code indicates to the compiler that we’re checking the rules manually instead of relying on the compiler to check them -for us; we will discuss unsafe code more in Chapter 19. +for us; we will discuss unsafe code more in Chapter 20. We can use types that use the interior mutability pattern only when we can ensure that the borrowing rules will be followed at runtime, even though the @@ -1125,14 +1189,18 @@ safe API, and the outer type is still immutable. Let’s explore this concept by looking at the `RefCell` type that follows the interior mutability pattern. -### Enforcing Borrowing Rules at Runtime with RefCell + + + + +### Enforcing Borrowing Rules at Runtime Unlike `Rc`, the `RefCell` type represents single ownership over the data -it holds. So what makes `RefCell` different from a type like `Box`? +it holds. So, what makes `RefCell` different from a type like `Box`? Recall the borrowing rules you learned in Chapter 4: * At any given time, you can have *either* one mutable reference or any number -of immutable references (but not both). + of immutable references (but not both). * References must always be valid. With references and `Box`, the borrowing rules’ invariants are enforced at @@ -1150,14 +1218,14 @@ The advantage of checking the borrowing rules at runtime instead is that certain memory-safe scenarios are then allowed, where they would’ve been disallowed by the compile-time checks. Static analysis, like the Rust compiler, is inherently conservative. Some properties of code are impossible to detect by -analyzing the code: the most famous example is the Halting Problem, which is +analyzing the code: The most famous example is the Halting Problem, which is beyond the scope of this book but is an interesting topic to research. Because some analysis is impossible, if the Rust compiler can’t be sure the code complies with the ownership rules, it might reject a correct program; in this way, it’s conservative. If Rust accepted an incorrect program, users -wouldn’t be able to trust in the guarantees Rust makes. However, if Rust -rejects a correct program, the programmer will be inconvenienced, but nothing +wouldn’t be able to trust the guarantees Rust makes. However, if Rust rejects a +correct program, the programmer will be inconvenienced, but nothing catastrophic can occur. The `RefCell` type is useful when you’re sure your code follows the borrowing rules but the compiler is unable to understand and guarantee that. @@ -1170,25 +1238,27 @@ multithreaded program in Chapter 16. Here is a recap of the reasons to choose `Box`, `Rc`, or `RefCell`: * `Rc` enables multiple owners of the same data; `Box` and `RefCell` -have single owners. + have single owners. * `Box` allows immutable or mutable borrows checked at compile time; `Rc` -allows only immutable borrows checked at compile time; `RefCell` allows -immutable or mutable borrows checked at runtime. + allows only immutable borrows checked at compile time; `RefCell` allows + immutable or mutable borrows checked at runtime. * Because `RefCell` allows mutable borrows checked at runtime, you can -mutate the value inside the `RefCell` even when the `RefCell` is -immutable. + mutate the value inside the `RefCell` even when the `RefCell` is + immutable. -Mutating the value inside an immutable value is the *interior mutability* +Mutating the value inside an immutable value is the interior mutability pattern. Let’s look at a situation in which interior mutability is useful and examine how it’s possible. -### Interior Mutability: A Mutable Borrow to an Immutable Value + + + + +### Using Interior Mutability A consequence of the borrowing rules is that when you have an immutable value, you can’t borrow it mutably. For example, this code won’t compile: -Filename: src/main.rs - ``` fn main() { let x = 5; @@ -1199,21 +1269,28 @@ fn main() { If you tried to compile this code, you’d get the following error: ``` -error[E0596]: cannot borrow `x` as mutable, as it is not declared -as mutable +$ cargo run + Compiling borrowing v0.1.0 (file:///projects/borrowing) +error[E0596]: cannot borrow `x` as mutable, as it is not declared as mutable --> src/main.rs:3:13 | -2 | let x = 5; - | - help: consider changing this to be mutable: `mut x` 3 | let y = &mut x; | ^^^^^^ cannot borrow as mutable + | +help: consider changing this to be mutable + | +2 | let mut x = 5; + | +++ + +For more information about this error, try `rustc --explain E0596`. +error: could not compile `borrowing` (bin "borrowing") due to 1 previous error ``` However, there are situations in which it would be useful for a value to mutate itself in its methods but appear immutable to other code. Code outside the value’s methods would not be able to mutate the value. Using `RefCell` is one way to get the ability to have interior mutability, but `RefCell` -doesn’t get around the borrowing rules completely: the borrow checker in the +doesn’t get around the borrowing rules completely: The borrow checker in the compiler allows this interior mutability, and the borrowing rules are checked at runtime instead. If you violate the rules, you’ll get a `panic!` instead of a compiler error. @@ -1221,7 +1298,11 @@ a compiler error. Let’s work through a practical example where we can use `RefCell` to mutate an immutable value and see why that is useful. -#### A Use Case for Interior Mutability: Mock Objects + + + + +#### Testing with Mock Objects Sometimes during testing a programmer will use a type in place of another type, in order to observe particular behavior and assert that it’s implemented @@ -1229,7 +1310,7 @@ correctly. This placeholder type is called a *test double*. Think of it in the sense of a stunt double in filmmaking, where a person steps in and substitutes for an actor to do a particularly tricky scene. Test doubles stand in for other types when we’re running tests. *Mock objects* are specific types of test -doubles that record what happens during a test so you can assert that the +doubles that record what happens during a test so that you can assert that the correct actions took place. Rust doesn’t have objects in the same sense as other languages have objects, @@ -1237,7 +1318,7 @@ and Rust doesn’t have mock object functionality built into the standard librar as some other languages do. However, you can definitely create a struct that will serve the same purposes as a mock object. -Here’s the scenario we’ll test: we’ll create a library that tracks a value +Here’s the scenario we’ll test: We’ll create a library that tracks a value against a maximum value and sends messages based on how close to the maximum value the current value is. This library could be used to keep track of a user’s quota for the number of API calls they’re allowed to make, for example. @@ -1245,16 +1326,16 @@ user’s quota for the number of API calls they’re allowed to make, for exampl Our library will only provide the functionality of tracking how close to the maximum a value is and what the messages should be at what times. Applications that use our library will be expected to provide the mechanism for sending the -messages: the application could put a message in the application, send an +messages: The application could show the message to the user directly, send an email, send a text message, or do something else. The library doesn’t need to know that detail. All it needs is something that implements a trait we’ll -provide called `Messenger`. Listing 15-20 shows the library code. +provide, called `Messenger`. Listing 15-20 shows the library code. -Filename: src/lib.rs +src/lib.rs ``` pub trait Messenger { - 1 fn send(&self, msg: &str); + fn send(&self, msg: &str); } pub struct LimitTracker<'a, T: Messenger> { @@ -1267,10 +1348,7 @@ impl<'a, T> LimitTracker<'a, T> where T: Messenger, { - pub fn new( - messenger: &'a T, - max: usize - ) -> LimitTracker<'a, T> { + pub fn new(messenger: &'a T, max: usize) -> LimitTracker<'a, T> { LimitTracker { messenger, value: 0, @@ -1278,40 +1356,36 @@ where } } - 2 pub fn set_value(&mut self, value: usize) { + pub fn set_value(&mut self, value: usize) { self.value = value; - let percentage_of_max = - self.value as f64 / self.max as f64; + let percentage_of_max = self.value as f64 / self.max as f64; if percentage_of_max >= 1.0 { - self.messenger - .send("Error: You are over your quota!"); + self.messenger.send("Error: You are over your quota!"); } else if percentage_of_max >= 0.9 { self.messenger - .send("Urgent: You're at 90% of your quota!"); + .send("Urgent warning: You've used up over 90% of your quota!"); } else if percentage_of_max >= 0.75 { self.messenger - .send("Warning: You're at 75% of your quota!"); + .send("Warning: You've used up over 75% of your quota!"); } } } ``` -Listing 15-20: A library to keep track of how close a value is to a maximum -value and warn when the value is at certain levels +Listing 15-20: A library to keep track of how close a value is to a maximum value and warn when the value is at certain levels One important part of this code is that the `Messenger` trait has one method called `send` that takes an immutable reference to `self` and the text of the -message [1]. This trait is the interface our mock object needs to implement so -that the mock can be used in the same way a real object is. The other important -part is that we want to test the behavior of the `set_value` method on the -`LimitTracker` [2]. We can change what we pass in for the `value` parameter, -but `set_value` doesn’t return anything for us to make assertions on. We want -to be able to say that if we create a `LimitTracker` with something that -implements the `Messenger` trait and a particular value for `max`, when we pass -different numbers for `value` the messenger is told to send the appropriate -messages. +message. This trait is the interface our mock object needs to implement so that +the mock can be used in the same way a real object is. The other important part +is that we want to test the behavior of the `set_value` method on the +`LimitTracker`. We can change what we pass in for the `value` parameter, but +`set_value` doesn’t return anything for us to make assertions on. We want to be +able to say that if we create a `LimitTracker` with something that implements +the `Messenger` trait and a particular value for `max`, the messenger is told +to send the appropriate messages when we pass different numbers for `value`. We need a mock object that, instead of sending an email or text message when we call `send`, will only keep track of the messages it’s told to send. We can @@ -1320,38 +1394,35 @@ mock object, call the `set_value` method on `LimitTracker`, and then check that the mock object has the messages we expect. Listing 15-21 shows an attempt to implement a mock object to do just that, but the borrow checker won’t allow it. -Filename: src/lib.rs +src/lib.rs ``` #[cfg(test)] mod tests { use super::*; - 1 struct MockMessenger { - 2 sent_messages: Vec, + struct MockMessenger { + sent_messages: Vec, } impl MockMessenger { - 3 fn new() -> MockMessenger { + fn new() -> MockMessenger { MockMessenger { sent_messages: vec![], } } } - 4 impl Messenger for MockMessenger { + impl Messenger for MockMessenger { fn send(&self, message: &str) { - 5 self.sent_messages.push(String::from(message)); + self.sent_messages.push(String::from(message)); } } #[test] - 6 fn it_sends_an_over_75_percent_warning_message() { + fn it_sends_an_over_75_percent_warning_message() { let mock_messenger = MockMessenger::new(); - let mut limit_tracker = LimitTracker::new( - &mock_messenger, - 100 - ); + let mut limit_tracker = LimitTracker::new(&mock_messenger, 100); limit_tracker.set_value(80); @@ -1360,55 +1431,63 @@ mod tests { } ``` -Listing 15-21: An attempt to implement a `MockMessenger` that isn’t allowed by -the borrow checker +Listing 15-21: An attempt to implement a `MockMessenger` that isn’t allowed by the borrow checker -This test code defines a `MockMessenger` struct [1] that has a `sent_messages` -field with a `Vec` of `String` values [2] to keep track of the messages it’s -told to send. We also define an associated function `new` [3] to make it -convenient to create new `MockMessenger` values that start with an empty list -of messages. We then implement the `Messenger` trait for `MockMessenger` [4] so -we can give a `MockMessenger` to a `LimitTracker`. In the definition of the -`send` method [5], we take the message passed in as a parameter and store it in -the `MockMessenger` list of `sent_messages`. +This test code defines a `MockMessenger` struct that has a `sent_messages` +field with a `Vec` of `String` values to keep track of the messages it’s told +to send. We also define an associated function `new` to make it convenient to +create new `MockMessenger` values that start with an empty list of messages. We +then implement the `Messenger` trait for `MockMessenger` so that we can give a +`MockMessenger` to a `LimitTracker`. In the definition of the `send` method, we +take the message passed in as a parameter and store it in the `MockMessenger` +list of `sent_messages`. In the test, we’re testing what happens when the `LimitTracker` is told to set -`value` to something that is more than 75 percent of the `max` value [6]. First -we create a new `MockMessenger`, which will start with an empty list of -messages. Then we create a new `LimitTracker` and give it a reference to the -new `MockMessenger` and a `max` value of `100`. We call the `set_value` method -on the `LimitTracker` with a value of `80`, which is more than 75 percent of -100. Then we assert that the list of messages that the `MockMessenger` is -keeping track of should now have one message in it. +`value` to something that is more than 75 percent of the `max` value. First, we +create a new `MockMessenger`, which will start with an empty list of messages. +Then, we create a new `LimitTracker` and give it a reference to the new +`MockMessenger` and a `max` value of `100`. We call the `set_value` method on +the `LimitTracker` with a value of `80`, which is more than 75 percent of 100. +Then, we assert that the list of messages that the `MockMessenger` is keeping +track of should now have one message in it. However, there’s one problem with this test, as shown here: ``` -error[E0596]: cannot borrow `self.sent_messages` as mutable, as it is behind a -`&` reference +$ cargo test + Compiling limit-tracker v0.1.0 (file:///projects/limit-tracker) +error[E0596]: cannot borrow `self.sent_messages` as mutable, as it is behind a `&` reference --> src/lib.rs:58:13 | -2 | fn send(&self, msg: &str); - | ----- help: consider changing that to be a mutable reference: -`&mut self` -... 58 | self.sent_messages.push(String::from(message)); - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `self` is a -`&` reference, so the data it refers to cannot be borrowed as mutable + | ^^^^^^^^^^^^^^^^^^ `self` is a `&` reference, so the data it refers to cannot be borrowed as mutable + | +help: consider changing this to be a mutable reference in the `impl` method and the `trait` definition + | +2 ~ fn send(&mut self, msg: &str); +3 | } +... +56 | impl Messenger for MockMessenger { +57 ~ fn send(&mut self, message: &str) { + | + +For more information about this error, try `rustc --explain E0596`. +error: could not compile `limit-tracker` (lib test) due to 1 previous error ``` -We can’t modify the `MockMessenger` to keep track of the messages because the +We can’t modify the `MockMessenger` to keep track of the messages, because the `send` method takes an immutable reference to `self`. We also can’t take the -suggestion from the error text to use `&mut self` instead because then the -signature of `send` wouldn’t match the signature in the `Messenger` trait -definition (feel free to try it and see what error message you get). +suggestion from the error text to use `&mut self` in both the `impl` method and +the trait definition. We do not want to change the `Messenger` trait solely for +the sake of testing. Instead, we need to find a way to make our test code work +correctly with our existing design. This is a situation in which interior mutability can help! We’ll store the `sent_messages` within a `RefCell`, and then the `send` method will be able to modify `sent_messages` to store the messages we’ve seen. Listing 15-22 shows what that looks like. -Filename: src/lib.rs +src/lib.rs ``` #[cfg(test)] @@ -1417,58 +1496,56 @@ mod tests { use std::cell::RefCell; struct MockMessenger { - 1 sent_messages: RefCell>, + sent_messages: RefCell>, } impl MockMessenger { fn new() -> MockMessenger { MockMessenger { - 2 sent_messages: RefCell::new(vec![]), + sent_messages: RefCell::new(vec![]), } } } impl Messenger for MockMessenger { fn send(&self, message: &str) { - self.sent_messages - 3 .borrow_mut() - .push(String::from(message)); + self.sent_messages.borrow_mut().push(String::from(message)); } } #[test] fn it_sends_an_over_75_percent_warning_message() { - --snip-- + // --snip-- - assert_eq!( - 4 mock_messenger.sent_messages.borrow().len(), - 1 - ); + assert_eq!(mock_messenger.sent_messages.borrow().len(), 1); } } ``` -Listing 15-22: Using `RefCell` to mutate an inner value while the outer -value is considered immutable +Listing 15-22: Using `RefCell` to mutate an inner value while the outer value is considered immutable -The `sent_messages` field is now of type `RefCell>` [1] instead of +The `sent_messages` field is now of type `RefCell>` instead of `Vec`. In the `new` function, we create a new `RefCell>` -instance around the empty vector [2]. +instance around the empty vector. For the implementation of the `send` method, the first parameter is still an immutable borrow of `self`, which matches the trait definition. We call -`borrow_mut` on the `RefCell>` in `self.sent_messages` [3] to get a +`borrow_mut` on the `RefCell>` in `self.sent_messages` to get a mutable reference to the value inside the `RefCell>`, which is the -vector. Then we can call `push` on the mutable reference to the vector to keep +vector. Then, we can call `push` on the mutable reference to the vector to keep track of the messages sent during the test. -The last change we have to make is in the assertion: to see how many items are +The last change we have to make is in the assertion: To see how many items are in the inner vector, we call `borrow` on the `RefCell>` to get an -immutable reference to the vector [4]. +immutable reference to the vector. Now that you’ve seen how to use `RefCell`, let’s dig into how it works! -#### Keeping Track of Borrows at Runtime with RefCell + + + + +#### Tracking Borrows at Runtime When creating immutable and mutable references, we use the `&` and `&mut` syntax, respectively. With `RefCell`, we use the `borrow` and `borrow_mut` @@ -1491,37 +1568,55 @@ Listing 15-22. We’re deliberately trying to create two mutable borrows active for the same scope to illustrate that `RefCell` prevents us from doing this at runtime. -Filename: src/lib.rs +src/lib.rs ``` -impl Messenger for MockMessenger { - fn send(&self, message: &str) { - let mut one_borrow = self.sent_messages.borrow_mut(); - let mut two_borrow = self.sent_messages.borrow_mut(); + impl Messenger for MockMessenger { + fn send(&self, message: &str) { + let mut one_borrow = self.sent_messages.borrow_mut(); + let mut two_borrow = self.sent_messages.borrow_mut(); - one_borrow.push(String::from(message)); - two_borrow.push(String::from(message)); + one_borrow.push(String::from(message)); + two_borrow.push(String::from(message)); + } } -} ``` -Listing 15-23: Creating two mutable references in the same scope to see that -`RefCell` will panic +Listing 15-23: Creating two mutable references in the same scope to see that `RefCell` will panic We create a variable `one_borrow` for the `RefMut` smart pointer returned -from `borrow_mut`. Then we create another mutable borrow in the same way in the -variable `two_borrow`. This makes two mutable references in the same scope, +from `borrow_mut`. Then, we create another mutable borrow in the same way in +the variable `two_borrow`. This makes two mutable references in the same scope, which isn’t allowed. When we run the tests for our library, the code in Listing 15-23 will compile without any errors, but the test will fail: ``` +$ cargo test + Compiling limit-tracker v0.1.0 (file:///projects/limit-tracker) + Finished `test` profile [unoptimized + debuginfo] target(s) in 0.91s + Running unittests src/lib.rs (target/debug/deps/limit_tracker-e599811fa246dbde) + +running 1 test +test tests::it_sends_an_over_75_percent_warning_message ... FAILED + +failures: + ---- tests::it_sends_an_over_75_percent_warning_message stdout ---- -thread 'main' panicked at 'already borrowed: BorrowMutError', src/lib.rs:60:53 + +thread 'tests::it_sends_an_over_75_percent_warning_message' panicked at src/lib.rs:60:53: +already borrowed: BorrowMutError note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace + + +failures: + tests::it_sends_an_over_75_percent_warning_message + +test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s + +error: test failed, to rerun pass `--lib` ``` -Notice that the code panicked with the message `already borrowed: -BorrowMutError`. This is how `RefCell` handles violations of the borrowing +Notice that the code panicked with the message `already borrowed: BorrowMutError`. This is how `RefCell` handles violations of the borrowing rules at runtime. Choosing to catch borrowing errors at runtime rather than compile time, as @@ -1535,7 +1630,12 @@ in a context where only immutable values are allowed. You can use `RefCell` despite its trade-offs to get more functionality than regular references provide. -### Allowing Multiple Owners of Mutable Data with Rc and RefCell + + + + + +### Allowing Multiple Owners of Mutable Data A common way to use `RefCell` is in combination with `Rc`. Recall that `Rc` lets you have multiple owners of some data, but it only gives immutable @@ -1550,7 +1650,7 @@ change the values in the lists. Listing 15-24 shows that by using a `RefCell` in the `Cons` definition, we can modify the value stored in all the lists. -Filename: src/main.rs +src/main.rs ``` #[derive(Debug)] @@ -1564,44 +1664,49 @@ use std::cell::RefCell; use std::rc::Rc; fn main() { - 1 let value = Rc::new(RefCell::new(5)); + let value = Rc::new(RefCell::new(5)); - 2 let a = Rc::new(Cons(Rc::clone(&value), Rc::new(Nil))); + let a = Rc::new(Cons(Rc::clone(&value), Rc::new(Nil))); let b = Cons(Rc::new(RefCell::new(3)), Rc::clone(&a)); let c = Cons(Rc::new(RefCell::new(4)), Rc::clone(&a)); - 3 *value.borrow_mut() += 10; + *value.borrow_mut() += 10; - println!("a after = {:?}", a); - println!("b after = {:?}", b); - println!("c after = {:?}", c); + println!("a after = {a:?}"); + println!("b after = {b:?}"); + println!("c after = {c:?}"); } ``` Listing 15-24: Using `Rc>` to create a `List` that we can mutate We create a value that is an instance of `Rc>` and store it in a -variable named `value` [1] so we can access it directly later. Then we create a -`List` in `a` with a `Cons` variant that holds `value` [2]. We need to clone -`value` so both `a` and `value` have ownership of the inner `5` value rather -than transferring ownership from `value` to `a` or having `a` borrow from -`value`. +variable named `value` so that we can access it directly later. Then, we create +a `List` in `a` with a `Cons` variant that holds `value`. We need to clone +`value` so that both `a` and `value` have ownership of the inner `5` value +rather than transferring ownership from `value` to `a` or having `a` borrow +from `value`. -We wrap the list `a` in an `Rc` so when we create lists `b` and `c`, they -can both refer to `a`, which is what we did in Listing 15-18. +We wrap the list `a` in an `Rc` so that when we create lists `b` and `c`, +they can both refer to `a`, which is what we did in Listing 15-18. After we’ve created the lists in `a`, `b`, and `c`, we want to add 10 to the -value in `value` [3]. We do this by calling `borrow_mut` on `value`, which uses -the automatic dereferencing feature we discussed in “Where’s the -> Operator?” -on page XX to dereference the `Rc` to the inner `RefCell` value. The -`borrow_mut` method returns a `RefMut` smart pointer, and we use the -dereference operator on it and change the inner value. +value in `value`. We do this by calling `borrow_mut` on `value`, which uses the +automatic dereferencing feature we discussed in “Where’s the `->` +Operator?” in Chapter 5 to dereference +the `Rc` to the inner `RefCell` value. The `borrow_mut` method returns a +`RefMut` smart pointer, and we use the dereference operator on it and change +the inner value. When we print `a`, `b`, and `c`, we can see that they all have the modified value of `15` rather than `5`: ``` +$ cargo run + Compiling cons-list v0.1.0 (file:///projects/cons-list) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.63s + Running `target/debug/cons-list` a after = Cons(RefCell { value: 15 }, Nil) b after = Cons(RefCell { value: 3 }, Cons(RefCell { value: 15 }, Nil)) c after = Cons(RefCell { value: 4 }, Cons(RefCell { value: 15 }, Nil)) @@ -1609,9 +1714,9 @@ c after = Cons(RefCell { value: 4 }, Cons(RefCell { value: 15 }, Nil)) This technique is pretty neat! By using `RefCell`, we have an outwardly immutable `List` value. But we can use the methods on `RefCell` that provide -access to its interior mutability so we can modify our data when we need to. -The runtime checks of the borrowing rules protect us from data races, and it’s -sometimes worth trading a bit of speed for this flexibility in our data +access to its interior mutability so that we can modify our data when we need +to. The runtime checks of the borrowing rules protect us from data races, and +it’s sometimes worth trading a bit of speed for this flexibility in our data structures. Note that `RefCell` does not work for multithreaded code! `Mutex` is the thread-safe version of `RefCell`, and we’ll discuss `Mutex` in Chapter 16. @@ -1622,7 +1727,7 @@ Rust’s memory safety guarantees make it difficult, but not impossible, to accidentally create memory that is never cleaned up (known as a *memory leak*). Preventing memory leaks entirely is not one of Rust’s guarantees, meaning memory leaks are memory safe in Rust. We can see that Rust allows memory leaks -by using `Rc` and `RefCell`: it’s possible to create references where +by using `Rc` and `RefCell`: It’s possible to create references where items refer to each other in a cycle. This creates memory leaks because the reference count of each item in the cycle will never reach 0, and the values will never be dropped. @@ -1633,7 +1738,7 @@ Let’s look at how a reference cycle might happen and how to prevent it, starting with the definition of the `List` enum and a `tail` method in Listing 15-25. -Filename: src/main.rs +src/main.rs ``` use crate::List::{Cons, Nil}; @@ -1642,12 +1747,12 @@ use std::rc::Rc; #[derive(Debug)] enum List { - 1 Cons(i32, RefCell>), + Cons(i32, RefCell>), Nil, } impl List { - 2 fn tail(&self) -> Option<&RefCell>> { + fn tail(&self) -> Option<&RefCell>> { match self { Cons(_, item) => Some(item), Nil => None, @@ -1656,77 +1761,70 @@ impl List { } ``` -Listing 15-25: A cons list definition that holds a `RefCell` so we can -modify what a `Cons` variant is referring to +Listing 15-25: A cons list definition that holds a `RefCell` so that we can modify what a `Cons` variant is referring to We’re using another variation of the `List` definition from Listing 15-5. The -second element in the `Cons` variant is now `RefCell>` [1], meaning -that instead of having the ability to modify the `i32` value as we did in -Listing 15-24, we want to modify the `List` value a `Cons` variant is pointing -to. We’re also adding a `tail` method [2] to make it convenient for us to -access the second item if we have a `Cons` variant. +second element in the `Cons` variant is now `RefCell>`, meaning that +instead of having the ability to modify the `i32` value as we did in Listing +15-24, we want to modify the `List` value a `Cons` variant is pointing to. +We’re also adding a `tail` method to make it convenient for us to access the +second item if we have a `Cons` variant. In Listing 15-26, we’re adding a `main` function that uses the definitions in Listing 15-25. This code creates a list in `a` and a list in `b` that points to -the list in `a`. Then it modifies the list in `a` to point to `b`, creating a +the list in `a`. Then, it modifies the list in `a` to point to `b`, creating a reference cycle. There are `println!` statements along the way to show what the reference counts are at various points in this process. -Filename: src/main.rs +src/main.rs ``` fn main() { - 1 let a = Rc::new(Cons(5, RefCell::new(Rc::new(Nil)))); + let a = Rc::new(Cons(5, RefCell::new(Rc::new(Nil)))); println!("a initial rc count = {}", Rc::strong_count(&a)); println!("a next item = {:?}", a.tail()); - 2 let b = Rc::new(Cons(10, RefCell::new(Rc::clone(&a)))); + let b = Rc::new(Cons(10, RefCell::new(Rc::clone(&a)))); - println!( - "a rc count after b creation = {}", - Rc::strong_count(&a) - ); + println!("a rc count after b creation = {}", Rc::strong_count(&a)); println!("b initial rc count = {}", Rc::strong_count(&b)); println!("b next item = {:?}", b.tail()); - 3 if let Some(link) = a.tail() { - 4 *link.borrow_mut() = Rc::clone(&b); + if let Some(link) = a.tail() { + *link.borrow_mut() = Rc::clone(&b); } - println!( - "b rc count after changing a = {}", - Rc::strong_count(&b) - ); - println!( - "a rc count after changing a = {}", - Rc::strong_count(&a) - ); + println!("b rc count after changing a = {}", Rc::strong_count(&b)); + println!("a rc count after changing a = {}", Rc::strong_count(&a)); // Uncomment the next line to see that we have a cycle; - // it will overflow the stack + // it will overflow the stack. // println!("a next item = {:?}", a.tail()); } ``` -Listing 15-26: Creating a reference cycle of two `List` values pointing to each -other +Listing 15-26: Creating a reference cycle of two `List` values pointing to each other We create an `Rc` instance holding a `List` value in the variable `a` -with an initial list of `5, Nil` [1]. We then create an `Rc` instance -holding another `List` value in the variable `b` that contains the value `10` -and points to the list in `a` [2]. +with an initial list of `5, Nil`. We then create an `Rc` instance holding +another `List` value in the variable `b` that contains the value `10` and +points to the list in `a`. -We modify `a` so it points to `b` instead of `Nil`, creating a cycle. We do -that by using the `tail` method to get a reference to the `RefCell>` -in `a`, which we put in the variable `link` [3]. Then we use the `borrow_mut` -method on the `RefCell>` to change the value inside from an `Rc` -that holds a `Nil` value to the `Rc` in `b` [4]. +We modify `a` so that it points to `b` instead of `Nil`, creating a cycle. We +do that by using the `tail` method to get a reference to the +`RefCell>` in `a`, which we put in the variable `link`. Then, we use +the `borrow_mut` method on the `RefCell>` to change the value inside +from an `Rc` that holds a `Nil` value to the `Rc` in `b`. When we run this code, keeping the last `println!` commented out for the moment, we’ll get this output: ``` +$ cargo run + Compiling cons-list v0.1.0 (file:///projects/cons-list) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.53s + Running `target/debug/cons-list` a initial rc count = 1 a next item = Some(RefCell { value: Nil }) a rc count after b creation = 2 @@ -1740,21 +1838,24 @@ The reference count of the `Rc` instances in both `a` and `b` is 2 after we change the list in `a` to point to `b`. At the end of `main`, Rust drops the variable `b`, which decreases the reference count of the `b` `Rc` instance from 2 to 1. The memory that `Rc` has on the heap won’t be -dropped at this point because its reference count is 1, not 0. Then Rust drops +dropped at this point because its reference count is 1, not 0. Then, Rust drops `a`, which decreases the reference count of the `a` `Rc` instance from 2 to 1 as well. This instance’s memory can’t be dropped either, because the other `Rc` instance still refers to it. The memory allocated to the list will -remain uncollected forever. To visualize this reference cycle, we’ve created a -diagram in Figure 15-4. +remain uncollected forever. To visualize this reference cycle, we’ve created +the diagram in Figure 15-4. -Figure 15-4: A reference cycle of lists `a` and `b` pointing to each other +A rectangle labeled 'a' that points to a rectangle containing the integer 5. A rectangle labeled 'b' that points to a rectangle containing the integer 10. The rectangle containing 5 points to the rectangle containing 10, and the rectangle containing 10 points back to the rectangle containing 5, creating a cycle. + +Figure 15-4: A reference cycle of lists `a` and `b` +pointing to each other If you uncomment the last `println!` and run the program, Rust will try to print this cycle with `a` pointing to `b` pointing to `a` and so forth until it overflows the stack. Compared to a real-world program, the consequences of creating a reference -cycle in this example aren’t very dire: right after we create the reference +cycle in this example aren’t very dire: Right after we create the reference cycle, the program ends. However, if a more complex program allocated lots of memory in a cycle and held onto it for a long time, the program would use more memory than it needed and might overwhelm the system, causing it to run out of @@ -1778,17 +1879,22 @@ Let’s look at an example using graphs made up of parent nodes and child nodes to see when non-ownership relationships are an appropriate way to prevent reference cycles. + + + + ### Preventing Reference Cycles Using Weak So far, we’ve demonstrated that calling `Rc::clone` increases the `strong_count` of an `Rc` instance, and an `Rc` instance is only cleaned -up if its `strong_count` is 0. You can also create a *weak reference* to the +up if its `strong_count` is 0. You can also create a weak reference to the value within an `Rc` instance by calling `Rc::downgrade` and passing a -reference to the `Rc`. Strong references are how you can share ownership of -an `Rc` instance. Weak references don’t express an ownership relationship, -and their count doesn’t affect when an `Rc` instance is cleaned up. They -won’t cause a reference cycle because any cycle involving some weak references -will be broken once the strong reference count of values involved is 0. +reference to the `Rc`. *Strong references* are how you can share ownership +of an `Rc` instance. *Weak references* don’t express an ownership +relationship, and their count doesn’t affect when an `Rc` instance is +cleaned up. They won’t cause a reference cycle, because any cycle involving +some weak references will be broken once the strong reference count of values +involved is 0. When you call `Rc::downgrade`, you get a smart pointer of type `Weak`. Instead of increasing the `strong_count` in the `Rc` instance by 1, calling @@ -1807,14 +1913,18 @@ Rust will ensure that the `Some` case and the `None` case are handled, and there won’t be an invalid pointer. As an example, rather than using a list whose items know only about the next -item, we’ll create a tree whose items know about their children items *and* -their parent items. +item, we’ll create a tree whose items know about their child items *and* their +parent items. + + + + -#### Creating a Tree Data Structure: A Node with Child Nodes +#### Creating a Tree Data Structure To start, we’ll build a tree with nodes that know about their child nodes. We’ll create a struct named `Node` that holds its own `i32` value as well as -references to its children `Node` values: +references to its child `Node` values: Filename: src/main.rs @@ -1830,8 +1940,8 @@ struct Node { ``` We want a `Node` to own its children, and we want to share that ownership with -variables so we can access each `Node` in the tree directly. To do this, we -define the `Vec` items to be values of type `Rc`. We also want to +variables so that we can access each `Node` in the tree directly. To do this, +we define the `Vec` items to be values of type `Rc`. We also want to modify which nodes are children of another node, so we have a `RefCell` in `children` around the `Vec>`. @@ -1839,7 +1949,7 @@ Next, we’ll use our struct definition and create one `Node` instance named `leaf` with the value `3` and no children, and another instance named `branch` with the value `5` and `leaf` as one of its children, as shown in Listing 15-27. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1855,8 +1965,7 @@ fn main() { } ``` -Listing 15-27: Creating a `leaf` node with no children and a `branch` node with -`leaf` as one of its children +Listing 15-27: Creating a `leaf` node with no children and a `branch` node with `leaf` as one of its children We clone the `Rc` in `leaf` and store that in `branch`, meaning the `Node` in `leaf` now has two owners: `leaf` and `branch`. We can get from @@ -1869,14 +1978,14 @@ parent. We’ll do that next. To make the child node aware of its parent, we need to add a `parent` field to our `Node` struct definition. The trouble is in deciding what the type of -`parent` should be. We know it can’t contain an `Rc` because that would +`parent` should be. We know it can’t contain an `Rc`, because that would create a reference cycle with `leaf.parent` pointing to `branch` and `branch.children` pointing to `leaf`, which would cause their `strong_count` values to never be 0. Thinking about the relationships another way, a parent node should own its -children: if a parent node is dropped, its child nodes should be dropped as -well. However, a child should not own its parent: if we drop a child node, the +children: If a parent node is dropped, its child nodes should be dropped as +well. However, a child should not own its parent: If we drop a child node, the parent should still exist. This is a case for weak references! So, instead of `Rc`, we’ll make the type of `parent` use `Weak`, @@ -1898,36 +2007,30 @@ struct Node { ``` A node will be able to refer to its parent node but doesn’t own its parent. In -Listing 15-28, we update `main` to use this new definition so the `leaf` node -will have a way to refer to its parent, `branch`. +Listing 15-28, we update `main` to use this new definition so that the `leaf` +node will have a way to refer to its parent, `branch`. -Filename: src/main.rs +src/main.rs ``` fn main() { let leaf = Rc::new(Node { value: 3, - 1 parent: RefCell::new(Weak::new()), + parent: RefCell::new(Weak::new()), children: RefCell::new(vec![]), }); - 2 println!( - "leaf parent = {:?}", - leaf.parent.borrow().upgrade() - ); + println!("leaf parent = {:?}", leaf.parent.borrow().upgrade()); let branch = Rc::new(Node { value: 5, - 3 parent: RefCell::new(Weak::new()), + parent: RefCell::new(Weak::new()), children: RefCell::new(vec![Rc::clone(&leaf)]), }); - 4 *leaf.parent.borrow_mut() = Rc::downgrade(&branch); + *leaf.parent.borrow_mut() = Rc::downgrade(&branch); - 5 println!( - "leaf parent = {:?}", - leaf.parent.borrow().upgrade() - ); + println!("leaf parent = {:?}", leaf.parent.borrow().upgrade()); } ``` @@ -1935,29 +2038,28 @@ Listing 15-28: A `leaf` node with a weak reference to its parent node, `branch` Creating the `leaf` node looks similar to Listing 15-27 with the exception of the `parent` field: `leaf` starts out without a parent, so we create a new, -empty `Weak` reference instance [1]. +empty `Weak` reference instance. At this point, when we try to get a reference to the parent of `leaf` by using the `upgrade` method, we get a `None` value. We see this in the output from the -first `println!` statement [2]: +first `println!` statement: ``` leaf parent = None ``` When we create the `branch` node, it will also have a new `Weak` -reference in the `parent` field [3] because `branch` doesn’t have a parent -node. We still have `leaf` as one of the children of `branch`. Once we have the -`Node` instance in `branch`, we can modify `leaf` to give it a `Weak` -reference to its parent [4]. We use the `borrow_mut` method on the -`RefCell>` in the `parent` field of `leaf`, and then we use the -`Rc::downgrade` function to create a `Weak` reference to `branch` from -the `Rc` in `branch`. +reference in the `parent` field because `branch` doesn’t have a parent node. We +still have `leaf` as one of the children of `branch`. Once we have the `Node` +instance in `branch`, we can modify `leaf` to give it a `Weak` reference +to its parent. We use the `borrow_mut` method on the `RefCell>` in +the `parent` field of `leaf`, and then we use the `Rc::downgrade` function to +create a `Weak` reference to `branch` from the `Rc` in `branch`. -When we print the parent of `leaf` again [5], this time we’ll get a `Some` -variant holding `branch`: now `leaf` can access its parent! When we print -`leaf`, we also avoid the cycle that eventually ended in a stack overflow like -we had in Listing 15-26; the `Weak` references are printed as `(Weak)`: +When we print the parent of `leaf` again, this time we’ll get a `Some` variant +holding `branch`: Now `leaf` can access its parent! When we print `leaf`, we +also avoid the cycle that eventually ended in a stack overflow like we had in +Listing 15-26; the `Weak` references are printed as `(Weak)`: ``` leaf parent = Some(Node { value: 5, parent: RefCell { value: (Weak) }, @@ -1977,7 +2079,7 @@ instances change by creating a new inner scope and moving the creation of created and then dropped when it goes out of scope. The modifications are shown in Listing 15-29. -Filename: src/main.rs +src/main.rs ``` fn main() { @@ -1987,13 +2089,13 @@ fn main() { children: RefCell::new(vec![]), }); - 1 println!( + println!( "leaf strong = {}, weak = {}", Rc::strong_count(&leaf), Rc::weak_count(&leaf), ); - 2 { + { let branch = Rc::new(Node { value: 5, parent: RefCell::new(Weak::new()), @@ -2002,24 +2104,21 @@ fn main() { *leaf.parent.borrow_mut() = Rc::downgrade(&branch); - 3 println!( + println!( "branch strong = {}, weak = {}", Rc::strong_count(&branch), Rc::weak_count(&branch), ); - 4 println!( + println!( "leaf strong = {}, weak = {}", Rc::strong_count(&leaf), Rc::weak_count(&leaf), ); - 5 } + } - 6 println!( - "leaf parent = {:?}", - leaf.parent.borrow().upgrade() - ); - 7 println!( + println!("leaf parent = {:?}", leaf.parent.borrow().upgrade()); + println!( "leaf strong = {}, weak = {}", Rc::strong_count(&leaf), Rc::weak_count(&leaf), @@ -2027,27 +2126,26 @@ fn main() { } ``` -Listing 15-29: Creating `branch` in an inner scope and examining strong and -weak reference counts +Listing 15-29: Creating `branch` in an inner scope and examining strong and weak reference counts After `leaf` is created, its `Rc` has a strong count of 1 and a weak -count of 0 [1]. In the inner scope [2], we create `branch` and associate it -with `leaf`, at which point when we print the counts [3], the `Rc` in -`branch` will have a strong count of 1 and a weak count of 1 (for `leaf.parent` -pointing to `branch` with a `Weak`). When we print the counts in `leaf` -[4], we’ll see it will have a strong count of 2 because `branch` now has a -clone of the `Rc` of `leaf` stored in `branch.children`, but will still -have a weak count of 0. - -When the inner scope ends [5], `branch` goes out of scope and the strong count -of the `Rc` decreases to 0, so its `Node` is dropped. The weak count of 1 +count of 0. In the inner scope, we create `branch` and associate it with +`leaf`, at which point when we print the counts, the `Rc` in `branch` +will have a strong count of 1 and a weak count of 1 (for `leaf.parent` pointing +to `branch` with a `Weak`). When we print the counts in `leaf`, we’ll see +it will have a strong count of 2 because `branch` now has a clone of the +`Rc` of `leaf` stored in `branch.children` but will still have a weak +count of 0. + +When the inner scope ends, `branch` goes out of scope and the strong count of +the `Rc` decreases to 0, so its `Node` is dropped. The weak count of 1 from `leaf.parent` has no bearing on whether or not `Node` is dropped, so we don’t get any memory leaks! If we try to access the parent of `leaf` after the end of the scope, we’ll get -`None` again [6]. At the end of the program [7], the `Rc` in `leaf` has a -strong count of 1 and a weak count of 0 because the variable `leaf` is now the -only reference to the `Rc` again. +`None` again. At the end of the program, the `Rc` in `leaf` has a strong +count of 1 and a weak count of 0 because the variable `leaf` is now the only +reference to the `Rc` again. All of the logic that manages the counts and value dropping is built into `Rc` and `Weak` and their implementations of the `Drop` trait. By @@ -2062,7 +2160,7 @@ This chapter covered how to use smart pointers to make different guarantees and trade-offs from those Rust makes by default with regular references. The `Box` type has a known size and points to data allocated on the heap. The `Rc` type keeps track of the number of references to data on the heap so -that data can have multiple owners. The `RefCell` type with its interior +that the data can have multiple owners. The `RefCell` type with its interior mutability gives us a type that we can use when we need an immutable type but need to change an inner value of that type; it also enforces the borrowing rules at runtime instead of at compile time. @@ -2072,9 +2170,8 @@ functionality of smart pointers. We explored reference cycles that can cause memory leaks and how to prevent them using `Weak`. If this chapter has piqued your interest and you want to implement your own -smart pointers, check out “The Rustonomicon” at -*https://doc.rust-lang.org/stable/nomicon* for more useful information. +smart pointers, check out “The Rustonomicon” at *../nomicon/index.html* for more useful +information. Next, we’ll talk about concurrency in Rust. You’ll even learn about a few new smart pointers. - diff --git a/nostarch/chapter16.md b/nostarch/chapter16.md index 7c5389e4f4..1877883b2f 100644 --- a/nostarch/chapter16.md +++ b/nostarch/chapter16.md @@ -9,11 +9,11 @@ directory, so all fixes need to be made in `/src/`. # Fearless Concurrency Handling concurrent programming safely and efficiently is another of Rust’s -major goals. *Concurrent programming*, where different parts of a program -execute independently, and *parallel programming*, where different parts of a -program execute at the same time, are becoming increasingly important as more +major goals. *Concurrent programming*, in which different parts of a program +execute independently, and *parallel programming*, in which different parts of +a program execute at the same time, are becoming increasingly important as more computers take advantage of their multiple processors. Historically, -programming in these contexts has been difficult and error prone: Rust hopes to +programming in these contexts has been difficult and error-prone. Rust hopes to change that. Initially, the Rust team thought that ensuring memory safety and preventing @@ -26,15 +26,15 @@ than making you spend lots of time trying to reproduce the exact circumstances under which a runtime concurrency bug occurs, incorrect code will refuse to compile and present an error explaining the problem. As a result, you can fix your code while you’re working on it rather than potentially after it has been -shipped to production. We’ve nicknamed this aspect of Rust *fearless* -*concurrency*. Fearless concurrency allows you to write code that is free of +shipped to production. We’ve nicknamed this aspect of Rust *fearless +concurrency*. Fearless concurrency allows you to write code that is free of subtle bugs and is easy to refactor without introducing new bugs. > Note: For simplicity’s sake, we’ll refer to many of the problems as -*concurrent* rather than being more precise by saying *concurrent and/or -parallel*. If this book were about concurrency and/or parallelism, we’d be more -specific. For this chapter, please mentally substitute *concurrent and/or -parallel* whenever we use *concurrent*. +> *concurrent* rather than being more precise by saying *concurrent and/or +> parallel*. For this chapter, please mentally substitute *concurrent and/or +> parallel* whenever we use *concurrent*. In the next chapter, where the +> distinction matters more, we’ll be more specific. Many languages are dogmatic about the solutions they offer for handling concurrent problems. For example, Erlang has elegant functionality for @@ -52,9 +52,9 @@ Here are the topics we’ll cover in this chapter: * How to create threads to run multiple pieces of code at the same time * *Message-passing* concurrency, where channels send messages between threads * *Shared-state* concurrency, where multiple threads have access to some piece -of data + of data * The `Sync` and `Send` traits, which extend Rust’s concurrency guarantees to -user-defined types as well as types provided by the standard library + user-defined types as well as types provided by the standard library ## Using Threads to Run Code Simultaneously @@ -62,7 +62,7 @@ In most current operating systems, an executed program’s code is run in a *process*, and the operating system will manage multiple processes at once. Within a program, you can also have independent parts that run simultaneously. The features that run these independent parts are called *threads*. For -example, a web server could have multiple threads so that it could respond to +example, a web server could have multiple threads so that it can respond to more than one request at the same time. Splitting the computation in your program into multiple threads to run multiple @@ -71,12 +71,12 @@ Because threads can run simultaneously, there’s no inherent guarantee about th order in which parts of your code on different threads will run. This can lead to problems, such as: -* Race conditions, where threads are accessing data or resources in an -inconsistent order -* Deadlocks, where two threads are waiting for each other, preventing both -threads from continuing -* Bugs that happen only in certain situations and are hard to reproduce and fix -reliably +* Race conditions, in which threads are accessing data or resources in an + inconsistent order +* Deadlocks, in which two threads are waiting for each other, preventing both + threads from continuing +* Bugs that only happen in certain situations and are hard to reproduce and fix + reliably Rust attempts to mitigate the negative effects of using threads, but programming in a multithreaded context still takes careful thought and requires @@ -84,11 +84,12 @@ a code structure that is different from that in programs running in a single thread. Programming languages implement threads in a few different ways, and many -operating systems provide an API the language can call for creating new -threads. The Rust standard library uses a *1:1* model of thread implementation, -whereby a program uses one operating system thread per one language thread. -There are crates that implement other models of threading that make different -trade-offs to the 1:1 model. +operating systems provide an API the programming language can call for creating +new threads. The Rust standard library uses a *1:1* model of thread +implementation, whereby a program uses one operating system thread per one +language thread. There are crates that implement other models of threading that +make different trade-offs to the 1:1 model. (Rust’s async system, which we will +see in the next chapter, provides another approach to concurrency as well.) ### Creating a New Thread with spawn @@ -97,7 +98,7 @@ closure (we talked about closures in Chapter 13) containing the code we want to run in the new thread. The example in Listing 16-1 prints some text from a main thread and other text from a new thread. -Filename: src/main.rs +src/main.rs ``` use std::thread; @@ -118,14 +119,17 @@ fn main() { } ``` -Listing 16-1: Creating a new thread to print one thing while the main thread -prints something else +Listing 16-1: Creating a new thread to print one thing while the main thread prints something else Note that when the main thread of a Rust program completes, all spawned threads are shut down, whether or not they have finished running. The output from this program might be a little different every time, but it will look similar to the following: + + ``` hi number 1 from the main thread! hi number 1 from the spawned thread! @@ -140,17 +144,21 @@ hi number 5 from the spawned thread! The calls to `thread::sleep` force a thread to stop its execution for a short duration, allowing a different thread to run. The threads will probably take -turns, but that isn’t guaranteed: it depends on how your operating system +turns, but that isn’t guaranteed: It depends on how your operating system schedules the threads. In this run, the main thread printed first, even though the print statement from the spawned thread appears first in the code. And even -though we told the spawned thread to print until `i` is 9, it only got to 5 +though we told the spawned thread to print until `i` is `9`, it only got to `5` before the main thread shut down. If you run this code and only see output from the main thread, or don’t see any overlap, try increasing the numbers in the ranges to create more opportunities for the operating system to switch between the threads. -### Waiting for All Threads to Finish Using join Handles + + + + +### Waiting for All Threads to Finish The code in Listing 16-1 not only stops the spawned thread prematurely most of the time due to the main thread ending, but because there is no guarantee on @@ -162,10 +170,10 @@ prematurely by saving the return value of `thread::spawn` in a variable. The return type of `thread::spawn` is `JoinHandle`. A `JoinHandle` is an owned value that, when we call the `join` method on it, will wait for its thread to finish. Listing 16-2 shows how to use the `JoinHandle` of the -thread we created in Listing 16-1 and call `join` to make sure the spawned -thread finishes before `main` exits. +thread we created in Listing 16-1 and how to call `join` to make sure the +spawned thread finishes before `main` exits. -Filename: src/main.rs +src/main.rs ``` use std::thread; @@ -188,8 +196,7 @@ fn main() { } ``` -Listing 16-2: Saving a `JoinHandle` from `thread::spawn` to guarantee the -thread is run to completion +Listing 16-2: Saving a `JoinHandle` from `thread::spawn` to guarantee the thread is run to completion Calling `join` on the handle blocks the thread currently running until the thread represented by the handle terminates. *Blocking* a thread means that @@ -197,6 +204,10 @@ thread is prevented from performing work or exiting. Because we’ve put the cal to `join` after the main thread’s `for` loop, running Listing 16-2 should produce output similar to this: + + ``` hi number 1 from the main thread! hi number 2 from the main thread! @@ -219,7 +230,7 @@ call to `handle.join()` and does not end until the spawned thread is finished. But let’s see what happens when we instead move `handle.join()` before the `for` loop in `main`, like this: -Filename: src/main.rs +src/main.rs ``` use std::thread; @@ -242,9 +253,15 @@ fn main() { } ``` + + The main thread will wait for the spawned thread to finish and then run its `for` loop, so the output won’t be interleaved anymore, as shown here: + + ``` hi number 1 from the spawned thread! hi number 2 from the spawned thread! @@ -269,18 +286,17 @@ threads run at the same time. We’ll often use the `move` keyword with closures passed to `thread::spawn` because the closure will then take ownership of the values it uses from the environment, thus transferring ownership of those values from one thread to -another. In “Capturing the Environment with Closures” on page XX, we discussed -`move` in the context of closures. Now we’ll concentrate more on the -interaction between `move` and `thread::spawn`. +another. In “Capturing References or Moving Ownership” in Chapter 13, we discussed `move` in the context of closures. Now we’ll +concentrate more on the interaction between `move` and `thread::spawn`. Notice in Listing 16-1 that the closure we pass to `thread::spawn` takes no -arguments: we’re not using any data from the main thread in the spawned +arguments: We’re not using any data from the main thread in the spawned thread’s code. To use data from the main thread in the spawned thread, the spawned thread’s closure must capture the values it needs. Listing 16-3 shows an attempt to create a vector in the main thread and use it in the spawned thread. However, this won’t work yet, as you’ll see in a moment. -Filename: src/main.rs +src/main.rs ``` use std::thread; @@ -289,15 +305,14 @@ fn main() { let v = vec![1, 2, 3]; let handle = thread::spawn(|| { - println!("Here's a vector: {:?}", v); + println!("Here's a vector: {v:?}"); }); handle.join().unwrap(); } ``` -Listing 16-3: Attempting to use a vector created by the main thread in another -thread +Listing 16-3: Attempting to use a vector created by the main thread in another thread The closure uses `v`, so it will capture `v` and make it part of the closure’s environment. Because `thread::spawn` runs this closure in a new thread, we @@ -305,28 +320,31 @@ should be able to access `v` inside that new thread. But when we compile this example, we get the following error: ``` -error[E0373]: closure may outlive the current function, but it borrows `v`, -which is owned by the current function +$ cargo run + Compiling threads v0.1.0 (file:///projects/threads) +error[E0373]: closure may outlive the current function, but it borrows `v`, which is owned by the current function --> src/main.rs:6:32 | 6 | let handle = thread::spawn(|| { | ^^ may outlive borrowed value `v` -7 | println!("Here's a vector: {:?}", v); - | - `v` is borrowed here +7 | println!("Here's a vector: {v:?}"); + | - `v` is borrowed here | note: function requires argument type to outlive `'static` --> src/main.rs:6:18 | 6 | let handle = thread::spawn(|| { | __________________^ -7 | | println!("Here's a vector: {:?}", v); +7 | | println!("Here's a vector: {v:?}"); 8 | | }); | |______^ -help: to force the closure to take ownership of `v` (and any other referenced -variables), use the `move` keyword +help: to force the closure to take ownership of `v` (and any other referenced variables), use the `move` keyword | 6 | let handle = thread::spawn(move || { | ++++ + +For more information about this error, try `rustc --explain E0373`. +error: could not compile `threads` (bin "threads") due to 1 previous error ``` Rust *infers* how to capture `v`, and because `println!` only needs a reference @@ -337,7 +355,7 @@ reference to `v` will always be valid. Listing 16-4 provides a scenario that’s more likely to have a reference to `v` that won’t be valid. -Filename: src/main.rs +src/main.rs ``` use std::thread; @@ -346,7 +364,7 @@ fn main() { let v = vec![1, 2, 3]; let handle = thread::spawn(|| { - println!("Here's a vector: {:?}", v); + println!("Here's a vector: {v:?}"); }); drop(v); // oh no! @@ -355,8 +373,7 @@ fn main() { } ``` -Listing 16-4: A thread with a closure that attempts to capture a reference to -`v` from a main thread that drops `v` +Listing 16-4: A thread with a closure that attempts to capture a reference to `v` from a main thread that drops `v` If Rust allowed us to run this code, there’s a possibility that the spawned thread would be immediately put in the background without running at all. The @@ -368,9 +385,12 @@ is also invalid. Oh no! To fix the compiler error in Listing 16-3, we can use the error message’s advice: + + ``` -help: to force the closure to take ownership of `v` (and any other referenced -variables), use the `move` keyword +help: to force the closure to take ownership of `v` (and any other referenced variables), use the `move` keyword | 6 | let handle = thread::spawn(move || { | ++++ @@ -381,7 +401,7 @@ ownership of the values it’s using rather than allowing Rust to infer that it should borrow the values. The modification to Listing 16-3 shown in Listing 16-5 will compile and run as we intend. -Filename: src/main.rs +src/main.rs ``` use std::thread; @@ -390,15 +410,14 @@ fn main() { let v = vec![1, 2, 3]; let handle = thread::spawn(move || { - println!("Here's a vector: {:?}", v); + println!("Here's a vector: {v:?}"); }); handle.join().unwrap(); } ``` -Listing 16-5: Using the `move` keyword to force a closure to take ownership of -the values it uses +Listing 16-5: Using the `move` keyword to force a closure to take ownership of the values it uses We might be tempted to try the same thing to fix the code in Listing 16-4 where the main thread called `drop` by using a `move` closure. However, this fix will @@ -408,29 +427,32 @@ closure’s environment, and we could no longer call `drop` on it in the main thread. We would get this compiler error instead: ``` +$ cargo run + Compiling threads v0.1.0 (file:///projects/threads) error[E0382]: use of moved value: `v` --> src/main.rs:10:10 | 4 | let v = vec![1, 2, 3]; - | - move occurs because `v` has type `Vec`, which does not -implement the `Copy` trait + | - move occurs because `v` has type `Vec`, which does not implement the `Copy` trait 5 | 6 | let handle = thread::spawn(move || { | ------- value moved into closure here -7 | println!("Here's a vector: {:?}", v); - | - variable moved due to use in -closure +7 | println!("Here's a vector: {v:?}"); + | - variable moved due to use in closure ... 10 | drop(v); // oh no! | ^ value used here after move + +For more information about this error, try `rustc --explain E0382`. +error: could not compile `threads` (bin "threads") due to 1 previous error ``` Rust’s ownership rules have saved us again! We got an error from the code in Listing 16-3 because Rust was being conservative and only borrowing `v` for the thread, which meant the main thread could theoretically invalidate the spawned thread’s reference. By telling Rust to move ownership of `v` to the spawned -thread, we’re guaranteeing Rust that the main thread won’t use `v` anymore. If -we change Listing 16-4 in the same way, we’re then violating the ownership +thread, we’re guaranteeing to Rust that the main thread won’t use `v` anymore. +If we change Listing 16-4 in the same way, we’re then violating the ownership rules when we try to use `v` in the main thread. The `move` keyword overrides Rust’s conservative default of borrowing; it doesn’t let us violate the ownership rules. @@ -438,16 +460,19 @@ ownership rules. Now that we’ve covered what threads are and the methods supplied by the thread API, let’s look at some situations in which we can use threads. -## Using Message Passing to Transfer Data Between Threads + + + -One increasingly popular approach to ensuring safe concurrency is *message -passing*, where threads or actors communicate by sending each other messages -containing data. Here’s the idea in a slogan from the Go language documentation -at *https://golang.org/doc/effective_go.html#concurrency*: “Do not communicate -by sharing memory; instead, share memory by communicating.” +## Transfer Data Between Threads with Message Passing + +One increasingly popular approach to ensuring safe concurrency is message +passing, where threads or actors communicate by sending each other messages +containing data. Here’s the idea in a slogan from the Go language documentation at *https://golang.org/doc/effective_go.html#concurrency*: +“Do not communicate by sharing memory; instead, share memory by communicating.” To accomplish message-sending concurrency, Rust’s standard library provides an -implementation of *channels*. A channel is a general programming concept by +implementation of channels. A *channel* is a general programming concept by which data is sent from one thread to another. You can imagine a channel in programming as being like a directional channel of @@ -473,7 +498,7 @@ First, in Listing 16-6, we’ll create a channel but not do anything with it. Note that this won’t compile yet because Rust can’t tell what type of values we want to send over the channel. -Filename: src/main.rs +src/main.rs ``` use std::sync::mpsc; @@ -489,7 +514,7 @@ We create a new channel using the `mpsc::channel` function; `mpsc` stands for *multiple producer, single consumer*. In short, the way Rust’s standard library implements channels means a channel can have multiple *sending* ends that produce values but only one *receiving* end that consumes those values. Imagine -multiple streams flowing together into one big river: everything sent down any +multiple streams flowing together into one big river: Everything sent down any of the streams will end up in one river at the end. We’ll start with a single producer for now, but we’ll add multiple producers when we get this example working. @@ -500,16 +525,16 @@ end—the receiver. The abbreviations `tx` and `rx` are traditionally used in many fields for *transmitter* and *receiver*, respectively, so we name our variables as such to indicate each end. We’re using a `let` statement with a pattern that destructures the tuples; we’ll discuss the use of patterns in -`let` statements and destructuring in Chapter 18. For now, know that using a +`let` statements and destructuring in Chapter 19. For now, know that using a `let` statement in this way is a convenient approach to extract the pieces of the tuple returned by `mpsc::channel`. Let’s move the transmitting end into a spawned thread and have it send one -string so the spawned thread is communicating with the main thread, as shown in -Listing 16-7. This is like putting a rubber duck in the river upstream or -sending a chat message from one thread to another. +string so that the spawned thread is communicating with the main thread, as +shown in Listing 16-7. This is like putting a rubber duck in the river upstream +or sending a chat message from one thread to another. -Filename: src/main.rs +src/main.rs ``` use std::sync::mpsc; @@ -528,7 +553,7 @@ fn main() { Listing 16-7: Moving `tx` to a spawned thread and sending `"hi"` Again, we’re using `thread::spawn` to create a new thread and then using `move` -to move `tx` into the closure so the spawned thread owns `tx`. The spawned +to move `tx` into the closure so that the spawned thread owns `tx`. The spawned thread needs to own the transmitter to be able to send messages through the channel. @@ -536,14 +561,14 @@ The transmitter has a `send` method that takes the value we want to send. The `send` method returns a `Result` type, so if the receiver has already been dropped and there’s nowhere to send a value, the send operation will return an error. In this example, we’re calling `unwrap` to panic in case of an -error. But in a real application, we would handle it properly: return to +error. But in a real application, we would handle it properly: Return to Chapter 9 to review strategies for proper error handling. In Listing 16-8, we’ll get the value from the receiver in the main thread. This is like retrieving the rubber duck from the water at the end of the river or receiving a chat message. -Filename: src/main.rs +src/main.rs ``` use std::sync::mpsc; @@ -573,7 +598,7 @@ an error to signal that no more values will be coming. The `try_recv` method doesn’t block, but will instead return a `Result` immediately: an `Ok` value holding a message if one is available and an `Err` value if there aren’t any messages this time. Using `try_recv` is useful if -this thread has other work to do while waiting for messages: we could write a +this thread has other work to do while waiting for messages: We could write a loop that calls `try_recv` every so often, handles a message if one is available, and otherwise does other work for a little while until checking again. @@ -585,23 +610,31 @@ thread is appropriate. When we run the code in Listing 16-8, we’ll see the value printed from the main thread: + + ``` Got: hi ``` Perfect! -### Channels and Ownership Transference + + + + +### Transferring Ownership Through Channels The ownership rules play a vital role in message sending because they help you write safe, concurrent code. Preventing errors in concurrent programming is the advantage of thinking about ownership throughout your Rust programs. Let’s do an experiment to show how channels and ownership work together to prevent -problems: we’ll try to use a `val` value in the spawned thread *after* we’ve +problems: We’ll try to use a `val` value in the spawned thread *after* we’ve sent it down the channel. Try compiling the code in Listing 16-9 to see why this code isn’t allowed. -Filename: src/main.rs +src/main.rs ``` use std::sync::mpsc; @@ -624,23 +657,29 @@ fn main() { Listing 16-9: Attempting to use `val` after we’ve sent it down the channel Here, we try to print `val` after we’ve sent it down the channel via `tx.send`. -Allowing this would be a bad idea: once the value has been sent to another +Allowing this would be a bad idea: Once the value has been sent to another thread, that thread could modify or drop it before we try to use the value again. Potentially, the other thread’s modifications could cause errors or unexpected results due to inconsistent or nonexistent data. However, Rust gives us an error if we try to compile the code in Listing 16-9: ``` +$ cargo run + Compiling message-passing v0.1.0 (file:///projects/message-passing) error[E0382]: borrow of moved value: `val` - --> src/main.rs:10:31 + --> src/main.rs:10:26 | 8 | let val = String::from("hi"); - | --- move occurs because `val` has type `String`, which does -not implement the `Copy` trait + | --- move occurs because `val` has type `String`, which does not implement the `Copy` trait 9 | tx.send(val).unwrap(); | --- value moved here 10 | println!("val is {val}"); - | ^^^ value borrowed here after move + | ^^^^^ value borrowed here after move + | + = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) + +For more information about this error, try `rustc --explain E0382`. +error: could not compile `message-passing` (bin "message-passing") due to 1 previous error ``` Our concurrency mistake has caused a compile-time error. The `send` function @@ -648,15 +687,20 @@ takes ownership of its parameter, and when the value is moved the receiver takes ownership of it. This stops us from accidentally using the value again after sending it; the ownership system checks that everything is okay. -### Sending Multiple Values and Seeing the Receiver Waiting + + + + +### Sending Multiple Values The code in Listing 16-8 compiled and ran, but it didn’t clearly show us that -two separate threads were talking to each other over the channel. In Listing -16-10 we’ve made some modifications that will prove the code in Listing 16-8 is -running concurrently: the spawned thread will now send multiple messages and -pause for a second between each message. +two separate threads were talking to each other over the channel. + +In Listing 16-10, we’ve made some modifications that will prove the code in +Listing 16-8 is running concurrently: The spawned thread will now send multiple +messages and pause for a second between each message. -Filename: src/main.rs +src/main.rs ``` use std::sync::mpsc; @@ -694,12 +738,16 @@ between each by calling the `thread::sleep` function with a `Duration` value of one second. In the main thread, we’re not calling the `recv` function explicitly anymore: -instead, we’re treating `rx` as an iterator. For each value received, we’re +Instead, we’re treating `rx` as an iterator. For each value received, we’re printing it. When the channel is closed, iteration will end. When running the code in Listing 16-10, you should see the following output with a one-second pause in between each line: + + ``` Got: hi Got: from @@ -711,54 +759,58 @@ Because we don’t have any code that pauses or delays in the `for` loop in the main thread, we can tell that the main thread is waiting to receive values from the spawned thread. -### Creating Multiple Producers by Cloning the Transmitter + + + + +### Creating Multiple Producers Earlier we mentioned that `mpsc` was an acronym for *multiple producer, single consumer*. Let’s put `mpsc` to use and expand the code in Listing 16-10 to create multiple threads that all send values to the same receiver. We can do so by cloning the transmitter, as shown in Listing 16-11. -Filename: src/main.rs +src/main.rs ``` ---snip-- - -let (tx, rx) = mpsc::channel(); - -let tx1 = tx.clone(); -thread::spawn(move || { - let vals = vec![ - String::from("hi"), - String::from("from"), - String::from("the"), - String::from("thread"), - ]; - - for val in vals { - tx1.send(val).unwrap(); - thread::sleep(Duration::from_secs(1)); - } -}); + // --snip-- -thread::spawn(move || { - let vals = vec![ - String::from("more"), - String::from("messages"), - String::from("for"), - String::from("you"), - ]; + let (tx, rx) = mpsc::channel(); - for val in vals { - tx.send(val).unwrap(); - thread::sleep(Duration::from_secs(1)); - } -}); + let tx1 = tx.clone(); + thread::spawn(move || { + let vals = vec![ + String::from("hi"), + String::from("from"), + String::from("the"), + String::from("thread"), + ]; -for received in rx { - println!("Got: {received}"); -} + for val in vals { + tx1.send(val).unwrap(); + thread::sleep(Duration::from_secs(1)); + } + }); + + thread::spawn(move || { + let vals = vec![ + String::from("more"), + String::from("messages"), + String::from("for"), + String::from("you"), + ]; ---snip-- + for val in vals { + tx.send(val).unwrap(); + thread::sleep(Duration::from_secs(1)); + } + }); + + for received in rx { + println!("Got: {received}"); + } + + // --snip-- ``` Listing 16-11: Sending multiple messages from multiple producers @@ -770,6 +822,10 @@ This gives us two threads, each sending different messages to the one receiver. When you run the code, your output should look something like this: + + ``` Got: hi Got: more @@ -801,7 +857,7 @@ message-passing enthusiasts caution not to use memory sharing? In a way, channels in any programming language are similar to single ownership because once you transfer a value down a channel, you should no longer use that -value. Shared-memory concurrency is like multiple ownership: multiple threads +value. Shared-memory concurrency is like multiple ownership: Multiple threads can access the same memory location at the same time. As you saw in Chapter 15, where smart pointers made multiple ownership possible, multiple ownership can add complexity because these different owners need managing. Rust’s type system @@ -809,12 +865,16 @@ and ownership rules greatly assist in getting this management correct. For an example, let’s look at mutexes, one of the more common concurrency primitives for shared memory. -### Using Mutexes to Allow Access to Data from One Thread at a Time + + + + +### Controlling Access with Mutexes *Mutex* is an abbreviation for *mutual exclusion*, as in a mutex allows only one thread to access some data at any given time. To access the data in a mutex, a thread must first signal that it wants access by asking to acquire the -mutex’s *lock*. The lock is a data structure that is part of the mutex that +mutex’s lock. The *lock* is a data structure that is part of the mutex that keeps track of who currently has exclusive access to the data. Therefore, the mutex is described as *guarding* the data it holds via the locking system. @@ -823,7 +883,7 @@ remember two rules: 1. You must attempt to acquire the lock before using the data. 1. When you’re done with the data that the mutex guards, you must unlock the -data so other threads can acquire the lock. + data so that other threads can acquire the lock. For a real-world metaphor for a mutex, imagine a panel discussion at a conference with only one microphone. Before a panelist can speak, they have to @@ -843,29 +903,28 @@ system and ownership rules, you can’t get locking and unlocking wrong. As an example of how to use a mutex, let’s start by using a mutex in a single-threaded context, as shown in Listing 16-12. -Filename: src/main.rs +src/main.rs ``` use std::sync::Mutex; fn main() { - 1 let m = Mutex::new(5); + let m = Mutex::new(5); { - 2 let mut num = m.lock().unwrap(); - 3 *num = 6; - 4 } + let mut num = m.lock().unwrap(); + *num = 6; + } - 5 println!("m = {:?}", m); + println!("m = {m:?}"); } ``` -Listing 16-12: Exploring the API of `Mutex` in a single-threaded context for -simplicity +Listing 16-12: Exploring the API of `Mutex` in a single-threaded context for simplicity -As with many types, we create a `Mutex` using the associated function `new` -[1]. To access the data inside the mutex, we use the `lock` method to acquire -the lock [2]. This call will block the current thread so it can’t do any work +As with many types, we create a `Mutex` using the associated function `new`. +To access the data inside the mutex, we use the `lock` method to acquire the +lock. This call will block the current thread so that it can’t do any work until it’s our turn to have the lock. The call to `lock` would fail if another thread holding the lock panicked. In @@ -879,20 +938,22 @@ that we acquire a lock before using the value in `m`. The type of `m` is value. We can’t forget; the type system won’t let us access the inner `i32` otherwise. -As you might suspect, `Mutex` is a smart pointer. More accurately, the call -to `lock` *returns* a smart pointer called `MutexGuard`, wrapped in a -`LockResult` that we handled with the call to `unwrap`. The `MutexGuard` smart -pointer implements `Deref` to point at our inner data; the smart pointer also -has a `Drop` implementation that releases the lock automatically when a -`MutexGuard` goes out of scope, which happens at the end of the inner scope -[4]. As a result, we don’t risk forgetting to release the lock and blocking the -mutex from being used by other threads because the lock release happens -automatically. +The call to `lock` returns a type called `MutexGuard`, wrapped in a +`LockResult` that we handled with the call to `unwrap`. The `MutexGuard` type +implements `Deref` to point at our inner data; the type also has a `Drop` +implementation that releases the lock automatically when a `MutexGuard` goes +out of scope, which happens at the end of the inner scope. As a result, we +don’t risk forgetting to release the lock and blocking the mutex from being +used by other threads because the lock release happens automatically. After dropping the lock, we can print the mutex value and see that we were able -to change the inner `i32` to `6` [5]. +to change the inner `i32` to `6`. -#### Sharing a Mutex Between Multiple Threads + + + + +#### Shared Access to Mutex Now let’s try to share a value between multiple threads using `Mutex`. We’ll spin up 10 threads and have them each increment a counter value by 1, so the @@ -900,63 +961,77 @@ counter goes from 0 to 10. The example in Listing 16-13 will have a compiler error, and we’ll use that error to learn more about using `Mutex` and how Rust helps us use it correctly. -Filename: src/main.rs +src/main.rs ``` use std::sync::Mutex; use std::thread; fn main() { - 1 let counter = Mutex::new(0); + let counter = Mutex::new(0); let mut handles = vec![]; - 2 for _ in 0..10 { - 3 let handle = thread::spawn(move || { - 4 let mut num = counter.lock().unwrap(); + for _ in 0..10 { + let handle = thread::spawn(move || { + let mut num = counter.lock().unwrap(); - 5 *num += 1; + *num += 1; }); - 6 handles.push(handle); + handles.push(handle); } for handle in handles { - 7 handle.join().unwrap(); + handle.join().unwrap(); } - 8 println!("Result: {}", *counter.lock().unwrap()); + println!("Result: {}", *counter.lock().unwrap()); } ``` Listing 16-13: Ten threads, each incrementing a counter guarded by a `Mutex` -We create a `counter` variable to hold an `i32` inside a `Mutex` [1], as we -did in Listing 16-12. Next, we create 10 threads by iterating over a range of -numbers [2]. We use `thread::spawn` and give all the threads the same closure: -one that moves the counter into the thread [3], acquires a lock on the -`Mutex` by calling the `lock` method [4], and then adds 1 to the value in -the mutex [5]. When a thread finishes running its closure, `num` will go out of -scope and release the lock so another thread can acquire it. +We create a `counter` variable to hold an `i32` inside a `Mutex`, as we did +in Listing 16-12. Next, we create 10 threads by iterating over a range of +numbers. We use `thread::spawn` and give all the threads the same closure: one +that moves the counter into the thread, acquires a lock on the `Mutex` by +calling the `lock` method, and then adds 1 to the value in the mutex. When a +thread finishes running its closure, `num` will go out of scope and release the +lock so that another thread can acquire it. -In the main thread, we collect all the join handles [6]. Then, as we did in -Listing 16-2, we call `join` on each handle to make sure all the threads finish -[7]. At that point, the main thread will acquire the lock and print the result -of this program [8]. +In the main thread, we collect all the join handles. Then, as we did in Listing +16-2, we call `join` on each handle to make sure all the threads finish. At +that point, the main thread will acquire the lock and print the result of this +program. We hinted that this example wouldn’t compile. Now let’s find out why! ``` -error[E0382]: use of moved value: `counter` - --> src/main.rs:9:36 +$ cargo run + Compiling shared-state v0.1.0 (file:///projects/shared-state) +error[E0382]: borrow of moved value: `counter` + --> src/main.rs:21:29 | 5 | let counter = Mutex::new(0); - | ------- move occurs because `counter` has type `Mutex`, which -does not implement the `Copy` trait + | ------- move occurs because `counter` has type `Mutex`, which does not implement the `Copy` trait ... +8 | for _ in 0..10 { + | -------------- inside of this loop 9 | let handle = thread::spawn(move || { - | ^^^^^^^ value moved into closure here, -in previous iteration of loop -10 | let mut num = counter.lock().unwrap(); - | ------- use occurs due to use in closure + | ------- value moved into closure here, in previous iteration of loop +... +21 | println!("Result: {}", *counter.lock().unwrap()); + | ^^^^^^^ value borrowed here after move + | +help: consider moving the expression out of the loop so it is only moved once + | +8 ~ let mut value = counter.lock(); +9 ~ for _ in 0..10 { +10 | let handle = thread::spawn(move || { +11 ~ let mut num = value.unwrap(); + | + +For more information about this error, try `rustc --explain E0382`. +error: could not compile `shared-state` (bin "shared-state") due to 1 previous error ``` The error message states that the `counter` value was moved in the previous @@ -967,11 +1042,11 @@ multiple-ownership method we discussed in Chapter 15. #### Multiple Ownership with Multiple Threads In Chapter 15, we gave a value to multiple owners by using the smart pointer -`Rc` to create a reference counted value. Let’s do the same here and see +`Rc` to create a reference-counted value. Let’s do the same here and see what happens. We’ll wrap the `Mutex` in `Rc` in Listing 16-14 and clone the `Rc` before moving ownership to the thread. -Filename: src/main.rs +src/main.rs ``` use std::rc::Rc; @@ -1000,39 +1075,46 @@ fn main() { } ``` -Listing 16-14: Attempting to use `Rc` to allow multiple threads to own the -`Mutex` +Listing 16-14: Attempting to use `Rc` to allow multiple threads to own the `Mutex` -Once again, we compile and get… different errors! The compiler is teaching us a -lot. +Once again, we compile and get… different errors! The compiler is teaching us +a lot: ``` -error[E0277]: `Rc>` cannot be sent between threads safely 1 - --> src/main.rs:11:22 - | -11 | let handle = thread::spawn(move || { - | ______________________^^^^^^^^^^^^^_- - | | | - | | `Rc>` cannot be sent between threads -safely -12 | | let mut num = counter.lock().unwrap(); -13 | | -14 | | *num += 1; -15 | | }); - | |_________- within this `[closure@src/main.rs:11:36: 15:10]` - | -= help: within `[closure@src/main.rs:11:36: 15:10]`, the trait `Send` is not -implemented for `Rc>` 2 - = note: required because it appears within the type -`[closure@src/main.rs:11:36: 15:10]` +$ cargo run + Compiling shared-state v0.1.0 (file:///projects/shared-state) +error[E0277]: `Rc>` cannot be sent between threads safely + --> src/main.rs:11:36 + | +11 | let handle = thread::spawn(move || { + | ------------- ^------ + | | | + | ______________________|_____________within this `{closure@src/main.rs:11:36: 11:43}` + | | | + | | required by a bound introduced by this call +12 | | let mut num = counter.lock().unwrap(); +13 | | +14 | | *num += 1; +15 | | }); + | |_________^ `Rc>` cannot be sent between threads safely + | + = help: within `{closure@src/main.rs:11:36: 11:43}`, the trait `Send` is not implemented for `Rc>` +note: required because it's used within this closure + --> src/main.rs:11:36 + | +11 | let handle = thread::spawn(move || { + | ^^^^^^^ note: required by a bound in `spawn` + --> /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/std/src/thread/mod.rs:728:1 + +For more information about this error, try `rustc --explain E0277`. +error: could not compile `shared-state` (bin "shared-state") due to 1 previous error ``` Wow, that error message is very wordy! Here’s the important part to focus on: -``Rc>` cannot be sent between threads safely` [1]. The compiler is -also telling us the reason why: `the trait `Send` is not implemented for -`Rc>`` [2]. We’ll talk about `Send` in the next section: it’s one of -the traits that ensures the types we use with threads are meant for use in +`` `Rc>` cannot be sent between threads safely ``. The compiler is +also telling us the reason why: `` the trait `Send` is not implemented for `Rc>` ``. We’ll talk about `Send` in the next section: It’s one of +the traits that ensures that the types we use with threads are meant for use in concurrent situations. Unfortunately, `Rc` is not safe to share across threads. When `Rc` @@ -1041,18 +1123,18 @@ subtracts from the count when each clone is dropped. But it doesn’t use any concurrency primitives to make sure that changes to the count can’t be interrupted by another thread. This could lead to wrong counts—subtle bugs that could in turn lead to memory leaks or a value being dropped before we’re done -with it. What we need is a type exactly like `Rc` but one that makes changes -to the reference count in a thread-safe way. +with it. What we need is a type that is exactly like `Rc`, but that makes +changes to the reference count in a thread-safe way. #### Atomic Reference Counting with Arc Fortunately, `Arc` *is* a type like `Rc` that is safe to use in concurrent situations. The *a* stands for *atomic*, meaning it’s an *atomically -reference counted* type. Atomics are an additional kind of concurrency -primitive that we won’t cover in detail here: see the standard library -documentation for `std::sync::atomic` for more details. At this point, you just -need to know that atomics work like primitive types but are safe to share -across threads. +reference-counted* type. Atomics are an additional kind of concurrency +primitive that we won’t cover in detail here: See the standard library +documentation for `std::sync::atomic` for more +details. At this point, you just need to know that atomics work like primitive +types but are safe to share across threads. You might then wonder why all primitive types aren’t atomic and why standard library types aren’t implemented to use `Arc` by default. The reason is that @@ -1065,7 +1147,7 @@ Let’s return to our example: `Arc` and `Rc` have the same API, so we fix our program by changing the `use` line, the call to `new`, and the call to `clone`. The code in Listing 16-15 will finally compile and run. -Filename: src/main.rs +src/main.rs ``` use std::sync::{Arc, Mutex}; @@ -1093,11 +1175,14 @@ fn main() { } ``` -Listing 16-15: Using an `Arc` to wrap the `Mutex` to be able to share -ownership across multiple threads +Listing 16-15: Using an `Arc` to wrap the `Mutex` to be able to share ownership across multiple threads This code will print the following: + + ``` Result: 10 ``` @@ -1111,26 +1196,30 @@ thread update the final result with its part. Note that if you are doing simple numerical operations, there are types simpler than `Mutex` types provided by the `std::sync::atomic` module of the -standard library. These types provide safe, concurrent, atomic access to -primitive types. We chose to use `Mutex` with a primitive type for this -example so we could concentrate on how `Mutex` works. +standard library. These types provide safe, concurrent, +atomic access to primitive types. We chose to use `Mutex` with a primitive +type for this example so that we could concentrate on how `Mutex` works. -### Similarities Between RefCell/Rc and Mutex/Arc + -You might have noticed that `counter` is immutable but we could get a mutable -reference to the value inside it; this means `Mutex` provides interior -mutability, as the `Cell` family does. In the same way we used `RefCell` in -Chapter 15 to allow us to mutate contents inside an `Rc`, we use `Mutex` -to mutate contents inside an `Arc`. + + +### Comparing RefCell/Rc and Mutex/Arc + +You might have noticed that `counter` is immutable but that we could get a +mutable reference to the value inside it; this means `Mutex` provides +interior mutability, as the `Cell` family does. In the same way we used +`RefCell` in Chapter 15 to allow us to mutate contents inside an `Rc`, we +use `Mutex` to mutate contents inside an `Arc`. Another detail to note is that Rust can’t protect you from all kinds of logic -errors when you use `Mutex`. Recall in Chapter 15 that using `Rc` came +errors when you use `Mutex`. Recall from Chapter 15 that using `Rc` came with the risk of creating reference cycles, where two `Rc` values refer to each other, causing memory leaks. Similarly, `Mutex` comes with the risk of creating *deadlocks*. These occur when an operation needs to lock two resources and two threads have each acquired one of the locks, causing them to wait for each other forever. If you’re interested in deadlocks, try creating a Rust -program that has a deadlock; then research deadlock mitigation strategies for +program that has a deadlock; then, research deadlock mitigation strategies for mutexes in any language and have a go at implementing them in Rust. The standard library API documentation for `Mutex` and `MutexGuard` offers useful information. @@ -1138,72 +1227,88 @@ useful information. We’ll round out this chapter by talking about the `Send` and `Sync` traits and how we can use them with custom types. -## Extensible Concurrency with the Send and Sync Traits + + + + + +## Extensible Concurrency with Send and Sync + +Interestingly, almost every concurrency feature we’ve talked about so far in +this chapter has been part of the standard library, not the language. Your +options for handling concurrency are not limited to the language or the +standard library; you can write your own concurrency features or use those +written by others. + +However, among the key concurrency concepts that are embedded in the language +rather than the standard library are the `std::marker` traits `Send` and `Sync`. -Interestingly, the Rust language has *very* few concurrency features. Almost -every concurrency feature we’ve talked about so far in this chapter has been -part of the standard library, not the language. Your options for handling -concurrency are not limited to the language or the standard library; you can -write your own concurrency features or use those written by others. + -However, two concurrency concepts are embedded in the language: the -`std::marker` traits `Send` and `Sync` . + -### Allowing Transference of Ownership Between Threads with Send +### Transferring Ownership Between Threads The `Send` marker trait indicates that ownership of values of the type implementing `Send` can be transferred between threads. Almost every Rust type -is `Send`, but there are some exceptions, including `Rc`: this cannot be -`Send` because if you cloned an `Rc` value and tried to transfer ownership -of the clone to another thread, both threads might update the reference count -at the same time. For this reason, `Rc` is implemented for use in -single-threaded situations where you don’t want to pay the thread-safe -performance penalty. +implements `Send`, but there are some exceptions, including `Rc`: This +cannot implement `Send` because if you cloned an `Rc` value and tried to +transfer ownership of the clone to another thread, both threads might update +the reference count at the same time. For this reason, `Rc` is implemented +for use in single-threaded situations where you don’t want to pay the +thread-safe performance penalty. Therefore, Rust’s type system and trait bounds ensure that you can never accidentally send an `Rc` value across threads unsafely. When we tried to do -this in Listing 16-14, we got the error `the trait `Send` is not implemented -for `Rc>``. When we switched to `Arc`, which is `Send`, the code -compiled. +this in Listing 16-14, we got the error `` the trait `Send` is not implemented for `Rc>` ``. When we switched to `Arc`, which does implement +`Send`, the code compiled. Any type composed entirely of `Send` types is automatically marked as `Send` as well. Almost all primitive types are `Send`, aside from raw pointers, which -we’ll discuss in Chapter 19. +we’ll discuss in Chapter 20. -### Allowing Access from Multiple Threads with Sync + + + + +### Accessing from Multiple Threads The `Sync` marker trait indicates that it is safe for the type implementing -`Sync` to be referenced from multiple threads. In other words, any type `T` is -`Sync` if `&T` (an immutable reference to `T`) is `Send`, meaning the reference -can be sent safely to another thread. Similar to `Send`, primitive types are -`Sync`, and types composed entirely of types that are `Sync` are also `Sync`. - -The smart pointer `Rc` is also not `Sync` for the same reasons that it’s not -`Send`. The `RefCell` type (which we talked about in Chapter 15) and the -family of related `Cell` types are not `Sync`. The implementation of borrow -checking that `RefCell` does at runtime is not thread-safe. The smart -pointer `Mutex` is `Sync` and can be used to share access with multiple -threads, as you saw in “Sharing a Mutex Between Multiple Threads” on page XX. +`Sync` to be referenced from multiple threads. In other words, any type `T` +implements `Sync` if `&T` (an immutable reference to `T`) implements `Send`, +meaning the reference can be sent safely to another thread. Similar to `Send`, +primitive types all implement `Sync`, and types composed entirely of types that +implement `Sync` also implement `Sync`. + +The smart pointer `Rc` also doesn’t implement `Sync` for the same reasons +that it doesn’t implement `Send`. The `RefCell` type (which we talked about +in Chapter 15) and the family of related `Cell` types don’t implement +`Sync`. The implementation of borrow checking that `RefCell` does at runtime +is not thread-safe. The smart pointer `Mutex` implements `Sync` and can be +used to share access with multiple threads, as you saw in “Shared Access to +`Mutex`”. ### Implementing Send and Sync Manually Is Unsafe -Because types that are made up of `Send` and `Sync` traits are automatically -also `Send` and `Sync`, we don’t have to implement those traits manually. As -marker traits, they don’t even have any methods to implement. They’re just -useful for enforcing invariants related to concurrency. +Because types composed entirely of other types that implement the `Send` and +`Sync` traits also automatically implement `Send` and `Sync`, we don’t have to +implement those traits manually. As marker traits, they don’t even have any +methods to implement. They’re just useful for enforcing invariants related to +concurrency. Manually implementing these traits involves implementing unsafe Rust code. -We’ll talk about using unsafe Rust code in Chapter 19; for now, the important +We’ll talk about using unsafe Rust code in Chapter 20; for now, the important information is that building new concurrent types not made up of `Send` and `Sync` parts requires careful thought to uphold the safety guarantees. “The -Rustonomicon” at *https://doc.rust-lang.org/stable/nomicon* has more -information about these guarantees and how to uphold them. +Rustonomicon” at *../nomicon/index.html* has more information about these guarantees and how to +uphold them. ## Summary -This isn’t the last you’ll see of concurrency in this book: the project in -Chapter 20 will use the concepts in this chapter in a more realistic situation -than the smaller examples discussed here. +This isn’t the last you’ll see of concurrency in this book: The next chapter +focuses on async programming, and the project in Chapter 21 will use the +concepts in this chapter in a more realistic situation than the smaller +examples discussed here. As mentioned earlier, because very little of how Rust handles concurrency is part of the language, many concurrency solutions are implemented as crates. @@ -1218,9 +1323,4 @@ code using these solutions won’t end up with data races or invalid references. Once you get your code to compile, you can rest assured that it will happily run on multiple threads without the kinds of hard-to-track-down bugs common in other languages. Concurrent programming is no longer a concept to be afraid of: -go forth and make your programs concurrent, fearlessly! - -Next, we’ll talk about idiomatic ways to model problems and structure solutions -as your Rust programs get bigger. In addition, we’ll discuss how Rust’s idioms -relate to those you might be familiar with from object-oriented programming. - +Go forth and make your programs concurrent, fearlessly! diff --git a/nostarch/chapter17.md b/nostarch/chapter17.md index 946d20a112..efab2a38e8 100644 --- a/nostarch/chapter17.md +++ b/nostarch/chapter17.md @@ -6,1228 +6,2267 @@ directory, so all fixes need to be made in `/src/`. [TOC] -# Object-Oriented Programming Features - -Object-oriented programming (OOP) is a way of modeling programs. Objects as a -programmatic concept were introduced in the programming language Simula in the -1960s. Those objects influenced Alan Kay’s programming architecture in which -objects pass messages to each other. To describe this architecture, he coined -the term *object-oriented programming* in 1967. Many competing definitions -describe what OOP is, and by some of these definitions Rust is object oriented -but by others it is not. In this chapter, we’ll explore certain characteristics -that are commonly considered object oriented and how those characteristics -translate to idiomatic Rust. We’ll then show you how to implement an -object-oriented design pattern in Rust and discuss the trade-offs of doing so -versus implementing a solution using some of Rust’s strengths instead. - -## Characteristics of Object-Oriented Languages - -There is no consensus in the programming community about what features a -language must have to be considered object oriented. Rust is influenced by many -programming paradigms, including OOP; for example, we explored the features -that came from functional programming in Chapter 13. Arguably, OOP languages -share certain common characteristics, namely objects, encapsulation, and -inheritance. Let’s look at what each of those characteristics means and whether -Rust supports it. - -### Objects Contain Data and Behavior - -The book *Design Patterns: Elements of Reusable Object-Oriented Software* by -Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (Addison-Wesley, -1994), colloquially referred to as *The Gang of Four* book, is a catalog of -object-oriented design patterns. It defines OOP in this way: - -Object-oriented programs are made up of objects. An *object* packages both data -and the procedures that operate on that data. The procedures are typically -called *methods* or *operations*. - -Using this definition, Rust is object oriented: structs and enums have data, -and `impl` blocks provide methods on structs and enums. Even though structs and -enums with methods aren’t *called* objects, they provide the same -functionality, according to the Gang of Four’s definition of objects. - -### Encapsulation That Hides Implementation Details - -Another aspect commonly associated with OOP is the idea of *encapsulation*, -which means that the implementation details of an object aren’t accessible to -code using that object. Therefore, the only way to interact with an object is -through its public API; code using the object shouldn’t be able to reach into -the object’s internals and change data or behavior directly. This enables the -programmer to change and refactor an object’s internals without needing to -change the code that uses the object. - -We discussed how to control encapsulation in Chapter 7: we can use the `pub` -keyword to decide which modules, types, functions, and methods in our code -should be public, and by default everything else is private. For example, we -can define a struct `AveragedCollection` that has a field containing a vector -of `i32` values. The struct can also have a field that contains the average of -the values in the vector, meaning the average doesn’t have to be computed on -demand whenever anyone needs it. In other words, `AveragedCollection` will -cache the calculated average for us. Listing 17-1 has the definition of the -`AveragedCollection` struct. - -Filename: src/lib.rs - -``` -pub struct AveragedCollection { - list: Vec, - average: f64, -} +# Fundamentals of Asynchronous Programming: Async, Await, Futures, and Streams + +Many operations we ask the computer to do can take a while to finish. It would +be nice if we could do something else while we’re waiting for those +long-running processes to complete. Modern computers offer two techniques for +working on more than one operation at a time: parallelism and concurrency. Our +programs’ logic, however, is written in a mostly linear fashion. We’d like to +be able to specify the operations a program should perform and points at which +a function could pause and some other part of the program could run instead, +without needing to specify up front exactly the order and manner in which each +bit of code should run. *Asynchronous programming* is an abstraction that lets +us express our code in terms of potential pausing points and eventual results +that takes care of the details of coordination for us. + +This chapter builds on Chapter 16’s use of threads for parallelism and +concurrency by introducing an alternative approach to writing code: Rust’s +futures, streams, and the `async` and `await` syntax that let us express how +operations could be asynchronous, and the third-party crates that implement +asynchronous runtimes: code that manages and coordinates the execution of +asynchronous operations. + +Let’s consider an example. Say you’re exporting a video you’ve created of a +family celebration, an operation that could take anywhere from minutes to +hours. The video export will use as much CPU and GPU power as it can. If you +had only one CPU core and your operating system didn’t pause that export until +it completed—that is, if it executed the export *synchronously*—you couldn’t do +anything else on your computer while that task was running. That would be a +pretty frustrating experience. Fortunately, your computer’s operating system +can, and does, invisibly interrupt the export often enough to let you get other +work done simultaneously. + +Now say you’re downloading a video shared by someone else, which can also take +a while but does not take up as much CPU time. In this case, the CPU has to +wait for data to arrive from the network. While you can start reading the data +once it starts to arrive, it might take some time for all of it to show up. +Even once the data is all present, if the video is quite large, it could take +at least a second or two to load it all. That might not sound like much, but +it’s a very long time for a modern processor, which can perform billions of +operations every second. Again, your operating system will invisibly interrupt +your program to allow the CPU to perform other work while waiting for the +network call to finish. + +The video export is an example of a *CPU-bound* or *compute-bound* operation. +It’s limited by the computer’s potential data processing speed within the CPU +or GPU, and how much of that speed it can dedicate to the operation. The video +download is an example of an *I/O-bound* operation, because it’s limited by the +speed of the computer’s *input and output*; it can only go as fast as the data +can be sent across the network. + +In both of these examples, the operating system’s invisible interrupts provide +a form of concurrency. That concurrency happens only at the level of the entire +program, though: the operating system interrupts one program to let other +programs get work done. In many cases, because we understand our programs at a +much more granular level than the operating system does, we can spot +opportunities for concurrency that the operating system can’t see. + +For example, if we’re building a tool to manage file downloads, we should be +able to write our program so that starting one download won’t lock up the UI, +and users should be able to start multiple downloads at the same time. Many +operating system APIs for interacting with the network are *blocking*, though; +that is, they block the program’s progress until the data they’re processing is +completely ready. + +> Note: This is how *most* function calls work, if you think about it. However, +> the term *blocking* is usually reserved for function calls that interact with +> files, the network, or other resources on the computer, because those are the +> cases where an individual program would benefit from the operation being +> *non*-blocking. + +We could avoid blocking our main thread by spawning a dedicated thread to +download each file. However, the overhead of the system resources used by those +threads would eventually become a problem. It would be preferable if the call +didn’t block in the first place, and instead we could define a number of tasks +that we’d like our program to complete and allow the runtime to choose the best +order and manner in which to run them. + +That is exactly what Rust’s *async* (short for *asynchronous*) abstraction +gives us. In this chapter, you’ll learn all about async as we cover the +following topics: + +* How to use Rust’s `async` and `await` syntax and execute asynchronous + functions with a runtime +* How to use the async model to solve some of the same challenges we looked at + in Chapter 16 +* How multithreading and async provide complementary solutions that you can + combine in many cases + +Before we see how async works in practice, though, we need to take a short +detour to discuss the differences between parallelism and concurrency. + +## Parallelism and Concurrency + +We’ve treated parallelism and concurrency as mostly interchangeable so far. Now +we need to distinguish between them more precisely, because the differences +will show up as we start working. + +Consider the different ways a team could split up work on a software project. +You could assign a single member multiple tasks, assign each member one task, +or use a mix of the two approaches. + +When an individual works on several different tasks before any of them is +complete, this is *concurrency*. One way to implement concurrency is similar to +having two different projects checked out on your computer, and when you get +bored or stuck on one project, you switch to the other. You’re just one person, +so you can’t make progress on both tasks at the exact same time, but you can +multitask, making progress on one at a time by switching between them (see +Figure 17-1). + +A diagram with stacked boxes labeled Task A and Task B, with diamonds in them representing subtasks. Arrows point from A1 to B1, B1 to A2, A2 to B2, B2 to A3, A3 to A4, and A4 to B3. The arrows between the subtasks cross the boxes between Task A and Task B. + +Figure 17-1: A concurrent workflow, switching between Task A and Task B + +When the team splits up a group of tasks by having each member take one task +and work on it alone, this is *parallelism*. Each person on the team can make +progress at the exact same time (see Figure 17-2). + +A diagram with stacked boxes labeled Task A and Task B, with diamonds in them representing subtasks. Arrows point from A1 to A2, A2 to A3, A3 to A4, B1 to B2, and B2 to B3. No arrows cross between the boxes for Task A and Task B. + +Figure 17-2: A parallel workflow, where work happens on Task A and Task B independently + +In both of these workflows, you might have to coordinate between different +tasks. Maybe you thought the task assigned to one person was totally +independent from everyone else’s work, but it actually requires another person +on the team to finish their task first. Some of the work could be done in +parallel, but some of it was actually *serial*: it could only happen in a +series, one task after the other, as in Figure 17-3. + +A diagram with stacked boxes labeled Task A and Task B, with diamonds in them representing subtasks. In Task A, arrows point from A1 to A2, from A2 to a pair of thick vertical lines like a “pause” symbol, and from that symbol to A3. In task B, arrows point from B1 to B2, from B2 to B3, from B3 to A3, and from B3 to B4. + +Figure 17-3: A partially parallel workflow, where work happens on Task A and Task B independently until Task A3 is blocked on the results of Task B3. + +Likewise, you might realize that one of your own tasks depends on another of +your tasks. Now your concurrent work has also become serial. + +Parallelism and concurrency can intersect with each other, too. If you learn +that a colleague is stuck until you finish one of your tasks, you’ll probably +focus all your efforts on that task to “unblock” your colleague. You and your +coworker are no longer able to work in parallel, and you’re also no longer able +to work concurrently on your own tasks. + +The same basic dynamics come into play with software and hardware. On a machine +with a single CPU core, the CPU can perform only one operation at a time, but +it can still work concurrently. Using tools such as threads, processes, and +async, the computer can pause one activity and switch to others before +eventually cycling back to that first activity again. On a machine with +multiple CPU cores, it can also do work in parallel. One core can be performing +one task while another core performs a completely unrelated one, and those +operations actually happen at the same time. + +Running async code in Rust usually happens concurrently. Depending on the +hardware, the operating system, and the async runtime we are using (more on +async runtimes shortly), that concurrency may also use parallelism under the +hood. + +Now, let’s dive into how async programming in Rust actually works. + +## Futures and the Async Syntax + +The key elements of asynchronous programming in Rust are *futures* and Rust’s +`async` and `await` keywords. + +A *future* is a value that may not be ready now but will become ready at some +point in the future. (This same concept shows up in many languages, sometimes +under other names such as *task* or *promise*.) Rust provides a `Future` trait +as a building block so that different async operations can be implemented with +different data structures but with a common interface. In Rust, futures are +types that implement the `Future` trait. Each future holds its own information +about the progress that has been made and what “ready” means. + +You can apply the `async` keyword to blocks and functions to specify that they +can be interrupted and resumed. Within an async block or async function, you +can use the `await` keyword to *await a future* (that is, wait for it to become +ready). Any point where you await a future within an async block or function is +a potential spot for that block or function to pause and resume. The process of +checking with a future to see if its value is available yet is called *polling*. + +Some other languages, such as C# and JavaScript, also use `async` and `await` +keywords for async programming. If you’re familiar with those languages, you +may notice some significant differences in how Rust handles the syntax. That’s +for good reason, as we’ll see! + +When writing async Rust, we use the `async` and `await` keywords most of the +time. Rust compiles them into equivalent code using the `Future` trait, much as +it compiles `for` loops into equivalent code using the `Iterator` trait. +Because Rust provides the `Future` trait, though, you can also implement it for +your own data types when you need to. Many of the functions we’ll see +throughout this chapter return types with their own implementations of +`Future`. We’ll return to the definition of the trait at the end of the chapter +and dig into more of how it works, but this is enough detail to keep us moving +forward. + +This may all feel a bit abstract, so let’s write our first async program: a +little web scraper. We’ll pass in two URLs from the command line, fetch both of +them concurrently, and return the result of whichever one finishes first. This +example will have a fair bit of new syntax, but don’t worry—we’ll explain +everything you need to know as we go. + +## Our First Async Program + +To keep the focus of this chapter on learning async rather than juggling parts +of the ecosystem, we’ve created the `trpl` crate (`trpl` is short for “The Rust +Programming Language”). It re-exports all the types, traits, and functions +you’ll need, primarily from the `futures` and +`tokio` crates. The `futures` crate is an official home +for Rust experimentation for async code, and it’s actually where the `Future` +trait was originally designed. Tokio is the most widely used async runtime in +Rust today, especially for web applications. There are other great runtimes out +there, and they may be more suitable for your purposes. We use the `tokio` +crate under the hood for `trpl` because it’s well tested and widely used. + +In some cases, `trpl` also renames or wraps the original APIs to keep you +focused on the details relevant to this chapter. If you want to understand what +the crate does, we encourage you to check out its source code at *https://github.com/rust-lang/book/tree/main/packages/trpl*. +You’ll be able to see what crate each re-export comes from, and we’ve left +extensive comments explaining what the crate does. + +Create a new binary project named `hello-async` and add the `trpl` crate as a +dependency: + +``` +$ cargo new hello-async +$ cd hello-async +$ cargo add trpl ``` -Listing 17-1: An `AveragedCollection` struct that maintains a list of integers -and the average of the items in the collection +Now we can use the various pieces provided by `trpl` to write our first async +program. We’ll build a little command line tool that fetches two web pages, +pulls the `` element from each, and prints out the title of whichever +page finishes that whole process first. -The struct is marked `pub` so that other code can use it, but the fields within -the struct remain private. This is important in this case because we want to -ensure that whenever a value is added or removed from the list, the average is -also updated. We do this by implementing `add`, `remove`, and `average` methods -on the struct, as shown in Listing 17-2. +### Defining the page_title Function -Filename: src/lib.rs +Let’s start by writing a function that takes one page URL as a parameter, makes +a request to it, and returns the text of the `<title>` element (see Listing +17-1). + +src/main.rs ``` -impl AveragedCollection { - pub fn add(&mut self, value: i32) { - self.list.push(value); - self.update_average(); - } +use trpl::Html; + +async fn page_title(url: &str) -> Option<String> { + let response = trpl::get(url).await; + let response_text = response.text().await; + Html::parse(&response_text) + .select_first("title") + .map(|title| title.inner_html()) +} +``` - pub fn remove(&mut self) -> Option<i32> { - let result = self.list.pop(); - match result { - Some(value) => { - self.update_average(); - Some(value) - } - None => None, - } - } +Listing 17-1: Defining an async function to get the title element from an HTML page + +First, we define a function named `page_title` and mark it with the `async` +keyword. Then we use the `trpl::get` function to fetch whatever URL is passed +in and add the `await` keyword to await the response. To get the text of the +`response`, we call its `text` method and once again await it with the `await` +keyword. Both of these steps are asynchronous. For the `get` function, we have +to wait for the server to send back the first part of its response, which will +include HTTP headers, cookies, and so on and can be delivered separately from +the response body. Especially if the body is very large, it can take some time +for it all to arrive. Because we have to wait for the *entirety* of the +response to arrive, the `text` method is also async. + +We have to explicitly await both of these futures, because futures in Rust are +*lazy*: they don’t do anything until you ask them to with the `await` keyword. +(In fact, Rust will show a compiler warning if you don’t use a future.) This +might remind you of the discussion of iterators in the “Processing a Series of +Items with Iterators” section in Chapter 13. +Iterators do nothing unless you call their `next` method—whether directly or by +using `for` loops or methods such as `map` that use `next` under the hood. +Likewise, futures do nothing unless you explicitly ask them to. This laziness +allows Rust to avoid running async code until it’s actually needed. + +> Note: This is different from the behavior we saw when using `thread::spawn` +> in the “Creating a New Thread with spawn” +> section in Chapter 16, where the closure we passed to another thread started +> running immediately. It’s also different from how many other languages +> approach async. But it’s important for Rust to be able to provide its +> performance guarantees, just as it is with iterators. + +Once we have `response_text`, we can parse it into an instance of the `Html` +type using `Html::parse`. Instead of a raw string, we now have a data type we +can use to work with the HTML as a richer data structure. In particular, we can +use the `select_first` method to find the first instance of a given CSS +selector. By passing the string `"title"`, we’ll get the first `<title>` +element in the document, if there is one. Because there may not be any matching +element, `select_first` returns an `Option<ElementRef>`. Finally, we use the +`Option::map` method, which lets us work with the item in the `Option` if it’s +present, and do nothing if it isn’t. (We could also use a `match` expression +here, but `map` is more idiomatic.) In the body of the function we supply to +`map`, we call `inner_html` on the `title` to get its content, which is a +`String`. When all is said and done, we have an `Option<String>`. + +Notice that Rust’s `await` keyword goes *after* the expression you’re awaiting, +not before it. That is, it’s a *postfix* keyword. This may differ from what +you’re used to if you’ve used `async` in other languages, but in Rust it makes +chains of methods much nicer to work with. As a result, we could change the +body of `page_title` to chain the `trpl::get` and `text` function calls +together with `await` between them, as shown in Listing 17-2. + +src/main.rs - pub fn average(&self) -> f64 { - self.average - } +``` + let response_text = trpl::get(url).await.text().await; +``` + +Listing 17-2: Chaining with the `await` keyword - fn update_average(&mut self) { - let total: i32 = self.list.iter().sum(); - self.average = total as f64 / self.list.len() as f64; +With that, we have successfully written our first async function! Before we add +some code in `main` to call it, let’s talk a little more about what we’ve +written and what it means. + +When Rust sees a *block* marked with the `async` keyword, it compiles it into a +unique, anonymous data type that implements the `Future` trait. When Rust sees +a *function* marked with `async`, it compiles it into a non-async function +whose body is an async block. An async function’s return type is the type of +the anonymous data type the compiler creates for that async block. + +Thus, writing `async fn` is equivalent to writing a function that returns a +*future* of the return type. To the compiler, a function definition such as the +`async fn page_title` in Listing 17-1 is roughly equivalent to a non-async +function defined like this: + +``` +use std::future::Future; +use trpl::Html; + +fn page_title(url: &str) -> impl Future<Output = Option<String>> { + async move { + let text = trpl::get(url).await.text().await; + Html::parse(&text) + .select_first("title") + .map(|title| title.inner_html()) } } ``` -Listing 17-2: Implementations of the public methods `add`, `remove`, and -`average` on `AveragedCollection` - -The public methods `add`, `remove`, and `average` are the only ways to access -or modify data in an instance of `AveragedCollection`. When an item is added to -`list` using the `add` method or removed using the `remove` method, the -implementations of each call the private `update_average` method that handles -updating the `average` field as well. - -We leave the `list` and `average` fields private so there is no way for -external code to add or remove items to or from the `list` field directly; -otherwise, the `average` field might become out of sync when the `list` -changes. The `average` method returns the value in the `average` field, -allowing external code to read the `average` but not modify it. - -Because we’ve encapsulated the implementation details of the struct -`AveragedCollection`, we can easily change aspects, such as the data structure, -in the future. For instance, we could use a `HashSet<i32>` instead of a -`Vec<i32>` for the `list` field. As long as the signatures of the `add`, -`remove`, and `average` public methods stayed the same, code using -`AveragedCollection` wouldn’t need to change. If we made `list` public instead, -this wouldn’t necessarily be the case: `HashSet<i32>` and `Vec<i32>` have -different methods for adding and removing items, so the external code would -likely have to change if it were modifying `list` directly. - -If encapsulation is a required aspect for a language to be considered object -oriented, then Rust meets that requirement. The option to use `pub` or not for -different parts of code enables encapsulation of implementation details. - -### Inheritance as a Type System and as Code Sharing - -*Inheritance* is a mechanism whereby an object can inherit elements from -another object’s definition, thus gaining the parent object’s data and behavior -without you having to define them again. - -If a language must have inheritance to be object oriented, then Rust is not -such a language. There is no way to define a struct that inherits the parent -struct’s fields and method implementations without using a macro. - -However, if you’re used to having inheritance in your programming toolbox, you -can use other solutions in Rust, depending on your reason for reaching for -inheritance in the first place. - -You would choose inheritance for two main reasons. One is for reuse of code: -you can implement particular behavior for one type, and inheritance enables you -to reuse that implementation for a different type. You can do this in a limited -way in Rust code using default trait method implementations, which you saw in -Listing 10-14 when we added a default implementation of the `summarize` method -on the `Summary` trait. Any type implementing the `Summary` trait would have -the `summarize` method available on it without any further code. This is -similar to a parent class having an implementation of a method and an -inheriting child class also having the implementation of the method. We can -also override the default implementation of the `summarize` method when we -implement the `Summary` trait, which is similar to a child class overriding the -implementation of a method inherited from a parent class. - -The other reason to use inheritance relates to the type system: to enable a -child type to be used in the same places as the parent type. This is also -called *polymorphism*, which means that you can substitute multiple objects for -each other at runtime if they share certain characteristics. - -> ### Polymorphism -> -> To many people, polymorphism is synonymous with inheritance. But it’s -actually a more general concept that refers to code that can work with data of -multiple types. For inheritance, those types are generally subclasses. -> -> Rust instead uses generics to abstract over different possible types and -trait bounds to impose constraints on what those types must provide. This is -sometimes called *bounded parametric polymorphism*. - -Inheritance has recently fallen out of favor as a programming design solution -in many programming languages because it’s often at risk of sharing more code -than necessary. Subclasses shouldn’t always share all characteristics of their -parent class but will do so with inheritance. This can make a program’s design -less flexible. It also introduces the possibility of calling methods on -subclasses that don’t make sense or that cause errors because the methods don’t -apply to the subclass. In addition, some languages will only allow single -inheritance (meaning a subclass can only inherit from one class), further -restricting the flexibility of a program’s design. - -For these reasons, Rust takes the different approach of using trait objects -instead of inheritance. Let’s look at how trait objects enable polymorphism in -Rust. - -## Using Trait Objects That Allow for Values of Different Types - -In Chapter 8, we mentioned that one limitation of vectors is that they can -store elements of only one type. We created a workaround in Listing 8-9 where -we defined a `SpreadsheetCell` enum that had variants to hold integers, floats, -and text. This meant we could store different types of data in each cell and -still have a vector that represented a row of cells. This is a perfectly good -solution when our interchangeable items are a fixed set of types that we know -when our code is compiled. - -However, sometimes we want our library user to be able to extend the set of -types that are valid in a particular situation. To show how we might achieve -this, we’ll create an example graphical user interface (GUI) tool that iterates -through a list of items, calling a `draw` method on each one to draw it to the -screen—a common technique for GUI tools. We’ll create a library crate called -`gui` that contains the structure of a GUI library. This crate might include -some types for people to use, such as `Button` or `TextField`. In addition, -`gui` users will want to create their own types that can be drawn: for -instance, one programmer might add an `Image` and another might add a -`SelectBox`. - -We won’t implement a full-fledged GUI library for this example but will show -how the pieces would fit together. At the time of writing the library, we can’t -know and define all the types other programmers might want to create. But we do -know that `gui` needs to keep track of many values of different types, and it -needs to call a `draw` method on each of these differently typed values. It -doesn’t need to know exactly what will happen when we call the `draw` method, -just that the value will have that method available for us to call. - -To do this in a language with inheritance, we might define a class named -`Component` that has a method named `draw` on it. The other classes, such as -`Button`, `Image`, and `SelectBox`, would inherit from `Component` and thus -inherit the `draw` method. They could each override the `draw` method to define -their custom behavior, but the framework could treat all of the types as if -they were `Component` instances and call `draw` on them. But because Rust -doesn’t have inheritance, we need another way to structure the `gui` library to -allow users to extend it with new types. - -### Defining a Trait for Common Behavior - -To implement the behavior we want `gui` to have, we’ll define a trait named -`Draw` that will have one method named `draw`. Then we can define a vector that -takes a *trait object*. A trait object points to both an instance of a type -implementing our specified trait and a table used to look up trait methods on -that type at runtime. We create a trait object by specifying some sort of -pointer, such as a `&` reference or a `Box<T>` smart pointer, then the `dyn` -keyword, and then specifying the relevant trait. (We’ll talk about the reason -trait objects must use a pointer in “Dynamically Sized Types and the Sized -Trait” on page XX.) We can use trait objects in place of a generic or concrete -type. Wherever we use a trait object, Rust’s type system will ensure at compile -time that any value used in that context will implement the trait object’s -trait. Consequently, we don’t need to know all the possible types at compile -time. - -We’ve mentioned that, in Rust, we refrain from calling structs and enums -“objects” to distinguish them from other languages’ objects. In a struct or -enum, the data in the struct fields and the behavior in `impl` blocks are -separated, whereas in other languages, the data and behavior combined into one -concept is often labeled an object. However, trait objects *are* more like -objects in other languages in the sense that they combine data and behavior. -But trait objects differ from traditional objects in that we can’t add data to -a trait object. Trait objects aren’t as generally useful as objects in other -languages: their specific purpose is to allow abstraction across common -behavior. - -Listing 17-3 shows how to define a trait named `Draw` with one method named -`draw`. - -Filename: src/lib.rs - -``` -pub trait Draw { - fn draw(&self); -} -``` +Let’s walk through each part of the transformed version: + +* It uses the `impl Trait` syntax we discussed back in Chapter 10 in the + “Traits as Parameters” section. +* The returned value implements the `Future` trait with an associated type of + `Output`. Notice that the `Output` type is `Option<String>`, which is the + same as the original return type from the `async fn` version of `page_title`. +* All of the code called in the body of the original function is wrapped in + an `async move` block. Remember that blocks are expressions. This whole block + is the expression returned from the function. +* This async block produces a value with the type `Option<String>`, as just + described. That value matches the `Output` type in the return type. This is + just like other blocks you have seen. +* The new function body is an `async move` block because of how it uses the + `url` parameter. (We’ll talk much more about `async` versus `async move` + later in the chapter.) + +Now we can call `page_title` in `main`. + +<!-- Old headings. Do not remove or links may break. --> -Listing 17-3: Definition of the `Draw` trait +<a id ="determining-a-single-pages-title"></a> -This syntax should look familiar from our discussions on how to define traits -in Chapter 10. Next comes some new syntax: Listing 17-4 defines a struct named -`Screen` that holds a vector named `components`. This vector is of type -`Box<dyn Draw>`, which is a trait object; it’s a stand-in for any type inside a -`Box` that implements the `Draw` trait. +### Executing an Async Function with a Runtime -Filename: src/lib.rs +To start, we’ll get the title for a single page, shown in Listing 17-3. +Unfortunately, this code doesn’t compile yet. + +src/main.rs ``` -pub struct Screen { - pub components: Vec<Box<dyn Draw>>, +async fn main() { + let args: Vec<String> = std::env::args().collect(); + let url = &args[1]; + match page_title(url).await { + Some(title) => println!("The title for {url} was {title}"), + None => println!("{url} had no title"), + } } ``` -Listing 17-4: Definition of the `Screen` struct with a `components` field -holding a vector of trait objects that implement the `Draw` trait +Listing 17-3: Calling the `page_title` function from `main` with a user-supplied argument + +We follow the same pattern we used to get command line arguments in the +“Accepting Command Line Arguments” section in +Chapter 12. Then we pass the URL argument to `page_title` and await the result. +Because the value produced by the future is an `Option<String>`, we use a +`match` expression to print different messages to account for whether the page +had a `<title>`. + +The only place we can use the `await` keyword is in async functions or blocks, +and Rust won’t let us mark the special `main` function as `async`. -On the `Screen` struct, we’ll define a method named `run` that will call the -`draw` method on each of its `components`, as shown in Listing 17-5. +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-03 +cargo build +copy just the compiler error +--> + +``` +error[E0752]: `main` function is not allowed to be `async` + --> src/main.rs:6:1 + | +6 | async fn main() { + | ^^^^^^^^^^^^^^^ `main` function is not allowed to be `async` +``` -Filename: src/lib.rs +The reason `main` can’t be marked `async` is that async code needs a *runtime*: +a Rust crate that manages the details of executing asynchronous code. A +program’s `main` function can *initialize* a runtime, but it’s not a runtime +*itself*. (We’ll see more about why this is the case in a bit.) Every Rust +program that executes async code has at least one place where it sets up a +runtime that executes the futures. + +Most languages that support async bundle a runtime, but Rust does not. Instead, +there are many different async runtimes available, each of which makes different +tradeoffs suitable to the use case it targets. For example, a high-throughput +web server with many CPU cores and a large amount of RAM has very different +needs than a microcontroller with a single core, a small amount of RAM, and no +heap allocation ability. The crates that provide those runtimes also often +supply async versions of common functionality such as file or network I/O. + +Here, and throughout the rest of this chapter, we’ll use the `block_on` +function from the `trpl` crate, which takes a future as an argument and blocks +the current thread until this future runs to completion. Behind the scenes, +calling `block_on` sets up a runtime using the `tokio` crate that’s used to run +the future passed in (the `trpl` crate’s `block_on` behavior is similar to +other runtime crates’ `block_on` functions). Once the future completes, +`block_on` returns whatever value the future produced. + +We could pass the future returned by `page_title` directly to `block_on` and, +once it completed, we could match on the resulting `Option<String>` as we tried +to do in Listing 17-3. However, for most of the examples in the chapter (and +most async code in the real world), we’ll be doing more than just one async +function call, so instead we’ll pass an `async` block and explicitly await the +result of the `page_title` call, as in Listing 17-4. + +src/main.rs + +<!-- should_panic,noplayground because mdbook test does not pass args --> ``` -impl Screen { - pub fn run(&self) { - for component in self.components.iter() { - component.draw(); +fn main() { + let args: Vec<String> = std::env::args().collect(); + + trpl::block_on(async { + let url = &args[1]; + match page_title(url).await { + Some(title) => println!("The title for {url} was {title}"), + None => println!("{url} had no title"), } - } + }) } ``` -Listing 17-5: A `run` method on `Screen` that calls the `draw` method on each -component +Listing 17-4: Awaiting an async block with `trpl::block_on` -This works differently from defining a struct that uses a generic type -parameter with trait bounds. A generic type parameter can only be substituted -with one concrete type at a time, whereas trait objects allow for multiple -concrete types to fill in for the trait object at runtime. For example, we -could have defined the `Screen` struct using a generic type and a trait bound, -as in Listing 17-6. +When we run this code, we get the behavior we expected initially: -Filename: src/lib.rs +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-04 +cargo build # skip all the build noise +cargo run -- "https://www.rust-lang.org" +# copy the output here +--> ``` -pub struct Screen<T: Draw> { - pub components: Vec<T>, -} +$ cargo run -- "https://www.rust-lang.org" + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s + Running `target/debug/async_await 'https://www.rust-lang.org'` +The title for https://www.rust-lang.org was + Rust Programming Language +``` -impl<T> Screen<T> -where - T: Draw, -{ - pub fn run(&self) { - for component in self.components.iter() { - component.draw(); - } - } +Phew—we finally have some working async code! But before we add the code to +race two sites against each other, let’s briefly turn our attention back to how +futures work. + +Each *await point*—that is, every place where the code uses the `await` +keyword—represents a place where control is handed back to the runtime. To make +that work, Rust needs to keep track of the state involved in the async block so +that the runtime could kick off some other work and then come back when it’s +ready to try advancing the first one again. This is an invisible state machine, +as if you’d written an enum like this to save the current state at each await +point: + +``` +enum PageTitleFuture<'a> { + Initial { url: &'a str }, + GetAwaitPoint { url: &'a str }, + TextAwaitPoint { response: trpl::Response }, } ``` -Listing 17-6: An alternate implementation of the `Screen` struct and its `run` -method using generics and trait bounds +Writing the code to transition between each state by hand would be tedious and +error-prone, however, especially when you need to add more functionality and +more states to the code later. Fortunately, the Rust compiler creates and +manages the state machine data structures for async code automatically. The +normal borrowing and ownership rules around data structures all still apply, +and happily, the compiler also handles checking those for us and provides +useful error messages. We’ll work through a few of those later in the chapter. + +Ultimately, something has to execute this state machine, and that something is +a runtime. (This is why you may come across mentions of *executors* when +looking into runtimes: an executor is the part of a runtime responsible for +executing the async code.) + +Now you can see why the compiler stopped us from making `main` itself an async +function back in Listing 17-3. If `main` were an async function, something else +would need to manage the state machine for whatever future `main` returned, but +`main` is the starting point for the program! Instead, we called the +`trpl::block_on` function in `main` to set up a runtime and run the future +returned by the `async` block until it’s done. -This restricts us to a `Screen` instance that has a list of components all of -type `Button` or all of type `TextField`. If you’ll only ever have homogeneous -collections, using generics and trait bounds is preferable because the -definitions will be monomorphized at compile time to use the concrete types. +> Note: Some runtimes provide macros so you *can* write an async `main` +> function. Those macros rewrite `async fn main() { ... }` to be a normal `fn main`, which does the same thing we did by hand in Listing 17-4: call a +> function that runs a future to completion the way `trpl::block_on` does. -On the other hand, with the method using trait objects, one `Screen` instance -can hold a `Vec<T>` that contains a `Box<Button>` as well as a -`Box<TextField>`. Let’s look at how this works, and then we’ll talk about the -runtime performance implications. +Now let’s put these pieces together and see how we can write concurrent code. -### Implementing the Trait +<!-- Old headings. Do not remove or links may break. --> -Now we’ll add some types that implement the `Draw` trait. We’ll provide the -`Button` type. Again, actually implementing a GUI library is beyond the scope -of this book, so the `draw` method won’t have any useful implementation in its -body. To imagine what the implementation might look like, a `Button` struct -might have fields for `width`, `height`, and `label`, as shown in Listing 17-7. +<a id="racing-our-two-urls-against-each-other"></a> -Filename: src/lib.rs +### Racing Two URLs Against Each Other Concurrently + +In Listing 17-5, we call `page_title` with two different URLs passed in from the +command line and race them by selecting whichever future finishes first. + +src/main.rs + +<!-- should_panic,noplayground because mdbook does not pass args --> ``` -pub struct Button { - pub width: u32, - pub height: u32, - pub label: String, +use trpl::{Either, Html}; + +fn main() { + let args: Vec<String> = std::env::args().collect(); + + trpl::block_on(async { + let title_fut_1 = page_title(&args[1]); + let title_fut_2 = page_title(&args[2]); + + let (url, maybe_title) = + match trpl::select(title_fut_1, title_fut_2).await { + Either::Left(left) => left, + Either::Right(right) => right, + }; + + println!("{url} returned first"); + match maybe_title { + Some(title) => println!("Its page title was: '{title}'"), + None => println!("It had no title."), + } + }) } -impl Draw for Button { - fn draw(&self) { - // code to actually draw a button - } +async fn page_title(url: &str) -> (&str, Option<String>) { + let response_text = trpl::get(url).await.text().await; + let title = Html::parse(&response_text) + .select_first("title") + .map(|title| title.inner_html()); + (url, title) } ``` -Listing 17-7: A `Button` struct that implements the `Draw` trait +Listing 17-5: Calling `page_title` for two URLs to see which returns first -The `width`, `height`, and `label` fields on `Button` will differ from the -fields on other components; for example, a `TextField` type might have those -same fields plus a `placeholder` field. Each of the types we want to draw on -the screen will implement the `Draw` trait but will use different code in the -`draw` method to define how to draw that particular type, as `Button` has here -(without the actual GUI code, as mentioned). The `Button` type, for instance, -might have an additional `impl` block containing methods related to what -happens when a user clicks the button. These kinds of methods won’t apply to -types like `TextField`. +We begin by calling `page_title` for each of the user-supplied URLs. We save +the resulting futures as `title_fut_1` and `title_fut_2`. Remember, these don’t +do anything yet, because futures are lazy and we haven’t yet awaited them. Then +we pass the futures to `trpl::select`, which returns a value to indicate which +of the futures passed to it finishes first. -If someone using our library decides to implement a `SelectBox` struct that has -`width`, `height`, and `options` fields, they would implement the `Draw` trait -on the `SelectBox` type as well, as shown in Listing 17-8. +> Note: Under the hood, `trpl::select` is built on a more general `select` +> function defined in the `futures` crate. The `futures` crate’s `select` +> function can do a lot of things that the `trpl::select` function can’t, but +> it also has some additional complexity that we can skip over for now. -Filename: src/main.rs +Either future can legitimately “win,” so it doesn’t make sense to return a +`Result`. Instead, `trpl::select` returns a type we haven’t seen before, +`trpl::Either`. The `Either` type is somewhat similar to a `Result` in that it +has two cases. Unlike `Result`, though, there is no notion of success or +failure baked into `Either`. Instead, it uses `Left` and `Right` to indicate +“one or the other”: ``` -use gui::Draw; - -struct SelectBox { - width: u32, - height: u32, - options: Vec<String>, -} - -impl Draw for SelectBox { - fn draw(&self) { - // code to actually draw a select box - } +enum Either<A, B> { + Left(A), + Right(B), } ``` -Listing 17-8: Another crate using `gui` and implementing the `Draw` trait on a -`SelectBox` struct +The `select` function returns `Left` with that future’s output if the first +argument wins, and `Right` with the second future argument’s output if *that* +one wins. This matches the order the arguments appear in when calling the +function: the first argument is to the left of the second argument. + +We also update `page_title` to return the same URL passed in. That way, if the +page that returns first does not have a `<title>` we can resolve, we can still +print a meaningful message. With that information available, we wrap up by +updating our `println!` output to indicate both which URL finished first and +what, if any, the `<title>` is for the web page at that URL. + +You have built a small working web scraper now! Pick a couple URLs and run the +command line tool. You may discover that some sites are consistently faster +than others, while in other cases the faster site varies from run to run. More +importantly, you’ve learned the basics of working with futures, so now we can +dig deeper into what we can do with async. + +<!-- TODO: map source link version to version of Rust? --> + +<!-- Old headings. Do not remove or links may break. --> + +<a id="concurrency-with-async"></a> + +## Applying Concurrency with Async + +In this section, we’ll apply async to some of the same concurrency challenges +we tackled with threads in Chapter 16. Because we already talked about a lot of +the key ideas there, in this section we’ll focus on what’s different between +threads and futures. -Our library’s user can now write their `main` function to create a `Screen` -instance. To the `Screen` instance, they can add a `SelectBox` and a `Button` -by putting each in a `Box<T>` to become a trait object. They can then call the -`run` method on the `Screen` instance, which will call `draw` on each of the -components. Listing 17-9 shows this implementation. +In many cases, the APIs for working with concurrency using async are very +similar to those for using threads. In other cases, they end up being quite +different. Even when the APIs *look* similar between threads and async, they +often have different behavior—and they nearly always have different performance +characteristics. -Filename: src/main.rs +<!-- Old headings. Do not remove or links may break. --> + +<a id="counting"></a> + +### Creating a New Task with spawn_task + +The first operation we tackled in the “Creating a New Thread with +`spawn`” section in Chapter 16 was counting up on +two separate threads. Let’s do the same using async. The `trpl` crate supplies +a `spawn_task` function that looks very similar to the `thread::spawn` API, and +a `sleep` function that is an async version of the `thread::sleep` API. We can +use these together to implement the counting example, as shown in Listing 17-6. + +src/main.rs ``` -use gui::{Button, Screen}; +use std::time::Duration; fn main() { - let screen = Screen { - components: vec![ - Box::new(SelectBox { - width: 75, - height: 10, - options: vec![ - String::from("Yes"), - String::from("Maybe"), - String::from("No"), - ], - }), - Box::new(Button { - width: 50, - height: 10, - label: String::from("OK"), - }), - ], - }; - - screen.run(); + trpl::block_on(async { + trpl::spawn_task(async { + for i in 1..10 { + println!("hi number {i} from the first task!"); + trpl::sleep(Duration::from_millis(500)).await; + } + }); + + for i in 1..5 { + println!("hi number {i} from the second task!"); + trpl::sleep(Duration::from_millis(500)).await; + } + }); } ``` -Listing 17-9: Using trait objects to store values of different types that -implement the same trait +Listing 17-6: Creating a new task to print one thing while the main task prints something else -When we wrote the library, we didn’t know that someone might add the -`SelectBox` type, but our `Screen` implementation was able to operate on the -new type and draw it because `SelectBox` implements the `Draw` trait, which -means it implements the `draw` method. +As our starting point, we set up our `main` function with `trpl::block_on` so +that our top-level function can be async. -This concept—of being concerned only with the messages a value responds to -rather than the value’s concrete type—is similar to the concept of *duck -typing* in dynamically typed languages: if it walks like a duck and quacks like -a duck, then it must be a duck! In the implementation of `run` on `Screen` in -Listing 17-5, `run` doesn’t need to know what the concrete type of each -component is. It doesn’t check whether a component is an instance of a `Button` -or a `SelectBox`, it just calls the `draw` method on the component. By -specifying `Box<dyn Draw>` as the type of the values in the `components` -vector, we’ve defined `Screen` to need values that we can call the `draw` -method on. +> Note: From this point forward in the chapter, every example will include this +> exact same wrapping code with `trpl::block_on` in `main`, so we’ll often skip it +> just as we do with `main`. Remember to include it in your code! -The advantage of using trait objects and Rust’s type system to write code -similar to code using duck typing is that we never have to check whether a -value implements a particular method at runtime or worry about getting errors -if a value doesn’t implement a method but we call it anyway. Rust won’t compile -our code if the values don’t implement the traits that the trait objects need. +Then we write two loops within that block, each containing a `trpl::sleep` +call, which waits for half a second (500 milliseconds) before sending the next +message. We put one loop in the body of a `trpl::spawn_task` and the other in a +top-level `for` loop. We also add an `await` after the `sleep` calls. -For example, Listing 17-10 shows what happens if we try to create a `Screen` -with a `String` as a component. +This code behaves similarly to the thread-based implementation—including the +fact that you may see the messages appear in a different order in your own +terminal when you run it: -Filename: src/main.rs +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> ``` -use gui::Screen; +hi number 1 from the second task! +hi number 1 from the first task! +hi number 2 from the first task! +hi number 2 from the second task! +hi number 3 from the first task! +hi number 3 from the second task! +hi number 4 from the first task! +hi number 4 from the second task! +hi number 5 from the first task! +``` -fn main() { - let screen = Screen { - components: vec![Box::new(String::from("Hi"))], - }; +This version stops as soon as the `for` loop in the body of the main async +block finishes, because the task spawned by `spawn_task` is shut down when the +`main` function ends. If you want it to run all the way to the task’s +completion, you will need to use a join handle to wait for the first task to +complete. With threads, we used the `join` method to “block” until the thread +was done running. In Listing 17-7, we can use `await` to do the same thing, +because the task handle itself is a future. Its `Output` type is a `Result`, so +we also unwrap it after awaiting it. + +src/main.rs - screen.run(); -} ``` + let handle = trpl::spawn_task(async { + for i in 1..10 { + println!("hi number {i} from the first task!"); + trpl::sleep(Duration::from_millis(500)).await; + } + }); -Listing 17-10: Attempting to use a type that doesn’t implement the trait -object’s trait + for i in 1..5 { + println!("hi number {i} from the second task!"); + trpl::sleep(Duration::from_millis(500)).await; + } -We’ll get this error because `String` doesn’t implement the `Draw` trait: + handle.await.unwrap(); +``` + +Listing 17-7: Using `await` with a join handle to run a task to completion + +This updated version runs until *both* loops finish: + +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> ``` -error[E0277]: the trait bound `String: Draw` is not satisfied - --> src/main.rs:5:26 - | -5 | components: vec![Box::new(String::from("Hi"))], - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Draw` is -not implemented for `String` - | - = note: required for the cast to the object type `dyn Draw` -``` - -This error lets us know that either we’re passing something to `Screen` that we -didn’t mean to pass and so should pass a different type, or we should implement -`Draw` on `String` so that `Screen` is able to call `draw` on it. - -### Trait Objects Perform Dynamic Dispatch - -Recall in “Performance of Code Using Generics” on page XX our discussion on the -monomorphization process performed by the compiler when we use trait bounds on -generics: the compiler generates nongeneric implementations of functions and -methods for each concrete type that we use in place of a generic type -parameter. The code that results from monomorphization is doing *static -dispatch*, which is when the compiler knows what method you’re calling at -compile time. This is opposed to *dynamic dispatch*, which is when the compiler -can’t tell at compile time which method you’re calling. In dynamic dispatch -cases, the compiler emits code that at runtime will figure out which method to -call. - -When we use trait objects, Rust must use dynamic dispatch. The compiler doesn’t -know all the types that might be used with the code that’s using trait objects, -so it doesn’t know which method implemented on which type to call. Instead, at -runtime, Rust uses the pointers inside the trait object to know which method to -call. This lookup incurs a runtime cost that doesn’t occur with static -dispatch. Dynamic dispatch also prevents the compiler from choosing to inline a -method’s code, which in turn prevents some optimizations. However, we did get -extra flexibility in the code that we wrote in Listing 17-5 and were able to -support in Listing 17-9, so it’s a trade-off to consider. - -## Implementing an Object-Oriented Design Pattern - -The *state pattern* is an object-oriented design pattern. The crux of the -pattern is that we define a set of states a value can have internally. The -states are represented by a set of *state objects*, and the value’s behavior -changes based on its state. We’re going to work through an example of a blog -post struct that has a field to hold its state, which will be a state object -from the set “draft,” “review,” or “published.” - -The state objects share functionality: in Rust, of course, we use structs and -traits rather than objects and inheritance. Each state object is responsible -for its own behavior and for governing when it should change into another -state. The value that holds a state object knows nothing about the different -behavior of the states or when to transition between states. - -The advantage of using the state pattern is that, when the business -requirements of the program change, we won’t need to change the code of the -value holding the state or the code that uses the value. We’ll only need to -update the code inside one of the state objects to change its rules or perhaps -add more state objects. - -First we’re going to implement the state pattern in a more traditional -object-oriented way, then we’ll use an approach that’s a bit more natural in -Rust. Let’s dig in to incrementally implement a blog post workflow using the -state pattern. - -The final functionality will look like this: - -1. A blog post starts as an empty draft. -1. When the draft is done, a review of the post is requested. -1. When the post is approved, it gets published. -1. Only published blog posts return content to print, so unapproved posts can’t -accidentally be published. - -Any other changes attempted on a post should have no effect. For example, if we -try to approve a draft blog post before we’ve requested a review, the post -should remain an unpublished draft. - -Listing 17-11 shows this workflow in code form: this is an example usage of the -API we’ll implement in a library crate named `blog`. This won’t compile yet -because we haven’t implemented the `blog` crate. - -Filename: src/main.rs - -``` -use blog::Post; +hi number 1 from the second task! +hi number 1 from the first task! +hi number 2 from the first task! +hi number 2 from the second task! +hi number 3 from the first task! +hi number 3 from the second task! +hi number 4 from the first task! +hi number 4 from the second task! +hi number 5 from the first task! +hi number 6 from the first task! +hi number 7 from the first task! +hi number 8 from the first task! +hi number 9 from the first task! +``` -fn main() { - 1 let mut post = Post::new(); +So far, it looks like async and threads give us similar outcomes, just with +different syntax: using `await` instead of calling `join` on the join handle, +and awaiting the `sleep` calls. - 2 post.add_text("I ate a salad for lunch today"); - 3 assert_eq!("", post.content()); +The bigger difference is that we didn’t need to spawn another operating system +thread to do this. In fact, we don’t even need to spawn a task here. Because +async blocks compile to anonymous futures, we can put each loop in an async +block and have the runtime run them both to completion using the `trpl::join` +function. - 4 post.request_review(); - 5 assert_eq!("", post.content()); +In the “Waiting for All Threads to Finish” +section in Chapter 16, we showed how to use the `join` method on the +`JoinHandle` type returned when you call `std::thread::spawn`. The `trpl::join` +function is similar, but for futures. When you give it two futures, it produces +a single new future whose output is a tuple containing the output of each +future you passed in once they *both* complete. Thus, in Listing 17-8, we use +`trpl::join` to wait for both `fut1` and `fut2` to finish. We do *not* await +`fut1` and `fut2` but instead the new future produced by `trpl::join`. We +ignore the output, because it’s just a tuple containing two unit values. - 6 post.approve(); - 7 assert_eq!("I ate a salad for lunch today", post.content()); -} +src/main.rs + +``` + let fut1 = async { + for i in 1..10 { + println!("hi number {i} from the first task!"); + trpl::sleep(Duration::from_millis(500)).await; + } + }; + + let fut2 = async { + for i in 1..5 { + println!("hi number {i} from the second task!"); + trpl::sleep(Duration::from_millis(500)).await; + } + }; + + trpl::join(fut1, fut2).await; ``` -Listing 17-11: Code that demonstrates the desired behavior we want our `blog` -crate to have +Listing 17-8: Using `trpl::join` to await two anonymous futures + +When we run this, we see both futures run to completion: + +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> -We want to allow the user to create a new draft blog post with `Post::new` [1]. -We want to allow text to be added to the blog post [2]. If we try to get the -post’s content immediately, before approval, we shouldn’t get any text because -the post is still a draft. We’ve added `assert_eq!` in the code for -demonstration purposes [3]. An excellent unit test for this would be to assert -that a draft blog post returns an empty string from the `content` method, but -we’re not going to write tests for this example. +``` +hi number 1 from the first task! +hi number 1 from the second task! +hi number 2 from the first task! +hi number 2 from the second task! +hi number 3 from the first task! +hi number 3 from the second task! +hi number 4 from the first task! +hi number 4 from the second task! +hi number 5 from the first task! +hi number 6 from the first task! +hi number 7 from the first task! +hi number 8 from the first task! +hi number 9 from the first task! +``` -Next, we want to enable a request for a review of the post [4], and we want -`content` to return an empty string while waiting for the review [5]. When the -post receives approval [6], it should get published, meaning the text of the -post will be returned when `content` is called [7]. +Now, you’ll see the exact same order every time, which is very different from +what we saw with threads and with `trpl::spawn_task` in Listing 17-7. That is +because the `trpl::join` function is *fair*, meaning it checks each future +equally often, alternating between them, and never lets one race ahead if the +other is ready. With threads, the operating system decides which thread to +check and how long to let it run. With async Rust, the runtime decides which +task to check. (In practice, the details get complicated because an async +runtime might use operating system threads under the hood as part of how it +manages concurrency, so guaranteeing fairness can be more work for a +runtime—but it’s still possible!) Runtimes don’t have to guarantee fairness for +any given operation, and they often offer different APIs to let you choose +whether or not you want fairness. -Notice that the only type we’re interacting with from the crate is the `Post` -type. This type will use the state pattern and will hold a value that will be -one of three state objects representing the various states a post can be -in—draft, review, or published. Changing from one state to another will be -managed internally within the `Post` type. The states change in response to the -methods called by our library’s users on the `Post` instance, but they don’t -have to manage the state changes directly. Also, users can’t make a mistake -with the states, such as publishing a post before it’s reviewed. +Try some of these variations on awaiting the futures and see what they do: -### Defining Post and Creating a New Instance in the Draft State +* Remove the async block from around either or both of the loops. +* Await each async block immediately after defining it. +* Wrap only the first loop in an async block, and await the resulting future + after the body of second loop. -Let’s get started on the implementation of the library! We know we need a -public `Post` struct that holds some content, so we’ll start with the -definition of the struct and an associated public `new` function to create an -instance of `Post`, as shown in Listing 17-12. We’ll also make a private -`State` trait that will define the behavior that all state objects for a `Post` -must have. +For an extra challenge, see if you can figure out what the output will be in +each case *before* running the code! -Then `Post` will hold a trait object of `Box<dyn State>` inside an `Option<T>` -in a private field named `state` to hold the state object. You’ll see why the -`Option<T>` is necessary in a bit. +<!-- Old headings. Do not remove or links may break. --> -Filename: src/lib.rs +<a id="message-passing"></a> +<a id="counting-up-on-two-tasks-using-message-passing"></a> + +### Sending Data Between Two Tasks Using Message Passing + +Sharing data between futures will also be familiar: we’ll use message passing +again, but this time with async versions of the types and functions. We’ll take +a slightly different path than we did in the “Transfer Data Between Threads +with Message Passing” section in +Chapter 16 to illustrate some of the key differences between thread-based and +futures-based concurrency. In Listing 17-9, we’ll begin with just a single +async block—*not* spawning a separate task as we spawned a separate thread. + +src/main.rs ``` -pub struct Post { - state: Option<Box<dyn State>>, - content: String, -} + let (tx, mut rx) = trpl::channel(); + + let val = String::from("hi"); + tx.send(val).unwrap(); + + let received = rx.recv().await.unwrap(); + println!("received '{received}'"); +``` + +Listing 17-9: Creating an async channel and assigning the two halves to `tx` and `rx` + +Here, we use `trpl::channel`, an async version of the multiple-producer, +single-consumer channel API we used with threads back in Chapter 16. The async +version of the API is only a little different from the thread-based version: it +uses a mutable rather than an immutable receiver `rx`, and its `recv` method +produces a future we need to await rather than producing the value directly. +Now we can send messages from the sender to the receiver. Notice that we don’t +have to spawn a separate thread or even a task; we merely need to await the +`rx.recv` call. + +The synchronous `Receiver::recv` method in `std::mpsc::channel` blocks until it +receives a message. The `trpl::Receiver::recv` method does not, because it is +async. Instead of blocking, it hands control back to the runtime until either a +message is received or the send side of the channel closes. By contrast, we +don’t await the `send` call, because it doesn’t block. It doesn’t need to, +because the channel we’re sending it into is unbounded. + +> Note: Because all of this async code runs in an async block in a +> `trpl::block_on` call, everything within it can avoid blocking. However, the +> code *outside* it will block on the `block_on` function returning. That’s the +> whole point of the `trpl::block_on` function: it lets you *choose* where to +> block on some set of async code, and thus where to transition between sync +> and async code. + +Notice two things about this example. First, the message will arrive right +away. Second, although we use a future here, there’s no concurrency yet. +Everything in the listing happens in sequence, just as it would if there were +no futures involved. + +Let’s address the first part by sending a series of messages and sleeping in +between them, as shown in Listing 17-10. -impl Post { - pub fn new() -> Post { - Post { - 1 state: Some(Box::new(Draft {})), - 2 content: String::new(), +<!-- We cannot test this one because it never stops! --> + +src/main.rs + +``` + let (tx, mut rx) = trpl::channel(); + + let vals = vec![ + String::from("hi"), + String::from("from"), + String::from("the"), + String::from("future"), + ]; + + for val in vals { + tx.send(val).unwrap(); + trpl::sleep(Duration::from_millis(500)).await; } - } -} -trait State {} + while let Some(value) = rx.recv().await { + println!("received '{value}'"); + } +``` + +Listing 17-10: Sending and receiving multiple messages over the async channel and sleeping with an `await` between each message + +In addition to sending the messages, we need to receive them. In this case, +because we know how many messages are coming in, we could do that manually by +calling `rx.recv().await` four times. In the real world, though, we’ll generally +be waiting on some *unknown* number of messages, so we need to keep waiting +until we determine that there are no more messages. + +In Listing 16-10, we used a `for` loop to process all the items received from a +synchronous channel. Rust doesn’t yet have a way to use a `for` loop with an +*asynchronously produced* series of items, however, so we need to use a loop we +haven’t seen before: the `while let` conditional loop. This is the loop version +of the `if let` construct we saw back in the “Concise Control Flow with `if let` and `let else`” section in Chapter 6. The loop +will continue executing as long as the pattern it specifies continues to match +the value. + +The `rx.recv` call produces a future, which we await. The runtime will pause +the future until it is ready. Once a message arrives, the future will resolve +to `Some(message)` as many times as a message arrives. When the channel closes, +regardless of whether *any* messages have arrived, the future will instead +resolve to `None` to indicate that there are no more values and thus we should +stop polling—that is, stop awaiting. + +The `while let` loop pulls all of this together. If the result of calling +`rx.recv().await` is `Some(message)`, we get access to the message and we can +use it in the loop body, just as we could with `if let`. If the result is +`None`, the loop ends. Every time the loop completes, it hits the await point +again, so the runtime pauses it again until another message arrives. + +The code now successfully sends and receives all of the messages. +Unfortunately, there are still a couple of problems. For one thing, the +messages do not arrive at half-second intervals. They arrive all at once, 2 +seconds (2,000 milliseconds) after we start the program. For another, this +program also never exits! Instead, it waits forever for new messages. You will +need to shut it down using <kbd>ctrl</kbd>-<kbd>C</kbd>. + +#### Code Within One Async Block Executes Linearly + +Let’s start by examining why the messages come in all at once after the full +delay, rather than coming in with delays between each one. Within a given async +block, the order in which `await` keywords appear in the code is also the order +in which they’re executed when the program runs. + +There’s only one async block in Listing 17-10, so everything in it runs +linearly. There’s still no concurrency. All the `tx.send` calls happen, +interspersed with all of the `trpl::sleep` calls and their associated await +points. Only then does the `while let` loop get to go through any of the +`await` points on the `recv` calls. + +To get the behavior we want, where the sleep delay happens between each +message, we need to put the `tx` and `rx` operations in their own async blocks, +as shown in Listing 17-11. Then the runtime can execute each of them separately +using `trpl::join`, just as in Listing 17-8. Once again, we await the result of +calling `trpl::join`, not the individual futures. If we awaited the individual +futures in sequence, we would just end up back in a sequential flow—exactly +what we’re trying *not* to do. + +<!-- We cannot test this one because it never stops! --> + +src/main.rs + +``` + let tx_fut = async { + let vals = vec![ + String::from("hi"), + String::from("from"), + String::from("the"), + String::from("future"), + ]; + + for val in vals { + tx.send(val).unwrap(); + trpl::sleep(Duration::from_millis(500)).await; + } + }; -struct Draft {} + let rx_fut = async { + while let Some(value) = rx.recv().await { + println!("received '{value}'"); + } + }; -impl State for Draft {} + trpl::join(tx_fut, rx_fut).await; ``` -Listing 17-12: Definition of a `Post` struct and a `new` function that creates -a new `Post` instance, a `State` trait, and a `Draft` struct +Listing 17-11: Separating `send` and `recv` into their own `async` blocks and awaiting the futures for those blocks + +With the updated code in Listing 17-11, the messages get printed at +500-millisecond intervals, rather than all in a rush after 2 seconds. + +#### Moving Ownership Into an Async Block + +The program still never exits, though, because of the way the `while let` loop +interacts with `trpl::join`: + +* The future returned from `trpl::join` completes only once *both* futures + passed to it have completed. +* The `tx_fut` future completes once it finishes sleeping after sending the last + message in `vals`. +* The `rx_fut` future won’t complete until the `while let` loop ends. +* The `while let` loop won’t end until awaiting `rx.recv` produces `None`. +* Awaiting `rx.recv` will return `None` only once the other end of the channel + is closed. +* The channel will close only if we call `rx.close` or when the sender side, + `tx`, is dropped. +* We don’t call `rx.close` anywhere, and `tx` won’t be dropped until the + outermost async block passed to `trpl::block_on` ends. +* The block can’t end because it is blocked on `trpl::join` completing, which + takes us back to the top of this list. + +Right now, the async block where we send the messages only *borrows* `tx` +because sending a message doesn’t require ownership, but if we could *move* +`tx` into that async block, it would be dropped once that block ends. In the +“Capturing References or Moving Ownership” +section in Chapter 13, you learned how to use the `move` keyword with closures, +and, as discussed in the “Using `move` Closures with +Threads” section in Chapter 16, we often need to +move data into closures when working with threads. The same basic dynamics +apply to async blocks, so the `move` keyword works with async blocks just as it +does with closures. + +In Listing 17-12, we change the block used to send messages from `async` to +`async move`. + +src/main.rs -The `State` trait defines the behavior shared by different post states. The -state objects are `Draft`, `PendingReview`, and `Published`, and they will all -implement the `State` trait. For now, the trait doesn’t have any methods, and -we’ll start by defining just the `Draft` state because that is the state we -want a post to start in. +``` + let (tx, mut rx) = trpl::channel(); -When we create a new `Post`, we set its `state` field to a `Some` value that -holds a `Box` [1]. This `Box` points to a new instance of the `Draft` struct. -This ensures that whenever we create a new instance of `Post`, it will start -out as a draft. Because the `state` field of `Post` is private, there is no way -to create a `Post` in any other state! In the `Post::new` function, we set the -`content` field to a new, empty `String` [2]. + let tx_fut = async move { + // --snip-- +``` -### Storing the Text of the Post Content +Listing 17-12: A revision of the code from Listing 17-11 that correctly shuts down when complete -We saw in Listing 17-11 that we want to be able to call a method named -`add_text` and pass it a `&str` that is then added as the text content of the -blog post. We implement this as a method, rather than exposing the `content` -field as `pub`, so that later we can implement a method that will control how -the `content` field’s data is read. The `add_text` method is pretty -straightforward, so let’s add the implementation in Listing 17-13 to the `impl -Post` block. +When we run *this* version of the code, it shuts down gracefully after the last +message is sent and received. Next, let’s see what would need to change to send +data from more than one future. -Filename: src/lib.rs +#### Joining a Number of Futures with the join! Macro + +This async channel is also a multiple-producer channel, so we can call `clone` +on `tx` if we want to send messages from multiple futures, as shown in Listing +17-13. + +src/main.rs ``` -impl Post { - --snip-- - pub fn add_text(&mut self, text: &str) { - self.content.push_str(text); - } -} + let (tx, mut rx) = trpl::channel(); + + let tx1 = tx.clone(); + let tx1_fut = async move { + let vals = vec![ + String::from("hi"), + String::from("from"), + String::from("the"), + String::from("future"), + ]; + + for val in vals { + tx1.send(val).unwrap(); + trpl::sleep(Duration::from_millis(500)).await; + } + }; + + let rx_fut = async { + while let Some(value) = rx.recv().await { + println!("received '{value}'"); + } + }; + + let tx_fut = async move { + let vals = vec![ + String::from("more"), + String::from("messages"), + String::from("for"), + String::from("you"), + ]; + + for val in vals { + tx.send(val).unwrap(); + trpl::sleep(Duration::from_millis(1500)).await; + } + }; + + trpl::join!(tx1_fut, tx_fut, rx_fut); ``` -Listing 17-13: Implementing the `add_text` method to add text to a post’s -`content` +Listing 17-13: Using multiple producers with async blocks -The `add_text` method takes a mutable reference to `self` because we’re -changing the `Post` instance that we’re calling `add_text` on. We then call -`push_str` on the `String` in `content` and pass the `text` argument to add to -the saved `content`. This behavior doesn’t depend on the state the post is in, -so it’s not part of the state pattern. The `add_text` method doesn’t interact -with the `state` field at all, but it is part of the behavior we want to -support. +First, we clone `tx`, creating `tx1` outside the first async block. We move +`tx1` into that block just as we did before with `tx`. Then, later, we move the +original `tx` into a *new* async block, where we send more messages on a +slightly slower delay. We happen to put this new async block after the async +block for receiving messages, but it could go before it just as well. The key is +the order in which the futures are awaited, not in which they’re created. -### Ensuring the Content of a Draft Post Is Empty +Both of the async blocks for sending messages need to be `async move` blocks so +that both `tx` and `tx1` get dropped when those blocks finish. Otherwise, we’ll +end up back in the same infinite loop we started out in. -Even after we’ve called `add_text` and added some content to our post, we still -want the `content` method to return an empty string slice because the post is -still in the draft state, as shown at [3] in Listing 17-11. For now, let’s -implement the `content` method with the simplest thing that will fulfill this -requirement: always returning an empty string slice. We’ll change this later -once we implement the ability to change a post’s state so it can be published. -So far, posts can only be in the draft state, so the post content should always -be empty. Listing 17-14 shows this placeholder implementation. +Finally, we switch from `trpl::join` to `trpl::join!` to handle the additional +future: the `join!` macro awaits an arbitrary number of futures where we know +the number of futures at compile time. We’ll discuss awaiting a collection of +an unknown number of futures later in this chapter. -Filename: src/lib.rs +Now we see all the messages from both sending futures, and because the sending +futures use slightly different delays after sending, the messages are also +received at those different intervals: + +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> ``` -impl Post { - --snip-- - pub fn content(&self) -> &str { - "" - } -} +received 'hi' +received 'more' +received 'from' +received 'the' +received 'messages' +received 'future' +received 'for' +received 'you' ``` -Listing 17-14: Adding a placeholder implementation for the `content` method on -`Post` that always returns an empty string slice +We’ve explored how to use message passing to send data between futures, how +code within an async block runs sequentially, how to move ownership into an +async block, and how to join multiple futures. Next, let’s discuss how and why +to tell the runtime it can switch to another task. + +<!-- Old headings. Do not remove or links may break. --> -With this added `content` method, everything in Listing 17-11 up to the line at -[3] works as intended. +<a id="yielding"></a> -### Requesting a Review Changes the Post’s State +### Yielding Control to the Runtime -Next, we need to add functionality to request a review of a post, which should -change its state from `Draft` to `PendingReview`. Listing 17-15 shows this code. +Recall from the “Our First Async Program” +section that at each await point, Rust gives a runtime a chance to pause the +task and switch to another one if the future being awaited isn’t ready. The +inverse is also true: Rust *only* pauses async blocks and hands control back to +a runtime at an await point. Everything between await points is synchronous. -Filename: src/lib.rs +That means if you do a bunch of work in an async block without an await point, +that future will block any other futures from making progress. You may sometimes +hear this referred to as one future *starving* other futures. In some cases, +that may not be a big deal. However, if you are doing some kind of expensive +setup or long-running work, or if you have a future that will keep doing some +particular task indefinitely, you’ll need to think about when and where to hand +control back to the runtime. + +Let’s simulate a long-running operation to illustrate the starvation problem, +then explore how to solve it. Listing 17-14 introduces a `slow` function. + +src/main.rs ``` -impl Post { - --snip-- - 1 pub fn request_review(&mut self) { - 2 if let Some(s) = self.state.take() { - 3 self.state = Some(s.request_review()) - } - } +fn slow(name: &str, ms: u64) { + thread::sleep(Duration::from_millis(ms)); + println!("'{name}' ran for {ms}ms"); } +``` -trait State { - 4 fn request_review(self: Box<Self>) -> Box<dyn State>; -} +Listing 17-14: Using `thread::sleep` to simulate slow operations -struct Draft {} +This code uses `std::thread::sleep` instead of `trpl::sleep` so that calling +`slow` will block the current thread for some number of milliseconds. We can +use `slow` to stand in for real-world operations that are both long-running and +blocking. -impl State for Draft { - fn request_review(self: Box<Self>) -> Box<dyn State> { - 5 Box::new(PendingReview {}) - } -} +In Listing 17-15, we use `slow` to emulate doing this kind of CPU-bound work in +a pair of futures. -struct PendingReview {} +src/main.rs -impl State for PendingReview { - fn request_review(self: Box<Self>) -> Box<dyn State> { - 6 self - } -} +``` + let a = async { + println!("'a' started."); + slow("a", 30); + slow("a", 10); + slow("a", 20); + trpl::sleep(Duration::from_millis(50)).await; + println!("'a' finished."); + }; + + let b = async { + println!("'b' started."); + slow("b", 75); + slow("b", 10); + slow("b", 15); + slow("b", 350); + trpl::sleep(Duration::from_millis(50)).await; + println!("'b' finished."); + }; + + trpl::select(a, b).await; ``` -Listing 17-15: Implementing `request_review` methods on `Post` and the `State` -trait - -We give `Post` a public method named `request_review` that will take a mutable -reference to `self` [1]. Then we call an internal `request_review` method on -the current state of `Post` [3], and this second `request_review` method -consumes the current state and returns a new state. - -We add the `request_review` method to the `State` trait [4]; all types that -implement the trait will now need to implement the `request_review` method. -Note that rather than having `self`, `&self`, or `&mut self` as the first -parameter of the method, we have `self: Box<Self>`. This syntax means the -method is only valid when called on a `Box` holding the type. This syntax takes -ownership of `Box<Self>`, invalidating the old state so the state value of the -`Post` can transform into a new state. - -To consume the old state, the `request_review` method needs to take ownership -of the state value. This is where the `Option` in the `state` field of `Post` -comes in: we call the `take` method to take the `Some` value out of the `state` -field and leave a `None` in its place because Rust doesn’t let us have -unpopulated fields in structs [2]. This lets us move the `state` value out of -`Post` rather than borrowing it. Then we’ll set the post’s `state` value to the -result of this operation. - -We need to set `state` to `None` temporarily rather than setting it directly -with code like `self.state = self.state.request_review();` to get ownership of -the `state` value. This ensures `Post` can’t use the old `state` value after -we’ve transformed it into a new state. - -The `request_review` method on `Draft` returns a new, boxed instance of a new -`PendingReview` struct [5], which represents the state when a post is waiting -for a review. The `PendingReview` struct also implements the `request_review` -method but doesn’t do any transformations. Rather, it returns itself [6] -because when we request a review on a post already in the `PendingReview` -state, it should stay in the `PendingReview` state. - -Now we can start seeing the advantages of the state pattern: the -`request_review` method on `Post` is the same no matter its `state` value. Each -state is responsible for its own rules. - -We’ll leave the `content` method on `Post` as is, returning an empty string -slice. We can now have a `Post` in the `PendingReview` state as well as in the -`Draft` state, but we want the same behavior in the `PendingReview` state. -Listing 17-11 now works up to the line at [5]! - -### Adding approve to Change the Behavior of content - -The `approve` method will be similar to the `request_review` method: it will -set `state` to the value that the current state says it should have when that -state is approved, as shown in Listing 17-16. - -Filename: src/lib.rs - -``` -impl Post { - --snip-- - pub fn approve(&mut self) { - if let Some(s) = self.state.take() { - self.state = Some(s.approve()) - } - } -} +Listing 17-15: Calling `slow` to simulate running slow operations -trait State { - fn request_review(self: Box<Self>) -> Box<dyn State>; - fn approve(self: Box<Self>) -> Box<dyn State>; -} +Each future hands control back to the runtime only *after* carrying out a bunch +of slow operations. If you run this code, you will see this output: -struct Draft {} +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-15/ +cargo run +copy just the output +--> -impl State for Draft { - --snip-- - fn approve(self: Box<Self>) -> Box<dyn State> { - 1 self - } -} +``` +'a' started. +'a' ran for 30ms +'a' ran for 10ms +'a' ran for 20ms +'b' started. +'b' ran for 75ms +'b' ran for 10ms +'b' ran for 15ms +'b' ran for 350ms +'a' finished. +``` -struct PendingReview {} +As with Listing 17-5 where we used `trpl::select` to race futures fetching two +URLs, `select` still finishes as soon as `a` is done. There’s no interleaving +between the calls to `slow` in the two futures, though. The `a` future does all +of its work until the `trpl::sleep` call is awaited, then the `b` future does +all of its work until its own `trpl::sleep` call is awaited, and finally the +`a` future completes. To allow both futures to make progress between their slow +tasks, we need await points so we can hand control back to the runtime. That +means we need something we can await! -impl State for PendingReview { - --snip-- - fn approve(self: Box<Self>) -> Box<dyn State> { - 2 Box::new(Published {}) - } -} +We can already see this kind of handoff happening in Listing 17-15: if we +removed the `trpl::sleep` at the end of the `a` future, it would complete +without the `b` future running *at all*. Let’s try using the `trpl::sleep` +function as a starting point for letting operations switch off making progress, +as shown in Listing 17-16. -struct Published {} +src/main.rs -impl State for Published { - fn request_review(self: Box<Self>) -> Box<dyn State> { - self - } +``` + let one_ms = Duration::from_millis(1); + + let a = async { + println!("'a' started."); + slow("a", 30); + trpl::sleep(one_ms).await; + slow("a", 10); + trpl::sleep(one_ms).await; + slow("a", 20); + trpl::sleep(one_ms).await; + println!("'a' finished."); + }; + + let b = async { + println!("'b' started."); + slow("b", 75); + trpl::sleep(one_ms).await; + slow("b", 10); + trpl::sleep(one_ms).await; + slow("b", 15); + trpl::sleep(one_ms).await; + slow("b", 350); + trpl::sleep(one_ms).await; + println!("'b' finished."); + }; +``` + +Listing 17-16: Using `trpl::sleep` to let operations switch off making progress + +We’ve added `trpl::sleep` calls with await points between each call to `slow`. +Now the two futures’ work is interleaved: + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-16 +cargo run +copy just the output +--> - fn approve(self: Box<Self>) -> Box<dyn State> { - self - } -} +``` +'a' started. +'a' ran for 30ms +'b' started. +'b' ran for 75ms +'a' ran for 10ms +'b' ran for 10ms +'a' ran for 20ms +'b' ran for 15ms +'a' finished. ``` -Listing 17-16: Implementing the `approve` method on `Post` and the `State` trait +The `a` future still runs for a bit before handing off control to `b`, because +it calls `slow` before ever calling `trpl::sleep`, but after that the futures +swap back and forth each time one of them hits an await point. In this case, we +have done that after every call to `slow`, but we could break up the work in +whatever way makes the most sense to us. -We add the `approve` method to the `State` trait and add a new struct that -implements `State`, the `Published` state. +We don’t really want to *sleep* here, though: we want to make progress as fast +as we can. We just need to hand back control to the runtime. We can do that +directly, using the `trpl::yield_now` function. In Listing 17-17, we replace +all those `trpl::sleep` calls with `trpl::yield_now`. -Similar to the way `request_review` on `PendingReview` works, if we call the -`approve` method on a `Draft`, it will have no effect because `approve` will -return `self` [1]. When we call `approve` on `PendingReview`, it returns a new, -boxed instance of the `Published` struct [2]. The `Published` struct implements -the `State` trait, and for both the `request_review` method and the `approve` -method, it returns itself because the post should stay in the `Published` state -in those cases. +src/main.rs -Now we need to update the `content` method on `Post`. We want the value -returned from `content` to depend on the current state of the `Post`, so we’re -going to have the `Post` delegate to a `content` method defined on its `state`, -as shown in Listing 17-17. +``` + let a = async { + println!("'a' started."); + slow("a", 30); + trpl::yield_now().await; + slow("a", 10); + trpl::yield_now().await; + slow("a", 20); + trpl::yield_now().await; + println!("'a' finished."); + }; + + let b = async { + println!("'b' started."); + slow("b", 75); + trpl::yield_now().await; + slow("b", 10); + trpl::yield_now().await; + slow("b", 15); + trpl::yield_now().await; + slow("b", 350); + trpl::yield_now().await; + println!("'b' finished."); + }; +``` -Filename: src/lib.rs +Listing 17-17: Using `yield_now` to let operations switch off making progress + +This code is both clearer about the actual intent and can be significantly +faster than using `sleep`, because timers such as the one used by `sleep` often +have limits on how granular they can be. The version of `sleep` we are using, +for example, will always sleep for at least a millisecond, even if we pass it a +`Duration` of one nanosecond. Again, modern computers are *fast*: they can do a +lot in one millisecond! + +This means that async can be useful even for compute-bound tasks, depending on +what else your program is doing, because it provides a useful tool for +structuring the relationships between different parts of the program (but at a +cost of the overhead of the async state machine). This is a form of +*cooperative multitasking*, where each future has the power to determine when +it hands over control via await points. Each future therefore also has the +responsibility to avoid blocking for too long. In some Rust-based embedded +operating systems, this is the *only* kind of multitasking! + +In real-world code, you won’t usually be alternating function calls with await +points on every single line, of course. While yielding control in this way is +relatively inexpensive, it’s not free. In many cases, trying to break up a +compute-bound task might make it significantly slower, so sometimes it’s better +for *overall* performance to let an operation block briefly. Always +measure to see what your code’s actual performance bottlenecks are. The +underlying dynamic is important to keep in mind, though, if you *are* seeing a +lot of work happening in serial that you expected to happen concurrently! + +### Building Our Own Async Abstractions + +We can also compose futures together to create new patterns. For example, we can +build a `timeout` function with async building blocks we already have. When +we’re done, the result will be another building block we could use to create +still more async abstractions. + +Listing 17-18 shows how we would expect this `timeout` to work with a slow +future. + +src/main.rs ``` -impl Post { - --snip-- - pub fn content(&self) -> &str { - self.state.as_ref().unwrap().content(self) - } - --snip-- -} + let slow = async { + trpl::sleep(Duration::from_secs(5)).await; + "Finally finished" + }; + + match timeout(slow, Duration::from_secs(2)).await { + Ok(message) => println!("Succeeded with '{message}'"), + Err(duration) => { + println!("Failed after {} seconds", duration.as_secs()) + } + } ``` -Listing 17-17: Updating the `content` method on `Post` to delegate to a -`content` method on `State` +Listing 17-18: Using our imagined `timeout` to run a slow operation with a time limit -Because the goal is to keep all of these rules inside the structs that -implement `State`, we call a `content` method on the value in `state` and pass -the post instance (that is, `self`) as an argument. Then we return the value -that’s returned from using the `content` method on the `state` value. +Let’s implement this! To begin, let’s think about the API for `timeout`: -We call the `as_ref` method on the `Option` because we want a reference to the -value inside the `Option` rather than ownership of the value. Because `state` -is an `Option<Box<dyn State>>`, when we call `as_ref`, an `Option<&Box<dyn -State>>` is returned. If we didn’t call `as_ref`, we would get an error because -we can’t move `state` out of the borrowed `&self` of the function parameter. +* It needs to be an async function itself so we can await it. +* Its first parameter should be a future to run. We can make it generic to allow + it to work with any future. +* Its second parameter will be the maximum time to wait. If we use a `Duration`, + that will make it easy to pass along to `trpl::sleep`. +* It should return a `Result`. If the future completes successfully, the + `Result` will be `Ok` with the value produced by the future. If the timeout + elapses first, the `Result` will be `Err` with the duration that the timeout + waited for. -We then call the `unwrap` method, which we know will never panic because we -know the methods on `Post` ensure that `state` will always contain a `Some` -value when those methods are done. This is one of the cases we talked about in -“Cases in Which You Have More Information Than the Compiler” on page XX when we -know that a `None` value is never possible, even though the compiler isn’t able -to understand that. +Listing 17-19 shows this declaration. -At this point, when we call `content` on the `&Box<dyn State>`, deref coercion -will take effect on the `&` and the `Box` so the `content` method will -ultimately be called on the type that implements the `State` trait. That means -we need to add `content` to the `State` trait definition, and that is where -we’ll put the logic for what content to return depending on which state we -have, as shown in Listing 17-18. +<!-- This is not tested because it intentionally does not compile. --> -Filename: src/lib.rs +src/main.rs ``` -trait State { - --snip-- - fn content<'a>(&self, post: &'a Post) -> &'a str { - 1 "" - } +async fn timeout<F: Future>( + future_to_try: F, + max_time: Duration, +) -> Result<F::Output, Duration> { + // Here is where our implementation will go! } +``` + +Listing 17-19: Defining the signature of `timeout` + +That satisfies our goals for the types. Now let’s think about the *behavior* we +need: we want to race the future passed in against the duration. We can use +`trpl::sleep` to make a timer future from the duration, and use `trpl::select` +to run that timer with the future the caller passes in. + +In Listing 17-20, we implement `timeout` by matching on the result of awaiting +`trpl::select`. + +src/main.rs ---snip-- -struct Published {} +``` +use trpl::Either; + +// --snip-- -impl State for Published { - --snip-- - fn content<'a>(&self, post: &'a Post) -> &'a str { - 2 &post.content +async fn timeout<F: Future>( + future_to_try: F, + max_time: Duration, +) -> Result<F::Output, Duration> { + match trpl::select(future_to_try, trpl::sleep(max_time)).await { + Either::Left(output) => Ok(output), + Either::Right(_) => Err(max_time), } } ``` -Listing 17-18: Adding the `content` method to the `State` trait - -We add a default implementation for the `content` method that returns an empty -string slice [1]. That means we don’t need to implement `content` on the -`Draft` and `PendingReview` structs. The `Published` struct will override the -`content` method and return the value in `post.content` [2]. - -Note that we need lifetime annotations on this method, as we discussed in -Chapter 10. We’re taking a reference to a `post` as an argument and returning a -reference to part of that `post`, so the lifetime of the returned reference is -related to the lifetime of the `post` argument. - -And we’re done—all of Listing 17-11 now works! We’ve implemented the state -pattern with the rules of the blog post workflow. The logic related to the -rules lives in the state objects rather than being scattered throughout `Post`. - -> ### Why Not An Enum? -> -> You may have been wondering why we didn’t use an `enum` with the different -possible post states as variants. That’s certainly a possible solution; try it -and compare the end results to see which you prefer! One disadvantage of using -an enum is that every place that checks the value of the enum will need a -`match` expression or similar to handle every possible variant. This could get -more repetitive than this trait object solution. - -### Trade-offs of the State Pattern - -We’ve shown that Rust is capable of implementing the object-oriented state -pattern to encapsulate the different kinds of behavior a post should have in -each state. The methods on `Post` know nothing about the various behaviors. The -way we organized the code, we have to look in only one place to know the -different ways a published post can behave: the implementation of the `State` -trait on the `Published` struct. - -If we were to create an alternative implementation that didn’t use the state -pattern, we might instead use `match` expressions in the methods on `Post` or -even in the `main` code that checks the state of the post and changes behavior -in those places. That would mean we would have to look in several places to -understand all the implications of a post being in the published state! This -would only increase the more states we added: each of those `match` expressions -would need another arm. - -With the state pattern, the `Post` methods and the places we use `Post` don’t -need `match` expressions, and to add a new state, we would only need to add a -new struct and implement the trait methods on that one struct. - -The implementation using the state pattern is easy to extend to add more -functionality. To see the simplicity of maintaining code that uses the state -pattern, try a few of these suggestions: - -* Add a `reject` method that changes the post’s state from `PendingReview` back -to `Draft`. -* Require two calls to `approve` before the state can be changed to `Published`. -* Allow users to add text content only when a post is in the `Draft` state. -Hint: have the state object responsible for what might change about the content -but not responsible for modifying the `Post`. - -One downside of the state pattern is that, because the states implement the -transitions between states, some of the states are coupled to each other. If we -add another state between `PendingReview` and `Published`, such as `Scheduled`, -we would have to change the code in `PendingReview` to transition to -`Scheduled` instead. It would be less work if `PendingReview` didn’t need to -change with the addition of a new state, but that would mean switching to -another design pattern. - -Another downside is that we’ve duplicated some logic. To eliminate some of the -duplication, we might try to make default implementations for the -`request_review` and `approve` methods on the `State` trait that return `self`. -However, this wouldn’t work: when using `State` as a trait object, the trait -doesn’t know what the concrete `self` will be exactly, so the return type isn’t -known at compile time. - -Other duplication includes the similar implementations of the `request_review` -and `approve` methods on `Post`. Both methods delegate to the implementation of -the same method on the value in the `state` field of `Option` and set the new -value of the `state` field to the result. If we had a lot of methods on `Post` -that followed this pattern, we might consider defining a macro to eliminate the -repetition (see “Macros” on page XX). - -By implementing the state pattern exactly as it’s defined for object-oriented -languages, we’re not taking as full advantage of Rust’s strengths as we could. -Let’s look at some changes we can make to the `blog` crate that can make -invalid states and transitions into compile-time errors. - -#### Encoding States and Behavior as Types - -We’ll show you how to rethink the state pattern to get a different set of -trade-offs. Rather than encapsulating the states and transitions completely so -outside code has no knowledge of them, we’ll encode the states into different -types. Consequently, Rust’s type checking system will prevent attempts to use -draft posts where only published posts are allowed by issuing a compiler error. - -Let’s consider the first part of `main` in Listing 17-11: - -Filename: src/main.rs +Listing 17-20: Defining `timeout` with `select` and `sleep` + +The implementation of `trpl::select` is not fair: it always polls arguments in +the order in which they are passed (other `select` implementations will +randomly choose which argument to poll first). Thus, we pass `future_to_try` to +`select` first so it gets a chance to complete even if `max_time` is a very +short duration. If `future_to_try` finishes first, `select` will return `Left` +with the output from `future_to_try`. If `timer` finishes first, `select` will +return `Right` with the timer’s output of `()`. + +If the `future_to_try` succeeds and we get a `Left(output)`, we return +`Ok(output)`. If the sleep timer elapses instead and we get a `Right(())`, we +ignore the `()` with `_` and return `Err(max_time)` instead. + +With that, we have a working `timeout` built out of two other async helpers. If +we run our code, it will print the failure mode after the timeout: + +``` +Failed after 2 seconds +``` + +Because futures compose with other futures, you can build really powerful tools +using smaller async building blocks. For example, you can use this same +approach to combine timeouts with retries, and in turn use those with +operations such as network calls (such as those in Listing 17-5). + +In practice, you’ll usually work directly with `async` and `await`, and +secondarily with functions such as `select` and macros such as the `join!` +macro to control how the outermost futures are executed. + +We’ve now seen a number of ways to work with multiple futures at the same time. +Up next, we’ll look at how we can work with multiple futures in a sequence over +time with *streams*. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="streams"></a> + +## Streams: Futures in Sequence + +Recall how we used the receiver for our async channel earlier in this chapter +in the “Message Passing” section. The async +`recv` method produces a sequence of items over time. This is an instance of a +much more general pattern known as a *stream*. Many concepts are naturally +represented as streams: items becoming available in a queue, chunks of data +being pulled incrementally from the filesystem when the full data set is too +large for the computer’s memory, or data arriving over the network over time. +Because streams are futures, we can use them with any other kind of future and +combine them in interesting ways. For example, we can batch up events to avoid +triggering too many network calls, set timeouts on sequences of long-running +operations, or throttle user interface events to avoid doing needless work. + +We saw a sequence of items back in Chapter 13, when we looked at the Iterator +trait in “The Iterator Trait and the `next` Method” section, but there are two differences between iterators and the +async channel receiver. The first difference is time: iterators are +synchronous, while the channel receiver is asynchronous. The second difference +is the API. When working directly with `Iterator`, we call its synchronous +`next` method. With the `trpl::Receiver` stream in particular, we called an +asynchronous `recv` method instead. Otherwise, these APIs feel very similar, +and that similarity isn’t a coincidence. A stream is like an asynchronous form +of iteration. Whereas the `trpl::Receiver` specifically waits to receive +messages, though, the general-purpose stream API is much broader: it provides +the next item the way `Iterator` does, but asynchronously. + +The similarity between iterators and streams in Rust means we can actually +create a stream from any iterator. As with an iterator, we can work with a +stream by calling its `next` method and then awaiting the output, as in Listing +17-21, which won’t compile yet. + +src/main.rs + +``` + let values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; + let iter = values.iter().map(|n| n * 2); + let mut stream = trpl::stream_from_iter(iter); + + while let Some(value) = stream.next().await { + println!("The value was: {value}"); + } +``` + +Listing 17-21: Creating a stream from an iterator and printing its values + +We start with an array of numbers, which we convert to an iterator and then +call `map` on to double all the values. Then we convert the iterator into a +stream using the `trpl::stream_from_iter` function. Next, we loop over the +items in the stream as they arrive with the `while let` loop. + +Unfortunately, when we try to run the code, it doesn’t compile but instead +reports that there’s no `next` method available: + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-21 +cargo build +copy only the error output +--> + +``` +error[E0599]: no method named `next` found for struct `tokio_stream::iter::Iter` in the current scope + --> src/main.rs:10:40 + | +10 | while let Some(value) = stream.next().await { + | ^^^^ + | + = help: items from traits can only be used if the trait is in scope +help: the following traits which provide `next` are implemented but not in scope; perhaps you want to import one of them + | +1 + use crate::trpl::StreamExt; + | +1 + use futures_util::stream::stream::StreamExt; + | +1 + use std::iter::Iterator; + | +1 + use std::str::pattern::Searcher; + | +help: there is a method `try_next` with a similar name + | +10 | while let Some(value) = stream.try_next().await { + | ~~~~~~~~ +``` + +As this output explains, the reason for the compiler error is that we need the +right trait in scope to be able to use the `next` method. Given our discussion +so far, you might reasonably expect that trait to be `Stream`, but it’s +actually `StreamExt`. Short for *extension*, `Ext` is a common pattern in the +Rust community for extending one trait with another. + +The `Stream` trait defines a low-level interface that effectively combines the +`Iterator` and `Future` traits. `StreamExt` supplies a higher-level set of APIs +on top of `Stream`, including the `next` method as well as other utility +methods similar to those provided by the `Iterator` trait. `Stream` and +`StreamExt` are not yet part of Rust’s standard library, but most ecosystem +crates use similar definitions. + +The fix to the compiler error is to add a `use` statement for +`trpl::StreamExt`, as in Listing 17-22. + +src/main.rs ``` +use trpl::StreamExt; + fn main() { - let mut post = Post::new(); + trpl::block_on(async { + let values = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; + // --snip-- +``` + +Listing 17-22: Successfully using an iterator as the basis for a stream + +With all those pieces put together, this code works the way we want! What’s +more, now that we have `StreamExt` in scope, we can use all of its utility +methods, just as with iterators. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="digging-into-the-traits-for-async"></a> + +## A Closer Look at the Traits for Async + +Throughout the chapter, we’ve used the `Future`, `Stream`, and `StreamExt` +traits in various ways. So far, though, we’ve avoided getting too far into the +details of how they work or how they fit together, which is fine most of the +time for your day-to-day Rust work. Sometimes, though, you’ll encounter +situations where you’ll need to understand a few more of these traits’ details, +along with the `Pin` type and the `Unpin` trait. In this section, we’ll dig in +just enough to help in those scenarios, still leaving the *really* deep dive +for other documentation. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="future"></a> - post.add_text("I ate a salad for lunch today"); - assert_eq!("", post.content()); +### The Future Trait + +Let’s start by taking a closer look at how the `Future` trait works. Here’s how +Rust defines it: + +``` +use std::pin::Pin; +use std::task::{Context, Poll}; + +pub trait Future { + type Output; + + fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>; } ``` -We still enable the creation of new posts in the draft state using `Post::new` -and the ability to add text to the post’s content. But instead of having a -`content` method on a draft post that returns an empty string, we’ll make it so -draft posts don’t have the `content` method at all. That way, if we try to get -a draft post’s content, we’ll get a compiler error telling us the method -doesn’t exist. As a result, it will be impossible for us to accidentally -display draft post content in production because that code won’t even compile. -Listing 17-19 shows the definition of a `Post` struct and a `DraftPost` struct, -as well as methods on each. +That trait definition includes a bunch of new types and also some syntax we +haven’t seen before, so let’s walk through the definition piece by piece. -Filename: src/lib.rs +First, `Future`’s associated type `Output` says what the future resolves to. +This is analogous to the `Item` associated type for the `Iterator` trait. +Second, `Future` has the `poll` method, which takes a special `Pin` reference +for its `self` parameter and a mutable reference to a `Context` type, and +returns a `Poll<Self::Output>`. We’ll talk more about `Pin` and `Context` in a +moment. For now, let’s focus on what the method returns, the `Poll` type: ``` -pub struct Post { - content: String, +pub enum Poll<T> { + Ready(T), + Pending, } +``` -pub struct DraftPost { - content: String, -} +This `Poll` type is similar to an `Option`. It has one variant that has a value, +`Ready(T)`, and one that does not, `Pending`. `Poll` means something quite +different from `Option`, though! The `Pending` variant indicates that the future +still has work to do, so the caller will need to check again later. The `Ready` +variant indicates that the `Future` has finished its work and the `T` value is +available. -impl Post { - 1 pub fn new() -> DraftPost { - DraftPost { - content: String::new(), - } - } +> Note: It’s rare to need to call `poll` directly, but if you do need to, keep +> in mind that with most futures, the caller should not call `poll` again after +> the future has returned `Ready`. Many futures will panic if polled again after +> becoming ready. Futures that are safe to poll again will say so explicitly in +> their documentation. This is similar to how `Iterator::next` behaves. - 2 pub fn content(&self) -> &str { - &self.content +When you see code that uses `await`, Rust compiles it under the hood to code +that calls `poll`. If you look back at Listing 17-4, where we printed out the +page title for a single URL once it resolved, Rust compiles it into something +kind of (although not exactly) like this: + +``` +match page_title(url).poll() { + Ready(page_title) => match page_title { + Some(title) => println!("The title for {url} was {title}"), + None => println!("{url} had no title"), + } + Pending => { + // But what goes here? } } +``` + +What should we do when the future is still `Pending`? We need some way to try +again, and again, and again, until the future is finally ready. In other words, +we need a loop: -impl DraftPost { - 3 pub fn add_text(&mut self, text: &str) { - self.content.push_str(text); +``` +let mut page_title_fut = page_title(url); +loop { + match page_title_fut.poll() { + Ready(value) => match page_title { + Some(title) => println!("The title for {url} was {title}"), + None => println!("{url} had no title"), + } + Pending => { + // continue + } } } ``` -Listing 17-19: A `Post` with a `content` method and a `DraftPost` without a -`content` method +If Rust compiled it to exactly that code, though, every `await` would be +blocking—exactly the opposite of what we were going for! Instead, Rust ensures +that the loop can hand off control to something that can pause work on this +future to work on other futures and then check this one again later. As we’ve +seen, that something is an async runtime, and this scheduling and coordination +work is one of its main jobs. + +In the “Sending Data Between Two Tasks Using Message +Passing” section, we described waiting on +`rx.recv`. The `recv` call returns a future, and awaiting the future polls it. +We noted that a runtime will pause the future until it’s ready with either +`Some(message)` or `None` when the channel closes. With our deeper +understanding of the `Future` trait, and specifically `Future::poll`, we can +see how that works. The runtime knows the future isn’t ready when it returns +`Poll::Pending`. Conversely, the runtime knows the future *is* ready and +advances it when `poll` returns `Poll::Ready(Some(message))` or +`Poll::Ready(None)`. -Both the `Post` and `DraftPost` structs have a private `content` field that -stores the blog post text. The structs no longer have the `state` field because -we’re moving the encoding of the state to the types of the structs. The `Post` -struct will represent a published post, and it has a `content` method that -returns the `content` [2]. +The exact details of how a runtime does that are beyond the scope of this book, +but the key is to see the basic mechanics of futures: a runtime *polls* each +future it is responsible for, putting the future back to sleep when it is not +yet ready. -We still have a `Post::new` function, but instead of returning an instance of -`Post`, it returns an instance of `DraftPost` [1]. Because `content` is private -and there aren’t any functions that return `Post`, it’s not possible to create -an instance of `Post` right now. +<!-- Old headings. Do not remove or links may break. --> -The `DraftPost` struct has an `add_text` method, so we can add text to -`content` as before [3], but note that `DraftPost` does not have a `content` -method defined! So now the program ensures all posts start as draft posts, and -draft posts don’t have their content available for display. Any attempt to get -around these constraints will result in a compiler error. +<a id="pinning-and-the-pin-and-unpin-traits"></a> +<a id="the-pin-and-unpin-traits"></a> -#### Implementing Transitions as Transformations into Different Types +### The Pin Type and the Unpin Trait -So how do we get a published post? We want to enforce the rule that a draft -post has to be reviewed and approved before it can be published. A post in the -pending review state should still not display any content. Let’s implement -these constraints by adding another struct, `PendingReviewPost`, defining the -`request_review` method on `DraftPost` to return a `PendingReviewPost` and -defining an `approve` method on `PendingReviewPost` to return a `Post`, as -shown in Listing 17-20. +Back in Listing 17-13, we used the `trpl::join!` macro to await three +futures. However, it’s common to have a collection such as a vector containing +some number futures that won’t be known until runtime. Let’s change Listing +17-13 to the code in Listing 17-23 that puts the three futures into a vector +and calls the `trpl::join_all` function instead, which won’t compile yet. -Filename: src/lib.rs +src/main.rs ``` -impl DraftPost { - --snip-- - pub fn request_review(self) -> PendingReviewPost { - PendingReviewPost { - content: self.content, - } - } -} + let tx_fut = async move { + // --snip-- + }; -pub struct PendingReviewPost { - content: String, -} + let futures: Vec<Box<dyn Future<Output = ()>>> = + vec![Box::new(tx1_fut), Box::new(rx_fut), Box::new(tx_fut)]; -impl PendingReviewPost { - pub fn approve(self) -> Post { - Post { - content: self.content, - } - } + trpl::join_all(futures).await; +``` + +Listing 17-23: Awaiting futures in a collection + +We put each future within a `Box` to make them into *trait objects*, just as +we did in the “Returning Errors from `run`” section in Chapter 12. (We’ll cover +trait objects in detail in Chapter 18.) Using trait objects lets us treat each +of the anonymous futures produced by these types as the same type, because all +of them implement the `Future` trait. + +This might be surprising. After all, none of the async blocks returns anything, +so each one produces a `Future<Output = ()>`. Remember that `Future` is a +trait, though, and that the compiler creates a unique enum for each async +block, even when they have identical output types. Just as you can’t put two +different handwritten structs in a `Vec`, you can’t mix compiler-generated +enums. + +Then we pass the collection of futures to the `trpl::join_all` function and +await the result. However, this doesn’t compile; here’s the relevant part of +the error messages. + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-23 +cargo build +copy *only* the final `error` block from the errors +--> + +``` +error[E0277]: `dyn Future<Output = ()>` cannot be unpinned + --> src/main.rs:48:33 + | +48 | trpl::join_all(futures).await; + | ^^^^^ the trait `Unpin` is not implemented for `dyn Future<Output = ()>` + | + = note: consider using the `pin!` macro + consider using `Box::pin` if you need to access the pinned value outside of the current scope + = note: required for `Box<dyn Future<Output = ()>>` to implement `Future` +note: required by a bound in `futures_util::future::join_all::JoinAll` + --> file:///home/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/futures-util-0.3.30/src/future/join_all.rs:29:8 + | +27 | pub struct JoinAll<F> + | ------- required by a bound in this struct +28 | where +29 | F: Future, + | ^^^^^^ required by this bound in `JoinAll` +``` + +The note in this error message tells us that we should use the `pin!` macro to +*pin* the values, which means putting them inside the `Pin` type that +guarantees the values won’t be moved in memory. The error message says pinning +is required because `dyn Future<Output = ()>` needs to implement the `Unpin` +trait and it currently does not. + +The `trpl::join_all` function returns a struct called `JoinAll`. That struct is +generic over a type `F`, which is constrained to implement the `Future` trait. +Directly awaiting a future with `await` pins the future implicitly. That’s why +we don’t need to use `pin!` everywhere we want to await futures. + +However, we’re not directly awaiting a future here. Instead, we construct a new +future, JoinAll, by passing a collection of futures to the `join_all` function. +The signature for `join_all` requires that the types of the items in the +collection all implement the `Future` trait, and `Box<T>` implements `Future` +only if the `T` it wraps is a future that implements the `Unpin` trait. + +That’s a lot to absorb! To really understand it, let’s dive a little further +into how the `Future` trait actually works, in particular around pinning. Look +again at the definition of the `Future` trait: + +``` +use std::pin::Pin; +use std::task::{Context, Poll}; + +pub trait Future { + type Output; + + // Required method + fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>; } ``` -Listing 17-20: A `PendingReviewPost` that gets created by calling -`request_review` on `DraftPost` and an `approve` method that turns a -`PendingReviewPost` into a published `Post` +The `cx` parameter and its `Context` type are the key to how a runtime actually +knows when to check any given future while still being lazy. Again, the details +of how that works are beyond the scope of this chapter, and you generally only +need to think about this when writing a custom `Future` implementation. We’ll +focus instead on the type for `self`, as this is the first time we’ve seen a +method where `self` has a type annotation. A type annotation for `self` works +like type annotations for other function parameters but with two key +differences: + +* It tells Rust what type `self` must be for the method to be called. +* It can’t be just any type. It’s restricted to the type on which the method is + implemented, a reference or smart pointer to that type, or a `Pin` wrapping a + reference to that type. + +We’ll see more on this syntax in Chapter 18. For now, +it’s enough to know that if we want to poll a future to check whether it is +`Pending` or `Ready(Output)`, we need a `Pin`-wrapped mutable reference to the +type. + +`Pin` is a wrapper for pointer-like types such as `&`, `&mut`, `Box`, and `Rc`. +(Technically, `Pin` works with types that implement the `Deref` or `DerefMut` +traits, but this is effectively equivalent to working only with references and +smart pointers.) `Pin` is not a pointer itself and doesn’t have any behavior of +its own like `Rc` and `Arc` do with reference counting; it’s purely a tool the +compiler can use to enforce constraints on pointer usage. + +Recalling that `await` is implemented in terms of calls to `poll` starts to +explain the error message we saw earlier, but that was in terms of `Unpin`, not +`Pin`. So how exactly does `Pin` relate to `Unpin`, and why does `Future` need +`self` to be in a `Pin` type to call `poll`? + +Remember from earlier in this chapter that a series of await points in a future +get compiled into a state machine, and the compiler makes sure that state +machine follows all of Rust’s normal rules around safety, including borrowing +and ownership. To make that work, Rust looks at what data is needed between one +await point and either the next await point or the end of the async block. It +then creates a corresponding variant in the compiled state machine. Each +variant gets the access it needs to the data that will be used in that section +of the source code, whether by taking ownership of that data or by getting a +mutable or immutable reference to it. + +So far, so good: if we get anything wrong about the ownership or references in +a given async block, the borrow checker will tell us. When we want to move +around the future that corresponds to that block—like moving it into a `Vec` to +pass to `join_all`—things get trickier. + +When we move a future—whether by pushing it into a data structure to use as an +iterator with `join_all` or by returning it from a function—that actually means +moving the state machine Rust creates for us. And unlike most other types in +Rust, the futures Rust creates for async blocks can end up with references to +themselves in the fields of any given variant, as shown in the simplified illustration in Figure 17-4. + +<img alt="A single-column, three-row table representing a future, fut1, which has data values 0 and 1 in the first two rows and an arrow pointing from the third row back to the second row, representing an internal reference within the future." src="img/trpl17-04.svg" class="center" /> + +Figure 17-4: A self-referential data type + +By default, though, any object that has a reference to itself is unsafe to move, +because references always point to the actual memory address of whatever they +refer to (see Figure 17-5). If you move the data structure itself, those +internal references will be left pointing to the old location. However, that +memory location is now invalid. For one thing, its value will not be updated +when you make changes to the data structure. For another—more important—thing, +the computer is now free to reuse that memory for other purposes! You could end +up reading completely unrelated data later. + +<img alt="Two tables, depicting two futures, fut1 and fut2, each of which has one column and three rows, representing the result of having moved a future out of fut1 into fut2. The first, fut1, is grayed out, with a question mark in each index, representing unknown memory. The second, fut2, has 0 and 1 in the first and second rows and an arrow pointing from its third row back to the second row of fut1, representing a pointer that is referencing the old location in memory of the future before it was moved." src="img/trpl17-05.svg" class="center" /> + +Figure 17-5: The unsafe result of moving a self-referential data type + +Theoretically, the Rust compiler could try to update every reference to an +object whenever it gets moved, but that could add a lot of performance overhead, +especially if a whole web of references needs updating. If we could instead make +sure the data structure in question *doesn’t move in memory*, we wouldn’t have +to update any references. This is exactly what Rust’s borrow checker is for: +in safe code, it prevents you from moving any item with an active reference to +it. + +`Pin` builds on that to give us the exact guarantee we need. When we *pin* a +value by wrapping a pointer to that value in `Pin`, it can no longer move. Thus, +if you have `Pin<Box<SomeType>>`, you actually pin the `SomeType` value, *not* +the `Box` pointer. Figure 17-6 illustrates this process. + +<img alt="Three boxes laid out side by side. The first is labeled “Pin”, the second “b1”, and the third “pinned”. Within “pinned” is a table labeled “fut”, with a single column; it represents a future with cells for each part of the data structure. Its first cell has the value “0”, its second cell has an arrow coming out of it and pointing to the fourth and final cell, which has the value “1” in it, and the third cell has dashed lines and an ellipsis to indicate there may be other parts to the data structure. All together, the “fut” table represents a future which is self-referential. An arrow leaves the box labeled “Pin”, goes through the box labeled “b1” and terminates inside the “pinned” box at the “fut” table." src="img/trpl17-06.svg" class="center" /> + +Figure 17-6: Pinning a `Box` that points to a self-referential future type + +In fact, the `Box` pointer can still move around freely. Remember: we care about +making sure the data ultimately being referenced stays in place. If a pointer +moves around, *but the data it points to* is in the same place, as in Figure +17-7, there’s no potential problem. (As an independent exercise, look at the docs +for the types as well as the `std::pin` module and try to work out how you’d do +this with a `Pin` wrapping a `Box`.) The key is that the self-referential type +itself cannot move, because it is still pinned. + +<img alt="Four boxes laid out in three rough columns, identical to the previous diagram with a change to the second column. Now there are two boxes in the second column, labeled “b1” and “b2”, “b1” is grayed out, and the arrow from “Pin” goes through “b2” instead of “b1”, indicating that the pointer has moved from “b1” to “b2”, but the data in “pinned” has not moved." src="img/trpl17-07.svg" class="center" /> + +Figure 17-7: Moving a `Box` which points to a self-referential future type + +However, most types are perfectly safe to move around, even if they happen to be +behind a `Pin` pointer. We only need to think about pinning when items have +internal references. Primitive values such as numbers and Booleans are safe +because they obviously don’t have any internal references. +Neither do most types you normally work with in Rust. You can move around +a `Vec`, for example, without worrying. Given what we have seen so far, if +you have a `Pin<Vec<String>>`, you’d have to do everything via the safe but +restrictive APIs provided by `Pin`, even though a `Vec<String>` is always safe +to move if there are no other references to it. We need a way to tell the +compiler that it’s fine to move items around in cases like this—and that’s +where `Unpin` comes into play. + +`Unpin` is a marker trait, similar to the `Send` and `Sync` traits we saw in +Chapter 16, and thus has no functionality of its own. Marker traits exist only +to tell the compiler it’s safe to use the type implementing a given trait in a +particular context. `Unpin` informs the compiler that a given type does *not* +need to uphold any guarantees about whether the value in question can be safely +moved. + +<!-- + The inline `<code>` in the next block is to allow the inline `<em>` inside it, + matching what NoStarch does style-wise, and emphasizing within the text here + that it is something distinct from a normal type. +--> + +Just as with `Send` and `Sync`, the compiler implements `Unpin` automatically +for all types where it can prove it is safe. A special case, again similar to +`Send` and `Sync`, is where `Unpin` is *not* implemented for a type. The +notation for this is <code>impl !Unpin for <em>SomeType</em></code>, where +<code><em>SomeType</em></code> is the name of a type that *does* need to uphold +those guarantees to be safe whenever a pointer to that type is used in a `Pin`. + +In other words, there are two things to keep in mind about the relationship +between `Pin` and `Unpin`. First, `Unpin` is the “normal” case, and `!Unpin` is +the special case. Second, whether a type implements `Unpin` or `!Unpin` *only* +matters when you’re using a pinned pointer to that type like <code>Pin\<&mut +<em>SomeType</em>\></code>. + +To make that concrete, think about a `String`: it has a length and the Unicode +characters that make it up. We can wrap a `String` in `Pin`, as seen in Figure +17-8. However, `String` automatically implements `Unpin`, as do most other types +in Rust. + +<img alt="A box labeled “Pin” on the left with an arrow going from it to a box labeled “String” on the right. The “String” box contains the data 5usize, representing the length of the string, and the letters “h”, “e”, “l”, “l”, and “o” representing the characters of the string “hello” stored in this String instance. A dotted rectangle surrounds the “String” box and its label, but not the “Pin” box." src="img/trpl17-08.svg" class="center" /> + +Figure 17-8: Pinning a `String`; the dotted line indicates that the `String` implements the `Unpin` trait and thus is not pinned + +As a result, we can do things that would be illegal if `String` implemented +`!Unpin` instead, such as replacing one string with another at the exact same +location in memory as in Figure 17-9. This doesn’t violate the `Pin` contract, +because `String` has no internal references that make it unsafe to move around. +That is precisely why it implements `Unpin` rather than `!Unpin`. -The `request_review` and `approve` methods take ownership of `self`, thus -consuming the `DraftPost` and `PendingReviewPost` instances and transforming -them into a `PendingReviewPost` and a published `Post`, respectively. This way, -we won’t have any lingering `DraftPost` instances after we’ve called -`request_review` on them, and so forth. The `PendingReviewPost` struct doesn’t -have a `content` method defined on it, so attempting to read its content -results in a compiler error, as with `DraftPost`. Because the only way to get a -published `Post` instance that does have a `content` method defined is to call -the `approve` method on a `PendingReviewPost`, and the only way to get a -`PendingReviewPost` is to call the `request_review` method on a `DraftPost`, -we’ve now encoded the blog post workflow into the type system. +<img alt="The same “hello” string data from the previous example, now labeled “s1” and grayed out. The “Pin” box from the previous example now points to a different String instance, one that is labeled “s2”, is valid, has a length of 7usize, and contains the characters of the string “goodbye”. s2 is surrounded by a dotted rectangle because it, too, implements the Unpin trait." src="img/trpl17-09.svg" class="center" /> -But we also have to make some small changes to `main`. The `request_review` and -`approve` methods return new instances rather than modifying the struct they’re -called on, so we need to add more `let post =` shadowing assignments to save -the returned instances. We also can’t have the assertions about the draft and -pending review posts’ contents be empty strings, nor do we need them: we can’t -compile code that tries to use the content of posts in those states any longer. -The updated code in `main` is shown in Listing 17-21. +Figure 17-9: Replacing the `String` with an entirely different `String` in memory + +Now we know enough to understand the errors reported for that `join_all` call +from back in Listing 17-23. We originally tried to move the futures produced by +async blocks into a `Vec<Box<dyn Future<Output = ()>>>`, but as we’ve seen, +those futures may have internal references, so they don’t automatically +implement `Unpin`. Once we pin them, we can pass the resulting `Pin` type into +the `Vec`, confident that the underlying data in the futures will *not* be +moved. Listing 17-24 shows how to fix the code by calling the `pin!` macro +where each of the three futures are defined and adjusting the trait object type. -Filename: src/main.rs ``` -use blog::Post; +use std::pin::{Pin, pin}; -fn main() { - let mut post = Post::new(); +// --snip-- + + let tx1_fut = pin!(async move { + // --snip-- + }); - post.add_text("I ate a salad for lunch today"); + let rx_fut = pin!(async { + // --snip-- + }); - let post = post.request_review(); + let tx_fut = pin!(async move { + // --snip-- + }); + + let futures: Vec<Pin<&mut dyn Future<Output = ()>>> = + vec![tx1_fut, rx_fut, tx_fut]; +``` - let post = post.approve(); +Listing 17-24: Pinning the futures to enable moving them into the vector + +This example now compiles and runs, and we could add or remove futures from the +vector at runtime and join them all. + +`Pin` and `Unpin` are mostly important for building lower-level libraries, or +when you’re building a runtime itself, rather than for day-to-day Rust code. +When you see these traits in error messages, though, now you’ll have a better +idea of how to fix your code! + +> Note: This combination of `Pin` and `Unpin` makes it possible to safely +> implement a whole class of complex types in Rust that would otherwise prove +> challenging because they’re self-referential. Types that require `Pin` show up +> most commonly in async Rust today, but every once in a while, you might see +> them in other contexts, too. +> +> The specifics of how `Pin` and `Unpin` work, and the rules they’re required +> to uphold, are covered extensively in the API documentation for `std::pin`, so +> if you’re interested in learning more, that’s a great place to start. +> +> If you want to understand how things work under the hood in even more detail, +> see Chapters 2 and +> 4 of +> *Asynchronous Programming in Rust* at *https://rust-lang.github.io/async-book/*. + +### The Stream Trait + +Now that you have a deeper grasp on the `Future`, `Pin`, and `Unpin` traits, we +can turn our attention to the `Stream` trait. As you learned earlier in the +chapter, streams are similar to asynchronous iterators. Unlike `Iterator` and +`Future`, however, `Stream` has no definition in the standard library as of +this writing, but there *is* a very common definition from the `futures` crate +used throughout the ecosystem. + +Let’s review the definitions of the `Iterator` and `Future` traits before +looking at how a `Stream` trait might merge them together. From `Iterator`, we +have the idea of a sequence: its `next` method provides an +`Option<Self::Item>`. From `Future`, we have the idea of readiness over time: +its `poll` method provides a `Poll<Self::Output>`. To represent a sequence of +items that become ready over time, we define a `Stream` trait that puts those +features together: - assert_eq!("I ate a salad for lunch today", post.content()); +``` +use std::pin::Pin; +use std::task::{Context, Poll}; + +trait Stream { + type Item; + + fn poll_next( + self: Pin<&mut Self>, + cx: &mut Context<'_> + ) -> Poll<Option<Self::Item>>; } ``` -Listing 17-21: Modifications to `main` to use the new implementation of the -blog post workflow +The `Stream` trait defines an associated type called `Item` for the type of the +items produced by the stream. This is similar to `Iterator`, where there may be +zero to many items, and unlike `Future`, where there is always a single +`Output`, even if it’s the unit type `()`. + +`Stream` also defines a method to get those items. We call it `poll_next`, to +make it clear that it polls in the same way `Future::poll` does and produces a +sequence of items in the same way `Iterator::next` does. Its return type +combines `Poll` with `Option`. The outer type is `Poll`, because it has to be +checked for readiness, just as a future does. The inner type is `Option`, +because it needs to signal whether there are more messages, just as an iterator +does. + +Something very similar to this definition will likely end up as part of Rust’s +standard library. In the meantime, it’s part of the toolkit of most runtimes, +so you can rely on it, and everything we cover next should generally apply! + +In the examples we saw in the “Streams: Futures in Sequence” section, though, we didn’t use `poll_next` *or* `Stream`, but +instead used `next` and `StreamExt`. We *could* work directly in terms of the +`poll_next` API by hand-writing our own `Stream` state machines, of course, +just as we *could* work with futures directly via their `poll` method. Using +`await` is much nicer, though, and the `StreamExt` trait supplies the `next` +method so we can do just that: + +``` +trait StreamExt: Stream { + async fn next(&mut self) -> Option<Self::Item> + where + Self: Unpin; + + // other methods... +} +``` + +<!-- +TODO: update this if/when tokio/etc. update their MSRV and switch to using async functions +in traits, since the lack thereof is the reason they do not yet have this. +--> + +> Note: The actual definition we used earlier in the chapter looks slightly +> different than this, because it supports versions of Rust that did not yet +> support using async functions in traits. As a result, it looks like this: +> +> ````rust,ignore +> fn next(&mut self) -> Next<'_, Self> where Self: Unpin; +> ```` +> +> That `Next` type is a `struct` that implements `Future` and allows us to name +> the lifetime of the reference to `self` with `Next<'_, Self>`, so that `await` +> can work with this method. + +The `StreamExt` trait is also the home of all the interesting methods available +to use with streams. `StreamExt` is automatically implemented for every type +that implements `Stream`, but these traits are defined separately to enable the +community to iterate on convenience APIs without affecting the foundational +trait. + +In the version of `StreamExt` used in the `trpl` crate, the trait not only +defines the `next` method but also supplies a default implementation of `next` +that correctly handles the details of calling `Stream::poll_next`. This means +that even when you need to write your own streaming data type, you *only* have +to implement `Stream`, and then anyone who uses your data type can use +`StreamExt` and its methods with it automatically. + +That’s all we’re going to cover for the lower-level details on these traits. To +wrap up, let’s consider how futures (including streams), tasks, and threads all +fit together! + +## Putting It All Together: Futures, Tasks, and Threads + +As we saw in Chapter 16, threads provide one approach to +concurrency. We’ve seen another approach in this chapter: using async with +futures and streams. If you’re wondering when to choose one method over the other, +the answer is: it depends! And in many cases, the choice isn’t threads *or* +async but rather threads *and* async. + +Many operating systems have supplied threading-based concurrency models for +decades now, and many programming languages support them as a result. However, +these models are not without their tradeoffs. On many operating systems, they +use a fair bit of memory for each thread. Threads are also only an option when +your operating system and hardware support them. Unlike mainstream desktop and +mobile computers, some embedded systems don’t have an OS at all, so they also +don’t have threads. + +The async model provides a different—and ultimately complementary—set of +tradeoffs. In the async model, concurrent operations don’t require their own +threads. Instead, they can run on tasks, as when we used `trpl::spawn_task` to +kick off work from a synchronous function in the streams section. A task is +similar to a thread, but instead of being managed by the operating system, it’s +managed by library-level code: the runtime. + +There’s a reason the APIs for spawning threads and spawning tasks are so +similar. Threads act as a boundary for sets of synchronous operations; +concurrency is possible *between* threads. Tasks act as a boundary for sets of +*asynchronous* operations; concurrency is possible both *between* and *within* +tasks, because a task can switch between futures in its body. Finally, futures +are Rust’s most granular unit of concurrency, and each future may represent a +tree of other futures. The runtime—specifically, its executor—manages tasks, +and tasks manage futures. In that regard, tasks are similar to lightweight, +runtime-managed threads with added capabilities that come from being managed by +a runtime instead of by the operating system. + +This doesn’t mean that async tasks are always better than threads (or vice +versa). Concurrency with threads is in some ways a simpler programming model +than concurrency with `async`. That can be a strength or a weakness. Threads are +somewhat “fire and forget”; they have no native equivalent to a future, so they +simply run to completion without being interrupted except by the operating +system itself. + +And it turns out that threads and tasks often work +very well together, because tasks can (at least in some runtimes) be moved +around between threads. In fact, under the hood, the runtime we’ve been +using—including the `spawn_blocking` and `spawn_task` functions—is multithreaded +by default! Many runtimes use an approach called *work stealing* to +transparently move tasks around between threads, based on how the threads are +currently being utilized, to improve the system’s overall performance. That +approach actually requires threads *and* tasks, and therefore futures. + +When thinking about which method to use when, consider these rules of thumb: + +* If the work is *very parallelizable* (that is, CPU-bound), such as processing + a bunch of data where each part can be processed separately, threads are a + better choice. +* If the work is *very concurrent* (that is, I/O-bound), such as handling + messages from a bunch of different sources that may come in at different + intervals or different rates, async is a better choice. + +And if you need both parallelism and concurrency, you don’t have to choose +between threads and async. You can use them together freely, letting each +play the part it’s best at. For example, Listing 17-25 shows a fairly common +example of this kind of mix in real-world Rust code. + +src/main.rs + +``` +use std::{thread, time::Duration}; + +fn main() { + let (tx, mut rx) = trpl::channel(); + + thread::spawn(move || { + for i in 1..11 { + tx.send(i).unwrap(); + thread::sleep(Duration::from_secs(1)); + } + }); + + trpl::block_on(async { + while let Some(message) = rx.recv().await { + println!("{message}"); + } + }); +} +``` -The changes we needed to make to `main` to reassign `post` mean that this -implementation doesn’t quite follow the object-oriented state pattern anymore: -the transformations between the states are no longer encapsulated entirely -within the `Post` implementation. However, our gain is that invalid states are -now impossible because of the type system and the type checking that happens at -compile time! This ensures that certain bugs, such as display of the content of -an unpublished post, will be discovered before they make it to production. +Listing 17-25: Sending messages with blocking code in a thread and awaiting the messages in an async block -Try the tasks suggested at the start of this section on the `blog` crate as it -is after Listing 17-21 to see what you think about the design of this version -of the code. Note that some of the tasks might be completed already in this -design. +We begin by creating an async channel, then spawning a thread that takes +ownership of the sender side of the channel using the `move` keyword. Within +the thread, we send the numbers 1 through 10, sleeping for a second between +each. Finally, we run a future created with an async block passed to +`trpl::block_on` just as we have throughout the chapter. In that future, we +await those messages, just as in the other message-passing examples we have +seen. -We’ve seen that even though Rust is capable of implementing object-oriented -design patterns, other patterns, such as encoding state into the type system, -are also available in Rust. These patterns have different trade-offs. Although -you might be very familiar with object-oriented patterns, rethinking the -problem to take advantage of Rust’s features can provide benefits, such as -preventing some bugs at compile time. Object-oriented patterns won’t always be -the best solution in Rust due to certain features, like ownership, that -object-oriented languages don’t have. +To return to the scenario we opened the chapter with, imagine running a set of +video encoding tasks using a dedicated thread (because video encoding is +compute-bound) but notifying the UI that those operations are done with an +async channel. There are countless examples of these kinds of combinations in +real-world use cases. ## Summary -Regardless of whether you think Rust is an object-oriented language after -reading this chapter, you now know that you can use trait objects to get some -object-oriented features in Rust. Dynamic dispatch can give your code some -flexibility in exchange for a bit of runtime performance. You can use this -flexibility to implement object-oriented patterns that can help your code’s -maintainability. Rust also has other features, like ownership, that -object-oriented languages don’t have. An object-oriented pattern won’t always -be the best way to take advantage of Rust’s strengths, but it is an available -option. +This isn’t the last you’ll see of concurrency in this book. The project in +Chapter 21 will apply these concepts in a more realistic +situation than the simpler examples discussed here and compare problem-solving +with threading versus tasks and futures more directly. -Next, we’ll look at patterns, which are another of Rust’s features that enable -lots of flexibility. We’ve looked at them briefly throughout the book but -haven’t seen their full capability yet. Let’s go! +No matter which of these approaches you choose, Rust gives you the tools you +need to write safe, fast, concurrent code—whether for a high-throughput web +server or an embedded operating system. +Next, we’ll talk about idiomatic ways to model problems and structure solutions +as your Rust programs get bigger. In addition, we’ll discuss how Rust’s idioms +relate to those you might be familiar with from object-oriented programming. diff --git a/nostarch/chapter18.md b/nostarch/chapter18.md index 40c7f10a1c..d2f56ea790 100644 --- a/nostarch/chapter18.md +++ b/nostarch/chapter18.md @@ -6,1287 +6,1271 @@ directory, so all fixes need to be made in `/src/`. [TOC] -# Patterns and Matching - -*Patterns* are a special syntax in Rust for matching against the structure of -types, both complex and simple. Using patterns in conjunction with `match` -expressions and other constructs gives you more control over a program’s -control flow. A pattern consists of some combination of the following: - -* Literals -* Destructured arrays, enums, structs, or tuples -* Variables -* Wildcards -* Placeholders - -Some example patterns include `x`, `(a, 3)`, and `Some(Color::Red)`. In the -contexts in which patterns are valid, these components describe the shape of -data. Our program then matches values against the patterns to determine whether -it has the correct shape of data to continue running a particular piece of code. +# Object-Oriented Programming Features + +<!-- Old headings. Do not remove or links may break. --> + +<a id="object-oriented-programming-features-of-rust"></a> + +Object-oriented programming (OOP) is a way of modeling programs. Objects as a +programmatic concept were introduced in the programming language Simula in the +1960s. Those objects influenced Alan Kay’s programming architecture in which +objects pass messages to each other. To describe this architecture, he coined +the term *object-oriented programming* in 1967. Many competing definitions +describe what OOP is, and by some of these definitions Rust is object oriented +but by others it is not. In this chapter, we’ll explore certain characteristics +that are commonly considered object oriented and how those characteristics +translate to idiomatic Rust. We’ll then show you how to implement an +object-oriented design pattern in Rust and discuss the trade-offs of doing so +versus implementing a solution using some of Rust’s strengths instead. + +## Characteristics of Object-Oriented Languages + +There is no consensus in the programming community about what features a +language must have to be considered object oriented. Rust is influenced by many +programming paradigms, including OOP; for example, we explored the features +that came from functional programming in Chapter 13. Arguably, OOP languages +share certain common characteristics—namely, objects, encapsulation, and +inheritance. Let’s look at what each of those characteristics means and whether +Rust supports it. + +### Objects Contain Data and Behavior + +The book *Design Patterns: Elements of Reusable Object-Oriented Software* by +Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (Addison-Wesley, +1994), colloquially referred to as *The Gang of Four* book, is a catalog of +object-oriented design patterns. It defines OOP in this way: + +> Object-oriented programs are made up of objects. An **object** packages both +> data and the procedures that operate on that data. The procedures are +> typically called **methods** or **operations**. + +Using this definition, Rust is object oriented: Structs and enums have data, +and `impl` blocks provide methods on structs and enums. Even though structs and +enums with methods aren’t *called* objects, they provide the same +functionality, according to the Gang of Four’s definition of objects. + +### Encapsulation That Hides Implementation Details + +Another aspect commonly associated with OOP is the idea of *encapsulation*, +which means that the implementation details of an object aren’t accessible to +code using that object. Therefore, the only way to interact with an object is +through its public API; code using the object shouldn’t be able to reach into +the object’s internals and change data or behavior directly. This enables the +programmer to change and refactor an object’s internals without needing to +change the code that uses the object. + +We discussed how to control encapsulation in Chapter 7: We can use the `pub` +keyword to decide which modules, types, functions, and methods in our code +should be public, and by default everything else is private. For example, we +can define a struct `AveragedCollection` that has a field containing a vector +of `i32` values. The struct can also have a field that contains the average of +the values in the vector, meaning the average doesn’t have to be computed on +demand whenever anyone needs it. In other words, `AveragedCollection` will +cache the calculated average for us. Listing 18-1 has the definition of the +`AveragedCollection` struct. + +src/lib.rs + +``` +pub struct AveragedCollection { + list: Vec<i32>, + average: f64, +} +``` -To use a pattern, we compare it to some value. If the pattern matches the -value, we use the value parts in our code. Recall the `match` expressions in -Chapter 6 that used patterns, such as the coin-sorting machine example. If the -value fits the shape of the pattern, we can use the named pieces. If it -doesn’t, the code associated with the pattern won’t run. +Listing 18-1: An `AveragedCollection` struct that maintains a list of integers and the average of the items in the collection -This chapter is a reference on all things related to patterns. We’ll cover the -valid places to use patterns, the difference between refutable and irrefutable -patterns, and the different kinds of pattern syntax that you might see. By the -end of the chapter, you’ll know how to use patterns to express many concepts in -a clear way. +The struct is marked `pub` so that other code can use it, but the fields within +the struct remain private. This is important in this case because we want to +ensure that whenever a value is added or removed from the list, the average is +also updated. We do this by implementing `add`, `remove`, and `average` methods +on the struct, as shown in Listing 18-2. -## All the Places Patterns Can Be Used +src/lib.rs -Patterns pop up in a number of places in Rust, and you’ve been using them a lot -without realizing it! This section discusses all the places where patterns are -valid. +``` +impl AveragedCollection { + pub fn add(&mut self, value: i32) { + self.list.push(value); + self.update_average(); + } -### match Arms + pub fn remove(&mut self) -> Option<i32> { + let result = self.list.pop(); + match result { + Some(value) => { + self.update_average(); + Some(value) + } + None => None, + } + } -As discussed in Chapter 6, we use patterns in the arms of `match` expressions. -Formally, `match` expressions are defined as the keyword `match`, a value to -match on, and one or more match arms that consist of a pattern and an -expression to run if the value matches that arm’s pattern, like this: + pub fn average(&self) -> f64 { + self.average + } -``` -match VALUE { - PATTERN => EXPRESSION, - PATTERN => EXPRESSION, - PATTERN => EXPRESSION, + fn update_average(&mut self) { + let total: i32 = self.list.iter().sum(); + self.average = total as f64 / self.list.len() as f64; + } } ``` -For example, here’s the `match` expression from Listing 6-5 that matches on an -`Option<i32>` value in the variable `x`: - -``` -match x { - None => None, - Some(i) => Some(i + 1), +Listing 18-2: Implementations of the public methods `add`, `remove`, and `average` on `AveragedCollection` + +The public methods `add`, `remove`, and `average` are the only ways to access +or modify data in an instance of `AveragedCollection`. When an item is added to +`list` using the `add` method or removed using the `remove` method, the +implementations of each call the private `update_average` method that handles +updating the `average` field as well. + +We leave the `list` and `average` fields private so that there is no way for +external code to add or remove items to or from the `list` field directly; +otherwise, the `average` field might become out of sync when the `list` +changes. The `average` method returns the value in the `average` field, +allowing external code to read the `average` but not modify it. + +Because we’ve encapsulated the implementation details of the struct +`AveragedCollection`, we can easily change aspects, such as the data structure, +in the future. For instance, we could use a `HashSet<i32>` instead of a +`Vec<i32>` for the `list` field. As long as the signatures of the `add`, +`remove`, and `average` public methods stayed the same, code using +`AveragedCollection` wouldn’t need to change. If we made `list` public instead, +this wouldn’t necessarily be the case: `HashSet<i32>` and `Vec<i32>` have +different methods for adding and removing items, so the external code would +likely have to change if it were modifying `list` directly. + +If encapsulation is a required aspect for a language to be considered object +oriented, then Rust meets that requirement. The option to use `pub` or not for +different parts of code enables encapsulation of implementation details. + +### Inheritance as a Type System and as Code Sharing + +*Inheritance* is a mechanism whereby an object can inherit elements from +another object’s definition, thus gaining the parent object’s data and behavior +without you having to define them again. + +If a language must have inheritance to be object oriented, then Rust is not +such a language. There is no way to define a struct that inherits the parent +struct’s fields and method implementations without using a macro. + +However, if you’re used to having inheritance in your programming toolbox, you +can use other solutions in Rust, depending on your reason for reaching for +inheritance in the first place. + +You would choose inheritance for two main reasons. One is for reuse of code: +You can implement particular behavior for one type, and inheritance enables you +to reuse that implementation for a different type. You can do this in a limited +way in Rust code using default trait method implementations, which you saw in +Listing 10-14 when we added a default implementation of the `summarize` method +on the `Summary` trait. Any type implementing the `Summary` trait would have +the `summarize` method available on it without any further code. This is +similar to a parent class having an implementation of a method and an +inheriting child class also having the implementation of the method. We can +also override the default implementation of the `summarize` method when we +implement the `Summary` trait, which is similar to a child class overriding the +implementation of a method inherited from a parent class. + +The other reason to use inheritance relates to the type system: to enable a +child type to be used in the same places as the parent type. This is also +called *polymorphism*, which means that you can substitute multiple objects for +each other at runtime if they share certain characteristics. + +> ### Polymorphism +> +> To many people, polymorphism is synonymous with inheritance. But it’s +> actually a more general concept that refers to code that can work with data of +> multiple types. For inheritance, those types are generally subclasses. +> +> Rust instead uses generics to abstract over different possible types and +> trait bounds to impose constraints on what those types must provide. This is +> sometimes called *bounded parametric polymorphism*. + +Rust has chosen a different set of trade-offs by not offering inheritance. +Inheritance is often at risk of sharing more code than necessary. Subclasses +shouldn’t always share all characteristics of their parent class but will do so +with inheritance. This can make a program’s design less flexible. It also +introduces the possibility of calling methods on subclasses that don’t make +sense or that cause errors because the methods don’t apply to the subclass. In +addition, some languages will only allow *single inheritance* (meaning a +subclass can only inherit from one class), further restricting the flexibility +of a program’s design. + +For these reasons, Rust takes the different approach of using trait objects +instead of inheritance to achieve polymorphism at runtime. Let’s look at how +trait objects work. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="using-trait-objects-that-allow-for-values-of-different-types"></a> + +## Using Trait Objects to Abstract over Shared Behavior + +In Chapter 8, we mentioned that one limitation of vectors is that they can +store elements of only one type. We created a workaround in Listing 8-9 where +we defined a `SpreadsheetCell` enum that had variants to hold integers, floats, +and text. This meant we could store different types of data in each cell and +still have a vector that represented a row of cells. This is a perfectly good +solution when our interchangeable items are a fixed set of types that we know +when our code is compiled. + +However, sometimes we want our library user to be able to extend the set of +types that are valid in a particular situation. To show how we might achieve +this, we’ll create an example graphical user interface (GUI) tool that iterates +through a list of items, calling a `draw` method on each one to draw it to the +screen—a common technique for GUI tools. We’ll create a library crate called +`gui` that contains the structure of a GUI library. This crate might include +some types for people to use, such as `Button` or `TextField`. In addition, +`gui` users will want to create their own types that can be drawn: For +instance, one programmer might add an `Image`, and another might add a +`SelectBox`. + +At the time of writing the library, we can’t know and define all the types +other programmers might want to create. But we do know that `gui` needs to keep +track of many values of different types, and it needs to call a `draw` method +on each of these differently typed values. It doesn’t need to know exactly what +will happen when we call the `draw` method, just that the value will have that +method available for us to call. + +To do this in a language with inheritance, we might define a class named +`Component` that has a method named `draw` on it. The other classes, such as +`Button`, `Image`, and `SelectBox`, would inherit from `Component` and thus +inherit the `draw` method. They could each override the `draw` method to define +their custom behavior, but the framework could treat all of the types as if +they were `Component` instances and call `draw` on them. But because Rust +doesn’t have inheritance, we need another way to structure the `gui` library to +allow users to create new types compatible with the library. + +### Defining a Trait for Common Behavior + +To implement the behavior that we want `gui` to have, we’ll define a trait +named `Draw` that will have one method named `draw`. Then, we can define a +vector that takes a trait object. A *trait object* points to both an instance +of a type implementing our specified trait and a table used to look up trait +methods on that type at runtime. We create a trait object by specifying some +sort of pointer, such as a reference or a `Box<T>` smart pointer, then the +`dyn` keyword, and then specifying the relevant trait. (We’ll talk about the +reason trait objects must use a pointer in “Dynamically Sized Types and the +`Sized` Trait” in Chapter 20.) We can use +trait objects in place of a generic or concrete type. Wherever we use a trait +object, Rust’s type system will ensure at compile time that any value used in +that context will implement the trait object’s trait. Consequently, we don’t +need to know all the possible types at compile time. + +We’ve mentioned that, in Rust, we refrain from calling structs and enums +“objects” to distinguish them from other languages’ objects. In a struct or +enum, the data in the struct fields and the behavior in `impl` blocks are +separated, whereas in other languages, the data and behavior combined into one +concept is often labeled an object. Trait objects differ from objects in other +languages in that we can’t add data to a trait object. Trait objects aren’t as +generally useful as objects in other languages: Their specific purpose is to +allow abstraction across common behavior. + +Listing 18-3 shows how to define a trait named `Draw` with one method named +`draw`. + +src/lib.rs + +``` +pub trait Draw { + fn draw(&self); } ``` -The patterns in this `match` expression are the `None` and `Some(i)` to the -left of each arrow. +Listing 18-3: Definition of the `Draw` trait -One requirement for `match` expressions is that they need to be *exhaustive* in -the sense that all possibilities for the value in the `match` expression must -be accounted for. One way to ensure you’ve covered every possibility is to have -a catchall pattern for the last arm: for example, a variable name matching any -value can never fail and thus covers every remaining case. +This syntax should look familiar from our discussions on how to define traits +in Chapter 10. Next comes some new syntax: Listing 18-4 defines a struct named +`Screen` that holds a vector named `components`. This vector is of type +`Box<dyn Draw>`, which is a trait object; it’s a stand-in for any type inside a +`Box` that implements the `Draw` trait. -The particular pattern `_` will match anything, but it never binds to a -variable, so it’s often used in the last match arm. The `_` pattern can be -useful when you want to ignore any value not specified, for example. We’ll -cover the `_` pattern in more detail in “Ignoring Values in a Pattern” on page -XX. - -### Conditional if let Expressions - -In Chapter 6, we discussed how to use `if let` expressions mainly as a shorter -way to write the equivalent of a `match` that only matches one case. -Optionally, `if let` can have a corresponding `else` containing code to run if -the pattern in the `if let` doesn’t match. - -Listing 18-1 shows that it’s also possible to mix and match `if let`, `else -if`, and `else if let` expressions. Doing so gives us more flexibility than a -`match` expression in which we can express only one value to compare with the -patterns. Also, Rust doesn’t require that the conditions in a series of `if -let`, `else if`, and `else if let` arms relate to each other. - -The code in Listing 18-1 determines what color to make your background based on -a series of checks for several conditions. For this example, we’ve created -variables with hardcoded values that a real program might receive from user -input. - -Filename: src/main.rs +src/lib.rs ``` -fn main() { - let favorite_color: Option<&str> = None; - let is_tuesday = false; - let age: Result<u8, _> = "34".parse(); - - 1 if let Some(color) = favorite_color { - 2 println!( - "Using your favorite, {color}, as the background" - ); - 3 } else if is_tuesday { - 4 println!("Tuesday is green day!"); - 5 } else if let Ok(age) = age { - 6 if age > 30 { - 7 println!("Using purple as the background color"); - } else { - 8 println!("Using orange as the background color"); - } - 9 } else { - 10 println!("Using blue as the background color"); - } +pub struct Screen { + pub components: Vec<Box<dyn Draw>>, } ``` -Listing 18-1: Mixing `if let`, `else if`, `else if let`, and `else` - -If the user specifies a favorite color [1], that color is used as the -background [2]. If no favorite color is specified and today is Tuesday [3], the -background color is green [4]. Otherwise, if the user specifies their age as a -string and we can parse it as a number successfully [5], the color is either -purple [7] or orange [8] depending on the value of the number [6]. If none of -these conditions apply [9], the background color is blue [10]. - -This conditional structure lets us support complex requirements. With the -hardcoded values we have here, this example will print `Using purple as the -background color`. - -You can see that `if let` can also introduce shadowed variables in the same way -that `match` arms can: the line `if let Ok(age) = age` [5] introduces a new -shadowed `age` variable that contains the value inside the `Ok` variant. This -means we need to place the `if age > 30` condition [6] within that block: we -can’t combine these two conditions into `if let Ok(age) = age && age > 30`. The -shadowed `age` we want to compare to 30 isn’t valid until the new scope starts -with the curly bracket. +Listing 18-4: Definition of the `Screen` struct with a `components` field holding a vector of trait objects that implement the `Draw` trait -The downside of using `if let` expressions is that the compiler doesn’t check -for exhaustiveness, whereas with `match` expressions it does. If we omitted the -last `else` block [9] and therefore missed handling some cases, the compiler -would not alert us to the possible logic bug. +On the `Screen` struct, we’ll define a method named `run` that will call the +`draw` method on each of its `components`, as shown in Listing 18-5. -### while let Conditional Loops - -Similar in construction to `if let`, the `while let` conditional loop allows a -`while` loop to run for as long as a pattern continues to match. In Listing -18-2, we code a `while let` loop that uses a vector as a stack and prints the -values in the vector in the opposite order in which they were pushed. - -Filename: src/main.rs +src/lib.rs ``` -let mut stack = Vec::new(); - -stack.push(1); -stack.push(2); -stack.push(3); - -while let Some(top) = stack.pop() { - println!("{top}"); +impl Screen { + pub fn run(&self) { + for component in self.components.iter() { + component.draw(); + } + } } ``` -Listing 18-2: Using a `while let` loop to print values for as long as -`stack.pop()` returns `Some` - -This example prints `3`, `2`, and then `1`. The `pop` method takes the last -element out of the vector and returns `Some(value)`. If the vector is empty, -`pop` returns `None`. The `while` loop continues running the code in its block -as long as `pop` returns `Some`. When `pop` returns `None`, the loop stops. We -can use `while let` to pop every element off our stack. +Listing 18-5: A `run` method on `Screen` that calls the `draw` method on each component -### for Loops +This works differently from defining a struct that uses a generic type +parameter with trait bounds. A generic type parameter can be substituted with +only one concrete type at a time, whereas trait objects allow for multiple +concrete types to fill in for the trait object at runtime. For example, we +could have defined the `Screen` struct using a generic type and a trait bound, +as in Listing 18-6. -In a `for` loop, the value that directly follows the keyword `for` is a -pattern. For example, in `for x in y`, the `x` is the pattern. Listing 18-3 -demonstrates how to use a pattern in a `for` loop to *destructure*, or break -apart, a tuple as part of the `for` loop. - -Filename: src/main.rs +src/lib.rs ``` -let v = vec!['a', 'b', 'c']; +pub struct Screen<T: Draw> { + pub components: Vec<T>, +} -for (index, value) in v.iter().enumerate() { - println!("{value} is at index {index}"); +impl<T> Screen<T> +where + T: Draw, +{ + pub fn run(&self) { + for component in self.components.iter() { + component.draw(); + } + } } ``` -Listing 18-3: Using a pattern in a `for` loop to destructure a tuple - -The code in Listing 18-3 will print the following: +Listing 18-6: An alternate implementation of the `Screen` struct and its `run` method using generics and trait bounds -``` -a is at index 0 -b is at index 1 -c is at index 2 -``` +This restricts us to a `Screen` instance that has a list of components all of +type `Button` or all of type `TextField`. If you’ll only ever have homogeneous +collections, using generics and trait bounds is preferable because the +definitions will be monomorphized at compile time to use the concrete types. -We adapt an iterator using the `enumerate` method so it produces a value and -the index for that value, placed into a tuple. The first value produced is the -tuple `(0, 'a')`. When this value is matched to the pattern `(index, value)`, -`index` will be `0` and `value` will be `'a'`, printing the first line of the -output. +On the other hand, with the method using trait objects, one `Screen` instance +can hold a `Vec<T>` that contains a `Box<Button>` as well as a +`Box<TextField>`. Let’s look at how this works, and then we’ll talk about the +runtime performance implications. -### let Statements +### Implementing the Trait -Prior to this chapter, we had only explicitly discussed using patterns with -`match` and `if let`, but in fact, we’ve used patterns in other places as well, -including in `let` statements. For example, consider this straightforward -variable assignment with `let`: - -``` -let x = 5; -``` +Now we’ll add some types that implement the `Draw` trait. We’ll provide the +`Button` type. Again, actually implementing a GUI library is beyond the scope +of this book, so the `draw` method won’t have any useful implementation in its +body. To imagine what the implementation might look like, a `Button` struct +might have fields for `width`, `height`, and `label`, as shown in Listing 18-7. -Every time you’ve used a `let` statement like this you’ve been using patterns, -although you might not have realized it! More formally, a `let` statement looks -like this: +src/lib.rs ``` -let PATTERN = EXPRESSION; -``` - -In statements like `let x = 5;` with a variable name in the PATTERN slot, the -variable name is just a particularly simple form of a pattern. Rust compares -the expression against the pattern and assigns any names it finds. So, in the -`let x = 5;` example, `x` is a pattern that means “bind what matches here to -the variable `x`.” Because the name `x` is the whole pattern, this pattern -effectively means “bind everything to the variable `x`, whatever the value is.” - -To see the pattern-matching aspect of `let` more clearly, consider Listing -18-4, which uses a pattern with `let` to destructure a tuple. +pub struct Button { + pub width: u32, + pub height: u32, + pub label: String, +} -``` -let (x, y, z) = (1, 2, 3); +impl Draw for Button { + fn draw(&self) { + // code to actually draw a button + } +} ``` -Listing 18-4: Using a pattern to destructure a tuple and create three variables -at once +Listing 18-7: A `Button` struct that implements the `Draw` trait -Here, we match a tuple against a pattern. Rust compares the value `(1, 2, 3)` -to the pattern `(x, y, z)` and sees that the value matches the pattern, in that -it sees that the number of elements is the same in both, so Rust binds `1` to -`x`, `2` to `y`, and `3` to `z`. You can think of this tuple pattern as nesting -three individual variable patterns inside it. +The `width`, `height`, and `label` fields on `Button` will differ from the +fields on other components; for example, a `TextField` type might have those +same fields plus a `placeholder` field. Each of the types we want to draw on +the screen will implement the `Draw` trait but will use different code in the +`draw` method to define how to draw that particular type, as `Button` has here +(without the actual GUI code, as mentioned). The `Button` type, for instance, +might have an additional `impl` block containing methods related to what +happens when a user clicks the button. These kinds of methods won’t apply to +types like `TextField`. -If the number of elements in the pattern doesn’t match the number of elements -in the tuple, the overall type won’t match and we’ll get a compiler error. For -example, Listing 18-5 shows an attempt to destructure a tuple with three -elements into two variables, which won’t work. +If someone using our library decides to implement a `SelectBox` struct that has +`width`, `height`, and `options` fields, they would implement the `Draw` trait +on the `SelectBox` type as well, as shown in Listing 18-8. -``` -let (x, y) = (1, 2, 3); -``` - -Listing 18-5: Incorrectly constructing a pattern whose variables don’t match -the number of elements in the tuple - -Attempting to compile this code results in this type error: +src/main.rs ``` -error[E0308]: mismatched types - --> src/main.rs:2:9 - | -2 | let (x, y) = (1, 2, 3); - | ^^^^^^ --------- this expression has type `({integer}, {integer}, -{integer})` - | | - | expected a tuple with 3 elements, found one with 2 elements - | - = note: expected tuple `({integer}, {integer}, {integer})` - found tuple `(_, _)` -``` +use gui::Draw; -To fix the error, we could ignore one or more of the values in the tuple using -`_` or `..`, as you’ll see in “Ignoring Values in a Pattern” on page XX. If the -problem is that we have too many variables in the pattern, the solution is to -make the types match by removing variables so the number of variables equals -the number of elements in the tuple. - -### Function Parameters - -Function parameters can also be patterns. The code in Listing 18-6, which -declares a function named `foo` that takes one parameter named `x` of type -`i32`, should by now look familiar. +struct SelectBox { + width: u32, + height: u32, + options: Vec<String>, +} -``` -fn foo(x: i32) { - // code goes here +impl Draw for SelectBox { + fn draw(&self) { + // code to actually draw a select box + } } ``` -Listing 18-6: A function signature using patterns in the parameters +Listing 18-8: Another crate using `gui` and implementing the `Draw` trait on a `SelectBox` struct -The `x` part is a pattern! As we did with `let`, we could match a tuple in a -function’s arguments to the pattern. Listing 18-7 splits the values in a tuple -as we pass it to a function. +Our library’s user can now write their `main` function to create a `Screen` +instance. To the `Screen` instance, they can add a `SelectBox` and a `Button` +by putting each in a `Box<T>` to become a trait object. They can then call the +`run` method on the `Screen` instance, which will call `draw` on each of the +components. Listing 18-9 shows this implementation. -Filename: src/main.rs +src/main.rs ``` -fn print_coordinates(&(x, y): &(i32, i32)) { - println!("Current location: ({x}, {y})"); -} +use gui::{Button, Screen}; fn main() { - let point = (3, 5); - print_coordinates(&point); + let screen = Screen { + components: vec![ + Box::new(SelectBox { + width: 75, + height: 10, + options: vec![ + String::from("Yes"), + String::from("Maybe"), + String::from("No"), + ], + }), + Box::new(Button { + width: 50, + height: 10, + label: String::from("OK"), + }), + ], + }; + + screen.run(); } ``` -Listing 18-7: A function with parameters that destructure a tuple - -This code prints `Current location: (3, 5)`. The values `&(3, 5)` match the -pattern `&(x, y)`, so `x` is the value `3` and `y` is the value `5`. - -We can also use patterns in closure parameter lists in the same way as in -function parameter lists because closures are similar to functions, as -discussed in Chapter 13. - -At this point, you’ve seen several ways to use patterns, but patterns don’t -work the same in every place we can use them. In some places, the patterns must -be irrefutable; in other circumstances, they can be refutable. We’ll discuss -these two concepts next. - -## Refutability: Whether a Pattern Might Fail to Match - -Patterns come in two forms: refutable and irrefutable. Patterns that will match -for any possible value passed are *irrefutable*. An example would be `x` in the -statement `let x = 5;` because `x` matches anything and therefore cannot fail -to match. Patterns that can fail to match for some possible value are -*refutable*. An example would be `Some(x)` in the expression `if let Some(x) = -a_value` because if the value in the `a_value` variable is `None` rather than -`Some`, the `Some(x)` pattern will not match. - -Function parameters, `let` statements, and `for` loops can only accept -irrefutable patterns because the program cannot do anything meaningful when -values don’t match. The `if let` and `while let` expressions accept refutable -and irrefutable patterns, but the compiler warns against irrefutable patterns -because, by definition, they’re intended to handle possible failure: the -functionality of a conditional is in its ability to perform differently -depending on success or failure. - -In general, you shouldn’t have to worry about the distinction between refutable -and irrefutable patterns; however, you do need to be familiar with the concept -of refutability so you can respond when you see it in an error message. In -those cases, you’ll need to change either the pattern or the construct you’re -using the pattern with, depending on the intended behavior of the code. - -Let’s look at an example of what happens when we try to use a refutable pattern -where Rust requires an irrefutable pattern and vice versa. Listing 18-8 shows a -`let` statement, but for the pattern, we’ve specified `Some(x)`, a refutable -pattern. As you might expect, this code will not compile. - -``` -let Some(x) = some_option_value; -``` +Listing 18-9: Using trait objects to store values of different types that implement the same trait -Listing 18-8: Attempting to use a refutable pattern with `let` +When we wrote the library, we didn’t know that someone might add the +`SelectBox` type, but our `Screen` implementation was able to operate on the +new type and draw it because `SelectBox` implements the `Draw` trait, which +means it implements the `draw` method. -If `some_option_value` were a `None` value, it would fail to match the pattern -`Some(x)`, meaning the pattern is refutable. However, the `let` statement can -only accept an irrefutable pattern because there is nothing valid the code can -do with a `None` value. At compile time, Rust will complain that we’ve tried to -use a refutable pattern where an irrefutable pattern is required: +This concept—of being concerned only with the messages a value responds to +rather than the value’s concrete type—is similar to the concept of *duck +typing* in dynamically typed languages: If it walks like a duck and quacks like +a duck, then it must be a duck! In the implementation of `run` on `Screen` in +Listing 18-5, `run` doesn’t need to know what the concrete type of each +component is. It doesn’t check whether a component is an instance of a `Button` +or a `SelectBox`, it just calls the `draw` method on the component. By +specifying `Box<dyn Draw>` as the type of the values in the `components` +vector, we’ve defined `Screen` to need values that we can call the `draw` +method on. -``` -error[E0005]: refutable pattern in local binding: `None` not covered - --> src/main.rs:3:9 - | -3 | let Some(x) = some_option_value; - | ^^^^^^^ pattern `None` not covered - | - = note: `let` bindings require an "irrefutable pattern", like a `struct` or -an `enum` with only one variant - = note: for more information, visit -https://doc.rust-lang.org/book/ch18-02-refutability.html - = note: the matched value is of type `Option<i32>` -help: you might want to use `if let` to ignore the variant that isn't matched - | -3 | let x = if let Some(x) = some_option_value { x } else { todo!() }; - | ++++++++++ ++++++++++++++++++++++ -``` +The advantage of using trait objects and Rust’s type system to write code +similar to code using duck typing is that we never have to check whether a +value implements a particular method at runtime or worry about getting errors +if a value doesn’t implement a method but we call it anyway. Rust won’t compile +our code if the values don’t implement the traits that the trait objects need. -Because we didn’t cover (and couldn’t cover!) every valid value with the -pattern `Some(x)`, Rust rightfully produces a compiler error. +For example, Listing 18-10 shows what happens if we try to create a `Screen` +with a `String` as a component. -If we have a refutable pattern where an irrefutable pattern is needed, we can -fix it by changing the code that uses the pattern: instead of using `let`, we -can use `if let`. Then, if the pattern doesn’t match, the code will just skip -the code in the curly brackets, giving it a way to continue validly. Listing -18-9 shows how to fix the code in Listing 18-8. +src/main.rs ``` -if let Some(x) = some_option_value { - println!("{x}"); -} -``` - -Listing 18-9: Using `if let` and a block with refutable patterns instead of -`let` +use gui::Screen; -We’ve given the code an out! This code is perfectly valid, although it means we -cannot use an irrefutable pattern without receiving an error. If we give `if -let` a pattern that will always match, such as `x`, as shown in Listing 18-10, -the compiler will give a warning. +fn main() { + let screen = Screen { + components: vec![Box::new(String::from("Hi"))], + }; -``` -if let x = 5 { - println!("{x}"); -}; + screen.run(); +} ``` -Listing 18-10: Attempting to use an irrefutable pattern with `if let` +Listing 18-10: Attempting to use a type that doesn’t implement the trait object’s trait -Rust complains that it doesn’t make sense to use `if let` with an irrefutable -pattern: +We’ll get this error because `String` doesn’t implement the `Draw` trait: ``` -warning: irrefutable `if let` pattern - --> src/main.rs:2:8 +$ cargo run + Compiling gui v0.1.0 (file:///projects/gui) +error[E0277]: the trait bound `String: Draw` is not satisfied + --> src/main.rs:5:26 | -2 | if let x = 5 { - | ^^^^^^^^^ +5 | components: vec![Box::new(String::from("Hi"))], + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Draw` is not implemented for `String` | - = note: `#[warn(irrefutable_let_patterns)]` on by default - = note: this pattern will always match, so the `if let` is -useless - = help: consider replacing the `if let` with a `let` -``` - -For this reason, match arms must use refutable patterns, except for the last -arm, which should match any remaining values with an irrefutable pattern. Rust -allows us to use an irrefutable pattern in a `match` with only one arm, but -this syntax isn’t particularly useful and could be replaced with a simpler -`let` statement. - -Now that you know where to use patterns and the difference between refutable -and irrefutable patterns, let’s cover all the syntax we can use to create -patterns. - -## Pattern Syntax - -In this section, we gather all the syntax that is valid in patterns and discuss -why and when you might want to use each one. - -### Matching Literals - -As you saw in Chapter 6, you can match patterns against literals directly. The -following code gives some examples: - -Filename: src/main.rs + = help: the trait `Draw` is implemented for `Button` + = note: required for the cast from `Box<String>` to `Box<dyn Draw>` +For more information about this error, try `rustc --explain E0277`. +error: could not compile `gui` (bin "gui") due to 1 previous error ``` -let x = 1; -match x { - 1 => println!("one"), - 2 => println!("two"), - 3 => println!("three"), - _ => println!("anything"), -} -``` +This error lets us know that either we’re passing something to `Screen` that we +didn’t mean to pass and so should pass a different type, or we should implement +`Draw` on `String` so that `Screen` is able to call `draw` on it. -This code prints `one` because the value in `x` is `1`. This syntax is useful -when you want your code to take an action if it gets a particular concrete -value. +<!-- Old headings. Do not remove or links may break. --> -### Matching Named Variables +<a id="trait-objects-perform-dynamic-dispatch"></a> -Named variables are irrefutable patterns that match any value, and we’ve used -them many times in this book. However, there is a complication when you use -named variables in `match` expressions. Because `match` starts a new scope, -variables declared as part of a pattern inside the `match` expression will -shadow those with the same name outside the `match` construct, as is the case -with all variables. In Listing 18-11, we declare a variable named `x` with the -value `Some(5)` and a variable `y` with the value `10`. We then create a -`match` expression on the value `x`. Look at the patterns in the match arms and -`println!` at the end, and try to figure out what the code will print before -running this code or reading further. +### Performing Dynamic Dispatch -Filename: src/main.rs +Recall in “Performance of Code Using +Generics” in Chapter 10 our +discussion on the monomorphization process performed on generics by the +compiler: The compiler generates nongeneric implementations of functions and +methods for each concrete type that we use in place of a generic type +parameter. The code that results from monomorphization is doing *static +dispatch*, which is when the compiler knows what method you’re calling at +compile time. This is opposed to *dynamic dispatch*, which is when the compiler +can’t tell at compile time which method you’re calling. In dynamic dispatch +cases, the compiler emits code that at runtime will know which method to call. -``` -fn main() { - 1 let x = Some(5); - 2 let y = 10; +When we use trait objects, Rust must use dynamic dispatch. The compiler doesn’t +know all the types that might be used with the code that’s using trait objects, +so it doesn’t know which method implemented on which type to call. Instead, at +runtime, Rust uses the pointers inside the trait object to know which method to +call. This lookup incurs a runtime cost that doesn’t occur with static dispatch. +Dynamic dispatch also prevents the compiler from choosing to inline a method’s +code, which in turn prevents some optimizations, and Rust has some rules about +where you can and cannot use dynamic dispatch, called *dyn compatibility*. Those +rules are beyond the scope of this discussion, but you can read more about them +in the reference. However, we did get extra +flexibility in the code that we wrote in Listing 18-5 and were able to support +in Listing 18-9, so it’s a trade-off to consider. - match x { - 3 Some(50) => println!("Got 50"), - 4 Some(y) => println!("Matched, y = {y}"), - 5 _ => println!("Default case, x = {:?}", x), - } +## Implementing an Object-Oriented Design Pattern - 6 println!("at the end: x = {:?}, y = {y}", x); -} -``` +The *state pattern* is an object-oriented design pattern. The crux of the +pattern is that we define a set of states a value can have internally. The +states are represented by a set of *state objects*, and the value’s behavior +changes based on its state. We’re going to work through an example of a blog +post struct that has a field to hold its state, which will be a state object +from the set “draft,” “review,” or “published.” -Listing 18-11: A `match` expression with an arm that introduces a shadowed -variable `y` +The state objects share functionality: In Rust, of course, we use structs and +traits rather than objects and inheritance. Each state object is responsible +for its own behavior and for governing when it should change into another +state. The value that holds a state object knows nothing about the different +behavior of the states or when to transition between states. -Let’s walk through what happens when the `match` expression runs. The pattern -in the first match arm [3] doesn’t match the defined value of `x` [1], so the -code continues. +The advantage of using the state pattern is that, when the business +requirements of the program change, we won’t need to change the code of the +value holding the state or the code that uses the value. We’ll only need to +update the code inside one of the state objects to change its rules or perhaps +add more state objects. -The pattern in the second match arm [4] introduces a new variable named `y` -that will match any value inside a `Some` value. Because we’re in a new scope -inside the `match` expression, this is a new `y` variable, not the `y` we -declared at the beginning with the value `10` [2]. This new `y` binding will -match any value inside a `Some`, which is what we have in `x`. Therefore, this -new `y` binds to the inner value of the `Some` in `x`. That value is `5`, so -the expression for that arm executes and prints `Matched, y = 5`. +First, we’re going to implement the state pattern in a more traditional +object-oriented way. Then, we’ll use an approach that’s a bit more natural in +Rust. Let’s dig in to incrementally implement a blog post workflow using the +state pattern. -If `x` had been a `None` value instead of `Some(5)`, the patterns in the first -two arms wouldn’t have matched, so the value would have matched to the -underscore [5]. We didn’t introduce the `x` variable in the pattern of the -underscore arm, so the `x` in the expression is still the outer `x` that hasn’t -been shadowed. In this hypothetical case, the `match` would print `Default -case, x = None`. +The final functionality will look like this: -When the `match` expression is done, its scope ends, and so does the scope of -the inner `y`. The last `println!` [6] produces `at the end: x = Some(5), y = -10`. +1. A blog post starts as an empty draft. +1. When the draft is done, a review of the post is requested. +1. When the post is approved, it gets published. +1. Only published blog posts return content to print so that unapproved posts + can’t accidentally be published. -To create a `match` expression that compares the values of the outer `x` and -`y`, rather than introducing a shadowed variable, we would need to use a match -guard conditional instead. We’ll talk about match guards in “Extra Conditionals -with Match Guards” on page XX. +Any other changes attempted on a post should have no effect. For example, if we +try to approve a draft blog post before we’ve requested a review, the post +should remain an unpublished draft. -### Multiple Patterns +<!-- Old headings. Do not remove or links may break. --> -In `match` expressions, you can match multiple patterns using the `|` syntax, -which is the pattern *or* operator. For example, in the following code we match -the value of `x` against the match arms, the first of which has an *or* option, -meaning if the value of `x` matches either of the values in that arm, that -arm’s code will run: +<a id="a-traditional-object-oriented-attempt"></a> -Filename: src/main.rs +### Attempting Traditional Object-Oriented Style -``` -let x = 1; +There are infinite ways to structure code to solve the same problem, each with +different trade-offs. This section’s implementation is more of a traditional +object-oriented style, which is possible to write in Rust, but doesn’t take +advantage of some of Rust’s strengths. Later, we’ll demonstrate a different +solution that still uses the object-oriented design pattern but is structured +in a way that might look less familiar to programmers with object-oriented +experience. We’ll compare the two solutions to experience the trade-offs of +designing Rust code differently than code in other languages. -match x { - 1 | 2 => println!("one or two"), - 3 => println!("three"), - _ => println!("anything"), -} -``` +Listing 18-11 shows this workflow in code form: This is an example usage of the +API we’ll implement in a library crate named `blog`. This won’t compile yet +because we haven’t implemented the `blog` crate. -This code prints `one or two`. +src/main.rs -### Matching Ranges of Values with ..= +``` +use blog::Post; -The `..=` syntax allows us to match to an inclusive range of values. In the -following code, when a pattern matches any of the values within the given -range, that arm will execute: +fn main() { + let mut post = Post::new(); -Filename: src/main.rs + post.add_text("I ate a salad for lunch today"); + assert_eq!("", post.content()); -``` -let x = 5; + post.request_review(); + assert_eq!("", post.content()); -match x { - 1..=5 => println!("one through five"), - _ => println!("something else"), + post.approve(); + assert_eq!("I ate a salad for lunch today", post.content()); } ``` -If `x` is `1`, `2`, `3`, `4`, or `5`, the first arm will match. This syntax is -more convenient for multiple match values than using the `|` operator to -express the same idea; if we were to use `|`, we would have to specify `1 | 2 | -3 | 4 | 5`. Specifying a range is much shorter, especially if we want to match, -say, any number between 1 and 1,000! +Listing 18-11: Code that demonstrates the desired behavior we want our `blog` crate to have -The compiler checks that the range isn’t empty at compile time, and because the -only types for which Rust can tell if a range is empty or not are `char` and -numeric values, ranges are only allowed with numeric or `char` values. +We want to allow the user to create a new draft blog post with `Post::new`. We +want to allow text to be added to the blog post. If we try to get the post’s +content immediately, before approval, we shouldn’t get any text because the +post is still a draft. We’ve added `assert_eq!` in the code for demonstration +purposes. An excellent unit test for this would be to assert that a draft blog +post returns an empty string from the `content` method, but we’re not going to +write tests for this example. -Here is an example using ranges of `char` values: +Next, we want to enable a request for a review of the post, and we want +`content` to return an empty string while waiting for the review. When the post +receives approval, it should get published, meaning the text of the post will +be returned when `content` is called. -Filename: src/main.rs +Notice that the only type we’re interacting with from the crate is the `Post` +type. This type will use the state pattern and will hold a value that will be +one of three state objects representing the various states a post can be +in—draft, review, or published. Changing from one state to another will be +managed internally within the `Post` type. The states change in response to the +methods called by our library’s users on the `Post` instance, but they don’t +have to manage the state changes directly. Also, users can’t make a mistake +with the states, such as publishing a post before it’s reviewed. -``` -let x = 'c'; - -match x { - 'a'..='j' => println!("early ASCII letter"), - 'k'..='z' => println!("late ASCII letter"), - _ => println!("something else"), -} -``` +<!-- Old headings. Do not remove or links may break. --> -Rust can tell that `'c'` is within the first pattern’s range and prints `early -ASCII letter`. +<a id="defining-post-and-creating-a-new-instance-in-the-draft-state"></a> -### Destructuring to Break Apart Values +#### Defining Post and Creating a New Instance -We can also use patterns to destructure structs, enums, and tuples to use -different parts of these values. Let’s walk through each value. +Let’s get started on the implementation of the library! We know we need a +public `Post` struct that holds some content, so we’ll start with the +definition of the struct and an associated public `new` function to create an +instance of `Post`, as shown in Listing 18-12. We’ll also make a private +`State` trait that will define the behavior that all state objects for a `Post` +must have. -#### Destructuring Structs +Then, `Post` will hold a trait object of `Box<dyn State>` inside an `Option<T>` +in a private field named `state` to hold the state object. You’ll see why the +`Option<T>` is necessary in a bit. -Listing 18-12 shows a `Point` struct with two fields, `x` and `y`, that we can -break apart using a pattern with a `let` statement. - -Filename: src/main.rs +src/lib.rs ``` -struct Point { - x: i32, - y: i32, +pub struct Post { + state: Option<Box<dyn State>>, + content: String, } -fn main() { - let p = Point { x: 0, y: 7 }; - - let Point { x: a, y: b } = p; - assert_eq!(0, a); - assert_eq!(7, b); +impl Post { + pub fn new() -> Post { + Post { + state: Some(Box::new(Draft {})), + content: String::new(), + } + } } -``` - -Listing 18-12: Destructuring a struct’s fields into separate variables -This code creates the variables `a` and `b` that match the values of the `x` -and `y` fields of the `p` struct. This example shows that the names of the -variables in the pattern don’t have to match the field names of the struct. -However, it’s common to match the variable names to the field names to make it -easier to remember which variables came from which fields. Because of this -common usage, and because writing `let Point { x: x, y: y } = p;` contains a -lot of duplication, Rust has a shorthand for patterns that match struct fields: -you only need to list the name of the struct field, and the variables created -from the pattern will have the same names. Listing 18-13 behaves in the same -way as the code in Listing 18-12, but the variables created in the `let` -pattern are `x` and `y` instead of `a` and `b`. +trait State {} -Filename: src/main.rs +struct Draft {} +impl State for Draft {} ``` -struct Point { - x: i32, - y: i32, -} - -fn main() { - let p = Point { x: 0, y: 7 }; - let Point { x, y } = p; - assert_eq!(0, x); - assert_eq!(7, y); -} -``` +Listing 18-12: Definition of a `Post` struct and a `new` function that creates a new `Post` instance, a `State` trait, and a `Draft` struct -Listing 18-13: Destructuring struct fields using struct field shorthand +The `State` trait defines the behavior shared by different post states. The +state objects are `Draft`, `PendingReview`, and `Published`, and they will all +implement the `State` trait. For now, the trait doesn’t have any methods, and +we’ll start by defining just the `Draft` state because that is the state we +want a post to start in. -This code creates the variables `x` and `y` that match the `x` and `y` fields -of the `p` variable. The outcome is that the variables `x` and `y` contain the -values from the `p` struct. +When we create a new `Post`, we set its `state` field to a `Some` value that +holds a `Box`. This `Box` points to a new instance of the `Draft` struct. This +ensures that whenever we create a new instance of `Post`, it will start out as +a draft. Because the `state` field of `Post` is private, there is no way to +create a `Post` in any other state! In the `Post::new` function, we set the +`content` field to a new, empty `String`. -We can also destructure with literal values as part of the struct pattern -rather than creating variables for all the fields. Doing so allows us to test -some of the fields for particular values while creating variables to -destructure the other fields. +#### Storing the Text of the Post Content -In Listing 18-14, we have a `match` expression that separates `Point` values -into three cases: points that lie directly on the `x` axis (which is true when -`y = 0`), on the `y` axis (`x = 0`), or on neither axis. +We saw in Listing 18-11 that we want to be able to call a method named +`add_text` and pass it a `&str` that is then added as the text content of the +blog post. We implement this as a method, rather than exposing the `content` +field as `pub`, so that later we can implement a method that will control how +the `content` field’s data is read. The `add_text` method is pretty +straightforward, so let’s add the implementation in Listing 18-13 to the `impl Post` block. -Filename: src/main.rs +src/lib.rs ``` -fn main() { - let p = Point { x: 0, y: 7 }; - - match p { - Point { x, y: 0 } => println!("On the x axis at {x}"), - Point { x: 0, y } => println!("On the y axis at {y}"), - Point { x, y } => { - println!("On neither axis: ({x}, {y})"); - } +impl Post { + // --snip-- + pub fn add_text(&mut self, text: &str) { + self.content.push_str(text); } } ``` -Listing 18-14: Destructuring and matching literal values in one pattern +Listing 18-13: Implementing the `add_text` method to add text to a post’s `content` -The first arm will match any point that lies on the `x` axis by specifying that -the `y` field matches if its value matches the literal `0`. The pattern still -creates an `x` variable that we can use in the code for this arm. +The `add_text` method takes a mutable reference to `self` because we’re +changing the `Post` instance that we’re calling `add_text` on. We then call +`push_str` on the `String` in `content` and pass the `text` argument to add to +the saved `content`. This behavior doesn’t depend on the state the post is in, +so it’s not part of the state pattern. The `add_text` method doesn’t interact +with the `state` field at all, but it is part of the behavior we want to +support. -Similarly, the second arm matches any point on the `y` axis by specifying that -the `x` field matches if its value is `0` and creates a variable `y` for the -value of the `y` field. The third arm doesn’t specify any literals, so it -matches any other `Point` and creates variables for both the `x` and `y` fields. +<!-- Old headings. Do not remove or links may break. --> -In this example, the value `p` matches the second arm by virtue of `x` -containing a `0`, so this code will print `On the y axis at 7`. +<a id="ensuring-the-content-of-a-draft-post-is-empty"></a> -Remember that a `match` expression stops checking arms once it has found the -first matching pattern, so even though `Point { x: 0, y: 0}` is on the `x` axis -and the `y` axis, this code would only print `On the x axis at 0`. +#### Ensuring That the Content of a Draft Post Is Empty -#### Destructuring Enums +Even after we’ve called `add_text` and added some content to our post, we still +want the `content` method to return an empty string slice because the post is +still in the draft state, as shown by the first `assert_eq!` in Listing 18-11. +For now, let’s implement the `content` method with the simplest thing that will +fulfill this requirement: always returning an empty string slice. We’ll change +this later once we implement the ability to change a post’s state so that it +can be published. So far, posts can only be in the draft state, so the post +content should always be empty. Listing 18-14 shows this placeholder +implementation. -We’ve destructured enums in this book (for example, Listing 6-5), but we -haven’t yet explicitly discussed that the pattern to destructure an enum -corresponds to the way the data stored within the enum is defined. As an -example, in Listing 18-15 we use the `Message` enum from Listing 6-2 and write -a `match` with patterns that will destructure each inner value. - -Filename: src/main.rs +src/lib.rs ``` -enum Message { - Quit, - Move { x: i32, y: i32 }, - Write(String), - ChangeColor(i32, i32, i32), -} - -fn main() { - 1 let msg = Message::ChangeColor(0, 160, 255); - - match msg { - 2 Message::Quit => { - println!( - "The Quit variant has no data to destructure." - ); - } - 3 Message::Move { x, y } => { - println!( - "Move in the x dir {x}, in the y dir {y}" - ); - } - 4 Message::Write(text) => { - println!("Text message: {text}"); - } - 5 Message::ChangeColor(r, g, b) => println!( - "Change color to red {r}, green {g}, and blue {b}" - ), +impl Post { + // --snip-- + pub fn content(&self) -> &str { + "" } } ``` -Listing 18-15: Destructuring enum variants that hold different kinds of values - -This code will print `Change color to red 0, green 160, and blue 255`. Try -changing the value of `msg` [1] to see the code from the other arms run. +Listing 18-14: Adding a placeholder implementation for the `content` method on `Post` that always returns an empty string slice -For enum variants without any data, like `Message::Quit` [2], we can’t -destructure the value any further. We can only match on the literal -`Message::Quit` value, and no variables are in that pattern. +With this added `content` method, everything in Listing 18-11 through the first +`assert_eq!` works as intended. -For struct-like enum variants, such as `Message::Move` [3], we can use a -pattern similar to the pattern we specify to match structs. After the variant -name, we place curly brackets and then list the fields with variables so we -break apart the pieces to use in the code for this arm. Here we use the -shorthand form as we did in Listing 18-13. +<!-- Old headings. Do not remove or links may break. --> -For tuple-like enum variants, like `Message::Write` that holds a tuple with one -element [4] and `Message::ChangeColor` that holds a tuple with three elements -[5], the pattern is similar to the pattern we specify to match tuples. The -number of variables in the pattern must match the number of elements in the -variant we’re matching. +<a id="requesting-a-review-of-the-post-changes-its-state"></a> +<a id="requesting-a-review-changes-the-posts-state"></a> -#### Destructuring Nested Structs and Enums +#### Requesting a Review, Which Changes the Post’s State -So far, our examples have all been matching structs or enums one level deep, -but matching can work on nested items too! For example, we can refactor the -code in Listing 18-15 to support RGB and HSV colors in the `ChangeColor` -message, as shown in Listing 18-16. +Next, we need to add functionality to request a review of a post, which should +change its state from `Draft` to `PendingReview`. Listing 18-15 shows this code. -Filename: src/main.rs +src/lib.rs ``` -enum Color { - Rgb(i32, i32, i32), - Hsv(i32, i32, i32), +impl Post { + // --snip-- + pub fn request_review(&mut self) { + if let Some(s) = self.state.take() { + self.state = Some(s.request_review()) + } + } } -enum Message { - Quit, - Move { x: i32, y: i32 }, - Write(String), - ChangeColor(Color), +trait State { + fn request_review(self: Box<Self>) -> Box<dyn State>; } -fn main() { - let msg = Message::ChangeColor(Color::Hsv(0, 160, 255)); - - match msg { - Message::ChangeColor(Color::Rgb(r, g, b)) => println!( - "Change color to red {r}, green {g}, and blue {b}" - ), - Message::ChangeColor(Color::Hsv(h, s, v)) => println!( - "Change color to hue {h}, saturation {s}, value {v}" - ), - _ => (), +struct Draft {} + +impl State for Draft { + fn request_review(self: Box<Self>) -> Box<dyn State> { + Box::new(PendingReview {}) } } -``` - -Listing 18-16: Matching on nested enums - -The pattern of the first arm in the `match` expression matches a -`Message::ChangeColor` enum variant that contains a `Color::Rgb` variant; then -the pattern binds to the three inner `i32` values. The pattern of the second -arm also matches a `Message::ChangeColor` enum variant, but the inner enum -matches `Color::Hsv` instead. We can specify these complex conditions in one -`match` expression, even though two enums are involved. -#### Destructuring Structs and Tuples +struct PendingReview {} -We can mix, match, and nest destructuring patterns in even more complex ways. -The following example shows a complicated destructure where we nest structs and -tuples inside a tuple and destructure all the primitive values out: - -``` -let ((feet, inches), Point { x, y }) = - ((3, 10), Point { x: 3, y: -10 }); +impl State for PendingReview { + fn request_review(self: Box<Self>) -> Box<dyn State> { + self + } +} ``` -This code lets us break complex types into their component parts so we can use -the values we’re interested in separately. - -Destructuring with patterns is a convenient way to use pieces of values, such -as the value from each field in a struct, separately from each other. +Listing 18-15: Implementing `request_review` methods on `Post` and the `State` trait -### Ignoring Values in a Pattern +We give `Post` a public method named `request_review` that will take a mutable +reference to `self`. Then, we call an internal `request_review` method on the +current state of `Post`, and this second `request_review` method consumes the +current state and returns a new state. -You’ve seen that it’s sometimes useful to ignore values in a pattern, such as -in the last arm of a `match`, to get a catchall that doesn’t actually do -anything but does account for all remaining possible values. There are a few -ways to ignore entire values or parts of values in a pattern: using the `_` -pattern (which you’ve seen), using the `_` pattern within another pattern, -using a name that starts with an underscore, or using `..` to ignore remaining -parts of a value. Let’s explore how and why to use each of these patterns. +We add the `request_review` method to the `State` trait; all types that +implement the trait will now need to implement the `request_review` method. +Note that rather than having `self`, `&self`, or `&mut self` as the first +parameter of the method, we have `self: Box<Self>`. This syntax means the +method is only valid when called on a `Box` holding the type. This syntax takes +ownership of `Box<Self>`, invalidating the old state so that the state value of +the `Post` can transform into a new state. -#### An Entire Value with _ +To consume the old state, the `request_review` method needs to take ownership +of the state value. This is where the `Option` in the `state` field of `Post` +comes in: We call the `take` method to take the `Some` value out of the `state` +field and leave a `None` in its place because Rust doesn’t let us have +unpopulated fields in structs. This lets us move the `state` value out of +`Post` rather than borrowing it. Then, we’ll set the post’s `state` value to +the result of this operation. -We’ve used the underscore as a wildcard pattern that will match any value but -not bind to the value. This is especially useful as the last arm in a `match` -expression, but we can also use it in any pattern, including function -parameters, as shown in Listing 18-17. +We need to set `state` to `None` temporarily rather than setting it directly +with code like `self.state = self.state.request_review();` to get ownership of +the `state` value. This ensures that `Post` can’t use the old `state` value +after we’ve transformed it into a new state. -Filename: src/main.rs +The `request_review` method on `Draft` returns a new, boxed instance of a new +`PendingReview` struct, which represents the state when a post is waiting for a +review. The `PendingReview` struct also implements the `request_review` method +but doesn’t do any transformations. Rather, it returns itself because when we +request a review on a post already in the `PendingReview` state, it should stay +in the `PendingReview` state. -``` -fn foo(_: i32, y: i32) { - println!("This code only uses the y parameter: {y}"); -} - -fn main() { - foo(3, 4); -} -``` +Now we can start seeing the advantages of the state pattern: The +`request_review` method on `Post` is the same no matter its `state` value. Each +state is responsible for its own rules. -Listing 18-17: Using `_` in a function signature +We’ll leave the `content` method on `Post` as is, returning an empty string +slice. We can now have a `Post` in the `PendingReview` state as well as in the +`Draft` state, but we want the same behavior in the `PendingReview` state. +Listing 18-11 now works up to the second `assert_eq!` call! -This code will completely ignore the value `3` passed as the first argument, -and will print `This code only uses the y parameter: 4`. +<!-- Old headings. Do not remove or links may break. --> -In most cases when you no longer need a particular function parameter, you -would change the signature so it doesn’t include the unused parameter. Ignoring -a function parameter can be especially useful in cases when, for example, -you’re implementing a trait when you need a certain type signature but the -function body in your implementation doesn’t need one of the parameters. You -then avoid getting a compiler warning about unused function parameters, as you -would if you used a name instead. +<a id="adding-the-approve-method-that-changes-the-behavior-of-content"></a> +<a id="adding-approve-to-change-the-behavior-of-content"></a> -#### Parts of a Value with a Nested _ +#### Adding approve to Change content’s Behavior -We can also use `_` inside another pattern to ignore just part of a value, for -example, when we want to test for only part of a value but have no use for the -other parts in the corresponding code we want to run. Listing 18-18 shows code -responsible for managing a setting’s value. The business requirements are that -the user should not be allowed to overwrite an existing customization of a -setting but can unset the setting and give it a value if it is currently unset. +The `approve` method will be similar to the `request_review` method: It will +set `state` to the value that the current state says it should have when that +state is approved, as shown in Listing 18-16. -Filename: src/main.rs +src/lib.rs ``` -let mut setting_value = Some(5); -let new_setting_value = Some(10); - -match (setting_value, new_setting_value) { - (Some(_), Some(_)) => { - println!("Can't overwrite an existing customized value"); - } - _ => { - setting_value = new_setting_value; +impl Post { + // --snip-- + pub fn approve(&mut self) { + if let Some(s) = self.state.take() { + self.state = Some(s.approve()) + } } } -println!("setting is {:?}", setting_value); -``` +trait State { + fn request_review(self: Box<Self>) -> Box<dyn State>; + fn approve(self: Box<Self>) -> Box<dyn State>; +} -Listing 18-18: Using an underscore within patterns that match `Some` variants -when we don’t need to use the value inside the `Some` +struct Draft {} -This code will print `Can't overwrite an existing customized value` and then -`setting is Some(5)`. In the first match arm, we don’t need to match on or use -the values inside either `Some` variant, but we do need to test for the case -when `setting_value` and `new_setting_value` are the `Some` variant. In that -case, we print the reason for not changing `setting_value`, and it doesn’t get -changed. +impl State for Draft { + // --snip-- + fn approve(self: Box<Self>) -> Box<dyn State> { + self + } +} -In all other cases (if either `setting_value` or `new_setting_value` is `None`) -expressed by the `_` pattern in the second arm, we want to allow -`new_setting_value` to become `setting_value`. +struct PendingReview {} -We can also use underscores in multiple places within one pattern to ignore -particular values. Listing 18-19 shows an example of ignoring the second and -fourth values in a tuple of five items. +impl State for PendingReview { + // --snip-- + fn approve(self: Box<Self>) -> Box<dyn State> { + Box::new(Published {}) + } +} -Filename: src/main.rs +struct Published {} -``` -let numbers = (2, 4, 8, 16, 32); +impl State for Published { + fn request_review(self: Box<Self>) -> Box<dyn State> { + self + } -match numbers { - (first, _, third, _, fifth) => { - println!("Some numbers: {first}, {third}, {fifth}"); + fn approve(self: Box<Self>) -> Box<dyn State> { + self } } ``` -Listing 18-19: Ignoring multiple parts of a tuple +Listing 18-16: Implementing the `approve` method on `Post` and the `State` trait -This code will print `Some numbers: 2, 8, 32`, and the values `4` and `16` will -be ignored. +We add the `approve` method to the `State` trait and add a new struct that +implements `State`, the `Published` state. -#### An Unused Variable by Starting Its Name with _ +Similar to the way `request_review` on `PendingReview` works, if we call the +`approve` method on a `Draft`, it will have no effect because `approve` will +return `self`. When we call `approve` on `PendingReview`, it returns a new, +boxed instance of the `Published` struct. The `Published` struct implements the +`State` trait, and for both the `request_review` method and the `approve` +method, it returns itself because the post should stay in the `Published` state +in those cases. -If you create a variable but don’t use it anywhere, Rust will usually issue a -warning because an unused variable could be a bug. However, sometimes it’s -useful to be able to create a variable you won’t use yet, such as when you’re -prototyping or just starting a project. In this situation, you can tell Rust -not to warn you about the unused variable by starting the name of the variable -with an underscore. In Listing 18-20, we create two unused variables, but when -we compile this code, we should only get a warning about one of them. +Now we need to update the `content` method on `Post`. We want the value +returned from `content` to depend on the current state of the `Post`, so we’re +going to have the `Post` delegate to a `content` method defined on its `state`, +as shown in Listing 18-17. -Filename: src/main.rs +src/lib.rs ``` -fn main() { - let _x = 5; - let y = 10; +impl Post { + // --snip-- + pub fn content(&self) -> &str { + self.state.as_ref().unwrap().content(self) + } + // --snip-- } ``` -Listing 18-20: Starting a variable name with an underscore to avoid getting -unused variable warnings +Listing 18-17: Updating the `content` method on `Post` to delegate to a `content` method on `State` -Here, we get a warning about not using the variable `y`, but we don’t get a -warning about not using `_x`. +Because the goal is to keep all of these rules inside the structs that +implement `State`, we call a `content` method on the value in `state` and pass +the post instance (that is, `self`) as an argument. Then, we return the value +that’s returned from using the `content` method on the `state` value. -Note that there is a subtle difference between using only `_` and using a name -that starts with an underscore. The syntax `_x` still binds the value to the -variable, whereas `_` doesn’t bind at all. To show a case where this -distinction matters, Listing 18-21 will provide us with an error. +We call the `as_ref` method on the `Option` because we want a reference to the +value inside the `Option` rather than ownership of the value. Because `state` is +an `Option<Box<dyn State>>`, when we call `as_ref`, an `Option<&Box<dyn State>>` is returned. If we didn’t call `as_ref`, we would get an error because +we can’t move `state` out of the borrowed `&self` of the function parameter. -Filename: src/main.rs +We then call the `unwrap` method, which we know will never panic because we +know the methods on `Post` ensure that `state` will always contain a `Some` +value when those methods are done. This is one of the cases we talked about in +the “When You Have More Information Than the +Compiler” section of Chapter 9 when we +know that a `None` value is never possible, even though the compiler isn’t able +to understand that. -``` -let s = Some(String::from("Hello!")); +At this point, when we call `content` on the `&Box<dyn State>`, deref coercion +will take effect on the `&` and the `Box` so that the `content` method will +ultimately be called on the type that implements the `State` trait. That means +we need to add `content` to the `State` trait definition, and that is where +we’ll put the logic for what content to return depending on which state we +have, as shown in Listing 18-18. -if let Some(_s) = s { - println!("found a string"); -} +src/lib.rs -println!("{:?}", s); ``` +trait State { + // --snip-- + fn content<'a>(&self, post: &'a Post) -> &'a str { + "" + } +} -Listing 18-21: An unused variable starting with an underscore still binds the -value, which might take ownership of the value. +// --snip-- +struct Published {} -We’ll receive an error because the `s` value will still be moved into `_s`, -which prevents us from using `s` again. However, using the underscore by itself -doesn’t ever bind to the value. Listing 18-22 will compile without any errors -because `s` doesn’t get moved into `_`. +impl State for Published { + // --snip-- + fn content<'a>(&self, post: &'a Post) -> &'a str { + &post.content + } +} +``` -Filename: src/main.rs +Listing 18-18: Adding the `content` method to the `State` trait + +We add a default implementation for the `content` method that returns an empty +string slice. That means we don’t need to implement `content` on the `Draft` +and `PendingReview` structs. The `Published` struct will override the `content` +method and return the value in `post.content`. While convenient, having the +`content` method on `State` determine the content of the `Post` is blurring +the lines between the responsibility of `State` and the responsibility of +`Post`. + +Note that we need lifetime annotations on this method, as we discussed in +Chapter 10. We’re taking a reference to a `post` as an argument and returning a +reference to part of that `post`, so the lifetime of the returned reference is +related to the lifetime of the `post` argument. + +And we’re done—all of Listing 18-11 now works! We’ve implemented the state +pattern with the rules of the blog post workflow. The logic related to the +rules lives in the state objects rather than being scattered throughout `Post`. + +> ### Why Not An Enum? +> +> You may have been wondering why we didn’t use an enum with the different +> possible post states as variants. That’s certainly a possible solution; try it +> and compare the end results to see which you prefer! One disadvantage of using +> an enum is that every place that checks the value of the enum will need a +> `match` expression or similar to handle every possible variant. This could get +> more repetitive than this trait object solution. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="trade-offs-of-the-state-pattern"></a> + +#### Evaluating the State Pattern + +We’ve shown that Rust is capable of implementing the object-oriented state +pattern to encapsulate the different kinds of behavior a post should have in +each state. The methods on `Post` know nothing about the various behaviors. +Because of the way we organized the code, we have to look in only one place to +know the different ways a published post can behave: the implementation of the +`State` trait on the `Published` struct. + +If we were to create an alternative implementation that didn’t use the state +pattern, we might instead use `match` expressions in the methods on `Post` or +even in the `main` code that checks the state of the post and changes behavior +in those places. That would mean we would have to look in several places to +understand all the implications of a post being in the published state. + +With the state pattern, the `Post` methods and the places we use `Post` don’t +need `match` expressions, and to add a new state, we would only need to add a +new struct and implement the trait methods on that one struct in one location. + +The implementation using the state pattern is easy to extend to add more +functionality. To see the simplicity of maintaining code that uses the state +pattern, try a few of these suggestions: + +* Add a `reject` method that changes the post’s state from `PendingReview` back + to `Draft`. +* Require two calls to `approve` before the state can be changed to `Published`. +* Allow users to add text content only when a post is in the `Draft` state. + Hint: have the state object responsible for what might change about the + content but not responsible for modifying the `Post`. + +One downside of the state pattern is that, because the states implement the +transitions between states, some of the states are coupled to each other. If we +add another state between `PendingReview` and `Published`, such as `Scheduled`, +we would have to change the code in `PendingReview` to transition to +`Scheduled` instead. It would be less work if `PendingReview` didn’t need to +change with the addition of a new state, but that would mean switching to +another design pattern. + +Another downside is that we’ve duplicated some logic. To eliminate some of the +duplication, we might try to make default implementations for the +`request_review` and `approve` methods on the `State` trait that return `self`. +However, this wouldn’t work: When using `State` as a trait object, the trait +doesn’t know what the concrete `self` will be exactly, so the return type isn’t +known at compile time. (This is one of the dyn compatibility rules mentioned +earlier.) + +Other duplication includes the similar implementations of the `request_review` +and `approve` methods on `Post`. Both methods use `Option::take` with the +`state` field of `Post`, and if `state` is `Some`, they delegate to the wrapped +value’s implementation of the same method and set the new value of the `state` +field to the result. If we had a lot of methods on `Post` that followed this +pattern, we might consider defining a macro to eliminate the repetition (see +the “Macros” section in Chapter 20). + +By implementing the state pattern exactly as it’s defined for object-oriented +languages, we’re not taking as full advantage of Rust’s strengths as we could. +Let’s look at some changes we can make to the `blog` crate that can make +invalid states and transitions into compile-time errors. + +### Encoding States and Behavior as Types + +We’ll show you how to rethink the state pattern to get a different set of +trade-offs. Rather than encapsulating the states and transitions completely so +that outside code has no knowledge of them, we’ll encode the states into +different types. Consequently, Rust’s type-checking system will prevent +attempts to use draft posts where only published posts are allowed by issuing a +compiler error. + +Let’s consider the first part of `main` in Listing 18-11: + +src/main.rs ``` -let s = Some(String::from("Hello!")); +fn main() { + let mut post = Post::new(); -if let Some(_) = s { - println!("found a string"); + post.add_text("I ate a salad for lunch today"); + assert_eq!("", post.content()); } - -println!("{:?}", s); ``` -Listing 18-22: Using an underscore does not bind the value. -This code works just fine because we never bind `s` to anything; it isn’t moved. -#### Remaining Parts of a Value with .. +We still enable the creation of new posts in the draft state using `Post::new` +and the ability to add text to the post’s content. But instead of having a +`content` method on a draft post that returns an empty string, we’ll make it so +that draft posts don’t have the `content` method at all. That way, if we try to +get a draft post’s content, we’ll get a compiler error telling us the method +doesn’t exist. As a result, it will be impossible for us to accidentally +display draft post content in production because that code won’t even compile. +Listing 18-19 shows the definition of a `Post` struct and a `DraftPost` struct, +as well as methods on each. -With values that have many parts, we can use the `..` syntax to use specific -parts and ignore the rest, avoiding the need to list underscores for each -ignored value. The `..` pattern ignores any parts of a value that we haven’t -explicitly matched in the rest of the pattern. In Listing 18-23, we have a -`Point` struct that holds a coordinate in three-dimensional space. In the -`match` expression, we want to operate only on the `x` coordinate and ignore -the values in the `y` and `z` fields. - -Filename: src/main.rs +src/lib.rs ``` -struct Point { - x: i32, - y: i32, - z: i32, +pub struct Post { + content: String, } -let origin = Point { x: 0, y: 0, z: 0 }; - -match origin { - Point { x, .. } => println!("x is {x}"), +pub struct DraftPost { + content: String, } -``` - -Listing 18-23: Ignoring all fields of a `Point` except for `x` by using `..` - -We list the `x` value and then just include the `..` pattern. This is quicker -than having to list `y: _` and `z: _`, particularly when we’re working with -structs that have lots of fields in situations where only one or two fields are -relevant. -The syntax `..` will expand to as many values as it needs to be. Listing 18-24 -shows how to use `..` with a tuple. - -Filename: src/main.rs - -``` -fn main() { - let numbers = (2, 4, 8, 16, 32); - - match numbers { - (first, .., last) => { - println!("Some numbers: {first}, {last}"); +impl Post { + pub fn new() -> DraftPost { + DraftPost { + content: String::new(), } } -} -``` -Listing 18-24: Matching only the first and last values in a tuple and ignoring -all other values - -In this code, the first and last values are matched with `first` and `last`. -The `..` will match and ignore everything in the middle. - -However, using `..` must be unambiguous. If it is unclear which values are -intended for matching and which should be ignored, Rust will give us an error. -Listing 18-25 shows an example of using `..` ambiguously, so it will not -compile. - -Filename: src/main.rs - -``` -fn main() { - let numbers = (2, 4, 8, 16, 32); + pub fn content(&self) -> &str { + &self.content + } +} - match numbers { - (.., second, ..) => { - println!("Some numbers: {second}"); - }, +impl DraftPost { + pub fn add_text(&mut self, text: &str) { + self.content.push_str(text); } } ``` -Listing 18-25: An attempt to use `..` in an ambiguous way +Listing 18-19: A `Post` with a `content` method and a `DraftPost` without a `content` method -When we compile this example, we get this error: +Both the `Post` and `DraftPost` structs have a private `content` field that +stores the blog post text. The structs no longer have the `state` field because +we’re moving the encoding of the state to the types of the structs. The `Post` +struct will represent a published post, and it has a `content` method that +returns the `content`. -``` -error: `..` can only be used once per tuple pattern - --> src/main.rs:5:22 - | -5 | (.., second, ..) => { - | -- ^^ can only be used once per tuple pattern - | | - | previously used here -``` +We still have a `Post::new` function, but instead of returning an instance of +`Post`, it returns an instance of `DraftPost`. Because `content` is private and +there aren’t any functions that return `Post`, it’s not possible to create an +instance of `Post` right now. -It’s impossible for Rust to determine how many values in the tuple to ignore -before matching a value with `second` and then how many further values to -ignore thereafter. This code could mean that we want to ignore `2`, bind -`second` to `4`, and then ignore `8`, `16`, and `32`; or that we want to ignore -`2` and `4`, bind `second` to `8`, and then ignore `16` and `32`; and so forth. -The variable name `second` doesn’t mean anything special to Rust, so we get a -compiler error because using `..` in two places like this is ambiguous. +The `DraftPost` struct has an `add_text` method, so we can add text to +`content` as before, but note that `DraftPost` does not have a `content` method +defined! So now the program ensures that all posts start as draft posts, and +draft posts don’t have their content available for display. Any attempt to get +around these constraints will result in a compiler error. -### Extra Conditionals with Match Guards +<!-- Old headings. Do not remove or links may break. --> -A *match guard* is an additional `if` condition, specified after the pattern in -a `match` arm, that must also match for that arm to be chosen. Match guards are -useful for expressing more complex ideas than a pattern alone allows. +<a id="implementing-transitions-as-transformations-into-different-types"></a> -The condition can use variables created in the pattern. Listing 18-26 shows a -`match` where the first arm has the pattern `Some(x)` and also has a match -guard of `if x % 2 == 0` (which will be `true` if the number is even). +So, how do we get a published post? We want to enforce the rule that a draft +post has to be reviewed and approved before it can be published. A post in the +pending review state should still not display any content. Let’s implement +these constraints by adding another struct, `PendingReviewPost`, defining the +`request_review` method on `DraftPost` to return a `PendingReviewPost` and +defining an `approve` method on `PendingReviewPost` to return a `Post`, as +shown in Listing 18-20. -Filename: src/main.rs +src/lib.rs ``` -let num = Some(4); - -match num { - Some(x) if x % 2 == 0 => println!("The number {x} is even"), - Some(x) => println!("The number {x} is odd"), - None => (), -} -``` - -Listing 18-26: Adding a match guard to a pattern - -This example will print `The number 4 is even`. When `num` is compared to the -pattern in the first arm, it matches because `Some(4)` matches `Some(x)`. Then -the match guard checks whether the remainder of dividing `x` by 2 is equal to -0, and because it is, the first arm is selected. - -If `num` had been `Some(5)` instead, the match guard in the first arm would -have been `false` because the remainder of 5 divided by 2 is 1, which is not -equal to 0. Rust would then go to the second arm, which would match because the -second arm doesn’t have a match guard and therefore matches any `Some` variant. - -There is no way to express the `if x % 2 == 0` condition within a pattern, so -the match guard gives us the ability to express this logic. The downside of -this additional expressiveness is that the compiler doesn’t try to check for -exhaustiveness when match guard expressions are involved. - -In Listing 18-11, we mentioned that we could use match guards to solve our -pattern-shadowing problem. Recall that we created a new variable inside the -pattern in the `match` expression instead of using the variable outside the -`match`. That new variable meant we couldn’t test against the value of the -outer variable. Listing 18-27 shows how we can use a match guard to fix this -problem. - -Filename: src/main.rs - -``` -fn main() { - let x = Some(5); - let y = 10; - - match x { - Some(50) => println!("Got 50"), - Some(n) if n == y => println!("Matched, n = {n}"), - _ => println!("Default case, x = {:?}", x), +impl DraftPost { + // --snip-- + pub fn request_review(self) -> PendingReviewPost { + PendingReviewPost { + content: self.content, + } } - - println!("at the end: x = {:?}, y = {y}", x); } -``` - -Listing 18-27: Using a match guard to test for equality with an outer variable -This code will now print `Default case, x = Some(5)`. The pattern in the second -match arm doesn’t introduce a new variable `y` that would shadow the outer `y`, -meaning we can use the outer `y` in the match guard. Instead of specifying the -pattern as `Some(y)`, which would have shadowed the outer `y`, we specify -`Some(n)`. This creates a new variable `n` that doesn’t shadow anything because -there is no `n` variable outside the `match`. - -The match guard `if n == y` is not a pattern and therefore doesn’t introduce -new variables. This `y` *is* the outer `y` rather than a new shadowed `y`, and -we can look for a value that has the same value as the outer `y` by comparing -`n` to `y`. - -You can also use the *or* operator `|` in a match guard to specify multiple -patterns; the match guard condition will apply to all the patterns. Listing -18-28 shows the precedence when combining a pattern that uses `|` with a match -guard. The important part of this example is that the `if y` match guard -applies to `4`, `5`, *and* `6`, even though it might look like `if y` only -applies to `6`. - -Filename: src/main.rs - -``` -let x = 4; -let y = false; +pub struct PendingReviewPost { + content: String, +} -match x { - 4 | 5 | 6 if y => println!("yes"), - _ => println!("no"), +impl PendingReviewPost { + pub fn approve(self) -> Post { + Post { + content: self.content, + } + } } ``` -Listing 18-28: Combining multiple patterns with a match guard +Listing 18-20: A `PendingReviewPost` that gets created by calling `request_review` on `DraftPost` and an `approve` method that turns a `PendingReviewPost` into a published `Post` -The match condition states that the arm only matches if the value of `x` is -equal to `4`, `5`, or `6` *and* if `y` is `true`. When this code runs, the -pattern of the first arm matches because `x` is `4`, but the match guard `if y` -is `false`, so the first arm is not chosen. The code moves on to the second -arm, which does match, and this program prints `no`. The reason is that the -`if` condition applies to the whole pattern `4 | 5 | 6`, not just to the last -value `6`. In other words, the precedence of a match guard in relation to a -pattern behaves like this: +The `request_review` and `approve` methods take ownership of `self`, thus +consuming the `DraftPost` and `PendingReviewPost` instances and transforming +them into a `PendingReviewPost` and a published `Post`, respectively. This way, +we won’t have any lingering `DraftPost` instances after we’ve called +`request_review` on them, and so forth. The `PendingReviewPost` struct doesn’t +have a `content` method defined on it, so attempting to read its content +results in a compiler error, as with `DraftPost`. Because the only way to get a +published `Post` instance that does have a `content` method defined is to call +the `approve` method on a `PendingReviewPost`, and the only way to get a +`PendingReviewPost` is to call the `request_review` method on a `DraftPost`, +we’ve now encoded the blog post workflow into the type system. -``` -(4 | 5 | 6) if y => ... -``` +But we also have to make some small changes to `main`. The `request_review` and +`approve` methods return new instances rather than modifying the struct they’re +called on, so we need to add more `let post =` shadowing assignments to save +the returned instances. We also can’t have the assertions about the draft and +pending review posts’ contents be empty strings, nor do we need them: We can’t +compile code that tries to use the content of posts in those states any longer. +The updated code in `main` is shown in Listing 18-21. -rather than this: +src/main.rs ``` -4 | 5 | (6 if y) => ... -``` +use blog::Post; -After running the code, the precedence behavior is evident: if the match guard -were applied only to the final value in the list of values specified using the -`|` operator, the arm would have matched and the program would have printed -`yes`. +fn main() { + let mut post = Post::new(); -### @ Bindings + post.add_text("I ate a salad for lunch today"); -The *at* operator `@` lets us create a variable that holds a value at the same -time we’re testing that value for a pattern match. In Listing 18-29, we want to -test that a `Message::Hello` `id` field is within the range `3..=7`. We also -want to bind the value to the variable `id_variable` so we can use it in the -code associated with the arm. We could name this variable `id`, the same as the -field, but for this example we’ll use a different name. + let post = post.request_review(); -Filename: src/main.rs + let post = post.approve(); -``` -enum Message { - Hello { id: i32 }, -} - -let msg = Message::Hello { id: 5 }; - -match msg { - Message::Hello { - id: id_variable @ 3..=7, - } => println!("Found an id in range: {id_variable}"), - Message::Hello { id: 10..=12 } => { - println!("Found an id in another range") - } - Message::Hello { id } => println!("Some other id: {id}"), + assert_eq!("I ate a salad for lunch today", post.content()); } ``` -Listing 18-29: Using `@` to bind to a value in a pattern while also testing it +Listing 18-21: Modifications to `main` to use the new implementation of the blog post workflow -This example will print `Found an id in range: 5`. By specifying `id_variable -@` before the range `3..=7`, we’re capturing whatever value matched the range -while also testing that the value matched the range pattern. +The changes we needed to make to `main` to reassign `post` mean that this +implementation doesn’t quite follow the object-oriented state pattern anymore: +The transformations between the states are no longer encapsulated entirely +within the `Post` implementation. However, our gain is that invalid states are +now impossible because of the type system and the type checking that happens at +compile time! This ensures that certain bugs, such as display of the content of +an unpublished post, will be discovered before they make it to production. -In the second arm, where we only have a range specified in the pattern, the -code associated with the arm doesn’t have a variable that contains the actual -value of the `id` field. The `id` field’s value could have been 10, 11, or 12, -but the code that goes with that pattern doesn’t know which it is. The pattern -code isn’t able to use the value from the `id` field because we haven’t saved -the `id` value in a variable. +Try the tasks suggested at the start of this section on the `blog` crate as it +is after Listing 18-21 to see what you think about the design of this version +of the code. Note that some of the tasks might be completed already in this +design. -In the last arm, where we’ve specified a variable without a range, we do have -the value available to use in the arm’s code in a variable named `id`. The -reason is that we’ve used the struct field shorthand syntax. But we haven’t -applied any test to the value in the `id` field in this arm, as we did with the -first two arms: any value would match this pattern. - -Using `@` lets us test a value and save it in a variable within one pattern. +We’ve seen that even though Rust is capable of implementing object-oriented +design patterns, other patterns, such as encoding state into the type system, +are also available in Rust. These patterns have different trade-offs. Although +you might be very familiar with object-oriented patterns, rethinking the +problem to take advantage of Rust’s features can provide benefits, such as +preventing some bugs at compile time. Object-oriented patterns won’t always be +the best solution in Rust due to certain features, like ownership, that +object-oriented languages don’t have. ## Summary -Rust’s patterns are very useful in distinguishing between different kinds of -data. When used in `match` expressions, Rust ensures your patterns cover every -possible value, or your program won’t compile. Patterns in `let` statements and -function parameters make those constructs more useful, enabling the -destructuring of values into smaller parts at the same time as assigning to -variables. We can create simple or complex patterns to suit our needs. - -Next, for the penultimate chapter of the book, we’ll look at some advanced -aspects of a variety of Rust’s features. - +Regardless of whether you think Rust is an object-oriented language after +reading this chapter, you now know that you can use trait objects to get some +object-oriented features in Rust. Dynamic dispatch can give your code some +flexibility in exchange for a bit of runtime performance. You can use this +flexibility to implement object-oriented patterns that can help your code’s +maintainability. Rust also has other features, like ownership, that +object-oriented languages don’t have. An object-oriented pattern won’t always +be the best way to take advantage of Rust’s strengths, but it is an available +option. + +Next, we’ll look at patterns, which are another of Rust’s features that enable +lots of flexibility. We’ve looked at them briefly throughout the book but +haven’t seen their full capability yet. Let’s go! diff --git a/nostarch/chapter19.md b/nostarch/chapter19.md index 410e7eb62d..b7df52a9b4 100644 --- a/nostarch/chapter19.md +++ b/nostarch/chapter19.md @@ -6,1086 +6,661 @@ directory, so all fixes need to be made in `/src/`. [TOC] -# Advanced Features - -By now, you’ve learned the most commonly used parts of the Rust programming -language. Before we do one more project, in Chapter 20, we’ll look at a few -aspects of the language you might run into every once in a while, but may not -use every day. You can use this chapter as a reference for when you encounter -any unknowns. The features covered here are useful in very specific situations. -Although you might not reach for them often, we want to make sure you have a -grasp of all the features Rust has to offer. - -In this chapter, we’ll cover: - -* Unsafe Rust: how to opt out of some of Rust’s guarantees and take -responsibility for manually upholding those guarantees -* Advanced traits: associated types, default type parameters, fully qualified -syntax, supertraits, and the newtype pattern in relation to traits -* Advanced types: more about the newtype pattern, type aliases, the never type, -and dynamically sized types -* Advanced functions and closures: function pointers and returning closures -* Macros: ways to define code that defines more code at compile time - -It’s a panoply of Rust features with something for everyone! Let’s dive in! - -## Unsafe Rust - -All the code we’ve discussed so far has had Rust’s memory safety guarantees -enforced at compile time. However, Rust has a second language hidden inside it -that doesn’t enforce these memory safety guarantees: it’s called *unsafe Rust* -and works just like regular Rust, but gives us extra superpowers. - -Unsafe Rust exists because, by nature, static analysis is conservative. When -the compiler tries to determine whether or not code upholds the guarantees, -it’s better for it to reject some valid programs than to accept some invalid -programs. Although the code *might* be okay, if the Rust compiler doesn’t have -enough information to be confident, it will reject the code. In these cases, -you can use unsafe code to tell the compiler, “Trust me, I know what I’m -doing.” Be warned, however, that you use unsafe Rust at your own risk: if you -use unsafe code incorrectly, problems can occur due to memory unsafety, such as -null pointer dereferencing. - -Another reason Rust has an unsafe alter ego is that the underlying computer -hardware is inherently unsafe. If Rust didn’t let you do unsafe operations, you -couldn’t do certain tasks. Rust needs to allow you to do low-level systems -programming, such as directly interacting with the operating system or even -writing your own operating system. Working with low-level systems programming -is one of the goals of the language. Let’s explore what we can do with unsafe -Rust and how to do it. - -### Unsafe Superpowers - -To switch to unsafe Rust, use the `unsafe` keyword and then start a new block -that holds the unsafe code. You can take five actions in unsafe Rust that you -can’t in safe Rust, which we call *unsafe superpowers*. Those superpowers -include the ability to: - -1. Dereference a raw pointer -1. Call an unsafe function or method -1. Access or modify a mutable static variable -1. Implement an unsafe trait -1. Access fields of `union`s - -It’s important to understand that `unsafe` doesn’t turn off the borrow checker -or disable any of Rust’s other safety checks: if you use a reference in unsafe -code, it will still be checked. The `unsafe` keyword only gives you access to -these five features that are then not checked by the compiler for memory -safety. You’ll still get some degree of safety inside an unsafe block. - -In addition, `unsafe` does not mean the code inside the block is necessarily -dangerous or that it will definitely have memory safety problems: the intent is -that as the programmer, you’ll ensure the code inside an `unsafe` block will -access memory in a valid way. - -People are fallible and mistakes will happen, but by requiring these five -unsafe operations to be inside blocks annotated with `unsafe`, you’ll know that -any errors related to memory safety must be within an `unsafe` block. Keep -`unsafe` blocks small; you’ll be thankful later when you investigate memory -bugs. - -To isolate unsafe code as much as possible, it’s best to enclose such code -within a safe abstraction and provide a safe API, which we’ll discuss later in -the chapter when we examine unsafe functions and methods. Parts of the standard -library are implemented as safe abstractions over unsafe code that has been -audited. Wrapping unsafe code in a safe abstraction prevents uses of `unsafe` -from leaking out into all the places that you or your users might want to use -the functionality implemented with `unsafe` code, because using a safe -abstraction is safe. - -Let’s look at each of the five unsafe superpowers in turn. We’ll also look at -some abstractions that provide a safe interface to unsafe code. - -### Dereferencing a Raw Pointer - -In “Dangling References” on page XX, we mentioned that the compiler ensures -references are always valid. Unsafe Rust has two new types called *raw -pointers* that are similar to references. As with references, raw pointers can -be immutable or mutable and are written as `*const T` and `*mut T`, -respectively. The asterisk isn’t the dereference operator; it’s part of the -type name. In the context of raw pointers, *immutable* means that the pointer -can’t be directly assigned to after being dereferenced. - -Different from references and smart pointers, raw pointers: - -* Are allowed to ignore the borrowing rules by having both immutable and -mutable pointers or multiple mutable pointers to the same location -* Aren’t guaranteed to point to valid memory -* Are allowed to be null -* Don’t implement any automatic cleanup +# Patterns and Matching + +Patterns are a special syntax in Rust for matching against the structure of +types, both complex and simple. Using patterns in conjunction with `match` +expressions and other constructs gives you more control over a program’s +control flow. A pattern consists of some combination of the following: + +* Literals +* Destructured arrays, enums, structs, or tuples +* Variables +* Wildcards +* Placeholders + +Some example patterns include `x`, `(a, 3)`, and `Some(Color::Red)`. In the +contexts in which patterns are valid, these components describe the shape of +data. Our program then matches values against the patterns to determine whether +it has the correct shape of data to continue running a particular piece of code. + +To use a pattern, we compare it to some value. If the pattern matches the +value, we use the value parts in our code. Recall the `match` expressions in +Chapter 6 that used patterns, such as the coin-sorting machine example. If the +value fits the shape of the pattern, we can use the named pieces. If it +doesn’t, the code associated with the pattern won’t run. + +This chapter is a reference on all things related to patterns. We’ll cover the +valid places to use patterns, the difference between refutable and irrefutable +patterns, and the different kinds of pattern syntax that you might see. By the +end of the chapter, you’ll know how to use patterns to express many concepts in +a clear way. + +## All the Places Patterns Can Be Used + +Patterns pop up in a number of places in Rust, and you’ve been using them a lot +without realizing it! This section discusses all the places where patterns are +valid. + +### match Arms + +As discussed in Chapter 6, we use patterns in the arms of `match` expressions. +Formally, `match` expressions are defined as the keyword `match`, a value to +match on, and one or more match arms that consist of a pattern and an +expression to run if the value matches that arm’s pattern, like this: + +<!-- + Manually formatted rather than using Markdown intentionally: Markdown does not + support italicizing code in the body of a block like this! +--> -By opting out of having Rust enforce these guarantees, you can give up -guaranteed safety in exchange for greater performance or the ability to -interface with another language or hardware where Rust’s guarantees don’t apply. +<pre><code>match <em>VALUE</em> { + <em>PATTERN</em> => <em>EXPRESSION</em>, + <em>PATTERN</em> => <em>EXPRESSION</em>, + <em>PATTERN</em> => <em>EXPRESSION</em>, +}</code></pre> -Listing 19-1 shows how to create an immutable and a mutable raw pointer from -references. - -``` -let mut num = 5; +For example, here’s the `match` expression from Listing 6-5 that matches on an +`Option<i32>` value in the variable `x`: -let r1 = &num as *const i32; -let r2 = &mut num as *mut i32; +``` +match x { + None => None, + Some(i) => Some(i + 1), +} ``` -Listing 19-1: Creating raw pointers from references +The patterns in this `match` expression are the `None` and `Some(i)` to the +left of each arrow. -Notice that we don’t include the `unsafe` keyword in this code. We can create -raw pointers in safe code; we just can’t dereference raw pointers outside an -unsafe block, as you’ll see in a bit. +One requirement for `match` expressions is that they need to be exhaustive in +the sense that all possibilities for the value in the `match` expression must +be accounted for. One way to ensure that you’ve covered every possibility is to +have a catch-all pattern for the last arm: For example, a variable name +matching any value can never fail and thus covers every remaining case. -We’ve created raw pointers by using `as` to cast an immutable and a mutable -reference into their corresponding raw pointer types. Because we created them -directly from references guaranteed to be valid, we know these particular raw -pointers are valid, but we can’t make that assumption about just any raw -pointer. +The particular pattern `_` will match anything, but it never binds to a +variable, so it’s often used in the last match arm. The `_` pattern can be +useful when you want to ignore any value not specified, for example. We’ll +cover the `_` pattern in more detail in “Ignoring Values in a +Pattern” later in this chapter. -To demonstrate this, next we’ll create a raw pointer whose validity we can’t be -so certain of. Listing 19-2 shows how to create a raw pointer to an arbitrary -location in memory. Trying to use arbitrary memory is undefined: there might be -data at that address or there might not, the compiler might optimize the code -so there is no memory access, or the program might terminate with a -segmentation fault. Usually, there is no good reason to write code like this, -but it is possible. +### let Statements -``` -let address = 0x012345usize; -let r = address as *const i32; -``` - -Listing 19-2: Creating a raw pointer to an arbitrary memory address - -Recall that we can create raw pointers in safe code, but we can’t *dereference* -raw pointers and read the data being pointed to. In Listing 19-3, we use the -dereference operator `*` on a raw pointer that requires an `unsafe` block. +Prior to this chapter, we had only explicitly discussed using patterns with +`match` and `if let`, but in fact, we’ve used patterns in other places as well, +including in `let` statements. For example, consider this straightforward +variable assignment with `let`: ``` -let mut num = 5; - -let r1 = &num as *const i32; -let r2 = &mut num as *mut i32; - -unsafe { - println!("r1 is: {}", *r1); - println!("r2 is: {}", *r2); -} +let x = 5; ``` -Listing 19-3: Dereferencing raw pointers within an `unsafe` block - -Creating a pointer does no harm; it’s only when we try to access the value that -it points at that we might end up dealing with an invalid value. - -Note also that in Listings 19-1 and 19-3, we created `*const i32` and `*mut -i32` raw pointers that both pointed to the same memory location, where `num` is -stored. If we instead tried to create an immutable and a mutable reference to -`num`, the code would not have compiled because Rust’s ownership rules don’t -allow a mutable reference at the same time as any immutable references. With -raw pointers, we can create a mutable pointer and an immutable pointer to the -same location and change data through the mutable pointer, potentially creating -a data race. Be careful! +Every time you’ve used a `let` statement like this you’ve been using patterns, +although you might not have realized it! More formally, a `let` statement looks +like this: -With all of these dangers, why would you ever use raw pointers? One major use -case is when interfacing with C code, as you’ll see in “Calling an Unsafe -Function or Method” on page XX. Another case is when building up safe -abstractions that the borrow checker doesn’t understand. We’ll introduce unsafe -functions and then look at an example of a safe abstraction that uses unsafe -code. +<!-- + Manually formatted rather than using Markdown intentionally: Markdown does not + support italicizing code in the body of a block like this! +--> -### Calling an Unsafe Function or Method +<pre> +<code>let <em>PATTERN</em> = <em>EXPRESSION</em>;</code> +</pre> -The second type of operation you can perform in an unsafe block is calling -unsafe functions. Unsafe functions and methods look exactly like regular -functions and methods, but they have an extra `unsafe` before the rest of the -definition. The `unsafe` keyword in this context indicates the function has -requirements we need to uphold when we call this function, because Rust can’t -guarantee we’ve met these requirements. By calling an unsafe function within an -`unsafe` block, we’re saying that we’ve read this function’s documentation and -we take responsibility for upholding the function’s contracts. +In statements like `let x = 5;` with a variable name in the PATTERN slot, the +variable name is just a particularly simple form of a pattern. Rust compares +the expression against the pattern and assigns any names it finds. So, in the +`let x = 5;` example, `x` is a pattern that means “bind what matches here to +the variable `x`.” Because the name `x` is the whole pattern, this pattern +effectively means “bind everything to the variable `x`, whatever the value is.” -Here is an unsafe function named `dangerous` that doesn’t do anything in its -body: +To see the pattern-matching aspect of `let` more clearly, consider Listing +19-1, which uses a pattern with `let` to destructure a tuple. -``` -unsafe fn dangerous() {} -unsafe { - dangerous(); -} ``` - -We must call the `dangerous` function within a separate `unsafe` block. If we -try to call `dangerous` without the `unsafe` block, we’ll get an error: - -``` -error[E0133]: call to unsafe function is unsafe and requires -unsafe function or block - --> src/main.rs:4:5 - | -4 | dangerous(); - | ^^^^^^^^^^^ call to unsafe function - | - = note: consult the function's documentation for information on -how to avoid undefined behavior + let (x, y, z) = (1, 2, 3); ``` -With the `unsafe` block, we’re asserting to Rust that we’ve read the function’s -documentation, we understand how to use it properly, and we’ve verified that -we’re fulfilling the contract of the function. +Listing 19-1: Using a pattern to destructure a tuple and create three variables at once -Bodies of unsafe functions are effectively `unsafe` blocks, so to perform other -unsafe operations within an unsafe function, we don’t need to add another -`unsafe` block. +Here, we match a tuple against a pattern. Rust compares the value `(1, 2, 3)` +to the pattern `(x, y, z)` and sees that the value matches the pattern—that is, +it sees that the number of elements is the same in both—so Rust binds `1` to +`x`, `2` to `y`, and `3` to `z`. You can think of this tuple pattern as nesting +three individual variable patterns inside it. -#### Creating a Safe Abstraction over Unsafe Code +If the number of elements in the pattern doesn’t match the number of elements +in the tuple, the overall type won’t match and we’ll get a compiler error. For +example, Listing 19-2 shows an attempt to destructure a tuple with three +elements into two variables, which won’t work. -Just because a function contains unsafe code doesn’t mean we need to mark the -entire function as unsafe. In fact, wrapping unsafe code in a safe function is -a common abstraction. As an example, let’s study the `split_at_mut` function -from the standard library, which requires some unsafe code. We’ll explore how -we might implement it. This safe method is defined on mutable slices: it takes -one slice and makes it two by splitting the slice at the index given as an -argument. Listing 19-4 shows how to use `split_at_mut`. ``` -let mut v = vec![1, 2, 3, 4, 5, 6]; + let (x, y) = (1, 2, 3); +``` -let r = &mut v[..]; +Listing 19-2: Incorrectly constructing a pattern whose variables don’t match the number of elements in the tuple -let (a, b) = r.split_at_mut(3); +Attempting to compile this code results in this type error: -assert_eq!(a, &mut [1, 2, 3]); -assert_eq!(b, &mut [4, 5, 6]); ``` +$ cargo run + Compiling patterns v0.1.0 (file:///projects/patterns) +error[E0308]: mismatched types + --> src/main.rs:2:9 + | +2 | let (x, y) = (1, 2, 3); + | ^^^^^^ --------- this expression has type `({integer}, {integer}, {integer})` + | | + | expected a tuple with 3 elements, found one with 2 elements + | + = note: expected tuple `({integer}, {integer}, {integer})` + found tuple `(_, _)` -Listing 19-4: Using the safe `split_at_mut` function - -We can’t implement this function using only safe Rust. An attempt might look -something like Listing 19-5, which won’t compile. For simplicity, we’ll -implement `split_at_mut` as a function rather than a method and only for slices -of `i32` values rather than for a generic type `T`. - +For more information about this error, try `rustc --explain E0308`. +error: could not compile `patterns` (bin "patterns") due to 1 previous error ``` -fn split_at_mut( - values: &mut [i32], - mid: usize, -) -> (&mut [i32], &mut [i32]) { - let len = values.len(); - assert!(mid <= len); +To fix the error, we could ignore one or more of the values in the tuple using +`_` or `..`, as you’ll see in the “Ignoring Values in a +Pattern” section. If the problem +is that we have too many variables in the pattern, the solution is to make the +types match by removing variables so that the number of variables equals the +number of elements in the tuple. - (&mut values[..mid], &mut values[mid..]) -} -``` +### Conditional if let Expressions -Listing 19-5: An attempted implementation of `split_at_mut` using only safe Rust +In Chapter 6, we discussed how to use `if let` expressions mainly as a shorter +way to write the equivalent of a `match` that only matches one case. +Optionally, `if let` can have a corresponding `else` containing code to run if +the pattern in the `if let` doesn’t match. -This function first gets the total length of the slice. Then it asserts that -the index given as a parameter is within the slice by checking whether it’s -less than or equal to the length. The assertion means that if we pass an index -that is greater than the length to split the slice at, the function will panic -before it attempts to use that index. +Listing 19-3 shows that it’s also possible to mix and match `if let`, `else if`, and `else if let` expressions. Doing so gives us more flexibility than a +`match` expression in which we can express only one value to compare with the +patterns. Also, Rust doesn’t require that the conditions in a series of `if let`, `else if`, and `else if let` arms relate to each other. -Then we return two mutable slices in a tuple: one from the start of the -original slice to the `mid` index and another from `mid` to the end of the -slice. +The code in Listing 19-3 determines what color to make your background based on +a series of checks for several conditions. For this example, we’ve created +variables with hardcoded values that a real program might receive from user +input. -When we try to compile the code in Listing 19-5, we’ll get an error: +src/main.rs ``` -error[E0499]: cannot borrow `*values` as mutable more than once at a time - --> src/main.rs:9:31 - | -2 | values: &mut [i32], - | - let's call the lifetime of this reference `'1` -... -9 | (&mut values[..mid], &mut values[mid..]) - | --------------------------^^^^^^-------- - | | | | - | | | second mutable borrow occurs here - | | first mutable borrow occurs here - | returning this value requires that `*values` is borrowed for `'1` -``` - -Rust’s borrow checker can’t understand that we’re borrowing different parts of -the slice; it only knows that we’re borrowing from the same slice twice. -Borrowing different parts of a slice is fundamentally okay because the two -slices aren’t overlapping, but Rust isn’t smart enough to know this. When we -know code is okay, but Rust doesn’t, it’s time to reach for unsafe code. - -Listing 19-6 shows how to use an `unsafe` block, a raw pointer, and some calls -to unsafe functions to make the implementation of `split_at_mut` work. - -``` -use std::slice; - -fn split_at_mut( - values: &mut [i32], - mid: usize, -) -> (&mut [i32], &mut [i32]) { - 1 let len = values.len(); - 2 let ptr = values.as_mut_ptr(); - - 3 assert!(mid <= len); - - 4 unsafe { - ( - 5 slice::from_raw_parts_mut(ptr, mid), - 6 slice::from_raw_parts_mut(ptr.add(mid), len - mid), - ) +fn main() { + let favorite_color: Option<&str> = None; + let is_tuesday = false; + let age: Result<u8, _> = "34".parse(); + + if let Some(color) = favorite_color { + println!("Using your favorite color, {color}, as the background"); + } else if is_tuesday { + println!("Tuesday is green day!"); + } else if let Ok(age) = age { + if age > 30 { + println!("Using purple as the background color"); + } else { + println!("Using orange as the background color"); + } + } else { + println!("Using blue as the background color"); } } ``` -Listing 19-6: Using unsafe code in the implementation of the `split_at_mut` -function +Listing 19-3: Mixing `if let`, `else if`, `else if let`, and `else` -Recall from “The Slice Type” on page XX that a slice is a pointer to some data -and the length of the slice. We use the `len` method to get the length of a -slice [1] and the `as_mut_ptr` method to access the raw pointer of a slice [2]. -In this case, because we have a mutable slice to `i32` values, `as_mut_ptr` -returns a raw pointer with the type `*mut i32`, which we’ve stored in the -variable `ptr`. +If the user specifies a favorite color, that color is used as the background. +If no favorite color is specified and today is Tuesday, the background color is +green. Otherwise, if the user specifies their age as a string and we can parse +it as a number successfully, the color is either purple or orange depending on +the value of the number. If none of these conditions apply, the background +color is blue. -We keep the assertion that the `mid` index is within the slice [3]. Then we get -to the unsafe code [4]: the `slice::from_raw_parts_mut` function takes a raw -pointer and a length, and it creates a slice. We use it to create a slice that -starts from `ptr` and is `mid` items long [5]. Then we call the `add` method on -`ptr` with `mid` as an argument to get a raw pointer that starts at `mid`, and -we create a slice using that pointer and the remaining number of items after -`mid` as the length [6]. +This conditional structure lets us support complex requirements. With the +hardcoded values we have here, this example will print `Using purple as the background color`. -The function `slice::from_raw_parts_mut` is unsafe because it takes a raw -pointer and must trust that this pointer is valid. The `add` method on raw -pointers is also unsafe because it must trust that the offset location is also -a valid pointer. Therefore, we had to put an `unsafe` block around our calls to -`slice::from_raw_parts_mut` and `add` so we could call them. By looking at the -code and by adding the assertion that `mid` must be less than or equal to -`len`, we can tell that all the raw pointers used within the `unsafe` block -will be valid pointers to data within the slice. This is an acceptable and -appropriate use of `unsafe`. +You can see that `if let` can also introduce new variables that shadow existing +variables in the same way that `match` arms can: The line `if let Ok(age) = age` +introduces a new `age` variable that contains the value inside the `Ok` variant, +shadowing the existing `age` variable. This means we need to place the `if age > 30` condition within that block: We can’t combine these two conditions into `if let Ok(age) = age && age > 30`. The new `age` we want to compare to 30 isn’t +valid until the new scope starts with the curly bracket. -Note that we don’t need to mark the resultant `split_at_mut` function as -`unsafe`, and we can call this function from safe Rust. We’ve created a safe -abstraction to the unsafe code with an implementation of the function that uses -`unsafe` code in a safe way, because it creates only valid pointers from the -data this function has access to. +The downside of using `if let` expressions is that the compiler doesn’t check +for exhaustiveness, whereas with `match` expressions it does. If we omitted the +last `else` block and therefore missed handling some cases, the compiler would +not alert us to the possible logic bug. -In contrast, the use of `slice::from_raw_parts_mut` in Listing 19-7 would -likely crash when the slice is used. This code takes an arbitrary memory -location and creates a slice 10,000 items long. +### while let Conditional Loops -``` -use std::slice; +Similar in construction to `if let`, the `while let` conditional loop allows a +`while` loop to run for as long as a pattern continues to match. In Listing +19-4, we show a `while let` loop that waits on messages sent between threads, +but in this case checking a `Result` instead of an `Option`. -let address = 0x01234usize; -let r = address as *mut i32; -let values: &[i32] = unsafe { - slice::from_raw_parts_mut(r, 10000) -}; ``` + let (tx, rx) = std::sync::mpsc::channel(); + std::thread::spawn(move || { + for val in [1, 2, 3] { + tx.send(val).unwrap(); + } + }); -Listing 19-7: Creating a slice from an arbitrary memory location + while let Ok(value) = rx.recv() { + println!("{value}"); + } +``` -We don’t own the memory at this arbitrary location, and there is no guarantee -that the slice this code creates contains valid `i32` values. Attempting to use -`values` as though it’s a valid slice results in undefined behavior. +Listing 19-4: Using a `while let` loop to print values for as long as `rx.recv()` returns `Ok` -#### Using extern Functions to Call External Code +This example prints `1`, `2`, and then `3`. The `recv` method takes the first +message out of the receiver side of the channel and returns an `Ok(value)`. When +we first saw `recv` back in Chapter 16, we unwrapped the error directly, or +we interacted with it as an iterator using a `for` loop. As Listing 19-4 shows, +though, we can also use `while let`, because the `recv` method returns an `Ok` +each time a message arrives, as long as the sender exists, and then produces an +`Err` once the sender side disconnects. -Sometimes your Rust code might need to interact with code written in another -language. For this, Rust has the keyword `extern` that facilitates the creation -and use of a *Foreign Function Interface* *(FFI)*, which is a way for a -programming language to define functions and enable a different (foreign) -programming language to call those functions. +### for Loops -Listing 19-8 demonstrates how to set up an integration with the `abs` function -from the C standard library. Functions declared within `extern` blocks are -always unsafe to call from Rust code. The reason is that other languages don’t -enforce Rust’s rules and guarantees, and Rust can’t check them, so -responsibility falls on the programmer to ensure safety. +In a `for` loop, the value that directly follows the keyword `for` is a +pattern. For example, in `for x in y`, the `x` is the pattern. Listing 19-5 +demonstrates how to use a pattern in a `for` loop to destructure, or break +apart, a tuple as part of the `for` loop. -Filename: src/main.rs ``` -extern "C" { - fn abs(input: i32) -> i32; -} + let v = vec!['a', 'b', 'c']; -fn main() { - unsafe { - println!( - "Absolute value of -3 according to C: {}", - abs(-3) - ); + for (index, value) in v.iter().enumerate() { + println!("{value} is at index {index}"); } -} ``` -Listing 19-8: Declaring and calling an `extern` function defined in another -language - -Within the `extern "C"` block, we list the names and signatures of external -functions from another language we want to call. The `"C"` part defines which -*application binary interface* *(ABI)* the external function uses: the ABI -defines how to call the function at the assembly level. The `"C"` ABI is the -most common and follows the C programming language’s ABI. - -> ### Calling Rust Functions from Other Languages -> -> We can also use `extern` to create an interface that allows other languages -to call Rust functions. Instead of creating a whole `extern` block, we add the -`extern` keyword and specify the ABI to use just before the `fn` keyword for -the relevant function. We also need to add a `#[no_mangle]` annotation to tell -the Rust compiler not to mangle the name of this function. *Mangling* is when a -compiler changes the name we’ve given a function to a different name that -contains more information for other parts of the compilation process to consume -but is less human readable. Every programming language compiler mangles names -slightly differently, so for a Rust function to be nameable by other languages, -we must disable the Rust compiler’s name mangling. -> -> In the following example, we make the `call_from_c` function accessible from -C code, after it’s compiled to a shared library and linked from C: -> -> ``` -> #[no_mangle] -> pub extern "C" fn call_from_c() { -> println!("Just called a Rust function from C!"); -> } -> ``` -> -> This usage of `extern` does not require `unsafe`. - -### Accessing or Modifying a Mutable Static Variable - -In this book, we’ve not yet talked about global variables, which Rust does -support but can be problematic with Rust’s ownership rules. If two threads are -accessing the same mutable global variable, it can cause a data race. - -In Rust, global variables are called *static* variables. Listing 19-9 shows an -example declaration and use of a static variable with a string slice as a value. - -Filename: src/main.rs - -``` -static HELLO_WORLD: &str = "Hello, world!"; +Listing 19-5: Using a pattern in a `for` loop to destructure a tuple + +The code in Listing 19-5 will print the following: -fn main() { - println!("value is: {HELLO_WORLD}"); -} +``` +$ cargo run + Compiling patterns v0.1.0 (file:///projects/patterns) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.52s + Running `target/debug/patterns` +a is at index 0 +b is at index 1 +c is at index 2 ``` -Listing 19-9: Defining and using an immutable static variable +We adapt an iterator using the `enumerate` method so that it produces a value +and the index for that value, placed into a tuple. The first value produced is +the tuple `(0, 'a')`. When this value is matched to the pattern `(index, value)`, index will be `0` and value will be `'a'`, printing the first line of +the output. -Static variables are similar to constants, which we discussed in “Constants” on -page XX. The names of static variables are in `SCREAMING_SNAKE_CASE` by -convention. Static variables can only store references with the `'static` -lifetime, which means the Rust compiler can figure out the lifetime and we -aren’t required to annotate it explicitly. Accessing an immutable static -variable is safe. +### Function Parameters -A subtle difference between constants and immutable static variables is that -values in a static variable have a fixed address in memory. Using the value -will always access the same data. Constants, on the other hand, are allowed to -duplicate their data whenever they’re used. Another difference is that static -variables can be mutable. Accessing and modifying mutable static variables is -*unsafe*. Listing 19-10 shows how to declare, access, and modify a mutable -static variable named `COUNTER`. +Function parameters can also be patterns. The code in Listing 19-6, which +declares a function named `foo` that takes one parameter named `x` of type +`i32`, should by now look familiar. -Filename: src/main.rs ``` -static mut COUNTER: u32 = 0; - -fn add_to_count(inc: u32) { - unsafe { - COUNTER += inc; - } -} - -fn main() { - add_to_count(3); - - unsafe { - println!("COUNTER: {COUNTER}"); - } +fn foo(x: i32) { + // code goes here } ``` -Listing 19-10: Reading from or writing to a mutable static variable is unsafe. +Listing 19-6: A function signature using patterns in the parameters -As with regular variables, we specify mutability using the `mut` keyword. Any -code that reads or writes from `COUNTER` must be within an `unsafe` block. This -code compiles and prints `COUNTER: 3` as we would expect because it’s single -threaded. Having multiple threads access `COUNTER` would likely result in data -races. +The `x` part is a pattern! As we did with `let`, we could match a tuple in a +function’s arguments to the pattern. Listing 19-7 splits the values in a tuple +as we pass it to a function. -With mutable data that is globally accessible, it’s difficult to ensure there -are no data races, which is why Rust considers mutable static variables to be -unsafe. Where possible, it’s preferable to use the concurrency techniques and -thread-safe smart pointers we discussed in Chapter 16 so the compiler checks -that data access from different threads is done safely. - -### Implementing an Unsafe Trait - -We can use `unsafe` to implement an unsafe trait. A trait is unsafe when at -least one of its methods has some invariant that the compiler can’t verify. We -declare that a trait is `unsafe` by adding the `unsafe` keyword before `trait` -and marking the implementation of the trait as `unsafe` too, as shown in -Listing 19-11. +src/main.rs ``` -unsafe trait Foo { - // methods go here +fn print_coordinates(&(x, y): &(i32, i32)) { + println!("Current location: ({x}, {y})"); } -unsafe impl Foo for i32 { - // method implementations go here +fn main() { + let point = (3, 5); + print_coordinates(&point); } ``` -Listing 19-11: Defining and implementing an unsafe trait - -By using `unsafe impl`, we’re promising that we’ll uphold the invariants that -the compiler can’t verify. - -As an example, recall the `Send` and `Sync` marker traits we discussed in -“Extensible Concurrency with the Send and Sync Traits” on page XX: the compiler -implements these traits automatically if our types are composed entirely of -`Send` and `Sync` types. If we implement a type that contains a type that is -not `Send` or `Sync`, such as raw pointers, and we want to mark that type as -`Send` or `Sync`, we must use `unsafe`. Rust can’t verify that our type upholds -the guarantees that it can be safely sent across threads or accessed from -multiple threads; therefore, we need to do those checks manually and indicate -as such with `unsafe`. +Listing 19-7: A function with parameters that destructure a tuple -### Accessing Fields of a Union +This code prints `Current location: (3, 5)`. The values `&(3, 5)` match the +pattern `&(x, y)`, so `x` is the value `3` and `y` is the value `5`. -The final action that works only with `unsafe` is accessing fields of a union. -A `union` is similar to a `struct`, but only one declared field is used in a -particular instance at one time. Unions are primarily used to interface with -unions in C code. Accessing union fields is unsafe because Rust can’t guarantee -the type of the data currently being stored in the union instance. You can -learn more about unions in the Rust Reference at -*https://doc.rust-lang.org/reference/items/unions.html**.* +We can also use patterns in closure parameter lists in the same way as in +function parameter lists because closures are similar to functions, as +discussed in Chapter 13. -### When to Use Unsafe Code +At this point, you’ve seen several ways to use patterns, but patterns don’t +work the same in every place we can use them. In some places, the patterns must +be irrefutable; in other circumstances, they can be refutable. We’ll discuss +these two concepts next. -Using `unsafe` to use one of the five superpowers just discussed isn’t wrong or -even frowned upon, but it is trickier to get `unsafe` code correct because the -compiler can’t help uphold memory safety. When you have a reason to use -`unsafe` code, you can do so, and having the explicit `unsafe` annotation makes -it easier to track down the source of problems when they occur. +## Refutability: Whether a Pattern Might Fail to Match -## Advanced Traits +Patterns come in two forms: refutable and irrefutable. Patterns that will match +for any possible value passed are *irrefutable*. An example would be `x` in the +statement `let x = 5;` because `x` matches anything and therefore cannot fail +to match. Patterns that can fail to match for some possible value are +*refutable*. An example would be `Some(x)` in the expression `if let Some(x) = a_value` because if the value in the `a_value` variable is `None` rather than +`Some`, the `Some(x)` pattern will not match. -We first covered traits in “Traits: Defining Shared Behavior” on page XX, but -we didn’t discuss the more advanced details. Now that you know more about Rust, -we can get into the nitty-gritty. +Function parameters, `let` statements, and `for` loops can only accept +irrefutable patterns because the program cannot do anything meaningful when +values don’t match. The `if let` and `while let` expressions and the +`let...else` statement accept refutable and irrefutable patterns, but the +compiler warns against irrefutable patterns because, by definition, they’re +intended to handle possible failure: The functionality of a conditional is in +its ability to perform differently depending on success or failure. -### Associated Types +In general, you shouldn’t have to worry about the distinction between refutable +and irrefutable patterns; however, you do need to be familiar with the concept +of refutability so that you can respond when you see it in an error message. In +those cases, you’ll need to change either the pattern or the construct you’re +using the pattern with, depending on the intended behavior of the code. -*Associated types* connect a type placeholder with a trait such that the trait -method definitions can use these placeholder types in their signatures. The -implementor of a trait will specify the concrete type to be used instead of the -placeholder type for the particular implementation. That way, we can define a -trait that uses some types without needing to know exactly what those types are -until the trait is implemented. +Let’s look at an example of what happens when we try to use a refutable pattern +where Rust requires an irrefutable pattern and vice versa. Listing 19-8 shows a +`let` statement, but for the pattern, we’ve specified `Some(x)`, a refutable +pattern. As you might expect, this code will not compile. -We’ve described most of the advanced features in this chapter as being rarely -needed. Associated types are somewhere in the middle: they’re used more rarely -than features explained in the rest of the book but more commonly than many of -the other features discussed in this chapter. - -One example of a trait with an associated type is the `Iterator` trait that the -standard library provides. The associated type is named `Item` and stands in -for the type of the values the type implementing the `Iterator` trait is -iterating over. The definition of the `Iterator` trait is as shown in Listing -19-12. ``` -pub trait Iterator { - type Item; - - fn next(&mut self) -> Option<Self::Item>; -} + let Some(x) = some_option_value; ``` -Listing 19-12: The definition of the `Iterator` trait that has an associated -type `Item` +Listing 19-8: Attempting to use a refutable pattern with `let` -The type `Item` is a placeholder, and the `next` method’s definition shows that -it will return values of type `Option<Self::Item>`. Implementors of the -`Iterator` trait will specify the concrete type for `Item`, and the `next` -method will return an `Option` containing a value of that concrete type. - -Associated types might seem like a similar concept to generics, in that the -latter allow us to define a function without specifying what types it can -handle. To examine the difference between the two concepts, we’ll look at an -implementation of the `Iterator` trait on a type named `Counter` that specifies -the `Item` type is `u32`: - -Filename: src/lib.rs +If `some_option_value` were a `None` value, it would fail to match the pattern +`Some(x)`, meaning the pattern is refutable. However, the `let` statement can +only accept an irrefutable pattern because there is nothing valid the code can +do with a `None` value. At compile time, Rust will complain that we’ve tried to +use a refutable pattern where an irrefutable pattern is required: ``` -impl Iterator for Counter { - type Item = u32; - - fn next(&mut self) -> Option<Self::Item> { - --snip-- -``` - -This syntax seems comparable to that of generics. So why not just define the -`Iterator` trait with generics, as shown in Listing 19-13? +$ cargo run + Compiling patterns v0.1.0 (file:///projects/patterns) +error[E0005]: refutable pattern in local binding + --> src/main.rs:3:9 + | +3 | let Some(x) = some_option_value; + | ^^^^^^^ pattern `None` not covered + | + = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant + = note: for more information, visit https://doc.rust-lang.org/book/ch19-02-refutability.html + = note: the matched value is of type `Option<i32>` +help: you might want to use `let else` to handle the variant that isn't matched + | +3 | let Some(x) = some_option_value else { todo!() }; + | ++++++++++++++++ +For more information about this error, try `rustc --explain E0005`. +error: could not compile `patterns` (bin "patterns") due to 1 previous error ``` -pub trait Iterator<T> { - fn next(&mut self) -> Option<T>; -} -``` - -Listing 19-13: A hypothetical definition of the `Iterator` trait using generics - -The difference is that when using generics, as in Listing 19-13, we must -annotate the types in each implementation; because we can also implement -`Iterator<``String``> for Counter` or any other type, we could have multiple -implementations of `Iterator` for `Counter`. In other words, when a trait has a -generic parameter, it can be implemented for a type multiple times, changing -the concrete types of the generic type parameters each time. When we use the -`next` method on `Counter`, we would have to provide type annotations to -indicate which implementation of `Iterator` we want to use. - -With associated types, we don’t need to annotate types because we can’t -implement a trait on a type multiple times. In Listing 19-12 with the -definition that uses associated types, we can choose what the type of `Item` -will be only once because there can be only one `impl Iterator for Counter`. We -don’t have to specify that we want an iterator of `u32` values everywhere we -call `next` on `Counter`. - -Associated types also become part of the trait’s contract: implementors of the -trait must provide a type to stand in for the associated type placeholder. -Associated types often have a name that describes how the type will be used, -and documenting the associated type in the API documentation is a good practice. -### Default Generic Type Parameters and Operator Overloading +Because we didn’t cover (and couldn’t cover!) every valid value with the +pattern `Some(x)`, Rust rightfully produces a compiler error. -When we use generic type parameters, we can specify a default concrete type for -the generic type. This eliminates the need for implementors of the trait to -specify a concrete type if the default type works. You specify a default type -when declaring a generic type with the `<`PlaceholderType`=`ConcreteType`>` -syntax. +If we have a refutable pattern where an irrefutable pattern is needed, we can +fix it by changing the code that uses the pattern: Instead of using `let`, we +can use `let else`. Then, if the pattern doesn’t match, the code will just skip +the code in the curly brackets, giving it a way to continue validly. Listing +19-9 shows how to fix the code in Listing 19-8. -A great example of a situation where this technique is useful is with *operator -overloading*, in which you customize the behavior of an operator (such as `+`) -in particular situations. - -Rust doesn’t allow you to create your own operators or overload arbitrary -operators. But you can overload the operations and corresponding traits listed -in `std::ops` by implementing the traits associated with the operator. For -example, in Listing 19-14 we overload the `+` operator to add two `Point` -instances together. We do this by implementing the `Add` trait on a `Point` -struct. - -Filename: src/main.rs ``` -use std::ops::Add; - -#[derive(Debug, Copy, Clone, PartialEq)] -struct Point { - x: i32, - y: i32, -} - -impl Add for Point { - type Output = Point; - - fn add(self, other: Point) -> Point { - Point { - x: self.x + other.x, - y: self.y + other.y, - } - } -} - -fn main() { - assert_eq!( - Point { x: 1, y: 0 } + Point { x: 2, y: 3 }, - Point { x: 3, y: 3 } - ); -} + let Some(x) = some_option_value else { + return; + }; ``` -Listing 19-14: Implementing the `Add` trait to overload the `+` operator for -`Point` instances +Listing 19-9: Using `let...else` and a block with refutable patterns instead of `let` -The `add` method adds the `x` values of two `Point` instances and the `y` -values of two `Point` instances to create a new `Point`. The `Add` trait has an -associated type named `Output` that determines the type returned from the `add` -method. +We’ve given the code an out! This code is perfectly valid, although it means we +cannot use an irrefutable pattern without receiving a warning. If we give +`let...else` a pattern that will always match, such as `x`, as shown in Listing +19-10, the compiler will give a warning. -The default generic type in this code is within the `Add` trait. Here is its -definition: ``` -trait Add<Rhs=Self> { - type Output; - - fn add(self, rhs: Rhs) -> Self::Output; -} + let x = 5 else { + return; + }; ``` -This code should look generally familiar: a trait with one method and an -associated type. The new part is `Rhs=Self`: this syntax is called *default -type parameters*. The `Rhs` generic type parameter (short for “right-hand -side”) defines the type of the `rhs` parameter in the `add` method. If we don’t -specify a concrete type for `Rhs` when we implement the `Add` trait, the type -of `Rhs` will default to `Self`, which will be the type we’re implementing -`Add` on. +Listing 19-10: Attempting to use an irrefutable pattern with `let...else` -When we implemented `Add` for `Point`, we used the default for `Rhs` because we -wanted to add two `Point` instances. Let’s look at an example of implementing -the `Add` trait where we want to customize the `Rhs` type rather than using the -default. - -We have two structs, `Millimeters` and `Meters`, holding values in different -units. This thin wrapping of an existing type in another struct is known as the -*newtype pattern*, which we describe in more detail in “Using the Newtype -Pattern to Implement External Traits on External Types” on page XX. We want to -add values in millimeters to values in meters and have the implementation of -`Add` do the conversion correctly. We can implement `Add` for `Millimeters` -with `Meters` as the `Rhs`, as shown in Listing 19-15. - -Filename: src/lib.rs +Rust complains that it doesn’t make sense to use `let...else` with an +irrefutable pattern: ``` -use std::ops::Add; - -struct Millimeters(u32); -struct Meters(u32); - -impl Add<Meters> for Millimeters { - type Output = Millimeters; +$ cargo run + Compiling patterns v0.1.0 (file:///projects/patterns) +warning: irrefutable `let...else` pattern + --> src/main.rs:2:5 + | +2 | let x = 5 else { + | ^^^^^^^^^ + | + = note: this pattern will always match, so the `else` clause is useless + = help: consider removing the `else` clause + = note: `#[warn(irrefutable_let_patterns)]` on by default - fn add(self, other: Meters) -> Millimeters { - Millimeters(self.0 + (other.0 * 1000)) - } -} +warning: `patterns` (bin "patterns") generated 1 warning + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.39s + Running `target/debug/patterns` ``` -Listing 19-15: Implementing the `Add` trait on `Millimeters` to add -`Millimeters` and `Meters` +For this reason, match arms must use refutable patterns, except for the last +arm, which should match any remaining values with an irrefutable pattern. Rust +allows us to use an irrefutable pattern in a `match` with only one arm, but +this syntax isn’t particularly useful and could be replaced with a simpler +`let` statement. -To add `Millimeters` and `Meters`, we specify `impl Add<Meters>` to set the -value of the `Rhs` type parameter instead of using the default of `Self`. +Now that you know where to use patterns and the difference between refutable +and irrefutable patterns, let’s cover all the syntax we can use to create +patterns. -You’ll use default type parameters in two main ways: +## Pattern Syntax -1. To extend a type without breaking existing code -1. To allow customization in specific cases most users won’t need +In this section, we gather all the syntax that is valid in patterns and discuss +why and when you might want to use each one. -The standard library’s `Add` trait is an example of the second purpose: -usually, you’ll add two like types, but the `Add` trait provides the ability to -customize beyond that. Using a default type parameter in the `Add` trait -definition means you don’t have to specify the extra parameter most of the -time. In other words, a bit of implementation boilerplate isn’t needed, making -it easier to use the trait. +### Matching Literals -The first purpose is similar to the second but in reverse: if you want to add a -type parameter to an existing trait, you can give it a default to allow -extension of the functionality of the trait without breaking the existing -implementation code. - -### Disambiguating Between Methods with the Same Name - -Nothing in Rust prevents a trait from having a method with the same name as -another trait’s method, nor does Rust prevent you from implementing both traits -on one type. It’s also possible to implement a method directly on the type with -the same name as methods from traits. - -When calling methods with the same name, you’ll need to tell Rust which one you -want to use. Consider the code in Listing 19-16 where we’ve defined two traits, -`Pilot` and `Wizard`, that both have a method called `fly`. We then implement -both traits on a type `Human` that already has a method named `fly` implemented -on it. Each `fly` method does something different. - -Filename: src/main.rs +As you saw in Chapter 6, you can match patterns against literals directly. The +following code gives some examples: ``` -trait Pilot { - fn fly(&self); -} - -trait Wizard { - fn fly(&self); -} - -struct Human; - -impl Pilot for Human { - fn fly(&self) { - println!("This is your captain speaking."); - } -} + let x = 1; -impl Wizard for Human { - fn fly(&self) { - println!("Up!"); + match x { + 1 => println!("one"), + 2 => println!("two"), + 3 => println!("three"), + _ => println!("anything"), } -} - -impl Human { - fn fly(&self) { - println!("*waving arms furiously*"); - } -} ``` -Listing 19-16: Two traits are defined to have a `fly` method and are -implemented on the `Human` type, and a `fly` method is implemented on `Human` -directly. +This code prints `one` because the value in `x` is `1`. This syntax is useful +when you want your code to take an action if it gets a particular concrete +value. -When we call `fly` on an instance of `Human`, the compiler defaults to calling -the method that is directly implemented on the type, as shown in Listing 19-17. +### Matching Named Variables -Filename: src/main.rs +Named variables are irrefutable patterns that match any value, and we’ve used +them many times in this book. However, there is a complication when you use +named variables in `match`, `if let`, or `while let` expressions. Because each +of these kinds of expressions starts a new scope, variables declared as part of +a pattern inside these expressions will shadow those with the same name outside +the constructs, as is the case with all variables. In Listing 19-11, we declare +a variable named `x` with the value `Some(5)` and a variable `y` with the value +`10`. We then create a `match` expression on the value `x`. Look at the +patterns in the match arms and `println!` at the end, and try to figure out +what the code will print before running this code or reading further. + +src/main.rs ``` -fn main() { - let person = Human; - person.fly(); -} -``` + let x = Some(5); + let y = 10; -Listing 19-17: Calling `fly` on an instance of `Human` + match x { + Some(50) => println!("Got 50"), + Some(y) => println!("Matched, y = {y}"), + _ => println!("Default case, x = {x:?}"), + } -Running this code will print `*waving arms furiously*`, showing that Rust -called the `fly` method implemented on `Human` directly. + println!("at the end: x = {x:?}, y = {y}"); +``` -To call the `fly` methods from either the `Pilot` trait or the `Wizard` trait, -we need to use more explicit syntax to specify which `fly` method we mean. -Listing 19-18 demonstrates this syntax. +Listing 19-11: A `match` expression with an arm that introduces a new variable which shadows an existing variable `y` -Filename: src/main.rs +Let’s walk through what happens when the `match` expression runs. The pattern +in the first match arm doesn’t match the defined value of `x`, so the code +continues. -``` -fn main() { - let person = Human; - Pilot::fly(&person); - Wizard::fly(&person); - person.fly(); -} -``` +The pattern in the second match arm introduces a new variable named `y` that +will match any value inside a `Some` value. Because we’re in a new scope inside +the `match` expression, this is a new `y` variable, not the `y` we declared at +the beginning with the value `10`. This new `y` binding will match any value +inside a `Some`, which is what we have in `x`. Therefore, this new `y` binds to +the inner value of the `Some` in `x`. That value is `5`, so the expression for +that arm executes and prints `Matched, y = 5`. -Listing 19-18: Specifying which trait’s `fly` method we want to call +If `x` had been a `None` value instead of `Some(5)`, the patterns in the first +two arms wouldn’t have matched, so the value would have matched to the +underscore. We didn’t introduce the `x` variable in the pattern of the +underscore arm, so the `x` in the expression is still the outer `x` that hasn’t +been shadowed. In this hypothetical case, the `match` would print `Default case, x = None`. -Specifying the trait name before the method name clarifies to Rust which -implementation of `fly` we want to call. We could also write -`Human::fly(&person)`, which is equivalent to the `person.fly()` that we used -in Listing 19-18, but this is a bit longer to write if we don’t need to -disambiguate. +When the `match` expression is done, its scope ends, and so does the scope of +the inner `y`. The last `println!` produces `at the end: x = Some(5), y = 10`. -Running this code prints the following: +To create a `match` expression that compares the values of the outer `x` and +`y`, rather than introducing a new variable that shadows the existing `y` +variable, we would need to use a match guard conditional instead. We’ll talk +about match guards later in the “Adding Conditionals with Match +Guards” section. -``` -This is your captain speaking. -Up! -*waving arms furiously* -``` +<!-- Old headings. Do not remove or links may break. --> -Because the `fly` method takes a `self` parameter, if we had two *types* that -both implement one *trait*, Rust could figure out which implementation of a -trait to use based on the type of `self`. +<a id="multiple-patterns"></a> -However, associated functions that are not methods don’t have a `self` -parameter. When there are multiple types or traits that define non-method -functions with the same function name, Rust doesn’t always know which type you -mean unless you use fully qualified syntax. For example, in Listing 19-19 we -create a trait for an animal shelter that wants to name all baby dogs Spot. We -make an `Animal` trait with an associated non-method function `baby_name`. The -`Animal` trait is implemented for the struct `Dog`, on which we also provide an -associated non-method function `baby_name` directly. +### Matching Multiple Patterns -Filename: src/main.rs +In `match` expressions, you can match multiple patterns using the `|` syntax, +which is the pattern *or* operator. For example, in the following code, we match +the value of `x` against the match arms, the first of which has an *or* option, +meaning if the value of `x` matches either of the values in that arm, that +arm’s code will run: ``` -trait Animal { - fn baby_name() -> String; -} + let x = 1; -struct Dog; - -impl Dog { - fn baby_name() -> String { - String::from("Spot") + match x { + 1 | 2 => println!("one or two"), + 3 => println!("three"), + _ => println!("anything"), } -} - -impl Animal for Dog { - fn baby_name() -> String { - String::from("puppy") - } -} - -fn main() { - println!("A baby dog is called a {}", Dog::baby_name()); -} ``` -Listing 19-19: A trait with an associated function and a type with an -associated function of the same name that also implements the trait +This code prints `one or two`. -We implement the code for naming all puppies Spot in the `baby_name` associated -function that is defined on `Dog`. The `Dog` type also implements the trait -`Animal`, which describes characteristics that all animals have. Baby dogs are -called puppies, and that is expressed in the implementation of the `Animal` -trait on `Dog` in the `baby_name` function associated with the `Animal` trait. +### Matching Ranges of Values with ..= -In `main`, we call the `Dog::baby_name` function, which calls the associated -function defined on `Dog` directly. This code prints the following: +The `..=` syntax allows us to match to an inclusive range of values. In the +following code, when a pattern matches any of the values within the given +range, that arm will execute: ``` -A baby dog is called a Spot -``` - -This output isn’t what we wanted. We want to call the `baby_name` function that -is part of the `Animal` trait that we implemented on `Dog` so the code prints -`A baby dog is called a puppy`. The technique of specifying the trait name that -we used in Listing 19-18 doesn’t help here; if we change `main` to the code in -Listing 19-20, we’ll get a compilation error. - -Filename: src/main.rs + let x = 5; + match x { + 1..=5 => println!("one through five"), + _ => println!("something else"), + } ``` -fn main() { - println!("A baby dog is called a {}", Animal::baby_name()); -} -``` - -Listing 19-20: Attempting to call the `baby_name` function from the `Animal` -trait, but Rust doesn’t know which implementation to use -Because `Animal::baby_name` doesn’t have a `self` parameter, and there could be -other types that implement the `Animal` trait, Rust can’t figure out which -implementation of `Animal::baby_name` we want. We’ll get this compiler error: +If `x` is `1`, `2`, `3`, `4`, or `5`, the first arm will match. This syntax is +more convenient for multiple match values than using the `|` operator to +express the same idea; if we were to use `|`, we would have to specify `1 | 2 | 3 | 4 | 5`. Specifying a range is much shorter, especially if we want to match, +say, any number between 1 and 1,000! -``` -error[E0283]: type annotations needed - --> src/main.rs:20:43 - | -20 | println!("A baby dog is called a {}", Animal::baby_name()); - | ^^^^^^^^^^^^^^^^^ cannot infer -type - | - = note: cannot satisfy `_: Animal` -``` - -To disambiguate and tell Rust that we want to use the implementation of -`Animal` for `Dog` as opposed to the implementation of `Animal` for some other -type, we need to use fully qualified syntax. Listing 19-21 demonstrates how to -use fully qualified syntax. +The compiler checks that the range isn’t empty at compile time, and because the +only types for which Rust can tell if a range is empty or not are `char` and +numeric values, ranges are only allowed with numeric or `char` values. -Filename: src/main.rs +Here is an example using ranges of `char` values: ``` -fn main() { - println!( - "A baby dog is called a {}", - <Dog as Animal>::baby_name() - ); -} -``` + let x = 'c'; -Listing 19-21: Using fully qualified syntax to specify that we want to call the -`baby_name` function from the `Animal` trait as implemented on `Dog` - -We’re providing Rust with a type annotation within the angle brackets, which -indicates we want to call the `baby_name` method from the `Animal` trait as -implemented on `Dog` by saying that we want to treat the `Dog` type as an -`Animal` for this function call. This code will now print what we want: - -``` -A baby dog is called a puppy + match x { + 'a'..='j' => println!("early ASCII letter"), + 'k'..='z' => println!("late ASCII letter"), + _ => println!("something else"), + } ``` -In general, fully qualified syntax is defined as follows: +Rust can tell that `'c'` is within the first pattern’s range and prints `early ASCII letter`. -``` -<Type as Trait>::function(receiver_if_method, next_arg, ...); -``` - -For associated functions that aren’t methods, there would not be a `receiver`: -there would only be the list of other arguments. You could use fully qualified -syntax everywhere that you call functions or methods. However, you’re allowed -to omit any part of this syntax that Rust can figure out from other information -in the program. You only need to use this more verbose syntax in cases where -there are multiple implementations that use the same name and Rust needs help -to identify which implementation you want to call. +### Destructuring to Break Apart Values -### Using Supertraits +We can also use patterns to destructure structs, enums, and tuples to use +different parts of these values. Let’s walk through each value. -Sometimes you might write a trait definition that depends on another trait: for -a type to implement the first trait, you want to require that type to also -implement the second trait. You would do this so that your trait definition can -make use of the associated items of the second trait. The trait your trait -definition is relying on is called a *supertrait* of your trait. +<!-- Old headings. Do not remove or links may break. --> -For example, let’s say we want to make an `OutlinePrint` trait with an -`outline_print` method that will print a given value formatted so that it’s -framed in asterisks. That is, given a `Point` struct that implements the -standard library trait `Display` to result in `(x, y)`, when we call -`outline_print` on a `Point` instance that has `1` for `x` and `3` for `y`, it -should print the following: +<a id="destructuring-structs"></a> -``` -********** -* * -* (1, 3) * -* * -********** -``` +#### Structs -In the implementation of the `outline_print` method, we want to use the -`Display` trait’s functionality. Therefore, we need to specify that the -`OutlinePrint` trait will work only for types that also implement `Display` and -provide the functionality that `OutlinePrint` needs. We can do that in the -trait definition by specifying `OutlinePrint: Display`. This technique is -similar to adding a trait bound to the trait. Listing 19-22 shows an -implementation of the `OutlinePrint` trait. +Listing 19-12 shows a `Point` struct with two fields, `x` and `y`, that we can +break apart using a pattern with a `let` statement. -Filename: src/main.rs +src/main.rs ``` -use std::fmt; +struct Point { + x: i32, + y: i32, +} -trait OutlinePrint: fmt::Display { - fn outline_print(&self) { - let output = self.to_string(); - let len = output.len(); - println!("{}", "*".repeat(len + 4)); - println!("*{}*", " ".repeat(len + 2)); - println!("* {} *", output); - println!("*{}*", " ".repeat(len + 2)); - println!("{}", "*".repeat(len + 4)); - } +fn main() { + let p = Point { x: 0, y: 7 }; + + let Point { x: a, y: b } = p; + assert_eq!(0, a); + assert_eq!(7, b); } ``` -Listing 19-22: Implementing the `OutlinePrint` trait that requires the -functionality from `Display` +Listing 19-12: Destructuring a struct’s fields into separate variables -Because we’ve specified that `OutlinePrint` requires the `Display` trait, we -can use the `to_string` function that is automatically implemented for any type -that implements `Display`. If we tried to use `to_string` without adding a -colon and specifying the `Display` trait after the trait name, we’d get an -error saying that no method named `to_string` was found for the type `&Self` in -the current scope. +This code creates the variables `a` and `b` that match the values of the `x` +and `y` fields of the `p` struct. This example shows that the names of the +variables in the pattern don’t have to match the field names of the struct. +However, it’s common to match the variable names to the field names to make it +easier to remember which variables came from which fields. Because of this +common usage, and because writing `let Point { x: x, y: y } = p;` contains a +lot of duplication, Rust has a shorthand for patterns that match struct fields: +You only need to list the name of the struct field, and the variables created +from the pattern will have the same names. Listing 19-13 behaves in the same +way as the code in Listing 19-12, but the variables created in the `let` +pattern are `x` and `y` instead of `a` and `b`. -Let’s see what happens when we try to implement `OutlinePrint` on a type that -doesn’t implement `Display`, such as the `Point` struct: - -Filename: src/main.rs +src/main.rs ``` struct Point { @@ -1093,1204 +668,658 @@ struct Point { y: i32, } -impl OutlinePrint for Point {} -``` - -We get an error saying that `Display` is required but not implemented: - -``` -error[E0277]: `Point` doesn't implement `std::fmt::Display` - --> src/main.rs:20:6 - | -20 | impl OutlinePrint for Point {} - | ^^^^^^^^^^^^ `Point` cannot be formatted with the default formatter - | - = help: the trait `std::fmt::Display` is not implemented for `Point` - = note: in format strings you may be able to use `{:?}` (or {:#?} for -pretty-print) instead -note: required by a bound in `OutlinePrint` - --> src/main.rs:3:21 - | -3 | trait OutlinePrint: fmt::Display { - | ^^^^^^^^^^^^ required by this bound in `OutlinePrint` -``` - -To fix this, we implement `Display` on `Point` and satisfy the constraint that -`OutlinePrint` requires, like so: - -Filename: src/main.rs - -``` -use std::fmt; +fn main() { + let p = Point { x: 0, y: 7 }; -impl fmt::Display for Point { - fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { - write!(f, "({}, {})", self.x, self.y) - } + let Point { x, y } = p; + assert_eq!(0, x); + assert_eq!(7, y); } ``` -Then, implementing the `OutlinePrint` trait on `Point` will compile -successfully, and we can call `outline_print` on a `Point` instance to display -it within an outline of asterisks. +Listing 19-13: Destructuring struct fields using struct field shorthand -### Using the Newtype Pattern to Implement External Traits +This code creates the variables `x` and `y` that match the `x` and `y` fields +of the `p` variable. The outcome is that the variables `x` and `y` contain the +values from the `p` struct. -In “Implementing a Trait on a Type” on page XX, we mentioned the orphan rule -that states we’re only allowed to implement a trait on a type if either the -trait or the type, or both, are local to our crate. It’s possible to get around -this restriction using the *newtype pattern*, which involves creating a new -type in a tuple struct. (We covered tuple structs in “Using Tuple Structs -Without Named Fields to Create Different Types” on page XX.) The tuple struct -will have one field and be a thin wrapper around the type for which we want to -implement a trait. Then the wrapper type is local to our crate, and we can -implement the trait on the wrapper. *Newtype* is a term that originates from -the Haskell programming language. There is no runtime performance penalty for -using this pattern, and the wrapper type is elided at compile time. +We can also destructure with literal values as part of the struct pattern +rather than creating variables for all the fields. Doing so allows us to test +some of the fields for particular values while creating variables to +destructure the other fields. -As an example, let’s say we want to implement `Display` on `Vec<T>`, which the -orphan rule prevents us from doing directly because the `Display` trait and the -`Vec<T>` type are defined outside our crate. We can make a `Wrapper` struct -that holds an instance of `Vec<T>`; then we can implement `Display` on -`Wrapper` and use the `Vec<T>` value, as shown in Listing 19-23. +In Listing 19-14, we have a `match` expression that separates `Point` values +into three cases: points that lie directly on the `x` axis (which is true when +`y = 0`), on the `y` axis (`x = 0`), or on neither axis. -Filename: src/main.rs +src/main.rs ``` -use std::fmt; - -struct Wrapper(Vec<String>); +fn main() { + let p = Point { x: 0, y: 7 }; -impl fmt::Display for Wrapper { - fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { - write!(f, "[{}]", self.0.join(", ")) + match p { + Point { x, y: 0 } => println!("On the x axis at {x}"), + Point { x: 0, y } => println!("On the y axis at {y}"), + Point { x, y } => { + println!("On neither axis: ({x}, {y})"); + } } } - -fn main() { - let w = Wrapper(vec![ - String::from("hello"), - String::from("world"), - ]); - println!("w = {w}"); -} ``` -Listing 19-23: Creating a `Wrapper` type around `Vec<String>` to implement -`Display` - -The implementation of `Display` uses `self.0` to access the inner `Vec<T>` -because `Wrapper` is a tuple struct and `Vec<T>` is the item at index 0 in the -tuple. Then we can use the functionality of the `Display` type on `Wrapper`. - -The downside of using this technique is that `Wrapper` is a new type, so it -doesn’t have the methods of the value it’s holding. We would have to implement -all the methods of `Vec<T>` directly on `Wrapper` such that the methods -delegate to `self.0`, which would allow us to treat `Wrapper` exactly like a -`Vec<T>`. If we wanted the new type to have every method the inner type has, -implementing the `Deref` trait on the `Wrapper` to return the inner type would -be a solution (we discussed implementing the `Deref` trait in “Treating Smart -Pointers Like Regular References with Deref” on page XX). If we didn’t want the -`Wrapper` type to have all the methods of the inner type—for example, to -restrict the `Wrapper` type’s behavior—we would have to implement just the -methods we do want manually. - -This newtype pattern is also useful even when traits are not involved. Let’s -switch focus and look at some advanced ways to interact with Rust’s type system. +Listing 19-14: Destructuring and matching literal values in one pattern -## Advanced Types +The first arm will match any point that lies on the `x` axis by specifying that +the `y` field matches if its value matches the literal `0`. The pattern still +creates an `x` variable that we can use in the code for this arm. -The Rust type system has some features that we’ve so far mentioned but haven’t -yet discussed. We’ll start by discussing newtypes in general as we examine why -newtypes are useful as types. Then we’ll move on to type aliases, a feature -similar to newtypes but with slightly different semantics. We’ll also discuss -the `!` type and dynamically sized types. +Similarly, the second arm matches any point on the `y` axis by specifying that +the `x` field matches if its value is `0` and creates a variable `y` for the +value of the `y` field. The third arm doesn’t specify any literals, so it +matches any other `Point` and creates variables for both the `x` and `y` fields. -### Using the Newtype Pattern for Type Safety and Abstraction +In this example, the value `p` matches the second arm by virtue of `x` +containing a `0`, so this code will print `On the y axis at 7`. -> Note: This section assumes you’ve read the earlier section “Using the Newtype -Pattern to Implement External Traits” on page XX. +Remember that a `match` expression stops checking arms once it has found the +first matching pattern, so even though `Point { x: 0, y: 0}` is on the `x` axis +and the `y` axis, this code would only print `On the x axis at 0`. -The newtype pattern is also useful for tasks beyond those we’ve discussed so -far, including statically enforcing that values are never confused and -indicating the units of a value. You saw an example of using newtypes to -indicate units in Listing 19-15: recall that the `Millimeters` and `Meters` -structs wrapped `u32` values in a newtype. If we wrote a function with a -parameter of type `Millimeters`, we wouldn’t be able to compile a program that -accidentally tried to call that function with a value of type `Meters` or a -plain `u32`. +<!-- Old headings. Do not remove or links may break. --> -We can also use the newtype pattern to abstract away some implementation -details of a type: the new type can expose a public API that is different from -the API of the private inner type. +<a id="destructuring-enums"></a> -Newtypes can also hide internal implementation. For example, we could provide a -`People` type to wrap a `HashMap<i32, String>` that stores a person’s ID -associated with their name. Code using `People` would only interact with the -public API we provide, such as a method to add a name string to the `People` -collection; that code wouldn’t need to know that we assign an `i32` ID to names -internally. The newtype pattern is a lightweight way to achieve encapsulation -to hide implementation details, which we discussed in “Encapsulation That Hides -Implementation Details” on page XX. +#### Enums -### Creating Type Synonyms with Type Aliases +We’ve destructured enums in this book (for example, Listing 6-5 in Chapter 6), +but we haven’t yet explicitly discussed that the pattern to destructure an enum +corresponds to the way the data stored within the enum is defined. As an +example, in Listing 19-15, we use the `Message` enum from Listing 6-2 and write +a `match` with patterns that will destructure each inner value. -Rust provides the ability to declare a *type alias* to give an existing type -another name. For this we use the `type` keyword. For example, we can create -the alias `Kilometers` to `i32` like so: +src/main.rs ``` -type Kilometers = i32; -``` +enum Message { + Quit, + Move { x: i32, y: i32 }, + Write(String), + ChangeColor(i32, i32, i32), +} -Now the alias `Kilometers` is a *synonym* for `i32`; unlike the `Millimeters` -and `Meters` types we created in Listing 19-15, `Kilometers` is not a separate, -new type. Values that have the type `Kilometers` will be treated the same as -values of type `i32`: +fn main() { + let msg = Message::ChangeColor(0, 160, 255); + match msg { + Message::Quit => { + println!("The Quit variant has no data to destructure."); + } + Message::Move { x, y } => { + println!("Move in the x direction {x} and in the y direction {y}"); + } + Message::Write(text) => { + println!("Text message: {text}"); + } + Message::ChangeColor(r, g, b) => { + println!("Change color to red {r}, green {g}, and blue {b}"); + } + } +} ``` -type Kilometers = i32; -let x: i32 = 5; -let y: Kilometers = 5; - -println!("x + y = {}", x + y); -``` +Listing 19-15: Destructuring enum variants that hold different kinds of values -Because `Kilometers` and `i32` are the same type, we can add values of both -types and we can pass `Kilometers` values to functions that take `i32` -parameters. However, using this method, we don’t get the type-checking benefits -that we get from the newtype pattern discussed earlier. In other words, if we -mix up `Kilometers` and `i32` values somewhere, the compiler will not give us -an error. +This code will print `Change color to red 0, green 160, and blue 255`. Try +changing the value of `msg` to see the code from the other arms run. -The main use case for type synonyms is to reduce repetition. For example, we -might have a lengthy type like this: +For enum variants without any data, like `Message::Quit`, we can’t destructure +the value any further. We can only match on the literal `Message::Quit` value, +and no variables are in that pattern. -``` -Box<dyn Fn() + Send + 'static> -``` +For struct-like enum variants, such as `Message::Move`, we can use a pattern +similar to the pattern we specify to match structs. After the variant name, we +place curly brackets and then list the fields with variables so that we break +apart the pieces to use in the code for this arm. Here we use the shorthand +form as we did in Listing 19-13. -Writing this lengthy type in function signatures and as type annotations all -over the code can be tiresome and error prone. Imagine having a project full of -code like that in Listing 19-24. +For tuple-like enum variants, like `Message::Write` that holds a tuple with one +element and `Message::ChangeColor` that holds a tuple with three elements, the +pattern is similar to the pattern we specify to match tuples. The number of +variables in the pattern must match the number of elements in the variant we’re +matching. -``` -let f: Box<dyn Fn() + Send + 'static> = Box::new(|| { - println!("hi"); -}); +<!-- Old headings. Do not remove or links may break. --> -fn takes_long_type(f: Box<dyn Fn() + Send + 'static>) { - --snip-- -} +<a id="destructuring-nested-structs-and-enums"></a> -fn returns_long_type() -> Box<dyn Fn() + Send + 'static> { - --snip-- -} -``` +#### Nested Structs and Enums -Listing 19-24: Using a long type in many places +So far, our examples have all been matching structs or enums one level deep, +but matching can work on nested items too! For example, we can refactor the +code in Listing 19-15 to support RGB and HSV colors in the `ChangeColor` +message, as shown in Listing 19-16. -A type alias makes this code more manageable by reducing the repetition. In -Listing 19-25, we’ve introduced an alias named `Thunk` for the verbose type and -can replace all uses of the type with the shorter alias `Thunk`. ``` -type Thunk = Box<dyn Fn() + Send + 'static>; - -let f: Thunk = Box::new(|| println!("hi")); +enum Color { + Rgb(i32, i32, i32), + Hsv(i32, i32, i32), +} -fn takes_long_type(f: Thunk) { - --snip-- +enum Message { + Quit, + Move { x: i32, y: i32 }, + Write(String), + ChangeColor(Color), } -fn returns_long_type() -> Thunk { - --snip-- +fn main() { + let msg = Message::ChangeColor(Color::Hsv(0, 160, 255)); + + match msg { + Message::ChangeColor(Color::Rgb(r, g, b)) => { + println!("Change color to red {r}, green {g}, and blue {b}"); + } + Message::ChangeColor(Color::Hsv(h, s, v)) => { + println!("Change color to hue {h}, saturation {s}, value {v}"); + } + _ => (), + } } ``` -Listing 19-25: Introducing a type alias `Thunk` to reduce repetition - -This code is much easier to read and write! Choosing a meaningful name for a -type alias can help communicate your intent as well (*thunk* is a word for code -to be evaluated at a later time, so it’s an appropriate name for a closure that -gets stored). +Listing 19-16: Matching on nested enums -Type aliases are also commonly used with the `Result<T, E>` type for reducing -repetition. Consider the `std::io` module in the standard library. I/O -operations often return a `Result<T, E>` to handle situations when operations -fail to work. This library has a `std::io::Error` struct that represents all -possible I/O errors. Many of the functions in `std::io` will be returning -`Result<T, E>` where the `E` is `std::io::Error`, such as these functions in -the `Write` trait: +The pattern of the first arm in the `match` expression matches a +`Message::ChangeColor` enum variant that contains a `Color::Rgb` variant; then, +the pattern binds to the three inner `i32` values. The pattern of the second +arm also matches a `Message::ChangeColor` enum variant, but the inner enum +matches `Color::Hsv` instead. We can specify these complex conditions in one +`match` expression, even though two enums are involved. -``` -use std::fmt; -use std::io::Error; +<!-- Old headings. Do not remove or links may break. --> -pub trait Write { - fn write(&mut self, buf: &[u8]) -> Result<usize, Error>; - fn flush(&mut self) -> Result<(), Error>; +<a id="destructuring-structs-and-tuples"></a> - fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>; - fn write_fmt( - &mut self, - fmt: fmt::Arguments, - ) -> Result<(), Error>; -} -``` +#### Structs and Tuples -The `Result<..., Error>` is repeated a lot. As such, `std::io` has this type -alias declaration: +We can mix, match, and nest destructuring patterns in even more complex ways. +The following example shows a complicated destructure where we nest structs and +tuples inside a tuple and destructure all the primitive values out: ``` -type Result<T> = std::result::Result<T, std::io::Error>; + let ((feet, inches), Point { x, y }) = ((3, 10), Point { x: 3, y: -10 }); ``` -Because this declaration is in the `std::io` module, we can use the fully -qualified alias `std::io::Result<T>`; that is, a `Result<T, E>` with the `E` -filled in as `std::io::Error`. The `Write` trait function signatures end up -looking like this: +This code lets us break complex types into their component parts so that we can +use the values we’re interested in separately. -``` -pub trait Write { - fn write(&mut self, buf: &[u8]) -> Result<usize>; - fn flush(&mut self) -> Result<()>; +Destructuring with patterns is a convenient way to use pieces of values, such +as the value from each field in a struct, separately from each other. - fn write_all(&mut self, buf: &[u8]) -> Result<()>; - fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()>; -} -``` +### Ignoring Values in a Pattern -The type alias helps in two ways: it makes code easier to write *and* it gives -us a consistent interface across all of `std::io`. Because it’s an alias, it’s -just another `Result<T, E>`, which means we can use any methods that work on -`Result<T, E>` with it, as well as special syntax like the `?` operator. +You’ve seen that it’s sometimes useful to ignore values in a pattern, such as +in the last arm of a `match`, to get a catch-all that doesn’t actually do +anything but does account for all remaining possible values. There are a few +ways to ignore entire values or parts of values in a pattern: using the `_` +pattern (which you’ve seen), using the `_` pattern within another pattern, +using a name that starts with an underscore, or using `..` to ignore remaining +parts of a value. Let’s explore how and why to use each of these patterns. -### The Never Type That Never Returns +<!-- Old headings. Do not remove or links may break. --> -Rust has a special type named `!` that’s known in type theory lingo as the -*empty type* because it has no values. We prefer to call it the *never type* -because it stands in the place of the return type when a function will never -return. Here is an example: +<a id="ignoring-an-entire-value-with-_"></a> -``` -fn bar() -> ! { - --snip-- -} -``` +#### An Entire Value with \_ -This code is read as “the function `bar` returns never.” Functions that return -never are called *diverging functions*. We can’t create values of the type `!`, -so `bar` can never possibly return. +We’ve used the underscore as a wildcard pattern that will match any value but +not bind to the value. This is especially useful as the last arm in a `match` +expression, but we can also use it in any pattern, including function +parameters, as shown in Listing 19-17. -But what use is a type you can never create values for? Recall the code from -Listing 2-5, part of the number-guessing game; we’ve reproduced a bit of it -here in Listing 19-26. +src/main.rs ``` -let guess: u32 = match guess.trim().parse() { - Ok(num) => num, - Err(_) => continue, -}; +fn foo(_: i32, y: i32) { + println!("This code only uses the y parameter: {y}"); +} + +fn main() { + foo(3, 4); +} ``` -Listing 19-26: A `match` with an arm that ends in `continue` +Listing 19-17: Using `_` in a function signature -At the time, we skipped over some details in this code. In “The match Control -Flow Construct” on page XX, we discussed that `match` arms must all return the -same type. So, for example, the following code doesn’t work: +This code will completely ignore the value `3` passed as the first argument, +and will print `This code only uses the y parameter: 4`. -``` -let guess = match guess.trim().parse() { - Ok(_) => 5, - Err(_) => "hello", -}; -``` +In most cases when you no longer need a particular function parameter, you +would change the signature so that it doesn’t include the unused parameter. +Ignoring a function parameter can be especially useful in cases when, for +example, you’re implementing a trait when you need a certain type signature but +the function body in your implementation doesn’t need one of the parameters. +You then avoid getting a compiler warning about unused function parameters, as +you would if you used a name instead. + +<!-- Old headings. Do not remove or links may break. --> -The type of `guess` in this code would have to be an integer *and* a string, -and Rust requires that `guess` have only one type. So what does `continue` -return? How were we allowed to return a `u32` from one arm and have another arm -that ends with `continue` in Listing 19-26? +<a id="ignoring-parts-of-a-value-with-a-nested-_"></a> -As you might have guessed, `continue` has a `!` value. That is, when Rust -computes the type of `guess`, it looks at both match arms, the former with a -value of `u32` and the latter with a `!` value. Because `!` can never have a -value, Rust decides that the type of `guess` is `u32`. +#### Parts of a Value with a Nested \_ -The formal way of describing this behavior is that expressions of type `!` can -be coerced into any other type. We’re allowed to end this `match` arm with -`continue` because `continue` doesn’t return a value; instead, it moves control -back to the top of the loop, so in the `Err` case, we never assign a value to -`guess`. +We can also use `_` inside another pattern to ignore just part of a value, for +example, when we want to test for only part of a value but have no use for the +other parts in the corresponding code we want to run. Listing 19-18 shows code +responsible for managing a setting’s value. The business requirements are that +the user should not be allowed to overwrite an existing customization of a +setting but can unset the setting and give it a value if it is currently unset. -The never type is useful with the `panic!` macro as well. Recall the `unwrap` -function that we call on `Option<T>` values to produce a value or panic with -this definition: ``` -impl<T> Option<T> { - pub fn unwrap(self) -> T { - match self { - Some(val) => val, - None => panic!( - "called `Option::unwrap()` on a `None` value" - ), + let mut setting_value = Some(5); + let new_setting_value = Some(10); + + match (setting_value, new_setting_value) { + (Some(_), Some(_)) => { + println!("Can't overwrite an existing customized value"); + } + _ => { + setting_value = new_setting_value; } } -} -``` - -In this code, the same thing happens as in the `match` in Listing 19-26: Rust -sees that `val` has the type `T` and `panic!` has the type `!`, so the result -of the overall `match` expression is `T`. This code works because `panic!` -doesn’t produce a value; it ends the program. In the `None` case, we won’t be -returning a value from `unwrap`, so this code is valid. - -One final expression that has the type `!` is a `loop`: + println!("setting is {setting_value:?}"); ``` -print!("forever "); -loop { - print!("and ever "); -} -``` +Listing 19-18: Using an underscore within patterns that match `Some` variants when we don’t need to use the value inside the `Some` -Here, the loop never ends, so `!` is the value of the expression. However, this -wouldn’t be true if we included a `break`, because the loop would terminate -when it got to the `break`. - -### Dynamically Sized Types and the Sized Trait - -Rust needs to know certain details about its types, such as how much space to -allocate for a value of a particular type. This leaves one corner of its type -system a little confusing at first: the concept of *dynamically sized types*. -Sometimes referred to as *DSTs* or *unsized types*, these types let us write -code using values whose size we can know only at runtime. - -Let’s dig into the details of a dynamically sized type called `str`, which -we’ve been using throughout the book. That’s right, not `&str`, but `str` on -its own, is a DST. We can’t know how long the string is until runtime, meaning -we can’t create a variable of type `str`, nor can we take an argument of type -`str`. Consider the following code, which does not work: - -``` -let s1: str = "Hello there!"; -let s2: str = "How's it going?"; -``` - -Rust needs to know how much memory to allocate for any value of a particular -type, and all values of a type must use the same amount of memory. If Rust -allowed us to write this code, these two `str` values would need to take up the -same amount of space. But they have different lengths: `s1` needs 12 bytes of -storage and `s2` needs 15. This is why it’s not possible to create a variable -holding a dynamically sized type. - -So what do we do? In this case, you already know the answer: we make the types -of `s1` and `s2` a `&str` rather than a `str`. Recall from “String Slices” on -page XX that the slice data structure just stores the starting position and the -length of the slice. So, although a `&T` is a single value that stores the -memory address of where the `T` is located, a `&str` is *two* values: the -address of the `str` and its length. As such, we can know the size of a `&str` -value at compile time: it’s twice the length of a `usize`. That is, we always -know the size of a `&str`, no matter how long the string it refers to is. In -general, this is the way in which dynamically sized types are used in Rust: -they have an extra bit of metadata that stores the size of the dynamic -information. The golden rule of dynamically sized types is that we must always -put values of dynamically sized types behind a pointer of some kind. - -We can combine `str` with all kinds of pointers: for example, `Box<str>` or -`Rc<str>`. In fact, you’ve seen this before but with a different dynamically -sized type: traits. Every trait is a dynamically sized type we can refer to by -using the name of the trait. In “Using Trait Objects That Allow for Values of -Different Types” on page XX, we mentioned that to use traits as trait objects, -we must put them behind a pointer, such as `&dyn Trait` or `Box<dyn Trait>` -(`Rc<dyn Trait>` would work too). - -To work with DSTs, Rust provides the `Sized` trait to determine whether or not -a type’s size is known at compile time. This trait is automatically implemented -for everything whose size is known at compile time. In addition, Rust -implicitly adds a bound on `Sized` to every generic function. That is, a -generic function definition like this: - -``` -fn generic<T>(t: T) { - --snip-- -} -``` +This code will print `Can't overwrite an existing customized value` and then +`setting is Some(5)`. In the first match arm, we don’t need to match on or use +the values inside either `Some` variant, but we do need to test for the case +when `setting_value` and `new_setting_value` are the `Some` variant. In that +case, we print the reason for not changing `setting_value`, and it doesn’t get +changed. -is actually treated as though we had written this: +In all other cases (if either `setting_value` or `new_setting_value` is `None`) +expressed by the `_` pattern in the second arm, we want to allow +`new_setting_value` to become `setting_value`. -``` -fn generic<T: Sized>(t: T) { - --snip-- -} -``` +We can also use underscores in multiple places within one pattern to ignore +particular values. Listing 19-19 shows an example of ignoring the second and +fourth values in a tuple of five items. -By default, generic functions will work only on types that have a known size at -compile time. However, you can use the following special syntax to relax this -restriction: ``` -fn generic<T: ?Sized>(t: &T) { - --snip-- -} -``` - -A trait bound on `?Sized` means “`T` may or may not be `Sized`” and this -notation overrides the default that generic types must have a known size at -compile time. The `?Trait` syntax with this meaning is only available for -`Sized`, not any other traits. + let numbers = (2, 4, 8, 16, 32); -Also note that we switched the type of the `t` parameter from `T` to `&T`. -Because the type might not be `Sized`, we need to use it behind some kind of -pointer. In this case, we’ve chosen a reference. + match numbers { + (first, _, third, _, fifth) => { + println!("Some numbers: {first}, {third}, {fifth}"); + } + } +``` -Next, we’ll talk about functions and closures! +Listing 19-19: Ignoring multiple parts of a tuple -## Advanced Functions and Closures +This code will print `Some numbers: 2, 8, 32`, and the values `4` and `16` will +be ignored. -This section explores some advanced features related to functions and closures, -including function pointers and returning closures. +<!-- Old headings. Do not remove or links may break. --> -### Function Pointers +<a id="ignoring-an-unused-variable-by-starting-its-name-with-_"></a> -We’ve talked about how to pass closures to functions; you can also pass regular -functions to functions! This technique is useful when you want to pass a -function you’ve already defined rather than defining a new closure. Functions -coerce to the type `fn` (with a lowercase *f*), not to be confused with the -`Fn` closure trait. The `fn` type is called a *function pointer*. Passing -functions with function pointers will allow you to use functions as arguments -to other functions. +#### An Unused Variable by Starting Its Name with \_ -The syntax for specifying that a parameter is a function pointer is similar to -that of closures, as shown in Listing 19-27, where we’ve defined a function -`add_one` that adds 1 to its parameter. The function `do_twice` takes two -parameters: a function pointer to any function that takes an `i32` parameter -and returns an `i32`, and one `i32 value`. The `do_twice` function calls the -function `f` twice, passing it the `arg` value, then adds the two function call -results together. The `main` function calls `do_twice` with the arguments -`add_one` and `5`. +If you create a variable but don’t use it anywhere, Rust will usually issue a +warning because an unused variable could be a bug. However, sometimes it’s +useful to be able to create a variable you won’t use yet, such as when you’re +prototyping or just starting a project. In this situation, you can tell Rust +not to warn you about the unused variable by starting the name of the variable +with an underscore. In Listing 19-20, we create two unused variables, but when +we compile this code, we should only get a warning about one of them. -Filename: src/main.rs +src/main.rs ``` -fn add_one(x: i32) -> i32 { - x + 1 -} - -fn do_twice(f: fn(i32) -> i32, arg: i32) -> i32 { - f(arg) + f(arg) -} - fn main() { - let answer = do_twice(add_one, 5); - - println!("The answer is: {answer}"); + let _x = 5; + let y = 10; } ``` -Listing 19-27: Using the `fn` type to accept a function pointer as an argument - -This code prints `The answer is: 12`. We specify that the parameter `f` in -`do_twice` is an `fn` that takes one parameter of type `i32` and returns an -`i32`. We can then call `f` in the body of `do_twice`. In `main`, we can pass -the function name `add_one` as the first argument to `do_twice`. +Listing 19-20: Starting a variable name with an underscore to avoid getting unused variable warnings -Unlike closures, `fn` is a type rather than a trait, so we specify `fn` as the -parameter type directly rather than declaring a generic type parameter with one -of the `Fn` traits as a trait bound. +Here, we get a warning about not using the variable `y`, but we don’t get a +warning about not using `_x`. -Function pointers implement all three of the closure traits (`Fn`, `FnMut`, and -`FnOnce`), meaning you can always pass a function pointer as an argument for a -function that expects a closure. It’s best to write functions using a generic -type and one of the closure traits so your functions can accept either -functions or closures. +Note that there is a subtle difference between using only `_` and using a name +that starts with an underscore. The syntax `_x` still binds the value to the +variable, whereas `_` doesn’t bind at all. To show a case where this +distinction matters, Listing 19-21 will provide us with an error. -That said, one example of where you would want to only accept `fn` and not -closures is when interfacing with external code that doesn’t have closures: C -functions can accept functions as arguments, but C doesn’t have closures. -As an example of where you could use either a closure defined inline or a named -function, let’s look at a use of the `map` method provided by the `Iterator` -trait in the standard library. To use the `map` function to turn a vector of -numbers into a vector of strings, we could use a closure, like this: - -``` -let list_of_numbers = vec![1, 2, 3]; -let list_of_strings: Vec<String> = list_of_numbers - .iter() - .map(|i| i.to_string()) - .collect(); ``` + let s = Some(String::from("Hello!")); -Or we could name a function as the argument to `map` instead of the closure, -like this: + if let Some(_s) = s { + println!("found a string"); + } -``` -let list_of_numbers = vec![1, 2, 3]; -let list_of_strings: Vec<String> = list_of_numbers - .iter() - .map(ToString::to_string) - .collect(); + println!("{s:?}"); ``` -Note that we must use the fully qualified syntax that we talked about in -“Advanced Traits” on page XX because there are multiple functions available -named `to_string`. +Listing 19-21: An unused variable starting with an underscore still binds the value, which might take ownership of the value. -Here, we’re using the `to_string` function defined in the `ToString` trait, -which the standard library has implemented for any type that implements -`Display`. +We’ll receive an error because the `s` value will still be moved into `_s`, +which prevents us from using `s` again. However, using the underscore by itself +doesn’t ever bind to the value. Listing 19-22 will compile without any errors +because `s` doesn’t get moved into `_`. -Recall from “Enum Values” on page XX that the name of each enum variant that we -define also becomes an initializer function. We can use these initializer -functions as function pointers that implement the closure traits, which means -we can specify the initializer functions as arguments for methods that take -closures, like so: ``` -enum Status { - Value(u32), - Stop, -} + let s = Some(String::from("Hello!")); -let list_of_statuses: Vec<Status> = (0u32..20) - .map(Status::Value) - .collect(); + if let Some(_) = s { + println!("found a string"); + } + + println!("{s:?}"); ``` -Here, we create `Status::Value` instances using each `u32` value in the range -that `map` is called on by using the initializer function of `Status::Value`. -Some people prefer this style and some people prefer to use closures. They -compile to the same code, so use whichever style is clearer to you. +Listing 19-22: Using an underscore does not bind the value. -### Returning Closures +This code works just fine because we never bind `s` to anything; it isn’t moved. -Closures are represented by traits, which means you can’t return closures -directly. In most cases where you might want to return a trait, you can instead -use the concrete type that implements the trait as the return value of the -function. However, you can’t do that with closures because they don’t have a -concrete type that is returnable; you’re not allowed to use the function -pointer `fn` as a return type, for example. +<a id="ignoring-remaining-parts-of-a-value-with-"></a> -The following code tries to return a closure directly, but it won’t compile: +#### Remaining Parts of a Value with .. -``` -fn returns_closure() -> dyn Fn(i32) -> i32 { - |x| x + 1 -} -``` +With values that have many parts, we can use the `..` syntax to use specific +parts and ignore the rest, avoiding the need to list underscores for each +ignored value. The `..` pattern ignores any parts of a value that we haven’t +explicitly matched in the rest of the pattern. In Listing 19-23, we have a +`Point` struct that holds a coordinate in three-dimensional space. In the +`match` expression, we want to operate only on the `x` coordinate and ignore +the values in the `y` and `z` fields. -The compiler error is as follows: ``` -error[E0746]: return type cannot have an unboxed trait object - --> src/lib.rs:1:25 - | -1 | fn returns_closure() -> dyn Fn(i32) -> i32 { - | ^^^^^^^^^^^^^^^^^^ doesn't have a size known at -compile-time - | - = note: for information on `impl Trait`, see -<https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that- -implement-traits> -help: use `impl Fn(i32) -> i32` as the return type, as all return paths are of -type `[closure@src/lib.rs:2:5: 2:14]`, which implements `Fn(i32) -> i32` - | -1 | fn returns_closure() -> impl Fn(i32) -> i32 { - | ~~~~~~~~~~~~~~~~~~~ -``` + struct Point { + x: i32, + y: i32, + z: i32, + } -The error references the `Sized` trait again! Rust doesn’t know how much space -it will need to store the closure. We saw a solution to this problem earlier. -We can use a trait object: + let origin = Point { x: 0, y: 0, z: 0 }; + match origin { + Point { x, .. } => println!("x is {x}"), + } ``` -fn returns_closure() -> Box<dyn Fn(i32) -> i32> { - Box::new(|x| x + 1) -} -``` - -This code will compile just fine. For more about trait objects, refer to “Using -Trait Objects That Allow for Values of Different Types” on page XX. - -Next, let’s look at macros! - -## Macros -We’ve used macros like `println!` throughout this book, but we haven’t fully -explored what a macro is and how it works. The term *macro* refers to a family -of features in Rust: *declarative* macros with `macro_rules!` and three kinds -of *procedural* macros: +Listing 19-23: Ignoring all fields of a `Point` except for `x` by using `..` -* Custom `#[derive]` macros that specify code added with the `derive` attribute -used on structs and enums -* Attribute-like macros that define custom attributes usable on any item -* Function-like macros that look like function calls but operate on the tokens -specified as their argument +We list the `x` value and then just include the `..` pattern. This is quicker +than having to list `y: _` and `z: _`, particularly when we’re working with +structs that have lots of fields in situations where only one or two fields are +relevant. -We’ll talk about each of these in turn, but first, let’s look at why we even -need macros when we already have functions. +The syntax `..` will expand to as many values as it needs to be. Listing 19-24 +shows how to use `..` with a tuple. -### The Difference Between Macros and Functions +src/main.rs -Fundamentally, macros are a way of writing code that writes other code, which -is known as *metaprogramming*. In Appendix C, we discuss the `derive` -attribute, which generates an implementation of various traits for you. We’ve -also used the `println!` and `vec!` macros throughout the book. All of these -macros *expand* to produce more code than the code you’ve written manually. - -Metaprogramming is useful for reducing the amount of code you have to write and -maintain, which is also one of the roles of functions. However, macros have -some additional powers that functions don’t have. - -A function signature must declare the number and type of parameters the -function has. Macros, on the other hand, can take a variable number of -parameters: we can call `println!("hello")` with one argument or -`println!("hello {}", name)` with two arguments. Also, macros are expanded -before the compiler interprets the meaning of the code, so a macro can, for -example, implement a trait on a given type. A function can’t, because it gets -called at runtime and a trait needs to be implemented at compile time. - -The downside to implementing a macro instead of a function is that macro -definitions are more complex than function definitions because you’re writing -Rust code that writes Rust code. Due to this indirection, macro definitions are -generally more difficult to read, understand, and maintain than function -definitions. - -Another important difference between macros and functions is that you must -define macros or bring them into scope *before* you call them in a file, as -opposed to functions you can define anywhere and call anywhere. - -### Declarative Macros with macro_rules! for General Metaprogramming - -The most widely used form of macros in Rust is the *declarative macro*. These -are also sometimes referred to as “macros by example,” “`macro_rules!` macros,” -or just plain “macros.” At their core, declarative macros allow you to write -something similar to a Rust `match` expression. As discussed in Chapter 6, -`match` expressions are control structures that take an expression, compare the -resultant value of the expression to patterns, and then run the code associated -with the matching pattern. Macros also compare a value to patterns that are -associated with particular code: in this situation, the value is the literal -Rust source code passed to the macro; the patterns are compared with the -structure of that source code; and the code associated with each pattern, when -matched, replaces the code passed to the macro. This all happens during -compilation. - -To define a macro, you use the `macro_rules!` construct. Let’s explore how to -use `macro_rules!` by looking at how the `vec!` macro is defined. Chapter 8 -covered how we can use the `vec!` macro to create a new vector with particular -values. For example, the following macro creates a new vector containing three -integers: - -``` -let v: Vec<u32> = vec![1, 2, 3]; ``` +fn main() { + let numbers = (2, 4, 8, 16, 32); -We could also use the `vec!` macro to make a vector of two integers or a vector -of five string slices. We wouldn’t be able to use a function to do the same -because we wouldn’t know the number or type of values up front. - -Listing 19-28 shows a slightly simplified definition of the `vec!` macro. - -Filename: src/lib.rs - -``` -1 #[macro_export] -2 macro_rules! vec { - 3 ( $( $x:expr ),* ) => { - { - let mut temp_vec = Vec::new(); - 4 $( - 5 temp_vec.push(6 $x); - )* - 7 temp_vec + match numbers { + (first, .., last) => { + println!("Some numbers: {first}, {last}"); } - }; -} -``` - -Listing 19-28: A simplified version of the `vec!` macro definition - -> Note: The actual definition of the `vec!` macro in the standard library -includes code to pre-allocate the correct amount of memory up front. That code -is an optimization that we don’t include here, to make the example simpler. - -The `#[macro_export]` annotation [1] indicates that this macro should be made -available whenever the crate in which the macro is defined is brought into -scope. Without this annotation, the macro can’t be brought into scope. - -We then start the macro definition with `macro_rules!` and the name of the -macro we’re defining *without* the exclamation mark [2]. The name, in this case -`vec`, is followed by curly brackets denoting the body of the macro definition. - -The structure in the `vec!` body is similar to the structure of a `match` -expression. Here we have one arm with the pattern `( $( $x:expr ),* )`, -followed by `=>` and the block of code associated with this pattern [3]. If the -pattern matches, the associated block of code will be emitted. Given that this -is the only pattern in this macro, there is only one valid way to match; any -other pattern will result in an error. More complex macros will have more than -one arm. - -Valid pattern syntax in macro definitions is different from the pattern syntax -covered in Chapter 18 because macro patterns are matched against Rust code -structure rather than values. Let’s walk through what the pattern pieces in -Listing 19-28 mean; for the full macro pattern syntax, see the Rust Reference -at *https://doc.rust-lang.org/reference/macros-by-example.html*. - -First we use a set of parentheses to encompass the whole pattern. We use a -dollar sign (`$`) to declare a variable in the macro system that will contain -the Rust code matching the pattern. The dollar sign makes it clear this is a -macro variable as opposed to a regular Rust variable. Next comes a set of -parentheses that captures values that match the pattern within the parentheses -for use in the replacement code. Within `$()` is `$x:expr`, which matches any -Rust expression and gives the expression the name `$x`. - -The comma following `$()` indicates that a literal comma separator character -could optionally appear after the code that matches the code in `$()`. The `*` -specifies that the pattern matches zero or more of whatever precedes the `*`. - -When we call this macro with `vec![1, 2, 3];`, the `$x` pattern matches three -times with the three expressions `1`, `2`, and `3`. - -Now let’s look at the pattern in the body of the code associated with this arm: -`temp_vec.push()` [5] within `$()* at [4] and [7] is generated for each part -that matches `$()` in the pattern zero or more times depending on how many -times the pattern matches. The `$x` [6] is replaced with each expression -matched. When we call this macro with `vec![1, 2, 3];`, the code generated that -replaces this macro call will be the following: - -``` -{ - let mut temp_vec = Vec::new(); - temp_vec.push(1); - temp_vec.push(2); - temp_vec.push(3); - temp_vec + } } ``` -We’ve defined a macro that can take any number of arguments of any type and can -generate code to create a vector containing the specified elements. - -To learn more about how to write macros, consult the online documentation or -other resources, such as “The Little Book of Rust Macros” at -*https://veykril.github.io/tlborm* started by Daniel Keep and continued by -Lukas Wirth. +Listing 19-24: Matching only the first and last values in a tuple and ignoring all other values -### Procedural Macros for Generating Code from Attributes +In this code, the first and last values are matched with `first` and `last`. +The `..` will match and ignore everything in the middle. -The second form of macros is the procedural macro, which acts more like a -function (and is a type of procedure). *Procedural macros* accept some code as -an input, operate on that code, and produce some code as an output rather than -matching against patterns and replacing the code with other code as declarative -macros do. The three kinds of procedural macros are custom `derive`, -attribute-like, and function-like, and all work in a similar fashion. +However, using `..` must be unambiguous. If it is unclear which values are +intended for matching and which should be ignored, Rust will give us an error. +Listing 19-25 shows an example of using `..` ambiguously, so it will not +compile. -When creating procedural macros, the definitions must reside in their own crate -with a special crate type. This is for complex technical reasons that we hope -to eliminate in the future. In Listing 19-29, we show how to define a -procedural macro, where `some_attribute` is a placeholder for using a specific -macro variety. - -Filename: src/lib.rs +src/main.rs ``` -use proc_macro::TokenStream; +fn main() { + let numbers = (2, 4, 8, 16, 32); -#[some_attribute] -pub fn some_name(input: TokenStream) -> TokenStream { + match numbers { + (.., second, ..) => { + println!("Some numbers: {second}") + }, + } } ``` -Listing 19-29: An example of defining a procedural macro - -The function that defines a procedural macro takes a `TokenStream` as an input -and produces a `TokenStream` as an output. The `TokenStream` type is defined by -the `proc_macro` crate that is included with Rust and represents a sequence of -tokens. This is the core of the macro: the source code that the macro is -operating on makes up the input `TokenStream`, and the code the macro produces -is the output `TokenStream`. The function also has an attribute attached to it -that specifies which kind of procedural macro we’re creating. We can have -multiple kinds of procedural macros in the same crate. - -Let’s look at the different kinds of procedural macros. We’ll start with a -custom `derive` macro and then explain the small dissimilarities that make the -other forms different. +Listing 19-25: An attempt to use `..` in an ambiguous way -### How to Write a Custom derive Macro - -Let’s create a crate named `hello_macro` that defines a trait named -`HelloMacro` with one associated function named `hello_macro`. Rather than -making our users implement the `HelloMacro` trait for each of their types, -we’ll provide a procedural macro so users can annotate their type with -`#[derive(HelloMacro)]` to get a default implementation of the `hello_macro` -function. The default implementation will print `Hello, Macro! My name is` -TypeName`!` where TypeName is the name of the type on which this trait has been -defined. In other words, we’ll write a crate that enables another programmer to -write code like Listing 19-30 using our crate. - -Filename: src/main.rs +When we compile this example, we get this error: ``` -use hello_macro::HelloMacro; -use hello_macro_derive::HelloMacro; - -#[derive(HelloMacro)] -struct Pancakes; +$ cargo run + Compiling patterns v0.1.0 (file:///projects/patterns) +error: `..` can only be used once per tuple pattern + --> src/main.rs:5:22 + | +5 | (.., second, ..) => { + | -- ^^ can only be used once per tuple pattern + | | + | previously used here -fn main() { - Pancakes::hello_macro(); -} +error: could not compile `patterns` (bin "patterns") due to 1 previous error ``` -Listing 19-30: The code a user of our crate will be able to write when using -our procedural macro +It’s impossible for Rust to determine how many values in the tuple to ignore +before matching a value with `second` and then how many further values to +ignore thereafter. This code could mean that we want to ignore `2`, bind +`second` to `4`, and then ignore `8`, `16`, and `32`; or that we want to ignore +`2` and `4`, bind `second` to `8`, and then ignore `16` and `32`; and so forth. +The variable name `second` doesn’t mean anything special to Rust, so we get a +compiler error because using `..` in two places like this is ambiguous. -This code will print `Hello, Macro! My name is Pancakes!` when we’re done. The -first step is to make a new library crate, like this: +<!-- Old headings. Do not remove or links may break. --> -``` -$ cargo new hello_macro --lib -``` +<a id="extra-conditionals-with-match-guards"></a> -Next, we’ll define the `HelloMacro` trait and its associated function: +### Adding Conditionals with Match Guards -Filename: src/lib.rs +A *match guard* is an additional `if` condition, specified after the pattern in +a `match` arm, that must also match for that arm to be chosen. Match guards are +useful for expressing more complex ideas than a pattern alone allows. Note, +however, that they are only available in `match` expressions, not `if let` or +`while let` expressions. -``` -pub trait HelloMacro { - fn hello_macro(); -} -``` +The condition can use variables created in the pattern. Listing 19-26 shows a +`match` where the first arm has the pattern `Some(x)` and also has a match +guard of `if x % 2 == 0` (which will be `true` if the number is even). -We have a trait and its function. At this point, our crate user could implement -the trait to achieve the desired functionality, like so: ``` -use hello_macro::HelloMacro; + let num = Some(4); -struct Pancakes; - -impl HelloMacro for Pancakes { - fn hello_macro() { - println!("Hello, Macro! My name is Pancakes!"); + match num { + Some(x) if x % 2 == 0 => println!("The number {x} is even"), + Some(x) => println!("The number {x} is odd"), + None => (), } -} - -fn main() { - Pancakes::hello_macro(); -} ``` -However, they would need to write the implementation block for each type they -wanted to use with `hello_macro`; we want to spare them from having to do this -work. - -Additionally, we can’t yet provide the `hello_macro` function with default -implementation that will print the name of the type the trait is implemented -on: Rust doesn’t have reflection capabilities, so it can’t look up the type’s -name at runtime. We need a macro to generate code at compile time. +Listing 19-26: Adding a match guard to a pattern -The next step is to define the procedural macro. At the time of this writing, -procedural macros need to be in their own crate. Eventually, this restriction -might be lifted. The convention for structuring crates and macro crates is as -follows: for a crate named foo, a custom `derive` procedural macro crate is -called foo`_derive`. Let’s start a new crate called `hello_macro_derive` inside -our `hello_macro` project: +This example will print `The number 4 is even`. When `num` is compared to the +pattern in the first arm, it matches because `Some(4)` matches `Some(x)`. Then, +the match guard checks whether the remainder of dividing `x` by 2 is equal to +0, and because it is, the first arm is selected. -``` -$ cargo new hello_macro_derive --lib -``` +If `num` had been `Some(5)` instead, the match guard in the first arm would +have been `false` because the remainder of 5 divided by 2 is 1, which is not +equal to 0. Rust would then go to the second arm, which would match because the +second arm doesn’t have a match guard and therefore matches any `Some` variant. -Our two crates are tightly related, so we create the procedural macro crate -within the directory of our `hello_macro` crate. If we change the trait -definition in `hello_macro`, we’ll have to change the implementation of the -procedural macro in `hello_macro_derive` as well. The two crates will need to -be published separately, and programmers using these crates will need to add -both as dependencies and bring them both into scope. We could instead have the -`hello_macro` crate use `hello_macro_derive` as a dependency and re-export the -procedural macro code. However, the way we’ve structured the project makes it -possible for programmers to use `hello_macro` even if they don’t want the -`derive` functionality. +There is no way to express the `if x % 2 == 0` condition within a pattern, so +the match guard gives us the ability to express this logic. The downside of +this additional expressiveness is that the compiler doesn’t try to check for +exhaustiveness when match guard expressions are involved. -We need to declare the `hello_macro_derive` crate as a procedural macro crate. -We’ll also need functionality from the `syn` and `quote` crates, as you’ll see -in a moment, so we need to add them as dependencies. Add the following to the -*Cargo.toml* file for `hello_macro_derive`: +When discussing Listing 19-11, we mentioned that we could use match guards to +solve our pattern-shadowing problem. Recall that we created a new variable +inside the pattern in the `match` expression instead of using the variable +outside the `match`. That new variable meant we couldn’t test against the value +of the outer variable. Listing 19-27 shows how we can use a match guard to fix +this problem. -Filename: hello_macro_derive/Cargo.toml +src/main.rs ``` -[lib] -proc-macro = true +fn main() { + let x = Some(5); + let y = 10; + + match x { + Some(50) => println!("Got 50"), + Some(n) if n == y => println!("Matched, n = {n}"), + _ => println!("Default case, x = {x:?}"), + } -[dependencies] -syn = "1.0" -quote = "1.0" + println!("at the end: x = {x:?}, y = {y}"); +} ``` -To start defining the procedural macro, place the code in Listing 19-31 into -your *src/lib.rs* file for the `hello_macro_derive` crate. Note that this code -won’t compile until we add a definition for the `impl_hello_macro` function. +Listing 19-27: Using a match guard to test for equality with an outer variable -Filename: hello_macro_derive/src/lib.rs +This code will now print `Default case, x = Some(5)`. The pattern in the second +match arm doesn’t introduce a new variable `y` that would shadow the outer `y`, +meaning we can use the outer `y` in the match guard. Instead of specifying the +pattern as `Some(y)`, which would have shadowed the outer `y`, we specify +`Some(n)`. This creates a new variable `n` that doesn’t shadow anything because +there is no `n` variable outside the `match`. -``` -use proc_macro::TokenStream; -use quote::quote; -use syn; +The match guard `if n == y` is not a pattern and therefore doesn’t introduce new +variables. This `y` *is* the outer `y` rather than a new `y` shadowing it, and +we can look for a value that has the same value as the outer `y` by comparing +`n` to `y`. -#[proc_macro_derive(HelloMacro)] -pub fn hello_macro_derive(input: TokenStream) -> TokenStream { - // Construct a representation of Rust code as a syntax tree - // that we can manipulate - let ast = syn::parse(input).unwrap(); +You can also use the *or* operator `|` in a match guard to specify multiple +patterns; the match guard condition will apply to all the patterns. Listing +19-28 shows the precedence when combining a pattern that uses `|` with a match +guard. The important part of this example is that the `if y` match guard +applies to `4`, `5`, *and* `6`, even though it might look like `if y` only +applies to `6`. - // Build the trait implementation - impl_hello_macro(&ast) -} -``` -Listing 19-31: Code that most procedural macro crates will require in order to -process Rust code - -Notice that we’ve split the code into the `hello_macro_derive` function, which -is responsible for parsing the `TokenStream`, and the `impl_hello_macro` -function, which is responsible for transforming the syntax tree: this makes -writing a procedural macro more convenient. The code in the outer function -(`hello_macro_derive` in this case) will be the same for almost every -procedural macro crate you see or create. The code you specify in the body of -the inner function (`impl_hello_macro` in this case) will be different -depending on your procedural macro’s purpose. - -We’ve introduced three new crates: `proc_macro`, `syn` (available from -*https://crates.io/crates/syn*), and `quote` (available from -*https://crates.io/crates/quote*). The `proc_macro` crate comes with Rust, so -we didn’t need to add that to the dependencies in *Cargo.toml*. The -`proc_macro` crate is the compiler’s API that allows us to read and manipulate -Rust code from our code. - -The `syn` crate parses Rust code from a string into a data structure that we -can perform operations on. The `quote` crate turns `syn` data structures back -into Rust code. These crates make it much simpler to parse any sort of Rust -code we might want to handle: writing a full parser for Rust code is no simple -task. - -The `hello_macro_derive` function will be called when a user of our library -specifies `#[derive(HelloMacro)]` on a type. This is possible because we’ve -annotated the `hello_macro_derive` function here with `proc_macro_derive` and -specified the name `HelloMacro`, which matches our trait name; this is the -convention most procedural macros follow. - -The `hello_macro_derive` function first converts the `input` from a -`TokenStream` to a data structure that we can then interpret and perform -operations on. This is where `syn` comes into play. The `parse` function in -`syn` takes a `TokenStream` and returns a `DeriveInput` struct representing the -parsed Rust code. Listing 19-32 shows the relevant parts of the `DeriveInput` -struct we get from parsing the `struct Pancakes;` string. - -``` -DeriveInput { - --snip-- - - ident: Ident { - ident: "Pancakes", - span: #0 bytes(95..103) - }, - data: Struct( - DataStruct { - struct_token: Struct, - fields: Unit, - semi_token: Some( - Semi - ) - } - ) -} ``` + let x = 4; + let y = false; -Listing 19-32: The `DeriveInput` instance we get when parsing the code that has -the macro’s attribute in Listing 19-30 - -The fields of this struct show that the Rust code we’ve parsed is a unit struct -with the `ident` (*identifier*, meaning the name) of `Pancakes`. There are more -fields on this struct for describing all sorts of Rust code; check the `syn` -documentation for `DeriveInput` at -*https://docs.rs/syn/1.0/syn/struct.DeriveInput.html* for more information. - -Soon we’ll define the `impl_hello_macro` function, which is where we’ll build -the new Rust code we want to include. But before we do, note that the output -for our `derive` macro is also a `TokenStream`. The returned `TokenStream` is -added to the code that our crate users write, so when they compile their crate, -they’ll get the extra functionality that we provide in the modified -`TokenStream`. - -You might have noticed that we’re calling `unwrap` to cause the -`hello_macro_derive` function to panic if the call to the `syn::parse` function -fails here. It’s necessary for our procedural macro to panic on errors because -`proc_macro_derive` functions must return `TokenStream` rather than `Result` to -conform to the procedural macro API. We’ve simplified this example by using -`unwrap`; in production code, you should provide more specific error messages -about what went wrong by using `panic!` or `expect`. - -Now that we have the code to turn the annotated Rust code from a `TokenStream` -into a `DeriveInput` instance, let’s generate the code that implements the -`HelloMacro` trait on the annotated type, as shown in Listing 19-33. - -Filename: hello_macro_derive/src/lib.rs - -``` -fn impl_hello_macro(ast: &syn::DeriveInput) -> TokenStream { - let name = &ast.ident; - let gen = quote! { - impl HelloMacro for #name { - fn hello_macro() { - println!( - "Hello, Macro! My name is {}!", - stringify!(#name) - ); - } - } - }; - gen.into() -} + match x { + 4 | 5 | 6 if y => println!("yes"), + _ => println!("no"), + } ``` -Listing 19-33: Implementing the `HelloMacro` trait using the parsed Rust code - -We get an `Ident` struct instance containing the name (identifier) of the -annotated type using `ast.ident`. The struct in Listing 19-32 shows that when -we run the `impl_hello_macro` function on the code in Listing 19-30, the -`ident` we get will have the `ident` field with a value of `"Pancakes"`. Thus -the `name` variable in Listing 19-33 will contain an `Ident` struct instance -that, when printed, will be the string `"Pancakes"`, the name of the struct in -Listing 19-30. +Listing 19-28: Combining multiple patterns with a match guard -The `quote!` macro lets us define the Rust code that we want to return. The -compiler expects something different to the direct result of the `quote!` -macro’s execution, so we need to convert it to a `TokenStream`. We do this by -calling the `into` method, which consumes this intermediate representation and -returns a value of the required `TokenStream` type. +The match condition states that the arm only matches if the value of `x` is +equal to `4`, `5`, or `6` *and* if `y` is `true`. When this code runs, the +pattern of the first arm matches because `x` is `4`, but the match guard `if y` +is `false`, so the first arm is not chosen. The code moves on to the second +arm, which does match, and this program prints `no`. The reason is that the +`if` condition applies to the whole pattern `4 | 5 | 6`, not just to the last +value `6`. In other words, the precedence of a match guard in relation to a +pattern behaves like this: -The `quote!` macro also provides some very cool templating mechanics: we can -enter `#name`, and `quote!` will replace it with the value in the variable -`name`. You can even do some repetition similar to the way regular macros work. -Check out the `quote` crate’s docs at *https://docs.rs/quote* for a thorough -introduction. - -We want our procedural macro to generate an implementation of our `HelloMacro` -trait for the type the user annotated, which we can get by using `#name`. The -trait implementation has the one function `hello_macro`, whose body contains -the functionality we want to provide: printing `Hello, Macro! My name is` and -then the name of the annotated type. - -The `stringify!` macro used here is built into Rust. It takes a Rust -expression, such as `1 + 2`, and at compile time turns the expression into a -string literal, such as `"1 + 2"`. This is different from `format!` or -`println!`, macros which evaluate the expression and then turn the result into -a `String`. There is a possibility that the `#name` input might be an -expression to print literally, so we use `stringify!`. Using `stringify!` also -saves an allocation by converting `#name` to a string literal at compile time. +``` +(4 | 5 | 6) if y => ... +``` -At this point, `cargo build` should complete successfully in both `hello_macro` -and `hello_macro_derive`. Let’s hook up these crates to the code in Listing -19-30 to see the procedural macro in action! Create a new binary project in -your *projects* directory using `cargo new pancakes`. We need to add -`hello_macro` and `hello_macro_derive` as dependencies in the `pancakes` -crate’s *Cargo.toml*. If you’re publishing your versions of `hello_macro` and -`hello_macro_derive` to *https://crates.io*, they would be regular -dependencies; if not, you can specify them as `path` dependencies as follows: +rather than this: ``` -[dependencies] -hello_macro = { path = "../hello_macro" } -hello_macro_derive = { path = "../hello_macro/hello_macro_derive" } +4 | 5 | (6 if y) => ... ``` -Put the code in Listing 19-30 into *src/main.rs*, and run `cargo run`: it -should print `Hello, Macro! My name is Pancakes!` The implementation of the -`HelloMacro` trait from the procedural macro was included without the -`pancakes` crate needing to implement it; the `#[derive(HelloMacro)]` added the -trait implementation. +After running the code, the precedence behavior is evident: If the match guard +were applied only to the final value in the list of values specified using the +`|` operator, the arm would have matched, and the program would have printed +`yes`. -Next, let’s explore how the other kinds of procedural macros differ from custom -`derive` macros. +<!-- Old headings. Do not remove or links may break. --> -### Attribute-like Macros +<a id="-bindings"></a> -Attribute-like macros are similar to custom `derive` macros, but instead of -generating code for the `derive` attribute, they allow you to create new -attributes. They’re also more flexible: `derive` only works for structs and -enums; attributes can be applied to other items as well, such as functions. -Here’s an example of using an attribute-like macro. Say you have an attribute -named `route` that annotates functions when using a web application framework: +### Using @ Bindings -``` -#[route(GET, "/")] -fn index() { -``` +The *at* operator `@` lets us create a variable that holds a value at the same +time we’re testing that value for a pattern match. In Listing 19-29, we want to +test that a `Message::Hello` `id` field is within the range `3..=7`. We also +want to bind the value to the variable `id` so that we can use it in the code +associated with the arm. -This `#[route]` attribute would be defined by the framework as a procedural -macro. The signature of the macro definition function would look like this: ``` -#[proc_macro_attribute] -pub fn route( - attr: TokenStream, - item: TokenStream -) -> TokenStream { -``` - -Here, we have two parameters of type `TokenStream`. The first is for the -contents of the attribute: the `GET, "/"` part. The second is the body of the -item the attribute is attached to: in this case, `fn index() {}` and the rest -of the function’s body. + enum Message { + Hello { id: i32 }, + } -Other than that, attribute-like macros work the same way as custom `derive` -macros: you create a crate with the `proc-macro` crate type and implement a -function that generates the code you want! + let msg = Message::Hello { id: 5 }; -### Function-like Macros + match msg { + Message::Hello { id: id @ 3..=7 } => { + println!("Found an id in range: {id}") + } + Message::Hello { id: 10..=12 } => { + println!("Found an id in another range") + } + Message::Hello { id } => println!("Found some other id: {id}"), + } +``` -Function-like macros define macros that look like function calls. Similarly to -`macro_rules!` macros, they’re more flexible than functions; for example, they -can take an unknown number of arguments. However, `macro_rules!` macros can -only be defined using the match-like syntax we discussed in “Declarative Macros -with macro_rules! for General Metaprogramming” on page XX. Function-like macros -take a `TokenStream` parameter, and their definition manipulates that -`TokenStream` using Rust code as the other two types of procedural macros do. -An example of a function-like macro is an `sql!` macro that might be called -like so: +Listing 19-29: Using `@` to bind to a value in a pattern while also testing it -``` -let sql = sql!(SELECT * FROM posts WHERE id=1); -``` +This example will print `Found an id in range: 5`. By specifying `id @` before +the range `3..=7`, we’re capturing whatever value matched the range in a +variable named `id` while also testing that the value matched the range pattern. -This macro would parse the SQL statement inside it and check that it’s -syntactically correct, which is much more complex processing than a -`macro_rules!` macro can do. The `sql!` macro would be defined like this: +In the second arm, where we only have a range specified in the pattern, the code +associated with the arm doesn’t have a variable that contains the actual value +of the `id` field. The `id` field’s value could have been 10, 11, or 12, but +the code that goes with that pattern doesn’t know which it is. The pattern code +isn’t able to use the value from the `id` field because we haven’t saved the +`id` value in a variable. -``` -#[proc_macro] -pub fn sql(input: TokenStream) -> TokenStream { -``` +In the last arm, where we’ve specified a variable without a range, we do have +the value available to use in the arm’s code in a variable named `id`. The +reason is that we’ve used the struct field shorthand syntax. But we haven’t +applied any test to the value in the `id` field in this arm, as we did with the +first two arms: Any value would match this pattern. -This definition is similar to the custom `derive` macro’s signature: we receive -the tokens that are inside the parentheses and return the code we wanted to -generate. +Using `@` lets us test a value and save it in a variable within one pattern. ## Summary -Whew! Now you have some Rust features in your toolbox that you likely won’t use -often, but you’ll know they’re available in very particular circumstances. -We’ve introduced several complex topics so that when you encounter them in -error message suggestions or in other people’s code, you’ll be able to -recognize these concepts and syntax. Use this chapter as a reference to guide -you to solutions. - -Next, we’ll put everything we’ve discussed throughout the book into practice -and do one more project! +Rust’s patterns are very useful in distinguishing between different kinds of +data. When used in `match` expressions, Rust ensures that your patterns cover +every possible value, or your program won’t compile. Patterns in `let` +statements and function parameters make those constructs more useful, enabling +the destructuring of values into smaller parts and assigning those parts to +variables. We can create simple or complex patterns to suit our needs. +Next, for the penultimate chapter of the book, we’ll look at some advanced +aspects of a variety of Rust’s features. diff --git a/nostarch/chapter20.md b/nostarch/chapter20.md index 9d4e22cd77..77a69459de 100644 --- a/nostarch/chapter20.md +++ b/nostarch/chapter20.md @@ -6,1989 +6,2571 @@ directory, so all fixes need to be made in `/src/`. [TOC] -# Final Project: Building a Multithreaded Web Server +# Advanced Features + +By now, you’ve learned the most commonly used parts of the Rust programming +language. Before we do one more project, in Chapter 21, we’ll look at a few +aspects of the language you might run into every once in a while but may not +use every day. You can use this chapter as a reference for when you encounter +any unknowns. The features covered here are useful in very specific situations. +Although you might not reach for them often, we want to make sure you have a +grasp of all the features Rust has to offer. + +In this chapter, we’ll cover: + +* Unsafe Rust: How to opt out of some of Rust’s guarantees and take + responsibility for manually upholding those guarantees +* Advanced traits: Associated types, default type parameters, fully qualified + syntax, supertraits, and the newtype pattern in relation to traits +* Advanced types: More about the newtype pattern, type aliases, the never type, + and dynamically sized types +* Advanced functions and closures: Function pointers and returning closures +* Macros: Ways to define code that defines more code at compile time + +It’s a panoply of Rust features with something for everyone! Let’s dive in! + +## Unsafe Rust + +All the code we’ve discussed so far has had Rust’s memory safety guarantees +enforced at compile time. However, Rust has a second language hidden inside it +that doesn’t enforce these memory safety guarantees: It’s called *unsafe Rust* +and works just like regular Rust but gives us extra superpowers. + +Unsafe Rust exists because, by nature, static analysis is conservative. When +the compiler tries to determine whether or not code upholds the guarantees, +it’s better for it to reject some valid programs than to accept some invalid +programs. Although the code *might* be okay, if the Rust compiler doesn’t have +enough information to be confident, it will reject the code. In these cases, +you can use unsafe code to tell the compiler, “Trust me, I know what I’m +doing.” Be warned, however, that you use unsafe Rust at your own risk: If you +use unsafe code incorrectly, problems can occur due to memory unsafety, such as +null pointer dereferencing. + +Another reason Rust has an unsafe alter ego is that the underlying computer +hardware is inherently unsafe. If Rust didn’t let you do unsafe operations, you +couldn’t do certain tasks. Rust needs to allow you to do low-level systems +programming, such as directly interacting with the operating system or even +writing your own operating system. Working with low-level systems programming +is one of the goals of the language. Let’s explore what we can do with unsafe +Rust and how to do it. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="unsafe-superpowers"></a> + +### Performing Unsafe Superpowers -It’s been a long journey, but we’ve reached the end of the book. In this -chapter, we’ll build one more project together to demonstrate some of the -concepts we covered in the final chapters, as well as recap some earlier -lessons. +To switch to unsafe Rust, use the `unsafe` keyword and then start a new block +that holds the unsafe code. You can take five actions in unsafe Rust that you +can’t in safe Rust, which we call *unsafe superpowers*. Those superpowers +include the ability to: -For our final project, we’ll make a web server that says “hello” and looks like -Figure 20-1 in a web browser. +1. Dereference a raw pointer. +1. Call an unsafe function or method. +1. Access or modify a mutable static variable. +1. Implement an unsafe trait. +1. Access fields of `union`s. -Figure 20-1: Our final shared project +It’s important to understand that `unsafe` doesn’t turn off the borrow checker +or disable any of Rust’s other safety checks: If you use a reference in unsafe +code, it will still be checked. The `unsafe` keyword only gives you access to +these five features that are then not checked by the compiler for memory +safety. You’ll still get some degree of safety inside an unsafe block. -Here is our plan for building the web server: +In addition, `unsafe` does not mean the code inside the block is necessarily +dangerous or that it will definitely have memory safety problems: The intent is +that as the programmer, you’ll ensure that the code inside an `unsafe` block +will access memory in a valid way. -1. Learn a bit about TCP and HTTP. -1. Listen for TCP connections on a socket. -1. Parse a small number of HTTP requests. -1. Create a proper HTTP response. -1. Improve the throughput of our server with a thread pool. +People are fallible and mistakes will happen, but by requiring these five +unsafe operations to be inside blocks annotated with `unsafe`, you’ll know that +any errors related to memory safety must be within an `unsafe` block. Keep +`unsafe` blocks small; you’ll be thankful later when you investigate memory +bugs. -Before we get started, we should mention one detail: the method we’ll use won’t -be the best way to build a web server with Rust. Community members have -published a number of production-ready crates available at *https://crates.io* -that provide more complete web server and thread pool implementations than -we’ll build. However, our intention in this chapter is to help you learn, not -to take the easy route. Because Rust is a systems programming language, we can -choose the level of abstraction we want to work with and can go to a lower -level than is possible or practical in other languages. We’ll therefore write -the basic HTTP server and thread pool manually so you can learn the general -ideas and techniques behind the crates you might use in the future. +To isolate unsafe code as much as possible, it’s best to enclose such code +within a safe abstraction and provide a safe API, which we’ll discuss later in +the chapter when we examine unsafe functions and methods. Parts of the standard +library are implemented as safe abstractions over unsafe code that has been +audited. Wrapping unsafe code in a safe abstraction prevents uses of `unsafe` +from leaking out into all the places that you or your users might want to use +the functionality implemented with `unsafe` code, because using a safe +abstraction is safe. -## Building a Single-Threaded Web Server +Let’s look at each of the five unsafe superpowers in turn. We’ll also look at +some abstractions that provide a safe interface to unsafe code. -We’ll start by getting a single-threaded web server working. Before we begin, -let’s look at a quick overview of the protocols involved in building web -servers. The details of these protocols are beyond the scope of this book, but -a brief overview will give you the information you need. +### Dereferencing a Raw Pointer -The two main protocols involved in web servers are *Hypertext Transfer -Protocol* *(HTTP)* and *Transmission Control Protocol* *(TCP)*. Both protocols -are *request-response* protocols, meaning a *client* initiates requests and a -*server* listens to the requests and provides a response to the client. The -contents of those requests and responses are defined by the protocols. +In Chapter 4, in the “Dangling References” section, we mentioned that the compiler ensures that references are always +valid. Unsafe Rust has two new types called *raw pointers* that are similar to +references. As with references, raw pointers can be immutable or mutable and +are written as `*const T` and `*mut T`, respectively. The asterisk isn’t the +dereference operator; it’s part of the type name. In the context of raw +pointers, *immutable* means that the pointer can’t be directly assigned to +after being dereferenced. -TCP is the lower-level protocol that describes the details of how information -gets from one server to another but doesn’t specify what that information is. -HTTP builds on top of TCP by defining the contents of the requests and -responses. It’s technically possible to use HTTP with other protocols, but in -the vast majority of cases, HTTP sends its data over TCP. We’ll work with the -raw bytes of TCP and HTTP requests and responses. +Different from references and smart pointers, raw pointers: -### Listening to the TCP Connection +* Are allowed to ignore the borrowing rules by having both immutable and + mutable pointers or multiple mutable pointers to the same location +* Aren’t guaranteed to point to valid memory +* Are allowed to be null +* Don’t implement any automatic cleanup + +By opting out of having Rust enforce these guarantees, you can give up +guaranteed safety in exchange for greater performance or the ability to +interface with another language or hardware where Rust’s guarantees don’t apply. + +Listing 20-1 shows how to create an immutable and a mutable raw pointer. -Our web server needs to listen to a TCP connection, so that’s the first part -we’ll work on. The standard library offers a `std::net` module that lets us do -this. Let’s make a new project in the usual fashion: ``` -$ cargo new hello - Created binary (application) `hello` project -$ cd hello + let mut num = 5; + + let r1 = &raw const num; + let r2 = &raw mut num; ``` -Now enter the code in Listing 20-1 in *src/main.rs* to start. This code will -listen at the local address `127.0.0.1:7878` for incoming TCP streams. When it -gets an incoming stream, it will print `Connection established!`. +Listing 20-1: Creating raw pointers with the raw borrow operators -Filename: src/main.rs +Notice that we don’t include the `unsafe` keyword in this code. We can create +raw pointers in safe code; we just can’t dereference raw pointers outside an +unsafe block, as you’ll see in a bit. -``` -use std::net::TcpListener; +We’ve created raw pointers by using the raw borrow operators: `&raw const num` +creates a `*const i32` immutable raw pointer, and `&raw mut num` creates a `*mut i32` mutable raw pointer. Because we created them directly from a local +variable, we know these particular raw pointers are valid, but we can’t make +that assumption about just any raw pointer. -fn main() { - 1 let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); +To demonstrate this, next we’ll create a raw pointer whose validity we can’t be +so certain of, using the keyword `as` to cast a value instead of using the raw +borrow operator. Listing 20-2 shows how to create a raw pointer to an arbitrary +location in memory. Trying to use arbitrary memory is undefined: There might be +data at that address or there might not, the compiler might optimize the code +so that there is no memory access, or the program might terminate with a +segmentation fault. Usually, there is no good reason to write code like this, +especially in cases where you can use a raw borrow operator instead, but it is +possible. - 2 for stream in listener.incoming() { - 3 let stream = stream.unwrap(); - 4 println!("Connection established!"); - } -} +``` + let address = 0x012345usize; + let r = address as *const i32; ``` -Listing 20-1: Listening for incoming streams and printing a message when we -receive a stream - -Using `TcpListener`, we can listen for TCP connections at the address -`127.0.0.1:7878` [1]. In the address, the section before the colon is an IP -address representing your computer (this is the same on every computer and -doesn’t represent the authors’ computer specifically), and `7878` is the port. -We’ve chosen this port for two reasons: HTTP isn’t normally accepted on this -port, so our server is unlikely to conflict with any other web server you might -have running on your machine, and 7878 is *rust* typed on a telephone. - -The `bind` function in this scenario works like the `new` function in that it -will return a new `TcpListener` instance. The function is called `bind` -because, in networking, connecting to a port to listen to is known as “binding -to a port.” - -The `bind` function returns a `Result<T, E>`, which indicates that it’s -possible for binding to fail. For example, connecting to port 80 requires -administrator privileges (non-administrators can listen only on ports higher -than 1023), so if we tried to connect to port 80 without being an -administrator, binding wouldn’t work. Binding also wouldn’t work, for example, -if we ran two instances of our program and so had two programs listening to the -same port. Because we’re writing a basic server just for learning purposes, we -won’t worry about handling these kinds of errors; instead, we use `unwrap` to -stop the program if errors happen. - -The `incoming` method on `TcpListener` returns an iterator that gives us a -sequence of streams [2] (more specifically, streams of type `TcpStream`). A -single *stream* represents an open connection between the client and the -server. A *connection* is the name for the full request and response process in -which a client connects to the server, the server generates a response, and the -server closes the connection. As such, we will read from the `TcpStream` to see -what the client sent and then write our response to the stream to send data -back to the client. Overall, this `for` loop will process each connection in -turn and produce a series of streams for us to handle. - -For now, our handling of the stream consists of calling `unwrap` to terminate -our program if the stream has any errors [3]; if there aren’t any errors, the -program prints a message [4]. We’ll add more functionality for the success case -in the next listing. The reason we might receive errors from the `incoming` -method when a client connects to the server is that we’re not actually -iterating over connections. Instead, we’re iterating over *connection -attempts*. The connection might not be successful for a number of reasons, many -of them operating system specific. For example, many operating systems have a -limit to the number of simultaneous open connections they can support; new -connection attempts beyond that number will produce an error until some of the -open connections are closed. - -Let’s try running this code! Invoke `cargo run` in the terminal and then load -*127.0.0.1:7878* in a web browser. The browser should show an error message -like “Connection reset” because the server isn’t currently sending back any -data. But when you look at your terminal, you should see several messages that -were printed when the browser connected to the server! - -``` - Running `target/debug/hello` -Connection established! -Connection established! -Connection established! -``` - -Sometimes you’ll see multiple messages printed for one browser request; the -reason might be that the browser is making a request for the page as well as a -request for other resources, like the *favicon.ico* icon that appears in the -browser tab. - -It could also be that the browser is trying to connect to the server multiple -times because the server isn’t responding with any data. When `stream` goes out -of scope and is dropped at the end of the loop, the connection is closed as -part of the `drop` implementation. Browsers sometimes deal with closed -connections by retrying, because the problem might be temporary. The important -factor is that we’ve successfully gotten a handle to a TCP connection! - -Remember to stop the program by pressing ctrl-C when you’re done running a -particular version of the code. Then restart the program by invoking the `cargo -run` command after you’ve made each set of code changes to make sure you’re -running the newest code. - -### Reading the Request - -Let’s implement the functionality to read the request from the browser! To -separate the concerns of first getting a connection and then taking some action -with the connection, we’ll start a new function for processing connections. In -this new `handle_connection` function, we’ll read data from the TCP stream and -print it so we can see the data being sent from the browser. Change the code to -look like Listing 20-2. - -Filename: src/main.rs - -``` -1 use std::{ - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, -}; +Listing 20-2: Creating a raw pointer to an arbitrary memory address -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); +Recall that we can create raw pointers in safe code, but we can’t dereference +raw pointers and read the data being pointed to. In Listing 20-3, we use the +dereference operator `*` on a raw pointer that requires an `unsafe` block. - for stream in listener.incoming() { - let stream = stream.unwrap(); - 2 handle_connection(stream); - } -} +``` + let mut num = 5; -fn handle_connection(mut stream: TcpStream) { - 3 let buf_reader = BufReader::new(&mut stream); - 4 let http_request: Vec<_> = buf_reader - 5 .lines() - 6 .map(|result| result.unwrap()) - 7 .take_while(|line| !line.is_empty()) - .collect(); + let r1 = &raw const num; + let r2 = &raw mut num; - 8 println!("Request: {:#?}", http_request); -} + unsafe { + println!("r1 is: {}", *r1); + println!("r2 is: {}", *r2); + } ``` -Listing 20-2: Reading from the `TcpStream` and printing the data +Listing 20-3: Dereferencing raw pointers within an `unsafe` block -We bring `std::io::prelude` and `std::io::BufReader` into scope to get access -to traits and types that let us read from and write to the stream [1]. In the -`for` loop in the `main` function, instead of printing a message that says we -made a connection, we now call the new `handle_connection` function and pass -the `stream` to it [2]. +Creating a pointer does no harm; it’s only when we try to access the value that +it points at that we might end up dealing with an invalid value. -In the `handle_connection` function, we create a new `BufReader` instance that -wraps a mutable reference to the `stream` [3]. `BufReader` adds buffering by -managing calls to the `std::io::Read` trait methods for us. +Note also that in Listings 20-1 and 20-3, we created `*const i32` and `*mut i32` raw pointers that both pointed to the same memory location, where `num` is +stored. If we instead tried to create an immutable and a mutable reference to +`num`, the code would not have compiled because Rust’s ownership rules don’t +allow a mutable reference at the same time as any immutable references. With +raw pointers, we can create a mutable pointer and an immutable pointer to the +same location and change data through the mutable pointer, potentially creating +a data race. Be careful! -We create a variable named `http_request` to collect the lines of the request -the browser sends to our server. We indicate that we want to collect these -lines in a vector by adding the `Vec<_>` type annotation [4]. +With all of these dangers, why would you ever use raw pointers? One major use +case is when interfacing with C code, as you’ll see in the next section. +Another case is when building up safe abstractions that the borrow checker +doesn’t understand. We’ll introduce unsafe functions and then look at an +example of a safe abstraction that uses unsafe code. -`BufReader` implements the `std::io::BufRead` trait, which provides the `lines` -method [5]. The `lines` method returns an iterator of `Result<String, -std::io::Error>` by splitting the stream of data whenever it sees a newline -byte. To get each `String`, we map and `unwrap` each `Result` [6]. The `Result` -might be an error if the data isn’t valid UTF-8 or if there was a problem -reading from the stream. Again, a production program should handle these errors -more gracefully, but we’re choosing to stop the program in the error case for -simplicity. +### Calling an Unsafe Function or Method -The browser signals the end of an HTTP request by sending two newline -characters in a row, so to get one request from the stream, we take lines until -we get a line that is the empty string [7]. Once we’ve collected the lines into -the vector, we’re printing them out using pretty debug formatting [8] so we can -take a look at the instructions the web browser is sending to our server. +The second type of operation you can perform in an unsafe block is calling +unsafe functions. Unsafe functions and methods look exactly like regular +functions and methods, but they have an extra `unsafe` before the rest of the +definition. The `unsafe` keyword in this context indicates the function has +requirements we need to uphold when we call this function, because Rust can’t +guarantee we’ve met these requirements. By calling an unsafe function within an +`unsafe` block, we’re saying that we’ve read this function’s documentation and +we take responsibility for upholding the function’s contracts. -Let’s try this code! Start the program and make a request in a web browser -again. Note that we’ll still get an error page in the browser, but our -program’s output in the terminal will now look similar to this: +Here is an unsafe function named `dangerous` that doesn’t do anything in its +body: + +``` + unsafe fn dangerous() {} + + unsafe { + dangerous(); + } +``` + +We must call the `dangerous` function within a separate `unsafe` block. If we +try to call `dangerous` without the `unsafe` block, we’ll get an error: ``` $ cargo run - Compiling hello v0.1.0 (file:///projects/hello) - Finished dev [unoptimized + debuginfo] target(s) in 0.42s - Running `target/debug/hello` -Request: [ - "GET / HTTP/1.1", - "Host: 127.0.0.1:7878", - "User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:99.0) -Gecko/20100101 Firefox/99.0", - "Accept: -text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/* -;q=0.8", - "Accept-Language: en-US,en;q=0.5", - "Accept-Encoding: gzip, deflate, br", - "DNT: 1", - "Connection: keep-alive", - "Upgrade-Insecure-Requests: 1", - "Sec-Fetch-Dest: document", - "Sec-Fetch-Mode: navigate", - "Sec-Fetch-Site: none", - "Sec-Fetch-User: ?1", - "Cache-Control: max-age=0", -] + Compiling unsafe-example v0.1.0 (file:///projects/unsafe-example) +error[E0133]: call to unsafe function `dangerous` is unsafe and requires unsafe block + --> src/main.rs:4:5 + | +4 | dangerous(); + | ^^^^^^^^^^^ call to unsafe function + | + = note: consult the function's documentation for information on how to avoid undefined behavior + +For more information about this error, try `rustc --explain E0133`. +error: could not compile `unsafe-example` (bin "unsafe-example") due to 1 previous error ``` -Depending on your browser, you might get slightly different output. Now that -we’re printing the request data, we can see why we get multiple connections -from one browser request by looking at the path after `GET` in the first line -of the request. If the repeated connections are all requesting */*, we know the -browser is trying to fetch */* repeatedly because it’s not getting a response -from our program. +With the `unsafe` block, we’re asserting to Rust that we’ve read the function’s +documentation, we understand how to use it properly, and we’ve verified that +we’re fulfilling the contract of the function. + +To perform unsafe operations in the body of an `unsafe` function, you still +need to use an `unsafe` block, just as within a regular function, and the +compiler will warn you if you forget. This helps us keep `unsafe` blocks as +small as possible, as unsafe operations may not be needed across the whole +function body. -Let’s break down this request data to understand what the browser is asking of -our program. +#### Creating a Safe Abstraction over Unsafe Code -### A Closer Look at an HTTP Request +Just because a function contains unsafe code doesn’t mean we need to mark the +entire function as unsafe. In fact, wrapping unsafe code in a safe function is +a common abstraction. As an example, let’s study the `split_at_mut` function +from the standard library, which requires some unsafe code. We’ll explore how +we might implement it. This safe method is defined on mutable slices: It takes +one slice and makes it two by splitting the slice at the index given as an +argument. Listing 20-4 shows how to use `split_at_mut`. -HTTP is a text-based protocol, and a request takes this format: ``` -Method Request-URI HTTP-Version CRLF -headers CRLF -message-body + let mut v = vec![1, 2, 3, 4, 5, 6]; + + let r = &mut v[..]; + + let (a, b) = r.split_at_mut(3); + + assert_eq!(a, &mut [1, 2, 3]); + assert_eq!(b, &mut [4, 5, 6]); ``` -The first line is the *request line* that holds information about what the -client is requesting. The first part of the request line indicates the *method* -being used, such as `GET` or `POST`, which describes how the client is making -this request. Our client used a `GET` request, which means it is asking for -information. +Listing 20-4: Using the safe `split_at_mut` function -The next part of the request line is */*, which indicates the *uniform resource -identifier* *(URI)* the client is requesting: a URI is almost, but not quite, -the same as a *uniform resource locator* *(URL)*. The difference between URIs -and URLs isn’t important for our purposes in this chapter, but the HTTP spec -uses the term *URI*, so we can just mentally substitute *URL* for *URI* here. +We can’t implement this function using only safe Rust. An attempt might look +something like Listing 20-5, which won’t compile. For simplicity, we’ll +implement `split_at_mut` as a function rather than a method and only for slices +of `i32` values rather than for a generic type `T`. -The last part is the HTTP version the client uses, and then the request line -ends in a CRLF sequence. (CRLF stands for *carriage return* and *line feed*, -which are terms from the typewriter days!) The CRLF sequence can also be -written as `\r\n`, where `\r` is a carriage return and `\n` is a line feed. The -*CRLF sequence* separates the request line from the rest of the request data. -Note that when the CRLF is printed, we see a new line start rather than `\r\n`. -Looking at the request line data we received from running our program so far, -we see that `GET` is the method, */* is the request URI, and `HTTP/1.1` is the -version. +``` +fn split_at_mut(values: &mut [i32], mid: usize) -> (&mut [i32], &mut [i32]) { + let len = values.len(); + + assert!(mid <= len); -After the request line, the remaining lines starting from `Host:` onward are -headers. `GET` requests have no body. + (&mut values[..mid], &mut values[mid..]) +} +``` -Try making a request from a different browser or asking for a different -address, such as *127.0.0.1:7878/test*, to see how the request data changes. +Listing 20-5: An attempted implementation of `split_at_mut` using only safe Rust -Now that we know what the browser is asking for, let’s send back some data! +This function first gets the total length of the slice. Then, it asserts that +the index given as a parameter is within the slice by checking whether it’s +less than or equal to the length. The assertion means that if we pass an index +that is greater than the length to split the slice at, the function will panic +before it attempts to use that index. -### Writing a Response +Then, we return two mutable slices in a tuple: one from the start of the +original slice to the `mid` index and another from `mid` to the end of the +slice. -We’re going to implement sending data in response to a client request. -Responses have the following format: +When we try to compile the code in Listing 20-5, we’ll get an error: ``` -HTTP-Version Status-Code Reason-Phrase CRLF -headers CRLF -message-body +$ cargo run + Compiling unsafe-example v0.1.0 (file:///projects/unsafe-example) +error[E0499]: cannot borrow `*values` as mutable more than once at a time + --> src/main.rs:6:31 + | +1 | fn split_at_mut(values: &mut [i32], mid: usize) -> (&mut [i32], &mut [i32]) { + | - let's call the lifetime of this reference `'1` +... +6 | (&mut values[..mid], &mut values[mid..]) + | --------------------------^^^^^^-------- + | | | | + | | | second mutable borrow occurs here + | | first mutable borrow occurs here + | returning this value requires that `*values` is borrowed for `'1` + | + = help: use `.split_at_mut(position)` to obtain two mutable non-overlapping sub-slices + +For more information about this error, try `rustc --explain E0499`. +error: could not compile `unsafe-example` (bin "unsafe-example") due to 1 previous error ``` -The first line is a *status line* that contains the HTTP version used in the -response, a numeric status code that summarizes the result of the request, and -a reason phrase that provides a text description of the status code. After the -CRLF sequence are any headers, another CRLF sequence, and the body of the -response. +Rust’s borrow checker can’t understand that we’re borrowing different parts of +the slice; it only knows that we’re borrowing from the same slice twice. +Borrowing different parts of a slice is fundamentally okay because the two +slices aren’t overlapping, but Rust isn’t smart enough to know this. When we +know code is okay, but Rust doesn’t, it’s time to reach for unsafe code. + +Listing 20-6 shows how to use an `unsafe` block, a raw pointer, and some calls +to unsafe functions to make the implementation of `split_at_mut` work. -Here is an example response that uses HTTP version 1.1, and has a status code -of 200, an OK reason phrase, no headers, and no body: ``` -HTTP/1.1 200 OK\r\n\r\n +use std::slice; + +fn split_at_mut(values: &mut [i32], mid: usize) -> (&mut [i32], &mut [i32]) { + let len = values.len(); + let ptr = values.as_mut_ptr(); + + assert!(mid <= len); + + unsafe { + ( + slice::from_raw_parts_mut(ptr, mid), + slice::from_raw_parts_mut(ptr.add(mid), len - mid), + ) + } +} ``` -The status code 200 is the standard success response. The text is a tiny -successful HTTP response. Let’s write this to the stream as our response to a -successful request! From the `handle_connection` function, remove the -`println!` that was printing the request data and replace it with the code in -Listing 20-3. +Listing 20-6: Using unsafe code in the implementation of the `split_at_mut` function + +Recall from “The Slice Type” section in +Chapter 4 that a slice is a pointer to some data and the length of the slice. +We use the `len` method to get the length of a slice and the `as_mut_ptr` +method to access the raw pointer of a slice. In this case, because we have a +mutable slice to `i32` values, `as_mut_ptr` returns a raw pointer with the type +`*mut i32`, which we’ve stored in the variable `ptr`. + +We keep the assertion that the `mid` index is within the slice. Then, we get to +the unsafe code: The `slice::from_raw_parts_mut` function takes a raw pointer +and a length, and it creates a slice. We use this function to create a slice +that starts from `ptr` and is `mid` items long. Then, we call the `add` method +on `ptr` with `mid` as an argument to get a raw pointer that starts at `mid`, +and we create a slice using that pointer and the remaining number of items +after `mid` as the length. + +The function `slice::from_raw_parts_mut` is unsafe because it takes a raw +pointer and must trust that this pointer is valid. The `add` method on raw +pointers is also unsafe because it must trust that the offset location is also +a valid pointer. Therefore, we had to put an `unsafe` block around our calls to +`slice::from_raw_parts_mut` and `add` so that we could call them. By looking at +the code and by adding the assertion that `mid` must be less than or equal to +`len`, we can tell that all the raw pointers used within the `unsafe` block +will be valid pointers to data within the slice. This is an acceptable and +appropriate use of `unsafe`. + +Note that we don’t need to mark the resultant `split_at_mut` function as +`unsafe`, and we can call this function from safe Rust. We’ve created a safe +abstraction to the unsafe code with an implementation of the function that uses +`unsafe` code in a safe way, because it creates only valid pointers from the +data this function has access to. + +In contrast, the use of `slice::from_raw_parts_mut` in Listing 20-7 would +likely crash when the slice is used. This code takes an arbitrary memory +location and creates a slice 10,000 items long. -Filename: src/main.rs ``` -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let http_request: Vec<_> = buf_reader - .lines() - .map(|result| result.unwrap()) - .take_while(|line| !line.is_empty()) - .collect(); + use std::slice; - 1 let response = "HTTP/1.1 200 OK\r\n\r\n"; + let address = 0x01234usize; + let r = address as *mut i32; - 2 stream.write_all(response.3 as_bytes()).unwrap(); -} + let values: &[i32] = unsafe { slice::from_raw_parts_mut(r, 10000) }; ``` -Listing 20-3: Writing a tiny successful HTTP response to the stream +Listing 20-7: Creating a slice from an arbitrary memory location -The first new line defines the `response` variable that holds the success -message’s data [1]. Then we call `as_bytes` on our `response` to convert the -string data to bytes [3]. The `write_all` method on `stream` takes a `&[u8]` -and sends those bytes directly down the connection [2]. Because the `write_all` -operation could fail, we use `unwrap` on any error result as before. Again, in -a real application you would add error handling here. +We don’t own the memory at this arbitrary location, and there is no guarantee +that the slice this code creates contains valid `i32` values. Attempting to use +`values` as though it’s a valid slice results in undefined behavior. -With these changes, let’s run our code and make a request. We’re no longer -printing any data to the terminal, so we won’t see any output other than the -output from Cargo. When you load *127.0.0.1:7878* in a web browser, you should -get a blank page instead of an error. You’ve just handcoded receiving an HTTP -request and sending a response! +#### Using extern Functions to Call External Code -### Returning Real HTML +Sometimes your Rust code might need to interact with code written in another +language. For this, Rust has the keyword `extern` that facilitates the creation +and use of a *Foreign Function Interface (FFI)*, which is a way for a +programming language to define functions and enable a different (foreign) +programming language to call those functions. -Let’s implement the functionality for returning more than a blank page. Create -the new file *hello.html* in the root of your project directory, not in the -*src* directory. You can input any HTML you want; Listing 20-4 shows one -possibility. +Listing 20-8 demonstrates how to set up an integration with the `abs` function +from the C standard library. Functions declared within `extern` blocks are +generally unsafe to call from Rust code, so `extern` blocks must also be marked +`unsafe`. The reason is that other languages don’t enforce Rust’s rules and +guarantees, and Rust can’t check them, so responsibility falls on the +programmer to ensure safety. -Filename: hello.html +src/main.rs ``` -<!DOCTYPE html> -<html lang="en"> - <head> - <meta charset="utf-8"> - <title>Hello! - - -

Hello!

-

Hi from Rust

- - +unsafe extern "C" { + fn abs(input: i32) -> i32; +} + +fn main() { + unsafe { + println!("Absolute value of -3 according to C: {}", abs(-3)); + } +} ``` -Listing 20-4: A sample HTML file to return in a response +Listing 20-8: Declaring and calling an `extern` function defined in another language + +Within the `unsafe extern "C"` block, we list the names and signatures of +external functions from another language we want to call. The `"C"` part +defines which *application binary interface (ABI)* the external function uses: +The ABI defines how to call the function at the assembly level. The `"C"` ABI +is the most common and follows the C programming language’s ABI. Information +about all the ABIs Rust supports is available in the Rust Reference at *../reference/items/external-blocks.html#abi*. -This is a minimal HTML5 document with a heading and some text. To return this -from the server when a request is received, we’ll modify `handle_connection` as -shown in Listing 20-5 to read the HTML file, add it to the response as a body, -and send it. +Every item declared within an `unsafe extern` block is implicitly unsafe. +However, some FFI functions *are* safe to call. For example, the `abs` function +from C’s standard library does not have any memory safety considerations, and we +know it can be called with any `i32`. In cases like this, we can use the `safe` +keyword to say that this specific function is safe to call even though it is in +an `unsafe extern` block. Once we make that change, calling it no longer +requires an `unsafe` block, as shown in Listing 20-9. -Filename: src/main.rs +src/main.rs ``` -use std::{ - 1 fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, -}; ---snip-- +unsafe extern "C" { + safe fn abs(input: i32) -> i32; +} -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - let http_request: Vec<_> = buf_reader - .lines() - .map(|result| result.unwrap()) - .take_while(|line| !line.is_empty()) - .collect(); +fn main() { + println!("Absolute value of -3 according to C: {}", abs(-3)); +} +``` - let status_line = "HTTP/1.1 200 OK"; - let contents = fs::read_to_string("hello.html").unwrap(); - let length = contents.len(); +Listing 20-9: Explicitly marking a function as `safe` within an `unsafe extern` block and calling it safely - 2 let response = format!( - "{status_line}\r\n\ - Content-Length: {length}\r\n\r\n\ - {contents}" - ); +Marking a function as `safe` does not inherently make it safe! Instead, it is +like a promise you are making to Rust that it is safe. It is still your +responsibility to make sure that promise is kept! + +#### Calling Rust Functions from Other Languages + +We can also use `extern` to create an interface that allows other languages to +call Rust functions. Instead of creating a whole `extern` block, we add the +`extern` keyword and specify the ABI to use just before the `fn` keyword for +the relevant function. We also need to add an `#[unsafe(no_mangle)]` annotation +to tell the Rust compiler not to mangle the name of this function. *Mangling* +is when a compiler changes the name we’ve given a function to a different name +that contains more information for other parts of the compilation process to +consume but is less human readable. Every programming language compiler mangles +names slightly differently, so for a Rust function to be nameable by other +languages, we must disable the Rust compiler’s name mangling. This is unsafe +because there might be name collisions across libraries without the built-in +mangling, so it is our responsibility to make sure the name we choose is safe +to export without mangling. - stream.write_all(response.as_bytes()).unwrap(); +In the following example, we make the `call_from_c` function accessible from C +code, after it’s compiled to a shared library and linked from C: + +``` +#[unsafe(no_mangle)] +pub extern "C" fn call_from_c() { + println!("Just called a Rust function from C!"); } ``` -Listing 20-5: Sending the contents of *hello.html* as the body of the response +This usage of `extern` requires `unsafe` only in the attribute, not on the +`extern` block. -We’ve added `fs` to the `use` statement to bring the standard library’s -filesystem module into scope [1]. The code for reading the contents of a file -to a string should look familiar; we used it when we read the contents of a -file for our I/O project in Listing 12-4. +### Accessing or Modifying a Mutable Static Variable -Next, we use `format!` to add the file’s contents as the body of the success -response [2]. To ensure a valid HTTP response, we add the `Content-Length` -header which is set to the size of our response body, in this case the size of -`hello.html`. +In this book, we’ve not yet talked about global variables, which Rust does +support but which can be problematic with Rust’s ownership rules. If two +threads are accessing the same mutable global variable, it can cause a data +race. -Run this code with `cargo run` and load *127.0.0.1:7878* in your browser; you -should see your HTML rendered! +In Rust, global variables are called *static* variables. Listing 20-10 shows an +example declaration and use of a static variable with a string slice as a +value. -Currently, we’re ignoring the request data in `http_request` and just sending -back the contents of the HTML file unconditionally. That means if you try -requesting *127.0.0.1:7878/something-else* in your browser, you’ll still get -back this same HTML response. At the moment, our server is very limited and -does not do what most web servers do. We want to customize our responses -depending on the request and only send back the HTML file for a well-formed -request to */*. +src/main.rs -### Validating the Request and Selectively Responding +``` +static HELLO_WORLD: &str = "Hello, world!"; -Right now, our web server will return the HTML in the file no matter what the -client requested. Let’s add functionality to check that the browser is -requesting */* before returning the HTML file, and return an error if the -browser requests anything else. For this we need to modify `handle_connection`, -as shown in Listing 20-6. This new code checks the content of the request -received against what we know a request for */* looks like and adds `if` and -`else` blocks to treat requests differently. +fn main() { + println!("value is: {HELLO_WORLD}"); +} +``` -Filename: src/main.rs +Listing 20-10: Defining and using an immutable static variable -``` ---snip-- +Static variables are similar to constants, which we discussed in the +“Declaring Constants” section in Chapter 3. The +names of static variables are in `SCREAMING_SNAKE_CASE` by convention. Static +variables can only store references with the `'static` lifetime, which means +the Rust compiler can figure out the lifetime and we aren’t required to +annotate it explicitly. Accessing an immutable static variable is safe. -fn handle_connection(mut stream: TcpStream) { - let buf_reader = BufReader::new(&mut stream); - 1 let request_line = buf_reader - .lines() - .next() - .unwrap() - .unwrap(); +A subtle difference between constants and immutable static variables is that +values in a static variable have a fixed address in memory. Using the value +will always access the same data. Constants, on the other hand, are allowed to +duplicate their data whenever they’re used. Another difference is that static +variables can be mutable. Accessing and modifying mutable static variables is +*unsafe*. Listing 20-11 shows how to declare, access, and modify a mutable +static variable named `COUNTER`. - 2 if request_line == "GET / HTTP/1.1" { - let status_line = "HTTP/1.1 200 OK"; - let contents = fs::read_to_string("hello.html").unwrap(); - let length = contents.len(); +src/main.rs - let response = format!( - "{status_line}\r\n\ - Content-Length: {length}\r\n\r\n\ - {contents}" - ); +``` +static mut COUNTER: u32 = 0; - stream.write_all(response.as_bytes()).unwrap(); - 3 } else { - // some other request +/// SAFETY: Calling this from more than a single thread at a time is undefined +/// behavior, so you *must* guarantee you only call it from a single thread at +/// a time. +unsafe fn add_to_count(inc: u32) { + unsafe { + COUNTER += inc; + } +} + +fn main() { + unsafe { + // SAFETY: This is only called from a single thread in `main`. + add_to_count(3); + println!("COUNTER: {}", *(&raw const COUNTER)); } } ``` -Listing 20-6: Handling requests to */* differently from other requests +Listing 20-11: Reading from or writing to a mutable static variable is unsafe. -We’re only going to be looking at the first line of the HTTP request, so rather -than reading the entire request into a vector, we’re calling `next` to get the -first item from the iterator [1]. The first `unwrap` takes care of the `Option` -and stops the program if the iterator has no items. The second `unwrap` handles -the `Result` and has the same effect as the `unwrap` that was in the `map` -added in Listing 20-2. +As with regular variables, we specify mutability using the `mut` keyword. Any +code that reads or writes from `COUNTER` must be within an `unsafe` block. The +code in Listing 20-11 compiles and prints `COUNTER: 3` as we would expect +because it’s single threaded. Having multiple threads access `COUNTER` would +likely result in data races, so it is undefined behavior. Therefore, we need to +mark the entire function as `unsafe` and document the safety limitation so that +anyone calling the function knows what they are and are not allowed to do +safely. -Next, we check the `request_line` to see if it equals the request line of a GET -request to the */* path [2]. If it does, the `if` block returns the contents of -our HTML file. +Whenever we write an unsafe function, it is idiomatic to write a comment +starting with `SAFETY` and explaining what the caller needs to do to call the +function safely. Likewise, whenever we perform an unsafe operation, it is +idiomatic to write a comment starting with `SAFETY` to explain how the safety +rules are upheld. -If the `request_line` does *not* equal the GET request to the */* path, it -means we’ve received some other request. We’ll add code to the `else` block [3] -in a moment to respond to all other requests. +Additionally, the compiler will deny by default any attempt to create +references to a mutable static variable through a compiler lint. You must +either explicitly opt out of that lint’s protections by adding an +`#[allow(static_mut_refs)]` annotation or access the mutable static variable +via a raw pointer created with one of the raw borrow operators. That includes +cases where the reference is created invisibly, as when it is used in the +`println!` in this code listing. Requiring references to static mutable +variables to be created via raw pointers helps make the safety requirements for +using them more obvious. -Run this code now and request *127.0.0.1:7878*; you should get the HTML in -*hello.html*. If you make any other request, such as -*127.0.0.1:7878/something-else*, you’ll get a connection error like those you -saw when running the code in Listing 20-1 and Listing 20-2. +With mutable data that is globally accessible, it’s difficult to ensure that +there are no data races, which is why Rust considers mutable static variables +to be unsafe. Where possible, it’s preferable to use the concurrency techniques +and thread-safe smart pointers we discussed in Chapter 16 so that the compiler +checks that data access from different threads is done safely. -Now let’s add the code in Listing 20-7 to the `else` block to return a response -with the status code 404, which signals that the content for the request was -not found. We’ll also return some HTML for a page to render in the browser -indicating the response to the end user. +### Implementing an Unsafe Trait -Filename: src/main.rs +We can use `unsafe` to implement an unsafe trait. A trait is unsafe when at +least one of its methods has some invariant that the compiler can’t verify. We +declare that a trait is `unsafe` by adding the `unsafe` keyword before `trait` +and marking the implementation of the trait as `unsafe` too, as shown in +Listing 20-12. -``` ---snip-- -} else { - 1 let status_line = "HTTP/1.1 404 NOT FOUND"; - 2 let contents = fs::read_to_string("404.html").unwrap(); - let length = contents.len(); - let response = format!( - "{status_line}\r\n\ - Content-Length: {length}\r\n\r\n - {contents}" - ); +``` +unsafe trait Foo { + // methods go here +} - stream.write_all(response.as_bytes()).unwrap(); +unsafe impl Foo for i32 { + // method implementations go here } ``` -Listing 20-7: Responding with status code 404 and an error page if anything -other than */* was requested +Listing 20-12: Defining and implementing an unsafe trait + +By using `unsafe impl`, we’re promising that we’ll uphold the invariants that +the compiler can’t verify. + +As an example, recall the `Send` and `Sync` marker traits we discussed in the +“Extensible Concurrency with `Send` and `Sync`” +section in Chapter 16: The compiler implements these traits automatically if +our types are composed entirely of other types that implement `Send` and +`Sync`. If we implement a type that contains a type that does not implement +`Send` or `Sync`, such as raw pointers, and we want to mark that type as `Send` +or `Sync`, we must use `unsafe`. Rust can’t verify that our type upholds the +guarantees that it can be safely sent across threads or accessed from multiple +threads; therefore, we need to do those checks manually and indicate as such +with `unsafe`. + +### Accessing Fields of a Union + +The final action that works only with `unsafe` is accessing fields of a union. +A *union* is similar to a `struct`, but only one declared field is used in a +particular instance at one time. Unions are primarily used to interface with +unions in C code. Accessing union fields is unsafe because Rust can’t guarantee +the type of the data currently being stored in the union instance. You can +learn more about unions in the Rust Reference at *../reference/items/unions.html*. + +### Using Miri to Check Unsafe Code + +When writing unsafe code, you might want to check that what you have written +actually is safe and correct. One of the best ways to do that is to use Miri, +an official Rust tool for detecting undefined behavior. Whereas the borrow +checker is a *static* tool that works at compile time, Miri is a *dynamic* +tool that works at runtime. It checks your code by running your program, or +its test suite, and detecting when you violate the rules it understands about +how Rust should work. + +Using Miri requires a nightly build of Rust (which we talk about more in +Appendix G: How Rust is Made and “Nightly Rust”). You +can install both a nightly version of Rust and the Miri tool by typing `rustup +nightly component add miri`. This does not change what version of Rust your +project uses; it only adds the tool to your system so you can use it when you +want to. You can run Miri on a project by typing `cargo +nightly miri run` or +`cargo +nightly miri test`. + +For an example of how helpful this can be, consider what happens when we run it +against Listing 20-7. + +``` +$ cargo +nightly miri run + Compiling unsafe-example v0.1.0 (file:///projects/unsafe-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.01s + Running `file:///home/.rustup/toolchains/nightly/bin/cargo-miri runner target/miri/debug/unsafe-example` +warning: integer-to-pointer cast + --> src/main.rs:5:13 + | +5 | let r = address as *mut i32; + | ^^^^^^^^^^^^^^^^^^^ integer-to-pointer cast + | + = help: this program is using integer-to-pointer casts or (equivalently) `ptr::with_exposed_provenance`, which means that Miri might miss pointer bugs in this program + = help: see https://doc.rust-lang.org/nightly/std/ptr/fn.with_exposed_provenance.html for more details on that operation + = help: to ensure that Miri does not miss bugs in your program, use Strict Provenance APIs (https://doc.rust-lang.org/nightly/std/ptr/index.html#strict-provenance, https://crates.io/crates/sptr) instead + = help: you can then set `MIRIFLAGS=-Zmiri-strict-provenance` to ensure you are not relying on `with_exposed_provenance` semantics + = help: alternatively, `MIRIFLAGS=-Zmiri-permissive-provenance` disables this warning + = note: BACKTRACE: + = note: inside `main` at src/main.rs:5:13: 5:32 + +error: Undefined Behavior: pointer not dereferenceable: pointer must be dereferenceable for 40000 bytes, but got 0x1234[noalloc] which is a dangling pointer (it has no provenance) + --> src/main.rs:7:35 + | +7 | let values: &[i32] = unsafe { slice::from_raw_parts_mut(r, 10000) }; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here + | + = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior + = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information + = note: BACKTRACE: + = note: inside `main` at src/main.rs:7:35: 7:70 + +note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace + +error: aborting due to 1 previous error; 1 warning emitted + +``` + +Miri correctly warns us that we’re casting an integer to a pointer, which might +be a problem, but Miri can’t determine whether a problem exists because it +doesn’t know how the pointer originated. Then, Miri returns an error where +Listing 20-7 has undefined behavior because we have a dangling pointer. Thanks +to Miri, we now know there is a risk of undefined behavior, and we can think +about how to make the code safe. In some cases, Miri can even make +recommendations about how to fix errors. + +Miri doesn’t catch everything you might get wrong when writing unsafe code. +Miri is a dynamic analysis tool, so it only catches problems with code that +actually gets run. That means you will need to use it in conjunction with good +testing techniques to increase your confidence about the unsafe code you have +written. Miri also does not cover every possible way your code can be unsound. + +Put another way: If Miri *does* catch a problem, you know there’s a bug, but +just because Miri *doesn’t* catch a bug doesn’t mean there isn’t a problem. It +can catch a lot, though. Try running it on the other examples of unsafe code in +this chapter and see what it says! + +You can learn more about Miri at its GitHub repository at *https://github.com/rust-lang/miri*. + + + + + +### Using Unsafe Code Correctly + +Using `unsafe` to use one of the five superpowers just discussed isn’t wrong or +even frowned upon, but it is trickier to get `unsafe` code correct because the +compiler can’t help uphold memory safety. When you have a reason to use +`unsafe` code, you can do so, and having the explicit `unsafe` annotation makes +it easier to track down the source of problems when they occur. Whenever you +write unsafe code, you can use Miri to help you be more confident that the code +you have written upholds Rust’s rules. + +For a much deeper exploration of how to work effectively with unsafe Rust, read +Rust’s official guide for `unsafe`, The Rustonomicon at *https://doc.rust-lang.org/nomicon/*. + +## Advanced Traits -Here, our response has a status line with status code 404 and the reason phrase -`NOT FOUND` [1]. The body of the response will be the HTML in the file -*404.html* [1]. You’ll need to create a *404.html* file next to *hello.html* -for the error page; again feel free to use any HTML you want, or use the -example HTML in Listing 20-8. +We first covered traits in the “Defining Shared Behavior with +Traits” section in Chapter 10, but we didn’t discuss +the more advanced details. Now that you know more about Rust, we can get into +the nitty-gritty. + + + + + + +### Defining Traits with Associated Types + +*Associated types* connect a type placeholder with a trait such that the trait +method definitions can use these placeholder types in their signatures. The +implementor of a trait will specify the concrete type to be used instead of the +placeholder type for the particular implementation. That way, we can define a +trait that uses some types without needing to know exactly what those types are +until the trait is implemented. + +We’ve described most of the advanced features in this chapter as being rarely +needed. Associated types are somewhere in the middle: They’re used more rarely +than features explained in the rest of the book but more commonly than many of +the other features discussed in this chapter. + +One example of a trait with an associated type is the `Iterator` trait that the +standard library provides. The associated type is named `Item` and stands in +for the type of the values the type implementing the `Iterator` trait is +iterating over. The definition of the `Iterator` trait is as shown in Listing +20-13. -Filename: 404.html ``` - - - - - Hello! - - -

Oops!

-

Sorry, I don't know what you're asking for.

- - +pub trait Iterator { + type Item; + + fn next(&mut self) -> Option; +} ``` -Listing 20-8: Sample content for the page to send back with any 404 response +Listing 20-13: The definition of the `Iterator` trait that has an associated type `Item` -With these changes, run your server again. Requesting *127.0.0.1:7878* should -return the contents of *hello.html*, and any other request, like -*127.0.0.1:7878/foo*, should return the error HTML from *404.html*. +The type `Item` is a placeholder, and the `next` method’s definition shows that +it will return values of type `Option`. Implementors of the +`Iterator` trait will specify the concrete type for `Item`, and the `next` +method will return an `Option` containing a value of that concrete type. -### A Touch of Refactoring +Associated types might seem like a similar concept to generics, in that the +latter allow us to define a function without specifying what types it can +handle. To examine the difference between the two concepts, we’ll look at an +implementation of the `Iterator` trait on a type named `Counter` that specifies +the `Item` type is `u32`: -At the moment, the `if` and `else` blocks have a lot of repetition: they’re -both reading files and writing the contents of the files to the stream. The -only differences are the status line and the filename. Let’s make the code more -concise by pulling out those differences into separate `if` and `else` lines -that will assign the values of the status line and the filename to variables; -we can then use those variables unconditionally in the code to read the file -and write the response. Listing 20-9 shows the resultant code after replacing -the large `if` and `else` blocks. +src/lib.rs -Filename: src/main.rs +``` +impl Iterator for Counter { + type Item = u32; + fn next(&mut self) -> Option { + // --snip-- ``` ---snip-- -fn handle_connection(mut stream: TcpStream) { - --snip-- - let (status_line, filename) = - if request_line == "GET / HTTP/1.1" { - ("HTTP/1.1 200 OK", "hello.html") - } else { - ("HTTP/1.1 404 NOT FOUND", "404.html") - }; - let contents = fs::read_to_string(filename).unwrap(); - let length = contents.len(); +This syntax seems comparable to that of generics. So, why not just define the +`Iterator` trait with generics, as shown in Listing 20-14? - let response = format!( - "{status_line}\r\n\ - Content-Length: {length}\r\n\r\n\ - {contents}" - ); - stream.write_all(response.as_bytes()).unwrap(); +``` +pub trait Iterator { + fn next(&mut self) -> Option; } ``` -Listing 20-9: Refactoring the `if` and `else` blocks to contain only the code -that differs between the two cases +Listing 20-14: A hypothetical definition of the `Iterator` trait using generics + +The difference is that when using generics, as in Listing 20-14, we must +annotate the types in each implementation; because we can also implement +`Iterator for Counter` or any other type, we could have multiple +implementations of `Iterator` for `Counter`. In other words, when a trait has a +generic parameter, it can be implemented for a type multiple times, changing +the concrete types of the generic type parameters each time. When we use the +`next` method on `Counter`, we would have to provide type annotations to +indicate which implementation of `Iterator` we want to use. -Now the `if` and `else` blocks only return the appropriate values for the -status line and filename in a tuple; we then use destructuring to assign these -two values to `status_line` and `filename` using a pattern in the `let` -statement, as discussed in Chapter 18. +With associated types, we don’t need to annotate types, because we can’t +implement a trait on a type multiple times. In Listing 20-13 with the +definition that uses associated types, we can choose what the type of `Item` +will be only once because there can be only one `impl Iterator for Counter`. We +don’t have to specify that we want an iterator of `u32` values everywhere we +call `next` on `Counter`. -The previously duplicated code is now outside the `if` and `else` blocks and -uses the `status_line` and `filename` variables. This makes it easier to see -the difference between the two cases, and it means we have only one place to -update the code if we want to change how the file reading and response writing -work. The behavior of the code in Listing 20-9 will be the same as that in -Listing 20-8. +Associated types also become part of the trait’s contract: Implementors of the +trait must provide a type to stand in for the associated type placeholder. +Associated types often have a name that describes how the type will be used, +and documenting the associated type in the API documentation is a good practice. -Awesome! We now have a simple web server in approximately 40 lines of Rust code -that responds to one request with a page of content and responds to all other -requests with a 404 response. + -Currently, our server runs in a single thread, meaning it can only serve one -request at a time. Let’s examine how that can be a problem by simulating some -slow requests. Then we’ll fix it so our server can handle multiple requests at -once. + -## Turning Our Single-Threaded Server into a Multithreaded Server +### Using Default Generic Parameters and Operator Overloading -Right now, the server will process each request in turn, meaning it won’t -process a second connection until the first is finished processing. If the -server received more and more requests, this serial execution would be less and -less optimal. If the server receives a request that takes a long time to -process, subsequent requests will have to wait until the long request is -finished, even if the new requests can be processed quickly. We’ll need to fix -this, but first we’ll look at the problem in action. +When we use generic type parameters, we can specify a default concrete type for +the generic type. This eliminates the need for implementors of the trait to +specify a concrete type if the default type works. You specify a default type +when declaring a generic type with the `` syntax. -### Simulating a Slow Request +A great example of a situation where this technique is useful is with *operator +overloading*, in which you customize the behavior of an operator (such as `+`) +in particular situations. -We’ll look at how a slow-processing request can affect other requests made to -our current server implementation. Listing 20-10 implements handling a request -to */sleep* with a simulated slow response that will cause the server to sleep -for five seconds before responding. +Rust doesn’t allow you to create your own operators or overload arbitrary +operators. But you can overload the operations and corresponding traits listed +in `std::ops` by implementing the traits associated with the operator. For +example, in Listing 20-15, we overload the `+` operator to add two `Point` +instances together. We do this by implementing the `Add` trait on a `Point` +struct. -Filename: src/main.rs +src/main.rs ``` -use std::{ - fs, - io::{prelude::*, BufReader}, - net::{TcpListener, TcpStream}, - thread, - time::Duration, -}; ---snip-- +use std::ops::Add; -fn handle_connection(mut stream: TcpStream) { - --snip-- +#[derive(Debug, Copy, Clone, PartialEq)] +struct Point { + x: i32, + y: i32, +} + +impl Add for Point { + type Output = Point; - let (status_line, filename) = 1 match &request_line[..] { - 2 "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), - 3 "GET /sleep HTTP/1.1" => { - thread::sleep(Duration::from_secs(5)); - ("HTTP/1.1 200 OK", "hello.html") + fn add(self, other: Point) -> Point { + Point { + x: self.x + other.x, + y: self.y + other.y, } - 4 _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), - }; + } +} - --snip-- +fn main() { + assert_eq!( + Point { x: 1, y: 0 } + Point { x: 2, y: 3 }, + Point { x: 3, y: 3 } + ); } ``` -Listing 20-10: Simulating a slow request by sleeping for five seconds - -We switched from `if` to `match` now that we have three cases [1]. We need to -explicitly match on a slice of `request_line` to pattern-match against the -string literal values; `match` doesn’t do automatic referencing and -dereferencing, like the equality method does. - -The first arm [2] is the same as the `if` block from Listing 20-9. The second -arm [3] matches a request to */sleep*. When that request is received, the -server will sleep for five seconds before rendering the successful HTML page. -The third arm [4] is the same as the `else` block from Listing 20-9. - -You can see how primitive our server is: real libraries would handle the -recognition of multiple requests in a much less verbose way! - -Start the server using `cargo run`. Then open two browser windows: one for -*http://127.0.0.1:7878* and the other for *http://127.0.0.1:7878/sleep*. If you -enter the */* URI a few times, as before, you’ll see it respond quickly. But if -you enter */sleep* and then load */*, you’ll see that */* waits until `sleep` -has slept for its full five seconds before loading. - -There are multiple techniques we could use to avoid requests backing up behind -a slow request; the one we’ll implement is a thread pool. - -### Improving Throughput with a Thread Pool - -A *thread pool* is a group of spawned threads that are waiting and ready to -handle a task. When the program receives a new task, it assigns one of the -threads in the pool to the task, and that thread will process the task. The -remaining threads in the pool are available to handle any other tasks that come -in while the first thread is processing. When the first thread is done -processing its task, it’s returned to the pool of idle threads, ready to handle -a new task. A thread pool allows you to process connections concurrently, -increasing the throughput of your server. - -We’ll limit the number of threads in the pool to a small number to protect us -from DoS attacks; if we had our program create a new thread for each request as -it came in, someone making 10 million requests to our server could create havoc -by using up all our server’s resources and grinding the processing of requests -to a halt. - -Rather than spawning unlimited threads, then, we’ll have a fixed number of -threads waiting in the pool. Requests that come in are sent to the pool for -processing. The pool will maintain a queue of incoming requests. Each of the -threads in the pool will pop off a request from this queue, handle the request, -and then ask the queue for another request. With this design, we can process up -to N requests concurrently, where N is the number of threads. If each thread is -responding to a long-running request, subsequent requests can still back up in -the queue, but we’ve increased the number of long-running requests we can -handle before reaching that point. - -This technique is just one of many ways to improve the throughput of a web -server. Other options you might explore are the fork/join model, the -single-threaded async I/O model, and the multithreaded async I/O model. If -you’re interested in this topic, you can read more about other solutions and -try to implement them; with a low-level language like Rust, all of these -options are possible. - -Before we begin implementing a thread pool, let’s talk about what using the -pool should look like. When you’re trying to design code, writing the client -interface first can help guide your design. Write the API of the code so it’s -structured in the way you want to call it; then implement the functionality -within that structure rather than implementing the functionality and then -designing the public API. - -Similar to how we used test-driven development in the project in Chapter 12, -we’ll use compiler-driven development here. We’ll write the code that calls the -functions we want, and then we’ll look at errors from the compiler to determine -what we should change next to get the code to work. Before we do that, however, -we’ll explore the technique we’re not going to use as a starting point. - -#### Spawning a Thread for Each Request - -First, let’s explore how our code might look if it did create a new thread for -every connection. As mentioned earlier, this isn’t our final plan due to the -problems with potentially spawning an unlimited number of threads, but it is a -starting point to get a working multithreaded server first. Then we’ll add the -thread pool as an improvement, and contrasting the two solutions will be easier. - -Listing 20-11 shows the changes to make to `main` to spawn a new thread to -handle each stream within the `for` loop. - -Filename: src/main.rs +Listing 20-15: Implementing the `Add` trait to overload the `+` operator for `Point` instances + +The `add` method adds the `x` values of two `Point` instances and the `y` +values of two `Point` instances to create a new `Point`. The `Add` trait has an +associated type named `Output` that determines the type returned from the `add` +method. + +The default generic type in this code is within the `Add` trait. Here is its +definition: ``` -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); +trait Add { + type Output; + + fn add(self, rhs: Rhs) -> Self::Output; +} +``` + +This code should look generally familiar: a trait with one method and an +associated type. The new part is `Rhs=Self`: This syntax is called *default +type parameters*. The `Rhs` generic type parameter (short for “right-hand +side”) defines the type of the `rhs` parameter in the `add` method. If we don’t +specify a concrete type for `Rhs` when we implement the `Add` trait, the type +of `Rhs` will default to `Self`, which will be the type we’re implementing +`Add` on. - for stream in listener.incoming() { - let stream = stream.unwrap(); +When we implemented `Add` for `Point`, we used the default for `Rhs` because we +wanted to add two `Point` instances. Let’s look at an example of implementing +the `Add` trait where we want to customize the `Rhs` type rather than using the +default. - thread::spawn(|| { - handle_connection(stream); - }); +We have two structs, `Millimeters` and `Meters`, holding values in different +units. This thin wrapping of an existing type in another struct is known as the +*newtype pattern*, which we describe in more detail in the “Implementing +External Traits with the Newtype Pattern” section. We +want to add values in millimeters to values in meters and have the +implementation of `Add` do the conversion correctly. We can implement `Add` for +`Millimeters` with `Meters` as the `Rhs`, as shown in Listing 20-16. + +src/lib.rs + +``` +use std::ops::Add; + +struct Millimeters(u32); +struct Meters(u32); + +impl Add for Millimeters { + type Output = Millimeters; + + fn add(self, other: Meters) -> Millimeters { + Millimeters(self.0 + (other.0 * 1000)) } } ``` -Listing 20-11: Spawning a new thread for each stream +Listing 20-16: Implementing the `Add` trait on `Millimeters` to add `Millimeters` and `Meters` + +To add `Millimeters` and `Meters`, we specify `impl Add` to set the +value of the `Rhs` type parameter instead of using the default of `Self`. + +You’ll use default type parameters in two main ways: + +1. To extend a type without breaking existing code +1. To allow customization in specific cases most users won’t need + +The standard library’s `Add` trait is an example of the second purpose: +Usually, you’ll add two like types, but the `Add` trait provides the ability to +customize beyond that. Using a default type parameter in the `Add` trait +definition means you don’t have to specify the extra parameter most of the +time. In other words, a bit of implementation boilerplate isn’t needed, making +it easier to use the trait. + +The first purpose is similar to the second but in reverse: If you want to add a +type parameter to an existing trait, you can give it a default to allow +extension of the functionality of the trait without breaking the existing +implementation code. + + + + + -As you learned in Chapter 16, `thread::spawn` will create a new thread and then -run the code in the closure in the new thread. If you run this code and load -*/sleep* in your browser, then */* in two more browser tabs, you’ll indeed see -that the requests to */* don’t have to wait for */sleep* to finish. However, as -we mentioned, this will eventually overwhelm the system because you’d be making -new threads without any limit. +### Disambiguating Between Identically Named Methods -#### Creating a Finite Number of Threads +Nothing in Rust prevents a trait from having a method with the same name as +another trait’s method, nor does Rust prevent you from implementing both traits +on one type. It’s also possible to implement a method directly on the type with +the same name as methods from traits. -We want our thread pool to work in a similar, familiar way so that switching -from threads to a thread pool doesn’t require large changes to the code that -uses our API. Listing 20-12 shows the hypothetical interface for a `ThreadPool` -struct we want to use instead of `thread::spawn`. +When calling methods with the same name, you’ll need to tell Rust which one you +want to use. Consider the code in Listing 20-17 where we’ve defined two traits, +`Pilot` and `Wizard`, that both have a method called `fly`. We then implement +both traits on a type `Human` that already has a method named `fly` implemented +on it. Each `fly` method does something different. -Filename: src/main.rs +src/main.rs ``` -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - 1 let pool = ThreadPool::new(4); +trait Pilot { + fn fly(&self); +} + +trait Wizard { + fn fly(&self); +} - for stream in listener.incoming() { - let stream = stream.unwrap(); +struct Human; - 2 pool.execute(|| { - handle_connection(stream); - }); +impl Pilot for Human { + fn fly(&self) { + println!("This is your captain speaking."); + } +} + +impl Wizard for Human { + fn fly(&self) { + println!("Up!"); } } -``` -Listing 20-12: Our ideal `ThreadPool` interface +impl Human { + fn fly(&self) { + println!("*waving arms furiously*"); + } +} +``` -We use `ThreadPool::new` to create a new thread pool with a configurable number -of threads, in this case four [1]. Then, in the `for` loop, `pool.execute` has -a similar interface as `thread::spawn` in that it takes a closure the pool -should run for each stream [2]. We need to implement `pool.execute` so it takes -the closure and gives it to a thread in the pool to run. This code won’t yet -compile, but we’ll try so that the compiler can guide us in how to fix it. +Listing 20-17: Two traits are defined to have a `fly` method and are implemented on the `Human` type, and a `fly` method is implemented on `Human` directly. -#### Building ThreadPool Using Compiler-Driven Development +When we call `fly` on an instance of `Human`, the compiler defaults to calling +the method that is directly implemented on the type, as shown in Listing 20-18. -Make the changes in Listing 20-12 to *src/main.rs*, and then let’s use the -compiler errors from `cargo check` to drive our development. Here is the first -error we get: +src/main.rs ``` -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) -error[E0433]: failed to resolve: use of undeclared type `ThreadPool` - --> src/main.rs:11:16 - | -11 | let pool = ThreadPool::new(4); - | ^^^^^^^^^^ use of undeclared type `ThreadPool` +fn main() { + let person = Human; + person.fly(); +} ``` -Great! This error tells us we need a `ThreadPool` type or module, so we’ll -build one now. Our `ThreadPool` implementation will be independent of the kind -of work our web server is doing. So let’s switch the `hello` crate from a -binary crate to a library crate to hold our `ThreadPool` implementation. After -we change to a library crate, we could also use the separate thread pool -library for any work we want to do using a thread pool, not just for serving -web requests. +Listing 20-18: Calling `fly` on an instance of `Human` -Create a *src/lib.rs* file that contains the following, which is the simplest -definition of a `ThreadPool` struct that we can have for now: +Running this code will print `*waving arms furiously*`, showing that Rust +called the `fly` method implemented on `Human` directly. -Filename: src/lib.rs +To call the `fly` methods from either the `Pilot` trait or the `Wizard` trait, +we need to use more explicit syntax to specify which `fly` method we mean. +Listing 20-19 demonstrates this syntax. + +src/main.rs ``` -pub struct ThreadPool; +fn main() { + let person = Human; + Pilot::fly(&person); + Wizard::fly(&person); + person.fly(); +} ``` -Then edit the *main.rs* file to bring `ThreadPool` into scope from the library -crate by adding the following code to the top of *src/main.rs*: +Listing 20-19: Specifying which trait’s `fly` method we want to call + +Specifying the trait name before the method name clarifies to Rust which +implementation of `fly` we want to call. We could also write +`Human::fly(&person)`, which is equivalent to the `person.fly()` that we used +in Listing 20-19, but this is a bit longer to write if we don’t need to +disambiguate. -Filename: src/main.rs +Running this code prints the following: ``` -use hello::ThreadPool; +$ cargo run + Compiling traits-example v0.1.0 (file:///projects/traits-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.46s + Running `target/debug/traits-example` +This is your captain speaking. +Up! +*waving arms furiously* ``` -This code still won’t work, but let’s check it again to get the next error that -we need to address: +Because the `fly` method takes a `self` parameter, if we had two *types* that +both implement one *trait*, Rust could figure out which implementation of a +trait to use based on the type of `self`. + +However, associated functions that are not methods don’t have a `self` +parameter. When there are multiple types or traits that define non-method +functions with the same function name, Rust doesn’t always know which type you +mean unless you use fully qualified syntax. For example, in Listing 20-20, we +create a trait for an animal shelter that wants to name all baby dogs Spot. We +make an `Animal` trait with an associated non-method function `baby_name`. The +`Animal` trait is implemented for the struct `Dog`, on which we also provide an +associated non-method function `baby_name` directly. + +src/main.rs ``` -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) -error[E0599]: no function or associated item named `new` found for struct -`ThreadPool` in the current scope - --> src/main.rs:12:28 - | -12 | let pool = ThreadPool::new(4); - | ^^^ function or associated item not found in -`ThreadPool` +trait Animal { + fn baby_name() -> String; +} + +struct Dog; + +impl Dog { + fn baby_name() -> String { + String::from("Spot") + } +} + +impl Animal for Dog { + fn baby_name() -> String { + String::from("puppy") + } +} + +fn main() { + println!("A baby dog is called a {}", Dog::baby_name()); +} ``` -This error indicates that next we need to create an associated function named -`new` for `ThreadPool`. We also know that `new` needs to have one parameter -that can accept `4` as an argument and should return a `ThreadPool` instance. -Let’s implement the simplest `new` function that will have those -characteristics: +Listing 20-20: A trait with an associated function and a type with an associated function of the same name that also implements the trait + +We implement the code for naming all puppies Spot in the `baby_name` associated +function that is defined on `Dog`. The `Dog` type also implements the trait +`Animal`, which describes characteristics that all animals have. Baby dogs are +called puppies, and that is expressed in the implementation of the `Animal` +trait on `Dog` in the `baby_name` function associated with the `Animal` trait. -Filename: src/lib.rs +In `main`, we call the `Dog::baby_name` function, which calls the associated +function defined on `Dog` directly. This code prints the following: ``` -pub struct ThreadPool; +$ cargo run + Compiling traits-example v0.1.0 (file:///projects/traits-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.54s + Running `target/debug/traits-example` +A baby dog is called a Spot +``` -impl ThreadPool { - pub fn new(size: usize) -> ThreadPool { - ThreadPool - } +This output isn’t what we wanted. We want to call the `baby_name` function that +is part of the `Animal` trait that we implemented on `Dog` so that the code +prints `A baby dog is called a puppy`. The technique of specifying the trait +name that we used in Listing 20-19 doesn’t help here; if we change `main` to +the code in Listing 20-21, we’ll get a compilation error. + +src/main.rs + +``` +fn main() { + println!("A baby dog is called a {}", Animal::baby_name()); } ``` -We chose `usize` as the type of the `size` parameter because we know that a -negative number of threads doesn’t make any sense. We also know we’ll use this -`4` as the number of elements in a collection of threads, which is what the -`usize` type is for, as discussed in “Integer Types” on page XX. +Listing 20-21: Attempting to call the `baby_name` function from the `Animal` trait, but Rust doesn’t know which implementation to use -Let’s check the code again: +Because `Animal::baby_name` doesn’t have a `self` parameter, and there could be +other types that implement the `Animal` trait, Rust can’t figure out which +implementation of `Animal::baby_name` we want. We’ll get this compiler error: ``` -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) -error[E0599]: no method named `execute` found for struct `ThreadPool` in the -current scope - --> src/main.rs:17:14 +$ cargo run + Compiling traits-example v0.1.0 (file:///projects/traits-example) +error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type + --> src/main.rs:20:43 | -17 | pool.execute(|| { - | ^^^^^^^ method not found in `ThreadPool` -``` - -Now the error occurs because we don’t have an `execute` method on `ThreadPool`. -Recall from “Creating a Finite Number of Threads” on page XX that we decided -our thread pool should have an interface similar to `thread::spawn`. In -addition, we’ll implement the `execute` function so it takes the closure it’s -given and gives it to an idle thread in the pool to run. - -We’ll define the `execute` method on `ThreadPool` to take a closure as a -parameter. Recall from “Moving Captured Values Out of Closures and the Fn -Traits” on page XX that we can take closures as parameters with three different -traits: `Fn`, `FnMut`, and `FnOnce`. We need to decide which kind of closure to -use here. We know we’ll end up doing something similar to the standard library -`thread::spawn` implementation, so we can look at what bounds the signature of -`thread::spawn` has on its parameter. The documentation shows us the following: - -``` -pub fn spawn(f: F) -> JoinHandle - where - F: FnOnce() -> T, - F: Send + 'static, - T: Send + 'static, -``` - -The `F` type parameter is the one we’re concerned with here; the `T` type -parameter is related to the return value, and we’re not concerned with that. We -can see that `spawn` uses `FnOnce` as the trait bound on `F`. This is probably -what we want as well, because we’ll eventually pass the argument we get in -`execute` to `spawn`. We can be further confident that `FnOnce` is the trait we -want to use because the thread for running a request will only execute that -request’s closure one time, which matches the `Once` in `FnOnce`. - -The `F` type parameter also has the trait bound `Send` and the lifetime bound -`'static`, which are useful in our situation: we need `Send` to transfer the -closure from one thread to another and `'static` because we don’t know how long -the thread will take to execute. Let’s create an `execute` method on -`ThreadPool` that will take a generic parameter of type `F` with these bounds: - -Filename: src/lib.rs - -``` -impl ThreadPool { - --snip-- - pub fn execute(&self, f: F) - where - F: FnOnce() 1 + Send + 'static, - { - } +2 | fn baby_name() -> String; + | ------------------------- `Animal::baby_name` defined here +... +20 | println!("A baby dog is called a {}", Animal::baby_name()); + | ^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait + | +help: use the fully-qualified path to the only available implementation + | +20 | println!("A baby dog is called a {}", ::baby_name()); + | +++++++ + + +For more information about this error, try `rustc --explain E0790`. +error: could not compile `traits-example` (bin "traits-example") due to 1 previous error +``` + +To disambiguate and tell Rust that we want to use the implementation of +`Animal` for `Dog` as opposed to the implementation of `Animal` for some other +type, we need to use fully qualified syntax. Listing 20-22 demonstrates how to +use fully qualified syntax. + +src/main.rs + +``` +fn main() { + println!("A baby dog is called a {}", ::baby_name()); } ``` -We still use the `()` after `FnOnce` [1] because this `FnOnce` represents a -closure that takes no parameters and returns the unit type `()`. Just like -function definitions, the return type can be omitted from the signature, but -even if we have no parameters, we still need the parentheses. +Listing 20-22: Using fully qualified syntax to specify that we want to call the `baby_name` function from the `Animal` trait as implemented on `Dog` -Again, this is the simplest implementation of the `execute` method: it does -nothing, but we’re only trying to make our code compile. Let’s check it again: +We’re providing Rust with a type annotation within the angle brackets, which +indicates we want to call the `baby_name` method from the `Animal` trait as +implemented on `Dog` by saying that we want to treat the `Dog` type as an +`Animal` for this function call. This code will now print what we want: ``` -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) - Finished dev [unoptimized + debuginfo] target(s) in 0.24s +$ cargo run + Compiling traits-example v0.1.0 (file:///projects/traits-example) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.48s + Running `target/debug/traits-example` +A baby dog is called a puppy ``` -It compiles! But note that if you try `cargo run` and make a request in the -browser, you’ll see the errors in the browser that we saw at the beginning of -the chapter. Our library isn’t actually calling the closure passed to `execute` -yet! +In general, fully qualified syntax is defined as follows: -> Note: A saying you might hear about languages with strict compilers, such as -Haskell and Rust, is “if the code compiles, it works.” But this saying is not -universally true. Our project compiles, but it does absolutely nothing! If we -were building a real, complete project, this would be a good time to start -writing unit tests to check that the code compiles *and* has the behavior we -want. +``` +::function(receiver_if_method, next_arg, ...); +``` + +For associated functions that aren’t methods, there would not be a `receiver`: +There would only be the list of other arguments. You could use fully qualified +syntax everywhere that you call functions or methods. However, you’re allowed +to omit any part of this syntax that Rust can figure out from other information +in the program. You only need to use this more verbose syntax in cases where +there are multiple implementations that use the same name and Rust needs help +to identify which implementation you want to call. + + -#### Validating the Number of Threads in new + -We aren’t doing anything with the parameters to `new` and `execute`. Let’s -implement the bodies of these functions with the behavior we want. To start, -let’s think about `new`. Earlier we chose an unsigned type for the `size` -parameter because a pool with a negative number of threads makes no sense. -However, a pool with zero threads also makes no sense, yet zero is a perfectly -valid `usize`. We’ll add code to check that `size` is greater than zero before -we return a `ThreadPool` instance and have the program panic if it receives a -zero by using the `assert!` macro, as shown in Listing 20-13. +### Using Supertraits -Filename: src/lib.rs +Sometimes you might write a trait definition that depends on another trait: For +a type to implement the first trait, you want to require that type to also +implement the second trait. You would do this so that your trait definition can +make use of the associated items of the second trait. The trait your trait +definition is relying on is called a *supertrait* of your trait. +For example, let’s say we want to make an `OutlinePrint` trait with an +`outline_print` method that will print a given value formatted so that it’s +framed in asterisks. That is, given a `Point` struct that implements the +standard library trait `Display` to result in `(x, y)`, when we call +`outline_print` on a `Point` instance that has `1` for `x` and `3` for `y`, it +should print the following: + +``` +********** +* * +* (1, 3) * +* * +********** ``` -impl ThreadPool { - /// Create a new ThreadPool. - /// - /// The size is the number of threads in the pool. - /// - 1 /// # Panics - /// - /// The `new` function will panic if the size is zero. - pub fn new(size: usize) -> ThreadPool { - 2 assert!(size > 0); - ThreadPool - } +In the implementation of the `outline_print` method, we want to use the +`Display` trait’s functionality. Therefore, we need to specify that the +`OutlinePrint` trait will work only for types that also implement `Display` and +provide the functionality that `OutlinePrint` needs. We can do that in the +trait definition by specifying `OutlinePrint: Display`. This technique is +similar to adding a trait bound to the trait. Listing 20-23 shows an +implementation of the `OutlinePrint` trait. - --snip-- +src/main.rs + +``` +use std::fmt; + +trait OutlinePrint: fmt::Display { + fn outline_print(&self) { + let output = self.to_string(); + let len = output.len(); + println!("{}", "*".repeat(len + 4)); + println!("*{}*", " ".repeat(len + 2)); + println!("* {output} *"); + println!("*{}*", " ".repeat(len + 2)); + println!("{}", "*".repeat(len + 4)); + } } ``` -Listing 20-13: Implementing `ThreadPool::new` to panic if `size` is zero +Listing 20-23: Implementing the `OutlinePrint` trait that requires the functionality from `Display` + +Because we’ve specified that `OutlinePrint` requires the `Display` trait, we +can use the `to_string` function that is automatically implemented for any type +that implements `Display`. If we tried to use `to_string` without adding a +colon and specifying the `Display` trait after the trait name, we’d get an +error saying that no method named `to_string` was found for the type `&Self` in +the current scope. -We’ve also added some documentation for our `ThreadPool` with doc comments. -Note that we followed good documentation practices by adding a section that -calls out the situations in which our function can panic [1], as discussed in -Chapter 14. Try running `cargo doc --open` and clicking the `ThreadPool` struct -to see what the generated docs for `new` look like! +Let’s see what happens when we try to implement `OutlinePrint` on a type that +doesn’t implement `Display`, such as the `Point` struct: -Instead of adding the `assert!` macro as we’ve done here [2], we could change -`new` into `build` and return a `Result` like we did with `Config::build` in -the I/O project in Listing 12-9. But we’ve decided in this case that trying to -create a thread pool without any threads should be an unrecoverable error. If -you’re feeling ambitious, try to write a function named `build` with the -following signature to compare with the `new` function: +src/main.rs ``` -pub fn build( - size: usize -) -> Result { +struct Point { + x: i32, + y: i32, +} + +impl OutlinePrint for Point {} ``` -#### Creating Space to Store the Threads -Now that we have a way to know we have a valid number of threads to store in -the pool, we can create those threads and store them in the `ThreadPool` struct -before returning the struct. But how do we “store” a thread? Let’s take another -look at the `thread::spawn` signature: + +We get an error saying that `Display` is required but not implemented: ``` -pub fn spawn(f: F) -> JoinHandle - where - F: FnOnce() -> T, - F: Send + 'static, - T: Send + 'static, -``` +$ cargo run + Compiling traits-example v0.1.0 (file:///projects/traits-example) +error[E0277]: `Point` doesn't implement `std::fmt::Display` + --> src/main.rs:20:23 + | +20 | impl OutlinePrint for Point {} + | ^^^^^ `Point` cannot be formatted with the default formatter + | + = help: the trait `std::fmt::Display` is not implemented for `Point` + = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead +note: required by a bound in `OutlinePrint` + --> src/main.rs:3:21 + | +3 | trait OutlinePrint: fmt::Display { + | ^^^^^^^^^^^^ required by this bound in `OutlinePrint` -The `spawn` function returns a `JoinHandle`, where `T` is the type that the -closure returns. Let’s try using `JoinHandle` too and see what happens. In our -case, the closures we’re passing to the thread pool will handle the connection -and not return anything, so `T` will be the unit type `()`. +error[E0277]: `Point` doesn't implement `std::fmt::Display` + --> src/main.rs:24:7 + | +24 | p.outline_print(); + | ^^^^^^^^^^^^^ `Point` cannot be formatted with the default formatter + | + = help: the trait `std::fmt::Display` is not implemented for `Point` + = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead +note: required by a bound in `OutlinePrint::outline_print` + --> src/main.rs:3:21 + | +3 | trait OutlinePrint: fmt::Display { + | ^^^^^^^^^^^^ required by this bound in `OutlinePrint::outline_print` +4 | fn outline_print(&self) { + | ------------- required by a bound in this associated function -The code in Listing 20-14 will compile but doesn’t create any threads yet. -We’ve changed the definition of `ThreadPool` to hold a vector of -`thread::JoinHandle<()>` instances, initialized the vector with a capacity of -`size`, set up a `for` loop that will run some code to create the threads, and -returned a `ThreadPool` instance containing them. +For more information about this error, try `rustc --explain E0277`. +error: could not compile `traits-example` (bin "traits-example") due to 2 previous errors +``` + +To fix this, we implement `Display` on `Point` and satisfy the constraint that +`OutlinePrint` requires, like so: -Filename: src/lib.rs +src/main.rs ``` -1 use std::thread; +use std::fmt; -pub struct ThreadPool { - 2 threads: Vec>, +impl fmt::Display for Point { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + write!(f, "({}, {})", self.x, self.y) + } } +``` -impl ThreadPool { - --snip-- - pub fn new(size: usize) -> ThreadPool { - assert!(size > 0); - 3 let mut threads = Vec::with_capacity(size); - for _ in 0..size { - // create some threads and store them in the vector - } +Then, implementing the `OutlinePrint` trait on `Point` will compile +successfully, and we can call `outline_print` on a `Point` instance to display +it within an outline of asterisks. + + + + + + +### Implementing External Traits with the Newtype Pattern + +In the “Implementing a Trait on a Type” section in Chapter 10, we mentioned the orphan rule that states +we’re only allowed to implement a trait on a type if either the trait or the +type, or both, are local to our crate. It’s possible to get around this +restriction using the newtype pattern, which involves creating a new type in a +tuple struct. (We covered tuple structs in the “Creating Different Types with +Tuple Structs” section in Chapter 5.) The tuple +struct will have one field and be a thin wrapper around the type for which we +want to implement a trait. Then, the wrapper type is local to our crate, and we +can implement the trait on the wrapper. *Newtype* is a term that originates +from the Haskell programming language. There is no runtime performance penalty +for using this pattern, and the wrapper type is elided at compile time. + +As an example, let’s say we want to implement `Display` on `Vec`, which the +orphan rule prevents us from doing directly because the `Display` trait and the +`Vec` type are defined outside our crate. We can make a `Wrapper` struct +that holds an instance of `Vec`; then, we can implement `Display` on +`Wrapper` and use the `Vec` value, as shown in Listing 20-24. - ThreadPool { threads } +src/main.rs + +``` +use std::fmt; + +struct Wrapper(Vec); + +impl fmt::Display for Wrapper { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + write!(f, "[{}]", self.0.join(", ")) } - --snip-- +} + +fn main() { + let w = Wrapper(vec![String::from("hello"), String::from("world")]); + println!("w = {w}"); } ``` -Listing 20-14: Creating a vector for `ThreadPool` to hold the threads +Listing 20-24: Creating a `Wrapper` type around `Vec` to implement `Display` -We’ve brought `std::thread` into scope in the library crate [1] because we’re -using `thread::JoinHandle` as the type of the items in the vector in -`ThreadPool` [2]. +The implementation of `Display` uses `self.0` to access the inner `Vec` +because `Wrapper` is a tuple struct and `Vec` is the item at index 0 in the +tuple. Then, we can use the functionality of the `Display` trait on `Wrapper`. -Once a valid size is received, our `ThreadPool` creates a new vector that can -hold `size` items [3]. The `with_capacity` function performs the same task as -`Vec::new` but with an important difference: it pre-allocates space in the -vector. Because we know we need to store `size` elements in the vector, doing -this allocation up front is slightly more efficient than using `Vec::new`, -which resizes itself as elements are inserted. +The downside of using this technique is that `Wrapper` is a new type, so it +doesn’t have the methods of the value it’s holding. We would have to implement +all the methods of `Vec` directly on `Wrapper` such that the methods +delegate to `self.0`, which would allow us to treat `Wrapper` exactly like a +`Vec`. If we wanted the new type to have every method the inner type has, +implementing the `Deref` trait on the `Wrapper` to return the inner type would +be a solution (we discussed implementing the `Deref` trait in the “Treating +Smart Pointers Like Regular References” +section in Chapter 15). If we didn’t want the `Wrapper` type to have all the +methods of the inner type—for example, to restrict the `Wrapper` type’s +behavior—we would have to implement just the methods we do want manually. -When you run `cargo check` again, it should succeed. +This newtype pattern is also useful even when traits are not involved. Let’s +switch focus and look at some advanced ways to interact with Rust’s type system. -#### Sending Code from the ThreadPool to a Thread +## Advanced Types -We left a comment in the `for` loop in Listing 20-14 regarding the creation of -threads. Here, we’ll look at how we actually create threads. The standard -library provides `thread::spawn` as a way to create threads, and -`thread::spawn` expects to get some code the thread should run as soon as the -thread is created. However, in our case, we want to create the threads and have -them *wait* for code that we’ll send later. The standard library’s -implementation of threads doesn’t include any way to do that; we have to -implement it manually. +The Rust type system has some features that we’ve so far mentioned but haven’t +yet discussed. We’ll start by discussing newtypes in general as we examine why +they are useful as types. Then, we’ll move on to type aliases, a feature +similar to newtypes but with slightly different semantics. We’ll also discuss +the `!` type and dynamically sized types. -We’ll implement this behavior by introducing a new data structure between the -`ThreadPool` and the threads that will manage this new behavior. We’ll call -this data structure *Worker*, which is a common term in pooling -implementations. The `Worker` picks up code that needs to be run and runs the -code in its thread. + -Think of people working in the kitchen at a restaurant: the workers wait until -orders come in from customers, and then they’re responsible for taking those -orders and filling them. + -Instead of storing a vector of `JoinHandle<()>` instances in the thread pool, -we’ll store instances of the `Worker` struct. Each `Worker` will store a single -`JoinHandle<()>` instance. Then we’ll implement a method on `Worker` that will -take a closure of code to run and send it to the already running thread for -execution. We’ll also give each `Worker` an `id` so we can distinguish between -the different instances of `Worker` in the pool when logging or debugging. +### Type Safety and Abstraction with the Newtype Pattern -Here is the new process that will happen when we create a `ThreadPool`. We’ll -implement the code that sends the closure to the thread after we have `Worker` -set up in this way: +This section assumes you’ve read the earlier section “Implementing External +Traits with the Newtype Pattern”. The newtype pattern +is also useful for tasks beyond those we’ve discussed so far, including +statically enforcing that values are never confused and indicating the units of +a value. You saw an example of using newtypes to indicate units in Listing +20-16: Recall that the `Millimeters` and `Meters` structs wrapped `u32` values +in a newtype. If we wrote a function with a parameter of type `Millimeters`, we +wouldn’t be able to compile a program that accidentally tried to call that +function with a value of type `Meters` or a plain `u32`. -1. Define a `Worker` struct that holds an `id` and a `JoinHandle<()>`. -1. Change `ThreadPool` to hold a vector of `Worker` instances. -1. Define a `Worker::new` function that takes an `id` number and returns a -`Worker` instance that holds the `id` and a thread spawned with an empty -closure. -1. In `ThreadPool::new`, use the `for` loop counter to generate an `id`, create -a new `Worker` with that `id`, and store the `Worker` in the vector. +We can also use the newtype pattern to abstract away some implementation +details of a type: The new type can expose a public API that is different from +the API of the private inner type. -If you’re up for a challenge, try implementing these changes on your own before -looking at the code in Listing 20-15. +Newtypes can also hide internal implementation. For example, we could provide a +`People` type to wrap a `HashMap` that stores a person’s ID +associated with their name. Code using `People` would only interact with the +public API we provide, such as a method to add a name string to the `People` +collection; that code wouldn’t need to know that we assign an `i32` ID to names +internally. The newtype pattern is a lightweight way to achieve encapsulation +to hide implementation details, which we discussed in the “Encapsulation that +Hides Implementation +Details” +section in Chapter 18. -Ready? Here is Listing 20-15 with one way to make the preceding modifications. + -Filename: src/lib.rs + + +### Type Synonyms and Type Aliases + +Rust provides the ability to declare a *type alias* to give an existing type +another name. For this we use the `type` keyword. For example, we can create +the alias `Kilometers` to `i32` like so: ``` -use std::thread; + type Kilometers = i32; +``` -pub struct ThreadPool { - 1 workers: Vec, -} +Now the alias `Kilometers` is a *synonym* for `i32`; unlike the `Millimeters` +and `Meters` types we created in Listing 20-16, `Kilometers` is not a separate, +new type. Values that have the type `Kilometers` will be treated the same as +values of type `i32`: -impl ThreadPool { - --snip-- - pub fn new(size: usize) -> ThreadPool { - assert!(size > 0); +``` + type Kilometers = i32; - let mut workers = Vec::with_capacity(size); + let x: i32 = 5; + let y: Kilometers = 5; - 2 for id in 0..size { - 3 workers.push(Worker::new(id)); - } + println!("x + y = {}", x + y); +``` - ThreadPool { workers } - } - --snip-- -} +Because `Kilometers` and `i32` are the same type, we can add values of both +types and can pass `Kilometers` values to functions that take `i32` +parameters. However, using this method, we don’t get the type-checking benefits +that we get from the newtype pattern discussed earlier. In other words, if we +mix up `Kilometers` and `i32` values somewhere, the compiler will not give us +an error. -4 struct Worker { - id: usize, - thread: thread::JoinHandle<()>, -} +The main use case for type synonyms is to reduce repetition. For example, we +might have a lengthy type like this: + +``` +Box +``` + +Writing this lengthy type in function signatures and as type annotations all +over the code can be tiresome and error-prone. Imagine having a project full of +code like that in Listing 20-25. -impl Worker { - 5 fn new(id: usize) -> Worker { - 6 let thread = thread::spawn(|| {}); - Worker { 7 id, 8 thread } - } -} ``` + let f: Box = Box::new(|| println!("hi")); -Listing 20-15: Modifying `ThreadPool` to hold `Worker` instances instead of -holding threads directly + fn takes_long_type(f: Box) { + // --snip-- + } -We’ve changed the name of the field on `ThreadPool` from `threads` to `workers` -because it’s now holding `Worker` instances instead of `JoinHandle<()>` -instances [1]. We use the counter in the `for` loop [2] as an argument to -`Worker::new`, and we store each new `Worker` in the vector named `workers` [3]. + fn returns_long_type() -> Box { + // --snip-- + } +``` -External code (like our server in *src/main.rs*) doesn’t need to know the -implementation details regarding using a `Worker` struct within `ThreadPool`, -so we make the `Worker` struct [4] and its `new` function [5] private. The -`Worker::new` function uses the `id` we give it [7] and stores a -`JoinHandle<()>` instance [8] that is created by spawning a new thread using an -empty closure [6]. +Listing 20-25: Using a long type in many places -> Note: If the operating system can’t create a thread because there aren’t -enough system resources, `thread::spawn` will panic. That will cause our whole -server to panic, even though the creation of some threads might succeed. For -simplicity’s sake, this behavior is fine, but in a production thread pool -implementation, you’d likely want to use `std::thread::Builder` and its `spawn` -method that returns `Result` instead. +A type alias makes this code more manageable by reducing the repetition. In +Listing 20-26, we’ve introduced an alias named `Thunk` for the verbose type and +can replace all uses of the type with the shorter alias `Thunk`. -This code will compile and will store the number of `Worker` instances we -specified as an argument to `ThreadPool::new`. But we’re *still* not processing -the closure that we get in `execute`. Let’s look at how to do that next. -#### Sending Requests to Threads via Channels +``` + type Thunk = Box; -The next problem we’ll tackle is that the closures given to `thread::spawn` do -absolutely nothing. Currently, we get the closure we want to execute in the -`execute` method. But we need to give `thread::spawn` a closure to run when we -create each `Worker` during the creation of the `ThreadPool`. + let f: Thunk = Box::new(|| println!("hi")); -We want the `Worker` structs that we just created to fetch the code to run from -a queue held in the `ThreadPool` and send that code to its thread to run. + fn takes_long_type(f: Thunk) { + // --snip-- + } -The channels we learned about in Chapter 16—a simple way to communicate between -two threads—would be perfect for this use case. We’ll use a channel to function -as the queue of jobs, and `execute` will send a job from the `ThreadPool` to -the `Worker` instances, which will send the job to its thread. Here is the plan: + fn returns_long_type() -> Thunk { + // --snip-- + } +``` -1. The `ThreadPool` will create a channel and hold on to the sender. -1. Each `Worker` will hold on to the receiver. -1. We’ll create a new `Job` struct that will hold the closures we want to send -down the channel. -1. The `execute` method will send the job it wants to execute through the -sender. -1. In its thread, the `Worker` will loop over its receiver and execute the -closures of any jobs it receives. +Listing 20-26: Introducing a type alias, `Thunk`, to reduce repetition -Let’s start by creating a channel in `ThreadPool::new` and holding the sender -in the `ThreadPool` instance, as shown in Listing 20-16. The `Job` struct -doesn’t hold anything for now but will be the type of item we’re sending down -the channel. +This code is much easier to read and write! Choosing a meaningful name for a +type alias can help communicate your intent as well (*thunk* is a word for code +to be evaluated at a later time, so it’s an appropriate name for a closure that +gets stored). -Filename: src/lib.rs +Type aliases are also commonly used with the `Result` type for reducing +repetition. Consider the `std::io` module in the standard library. I/O +operations often return a `Result` to handle situations when operations +fail to work. This library has a `std::io::Error` struct that represents all +possible I/O errors. Many of the functions in `std::io` will be returning +`Result` where the `E` is `std::io::Error`, such as these functions in +the `Write` trait: ``` -use std::{sync::mpsc, thread}; +use std::fmt; +use std::io::Error; + +pub trait Write { + fn write(&mut self, buf: &[u8]) -> Result; + fn flush(&mut self) -> Result<(), Error>; -pub struct ThreadPool { - workers: Vec, - sender: mpsc::Sender, + fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>; + fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<(), Error>; } +``` -struct Job; +The `Result<..., Error>` is repeated a lot. As such, `std::io` has this type +alias declaration: -impl ThreadPool { - --snip-- - pub fn new(size: usize) -> ThreadPool { - assert!(size > 0); +``` +type Result = std::result::Result; +``` - 1 let (sender, receiver) = mpsc::channel(); +Because this declaration is in the `std::io` module, we can use the fully +qualified alias `std::io::Result`; that is, a `Result` with the `E` +filled in as `std::io::Error`. The `Write` trait function signatures end up +looking like this: - let mut workers = Vec::with_capacity(size); +``` +pub trait Write { + fn write(&mut self, buf: &[u8]) -> Result; + fn flush(&mut self) -> Result<()>; - for id in 0..size { - workers.push(Worker::new(id)); - } + fn write_all(&mut self, buf: &[u8]) -> Result<()>; + fn write_fmt(&mut self, fmt: fmt::Arguments) -> Result<()>; +} +``` - ThreadPool { workers, 2 sender } - } - --snip-- +The type alias helps in two ways: It makes code easier to write *and* it gives +us a consistent interface across all of `std::io`. Because it’s an alias, it’s +just another `Result`, which means we can use any methods that work on +`Result` with it, as well as special syntax like the `?` operator. + +### The Never Type That Never Returns + +Rust has a special type named `!` that’s known in type theory lingo as the +*empty type* because it has no values. We prefer to call it the *never type* +because it stands in the place of the return type when a function will never +return. Here is an example: + +``` +fn bar() -> ! { + // --snip-- } ``` -Listing 20-16: Modifying `ThreadPool` to store the sender of a channel that -transmits `Job` instances +This code is read as “the function `bar` returns never.” Functions that return +never are called *diverging functions*. We can’t create values of the type `!`, +so `bar` can never possibly return. + +But what use is a type you can never create values for? Recall the code from +Listing 2-5, part of the number-guessing game; we’ve reproduced a bit of it +here in Listing 20-27. -In `ThreadPool::new`, we create our new channel [1] and have the pool hold the -sender [2]. This will successfully compile. -Let’s try passing a receiver of the channel into each `Worker` as the thread -pool creates the channel. We know we want to use the receiver in the thread -that the `Worker` instances spawn, so we’ll reference the `receiver` parameter -in the closure. The code in Listing 20-17 won’t quite compile yet. +``` + let guess: u32 = match guess.trim().parse() { + Ok(num) => num, + Err(_) => continue, + }; +``` + +Listing 20-27: A `match` with an arm that ends in `continue` -Filename: src/lib.rs +At the time, we skipped over some details in this code. In “The `match` +Control Flow Construct” +section in Chapter 6, we discussed that `match` arms must all return the same +type. So, for example, the following code doesn’t work: ``` -impl ThreadPool { - --snip-- - pub fn new(size: usize) -> ThreadPool { - assert!(size > 0); + let guess = match guess.trim().parse() { + Ok(_) => 5, + Err(_) => "hello", + }; +``` - let (sender, receiver) = mpsc::channel(); +The type of `guess` in this code would have to be an integer *and* a string, +and Rust requires that `guess` have only one type. So, what does `continue` +return? How were we allowed to return a `u32` from one arm and have another arm +that ends with `continue` in Listing 20-27? - let mut workers = Vec::with_capacity(size); +As you might have guessed, `continue` has a `!` value. That is, when Rust +computes the type of `guess`, it looks at both match arms, the former with a +value of `u32` and the latter with a `!` value. Because `!` can never have a +value, Rust decides that the type of `guess` is `u32`. - for id in 0..size { - 1 workers.push(Worker::new(id, receiver)); - } +The formal way of describing this behavior is that expressions of type `!` can +be coerced into any other type. We’re allowed to end this `match` arm with +`continue` because `continue` doesn’t return a value; instead, it moves control +back to the top of the loop, so in the `Err` case, we never assign a value to +`guess`. - ThreadPool { workers, sender } +The never type is useful with the `panic!` macro as well. Recall the `unwrap` +function that we call on `Option` values to produce a value or panic with +this definition: + +``` +impl Option { + pub fn unwrap(self) -> T { + match self { + Some(val) => val, + None => panic!("called `Option::unwrap()` on a `None` value"), + } } - --snip-- } +``` + +In this code, the same thing happens as in the `match` in Listing 20-27: Rust +sees that `val` has the type `T` and `panic!` has the type `!`, so the result +of the overall `match` expression is `T`. This code works because `panic!` +doesn’t produce a value; it ends the program. In the `None` case, we won’t be +returning a value from `unwrap`, so this code is valid. ---snip-- +One final expression that has the type `!` is a loop: -impl Worker { - fn new(id: usize, receiver: mpsc::Receiver) -> Worker { - let thread = thread::spawn(|| { - 2 receiver; - }); +``` + print!("forever "); - Worker { id, thread } + loop { + print!("and ever "); } +``` + +Here, the loop never ends, so `!` is the value of the expression. However, this +wouldn’t be true if we included a `break`, because the loop would terminate +when it got to the `break`. + +### Dynamically Sized Types and the Sized Trait + +Rust needs to know certain details about its types, such as how much space to +allocate for a value of a particular type. This leaves one corner of its type +system a little confusing at first: the concept of *dynamically sized types*. +Sometimes referred to as *DSTs* or *unsized types*, these types let us write +code using values whose size we can know only at runtime. + +Let’s dig into the details of a dynamically sized type called `str`, which +we’ve been using throughout the book. That’s right, not `&str`, but `str` on +its own, is a DST. In many cases, such as when storing text entered by a user, +we can’t know how long the string is until runtime. That means we can’t create +a variable of type `str`, nor can we take an argument of type `str`. Consider +the following code, which does not work: + +``` + let s1: str = "Hello there!"; + let s2: str = "How's it going?"; +``` + +Rust needs to know how much memory to allocate for any value of a particular +type, and all values of a type must use the same amount of memory. If Rust +allowed us to write this code, these two `str` values would need to take up the +same amount of space. But they have different lengths: `s1` needs 12 bytes of +storage and `s2` needs 15. This is why it’s not possible to create a variable +holding a dynamically sized type. + +So, what do we do? In this case, you already know the answer: We make the type +of `s1` and `s2` string slice (`&str`) rather than `str`. Recall from the +“String Slices” section in Chapter 4 that the +slice data structure only stores the starting position and the length of the +slice. So, although `&T` is a single value that stores the memory address of +where the `T` is located, a string slice is *two* values: the address of the +`str` and its length. As such, we can know the size of a string slice value at +compile time: It’s twice the length of a `usize`. That is, we always know the +size of a string slice, no matter how long the string it refers to is. In +general, this is the way in which dynamically sized types are used in Rust: +They have an extra bit of metadata that stores the size of the dynamic +information. The golden rule of dynamically sized types is that we must always +put values of dynamically sized types behind a pointer of some kind. + +We can combine `str` with all kinds of pointers: for example, `Box` or +`Rc`. In fact, you’ve seen this before but with a different dynamically +sized type: traits. Every trait is a dynamically sized type we can refer to by +using the name of the trait. In the “Using Trait Objects to Abstract over +Shared Behavior” section in Chapter 18, we mentioned that to use traits as trait +objects, we must put them behind a pointer, such as `&dyn Trait` or `Box` (`Rc` would work too). + +To work with DSTs, Rust provides the `Sized` trait to determine whether or not +a type’s size is known at compile time. This trait is automatically implemented +for everything whose size is known at compile time. In addition, Rust +implicitly adds a bound on `Sized` to every generic function. That is, a +generic function definition like this: + +``` +fn generic(t: T) { + // --snip-- } ``` -Listing 20-17: Passing the receiver to each `Worker` +is actually treated as though we had written this: -We’ve made some small and straightforward changes: we pass the receiver into -`Worker::new` [1], and then we use it inside the closure [2]. +``` +fn generic(t: T) { + // --snip-- +} +``` -When we try to check this code, we get this error: +By default, generic functions will work only on types that have a known size at +compile time. However, you can use the following special syntax to relax this +restriction: ``` -$ cargo check - Checking hello v0.1.0 (file:///projects/hello) -error[E0382]: use of moved value: `receiver` - --> src/lib.rs:26:42 - | -21 | let (sender, receiver) = mpsc::channel(); - | -------- move occurs because `receiver` has type -`std::sync::mpsc::Receiver`, which does not implement the `Copy` trait -... -26 | workers.push(Worker::new(id, receiver)); - | ^^^^^^^^ value moved here, in -previous iteration of loop +fn generic(t: &T) { + // --snip-- +} ``` -The code is trying to pass `receiver` to multiple `Worker` instances. This -won’t work, as you’ll recall from Chapter 16: the channel implementation that -Rust provides is multiple *producer*, single *consumer*. This means we can’t -just clone the consuming end of the channel to fix this code. We also don’t -want to send a message multiple times to multiple consumers; we want one list -of messages with multiple `Worker` instances such that each message gets -processed once. +A trait bound on `?Sized` means “`T` may or may not be `Sized`,” and this +notation overrides the default that generic types must have a known size at +compile time. The `?Trait` syntax with this meaning is only available for +`Sized`, not any other traits. -Additionally, taking a job off the channel queue involves mutating the -`receiver`, so the threads need a safe way to share and modify `receiver`; -otherwise, we might get race conditions (as covered in Chapter 16). +Also note that we switched the type of the `t` parameter from `T` to `&T`. +Because the type might not be `Sized`, we need to use it behind some kind of +pointer. In this case, we’ve chosen a reference. -Recall the thread-safe smart pointers discussed in Chapter 16: to share -ownership across multiple threads and allow the threads to mutate the value, we -need to use `Arc>`. The `Arc` type will let multiple `Worker` -instances own the receiver, and `Mutex` will ensure that only one `Worker` gets -a job from the receiver at a time. Listing 20-18 shows the changes we need to -make. +Next, we’ll talk about functions and closures! -Filename: src/lib.rs +## Advanced Functions and Closures -``` -use std::{ - sync::{mpsc, Arc, Mutex}, - thread, -}; ---snip-- - -impl ThreadPool { - --snip-- - pub fn new(size: usize) -> ThreadPool { - assert!(size > 0); +This section explores some advanced features related to functions and closures, +including function pointers and returning closures. - let (sender, receiver) = mpsc::channel(); +### Function Pointers - 1 let receiver = Arc::new(Mutex::new(receiver)); +We’ve talked about how to pass closures to functions; you can also pass regular +functions to functions! This technique is useful when you want to pass a +function you’ve already defined rather than defining a new closure. Functions +coerce to the type `fn` (with a lowercase *f*), not to be confused with the +`Fn` closure trait. The `fn` type is called a *function pointer*. Passing +functions with function pointers will allow you to use functions as arguments +to other functions. - let mut workers = Vec::with_capacity(size); +The syntax for specifying that a parameter is a function pointer is similar to +that of closures, as shown in Listing 20-28, where we’ve defined a function +`add_one` that adds 1 to its parameter. The function `do_twice` takes two +parameters: a function pointer to any function that takes an `i32` parameter +and returns an `i32`, and one `i32` value. The `do_twice` function calls the +function `f` twice, passing it the `arg` value, then adds the two function call +results together. The `main` function calls `do_twice` with the arguments +`add_one` and `5`. - for id in 0..size { - workers.push( - Worker::new(id, Arc::clone(& 2 receiver)) - ); - } +src/main.rs - ThreadPool { workers, sender } - } +``` +fn add_one(x: i32) -> i32 { + x + 1 +} - --snip-- +fn do_twice(f: fn(i32) -> i32, arg: i32) -> i32 { + f(arg) + f(arg) } ---snip-- +fn main() { + let answer = do_twice(add_one, 5); -impl Worker { - fn new( - id: usize, - receiver: Arc>>, - ) -> Worker { - --snip-- - } + println!("The answer is: {answer}"); } ``` -Listing 20-18: Sharing the receiver among the `Worker` instances using `Arc` -and `Mutex` +Listing 20-28: Using the `fn` type to accept a function pointer as an argument + +This code prints `The answer is: 12`. We specify that the parameter `f` in +`do_twice` is an `fn` that takes one parameter of type `i32` and returns an +`i32`. We can then call `f` in the body of `do_twice`. In `main`, we can pass +the function name `add_one` as the first argument to `do_twice`. -In `ThreadPool::new`, we put the receiver in an `Arc` and a `Mutex` [1]. For -each new `Worker`, we clone the `Arc` to bump the reference count so the -`Worker` instances can share ownership of the receiver [2]. +Unlike closures, `fn` is a type rather than a trait, so we specify `fn` as the +parameter type directly rather than declaring a generic type parameter with one +of the `Fn` traits as a trait bound. -With these changes, the code compiles! We’re getting there! +Function pointers implement all three of the closure traits (`Fn`, `FnMut`, and +`FnOnce`), meaning you can always pass a function pointer as an argument for a +function that expects a closure. It’s best to write functions using a generic +type and one of the closure traits so that your functions can accept either +functions or closures. -#### Implementing the execute Method +That said, one example of where you would want to only accept `fn` and not +closures is when interfacing with external code that doesn’t have closures: C +functions can accept functions as arguments, but C doesn’t have closures. -Let’s finally implement the `execute` method on `ThreadPool`. We’ll also change -`Job` from a struct to a type alias for a trait object that holds the type of -closure that `execute` receives. As discussed in “Creating Type Synonyms with -Type Aliases” on page XX, type aliases allow us to make long types shorter for -ease of use. Look at Listing 20-19. +As an example of where you could use either a closure defined inline or a named +function, let’s look at a use of the `map` method provided by the `Iterator` +trait in the standard library. To use the `map` method to turn a vector of +numbers into a vector of strings, we could use a closure, as in Listing 20-29. -Filename: src/lib.rs ``` ---snip-- + let list_of_numbers = vec![1, 2, 3]; + let list_of_strings: Vec = + list_of_numbers.iter().map(|i| i.to_string()).collect(); +``` + +Listing 20-29: Using a closure with the `map` method to convert numbers to strings + +Or we could name a function as the argument to `map` instead of the closure. +Listing 20-30 shows what this would look like. + + +``` + let list_of_numbers = vec![1, 2, 3]; + let list_of_strings: Vec = + list_of_numbers.iter().map(ToString::to_string).collect(); +``` -type Job = Box; +Listing 20-30: Using the `String::to_string` function with the `map` method to convert numbers to strings -impl ThreadPool { - --snip-- +Note that we must use the fully qualified syntax that we talked about in the +“Advanced Traits” section because there are +multiple functions available named `to_string`. - pub fn execute(&self, f: F) - where - F: FnOnce() + Send + 'static, - { - 1 let job = Box::new(f); +Here, we’re using the `to_string` function defined in the `ToString` trait, +which the standard library has implemented for any type that implements +`Display`. - 2 self.sender.send(job).unwrap(); +Recall from the “Enum Values” section in Chapter +6 that the name of each enum variant that we define also becomes an initializer +function. We can use these initializer functions as function pointers that +implement the closure traits, which means we can specify the initializer +functions as arguments for methods that take closures, as seen in Listing 20-31. + + +``` + enum Status { + Value(u32), + Stop, } -} ---snip-- + let list_of_statuses: Vec = (0u32..20).map(Status::Value).collect(); ``` -Listing 20-19: Creating a `Job` type alias for a `Box` that holds each closure -and then sending the job down the channel +Listing 20-31: Using an enum initializer with the `map` method to create a `Status` instance from numbers -After creating a new `Job` instance using the closure we get in `execute` [1], -we send that job down the sending end of the channel [2]. We’re calling -`unwrap` on `send` for the case that sending fails. This might happen if, for -example, we stop all our threads from executing, meaning the receiving end has -stopped receiving new messages. At the moment, we can’t stop our threads from -executing: our threads continue executing as long as the pool exists. The -reason we use `unwrap` is that we know the failure case won’t happen, but the -compiler doesn’t know that. +Here, we create `Status::Value` instances using each `u32` value in the range +that `map` is called on by using the initializer function of `Status::Value`. +Some people prefer this style and some people prefer to use closures. They +compile to the same code, so use whichever style is clearer to you. -But we’re not quite done yet! In the `Worker`, our closure being passed to -`thread::spawn` still only *references* the receiving end of the channel. -Instead, we need the closure to loop forever, asking the receiving end of the -channel for a job and running the job when it gets one. Let’s make the change -shown in Listing 20-20 to `Worker::new`. +### Returning Closures + +Closures are represented by traits, which means you can’t return closures +directly. In most cases where you might want to return a trait, you can instead +use the concrete type that implements the trait as the return value of the +function. However, you can’t usually do that with closures because they don’t +have a concrete type that is returnable; you’re not allowed to use the function +pointer `fn` as a return type if the closure captures any values from its +scope, for example. + +Instead, you will normally use the `impl Trait` syntax we learned about in +Chapter 10. You can return any function type, using `Fn`, `FnOnce`, and `FnMut`. +For example, the code in Listing 20-32 will compile just fine. -Filename: src/lib.rs ``` ---snip-- +fn returns_closure() -> impl Fn(i32) -> i32 { + |x| x + 1 +} +``` -impl Worker { - fn new( - id: usize, - receiver: Arc>>, - ) -> Worker { - let thread = thread::spawn(move || loop { - let job = receiver - 1 .lock() - 2 .unwrap() - 3 .recv() - 4 .unwrap(); +Listing 20-32: Returning a closure from a function using the `impl Trait` syntax - println!("Worker {id} got a job; executing."); +However, as we noted in the “Inferring and Annotating Closure +Types” section in Chapter 13, each closure is +also its own distinct type. If you need to work with multiple functions that +have the same signature but different implementations, you will need to use a +trait object for them. Consider what happens if you write code like that shown +in Listing 20-33. - job(); - }); +src/main.rs - Worker { id, thread } +``` +fn main() { + let handlers = vec![returns_closure(), returns_initialized_closure(123)]; + for handler in handlers { + let output = handler(5); + println!("{output}"); } } -``` -Listing 20-20: Receiving and executing the jobs in the `Worker` instance’s -thread +fn returns_closure() -> impl Fn(i32) -> i32 { + |x| x + 1 +} -Here, we first call `lock` on the `receiver` to acquire the mutex [1], and then -we call `unwrap` to panic on any errors [2]. Acquiring a lock might fail if the -mutex is in a *poisoned* state, which can happen if some other thread panicked -while holding the lock rather than releasing the lock. In this situation, -calling `unwrap` to have this thread panic is the correct action to take. Feel -free to change this `unwrap` to an `expect` with an error message that is -meaningful to you. +fn returns_initialized_closure(init: i32) -> impl Fn(i32) -> i32 { + move |x| x + init +} +``` -If we get the lock on the mutex, we call `recv` to receive a `Job` from the -channel [3]. A final `unwrap` moves past any errors here as well [4], which -might occur if the thread holding the sender has shut down, similar to how the -`send` method returns `Err` if the receiver shuts down. +Listing 20-33: Creating a `Vec` of closures defined by functions that return `impl Fn` types -The call to `recv` blocks, so if there is no job yet, the current thread will -wait until a job becomes available. The `Mutex` ensures that only one -`Worker` thread at a time is trying to request a job. +Here we have two functions, `returns_closure` and `returns_initialized_closure`, +which both return `impl Fn(i32) -> i32`. Notice that the closures that they +return are different, even though they implement the same type. If we try to +compile this, Rust lets us know that it won’t work: -Our thread pool is now in a working state! Give it a `cargo run` and make some -requests: +``` +$ cargo build + Compiling functions-example v0.1.0 (file:///projects/functions-example) +error[E0308]: mismatched types + --> src/main.rs:2:44 + | +2 | let handlers = vec![returns_closure(), returns_initialized_closure(123)]; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected opaque type, found a different opaque type +... +9 | fn returns_closure() -> impl Fn(i32) -> i32 { + | ------------------- the expected opaque type +... +13 | fn returns_initialized_closure(init: i32) -> impl Fn(i32) -> i32 { + | ------------------- the found opaque type + | + = note: expected opaque type `impl Fn(i32) -> i32` (opaque type at ) + found opaque type `impl Fn(i32) -> i32` (opaque type at ) + = note: distinct uses of `impl Trait` result in different opaque types +For more information about this error, try `rustc --explain E0308`. +error: could not compile `functions-example` (bin "functions-example") due to 1 previous error ``` -$ cargo run - Compiling hello v0.1.0 (file:///projects/hello) -warning: field is never read: `workers` - --> src/lib.rs:7:5 - | -7 | workers: Vec, - | ^^^^^^^^^^^^^^^^^^^^ - | - = note: `#[warn(dead_code)]` on by default -warning: field is never read: `id` - --> src/lib.rs:48:5 - | -48 | id: usize, - | ^^^^^^^^^ +The error message tells us that whenever we return an `impl Trait`, Rust +creates a unique *opaque type*, a type where we cannot see into the details of +what Rust constructs for us, nor can we guess the type Rust will generate to +write ourselves. So, even though these functions return closures that implement +the same trait, `Fn(i32) -> i32`, the opaque types Rust generates for each are +distinct. (This is similar to how Rust produces different concrete types for +distinct async blocks even when they have the same output type, as we saw in +“The `Pin` Type and the `Unpin` Trait” in +Chapter 17.) We have seen a solution to this problem a few times now: We can +use a trait object, as in Listing 20-34. -warning: field is never read: `thread` - --> src/lib.rs:49:5 - | -49 | thread: thread::JoinHandle<()>, - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -warning: `hello` (lib) generated 3 warnings - Finished dev [unoptimized + debuginfo] target(s) in 1.40s - Running `target/debug/hello` -Worker 0 got a job; executing. -Worker 2 got a job; executing. -Worker 1 got a job; executing. -Worker 3 got a job; executing. -Worker 0 got a job; executing. -Worker 2 got a job; executing. -Worker 1 got a job; executing. -Worker 3 got a job; executing. -Worker 0 got a job; executing. -Worker 2 got a job; executing. -``` - -Success! We now have a thread pool that executes connections asynchronously. -There are never more than four threads created, so our system won’t get -overloaded if the server receives a lot of requests. If we make a request to -*/sleep*, the server will be able to serve other requests by having another -thread run them. - -> Note: If you open */sleep* in multiple browser windows simultaneously, they -might load one at a time in five-second intervals. Some web browsers execute -multiple instances of the same request sequentially for caching reasons. This -limitation is not caused by our web server. - -After learning about the `while let` loop in Chapter 18, you might be wondering -why we didn’t write the `Worker` thread code as shown in Listing 20-21. - -Filename: src/lib.rs - -``` ---snip-- - -impl Worker { - fn new( - id: usize, - receiver: Arc>>, - ) -> Worker { - let thread = thread::spawn(move || { - while let Ok(job) = receiver.lock().unwrap().recv() { - println!("Worker {id} got a job; executing."); - - job(); - } - }); - Worker { id, thread } - } +``` +fn returns_closure() -> Box i32> { + Box::new(|x| x + 1) +} + +fn returns_initialized_closure(init: i32) -> Box i32> { + Box::new(move |x| x + init) } ``` -Listing 20-21: An alternative implementation of `Worker::new` using `while let` +Listing 20-34: Creating a `Vec` of closures defined by functions that return `Box` so that they have the same type + +This code will compile just fine. For more about trait objects, refer to the +section “Using Trait Objects To Abstract over Shared +Behavior” in Chapter 18. + +Next, let’s look at macros! + +## Macros + +We’ve used macros like `println!` throughout this book, but we haven’t fully +explored what a macro is and how it works. The term *macro* refers to a family +of features in Rust—declarative macros with `macro_rules!` and three kinds of +procedural macros: -This code compiles and runs but doesn’t result in the desired threading -behavior: a slow request will still cause other requests to wait to be -processed. The reason is somewhat subtle: the `Mutex` struct has no public -`unlock` method because the ownership of the lock is based on the lifetime of -the `MutexGuard` within the `LockResult>` that the `lock` -method returns. At compile time, the borrow checker can then enforce the rule -that a resource guarded by a `Mutex` cannot be accessed unless we hold the -lock. However, this implementation can also result in the lock being held -longer than intended if we aren’t mindful of the lifetime of the -`MutexGuard`. +* Custom `#[derive]` macros that specify code added with the `derive` attribute + used on structs and enums +* Attribute-like macros that define custom attributes usable on any item +* Function-like macros that look like function calls but operate on the tokens + specified as their argument -The code in Listing 20-20 that uses `let job = -receiver.lock().unwrap().recv().unwrap();` works because with `let`, any -temporary values used in the expression on the right-hand side of the equal -sign are immediately dropped when the `let` statement ends. However, `while -let` (and `if let` and `match`) does not drop temporary values until the end of -the associated block. In Listing 20-21, the lock remains held for the duration -of the call to `job()`, meaning other `Worker` instances cannot receive jobs. +We’ll talk about each of these in turn, but first, let’s look at why we even +need macros when we already have functions. -## Graceful Shutdown and Cleanup +### The Difference Between Macros and Functions -The code in Listing 20-20 is responding to requests asynchronously through the -use of a thread pool, as we intended. We get some warnings about the `workers`, -`id`, and `thread` fields that we’re not using in a direct way that reminds us -we’re not cleaning up anything. When we use the less elegant ctrl-C method to -halt the main thread, all other threads are stopped immediately as well, even -if they’re in the middle of serving a request. +Fundamentally, macros are a way of writing code that writes other code, which +is known as *metaprogramming*. In Appendix C, we discuss the `derive` +attribute, which generates an implementation of various traits for you. We’ve +also used the `println!` and `vec!` macros throughout the book. All of these +macros *expand* to produce more code than the code you’ve written manually. -Next, then, we’ll implement the `Drop` trait to call `join` on each of the -threads in the pool so they can finish the requests they’re working on before -closing. Then we’ll implement a way to tell the threads they should stop -accepting new requests and shut down. To see this code in action, we’ll modify -our server to accept only two requests before gracefully shutting down its -thread pool. +Metaprogramming is useful for reducing the amount of code you have to write and +maintain, which is also one of the roles of functions. However, macros have +some additional powers that functions don’t have. -### Implementing the Drop Trait on ThreadPool +A function signature must declare the number and type of parameters the +function has. Macros, on the other hand, can take a variable number of +parameters: We can call `println!("hello")` with one argument or +`println!("hello {}", name)` with two arguments. Also, macros are expanded +before the compiler interprets the meaning of the code, so a macro can, for +example, implement a trait on a given type. A function can’t, because it gets +called at runtime and a trait needs to be implemented at compile time. -Let’s start with implementing `Drop` on our thread pool. When the pool is -dropped, our threads should all join to make sure they finish their work. -Listing 20-22 shows a first attempt at a `Drop` implementation; this code won’t -quite work yet. +The downside to implementing a macro instead of a function is that macro +definitions are more complex than function definitions because you’re writing +Rust code that writes Rust code. Due to this indirection, macro definitions are +generally more difficult to read, understand, and maintain than function +definitions. -Filename: src/lib.rs +Another important difference between macros and functions is that you must +define macros or bring them into scope *before* you call them in a file, as +opposed to functions you can define anywhere and call anywhere. + + + + +### Declarative Macros for General Metaprogramming + +The most widely used form of macros in Rust is the *declarative macro*. These +are also sometimes referred to as “macros by example,” “`macro_rules!` macros,” +or just plain “macros.” At their core, declarative macros allow you to write +something similar to a Rust `match` expression. As discussed in Chapter 6, +`match` expressions are control structures that take an expression, compare the +resultant value of the expression to patterns, and then run the code associated +with the matching pattern. Macros also compare a value to patterns that are +associated with particular code: In this situation, the value is the literal +Rust source code passed to the macro; the patterns are compared with the +structure of that source code; and the code associated with each pattern, when +matched, replaces the code passed to the macro. This all happens during +compilation. + +To define a macro, you use the `macro_rules!` construct. Let’s explore how to +use `macro_rules!` by looking at how the `vec!` macro is defined. Chapter 8 +covered how we can use the `vec!` macro to create a new vector with particular +values. For example, the following macro creates a new vector containing three +integers: + +``` +let v: Vec = vec![1, 2, 3]; ``` -impl Drop for ThreadPool { - fn drop(&mut self) { - 1 for worker in &mut self.workers { - 2 println!("Shutting down worker {}", worker.id); - 3 worker.thread.join().unwrap(); +We could also use the `vec!` macro to make a vector of two integers or a vector +of five string slices. We wouldn’t be able to use a function to do the same +because we wouldn’t know the number or type of values up front. + +Listing 20-35 shows a slightly simplified definition of the `vec!` macro. + +src/lib.rs + +``` +#[macro_export] +macro_rules! vec { + ( $( $x:expr ),* ) => { + { + let mut temp_vec = Vec::new(); + $( + temp_vec.push($x); + )* + temp_vec } - } + }; +} +``` + +Listing 20-35: A simplified version of the `vec!` macro definition + +> Note: The actual definition of the `vec!` macro in the standard library +> includes code to pre-allocate the correct amount of memory up front. That code +> is an optimization that we don’t include here, to make the example simpler. + +The `#[macro_export]` annotation indicates that this macro should be made +available whenever the crate in which the macro is defined is brought into +scope. Without this annotation, the macro can’t be brought into scope. + +We then start the macro definition with `macro_rules!` and the name of the +macro we’re defining *without* the exclamation mark. The name, in this case +`vec`, is followed by curly brackets denoting the body of the macro definition. + +The structure in the `vec!` body is similar to the structure of a `match` +expression. Here we have one arm with the pattern `( $( $x:expr ),* )`, +followed by `=>` and the block of code associated with this pattern. If the +pattern matches, the associated block of code will be emitted. Given that this +is the only pattern in this macro, there is only one valid way to match; any +other pattern will result in an error. More complex macros will have more than +one arm. + +Valid pattern syntax in macro definitions is different from the pattern syntax +covered in Chapter 19 because macro patterns are matched against Rust code +structure rather than values. Let’s walk through what the pattern pieces in +Listing 20-29 mean; for the full macro pattern syntax, see the Rust +Reference at *../reference/macros-by-example.html*. + +First, we use a set of parentheses to encompass the whole pattern. We use a +dollar sign (`$`) to declare a variable in the macro system that will contain +the Rust code matching the pattern. The dollar sign makes it clear this is a +macro variable as opposed to a regular Rust variable. Next comes a set of +parentheses that captures values that match the pattern within the parentheses +for use in the replacement code. Within `$()` is `$x:expr`, which matches any +Rust expression and gives the expression the name `$x`. + +The comma following `$()` indicates that a literal comma separator character +must appear between each instance of the code that matches the code in `$()`. +The `*` specifies that the pattern matches zero or more of whatever precedes +the `*`. + +When we call this macro with `vec![1, 2, 3];`, the `$x` pattern matches three +times with the three expressions `1`, `2`, and `3`. + +Now let’s look at the pattern in the body of the code associated with this arm: +`temp_vec.push()` within `$()*` is generated for each part that matches `$()` +in the pattern zero or more times depending on how many times the pattern +matches. The `$x` is replaced with each expression matched. When we call this +macro with `vec![1, 2, 3];`, the code generated that replaces this macro call +will be the following: + +``` +{ + let mut temp_vec = Vec::new(); + temp_vec.push(1); + temp_vec.push(2); + temp_vec.push(3); + temp_vec } ``` -Listing 20-22: Joining each thread when the thread pool goes out of scope +We’ve defined a macro that can take any number of arguments of any type and can +generate code to create a vector containing the specified elements. + +To learn more about how to write macros, consult the online documentation or +other resources, such as “The Little Book of Rust Macros” at *https://veykril.github.io/tlborm/* started by +Daniel Keep and continued by Lukas Wirth. + +### Procedural Macros for Generating Code from Attributes -First we loop through each of the thread pool `workers` [1]. We use `&mut` for -this because `self` is a mutable reference, and we also need to be able to -mutate `worker`. For each `worker`, we print a message saying that this -particular `Worker` instance is shutting down [2], and then we call `join` on -that `Worker` instance’s thread [3]. If the call to `join` fails, we use -`unwrap` to make Rust panic and go into an ungraceful shutdown. +The second form of macros is the procedural macro, which acts more like a +function (and is a type of procedure). *Procedural macros* accept some code as +an input, operate on that code, and produce some code as an output rather than +matching against patterns and replacing the code with other code as declarative +macros do. The three kinds of procedural macros are custom `derive`, +attribute-like, and function-like, and all work in a similar fashion. -Here is the error we get when we compile this code: +When creating procedural macros, the definitions must reside in their own crate +with a special crate type. This is for complex technical reasons that we hope +to eliminate in the future. In Listing 20-36, we show how to define a +procedural macro, where `some_attribute` is a placeholder for using a specific +macro variety. + +src/lib.rs ``` -error[E0507]: cannot move out of `worker.thread` which is behind a mutable -reference - --> src/lib.rs:52:13 - | -52 | worker.thread.join().unwrap(); - | ^^^^^^^^^^^^^ ------ `worker.thread` moved due to this -method call - | | - | move occurs because `worker.thread` has type -`JoinHandle<()>`, which does not implement the `Copy` trait - | -note: this function takes ownership of the receiver `self`, which moves -`worker.thread` +use proc_macro::TokenStream; + +#[some_attribute] +pub fn some_name(input: TokenStream) -> TokenStream { +} ``` -The error tells us we can’t call `join` because we only have a mutable borrow -of each `worker` and `join` takes ownership of its argument. To solve this -issue, we need to move the thread out of the `Worker` instance that owns -`thread` so `join` can consume the thread. We did this in Listing 17-15: if -`Worker` holds an `Option>` instead, we can call the -`take` method on the `Option` to move the value out of the `Some` variant and -leave a `None` variant in its place. In other words, a `Worker` that is running -will have a `Some` variant in `thread`, and when we want to clean up a -`Worker`, we’ll replace `Some` with `None` so the `Worker` doesn’t have a -thread to run. +Listing 20-36: An example of defining a procedural macro -So we know we want to update the definition of `Worker` like this: +The function that defines a procedural macro takes a `TokenStream` as an input +and produces a `TokenStream` as an output. The `TokenStream` type is defined by +the `proc_macro` crate that is included with Rust and represents a sequence of +tokens. This is the core of the macro: The source code that the macro is +operating on makes up the input `TokenStream`, and the code the macro produces +is the output `TokenStream`. The function also has an attribute attached to it +that specifies which kind of procedural macro we’re creating. We can have +multiple kinds of procedural macros in the same crate. -Filename: src/lib.rs +Let’s look at the different kinds of procedural macros. We’ll start with a +custom `derive` macro and then explain the small dissimilarities that make the +other forms different. + + + + + +### Custom derive Macros + +Let’s create a crate named `hello_macro` that defines a trait named +`HelloMacro` with one associated function named `hello_macro`. Rather than +making our users implement the `HelloMacro` trait for each of their types, +we’ll provide a procedural macro so that users can annotate their type with +`#[derive(HelloMacro)]` to get a default implementation of the `hello_macro` +function. The default implementation will print `Hello, Macro! My name is TypeName!` where `TypeName` is the name of the type on which this trait has +been defined. In other words, we’ll write a crate that enables another +programmer to write code like Listing 20-37 using our crate. + +src/main.rs ``` -struct Worker { - id: usize, - thread: Option>, +use hello_macro::HelloMacro; +use hello_macro_derive::HelloMacro; + +#[derive(HelloMacro)] +struct Pancakes; + +fn main() { + Pancakes::hello_macro(); } ``` -Now let’s lean on the compiler to find the other places that need to change. -Checking this code, we get two errors: +Listing 20-37: The code a user of our crate will be able to write when using our procedural macro -``` -error[E0599]: no method named `join` found for enum `Option` in the current -scope - --> src/lib.rs:52:27 - | -52 | worker.thread.join().unwrap(); - | ^^^^ method not found in -`Option>` +This code will print `Hello, Macro! My name is Pancakes!` when we’re done. The +first step is to make a new library crate, like this: -error[E0308]: mismatched types - --> src/lib.rs:72:22 - | -72 | Worker { id, thread } - | ^^^^^^ expected enum `Option`, found struct -`JoinHandle` - | - = note: expected enum `Option>` - found struct `JoinHandle<_>` -help: try wrapping the expression in `Some` - | -72 | Worker { id, thread: Some(thread) } - | +++++++++++++ + +``` +$ cargo new hello_macro --lib ``` -Let’s address the second error, which points to the code at the end of -`Worker::new`; we need to wrap the `thread` value in `Some` when we create a -new `Worker`. Make the following changes to fix this error: +Next, in Listing 20-38, we’ll define the `HelloMacro` trait and its associated +function. -Filename: src/lib.rs +src/lib.rs ``` -impl Worker { - fn new( - id: usize, - receiver: Arc>>, - ) -> Worker { - --snip-- - - Worker { - id, - thread: Some(thread), - } - } +pub trait HelloMacro { + fn hello_macro(); } ``` -The first error is in our `Drop` implementation. We mentioned earlier that we -intended to call `take` on the `Option` value to move `thread` out of `worker`. -The following changes will do so: +Listing 20-38: A simple trait that we will use with the `derive` macro + +We have a trait and its function. At this point, our crate user could implement +the trait to achieve the desired functionality, as in Listing 20-39. -Filename: src/lib.rs +src/main.rs ``` -impl Drop for ThreadPool { - fn drop(&mut self) { - for worker in &mut self.workers { - println!("Shutting down worker {}", worker.id); +use hello_macro::HelloMacro; - 1 if let Some(thread) = worker.thread.take() { - 2 thread.join().unwrap(); - } - } +struct Pancakes; + +impl HelloMacro for Pancakes { + fn hello_macro() { + println!("Hello, Macro! My name is Pancakes!"); } } + +fn main() { + Pancakes::hello_macro(); +} ``` -As discussed in Chapter 17, the `take` method on `Option` takes the `Some` -variant out and leaves `None` in its place. We’re using `if let` to destructure -the `Some` and get the thread [1]; then we call `join` on the thread [2]. If a -`Worker` instance’s thread is already `None`, we know that `Worker` has already -had its thread cleaned up, so nothing happens in that case. +Listing 20-39: How it would look if users wrote a manual implementation of the `HelloMacro` trait + +However, they would need to write the implementation block for each type they +wanted to use with `hello_macro`; we want to spare them from having to do this +work. + +Additionally, we can’t yet provide the `hello_macro` function with default +implementation that will print the name of the type the trait is implemented +on: Rust doesn’t have reflection capabilities, so it can’t look up the type’s +name at runtime. We need a macro to generate code at compile time. -### Signaling to the Threads to Stop Listening for Jobs +The next step is to define the procedural macro. At the time of this writing, +procedural macros need to be in their own crate. Eventually, this restriction +might be lifted. The convention for structuring crates and macro crates is as +follows: For a crate named `foo`, a custom `derive` procedural macro crate is +called `foo_derive`. Let’s start a new crate called `hello_macro_derive` inside +our `hello_macro` project: -With all the changes we’ve made, our code compiles without any warnings. -However, the bad news is that this code doesn’t function the way we want it to -yet. The key is the logic in the closures run by the threads of the `Worker` -instances: at the moment, we call `join`, but that won’t shut down the threads, -because they `loop` forever looking for jobs. If we try to drop our -`ThreadPool` with our current implementation of `drop`, the main thread will -block forever, waiting for the first thread to finish. +``` +$ cargo new hello_macro_derive --lib +``` -To fix this problem, we’ll need a change in the `ThreadPool` `drop` -implementation and then a change in the `Worker` loop. +Our two crates are tightly related, so we create the procedural macro crate +within the directory of our `hello_macro` crate. If we change the trait +definition in `hello_macro`, we’ll have to change the implementation of the +procedural macro in `hello_macro_derive` as well. The two crates will need to +be published separately, and programmers using these crates will need to add +both as dependencies and bring them both into scope. We could instead have the +`hello_macro` crate use `hello_macro_derive` as a dependency and re-export the +procedural macro code. However, the way we’ve structured the project makes it +possible for programmers to use `hello_macro` even if they don’t want the +`derive` functionality. -First we’ll change the `ThreadPool` `drop` implementation to explicitly drop -the `sender` before waiting for the threads to finish. Listing 20-23 shows the -changes to `ThreadPool` to explicitly drop `sender`. We use the same `Option` -and `take` technique as we did with the thread to be able to move `sender` out -of `ThreadPool`. +We need to declare the `hello_macro_derive` crate as a procedural macro crate. +We’ll also need functionality from the `syn` and `quote` crates, as you’ll see +in a moment, so we need to add them as dependencies. Add the following to the +*Cargo.toml* file for `hello_macro_derive`: -Filename: src/lib.rs +hello_macro_derive/Cargo.toml ``` -pub struct ThreadPool { - workers: Vec, - sender: Option>, -} ---snip-- -impl ThreadPool { - pub fn new(size: usize) -> ThreadPool { - --snip-- - - ThreadPool { - workers, - sender: Some(sender), - } - } +[lib] +proc-macro = true - pub fn execute(&self, f: F) - where - F: FnOnce() + Send + 'static, - { - let job = Box::new(f); - - self.sender - .as_ref() - .unwrap() - .send(job) - .unwrap(); - } -} +[dependencies] +syn = "2.0" +quote = "1.0" +``` -impl Drop for ThreadPool { - fn drop(&mut self) { - 1 drop(self.sender.take()); - for worker in &mut self.workers { - println!("Shutting down worker {}", worker.id); - if let Some(thread) = worker.thread.take() { - thread.join().unwrap(); - } +To start defining the procedural macro, place the code in Listing 20-40 into +your *src/lib.rs* file for the `hello_macro_derive` crate. Note that this code +won’t compile until we add a definition for the `impl_hello_macro` function. + +hello_macro_derive/src/lib.rs + +``` +use proc_macro::TokenStream; +use quote::quote; + +#[proc_macro_derive(HelloMacro)] +pub fn hello_macro_derive(input: TokenStream) -> TokenStream { + // Construct a representation of Rust code as a syntax tree + // that we can manipulate. + let ast = syn::parse(input).unwrap(); + + // Build the trait implementation. + impl_hello_macro(&ast) +} +``` + +Listing 20-40: Code that most procedural macro crates will require in order to process Rust code + +Notice that we’ve split the code into the `hello_macro_derive` function, which +is responsible for parsing the `TokenStream`, and the `impl_hello_macro` +function, which is responsible for transforming the syntax tree: This makes +writing a procedural macro more convenient. The code in the outer function +(`hello_macro_derive` in this case) will be the same for almost every +procedural macro crate you see or create. The code you specify in the body of +the inner function (`impl_hello_macro` in this case) will be different +depending on your procedural macro’s purpose. + +We’ve introduced three new crates: `proc_macro`, `syn`, +and `quote`. The `proc_macro` crate comes with Rust, +so we didn’t need to add that to the dependencies in *Cargo.toml*. The +`proc_macro` crate is the compiler’s API that allows us to read and manipulate +Rust code from our code. + +The `syn` crate parses Rust code from a string into a data structure that we +can perform operations on. The `quote` crate turns `syn` data structures back +into Rust code. These crates make it much simpler to parse any sort of Rust +code we might want to handle: Writing a full parser for Rust code is no simple +task. + +The `hello_macro_derive` function will be called when a user of our library +specifies `#[derive(HelloMacro)]` on a type. This is possible because we’ve +annotated the `hello_macro_derive` function here with `proc_macro_derive` and +specified the name `HelloMacro`, which matches our trait name; this is the +convention most procedural macros follow. + +The `hello_macro_derive` function first converts the `input` from a +`TokenStream` to a data structure that we can then interpret and perform +operations on. This is where `syn` comes into play. The `parse` function in +`syn` takes a `TokenStream` and returns a `DeriveInput` struct representing the +parsed Rust code. Listing 20-41 shows the relevant parts of the `DeriveInput` +struct we get from parsing the `struct Pancakes;` string. + + +``` +DeriveInput { + // --snip-- + + ident: Ident { + ident: "Pancakes", + span: #0 bytes(95..103) + }, + data: Struct( + DataStruct { + struct_token: Struct, + fields: Unit, + semi_token: Some( + Semi + ) } - } + ) } ``` -Listing 20-23: Explicitly dropping `sender` before joining the `Worker` threads +Listing 20-41: The `DeriveInput` instance we get when parsing the code that has the macro’s attribute in Listing 20-37 -Dropping `sender` [1] closes the channel, which indicates no more messages will -be sent. When that happens, all the calls to `recv` that the `Worker` instances -do in the infinite loop will return an error. In Listing 20-24, we change the -`Worker` loop to gracefully exit the loop in that case, which means the threads -will finish when the `ThreadPool` `drop` implementation calls `join` on them. +The fields of this struct show that the Rust code we’ve parsed is a unit struct +with the `ident` (*identifier*, meaning the name) of `Pancakes`. There are more +fields on this struct for describing all sorts of Rust code; check the `syn` +documentation for `DeriveInput` at *https://docs.rs/syn/2.0/syn/struct.DeriveInput.html* for more information. -Filename: src/lib.rs +Soon we’ll define the `impl_hello_macro` function, which is where we’ll build +the new Rust code we want to include. But before we do, note that the output +for our `derive` macro is also a `TokenStream`. The returned `TokenStream` is +added to the code that our crate users write, so when they compile their crate, +they’ll get the extra functionality that we provide in the modified +`TokenStream`. -``` -impl Worker { - fn new( - id: usize, - receiver: Arc>>, - ) -> Worker { - let thread = thread::spawn(move || loop { - let message = receiver.lock().unwrap().recv(); +You might have noticed that we’re calling `unwrap` to cause the +`hello_macro_derive` function to panic if the call to the `syn::parse` function +fails here. It’s necessary for our procedural macro to panic on errors because +`proc_macro_derive` functions must return `TokenStream` rather than `Result` to +conform to the procedural macro API. We’ve simplified this example by using +`unwrap`; in production code, you should provide more specific error messages +about what went wrong by using `panic!` or `expect`. - match message { - Ok(job) => { - println!( - "Worker {id} got a job; executing." - ); +Now that we have the code to turn the annotated Rust code from a `TokenStream` +into a `DeriveInput` instance, let’s generate the code that implements the +`HelloMacro` trait on the annotated type, as shown in Listing 20-42. - job(); - } - Err(_) => { - println!( - "Worker {id} shutting down." - ); - break; - } - } - }); +hello_macro_derive/src/lib.rs - Worker { - id, - thread: Some(thread), +``` +fn impl_hello_macro(ast: &syn::DeriveInput) -> TokenStream { + let name = &ast.ident; + let generated = quote! { + impl HelloMacro for #name { + fn hello_macro() { + println!("Hello, Macro! My name is {}!", stringify!(#name)); + } } - } + }; + generated.into() } ``` -Listing 20-24: Explicitly breaking out of the loop when `recv` returns an error +Listing 20-42: Implementing the `HelloMacro` trait using the parsed Rust code + +We get an `Ident` struct instance containing the name (identifier) of the +annotated type using `ast.ident`. The struct in Listing 20-41 shows that when +we run the `impl_hello_macro` function on the code in Listing 20-37, the +`ident` we get will have the `ident` field with a value of `"Pancakes"`. Thus, +the `name` variable in Listing 20-42 will contain an `Ident` struct instance +that, when printed, will be the string `"Pancakes"`, the name of the struct in +Listing 20-37. + +The `quote!` macro lets us define the Rust code that we want to return. The +compiler expects something different from the direct result of the `quote!` +macro’s execution, so we need to convert it to a `TokenStream`. We do this by +calling the `into` method, which consumes this intermediate representation and +returns a value of the required `TokenStream` type. + +The `quote!` macro also provides some very cool templating mechanics: We can +enter `#name`, and `quote!` will replace it with the value in the variable +`name`. You can even do some repetition similar to the way regular macros work. +Check out the `quote` crate’s docs at *https://docs.rs/quote* for a thorough introduction. -To see this code in action, let’s modify `main` to accept only two requests -before gracefully shutting down the server, as shown in Listing 20-25. +We want our procedural macro to generate an implementation of our `HelloMacro` +trait for the type the user annotated, which we can get by using `#name`. The +trait implementation has the one function `hello_macro`, whose body contains the +functionality we want to provide: printing `Hello, Macro! My name is` and then +the name of the annotated type. -Filename: src/main.rs +The `stringify!` macro used here is built into Rust. It takes a Rust +expression, such as `1 + 2`, and at compile time turns the expression into a +string literal, such as `"1 + 2"`. This is different from `format!` or +`println!`, which are macros that evaluate the expression and then turn the +result into a `String`. There is a possibility that the `#name` input might be +an expression to print literally, so we use `stringify!`. Using `stringify!` +also saves an allocation by converting `#name` to a string literal at compile +time. + +At this point, `cargo build` should complete successfully in both `hello_macro` +and `hello_macro_derive`. Let’s hook up these crates to the code in Listing +20-37 to see the procedural macro in action! Create a new binary project in +your *projects* directory using `cargo new pancakes`. We need to add +`hello_macro` and `hello_macro_derive` as dependencies in the `pancakes` +crate’s *Cargo.toml*. If you’re publishing your versions of `hello_macro` and +`hello_macro_derive` to crates.io, they +would be regular dependencies; if not, you can specify them as `path` +dependencies as follows: ``` -fn main() { - let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); - let pool = ThreadPool::new(4); +[dependencies] +hello_macro = { path = "../hello_macro" } +hello_macro_derive = { path = "../hello_macro/hello_macro_derive" } +``` - for stream in listener.incoming().take(2) { - let stream = stream.unwrap(); +Put the code in Listing 20-37 into *src/main.rs*, and run `cargo run`: It +should print `Hello, Macro! My name is Pancakes!`. The implementation of the +`HelloMacro` trait from the procedural macro was included without the +`pancakes` crate needing to implement it; the `#[derive(HelloMacro)]` added the +trait implementation. - pool.execute(|| { - handle_connection(stream); - }); - } +Next, let’s explore how the other kinds of procedural macros differ from custom +`derive` macros. - println!("Shutting down."); -} +### Attribute-Like Macros + +Attribute-like macros are similar to custom `derive` macros, but instead of +generating code for the `derive` attribute, they allow you to create new +attributes. They’re also more flexible: `derive` only works for structs and +enums; attributes can be applied to other items as well, such as functions. +Here’s an example of using an attribute-like macro. Say you have an attribute +named `route` that annotates functions when using a web application framework: + +``` +#[route(GET, "/")] +fn index() { ``` -Listing 20-25: Shutting down the server after serving two requests by exiting -the loop +This `#[route]` attribute would be defined by the framework as a procedural +macro. The signature of the macro definition function would look like this: -You wouldn’t want a real-world web server to shut down after serving only two -requests. This code just demonstrates that the graceful shutdown and cleanup is -in working order. +``` +#[proc_macro_attribute] +pub fn route(attr: TokenStream, item: TokenStream) -> TokenStream { +``` -The `take` method is defined in the `Iterator` trait and limits the iteration -to the first two items at most. The `ThreadPool` will go out of scope at the -end of `main`, and the `drop` implementation will run. +Here, we have two parameters of type `TokenStream`. The first is for the +contents of the attribute: the `GET, "/"` part. The second is the body of the +item the attribute is attached to: in this case, `fn index() {}` and the rest +of the function’s body. -Start the server with `cargo run`, and make three requests. The third request -should error, and in your terminal you should see output similar to this: +Other than that, attribute-like macros work the same way as custom `derive` +macros: You create a crate with the `proc-macro` crate type and implement a +function that generates the code you want! + +### Function-Like Macros + +Function-like macros define macros that look like function calls. Similarly to +`macro_rules!` macros, they’re more flexible than functions; for example, they +can take an unknown number of arguments. However, `macro_rules!` macros can +only be defined using the match-like syntax we discussed in the “Declarative +Macros for General Metaprogramming” section earlier. +Function-like macros take a `TokenStream` parameter, and their definition +manipulates that `TokenStream` using Rust code as the other two types of +procedural macros do. An example of a function-like macro is an `sql!` macro +that might be called like so: ``` -$ cargo run - Compiling hello v0.1.0 (file:///projects/hello) - Finished dev [unoptimized + debuginfo] target(s) in 1.0s - Running `target/debug/hello` -Worker 0 got a job; executing. -Shutting down. -Shutting down worker 0 -Worker 3 got a job; executing. -Worker 1 disconnected; shutting down. -Worker 2 disconnected; shutting down. -Worker 3 disconnected; shutting down. -Worker 0 disconnected; shutting down. -Shutting down worker 1 -Shutting down worker 2 -Shutting down worker 3 -``` - -You might see a different ordering of `Worker` IDs and messages printed. We can -see how this code works from the messages: `Worker` instances 0 and 3 got the -first two requests. The server stopped accepting connections after the second -connection, and the `Drop` implementation on `ThreadPool` starts executing -before `Worker` 3 even starts its job. Dropping the `sender` disconnects all -the `Worker` instances and tells them to shut down. The `Worker` instances each -print a message when they disconnect, and then the thread pool calls `join` to -wait for each `Worker` thread to finish. - -Notice one interesting aspect of this particular execution: the `ThreadPool` -dropped the `sender`, and before any `Worker` received an error, we tried to -join `Worker` 0. `Worker` 0 had not yet gotten an error from `recv`, so the -main thread blocked, waiting for `Worker` 0 to finish. In the meantime, -`Worker` 3 received a job and then all threads received an error. When `Worker` -0 finished, the main thread waited for the rest of the `Worker` instances to -finish. At that point, they had all exited their loops and stopped. - -Congrats! We’ve now completed our project; we have a basic web server that uses -a thread pool to respond asynchronously. We’re able to perform a graceful -shutdown of the server, which cleans up all the threads in the pool. See -*https://www.nostarch.com/Rust2021* to download the full code for this chapter -for reference. - -We could do more here! If you want to continue enhancing this project, here are -some ideas: - -* Add more documentation to `ThreadPool` and its public methods. -* Add tests of the library’s functionality. -* Change calls to `unwrap` to more robust error handling. -* Use `ThreadPool` to perform some task other than serving web requests. -* Find a thread pool crate on *https://crates.io* and implement a similar web -server using the crate instead. Then compare its API and robustness to the -thread pool we implemented. +let sql = sql!(SELECT * FROM posts WHERE id=1); +``` + +This macro would parse the SQL statement inside it and check that it’s +syntactically correct, which is much more complex processing than a +`macro_rules!` macro can do. The `sql!` macro would be defined like this: + +``` +#[proc_macro] +pub fn sql(input: TokenStream) -> TokenStream { +``` + +This definition is similar to the custom `derive` macro’s signature: We receive +the tokens that are inside the parentheses and return the code we wanted to +generate. ## Summary -Well done! You’ve made it to the end of the book! We want to thank you for -joining us on this tour of Rust. You’re now ready to implement your own Rust -projects and help with other people’s projects. Keep in mind that there is a -welcoming community of other Rustaceans who would love to help you with any -challenges you encounter on your Rust journey. +Whew! Now you have some Rust features in your toolbox that you likely won’t use +often, but you’ll know they’re available in very particular circumstances. +We’ve introduced several complex topics so that when you encounter them in +error message suggestions or in other people’s code, you’ll be able to +recognize these concepts and syntax. Use this chapter as a reference to guide +you to solutions. +Next, we’ll put everything we’ve discussed throughout the book into practice +and do one more project! diff --git a/nostarch/chapter21.md b/nostarch/chapter21.md new file mode 100644 index 0000000000..32bcd7db9d --- /dev/null +++ b/nostarch/chapter21.md @@ -0,0 +1,2166 @@ + + +[TOC] + +# Final Project: Building a Multithreaded Web Server + +It’s been a long journey, but we’ve reached the end of the book. In this +chapter, we’ll build one more project together to demonstrate some of the +concepts we covered in the final chapters, as well as recap some earlier +lessons. + +For our final project, we’ll make a web server that says “Hello!” and looks like +Figure 21-1 in a web browser. + +Here is our plan for building the web server: + +1. Learn a bit about TCP and HTTP. +1. Listen for TCP connections on a socket. +1. Parse a small number of HTTP requests. +1. Create a proper HTTP response. +1. Improve the throughput of our server with a thread pool. + +Screenshot of a web browser visiting the address 127.0.0.1:8080 displaying a webpage with the text content “Hello! Hi from Rust” + +Figure 21-1: Our final shared project + +Before we get started, we should mention two details. First, the method we’ll +use won’t be the best way to build a web server with Rust. Community members +have published a number of production-ready crates available at +crates.io at *https://crates.io/* that provide more complete web server and +thread pool implementations than we’ll build. However, our intention in this +chapter is to help you learn, not to take the easy route. Because Rust is a +systems programming language, we can choose the level of abstraction we want to +work with and can go to a lower level than is possible or practical in other +languages. + +Second, we will not be using async and await here. Building a thread pool is a +big enough challenge on its own, without adding in building an async runtime! +However, we will note how async and await might be applicable to some of the +same problems we will see in this chapter. Ultimately, as we noted back in +Chapter 17, many async runtimes use thread pools for managing their work. + +We’ll therefore write the basic HTTP server and thread pool manually so that +you can learn the general ideas and techniques behind the crates you might use +in the future. + +## Building a Single-Threaded Web Server + +We’ll start by getting a single-threaded web server working. Before we begin, +let’s look at a quick overview of the protocols involved in building web +servers. The details of these protocols are beyond the scope of this book, but +a brief overview will give you the information you need. + +The two main protocols involved in web servers are *Hypertext Transfer +Protocol* *(HTTP)* and *Transmission Control Protocol* *(TCP)*. Both protocols +are *request-response* protocols, meaning a *client* initiates requests and a +*server* listens to the requests and provides a response to the client. The +contents of those requests and responses are defined by the protocols. + +TCP is the lower-level protocol that describes the details of how information +gets from one server to another but doesn’t specify what that information is. +HTTP builds on top of TCP by defining the contents of the requests and +responses. It’s technically possible to use HTTP with other protocols, but in +the vast majority of cases, HTTP sends its data over TCP. We’ll work with the +raw bytes of TCP and HTTP requests and responses. + +### Listening to the TCP Connection + +Our web server needs to listen to a TCP connection, so that’s the first part +we’ll work on. The standard library offers a `std::net` module that lets us do +this. Let’s make a new project in the usual fashion: + +``` +$ cargo new hello + Created binary (application) `hello` project +$ cd hello +``` + +Now enter the code in Listing 21-1 in *src/main.rs* to start. This code will +listen at the local address `127.0.0.1:7878` for incoming TCP streams. When it +gets an incoming stream, it will print `Connection established!`. + +src/main.rs + +``` +use std::net::TcpListener; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + println!("Connection established!"); + } +} +``` + +Listing 21-1: Listening for incoming streams and printing a message when we receive a stream + +Using `TcpListener`, we can listen for TCP connections at the address +`127.0.0.1:7878`. In the address, the section before the colon is an IP address +representing your computer (this is the same on every computer and doesn’t +represent the authors’ computer specifically), and `7878` is the port. We’ve +chosen this port for two reasons: HTTP isn’t normally accepted on this port, so +our server is unlikely to conflict with any other web server you might have +running on your machine, and 7878 is *rust* typed on a telephone. + +The `bind` function in this scenario works like the `new` function in that it +will return a new `TcpListener` instance. The function is called `bind` +because, in networking, connecting to a port to listen to is known as “binding +to a port.” + +The `bind` function returns a `Result`, which indicates that it’s +possible for binding to fail, for example, if we ran two instances of our +program and so had two programs listening to the same port. Because we’re +writing a basic server just for learning purposes, we won’t worry about +handling these kinds of errors; instead, we use `unwrap` to stop the program if +errors happen. + +The `incoming` method on `TcpListener` returns an iterator that gives us a +sequence of streams (more specifically, streams of type `TcpStream`). A single +*stream* represents an open connection between the client and the server. +*Connection* is the name for the full request and response process in which a +client connects to the server, the server generates a response, and the server +closes the connection. As such, we will read from the `TcpStream` to see what +the client sent and then write our response to the stream to send data back to +the client. Overall, this `for` loop will process each connection in turn and +produce a series of streams for us to handle. + +For now, our handling of the stream consists of calling `unwrap` to terminate +our program if the stream has any errors; if there aren’t any errors, the +program prints a message. We’ll add more functionality for the success case in +the next listing. The reason we might receive errors from the `incoming` method +when a client connects to the server is that we’re not actually iterating over +connections. Instead, we’re iterating over *connection attempts*. The +connection might not be successful for a number of reasons, many of them +operating system specific. For example, many operating systems have a limit to +the number of simultaneous open connections they can support; new connection +attempts beyond that number will produce an error until some of the open +connections are closed. + +Let’s try running this code! Invoke `cargo run` in the terminal and then load +*127.0.0.1:7878* in a web browser. The browser should show an error message +like “Connection reset” because the server isn’t currently sending back any +data. But when you look at your terminal, you should see several messages that +were printed when the browser connected to the server! + +``` + Running `target/debug/hello` +Connection established! +Connection established! +Connection established! +``` + +Sometimes you’ll see multiple messages printed for one browser request; the +reason might be that the browser is making a request for the page as well as a +request for other resources, like the *favicon.ico* icon that appears in the +browser tab. + +It could also be that the browser is trying to connect to the server multiple +times because the server isn’t responding with any data. When `stream` goes out +of scope and is dropped at the end of the loop, the connection is closed as +part of the `drop` implementation. Browsers sometimes deal with closed +connections by retrying, because the problem might be temporary. + +Browsers also sometimes open multiple connections to the server without sending +any requests so that if they *do* later send requests, those requests can +happen more quickly. When this occurs, our server will see each connection, +regardless of whether there are any requests over that connection. Many +versions of Chrome-based browsers do this, for example; you can disable that +optimization by using private browsing mode or using a different browser. + +The important factor is that we’ve successfully gotten a handle to a TCP +connection! + +Remember to stop the program by pressing ctrl-C when +you’re done running a particular version of the code. Then, restart the program +by invoking the `cargo run` command after you’ve made each set of code changes +to make sure you’re running the newest code. + +### Reading the Request + +Let’s implement the functionality to read the request from the browser! To +separate the concerns of first getting a connection and then taking some action +with the connection, we’ll start a new function for processing connections. In +this new `handle_connection` function, we’ll read data from the TCP stream and +print it so that we can see the data being sent from the browser. Change the +code to look like Listing 21-2. + +src/main.rs + +``` +use std::{ + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + handle_connection(stream); + } +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let http_request: Vec<_> = buf_reader + .lines() + .map(|result| result.unwrap()) + .take_while(|line| !line.is_empty()) + .collect(); + + println!("Request: {http_request:#?}"); +} +``` + +Listing 21-2: Reading from the `TcpStream` and printing the data + +We bring `std::io::BufReader` and `std::io::prelude` into scope to get access +to traits and types that let us read from and write to the stream. In the `for` +loop in the `main` function, instead of printing a message that says we made a +connection, we now call the new `handle_connection` function and pass the +`stream` to it. + +In the `handle_connection` function, we create a new `BufReader` instance that +wraps a reference to the `stream`. The `BufReader` adds buffering by managing +calls to the `std::io::Read` trait methods for us. + +We create a variable named `http_request` to collect the lines of the request +the browser sends to our server. We indicate that we want to collect these +lines in a vector by adding the `Vec<_>` type annotation. + +`BufReader` implements the `std::io::BufRead` trait, which provides the `lines` +method. The `lines` method returns an iterator of `Result` by splitting the stream of data whenever it sees a newline +byte. To get each `String`, we `map` and `unwrap` each `Result`. The `Result` +might be an error if the data isn’t valid UTF-8 or if there was a problem +reading from the stream. Again, a production program should handle these errors +more gracefully, but we’re choosing to stop the program in the error case for +simplicity. + +The browser signals the end of an HTTP request by sending two newline +characters in a row, so to get one request from the stream, we take lines until +we get a line that is the empty string. Once we’ve collected the lines into the +vector, we’re printing them out using pretty debug formatting so that we can +take a look at the instructions the web browser is sending to our server. + +Let’s try this code! Start the program and make a request in a web browser +again. Note that we’ll still get an error page in the browser, but our +program’s output in the terminal will now look similar to this: + + + +``` +$ cargo run + Compiling hello v0.1.0 (file:///projects/hello) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.42s + Running `target/debug/hello` +Request: [ + "GET / HTTP/1.1", + "Host: 127.0.0.1:7878", + "User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:99.0) Gecko/20100101 Firefox/99.0", + "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8", + "Accept-Language: en-US,en;q=0.5", + "Accept-Encoding: gzip, deflate, br", + "DNT: 1", + "Connection: keep-alive", + "Upgrade-Insecure-Requests: 1", + "Sec-Fetch-Dest: document", + "Sec-Fetch-Mode: navigate", + "Sec-Fetch-Site: none", + "Sec-Fetch-User: ?1", + "Cache-Control: max-age=0", +] +``` + +Depending on your browser, you might get slightly different output. Now that +we’re printing the request data, we can see why we get multiple connections +from one browser request by looking at the path after `GET` in the first line +of the request. If the repeated connections are all requesting */*, we know the +browser is trying to fetch */* repeatedly because it’s not getting a response +from our program. + +Let’s break down this request data to understand what the browser is asking of +our program. + + + + + + +### Looking More Closely at an HTTP Request + +HTTP is a text-based protocol, and a request takes this format: + +``` +Method Request-URI HTTP-Version CRLF +headers CRLF +message-body +``` + +The first line is the *request line* that holds information about what the +client is requesting. The first part of the request line indicates the method +being used, such as `GET` or `POST`, which describes how the client is making +this request. Our client used a `GET` request, which means it is asking for +information. + +The next part of the request line is */*, which indicates the *uniform resource +identifier* *(URI)* the client is requesting: A URI is almost, but not quite, +the same as a *uniform resource locator* *(URL)*. The difference between URIs +and URLs isn’t important for our purposes in this chapter, but the HTTP spec +uses the term *URI*, so we can just mentally substitute *URL* for *URI* here. + +The last part is the HTTP version the client uses, and then the request line +ends in a CRLF sequence. (*CRLF* stands for *carriage return* and *line feed*, +which are terms from the typewriter days!) The CRLF sequence can also be +written as `\r\n`, where `\r` is a carriage return and `\n` is a line feed. The +*CRLF sequence* separates the request line from the rest of the request data. +Note that when the CRLF is printed, we see a new line start rather than `\r\n`. + +Looking at the request line data we received from running our program so far, +we see that `GET` is the method, */* is the request URI, and `HTTP/1.1` is the +version. + +After the request line, the remaining lines starting from `Host:` onward are +headers. `GET` requests have no body. + +Try making a request from a different browser or asking for a different +address, such as *127.0.0.1:7878/test*, to see how the request data changes. + +Now that we know what the browser is asking for, let’s send back some data! + +### Writing a Response + +We’re going to implement sending data in response to a client request. +Responses have the following format: + +``` +HTTP-Version Status-Code Reason-Phrase CRLF +headers CRLF +message-body +``` + +The first line is a *status line* that contains the HTTP version used in the +response, a numeric status code that summarizes the result of the request, and +a reason phrase that provides a text description of the status code. After the +CRLF sequence are any headers, another CRLF sequence, and the body of the +response. + +Here is an example response that uses HTTP version 1.1 and has a status code of +200, an OK reason phrase, no headers, and no body: + +``` +HTTP/1.1 200 OK\r\n\r\n +``` + +The status code 200 is the standard success response. The text is a tiny +successful HTTP response. Let’s write this to the stream as our response to a +successful request! From the `handle_connection` function, remove the +`println!` that was printing the request data and replace it with the code in +Listing 21-3. + +src/main.rs + +``` +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let http_request: Vec<_> = buf_reader + .lines() + .map(|result| result.unwrap()) + .take_while(|line| !line.is_empty()) + .collect(); + + let response = "HTTP/1.1 200 OK\r\n\r\n"; + + stream.write_all(response.as_bytes()).unwrap(); +} +``` + +Listing 21-3: Writing a tiny successful HTTP response to the stream + +The first new line defines the `response` variable that holds the success +message’s data. Then, we call `as_bytes` on our `response` to convert the +string data to bytes. The `write_all` method on `stream` takes a `&[u8]` and +sends those bytes directly down the connection. Because the `write_all` +operation could fail, we use `unwrap` on any error result as before. Again, in +a real application, you would add error handling here. + +With these changes, let’s run our code and make a request. We’re no longer +printing any data to the terminal, so we won’t see any output other than the +output from Cargo. When you load *127.0.0.1:7878* in a web browser, you should +get a blank page instead of an error. You’ve just handcoded receiving an HTTP +request and sending a response! + +### Returning Real HTML + +Let’s implement the functionality for returning more than a blank page. Create +the new file *hello.html* in the root of your project directory, not in the +*src* directory. You can input any HTML you want; Listing 21-4 shows one +possibility. + +hello.html + +``` + + + + + Hello! + + +

Hello!

+

Hi from Rust

+ + +``` + +Listing 21-4: A sample HTML file to return in a response + +This is a minimal HTML5 document with a heading and some text. To return this +from the server when a request is received, we’ll modify `handle_connection` as +shown in Listing 21-5 to read the HTML file, add it to the response as a body, +and send it. + +src/main.rs + +``` +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, +}; +// --snip-- + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let http_request: Vec<_> = buf_reader + .lines() + .map(|result| result.unwrap()) + .take_while(|line| !line.is_empty()) + .collect(); + + let status_line = "HTTP/1.1 200 OK"; + let contents = fs::read_to_string("hello.html").unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} +``` + +Listing 21-5: Sending the contents of *hello.html* as the body of the response + +We’ve added `fs` to the `use` statement to bring the standard library’s +filesystem module into scope. The code for reading the contents of a file to a +string should look familiar; we used it when we read the contents of a file for +our I/O project in Listing 12-4. + +Next, we use `format!` to add the file’s contents as the body of the success +response. To ensure a valid HTTP response, we add the `Content-Length` header, +which is set to the size of our response body—in this case, the size of +`hello.html`. + +Run this code with `cargo run` and load *127.0.0.1:7878* in your browser; you +should see your HTML rendered! + +Currently, we’re ignoring the request data in `http_request` and just sending +back the contents of the HTML file unconditionally. That means if you try +requesting *127.0.0.1:7878/something-else* in your browser, you’ll still get +back this same HTML response. At the moment, our server is very limited and +does not do what most web servers do. We want to customize our responses +depending on the request and only send back the HTML file for a well-formed +request to */*. + +### Validating the Request and Selectively Responding + +Right now, our web server will return the HTML in the file no matter what the +client requested. Let’s add functionality to check that the browser is +requesting */* before returning the HTML file and to return an error if the +browser requests anything else. For this we need to modify `handle_connection`, +as shown in Listing 21-6. This new code checks the content of the request +received against what we know a request for */* looks like and adds `if` and +`else` blocks to treat requests differently. + +src/main.rs + +``` +// --snip-- + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + if request_line == "GET / HTTP/1.1" { + let status_line = "HTTP/1.1 200 OK"; + let contents = fs::read_to_string("hello.html").unwrap(); + let length = contents.len(); + + let response = format!( + "{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}" + ); + + stream.write_all(response.as_bytes()).unwrap(); + } else { + // some other request + } +} +``` + +Listing 21-6: Handling requests to */* differently from other requests + +We’re only going to be looking at the first line of the HTTP request, so rather +than reading the entire request into a vector, we’re calling `next` to get the +first item from the iterator. The first `unwrap` takes care of the `Option` and +stops the program if the iterator has no items. The second `unwrap` handles the +`Result` and has the same effect as the `unwrap` that was in the `map` added in +Listing 21-2. + +Next, we check the `request_line` to see if it equals the request line of a GET +request to the */* path. If it does, the `if` block returns the contents of our +HTML file. + +If the `request_line` does *not* equal the GET request to the */* path, it +means we’ve received some other request. We’ll add code to the `else` block in +a moment to respond to all other requests. + +Run this code now and request *127.0.0.1:7878*; you should get the HTML in +*hello.html*. If you make any other request, such as +*127.0.0.1:7878/something-else*, you’ll get a connection error like those you +saw when running the code in Listing 21-1 and Listing 21-2. + +Now let’s add the code in Listing 21-7 to the `else` block to return a response +with the status code 404, which signals that the content for the request was +not found. We’ll also return some HTML for a page to render in the browser +indicating the response to the end user. + +src/main.rs + +``` + // --snip-- + } else { + let status_line = "HTTP/1.1 404 NOT FOUND"; + let contents = fs::read_to_string("404.html").unwrap(); + let length = contents.len(); + + let response = format!( + "{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}" + ); + + stream.write_all(response.as_bytes()).unwrap(); + } +``` + +Listing 21-7: Responding with status code 404 and an error page if anything other than */* was requested + +Here, our response has a status line with status code 404 and the reason phrase +`NOT FOUND`. The body of the response will be the HTML in the file *404.html*. +You’ll need to create a *404.html* file next to *hello.html* for the error +page; again, feel free to use any HTML you want, or use the example HTML in +Listing 21-8. + +404.html + +``` + + + + + Hello! + + +

Oops!

+

Sorry, I don't know what you're asking for.

+ + +``` + +Listing 21-8: Sample content for the page to send back with any 404 response + +With these changes, run your server again. Requesting *127.0.0.1:7878* should +return the contents of *hello.html*, and any other request, like +*127.0.0.1:7878/foo*, should return the error HTML from *404.html*. + + + + + +### Refactoring + +At the moment, the `if` and `else` blocks have a lot of repetition: They’re +both reading files and writing the contents of the files to the stream. The +only differences are the status line and the filename. Let’s make the code more +concise by pulling out those differences into separate `if` and `else` lines +that will assign the values of the status line and the filename to variables; +we can then use those variables unconditionally in the code to read the file +and write the response. Listing 21-9 shows the resultant code after replacing +the large `if` and `else` blocks. + +src/main.rs + +``` +// --snip-- + +fn handle_connection(mut stream: TcpStream) { + // --snip-- + + let (status_line, filename) = if request_line == "GET / HTTP/1.1" { + ("HTTP/1.1 200 OK", "hello.html") + } else { + ("HTTP/1.1 404 NOT FOUND", "404.html") + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} +``` + +Listing 21-9: Refactoring the `if` and `else` blocks to contain only the code that differs between the two cases + +Now the `if` and `else` blocks only return the appropriate values for the +status line and filename in a tuple; we then use destructuring to assign these +two values to `status_line` and `filename` using a pattern in the `let` +statement, as discussed in Chapter 19. + +The previously duplicated code is now outside the `if` and `else` blocks and +uses the `status_line` and `filename` variables. This makes it easier to see +the difference between the two cases, and it means we have only one place to +update the code if we want to change how the file reading and response writing +work. The behavior of the code in Listing 21-9 will be the same as that in +Listing 21-7. + +Awesome! We now have a simple web server in approximately 40 lines of Rust code +that responds to one request with a page of content and responds to all other +requests with a 404 response. + +Currently, our server runs in a single thread, meaning it can only serve one +request at a time. Let’s examine how that can be a problem by simulating some +slow requests. Then, we’ll fix it so that our server can handle multiple +requests at once. + + + + + + +## From a Single-Threaded to a Multithreaded Server + +Right now, the server will process each request in turn, meaning it won’t +process a second connection until the first connection is finished processing. +If the server received more and more requests, this serial execution would be +less and less optimal. If the server receives a request that takes a long time +to process, subsequent requests will have to wait until the long request is +finished, even if the new requests can be processed quickly. We’ll need to fix +this, but first we’ll look at the problem in action. + + + + + +### Simulating a Slow Request + +We’ll look at how a slowly processing request can affect other requests made to +our current server implementation. Listing 21-10 implements handling a request +to */sleep* with a simulated slow response that will cause the server to sleep +for five seconds before responding. + +src/main.rs + +``` +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; +// --snip-- + +fn handle_connection(mut stream: TcpStream) { + // --snip-- + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + // --snip-- +} +``` + +Listing 21-10: Simulating a slow request by sleeping for five seconds + +We switched from `if` to `match` now that we have three cases. We need to +explicitly match on a slice of `request_line` to pattern-match against the +string literal values; `match` doesn’t do automatic referencing and +dereferencing, like the equality method does. + +The first arm is the same as the `if` block from Listing 21-9. The second arm +matches a request to */sleep*. When that request is received, the server will +sleep for five seconds before rendering the successful HTML page. The third arm +is the same as the `else` block from Listing 21-9. + +You can see how primitive our server is: Real libraries would handle the +recognition of multiple requests in a much less verbose way! + +Start the server using `cargo run`. Then, open two browser windows: one for +*http://127.0.0.1:7878* and the other for *http://127.0.0.1:7878/sleep*. If you +enter the */* URI a few times, as before, you’ll see it respond quickly. But if +you enter */sleep* and then load */*, you’ll see that */* waits until `sleep` +has slept for its full five seconds before loading. + +There are multiple techniques we could use to avoid requests backing up behind +a slow request, including using async as we did Chapter 17; the one we’ll +implement is a thread pool. + +### Improving Throughput with a Thread Pool + +A *thread pool* is a group of spawned threads that are ready and waiting to +handle a task. When the program receives a new task, it assigns one of the +threads in the pool to the task, and that thread will process the task. The +remaining threads in the pool are available to handle any other tasks that come +in while the first thread is processing. When the first thread is done +processing its task, it’s returned to the pool of idle threads, ready to handle +a new task. A thread pool allows you to process connections concurrently, +increasing the throughput of your server. + +We’ll limit the number of threads in the pool to a small number to protect us +from DoS attacks; if we had our program create a new thread for each request as +it came in, someone making 10 million requests to our server could wreak havoc +by using up all our server’s resources and grinding the processing of requests +to a halt. + +Rather than spawning unlimited threads, then, we’ll have a fixed number of +threads waiting in the pool. Requests that come in are sent to the pool for +processing. The pool will maintain a queue of incoming requests. Each of the +threads in the pool will pop off a request from this queue, handle the request, +and then ask the queue for another request. With this design, we can process up +to *`N`* requests concurrently, where *`N`* is the number of threads. If each +thread is responding to a long-running request, subsequent requests can still +back up in the queue, but we’ve increased the number of long-running requests +we can handle before reaching that point. + +This technique is just one of many ways to improve the throughput of a web +server. Other options you might explore are the fork/join model, the +single-threaded async I/O model, and the multithreaded async I/O model. If +you’re interested in this topic, you can read more about other solutions and +try to implement them; with a low-level language like Rust, all of these +options are possible. + +Before we begin implementing a thread pool, let’s talk about what using the +pool should look like. When you’re trying to design code, writing the client +interface first can help guide your design. Write the API of the code so that +it’s structured in the way you want to call it; then, implement the +functionality within that structure rather than implementing the functionality +and then designing the public API. + +Similar to how we used test-driven development in the project in Chapter 12, +we’ll use compiler-driven development here. We’ll write the code that calls the +functions we want, and then we’ll look at errors from the compiler to determine +what we should change next to get the code to work. Before we do that, however, +we’ll explore the technique we’re not going to use as a starting point. + + + + + +#### Spawning a Thread for Each Request + +First, let’s explore how our code might look if it did create a new thread for +every connection. As mentioned earlier, this isn’t our final plan due to the +problems with potentially spawning an unlimited number of threads, but it is a +starting point to get a working multithreaded server first. Then, we’ll add the +thread pool as an improvement, and contrasting the two solutions will be easier. + +Listing 21-11 shows the changes to make to `main` to spawn a new thread to +handle each stream within the `for` loop. + +src/main.rs + +``` +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + thread::spawn(|| { + handle_connection(stream); + }); + } +} +``` + +Listing 21-11: Spawning a new thread for each stream + +As you learned in Chapter 16, `thread::spawn` will create a new thread and then +run the code in the closure in the new thread. If you run this code and load +*/sleep* in your browser, then */* in two more browser tabs, you’ll indeed see +that the requests to */* don’t have to wait for */sleep* to finish. However, as +we mentioned, this will eventually overwhelm the system because you’d be making +new threads without any limit. + +You may also recall from Chapter 17 that this is exactly the kind of situation +where async and await really shine! Keep that in mind as we build the thread +pool and think about how things would look different or the same with async. + + + + + +#### Creating a Finite Number of Threads + +We want our thread pool to work in a similar, familiar way so that switching +from threads to a thread pool doesn’t require large changes to the code that +uses our API. Listing 21-12 shows the hypothetical interface for a `ThreadPool` +struct we want to use instead of `thread::spawn`. + +src/main.rs + +``` +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming() { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } +} +``` + +Listing 21-12: Our ideal `ThreadPool` interface + +We use `ThreadPool::new` to create a new thread pool with a configurable number +of threads, in this case four. Then, in the `for` loop, `pool.execute` has a +similar interface as `thread::spawn` in that it takes a closure that the pool +should run for each stream. We need to implement `pool.execute` so that it +takes the closure and gives it to a thread in the pool to run. This code won’t +yet compile, but we’ll try so that the compiler can guide us in how to fix it. + + + + + +#### Building ThreadPool Using Compiler-Driven Development + +Make the changes in Listing 21-12 to *src/main.rs*, and then let’s use the +compiler errors from `cargo check` to drive our development. Here is the first +error we get: + +``` +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) +error[E0433]: failed to resolve: use of undeclared type `ThreadPool` + --> src/main.rs:11:16 + | +11 | let pool = ThreadPool::new(4); + | ^^^^^^^^^^ use of undeclared type `ThreadPool` + +For more information about this error, try `rustc --explain E0433`. +error: could not compile `hello` (bin "hello") due to 1 previous error +``` + +Great! This error tells us we need a `ThreadPool` type or module, so we’ll +build one now. Our `ThreadPool` implementation will be independent of the kind +of work our web server is doing. So, let’s switch the `hello` crate from a +binary crate to a library crate to hold our `ThreadPool` implementation. After +we change to a library crate, we could also use the separate thread pool +library for any work we want to do using a thread pool, not just for serving +web requests. + +Create a *src/lib.rs* file that contains the following, which is the simplest +definition of a `ThreadPool` struct that we can have for now: + +src/lib.rs + +``` +pub struct ThreadPool; +``` + + + +Then, edit the *main.rs* file to bring `ThreadPool` into scope from the library +crate by adding the following code to the top of *src/main.rs*: + +src/main.rs + +``` +use hello::ThreadPool; +``` + + + +This code still won’t work, but let’s check it again to get the next error that +we need to address: + +``` +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) +error[E0599]: no function or associated item named `new` found for struct `ThreadPool` in the current scope + --> src/main.rs:12:28 + | +12 | let pool = ThreadPool::new(4); + | ^^^ function or associated item not found in `ThreadPool` + +For more information about this error, try `rustc --explain E0599`. +error: could not compile `hello` (bin "hello") due to 1 previous error +``` + +This error indicates that next we need to create an associated function named +`new` for `ThreadPool`. We also know that `new` needs to have one parameter +that can accept `4` as an argument and should return a `ThreadPool` instance. +Let’s implement the simplest `new` function that will have those +characteristics: + +src/lib.rs + +``` +pub struct ThreadPool; + +impl ThreadPool { + pub fn new(size: usize) -> ThreadPool { + ThreadPool + } +} +``` + + + +We chose `usize` as the type of the `size` parameter because we know that a +negative number of threads doesn’t make any sense. We also know we’ll use this +`4` as the number of elements in a collection of threads, which is what the +`usize` type is for, as discussed in the “Integer Types” section in Chapter 3. + +Let’s check the code again: + +``` +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) +error[E0599]: no method named `execute` found for struct `ThreadPool` in the current scope + --> src/main.rs:17:14 + | +17 | pool.execute(|| { + | -----^^^^^^^ method not found in `ThreadPool` + +For more information about this error, try `rustc --explain E0599`. +error: could not compile `hello` (bin "hello") due to 1 previous error +``` + +Now the error occurs because we don’t have an `execute` method on `ThreadPool`. +Recall from the “Creating a Finite Number of +Threads” section that we +decided our thread pool should have an interface similar to `thread::spawn`. In +addition, we’ll implement the `execute` function so that it takes the closure +it’s given and gives it to an idle thread in the pool to run. + +We’ll define the `execute` method on `ThreadPool` to take a closure as a +parameter. Recall from the “Moving Captured Values Out of +Closures” in Chapter 13 that we can +take closures as parameters with three different traits: `Fn`, `FnMut`, and +`FnOnce`. We need to decide which kind of closure to use here. We know we’ll +end up doing something similar to the standard library `thread::spawn` +implementation, so we can look at what bounds the signature of `thread::spawn` +has on its parameter. The documentation shows us the following: + +``` +pub fn spawn(f: F) -> JoinHandle + where + F: FnOnce() -> T, + F: Send + 'static, + T: Send + 'static, +``` + +The `F` type parameter is the one we’re concerned with here; the `T` type +parameter is related to the return value, and we’re not concerned with that. We +can see that `spawn` uses `FnOnce` as the trait bound on `F`. This is probably +what we want as well, because we’ll eventually pass the argument we get in +`execute` to `spawn`. We can be further confident that `FnOnce` is the trait we +want to use because the thread for running a request will only execute that +request’s closure one time, which matches the `Once` in `FnOnce`. + +The `F` type parameter also has the trait bound `Send` and the lifetime bound +`'static`, which are useful in our situation: We need `Send` to transfer the +closure from one thread to another and `'static` because we don’t know how long +the thread will take to execute. Let’s create an `execute` method on +`ThreadPool` that will take a generic parameter of type `F` with these bounds: + +src/lib.rs + +``` +impl ThreadPool { + // --snip-- + pub fn execute(&self, f: F) + where + F: FnOnce() + Send + 'static, + { + } +} +``` + + + +We still use the `()` after `FnOnce` because this `FnOnce` represents a closure +that takes no parameters and returns the unit type `()`. Just like function +definitions, the return type can be omitted from the signature, but even if we +have no parameters, we still need the parentheses. + +Again, this is the simplest implementation of the `execute` method: It does +nothing, but we’re only trying to make our code compile. Let’s check it again: + +``` +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.24s +``` + +It compiles! But note that if you try `cargo run` and make a request in the +browser, you’ll see the errors in the browser that we saw at the beginning of +the chapter. Our library isn’t actually calling the closure passed to `execute` +yet! + +> Note: A saying you might hear about languages with strict compilers, such as +> Haskell and Rust, is “If the code compiles, it works.” But this saying is not +> universally true. Our project compiles, but it does absolutely nothing! If we +> were building a real, complete project, this would be a good time to start +> writing unit tests to check that the code compiles *and* has the behavior we +> want. + +Consider: What would be different here if we were going to execute a future +instead of a closure? + +#### Validating the Number of Threads in new + +We aren’t doing anything with the parameters to `new` and `execute`. Let’s +implement the bodies of these functions with the behavior we want. To start, +let’s think about `new`. Earlier we chose an unsigned type for the `size` +parameter because a pool with a negative number of threads makes no sense. +However, a pool with zero threads also makes no sense, yet zero is a perfectly +valid `usize`. We’ll add code to check that `size` is greater than zero before +we return a `ThreadPool` instance, and we’ll have the program panic if it +receives a zero by using the `assert!` macro, as shown in Listing 21-13. + +src/lib.rs + +``` +impl ThreadPool { + /// Create a new ThreadPool. + /// + /// The size is the number of threads in the pool. + /// + /// # Panics + /// + /// The `new` function will panic if the size is zero. + pub fn new(size: usize) -> ThreadPool { + assert!(size > 0); + + ThreadPool + } + + // --snip-- +} +``` + +Listing 21-13: Implementing `ThreadPool::new` to panic if `size` is zero + +We’ve also added some documentation for our `ThreadPool` with doc comments. +Note that we followed good documentation practices by adding a section that +calls out the situations in which our function can panic, as discussed in +Chapter 14. Try running `cargo doc --open` and clicking the `ThreadPool` struct +to see what the generated docs for `new` look like! + +Instead of adding the `assert!` macro as we’ve done here, we could change `new` +into `build` and return a `Result` like we did with `Config::build` in the I/O +project in Listing 12-9. But we’ve decided in this case that trying to create a +thread pool without any threads should be an unrecoverable error. If you’re +feeling ambitious, try to write a function named `build` with the following +signature to compare with the `new` function: + +``` +pub fn build(size: usize) -> Result { +``` + +#### Creating Space to Store the Threads + +Now that we have a way to know we have a valid number of threads to store in +the pool, we can create those threads and store them in the `ThreadPool` struct +before returning the struct. But how do we “store” a thread? Let’s take another +look at the `thread::spawn` signature: + +``` +pub fn spawn(f: F) -> JoinHandle + where + F: FnOnce() -> T, + F: Send + 'static, + T: Send + 'static, +``` + +The `spawn` function returns a `JoinHandle`, where `T` is the type that the +closure returns. Let’s try using `JoinHandle` too and see what happens. In our +case, the closures we’re passing to the thread pool will handle the connection +and not return anything, so `T` will be the unit type `()`. + +The code in Listing 21-14 will compile, but it doesn’t create any threads yet. +We’ve changed the definition of `ThreadPool` to hold a vector of +`thread::JoinHandle<()>` instances, initialized the vector with a capacity of +`size`, set up a `for` loop that will run some code to create the threads, and +returned a `ThreadPool` instance containing them. + +src/lib.rs + +``` +use std::thread; + +pub struct ThreadPool { + threads: Vec>, +} + +impl ThreadPool { + // --snip-- + pub fn new(size: usize) -> ThreadPool { + assert!(size > 0); + + let mut threads = Vec::with_capacity(size); + + for _ in 0..size { + // create some threads and store them in the vector + } + + ThreadPool { threads } + } + // --snip-- +} +``` + +Listing 21-14: Creating a vector for `ThreadPool` to hold the threads + +We’ve brought `std::thread` into scope in the library crate because we’re +using `thread::JoinHandle` as the type of the items in the vector in +`ThreadPool`. + +Once a valid size is received, our `ThreadPool` creates a new vector that can +hold `size` items. The `with_capacity` function performs the same task as +`Vec::new` but with an important difference: It pre-allocates space in the +vector. Because we know we need to store `size` elements in the vector, doing +this allocation up front is slightly more efficient than using `Vec::new`, +which resizes itself as elements are inserted. + +When you run `cargo check` again, it should succeed. + + + + + +#### Sending Code from the ThreadPool to a Thread + +We left a comment in the `for` loop in Listing 21-14 regarding the creation of +threads. Here, we’ll look at how we actually create threads. The standard +library provides `thread::spawn` as a way to create threads, and +`thread::spawn` expects to get some code the thread should run as soon as the +thread is created. However, in our case, we want to create the threads and have +them *wait* for code that we’ll send later. The standard library’s +implementation of threads doesn’t include any way to do that; we have to +implement it manually. + +We’ll implement this behavior by introducing a new data structure between the +`ThreadPool` and the threads that will manage this new behavior. We’ll call +this data structure *Worker*, which is a common term in pooling +implementations. The `Worker` picks up code that needs to be run and runs the +code in its thread. + +Think of people working in the kitchen at a restaurant: The workers wait until +orders come in from customers, and then they’re responsible for taking those +orders and filling them. + +Instead of storing a vector of `JoinHandle<()>` instances in the thread pool, +we’ll store instances of the `Worker` struct. Each `Worker` will store a single +`JoinHandle<()>` instance. Then, we’ll implement a method on `Worker` that will +take a closure of code to run and send it to the already running thread for +execution. We’ll also give each `Worker` an `id` so that we can distinguish +between the different instances of `Worker` in the pool when logging or +debugging. + +Here is the new process that will happen when we create a `ThreadPool`. We’ll +implement the code that sends the closure to the thread after we have `Worker` +set up in this way: + +1. Define a `Worker` struct that holds an `id` and a `JoinHandle<()>`. +1. Change `ThreadPool` to hold a vector of `Worker` instances. +1. Define a `Worker::new` function that takes an `id` number and returns a + `Worker` instance that holds the `id` and a thread spawned with an empty + closure. +1. In `ThreadPool::new`, use the `for` loop counter to generate an `id`, create + a new `Worker` with that `id`, and store the `Worker` in the vector. + +If you’re up for a challenge, try implementing these changes on your own before +looking at the code in Listing 21-15. + +Ready? Here is Listing 21-15 with one way to make the preceding modifications. + +src/lib.rs + +``` +use std::thread; + +pub struct ThreadPool { + workers: Vec, +} + +impl ThreadPool { + // --snip-- + pub fn new(size: usize) -> ThreadPool { + assert!(size > 0); + + let mut workers = Vec::with_capacity(size); + + for id in 0..size { + workers.push(Worker::new(id)); + } + + ThreadPool { workers } + } + // --snip-- +} + +struct Worker { + id: usize, + thread: thread::JoinHandle<()>, +} + +impl Worker { + fn new(id: usize) -> Worker { + let thread = thread::spawn(|| {}); + + Worker { id, thread } + } +} +``` + +Listing 21-15: Modifying `ThreadPool` to hold `Worker` instances instead of holding threads directly + +We’ve changed the name of the field on `ThreadPool` from `threads` to `workers` +because it’s now holding `Worker` instances instead of `JoinHandle<()>` +instances. We use the counter in the `for` loop as an argument to +`Worker::new`, and we store each new `Worker` in the vector named `workers`. + +External code (like our server in *src/main.rs*) doesn’t need to know the +implementation details regarding using a `Worker` struct within `ThreadPool`, +so we make the `Worker` struct and its `new` function private. The +`Worker::new` function uses the `id` we give it and stores a `JoinHandle<()>` +instance that is created by spawning a new thread using an empty closure. + +> Note: If the operating system can’t create a thread because there aren’t +> enough system resources, `thread::spawn` will panic. That will cause our +> whole server to panic, even though the creation of some threads might +> succeed. For simplicity’s sake, this behavior is fine, but in a production +> thread pool implementation, you’d likely want to use +> `std::thread::Builder` and its +> `spawn` method that returns `Result` instead. + +This code will compile and will store the number of `Worker` instances we +specified as an argument to `ThreadPool::new`. But we’re *still* not processing +the closure that we get in `execute`. Let’s look at how to do that next. + +#### Sending Requests to Threads via Channels + +The next problem we’ll tackle is that the closures given to `thread::spawn` do +absolutely nothing. Currently, we get the closure we want to execute in the +`execute` method. But we need to give `thread::spawn` a closure to run when we +create each `Worker` during the creation of the `ThreadPool`. + +We want the `Worker` structs that we just created to fetch the code to run from +a queue held in the `ThreadPool` and send that code to its thread to run. + +The channels we learned about in Chapter 16—a simple way to communicate between +two threads—would be perfect for this use case. We’ll use a channel to function +as the queue of jobs, and `execute` will send a job from the `ThreadPool` to +the `Worker` instances, which will send the job to its thread. Here is the plan: + +1. The `ThreadPool` will create a channel and hold on to the sender. +1. Each `Worker` will hold on to the receiver. +1. We’ll create a new `Job` struct that will hold the closures we want to send + down the channel. +1. The `execute` method will send the job it wants to execute through the + sender. +1. In its thread, the `Worker` will loop over its receiver and execute the + closures of any jobs it receives. + +Let’s start by creating a channel in `ThreadPool::new` and holding the sender +in the `ThreadPool` instance, as shown in Listing 21-16. The `Job` struct +doesn’t hold anything for now but will be the type of item we’re sending down +the channel. + +src/lib.rs + +``` +use std::{sync::mpsc, thread}; + +pub struct ThreadPool { + workers: Vec, + sender: mpsc::Sender, +} + +struct Job; + +impl ThreadPool { + // --snip-- + pub fn new(size: usize) -> ThreadPool { + assert!(size > 0); + + let (sender, receiver) = mpsc::channel(); + + let mut workers = Vec::with_capacity(size); + + for id in 0..size { + workers.push(Worker::new(id)); + } + + ThreadPool { workers, sender } + } + // --snip-- +} +``` + +Listing 21-16: Modifying `ThreadPool` to store the sender of a channel that transmits `Job` instances + +In `ThreadPool::new`, we create our new channel and have the pool hold the +sender. This will successfully compile. + +Let’s try passing a receiver of the channel into each `Worker` as the thread +pool creates the channel. We know we want to use the receiver in the thread that +the `Worker` instances spawn, so we’ll reference the `receiver` parameter in the +closure. The code in Listing 21-17 won’t quite compile yet. + +src/lib.rs + +``` +impl ThreadPool { + // --snip-- + pub fn new(size: usize) -> ThreadPool { + assert!(size > 0); + + let (sender, receiver) = mpsc::channel(); + + let mut workers = Vec::with_capacity(size); + + for id in 0..size { + workers.push(Worker::new(id, receiver)); + } + + ThreadPool { workers, sender } + } + // --snip-- +} + +// --snip-- + +impl Worker { + fn new(id: usize, receiver: mpsc::Receiver) -> Worker { + let thread = thread::spawn(|| { + receiver; + }); + + Worker { id, thread } + } +} +``` + +Listing 21-17: Passing the receiver to each `Worker` + +We’ve made some small and straightforward changes: We pass the receiver into +`Worker::new`, and then we use it inside the closure. + +When we try to check this code, we get this error: + +``` +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) +error[E0382]: use of moved value: `receiver` + --> src/lib.rs:26:42 + | +21 | let (sender, receiver) = mpsc::channel(); + | -------- move occurs because `receiver` has type `std::sync::mpsc::Receiver`, which does not implement the `Copy` trait +... +25 | for id in 0..size { + | ----------------- inside of this loop +26 | workers.push(Worker::new(id, receiver)); + | ^^^^^^^^ value moved here, in previous iteration of loop + | +note: consider changing this parameter type in method `new` to borrow instead if owning the value isn't necessary + --> src/lib.rs:47:33 + | +47 | fn new(id: usize, receiver: mpsc::Receiver) -> Worker { + | --- in this method ^^^^^^^^^^^^^^^^^^^ this parameter takes ownership of the value +help: consider moving the expression out of the loop so it is only moved once + | +25 ~ let mut value = Worker::new(id, receiver); +26 ~ for id in 0..size { +27 ~ workers.push(value); + | + +For more information about this error, try `rustc --explain E0382`. +error: could not compile `hello` (lib) due to 1 previous error +``` + +The code is trying to pass `receiver` to multiple `Worker` instances. This +won’t work, as you’ll recall from Chapter 16: The channel implementation that +Rust provides is multiple *producer*, single *consumer*. This means we can’t +just clone the consuming end of the channel to fix this code. We also don’t +want to send a message multiple times to multiple consumers; we want one list +of messages with multiple `Worker` instances such that each message gets +processed once. + +Additionally, taking a job off the channel queue involves mutating the +`receiver`, so the threads need a safe way to share and modify `receiver`; +otherwise, we might get race conditions (as covered in Chapter 16). + +Recall the thread-safe smart pointers discussed in Chapter 16: To share +ownership across multiple threads and allow the threads to mutate the value, we +need to use `Arc>`. The `Arc` type will let multiple `Worker` instances +own the receiver, and `Mutex` will ensure that only one `Worker` gets a job from +the receiver at a time. Listing 21-18 shows the changes we need to make. + +src/lib.rs + +``` +use std::{ + sync::{Arc, Mutex, mpsc}, + thread, +}; +// --snip-- + +impl ThreadPool { + // --snip-- + pub fn new(size: usize) -> ThreadPool { + assert!(size > 0); + + let (sender, receiver) = mpsc::channel(); + + let receiver = Arc::new(Mutex::new(receiver)); + + let mut workers = Vec::with_capacity(size); + + for id in 0..size { + workers.push(Worker::new(id, Arc::clone(&receiver))); + } + + ThreadPool { workers, sender } + } + + // --snip-- +} + +// --snip-- + +impl Worker { + fn new(id: usize, receiver: Arc>>) -> Worker { + // --snip-- + } +} +``` + +Listing 21-18: Sharing the receiver among the `Worker` instances using `Arc` and `Mutex` + +In `ThreadPool::new`, we put the receiver in an `Arc` and a `Mutex`. For each +new `Worker`, we clone the `Arc` to bump the reference count so that the +`Worker` instances can share ownership of the receiver. + +With these changes, the code compiles! We’re getting there! + +#### Implementing the execute Method + +Let’s finally implement the `execute` method on `ThreadPool`. We’ll also change +`Job` from a struct to a type alias for a trait object that holds the type of +closure that `execute` receives. As discussed in the “Type Synonyms and Type +Aliases” section in Chapter 20, type aliases +allow us to make long types shorter for ease of use. Look at Listing 21-19. + +src/lib.rs + +``` +// --snip-- + +type Job = Box; + +impl ThreadPool { + // --snip-- + + pub fn execute(&self, f: F) + where + F: FnOnce() + Send + 'static, + { + let job = Box::new(f); + + self.sender.send(job).unwrap(); + } +} + +// --snip-- +``` + +Listing 21-19: Creating a `Job` type alias for a `Box` that holds each closure and then sending the job down the channel + +After creating a new `Job` instance using the closure we get in `execute`, we +send that job down the sending end of the channel. We’re calling `unwrap` on +`send` for the case that sending fails. This might happen if, for example, we +stop all our threads from executing, meaning the receiving end has stopped +receiving new messages. At the moment, we can’t stop our threads from +executing: Our threads continue executing as long as the pool exists. The +reason we use `unwrap` is that we know the failure case won’t happen, but the +compiler doesn’t know that. + +But we’re not quite done yet! In the `Worker`, our closure being passed to +`thread::spawn` still only *references* the receiving end of the channel. +Instead, we need the closure to loop forever, asking the receiving end of the +channel for a job and running the job when it gets one. Let’s make the change +shown in Listing 21-20 to `Worker::new`. + +src/lib.rs + +``` +// --snip-- + +impl Worker { + fn new(id: usize, receiver: Arc>>) -> Worker { + let thread = thread::spawn(move || { + loop { + let job = receiver.lock().unwrap().recv().unwrap(); + + println!("Worker {id} got a job; executing."); + + job(); + } + }); + + Worker { id, thread } + } +} +``` + +Listing 21-20: Receiving and executing the jobs in the `Worker` instance’s thread + +Here, we first call `lock` on the `receiver` to acquire the mutex, and then we +call `unwrap` to panic on any errors. Acquiring a lock might fail if the mutex +is in a *poisoned* state, which can happen if some other thread panicked while +holding the lock rather than releasing the lock. In this situation, calling +`unwrap` to have this thread panic is the correct action to take. Feel free to +change this `unwrap` to an `expect` with an error message that is meaningful to +you. + +If we get the lock on the mutex, we call `recv` to receive a `Job` from the +channel. A final `unwrap` moves past any errors here as well, which might occur +if the thread holding the sender has shut down, similar to how the `send` +method returns `Err` if the receiver shuts down. + +The call to `recv` blocks, so if there is no job yet, the current thread will +wait until a job becomes available. The `Mutex` ensures that only one +`Worker` thread at a time is trying to request a job. + +Our thread pool is now in a working state! Give it a `cargo run` and make some +requests: + + + +``` +$ cargo run + Compiling hello v0.1.0 (file:///projects/hello) +warning: field `workers` is never read + --> src/lib.rs:7:5 + | +6 | pub struct ThreadPool { + | ---------- field in this struct +7 | workers: Vec, + | ^^^^^^^ + | + = note: `#[warn(dead_code)]` on by default + +warning: fields `id` and `thread` are never read + --> src/lib.rs:48:5 + | +47 | struct Worker { + | ------ fields in this struct +48 | id: usize, + | ^^ +49 | thread: thread::JoinHandle<()>, + | ^^^^^^ + +warning: `hello` (lib) generated 2 warnings + Finished `dev` profile [unoptimized + debuginfo] target(s) in 4.91s + Running `target/debug/hello` +Worker 0 got a job; executing. +Worker 2 got a job; executing. +Worker 1 got a job; executing. +Worker 3 got a job; executing. +Worker 0 got a job; executing. +Worker 2 got a job; executing. +Worker 1 got a job; executing. +Worker 3 got a job; executing. +Worker 0 got a job; executing. +Worker 2 got a job; executing. +``` + +Success! We now have a thread pool that executes connections asynchronously. +There are never more than four threads created, so our system won’t get +overloaded if the server receives a lot of requests. If we make a request to +*/sleep*, the server will be able to serve other requests by having another +thread run them. + +> Note: If you open */sleep* in multiple browser windows simultaneously, they +> might load one at a time in five-second intervals. Some web browsers execute +> multiple instances of the same request sequentially for caching reasons. This +> limitation is not caused by our web server. + +This is a good time to pause and consider how the code in Listings 21-18, 21-19, +and 21-20 would be different if we were using futures instead of a closure for +the work to be done. What types would change? How would the method signatures be +different, if at all? What parts of the code would stay the same? + +After learning about the `while let` loop in Chapter 17 and Chapter 19, you +might be wondering why we didn’t write the `Worker` thread code as shown in +Listing 21-21. + +src/lib.rs + +``` +// --snip-- + +impl Worker { + fn new(id: usize, receiver: Arc>>) -> Worker { + let thread = thread::spawn(move || { + while let Ok(job) = receiver.lock().unwrap().recv() { + println!("Worker {id} got a job; executing."); + + job(); + } + }); + + Worker { id, thread } + } +} +``` + +Listing 21-21: An alternative implementation of `Worker::new` using `while let` + +This code compiles and runs but doesn’t result in the desired threading +behavior: A slow request will still cause other requests to wait to be +processed. The reason is somewhat subtle: The `Mutex` struct has no public +`unlock` method because the ownership of the lock is based on the lifetime of +the `MutexGuard` within the `LockResult>` that the `lock` +method returns. At compile time, the borrow checker can then enforce the rule +that a resource guarded by a `Mutex` cannot be accessed unless we hold the +lock. However, this implementation can also result in the lock being held +longer than intended if we aren’t mindful of the lifetime of the +`MutexGuard`. + +The code in Listing 21-20 that uses `let job = receiver.lock().unwrap().recv().unwrap();` works because with `let`, any +temporary values used in the expression on the right-hand side of the equal +sign are immediately dropped when the `let` statement ends. However, `while let` (and `if let` and `match`) does not drop temporary values until the end of +the associated block. In Listing 21-21, the lock remains held for the duration +of the call to `job()`, meaning other `Worker` instances cannot receive jobs. + +## Graceful Shutdown and Cleanup + +The code in Listing 21-20 is responding to requests asynchronously through the +use of a thread pool, as we intended. We get some warnings about the `workers`, +`id`, and `thread` fields that we’re not using in a direct way that reminds us +we’re not cleaning up anything. When we use the less elegant +ctrl-C method to halt the main thread, all other threads +are stopped immediately as well, even if they’re in the middle of serving a +request. + +Next, then, we’ll implement the `Drop` trait to call `join` on each of the +threads in the pool so that they can finish the requests they’re working on +before closing. Then, we’ll implement a way to tell the threads they should +stop accepting new requests and shut down. To see this code in action, we’ll +modify our server to accept only two requests before gracefully shutting down +its thread pool. + +One thing to notice as we go: None of this affects the parts of the code that +handle executing the closures, so everything here would be the same if we were +using a thread pool for an async runtime. + +### Implementing the Drop Trait on ThreadPool + +Let’s start with implementing `Drop` on our thread pool. When the pool is +dropped, our threads should all join to make sure they finish their work. +Listing 21-22 shows a first attempt at a `Drop` implementation; this code won’t +quite work yet. + +src/lib.rs + +``` +impl Drop for ThreadPool { + fn drop(&mut self) { + for worker in &mut self.workers { + println!("Shutting down worker {}", worker.id); + + worker.thread.join().unwrap(); + } + } +} +``` + +Listing 21-22: Joining each thread when the thread pool goes out of scope + +First, we loop through each of the thread pool `workers`. We use `&mut` for this +because `self` is a mutable reference, and we also need to be able to mutate +`worker`. For each `worker`, we print a message saying that this particular +`Worker` instance is shutting down, and then we call `join` on that `Worker` +instance’s thread. If the call to `join` fails, we use `unwrap` to make Rust +panic and go into an ungraceful shutdown. + +Here is the error we get when we compile this code: + +``` +$ cargo check + Checking hello v0.1.0 (file:///projects/hello) +error[E0507]: cannot move out of `worker.thread` which is behind a mutable reference + --> src/lib.rs:52:13 + | +52 | worker.thread.join().unwrap(); + | ^^^^^^^^^^^^^ ------ `worker.thread` moved due to this method call + | | + | move occurs because `worker.thread` has type `JoinHandle<()>`, which does not implement the `Copy` trait + | +note: `JoinHandle::::join` takes ownership of the receiver `self`, which moves `worker.thread` + --> /rustc/4eb161250e340c8f48f66e2b929ef4a5bed7c181/library/std/src/thread/mod.rs:1876:17 + +For more information about this error, try `rustc --explain E0507`. +error: could not compile `hello` (lib) due to 1 previous error +``` + +The error tells us we can’t call `join` because we only have a mutable borrow +of each `worker` and `join` takes ownership of its argument. To solve this +issue, we need to move the thread out of the `Worker` instance that owns +`thread` so that `join` can consume the thread. One way to do this is to take +the same approach we took in Listing 18-15. If `Worker` held an +`Option>`, we could call the `take` method on the +`Option` to move the value out of the `Some` variant and leave a `None` variant +in its place. In other words, a `Worker` that is running would have a `Some` +variant in `thread`, and when we wanted to clean up a `Worker`, we’d replace +`Some` with `None` so that the `Worker` wouldn’t have a thread to run. + +However, the *only* time this would come up would be when dropping the +`Worker`. In exchange, we’d have to deal with an +`Option>` anywhere we accessed `worker.thread`. +Idiomatic Rust uses `Option` quite a bit, but when you find yourself wrapping +something you know will always be present in an `Option` as a workaround like +this, it’s a good idea to look for alternative approaches to make your code +cleaner and less error-prone. + +In this case, a better alternative exists: the `Vec::drain` method. It accepts +a range parameter to specify which items to remove from the vector and returns +an iterator of those items. Passing the `..` range syntax will remove *every* +value from the vector. + +So, we need to update the `ThreadPool` `drop` implementation like this: + +src/lib.rs + +``` +impl Drop for ThreadPool { + fn drop(&mut self) { + for worker in self.workers.drain(..) { + println!("Shutting down worker {}", worker.id); + + worker.thread.join().unwrap(); + } + } +} +``` + + + +This resolves the compiler error and does not require any other changes to our +code. Note that, because drop can be called when panicking, the unwrap +could also panic and cause a double panic, which immediately crashes the +program and ends any cleanup in progress. This is fine for an example program, +but it isn’t recommended for production code. + +### Signaling to the Threads to Stop Listening for Jobs + +With all the changes we’ve made, our code compiles without any warnings. +However, the bad news is that this code doesn’t function the way we want it to +yet. The key is the logic in the closures run by the threads of the `Worker` +instances: At the moment, we call `join`, but that won’t shut down the threads, +because they `loop` forever looking for jobs. If we try to drop our +`ThreadPool` with our current implementation of `drop`, the main thread will +block forever, waiting for the first thread to finish. + +To fix this problem, we’ll need a change in the `ThreadPool` `drop` +implementation and then a change in the `Worker` loop. + +First, we’ll change the `ThreadPool` `drop` implementation to explicitly drop +the `sender` before waiting for the threads to finish. Listing 21-23 shows the +changes to `ThreadPool` to explicitly drop `sender`. Unlike with the thread, +here we *do* need to use an `Option` to be able to move `sender` out of +`ThreadPool` with `Option::take`. + +src/lib.rs + +``` +pub struct ThreadPool { + workers: Vec, + sender: Option>, +} +// --snip-- +impl ThreadPool { + pub fn new(size: usize) -> ThreadPool { + // --snip-- + + ThreadPool { + workers, + sender: Some(sender), + } + } + + pub fn execute(&self, f: F) + where + F: FnOnce() + Send + 'static, + { + let job = Box::new(f); + + self.sender.as_ref().unwrap().send(job).unwrap(); + } +} + +impl Drop for ThreadPool { + fn drop(&mut self) { + drop(self.sender.take()); + + for worker in self.workers.drain(..) { + println!("Shutting down worker {}", worker.id); + + worker.thread.join().unwrap(); + } + } +} +``` + +Listing 21-23: Explicitly dropping `sender` before joining the `Worker` threads + +Dropping `sender` closes the channel, which indicates no more messages will be +sent. When that happens, all the calls to `recv` that the `Worker` instances do +in the infinite loop will return an error. In Listing 21-24, we change the +`Worker` loop to gracefully exit the loop in that case, which means the threads +will finish when the `ThreadPool` `drop` implementation calls `join` on them. + +src/lib.rs + +``` +impl Worker { + fn new(id: usize, receiver: Arc>>) -> Worker { + let thread = thread::spawn(move || { + loop { + let message = receiver.lock().unwrap().recv(); + + match message { + Ok(job) => { + println!("Worker {id} got a job; executing."); + + job(); + } + Err(_) => { + println!("Worker {id} disconnected; shutting down."); + break; + } + } + } + }); + + Worker { id, thread } + } +} +``` + +Listing 21-24: Explicitly breaking out of the loop when `recv` returns an error + +To see this code in action, let’s modify `main` to accept only two requests +before gracefully shutting down the server, as shown in Listing 21-25. + +src/main.rs + +``` +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming().take(2) { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } + + println!("Shutting down."); +} +``` + +Listing 21-25: Shutting down the server after serving two requests by exiting the loop + +You wouldn’t want a real-world web server to shut down after serving only two +requests. This code just demonstrates that the graceful shutdown and cleanup is +in working order. + +The `take` method is defined in the `Iterator` trait and limits the iteration +to the first two items at most. The `ThreadPool` will go out of scope at the +end of `main`, and the `drop` implementation will run. + +Start the server with `cargo run` and make three requests. The third request +should error, and in your terminal, you should see output similar to this: + + + +``` +$ cargo run + Compiling hello v0.1.0 (file:///projects/hello) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.41s + Running `target/debug/hello` +Worker 0 got a job; executing. +Shutting down. +Shutting down worker 0 +Worker 3 got a job; executing. +Worker 1 disconnected; shutting down. +Worker 2 disconnected; shutting down. +Worker 3 disconnected; shutting down. +Worker 0 disconnected; shutting down. +Shutting down worker 1 +Shutting down worker 2 +Shutting down worker 3 +``` + +You might see a different ordering of `Worker` IDs and messages printed. We can +see how this code works from the messages: `Worker` instances 0 and 3 got the +first two requests. The server stopped accepting connections after the second +connection, and the `Drop` implementation on `ThreadPool` starts executing +before `Worker 3` even starts its job. Dropping the `sender` disconnects all the +`Worker` instances and tells them to shut down. The `Worker` instances each +print a message when they disconnect, and then the thread pool calls `join` to +wait for each `Worker` thread to finish. + +Notice one interesting aspect of this particular execution: The `ThreadPool` +dropped the `sender`, and before any `Worker` received an error, we tried to +join `Worker 0`. `Worker 0` had not yet gotten an error from `recv`, so the main +thread blocked, waiting for `Worker 0` to finish. In the meantime, `Worker 3` +received a job and then all threads received an error. When `Worker 0` finished, +the main thread waited for the rest of the `Worker` instances to finish. At that +point, they had all exited their loops and stopped. + +Congrats! We’ve now completed our project; we have a basic web server that uses +a thread pool to respond asynchronously. We’re able to perform a graceful +shutdown of the server, which cleans up all the threads in the pool. + +Here’s the full code for reference: + +src/main.rs + +``` +use hello::ThreadPool; +use std::{ + fs, + io::{BufReader, prelude::*}, + net::{TcpListener, TcpStream}, + thread, + time::Duration, +}; + +fn main() { + let listener = TcpListener::bind("127.0.0.1:7878").unwrap(); + let pool = ThreadPool::new(4); + + for stream in listener.incoming().take(2) { + let stream = stream.unwrap(); + + pool.execute(|| { + handle_connection(stream); + }); + } + + println!("Shutting down."); +} + +fn handle_connection(mut stream: TcpStream) { + let buf_reader = BufReader::new(&stream); + let request_line = buf_reader.lines().next().unwrap().unwrap(); + + let (status_line, filename) = match &request_line[..] { + "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"), + "GET /sleep HTTP/1.1" => { + thread::sleep(Duration::from_secs(5)); + ("HTTP/1.1 200 OK", "hello.html") + } + _ => ("HTTP/1.1 404 NOT FOUND", "404.html"), + }; + + let contents = fs::read_to_string(filename).unwrap(); + let length = contents.len(); + + let response = + format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}"); + + stream.write_all(response.as_bytes()).unwrap(); +} +``` + + + +src/lib.rs + +``` +use std::{ + sync::{Arc, Mutex, mpsc}, + thread, +}; + +pub struct ThreadPool { + workers: Vec, + sender: Option>, +} + +type Job = Box; + +impl ThreadPool { + /// Create a new ThreadPool. + /// + /// The size is the number of threads in the pool. + /// + /// # Panics + /// + /// The `new` function will panic if the size is zero. + pub fn new(size: usize) -> ThreadPool { + assert!(size > 0); + + let (sender, receiver) = mpsc::channel(); + + let receiver = Arc::new(Mutex::new(receiver)); + + let mut workers = Vec::with_capacity(size); + + for id in 0..size { + workers.push(Worker::new(id, Arc::clone(&receiver))); + } + + ThreadPool { + workers, + sender: Some(sender), + } + } + + pub fn execute(&self, f: F) + where + F: FnOnce() + Send + 'static, + { + let job = Box::new(f); + + self.sender.as_ref().unwrap().send(job).unwrap(); + } +} + +impl Drop for ThreadPool { + fn drop(&mut self) { + drop(self.sender.take()); + + for worker in &mut self.workers { + println!("Shutting down worker {}", worker.id); + + if let Some(thread) = worker.thread.take() { + thread.join().unwrap(); + } + } + } +} + +struct Worker { + id: usize, + thread: Option>, +} + +impl Worker { + fn new(id: usize, receiver: Arc>>) -> Worker { + let thread = thread::spawn(move || { + loop { + let message = receiver.lock().unwrap().recv(); + + match message { + Ok(job) => { + println!("Worker {id} got a job; executing."); + + job(); + } + Err(_) => { + println!("Worker {id} disconnected; shutting down."); + break; + } + } + } + }); + + Worker { + id, + thread: Some(thread), + } + } +} +``` + + + +We could do more here! If you want to continue enhancing this project, here are +some ideas: + +* Add more documentation to `ThreadPool` and its public methods. +* Add tests of the library’s functionality. +* Change calls to `unwrap` to more robust error handling. +* Use `ThreadPool` to perform some task other than serving web requests. +* Find a thread pool crate on crates.io at *https://crates.io/* and implement a + similar web server using the crate instead. Then, compare its API and + robustness to the thread pool we implemented. + +## Summary + +Well done! You’ve made it to the end of the book! We want to thank you for +joining us on this tour of Rust. You’re now ready to implement your own Rust +projects and help with other people’s projects. 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all fixes need to be made in `/src/`. --> -## About the Authors -Carol Nichols is a member of the Rust Crates.io Team and a former member of the -Rust Core Team. She’s a co-founder of Integer 32, LLC, the world’s first -Rust-focused software consultancy. Nichols has also organized the Rust Belt -Rust Conference. +## About the Authors -Steve Klabnik was the lead for the Rust documentation team and was one of +**Steve Klabnik** was the lead for the Rust documentation team and was one of Rust’s core developers. A frequent speaker and a prolific open source contributor, he previously worked on projects such as Ruby and Ruby on Rails. +**Carol Nichols** is a member of the Rust Crates.io Team and a former member of +the Rust Core Team. She’s a co-founder of Integer 32, LLC, the world’s first +Rust-focused software consultancy. She has also organized the Rust Belt Rust +Conference. + +**Chris Krycho** is a software engineering leader with experience in avionics, +developer tools, web frameworks, and more. In addition to his open source +software contributions and regular public speaking, he created the *New +Rustacean* podcast (2015–2019). + ## About the Technical Reviewer -JT is a Rust core team member and the co-creator of the Rust error message -format, Rust Language Server (RLS), and Nushell. They first started using Rust -in 2011, and in 2016 joined Mozilla to work on Rust full time, helping to shape -its direction for widespread use. These days, they are a freelance Rust trainer -and advocate for safe systems programming. +**Sophia Turner** has been a long-time advocate of better programming +languages and tools. She helped create TypeScript and later joined Mozilla to +work on compiler errors, IDE support, and the larger Rust ergonomics +initiative. She also served on the Rust core team and helped create the Rust +Leadership Council. ## Brief Contents @@ -28,88 +34,103 @@ and advocate for safe systems programming. ## Foreword -It wasn’t always so clear, but the Rust programming language is fundamentally -about *empowerment*: no matter what kind of code you are writing now, Rust -empowers you to reach further, to program with confidence in a wider variety of -domains than you did before. - -Take, for example, “systems-level” work that deals with low-level details of -memory management, data representation, and concurrency. Traditionally, this -realm of programming is seen as arcane, accessible to only a select few who -have devoted the necessary years learning it to avoid its infamous pitfalls. -And even those who practice it do so with caution, lest their code be open to -exploits, crashes, or corruption. - -Rust breaks down these barriers by eliminating the old pitfalls and providing a -friendly, polished set of tools to help you along the way. Programmers who need -to “dip down” into lower-level control can do so with Rust, without taking on -the customary risk of crashes or security holes and without having to learn the -fine points of a fickle toolchain. Better yet, the language is designed to -guide you naturally toward reliable code that is efficient in terms of speed -and memory usage. - -Programmers who are already working with low-level code can use Rust to raise -their ambitions. For example, introducing parallelism in Rust is a relatively -low-risk operation: the compiler will catch the classical mistakes for you. And -you can tackle more aggressive optimizations in your code with the confidence -that you won’t accidentally introduce crashes or vulnerabilities. - -But Rust isn’t limited to low-level systems programming. It’s expressive and -ergonomic enough to make CLI apps, web servers, and many other kinds of code -quite pleasant to write—you’ll find simple examples later in the book. Working -with Rust allows you to build skills that transfer from one domain to another; -you can learn Rust by writing a web app, then apply those same skills to target -your Raspberry Pi. - -This book fully embraces the potential of Rust to empower its users. It’s a -friendly and approachable text intended to help you level up not just your -knowledge of Rust, but also your reach and confidence as a programmer in -general. So dive in, get ready to learn—and welcome to the Rust community! - -Nicholas Matsakis and Aaron Turon - -## ACKNOWLEDGMENTS - -We would like to thank everyone who has worked on the Rust language for -creating an amazing language worth writing a book about. We’re grateful to -everyone in the Rust community for being welcoming and creating an environment -worth welcoming more folks into. - -We’re especially thankful for everyone who read early versions of this book -online and provided feedback, bug reports, and pull requests. Special thanks to -Eduard-Mihai Burtescu, Alex Crichton, and JT for providing technical review, -and to Karen Rustad Tölva for the cover art. Thank you to our team at No -Starch, including Bill Pollock, Liz Chadwick, and Janelle Ludowise, for -improving this book and bringing it to print. - -Carol is grateful for the opportunity to work on this book. She thanks her -family for their constant love and support, especially her husband, Jake -Goulding, and her daughter, Vivian. +The Rust programming language has come a long way in a few short years, from +its creation and incubation by a small and nascent community of enthusiasts, to +becoming one of the most loved and in-demand programming languages in the +world. Looking back, it was inevitable that the power and promise of Rust would +turn heads and gain a foothold in systems programming. What was not inevitable +was the global growth in interest and innovation that permeated through open +source communities and catalyzed wide-scale adoption across industries. + +At this point in time, it is easy to point to the wonderful features that Rust +has to offer to explain this explosion in interest and adoption. Who doesn’t +want memory safety, *and* fast performance, *and* a friendly compiler, *and* +great tooling, among a host of other wonderful features? The Rust language you +see today combines years of research in systems programming with the practical +wisdom of a vibrant and passionate community. This language was designed with +purpose and crafted with care, offering developers a tool that makes it easier +to write safe, fast, and reliable code. + +But what makes Rust truly special is its roots in empowering you, the user, to +achieve your goals. This is a language that wants you to succeed, and the +principle of empowerment runs through the core of the community that builds, +maintains, and advocates for this language. Since the previous edition of this +definitive text, Rust has further developed into a truly global and trusted +language. The Rust Project is now robustly supported by the Rust Foundation, +which also invests in key initiatives to ensure that Rust is secure, stable, +and sustainable. + +This edition of *The Rust Programming Language* is a comprehensive update, +reflecting the language’s evolution over the years and providing valuable new +information. But it is not just a guide to syntax and libraries—it’s an +invitation to join a community that values quality, performance, and thoughtful +design. Whether you’re a seasoned developer looking to explore Rust for the +first time or an experienced Rustacean looking to refine your skills, this +edition offers something for everyone. + +The Rust journey has been one of collaboration, learning, and iteration. The +growth of the language and its ecosystem is a direct reflection of the vibrant, +diverse community behind it. The contributions of thousands of developers, from +core language designers to casual contributors, are what make Rust such a +unique and powerful tool. By picking up this book, you’re not just learning a +new programming language—you’re joining a movement to make software better, +safer, and more enjoyable to work with. + +Welcome to the Rust community! + +Bec Rumbul, Executive Director of the Rust Foundation ## Preface -This version of the text assumes you’re using Rust 1.62.0 (released 2022-06-30) -or later with `edition="2021"` in the *Cargo.toml* file of all projects to -configure them to use Rust 2021 edition idioms. See “Installation” on page XX +This version of the text assumes you’re using Rust 1.85.0 (released 2025-02-17) +or later with `edition = "2024"` in the *Cargo.toml* file of all projects to +configure them to use Rust 2024 Edition idioms. See “Installation” on page XX for instructions on installing or updating Rust, and see Appendix E for information on editions. -The 2021 edition of the Rust language includes a number of improvements that +The 2024 Edition of the Rust language includes a number of improvements that make Rust more ergonomic and that correct some inconsistencies. On top of a general update to reflect these improvements, this rendition of the book has a number of improvements to address specific feedback: -* Chapter 7 contains a new quick reference section on organizing your code into -multiple files with modules. -* Chapter 13 has new and improved closure examples that more clearly illustrate -captures, the `move` keyword, and the `Fn` traits. +* A new Chapter 17 introduces async programming in Rust, including `async` and +`await` along with the `Future` and `Stream` types. Later chapters have been +lightly adapted and renumbered to account for this update. +* Chapter 20 (Chapter 19 in previous editions) now includes an introduction to +Miri, Rust’s dynamic analysis tool for unsafe code. It also includes updates +for some of the more significant updates to Rust in the 2024 Edition. * We fixed a number of small errors and imprecise wording throughout the book. Thank you to the readers who reported them! Note that any code from earlier renditions of this book that compiled will continue to compile with the relevant edition in the project’s *Cargo.toml*, even as you update the Rust compiler version you’re using. That’s Rust’s -backward-compatibility guarantees at work! +backward-compatibility guarantee at work! + +## ACKNOWLEDGMENTS + +We would like to thank everyone who has worked on the Rust language for +creating an amazing language worth writing a book about. We’re grateful to +everyone in the Rust community for being welcoming and creating an environment +worth welcoming more folks into. + +We’re especially thankful for everyone who read early versions of this book +online and provided feedback, bug reports, and pull requests. Special thanks to +Eduard-Mihai Burtescu, Alex Crichton, and Sophia Turner for providing technical +review, and to Karen Rustad Tölva for the cover art. Thank you to our team at +No Starch Press, including Bill Pollock, Liz Chadwick, and Janelle Ludowise, +for improving this book and bringing it to print. + +Carol is grateful for the opportunity to work on this book. She thanks her +family for their constant love and support, especially her husband, Jake +Goulding, and her daughter, Vivian. + +Chris is profoundly grateful to Tim McNamara, Will Crichton, James Munns, Nick +Cameron, and Tyler Mandry for dedicated feedback on the new chapter on async +programming in Rust. He would also like to thank Integer 32 for making this +update for the 2024 Edition happen. Finally, and most of all, he is thankful to +his wife, Jaimie, and his daughters, Elayne and Katherine, for supporting him, +including many a “How is the book going, daddy?” over family dinners. ## Introduction @@ -134,7 +155,7 @@ is prone to various subtle bugs, which in most other languages can only be caught through extensive testing and careful code review by experienced developers. In Rust, the compiler plays a gatekeeper role by refusing to compile code with these elusive bugs, including concurrency bugs. By working -alongside the compiler, the team can spend their time focusing on the program’s +alongside the compiler, the team can spend its time focusing on the program’s logic rather than chasing down bugs. Rust also brings contemporary developer tools to the systems programming world: @@ -180,24 +201,25 @@ mean both how quickly Rust code can run and the speed at which Rust lets you write programs. The Rust compiler’s checks ensure stability through feature additions and refactoring. This is in contrast to the brittle legacy code in languages without these checks, which developers are often afraid to modify. By -striving for zero-cost abstractions, higher-level features that compile to -lower-level code as fast as code written manually, Rust endeavors to make safe +striving for zero-cost abstractions—higher-level features that compile to +lower-level code as fast as code written manually—Rust endeavors to make safe code be fast code as well. The Rust language hopes to support many other users as well; those mentioned here are merely some of the biggest stakeholders. Overall, Rust’s greatest ambition is to eliminate the trade-offs that programmers have accepted for decades by providing safety *and* productivity, speed *and* ergonomics. Give -Rust a try and see if its choices work for you. +Rust a try, and see if its choices work for you. ## Who This Book Is For This book assumes that you’ve written code in another programming language, but -doesn’t make any assumptions about which one. We’ve tried to make the material -broadly accessible to those from a wide variety of programming backgrounds. We -don’t spend a lot of time talking about what programming *is* or how to think -about it. If you’re entirely new to programming, you would be better served by -reading a book that specifically provides an introduction to programming. +it doesn’t make any assumptions about which one. We’ve tried to make the +material broadly accessible to those from a wide variety of programming +backgrounds. We don’t spend a lot of time talking about what programming *is* +or how to think about it. If you’re entirely new to programming, you would be +better served by reading a book that specifically provides an introduction to +programming. ## How to Use This Book @@ -209,7 +231,7 @@ the topic in a later chapter. You’ll find two kinds of chapters in this book: concept chapters and project chapters. In concept chapters, you’ll learn about an aspect of Rust. In project chapters, we’ll build small programs together, applying what you’ve learned so -far. Chapter 2, Chapter 12, and Chapter 20 are project chapters; the rest are +far. Chapter 2, Chapter 12, and Chapter 21 are project chapters; the rest are concept chapters. **Chapter 1** explains how to install Rust, how to write a “Hello, world!” @@ -217,27 +239,28 @@ program, and how to use Cargo, Rust’s package manager and build tool. **Chapte 2** is a hands-on introduction to writing a program in Rust, having you build up a number-guessing game. Here, we cover concepts at a high level, and later chapters will provide additional detail. If you want to get your hands dirty -right away, Chapter 2 is the place for that. **Chapter 3** covers Rust features -that are similar to those of other programming languages, and in **Chapter 4** -you’ll learn about Rust’s ownership system. If you’re a particularly meticulous -learner who prefers to learn every detail before moving on to the next, you -might want to skip Chapter 2 and go straight to Chapter 3, returning to Chapter -2 when you’d like to work on a project applying the details you’ve learned. - -**Chapter 5** discusses structs and methods, and **Chapter 6** covers enums, -`match` expressions, and the `if let` control flow construct. You’ll use -structs and enums to make custom types in Rust. +right away, Chapter 2 is the place for that. If you’re a particularly +meticulous learner who prefers to learn every detail before moving on to the +next, you might want to skip Chapter 2 and go straight to **Chapter 3**, which +covers Rust features that are similar to those of other programming languages; +then, you can return to Chapter 2 when you’d like to work on a project applying +the details you’ve learned. + +In **Chapter 4**, you’ll learn about Rust’s ownership system. **Chapter 5** +discusses structs and methods. **Chapter 6** covers enums, `match` expressions, +and the `if let` and `let...else` control flow constructs. You’ll use structs +and enums to make custom types. In **Chapter 7**, you’ll learn about Rust’s module system and about privacy rules for organizing your code and its public application programming interface (API). **Chapter 8** discusses some common collection data structures that the -standard library provides, such as vectors, strings, and hash maps. **Chapter -9** explores Rust’s error-handling philosophy and techniques. +standard library provides: vectors, strings, and hash maps. **Chapter 9** +explores Rust’s error-handling philosophy and techniques. **Chapter 10** digs into generics, traits, and lifetimes, which give you the power to define code that applies to multiple types. **Chapter 11** is all about testing, which even with Rust’s safety guarantees is necessary to ensure -your program’s logic is correct. In **Chapter 12**, we’ll build our own +that your program’s logic is correct. In **Chapter 12**, we’ll build our own implementation of a subset of functionality from the `grep` command line tool that searches for text within files. For this, we’ll use many of the concepts we discussed in the previous chapters. @@ -250,29 +273,32 @@ provides and the traits that enable their functionality. In **Chapter 16**, we’ll walk through different models of concurrent programming and talk about how Rust helps you program in multiple threads -fearlessly. **Chapter 17** looks at how Rust idioms compare to object-oriented -programming principles you might be familiar with. - -**Chapter 18** is a reference on patterns and pattern matching, which are -powerful ways of expressing ideas throughout Rust programs. **Chapter 19** -contains a smorgasbord of advanced topics of interest, including unsafe Rust, -macros, and more about lifetimes, traits, types, functions, and closures. - -In **Chapter 20**, we’ll complete a project in which we’ll implement a +fearlessly. In **Chapter 17**, we build on that by exploring Rust’s async and +await syntax, along with tasks, futures, and streams, and the lightweight +concurrency model they enable. + +**Chapter 18** looks at how Rust idioms compare to object-oriented programming +principles you might be familiar with. **Chapter 19** is a reference on +patterns and pattern matching, which are powerful ways of expressing ideas +throughout Rust programs. **Chapter 20** contains a smorgasbord of advanced +topics of interest, including unsafe Rust, macros, and more about lifetimes, +traits, types, functions, and closures. + +In **Chapter 21**, we’ll complete a project in which we’ll implement a low-level multithreaded web server! -Finally, some appendices contain useful information about the language in a -more reference-like format**. Appendix A** covers Rust’s keywords, **Appendix +Finally, some appendixes contain useful information about the language in a +more reference-like format. **Appendix A** covers Rust’s keywords, **Appendix B** covers Rust’s operators and symbols, **Appendix C** covers derivable traits provided by the standard library, **Appendix D** covers some useful development tools, and **Appendix E** explains Rust editions. -There is no wrong way to read this book: if you want to skip ahead, go for it! +There is no wrong way to read this book: If you want to skip ahead, go for it! You might have to jump back to earlier chapters if you experience any confusion. But do whatever works for you. An important part of the process of learning Rust is learning how to read the -error messages the compiler displays: these will guide you toward working code. +error messages the compiler displays: These will guide you toward working code. As such, we’ll provide many examples that don’t compile along with the error message the compiler will show you in each situation. Know that if you enter and run a random example, it may not compile! Make sure you read the @@ -288,5 +314,5 @@ an issue or send a pull request on GitHub at *https://github.com/rust-lang/book/blob/main/CONTRIBUTING.md* for more details. The source code for the examples in this book, errata, and other information -are available at *https://www.nostarch.com/Rust2021*. +are available at *https://nostarch.com/rust-programming-language-3rd-edition*. diff --git a/packages/mdbook-trpl/Cargo.lock b/packages/mdbook-trpl/Cargo.lock new file mode 100644 index 0000000000..e97f7c7e29 --- /dev/null +++ b/packages/mdbook-trpl/Cargo.lock @@ -0,0 +1,854 @@ +# This file is automatically @generated by Cargo. +# It is not intended for manual editing. +version = 4 + +[[package]] +name = "aho-corasick" +version = "1.1.3" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916" +dependencies = [ + "memchr", +] + +[[package]] +name = "anstream" +version = "0.6.18" +source = "registry+https://github.com/rust-lang/crates.io-index" +checksum = "8acc5369981196006228e28809f761875c0327210a891e941f4c683b3a99529b" +dependencies = [ + "anstyle", + "anstyle-parse", 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b/packages/mdbook-trpl/Cargo.toml @@ -0,0 +1,40 @@ +[package] +name = "mdbook-trpl" +version = "0.1.0" +edition = "2021" + +[[bin]] +name = "mdbook-trpl-note" +path = "src/bin/note.rs" + +[[bin]] +name = "mdbook-trpl-listing" +path = "src/bin/listing.rs" + +[[bin]] +name = "mdbook-trpl-heading" +path = "src/bin/heading.rs" + +[[bin]] +name = "mdbook-trpl-figure" +path = "src/bin/figure.rs" + +[dependencies] +anyhow = "1" +clap = { version = "4", features = ["derive"] } +html_parser = "0.7.0" +mdbook-preprocessor = "0.5.1" +pulldown-cmark = { version = "0.12", features = ["simd"] } +pulldown-cmark-to-cmark = "19" +serde = { version = "1.0.228", features = ["serde_derive"] } +serde_json = "1" +thiserror = "1.0.60" +toml = "0.8.12" + +[dev-dependencies] +assert_cmd = "2" + +# This package is used as a path dependency in `rust-lang/rust`, not published +# to crates.io, so it cannot be part of the `rust-lang/book` workspace, because +# path dependencies do not get built as a crate within the hosting workspace. +[workspace] diff --git a/packages/mdbook-trpl/README.md b/packages/mdbook-trpl/README.md new file mode 100644 index 0000000000..15aacced0d --- /dev/null +++ b/packages/mdbook-trpl/README.md @@ -0,0 +1,13 @@ +# mdbook_trpl + +A shared package for [mdbook][mdbook] [preprocessors][pre] used in [_The Rust +Programming Language_][trpl]. + +Supplies the following preprocessor binaries: + +- [mdbook-trpl-note](./src/bin/note) +- [mdbook-trpl-listing](./src/bin/listing) + +[mdbook]: https://crates.io/crates/mdbook +[pre]: https://rust-lang.github.io/mdBook/format/configuration/preprocessors.html +[trpl]: https://doc.rust-lang.org/book/ diff --git a/packages/mdbook-trpl/src/bin/README - mdbook-trpl-note.md b/packages/mdbook-trpl/src/bin/README - mdbook-trpl-note.md new file mode 100644 index 0000000000..3e54ae7fd1 --- /dev/null +++ b/packages/mdbook-trpl/src/bin/README - mdbook-trpl-note.md @@ -0,0 +1,51 @@ +# mdbook-trpl-note + +This is a _very_ simple [preprocessor][pre] for [mdBook][mdbook], focused specifically on the content of _The Rust Programming Language_ book. This preprocessor takes Markdown like this— + +```markdown +> Note: This is some material we want to provide more emphasis for, because it +> is important in some way! + +Some text. + +> ## Some subject +> +> Here is all the important things to know about that particular subject. +``` + +—and rewrites the Markdown to this: + +```html +
+ +This is some material we want to provide more emphasis for, because it is +important in some way! + +
+ +Some text. + +
+ +## Some subject + +Here is all the important things to know about that particular subject. + +
+``` + +This allows using the relatively standard Markdown convention of (incorrectly!) using blockquotes for “callouts” or “notes” like this, while still producing semantic HTML which conveys the actual intent. + +> [!NOTE] +> This is _not_ a full “admonition” preprocessor, and it is not remotely compliant with [the GitHub “alert” syntax][alerts]. It exists almost entirely for the sake of providing better semantic HTML for _The Rust Programming Language_ book with a minimum of disruption to existing workflows! +> +> You are probably better off using one of the other existing alert/admonition preprocessors: +> +> - [mdbook-alerts][mdbook-alerts] +> - [mdbook-admonish][mdbook-admonish] + +[pre]: https://rust-lang.github.io/mdBook/format/configuration/preprocessors.html +[mdbook]: https://github.com/rust-lang/mdBook +[alerts]: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts +[mdbook-alerts]: https://github.com/lambdalisue/rs-mdbook-alerts +[mdbook-admonish]: https://github.com/tommilligan/mdbook-admonish diff --git a/packages/mdbook-trpl/src/bin/figure.rs b/packages/mdbook-trpl/src/bin/figure.rs new file mode 100644 index 0000000000..44657877b5 --- /dev/null +++ b/packages/mdbook-trpl/src/bin/figure.rs @@ -0,0 +1,42 @@ +use std::io; + +use clap::{self, Parser, Subcommand}; + +use mdbook_preprocessor::Preprocessor; +use mdbook_trpl::Figure; + +fn main() -> Result<(), String> { + match Cli::parse().command { + Some(Command::Supports { renderer }) => { + if Figure.supports_renderer(&renderer) { + Ok(()) + } else { + Err(format!("Renderer '{renderer}' is unsupported")) + } + } + None => { + let (ctx, book) = mdbook_preprocessor::parse_input(io::stdin()) + .map_err(|e| format!("{e}"))?; + let processed = + Figure.run(&ctx, book).map_err(|e| format!("{e}"))?; + serde_json::to_writer(io::stdout(), &processed) + .map_err(|e| format!("{e}")) + } + } +} + +/// A simple preprocessor for handling figures with images in _The Rust +/// Programming Language_ book. +#[derive(Parser, Debug)] +struct Cli { + #[command(subcommand)] + command: Option, +} + +#[derive(Subcommand, Debug)] +enum Command { + /// Is the renderer supported? + /// + /// Supported renderers are `'html'`, `'markdown'`, and `'test'`. + Supports { renderer: String }, +} diff --git a/packages/mdbook-trpl/src/bin/heading.rs b/packages/mdbook-trpl/src/bin/heading.rs new file mode 100644 index 0000000000..1c53046389 --- /dev/null +++ b/packages/mdbook-trpl/src/bin/heading.rs @@ -0,0 +1,38 @@ +use std::io; + +use clap::{self, Parser, Subcommand}; +use mdbook_preprocessor::Preprocessor; + +use mdbook_trpl::Heading; + +fn main() -> Result<(), String> { + let cli = Cli::parse(); + if let Some(Command::Supports { renderer }) = cli.command { + return if Heading.supports_renderer(&renderer).unwrap() { + Ok(()) + } else { + Err(format!("Renderer '{renderer}' is unsupported")) + }; + } + + let (ctx, book) = mdbook_preprocessor::parse_input(io::stdin()) + .map_err(|e| format!("{e}"))?; + let processed = Heading.run(&ctx, book).map_err(|e| format!("{e}"))?; + serde_json::to_writer(io::stdout(), &processed).map_err(|e| format!("{e}")) +} + +/// A simple preprocessor for semantic markup for code listings in _The Rust +/// Programming Language_. +#[derive(Parser, Debug)] +struct Cli { + #[command(subcommand)] + command: Option, +} + +#[derive(Subcommand, Debug)] +enum Command { + /// Is the renderer supported? + /// + /// This supports the HTML + Supports { renderer: String }, +} diff --git a/packages/mdbook-trpl/src/bin/listing.rs b/packages/mdbook-trpl/src/bin/listing.rs new file mode 100644 index 0000000000..83c26a659a --- /dev/null +++ b/packages/mdbook-trpl/src/bin/listing.rs @@ -0,0 +1,38 @@ +use std::io; + +use clap::{self, Parser, Subcommand}; +use mdbook_preprocessor::Preprocessor; + +use mdbook_trpl::Listing; + +fn main() -> Result<(), String> { + let cli = Cli::parse(); + if let Some(Command::Supports { renderer }) = cli.command { + return if Listing.supports_renderer(&renderer).unwrap() { + Ok(()) + } else { + Err(format!("Renderer '{renderer}' is unsupported")) + }; + } + + let (ctx, book) = mdbook_preprocessor::parse_input(io::stdin()) + .map_err(|e| format!("{e}"))?; + let processed = Listing.run(&ctx, book).map_err(|e| format!("{e}"))?; + serde_json::to_writer(io::stdout(), &processed).map_err(|e| format!("{e}")) +} + +/// A simple preprocessor for semantic markup for code listings in _The Rust +/// Programming Language_. +#[derive(Parser, Debug)] +struct Cli { + #[command(subcommand)] + command: Option, +} + +#[derive(Subcommand, Debug)] +enum Command { + /// Is the renderer supported? + /// + /// All renderers are supported! This is the contract for mdBook. + Supports { renderer: String }, +} diff --git a/packages/mdbook-trpl/src/bin/note.rs b/packages/mdbook-trpl/src/bin/note.rs new file mode 100644 index 0000000000..0367fcbbcf --- /dev/null +++ b/packages/mdbook-trpl/src/bin/note.rs @@ -0,0 +1,38 @@ +use std::io; + +use clap::{self, Parser, Subcommand}; +use mdbook_preprocessor::Preprocessor; + +use mdbook_trpl::Note; + +fn main() -> Result<(), String> { + let cli = Cli::parse(); + let simple_note = Note; + if let Some(Command::Supports { renderer }) = cli.command { + return if simple_note.supports_renderer(&renderer).unwrap() { + Ok(()) + } else { + Err(format!("Renderer '{renderer}' is unsupported")) + }; + } + + let (ctx, book) = mdbook_preprocessor::parse_input(io::stdin()) + .map_err(|e| format!("blah: {e}"))?; + let processed = simple_note.run(&ctx, book).map_err(|e| format!("{e}"))?; + serde_json::to_writer(io::stdout(), &processed).map_err(|e| format!("{e}")) +} + +/// A simple preprocessor for semantic notes in _The Rust Programming Language_. +#[derive(Parser, Debug)] +struct Cli { + #[command(subcommand)] + command: Option, +} + +#[derive(Subcommand, Debug)] +enum Command { + /// Is the renderer supported? + /// + /// All renderers are supported! This is the contract for mdBook. + Supports { renderer: String }, +} diff --git a/packages/mdbook-trpl/src/config/mod.rs b/packages/mdbook-trpl/src/config/mod.rs new file mode 100644 index 0000000000..12ffba9152 --- /dev/null +++ b/packages/mdbook-trpl/src/config/mod.rs @@ -0,0 +1,43 @@ +//! Get any `preprocessor.trpl-*` config. + +use mdbook_preprocessor::PreprocessorContext; + +#[derive(Debug, Default, Clone, Copy, PartialEq, serde::Deserialize)] +#[serde(rename_all = "snake_case")] +pub enum Mode { + #[default] + Default, + Simple, +} + +impl Mode { + pub fn from_context( + ctx: &PreprocessorContext, + preprocessor_name: &str, + ) -> Result { + #[derive(Default, serde::Deserialize)] + #[serde(rename_all = "kebab-case")] + struct Config { + #[serde(default)] + output_mode: Mode, + } + + let config: Config = ctx + .config + .get(&format!("preprocessor.{preprocessor_name}"))? + .ok_or_else(|| Error::NoConfig(preprocessor_name.into()))?; + Ok(config.output_mode) + } +} + +#[derive(Debug, thiserror::Error)] +pub enum Error { + #[error(transparent)] + Mdbook(#[from] mdbook_preprocessor::errors::Error), + + #[error("No config for '{0}'")] + NoConfig(String), +} + +#[cfg(test)] +mod tests; diff --git a/packages/mdbook-trpl/src/config/tests.rs b/packages/mdbook-trpl/src/config/tests.rs new file mode 100644 index 0000000000..9bf855ac03 --- /dev/null +++ b/packages/mdbook-trpl/src/config/tests.rs @@ -0,0 +1,259 @@ +//! Check that the config options are correctly handled. +//! +//! Note: none of these tests particularly exercise the *wiring*. They just +//! assume that the config itself is done correctly. This is a small enough +//! chunk of code that it easy to verify by hand at present. If it becomes +//! more complex in the future, it would be good to revisit and integrate +//! the same kinds of tests as the unit tests above here. + +use mdbook_preprocessor::{ + book::{Book, BookItem}, + errors::Result, + Preprocessor, PreprocessorContext, +}; + +use crate::config::Mode; + +/// Dummy preprocessor for testing purposes to exercise config. +struct TestPreprocessor; + +impl Preprocessor for TestPreprocessor { + fn name(&self) -> &str { + "test-preprocessor" + } + + fn run(&self, ctx: &PreprocessorContext, mut book: Book) -> Result { + let mode = Mode::from_context(ctx, self.name())?; + book.push_item(BookItem::PartTitle(format!("{mode:?}"))); + Ok(book) + } +} + +#[test] +fn no_config() { + let input_json = r##"[ + { + "root": "/path/to/book", + "config": { + "book": { + "authors": ["AUTHOR"], + "language": "en", + "src": "src", + "title": "TITLE" + }, + "preprocessor": {} + }, + "renderer": "html", + "mdbook_version": "0.5.1" + }, + { + "items": [ + { + "Chapter": { + "name": "Chapter 1", + "content": "# Chapter 1\n", + "number": [1], + "sub_items": [], + "path": "chapter_1.md", + "source_path": "chapter_1.md", + "parent_names": [] + } + } + ], + "__non_exhaustive": null + } + ]"##; + let input_json = input_json.as_bytes(); + let (ctx, book) = mdbook_preprocessor::parse_input(input_json).unwrap(); + let result = TestPreprocessor.run(&ctx, book); + assert!(result.is_err()); + let err = result.unwrap_err(); + assert_eq!(format!("{err}"), "No config for 'test-preprocessor'"); +} + +#[test] +fn empty_config() { + let input_json = r##"[ + { + "root": "/path/to/book", + "config": { + "book": { + "authors": ["AUTHOR"], + "language": "en", + "src": "src", + "title": "TITLE" + }, + "preprocessor": { + "test-preprocessor": {} + } + }, + "renderer": "html", + "mdbook_version": "0.5.0" + }, + { + "items": [ + { + "Chapter": { + "name": "Chapter 1", + "content": "# Chapter 1\n", + "number": [1], + "sub_items": [], + "path": "chapter_1.md", + "source_path": "chapter_1.md", + "parent_names": [] + } + } + ], + "__non_exhaustive": null + } + ]"##; + let input_json = input_json.as_bytes(); + let (ctx, book) = mdbook_preprocessor::parse_input(input_json).unwrap(); + let book = TestPreprocessor.run(&ctx, book).unwrap(); + assert!(book.iter().any( + |item| matches!(item, BookItem::PartTitle(title) if title == &format!("{:?}", Mode::Default)) + )) +} + +#[test] +fn specify_default() { + let input_json = r##"[ + { + "root": "/path/to/book", + "config": { + "book": { + "authors": ["AUTHOR"], + "language": "en", + "src": "src", + "title": "TITLE" + }, + "preprocessor": { + "test-preprocessor": { + "output-mode": "default" + } + } + }, + "renderer": "html", + "mdbook_version": "0.5.1" + }, + { + "items": [ + { + "Chapter": { + "name": "Chapter 1", + "content": "# Chapter 1\n", + "number": [1], + "sub_items": [], + "path": "chapter_1.md", + "source_path": "chapter_1.md", + "parent_names": [] + } + } + ], + "__non_exhaustive": null + } + ]"##; + let input_json = input_json.as_bytes(); + let (ctx, book) = mdbook_preprocessor::parse_input(input_json).unwrap(); + let book = TestPreprocessor.run(&ctx, book).unwrap(); + assert!(book.iter().any( + |item| matches!(item, BookItem::PartTitle(title) if title == &format!("{:?}", Mode::Default)) + )); +} + +#[test] +fn specify_simple() { + let input_json = r##"[ + { + "root": "/path/to/book", + "config": { + "book": { + "authors": ["AUTHOR"], + "language": "en", + "src": "src", + "title": "TITLE" + }, + "preprocessor": { + "test-preprocessor": { + "output-mode": "simple" + } + } + }, + "renderer": "html", + "mdbook_version": "0.5.1" + }, + { + "items": [ + { + "Chapter": { + "name": "Chapter 1", + "content": "# Chapter 1\n", + "number": [1], + "sub_items": [], + "path": "chapter_1.md", + "source_path": "chapter_1.md", + "parent_names": [] + } + } + ], + "__non_exhaustive": null + } + ]"##; + let input_json = input_json.as_bytes(); + let (ctx, book) = mdbook_preprocessor::parse_input(input_json).unwrap(); + let book = TestPreprocessor.run(&ctx, book).unwrap(); + assert!(book.iter().any( + |item| matches!(item, BookItem::PartTitle(title) if title == &format!("{:?}", Mode::Simple)) + )) +} + +#[test] +fn specify_invalid() { + let input_json = r##"[ + { + "root": "/path/to/book", + "config": { + "book": { + "authors": ["AUTHOR"], + "language": "en", + "src": "src", + "title": "TITLE" + }, + "preprocessor": { + "test-preprocessor": { + "output-mode": "nonsense" + } + } + }, + "renderer": "html", + "mdbook_version": "0.5.1" + }, + { + "items": [ + { + "Chapter": { + "name": "Chapter 1", + "content": "# Chapter 1\n", + "number": [1], + "sub_items": [], + "path": "chapter_1.md", + "source_path": "chapter_1.md", + "parent_names": [] + } + } + ], + "__non_exhaustive": null + } + ]"##; + let input_json = input_json.as_bytes(); + let (ctx, book) = mdbook_preprocessor::parse_input(input_json).unwrap(); + let result = TestPreprocessor.run(&ctx, book).unwrap_err(); + assert_eq!( + format!("{result:?}"), + "Failed to deserialize `preprocessor.test-preprocessor`\n\ + \n\ + Caused by:\n \ + unknown variant `nonsense`, expected `default` or `simple`\n \ + in `output-mode`\n " + ); +} diff --git a/packages/mdbook-trpl/src/figure/mod.rs b/packages/mdbook-trpl/src/figure/mod.rs new file mode 100644 index 0000000000..87e37ebf0a --- /dev/null +++ b/packages/mdbook-trpl/src/figure/mod.rs @@ -0,0 +1,242 @@ +use anyhow::{anyhow, Result}; +use html_parser::{Dom, Node}; +use mdbook_preprocessor::{ + book::{Book, BookItem}, + Preprocessor, +}; + +use pulldown_cmark::Event; +use pulldown_cmark_to_cmark::cmark; + +use crate::{config::Mode, CompositeError}; + +/// A simple preprocessor to rewrite `
`s with ``s. +/// +/// This is a no-op by default; it only operates on the book chapters when the +/// `[preprocessor.trpl-figure]` has `output-mode = "simple"`. +/// +/// Takes in Markdown containing like this: +/// +/// ```markdown +///
+/// +/// +/// +///
Figure 1-2: A description of the image
+/// +///
+/// ``` +/// +/// Spits out Markdown like this: +/// +/// ```markdown +/// +/// +/// +/// Figure 1-2: A description of the image +/// +/// ``` +pub struct TrplFigure; + +impl TrplFigure { + pub fn supports_renderer(&self, renderer: &str) -> bool { + renderer == "html" || renderer == "markdown" || renderer == "test" + } +} + +impl Preprocessor for TrplFigure { + fn name(&self) -> &str { + "trpl-figure" + } + + fn run( + &self, + ctx: &mdbook_preprocessor::PreprocessorContext, + mut book: Book, + ) -> Result { + // The `
`-based output is only replaced in the `Simple` mode. + let Mode::Simple = Mode::from_context(ctx, self.name())? else { + return Ok(book); + }; + + let mut errors = vec![]; + book.for_each_mut(|item| { + if let BookItem::Chapter(ref mut chapter) = item { + match rewrite_figure(&chapter.content) { + Ok(rewritten) => chapter.content = rewritten, + Err(reason) => errors.push(reason), + } + } + }); + + if errors.is_empty() { + Ok(book) + } else { + Err(CompositeError(errors).into()) + } + } +} + +const OPEN_FIGURE: &'static str = "
"; +const CLOSE_FIGURE: &'static str = "
"; + +const OPEN_CAPTION: &'static str = "
"; +const CLOSE_CAPTION: &'static str = "
"; + +fn rewrite_figure(text: &str) -> Result { + let final_state = crate::parser(text).try_fold( + State { + current: None, + events: Vec::new(), + }, + |mut state, event| { + match (event, &mut state.current) { + // -- Open figure + (Event::Html(tag), None) if tag.starts_with(OPEN_FIGURE) => { + let mut figure = Figure::new(); + figure.events.push(Event::Text("\n".into())); + state.current.replace(figure); + } + + (Event::Html(tag), Some(_)) if tag.starts_with(OPEN_FIGURE) => { + return Err(anyhow!( + "Opening `
` when already in a `
`" + )) + } + + // -- Close figure + (Event::Html(tag), Some(figure)) + if tag.starts_with(CLOSE_FIGURE) => + { + if figure.in_caption { + return Err(anyhow!("Unclosed `
`")); + } + + state.events.append(&mut figure.events); + state.events.push(Event::Text("\n".into())); + let _ = state.current.take(); + } + + (Event::Html(tag), None) if tag.trim() == CLOSE_FIGURE => { + return Err(anyhow!(bad_close(CLOSE_FIGURE, OPEN_CAPTION))); + } + + // -- Start captions + // We do not allow nested captions, but if we have not yet + // started a caption, it is legal to start one, and we + // intentionally ignore that event entirely other than tracking + // that we have started a caption. We will push the body of the + // caption into the figure’s events when we hit them. + // + // Note: this does not support `
`. + (Event::Html(tag), Some(fig)) + if tag.starts_with(OPEN_CAPTION) => + { + if fig.in_caption { + return Err(anyhow!(bad_open(OPEN_CAPTION))); + } else { + if tag.trim().ends_with(CLOSE_CAPTION) { + let text = Dom::parse(tag.as_ref())? + .children + .into_iter() + .filter_map(text_of) + .collect::(); + + if text.is_empty() { + return Err(anyhow!( + "Missing caption in `
`" + )); + } + + fig.events.push(Event::Text(text.into())); + } else { + fig.events.push(Event::Text("\n".into())); + fig.in_caption = true; + } + } + } + + (Event::Html(tag), None) if tag.starts_with(OPEN_CAPTION) => { + return Err(anyhow!(bad_open(OPEN_CAPTION))) + } + + // -- Close captions + (Event::Html(tag), Some(fig)) + if tag.trim() == CLOSE_CAPTION => + { + if fig.in_caption { + fig.events.push(Event::Text("\n".into())); + fig.in_caption = false; + } else { + return Err(anyhow!(bad_close( + CLOSE_CAPTION, + OPEN_CAPTION + ))); + } + } + + (Event::Html(tag), None) if tag.trim() == CLOSE_CAPTION => { + return Err(anyhow!(bad_close(CLOSE_CAPTION, OPEN_FIGURE))); + } + + // Otherwise, if in the body of a figure, push whatever other + // events without modification into the figure state. + (ev, Some(ref mut figure)) => figure.events.push(ev), + + // And if not in a figure, no modifications whatsoever. + (ev, None) => state.events.push(ev), + } + Ok(state) + }, + )?; + + if final_state.current.is_some() { + return Err(anyhow!("Unclosed `
`")); + } + + let mut rewritten = String::new(); + cmark(final_state.events.into_iter(), &mut rewritten)?; + Ok(rewritten) +} + +fn text_of(node: Node) -> Option { + match node { + Node::Text(text) => Some(text), + Node::Element(element) => { + Some(element.children.into_iter().filter_map(text_of).collect()) + } + Node::Comment(_) => None, + } +} + +fn bad_open(tag: &str) -> String { + format!("Opening `<{tag}>` while not in a `
`.") +} + +fn bad_close(close: &str, required_open: &str) -> String { + format!("Closing `<{close}>` while not in a `<{required_open}>`.") +} + +#[derive(Debug)] +struct State<'e> { + current: Option>, + events: Vec>, +} + +#[derive(Debug)] +struct Figure<'e> { + events: Vec>, + in_caption: bool, +} + +impl<'e> Figure<'e> { + fn new() -> Figure<'e> { + Figure { + events: vec![], + in_caption: false, + } + } +} + +#[cfg(test)] +mod tests; diff --git a/packages/mdbook-trpl/src/figure/tests.rs b/packages/mdbook-trpl/src/figure/tests.rs new file mode 100644 index 0000000000..d99eb6d43e --- /dev/null +++ b/packages/mdbook-trpl/src/figure/tests.rs @@ -0,0 +1,60 @@ +use super::*; + +#[test] +fn text_without_figures_is_ignored() { + let actual = rewrite_figure("This is some basic text.").unwrap(); + assert_eq!(actual, "This is some basic text."); +} + +#[test] +fn text_with_figure_replaces_it_with_simple_text() { + let actual = rewrite_figure( + r#"
+ + + +
Figure 12-34: Look at this cool picture!
+ +
"#, + ) + .unwrap(); + + let expected = r#" + + + +Figure 12-34: Look at this cool picture! + +"#; + + assert_eq!(actual, expected); +} + +#[test] +fn unclosed_figure() { + let result = rewrite_figure("
"); + let actual = format!("{:?}", result.unwrap_err()); + assert_eq!(actual, "Unclosed `
`"); +} + +#[test] +fn empty_caption() { + let result = rewrite_figure( + "
+
+
", + ); + let actual = format!("{:?}", result.unwrap_err()); + assert_eq!(actual, "Missing caption in `
`"); +} + +#[test] +fn unclosed_caption() { + let result = rewrite_figure( + "
+
+
", + ); + let actual = format!("{:?}", result.unwrap_err()); + assert_eq!(actual, "Unclosed `
`"); +} diff --git a/packages/mdbook-trpl/src/heading/mod.rs b/packages/mdbook-trpl/src/heading/mod.rs new file mode 100644 index 0000000000..cf08dea54a --- /dev/null +++ b/packages/mdbook-trpl/src/heading/mod.rs @@ -0,0 +1,110 @@ +use anyhow::anyhow; +use mdbook_preprocessor::{ + book::{Book, BookItem}, + errors::Result, + Preprocessor, PreprocessorContext, +}; +use pulldown_cmark::{Event, Tag, TagEnd}; +use pulldown_cmark_to_cmark::cmark; + +use crate::{CompositeError, Mode}; + +pub struct TrplHeading; + +impl Preprocessor for TrplHeading { + fn name(&self) -> &str { + "trpl-heading" + } + + fn run(&self, ctx: &PreprocessorContext, mut book: Book) -> Result { + let mode = Mode::from_context(ctx, self.name())?; + + let mut errors = vec![]; + book.for_each_mut(|item| { + if let BookItem::Chapter(ref mut chapter) = item { + match rewrite_headings(&chapter.content, mode) { + Ok(rewritten) => chapter.content = rewritten, + Err(reason) => errors.push(reason), + } + } + }); + + if errors.is_empty() { + Ok(book) + } else { + Err(CompositeError(errors).into()) + } + } + + fn supports_renderer(&self, renderer: &str) -> Result { + Ok(renderer == "html" || renderer == "markdown" || renderer == "test") + } +} + +fn rewrite_headings(src: &str, mode: Mode) -> anyhow::Result { + // Don't rewrite anything for the default mode. + if mode == Mode::Default { + return Ok(src.into()); + } + + #[derive(Default)] + struct State<'e> { + in_heading: bool, + events: Vec>, + } + + let final_state: State = crate::parser(src).try_fold( + State::default(), + |mut state, event| -> anyhow::Result { + if state.in_heading { + match event { + // When we see the start or end of any of the inline tags + // (emphasis, strong emphasis, or strikethrough), or any + // inline HTML tags, we just skip emitting them. As dumb as + // that may seem, it does the job! + Event::Start( + Tag::Emphasis | Tag::Strong | Tag::Strikethrough, + ) + | Event::End( + TagEnd::Emphasis + | TagEnd::Strong + | TagEnd::Strikethrough, + ) + | Event::InlineHtml(_) => { /* skip */ } + + // For code, we just emit the body of the inline code block, + // unchanged (the wrapping backticks are not present here). + Event::Code(code) => { + state.events.push(Event::Text(code)); + } + + // Assume headings are well-formed; you cannot have a nested + // headings, so we don't have to check heading level. + Event::End(TagEnd::Heading(_)) => { + state.in_heading = false; + state.events.push(event); + } + _ => state.events.push(event), + } + } else if matches!(event, Event::Start(Tag::Heading { .. })) { + state.events.push(event); + state.in_heading = true; + } else { + state.events.push(event); + } + + Ok(state) + }, + )?; + + if final_state.in_heading { + return Err(anyhow!("Unclosed heading")); + } + + let mut rewritten = String::new(); + cmark(final_state.events.into_iter(), &mut rewritten)?; + Ok(rewritten) +} + +#[cfg(test)] +mod tests; diff --git a/packages/mdbook-trpl/src/heading/tests.rs b/packages/mdbook-trpl/src/heading/tests.rs new file mode 100644 index 0000000000..242904e98b --- /dev/null +++ b/packages/mdbook-trpl/src/heading/tests.rs @@ -0,0 +1,205 @@ +use super::*; + +#[test] +fn default_mode_is_unchanged() { + let result = rewrite_headings( + "# This is *emphasized* and **strong** and `code` +## Here is *another* and **strong** and `code` +### Third *level* **heading** with `code` +#### Fourth *heading* **level** and `code` +##### Fifth *level* **heading** and `code` +###### Last *heading* **level** with `code` +", + Mode::Default, + ); + + assert_eq!( + result.unwrap(), + "# This is *emphasized* and **strong** and `code` +## Here is *another* and **strong** and `code` +### Third *level* **heading** with `code` +#### Fourth *heading* **level** and `code` +##### Fifth *level* **heading** and `code` +###### Last *heading* **level** with `code` +" + ); +} + +// Note: these tests all check that the result of rewriting a header *with* and +// *without* the markup is the same, so that other “normalization” that happens +// along the way (inserting or removing newlines, e.g.) is ignored. +mod simple_mode { + use super::*; + + #[test] + fn strips_em() { + let result = rewrite_headings( + "# This is *emphasized* and _this is too_ +## Here is *another* and _emphasis style_ +### Third *level* _heading_ here +#### Fourth *heading* _level_ text +##### Fifth *level* _heading_ now +###### Last *heading* _level_ test +", + Mode::Simple, + ); + + let expected = rewrite_headings( + "# This is emphasized and this is too +## Here is another and emphasis style +### Third level heading here +#### Fourth heading level text +##### Fifth level heading now +###### Last heading level test +", + Mode::Simple, + ); + + assert_eq!(result.unwrap(), expected.unwrap()); + } + + #[test] + fn strips_nested_em() { + let result = rewrite_headings( + "# *This _is *extra* emphatic_ emphasis*.", + Mode::Simple, + ); + let expected = "# This is extra emphatic emphasis."; + + assert_eq!(result.unwrap(), expected); + } + + #[test] + fn strips_strong() { + let result = rewrite_headings( + "# This is **strong** and __this is too__ +## Here is **another** and __strong style__ +### Third **level** __heading__ here +#### Fourth **heading** __level__ text +##### Fifth **level** __heading__ now +###### Last **heading** __level__ test +", + Mode::Simple, + ); + + let expected = rewrite_headings( + "# This is strong and this is too +## Here is another and strong style +### Third level heading here +#### Fourth heading level text +##### Fifth level heading now +###### Last heading level test +", + Mode::Simple, + ); + + assert_eq!(result.unwrap(), expected.unwrap()); + } + + #[test] + fn strips_nested_strong() { + let result = rewrite_headings( + "# **This __is **extra** emphatic__ emphasis**.", + Mode::Simple, + ); + let expected = "# This is extra emphatic emphasis."; + + assert_eq!(result.unwrap(), expected); + } + + #[test] + fn strips_code() { + let result = rewrite_headings( + "# This is `code` +## Here is `another` +### Third `level` +#### Fourth `heading` +##### Fifth `level` +###### Last `heading` +", + Mode::Simple, + ); + + let expected = rewrite_headings( + "# This is code +## Here is another +### Third level +#### Fourth heading +##### Fifth level +###### Last heading +", + Mode::Simple, + ); + + assert_eq!(result.unwrap(), expected.unwrap()); + } + + #[test] + fn strips_html() { + let result = rewrite_headings( + "# This is html +## Here is another +### Third level +#### Fourth heading +##### Fifth level +###### Last heading +", + Mode::Simple, + ); + + let expected = rewrite_headings( + "# This is html +## Here is another +### Third level +#### Fourth heading +##### Fifth level +###### Last heading +", + Mode::Simple, + ); + + assert_eq!(result.unwrap(), expected.unwrap()); + } + + #[test] + fn strips_strikethrough() { + let result = rewrite_headings( + "# This is ~~strikethrough~~ +## Here is ~~another~~ +### Third ~~level~~ +#### Fourth ~~heading~~ +##### Fifth ~~level~~ +###### Last ~~heading~~ +", + Mode::Simple, + ); + + let expected = rewrite_headings( + "# This is strikethrough +## Here is another +### Third level +#### Fourth heading +##### Fifth level +###### Last heading +", + Mode::Simple, + ); + + assert_eq!(result.unwrap(), expected.unwrap()); + } + + #[test] + fn strips_nested_combinations() { + let result = rewrite_headings( + "# **Nested ~~strikethrough _emphasis_ fun~~ times**", + Mode::Simple, + ); + + let expected = rewrite_headings( + "# Nested strikethrough emphasis fun times", + Mode::Simple, + ); + + assert_eq!(result.unwrap(), expected.unwrap()) + } +} diff --git a/packages/mdbook-trpl/src/lib.rs b/packages/mdbook-trpl/src/lib.rs new file mode 100644 index 0000000000..2586a8ed7e --- /dev/null +++ b/packages/mdbook-trpl/src/lib.rs @@ -0,0 +1,50 @@ +mod config; +mod figure; +mod heading; +mod listing; +mod note; + +pub use config::Mode; +pub use figure::TrplFigure as Figure; +pub use heading::TrplHeading as Heading; +pub use listing::TrplListing as Listing; +pub use note::TrplNote as Note; +use pulldown_cmark::{Options, Parser}; + +/// Convenience function to get a parser matching `mdbook::new_cmark_parser`. +/// +/// This is implemented separately so we are decoupled from mdbook's dependency +/// versions and can update at will (albeit with care to stay aligned with what +/// mdbook does!) to later versions of `pulldown-cmark` and related tools. +/// +/// Notes: +/// +/// - `mdbook::new_cmark_parser` has an additional parameter which allows smart +/// punctuation to be enabled or disabled; we always enable it. +/// - We do not use footnotes in the text at present, but this goes out of its +/// way to match this up to the old footnotes behavior just to make sure the +/// parsing etc. is all the same. +pub fn parser(text: &str) -> Parser<'_> { + let mut opts = Options::empty(); + opts.insert(Options::ENABLE_TABLES); + opts.insert(Options::ENABLE_FOOTNOTES); + opts.insert(Options::ENABLE_OLD_FOOTNOTES); + opts.insert(Options::ENABLE_STRIKETHROUGH); + opts.insert(Options::ENABLE_TASKLISTS); + opts.insert(Options::ENABLE_HEADING_ATTRIBUTES); + opts.insert(Options::ENABLE_SMART_PUNCTUATION); + Parser::new_ext(text, opts) +} + +#[derive(Debug, thiserror::Error)] +struct CompositeError(Vec); + +impl std::fmt::Display for CompositeError { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + write!( + f, + "Error(s) rewriting input: {}", + self.0.iter().map(|e| format!("{e:?}")).collect::() + ) + } +} diff --git a/packages/mdbook-trpl/src/listing/mod.rs b/packages/mdbook-trpl/src/listing/mod.rs new file mode 100644 index 0000000000..f39b9e97b4 --- /dev/null +++ b/packages/mdbook-trpl/src/listing/mod.rs @@ -0,0 +1,372 @@ +use anyhow::anyhow; +use html_parser::Dom; +use mdbook_preprocessor::{ + book::{Book, BookItem}, + errors::Result, + Preprocessor, PreprocessorContext, +}; +use pulldown_cmark::{html, Event}; +use pulldown_cmark_to_cmark::cmark; + +use crate::{config::Mode, CompositeError}; + +/// A preprocessor for rendering listings more elegantly. +/// +/// Given input like this: +/// +/// ````markdown +/// +/// +/// ```rust +/// fn main() {} +/// ``` +/// +/// +/// +/// ```` +/// +/// With no configuration, or with `output-mode = "default"`, it renders the +/// following Markdown to be further preprocessed or rendered to HTML: +/// +/// ````markdown +///
+/// Filename: src/main.rs +/// +/// ```rust +/// fn main() {} +/// ``` +/// +///
Listing 1-2: Some text, yeah?
+/// +///
+/// ```` +/// +/// When `output-mode = "simple"` in the configuration, it instead emits: +/// +/// ````markdown +/// Filename: src/main.rs +/// +/// ```rust +/// fn main() {} +/// ``` +/// +/// Listing 1-2: Some *text*, yeah? +/// ```` +pub struct TrplListing; + +impl Preprocessor for TrplListing { + fn name(&self) -> &str { + "trpl-listing" + } + + fn run(&self, ctx: &PreprocessorContext, mut book: Book) -> Result { + let mode = Mode::from_context(ctx, self.name())?; + + let mut errors = vec![]; + book.for_each_mut(|item| { + if let BookItem::Chapter(ref mut chapter) = item { + match rewrite_listing(&chapter.content, mode) { + Ok(rewritten) => chapter.content = rewritten, + Err(reason) => errors.push(anyhow!(reason)), + } + } + }); + + if errors.is_empty() { + Ok(book) + } else { + Err(CompositeError(errors).into()) + } + } + + fn supports_renderer(&self, renderer: &str) -> Result { + Ok(renderer == "html" || renderer == "markdown" || renderer == "test") + } +} + +fn rewrite_listing(src: &str, mode: Mode) -> Result { + match mode { + Mode::Default => { + let final_state = crate::parser(src).try_fold( + RewriteState { + current: None, + events: vec![], + }, + |mut state, ev| -> Result { + match ev { + Event::Html(tag) => { + if tag.starts_with("") { + state.close_listing(tag); + } else { + state.events.push(Ok(Event::Html(tag))); + } + } + ev => state.events.push(Ok(ev)), + }; + Ok(state) + }, + )?; + + if final_state.current.is_some() { + return Err("Unclosed listing".into()); + } + + let (events, errors): (Vec<_>, Vec<_>) = + final_state.events.into_iter().partition(|e| e.is_ok()); + + if !errors.is_empty() { + return Err(errors + .into_iter() + .map(|e| e.unwrap_err()) + .collect::>() + .join("\n")); + } + + let mut buf = String::with_capacity(src.len() * 2); + cmark(events.into_iter().map(|ok| ok.unwrap()), &mut buf) + .map_err(|e| format!("{e}"))?; + + Ok(buf) + } + Mode::Simple => { + // The output text should be very slightly *shorter* than the input, + // so we know this is a reasonable size for the buffer. + let mut rewritten = String::with_capacity(src.len()); + let mut current_closing = None; + for line in src.lines() { + if line.starts_with("")) { + let listing = + ListingBuilder::from_tag(&line)?.build(Mode::Simple); + rewritten.push_str(&listing.opening_text()); + current_closing = Some(listing.closing_text("\n")); + } else if line == "" { + let closing = + current_closing.as_ref().ok_or_else(|| { + String::from( + "Closing `` without opening tag.", + ) + })?; + rewritten.push_str(closing); + } else { + rewritten.push_str(line); + rewritten.push('\n'); + } + } + + // Since we always push a `'\n'` onto the end of the new string and + // `.lines()` does not tell us whether there *was* such a character, + // this makes the output match the input, and thus avoids adding new + // newlines after conversion. + if !src.ends_with('\n') { + rewritten.pop(); + } + + Ok(rewritten) + } + } +} + +struct RewriteState<'e> { + current: Option, + events: Vec, String>>, +} + +impl<'e> RewriteState<'e> { + fn open_listing( + &mut self, + tag: pulldown_cmark::CowStr<'_>, + mode: Mode, + ) -> Result<(), String> { + let listing = ListingBuilder::from_tag(&tag)?.build(mode); + let opening_event = Event::Html(listing.opening_html().into()); + + self.current = Some(listing); + self.events.push(Ok(opening_event)); + Ok(()) + } + + fn close_listing(&mut self, tag: pulldown_cmark::CowStr<'_>) { + let trailing = if !tag.ends_with('>') { + tag.replace("", "") + } else { + String::from("") + }; + + match &self.current { + Some(listing) => { + let closing_event = + Event::Html(listing.closing_html(&trailing).into()); + + self.current = None; + self.events.push(Ok(closing_event)); + } + None => { + self.events.push(Err(String::from( + "Closing `` without opening tag.", + ))); + } + } + } +} + +#[derive(Debug)] +struct Listing { + number: Option, + caption: Option, + file_name: Option, +} + +impl Listing { + fn opening_html(&self) -> String { + let id_attribute = self + .number + .as_ref() + .map(|number| format!(" id=\"listing-{number}\"")) + .unwrap_or_default(); + + let figure = format!("
\n"); + + match self.file_name.as_ref() { + Some(file_name) => format!( + "{figure}Filename: {file_name}\n", + ), + None => figure, + } + } + + fn closing_html(&self, trailing: &str) -> String { + match (&self.number, &self.caption) { + (Some(number), caption) => { + let caption_text = caption + .as_ref() + .map(|caption| format!(": {}", caption)) + .unwrap_or_default(); + let listing_a_tag = format!( + "Listing {number}" + ); + format!( + r#"
{listing_a_tag}{caption_text}
+
{trailing}"# + ) + } + (None, Some(caption)) => format!( + r#"
{caption}
+
{trailing}"# + ), + (None, None) => format!("
{trailing}"), + } + } + + fn opening_text(&self) -> String { + self.file_name + .as_ref() + .map(|file_name| format!("{file_name}\n")) + .unwrap_or_default() + } + + fn closing_text(&self, trailing: &str) -> String { + match (&self.number, &self.caption) { + (Some(number), Some(caption)) => { + format!("Listing {number}: {caption}{trailing}") + } + (None, Some(caption)) => format!("{caption}{trailing}"), + (Some(number), None) => format!("Listing {number}{trailing}"), + (None, None) => trailing.into(), + } + } +} + +/// Note: Although this has the same structure as [`Listing`], it does not have +/// the same *semantics*. In particular, this has the *source* for the `caption` +/// while `Listing` has the *rendered* version. +struct ListingBuilder { + number: Option, + caption: Option, + file_name: Option, +} + +impl ListingBuilder { + fn from_tag(tag: &str) -> Result { + let to_parse = format!("{tag}"); + Dom::parse(&to_parse) + .map_err(|e| e.to_string())? + .children + .into_iter() + .filter_map(|node| match node { + html_parser::Node::Element(element) => Some(element.attributes), + html_parser::Node::Text(_) | html_parser::Node::Comment(_) => { + None + } + }) + .flatten() + .try_fold( + ListingBuilder { + number: None, + caption: None, + file_name: None, + }, + |builder, (key, maybe_value)| match (key.as_str(), maybe_value) + { + ("number", Some(value)) => Ok(builder.with_number(value)), + + ("caption", Some(value)) => Ok(builder.with_caption(value)), + + ("file-name", Some(value)) => { + Ok(builder.with_file_name(value)) + } + + (attr @ "file-name", None) + | (attr @ "caption", None) + | (attr @ "number", None) => { + Err(format!("Missing value for attribute: '{attr}'")) + } + + (attr, _) => { + Err(format!("Unsupported attribute name: '{attr}'")) + } + }, + ) + } + + fn with_number(mut self, value: String) -> Self { + self.number = Some(value); + self + } + + fn with_caption(mut self, value: String) -> Self { + self.caption = Some(value); + self + } + + fn with_file_name(mut self, value: String) -> Self { + self.file_name = Some(value); + self + } + + fn build(self, mode: Mode) -> Listing { + let caption = match mode { + Mode::Default => self.caption.map(|caption_source| { + let events = crate::parser(&caption_source); + let mut buf = String::with_capacity(caption_source.len() * 2); + html::push_html(&mut buf, events); + + // This is not particularly principled, but since the only + // place it is used is here, for caption source handling, it + // is “fine”. + buf.replace("

", "").replace("

", "").replace('\n', "") + }), + Mode::Simple => self.caption, + }; + + Listing { + number: self.number.map(String::from), + caption, + file_name: self.file_name.map(String::from), + } + } +} + +#[cfg(test)] +mod tests; diff --git a/packages/mdbook-trpl/src/listing/tests.rs b/packages/mdbook-trpl/src/listing/tests.rs new file mode 100644 index 0000000000..48f14ffb7d --- /dev/null +++ b/packages/mdbook-trpl/src/listing/tests.rs @@ -0,0 +1,296 @@ +use super::*; + +/// Note: This inserts an additional backtick around the re-emitted code. +/// It is not clear *why*, but that seems to be an artifact of the rendering +/// done by the `pulldown_cmark_to_cmark` crate. +#[test] +fn default_mode_works() { + let result = rewrite_listing( + r#"+ +```rust +fn main() {} +``` + +"#, + Mode::Default, + ); + + assert_eq!( + &result.unwrap(), + r##"
+Filename: src/main.rs + +````rust +fn main() {} +```` + +
Listing 1-2: A write-up which might include inline Markdown like code etc.
+
"## + ); +} + +#[test] +fn simple_mode_works() { + let result = rewrite_listing( + r#"Leading text. + ++ +```rust +fn main() {} +``` + + + +Trailing text."#, + Mode::Simple, + ); + + assert_eq!( + &result.unwrap(), + r#"Leading text. + +src/main.rs + +```rust +fn main() {} +``` + +Listing 1-2: A write-up which *might* include inline Markdown like `code` etc. + +Trailing text."# + ); +} + +#[test] +fn listing_with_embedded_angle_brackets() { + let result = rewrite_listing( + r#"+ +```rust +fn get_a_box_of(t: T) -> Box { + Box::new(T) +} +``` + +"#, + Mode::Default, + ); + + assert_eq!( + &result.unwrap(), + r##"
+ +````rust +fn get_a_box_of(t: T) -> Box { + Box::new(T) +} +```` + +
Listing 34-5: This has a Box<T> in it.
+
"## + ); +} + +#[test] +fn actual_listing() { + let result = rewrite_listing( + r#"Now open the *main.rs* file you just created and enter the code in Listing 1-1. + ++ +```rust +fn main() { + println!("Hello, world!"); +} +``` + + + +Save the file and go back to your terminal window"#, + Mode::Default, + ); + + assert!(result.is_ok()); + assert_eq!( + result.unwrap(), + r##"Now open the *main.rs* file you just created and enter the code in Listing 1-1. + +
+Filename: main.rs + +````rust +fn main() { + println!("Hello, world!"); +} +```` + +
Listing 1-1: A program that prints Hello, world!
+
+ +Save the file and go back to your terminal window"## + ); +} + +#[test] +fn no_filename() { + let result = rewrite_listing( + r#"This is the opening. + ++ +```rust +fn main() {} +``` + + + +This is the closing."#, + Mode::Default, + ); + + assert!(result.is_ok()); + assert_eq!( + result.unwrap(), + r##"This is the opening. + +
+ +````rust +fn main() {} +```` + +
Listing 1-1: This is the caption
+
+ +This is the closing."## + ); +} + +#[test] +fn without_number() { + let result = rewrite_listing( + r#"+ +```rust +fn main() {} +``` + +"#, + Mode::Default, + ); + + assert!(result.is_ok()); + assert_eq!( + result.unwrap(), + r#"
+Filename: src/main.rs + +````rust +fn main() {} +```` + +
"# + ); +} + +#[test] +fn with_unsupported_attr_name() { + let result = rewrite_listing( + "+ +```rust +fn main() {} +``` + +", + Mode::Default, + ); + + assert_eq!( + result, + Err(String::from("Unsupported attribute name: 'invalid-attr'")) + ) +} + +#[test] +fn with_unsupported_attr_name_with_arg() { + let result = rewrite_listing( + r#"+ +```rust +fn main() {} +``` + +"#, + Mode::Default, + ); + + assert_eq!( + result, + Err(String::from("Unsupported attribute name: 'invalid-attr'")) + ) +} + +#[cfg(test)] +mod missing_value { + use super::*; + + #[test] + fn for_number() { + let result = rewrite_listing( + r#"+ +```rust +fn main() {} +``` + +"#, + Mode::Default, + ); + + assert_eq!( + result, + Err(String::from("Missing value for attribute: 'number'")) + ) + } + + #[test] + fn for_caption() { + let result = rewrite_listing( + r#"+ +```rust +fn main() {} +``` + +"#, + Mode::Default, + ); + + assert_eq!( + result, + Err(String::from("Missing value for attribute: 'caption'")) + ) + } + + #[test] + fn for_file_name() { + let result = rewrite_listing( + r#"+ +```rust +fn main() {} +``` + +"#, + Mode::Default, + ); + + assert_eq!( + result, + Err(String::from("Missing value for attribute: 'file-name'")) + ) + } +} diff --git a/packages/mdbook-trpl/src/note/mod.rs b/packages/mdbook-trpl/src/note/mod.rs new file mode 100644 index 0000000000..4e52cf0dc7 --- /dev/null +++ b/packages/mdbook-trpl/src/note/mod.rs @@ -0,0 +1,144 @@ +use mdbook_preprocessor::{ + book::{Book, BookItem}, + errors::Result, + Preprocessor, PreprocessorContext, +}; +use pulldown_cmark::{ + Event::{self, *}, + Tag, TagEnd, +}; +use pulldown_cmark_to_cmark::cmark; + +/// A simple preprocessor for semantic notes in _The Rust Programming Language_. +/// +/// Takes in Markdown like this: +/// +/// ```markdown +/// > Note: This is a note. +/// ``` +/// +/// Spits out Markdown like this: +/// +/// ```markdown +///
+/// +/// This is a note. +/// +///
+/// ``` +pub struct TrplNote; + +impl Preprocessor for TrplNote { + fn name(&self) -> &str { + "trpl-note" + } + + fn run(&self, _ctx: &PreprocessorContext, mut book: Book) -> Result { + book.for_each_mut(|item| { + if let BookItem::Chapter(ref mut chapter) = item { + chapter.content = rewrite(&chapter.content); + } + }); + Ok(book) + } + + fn supports_renderer(&self, renderer: &str) -> Result { + Ok(renderer == "html" || renderer == "markdown" || renderer == "test") + } +} + +pub fn rewrite(text: &str) -> String { + let parser = crate::parser(text); + + let mut events = Vec::new(); + let mut state = Default; + + for event in parser { + match (&mut state, event) { + (Default, Start(Tag::BlockQuote(_))) => { + state = StartingBlockquote(vec![Start(Tag::BlockQuote(None))]); + } + + (StartingBlockquote(blockquote_events), Text(content)) => { + if content.starts_with("Note: ") { + // This needs the "extra" `SoftBreak`s so that when the final rendering pass + // happens, it does not end up treating the internal content as inline *or* + // treating the HTML tags as inline tags: + // + // - Content inside HTML blocks is only rendered as Markdown when it is + // separated from the block HTML elements: otherwise it gets treated as inline + // HTML and *not* rendered. + // - Along the same lines, an HTML tag that happens to be directly adjacent to + // the end of a previous Markdown block will end up being rendered as part of + // that block. + events.extend([ + SoftBreak, + SoftBreak, + Html( + r#"
"#.into(), + ), + SoftBreak, + SoftBreak, + Start(Tag::Paragraph), + Text(content), + ]); + state = InNote; + } else { + events.append(blockquote_events); + events.push(Text(content)); + state = Default; + } + } + + ( + StartingBlockquote(_blockquote_events), + heading @ Start(Tag::Heading { .. }), + ) => { + events.extend([ + SoftBreak, + SoftBreak, + Html(r#"
"#.into()), + SoftBreak, + SoftBreak, + heading, + ]); + state = InNote; + } + + (StartingBlockquote(ref mut events), Start(tag)) => { + events.push(Start(tag)); + } + + (InNote, End(TagEnd::BlockQuote(_))) => { + // As with the start of the block HTML, the closing HTML must be + // separated from the Markdown text by two newlines. + events.extend([ + SoftBreak, + SoftBreak, + Html("
".into()), + ]); + state = Default; + } + + (_, event) => { + events.push(event); + } + } + } + + let mut buf = String::new(); + cmark(events.into_iter(), &mut buf).unwrap(); + buf +} + +use State::*; + +#[derive(Debug)] +enum State<'e> { + Default, + StartingBlockquote(Vec>), + InNote, +} + +#[cfg(test)] +mod tests; diff --git a/packages/mdbook-trpl/src/note/tests.rs b/packages/mdbook-trpl/src/note/tests.rs new file mode 100644 index 0000000000..c67d2ec9dc --- /dev/null +++ b/packages/mdbook-trpl/src/note/tests.rs @@ -0,0 +1,195 @@ +use super::*; + +#[test] +fn no_note() { + let text = "Hello, world.\n\nThis is some text."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "

Hello, world.

\n

This is some text.

\n" + ); +} + +#[test] +fn with_note() { + let text = "> Note: This is some text.\n> It keeps going."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Note: This is some text.\nIt keeps going.

\n
" + ); +} + +#[test] +fn regular_blockquote() { + let text = "> This is some text.\n> It keeps going."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

This is some text.\nIt keeps going.

\n
\n" + ); +} + +#[test] +fn combined() { + let text = "> Note: This is some text.\n> It keeps going.\n\nThis is regular text.\n\n> This is a blockquote.\n"; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Note: This is some text.\nIt keeps going.

\n
\n

This is regular text.

\n
\n

This is a blockquote.

\n
\n" + ); +} + +#[test] +fn blockquote_then_note() { + let text = "> This is quoted.\n\n> Note: This is noted."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

This is quoted.

\n
\n
\n

Note: This is noted.

\n
" + ); +} + +#[test] +fn note_then_blockquote() { + let text = "> Note: This is noted.\n\n> This is quoted."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Note: This is noted.

\n
\n
\n

This is quoted.

\n
\n" + ); +} + +#[test] +fn with_h1_note() { + let text = "> # Header\n > And then some note content."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Header

\n

And then some note content.

\n
" + ); +} + +#[test] +fn with_h2_note() { + let text = "> ## Header\n > And then some note content."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Header

\n

And then some note content.

\n
" + ); +} + +#[test] +fn with_h3_note() { + let text = "> ### Header\n > And then some note content."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Header

\n

And then some note content.

\n
" + ); +} + +#[test] +fn with_h4_note() { + let text = "> #### Header\n > And then some note content."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Header

\n

And then some note content.

\n
" + ); +} + +#[test] +fn with_h5_note() { + let text = "> ##### Header\n > And then some note content."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n
Header
\n

And then some note content.

\n
" + ); +} + +#[test] +fn with_h6_note() { + let text = "> ###### Header\n > And then some note content."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n
Header
\n

And then some note content.

\n
" + ); +} + +#[test] +fn h1_then_blockquote() { + let text = + "> # Header\n > And then some note content.\n\n> This is quoted."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Header

\n

And then some note content.

\n
\n
\n

This is quoted.

\n
\n" + ); +} + +#[test] +fn blockquote_then_h1_note() { + let text = + "> This is quoted.\n\n> # Header\n > And then some note content."; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

This is quoted.

\n
\n
\n

Header

\n

And then some note content.

\n
" + ); +} + +#[test] +fn blockquote_with_strong() { + let text = "> **Bold text in a paragraph.**"; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

Bold text in a paragraph.

\n
\n" + ); +} + +#[test] +fn normal_table() { + let text = "| Header 1 | Header 2 |\n| -------- | -------- |\n| Text 123 | More 456 |"; + let processed = rewrite(text); + + assert_eq!( + processed, + "|Header 1|Header 2|\n|--------|--------|\n|Text 123|More 456|", + "It strips some whitespace but otherwise leaves the table intact." + ); +} + +#[test] +fn table_in_note() { + let text = "> Note: table stuff.\n\n| Header 1 | Header 2 |\n| -------- | -------- |\n| Text 123 | More 456 |"; + let processed = rewrite(text); + + assert_eq!( + processed, + "\n\n
\n\nNote: table stuff.\n\n
\n\n|Header 1|Header 2|\n|--------|--------|\n|Text 123|More 456|", + "It adds the note markup but leaves the table untouched, to be rendered as Markdown." + ); +} + +#[test] +fn table_in_quote() { + let text = "> A table.\n\n| Header 1 | Header 2 |\n| -------- | -------- |\n| Text 123 | More 456 |"; + let processed = rewrite(text); + assert_eq!( + render_markdown(&processed), + "
\n

A table.

\n
\n\n\n
Header 1Header 2
Text 123More 456
\n", + "It renders blockquotes with nested tables as expected." + ); +} + +fn render_markdown(text: &str) -> String { + let parser = crate::parser(text); + let mut buf = String::new(); + pulldown_cmark::html::push_html(&mut buf, parser); + buf +} diff --git a/packages/mdbook-trpl/tests/integration/main.rs b/packages/mdbook-trpl/tests/integration/main.rs new file mode 100644 index 0000000000..bc081a1204 --- /dev/null +++ b/packages/mdbook-trpl/tests/integration/main.rs @@ -0,0 +1,20 @@ +mod note { + use assert_cmd::Command; + #[test] + fn supports_html_renderer() { + let cmd = Command::cargo_bin("mdbook-trpl-note") + .unwrap() + .args(["supports", "html"]) + .ok(); + assert!(cmd.is_ok()); + } + + #[test] + fn errors_for_other_renderers() { + let cmd = Command::cargo_bin("mdbook-trpl-note") + .unwrap() + .args(["supports", "total-nonsense"]) + .ok(); + assert!(cmd.is_err()); + } +} diff --git a/packages/tools/Cargo.toml b/packages/tools/Cargo.toml new file mode 100644 index 0000000000..b7fdf35e83 --- /dev/null +++ b/packages/tools/Cargo.toml @@ -0,0 +1,51 @@ +[package] +name = "rust-book-tools" +version = "0.0.1" +description = "The Rust Book" +edition = "2024" + +[[bin]] +name = "concat_chapters" +path = "src/bin/concat_chapters.rs" + +[[bin]] +name = "convert_quotes" +path = "src/bin/convert_quotes.rs" + +[[bin]] +name = "lfp" +path = "src/bin/lfp.rs" + +[[bin]] +name = "link2print" +path = "src/bin/link2print.rs" + +[[bin]] +name = "release_listings" +path = "src/bin/release_listings.rs" + +[[bin]] +name = "remove_hidden_lines" +path = "src/bin/remove_hidden_lines.rs" + +[[bin]] +name = "remove_links" +path = "src/bin/remove_links.rs" + +[[bin]] +name = "remove_markup" +path = "src/bin/remove_markup.rs" + +[[bin]] +name = "cleanup_blockquotes" +path = "src/bin/cleanup_blockquotes.rs" + + +[dependencies] +walkdir = { workspace = true } +docopt = { workspace = true } +serde = { workspace = true } +regex = { workspace = true } +lazy_static = { workspace = true } +flate2 = { workspace = true } +tar = { workspace = true } diff --git a/packages/tools/src/bin/cleanup_blockquotes.rs b/packages/tools/src/bin/cleanup_blockquotes.rs new file mode 100644 index 0000000000..41c31b653c --- /dev/null +++ b/packages/tools/src/bin/cleanup_blockquotes.rs @@ -0,0 +1,147 @@ +//! Fix incorrect round-tripping of block quotes in `pulldown-cmark-to-cmark`: +//! +//! - Eliminate extraneous leading `>` +//! - Eliminate extraneous indent. +//! +//! Note: later versions of `pulldown-cmark-to-cmark` will likely fix this, so +//! check when upgrading it if it is still necessary! + +use std::io::{self, Read}; + +use lazy_static::lazy_static; +use regex::Regex; + +fn main() { + let input = { + let mut buffer = String::new(); + io::stdin() + .read_to_string(&mut buffer) + .unwrap_or_else(|e| panic!("{e}")); + buffer + }; + + let fixed = cleanup_blockquotes(input); + print!("{fixed}"); +} + +fn cleanup_blockquotes(input: String) -> String { + let normal_start = EXTRA_SPACE.replace_all(&input, ">"); + let sans_empty_leading = EMPTY_LEADING.replace_all(&normal_start, "\n\n"); + sans_empty_leading.to_string() +} + +lazy_static! { + static ref EXTRA_SPACE: Regex = Regex::new("(?m)^ >").unwrap(); + static ref EMPTY_LEADING: Regex = Regex::new("\n\n> ?\n").unwrap(); +} + +#[cfg(test)] +mod tests { + use super::*; + + #[test] + fn extra_space() { + let input = " > Hello".to_string(); + let actual = cleanup_blockquotes(input); + assert_eq!(actual, "> Hello"); + } + + #[test] + fn empty_leading() { + let input = "\n\n>\n> Hello".into(); + let actual = cleanup_blockquotes(input); + assert_eq!(actual, "\n\n> Hello"); + } + + #[test] + fn leading_after_extra_space_cleaned_up() { + let input = r#"Start + +> +> Note: Hey. + +Wrap."# + .into(); + + let actual = cleanup_blockquotes(input); + assert_eq!( + actual, + r#"Start + +> Note: Hey. + +Wrap."# + ); + } + + /// This particular input was the result of running any of the mdbook + /// preprocessors which use `pulldown-cmark-to-cmark@<=18.0.0`. + #[test] + fn regression_ch17_example() { + // This is an example of the original motivating input which we are fixing. + let input = r#" +We have to explicitly await both of these futures, because futures in Rust are +*lazy*: they don’t do anything until you ask them to with `await`. (In fact, +Rust will show a compiler warning if you don’t use a future.) This should +remind you of our discussion of iterators [back in Chapter 13][iterators-lazy]. +Iterators do nothing unless you call their `next` method—whether directly, or +using `for` loops or methods such as `map` which use `next` under the hood. With +futures, the same basic idea applies: they do nothing unless you explicitly ask +them to. This laziness allows Rust to avoid running async code until it’s +actually needed. + + > + > Note: This is different from the behavior we saw when using `thread::spawn` in + > the previous chapter, where the closure we passed to another thread started + > running immediately. It’s also different from how many other languages + > approach async! But it’s important for Rust. We’ll see why that is later. + +Once we have `response_text`, we can then parse it into an instance of the +`Html` type using `Html::parse`. Instead of a raw string, we now have a data +type we can use to work with the HTML as a richer data structure. In particular, +we can use the `select_first` method to find the first instance of a given CSS +selector. By passing the string `"title"`, we’ll get the first `` +element in the document, if there is one. Because there may not be any matching +element, `select_first` returns an `Option<ElementRef>`. Finally, we use the +`Option::map` method, which lets us work with the item in the `Option` if it’s +present, and do nothing if it isn’t. (We could also use a `match` expression +here, but `map` is more idiomatic.) In the body of the function we supply to +`map`, we call `inner_html` on the `title_element` to get its content, which is +a `String`. When all is said and done, we have an `Option<String>`. +"#.to_string(); + + let actual = cleanup_blockquotes(input); + assert_eq!( + actual, + r#" +We have to explicitly await both of these futures, because futures in Rust are +*lazy*: they don’t do anything until you ask them to with `await`. (In fact, +Rust will show a compiler warning if you don’t use a future.) This should +remind you of our discussion of iterators [back in Chapter 13][iterators-lazy]. +Iterators do nothing unless you call their `next` method—whether directly, or +using `for` loops or methods such as `map` which use `next` under the hood. With +futures, the same basic idea applies: they do nothing unless you explicitly ask +them to. This laziness allows Rust to avoid running async code until it’s +actually needed. + +> Note: This is different from the behavior we saw when using `thread::spawn` in +> the previous chapter, where the closure we passed to another thread started +> running immediately. It’s also different from how many other languages +> approach async! But it’s important for Rust. We’ll see why that is later. + +Once we have `response_text`, we can then parse it into an instance of the +`Html` type using `Html::parse`. Instead of a raw string, we now have a data +type we can use to work with the HTML as a richer data structure. In particular, +we can use the `select_first` method to find the first instance of a given CSS +selector. By passing the string `"title"`, we’ll get the first `<title>` +element in the document, if there is one. Because there may not be any matching +element, `select_first` returns an `Option<ElementRef>`. Finally, we use the +`Option::map` method, which lets us work with the item in the `Option` if it’s +present, and do nothing if it isn’t. (We could also use a `match` expression +here, but `map` is more idiomatic.) In the body of the function we supply to +`map`, we call `inner_html` on the `title_element` to get its content, which is +a `String`. When all is said and done, we have an `Option<String>`. +"# + ); + } +} diff --git a/tools/src/bin/concat_chapters.rs b/packages/tools/src/bin/concat_chapters.rs similarity index 97% rename from tools/src/bin/concat_chapters.rs rename to packages/tools/src/bin/concat_chapters.rs index 79ffec9b70..127e93a84e 100644 --- a/tools/src/bin/concat_chapters.rs +++ b/packages/tools/src/bin/concat_chapters.rs @@ -1,14 +1,12 @@ -#[macro_use] -extern crate lazy_static; - use std::collections::BTreeMap; use std::env; -use std::fs::{create_dir, read_dir, File}; +use std::fs::{File, create_dir, read_dir}; use std::io; use std::io::{Read, Write}; use std::path::{Path, PathBuf}; use std::process::exit; +use lazy_static::lazy_static; use regex::Regex; static PATTERNS: &[(&str, &str)] = &[ diff --git a/tools/src/bin/convert_quotes.rs b/packages/tools/src/bin/convert_quotes.rs similarity index 96% rename from tools/src/bin/convert_quotes.rs rename to packages/tools/src/bin/convert_quotes.rs index b4a9bdce2e..a6a8dae72b 100644 --- a/tools/src/bin/convert_quotes.rs +++ b/packages/tools/src/bin/convert_quotes.rs @@ -8,7 +8,7 @@ fn main() { let mut buffer = String::new(); if let Err(e) = io::stdin().read_to_string(&mut buffer) { - panic!("{}", e); + panic!("{e}"); } for line in buffer.lines() { @@ -21,7 +21,7 @@ fn main() { if is_in_code_block { is_in_inline_code = false; is_in_html_tag = false; - println!("{}", line); + println!("{line}"); } else { let modified_line = &mut String::new(); let mut previous_char = std::char::REPLACEMENT_CHARACTER; @@ -72,7 +72,7 @@ fn main() { modified_line.push(char_to_push); previous_char = char_to_push; } - println!("{}", modified_line); + println!("{modified_line}"); } } } diff --git a/tools/src/bin/lfp.rs b/packages/tools/src/bin/lfp.rs similarity index 96% rename from tools/src/bin/lfp.rs rename to packages/tools/src/bin/lfp.rs index c4d4bce036..d4ab62d5d4 100644 --- a/tools/src/bin/lfp.rs +++ b/packages/tools/src/bin/lfp.rs @@ -1,11 +1,12 @@ // We have some long regex literals, so: // ignore-tidy-linelength -use docopt::Docopt; -use serde::Deserialize; use std::io::BufRead; use std::{fs, io, path}; +use docopt::Docopt; +use serde::Deserialize; + fn main() { let args: Args = Docopt::new(USAGE) .and_then(|d| d.deserialize()) @@ -18,7 +19,7 @@ fn main() { .map(|entry| match entry { Ok(entry) => entry, Err(err) => { - eprintln!("{:?}", err); + eprintln!("{err:?}"); std::process::exit(911) } }) @@ -105,6 +106,8 @@ fn is_line_of_interest(line: &str) -> bool { line.split_whitespace().any(|sub_string| { sub_string.contains("file://") && !sub_string.contains("file:///projects/") + && !sub_string.contains("file:///home/.cargo") + && !sub_string.contains("file:///home/.rustup") }) } @@ -212,8 +215,8 @@ mod tests { } #[test] - fn is_file_of_interest_returns_false_when_the_filename_does_not_have_the_md_extension( - ) { + fn is_file_of_interest_returns_false_when_the_filename_does_not_have_the_md_extension() + { let uninteresting_fn = "src/img/foo1.png"; assert!(!super::is_file_of_interest(path::Path::new( @@ -230,8 +233,8 @@ mod tests { } #[test] - fn is_line_of_interest_does_not_report_a_line_if_the_line_contains_a_file_url_which_is_directly_followed_by_the_project_path( - ) { + fn is_line_of_interest_does_not_report_a_line_if_the_line_contains_a_file_url_which_is_directly_followed_by_the_project_path() + { let sample_line = "Compiling guessing_game v0.1.0 (file:///projects/guessing_game)"; @@ -239,8 +242,8 @@ mod tests { } #[test] - fn is_line_of_interest_reports_a_line_if_the_line_contains_a_file_url_which_is_not_directly_followed_by_the_project_path( - ) { + fn is_line_of_interest_reports_a_line_if_the_line_contains_a_file_url_which_is_not_directly_followed_by_the_project_path() + { let sample_line = "Compiling guessing_game v0.1.0 (file:///home/you/projects/guessing_game)"; assert!(super::is_line_of_interest(sample_line)); diff --git a/tools/src/bin/link2print.rs b/packages/tools/src/bin/link2print.rs similarity index 89% rename from tools/src/bin/link2print.rs rename to packages/tools/src/bin/link2print.rs index 1e92ecbccd..b763828a77 100644 --- a/tools/src/bin/link2print.rs +++ b/packages/tools/src/bin/link2print.rs @@ -1,11 +1,12 @@ // FIXME: we have some long lines that could be refactored, but it's not a big deal. // ignore-tidy-linelength -use regex::{Captures, Regex}; use std::collections::HashMap; use std::io; use std::io::Read; +use regex::{Captures, Regex}; + fn main() { write_md(parse_links(parse_references(read_md()))); } @@ -14,12 +15,12 @@ fn read_md() -> String { let mut buffer = String::new(); match io::stdin().read_to_string(&mut buffer) { Ok(_) => buffer, - Err(error) => panic!("{}", error), + Err(error) => panic!("{error}"), } } fn write_md(output: String) { - print!("{}", output); + print!("{output}"); } fn parse_references(buffer: String) -> (String, HashMap<String, String>) { @@ -29,12 +30,11 @@ fn parse_references(buffer: String) -> (String, HashMap<String, String>) { .unwrap(); let output = re .replace_all(&buffer, |caps: &Captures<'_>| { - let key = caps.get(1).unwrap().as_str().to_uppercase(); + let key_def = caps.get(1).unwrap().as_str(); + let key = key_def.to_uppercase(); let val = caps.get(2).unwrap().as_str().to_string(); if ref_map.insert(key, val).is_some() { - panic!( - "Did not expect markdown page to have duplicate reference" - ); + panic!("unexpected page had duplicate reference for {key_def}",); } "".to_string() }) @@ -45,23 +45,11 @@ fn parse_references(buffer: String) -> (String, HashMap<String, String>) { fn parse_links((buffer, ref_map): (String, HashMap<String, String>)) -> String { // FIXME: check which punctuation is allowed by spec. let re = Regex::new(r###"(?:(?P<pre>(?:```(?:[^`]|`[^`])*`?\n```\n)|(?:[^\[]`[^`\n]+[\n]?[^`\n]*`))|(?:\[(?P<name>[^]]+)\](?:(?:\([[:blank:]]*(?P<val>[^")]*[^ ])(?:[[:blank:]]*"[^"]*")?\))|(?:\[(?P<key>[^]]*)\]))?))"###).expect("could not create regex"); - let error_code = - Regex::new(r###"^E\d{4}$"###).expect("could not create regex"); let output = re.replace_all(&buffer, |caps: &Captures<'_>| { match caps.name("pre") { Some(pre_section) => pre_section.as_str().to_string(), None => { let name = caps.name("name").expect("could not get name").as_str(); - // Really we should ignore text inside code blocks, - // this is a hack to not try to treat `#[derive()]`, - // `[profile]`, `[test]`, or `[E\d\d\d\d]` like a link. - if name.starts_with("derive(") || - name.starts_with("profile") || - name.starts_with("test") || - name.starts_with("no_mangle") || - error_code.is_match(name) { - return name.to_string() - } let val = match caps.name("val") { // `[name](link)` @@ -71,17 +59,19 @@ fn parse_links((buffer, ref_map): (String, HashMap<String, String>)) -> String { Some(key) => { match key.as_str() { // `[name][]` - "" => ref_map.get(&name.to_uppercase()).unwrap_or_else(|| panic!("could not find url for the link text `{}`", name)).to_string(), + "" => ref_map.get(&name.to_uppercase()).unwrap_or_else(|| panic!("could not find url for the link text `{name}`")).to_string(), // `[name][reference]` _ => ref_map.get(&key.as_str().to_uppercase()).unwrap_or_else(|| panic!("could not find url for the link text `{}`", key.as_str())).to_string(), } } - // `[name]` as reference - None => ref_map.get(&name.to_uppercase()).unwrap_or_else(|| panic!("could not find url for the link text `{}`", name)).to_string(), + // `[name]` is within code and should not be treated as a link + None => { + return format!("[{name}]"); + } } } }; - format!("{} at *{}*", name, val) + format!("{name} at *{val}*") } } }); @@ -231,11 +221,11 @@ more text" } #[test] - fn parses_link_without_reference_as_reference() { + fn does_not_parse_link_without_reference_as_reference() { let source = r"[link] is alone [link]: The contents" .to_string(); - let target = r"link at *The contents* is alone".to_string(); + let target = r"[link] is alone".to_string(); assert_eq!(parse(source), target); } @@ -289,7 +279,7 @@ version = "0.1.0" [dependencies] ``` -Another [link] +Another [link][] more text [link]: http://gohere "### @@ -374,7 +364,7 @@ note: required by `std::fmt::Display::fmt` [I'm a reference-style link][Arbitrary case-insensitive reference text] -[I'm a relative reference to a repository file](../blob/master/LICENSE) +[I'm a relative reference to a repository file](../blob/HEAD/LICENSE) [You can use numbers for reference-style link definitions][1] @@ -397,7 +387,7 @@ I'm an inline-style link with title at *https://www.google.com* I'm a reference-style link at *https://www.mozilla.org* -I'm a relative reference to a repository file at *../blob/master/LICENSE* +I'm a relative reference to a repository file at *../blob/HEAD/LICENSE* You can use numbers for reference-style link definitions at *http://slashdot.org* diff --git a/tools/src/bin/release_listings.rs b/packages/tools/src/bin/release_listings.rs similarity index 68% rename from tools/src/bin/release_listings.rs rename to packages/tools/src/bin/release_listings.rs index c371d7b308..468c4637dd 100644 --- a/tools/src/bin/release_listings.rs +++ b/packages/tools/src/bin/release_listings.rs @@ -1,7 +1,3 @@ -#[macro_use] -extern crate lazy_static; - -use regex::Regex; use std::error::Error; use std::fs; use std::fs::File; @@ -9,6 +5,9 @@ use std::io::prelude::*; use std::io::{BufReader, BufWriter}; use std::path::{Path, PathBuf}; +use lazy_static::lazy_static; +use regex::Regex; + fn main() -> Result<(), Box<dyn Error>> { // Get all listings from the `listings` directory let listings_dir = Path::new("listings"); @@ -29,26 +28,59 @@ fn main() -> Result<(), Box<dyn Error>> { let chapter = chapter?; let chapter_path = chapter.path(); + if !chapter_path.is_dir() { + eprintln!( + "'{}' is not a directory, skipping", + chapter_path.display() + ); + continue; + } + let chapter_name = chapter_path .file_name() .expect("Chapter should've had a name"); // Create a corresponding chapter dir in `tmp/listings` let output_chapter_path = out_dir.join(chapter_name); - fs::create_dir(&output_chapter_path)?; + fs::create_dir(&output_chapter_path).map_err(|e| { + format!( + "could not create dir at '{}': {e}", + output_chapter_path.display() + ) + })?; // For each listing in the chapter directory, - for listing in fs::read_dir(chapter_path)? { - let listing = listing?; + for listing in fs::read_dir(&chapter_path).map_err(|e| { + format!("Could not read '{}': {e}", chapter_path.display()) + })? { + let listing = listing.map_err(|e| { + format!( + "bad dir entry listing in {}: {e}", + chapter_path.display() + ) + })?; let listing_path = listing.path(); + if !listing_path.is_dir() { + eprintln!( + "'{}' is not a directory, skipping", + listing_path.display(), + ); + continue; + } + let listing_name = listing_path .file_name() .expect("Listing should've had a name"); // Create a corresponding listing dir in the tmp chapter dir let output_listing_dir = output_chapter_path.join(listing_name); - fs::create_dir(&output_listing_dir)?; + fs::create_dir(&output_listing_dir).map_err(|e| { + format!( + "could not create dir '{}': {e}", + output_listing_dir.display() + ) + })?; // Copy all the cleaned files in the listing to the tmp directory copy_cleaned_listing_files(listing_path, output_listing_dir)?; @@ -80,8 +112,12 @@ fn copy_cleaned_listing_files( from: PathBuf, to: PathBuf, ) -> Result<(), Box<dyn Error>> { - for item in fs::read_dir(from)? { - let item = item?; + for item in fs::read_dir(&from).map_err(|e| { + format!("Could not read_dir on '{}': {e}", from.display()) + })? { + let item = item.map_err(|e| { + format!("invalid dir entry in {}: {e}", from.display()) + })?; let item_path = item.path(); let item_name = @@ -91,7 +127,12 @@ fn copy_cleaned_listing_files( if item_path.is_dir() { // Don't copy `target` directories if item_name != "target" { - fs::create_dir(&output_item)?; + fs::create_dir(&output_item).map_err(|e| { + format!( + "Could not create output directory '{}': {e}", + output_item.display() + ) + })?; copy_cleaned_listing_files(item_path, output_item)?; } } else { @@ -106,7 +147,13 @@ fn copy_cleaned_listing_files( )?; } else { // Copy any non-Rust files without modification - fs::copy(item_path, output_item)?; + fs::copy(&item_path, &output_item).map_err(|e| { + format!( + "Could not copy from '{}' to '{}': {e}", + item_path.display(), + output_item.display() + ) + })?; } } } @@ -149,7 +196,7 @@ fn copy_cleaned_rust_file( if !ANCHOR_OR_SNIP_COMMENTS.is_match(&line) && (item_name != "lib.rs" || !EMPTY_MAIN.is_match(&line)) { - writeln!(&mut to_buf, "{}", line)?; + writeln!(&mut to_buf, "{line}")?; } } diff --git a/tools/src/bin/remove_hidden_lines.rs b/packages/tools/src/bin/remove_hidden_lines.rs similarity index 95% rename from tools/src/bin/remove_hidden_lines.rs rename to packages/tools/src/bin/remove_hidden_lines.rs index dc3c593570..934b64eb69 100644 --- a/tools/src/bin/remove_hidden_lines.rs +++ b/packages/tools/src/bin/remove_hidden_lines.rs @@ -9,12 +9,12 @@ fn read_md() -> String { let mut buffer = String::new(); match io::stdin().read_to_string(&mut buffer) { Ok(_) => buffer, - Err(error) => panic!("{}", error), + Err(error) => panic!("{error}"), } } fn write_md(output: String) { - print!("{}", output); + print!("{output}"); } fn remove_hidden_lines(input: &str) -> String { diff --git a/tools/src/bin/remove_links.rs b/packages/tools/src/bin/remove_links.rs similarity index 94% rename from tools/src/bin/remove_links.rs rename to packages/tools/src/bin/remove_links.rs index b3f78d70a0..ebb46e2c25 100644 --- a/tools/src/bin/remove_links.rs +++ b/packages/tools/src/bin/remove_links.rs @@ -1,5 +1,3 @@ -extern crate regex; - use regex::{Captures, Regex}; use std::collections::HashSet; use std::io; @@ -8,7 +6,7 @@ use std::io::Read; fn main() { let mut buffer = String::new(); if let Err(e) = io::stdin().read_to_string(&mut buffer) { - panic!("{}", e); + panic!("{e}"); } let mut refs = HashSet::new(); @@ -41,5 +39,5 @@ fn main() { caps.get(0).unwrap().as_str().to_string() }); - print!("{}", out); + print!("{out}"); } diff --git a/tools/src/bin/remove_markup.rs b/packages/tools/src/bin/remove_markup.rs similarity index 89% rename from tools/src/bin/remove_markup.rs rename to packages/tools/src/bin/remove_markup.rs index c42e588e75..6ec0fdfb90 100644 --- a/tools/src/bin/remove_markup.rs +++ b/packages/tools/src/bin/remove_markup.rs @@ -1,9 +1,8 @@ -extern crate regex; - -use regex::{Captures, Regex}; use std::io; use std::io::Read; +use regex::{Captures, Regex}; + fn main() { write_md(remove_markup(read_md())); } @@ -12,12 +11,12 @@ fn read_md() -> String { let mut buffer = String::new(); match io::stdin().read_to_string(&mut buffer) { Ok(_) => buffer, - Err(error) => panic!("{}", error), + Err(error) => panic!("{error}"), } } fn write_md(output: String) { - print!("{}", output); + print!("{output}"); } fn remove_markup(input: String) -> String { @@ -27,7 +26,7 @@ fn remove_markup(input: String) -> String { let caption_start_regex = Regex::new(r#"\A<span class="caption">(.*)\z"#).unwrap(); let caption_end_regex = Regex::new(r#"(.*)</span>\z"#).unwrap(); - let regexen = vec![filename_regex, caption_start_regex, caption_end_regex]; + let regexen = [filename_regex, caption_start_regex, caption_end_regex]; let lines: Vec<_> = input .lines() diff --git a/packages/trpl/CHANGELOG.md b/packages/trpl/CHANGELOG.md new file mode 100644 index 0000000000..61ca499927 --- /dev/null +++ b/packages/trpl/CHANGELOG.md @@ -0,0 +1,21 @@ +# CHANGELOG + +## 0.3.0 + +This is intended to be a backwards-compatible release. + +- Added aliases of method names to better align with other async crates' terminology after tech + review feedback, including: + - `select` instead of `race` + - `block_on` instead of `run` +- Upgraded Rust, the edition, `ring`, and `quinn-proto` +- Switched to `rustls` + + +## 0.2.0 + +- Added `get`, `Response`, and `Html` to support more examples in chapter 17. + +## 0.1.0 + +Initial release! 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dependency for distribution with Rust, so it must not be +# built as part of the `rust-lang/book` or `rust-lang/rust` workspaces. +[workspace] diff --git a/packages/trpl/LICENSE-APACHE b/packages/trpl/LICENSE-APACHE new file mode 100644 index 0000000000..38634daab0 --- /dev/null +++ b/packages/trpl/LICENSE-APACHE @@ -0,0 +1,201 @@ + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + +TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + +1. 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We also recommend that a + file or class name and description of purpose be included on the + same "printed page" as the copyright notice for easier + identification within third-party archives. + +Copyright 2010 The Rust Project Developers + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. diff --git a/packages/trpl/LICENSE-MIT b/packages/trpl/LICENSE-MIT new file mode 100644 index 0000000000..25597d5838 --- /dev/null +++ b/packages/trpl/LICENSE-MIT @@ -0,0 +1,25 @@ +Copyright (c) 2010 The Rust Project Developers + +Permission is hereby granted, free of charge, to any +person obtaining a copy of this software and associated +documentation files (the "Software"), to deal in the +Software without restriction, including without +limitation the rights to use, copy, modify, merge, +publish, distribute, sublicense, and/or sell copies of +the Software, and to permit persons to whom the Software +is furnished to do so, subject to the following +conditions: + +The above copyright notice and this permission notice +shall be included in all copies or substantial portions +of the Software. + +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF +ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED +TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A +PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT +SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY +CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION +OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR +IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER +DEALINGS IN THE SOFTWARE. diff --git a/packages/trpl/README.md b/packages/trpl/README.md new file mode 100644 index 0000000000..3e97ac9b3b --- /dev/null +++ b/packages/trpl/README.md @@ -0,0 +1,22 @@ +# The Rust Programming Language Book Crate + +![Build Status](https://github.com/chriskrycho/trpl-crate/workflows/CI/badge.svg) + +This repository is the home of the `trpl` crate used in _The Rust Programming +Language_ book materials. + +This crate mostly just re-exports items from _other_ crates. It exists for two +main reasons: + +1. So that as you read along in _The Rust Programming Language_, you can add + just one dependency, rather than however many we end up with, and likewise + use only one set of imports. + +2. So that we can more easily guarantee it keeps building and working. Since we + control the contents of this crate and when it changes, readers will never be + broken by upstream changes, e.g. if Tokio does a breaking 2.0 release at some + point. + +## Requirements + +This crate currently requires at least Rust 1.79. diff --git a/packages/trpl/src/lib.rs b/packages/trpl/src/lib.rs new file mode 100644 index 0000000000..02a1dd8248 --- /dev/null +++ b/packages/trpl/src/lib.rs @@ -0,0 +1,167 @@ +//! A support crate for [_The Rust Programming Language_][trpl]. +//! +//! [trpl]: https://doc.rust-lang.org/book +//! +//! This crate mostly just re-exports items from *other* crates. It exists for +//! two main reasons: +//! +//! 1. So that as you read along in _The Rust Programming Language_, you can +//! add just one dependency, rather than however many we end up with, and +//! likewise use only one set of imports. +//! +//! 2. So that we can more easily guarantee it keeps building and working. Since +//! we control the contents of this crate and when it changes, readers will +//! never be broken by upstream changes, e.g. if Tokio does a breaking 2.0 +//! release at some point. + +// For direct use within the `trpl` crate, *not* re-exported. +use std::{future::Future, pin::pin}; + +use futures::future; + +// Re-exports, to be used like `trpl::join`. +pub use futures::{ + future::{Either, join, join_all, join3}, + join, +}; +pub use tokio::{ + fs::read_to_string, + runtime::Runtime, + // We use the `unbounded` variants because they most closely match the APIs + // from `std::sync::mpsc::channel`. Tokio's API choices are interesting: + // + // | `tokio::sync::mpsc` | `std::sync::mpsc` | + // | ------------------- | ----------------- | + // | `channel` | `sync_channel` | + // | `unbounded_channel` | `channel` | + // + // The book collapses these differences for pedagogical simplicity, so that + // readers are not asking why `unbounded` is now important and can focus on + // the more important differences between sync and async APIs. + sync::mpsc::{ + UnboundedReceiver as Receiver, UnboundedSender as Sender, + unbounded_channel as channel, + }, + task::{JoinHandle, spawn as spawn_task, yield_now}, + time::{interval, sleep}, +}; + +pub use tokio_stream::{ + Stream, StreamExt, iter as stream_from_iter, + wrappers::{IntervalStream, UnboundedReceiverStream as ReceiverStream}, +}; + +/// Run a single future to completion on a bespoke Tokio `Runtime`. +/// +/// Every time you call this, a new instance of `tokio::runtime::Runtime` will +/// be created (see the implementation for details: it is trivial). This is: +/// +/// - Reasonable for teaching purposes, in that you do not generally need to set +/// up more than one runtime anyway, and especially do not in basic code like +/// we are showing! +/// +/// - Not *that* far off from what Tokio itself does under the hood in its own +/// `tokio::main` macro for supporting `async fn main`. +pub fn block_on<F: Future>(future: F) -> F::Output { + let rt = Runtime::new().unwrap(); + rt.block_on(future) +} + +/// This function has been renamed to `block_on`; please see its documentation. +/// This function remains to maintain compatibility with the online versions +/// of the book that use the name `run`. +pub fn run<F: Future>(future: F) -> F::Output { + block_on(future) +} + +/// Run two futures, taking whichever finishes first and canceling the other. +/// +/// Notice that this is built on [`futures::future::select`], which has the +/// same overall semantics but does *not* drop the slower future. The idea there +/// is that you can work with the first result and then later *also* continue +/// waiting for the second future. +/// +/// We drop the slower future for the sake of simplicity in the examples: no +/// need to deal with the tuple and intentionally ignore the second future this +/// way! +/// +/// Note that this only works as “simply” as it does because: +/// +/// - It takes ownership of the futures. +/// - It internally *pins* the futures. +/// - It throws away (rather than returning) the unused future (which is why it +/// can get away with pinning them). +pub async fn select<A, B, F1, F2>(f1: F1, f2: F2) -> Either<A, B> +where + F1: Future<Output = A>, + F2: Future<Output = B>, +{ + let f1 = pin!(f1); + let f2 = pin!(f2); + match future::select(f1, f2).await { + Either::Left((a, _f2)) => Either::Left(a), + Either::Right((b, _f1)) => Either::Right(b), + } +} + +/// This function has been renamed to `select`; please see its documentation. +/// This function remains to maintain compatibility with the online versions +/// of the book that use the name `race`. +pub async fn race<A, B, F1, F2>(f1: F1, f2: F2) -> Either<A, B> +where + F1: Future<Output = A>, + F2: Future<Output = B>, +{ + select(f1, f2).await +} + +/// Fetch data from a URL. For more convenient use in _The Rust Programming +/// Language_, panics instead of returning a [`Result`] if the request fails. +pub async fn get(url: &str) -> Response { + Response(reqwest::get(url).await.unwrap()) +} + +/// A thin wrapper around [`reqwest::Response`] to make the demos in _The Rust +/// Programming Language_ substantially nicer to use. +pub struct Response(reqwest::Response); + +impl Response { + /// Get the full response text. + /// + /// If the response cannot be deserialized, this panics instead of returning + /// a [`Result`] (for convenience in the demo). + pub async fn text(self) -> String { + self.0.text().await.unwrap() + } +} + +/// A thin wrapper around [`scraper::Html`] to make the demos in _The Rust +/// Programming Language_ substantially nicer to use. +pub struct Html { + inner: scraper::Html, +} + +impl Html { + /// Parse an HTML document from a string. + /// + /// This is just a thin wrapper around `scraper::Html::parse_document` to + /// keep the exported API surface simpler. + pub fn parse(source: &str) -> Html { + Html { + inner: scraper::Html::parse_document(source), + } + } + + /// Get the first item in the document matching a string selector. Returns + /// Some() + /// + /// If the selector is not a valid CSS selector, panics rather than + /// returning a [`Result`] for convenience. + pub fn select_first<'a>( + &'a self, + selector: &'a str, + ) -> Option<scraper::ElementRef<'a>> { + let selector = scraper::Selector::parse(selector).unwrap(); + self.inner.select(&selector).nth(0) + } +} diff --git a/packages/trpl/tests/integration/main.rs b/packages/trpl/tests/integration/main.rs new file mode 100644 index 0000000000..65fce378ea --- /dev/null +++ b/packages/trpl/tests/integration/main.rs @@ -0,0 +1,277 @@ +//! Integration tests for the crate. +//! +//! These all live in a *single* integration test crate, `tests/integration`, +//! because each integration test is a dedicated binary crate which has to be +//! compiled separately. While that is not really a problem for a crate this +//! small, we have chosen to follow this “best practice” here as a good example. +//! +//! For more details on why you might prefer this pattern see [this post][post]. +//! +//! [post]: https://matklad.github.io/2021/02/27/delete-cargo-integration-tests.html + +use std::{pin::Pin, time::Duration}; + +use futures::Future; +use trpl::{Either, Receiver, Sender}; + +/// We initially named the function `run` and an online version of the async chapter +/// was released with that name, so we want to keep it working. We decided to rename +/// `run` to be `block_on` to more closely match other crates' names, so most of the +/// tests now use the `block_on` name. +#[test] +fn using_run_works() { + let val = trpl::run(async { "Hello" }); + assert_eq!(val, "Hello"); +} + +/// This test is foundational for all the others, as they depend on `block_on`. +/// +/// If we mess this up, *all* the tests below will fail -- so by the same token, +/// if all the tests below are failing, this one probably is too; fix it and the +/// others will likely start working again. +#[test] +fn re_exported_block_on_works() { + let val = trpl::block_on(async { "Hello" }); + assert_eq!(val, "Hello"); +} + +#[test] +fn re_exported_spawn_works() { + let result = trpl::block_on(async { + let handle_a = trpl::spawn_task(async { "Hello" }); + let handle_b = trpl::spawn_task(async { "Goodbye" }); + vec![handle_a.await.unwrap(), handle_b.await.unwrap()] + }); + + assert_eq!(result, vec!["Hello", "Goodbye"]); +} + +#[test] +fn re_exported_sleep_works() { + let val = trpl::block_on(async { + trpl::sleep(Duration::from_micros(1)).await; + "Done!" + }); + assert_eq!(val, "Done!"); +} + +#[test] +fn re_exported_channel_apis_work() { + trpl::block_on(async { + // Explicitly naming the type to confirm the re-exports are aligned. + let (tx, mut rx): (Sender<&str>, Receiver<&str>) = trpl::channel(); + + tx.send("Hello").unwrap(); + trpl::sleep(Duration::from_millis(1)).await; + tx.send("Goodbye").unwrap(); + drop(tx); + + assert_eq!(rx.recv().await, Some("Hello")); + assert_eq!(rx.recv().await, Some("Goodbye")); + assert_eq!(rx.recv().await, None); + }); +} + +mod re_exported_join_apis_work { + use super::*; + + #[test] + fn join_fn() { + let result = trpl::block_on(async { + let a = async { 1 }; + let b = async { 2 }; + trpl::join(a, b).await + }); + + assert_eq!(result, (1, 2)); + } + + #[test] + fn join3_fn() { + let result = trpl::block_on(async { + let a = async { 1 }; + let b = async { 2 }; + let c = async { 3 }; + + trpl::join3(a, b, c).await + }); + + assert_eq!(result, (1, 2, 3)); + } + + #[test] + fn join_all_fn() { + let result = trpl::block_on(async { + let a = async { format!("{}", 1) }; + + let b = async { "Hello".to_string() }; + + let outer = String::from("World"); + let c = async move { outer.to_string() }; + + let futures: Vec<Pin<Box<dyn Future<Output = String>>>> = + vec![Box::pin(a), Box::pin(b), Box::pin(c)]; + + trpl::join_all(futures).await + }); + + assert_eq!( + result, + vec![ + String::from("1"), + String::from("Hello"), + String::from("World") + ] + ); + } + + #[test] + fn join_macro() { + let result = trpl::block_on(async { + let a = async { 1 }; + let b = async { "Hello" }; + + let outer = vec![String::from("World")]; + let c = async move { outer }; + + trpl::join!(a, b, c) + }); + + assert_eq!(result, (1, "Hello", vec![String::from("World")])); + } +} + +#[test] +fn select() { + #[derive(Debug, PartialEq)] + struct Slow; + + #[derive(Debug, PartialEq)] + struct Fast; + + let val = trpl::block_on(async { + let slow = async { + trpl::sleep(Duration::from_millis(1_000)).await; + Slow + }; + + let fast = async { + trpl::sleep(Duration::from_millis(1)).await; + Fast + }; + + trpl::select(slow, fast).await + }); + + assert!(matches!(val, Either::Right(Fast))); +} + +#[test] +fn race_continues_to_work() { + #[derive(Debug, PartialEq)] + struct Slow; + + #[derive(Debug, PartialEq)] + struct Fast; + + let val = trpl::block_on(async { + let slow = async { + trpl::sleep(Duration::from_millis(1_000)).await; + Slow + }; + + let fast = async { + trpl::sleep(Duration::from_millis(1)).await; + Fast + }; + + trpl::race(slow, fast).await + }); + + assert!(matches!(val, Either::Right(Fast))); +} + +#[test] +fn yield_now() { + let result = trpl::block_on(async { + trpl::yield_now().await; + "done" + }); + + assert_eq!(result, "done"); +} + +#[test] +fn read_to_string() { + let result = trpl::block_on(async { + trpl::read_to_string("tests/integration/to-read.txt") + .await + .unwrap() + }); + + assert_eq!(result, String::from("This is some text!\n")); +} + +#[test] +fn stream_iter() { + use trpl::StreamExt; + + let result = trpl::block_on(async { + let ns = vec![1, 2, 3]; + let mut stream = trpl::stream_from_iter(ns); + let mut result = vec![]; + while let Some(n) = stream.next().await { + result.push(format!("{n}")); + } + result + }); + + assert_eq!( + result, + vec![String::from("1"), String::from("2"), String::from("3")] + ) +} + +#[test] +fn receiver_stream() { + use trpl::ReceiverStream; + use trpl::StreamExt; + + let result: Vec<u32> = trpl::block_on(async { + println!("startup"); + let (tx, rx) = trpl::channel(); + let rx_stream = ReceiverStream::new(rx); + println!("sending 123"); + tx.send(123).unwrap(); + drop(tx); // So the receiver channel closes! + + rx_stream.collect().await + }); + + assert_eq!(result, vec![123]); +} + +#[test] +fn re_exported_interval_stream_works() { + use trpl::{IntervalStream, StreamExt}; + + trpl::block_on(async { + let mut interval_stream = + IntervalStream::new(trpl::interval(Duration::from_millis(1))) + .take(1); + + assert!(interval_stream.next().await.is_some()); + assert!(interval_stream.next().await.is_none()); + }); +} + +#[test] +fn re_exported_html() { + use trpl::Html; + + let doc = Html::parse( + "<html><head><title>

Hello!

", + ); + let p = doc.select_first("p").map(|el| el.inner_html()); + assert_eq!(p, Some(String::from("Hello!"))); +} diff --git a/packages/trpl/tests/integration/to-read.txt b/packages/trpl/tests/integration/to-read.txt new file mode 100644 index 0000000000..2af04f5bdf --- /dev/null +++ b/packages/trpl/tests/integration/to-read.txt @@ -0,0 +1 @@ +This is some text! diff --git a/redirects/associated-types.md b/redirects/associated-types.md index b222f3298f..f91fc23d6f 100644 --- a/redirects/associated-types.md +++ b/redirects/associated-types.md @@ -14,4 +14,4 @@ pub trait Iterator { --- You can find the latest version of this information -[here](ch19-03-advanced-traits.html#specifying-placeholder-types-in-trait-definitions-with-associated-types). \ No newline at end of file +[here](ch20-02-advanced-traits.html#specifying-placeholder-types-in-trait-definitions-with-associated-types). diff --git a/redirects/choosing-your-guarantees.md b/redirects/choosing-your-guarantees.md index 3667258c66..d8a4e3a3f9 100644 --- a/redirects/choosing-your-guarantees.md +++ b/redirects/choosing-your-guarantees.md @@ -7,7 +7,7 @@ ```rust let b = Box::new(5); -println!("b = {}", b); +println!("b = {b}"); ``` --- diff --git a/redirects/const-and-static.md b/redirects/const-and-static.md index b87bdd3831..60b13f62ac 100644 --- a/redirects/const-and-static.md +++ b/redirects/const-and-static.md @@ -16,6 +16,6 @@ static HELLO_WORLD: &str = "Hello, world!"; You can find the latest version about constants [here](ch03-01-variables-and-mutability.html#constants), and about statics -[here](ch19-01-unsafe-rust.html#accessing-or-modifying-a-mutable-static-variable). +[here](ch20-01-unsafe-rust.html#accessing-or-modifying-a-mutable-static-variable). diff --git a/redirects/ffi.md b/redirects/ffi.md index 20ed3963ef..63308ab1de 100644 --- a/redirects/ffi.md +++ b/redirects/ffi.md @@ -20,4 +20,4 @@ fn main() { --- You can find the latest version of this information -[here](ch19-01-unsafe-rust.html#using-extern-functions-to-call-external-code) \ No newline at end of file +[here](ch20-01-unsafe-rust.html#using-extern-functions-to-call-external-code) diff --git a/redirects/iterators.md b/redirects/iterators.md index 26cb047668..d8a73dab87 100644 --- a/redirects/iterators.md +++ b/redirects/iterators.md @@ -11,7 +11,7 @@ let v1 = vec![1, 2, 3]; let v1_iter = v1.iter(); for val in v1_iter { - println!("Got: {}", val); + println!("Got: {val}"); } ``` diff --git a/redirects/lifetimes.md b/redirects/lifetimes.md index 21ddb38ce8..8a27ec1724 100644 --- a/redirects/lifetimes.md +++ b/redirects/lifetimes.md @@ -11,7 +11,7 @@ // | let r = &x; // --+--+-- 'a // | | - println!("r: {}", r); // | | + println!("r: {r}"); // | | // --+ | } // -----+ ``` diff --git a/redirects/loops.md b/redirects/loops.md index 1686c115ee..30c7d4059f 100644 --- a/redirects/loops.md +++ b/redirects/loops.md @@ -14,17 +14,17 @@ loop { let mut number = 3; while number != 0 { - println!("{}!", number); + println!("{number}!"); number = number - 1; } let a = [10, 20, 30, 40, 50]; for element in a.iter() { - println!("the value is: {}", element); + println!("the value is: {element}"); } ``` --- You can find the latest version of this information -[here](ch03-05-control-flow.html#repetition-with-loops). \ No newline at end of file +[here](ch03-05-control-flow.html#repetition-with-loops). diff --git a/redirects/macros.md b/redirects/macros.md index 08217d115d..f8ada9abf9 100644 --- a/redirects/macros.md +++ b/redirects/macros.md @@ -18,13 +18,13 @@ fn main() { Here are the relevant sections in the new and old books: -* **[In the current edition: Ch 19.06 Macros][2]** +* **[In the current edition: Ch 20.05 Macros][2]** * [Rust By Example: Macros][3] * [In the Rust Reference: Ch 3.1 — Macros by Example][4] * [In the first edition: Ch 3.34 — Macros][1] [1]: https://doc.rust-lang.org/1.30.0/book/first-edition/macros.html -[2]: ch19-06-macros.html +[2]: ch20-06-macros.html [3]: https://rustbyexample.com/macros.html [4]: ../reference/macros-by-example.html diff --git a/redirects/match.md b/redirects/match.md index fd28ba8dea..c76ffadb7a 100644 --- a/redirects/match.md +++ b/redirects/match.md @@ -28,11 +28,11 @@ fn value_in_cents(coin: Coin) -> u32 { Here are the relevant sections in the new and old books: * **[in the current edition: Ch 6.02 — The `match` Control Flow Operator][2]** -* [in the current edition: Ch 18.00 — Patterns][3] +* [in the current edition: Ch 19.00 — Patterns][3] * [In the first edition: Ch 3.14 — Match][1] [1]: https://doc.rust-lang.org/1.30.0/book/first-edition/match.html [2]: ch06-02-match.html -[3]: ch18-00-patterns.html +[3]: ch19-00-patterns.html diff --git a/redirects/mutability.md b/redirects/mutability.md index 89fc3b6f56..4e64953c10 100644 --- a/redirects/mutability.md +++ b/redirects/mutability.md @@ -6,9 +6,9 @@ ```rust let mut x = 5; -println!("The value of x is: {}", x); +println!("The value of x is: {x}"); x = 6; -println!("The value of x is: {}", x); +println!("The value of x is: {x}"); ``` --- diff --git a/redirects/operators-and-overloading.md b/redirects/operators-and-overloading.md index ff9a33048a..b77cf7c913 100644 --- a/redirects/operators-and-overloading.md +++ b/redirects/operators-and-overloading.md @@ -33,4 +33,4 @@ fn main() { --- You can find the latest version of this information -[here](ch19-03-advanced-traits.html). +[here](ch20-02-advanced-traits.html). diff --git a/redirects/procedural-macros.md b/redirects/procedural-macros.md index bf6665f1a6..7c72392b70 100644 --- a/redirects/procedural-macros.md +++ b/redirects/procedural-macros.md @@ -9,13 +9,13 @@ This chapter does not exist yet in [the second edition][2]. You can check out other resources that describe macros. -* **[In the current edition: Ch 19.06 Macros][2]** +* **[In the current edition: Ch 20.05 Macros][2]** * [In the Rust Reference: Ch 3.2 — Procedural Macros][4] * [The `proc_macro` crate documentation][3] * [In the first edition: Ch 4.13 — Procedural Macros (and custom Derive)][1] [1]: https://doc.rust-lang.org/1.30.0/book/first-edition/procedural-macros.html -[2]: ch19-06-macros.html +[2]: ch20-05-macros.html [3]: ../proc_macro/index.html [4]: ../reference/procedural-macros.html diff --git a/redirects/raw-pointers.md b/redirects/raw-pointers.md index 773f3abc48..4076907b5c 100644 --- a/redirects/raw-pointers.md +++ b/redirects/raw-pointers.md @@ -14,4 +14,4 @@ let r2 = &mut num as *mut i32; --- You can find the latest version of this information -[here](ch19-01-unsafe-rust.html#dereferencing-a-raw-pointer) \ No newline at end of file +[here](ch20-01-unsafe-rust.html#dereferencing-a-raw-pointer) diff --git a/redirects/release-channels.md b/redirects/release-channels.md index 6e01e227fe..bf2f87315d 100644 --- a/redirects/release-channels.md +++ b/redirects/release-channels.md @@ -22,7 +22,7 @@ You can check out other resources that describe release channels. [1]: https://doc.rust-lang.org/1.30.0/book/first-edition/release-channels.html [2]: appendix-07-nightly-rust.html -[3]: https://github.com/rust-lang/rfcs/blob/master/text/0507-release-channels.md -[4]: https://github.com/rust-lang-nursery/rustup.rs/blob/master/README.md#keeping-rust-up-to-date +[3]: https://github.com/rust-lang/rfcs/blob/HEAD/text/0507-release-channels.md +[4]: https://github.com/rust-lang-nursery/rustup.rs/blob/HEAD/README.md#keeping-rust-up-to-date [5]: https://www.rust-lang.org/en-US/tools/install diff --git a/redirects/trait-objects.md b/redirects/trait-objects.md index 3200e26a15..a0e7438d45 100644 --- a/redirects/trait-objects.md +++ b/redirects/trait-objects.md @@ -60,9 +60,9 @@ fn main() { Here are the relevant sections in the new and old books: -* **[in the current edition: Ch 17.02 — Trait Objects][2]** +* **[in the current edition: Ch 18.02 — Trait Objects][2]** * [In the first edition: Ch 3.22 — Trait Objects][1] [1]: https://doc.rust-lang.org/1.30.0/book/first-edition/trait-objects.html -[2]: ch17-02-trait-objects.html +[2]: ch18-02-trait-objects.html diff --git a/redirects/traits.md b/redirects/traits.md index dcb577e97b..2ff60daae2 100644 --- a/redirects/traits.md +++ b/redirects/traits.md @@ -15,10 +15,10 @@ pub trait Summarizable { Here are the relevant sections in the new and old books: * **[in the current edition: Ch 10.02 — Traits][2]** -* [in the current edition: Ch 19.03 — Advanced Traits][3] +* [in the current edition: Ch 20.02 — Advanced Traits][3] * [In the first edition: Ch 3.19 — Traits][1] [1]: https://doc.rust-lang.org/1.30.0/book/first-edition/traits.html [2]: ch10-02-traits.html -[3]: ch19-03-advanced-traits.html +[3]: ch20-02-advanced-traits.html diff --git a/redirects/type-aliases.md b/redirects/type-aliases.md index 85cd4c9ecc..986e7b9e33 100644 --- a/redirects/type-aliases.md +++ b/redirects/type-aliases.md @@ -11,4 +11,4 @@ type Kilometers = i32; --- You can find the latest version of this information -[here](ch19-04-advanced-types.html#creating-type-synonyms-with-type-aliases). \ No newline at end of file +[here](ch20-03-advanced-types.html#creating-type-synonyms-with-type-aliases). diff --git a/redirects/ufcs.md b/redirects/ufcs.md index 2959c06bd0..383465398b 100644 --- a/redirects/ufcs.md +++ b/redirects/ufcs.md @@ -45,4 +45,4 @@ fn main() { --- You can find the latest version of this information -[here](ch19-03-advanced-traits.html#fully-qualified-syntax-for-disambiguation-calling-methods-with-the-same-name). \ No newline at end of file +[here](ch20-02-advanced-traits.html#fully-qualified-syntax-for-disambiguation-calling-methods-with-the-same-name). diff --git a/redirects/unsafe.md b/redirects/unsafe.md index 8628c7aa95..7d9adb39d8 100644 --- a/redirects/unsafe.md +++ b/redirects/unsafe.md @@ -8,11 +8,11 @@ Here are the relevant sections in the new and old books: -* **[in the current edition: Ch 19.01 — Unsafe Rust][2]** +* **[in the current edition: Ch 20.01 — Unsafe Rust][2]** * [The Rustonomicon, The Dark Arts of Advanced and Unsafe Rust Programming][3] * [In the first edition: Ch 3.36 — `unsafe`][1] [1]: https://doc.rust-lang.org/1.30.0/book/first-edition/unsafe.html -[2]: ch19-01-unsafe-rust.html +[2]: ch20-01-unsafe-rust.html [3]: ../nomicon/index.html diff --git a/redirects/unsized-types.md b/redirects/unsized-types.md index bd9582cbac..a9ca1e03e0 100644 --- a/redirects/unsized-types.md +++ b/redirects/unsized-types.md @@ -15,4 +15,4 @@ fn generic(t: &T) { --- You can find the latest version of this information -[here](ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait). \ No newline at end of file +[here](ch20-03-advanced-types.html#dynamically-sized-types-and-the-sized-trait). diff --git a/rust-toolchain b/rust-toolchain index 9ebd7af328..e87fb34ea9 100644 --- a/rust-toolchain +++ b/rust-toolchain @@ -1 +1 @@ -1.67 +1.90 diff --git a/second-edition/book.toml b/second-edition/book.toml index 9789a435c2..64d5099081 100644 --- a/second-edition/book.toml +++ b/second-edition/book.toml @@ -1,3 +1,3 @@ [book] title = "The Rust Programming Language" -author = "Steve Klabnik and Carol Nichols, with Contributions from the Rust Community" +authors = ["Steve Klabnik", "Carol Nichols", "Contributions from the Rust Community"] diff --git a/second-edition/src/appendix-04-macros.md b/second-edition/src/appendix-04-macros.md index 2798b5d50a..f04f9eb4e8 100644 --- a/second-edition/src/appendix-04-macros.md +++ b/second-edition/src/appendix-04-macros.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-06-macros.html) instead. +version of the book](../ch20-05-macros.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/appendix-04-macros.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/appendix-04-macros.html). diff --git a/second-edition/src/ch17-00-oop.md b/second-edition/src/ch17-00-oop.md index 752130915e..e3633405f1 100644 --- a/second-edition/src/ch17-00-oop.md +++ b/second-edition/src/ch17-00-oop.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-00-oop.html) instead. +version of the book](../ch18-00-oop.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-00-oop.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-00-oop.html). diff --git a/second-edition/src/ch17-01-what-is-oo.md b/second-edition/src/ch17-01-what-is-oo.md index 82c1ed8f9c..a705d19416 100644 --- a/second-edition/src/ch17-01-what-is-oo.md +++ b/second-edition/src/ch17-01-what-is-oo.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-01-what-is-oo.html) instead. +version of the book](../ch18-01-what-is-oo.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-01-what-is-oo.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-01-what-is-oo.html). diff --git a/second-edition/src/ch17-02-trait-objects.md b/second-edition/src/ch17-02-trait-objects.md index 35f0c18835..16dad6368e 100644 --- a/second-edition/src/ch17-02-trait-objects.md +++ b/second-edition/src/ch17-02-trait-objects.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-02-trait-objects.html) instead. +version of the book](../ch18-02-trait-objects.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-02-trait-objects.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-02-trait-objects.html). diff --git a/second-edition/src/ch17-03-oo-design-patterns.md b/second-edition/src/ch17-03-oo-design-patterns.md index 46bec2692f..b29dc2393c 100644 --- a/second-edition/src/ch17-03-oo-design-patterns.md +++ b/second-edition/src/ch17-03-oo-design-patterns.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch17-03-oo-design-patterns.html) instead. +version of the book](../ch18-03-oo-design-patterns.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-03-oo-design-patterns.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch17-03-oo-design-patterns.html). diff --git a/second-edition/src/ch18-00-patterns.md b/second-edition/src/ch18-00-patterns.md index 6bd221fa3c..e315b35274 100644 --- a/second-edition/src/ch18-00-patterns.md +++ b/second-edition/src/ch18-00-patterns.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-00-patterns.html) instead. +version of the book](../ch19-00-patterns.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-00-patterns.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-00-patterns.html). diff --git a/second-edition/src/ch18-01-all-the-places-for-patterns.md b/second-edition/src/ch18-01-all-the-places-for-patterns.md index 0374a9a883..4a76aded0a 100644 --- a/second-edition/src/ch18-01-all-the-places-for-patterns.md +++ b/second-edition/src/ch18-01-all-the-places-for-patterns.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-01-all-the-places-for-patterns.html) instead. +version of the book](../ch19-01-all-the-places-for-patterns.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-01-all-the-places-for-patterns.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-01-all-the-places-for-patterns.html). diff --git a/second-edition/src/ch18-02-refutability.md b/second-edition/src/ch18-02-refutability.md index 2ef5206afd..768df16b25 100644 --- a/second-edition/src/ch18-02-refutability.md +++ b/second-edition/src/ch18-02-refutability.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-02-refutability.html) instead. +version of the book](../ch19-02-refutability.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-02-refutability.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-02-refutability.html). diff --git a/second-edition/src/ch18-03-pattern-syntax.md b/second-edition/src/ch18-03-pattern-syntax.md index 31c5f79203..08676091e1 100644 --- a/second-edition/src/ch18-03-pattern-syntax.md +++ b/second-edition/src/ch18-03-pattern-syntax.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch18-03-pattern-syntax.html) instead. +version of the book](../ch19-03-pattern-syntax.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-03-pattern-syntax.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch18-03-pattern-syntax.html). diff --git a/second-edition/src/ch19-00-advanced-features.md b/second-edition/src/ch19-00-advanced-features.md index f6df05f0aa..3633c0548e 100644 --- a/second-edition/src/ch19-00-advanced-features.md +++ b/second-edition/src/ch19-00-advanced-features.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-00-advanced-features.html) instead. +version of the book](../ch20-00-advanced-features.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-00-advanced-features.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-00-advanced-features.html). diff --git a/second-edition/src/ch19-01-unsafe-rust.md b/second-edition/src/ch19-01-unsafe-rust.md index 8a9a29c096..0e740ce03d 100644 --- a/second-edition/src/ch19-01-unsafe-rust.md +++ b/second-edition/src/ch19-01-unsafe-rust.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-01-unsafe-rust.html) instead. +version of the book](../ch20-01-unsafe-rust.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-01-unsafe-rust.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-01-unsafe-rust.html). diff --git a/second-edition/src/ch19-03-advanced-traits.md b/second-edition/src/ch19-03-advanced-traits.md index cc8433fb38..07c9d71a54 100644 --- a/second-edition/src/ch19-03-advanced-traits.md +++ b/second-edition/src/ch19-03-advanced-traits.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-03-advanced-traits.html) instead. +version of the book](../ch20-02-advanced-traits.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-03-advanced-traits.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-03-advanced-traits.html). diff --git a/second-edition/src/ch19-04-advanced-types.md b/second-edition/src/ch19-04-advanced-types.md index 5081457292..153ad9cf44 100644 --- a/second-edition/src/ch19-04-advanced-types.md +++ b/second-edition/src/ch19-04-advanced-types.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-04-advanced-types.html) instead. +version of the book](../ch20-03-advanced-types.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-04-advanced-types.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-04-advanced-types.html). diff --git a/second-edition/src/ch19-05-advanced-functions-and-closures.md b/second-edition/src/ch19-05-advanced-functions-and-closures.md index 18d369c60d..2d8b64c07d 100644 --- a/second-edition/src/ch19-05-advanced-functions-and-closures.md +++ b/second-edition/src/ch19-05-advanced-functions-and-closures.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch19-05-advanced-functions-and-closures.html) instead. +version of the book](../ch20-04-advanced-functions-and-closures.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-05-advanced-functions-and-closures.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch19-05-advanced-functions-and-closures.html). diff --git a/second-edition/src/ch20-00-final-project-a-web-server.md b/second-edition/src/ch20-00-final-project-a-web-server.md index 059d6824c3..0c99ac623b 100644 --- a/second-edition/src/ch20-00-final-project-a-web-server.md +++ b/second-edition/src/ch20-00-final-project-a-web-server.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-00-final-project-a-web-server.html) instead. +version of the book](../ch21-00-final-project-a-web-server.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-00-final-project-a-web-server.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-00-final-project-a-web-server.html). diff --git a/second-edition/src/ch20-01-single-threaded.md b/second-edition/src/ch20-01-single-threaded.md index 5ff97a2ee1..a06b0cbc1a 100644 --- a/second-edition/src/ch20-01-single-threaded.md +++ b/second-edition/src/ch20-01-single-threaded.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-01-single-threaded.html) instead. +version of the book](../ch21-01-single-threaded.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-01-single-threaded.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-01-single-threaded.html). diff --git a/second-edition/src/ch20-02-multithreaded.md b/second-edition/src/ch20-02-multithreaded.md index 0695d2451c..8826bd9f1a 100644 --- a/second-edition/src/ch20-02-multithreaded.md +++ b/second-edition/src/ch20-02-multithreaded.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-02-multithreaded.html) instead. +version of the book](../ch21-02-multithreaded.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-02-multithreaded.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-02-multithreaded.html). diff --git a/second-edition/src/ch20-03-graceful-shutdown-and-cleanup.md b/second-edition/src/ch20-03-graceful-shutdown-and-cleanup.md index eb7ed59879..457b294f90 100644 --- a/second-edition/src/ch20-03-graceful-shutdown-and-cleanup.md +++ b/second-edition/src/ch20-03-graceful-shutdown-and-cleanup.md @@ -3,8 +3,8 @@ The second edition of the book is no longer distributed with Rust's documentation. If you came here via a link or web search, you may want to check out [the current -version of the book](../ch20-03-graceful-shutdown-and-cleanup.html) instead. +version of the book](../ch21-03-graceful-shutdown-and-cleanup.html) instead. If you have an internet connection, you can [find a copy distributed with Rust -1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-03-graceful-shutdown-and-cleanup.html). \ No newline at end of file +1.30](https://doc.rust-lang.org/1.30.0/book/second-edition/ch20-03-graceful-shutdown-and-cleanup.html). diff --git a/src/SUMMARY.md b/src/SUMMARY.md index b4b58afdee..c641650c92 100644 --- a/src/SUMMARY.md +++ b/src/SUMMARY.md @@ -1,135 +1,134 @@ # The Rust Programming Language -[The Rust Programming Language](title-page.md) -[Foreword](foreword.md) +[The Rust Programming Language](title-page.md) [Foreword](foreword.md) [Introduction](ch00-00-introduction.md) -## Getting started - - [Getting Started](ch01-00-getting-started.md) - - [Installation](ch01-01-installation.md) - - [Hello, World!](ch01-02-hello-world.md) - - [Hello, Cargo!](ch01-03-hello-cargo.md) + - [Installation](ch01-01-installation.md) + - [Hello, World!](ch01-02-hello-world.md) + - [Hello, Cargo!](ch01-03-hello-cargo.md) -- [Programming a Guessing Game](ch02-00-guessing-game-tutorial.md) +- [Bikin Game Tebak Angka](ch02-00-guessing-game-tutorial.md) - [Common Programming Concepts](ch03-00-common-programming-concepts.md) - - [Variables and Mutability](ch03-01-variables-and-mutability.md) - - [Data Types](ch03-02-data-types.md) - - [Functions](ch03-03-how-functions-work.md) - - [Comments](ch03-04-comments.md) - - [Control Flow](ch03-05-control-flow.md) + - [Variables and Mutability](ch03-01-variables-and-mutability.md) + - [Data Types](ch03-02-data-types.md) + - [Functions](ch03-03-how-functions-work.md) + - [Comments](ch03-04-comments.md) + - [Control Flow](ch03-05-control-flow.md) - [Understanding Ownership](ch04-00-understanding-ownership.md) - - [What is Ownership?](ch04-01-what-is-ownership.md) - - [References and Borrowing](ch04-02-references-and-borrowing.md) - - [The Slice Type](ch04-03-slices.md) + - [What is Ownership?](ch04-01-what-is-ownership.md) + - [References and Borrowing](ch04-02-references-and-borrowing.md) + - [The Slice Type](ch04-03-slices.md) - [Using Structs to Structure Related Data](ch05-00-structs.md) - - [Defining and Instantiating Structs](ch05-01-defining-structs.md) - - [An Example Program Using Structs](ch05-02-example-structs.md) - - [Method Syntax](ch05-03-method-syntax.md) + - [Defining and Instantiating Structs](ch05-01-defining-structs.md) + - [An Example Program Using Structs](ch05-02-example-structs.md) + - [Methods](ch05-03-method-syntax.md) - [Enums and Pattern Matching](ch06-00-enums.md) - - [Defining an Enum](ch06-01-defining-an-enum.md) - - [The `match` Control Flow Construct](ch06-02-match.md) - - [Concise Control Flow with `if let`](ch06-03-if-let.md) - -## Basic Rust Literacy + - [Defining an Enum](ch06-01-defining-an-enum.md) + - [The `match` Control Flow Construct](ch06-02-match.md) + - [Concise Control Flow with `if let` and `let...else`](ch06-03-if-let.md) -- [Managing Growing Projects with Packages, Crates, and Modules](ch07-00-managing-growing-projects-with-packages-crates-and-modules.md) - - [Packages and Crates](ch07-01-packages-and-crates.md) - - [Defining Modules to Control Scope and Privacy](ch07-02-defining-modules-to-control-scope-and-privacy.md) - - [Paths for Referring to an Item in the Module Tree](ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md) - - [Bringing Paths Into Scope with the `use` Keyword](ch07-04-bringing-paths-into-scope-with-the-use-keyword.md) - - [Separating Modules into Different Files](ch07-05-separating-modules-into-different-files.md) +- [Packages, Crates, and Modules](ch07-00-managing-growing-projects-with-packages-crates-and-modules.md) + - [Packages and Crates](ch07-01-packages-and-crates.md) + - [Control Scope and Privacy with Modules](ch07-02-defining-modules-to-control-scope-and-privacy.md) + - [Paths for Referring to an Item in the Module Tree](ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md) + - [Bringing Paths Into Scope with the `use` Keyword](ch07-04-bringing-paths-into-scope-with-the-use-keyword.md) + - [Separating Modules into Different Files](ch07-05-separating-modules-into-different-files.md) - [Common Collections](ch08-00-common-collections.md) - - [Storing Lists of Values with Vectors](ch08-01-vectors.md) - - [Storing UTF-8 Encoded Text with Strings](ch08-02-strings.md) - - [Storing Keys with Associated Values in Hash Maps](ch08-03-hash-maps.md) + - [Storing Lists of Values with Vectors](ch08-01-vectors.md) + - [Storing UTF-8 Encoded Text with Strings](ch08-02-strings.md) + - [Storing Keys with Associated Values in Hash Maps](ch08-03-hash-maps.md) - [Error Handling](ch09-00-error-handling.md) - - [Unrecoverable Errors with `panic!`](ch09-01-unrecoverable-errors-with-panic.md) - - [Recoverable Errors with `Result`](ch09-02-recoverable-errors-with-result.md) - - [To `panic!` or Not to `panic!`](ch09-03-to-panic-or-not-to-panic.md) + - [Unrecoverable Errors with `panic!`](ch09-01-unrecoverable-errors-with-panic.md) + - [Recoverable Errors with `Result`](ch09-02-recoverable-errors-with-result.md) + - [To `panic!` or Not to `panic!`](ch09-03-to-panic-or-not-to-panic.md) - [Generic Types, Traits, and Lifetimes](ch10-00-generics.md) - - [Generic Data Types](ch10-01-syntax.md) - - [Traits: Defining Shared Behavior](ch10-02-traits.md) - - [Validating References with Lifetimes](ch10-03-lifetime-syntax.md) + - [Generic Data Types](ch10-01-syntax.md) + - [Defining Shared Behavior with Traits](ch10-02-traits.md) + - [Validating References with Lifetimes](ch10-03-lifetime-syntax.md) - [Writing Automated Tests](ch11-00-testing.md) - - [How to Write Tests](ch11-01-writing-tests.md) - - [Controlling How Tests Are Run](ch11-02-running-tests.md) - - [Test Organization](ch11-03-test-organization.md) - -- [An I/O Project: Building a Command Line Program](ch12-00-an-io-project.md) - - [Accepting Command Line Arguments](ch12-01-accepting-command-line-arguments.md) - - [Reading a File](ch12-02-reading-a-file.md) - - [Refactoring to Improve Modularity and Error Handling](ch12-03-improving-error-handling-and-modularity.md) - - [Developing the Library’s Functionality with Test Driven Development](ch12-04-testing-the-librarys-functionality.md) - - [Working with Environment Variables](ch12-05-working-with-environment-variables.md) - - [Writing Error Messages to Standard Error Instead of Standard Output](ch12-06-writing-to-stderr-instead-of-stdout.md) - -## Thinking in Rust + - [How to Write Tests](ch11-01-writing-tests.md) + - [Controlling How Tests Are Run](ch11-02-running-tests.md) + - [Test Organization](ch11-03-test-organization.md) + +- [Proyek I/O: Membangun Program Command Line](ch12-00-an-io-project.md) + - [Menerima Argumen dari Command Line](ch12-01-accepting-command-line-arguments.md) + - [Membaca File](ch12-02-reading-a-file.md) + - [Refactoring untuk Meningkatkan Modularitas dan Penanganan Error](ch12-03-improving-error-handling-and-modularity.md) + - [Nambahin Fungsionalitas pakai Test-Driven Development](ch12-04-testing-the-librarys-functionality.md) + - [Bekerja dengan Environment Variable](ch12-05-working-with-environment-variables.md) + - [Ngeredirect Error ke Standard Error](ch12-06-writing-to-stderr-instead-of-stdout.md) - [Functional Language Features: Iterators and Closures](ch13-00-functional-features.md) - - [Closures: Anonymous Functions that Capture Their Environment](ch13-01-closures.md) - - [Processing a Series of Items with Iterators](ch13-02-iterators.md) - - [Improving Our I/O Project](ch13-03-improving-our-io-project.md) - - [Comparing Performance: Loops vs. Iterators](ch13-04-performance.md) + - [Closures](ch13-01-closures.md) + - [Processing a Series of Items with Iterators](ch13-02-iterators.md) + - [Improving Our I/O Project](ch13-03-improving-our-io-project.md) + - [Performance in Loops vs. Iterators](ch13-04-performance.md) - [More about Cargo and Crates.io](ch14-00-more-about-cargo.md) - - [Customizing Builds with Release Profiles](ch14-01-release-profiles.md) - - [Publishing a Crate to Crates.io](ch14-02-publishing-to-crates-io.md) - - [Cargo Workspaces](ch14-03-cargo-workspaces.md) - - [Installing Binaries from Crates.io with `cargo install`](ch14-04-installing-binaries.md) - - [Extending Cargo with Custom Commands](ch14-05-extending-cargo.md) + - [Customizing Builds with Release Profiles](ch14-01-release-profiles.md) + - [Publishing a Crate to Crates.io](ch14-02-publishing-to-crates-io.md) + - [Cargo Workspaces](ch14-03-cargo-workspaces.md) + - [Installing Binaries with `cargo install`](ch14-04-installing-binaries.md) + - [Extending Cargo with Custom Commands](ch14-05-extending-cargo.md) - [Smart Pointers](ch15-00-smart-pointers.md) - - [Using `Box` to Point to Data on the Heap](ch15-01-box.md) - - [Treating Smart Pointers Like Regular References with the `Deref` Trait](ch15-02-deref.md) - - [Running Code on Cleanup with the `Drop` Trait](ch15-03-drop.md) - - [`Rc`, the Reference Counted Smart Pointer](ch15-04-rc.md) - - [`RefCell` and the Interior Mutability Pattern](ch15-05-interior-mutability.md) - - [Reference Cycles Can Leak Memory](ch15-06-reference-cycles.md) + - [Using `Box` to Point to Data on the Heap](ch15-01-box.md) + - [Treating Smart Pointers Like Regular References](ch15-02-deref.md) + - [Running Code on Cleanup with the `Drop` Trait](ch15-03-drop.md) + - [`Rc`, the Reference Counted Smart Pointer](ch15-04-rc.md) + - [`RefCell` and the Interior Mutability Pattern](ch15-05-interior-mutability.md) + - [Reference Cycles Can Leak Memory](ch15-06-reference-cycles.md) - [Fearless Concurrency](ch16-00-concurrency.md) - - [Using Threads to Run Code Simultaneously](ch16-01-threads.md) - - [Using Message Passing to Transfer Data Between Threads](ch16-02-message-passing.md) - - [Shared-State Concurrency](ch16-03-shared-state.md) - - [Extensible Concurrency with the `Sync` and `Send` Traits](ch16-04-extensible-concurrency-sync-and-send.md) - -- [Object Oriented Programming Features of Rust](ch17-00-oop.md) - - [Characteristics of Object-Oriented Languages](ch17-01-what-is-oo.md) - - [Using Trait Objects That Allow for Values of Different Types](ch17-02-trait-objects.md) - - [Implementing an Object-Oriented Design Pattern](ch17-03-oo-design-patterns.md) - -## Advanced Topics - -- [Patterns and Matching](ch18-00-patterns.md) - - [All the Places Patterns Can Be Used](ch18-01-all-the-places-for-patterns.md) - - [Refutability: Whether a Pattern Might Fail to Match](ch18-02-refutability.md) - - [Pattern Syntax](ch18-03-pattern-syntax.md) - -- [Advanced Features](ch19-00-advanced-features.md) - - [Unsafe Rust](ch19-01-unsafe-rust.md) - - [Advanced Traits](ch19-03-advanced-traits.md) - - [Advanced Types](ch19-04-advanced-types.md) - - [Advanced Functions and Closures](ch19-05-advanced-functions-and-closures.md) - - [Macros](ch19-06-macros.md) - -- [Final Project: Building a Multithreaded Web Server](ch20-00-final-project-a-web-server.md) - - [Building a Single-Threaded Web Server](ch20-01-single-threaded.md) - - [Turning Our Single-Threaded Server into a Multithreaded Server](ch20-02-multithreaded.md) - - [Graceful Shutdown and Cleanup](ch20-03-graceful-shutdown-and-cleanup.md) + - [Using Threads to Run Code Simultaneously](ch16-01-threads.md) + - [Transfer Data Between Threads with Message Passing](ch16-02-message-passing.md) + - [Shared-State Concurrency](ch16-03-shared-state.md) + - [Extensible Concurrency with `Send` and `Sync`](ch16-04-extensible-concurrency-sync-and-send.md) + +- [Fundamentals of Asynchronous Programming: Async, Await, Futures, and Streams](ch17-00-async-await.md) + - [Futures and the Async Syntax](ch17-01-futures-and-syntax.md) + - [Applying Concurrency with Async](ch17-02-concurrency-with-async.md) + - [Working With Any Number of Futures](ch17-03-more-futures.md) + - [Streams: Futures in Sequence](ch17-04-streams.md) + - [A Closer Look at the Traits for Async](ch17-05-traits-for-async.md) + - [Futures, Tasks, and Threads](ch17-06-futures-tasks-threads.md) + +- [Object Oriented Programming Features](ch18-00-oop.md) + - [Characteristics of Object-Oriented Languages](ch18-01-what-is-oo.md) + - [Using Trait Objects to Abstract over Shared Behavior](ch18-02-trait-objects.md) + - [Implementing an Object-Oriented Design Pattern](ch18-03-oo-design-patterns.md) + +- [Patterns and Matching](ch19-00-patterns.md) + - [All the Places Patterns Can Be Used](ch19-01-all-the-places-for-patterns.md) + - [Refutability: Whether a Pattern Might Fail to Match](ch19-02-refutability.md) + - [Pattern Syntax](ch19-03-pattern-syntax.md) + +- [Advanced Features](ch20-00-advanced-features.md) + - [Unsafe Rust](ch20-01-unsafe-rust.md) + - [Advanced Traits](ch20-02-advanced-traits.md) + - [Advanced Types](ch20-03-advanced-types.md) + - [Advanced Functions and Closures](ch20-04-advanced-functions-and-closures.md) + - [Macros](ch20-05-macros.md) + +- [Proyek Final: Membangun Web Server Multithreaded](ch21-00-final-project-a-web-server.md) + - [Membangun Web Server Single-Threaded](ch21-01-single-threaded.md) + - [Dari Server Single-Threaded ke Multithreaded](ch21-02-multithreaded.md) + - [Shutdown Santai & Cleanup yang Rapi](ch21-03-graceful-shutdown-and-cleanup.md) - [Appendix](appendix-00.md) - - [A - Keywords](appendix-01-keywords.md) - - [B - Operators and Symbols](appendix-02-operators.md) - - [C - Derivable Traits](appendix-03-derivable-traits.md) - - [D - Useful Development Tools](appendix-04-useful-development-tools.md) - - [E - Editions](appendix-05-editions.md) - - [F - Translations of the Book](appendix-06-translation.md) - - [G - How Rust is Made and “Nightly Rust”](appendix-07-nightly-rust.md) + - [A - Keywords](appendix-01-keywords.md) + - [B - Operators and Symbols](appendix-02-operators.md) + - [C - Derivable Traits](appendix-03-derivable-traits.md) + - [D - Useful Development Tools](appendix-04-useful-development-tools.md) + - [E - Editions](appendix-05-editions.md) + - [F - Translations of the Book](appendix-06-translation.md) + - [G - How Rust is Made and “Nightly Rust”](appendix-07-nightly-rust.md) diff --git a/src/appendix-01-keywords.md b/src/appendix-01-keywords.md index b848945915..5d4716b934 100644 --- a/src/appendix-01-keywords.md +++ b/src/appendix-01-keywords.md @@ -1,9 +1,9 @@ ## Appendix A: Keywords -The following list contains keywords that are reserved for current or future +The following lists contain keywords that are reserved for current or future use by the Rust language. As such, they cannot be used as identifiers (except -as raw identifiers as we’ll discuss in the “[Raw -Identifiers][raw-identifiers]” section). Identifiers are names +as raw identifiers, as we discuss in the [“Raw +Identifiers”][raw-identifiers] section). _Identifiers_ are names of functions, variables, parameters, struct fields, modules, crates, constants, macros, static values, attributes, types, traits, or lifetimes. @@ -14,73 +14,76 @@ macros, static values, attributes, types, traits, or lifetimes. The following is a list of keywords currently in use, with their functionality described. -* `as` - perform primitive casting, disambiguate the specific trait containing - an item, or rename items in `use` statements -* `async` - return a `Future` instead of blocking the current thread -* `await` - suspend execution until the result of a `Future` is ready -* `break` - exit a loop immediately -* `const` - define constant items or constant raw pointers -* `continue` - continue to the next loop iteration -* `crate` - in a module path, refers to the crate root -* `dyn` - dynamic dispatch to a trait object -* `else` - fallback for `if` and `if let` control flow constructs -* `enum` - define an enumeration -* `extern` - link an external function or variable -* `false` - Boolean false literal -* `fn` - define a function or the function pointer type -* `for` - loop over items from an iterator, implement a trait, or specify a - higher-ranked lifetime -* `if` - branch based on the result of a conditional expression -* `impl` - implement inherent or trait functionality -* `in` - part of `for` loop syntax -* `let` - bind a variable -* `loop` - loop unconditionally -* `match` - match a value to patterns -* `mod` - define a module -* `move` - make a closure take ownership of all its captures -* `mut` - denote mutability in references, raw pointers, or pattern bindings -* `pub` - denote public visibility in struct fields, `impl` blocks, or modules -* `ref` - bind by reference -* `return` - return from function -* `Self` - a type alias for the type we are defining or implementing -* `self` - method subject or current module -* `static` - global variable or lifetime lasting the entire program execution -* `struct` - define a structure -* `super` - parent module of the current module -* `trait` - define a trait -* `true` - Boolean true literal -* `type` - define a type alias or associated type -* `union` - define a [union][union]; is only a keyword when used - in a union declaration -* `unsafe` - denote unsafe code, functions, traits, or implementations -* `use` - bring symbols into scope -* `where` - denote clauses that constrain a type -* `while` - loop conditionally based on the result of an expression +- **`as`**: Perform primitive casting, disambiguate the specific trait + containing an item, or rename items in `use` statements. +- **`async`**: Return a `Future` instead of blocking the current thread. +- **`await`**: Suspend execution until the result of a `Future` is ready. +- **`break`**: Exit a loop immediately. +- **`const`**: Define constant items or constant raw pointers. +- **`continue`**: Continue to the next loop iteration. +- **`crate`**: In a module path, refers to the crate root. +- **`dyn`**: Dynamic dispatch to a trait object. +- **`else`**: Fallback for `if` and `if let` control flow constructs. +- **`enum`**: Define an enumeration. +- **`extern`**: Link an external function or variable. +- **`false`**: Boolean false literal. +- **`fn`**: Define a function or the function pointer type. +- **`for`**: Loop over items from an iterator, implement a trait, or specify a + higher ranked lifetime. +- **`if`**: Branch based on the result of a conditional expression. +- **`impl`**: Implement inherent or trait functionality. +- **`in`**: Part of `for` loop syntax. +- **`let`**: Bind a variable. +- **`loop`**: Loop unconditionally. +- **`match`**: Match a value to patterns. +- **`mod`**: Define a module. +- **`move`**: Make a closure take ownership of all its captures. +- **`mut`**: Denote mutability in references, raw pointers, or pattern bindings. +- **`pub`**: Denote public visibility in struct fields, `impl` blocks, or + modules. +- **`ref`**: Bind by reference. +- **`return`**: Return from function. +- **`Self`**: A type alias for the type we are defining or implementing. +- **`self`**: Method subject or current module. +- **`static`**: Global variable or lifetime lasting the entire program + execution. +- **`struct`**: Define a structure. +- **`super`**: Parent module of the current module. +- **`trait`**: Define a trait. +- **`true`**: Boolean true literal. +- **`type`**: Define a type alias or associated type. +- **`union`**: Define a [union][union]; is a keyword only when + used in a union declaration. +- **`unsafe`**: Denote unsafe code, functions, traits, or implementations. +- **`use`**: Bring symbols into scope. +- **`where`**: Denote clauses that constrain a type. +- **`while`**: Loop conditionally based on the result of an expression. [union]: ../reference/items/unions.html ### Keywords Reserved for Future Use The following keywords do not yet have any functionality but are reserved by -Rust for potential future use. - -* `abstract` -* `become` -* `box` -* `do` -* `final` -* `macro` -* `override` -* `priv` -* `try` -* `typeof` -* `unsized` -* `virtual` -* `yield` +Rust for potential future use: + +- `abstract` +- `become` +- `box` +- `do` +- `final` +- `gen` +- `macro` +- `override` +- `priv` +- `try` +- `typeof` +- `unsized` +- `virtual` +- `yield` ### Raw Identifiers -*Raw identifiers* are the syntax that lets you use keywords where they wouldn’t +_Raw identifiers_ are the syntax that lets you use keywords where they wouldn’t normally be allowed. You use a raw identifier by prefixing a keyword with `r#`. For example, `match` is a keyword. If you try to compile the following function @@ -124,14 +127,14 @@ This code will compile without any errors. Note the `r#` prefix on the function name in its definition as well as where the function is called in `main`. Raw identifiers allow you to use any word you choose as an identifier, even if -that word happens to be a reserved keyword. This gives us more freedom to -choose identifier names, as well as lets us integrate with programs written in -a language where these words aren’t keywords. In addition, raw identifiers -allow you to use libraries written in a different Rust edition than your crate -uses. For example, `try` isn’t a keyword in the 2015 edition but is in the 2018 -edition. If you depend on a library that’s written using the 2015 edition and -has a `try` function, you’ll need to use the raw identifier syntax, `r#try` in -this case, to call that function from your 2018 edition code. See [Appendix -E][appendix-e] for more information on editions. +that word happens to be a reserved keyword. This gives us more freedom to choose +identifier names, as well as lets us integrate with programs written in a +language where these words aren’t keywords. In addition, raw identifiers allow +you to use libraries written in a different Rust edition than your crate uses. +For example, `try` isn’t a keyword in the 2015 edition but is in the 2018, 2021, +and 2024 editions. If you depend on a library that is written using the 2015 +edition and has a `try` function, you’ll need to use the raw identifier syntax, +`r#try` in this case, to call that function from your code on later editions. +See [Appendix E][appendix-e] for more information on editions. [appendix-e]: appendix-05-editions.html diff --git a/src/appendix-02-operators.md b/src/appendix-02-operators.md index bc770c703e..e938b5e531 100644 --- a/src/appendix-02-operators.md +++ b/src/appendix-02-operators.md @@ -13,193 +13,194 @@ overload that operator is listed. Table B-1: Operators -| Operator | Example | Explanation | Overloadable? | -|----------|---------|-------------|---------------| -| `!` | `ident!(...)`, `ident!{...}`, `ident![...]` | Macro expansion | | -| `!` | `!expr` | Bitwise or logical complement | `Not` | -| `!=` | `expr != expr` | Nonequality comparison | `PartialEq` | -| `%` | `expr % expr` | Arithmetic remainder | `Rem` | -| `%=` | `var %= expr` | Arithmetic remainder and assignment | `RemAssign` | -| `&` | `&expr`, `&mut expr` | Borrow | | -| `&` | `&type`, `&mut type`, `&'a type`, `&'a mut type` | Borrowed pointer type | | -| `&` | `expr & expr` | Bitwise AND | `BitAnd` | -| `&=` | `var &= expr` | Bitwise AND and assignment | `BitAndAssign` | -| `&&` | `expr && expr` | Short-circuiting logical AND | | -| `*` | `expr * expr` | Arithmetic multiplication | `Mul` | -| `*=` | `var *= expr` | Arithmetic multiplication and assignment | `MulAssign` | -| `*` | `*expr` | Dereference | `Deref` | -| `*` | `*const type`, `*mut type` | Raw pointer | | -| `+` | `trait + trait`, `'a + trait` | Compound type constraint | | -| `+` | `expr + expr` | Arithmetic addition | `Add` | -| `+=` | `var += expr` | Arithmetic addition and assignment | `AddAssign` | -| `,` | `expr, expr` | Argument and element separator | | -| `-` | `- expr` | Arithmetic negation | `Neg` | -| `-` | `expr - expr` | Arithmetic subtraction | `Sub` | -| `-=` | `var -= expr` | Arithmetic subtraction and assignment | `SubAssign` | -| `->` | `fn(...) -> type`, |...| -> type | Function and closure return type | | -| `.` | `expr.ident` | Member access | | -| `..` | `..`, `expr..`, `..expr`, `expr..expr` | Right-exclusive range literal | `PartialOrd` | -| `..=` | `..=expr`, `expr..=expr` | Right-inclusive range literal | `PartialOrd` | -| `..` | `..expr` | Struct literal update syntax | | -| `..` | `variant(x, ..)`, `struct_type { x, .. }` | “And the rest” pattern binding | | -| `...` | `expr...expr` | (Deprecated, use `..=` instead) In a pattern: inclusive range pattern | | -| `/` | `expr / expr` | Arithmetic division | `Div` | -| `/=` | `var /= expr` | Arithmetic division and assignment | `DivAssign` | -| `:` | `pat: type`, `ident: type` | Constraints | | -| `:` | `ident: expr` | Struct field initializer | | -| `:` | `'a: loop {...}` | Loop label | | -| `;` | `expr;` | Statement and item terminator | | -| `;` | `[...; len]` | Part of fixed-size array syntax | | -| `<<` | `expr << expr` | Left-shift | `Shl` | -| `<<=` | `var <<= expr` | Left-shift and assignment | `ShlAssign` | -| `<` | `expr < expr` | Less than comparison | `PartialOrd` | -| `<=` | `expr <= expr` | Less than or equal to comparison | `PartialOrd` | -| `=` | `var = expr`, `ident = type` | Assignment/equivalence | | -| `==` | `expr == expr` | Equality comparison | `PartialEq` | -| `=>` | `pat => expr` | Part of match arm syntax | | -| `>` | `expr > expr` | Greater than comparison | `PartialOrd` | -| `>=` | `expr >= expr` | Greater than or equal to comparison | `PartialOrd` | -| `>>` | `expr >> expr` | Right-shift | `Shr` | -| `>>=` | `var >>= expr` | Right-shift and assignment | `ShrAssign` | -| `@` | `ident @ pat` | Pattern binding | | -| `^` | `expr ^ expr` | Bitwise exclusive OR | `BitXor` | -| `^=` | `var ^= expr` | Bitwise exclusive OR and assignment | `BitXorAssign` | -| | | pat | pat | Pattern alternatives | | -| | | expr | expr | Bitwise OR | `BitOr` | -| |= | var |= expr | Bitwise OR and assignment | `BitOrAssign` | -| || | expr || expr | Short-circuiting logical OR | | -| `?` | `expr?` | Error propagation | | +| Operator | Example | Explanation | Overloadable? | +| ------------------------- | ------------------------------------------------------- | --------------------------------------------------------------------- | -------------- | +| `!` | `ident!(...)`, `ident!{...}`, `ident![...]` | Macro expansion | | +| `!` | `!expr` | Bitwise or logical complement | `Not` | +| `!=` | `expr != expr` | Nonequality comparison | `PartialEq` | +| `%` | `expr % expr` | Arithmetic remainder | `Rem` | +| `%=` | `var %= expr` | Arithmetic remainder and assignment | `RemAssign` | +| `&` | `&expr`, `&mut expr` | Borrow | | +| `&` | `&type`, `&mut type`, `&'a type`, `&'a mut type` | Borrowed pointer type | | +| `&` | `expr & expr` | Bitwise AND | `BitAnd` | +| `&=` | `var &= expr` | Bitwise AND and assignment | `BitAndAssign` | +| `&&` | `expr && expr` | Short-circuiting logical AND | | +| `*` | `expr * expr` | Arithmetic multiplication | `Mul` | +| `*=` | `var *= expr` | Arithmetic multiplication and assignment | `MulAssign` | +| `*` | `*expr` | Dereference | `Deref` | +| `*` | `*const type`, `*mut type` | Raw pointer | | +| `+` | `trait + trait`, `'a + trait` | Compound type constraint | | +| `+` | `expr + expr` | Arithmetic addition | `Add` | +| `+=` | `var += expr` | Arithmetic addition and assignment | `AddAssign` | +| `,` | `expr, expr` | Argument and element separator | | +| `-` | `- expr` | Arithmetic negation | `Neg` | +| `-` | `expr - expr` | Arithmetic subtraction | `Sub` | +| `-=` | `var -= expr` | Arithmetic subtraction and assignment | `SubAssign` | +| `->` | `fn(...) -> type`, |...| -> type | Function and closure return type | | +| `.` | `expr.ident` | Field access | | +| `.` | `expr.ident(expr, ...)` | Method call | | +| `.` | `expr.0`, `expr.1`, and so on | Tuple indexing | | +| `..` | `..`, `expr..`, `..expr`, `expr..expr` | Right-exclusive range literal | `PartialOrd` | +| `..=` | `..=expr`, `expr..=expr` | Right-inclusive range literal | `PartialOrd` | +| `..` | `..expr` | Struct literal update syntax | | +| `..` | `variant(x, ..)`, `struct_type { x, .. }` | “And the rest” pattern binding | | +| `...` | `expr...expr` | (Deprecated, use `..=` instead) In a pattern: inclusive range pattern | | +| `/` | `expr / expr` | Arithmetic division | `Div` | +| `/=` | `var /= expr` | Arithmetic division and assignment | `DivAssign` | +| `:` | `pat: type`, `ident: type` | Constraints | | +| `:` | `ident: expr` | Struct field initializer | | +| `:` | `'a: loop {...}` | Loop label | | +| `;` | `expr;` | Statement and item terminator | | +| `;` | `[...; len]` | Part of fixed-size array syntax | | +| `<<` | `expr << expr` | Left-shift | `Shl` | +| `<<=` | `var <<= expr` | Left-shift and assignment | `ShlAssign` | +| `<` | `expr < expr` | Less than comparison | `PartialOrd` | +| `<=` | `expr <= expr` | Less than or equal to comparison | `PartialOrd` | +| `=` | `var = expr`, `ident = type` | Assignment/equivalence | | +| `==` | `expr == expr` | Equality comparison | `PartialEq` | +| `=>` | `pat => expr` | Part of match arm syntax | | +| `>` | `expr > expr` | Greater than comparison | `PartialOrd` | +| `>=` | `expr >= expr` | Greater than or equal to comparison | `PartialOrd` | +| `>>` | `expr >> expr` | Right-shift | `Shr` | +| `>>=` | `var >>= expr` | Right-shift and assignment | `ShrAssign` | +| `@` | `ident @ pat` | Pattern binding | | +| `^` | `expr ^ expr` | Bitwise exclusive OR | `BitXor` | +| `^=` | `var ^= expr` | Bitwise exclusive OR and assignment | `BitXorAssign` | +| | | pat | pat | Pattern alternatives | | +| | | expr | expr | Bitwise OR | `BitOr` | +| |= | var |= expr | Bitwise OR and assignment | `BitOrAssign` | +| || | expr || expr | Short-circuiting logical OR | | +| `?` | `expr?` | Error propagation | | ### Non-operator Symbols -The following list contains all symbols that don’t function as operators; that +The following tables contain all symbols that don’t function as operators; that is, they don’t behave like a function or method call. Table B-2 shows symbols that appear on their own and are valid in a variety of locations. -Table B-2: Stand-Alone Syntax - -| Symbol | Explanation | -|--------|-------------| -| `'ident` | Named lifetime or loop label | -| `...u8`, `...i32`, `...f64`, `...usize`, etc. | Numeric literal of specific type | -| `"..."` | String literal | -| `r"..."`, `r#"..."#`, `r##"..."##`, etc. | Raw string literal, escape characters not processed | -| `b"..."` | Byte string literal; constructs an array of bytes instead of a string | -| `br"..."`, `br#"..."#`, `br##"..."##`, etc. | Raw byte string literal, combination of raw and byte string literal | -| `'...'` | Character literal | -| `b'...'` | ASCII byte literal | -| |...| expr | Closure | -| `!` | Always empty bottom type for diverging functions | -| `_` | “Ignored” pattern binding; also used to make integer literals readable | +Table B-2: Stand-alone Syntax + +| Symbol | Explanation | +| ---------------------------------------------------------------------- | ---------------------------------------------------------------------- | +| `'ident` | Named lifetime or loop label | +| Digits immediately followed by `u8`, `i32`, `f64`, `usize`, and so on | Numeric literal of specific type | +| `"..."` | String literal | +| `r"..."`, `r#"..."#`, `r##"..."##`, and so on | Raw string literal; escape characters not processed | +| `b"..."` | Byte string literal; constructs an array of bytes instead of a string | +| `br"..."`, `br#"..."#`, `br##"..."##`, and so on | Raw byte string literal; combination of raw and byte string literal | +| `'...'` | Character literal | +| `b'...'` | ASCII byte literal | +| |...| expr | Closure | +| `!` | Always-empty bottom type for diverging functions | +| `_` | “Ignored” pattern binding; also used to make integer literals readable | Table B-3 shows symbols that appear in the context of a path through the module hierarchy to an item. Table B-3: Path-Related Syntax -| Symbol | Explanation | -|--------|-------------| -| `ident::ident` | Namespace path | -| `::path` | Path relative to the crate root (i.e., an explicitly absolute path) | -| `self::path` | Path relative to the current module (i.e., an explicitly relative path). -| `super::path` | Path relative to the parent of the current module | -| `type::ident`, `::ident` | Associated constants, functions, and types | -| `::...` | Associated item for a type that cannot be directly named (e.g., `<&T>::...`, `<[T]>::...`, etc.) | -| `trait::method(...)` | Disambiguating a method call by naming the trait that defines it | -| `type::method(...)` | Disambiguating a method call by naming the type for which it’s defined | -| `::method(...)` | Disambiguating a method call by naming the trait and type | +| Symbol | Explanation | +| --------------------------------------- | -------------------------------------------------------------------------------------------------------------| +| `ident::ident` | Namespace path | +| `::path` | Path relative to the crate root (that is, an explicitly absolute path) | +| `self::path` | Path relative to the current module (that is, an explicitly relative path) | +| `super::path` | Path relative to the parent of the current module | +| `type::ident`, `::ident` | Associated constants, functions, and types | +| `::...` | Associated item for a type that cannot be directly named (for example, `<&T>::...`, `<[T]>::...`, and so on) | +| `trait::method(...)` | Disambiguating a method call by naming the trait that defines it | +| `type::method(...)` | Disambiguating a method call by naming the type for which it’s defined | +| `::method(...)` | Disambiguating a method call by naming the trait and type | Table B-4 shows symbols that appear in the context of using generic type parameters. Table B-4: Generics -| Symbol | Explanation | -|--------|-------------| -| `path<...>` | Specifies parameters to generic type in a type (e.g., `Vec`) | -| `path::<...>`, `method::<...>` | Specifies parameters to generic type, function, or method in an expression; often referred to as turbofish (e.g., `"42".parse::()`) | -| `fn ident<...> ...` | Define generic function | -| `struct ident<...> ...` | Define generic structure | -| `enum ident<...> ...` | Define generic enumeration | -| `impl<...> ...` | Define generic implementation | -| `for<...> type` | Higher-ranked lifetime bounds | -| `type` | A generic type where one or more associated types have specific assignments (e.g., `Iterator`) | +| Symbol | Explanation | +| ------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------- | +| `path<...>` | Specifies parameters to a generic type in a type (for example, `Vec`) | +| `path::<...>`, `method::<...>` | Specifies parameters to a generic type, function, or method in an expression; often referred to as _turbofish_ (for example, `"42".parse::()`) | +| `fn ident<...> ...` | Define generic function | +| `struct ident<...> ...` | Define generic structure | +| `enum ident<...> ...` | Define generic enumeration | +| `impl<...> ...` | Define generic implementation | +| `for<...> type` | Higher ranked lifetime bounds | +| `type` | A generic type where one or more associated types have specific assignments (for example, `Iterator`) | Table B-5 shows symbols that appear in the context of constraining generic type parameters with trait bounds. Table B-5: Trait Bound Constraints -| Symbol | Explanation | -|--------|-------------| -| `T: U` | Generic parameter `T` constrained to types that implement `U` | -| `T: 'a` | Generic type `T` must outlive lifetime `'a` (meaning the type cannot transitively contain any references with lifetimes shorter than `'a`) | -| `T: 'static` | Generic type `T` contains no borrowed references other than `'static` ones | -| `'b: 'a` | Generic lifetime `'b` must outlive lifetime `'a` | -| `T: ?Sized` | Allow generic type parameter to be a dynamically sized type | -| `'a + trait`, `trait + trait` | Compound type constraint | +| Symbol | Explanation | +| ----------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ | +| `T: U` | Generic parameter `T` constrained to types that implement `U` | +| `T: 'a` | Generic type `T` must outlive lifetime `'a` (meaning the type cannot transitively contain any references with lifetimes shorter than `'a`) | +| `T: 'static` | Generic type `T` contains no borrowed references other than `'static` ones | +| `'b: 'a` | Generic lifetime `'b` must outlive lifetime `'a` | +| `T: ?Sized` | Allow generic type parameter to be a dynamically sized type | +| `'a + trait`, `trait + trait` | Compound type constraint | Table B-6 shows symbols that appear in the context of calling or defining macros and specifying attributes on an item. Table B-6: Macros and Attributes -| Symbol | Explanation | -|--------|-------------| -| `#[meta]` | Outer attribute | -| `#![meta]` | Inner attribute | -| `$ident` | Macro substitution | -| `$ident:kind` | Macro capture | -| `$(…)…` | Macro repetition | -| `ident!(...)`, `ident!{...}`, `ident![...]` | Macro invocation | +| Symbol | Explanation | +| ------------------------------------------- | ------------------ | +| `#[meta]` | Outer attribute | +| `#![meta]` | Inner attribute | +| `$ident` | Macro substitution | +| `$ident:kind` | Macro metavariable | +| `$(...)...` | Macro repetition | +| `ident!(...)`, `ident!{...}`, `ident![...]` | Macro invocation | Table B-7 shows symbols that create comments. Table B-7: Comments -| Symbol | Explanation | -|--------|-------------| -| `//` | Line comment | -| `//!` | Inner line doc comment | -| `///` | Outer line doc comment | -| `/*...*/` | Block comment | +| Symbol | Explanation | +| ---------- | ----------------------- | +| `//` | Line comment | +| `//!` | Inner line doc comment | +| `///` | Outer line doc comment | +| `/*...*/` | Block comment | | `/*!...*/` | Inner block doc comment | | `/**...*/` | Outer block doc comment | -Table B-8 shows symbols that appear in the context of using tuples. +Table B-8 shows the contexts in which parentheses are used. -Table B-8: Tuples +Table B-8: Parentheses -| Symbol | Explanation | -|--------|-------------| -| `()` | Empty tuple (aka unit), both literal and type | -| `(expr)` | Parenthesized expression | -| `(expr,)` | Single-element tuple expression | -| `(type,)` | Single-element tuple type | -| `(expr, ...)` | Tuple expression | -| `(type, ...)` | Tuple type | -| `expr(expr, ...)` | Function call expression; also used to initialize tuple `struct`s and tuple `enum` variants | -| `expr.0`, `expr.1`, etc. | Tuple indexing | +| Symbol | Explanation | +| ------------------------ | ------------------------------------------------------------------------------------------- | +| `()` | Empty tuple (aka unit), both literal and type | +| `(expr)` | Parenthesized expression | +| `(expr,)` | Single-element tuple expression | +| `(type,)` | Single-element tuple type | +| `(expr, ...)` | Tuple expression | +| `(type, ...)` | Tuple type | +| `expr(expr, ...)` | Function call expression; also used to initialize tuple `struct`s and tuple `enum` variants | -Table B-9 shows the contexts in which curly braces are used. +Table B-9 shows the contexts in which curly brackets are used. Table B-9: Curly Brackets -| Context | Explanation | -|---------|-------------| -| `{...}` | Block expression | -| `Type {...}` | `struct` literal | +| Context | Explanation | +| ------------ | ---------------- | +| `{...}` | Block expression | +| `Type {...}` | Struct literal | Table B-10 shows the contexts in which square brackets are used. Table B-10: Square Brackets -| Context | Explanation | -|---------|-------------| -| `[...]` | Array literal | -| `[expr; len]` | Array literal containing `len` copies of `expr` | -| `[type; len]` | Array type containing `len` instances of `type` | -| `expr[expr]` | Collection indexing. Overloadable (`Index`, `IndexMut`) | +| Context | Explanation | +| -------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------- | +| `[...]` | Array literal | +| `[expr; len]` | Array literal containing `len` copies of `expr` | +| `[type; len]` | Array type containing `len` instances of `type` | +| `expr[expr]` | Collection indexing; overloadable (`Index`, `IndexMut`) | | `expr[..]`, `expr[a..]`, `expr[..b]`, `expr[a..b]` | Collection indexing pretending to be collection slicing, using `Range`, `RangeFrom`, `RangeTo`, or `RangeFull` as the “index” | diff --git a/src/appendix-03-derivable-traits.md b/src/appendix-03-derivable-traits.md index 299796dbf7..1bcc1de931 100644 --- a/src/appendix-03-derivable-traits.md +++ b/src/appendix-03-derivable-traits.md @@ -8,17 +8,17 @@ type you’ve annotated with the `derive` syntax. In this appendix, we provide a reference of all the traits in the standard library that you can use with `derive`. Each section covers: -* What operators and methods deriving this trait will enable -* What the implementation of the trait provided by `derive` does -* What implementing the trait signifies about the type -* The conditions in which you’re allowed or not allowed to implement the trait -* Examples of operations that require the trait +- What operators and methods deriving this trait will enable +- What the implementation of the trait provided by `derive` does +- What implementing the trait signifies about the type +- The conditions in which you’re allowed or not allowed to implement the trait +- Examples of operations that require the trait If you want different behavior from that provided by the `derive` attribute, consult the [standard library documentation](../std/index.html) -for each trait for details of how to manually implement them. +for each trait for details on how to manually implement them. -These traits listed here are the only ones defined by the standard library that +The traits listed here are the only ones defined by the standard library that can be implemented on your types using `derive`. Other traits defined in the standard library don’t have sensible default behavior, so it’s up to you to implement them in the way that makes sense for what you’re trying to accomplish. @@ -31,10 +31,10 @@ would be most relevant to them? The Rust compiler doesn’t have this insight, s it can’t provide appropriate default behavior for you. The list of derivable traits provided in this appendix is not comprehensive: -libraries can implement `derive` for their own traits, making the list of -traits you can use `derive` with truly open-ended. Implementing `derive` -involves using a procedural macro, which is covered in the -[“Macros”][macros] section of Chapter 19. +Libraries can implement `derive` for their own traits, making the list of +traits you can use `derive` with truly open ended. Implementing `derive` +involves using a procedural macro, which is covered in the [“Custom `derive` +Macros”][custom-derive-macros] section in Chapter 20. ### `Debug` for Programmer Output @@ -45,9 +45,10 @@ The `Debug` trait allows you to print instances of a type for debugging purposes, so you and other programmers using your type can inspect an instance at a particular point in a program’s execution. -The `Debug` trait is required, for example, in use of the `assert_eq!` macro. -This macro prints the values of instances given as arguments if the equality -assertion fails so programmers can see why the two instances weren’t equal. +The `Debug` trait is required, for example, in the use of the `assert_eq!` +macro. This macro prints the values of instances given as arguments if the +equality assertion fails so that programmers can see why the two instances +weren’t equal. ### `PartialEq` and `Eq` for Equality Comparisons @@ -55,8 +56,8 @@ The `PartialEq` trait allows you to compare instances of a type to check for equality and enables use of the `==` and `!=` operators. Deriving `PartialEq` implements the `eq` method. When `PartialEq` is derived on -structs, two instances are equal only if *all* fields are equal, and the -instances are not equal if any fields are not equal. When derived on enums, +structs, two instances are equal only if _all_ fields are equal, and the +instances are not equal if _any_ fields are not equal. When derived on enums, each variant is equal to itself and not equal to the other variants. The `PartialEq` trait is required, for example, with the use of the @@ -66,12 +67,12 @@ for equality. The `Eq` trait has no methods. Its purpose is to signal that for every value of the annotated type, the value is equal to itself. The `Eq` trait can only be applied to types that also implement `PartialEq`, although not all types that -implement `PartialEq` can implement `Eq`. One example of this is floating point -number types: the implementation of floating point numbers states that two +implement `PartialEq` can implement `Eq`. One example of this is floating-point +number types: The implementation of floating-point numbers states that two instances of the not-a-number (`NaN`) value are not equal to each other. -An example of when `Eq` is required is for keys in a `HashMap` so the -`HashMap` can tell whether two keys are the same. +An example of when `Eq` is required is for keys in a `HashMap` so that +the `HashMap` can tell whether two keys are the same. ### `PartialOrd` and `Ord` for Ordering Comparisons @@ -83,9 +84,9 @@ that also implement `PartialEq`. Deriving `PartialOrd` implements the `partial_cmp` method, which returns an `Option` that will be `None` when the values given don’t produce an ordering. An example of a value that doesn’t produce an ordering, even though -most values of that type can be compared, is the not-a-number (`NaN`) floating -point value. Calling `partial_cmp` with any floating point number and the `NaN` -floating point value will return `None`. +most values of that type can be compared, is the `NaN` floating point value. +Calling `partial_cmp` with any floating-point number and the `NaN` +floating-point value will return `None`. When derived on structs, `PartialOrd` compares two instances by comparing the value in each field in the order in which the fields appear in the struct @@ -111,8 +112,8 @@ a data structure that stores data based on the sort order of the values. The `Clone` trait allows you to explicitly create a deep copy of a value, and the duplication process might involve running arbitrary code and copying heap -data. See the [“Ways Variables and Data Interact: -Clone”][ways-variables-and-data-interact-clone] section in +data. See the [“Variables and Data Interacting with +Clone”][variables-and-data-interacting-with-clone] section in Chapter 4 for more information on `Clone`. Deriving `Clone` implements the `clone` method, which when implemented for the @@ -135,7 +136,7 @@ is being run. That way, all programmers can assume that copying a value will be very fast. You can derive `Copy` on any type whose parts all implement `Copy`. A type that -implements `Copy` must also implement `Clone`, because a type that implements +implements `Copy` must also implement `Clone` because a type that implements `Copy` has a trivial implementation of `Clone` that performs the same task as `Copy`. @@ -166,11 +167,11 @@ meaning all fields or values in the type must also implement `Default` to derive `Default`. The `Default::default` function is commonly used in combination with the struct -update syntax discussed in the [“Creating Instances From Other Instances With +update syntax discussed in the [“Creating Instances from Other Instances with Struct Update -Syntax”][creating-instances-from-other-instances-with-struct-update-syntax] -section in Chapter 5. You can customize a few fields of a struct and then -set and use a default value for the rest of the fields by using +Syntax”][creating-instances-from-other-instances-with-struct-update-syntax] section in Chapter 5. You can customize a few fields of a struct and +then set and use a default value for the rest of the fields by using `..Default::default()`. The `Default` trait is required when you use the method `unwrap_or_default` on @@ -178,10 +179,7 @@ The `Default` trait is required when you use the method `unwrap_or_default` on `unwrap_or_default` will return the result of `Default::default` for the type `T` stored in the `Option`. -[creating-instances-from-other-instances-with-struct-update-syntax]: -ch05-01-defining-structs.html#creating-instances-from-other-instances-with-struct-update-syntax -[stack-only-data-copy]: -ch04-01-what-is-ownership.html#stack-only-data-copy -[ways-variables-and-data-interact-clone]: -ch04-01-what-is-ownership.html#ways-variables-and-data-interact-clone -[macros]: ch19-06-macros.html#macros +[creating-instances-from-other-instances-with-struct-update-syntax]: ch05-01-defining-structs.html#creating-instances-from-other-instances-with-struct-update-syntax +[stack-only-data-copy]: ch04-01-what-is-ownership.html#stack-only-data-copy +[variables-and-data-interacting-with-clone]: ch04-01-what-is-ownership.html#variables-and-data-interacting-with-clone +[custom-derive-macros]: ch20-05-macros.html#custom-derive-macros diff --git a/src/appendix-04-useful-development-tools.md b/src/appendix-04-useful-development-tools.md index 40b076153d..6719eaa26d 100644 --- a/src/appendix-04-useful-development-tools.md +++ b/src/appendix-04-useful-development-tools.md @@ -1,4 +1,4 @@ -## Appendix D - Useful Development Tools +## Appendix D: Useful Development Tools In this appendix, we talk about some useful development tools that the Rust project provides. We’ll look at automatic formatting, quick ways to apply @@ -8,16 +8,13 @@ warning fixes, a linter, and integrating with IDEs. The `rustfmt` tool reformats your code according to the community code style. Many collaborative projects use `rustfmt` to prevent arguments about which -style to use when writing Rust: everyone formats their code using the tool. +style to use when writing Rust: Everyone formats their code using the tool. -To install `rustfmt`, enter the following: - -```console -$ rustup component add rustfmt -``` - -This command gives you `rustfmt` and `cargo-fmt`, similar to how Rust gives you -both `rustc` and `cargo`. To format any Cargo project, enter the following: +Rust installations include `rustfmt` by default, so you should already have the +programs `rustfmt` and `cargo-fmt` on your system. These two commands are +analogous to `rustc` and `cargo` in that `rustfmt` allows finer grained control +and `cargo-fmt` understands conventions of a project that uses Cargo. To format +any Cargo project, enter the following: ```console $ cargo fmt @@ -27,46 +24,40 @@ Running this command reformats all the Rust code in the current crate. This should only change the code style, not the code semantics. For more information on `rustfmt`, see [its documentation][rustfmt]. -[rustfmt]: https://github.com/rust-lang/rustfmt - ### Fix Your Code with `rustfix` -The rustfix tool is included with Rust installations and can automatically fix -compiler warnings that have a clear way to correct the problem that’s likely -what you want. It’s likely you’ve seen compiler warnings before. For example, -consider this code: +The `rustfix` tool is included with Rust installations and can automatically +fix compiler warnings that have a clear way to correct the problem that’s +likely what you want. You’ve probably seen compiler warnings before. For +example, consider this code: Filename: src/main.rs ```rust -fn do_something() {} - fn main() { - for i in 0..100 { - do_something(); - } + let mut x = 42; + println!("{x}"); } ``` -Here, we’re calling the `do_something` function 100 times, but we never use the -variable `i` in the body of the `for` loop. Rust warns us about that: +Here, we’re defining the variable `x` as mutable, but we never actually mutate +it. Rust warns us about that: ```console $ cargo build Compiling myprogram v0.1.0 (file:///projects/myprogram) -warning: unused variable: `i` - --> src/main.rs:4:9 +warning: variable does not need to be mutable + --> src/main.rs:2:9 | -4 | for i in 0..100 { - | ^ help: consider using `_i` instead +2 | let mut x = 0; + | ----^ + | | + | help: remove this `mut` | - = note: #[warn(unused_variables)] on by default - - Finished dev [unoptimized + debuginfo] target(s) in 0.50s + = note: `#[warn(unused_mut)]` on by default ``` -The warning suggests that we use `_i` as a name instead: the underscore -indicates that we intend for this variable to be unused. We can automatically +The warning suggests that we remove the `mut` keyword. We can automatically apply that suggestion using the `rustfix` tool by running the command `cargo fix`: @@ -77,36 +68,29 @@ $ cargo fix Finished dev [unoptimized + debuginfo] target(s) in 0.59s ``` -When we look at *src/main.rs* again, we’ll see that `cargo fix` has changed the +When we look at _src/main.rs_ again, we’ll see that `cargo fix` has changed the code: Filename: src/main.rs ```rust -fn do_something() {} - fn main() { - for _i in 0..100 { - do_something(); - } + let x = 42; + println!("{x}"); } ``` -The `for` loop variable is now named `_i`, and the warning no longer appears. +The variable `x` is now immutable, and the warning no longer appears. You can also use the `cargo fix` command to transition your code between -different Rust editions. Editions are covered in Appendix E. +different Rust editions. Editions are covered in [Appendix E][editions]. ### More Lints with Clippy -The Clippy tool is a collection of lints to analyze your code so you can catch -common mistakes and improve your Rust code. - -To install Clippy, enter the following: - -```console -$ rustup component add clippy -``` +The Clippy tool is a collection of lints to analyze your code so that you can +catch common mistakes and improve your Rust code. Clippy is included with +standard Rust installations. To run Clippy’s lints on any Cargo project, enter the following: @@ -117,7 +101,7 @@ $ cargo clippy For example, say you write a program that uses an approximation of a mathematical constant, such as pi, as this program does: -Filename: src/main.rs + ```rust fn main() { @@ -127,6 +111,8 @@ fn main() { } ``` + + Running `cargo clippy` on this project results in this error: ```text @@ -143,10 +129,11 @@ error: approximate value of `f{32, 64}::consts::PI` found This error lets you know that Rust already has a more precise `PI` constant defined, and that your program would be more correct if you used the constant -instead. You would then change your code to use the `PI` constant. The -following code doesn’t result in any errors or warnings from Clippy: +instead. You would then change your code to use the `PI` constant. -Filename: src/main.rs +The following code doesn’t result in any errors or warnings from Clippy: + + ```rust fn main() { @@ -156,25 +143,27 @@ fn main() { } ``` -For more information on Clippy, see [its documentation][clippy]. + -[clippy]: https://github.com/rust-lang/rust-clippy +For more information on Clippy, see [its documentation][clippy]. ### IDE Integration Using `rust-analyzer` -To help IDE integration, the Rust community recommends using +To help with IDE integration, the Rust community recommends using [`rust-analyzer`][rust-analyzer]. This tool is a set of -compiler-centric utilities that speaks the [Language Server Protocol][lsp], which is a specification for IDEs and programming languages to communicate with each other. Different clients can use `rust-analyzer`, such as [the Rust analyzer plug-in for Visual Studio Code][vscode]. -[lsp]: http://langserver.org/ -[vscode]: https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer - Visit the `rust-analyzer` project’s [home page][rust-analyzer] for installation instructions, then install the language server support in your -particular IDE. Your IDE will gain abilities such as autocompletion, jump to +particular IDE. Your IDE will gain capabilities such as autocompletion, jump to definition, and inline errors. +[rustfmt]: https://github.com/rust-lang/rustfmt +[editions]: appendix-05-editions.md +[clippy]: https://github.com/rust-lang/rust-clippy [rust-analyzer]: https://rust-analyzer.github.io +[lsp]: http://langserver.org/ +[vscode]: https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer diff --git a/src/appendix-05-editions.md b/src/appendix-05-editions.md index 90828ebbaf..ef210ce6a4 100644 --- a/src/appendix-05-editions.md +++ b/src/appendix-05-editions.md @@ -1,7 +1,7 @@ -## Appendix E - Editions +## Appendix E: Editions In Chapter 1, you saw that `cargo new` adds a bit of metadata to your -*Cargo.toml* file about an edition. This appendix talks about what that means! +_Cargo.toml_ file about an edition. This appendix talks about what that means! The Rust language and compiler have a six-week release cycle, meaning users get a constant stream of new features. Other programming languages release larger @@ -10,24 +10,25 @@ while, all of these tiny changes add up. But from release to release, it can be difficult to look back and say, “Wow, between Rust 1.10 and Rust 1.31, Rust has changed a lot!” -Every two or three years, the Rust team produces a new Rust *edition*. Each +Every three years or so, the Rust team produces a new Rust _edition_. Each edition brings together the features that have landed into a clear package with fully updated documentation and tooling. New editions ship as part of the usual six-week release process. Editions serve different purposes for different people: -* For active Rust users, a new edition brings together incremental changes into +- For active Rust users, a new edition brings together incremental changes into an easy-to-understand package. -* For non-users, a new edition signals that some major advancements have +- For non-users, a new edition signals that some major advancements have landed, which might make Rust worth another look. -* For those developing Rust, a new edition provides a rallying point for the +- For those developing Rust, a new edition provides a rallying point for the project as a whole. -At the time of this writing, three Rust editions are available: Rust 2015, Rust -2018, and Rust 2021. This book is written using Rust 2021 edition idioms. +At the time of this writing, four Rust editions are available: Rust 2015, Rust +2018, Rust 2021, and Rust 2024. This book is written using Rust 2024 edition +idioms. -The `edition` key in *Cargo.toml* indicates which edition the compiler should +The `edition` key in _Cargo.toml_ indicates which edition the compiler should use for your code. If the key doesn’t exist, Rust uses `2015` as the edition value for backward compatibility reasons. @@ -45,13 +46,14 @@ Rust 2018, your project will compile and be able to use that dependency. The opposite situation, where your project uses Rust 2018 and a dependency uses Rust 2015, works as well. -To be clear: most features will be available on all editions. Developers using +To be clear: Most features will be available on all editions. Developers using any Rust edition will continue to see improvements as new stable releases are made. However, in some cases, mainly when new keywords are added, some new features might only be available in later editions. You will need to switch editions if you want to take advantage of such features. -For more details, the [*Edition -Guide*](https://doc.rust-lang.org/stable/edition-guide/) is a complete book -about editions that enumerates the differences between editions and explains -how to automatically upgrade your code to a new edition via `cargo fix`. +For more details, see [_The Rust Edition Guide_][edition-guide]. This is a +complete book that enumerates the differences between editions and explains how +to automatically upgrade your code to a new edition via `cargo fix`. + +[edition-guide]: https://doc.rust-lang.org/stable/edition-guide diff --git a/src/appendix-06-translation.md b/src/appendix-06-translation.md index 7e8c68d253..0933907757 100644 --- a/src/appendix-06-translation.md +++ b/src/appendix-06-translation.md @@ -7,13 +7,12 @@ For resources in languages other than English. Most are still in progress; see - [Português](https://github.com/rust-br/rust-book-pt-br) (BR) - [Português](https://github.com/nunojesus/rust-book-pt-pt) (PT) -- [简体中文](https://github.com/KaiserY/trpl-zh-cn) +- 简体中文: [KaiserY/trpl-zh-cn](https://github.com/KaiserY/trpl-zh-cn), [gnu4cn/rust-lang-Zh_CN](https://github.com/gnu4cn/rust-lang-Zh_CN) - [正體中文](https://github.com/rust-tw/book-tw) -- [Українська](https://github.com/pavloslav/rust-book-uk-ua) -- [Español](https://github.com/thecodix/book), [alternate](https://github.com/ManRR/rust-book-es) -- [Italiano](https://github.com/EmanueleGurini/book_it) +- [Українська](https://rust-lang-ua.github.io/rustbook_ukrainian) +- [Español](https://github.com/thecodix/book), [alternate](https://github.com/ManRR/rust-book-es), [Español por RustLangES](https://github.com/RustLangES/rust-book-es) - [Русский](https://github.com/rust-lang-ru/book) -- [한국어](https://github.com/rinthel/rust-lang-book-ko) +- [한국어](https://github.com/rust-kr/doc.rust-kr.org) - [日本語](https://github.com/rust-lang-ja/book-ja) - [Français](https://github.com/Jimskapt/rust-book-fr) - [Polski](https://github.com/paytchoo/book-pl) @@ -22,8 +21,12 @@ For resources in languages other than English. Most are still in progress; see - [Esperanto](https://github.com/psychoslave/Rust-libro) - [ελληνική](https://github.com/TChatzigiannakis/rust-book-greek) - [Svenska](https://github.com/sebras/book) -- [Farsi](https://github.com/pomokhtari/rust-book-fa) +- [Farsi](https://github.com/RustFarsi/book), [Persian (FA)](https://github.com/persian-rust/book) - [Deutsch](https://github.com/rust-lang-de/rustbook-de) - [हिंदी](https://github.com/venkatarun95/rust-book-hindi) - [ไทย](https://github.com/rust-lang-th/book-th) - [Danske](https://github.com/DanKHansen/book-dk) +- [O'zbek](https://github.com/rust-lang-uz/book) +- [Tiếng Việt](https://github.com/tuanemdev/rust-book-vn) +- [Italiano](https://nixxo.github.io/rust-lang-book-it/) +- [বাংলা](https://github.com/IsmailHosenIsmailJames/rust-book-bn) diff --git a/src/appendix-07-nightly-rust.md b/src/appendix-07-nightly-rust.md index 46e619c815..7108441fa3 100644 --- a/src/appendix-07-nightly-rust.md +++ b/src/appendix-07-nightly-rust.md @@ -5,7 +5,7 @@ developer. ### Stability Without Stagnation -As a language, Rust cares a *lot* about the stability of your code. We want +As a language, Rust cares a _lot_ about the stability of your code. We want Rust to be a rock-solid foundation you can build on, and if things were constantly changing, that would be impossible. At the same time, if we can’t experiment with new features, we may not find out important flaws until after @@ -18,14 +18,14 @@ bring you new features, fewer bugs, and faster compile times. ### Choo, Choo! Release Channels and Riding the Trains -Rust development operates on a *train schedule*. That is, all development is -done on the `master` branch of the Rust repository. Releases follow a software +Rust development operates on a _train schedule_. That is, all development is +done in the main branch of the Rust repository. Releases follow a software release train model, which has been used by Cisco IOS and other software -projects. There are three *release channels* for Rust: +projects. There are three _release channels_ for Rust: -* Nightly -* Beta -* Stable +- Nightly +- Beta +- Stable Most Rust developers primarily use the stable channel, but those who want to try out experimental new features may use nightly or beta. @@ -33,7 +33,7 @@ try out experimental new features may use nightly or beta. Here’s an example of how the development and release process works: let’s assume that the Rust team is working on the release of Rust 1.5. That release happened in December of 2015, but it will provide us with realistic version -numbers. A new feature is added to Rust: a new commit lands on the `master` +numbers. A new feature is added to Rust: a new commit lands on the main branch. Each night, a new nightly version of Rust is produced. Every day is a release day, and these releases are created by our release infrastructure automatically. So as time passes, our releases look like this, once a night: @@ -43,7 +43,7 @@ nightly: * - - * - - * ``` Every six weeks, it’s time to prepare a new release! The `beta` branch of the -Rust repository branches off from the `master` branch used by nightly. Now, +Rust repository branches off from the main branch used by nightly. Now, there are two releases: ```text @@ -64,8 +64,8 @@ beta: * Let’s say a regression is found. Good thing we had some time to test the beta release before the regression snuck into a stable release! The fix is applied -to `master`, so that nightly is fixed, and then the fix is backported to the -`beta` branch, and a new release of beta is produced: +to the main branch, so that nightly is fixed, and then the fix is backported to +the `beta` branch, and a new release of beta is produced: ```text nightly: * - - * - - * - - * - - * - - * @@ -85,7 +85,7 @@ stable: * ``` Hooray! Rust 1.5 is done! However, we’ve forgotten one thing: because the six -weeks have gone by, we also need a new beta of the *next* version of Rust, 1.6. +weeks have gone by, we also need a new beta of the _next_ version of Rust, 1.6. So after `stable` branches off of `beta`, the next version of `beta` branches off of `nightly` again: @@ -114,13 +114,19 @@ work as expected, you can report it to the team and get it fixed before the next stable release happens! Breakage in a beta release is relatively rare, but `rustc` is still a piece of software, and bugs do exist. +### Maintenance time + +The Rust project supports the most recent stable version. When a new stable +version is released, the old version reaches its end of life (EOL). This means +each version is supported for six weeks. + ### Unstable Features There’s one more catch with this release model: unstable features. Rust uses a technique called “feature flags” to determine what features are enabled in a -given release. If a new feature is under active development, it lands on -`master`, and therefore, in nightly, but behind a *feature flag*. If you, as a -user, wish to try out the work-in-progress feature, you can, but you must be +given release. If a new feature is under active development, it lands on the +main branch, and therefore, in nightly, but behind a _feature flag_. If you, as +a user, wish to try out the work-in-progress feature, you can, but you must be using a nightly release of Rust and annotate your source code with the appropriate flag to opt in. @@ -145,7 +151,7 @@ install nightly, for example: $ rustup toolchain install nightly ``` -You can see all of the *toolchains* (releases of Rust and associated +You can see all of the _toolchains_ (releases of Rust and associated components) you have installed with `rustup` as well. Here’s an example on one of your authors’ Windows computer: @@ -168,20 +174,19 @@ $ rustup override set nightly ``` Now, every time you call `rustc` or `cargo` inside of -*~/projects/needs-nightly*, `rustup` will make sure that you are using nightly +_~/projects/needs-nightly_, `rustup` will make sure that you are using nightly Rust, rather than your default of stable Rust. This comes in handy when you have a lot of Rust projects! ### The RFC Process and Teams So how do you learn about these new features? Rust’s development model follows -a *Request For Comments (RFC) process*. If you’d like an improvement in Rust, +a _Request For Comments (RFC) process_. If you’d like an improvement in Rust, you can write up a proposal, called an RFC. Anyone can write RFCs to improve Rust, and the proposals are reviewed and discussed by the Rust team, which is comprised of many topic subteams. There’s -a full list of the teams [on Rust’s -website](https://www.rust-lang.org/governance), which includes teams for +a full list of the teams [on Rust’s website](https://www.rust-lang.org/governance), which includes teams for each area of the project: language design, compiler implementation, infrastructure, documentation, and more. The appropriate team reads the proposal and the comments, writes some comments of their own, and eventually, @@ -190,8 +195,8 @@ there’s consensus to accept or reject the feature. If the feature is accepted, an issue is opened on the Rust repository, and someone can implement it. The person who implements it very well may not be the person who proposed the feature in the first place! When the implementation is -ready, it lands on the `master` branch behind a feature gate, as we discussed -in the [“Unstable Features”](#unstable-features) section. +ready, it lands on the main branch behind a feature gate, as we discussed in +the [“Unstable Features”](#unstable-features) section. After some time, once Rust developers who use nightly releases have been able to try out the new feature, team members will discuss the feature, how it’s diff --git a/src/ch00-00-introduction.md b/src/ch00-00-introduction.md index 536988cb19..4dfa272fcc 100644 --- a/src/ch00-00-introduction.md +++ b/src/ch00-00-introduction.md @@ -4,10 +4,10 @@ > Language][nsprust] available in print and ebook format from [No Starch > Press][nsp]. -[nsprust]: https://nostarch.com/rust-programming-language-2nd-edition +[nsprust]: https://nostarch.com/rust-programming-language-3rd-edition [nsp]: https://nostarch.com/ -Welcome to *The Rust Programming Language*, an introductory book about Rust. +Welcome to _The Rust Programming Language_, an introductory book about Rust. The Rust programming language helps you write faster, more reliable software. High-level ergonomics and low-level control are often at odds in programming language design; Rust challenges that conflict. Through balancing powerful @@ -24,21 +24,21 @@ the most important groups. Rust is proving to be a productive tool for collaborating among large teams of developers with varying levels of systems programming knowledge. Low-level code -is prone to various subtle bugs, which in most other languages can be caught -only through extensive testing and careful code review by experienced +is prone to various subtle bugs, which in most other languages can only be +caught through extensive testing and careful code review by experienced developers. In Rust, the compiler plays a gatekeeper role by refusing to compile code with these elusive bugs, including concurrency bugs. By working -alongside the compiler, the team can spend their time focusing on the program’s +alongside the compiler, the team can spend its time focusing on the program’s logic rather than chasing down bugs. Rust also brings contemporary developer tools to the systems programming world: -* Cargo, the included dependency manager and build tool, makes adding, +- Cargo, the included dependency manager and build tool, makes adding, compiling, and managing dependencies painless and consistent across the Rust ecosystem. -* The Rustfmt formatting tool ensures a consistent coding style across +- The `rustfmt` formatting tool ensures a consistent coding style across developers. -* The Rust Language Server powers Integrated Development Environment (IDE) +- The Rust Language Server powers integrated development environment (IDE) integration for code completion and inline error messages. By using these and other tools in the Rust ecosystem, developers can be @@ -49,7 +49,7 @@ productive while writing systems-level code. Rust is for students and those who are interested in learning about systems concepts. Using Rust, many people have learned about topics like operating systems development. The community is very welcoming and happy to answer -student questions. Through efforts such as this book, the Rust teams want to +students’ questions. Through efforts such as this book, the Rust teams want to make systems concepts more accessible to more people, especially those new to programming. @@ -74,24 +74,25 @@ mean both how quickly Rust code can run and the speed at which Rust lets you write programs. The Rust compiler’s checks ensure stability through feature additions and refactoring. This is in contrast to the brittle legacy code in languages without these checks, which developers are often afraid to modify. By -striving for zero-cost abstractions, higher-level features that compile to -lower-level code as fast as code written manually, Rust endeavors to make safe +striving for zero-cost abstractions—higher-level features that compile to +lower-level code as fast as code written manually—Rust endeavors to make safe code be fast code as well. The Rust language hopes to support many other users as well; those mentioned here are merely some of the biggest stakeholders. Overall, Rust’s greatest ambition is to eliminate the trade-offs that programmers have accepted for -decades by providing safety *and* productivity, speed *and* ergonomics. Give -Rust a try and see if its choices work for you. +decades by providing safety _and_ productivity, speed _and_ ergonomics. Give +Rust a try, and see if its choices work for you. ## Who This Book Is For -This book assumes that you’ve written code in another programming language but -doesn’t make any assumptions about which one. We’ve tried to make the material -broadly accessible to those from a wide variety of programming backgrounds. We -don’t spend a lot of time talking about what programming *is* or how to think -about it. If you’re entirely new to programming, you would be better served by -reading a book that specifically provides an introduction to programming. +This book assumes that you’ve written code in another programming language, but +it doesn’t make any assumptions about which one. We’ve tried to make the +material broadly accessible to those from a wide variety of programming +backgrounds. We don’t spend a lot of time talking about what programming _is_ +or how to think about it. If you’re entirely new to programming, you would be +better served by reading a book that specifically provides an introduction to +programming. ## How to Use This Book @@ -103,81 +104,88 @@ the topic in a later chapter. You’ll find two kinds of chapters in this book: concept chapters and project chapters. In concept chapters, you’ll learn about an aspect of Rust. In project chapters, we’ll build small programs together, applying what you’ve learned so -far. Chapters 2, 12, and 20 are project chapters; the rest are concept chapters. +far. Chapter 2, Chapter 12, and Chapter 21 are project chapters; the rest are +concept chapters. -Chapter 1 explains how to install Rust, how to write a “Hello, world!” program, -and how to use Cargo, Rust’s package manager and build tool. Chapter 2 is a -hands-on introduction to writing a program in Rust, having you build up a -number guessing game. Here we cover concepts at a high level, and later +**Chapter 1** explains how to install Rust, how to write a “Hello, world!” +program, and how to use Cargo, Rust’s package manager and build tool. **Chapter +2** is a hands-on introduction to writing a program in Rust, having you build +up a number-guessing game. Here, we cover concepts at a high level, and later chapters will provide additional detail. If you want to get your hands dirty -right away, Chapter 2 is the place for that. Chapter 3 covers Rust features -that are similar to those of other programming languages, and in Chapter 4 -you’ll learn about Rust’s ownership system. If you’re a particularly meticulous -learner who prefers to learn every detail before moving on to the next, you -might want to skip Chapter 2 and go straight to Chapter 3, returning to Chapter -2 when you’d like to work on a project applying the details you’ve learned. - -Chapter 5 discusses structs and methods, and Chapter 6 covers enums, `match` -expressions, and the `if let` control flow construct. You’ll use structs and -enums to make custom types in Rust. - -In Chapter 7, you’ll learn about Rust’s module system and about privacy rules -for organizing your code and its public Application Programming Interface -(API). Chapter 8 discusses some common collection data structures that the -standard library provides, such as vectors, strings, and hash maps. Chapter 9 +right away, Chapter 2 is the place for that. If you’re a particularly +meticulous learner who prefers to learn every detail before moving on to the +next, you might want to skip Chapter 2 and go straight to **Chapter 3**, which +covers Rust features that are similar to those of other programming languages; +then, you can return to Chapter 2 when you’d like to work on a project applying +the details you’ve learned. + +In **Chapter 4**, you’ll learn about Rust’s ownership system. **Chapter 5** +discusses structs and methods. **Chapter 6** covers enums, `match` expressions, +and the `if let` and `let...else` control flow constructs. You’ll use structs +and enums to make custom types. + +In **Chapter 7**, you’ll learn about Rust’s module system and about privacy +rules for organizing your code and its public application programming interface +(API). **Chapter 8** discusses some common collection data structures that the +standard library provides: vectors, strings, and hash maps. **Chapter 9** explores Rust’s error-handling philosophy and techniques. -Chapter 10 digs into generics, traits, and lifetimes, which give you the power -to define code that applies to multiple types. Chapter 11 is all about testing, -which even with Rust’s safety guarantees is necessary to ensure your program’s -logic is correct. In Chapter 12, we’ll build our own implementation of a subset -of functionality from the `grep` command line tool that searches for text -within files. For this, we’ll use many of the concepts we discussed in the -previous chapters. - -Chapter 13 explores closures and iterators: features of Rust that come from -functional programming languages. In Chapter 14, we’ll examine Cargo in more -depth and talk about best practices for sharing your libraries with others. -Chapter 15 discusses smart pointers that the standard library provides and the -traits that enable their functionality. - -In Chapter 16, we’ll walk through different models of concurrent programming -and talk about how Rust helps you to program in multiple threads fearlessly. -Chapter 17 looks at how Rust idioms compare to object-oriented programming -principles you might be familiar with. - -Chapter 18 is a reference on patterns and pattern matching, which are powerful -ways of expressing ideas throughout Rust programs. Chapter 19 contains a -smorgasbord of advanced topics of interest, including unsafe Rust, macros, and -more about lifetimes, traits, types, functions, and closures. - -In Chapter 20, we’ll complete a project in which we’ll implement a low-level -multithreaded web server! - -Finally, some appendices contain useful information about the language in a -more reference-like format. Appendix A covers Rust’s keywords, Appendix B -covers Rust’s operators and symbols, Appendix C covers derivable traits -provided by the standard library, Appendix D covers some useful development -tools, and Appendix E explains Rust editions. In Appendix F, you can find -translations of the book, and in Appendix G we’ll cover how Rust is made and -what nightly Rust is. - -There is no wrong way to read this book: if you want to skip ahead, go for it! +**Chapter 10** digs into generics, traits, and lifetimes, which give you the +power to define code that applies to multiple types. **Chapter 11** is all +about testing, which even with Rust’s safety guarantees is necessary to ensure +that your program’s logic is correct. In **Chapter 12**, we’ll build our own +implementation of a subset of functionality from the `grep` command line tool +that searches for text within files. For this, we’ll use many of the concepts +we discussed in the previous chapters. + +**Chapter 13** explores closures and iterators: features of Rust that come from +functional programming languages. In **Chapter 14**, we’ll examine Cargo in +more depth and talk about best practices for sharing your libraries with +others. **Chapter 15** discusses smart pointers that the standard library +provides and the traits that enable their functionality. + +In **Chapter 16**, we’ll walk through different models of concurrent +programming and talk about how Rust helps you program in multiple threads +fearlessly. In **Chapter 17**, we build on that by exploring Rust’s async and +await syntax, along with tasks, futures, and streams, and the lightweight +concurrency model they enable. + +**Chapter 18** looks at how Rust idioms compare to object-oriented programming +principles you might be familiar with. **Chapter 19** is a reference on +patterns and pattern matching, which are powerful ways of expressing ideas +throughout Rust programs. **Chapter 20** contains a smorgasbord of advanced +topics of interest, including unsafe Rust, macros, and more about lifetimes, +traits, types, functions, and closures. + +In **Chapter 21**, we’ll complete a project in which we’ll implement a +low-level multithreaded web server! + +Finally, some appendixes contain useful information about the language in a +more reference-like format. **Appendix A** covers Rust’s keywords, **Appendix +B** covers Rust’s operators and symbols, **Appendix C** covers derivable traits +provided by the standard library, **Appendix D** covers some useful development +tools, and **Appendix E** explains Rust editions. In **Appendix F**, you can +find translations of the book, and in **Appendix G** we’ll cover how Rust is +made and what nightly Rust is. + +There is no wrong way to read this book: If you want to skip ahead, go for it! You might have to jump back to earlier chapters if you experience any confusion. But do whatever works for you. An important part of the process of learning Rust is learning how to read the -error messages the compiler displays: these will guide you toward working code. +error messages the compiler displays: These will guide you toward working code. As such, we’ll provide many examples that don’t compile along with the error message the compiler will show you in each situation. Know that if you enter and run a random example, it may not compile! Make sure you read the surrounding text to see whether the example you’re trying to run is meant to -error. Ferris will also help you distinguish code that isn’t meant to work: +error. In most situations, we’ll lead you to the correct version of any code +that doesn’t compile. Ferris will also help you distinguish code that isn’t +meant to work: | Ferris | Meaning | -|------------------------------------------------------------------------------------------------------------------|--------------------------------------------------| +| ---------------------------------------------------------------------------------------------------------------- | ------------------------------------------------ | | Ferris with a question mark | This code does not compile! | | Ferris throwing up their hands | This code panics! | | Ferris with one claw up, shrugging | This code does not produce the desired behavior. | diff --git a/src/ch01-00-getting-started.md b/src/ch01-00-getting-started.md index ff5e324f7a..ccb10e884e 100644 --- a/src/ch01-00-getting-started.md +++ b/src/ch01-00-getting-started.md @@ -3,6 +3,6 @@ Let’s start your Rust journey! There’s a lot to learn, but every journey starts somewhere. In this chapter, we’ll discuss: -* Installing Rust on Linux, macOS, and Windows -* Writing a program that prints `Hello, world!` -* Using `cargo`, Rust’s package manager and build system +- Installing Rust on Linux, macOS, and Windows +- Writing a program that prints `Hello, world!` +- Using `cargo`, Rust’s package manager and build system diff --git a/src/ch01-01-installation.md b/src/ch01-01-installation.md index 87f37fab26..39d8371a6c 100644 --- a/src/ch01-01-installation.md +++ b/src/ch01-01-installation.md @@ -39,7 +39,7 @@ for your password. If the install is successful, the following line will appear: Rust is installed now. Great! ``` -You will also need a *linker*, which is a program that Rust uses to join its +You will also need a _linker_, which is a program that Rust uses to join its compiled outputs into one file. It is likely you already have one. If you get linker errors, you should install a C compiler, which will typically include a linker. A C compiler is also useful because some common Rust packages depend on @@ -57,20 +57,15 @@ the `build-essential` package. ### Installing `rustup` on Windows -On Windows, go to [https://www.rust-lang.org/tools/install][install] and follow -the instructions for installing Rust. At some point in the installation, you’ll -receive a message explaining that you’ll also need the MSVC build tools for -Visual Studio 2013 or later. +On Windows, go to [https://www.rust-lang.org/tools/install][install] and follow the instructions for installing Rust. At some point in the +installation, you’ll be prompted to install Visual Studio. This provides a +linker and the native libraries needed to compile programs. If you need more +help with this step, see +[https://rust-lang.github.io/rustup/installation/windows-msvc.html][msvc]. -To acquire the build tools, you’ll need to install [Visual Studio -2022][visualstudio]. When asked which workloads to install, include: - -* “Desktop Development with C++” -* The Windows 10 or 11 SDK -* The English language pack component, along with any other language pack of - your choosing - -The rest of this book uses commands that work in both *cmd.exe* and PowerShell. +The rest of this book uses commands that work in both _cmd.exe_ and PowerShell. If there are specific differences, we’ll explain which to use. ### Troubleshooting @@ -131,7 +126,10 @@ shell: $ rustup self uninstall ``` -### Local Documentation + + + +### Reading the Local Documentation The installation of Rust also includes a local copy of the documentation so that you can read it offline. Run `rustup doc` to open the local documentation @@ -141,7 +139,39 @@ Any time a type or function is provided by the standard library and you’re not sure what it does or how to use it, use the application programming interface (API) documentation to find out! + + + +### Using Text Editors and IDEs + +This book makes no assumptions about what tools you use to author Rust code. +Just about any text editor will get the job done! However, many text editors and +integrated development environments (IDEs) have built-in support for Rust. You +can always find a fairly current list of many editors and IDEs on [the tools +page][tools] on the Rust website. + +### Working Offline with This Book + +In several examples, we will use Rust packages beyond the standard library. To +work through those examples, you will either need to have an internet connection +or to have downloaded those dependencies ahead of time. To download the +dependencies ahead of time, you can run the following commands. (We’ll explain +what `cargo` is and what each of these commands does in detail later.) + +```console +$ cargo new get-dependencies +$ cd get-dependencies +$ cargo add rand@0.8.5 trpl@0.2.0 +``` + +This will cache the downloads for these packages so you will not need to +download them later. Once you have run this command, you do not need to keep the +`get-dependencies` folder. If you have run this command, you can use the +`--offline` flag with all `cargo` commands in the rest of the book to use these +cached versions instead of attempting to use the network. + [otherinstall]: https://forge.rust-lang.org/infra/other-installation-methods.html [install]: https://www.rust-lang.org/tools/install -[visualstudio]: https://visualstudio.microsoft.com/downloads/ +[msvc]: https://rust-lang.github.io/rustup/installation/windows-msvc.html [community]: https://www.rust-lang.org/community +[tools]: https://www.rust-lang.org/tools diff --git a/src/ch01-02-hello-world.md b/src/ch01-02-hello-world.md index f291463799..a70b2db6d3 100644 --- a/src/ch01-02-hello-world.md +++ b/src/ch01-02-hello-world.md @@ -6,21 +6,24 @@ prints the text `Hello, world!` to the screen, so we’ll do the same here! > Note: This book assumes basic familiarity with the command line. Rust makes > no specific demands about your editing or tooling or where your code lives, so -> if you prefer to use an integrated development environment (IDE) instead of -> the command line, feel free to use your favorite IDE. Many IDEs now have some -> degree of Rust support; check the IDE’s documentation for details. The Rust -> team has been focusing on enabling great IDE support via `rust-analyzer`. See -> [Appendix D][devtools] for more details. +> if you prefer to use an IDE instead of the command line, feel free to use your +> favorite IDE. Many IDEs now have some degree of Rust support; check the IDE’s +> documentation for details. The Rust team has been focusing on enabling great +> IDE support via `rust-analyzer`. See [Appendix D][devtools] +> for more details. -### Creating a Project Directory + + + +### Project Directory Setup You’ll start by making a directory to store your Rust code. It doesn’t matter to Rust where your code lives, but for the exercises and projects in this book, -we suggest making a *projects* directory in your home directory and keeping all +we suggest making a _projects_ directory in your home directory and keeping all your projects there. -Open a terminal and enter the following commands to make a *projects* directory -and a directory for the “Hello, world!” project within the *projects* directory. +Open a terminal and enter the following commands to make a _projects_ directory +and a directory for the “Hello, world!” project within the _projects_ directory. For Linux, macOS, and PowerShell on Windows, enter this: @@ -40,16 +43,19 @@ For Windows CMD, enter this: > cd hello_world ``` -### Writing and Running a Rust Program + + + +### Rust Program Basics -Next, make a new source file and call it *main.rs*. Rust files always end with -the *.rs* extension. If you’re using more than one word in your filename, the +Next, make a new source file and call it _main.rs_. Rust files always end with +the _.rs_ extension. If you’re using more than one word in your filename, the convention is to use an underscore to separate them. For example, use -*hello_world.rs* rather than *helloworld.rs*. +_hello_world.rs_ rather than _helloworld.rs_. -Now open the *main.rs* file you just created and enter the code in Listing 1-1. +Now open the _main.rs_ file you just created and enter the code in Listing 1-1. -Filename: main.rs + ```rust fn main() { @@ -57,10 +63,10 @@ fn main() { } ``` -Listing 1-1: A program that prints `Hello, world!` + Save the file and go back to your terminal window in the -*~/projects/hello_world* directory. On Linux or macOS, enter the following +_~/projects/hello_world_ directory. On Linux or macOS, enter the following commands to compile and run the file: ```console @@ -69,11 +75,11 @@ $ ./main Hello, world! ``` -On Windows, enter the command `.\main.exe` instead of `./main`: +On Windows, enter the command `.\main` instead of `./main`: ```powershell > rustc main.rs -> .\main.exe +> .\main Hello, world! ``` @@ -85,7 +91,11 @@ section for ways to get help. If `Hello, world!` did print, congratulations! You’ve officially written a Rust program. That makes you a Rust programmer—welcome! -### Anatomy of a Rust Program + + + + +### The Anatomy of a Rust Program Let’s review this “Hello, world!” program in detail. Here’s the first piece of the puzzle: @@ -96,10 +106,10 @@ fn main() { } ``` -These lines define a function named `main`. The `main` function is special: it +These lines define a function named `main`. The `main` function is special: It is always the first code that runs in every executable Rust program. Here, the first line declares a function named `main` that has no parameters and returns -nothing. If there were parameters, they would go inside the parentheses `()`. +nothing. If there were parameters, they would go inside the parentheses (`()`). The function body is wrapped in `{}`. Rust requires curly brackets around all function bodies. It’s good style to place the opening curly bracket on the same @@ -115,28 +125,30 @@ line as the function declaration, adding one space in between. The body of the `main` function holds the following code: ```rust - println!("Hello, world!"); +println!("Hello, world!"); ``` -This line does all the work in this little program: it prints text to the -screen. There are four important details to notice here. - -First, Rust style is to indent with four spaces, not a tab. +This line does all the work in this little program: It prints text to the +screen. There are three important details to notice here. -Second, `println!` calls a Rust macro. If it had called a function instead, it -would be entered as `println` (without the `!`). We’ll discuss Rust macros in -more detail in Chapter 19. For now, you just need to know that using a `!` -means that you’re calling a macro instead of a normal function and that macros -don’t always follow the same rules as functions. +First, `println!` calls a Rust macro. If it had called a function instead, it +would be entered as `println` (without the `!`). Rust macros are a way to write +code that generates code to extend Rust syntax, and we’ll discuss them in more +detail in [Chapter 20][ch20-macros]. For now, you just need to +know that using a `!` means that you’re calling a macro instead of a normal +function and that macros don’t always follow the same rules as functions. -Third, you see the `"Hello, world!"` string. We pass this string as an argument +Second, you see the `"Hello, world!"` string. We pass this string as an argument to `println!`, and the string is printed to the screen. -Fourth, we end the line with a semicolon (`;`), which indicates that this -expression is over and the next one is ready to begin. Most lines of Rust code +Third, we end the line with a semicolon (`;`), which indicates that this +expression is over, and the next one is ready to begin. Most lines of Rust code end with a semicolon. -### Compiling and Running Are Separate Steps + + + +### Compilation and Execution You’ve just run a newly created program, so let’s examine each step in the process. @@ -171,24 +183,24 @@ main.pdb main.rs ``` -This shows the source code file with the *.rs* extension, the executable file -(*main.exe* on Windows, but *main* on all other platforms), and, when using -Windows, a file containing debugging information with the *.pdb* extension. -From here, you run the *main* or *main.exe* file, like this: +This shows the source code file with the _.rs_ extension, the executable file +(_main.exe_ on Windows, but _main_ on all other platforms), and, when using +Windows, a file containing debugging information with the _.pdb_ extension. +From here, you run the _main_ or _main.exe_ file, like this: ```console -$ ./main # or .\main.exe on Windows +$ ./main # or .\main on Windows ``` -If your *main.rs* is your “Hello, world!” program, this line prints `Hello, +If your _main.rs_ is your “Hello, world!” program, this line prints `Hello, world!` to your terminal. If you’re more familiar with a dynamic language, such as Ruby, Python, or JavaScript, you might not be used to compiling and running a program as -separate steps. Rust is an *ahead-of-time compiled* language, meaning you can +separate steps. Rust is an _ahead-of-time compiled_ language, meaning you can compile a program and give the executable to someone else, and they can run it -even without having Rust installed. If you give someone a *.rb*, *.py*, or -*.js* file, they need to have a Ruby, Python, or JavaScript implementation +even without having Rust installed. If you give someone a _.rb_, _.py_, or +_.js_ file, they need to have a Ruby, Python, or JavaScript implementation installed (respectively). But in those languages, you only need one command to compile and run your program. Everything is a trade-off in language design. @@ -199,3 +211,4 @@ real-world Rust programs. [troubleshooting]: ch01-01-installation.html#troubleshooting [devtools]: appendix-04-useful-development-tools.html +[ch20-macros]: ch20-05-macros.html diff --git a/src/ch01-03-hello-cargo.md b/src/ch01-03-hello-cargo.md index 42cd0889c8..70898e1180 100644 --- a/src/ch01-03-hello-cargo.md +++ b/src/ch01-03-hello-cargo.md @@ -4,7 +4,7 @@ Cargo is Rust’s build system and package manager. Most Rustaceans use this too to manage their Rust projects because Cargo handles a lot of tasks for you, such as building your code, downloading the libraries your code depends on, and building those libraries. (We call the libraries that your code needs -*dependencies*.) +_dependencies_.) The simplest Rust programs, like the one we’ve written so far, don’t have any dependencies. If we had built the “Hello, world!” project with Cargo, it would @@ -30,7 +30,7 @@ determine how to install Cargo separately. ### Creating a Project with Cargo Let’s create a new project using Cargo and look at how it differs from our -original “Hello, world!” project. Navigate back to your *projects* directory +original “Hello, world!” project. Navigate back to your _projects_ directory (or wherever you decided to store your code). Then, on any operating system, run the following: @@ -39,15 +39,15 @@ $ cargo new hello_cargo $ cd hello_cargo ``` -The first command creates a new directory and project called *hello_cargo*. -We’ve named our project *hello_cargo*, and Cargo creates its files in a +The first command creates a new directory and project called _hello_cargo_. +We’ve named our project _hello_cargo_, and Cargo creates its files in a directory of the same name. -Go into the *hello_cargo* directory and list the files. You’ll see that Cargo -has generated two files and one directory for us: a *Cargo.toml* file and a -*src* directory with a *main.rs* file inside. +Go into the _hello_cargo_ directory and list the files. You’ll see that Cargo +has generated two files and one directory for us: a _Cargo.toml_ file and a +_src_ directory with a _main.rs_ file inside. -It has also initialized a new Git repository along with a *.gitignore* file. +It has also initialized a new Git repository along with a _.gitignore_ file. Git files won’t be generated if you run `cargo new` within an existing Git repository; you can override this behavior by using `cargo new --vcs=git`. @@ -55,27 +55,24 @@ repository; you can override this behavior by using `cargo new --vcs=git`. > use a different version control system or no version control system by using > the `--vcs` flag. Run `cargo new --help` to see the available options. -Open *Cargo.toml* in your text editor of choice. It should look similar to the +Open _Cargo.toml_ in your text editor of choice. It should look similar to the code in Listing 1-2. -Filename: Cargo.toml + ```toml [package] name = "hello_cargo" version = "0.1.0" -edition = "2021" - -# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html +edition = "2024" [dependencies] ``` -Listing 1-2: Contents of *Cargo.toml* generated by `cargo -new` + -This file is in the [*TOML*][toml] (*Tom’s Obvious, Minimal -Language*) format, which is Cargo’s configuration format. +This file is in the [_TOML_][toml] (_Tom’s Obvious, Minimal +Language_) format, which is Cargo’s configuration format. The first line, `[package]`, is a section heading that indicates that the following statements are configuring a package. As we add more information to @@ -87,10 +84,10 @@ about the `edition` key in [Appendix E][appendix-e]. The last line, `[dependencies]`, is the start of a section for you to list any of your project’s dependencies. In Rust, packages of code are referred to as -*crates*. We won’t need any other crates for this project, but we will in the +_crates_. We won’t need any other crates for this project, but we will in the first project in Chapter 2, so we’ll use this dependencies section then. -Now open *src/main.rs* and take a look: +Now open _src/main.rs_ and take a look: Filename: src/main.rs @@ -102,10 +99,10 @@ fn main() { Cargo has generated a “Hello, world!” program for you, just like the one we wrote in Listing 1-1! So far, the differences between our project and the -project Cargo generated are that Cargo placed the code in the *src* directory -and we have a *Cargo.toml* configuration file in the top directory. +project Cargo generated are that Cargo placed the code in the _src_ directory, +and we have a _Cargo.toml_ configuration file in the top directory. -Cargo expects your source files to live inside the *src* directory. The +Cargo expects your source files to live inside the _src_ directory. The top-level project directory is just for README files, license information, configuration files, and anything else not related to your code. Using Cargo helps you organize your projects. There’s a place for everything, and @@ -113,13 +110,14 @@ everything is in its place. If you started a project that doesn’t use Cargo, as we did with the “Hello, world!” project, you can convert it to a project that does use Cargo. Move the -project code into the *src* directory and create an appropriate *Cargo.toml* -file. +project code into the _src_ directory and create an appropriate _Cargo.toml_ +file. One easy way to get that _Cargo.toml_ file is to run `cargo init`, which +will create it for you automatically. ### Building and Running a Cargo Project Now let’s look at what’s different when we build and run the “Hello, world!” -program with Cargo! From your *hello_cargo* directory, build your project by +program with Cargo! From your _hello_cargo_ directory, build your project by entering the following command: ```console @@ -128,10 +126,10 @@ $ cargo build Finished dev [unoptimized + debuginfo] target(s) in 2.85 secs ``` -This command creates an executable file in *target/debug/hello_cargo* (or -*target\debug\hello_cargo.exe* on Windows) rather than in your current +This command creates an executable file in _target/debug/hello_cargo_ (or +_target\debug\hello_cargo.exe_ on Windows) rather than in your current directory. Because the default build is a debug build, Cargo puts the binary in -a directory named *debug*. You can run the executable with this command: +a directory named _debug_. You can run the executable with this command: ```console $ ./target/debug/hello_cargo # or .\target\debug\hello_cargo.exe on Windows @@ -140,7 +138,7 @@ Hello, world! If all goes well, `Hello, world!` should print to the terminal. Running `cargo build` for the first time also causes Cargo to create a new file at the top -level: *Cargo.lock*. This file keeps track of the exact versions of +level: _Cargo.lock_. This file keeps track of the exact versions of dependencies in your project. This project doesn’t have dependencies, so the file is a bit sparse. You won’t ever need to change this file manually; Cargo manages its contents for you. @@ -188,18 +186,18 @@ Why would you not want an executable? Often, `cargo check` is much faster than continually checking your work while writing the code, using `cargo check` will speed up the process of letting you know if your project is still compiling! As such, many Rustaceans run `cargo check` periodically as they write their -program to make sure it compiles. Then they run `cargo build` when they’re +program to make sure it compiles. Then, they run `cargo build` when they’re ready to use the executable. Let’s recap what we’ve learned so far about Cargo: -* We can create a project using `cargo new`. -* We can build a project using `cargo build`. -* We can build and run a project in one step using `cargo run`. -* We can build a project without producing a binary to check for errors using +- We can create a project using `cargo new`. +- We can build a project using `cargo build`. +- We can build and run a project in one step using `cargo run`. +- We can build a project without producing a binary to check for errors using `cargo check`. -* Instead of saving the result of the build in the same directory as our code, - Cargo stores it in the *target/debug* directory. +- Instead of saving the result of the build in the same directory as our code, + Cargo stores it in the _target/debug_ directory. An additional advantage of using Cargo is that the commands are the same no matter which operating system you’re working on. So, at this point, we’ll no @@ -209,16 +207,19 @@ longer provide specific instructions for Linux and macOS versus Windows. When your project is finally ready for release, you can use `cargo build --release` to compile it with optimizations. This command will create an -executable in *target/release* instead of *target/debug*. The optimizations +executable in _target/release_ instead of _target/debug_. The optimizations make your Rust code run faster, but turning them on lengthens the time it takes for your program to compile. This is why there are two different profiles: one for development, when you want to rebuild quickly and often, and another for building the final program you’ll give to a user that won’t be rebuilt repeatedly and that will run as fast as possible. If you’re benchmarking your code’s running time, be sure to run `cargo build --release` and benchmark with -the executable in *target/release*. +the executable in _target/release_. + + + -### Cargo as Convention +### Leveraging Cargo’s Conventions With simple projects, Cargo doesn’t provide a lot of value over just using `rustc`, but it will prove its worth as your programs become more intricate. @@ -240,14 +241,14 @@ For more information about Cargo, check out [its documentation][cargo]. ## Summary -You’re already off to a great start on your Rust journey! In this chapter, -you’ve learned how to: +You’re already off to a great start on your Rust journey! In this chapter, you +learned how to: -* Install the latest stable version of Rust using `rustup` -* Update to a newer Rust version -* Open locally installed documentation -* Write and run a “Hello, world!” program using `rustc` directly -* Create and run a new project using the conventions of Cargo +- Install the latest stable version of Rust using `rustup`. +- Update to a newer Rust version. +- Open locally installed documentation. +- Write and run a “Hello, world!” program using `rustc` directly. +- Create and run a new project using the conventions of Cargo. This is a great time to build a more substantial program to get used to reading and writing Rust code. So, in Chapter 2, we’ll build a guessing game program. diff --git a/src/ch02-00-guessing-game-tutorial.md b/src/ch02-00-guessing-game-tutorial.md index 5e27fb114d..b1aea365c3 100644 --- a/src/ch02-00-guessing-game-tutorial.md +++ b/src/ch02-00-guessing-game-tutorial.md @@ -1,33 +1,33 @@ -# Programming a Guessing Game +# Bikin Game Tebak Angka -Let’s jump into Rust by working through a hands-on project together! This -chapter introduces you to a few common Rust concepts by showing you how to use -them in a real program. You’ll learn about `let`, `match`, methods, associated -functions, external crates, and more! In the following chapters, we’ll explore -these ideas in more detail. In this chapter, you’ll just practice the -fundamentals. +Yuk langsung gas belajar Rust lewat proyek langsung praktek!. Di bab ini kamu +bakal kenalan sama konsep-konsep Rust yang sering dipakai, tapi bukan cuma teori +doang, langsung dipraktekin di program beneran. Kamu bakal ketemu `let`, +`match`, method, associated function, external crate, dan temen-temennya. Di bab +selanjutnya baru kita kupas lebih dalam. Sekarang fokus dulu ke basic-nya sambil +praktik. -We’ll implement a classic beginner programming problem: a guessing game. Here’s -how it works: the program will generate a random integer between 1 and 100. It -will then prompt the player to enter a guess. After a guess is entered, the -program will indicate whether the guess is too low or too high. If the guess is -correct, the game will print a congratulatory message and exit. +Kita bakal ngerjain problem klasik buat pemula: **game tebak angka**, Kurang +lebih gini cara mainnya: Program bakal bikin angka random dari 1 sampai 100 Kamu +diminta masukin tebakan Abis itu program bakal ngasih tau tebakan kamu +**kekecilan** atau **kegedean** kalo pas… **boom!** Tebakan kamu bener, program +bakal ngucapin selamat dan selesai -## Setting Up a New Project +## Setup Project Baru -To set up a new project, go to the *projects* directory that you created in -Chapter 1 and make a new project using Cargo, like so: +Biar bisa mulai, masuk dulu ke folder _projects_ yang kamu bikin di Chapter 1, +terus bikin project baru pakai Cargo kayak gini: ```console -$ cargo new guessing_game -$ cd guessing_game +cargo new guessing_game +cd guessing_game ``` -The first command, `cargo new`, takes the name of the project (`guessing_game`) -as the first argument. The second command changes to the new project’s -directory. +Perintah pertama, `cargo new`, pake nama project (`guessing_game`) sebagai +argumen pertamanya. Perintah kedua buat pindah ke folder project yang baru +dibuat. -Look at the generated *Cargo.toml* file: +Sekarang cek dulu file _Cargo.toml_ yang otomatis dibuat -section in Chapter 3. To make a variable mutable, we add `mut` before the -variable name: +Baris ini membuat variabel baru bernama `apples` dan mengikatnya ke nilai `5`. +Di Rust, variabel itu **immutable secara default**, artinya setelah kita kasih +nilai ke variabel, nilainya nggak bisa diubah lagi. Kita bakal bahas ini lebih +detail di bagian **“Variables and Mutability”** di Chapter 3. Untuk membuat +variabel bisa diubah (mutable), kita tambahkan `mut` sebelum nama variabel: ```rust,ignore let apples = 5; // immutable let mut bananas = 5; // mutable ``` -> Note: The `//` syntax starts a comment that continues until the end of the -> line. Rust ignores everything in comments. We’ll discuss comments in more -> detail in [Chapter 3][comments]. +> Catatan: Sintak `//` memulai komentar yang berlanjut sampai akhir baris. Rust +> mengabaikan semua yang ada di dalam komentar. Kita akan membahas komentar +> lebih detail di [Chapter3][comments]. -Returning to the guessing game program, you now know that `let mut guess` will -introduce a mutable variable named `guess`. The equal sign (`=`) tells Rust we -want to bind something to the variable now. On the right of the equal sign is -the value that `guess` is bound to, which is the result of calling -`String::new`, a function that returns a new instance of a `String`. -[`String`][string] is a string type provided by the standard -library that is a growable, UTF-8 encoded bit of text. +Kembali ke program tebak angka, sekarang kamu tahu bahwa `let mut guess` akan +memperkenalkan variabel mutable bernama `guess`. Tanda sama dengan (`=`) memberi +tahu Rust bahwa kita ingin langsung mengikat sesuatu ke variabel tersebut. Di +sebelah kanan tanda sama dengan adalah nilai yang diikat ke `guess`, yaitu hasil +pemanggilan `String::new`, sebuah fungsi yang mengembalikan instance baru dari +`String`. [`String`][string] adalah tipe string yang disediakan +oleh standard library yang bisa bertambah ukurannya dan berisi teks UTF-8. -The `::` syntax in the `::new` line indicates that `new` is an associated -function of the `String` type. An *associated function* is a function that’s -implemented on a type, in this case `String`. This `new` function creates a -new, empty string. You’ll find a `new` function on many types because it’s a -common name for a function that makes a new value of some kind. +Sintaks `::` pada baris `::new` menunjukkan bahwa `new` adalah **associated +function** dari tipe `String`. **Associated function** adalah fungsi yang +diimplementasikan pada sebuah tipe, dalam kasus ini `String`. Fungsi `new` ini +membuat string baru yang kosong. Kamu akan menemukan fungsi `new` pada banyak +tipe karena ini adalah nama umum untuk fungsi yang membuat nilai baru. -In full, the `let mut guess = String::new();` line has created a mutable -variable that is currently bound to a new, empty instance of a `String`. Whew! +Secara keseluruhan, baris `let mut guess = String::new();` telah membuat +variabel mutable yang saat ini terikat pada instance baru dan kosong dari +`String`. Whew! -### Receiving User Input +### Menerima Input dari User -Recall that we included the input/output functionality from the standard -library with `use std::io;` on the first line of the program. Now we’ll call -the `stdin` function from the `io` module, which will allow us to handle user -input: +Ingat, tadi kita sudah masukin fitur input/output dari standard library dengan +`use std::io;` di baris pertama program. Sekarang kita bakal manggil fungsi +`stdin` dari module `io`, yang bakal kita pakai buat ngurus input dari user: ```rust,ignore {{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:read}} ``` -If we hadn’t imported the `io` library with `use std::io;` at the beginning of -the program, we could still use the function by writing this function call as -`std::io::stdin`. The `stdin` function returns an instance of -[`std::io::Stdin`][iostdin], which is a type that represents a -handle to the standard input for your terminal. - -Next, the line `.read_line(&mut guess)` calls the [`read_line`][read_line] method on the standard input handle to get input from the user. -We’re also passing `&mut guess` as the argument to `read_line` to tell it what -string to store the user input in. The full job of `read_line` is to take -whatever the user types into standard input and append that into a string -(without overwriting its contents), so we therefore pass that string as an -argument. The string argument needs to be mutable so the method can change the -string’s content. - -The `&` indicates that this argument is a *reference*, which gives you a way to -let multiple parts of your code access one piece of data without needing to -copy that data into memory multiple times. References are a complex feature, -and one of Rust’s major advantages is how safe and easy it is to use -references. You don’t need to know a lot of those details to finish this -program. For now, all you need to know is that, like variables, references are -immutable by default. Hence, you need to write `&mut guess` rather than -`&guess` to make it mutable. (Chapter 4 will explain references more -thoroughly.) - - +Kalau kita **nggak** meng-import module `io` dengan `use std::io;` di awal +program, kita tetap bisa pakai fungsinya dengan nulis pemanggilannya sebagai +`std::io::stdin`. Fungsi `stdin` ini bakal balikin sebuah instance dari +[`std::io::Stdin`][iostdin], yaitu tipe yang mewakili _handle_ ke +input standar terminal kamu. + +Selanjutnya, baris `.read_line(&mut guess)` akan memanggil method +[`read_line`][read_line] pada _input handle standard_ untuk +mengambil input dari user. Kita juga mengoper `&mut guess` sebagai argumen ke +`read_line` untuk kasih tahu string mana yang harus dipakai buat nyimpen input +user. Tugas penuh `read_line` adalah mengambil apapun yang user ketik di +standard input dan **menambahkan** itu ke dalam sebuah string (tanpa menghapus +isi sebelumnya), jadi kita kasih string itu sebagai argumen. String tersebut +harus mutable supaya method-nya bisa mengubah isinya. + +Tanda `&` menunjukkan bahwa argumen ini adalah sebuah **reference**, yaitu cara +buat beberapa bagian kode mengakses data yang sama tanpa harus menyalin datanya +berkali-kali ke memori. Reference itu topik yang lumayan kompleks, dan salah +satu keunggulan besar Rust adalah reference-nya aman dan relatif mudah dipakai. +Kamu gak perlu paham detailnya untuk menyelesaikan program ini. Untuk sekarang, +semua yang perlu kamu ketahui bahwa, sama kayak variabel, reference itu +**immutable secara default**. Makanya kita perlu nulis `&mut guess` bukan +`&guess` supaya bisa diubah. (Chapter 4 bakal jelasin reference ini lebih +lengkap.) + + + -### Handling Potential Failure with `Result` +### Menangani Kemungkinan Error dengan `Result` -We’re still working on this line of code. We’re now discussing a third line of -text, but note that it’s still part of a single logical line of code. The next -part is this method: +Kita masih ngebahas baris kode yang sama. Sekarang kita masuk ke baris teks +ketiga, tapi perlu diingat ini sebenarnya masih bagian dari **satu baris logika +kode yang sama**. Bagian berikutnya adalah method ini: ```rust,ignore {{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:expect}} ``` -We could have written this code as: +Kita sebenarnya juga bisa nulis kodenya seperti ini: ```rust,ignore io::stdin().read_line(&mut guess).expect("Failed to read line"); ``` -However, one long line is difficult to read, so it’s best to divide it. It’s -often wise to introduce a newline and other whitespace to help break up long -lines when you call a method with the `.method_name()` syntax. Now let’s -discuss what this line does. +Namun, satu baris yang terlalu panjang bakal susah dibaca, jadi lebih baik +dibagi beberapa baris. Biasanya lebih baik untuk menambahkan newline dan +whitespace lain untuk “memecah” baris panjang saat kamu memanggil method dengan +sintaks `.method_name()`. Sekarang mari kita bahas apa yang sebenarnya dilakukan +baris ini. -As mentioned earlier, `read_line` puts whatever the user enters into the string -we pass to it, but it also returns a `Result` value. [`Result`][result] is an [*enumeration*][enums], often called an *enum*, -which is a type that can be in one of multiple possible states. We call each -possible state a *variant*. +Seperti yang sudah disebutkan sebelumnya, `read_line` akan memasukkan apa pun +yang diketik user ke dalam string yang kita berikan, tapi fungsi ini juga +mengembalikan nilai bertipe `Result`. [`Result`][result] adalah +sebuah [_enumeration_][enums] (sering disebut _enum_), yaitu tipe +yang bisa berada dalam beberapa kemungkinan keadaan. Setiap kemungkinan keadaan +itu disebut _variant_. -[Chapter 6][enums] will cover enums in more detail. The purpose -of these `Result` types is to encode error-handling information. +[Chapter 6][enums] akan membahas enum lebih dalam. Tujuan dari +tipe `Result` ini adalah untuk membawa informasi terkait penanganan error. -`Result`’s variants are `Ok` and `Err`. The `Ok` variant indicates the -operation was successful, and inside `Ok` is the successfully generated value. -The `Err` variant means the operation failed, and `Err` contains information -about how or why the operation failed. +Variant dari `Result` adalah `Ok` dan `Err`.`Ok` berarti operasi berhasil, dan +dia menyimpan nilai hasil keberhasilan tersebut. `Err` berarti operasi gagal, +dan dia menyimpan informasi tentang bagaimana atau kenapa kegagalan itu terjadi. -Values of the `Result` type, like values of any type, have methods defined on -them. An instance of `Result` has an [`expect` method][expect] -that you can call. If this instance of `Result` is an `Err` value, `expect` -will cause the program to crash and display the message that you passed as an -argument to `expect`. If the `read_line` method returns an `Err`, it would -likely be the result of an error coming from the underlying operating system. -If this instance of `Result` is an `Ok` value, `expect` will take the return -value that `Ok` is holding and return just that value to you so you can use it. -In this case, that value is the number of bytes in the user’s input. +Nilai bertipe `Result`, sama seperti tipe lain, juga punya method. Sebuah +instance `Result` punya method [`expect`][expect] yang bisa kamu +panggil. Jika instance `Result` tersebut adalah `Err`, `expect` akan membuat +program crash dan menampilkan pesan yang kamu berikan ke `expect`. Jika +`read_line` mengembalikan `Err`, biasanya itu karena ada masalah dari sistem +operasi. Kalau instance `Result` tersebut adalah `Ok`, `expect` akan mengambil +nilai yang ada di dalam `Ok` dan mengembalikannya ke kamu supaya bisa dipakai. +Dalam kasus ini, nilainya adalah jumlah byte dari input user. -If you don’t call `expect`, the program will compile, but you’ll get a warning: +Kalau kamu tidak memanggil `expect`, program tetap akan berhasil dikompilasi, +tapi kamu akan mendapatkan peringatan: ```console {{#include ../listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/output.txt}} ``` -Rust warns that you haven’t used the `Result` value returned from `read_line`, -indicating that the program hasn’t handled a possible error. +Rust ngasih peringatan karena kamu nggak pakai nilai `Result` yang dikembalikan +dari `read_line`, yang artinya program belum menangani kemungkinan terjadinya +error. -The right way to suppress the warning is to actually write error-handling code, -but in our case we just want to crash this program when a problem occurs, so we -can use `expect`. You’ll learn about recovering from errors in [Chapter -9][recover]. +Cara yang “benar” buat ngilangin peringatan itu adalah dengan benar-benar nulis +kode penanganan error. Tapi, dalam kasus kita sekarang, kita cuma pengin +programnya langsung crash kalau ada masalah, jadi kita bisa pakai `expect`. Kamu +bakal belajar cara “pulih” dari error di [Bab 9][recover]. -### Printing Values with `println!` Placeholders +### Nampilin Nilai dengan Placeholder `println!` -Aside from the closing curly bracket, there’s only one more line to discuss in -the code so far: +Selain kurung kurawal penutup, masih ada satu baris lagi yang perlu dibahas: ```rust,ignore {{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:print_guess}} ``` -This line prints the string that now contains the user’s input. The `{}` set of -curly brackets is a placeholder: think of `{}` as little crab pincers that hold -a value in place. When printing the value of a variable, the variable name can -go inside the curly brackets. When printing the result of evaluating an -expression, place empty curly brackets in the format string, then follow the -format string with a comma-separated list of expressions to print in each empty -curly bracket placeholder in the same order. Printing a variable and the result -of an expression in one call to `println!` would look like this: +Baris ini bakal nge-print string yang sekarang udah berisi input dari user. +Tanda kurung kurawal `{}` itu jadi semacam “tempat dudukan” nilai, anggap aja +`{}` kayak capit kepiting kecil yang megang nilai biar bisa ditampilin. Kalau +mau nge-print nilai dari sebuah variabel, tinggal taruh nama variabelnya di +dalam `{}`. Kalau mau nge-print hasil dari sebuah ekspresi, cukup pakai `{}` +yang kosong di format string, lalu setelah stringnya kasih daftar ekspresi yang +dipisahkan koma sesuai urutan placeholder `{}` tadi. Nge-print variabel dan +hasil ekspresi sekaligus dalam satu `println!` bakal kelihatan seperti ini: ```rust let x = 5; @@ -291,11 +295,12 @@ let y = 10; println!("x = {x} and y + 2 = {}", y + 2); ``` -This code would print `x = 5 and y + 2 = 12`. +Kode itu bakal nge-print: `x = 5 and y + 2 = 12` -### Testing the First Part +### Ngetes Bagian Pertama -Let’s test the first part of the guessing game. Run it using `cargo run`: +Sekarang kita tes dulu bagian pertama dari game tebak angkanya. Jalanin +programnya pakai: `cargo run` ```console $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 6.44s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 6.44s Running `target/debug/guessing_game` Guess the number! Please input your guess. @@ -314,31 +319,38 @@ Please input your guess. You guessed: 6 ``` -At this point, the first part of the game is done: we’re getting input from the -keyboard and then printing it. +Pada tahap ini, bagian pertama dari game-nya sudah kelar kita berhasil ngambil +input dari keyboard terus kita tampilin lagi. -## Generating a Secret Number +## Membuat Angka Rahasia -Next, we need to generate a secret number that the user will try to guess. The -secret number should be different every time so the game is fun to play more -than once. We’ll use a random number between 1 and 100 so the game isn’t too -difficult. Rust doesn’t yet include random number functionality in its standard -library. However, the Rust team does provide a [`rand` crate][randcrate] with -said functionality. +Selanjutnya, kita perlu bikin angka rahasia yang nanti harus ditebak sama user. +Angka ini harus beda setiap kali game dijalankan biar tetap seru dimainkan +berkali-kali. Kita bakal pakai angka random antara 1 sampai 100 supaya gamenya +nggak terlalu susah. -### Using a Crate to Get More Functionality +Rust sendiri belum punya fitur angka random di standard library-nya. Tapi tim +Rust sudah nyediain crate bernama [`rand`][randcrate] yang punya fitur itu. -Remember that a crate is a collection of Rust source code files. The project -we’ve been building is a *binary crate*, which is an executable. The `rand` -crate is a *library crate*, which contains code that is intended to be used in -other programs and can’t be executed on its own. + -Cargo’s coordination of external crates is where Cargo really shines. Before we -can write code that uses `rand`, we need to modify the *Cargo.toml* file to -include the `rand` crate as a dependency. Open that file now and add the -following line to the bottom, beneath the `[dependencies]` section header that -Cargo created for you. Be sure to specify `rand` exactly as we have here, with -this version number, or the code examples in this tutorial may not work: + + +### Nambah Fungsionalitas dengan Crate + +Ingat, **crate** itu kumpulan file kode sumber Rust. Project yang lagi kita +bikin sekarang adalah **binary crate**, yaitu program yang bisa dieksekusi. +Sementara itu, crate `rand` adalah **library crate**, yang isinya kode buat +dipakai di program lain dan nggak bisa dijalankan sendiri. + +Bagian ngatur crate eksternal ini adalah salah satu hal yang bikin Cargo +keliatan keren banget. Sebelum kita bisa nulis kode yang pakai `rand`, kita +harus ngubah file _Cargo.toml_ dulu buat nambahin `rand` sebagai dependency. + +Buka file itu sekarang, lalu tambahin baris berikut di bagian paling bawah, +tepat di bawah header `[dependencies]` yang sebelumnya udah dibuat Cargo buat +kamu. Pastikan kamu tulis `rand` persis kayak ini, termasuk versi nomornya, +karena kalau beda bisa bikin contoh kode di tutorial ini nggak jalan: (sometimes called *SemVer*), which is a -standard for writing version numbers. The specifier `0.8.5` is actually -shorthand for `^0.8.5`, which means any version that is at least 0.8.5 but -below 0.9.0. +Di file _Cargo.toml_, semua yang ada setelah sebuah header akan jadi bagian dari +section itu sampai ada section baru dimulai. Di bagian `[dependencies]`, kamu +kasih tahu Cargo crate eksternal apa aja yang dibutuhin project kamu dan versi +berapa yang ingin dipakai. + +Di kasus ini, kita nentuin crate `rand` dengan semantic version `0.8.5`. Cargo +paham soal [Semantic Versioning][semver] (sering disebut +_SemVer_), yaitu standar penulisan versi. Penulisan `0.8.5` ini sebenarnya +singkatan dari `^0.8.5`, yang artinya versi berapapun yang minimal 0.8.5 dan +masih di bawah 0.9.0. -Cargo considers these versions to have public APIs compatible with version -0.8.5, and this specification ensures you’ll get the latest patch release that -will still compile with the code in this chapter. Any version 0.9.0 or greater -is not guaranteed to have the same API as what the following examples use. +Cargo nganggep versi-versi dalam rentang itu punya API yang masih kompatibel +dengan 0.8.5. Dengan begitu, kamu bakal selalu dapet patch terbaru tapi tetap +aman dan bisa dikompilasi sesuai contoh di bab ini. Versi 0.9.0 ke atas nggak +dijamin punya API yang sama lagi. -Now, without changing any of the code, let’s build the project, as shown in -Listing 2-2. +Sekarang, tanpa mengubah kode apa pun, coba build project-nya dulu seperti yang +ditunjukkan di Listing 2-2. ++ +```console +$ cargo build + Updating crates.io index + Locking 15 packages to latest Rust 1.85.0 compatible versions + Adding rand v0.8.5 (available: v0.9.0) + Compiling proc-macro2 v1.0.93 + Compiling unicode-ident v1.0.17 + Compiling libc v0.2.170 + Compiling cfg-if v1.0.0 + Compiling byteorder v1.5.0 + Compiling getrandom v0.2.15 + Compiling rand_core v0.6.4 + Compiling quote v1.0.38 + Compiling syn v2.0.98 + Compiling zerocopy-derive v0.7.35 + Compiling zerocopy v0.7.35 + Compiling ppv-lite86 v0.2.20 + Compiling rand_chacha v0.3.1 + Compiling rand v0.8.5 + Compiling guessing_game v0.1.0 (file:///projects/guessing_game) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.48s +``` + + + +Kamu mungkin akan melihat nomor versi yang berbeda (tapi semuanya tetap +kompatibel kok berkat SemVer!) dan mungkin juga baris output yang berbeda +tergantung sistem operasi yang kamu pakai, bahkan urutannya juga bisa nggak +sama. + +Saat kita nambahin dependency eksternal, Cargo akan ngambil versi terbaru dari +semua dependency yang dibutuhin lewat _registry_, yaitu salinan data dari +[Crates.io][cratesio]. Crates.io itu tempat orang-orang di ekosistem Rust +nge-publish proyek Rust open source mereka supaya bisa dipakai orang lain. + +Setelah registry diperbarui, Cargo ngecek bagian `[dependencies]`, lalu +nge-download crate yang belum ada di lokal. Di kasus ini, meskipun kita cuma +nulis `rand` sebagai dependency, Cargo juga ikut ngambil crate lain yang +dibutuhin `rand` supaya bisa jalan. Setelah semua crate kelar di-download, Rust +akan nge-compile crate-crate itu, baru kemudian nge-compile project kamu dengan +dependency yang sudah siap dipakai. + +Kalau kamu langsung menjalankan `cargo build` lagi tanpa ada perubahan apa pun, +kamu nggak bakal lihat output apa pun selain baris `Finished`. Cargo tahu kalau +dependency-nya sudah didownload dan dikompilasi, dan kamu juga nggak ngubah apa +pun di _Cargo.toml_. Cargo juga sadar kode kamu nggak berubah, jadi dia nggak +perlu recompile. Karena nggak ada kerjaan, dia langsung selesai. + +Kalau kamu buka file _src/main.rs_, ubah sesuatu yang sepele aja, simpan, lalu +build lagi, kamu cuma bakal lihat dua baris output: + + + ```console $ cargo build - Updating crates.io index - Downloaded rand v0.8.5 - Downloaded libc v0.2.127 - Downloaded getrandom v0.2.7 - Downloaded cfg-if v1.0.0 - Downloaded ppv-lite86 v0.2.16 - Downloaded rand_chacha v0.3.1 - Downloaded rand_core v0.6.3 - Compiling libc v0.2.127 - Compiling getrandom v0.2.7 - Compiling cfg-if v1.0.0 - Compiling ppv-lite86 v0.2.16 - Compiling rand_core v0.6.3 - Compiling rand_chacha v0.3.1 - Compiling rand v0.8.5 Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 2.53s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.13s ``` -Listing 2-2: The output from running `cargo build` after -adding the rand crate as a dependency +Baris-baris tadi nunjukin kalau Cargo cuma nge-update build berdasarkan +perubahan kecil yang kamu lakukan di file _src/main.rs_. Karena dependency kamu +nggak berubah, Cargo tahu dia bisa langsung pakai ulang hasil download dan +compile sebelumnya tanpa perlu ngulang dari awal. -You may see different version numbers (but they will all be compatible with the -code, thanks to SemVer!) and different lines (depending on the operating -system), and the lines may be in a different order. + -When we include an external dependency, Cargo fetches the latest versions of -everything that dependency needs from the *registry*, which is a copy of data -from [Crates.io][cratesio]. Crates.io is where people in the Rust ecosystem -post their open source Rust projects for others to use. + -After updating the registry, Cargo checks the `[dependencies]` section and -downloads any crates listed that aren’t already downloaded. In this case, -although we only listed `rand` as a dependency, Cargo also grabbed other crates -that `rand` depends on to work. After downloading the crates, Rust compiles -them and then compiles the project with the dependencies available. +#### Memastikan Build Bisa Diulang dengan Hasil yang Sama -If you immediately run `cargo build` again without making any changes, you -won’t get any output aside from the `Finished` line. Cargo knows it has already -downloaded and compiled the dependencies, and you haven’t changed anything -about them in your *Cargo.toml* file. Cargo also knows that you haven’t changed -anything about your code, so it doesn’t recompile that either. With nothing to -do, it simply exits. +Cargo punya mekanisme supaya kamu bisa build proyek dengan hasil yang sama +setiap kali kamu atau orang lain nge-build kode kamu. Caranya: Cargo cuma bakal +pakai versi dependency yang sudah kamu tentuin, sampai kamu bilang mau ganti. -If you open the *src/main.rs* file, make a trivial change, and then save it and -build again, you’ll only see two lines of output: +Misalnya, minggu depan keluar `rand` versi 0.8.6. Versi itu punya bug fix +penting, tapi ternyata ada regresi yang bikin kode kamu rusak. Untuk ngatasi +hal-hal kayak gitu, Rust bikin file _**Cargo.lock**_ saat pertama kali kamu +jalanin `cargo build`, jadi sekarang file itu sudah ada di folder +_guessing_game_. - +Waktu kamu build project pertama kali, Cargo bakal nyari versi dependency yang +cocok sama aturan yang kamu tulis, lalu nyimpen hasilnya ke file _Cargo.lock_. +Build berikutnya, Cargo bakal lihat kalau _Cargo.lock_ sudah ada dan langsung +pakai versi yang tertulis di situ, tanpa repot-repot ngecek lagi. Ini bikin +build jadi **reproducible** alias hasilnya konsisten. Singkatnya: proyekmu bakal +tetap pakai versi 0.8.5 sampai kamu sengaja upgrade, berkat _Cargo.lock_. Karena +penting buat jaga konsistensi build, file ini biasanya ikut di-commit bareng +source code ke version control. -```console -$ cargo build - Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 2.53 secs -``` - -These lines show that Cargo only updates the build with your tiny change to the -*src/main.rs* file. Your dependencies haven’t changed, so Cargo knows it can -reuse what it has already downloaded and compiled for those. - -#### Ensuring Reproducible Builds with the *Cargo.lock* File - -Cargo has a mechanism that ensures you can rebuild the same artifact every time -you or anyone else builds your code: Cargo will use only the versions of the -dependencies you specified until you indicate otherwise. For example, say that -next week version 0.8.6 of the `rand` crate comes out, and that version -contains an important bug fix, but it also contains a regression that will -break your code. To handle this, Rust creates the *Cargo.lock* file the first -time you run `cargo build`, so we now have this in the *guessing_game* -directory. - -When you build a project for the first time, Cargo figures out all the versions -of the dependencies that fit the criteria and then writes them to the -*Cargo.lock* file. When you build your project in the future, Cargo will see -that the *Cargo.lock* file exists and will use the versions specified there -rather than doing all the work of figuring out versions again. This lets you -have a reproducible build automatically. In other words, your project will -remain at 0.8.5 until you explicitly upgrade, thanks to the *Cargo.lock* file. -Because the *Cargo.lock* file is important for reproducible builds, it’s often -checked into source control with the rest of the code in your project. - -#### Updating a Crate to Get a New Version - -When you *do* want to update a crate, Cargo provides the command `update`, -which will ignore the *Cargo.lock* file and figure out all the latest versions -that fit your specifications in *Cargo.toml*. Cargo will then write those -versions to the *Cargo.lock* file. Otherwise, by default, Cargo will only look -for versions greater than 0.8.5 and less than 0.9.0. If the `rand` crate has -released the two new versions 0.8.6 and 0.9.0, you would see the following if -you ran `cargo update`: +#### Update Crate ke Versi Baru + +Kalau kamu **memang pengin update** crate, Cargo nyediain perintah `update`. +Perintah ini bakal ngabaikan _Cargo.lock_ dan nyari versi terbaru yang masih +cocok sama aturan di _Cargo.toml_. Setelah itu, Cargo bakal nulis versi barunya +ke _Cargo.lock_. Secara default, Cargo cuma bakal nyari versi yang lebih besar +dari 0.8.5 tapi masih di bawah 0.9.0. + +Kalau misalnya crate `rand` udah keluar versi 0.8.6 dan 0.999.0, dan kamu +jalanin: + +``` +cargo update +``` ```console $ cargo update Updating crates.io index - Updating rand v0.8.5 -> v0.8.6 + Locking 1 package to latest Rust 1.85.0 compatible version + Updating rand v0.8.5 -> v0.8.6 (available: v0.999.0) ``` -Cargo ignores the 0.9.0 release. At this point, you would also notice a change -in your *Cargo.lock* file noting that the version of the `rand` crate you are -now using is 0.8.6. To use `rand` version 0.9.0 or any version in the 0.9.*x* -series, you’d have to update the *Cargo.toml* file to look like this instead: +Cargo mengabaikan rilis 0.999.0. Pada titik ini, kamu juga bakal lihat ada +perubahan di file _Cargo.lock_ yang nunjukin kalau sekarang versi `rand` yang +dipakai adalah 0.8.6. Kalau kamu mau pakai `rand` versi 0.999.0 atau versi lain +di seri 0.999._x_, kamu harus ngubah file _Cargo.toml_ jadi seperti ini (tapi +jangan beneran diubah, karena contoh-contoh selanjutnya diasumsikan masih pakai +`rand` 0.8): ```toml [dependencies] -rand = "0.9.0" +rand = "0.999.0" ``` -The next time you run `cargo build`, Cargo will update the registry of crates -available and reevaluate your `rand` requirements according to the new version -you have specified. +Saat kamu menjalankan `cargo build` lagi, Cargo bakal memperbarui daftar crate +yang tersedia lalu mengevaluasi ulang kebutuhan `rand` kamu sesuai versi baru +yang sudah kamu tentukan. -There’s a lot more to say about [Cargo][doccargo] and [its -ecosystem][doccratesio], which we’ll discuss in Chapter 14, but -for now, that’s all you need to know. Cargo makes it very easy to reuse -libraries, so Rustaceans are able to write smaller projects that are assembled -from a number of packages. +Sebenernya masih banyak hal lain soal [Cargo][doccargo] dan +[ekosistemnya][doccratesio] yang bakal dibahas lebih dalam di +Bab 14. Tapi untuk sekarang, itu aja yang perlu kamu tahu dulu. Cargo bikin +reuse library jadi super gampang, sehingga para Rustacean bisa nulis project +yang lebih kecil dan nyusunnya dari banyak package yang sudah ada. -### Generating a Random Number +### Membuat Angka Acak -Let’s start using `rand` to generate a number to guess. The next step is to -update *src/main.rs*, as shown in Listing 2-3. +Sekarang kita mulai pakai `rand` buat ngehasilin angka yang bakal ditebak. +Langkah selanjutnya adalah update file _src/main.rs_, seperti yang ditunjukkan +di Listing 2-3. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs:all}} ``` -Listing 2-3: Adding code to generate a random -number + + +Pertama, kita nambahin baris `use rand::Rng;`. Trait `Rng` ini berisi +method-method yang dipakai oleh random number generator, dan trait ini harus ada +di scope supaya kita bisa pakai method-nya. Detail soal trait bakal dibahas +lebih dalam di Chapter 10. -First we add the line `use rand::Rng;`. The `Rng` trait defines methods that -random number generators implement, and this trait must be in scope for us to -use those methods. Chapter 10 will cover traits in detail. +Selanjutnya, kita nambah dua baris di bagian tengah kode. Di baris pertama, kita +manggil fungsi `rand::thread_rng` untuk ngambil random number generator yang +bakal kita pakai. Generator ini terikat pada thread yang lagi jalan sekarang dan +“dibekali” (seeded) dari operating system. -Next, we’re adding two lines in the middle. In the first line, we call the -`rand::thread_rng` function that gives us the particular random number -generator we’re going to use: one that is local to the current thread of -execution and is seeded by the operating system. Then we call the `gen_range` -method on the random number generator. This method is defined by the `Rng` -trait that we brought into scope with the `use rand::Rng;` statement. The -`gen_range` method takes a range expression as an argument and generates a -random number in the range. The kind of range expression we’re using here takes -the form `start..=end` and is inclusive on the lower and upper bounds, so we -need to specify `1..=100` to request a number between 1 and 100. +Lalu, kita manggil method `gen_range` dari random number generator tadi. Method +ini didefinisikan oleh trait `Rng` yang tadi sudah kita masukin ke scope lewat +`use rand::Rng;`. Method `gen_range` menerima sebuah ekspresi range sebagai +argumen dan bakal ngasilin angka random di dalam range tersebut. Range yang kita +pakai bentuknya `start..=end`, yaitu range yang inklusif di batas bawah _dan_ +batas atas. Jadi kita tulis `1..=100` supaya dapet angka acak antara 1 +sampai 100. -> Note: You won’t just know which traits to use and which methods and functions -> to call from a crate, so each crate has documentation with instructions for -> using it. Another neat feature of Cargo is that running the `cargo doc -> --open` command will build documentation provided by all your dependencies -> locally and open it in your browser. If you’re interested in other -> functionality in the `rand` crate, for example, run `cargo doc --open` and -> click `rand` in the sidebar on the left. +> Catatan: Kamu nggak mungkin hafal begitu aja trait apa yang harus dipakai, +> method apa yang harus dipanggil, atau fungsi apa yang tersedia dari sebuah +> crate. Makanya setiap crate punya dokumentasi yang ngejelasin cara pakainya. +> Fitur keren Cargo lainnya: kalau kamu jalanin perintah `cargo doc --open` +> Cargo bakal bikin dokumentasi lokal untuk semua dependency kamu dan langsung +> buka di browser. Misalnya kamu pengin lihat fitur lain dari crate `rand`, +> tinggal jalankan `cargo doc --open` lalu klik `rand` di sidebar kiri. -The second new line prints the secret number. This is useful while we’re -developing the program to be able to test it, but we’ll delete it from the -final version. It’s not much of a game if the program prints the answer as soon -as it starts! +Baris baru kedua cuma buat nge-print angka rahasianya. Ini berguna selama masa +pengembangan biar gampang ngetes, tapi nanti bakal kita hapus di versi final. +Soalnya nggak seru dong kalau game langsung kasih jawabannya -Try running the program a few times: +Sekarang coba jalankan programnya beberapa kali: expression to decide what to do next based on -which variant of `Ordering` was returned from the call to `cmp` with the values -in `guess` and `secret_number`. - -A `match` expression is made up of *arms*. An arm consists of a *pattern* to -match against, and the code that should be run if the value given to `match` -fits that arm’s pattern. Rust takes the value given to `match` and looks -through each arm’s pattern in turn. Patterns and the `match` construct are -powerful Rust features: they let you express a variety of situations your code -might encounter and they make sure you handle them all. These features will be -covered in detail in Chapter 6 and Chapter 18, respectively. - -Let’s walk through an example with the `match` expression we use here. Say that -the user has guessed 50 and the randomly generated secret number this time is -38. - -When the code compares 50 to 38, the `cmp` method will return -`Ordering::Greater` because 50 is greater than 38. The `match` expression gets -the `Ordering::Greater` value and starts checking each arm’s pattern. It looks -at the first arm’s pattern, `Ordering::Less`, and sees that the value -`Ordering::Greater` does not match `Ordering::Less`, so it ignores the code in -that arm and moves to the next arm. The next arm’s pattern is -`Ordering::Greater`, which *does* match `Ordering::Greater`! The associated -code in that arm will execute and print `Too big!` to the screen. The `match` -expression ends after the first successful match, so it won’t look at the last -arm in this scenario. - -However, the code in Listing 2-4 won’t compile yet. Let’s try it: + + +Pertama, kita nambah satu `use` lagi buat masukin tipe `std::cmp::Ordering` ke +dalam scope dari standard library. Tipe `Ordering` ini adalah enum lain yang +punya tiga kemungkinan nilai: `Less`, `Greater`, dan `Equal`. Ini adalah tiga +hasil yang mungkin terjadi saat kita membandingkan dua nilai. + +Lalu, kita nambah lima baris kode baru di bagian bawah yang pakai `Ordering`. +Method `cmp` dipakai buat membandingkan dua nilai, dan bisa dipanggil di tipe +apa pun yang bisa dibandingkan. Method ini butuh referensi ke nilai yang mau +dibandingin: di sini, kita bandingin `guess` dengan `secret_number`. Setelah +itu, `cmp` bakal ngembalikan salah satu varian dari enum `Ordering` yang tadi +sudah kita masukin ke scope lewat `use`. Nah, kita pakai ekspresi +[`match`][match] buat nentuin langkah selanjutnya berdasarkan +varian `Ordering` yang dikembalikan dari `cmp` saat bandingin `guess` dan +`secret_number`. + +Ekspresi `match` tersusun dari beberapa _arm_. Satu arm terdiri dari _pattern_ +yang mau dicocokkan, plus kode yang bakal dijalankan kalau nilai yang dikasih ke +`match` cocok sama pattern tersebut. Rust bakal ngambil nilai yang dikasih ke +`match`, lalu ngecek tiap pattern dari atas ke bawah. Pattern matching dan +`match` ini fitur yang kuat banget di Rust: mereka bikin kamu bisa menangani +banyak kemungkinan kondisi program dengan rapi, dan memastikan semuanya +tertangani. Fitur ini bakal dibahas lebih dalam di Chapter 6 dan Chapter 19 +nanti. + +Sekarang kita lihat contohnya pakai `match` yang ada di sini. Misalnya user +nebak angka 50, dan angka rahasianya ternyata 38. + +Pas kode ngebandingin 50 dengan 38, method `cmp` bakal balikin +`Ordering::Greater` karena 50 lebih besar dari 38. Nilai `Ordering::Greater` ini +masuk ke `match`, lalu `match` mulai ngecek tiap arm. Pertama dia lihat pattern +`Ordering::Less`, tapi karena nggak cocok, arm itu dilewatin. Lanjut ke arm +berikutnya yang pattern-nya `Ordering::Greater`, dan ini cocok! Jadi kode di arm +itu dijalankan, dan program bakal nampilin `Too big!`. Setelah dapat kecocokan +pertama, `match` langsung selesai dan nggak ngecek arm terakhir. + +Tapi… kode di Listing 2-4 ini belum bisa dikompilasi. Yuk kita coba jalanin +dulu: , but for now, know that this feature is -often used when you want to convert a value from one type to another type. - -We bind this new variable to the expression `guess.trim().parse()`. The `guess` -in the expression refers to the original `guess` variable that contained the -input as a string. The `trim` method on a `String` instance will eliminate any -whitespace at the beginning and end, which we must do to be able to compare the -string to the `u32`, which can only contain numerical data. The user must press -enter to satisfy `read_line` and input their -guess, which adds a newline character to the string. For example, if the user -types 5 and presses enter, `guess` looks like this: `5\n`. The `\n` -represents “newline.” (On Windows, pressing enter results in a carriage return and a newline, -`\r\n`.) The `trim` method eliminates `\n` or `\r\n`, resulting in just `5`. - -The [`parse` method on strings][parse] converts a string to -another type. Here, we use it to convert from a string to a number. We need to -tell Rust the exact number type we want by using `let guess: u32`. The colon -(`:`) after `guess` tells Rust we’ll annotate the variable’s type. Rust has a -few built-in number types; the `u32` seen here is an unsigned, 32-bit integer. -It’s a good default choice for a small positive number. You’ll learn about -other number types in [Chapter 3][integers]. - -Additionally, the `u32` annotation in this example program and the comparison -with `secret_number` means Rust will infer that `secret_number` should be a -`u32` as well. So now the comparison will be between two values of the same -type! - -The `parse` method will only work on characters that can logically be converted -into numbers and so can easily cause errors. If, for example, the string -contained `A👍%`, there would be no way to convert that to a number. Because it -might fail, the `parse` method returns a `Result` type, much as the `read_line` -method does (discussed earlier in [“Handling Potential Failure with -`Result`”](#handling-potential-failure-with-result)). We’ll treat -this `Result` the same way by using the `expect` method again. If `parse` -returns an `Err` `Result` variant because it couldn’t create a number from the -string, the `expect` call will crash the game and print the message we give it. -If `parse` can successfully convert the string to a number, it will return the -`Ok` variant of `Result`, and `expect` will return the number that we want from -the `Ok` value. - -Let’s run the program now: +Kita bikin variabel baru bernama `guess`. Eh, tapi kan kita udah punya variabel +`guess` sebelumnya? Betul. Tapi enaknya Rust, kita boleh “menimpa” nilai lama +`guess` dengan nilai baru. Fitur ini disebut **shadowing**. Dengan shadowing, +kita bisa pakai lagi nama variabel `guess` tanpa harus bikin dua nama berbeda, +misalnya `guess_str` dan `guess`. Topik ini bakal dibahas lebih detail di +[Chapter 3][shadowing], tapi untuk sekarang cukup tahu kalau +fitur ini sering dipakai saat kita ingin mengubah suatu nilai dari satu tipe ke +tipe lain. + +Variabel baru ini kita isi dengan ekspresi `guess.trim().parse()`. `guess` yang +ada di ekspresi ini masih merujuk ke `guess` yang lama, yang isinya input user +dalam bentuk string. Method `trim` pada `String` bakal ngapus whitespace di awal +dan akhir teks, dan ini wajib dilakukan sebelum kita ubah string tersebut ke +`u32`, karena `u32` cuma boleh berisi angka doang. + +User harus tekan enter buat ngirim input ke `read_line`, dan itu +bakal nambahin karakter newline ke string. Misalnya user ngetik 5 +lalu tekan enter, isi `guess` bakal jadi kayak gini: `5\n`. Tanda +`\n` itu newline. (Di Windows malah jadi `\r\n`.) Nah, `trim` bakal ngilangin +`\n` atau `\r\n`, jadi tinggal `5`. + +Method [`parse` pada string][parse] dipakai buat ngubah string +jadi tipe lain. Di sini kita pakai buat ngubah string jadi angka. Kita harus +ngasih tahu Rust angka tipe apa yang kita mau, makanya kita tulis +`let guess: u32`. Titik dua (`:`) setelah `guess` artinya kita lagi nentuin tipe +variabelnya. `u32` sendiri adalah unsigned 32-bit integer, pilihan yang pas buat +angka kecil dan positif. Tipe angka lain bakal dibahas di +[Chapter 3][integers]. + +Selain itu, karena di contoh ini kita pakai `u32` untuk `guess` dan kita +bandingin sama `secret_number`, Rust jadi nge-infer kalau `secret_number` juga +harus `u32`. Jadi sekarang kedua nilai punya tipe yang sama — mantap, bisa +dibandingkan! + +Method `parse` cuma bakal berhasil kalau stringnya bener-bener bisa diubah ke +angka. Jadi gampang banget terjadi error kalau isinya aneh, misalnya `A👍%`, +jelas nggak bisa jadi angka. Karena bisa gagal, `parse` juga ngembalikan +`Result`, sama kayak `read_line` yang udah kita bahas di bagian +[“Handling Potential Failure with `Result`”](#handling-potential-failure-with-result). + +Kita tangani `Result` ini dengan cara yang sama: pakai `expect`. Kalau `parse` +gagal dan balikin `Err`, `expect` bakal bikin game crash dan nampilin pesan yang +kita kasih. Tapi kalau `parse` berhasil dan balikin `Ok`, `expect` bakal ngasih +kita angkanya. + +Sekarang, ayo jalanin programnya lagi: @@ -727,7 +761,7 @@ cargo run ```console $ cargo run Compiling guessing_game v0.1.0 (file:///projects/guessing_game) - Finished dev [unoptimized + debuginfo] target(s) in 0.43s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s Running `target/debug/guessing_game` Guess the number! The secret number is: 58 @@ -737,18 +771,18 @@ You guessed: 76 Too big! ``` -Nice! Even though spaces were added before the guess, the program still figured -out that the user guessed 76. Run the program a few times to verify the -different behavior with different kinds of input: guess the number correctly, -guess a number that is too high, and guess a number that is too low. +Keren! Meskipun ada spasi di depan tebakan, program tetap bisa ngerti kalau +user nebak angka 76. Coba jalanin programnya beberapa kali untuk ngetes berbagai +kondisi: tebak angka yang tepat, tebak angka yang terlalu besar, dan tebak angka +yang terlalu kecil. -We have most of the game working now, but the user can make only one guess. -Let’s change that by adding a loop! +Sekarang sebagian besar game-nya sudah jalan, tapi user baru bisa nebak **sekali +doang**. Kita perlu ubah itu dengan nambahin loop! -## Allowing Multiple Guesses with Looping +## Mengizinkan Banyak Tebakan dengan Loop -The `loop` keyword creates an infinite loop. We’ll add a loop to give users -more chances at guessing the number: +Keyword `loop` bakal bikin loop tak terbatas (infinite loop). Kita bakal +nambahin loop supaya user bisa punya banyak kesempatan buat nebak angkanya: Filename: src/main.rs @@ -756,20 +790,24 @@ more chances at guessing the number: {{#rustdoc_include ../listings/ch02-guessing-game-tutorial/no-listing-04-looping/src/main.rs:here}} ``` -As you can see, we’ve moved everything from the guess input prompt onward into -a loop. Be sure to indent the lines inside the loop another four spaces each -and run the program again. The program will now ask for another guess forever, -which actually introduces a new problem. It doesn’t seem like the user can quit! +Seperti yang kamu lihat, sekarang kita mindahin semua bagian mulai dari prompt +input tebakan ke dalam sebuah loop. Pastikan baris-baris di dalam loop +di-_indent_ empat spasi lagi, lalu jalankan programnya. Sekarang program bakal +terus minta tebakan baru tanpa henti… tapi itu bikin masalah baru: kelihatannya +user jadi nggak bisa keluar dari game! + +Sebenernya user masih bisa keluar pakai shortcut keyboard Ctrl + +C. Tapi ada cara lain buat kabur dari “monster tak pernah puas” ini, +seperti yang udah disinggung waktu bahas `parse` di bagian +[“Comparing the Guess to the Secret Number”](#comparing-the-guess-to-the-secret-number). -The user could always interrupt the program by using the keyboard shortcut -ctrl-c. But there’s another way to escape this -insatiable monster, as mentioned in the `parse` discussion in [“Comparing the -Guess to the Secret Number”](#comparing-the-guess-to-the-secret-number): if the user enters a non-number answer, the program will crash. We -can take advantage of that to allow the user to quit, as shown here: +Kalau user masukin input yang **bukan angka**, program bakal crash. Nah, kita +bisa manfaatin hal ini buat bikin cara keluar dari game, seperti di contoh +berikut: . +> can find the list of the keywords in [Appendix A][appendix_a]. [appendix_a]: appendix-01-keywords.md diff --git a/src/ch03-01-variables-and-mutability.md b/src/ch03-01-variables-and-mutability.md index 058f7bb5c4..ed15afc0fd 100644 --- a/src/ch03-01-variables-and-mutability.md +++ b/src/ch03-01-variables-and-mutability.md @@ -9,10 +9,10 @@ Let’s explore how and why Rust encourages you to favor immutability and why sometimes you might want to opt out. When a variable is immutable, once a value is bound to a name, you can’t change -that value. To illustrate this, generate a new project called *variables* in -your *projects* directory by using `cargo new variables`. +that value. To illustrate this, generate a new project called _variables_ in +your _projects_ directory by using `cargo new variables`. -Then, in your new *variables* directory, open *src/main.rs* and replace its +Then, in your new _variables_ directory, open _src/main.rs_ and replace its code with the following code, which won’t compile just yet: Filename: src/main.rs @@ -30,31 +30,30 @@ regarding an immutability error, as shown in this output: This example shows how the compiler helps you find errors in your programs. Compiler errors can be frustrating, but really they only mean your program -isn’t safely doing what you want it to do yet; they do *not* mean that you’re +isn’t safely doing what you want it to do yet; they do _not_ mean that you’re not a good programmer! Experienced Rustaceans still get compiler errors. -You received the error message `` cannot assign twice to immutable variable `x` -`` because you tried to assign a second value to the immutable `x` variable. +You received the error message `` cannot assign twice to immutable variable `x` `` because you tried to assign a second value to the immutable `x` variable. It’s important that we get compile-time errors when we attempt to change a -value that’s designated as immutable because this very situation can lead to +value that’s designated as immutable, because this very situation can lead to bugs. If one part of our code operates on the assumption that a value will never change and another part of our code changes that value, it’s possible that the first part of the code won’t do what it was designed to do. The cause of this kind of bug can be difficult to track down after the fact, especially -when the second piece of code changes the value only *sometimes*. The Rust +when the second piece of code changes the value only _sometimes_. The Rust compiler guarantees that when you state that a value won’t change, it really won’t change, so you don’t have to keep track of it yourself. Your code is thus easier to reason through. -But mutability can be very useful, and can make code more convenient to write. +But mutability can be very useful and can make code more convenient to write. Although variables are immutable by default, you can make them mutable by adding `mut` in front of the variable name as you did in [Chapter 2][storing-values-with-variables]. Adding `mut` also conveys intent to future readers of the code by indicating that other parts of the code will be changing this variable’s value. -For example, let’s change *src/main.rs* to the following: +For example, let’s change _src/main.rs_ to the following: Filename: src/main.rs @@ -72,15 +71,18 @@ We’re allowed to change the value bound to `x` from `5` to `6` when `mut` is used. Ultimately, deciding whether to use mutability or not is up to you and depends on what you think is clearest in that particular situation. -### Constants + + -Like immutable variables, *constants* are values that are bound to a name and +### Declaring Constants + +Like immutable variables, _constants_ are values that are bound to a name and are not allowed to change, but there are a few differences between constants and variables. First, you aren’t allowed to use `mut` with constants. Constants aren’t just immutable by default—they’re always immutable. You declare constants using the -`const` keyword instead of the `let` keyword, and the type of the value *must* +`const` keyword instead of the `let` keyword, and the type of the value _must_ be annotated. We’ll cover types and type annotations in the next section, [“Data Types”][data-types], so don’t worry about the details right now. Just know that you must always annotate the type. @@ -97,7 +99,7 @@ Here’s an example of a constant declaration: const THREE_HOURS_IN_SECONDS: u32 = 60 * 60 * 3; ``` -The constant’s name is `THREE_HOURS_IN_SECONDS` and its value is set to the +The constant’s name is `THREE_HOURS_IN_SECONDS`, and its value is set to the result of multiplying 60 (the number of seconds in a minute) by 60 (the number of minutes in an hour) by 3 (the number of hours we want to count in this program). Rust’s naming convention for constants is to use all uppercase with @@ -116,7 +118,7 @@ earn, or the speed of light. Naming hardcoded values used throughout your program as constants is useful in conveying the meaning of that value to future maintainers of the code. It also -helps to have only one place in your code you would need to change if the +helps to have only one place in your code that you would need to change if the hardcoded value needed to be updated in the future. ### Shadowing @@ -124,7 +126,7 @@ hardcoded value needed to be updated in the future. As you saw in the guessing game tutorial in [Chapter 2][comparing-the-guess-to-the-secret-number], you can declare a new variable with the same name as a previous variable. Rustaceans say that the -first variable is *shadowed* by the second, which means that the second +first variable is _shadowed_ by the second, which means that the second variable is what the compiler will see when you use the name of the variable. In effect, the second variable overshadows the first, taking any uses of the variable name to itself until either it itself is shadowed or the scope ends. @@ -137,9 +139,9 @@ use of the `let` keyword as follows: {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-03-shadowing/src/main.rs}} ``` -This program first binds `x` to a value of `5`. Then it creates a new variable -`x` by repeating `let x =`, taking the original value and adding `1` so the -value of `x` is then `6`. Then, within an inner scope created with the curly +This program first binds `x` to a value of `5`. Then, it creates a new variable +`x` by repeating `let x =`, taking the original value and adding `1` so that +the value of `x` is `6`. Then, within an inner scope created with the curly brackets, the third `let` statement also shadows `x` and creates a new variable, multiplying the previous value by `2` to give `x` a value of `12`. When that scope is over, the inner shadowing ends and `x` returns to being `6`. @@ -153,7 +155,7 @@ Shadowing is different from marking a variable as `mut` because we’ll get a compile-time error if we accidentally try to reassign to this variable without using the `let` keyword. By using `let`, we can perform a few transformations on a value but have the variable be immutable after those transformations have -been completed. +completed. The other difference between `mut` and shadowing is that because we’re effectively creating a new variable when we use the `let` keyword again, we can @@ -165,7 +167,7 @@ inputting space characters, and then we want to store that input as a number: {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-04-shadowing-can-change-types/src/main.rs:here}} ``` -The first `spaces` variable is a string type and the second `spaces` variable +The first `spaces` variable is a string type, and the second `spaces` variable is a number type. Shadowing thus spares us from having to come up with different names, such as `spaces_str` and `spaces_num`; instead, we can reuse the simpler `spaces` name. However, if we try to use `mut` for this, as shown @@ -184,8 +186,7 @@ The error says we’re not allowed to mutate a variable’s type: Now that we’ve explored how variables work, let’s look at more data types they can have. -[comparing-the-guess-to-the-secret-number]: -ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number +[comparing-the-guess-to-the-secret-number]: ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number [data-types]: ch03-02-data-types.html#data-types [storing-values-with-variables]: ch02-00-guessing-game-tutorial.html#storing-values-with-variables [const-eval]: ../reference/const_eval.html diff --git a/src/ch03-02-data-types.md b/src/ch03-02-data-types.md index bedf1450cc..2aa8b79cd8 100644 --- a/src/ch03-02-data-types.md +++ b/src/ch03-02-data-types.md @@ -1,10 +1,10 @@ ## Data Types -Every value in Rust is of a certain *data type*, which tells Rust what kind of -data is being specified so it knows how to work with that data. We’ll look at -two data type subsets: scalar and compound. +Every value in Rust is of a certain _data type_, which tells Rust what kind of +data is being specified so that it knows how to work with that data. We’ll look +at two data type subsets: scalar and compound. -Keep in mind that Rust is a *statically typed* language, which means that it +Keep in mind that Rust is a _statically typed_ language, which means that it must know the types of all variables at compile time. The compiler can usually infer what type we want to use based on the value and how we use it. In cases when many types are possible, such as when we converted a `String` to a numeric @@ -28,13 +28,13 @@ You’ll see different type annotations for other data types. ### Scalar Types -A *scalar* type represents a single value. Rust has four primary scalar types: +A _scalar_ type represents a single value. Rust has four primary scalar types: integers, floating-point numbers, Booleans, and characters. You may recognize these from other programming languages. Let’s jump into how they work in Rust. #### Integer Types -An *integer* is a number without a fractional component. We used one integer +An _integer_ is a number without a fractional component. We used one integer type in Chapter 2, the `u32` type. This type declaration indicates that the value it’s associated with should be an unsigned integer (signed integer types start with `i` instead of `u`) that takes up 32 bits of space. Table 3-1 shows @@ -44,34 +44,33 @@ the type of an integer value. Table 3-1: Integer Types in Rust | Length | Signed | Unsigned | -|---------|---------|----------| +| ------- | ------- | -------- | | 8-bit | `i8` | `u8` | | 16-bit | `i16` | `u16` | | 32-bit | `i32` | `u32` | | 64-bit | `i64` | `u64` | | 128-bit | `i128` | `u128` | -| arch | `isize` | `usize` | +| Architecture-dependent | `isize` | `usize` | Each variant can be either signed or unsigned and has an explicit size. -*Signed* and *unsigned* refer to whether it’s possible for the number to be +_Signed_ and _unsigned_ refer to whether it’s possible for the number to be negative—in other words, whether the number needs to have a sign with it (signed) or whether it will only ever be positive and can therefore be -represented without a sign (unsigned). It’s like writing numbers on paper: when +represented without a sign (unsigned). It’s like writing numbers on paper: When the sign matters, a number is shown with a plus sign or a minus sign; however, when it’s safe to assume the number is positive, it’s shown with no sign. Signed numbers are stored using [two’s complement][twos-complement] representation. -Each signed variant can store numbers from -(2n - 1) to 2n - -1 - 1 inclusive, where *n* is the number of bits that variant uses. So an -`i8` can store numbers from -(27) to 27 - 1, which equals --128 to 127. Unsigned variants can store numbers from 0 to 2n - 1, -so a `u8` can store numbers from 0 to 28 - 1, which equals 0 to 255. +Each signed variant can store numbers from −(2n − 1) to 2n − +1 − 1 inclusive, where _n_ is the number of bits that variant uses. So, an +`i8` can store numbers from −(27) to 27 − 1, which equals +−128 to 127. Unsigned variants can store numbers from 0 to 2n − 1, +so a `u8` can store numbers from 0 to 28 − 1, which equals 0 to 255. Additionally, the `isize` and `usize` types depend on the architecture of the -computer your program is running on, which is denoted in the table as “arch”: -64 bits if you’re on a 64-bit architecture and 32 bits if you’re on a 32-bit -architecture. +computer your program is running on: 64 bits if you’re on a 64-bit architecture +and 32 bits if you’re on a 32-bit architecture. You can write integer literals in any of the forms shown in Table 3-2. Note that number literals that can be multiple numeric types allow a type suffix, @@ -82,7 +81,7 @@ have the same value as if you had specified `1000`. Table 3-2: Integer Literals in Rust | Number literals | Example | -|------------------|---------------| +| ---------------- | ------------- | | Decimal | `98_222` | | Hex | `0xff` | | Octal | `0o77` | @@ -90,7 +89,7 @@ have the same value as if you had specified `1000`. | Byte (`u8` only) | `b'A'` | So how do you know which type of integer to use? If you’re unsure, Rust’s -defaults are generally good places to start: integer types default to `i32`. +defaults are generally good places to start: Integer types default to `i32`. The primary situation in which you’d use `isize` or `usize` is when indexing some sort of collection. @@ -98,17 +97,17 @@ some sort of collection. > > Let’s say you have a variable of type `u8` that can hold values between 0 and > 255. If you try to change the variable to a value outside that range, such as -> 256, *integer overflow* will occur, which can result in one of two behaviors. +> 256, _integer overflow_ will occur, which can result in one of two behaviors. > When you’re compiling in debug mode, Rust includes checks for integer overflow -> that cause your program to *panic* at runtime if this behavior occurs. Rust -> uses the term *panicking* when a program exits with an error; we’ll discuss +> that cause your program to _panic_ at runtime if this behavior occurs. Rust +> uses the term _panicking_ when a program exits with an error; we’ll discuss > panics in more depth in the [“Unrecoverable Errors with > `panic!`”][unrecoverable-errors-with-panic] section in Chapter > 9. > > When you’re compiling in release mode with the `--release` flag, Rust does -> *not* include checks for integer overflow that cause panics. Instead, if -> overflow occurs, Rust performs *two’s complement wrapping*. In short, values +> _not_ include checks for integer overflow that cause panics. Instead, if +> overflow occurs, Rust performs _two’s complement wrapping_. In short, values > greater than the maximum value the type can hold “wrap around” to the minimum > of the values the type can hold. In the case of a `u8`, the value 256 becomes > 0, the value 257 becomes 1, and so on. The program won’t panic, but the @@ -118,16 +117,16 @@ some sort of collection. > To explicitly handle the possibility of overflow, you can use these families > of methods provided by the standard library for primitive numeric types: > -> * Wrap in all modes with the `wrapping_*` methods, such as `wrapping_add`. -> * Return the `None` value if there is overflow with the `checked_*` methods. -> * Return the value and a boolean indicating whether there was overflow with +> - Wrap in all modes with the `wrapping_*` methods, such as `wrapping_add`. +> - Return the `None` value if there is overflow with the `checked_*` methods. +> - Return the value and a Boolean indicating whether there was overflow with > the `overflowing_*` methods. -> * Saturate at the value’s minimum or maximum values with the `saturating_*` +> - Saturate at the value’s minimum or maximum values with the `saturating_*` > methods. #### Floating-Point Types -Rust also has two primitive types for *floating-point numbers*, which are +Rust also has two primitive types for _floating-point numbers_, which are numbers with decimal points. Rust’s floating-point types are `f32` and `f64`, which are 32 bits and 64 bits in size, respectively. The default type is `f64` because on modern CPUs, it’s roughly the same speed as `f32` but is capable of @@ -141,8 +140,7 @@ Here’s an example that shows floating-point numbers in action: {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-06-floating-point/src/main.rs}} ``` -Floating-point numbers are represented according to the IEEE-754 standard. The -`f32` type is a single-precision float, and `f64` has double precision. +Floating-point numbers are represented according to the IEEE-754 standard. #### Numeric Operations @@ -189,26 +187,26 @@ some examples of declaring `char` values: {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-09-char/src/main.rs}} ``` -Note that we specify `char` literals with single quotes, as opposed to string -literals, which use double quotes. Rust’s `char` type is four bytes in size and -represents a Unicode Scalar Value, which means it can represent a lot more than -just ASCII. Accented letters; Chinese, Japanese, and Korean characters; emoji; -and zero-width spaces are all valid `char` values in Rust. Unicode Scalar -Values range from `U+0000` to `U+D7FF` and `U+E000` to `U+10FFFF` inclusive. -However, a “character” isn’t really a concept in Unicode, so your human -intuition for what a “character” is may not match up with what a `char` is in -Rust. We’ll discuss this topic in detail in [“Storing UTF-8 Encoded Text with -Strings”][strings] in Chapter 8. +Note that we specify `char` literals with single quotation marks, as opposed to +string literals, which use double quotation marks. Rust’s `char` type is 4 +bytes in size and represents a Unicode scalar value, which means it can +represent a lot more than just ASCII. Accented letters; Chinese, Japanese, and +Korean characters; emojis; and zero-width spaces are all valid `char` values in +Rust. Unicode scalar values range from `U+0000` to `U+D7FF` and `U+E000` to +`U+10FFFF` inclusive. However, a “character” isn’t really a concept in Unicode, +so your human intuition for what a “character” is may not match up with what a +`char` is in Rust. We’ll discuss this topic in detail in [“Storing UTF-8 +Encoded Text with Strings”][strings] in Chapter 8. ### Compound Types -*Compound types* can group multiple values into one type. Rust has two +_Compound types_ can group multiple values into one type. Rust has two primitive compound types: tuples and arrays. #### The Tuple Type -A *tuple* is a general way of grouping together a number of values with a -variety of types into one compound type. Tuples have a fixed length: once +A _tuple_ is a general way of grouping together a number of values with a +variety of types into one compound type. Tuples have a fixed length: Once declared, they cannot grow or shrink in size. We create a tuple by writing a comma-separated list of values inside @@ -234,7 +232,7 @@ use pattern matching to destructure a tuple value, like this: This program first creates a tuple and binds it to the variable `tup`. It then uses a pattern with `let` to take `tup` and turn it into three separate -variables, `x`, `y`, and `z`. This is called *destructuring* because it breaks +variables, `x`, `y`, and `z`. This is called _destructuring_ because it breaks the single tuple into three parts. Finally, the program prints the value of `y`, which is `6.4`. @@ -251,14 +249,14 @@ This program creates the tuple `x` and then accesses each element of the tuple using their respective indices. As with most programming languages, the first index in a tuple is 0. -The tuple without any values has a special name, *unit*. This value and its +The tuple without any values has a special name, _unit_. This value and its corresponding type are both written `()` and represent an empty value or an empty return type. Expressions implicitly return the unit value if they don’t return any other value. #### The Array Type -Another way to have a collection of multiple values is with an *array*. Unlike +Another way to have a collection of multiple values is with an _array_. Unlike a tuple, every element of an array must have the same type. Unlike arrays in some other languages, arrays in Rust have a fixed length. @@ -271,13 +269,14 @@ brackets: {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-13-arrays/src/main.rs}} ``` -Arrays are useful when you want your data allocated on the stack rather than -the heap (we will discuss the stack and the heap more in [Chapter -4][stack-and-heap]) or when you want to ensure you always have a -fixed number of elements. An array isn’t as flexible as the vector type, -though. A *vector* is a similar collection type provided by the standard -library that *is* allowed to grow or shrink in size. If you’re unsure whether -to use an array or a vector, chances are you should use a vector. [Chapter +Arrays are useful when you want your data allocated on the stack, the same as +the other types we have seen so far, rather than the heap (we will discuss the +stack and the heap more in [Chapter 4][stack-and-heap]) or when +you want to ensure that you always have a fixed number of elements. An array +isn’t as flexible as the vector type, though. A vector is a similar collection +type provided by the standard library that _is_ allowed to grow or shrink in +size because its contents live on the heap. If you’re unsure whether to use an +array or a vector, chances are you should use a vector. [Chapter 8][vectors] discusses vectors in more detail. However, arrays are more useful when you know the number of elements will not @@ -312,7 +311,10 @@ The array named `a` will contain `5` elements that will all be set to the value `3` initially. This is the same as writing `let a = [3, 3, 3, 3, 3];` but in a more concise way. -##### Accessing Array Elements + + + +#### Array Element Access An array is a single chunk of memory of a known, fixed size that can be allocated on the stack. You can access elements of an array using indexing, @@ -328,7 +330,7 @@ In this example, the variable named `first` will get the value `1` because that is the value at index `[0]` in the array. The variable named `second` will get the value `2` from index `[1]` in the array. -##### Invalid Array Element Access +#### Invalid Array Element Access Let’s see what happens if you try to access an element of an array that is past the end of the array. Say you run this code, similar to the guessing game in @@ -352,11 +354,12 @@ cargo run --> ```console -thread 'main' panicked at 'index out of bounds: the len is 5 but the index is 10', src/main.rs:19:19 +thread 'main' panicked at src/main.rs:19:19: +index out of bounds: the len is 5 but the index is 10 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace ``` -The program resulted in a *runtime* error at the point of using an invalid +The program resulted in a runtime error at the point of using an invalid value in the indexing operation. The program exited with an error message and didn’t execute the final `println!` statement. When you attempt to access an element using indexing, Rust will check that the index you’ve specified is less @@ -372,8 +375,7 @@ kind of error by immediately exiting instead of allowing the memory access and continuing. Chapter 9 discusses more of Rust’s error handling and how you can write readable, safe code that neither panics nor allows invalid memory access. -[comparing-the-guess-to-the-secret-number]: -ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number +[comparing-the-guess-to-the-secret-number]: ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number [twos-complement]: https://en.wikipedia.org/wiki/Two%27s_complement [control-flow]: ch03-05-control-flow.html#control-flow [strings]: ch08-02-strings.html#storing-utf-8-encoded-text-with-strings diff --git a/src/ch03-03-how-functions-work.md b/src/ch03-03-how-functions-work.md index 2b59f0cd45..5f9e512da2 100644 --- a/src/ch03-03-how-functions-work.md +++ b/src/ch03-03-how-functions-work.md @@ -5,7 +5,7 @@ important functions in the language: the `main` function, which is the entry point of many programs. You’ve also seen the `fn` keyword, which allows you to declare new functions. -Rust code uses *snake case* as the conventional style for function and variable +Rust code uses _snake case_ as the conventional style for function and variable names, in which all letters are lowercase and underscores separate words. Here’s a program that contains an example function definition: @@ -22,12 +22,12 @@ body begins and ends. We can call any function we’ve defined by entering its name followed by a set of parentheses. Because `another_function` is defined in the program, it can be called from inside the `main` function. Note that we defined `another_function` -*after* the `main` function in the source code; we could have defined it before +_after_ the `main` function in the source code; we could have defined it before as well. Rust doesn’t care where you define your functions, only that they’re defined somewhere in a scope that can be seen by the caller. -Let’s start a new binary project named *functions* to explore functions -further. Place the `another_function` example in *src/main.rs* and run it. You +Let’s start a new binary project named _functions_ to explore functions +further. Place the `another_function` example in _src/main.rs_ and run it. You should see the following output: ```console @@ -40,11 +40,11 @@ and its message is printed. ### Parameters -We can define functions to have *parameters*, which are special variables that +We can define functions to have _parameters_, which are special variables that are part of a function’s signature. When a function has parameters, you can provide it with concrete values for those parameters. Technically, the concrete -values are called *arguments*, but in casual conversation, people tend to use -the words *parameter* and *argument* interchangeably for either the variables +values are called _arguments_, but in casual conversation, people tend to use +the words _parameter_ and _argument_ interchangeably for either the variables in a function’s definition or the concrete values passed in when you call a function. @@ -67,11 +67,11 @@ The declaration of `another_function` has one parameter named `x`. The type of `println!` macro puts `5` where the pair of curly brackets containing `x` was in the format string. -In function signatures, you *must* declare the type of each parameter. This is -a deliberate decision in Rust’s design: requiring type annotations in function +In function signatures, you _must_ declare the type of each parameter. This is +a deliberate decision in Rust’s design: Requiring type annotations in function definitions means the compiler almost never needs you to use them elsewhere in the code to figure out what type you mean. The compiler is also able to give -more helpful error messages if it knows what types the function expects. +more-helpful error messages if it knows what types the function expects. When defining multiple parameters, separate the parameter declarations with commas, like this: @@ -87,8 +87,8 @@ parameters. The first parameter is named `value` and is an `i32`. The second is named `unit_label` and is type `char`. The function then prints text containing both the `value` and the `unit_label`. -Let’s try running this code. Replace the program currently in your *functions* -project’s *src/main.rs* file with the preceding example and run it using `cargo +Let’s try running this code. Replace the program currently in your _functions_ +project’s _src/main.rs_ file with the preceding example and run it using `cargo run`: ```console @@ -108,24 +108,27 @@ understand. Other languages don’t have the same distinctions, so let’s look what statements and expressions are and how their differences affect the bodies of functions. -* **Statements** are instructions that perform some action and do not return +- _Statements_ are instructions that perform some action and do not return a value. -* **Expressions** evaluate to a resultant value. Let’s look at some examples. +- _Expressions_ evaluate to a resultant value. + +Let’s look at some examples. We’ve actually already used statements and expressions. Creating a variable and assigning a value to it with the `let` keyword is a statement. In Listing 3-1, `let y = 6;` is a statement. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-01/src/main.rs}} ``` -Listing 3-1: A `main` function declaration containing one statement + Function definitions are also statements; the entire preceding example is a -statement in itself. +statement in itself. (As we’ll see shortly, calling a function is not a +statement, though.) Statements do not return values. Therefore, you can’t assign a `let` statement to another variable, as the following code tries to do; you’ll get an error: @@ -151,7 +154,7 @@ languages, you can write `x = y = 6` and have both `x` and `y` have the value Expressions evaluate to a value and make up most of the rest of the code that you’ll write in Rust. Consider a math operation, such as `5 + 6`, which is an expression that evaluates to the value `11`. Expressions can be part of -statements: in Listing 3-1, the `6` in the statement `let y = 6;` is an +statements: In Listing 3-1, the `6` in the statement `let y = 6;` is an expression that evaluates to the value `6`. Calling a function is an expression. Calling a macro is an expression. A new scope block created with curly brackets is an expression, for example: @@ -172,12 +175,11 @@ This expression: ``` is a block that, in this case, evaluates to `4`. That value gets bound to `y` -as part of the `let` statement. Note that the `x + 1` line doesn’t have a -semicolon at the end, which is unlike most of the lines you’ve seen so far. -Expressions do not include ending semicolons. If you add a semicolon to the end -of an expression, you turn it into a statement, and it will then not return a -value. Keep this in mind as you explore function return values and expressions -next. +as part of the `let` statement. Note the `x + 1` line without a semicolon at +the end, which is unlike most of the lines you’ve seen so far. Expressions do +not include ending semicolons. If you add a semicolon to the end of an +expression, you turn it into a statement, and it will then not return a value. +Keep this in mind as you explore function return values and expressions next. ### Functions with Return Values @@ -206,7 +208,7 @@ running this code; the output should look like this: The `5` in `five` is the function’s return value, which is why the return type is `i32`. Let’s examine this in more detail. There are two important bits: -first, the line `let x = five();` shows that we’re using the return value of a +First, the line `let x = five();` shows that we’re using the return value of a function to initialize a variable. Because the function `five` returns a `5`, that line is the same as the following: @@ -226,9 +228,9 @@ Let’s look at another example: {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-22-function-parameter-and-return/src/main.rs}} ``` -Running this code will print `The value of x is: 6`. But if we place a -semicolon at the end of the line containing `x + 1`, changing it from an -expression to a statement, we’ll get an error: +Running this code will print `The value of x is: 6`. But what happens if we +place a semicolon at the end of the line containing `x + 1`, changing it from +an expression to a statement? Filename: src/main.rs @@ -236,7 +238,7 @@ expression to a statement, we’ll get an error: {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/src/main.rs}} ``` -Compiling this code produces an error, as follows: +Compiling this code will produce an error, as follows: ```console {{#include ../listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/output.txt}} @@ -247,5 +249,5 @@ code. The definition of the function `plus_one` says that it will return an `i32`, but statements don’t evaluate to a value, which is expressed by `()`, the unit type. Therefore, nothing is returned, which contradicts the function definition and results in an error. In this output, Rust provides a message to -possibly help rectify this issue: it suggests removing the semicolon, which +possibly help rectify this issue: It suggests removing the semicolon, which would fix the error. diff --git a/src/ch03-04-comments.md b/src/ch03-04-comments.md index bfb0cfe177..fdcdbd48a1 100644 --- a/src/ch03-04-comments.md +++ b/src/ch03-04-comments.md @@ -1,9 +1,9 @@ ## Comments All programmers strive to make their code easy to understand, but sometimes -extra explanation is warranted. In these cases, programmers leave *comments* in -their source code that the compiler will ignore but people reading the source -code may find useful. +extra explanation is warranted. In these cases, programmers leave _comments_ in +their source code that the compiler will ignore but that people reading the +source code may find useful. Here’s a simple comment: @@ -16,9 +16,9 @@ comment continues until the end of the line. For comments that extend beyond a single line, you’ll need to include `//` on each line, like this: ```rust -// So we’re doing something complicated here, long enough that we need +// So we're doing something complicated here, long enough that we need // multiple lines of comments to do it! Whew! Hopefully, this comment will -// explain what’s going on. +// explain what's going on. ``` Comments can also be placed at the end of lines containing code: diff --git a/src/ch03-05-control-flow.md b/src/ch03-05-control-flow.md index 60d6b95a96..6bde6748fe 100644 --- a/src/ch03-05-control-flow.md +++ b/src/ch03-05-control-flow.md @@ -1,9 +1,10 @@ ## Control Flow -The ability to run some code depending on whether a condition is `true` and to -run some code repeatedly while a condition is `true` are basic building blocks -in most programming languages. The most common constructs that let you control -the flow of execution of Rust code are `if` expressions and loops. +The ability to run some code depending on whether a condition is `true` and the +ability to run some code repeatedly while a condition is `true` are basic +building blocks in most programming languages. The most common constructs that +let you control the flow of execution of Rust code are `if` expressions and +loops. ### `if` Expressions @@ -11,8 +12,8 @@ An `if` expression allows you to branch your code depending on conditions. You provide a condition and then state, “If this condition is met, run this block of code. If the condition is not met, do not run this block of code.” -Create a new project called *branches* in your *projects* directory to explore -the `if` expression. In the *src/main.rs* file, input the following: +Create a new project called _branches_ in your _projects_ directory to explore +the `if` expression. In the _src/main.rs_ file, input the following: Filename: src/main.rs @@ -24,7 +25,7 @@ All `if` expressions start with the keyword `if`, followed by a condition. In this case, the condition checks whether or not the variable `number` has a value less than 5. We place the block of code to execute if the condition is `true` immediately after the condition inside curly brackets. Blocks of code -associated with the conditions in `if` expressions are sometimes called *arms*, +associated with the conditions in `if` expressions are sometimes called _arms_, just like the arms in `match` expressions that we discussed in the [“Comparing the Guess to the Secret Number”][comparing-the-guess-to-the-secret-number] section of Chapter 2. @@ -54,7 +55,7 @@ Run the program again, and look at the output: {{#include ../listings/ch03-common-programming-concepts/no-listing-27-if-false/output.txt}} ``` -It’s also worth noting that the condition in this code *must* be a `bool`. If +It’s also worth noting that the condition in this code _must_ be a `bool`. If the condition isn’t a `bool`, we’ll get an error. For example, try running the following code: @@ -120,14 +121,13 @@ Rust branching construct called `match` for these cases. Because `if` is an expression, we can use it on the right side of a `let` statement to assign the outcome to a variable, as in Listing 3-2. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-02/src/main.rs}} ``` -Listing 3-2: Assigning the result of an `if` expression -to a variable + The `number` variable will be bound to a value based on the outcome of the `if` expression. Run this code to see what happens: @@ -159,29 +159,29 @@ find the problem in the program: ``` The expression in the `if` block evaluates to an integer, and the expression in -the `else` block evaluates to a string. This won’t work because variables must -have a single type, and Rust needs to know at compile time what type the -`number` variable is, definitively. Knowing the type of `number` lets the -compiler verify the type is valid everywhere we use `number`. Rust wouldn’t be -able to do that if the type of `number` was only determined at runtime; the -compiler would be more complex and would make fewer guarantees about the code -if it had to keep track of multiple hypothetical types for any variable. +the `else` block evaluates to a string. This won’t work, because variables must +have a single type, and Rust needs to know definitively at compile time what +type the `number` variable is. Knowing the type of `number` lets the compiler +verify the type is valid everywhere we use `number`. Rust wouldn’t be able to +do that if the type of `number` was only determined at runtime; the compiler +would be more complex and would make fewer guarantees about the code if it had +to keep track of multiple hypothetical types for any variable. ### Repetition with Loops It’s often useful to execute a block of code more than once. For this task, -Rust provides several *loops*, which will run through the code inside the loop +Rust provides several _loops_, which will run through the code inside the loop body to the end and then start immediately back at the beginning. To experiment -with loops, let’s make a new project called *loops*. +with loops, let’s make a new project called _loops_. Rust has three kinds of loops: `loop`, `while`, and `for`. Let’s try each one. #### Repeating Code with `loop` The `loop` keyword tells Rust to execute a block of code over and over again -forever or until you explicitly tell it to stop. +either forever or until you explicitly tell it to stop. -As an example, change the *src/main.rs* file in your *loops* directory to look +As an example, change the _src/main.rs_ file in your _loops_ directory to look like this: Filename: src/main.rs @@ -191,9 +191,9 @@ like this: ``` When we run this program, we’ll see `again!` printed over and over continuously -until we stop the program manually. Most terminals support the keyboard -shortcut ctrl-c to interrupt a program that is -stuck in a continual loop. Give it a try: +until we stop the program manually. Most terminals support the keyboard shortcut +ctrl-C to interrupt a program that is stuck in a continual +loop. Give it a try: + + +#### Disambiguating with Loop Labels If you have loops within loops, `break` and `continue` apply to the innermost -loop at that point. You can optionally specify a *loop label* on a loop that +loop at that point. You can optionally specify a _loop label_ on a loop that you can then use with `break` or `continue` to specify that those keywords apply to the labeled loop instead of the innermost loop. Loop labels must begin with a single quote. Here’s an example with two nested loops: @@ -271,7 +277,10 @@ doesn’t specify a label will exit the inner loop only. The `break {{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt}} ``` -#### Conditional Loops with `while` + + + +#### Streamlining Conditional Loops with while A program will often need to evaluate a condition within a loop. While the condition is `true`, the loop runs. When the condition ceases to be `true`, the @@ -280,16 +289,15 @@ like this using a combination of `loop`, `if`, `else`, and `break`; you could try that now in a program, if you’d like. However, this pattern is so common that Rust has a built-in language construct for it, called a `while` loop. In Listing 3-3, we use `while` to loop the program three times, counting down each -time, and then, after the loop, print a message and exit. +time, and then, after the loop, to print a message and exit. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-03/src/main.rs}} ``` -Listing 3-3: Using a `while` loop to run code while a -condition holds true + This construct eliminates a lot of nesting that would be necessary if you used `loop`, `if`, `else`, and `break`, and it’s clearer. While a condition @@ -301,17 +309,16 @@ You can choose to use the `while` construct to loop over the elements of a collection, such as an array. For example, the loop in Listing 3-4 prints each element in the array `a`. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-04/src/main.rs}} ``` -Listing 3-4: Looping through each element of a collection -using a `while` loop + Here, the code counts up through the elements in the array. It starts at index -`0`, and then loops until it reaches the final index in the array (that is, +`0` and then loops until it reaches the final index in the array (that is, when `index < 5` is no longer `true`). Running this code will print every element in the array: @@ -323,7 +330,7 @@ All five array values appear in the terminal, as expected. Even though `index` will reach a value of `5` at some point, the loop stops executing before trying to fetch a sixth value from the array. -However, this approach is error prone; we could cause the program to panic if +However, this approach is error-prone; we could cause the program to panic if the index value or test condition is incorrect. For example, if you changed the definition of the `a` array to have four elements but forgot to update the condition to `while index < 4`, the code would panic. It’s also slow, because @@ -333,19 +340,20 @@ index is within the bounds of the array on every iteration through the loop. As a more concise alternative, you can use a `for` loop and execute some code for each item in a collection. A `for` loop looks like the code in Listing 3-5. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-05/src/main.rs}} ``` -Listing 3-5: Looping through each element of a collection -using a `for` loop + When we run this code, we’ll see the same output as in Listing 3-4. More importantly, we’ve now increased the safety of the code and eliminated the chance of bugs that might result from going beyond the end of the array or not -going far enough and missing some items. +going far enough and missing some items. Machine code generated from `for` +loops can be more efficient as well because the index doesn’t need to be +compared to the length of the array at every iteration. Using the `for` loop, you wouldn’t need to remember to change any other code if you changed the number of values in the array, as you would with the method @@ -372,20 +380,18 @@ This code is a bit nicer, isn’t it? ## Summary -You made it! This was a sizable chapter: you learned about variables, scalar +You made it! This was a sizable chapter: You learned about variables, scalar and compound data types, functions, comments, `if` expressions, and loops! To practice with the concepts discussed in this chapter, try building programs to do the following: -* Convert temperatures between Fahrenheit and Celsius. -* Generate the *n*th Fibonacci number. -* Print the lyrics to the Christmas carol “The Twelve Days of Christmas,” +- Convert temperatures between Fahrenheit and Celsius. +- Generate the *n*th Fibonacci number. +- Print the lyrics to the Christmas carol “The Twelve Days of Christmas,” taking advantage of the repetition in the song. -When you’re ready to move on, we’ll talk about a concept in Rust that *doesn’t* +When you’re ready to move on, we’ll talk about a concept in Rust that _doesn’t_ commonly exist in other programming languages: ownership. -[comparing-the-guess-to-the-secret-number]: -ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number -[quitting-after-a-correct-guess]: -ch02-00-guessing-game-tutorial.html#quitting-after-a-correct-guess +[comparing-the-guess-to-the-secret-number]: ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number +[quitting-after-a-correct-guess]: ch02-00-guessing-game-tutorial.html#quitting-after-a-correct-guess diff --git a/src/ch04-01-what-is-ownership.md b/src/ch04-01-what-is-ownership.md index 5249c2dd77..70d4f1bdf5 100644 --- a/src/ch04-01-what-is-ownership.md +++ b/src/ch04-01-what-is-ownership.md @@ -1,10 +1,10 @@ ## What Is Ownership? -*Ownership* is a set of rules that govern how a Rust program manages memory. +_Ownership_ is a set of rules that govern how a Rust program manages memory. All programs have to manage the way they use a computer’s memory while running. Some languages have garbage collection that regularly looks for no-longer-used memory as the program runs; in other languages, the programmer must explicitly -allocate and free the memory. Rust uses a third approach: memory is managed +allocate and free the memory. Rust uses a third approach: Memory is managed through a system of ownership with a set of rules that the compiler checks. If any of the rules are violated, the program won’t compile. None of the features of ownership will slow down your program while it’s running. @@ -31,20 +31,20 @@ strings. > Both the stack and the heap are parts of memory available to your code to use > at runtime, but they are structured in different ways. The stack stores > values in the order it gets them and removes the values in the opposite -> order. This is referred to as *last in, first out*. Think of a stack of -> plates: when you add more plates, you put them on top of the pile, and when +> order. This is referred to as _last in, first out (LIFO)_. Think of a stack of +> plates: When you add more plates, you put them on top of the pile, and when > you need a plate, you take one off the top. Adding or removing plates from -> the middle or bottom wouldn’t work as well! Adding data is called *pushing -> onto the stack*, and removing data is called *popping off the stack*. All +> the middle or bottom wouldn’t work as well! Adding data is called _pushing +> onto the stack_, and removing data is called _popping off the stack_. All > data stored on the stack must have a known, fixed size. Data with an unknown > size at compile time or a size that might change must be stored on the heap > instead. > -> The heap is less organized: when you put data on the heap, you request a +> The heap is less organized: When you put data on the heap, you request a > certain amount of space. The memory allocator finds an empty spot in the heap -> that is big enough, marks it as being in use, and returns a *pointer*, which -> is the address of that location. This process is called *allocating on the -> heap* and is sometimes abbreviated as just *allocating* (pushing values onto +> that is big enough, marks it as being in use, and returns a _pointer_, which +> is the address of that location. This process is called _allocating on the +> heap_ and is sometimes abbreviated as just _allocating_ (pushing values onto > the stack is not considered allocating). Because the pointer to the heap is a > known, fixed size, you can store the pointer on the stack, but when you want > the actual data, you must follow the pointer. Think of being seated at a @@ -60,16 +60,16 @@ strings. > to hold the data and then perform bookkeeping to prepare for the next > allocation. > -> Accessing data in the heap is slower than accessing data on the stack because -> you have to follow a pointer to get there. Contemporary processors are faster -> if they jump around less in memory. Continuing the analogy, consider a server -> at a restaurant taking orders from many tables. It’s most efficient to get -> all the orders at one table before moving on to the next table. Taking an -> order from table A, then an order from table B, then one from A again, and -> then one from B again would be a much slower process. By the same token, a -> processor can do its job better if it works on data that’s close to other -> data (as it is on the stack) rather than farther away (as it can be on the -> heap). +> Accessing data in the heap is generally slower than accessing data on the +> stack because you have to follow a pointer to get there. Contemporary +> processors are faster if they jump around less in memory. Continuing the +> analogy, consider a server at a restaurant taking orders from many tables. +> It’s most efficient to get all the orders at one table before moving on to +> the next table. Taking an order from table A, then an order from table B, +> then one from A again, and then one from B again would be a much slower +> process. By the same token, a processor can usually do its job better if it +> works on data that’s close to other data (as it is on the stack) rather than +> farther away (as it can be on the heap). > > When your code calls a function, the values passed into the function > (including, potentially, pointers to data on the heap) and the function’s @@ -78,30 +78,31 @@ strings. > > Keeping track of what parts of code are using what data on the heap, > minimizing the amount of duplicate data on the heap, and cleaning up unused -> data on the heap so you don’t run out of space are all problems that ownership -> addresses. Once you understand ownership, you won’t need to think about the -> stack and the heap very often, but knowing that the main purpose of ownership -> is to manage heap data can help explain why it works the way it does. +> data on the heap so that you don’t run out of space are all problems that +> ownership addresses. Once you understand ownership, you won’t need to think +> about the stack and the heap very often. But knowing that the main purpose of +> ownership is to manage heap data can help explain why it works the way it +> does. ### Ownership Rules First, let’s take a look at the ownership rules. Keep these rules in mind as we work through the examples that illustrate them: -* Each value in Rust has an *owner*. -* There can only be one owner at a time. -* When the owner goes out of scope, the value will be dropped. +- Each value in Rust has an _owner_. +- There can only be one owner at a time. +- When the owner goes out of scope, the value will be dropped. ### Variable Scope Now that we’re past basic Rust syntax, we won’t include all the `fn main() {` -code in examples, so if you’re following along, make sure to put the following -examples inside a `main` function manually. As a result, our examples will be a -bit more concise, letting us focus on the actual details rather than +code in the examples, so if you’re following along, make sure to put the +following examples inside a `main` function manually. As a result, our examples +will be a bit more concise, letting us focus on the actual details rather than boilerplate code. -As a first example of ownership, we’ll look at the *scope* of some variables. A -scope is the range within a program for which an item is valid. Take the +As a first example of ownership, we’ll look at the scope of some variables. A +_scope_ is the range within a program for which an item is valid. Take the following variable: ```rust @@ -110,20 +111,21 @@ let s = "hello"; The variable `s` refers to a string literal, where the value of the string is hardcoded into the text of our program. The variable is valid from the point at -which it’s declared until the end of the current *scope*. Listing 4-1 shows a +which it’s declared until the end of the current scope. Listing 4-1 shows a program with comments annotating where the variable `s` would be valid. ++ ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-01/src/main.rs:here}} ``` -Listing 4-1: A variable and the scope in which it is -valid + In other words, there are two important points in time here: -* When `s` comes *into* scope, it is valid. -* It remains valid until it goes *out of* scope. +- When `s` comes _into_ scope, it is valid. +- It remains valid until it goes _out of_ scope. At this point, the relationship between scopes and when variables are valid is similar to that in other programming languages. Now we’ll build on top of this @@ -142,15 +144,15 @@ clean up that data, and the `String` type is a great example. We’ll concentrate on the parts of `String` that relate to ownership. These aspects also apply to other complex data types, whether they are provided by -the standard library or created by you. We’ll discuss `String` in more depth in -[Chapter 8][ch8]. +the standard library or created by you. We’ll discuss non-ownership aspects of +`String` in [Chapter 8][ch8]. We’ve already seen string literals, where a string value is hardcoded into our program. String literals are convenient, but they aren’t suitable for every situation in which we may want to use text. One reason is that they’re immutable. Another is that not every string value can be known when we write -our code: for example, what if we want to take user input and store it? For -these situations, Rust has a second string type, `String`. This type manages +our code: For example, what if we want to take user input and store it? It is +for these situations that Rust has the `String` type. This type manages data allocated on the heap and as such is able to store an amount of text that is unknown to us at compile time. You can create a `String` from a string literal using the `from` function, like so: @@ -161,12 +163,12 @@ let s = String::from("hello"); The double colon `::` operator allows us to namespace this particular `from` function under the `String` type rather than using some sort of name like -`string_from`. We’ll discuss this syntax more in the [“Method -Syntax”][method-syntax] section of Chapter 5, and when we talk -about namespacing with modules in [“Paths for Referring to an Item in the -Module Tree”][paths-module-tree] in Chapter 7. +`string_from`. We’ll discuss this syntax more in the [“Methods”][methods] section of Chapter 5, and when we talk about namespacing with +modules in [“Paths for Referring to an Item in the Module +Tree”][paths-module-tree] in Chapter 7. -This kind of string *can* be mutated: +This kind of string _can_ be mutated: ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/src/main.rs:here}} @@ -188,16 +190,16 @@ With the `String` type, in order to support a mutable, growable piece of text, we need to allocate an amount of memory on the heap, unknown at compile time, to hold the contents. This means: -* The memory must be requested from the memory allocator at runtime. -* We need a way of returning this memory to the allocator when we’re done with +- The memory must be requested from the memory allocator at runtime. +- We need a way of returning this memory to the allocator when we’re done with our `String`. -That first part is done by us: when we call `String::from`, its implementation +That first part is done by us: When we call `String::from`, its implementation requests the memory it needs. This is pretty much universal in programming languages. -However, the second part is different. In languages with a *garbage collector -(GC)*, the GC keeps track of and cleans up memory that isn’t being used +However, the second part is different. In languages with a _garbage collector +(GC)_, the GC keeps track of and cleans up memory that isn’t being used anymore, and we don’t need to think about it. In most languages without a GC, it’s our responsibility to identify when memory is no longer being used and to call code to explicitly free it, just as we did to request it. Doing this @@ -206,7 +208,7 @@ we’ll waste memory. If we do it too early, we’ll have an invalid variable. I we do it twice, that’s a bug too. We need to pair exactly one `allocate` with exactly one `free`. -Rust takes a different path: the memory is automatically returned once the +Rust takes a different path: The memory is automatically returned once the variable that owns it goes out of scope. Here’s a version of our scope example from Listing 4-1 using a `String` instead of a string literal: @@ -222,7 +224,7 @@ the code to return the memory. Rust calls `drop` automatically at the closing curly bracket. > Note: In C++, this pattern of deallocating resources at the end of an item’s -> lifetime is sometimes called *Resource Acquisition Is Initialization (RAII)*. +> lifetime is sometimes called _Resource Acquisition Is Initialization (RAII)_. > The `drop` function in Rust will be familiar to you if you’ve used RAII > patterns. @@ -231,22 +233,24 @@ simple right now, but the behavior of code can be unexpected in more complicated situations when we want to have multiple variables use the data we’ve allocated on the heap. Let’s explore some of those situations now. - + + #### Variables and Data Interacting with Move Multiple variables can interact with the same data in different ways in Rust. -Let’s look at an example using an integer in Listing 4-2. +Listing 4-2 shows an example using an integer. + + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-02/src/main.rs:here}} ``` -Listing 4-2: Assigning the integer value of variable `x` -to `y` + -We can probably guess what this is doing: “bind the value `5` to `x`; then make +We can probably guess what this is doing: “Bind the value `5` to `x`; then, make a copy of the value in `x` and bind it to `y`.” We now have two variables, `x` and `y`, and both equal `5`. This is indeed what is happening, because integers are simple values with a known, fixed size, and these two `5` values are pushed @@ -259,7 +263,7 @@ Now let’s look at the `String` version: ``` This looks very similar, so we might assume that the way it works would be the -same: that is, the second line would make a copy of the value in `s1` and bind +same: That is, the second line would make a copy of the value in `s1` and bind it to `s2`. But this isn’t quite what happens. Take a look at Figure 4-1 to see what is happening to `String` under the @@ -274,7 +278,7 @@ value in the second table. The second table contains the representation of the string data on the heap, byte by byte." src="img/trpl04-01.svg" class="center" style="width: 50%;" /> -Figure 4-1: Representation in memory of a `String` +Figure 4-1: The representation in memory of a `String` holding the value `"hello"` bound to `s1` The length is how much memory, in bytes, the contents of the `String` are @@ -292,10 +296,10 @@ representation in memory looks like Figure 4-2. stack, respectively, and both pointing to the same string data on the heap." src="img/trpl04-02.svg" class="center" style="width: 50%;" /> -Figure 4-2: Representation in memory of the variable `s2` -that has a copy of the pointer, length, and capacity of `s1` +Figure 4-2: The representation in memory of the variable +`s2` that has a copy of the pointer, length, and capacity of `s1` -The representation does *not* look like Figure 4-3, which is what memory would +The representation does _not_ look like Figure 4-3, which is what memory would look like if Rust instead copied the heap data as well. If Rust did this, the operation `s2 = s1` could be very expensive in terms of runtime performance if the data on the heap were large. @@ -310,8 +314,8 @@ do if Rust copied the heap data as well Earlier, we said that when a variable goes out of scope, Rust automatically calls the `drop` function and cleans up the heap memory for that variable. But Figure 4-2 shows both data pointers pointing to the same location. This is a -problem: when `s2` and `s1` go out of scope, they will both try to free the -same memory. This is known as a *double free* error and is one of the memory +problem: When `s2` and `s1` go out of scope, they will both try to free the +same memory. This is known as a _double free_ error and is one of the memory safety bugs we mentioned previously. Freeing memory twice can lead to memory corruption, which can potentially lead to security vulnerabilities. @@ -331,35 +335,64 @@ invalidated reference: {{#include ../listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/output.txt}} ``` -If you’ve heard the terms *shallow copy* and *deep copy* while working with +If you’ve heard the terms _shallow copy_ and _deep copy_ while working with other languages, the concept of copying the pointer, length, and capacity without copying the data probably sounds like making a shallow copy. But because Rust also invalidates the first variable, instead of being called a -shallow copy, it’s known as a *move*. In this example, we would say that `s1` -was *moved* into `s2`. So, what actually happens is shown in Figure 4-4. +shallow copy, it’s known as a _move_. In this example, we would say that `s1` +was _moved_ into `s2`. So, what actually happens is shown in Figure 4-4. Three tables: tables s1 and s2 representing those strings on the stack, respectively, and both pointing to the same string data on the heap. -Table s1 is grayed out be-cause s1 is no longer valid; only s2 can be used to +Table s1 is grayed out because s1 is no longer valid; only s2 can be used to access the heap data. -Figure 4-4: Representation in memory after `s1` has been -invalidated +Figure 4-4: The representation in memory after `s1` has +been invalidated That solves our problem! With only `s2` valid, when it goes out of scope it alone will free the memory, and we’re done. In addition, there’s a design choice that’s implied by this: Rust will never -automatically create “deep” copies of your data. Therefore, any *automatic* +automatically create “deep” copies of your data. Therefore, any _automatic_ copying can be assumed to be inexpensive in terms of runtime performance. - +#### Scope and Assignment + +The inverse of this is true for the relationship between scoping, ownership, and +memory being freed via the `drop` function as well. When you assign a completely +new value to an existing variable, Rust will call `drop` and free the original +value’s memory immediately. Consider this code, for example: + +```rust +{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/src/main.rs:here}} +``` + +We initially declare a variable `s` and bind it to a `String` with the value +`"hello"`. Then, we immediately create a new `String` with the value `"ahoy"` +and assign it to `s`. At this point, nothing is referring to the original value +on the heap at all. Figure 4-5 illustrates the stack and heap data now: + +One table representing the string value on the stack, pointing to +the second piece of string data (ahoy) on the heap, with the original string +data (hello) grayed out because it cannot be accessed anymore. + +Figure 4-5: The representation in memory after the initial +value has been replaced in its entirety + +The original string thus immediately goes out of scope. Rust will run the `drop` +function on it and its memory will be freed right away. When we print the value +at the end, it will be `"ahoy, world!"`. + + + #### Variables and Data Interacting with Clone -If we *do* want to deeply copy the heap data of the `String`, not just the +If we _do_ want to deeply copy the heap data of the `String`, not just the stack data, we can use a common method called `clone`. We’ll discuss method syntax in Chapter 5, but because methods are a common feature in many programming languages, you’ve probably seen them before. @@ -371,7 +404,7 @@ Here’s an example of the `clone` method in action: ``` This works just fine and explicitly produces the behavior shown in Figure 4-3, -where the heap data *does* get copied. +where the heap data _does_ get copied. When you see a call to `clone`, you know that some arbitrary code is being executed and that code may be expensive. It’s a visual indicator that something @@ -386,7 +419,7 @@ integers—part of which was shown in Listing 4-2—works and is valid: {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-06-copy/src/main.rs:here}} ``` -But this code seems to contradict what we just learned: we don’t have a call to +But this code seems to contradict what we just learned: We don’t have a call to `clone`, but `x` is still valid and wasn’t moved into `y`. The reason is that types such as integers that have a known size at compile @@ -415,11 +448,11 @@ values can implement `Copy`, and nothing that requires allocation or is some form of resource can implement `Copy`. Here are some of the types that implement `Copy`: -* All the integer types, such as `u32`. -* The Boolean type, `bool`, with values `true` and `false`. -* All the floating-point types, such as `f64`. -* The character type, `char`. -* Tuples, if they only contain types that also implement `Copy`. For example, +- All the integer types, such as `u32`. +- The Boolean type, `bool`, with values `true` and `false`. +- All the floating-point types, such as `f64`. +- The character type, `char`. +- Tuples, if they only contain types that also implement `Copy`. For example, `(i32, i32)` implements `Copy`, but `(i32, String)` does not. ### Ownership and Functions @@ -429,14 +462,13 @@ assigning a value to a variable. Passing a variable to a function will move or copy, just as assignment does. Listing 4-3 has an example with some annotations showing where variables go into and out of scope. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-03/src/main.rs}} ``` -Listing 4-3: Functions with ownership and scope -annotated + If we tried to use `s` after the call to `takes_ownership`, Rust would throw a compile-time error. These static checks protect us from mistakes. Try adding @@ -449,16 +481,15 @@ Returning values can also transfer ownership. Listing 4-4 shows an example of a function that returns some value, with similar annotations as those in Listing 4-3. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-04/src/main.rs}} ``` -Listing 4-4: Transferring ownership of return -values + -The ownership of a variable follows the same pattern every time: assigning a +The ownership of a variable follows the same pattern every time: Assigning a value to another variable moves it. When a variable that includes data on the heap goes out of scope, the value will be cleaned up by `drop` unless ownership of the data has been moved to another variable. @@ -471,22 +502,22 @@ from the body of the function that we might want to return as well. Rust does let us return multiple values using a tuple, as shown in Listing 4-5. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-05/src/main.rs}} ``` -Listing 4-5: Returning ownership of parameters + But this is too much ceremony and a lot of work for a concept that should be common. Luckily for us, Rust has a feature for using a value without -transferring ownership, called *references*. +transferring ownership: references. [data-types]: ch03-02-data-types.html#data-types [ch8]: ch08-02-strings.html [traits]: ch10-02-traits.html [derivable-traits]: appendix-03-derivable-traits.html -[method-syntax]: ch05-03-method-syntax.html#method-syntax +[methods]: ch05-03-method-syntax.html#methods [paths-module-tree]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html [drop]: ../std/ops/trait.Drop.html#tymethod.drop diff --git a/src/ch04-02-references-and-borrowing.md b/src/ch04-02-references-and-borrowing.md index ea2d8d2029..8c37601d57 100644 --- a/src/ch04-02-references-and-borrowing.md +++ b/src/ch04-02-references-and-borrowing.md @@ -1,10 +1,10 @@ ## References and Borrowing The issue with the tuple code in Listing 4-5 is that we have to return the -`String` to the calling function so we can still use the `String` after the -call to `calculate_length`, because the `String` was moved into +`String` to the calling function so that we can still use the `String` after +the call to `calculate_length`, because the `String` was moved into `calculate_length`. Instead, we can provide a reference to the `String` value. -A *reference* is like a pointer in that it’s an address we can follow to access +A reference is like a pointer in that it’s an address we can follow to access the data stored at that address; that data is owned by some other variable. Unlike a pointer, a reference is guaranteed to point to a valid value of a particular type for the life of that reference. @@ -12,26 +12,28 @@ particular type for the life of that reference. Here is how you would define and use a `calculate_length` function that has a reference to an object as a parameter instead of taking ownership of the value: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs:all}} ``` + + First, notice that all the tuple code in the variable declaration and the function return value is gone. Second, note that we pass `&s1` into `calculate_length` and, in its definition, we take `&String` rather than -`String`. These ampersands represent *references*, and they allow you to refer -to some value without taking ownership of it. Figure 4-5 depicts this concept. +`String`. These ampersands represent references, and they allow you to refer to +some value without taking ownership of it. Figure 4-6 depicts this concept. Three tables: the table for s contains only a pointer to the table for s1. The table for s1 contains the stack data for s1 and points to the -string data on the heap. +string data on the heap." src="img/trpl04-06.svg" class="center" /> -Figure 4-5: A diagram of `&String s` pointing at `String -s1` +Figure 4-6: A diagram of `&String` `s` pointing at +`String` `s1` -> Note: The opposite of referencing by using `&` is *dereferencing*, which is +> Note: The opposite of referencing by using `&` is _dereferencing_, which is > accomplished with the dereference operator, `*`. We’ll see some uses of the > dereference operator in Chapter 8 and discuss details of dereferencing in > Chapter 15. @@ -42,9 +44,9 @@ Let’s take a closer look at the function call here: {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs:here}} ``` -The `&s1` syntax lets us create a reference that *refers* to the value of `s1` -but does not own it. Because it does not own it, the value it points to will -not be dropped when the reference stops being used. +The `&s1` syntax lets us create a reference that _refers_ to the value of `s1` +but does not own it. Because the reference does not own it, the value it points +to will not be dropped when the reference stops being used. Likewise, the signature of the function uses `&` to indicate that the type of the parameter `s` is a reference. Let’s add some explanatory annotations: @@ -60,20 +62,20 @@ have references as parameters instead of the actual values, we won’t need to return the values in order to give back ownership, because we never had ownership. -We call the action of creating a reference *borrowing*. As in real life, if a +We call the action of creating a reference _borrowing_. As in real life, if a person owns something, you can borrow it from them. When you’re done, you have to give it back. You don’t own it. So, what happens if we try to modify something we’re borrowing? Try the code in -Listing 4-6. Spoiler alert: it doesn’t work! +Listing 4-6. Spoiler alert: It doesn’t work! -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-06/src/main.rs}} ``` -Listing 4-6: Attempting to modify a borrowed value + Here’s the error: @@ -87,29 +89,33 @@ allowed to modify something we have a reference to. ### Mutable References We can fix the code from Listing 4-6 to allow us to modify a borrowed value -with just a few small tweaks that use, instead, a *mutable reference*: +with just a few small tweaks that use, instead, a _mutable reference_: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-09-fixes-listing-04-06/src/main.rs}} ``` -First we change `s` to be `mut`. Then we create a mutable reference with `&mut -s` where we call the `change` function, and update the function signature to -accept a mutable reference with `some_string: &mut String`. This makes it very -clear that the `change` function will mutate the value it borrows. + + +First, we change `s` to be `mut`. Then, we create a mutable reference with +`&mut s` where we call the `change` function and update the function signature +to accept a mutable reference with `some_string: &mut String`. This makes it +very clear that the `change` function will mutate the value it borrows. -Mutable references have one big restriction: if you have a mutable reference to +Mutable references have one big restriction: If you have a mutable reference to a value, you can have no other references to that value. This code that attempts to create two mutable references to `s` will fail: -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/src/main.rs:here}} ``` + + Here’s the error: ```console @@ -126,19 +132,19 @@ The restriction preventing multiple mutable references to the same data at the same time allows for mutation but in a very controlled fashion. It’s something that new Rustaceans struggle with because most languages let you mutate whenever you’d like. The benefit of having this restriction is that Rust can -prevent data races at compile time. A *data race* is similar to a race +prevent data races at compile time. A _data race_ is similar to a race condition and happens when these three behaviors occur: -* Two or more pointers access the same data at the same time. -* At least one of the pointers is being used to write to the data. -* There’s no mechanism being used to synchronize access to the data. +- Two or more pointers access the same data at the same time. +- At least one of the pointers is being used to write to the data. +- There’s no mechanism being used to synchronize access to the data. Data races cause undefined behavior and can be difficult to diagnose and fix when you’re trying to track them down at runtime; Rust prevents this problem by refusing to compile code with data races! As always, we can use curly brackets to create a new scope, allowing for -multiple mutable references, just not *simultaneous* ones: +multiple mutable references, just not _simultaneous_ ones: ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-11-muts-in-separate-scopes/src/main.rs:here}} @@ -157,7 +163,7 @@ Here’s the error: {{#include ../listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/output.txt}} ``` -Whew! We *also* cannot have a mutable reference while we have an immutable one +Whew! We _also_ cannot have a mutable reference while we have an immutable one to the same value. Users of an immutable reference don’t expect the value to suddenly change out @@ -167,43 +173,45 @@ reading of the data. Note that a reference’s scope starts from where it is introduced and continues through the last time that reference is used. For instance, this code will -compile because the last usage of the immutable references, the `println!`, -occurs before the mutable reference is introduced: +compile because the last usage of the immutable references is in the `println!`, +before the mutable reference is introduced: -```rust,edition2021 +```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/src/main.rs:here}} ``` The scopes of the immutable references `r1` and `r2` end after the `println!` where they are last used, which is before the mutable reference `r3` is -created. These scopes don’t overlap, so this code is allowed: the compiler can +created. These scopes don’t overlap, so this code is allowed: The compiler can tell that the reference is no longer being used at a point before the end of the scope. Even though borrowing errors may be frustrating at times, remember that it’s the Rust compiler pointing out a potential bug early (at compile time rather -than at runtime) and showing you exactly where the problem is. Then you don’t +than at runtime) and showing you exactly where the problem is. Then, you don’t have to track down why your data isn’t what you thought it was. ### Dangling References -In languages with pointers, it’s easy to erroneously create a *dangling -pointer*—a pointer that references a location in memory that may have been +In languages with pointers, it’s easy to erroneously create a _dangling +pointer_—a pointer that references a location in memory that may have been given to someone else—by freeing some memory while preserving a pointer to that memory. In Rust, by contrast, the compiler guarantees that references will -never be dangling references: if you have a reference to some data, the +never be dangling references: If you have a reference to some data, the compiler will ensure that the data will not go out of scope before the reference to the data does. Let’s try to create a dangling reference to see how Rust prevents them with a compile-time error: -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-14-dangling-reference/src/main.rs}} ``` + + Here’s the error: ```console @@ -222,12 +230,14 @@ for it to be borrowed from Let’s take a closer look at exactly what’s happening at each stage of our `dangle` code: -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/src/main.rs:here}} ``` + + Because `s` is created inside `dangle`, when the code of `dangle` is finished, `s` will be deallocated. But we tried to return a reference to it. That means this reference would be pointing to an invalid `String`. That’s no good! Rust @@ -246,8 +256,8 @@ deallocated. Let’s recap what we’ve discussed about references: -* At any given time, you can have *either* one mutable reference *or* any +- At any given time, you can have _either_ one mutable reference _or_ any number of immutable references. -* References must always be valid. +- References must always be valid. Next, we’ll look at a different kind of reference: slices. diff --git a/src/ch04-03-slices.md b/src/ch04-03-slices.md index 6ffb1dc114..7f145baf1d 100644 --- a/src/ch04-03-slices.md +++ b/src/ch04-03-slices.md @@ -1,14 +1,19 @@ ## The Slice Type -*Slices* let you reference a contiguous sequence of elements in a collection -rather than the whole collection. A slice is a kind of reference, so it does -not have ownership. +_Slices_ let you reference a contiguous sequence of elements in a +[collection](ch08-00-common-collections.md). A slice is a kind +of reference, so it does not have ownership. -Here’s a small programming problem: write a function that takes a string of +Here’s a small programming problem: Write a function that takes a string of words separated by spaces and returns the first word it finds in that string. If the function doesn’t find a space in the string, the whole string must be one word, so the entire string should be returned. +> Note: For the purposes of introducing slices, we are assuming ASCII only in +> this section; a more thorough discussion of UTF-8 handling is in the +> [“Storing UTF-8 Encoded Text with Strings”][strings] section +> of Chapter 8. + Let’s work through how we’d write the signature of this function without using slices, to understand the problem that slices will solve: @@ -16,19 +21,20 @@ slices, to understand the problem that slices will solve: fn first_word(s: &String) -> ? ``` -The `first_word` function has a `&String` as a parameter. We don’t want -ownership, so this is fine. But what should we return? We don’t really have a -way to talk about *part* of a string. However, we could return the index of the -end of the word, indicated by a space. Let’s try that, as shown in Listing 4-7. +The `first_word` function has a parameter of type `&String`. We don’t need +ownership, so this is fine. (In idiomatic Rust, functions do not take ownership +of their arguments unless they need to, and the reasons for that will become +clear as we keep going.) But what should we return? We don’t really have a way +to talk about *part* of a string. However, we could return the index of the end +of the word, indicated by a space. Let’s try that, as shown in Listing 4-7. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-07/src/main.rs:here}} ``` -Listing 4-7: The `first_word` function that returns a -byte index value into the `String` parameter + Because we need to go through the `String` element by element and check whether a value is a space, we’ll convert our `String` to an array of bytes using the @@ -73,14 +79,13 @@ because it’s a separate value from the `String`, there’s no guarantee that i will still be valid in the future. Consider the program in Listing 4-8 that uses the `first_word` function from Listing 4-7. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-08/src/main.rs:here}} ``` -Listing 4-8: Storing the result from calling the -`first_word` function and then changing the `String` contents + This program compiles without any errors and would also do so if we used `word` after calling `s.clear()`. Because `word` isn’t connected to the state of `s` @@ -89,14 +94,14 @@ the variable `s` to try to extract the first word out, but this would be a bug because the contents of `s` have changed since we saved `5` in `word`. Having to worry about the index in `word` getting out of sync with the data in -`s` is tedious and error prone! Managing these indices is even more brittle if +`s` is tedious and error-prone! Managing these indices is even more brittle if we write a `second_word` function. Its signature would have to look like this: ```rust,ignore fn second_word(s: &String) -> (usize, usize) { ``` -Now we’re tracking a starting *and* an ending index, and we have even more +Now we’re tracking a starting _and_ an ending index, and we have even more values that were calculated from data in a particular state but aren’t tied to that state at all. We have three unrelated variables floating around that need to be kept in sync. @@ -105,7 +110,8 @@ Luckily, Rust has a solution to this problem: string slices. ### String Slices -A *string slice* is a reference to part of a `String`, and it looks like this: +A _string slice_ is a reference to a contiguous sequence of the elements of a +`String`, and it looks like this: ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-17-slice/src/main.rs:here}} @@ -113,23 +119,24 @@ A *string slice* is a reference to part of a `String`, and it looks like this: Rather than a reference to the entire `String`, `hello` is a reference to a portion of the `String`, specified in the extra `[0..5]` bit. We create slices -using a range within brackets by specifying `[starting_index..ending_index]`, -where `starting_index` is the first position in the slice and `ending_index` is -one more than the last position in the slice. Internally, the slice data -structure stores the starting position and the length of the slice, which -corresponds to `ending_index` minus `starting_index`. So, in the case of `let -world = &s[6..11];`, `world` would be a slice that contains a pointer to the -byte at index 6 of `s` with a length value of `5`. +using a range within square brackets by specifying +`[starting_index..ending_index]`, where _`starting_index`_ is the first +position in the slice and _`ending_index`_ is one more than the last position +in the slice. Internally, the slice data structure stores the starting position +and the length of the slice, which corresponds to _`ending_index`_ minus +_`starting_index`_. So, in the case of `let world = &s[6..11];`, `world` would +be a slice that contains a pointer to the byte at index 6 of `s` with a length +value of `5`. -Figure 4-6 shows this in a diagram. +Figure 4-7 shows this in a diagram. Three tables: a table representing the stack data of s, which points to the byte at index 0 in a table of the string data "hello world" on -the heap. The third table rep-resents the stack data of the slice world, which +the heap. The third table represents the stack data of the slice world, which has a length value of 5 and points to byte 6 of the heap data table. +src="img/trpl04-07.svg" class="center" style="width: 50%;" /> -Figure 4-6: String slice referring to part of a +Figure 4-7: A string slice referring to part of a `String` With Rust’s `..` range syntax, if you want to start at index 0, you can drop @@ -154,7 +161,7 @@ let slice = &s[3..len]; let slice = &s[3..]; ``` -You can also drop both values to take a slice of the entire string. So these +You can also drop both values to take a slice of the entire string. So, these are equal: ```rust @@ -168,20 +175,19 @@ let slice = &s[..]; > Note: String slice range indices must occur at valid UTF-8 character > boundaries. If you attempt to create a string slice in the middle of a -> multibyte character, your program will exit with an error. For the purposes -> of introducing string slices, we are assuming ASCII only in this section; a -> more thorough discussion of UTF-8 handling is in the [“Storing UTF-8 Encoded -> Text with Strings”][strings] section of Chapter 8. +> multibyte character, your program will exit with an error. With all this information in mind, let’s rewrite `first_word` to return a slice. The type that signifies “string slice” is written as `&str`: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-18-first-word-slice/src/main.rs:here}} ``` + + We get the index for the end of the word the same way we did in Listing 4-7, by looking for the first occurrence of a space. When we find a space, we return a string slice using the start of the string and the index of the space as the @@ -198,21 +204,23 @@ fn second_word(s: &String) -> &str { ``` We now have a straightforward API that’s much harder to mess up because the -compiler will ensure the references into the `String` remain valid. Remember -the bug in the program in Listing 4-8, when we got the index to the end of the -first word but then cleared the string so our index was invalid? That code was -logically incorrect but didn’t show any immediate errors. The problems would -show up later if we kept trying to use the first word index with an emptied -string. Slices make this bug impossible and let us know we have a problem with -our code much sooner. Using the slice version of `first_word` will throw a -compile-time error: +compiler will ensure that the references into the `String` remain valid. +Remember the bug in the program in Listing 4-8, when we got the index to the +end of the first word but then cleared the string so our index was invalid? +That code was logically incorrect but didn’t show any immediate errors. The +problems would show up later if we kept trying to use the first word index with +an emptied string. Slices make this bug impossible and let us know much sooner +that we have a problem with our code. Using the slice version of `first_word` +will throw a compile-time error: -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-19-slice-error/src/main.rs:here}} ``` + + Here’s the compiler error: ```console @@ -228,7 +236,8 @@ reference in `clear` and the immutable reference in `word` from existing at the same time, and compilation fails. Not only has Rust made our API easier to use, but it has also eliminated an entire class of errors at compile time! - + + #### String Literals as Slices @@ -240,7 +249,7 @@ that we know about slices, we can properly understand string literals: let s = "Hello, world!"; ``` -The type of `s` here is `&str`: it’s a slice pointing to that specific point of +The type of `s` here is `&str`: It’s a slice pointing to that specific point of the binary. This is also why string literals are immutable; `&str` is an immutable reference. @@ -257,28 +266,31 @@ A more experienced Rustacean would write the signature shown in Listing 4-9 instead because it allows us to use the same function on both `&String` values and `&str` values. ++ ```rust,ignore {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-09/src/main.rs:here}} ``` -Listing 4-9: Improving the `first_word` function by using -a string slice for the type of the `s` parameter + If we have a string slice, we can pass that directly. If we have a `String`, we can pass a slice of the `String` or a reference to the `String`. This -flexibility takes advantage of *deref coercions*, a feature we will cover in -[“Implicit Deref Coercions with Functions and -Methods”][deref-coercions] section of Chapter 15. +flexibility takes advantage of deref coercions, a feature we will cover in +the [“Using Deref Coercions in Functions and Methods”][deref-coercions] section of Chapter 15. Defining a function to take a string slice instead of a reference to a `String` makes our API more general and useful without losing any functionality: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-09/src/main.rs:usage}} ``` + + ### Other Slices String slices, as you might imagine, are specific to strings. But there’s a @@ -308,7 +320,7 @@ detail when we talk about vectors in Chapter 8. The concepts of ownership, borrowing, and slices ensure memory safety in Rust programs at compile time. The Rust language gives you control over your memory -usage in the same way as other systems programming languages, but having the +usage in the same way as other systems programming languages. But having the owner of data automatically clean up that data when the owner goes out of scope means you don’t have to write and debug extra code to get this control. @@ -319,4 +331,4 @@ Chapter 5 and look at grouping pieces of data together in a `struct`. [ch13]: ch13-02-iterators.html [ch6]: ch06-02-match.html#patterns-that-bind-to-values [strings]: ch08-02-strings.html#storing-utf-8-encoded-text-with-strings -[deref-coercions]: ch15-02-deref.html#implicit-deref-coercions-with-functions-and-methods +[deref-coercions]: ch15-02-deref.html#using-deref-coercions-in-functions-and-methods diff --git a/src/ch05-00-structs.md b/src/ch05-00-structs.md index d41482579a..4c0f7d35b9 100644 --- a/src/ch05-00-structs.md +++ b/src/ch05-00-structs.md @@ -1,14 +1,14 @@ # Using Structs to Structure Related Data -A *struct*, or *structure*, is a custom data type that lets you package +A _struct_, or _structure_, is a custom data type that lets you package together and name multiple related values that make up a meaningful group. If -you’re familiar with an object-oriented language, a *struct* is like an -object’s data attributes. In this chapter, we’ll compare and contrast tuples -with structs to build on what you already know and demonstrate when structs are -a better way to group data. +you’re familiar with an object-oriented language, a struct is like an object’s +data attributes. In this chapter, we’ll compare and contrast tuples with +structs to build on what you already know and demonstrate when structs are a +better way to group data. We’ll demonstrate how to define and instantiate structs. We’ll discuss how to define associated functions, especially the kind of associated functions called -*methods*, to specify behavior associated with a struct type. Structs and enums +_methods_, to specify behavior associated with a struct type. Structs and enums (discussed in Chapter 6) are the building blocks for creating new types in your program’s domain to take full advantage of Rust’s compile-time type checking. diff --git a/src/ch05-01-defining-structs.md b/src/ch05-01-defining-structs.md index d258d89cc5..66da938956 100644 --- a/src/ch05-01-defining-structs.md +++ b/src/ch05-01-defining-structs.md @@ -4,41 +4,40 @@ Structs are similar to tuples, discussed in [“The Tuple Type”][tuples] section, in that both hold multiple related values. Like tuples, the pieces of a struct can be different types. Unlike with tuples, in a struct you’ll name each piece of data so it’s clear what the values mean. Adding these -names means that structs are more flexible than tuples: you don’t have to rely +names means that structs are more flexible than tuples: You don’t have to rely on the order of the data to specify or access the values of an instance. To define a struct, we enter the keyword `struct` and name the entire struct. A struct’s name should describe the significance of the pieces of data being grouped together. Then, inside curly brackets, we define the names and types of -the pieces of data, which we call *fields*. For example, Listing 5-1 shows a +the pieces of data, which we call _fields_. For example, Listing 5-1 shows a struct that stores information about a user account. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-01/src/main.rs:here}} ``` -Listing 5-1: A `User` struct definition + -To use a struct after we’ve defined it, we create an *instance* of that struct +To use a struct after we’ve defined it, we create an _instance_ of that struct by specifying concrete values for each of the fields. We create an instance by -stating the name of the struct and then add curly brackets containing *key: -value* pairs, where the keys are the names of the fields and the values are the +stating the name of the struct and then add curly brackets containing _`key: +value`_ pairs, where the keys are the names of the fields and the values are the data we want to store in those fields. We don’t have to specify the fields in the same order in which we declared them in the struct. In other words, the struct definition is like a general template for the type, and instances fill in that template with particular data to create values of the type. For example, we can declare a particular user as shown in Listing 5-2. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-02/src/main.rs:here}} ``` -Listing 5-2: Creating an instance of the `User` -struct + To get a specific value from a struct, we use dot notation. For example, to access this user’s email address, we use `user1.email`. If the instance is @@ -46,14 +45,13 @@ mutable, we can change a value by using the dot notation and assigning into a particular field. Listing 5-3 shows how to change the value in the `email` field of a mutable `User` instance. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-03/src/main.rs:here}} ``` -Listing 5-3: Changing the value in the `email` field of a -`User` instance + Note that the entire instance must be mutable; Rust doesn’t allow us to mark only certain fields as mutable. As with any expression, we can construct a new @@ -61,42 +59,40 @@ instance of the struct as the last expression in the function body to implicitly return that new instance. Listing 5-4 shows a `build_user` function that returns a `User` instance with -the given email and username. The `active` field gets the value of `true`, and -the `sign_in_count` gets a value of `1`. +the given email and username. The `active` field gets the value `true`, and the +`sign_in_count` gets a value of `1`. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-04/src/main.rs:here}} ``` -Listing 5-4: A `build_user` function that takes an email -and username and returns a `User` instance + It makes sense to name the function parameters with the same name as the struct fields, but having to repeat the `email` and `username` field names and variables is a bit tedious. If the struct had more fields, repeating each name would get even more annoying. Luckily, there’s a convenient shorthand! - + + ### Using the Field Init Shorthand Because the parameter names and the struct field names are exactly the same in -Listing 5-4, we can use the *field init shorthand* syntax to rewrite -`build_user` so it behaves exactly the same but doesn’t have the repetition of -`username` and `email`, as shown in Listing 5-5. +Listing 5-4, we can use the _field init shorthand_ syntax to rewrite +`build_user` so that it behaves exactly the same but doesn’t have the +repetition of `username` and `email`, as shown in Listing 5-5. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-05/src/main.rs:here}} ``` -Listing 5-5: A `build_user` function that uses field init -shorthand because the `username` and `email` parameters have the same name as -struct fields + Here, we’re creating a new instance of the `User` struct, which has a field named `email`. We want to set the `email` field’s value to the value in the @@ -104,38 +100,39 @@ named `email`. We want to set the `email` field’s value to the value in the the `email` parameter have the same name, we only need to write `email` rather than `email: email`. -### Creating Instances from Other Instances with Struct Update Syntax + + + + +### Creating Instances with Struct Update Syntax It’s often useful to create a new instance of a struct that includes most of -the values from another instance, but changes some. You can do this using -*struct update syntax*. +the values from another instance of the same type, but changes some of them. +You can do this using struct update syntax. -First, in Listing 5-6 we show how to create a new `User` instance in `user2` -regularly, without the update syntax. We set a new value for `email` but +First, in Listing 5-6 we show how to create a new `User` instance in `user2` in +the regular way, without the update syntax. We set a new value for `email` but otherwise use the same values from `user1` that we created in Listing 5-2. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-06/src/main.rs:here}} ``` -Listing 5-6: Creating a new `User` instance using one of -the values from `user1` + Using struct update syntax, we can achieve the same effect with less code, as shown in Listing 5-7. The syntax `..` specifies that the remaining fields not explicitly set should have the same value as the fields in the given instance. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-07/src/main.rs:here}} ``` -Listing 5-7: Using struct update syntax to set a new -`email` value for a `User` instance but to use the rest of the values from -`user1` + The code in Listing 5-7 also creates an instance in `user2` that has a different value for `email` but has the same values for the `username`, @@ -148,17 +145,22 @@ the struct’s definition. Note that the struct update syntax uses `=` like an assignment; this is because it moves the data, just as we saw in the [“Variables and Data Interacting with Move”][move] section. In this example, we can no longer use -`user1` as a whole after creating `user2` because the `String` in the -`username` field of `user1` was moved into `user2`. If we had given `user2` new -`String` values for both `email` and `username`, and thus only used the -`active` and `sign_in_count` values from `user1`, then `user1` would still be -valid after creating `user2`. Both `active` and `sign_in_count` are types that -implement the `Copy` trait, so the behavior we discussed in the [“Stack-Only -Data: Copy”][copy] section would apply. +`user1` after creating `user2` because the `String` in the `username` field of +`user1` was moved into `user2`. If we had given `user2` new `String` values for +both `email` and `username`, and thus only used the `active` and `sign_in_count` +values from `user1`, then `user1` would still be valid after creating `user2`. +Both `active` and `sign_in_count` are types that implement the `Copy` trait, so +the behavior we discussed in the [“Stack-Only Data: Copy”][copy] +section would apply. We can also still use `user1.email` in this example, +because its value was not moved out of `user1`. + + + + -### Using Tuple Structs Without Named Fields to Create Different Types +### Creating Different Types with Tuple Structs -Rust also supports structs that look similar to tuples, called *tuple structs*. +Rust also supports structs that look similar to tuples, called _tuple structs_. Tuple structs have the added meaning the struct name provides but don’t have names associated with their fields; rather, they just have the types of the fields. Tuple structs are useful when you want to give the whole tuple a name @@ -169,12 +171,14 @@ To define a tuple struct, start with the `struct` keyword and the struct name followed by the types in the tuple. For example, here we define and use two tuple structs named `Color` and `Point`: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-01-tuple-structs/src/main.rs}} ``` + + Note that the `black` and `origin` values are different types because they’re instances of different tuple structs. Each struct you define is its own type, even though the fields within the struct might have the same types. For @@ -182,29 +186,38 @@ example, a function that takes a parameter of type `Color` cannot take a `Point` as an argument, even though both types are made up of three `i32` values. Otherwise, tuple struct instances are similar to tuples in that you can destructure them into their individual pieces, and you can use a `.` followed -by the index to access an individual value. +by the index to access an individual value. Unlike tuples, tuple structs +require you to name the type of the struct when you destructure them. For +example, we would write `let Point(x, y, z) = origin;` to destructure the +values in the `origin` point into variables named `x`, `y`, and `z`. + + + + -### Unit-Like Structs Without Any Fields +### Defining Unit-Like Structs You can also define structs that don’t have any fields! These are called -*unit-like structs* because they behave similarly to `()`, the unit type that +_unit-like structs_ because they behave similarly to `()`, the unit type that we mentioned in [“The Tuple Type”][tuples] section. Unit-like structs can be useful when you need to implement a trait on some type but don’t have any data that you want to store in the type itself. We’ll discuss traits in Chapter 10. Here’s an example of declaring and instantiating a unit struct named `AlwaysEqual`: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-04-unit-like-structs/src/main.rs}} ``` + + To define `AlwaysEqual`, we use the `struct` keyword, the name we want, and -then a semicolon. No need for curly brackets or parentheses! Then we can get an -instance of `AlwaysEqual` in the `subject` variable in a similar way: using the -name we defined, without any curly brackets or parentheses. Imagine that later -we’ll implement behavior for this type such that every instance of +then a semicolon. No need for curly brackets or parentheses! Then, we can get +an instance of `AlwaysEqual` in the `subject` variable in a similar way: using +the name we defined, without any curly brackets or parentheses. Imagine that +later we’ll implement behavior for this type such that every instance of `AlwaysEqual` is always equal to every instance of any other type, perhaps to have a known result for testing purposes. We wouldn’t need any data to implement that behavior! You’ll see in Chapter 10 how to define traits and @@ -218,12 +231,13 @@ implement them on any type, including unit-like structs. > that data to be valid for as long as the entire struct is valid. > > It’s also possible for structs to store references to data owned by something -> else, but to do so requires the use of *lifetimes*, a Rust feature that we’ll +> else, but to do so requires the use of _lifetimes_, a Rust feature that we’ll > discuss in Chapter 10. Lifetimes ensure that the data referenced by a struct > is valid for as long as the struct is. Let’s say you try to store a reference -> in a struct without specifying lifetimes, like the following; this won’t work: +> in a struct without specifying lifetimes, like the following in +> *src/main.rs*; this won’t work: > -> Filename: src/main.rs +> > > > @@ -245,6 +259,8 @@ implement them on any type, including unit-like structs. > } > ``` > +> +> > The compiler will complain that it needs lifetime specifiers: > > ```console @@ -278,10 +294,10 @@ implement them on any type, including unit-like structs. > | > > For more information about this error, try `rustc --explain E0106`. -> error: could not compile `structs` due to 2 previous errors +> error: could not compile `structs` (bin "structs") due to 2 previous errors > ``` > -> In Chapter 10, we’ll discuss how to fix these errors so you can store +> In Chapter 10, we’ll discuss how to fix these errors so that you can store > references in structs, but for now, we’ll fix errors like these using owned > types like `String` instead of references like `&str`. diff --git a/src/ch05-02-example-structs.md b/src/ch05-02-example-structs.md index b2416b743b..fe59bb402e 100644 --- a/src/ch05-02-example-structs.md +++ b/src/ch05-02-example-structs.md @@ -1,22 +1,21 @@ ## An Example Program Using Structs To understand when we might want to use structs, let’s write a program that -calculates the area of a rectangle. We’ll start by using single variables, and +calculates the area of a rectangle. We’ll start by using single variables and then refactor the program until we’re using structs instead. -Let’s make a new binary project with Cargo called *rectangles* that will take +Let’s make a new binary project with Cargo called _rectangles_ that will take the width and height of a rectangle specified in pixels and calculate the area of the rectangle. Listing 5-8 shows a short program with one way of doing -exactly that in our project’s *src/main.rs*. +exactly that in our project’s _src/main.rs_. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-08/src/main.rs:all}} ``` -Listing 5-8: Calculating the area of a rectangle -specified by separate width and height variables + Now, run this program using `cargo run`: @@ -45,18 +44,17 @@ of Chapter 3: by using tuples. Listing 5-9 shows another version of our program that uses tuples. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-09/src/main.rs}} ``` -Listing 5-9: Specifying the width and height of the -rectangle with a tuple + In one way, this program is better. Tuples let us add a bit of structure, and we’re now passing just one argument. But in another way, this version is less -clear: tuples don’t name their elements, so we have to index into the parts of +clear: Tuples don’t name their elements, so we have to index into the parts of the tuple, making our calculation less obvious. Mixing up the width and height wouldn’t matter for the area calculation, but if @@ -66,21 +64,25 @@ index `1`. This would be even harder for someone else to figure out and keep in mind if they were to use our code. Because we haven’t conveyed the meaning of our data in our code, it’s now easier to introduce errors. -### Refactoring with Structs: Adding More Meaning + + + + +### Refactoring with Structs We use structs to add meaning by labeling the data. We can transform the tuple we’re using into a struct with a name for the whole as well as names for the parts, as shown in Listing 5-10. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-10/src/main.rs}} ``` -Listing 5-10: Defining a `Rectangle` struct + -Here we’ve defined a struct and named it `Rectangle`. Inside the curly +Here, we’ve defined a struct and named it `Rectangle`. Inside the curly brackets, we defined the fields as `width` and `height`, both of which have type `u32`. Then, in `main`, we created a particular instance of `Rectangle` that has a width of `30` and a height of `50`. @@ -95,27 +97,30 @@ where we call the function. The `area` function accesses the `width` and `height` fields of the `Rectangle` instance (note that accessing fields of a borrowed struct instance does not move the field values, which is why you often see borrows of structs). Our -function signature for `area` now says exactly what we mean: calculate the area +function signature for `area` now says exactly what we mean: Calculate the area of `Rectangle`, using its `width` and `height` fields. This conveys that the width and height are related to each other, and it gives descriptive names to the values rather than using the tuple index values of `0` and `1`. This is a win for clarity. -### Adding Useful Functionality with Derived Traits + + + + +### Adding Functionality with Derived Traits It’d be useful to be able to print an instance of `Rectangle` while we’re debugging our program and see the values for all its fields. Listing 5-11 tries using the [`println!` macro][println] as we have used in previous chapters. This won’t work, however. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-11/src/main.rs}} ``` -Listing 5-11: Attempting to print a `Rectangle` -instance + When we compile this code, we get an error with this core message: @@ -141,10 +146,10 @@ If we continue reading the errors, we’ll find this helpful note: ``` Let’s try it! The `println!` macro call will now look like `println!("rect1 is -{:?}", rect1);`. Putting the specifier `:?` inside the curly brackets tells +{rect1:?}");`. Putting the specifier `:?` inside the curly brackets tells `println!` we want to use an output format called `Debug`. The `Debug` trait -enables us to print our struct in a way that is useful for developers so we can -see its value while we’re debugging our code. +enables us to print our struct in a way that is useful for developers so that +we can see its value while we’re debugging our code. Compile the code with this change. Drat! We still get an error: @@ -158,19 +163,18 @@ But again, the compiler gives us a helpful note: {{#include ../listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/output.txt:9:10}} ``` -Rust *does* include functionality to print out debugging information, but we +Rust _does_ include functionality to print out debugging information, but we have to explicitly opt in to make that functionality available for our struct. To do that, we add the outer attribute `#[derive(Debug)]` just before the struct definition, as shown in Listing 5-12. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-12/src/main.rs}} ``` -Listing 5-12: Adding the attribute to derive the `Debug` -trait and printing the `Rectangle` instance using debug formatting + Now when we run the program, we won’t get any errors, and we’ll see the following output: @@ -198,8 +202,8 @@ of that expression, and returns ownership of the value. > Note: Calling the `dbg!` macro prints to the standard error console stream > (`stderr`), as opposed to `println!`, which prints to the standard output > console stream (`stdout`). We’ll talk more about `stderr` and `stdout` in the -> [“Writing Error Messages to Standard Error Instead of Standard Output” -> section in Chapter 12][err]. +> [“Redirecting Errors to Standard Error” section in Chapter +> 12][err]. Here’s an example where we’re interested in the value that gets assigned to the `width` field, as well as the value of the whole struct in `rect1`: @@ -218,10 +222,10 @@ Here’s what the output of this example looks like: {{#include ../listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/output.txt}} ``` -We can see the first bit of output came from *src/main.rs* line 10 where we’re +We can see the first bit of output came from _src/main.rs_ line 10 where we’re debugging the expression `30 * scale`, and its resultant value is `60` (the `Debug` formatting implemented for integers is to print only their value). The -`dbg!` call on line 14 of *src/main.rs* outputs the value of `&rect1`, which is +`dbg!` call on line 14 of _src/main.rs_ outputs the value of `&rect1`, which is the `Rectangle` struct. This output uses the pretty `Debug` formatting of the `Rectangle` type. The `dbg!` macro can be really helpful when you’re trying to figure out what your code is doing! @@ -234,10 +238,10 @@ well as how to create your own traits in Chapter 10. There are also many attributes other than `derive`; for more information, see [the “Attributes” section of the Rust Reference][attributes]. -Our `area` function is very specific: it only computes the area of rectangles. +Our `area` function is very specific: It only computes the area of rectangles. It would be helpful to tie this behavior more closely to our `Rectangle` struct because it won’t work with any other type. Let’s look at how we can continue to -refactor this code by turning the `area` function into an `area` *method* +refactor this code by turning the `area` function into an `area` method defined on our `Rectangle` type. [the-tuple-type]: ch03-02-data-types.html#the-tuple-type diff --git a/src/ch05-03-method-syntax.md b/src/ch05-03-method-syntax.md index d25e55b18c..fe0c7e3a2f 100644 --- a/src/ch05-03-method-syntax.md +++ b/src/ch05-03-method-syntax.md @@ -1,37 +1,40 @@ -## Method Syntax +## Methods -*Methods* are similar to functions: we declare them with the `fn` keyword and a +Methods are similar to functions: We declare them with the `fn` keyword and a name, they can have parameters and a return value, and they contain some code that’s run when the method is called from somewhere else. Unlike functions, methods are defined within the context of a struct (or an enum or a trait object, which we cover in [Chapter 6][enums] and [Chapter -17][trait-objects], respectively), and their first parameter is +18][trait-objects], respectively), and their first parameter is always `self`, which represents the instance of the struct the method is being called on. -### Defining Methods + + + + +### Method Syntax Let’s change the `area` function that has a `Rectangle` instance as a parameter and instead make an `area` method defined on the `Rectangle` struct, as shown in Listing 5-13. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-13/src/main.rs}} ``` -Listing 5-13: Defining an `area` method on the -`Rectangle` struct + To define the function within the context of `Rectangle`, we start an `impl` (implementation) block for `Rectangle`. Everything within this `impl` block -will be associated with the `Rectangle` type. Then we move the `area` function +will be associated with the `Rectangle` type. Then, we move the `area` function within the `impl` curly brackets and change the first (and in this case, only) parameter to be `self` in the signature and everywhere within the body. In `main`, where we called the `area` function and passed `rect1` as an argument, -we can instead use *method syntax* to call the `area` method on our `Rectangle` -instance. The method syntax goes after an instance: we add a dot followed by +we can instead use _method syntax_ to call the `area` method on our `Rectangle` +instance. The method syntax goes after an instance: We add a dot followed by the method name, parentheses, and any arguments. In the signature for `area`, we use `&self` instead of `rectangle: &Rectangle`. @@ -46,7 +49,7 @@ immutably, as we’ve done here, or borrow `self` mutably, just as they can any other parameter. We chose `&self` here for the same reason we used `&Rectangle` in the function -version: we don’t want to take ownership, and we just want to read the data in +version: We don’t want to take ownership, and we just want to read the data in the struct, not write to it. If we wanted to change the instance that we’ve called the method on as part of what the method does, we’d use `&mut self` as the first parameter. Having a method that takes ownership of the instance by @@ -65,45 +68,48 @@ Note that we can choose to give a method the same name as one of the struct’s fields. For example, we can define a method on `Rectangle` that is also named `width`: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-06-method-field-interaction/src/main.rs:here}} ``` + + Here, we’re choosing to make the `width` method return `true` if the value in the instance’s `width` field is greater than `0` and `false` if the value is -`0`: we can use a field within a method of the same name for any purpose. In +`0`: We can use a field within a method of the same name for any purpose. In `main`, when we follow `rect1.width` with parentheses, Rust knows we mean the method `width`. When we don’t use parentheses, Rust knows we mean the field `width`. Often, but not always, when we give a method the same name as a field we want it to only return the value in the field and do nothing else. Methods like this -are called *getters*, and Rust does not implement them automatically for struct +are called _getters_, and Rust does not implement them automatically for struct fields as some other languages do. Getters are useful because you can make the -field private but the method public, and thus enable read-only access to that +field private but the method public and thus enable read-only access to that field as part of the type’s public API. We will discuss what public and private are and how to designate a field or method as public or private in [Chapter 7][public]. > ### Where’s the `->` Operator? > -> In C and C++, two different operators are used for calling methods: you use +> In C and C++, two different operators are used for calling methods: You use > `.` if you’re calling a method on the object directly and `->` if you’re > calling the method on a pointer to the object and need to dereference the > pointer first. In other words, if `object` is a pointer, > `object->something()` is similar to `(*object).something()`. > > Rust doesn’t have an equivalent to the `->` operator; instead, Rust has a -> feature called *automatic referencing and dereferencing*. Calling methods is -> one of the few places in Rust that has this behavior. +> feature called _automatic referencing and dereferencing_. Calling methods is +> one of the few places in Rust with this behavior. > -> Here’s how it works: when you call a method with `object.something()`, Rust -> automatically adds in `&`, `&mut`, or `*` so `object` matches the signature of -> the method. In other words, the following are the same: +> Here’s how it works: When you call a method with `object.something()`, Rust +> automatically adds in `&`, `&mut`, or `*` so that `object` matches the +> signature of the method. In other words, the following are the same: > > +> > ```rust > # #[derive(Debug,Copy,Clone)] > # struct Point { @@ -141,14 +147,13 @@ within `self` (the first `Rectangle`); otherwise, it should return `false`. That is, once we’ve defined the `can_hold` method, we want to be able to write the program shown in Listing 5-14. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-14/src/main.rs}} ``` -Listing 5-14: Using the as-yet-unwritten `can_hold` -method + The expected output would look like the following because both dimensions of `rect2` are smaller than the dimensions of `rect1`, but `rect3` is wider than @@ -166,21 +171,20 @@ parameter will be by looking at the code that calls the method: `rect1.can_hold(&rect2)` passes in `&rect2`, which is an immutable borrow to `rect2`, an instance of `Rectangle`. This makes sense because we only need to read `rect2` (rather than write, which would mean we’d need a mutable borrow), -and we want `main` to retain ownership of `rect2` so we can use it again after -calling the `can_hold` method. The return value of `can_hold` will be a +and we want `main` to retain ownership of `rect2` so that we can use it again +after calling the `can_hold` method. The return value of `can_hold` will be a Boolean, and the implementation will check whether the width and height of `self` are greater than the width and height of the other `Rectangle`, respectively. Let’s add the new `can_hold` method to the `impl` block from Listing 5-13, shown in Listing 5-15. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-15/src/main.rs:here}} ``` -Listing 5-15: Implementing the `can_hold` method on -`Rectangle` that takes another `Rectangle` instance as a parameter + When we run this code with the `main` function in Listing 5-14, we’ll get our desired output. Methods can take multiple parameters that we add to the @@ -189,7 +193,7 @@ parameters in functions. ### Associated Functions -All functions defined within an `impl` block are called *associated functions* +All functions defined within an `impl` block are called _associated functions_ because they’re associated with the type named after the `impl`. We can define associated functions that don’t have `self` as their first parameter (and thus are not methods) because they don’t need an instance of the type to work with. @@ -216,7 +220,7 @@ is `Rectangle`. To call this associated function, we use the `::` syntax with the struct name; `let sq = Rectangle::square(3);` is an example. This function is namespaced by -the struct: the `::` syntax is used for both associated functions and +the struct: The `::` syntax is used for both associated functions and namespaces created by modules. We’ll discuss modules in [Chapter 7][modules]. @@ -226,12 +230,13 @@ Each struct is allowed to have multiple `impl` blocks. For example, Listing 5-15 is equivalent to the code shown in Listing 5-16, which has each method in its own `impl` block. ++ ```rust {{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-16/src/main.rs:here}} ``` -Listing 5-16: Rewriting Listing 5-15 using multiple `impl` -blocks + There’s no reason to separate these methods into multiple `impl` blocks here, but this is valid syntax. We’ll see a case in which multiple `impl` blocks are @@ -246,10 +251,10 @@ functions that are associated with your type, and methods are a kind of associated function that let you specify the behavior that instances of your structs have. -But structs aren’t the only way you can create custom types: let’s turn to +But structs aren’t the only way you can create custom types: Let’s turn to Rust’s enum feature to add another tool to your toolbox. [enums]: ch06-00-enums.html -[trait-objects]: ch17-02-trait-objects.md +[trait-objects]: ch18-02-trait-objects.md [public]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html#exposing-paths-with-the-pub-keyword [modules]: ch07-02-defining-modules-to-control-scope-and-privacy.html diff --git a/src/ch06-00-enums.md b/src/ch06-00-enums.md index 8a7faa9f30..982e62c2b4 100644 --- a/src/ch06-00-enums.md +++ b/src/ch06-00-enums.md @@ -1,10 +1,10 @@ # Enums and Pattern Matching -In this chapter, we’ll look at *enumerations*, also referred to as *enums*. -Enums allow you to define a type by enumerating its possible *variants*. First +In this chapter, we’ll look at enumerations, also referred to as _enums_. +Enums allow you to define a type by enumerating its possible variants. First we’ll define and use an enum to show how an enum can encode meaning along with data. Next, we’ll explore a particularly useful enum, called `Option`, which -expresses that a value can be either something or nothing. Then we’ll look at +expresses that a value can be either something or nothing. Then, we’ll look at how pattern matching in the `match` expression makes it easy to run different code for different values of an enum. Finally, we’ll cover how the `if let` construct is another convenient and concise idiom available to handle enums in diff --git a/src/ch06-01-defining-an-enum.md b/src/ch06-01-defining-an-enum.md index eacd091bd4..74e460d1e4 100644 --- a/src/ch06-01-defining-an-enum.md +++ b/src/ch06-01-defining-an-enum.md @@ -10,7 +10,7 @@ Let’s look at a situation we might want to express in code and see why enums are useful and more appropriate than structs in this case. Say we need to work with IP addresses. Currently, two major standards are used for IP addresses: version four and version six. Because these are the only possibilities for an -IP address that our program will come across, we can *enumerate* all possible +IP address that our program will come across, we can _enumerate_ all possible variants, which is where enumeration gets its name. Any IP address can be either a version four or a version six address, but not @@ -54,17 +54,18 @@ And we can call this function with either variant: ``` Using enums has even more advantages. Thinking more about our IP address type, -at the moment we don’t have a way to store the actual IP address *data*; we -only know what *kind* it is. Given that you just learned about structs in +at the moment we don’t have a way to store the actual IP address _data_; we +only know what _kind_ it is. Given that you just learned about structs in Chapter 5, you might be tempted to tackle this problem with structs as shown in Listing 6-1. ++ ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-01/src/main.rs:here}} ``` -Listing 6-1: Storing the data and `IpAddrKind` variant of -an IP address using a `struct` + Here, we’ve defined a struct `IpAddr` that has two fields: a `kind` field that is of type `IpAddrKind` (the enum we defined previously) and an `address` field @@ -76,7 +77,7 @@ associated with it. We’ve used a struct to bundle the `kind` and `address` values together, so now the variant is associated with the value. However, representing the same concept using just an enum is more concise: -rather than an enum inside a struct, we can put data directly into each enum +Rather than an enum inside a struct, we can put data directly into each enum variant. This new definition of the `IpAddr` enum says that both `V4` and `V6` variants will have associated `String` values: @@ -86,13 +87,13 @@ variants will have associated `String` values: We attach data to each variant of the enum directly, so there is no need for an extra struct. Here, it’s also easier to see another detail of how enums work: -the name of each enum variant that we define also becomes a function that +The name of each enum variant that we define also becomes a function that constructs an instance of the enum. That is, `IpAddr::V4()` is a function call that takes a `String` argument and returns an instance of the `IpAddr` type. We automatically get this constructor function defined as a result of defining the enum. -There’s another advantage to using an enum rather than a struct: each variant +There’s another advantage to using an enum rather than a struct: Each variant can have different types and amounts of associated data. Version four IP addresses will always have four numeric components that will have values between 0 and 255. If we wanted to store `V4` addresses as four `u8` values but @@ -107,7 +108,7 @@ We’ve shown several different ways to define data structures to store version four and version six IP addresses. However, as it turns out, wanting to store IP addresses and encode which kind they are is so common that [the standard library has a definition we can use!][IpAddr] Let’s look at how -the standard library defines `IpAddr`: it has the exact enum and variants that +the standard library defines `IpAddr`. It has the exact enum and variants that we’ve defined and used, but it embeds the address data inside the variants in the form of two different structs, which are defined differently for each variant: @@ -137,22 +138,23 @@ we can still create and use our own definition without conflict because we haven’t brought the standard library’s definition into our scope. We’ll talk more about bringing types into scope in Chapter 7. -Let’s look at another example of an enum in Listing 6-2: this one has a wide +Let’s look at another example of an enum in Listing 6-2: This one has a wide variety of types embedded in its variants. ++ ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-02/src/main.rs:here}} ``` -Listing 6-2: A `Message` enum whose variants each store -different amounts and types of values + This enum has four variants with different types: -* `Quit` has no data associated with it at all. -* `Move` has named fields, like a struct does. -* `Write` includes a single `String`. -* `ChangeColor` includes three `i32` values. +- `Quit`: Has no data associated with it at all +- `Move`: Has named fields, like a struct does +- `Write`: Includes a single `String` +- `ChangeColor`: Includes three `i32` values Defining an enum with variants such as the ones in Listing 6-2 is similar to defining different kinds of struct definitions, except the enum doesn’t use the @@ -168,7 +170,7 @@ But if we used the different structs, each of which has its own type, we couldn’t as easily define a function to take any of these kinds of messages as we could with the `Message` enum defined in Listing 6-2, which is a single type. -There is one more similarity between enums and structs: just as we’re able to +There is one more similarity between enums and structs: Just as we’re able to define methods on structs using `impl`, we’re also able to define methods on enums. Here’s a method named `call` that we could define on our `Message` enum: @@ -184,11 +186,15 @@ body of the `call` method when `m.call()` runs. Let’s look at another enum in the standard library that is very common and useful: `Option`. -### The `Option` Enum and Its Advantages Over Null Values + + + + +### The `Option` Enum This section explores a case study of `Option`, which is another enum defined by the standard library. The `Option` type encodes the very common scenario in -which a value could be something or it could be nothing. +which a value could be something, or it could be nothing. For example, if you request the first item in a non-empty list, you would get a value. If you request the first item in an empty list, you would get nothing. @@ -199,12 +205,12 @@ languages. Programming language design is often thought of in terms of which features you include, but the features you exclude are important too. Rust doesn’t have the -null feature that many other languages have. *Null* is a value that means there +null feature that many other languages have. _Null_ is a value that means there is no value there. In languages with null, variables can always be in one of two states: null or not-null. In his 2009 presentation “Null References: The Billion Dollar Mistake,” Tony -Hoare, the inventor of null, has this to say: +Hoare, the inventor of null, had this to say: > I call it my billion-dollar mistake. At that time, I was designing the first > comprehensive type system for references in an object-oriented language. My @@ -219,7 +225,7 @@ The problem with null values is that if you try to use a null value as a not-null value, you’ll get an error of some kind. Because this null or not-null property is pervasive, it’s extremely easy to make this kind of error. -However, the concept that null is trying to express is still a useful one: a +However, the concept that null is trying to express is still a useful one: A null is a value that is currently invalid or absent for some reason. The problem isn’t really with the concept but with the particular @@ -237,7 +243,7 @@ enum Option { The `Option` enum is so useful that it’s even included in the prelude; you don’t need to bring it into scope explicitly. Its variants are also included in -the prelude: you can use `Some` and `None` directly without the `Option::` +the prelude: You can use `Some` and `None` directly without the `Option::` prefix. The `Option` enum is still just a regular enum, and `Some(T)` and `None` are still variants of type `Option`. @@ -247,7 +253,7 @@ For now, all you need to know is that `` means that the `Some` variant of the `Option` enum can hold one piece of data of any type, and that each concrete type that gets used in place of `T` makes the overall `Option` type a different type. Here are some examples of using `Option` values to hold -number types and string types: +number types and char types: ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-06-option-examples/src/main.rs:here}} @@ -256,14 +262,14 @@ number types and string types: The type of `some_number` is `Option`. The type of `some_char` is `Option`, which is a different type. Rust can infer these types because we’ve specified a value inside the `Some` variant. For `absent_number`, Rust -requires us to annotate the overall `Option` type: the compiler can’t infer the +requires us to annotate the overall `Option` type: The compiler can’t infer the type that the corresponding `Some` variant will hold by looking only at a `None` value. Here, we tell Rust that we mean for `absent_number` to be of type `Option`. -When we have a `Some` value, we know that a value is present and the value is +When we have a `Some` value, we know that a value is present, and the value is held within the `Some`. When we have a `None` value, in some sense it means the -same thing as null: we don’t have a valid value. So why is having `Option` +same thing as null: We don’t have a valid value. So, why is having `Option` any better than having null? In short, because `Option` and `T` (where `T` can be any type) are different @@ -294,14 +300,14 @@ In other words, you have to convert an `Option` to a `T` before you can perform `T` operations with it. Generally, this helps catch one of the most common issues with null: assuming that something isn’t null when it actually is. -Eliminating the risk of incorrectly assuming a not-null value helps you to be -more confident in your code. In order to have a value that can possibly be -null, you must explicitly opt in by making the type of that value `Option`. -Then, when you use that value, you are required to explicitly handle the case -when the value is null. Everywhere that a value has a type that isn’t an -`Option`, you *can* safely assume that the value isn’t null. This was a -deliberate design decision for Rust to limit null’s pervasiveness and increase -the safety of Rust code. +Eliminating the risk of incorrectly assuming a not-null value helps you be more +confident in your code. In order to have a value that can possibly be null, you +must explicitly opt in by making the type of that value `Option`. Then, when +you use that value, you are required to explicitly handle the case when the +value is null. Everywhere that a value has a type that isn’t an `Option`, +you _can_ safely assume that the value isn’t null. This was a deliberate design +decision for Rust to limit null’s pervasiveness and increase the safety of Rust +code. So how do you get the `T` value out of a `Some` variant when you have a value of type `Option` so that you can use that value? The `Option` enum has a @@ -315,7 +321,7 @@ will handle each variant. You want some code that will run only when you have a `Some(T)` value, and this code is allowed to use the inner `T`. You want some other code to run only if you have a `None` value, and that code doesn’t have a `T` value available. The `match` expression is a control flow construct that -does just this when used with enums: it will run different code depending on +does just this when used with enums: It will run different code depending on which variant of the enum it has, and that code can use the data inside the matching value. diff --git a/src/ch06-02-match.md b/src/ch06-02-match.md index 6a510df402..e96ec79ba3 100644 --- a/src/ch06-02-match.md +++ b/src/ch06-02-match.md @@ -1,17 +1,19 @@ - + + + ## The `match` Control Flow Construct Rust has an extremely powerful control flow construct called `match` that allows you to compare a value against a series of patterns and then execute code based on which pattern matches. Patterns can be made up of literal values, variable names, wildcards, and many other things; [Chapter -18][ch18-00-patterns] covers all the different kinds of patterns +19][ch19-00-patterns] covers all the different kinds of patterns and what they do. The power of `match` comes from the expressiveness of the patterns and the fact that the compiler confirms that all possible cases are handled. -Think of a `match` expression as being like a coin-sorting machine: coins slide +Think of a `match` expression as being like a coin-sorting machine: Coins slide down a track with variously sized holes along it, and each coin falls through the first hole it encounters that it fits into. In the same way, values go through each pattern in a `match`, and at the first pattern the value “fits,” @@ -22,17 +24,18 @@ function that takes an unknown US coin and, in a similar way as the counting machine, determines which coin it is and returns its value in cents, as shown in Listing 6-3. ++ ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-03/src/main.rs:here}} ``` -Listing 6-3: An enum and a `match` expression that has -the variants of the enum as its patterns + -Let’s break down the `match` in the `value_in_cents` function. First we list +Let’s break down the `match` in the `value_in_cents` function. First, we list the `match` keyword followed by an expression, which in this case is the value `coin`. This seems very similar to a conditional expression used with `if`, but -there’s a big difference: with `if`, the condition needs to evaluate to a +there’s a big difference: With `if`, the condition needs to evaluate to a Boolean value, but here it can be any type. The type of `coin` in this example is the `Coin` enum that we defined on the first line. @@ -45,7 +48,7 @@ When the `match` expression executes, it compares the resultant value against the pattern of each arm, in order. If a pattern matches the value, the code associated with that pattern is executed. If that pattern doesn’t match the value, execution continues to the next arm, much as in a coin-sorting machine. -We can have as many arms as we need: in Listing 6-3, our `match` has four arms. +We can have as many arms as we need: In Listing 6-3, our `match` has four arms. The code associated with each arm is an expression, and the resultant value of the expression in the matching arm is the value that gets returned for the @@ -55,8 +58,8 @@ We don’t typically use curly brackets if the match arm code is short, as it is in Listing 6-3 where each arm just returns a value. If you want to run multiple lines of code in a match arm, you must use curly brackets, and the comma following the arm is then optional. For example, the following code prints -“Lucky penny!” every time the method is called with a `Coin::Penny`, but still -returns the last value of the block, `1`: +“Lucky penny!” every time the method is called with a `Coin::Penny`, but it +still returns the last value of the block, `1`: ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-08-match-arm-multiple-lines/src/main.rs:here}} @@ -75,12 +78,13 @@ designs, so only quarters have this extra value. We can add this information to our `enum` by changing the `Quarter` variant to include a `UsState` value stored inside it, which we’ve done in Listing 6-4. ++ ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-04/src/main.rs:here}} ``` -Listing 6-4: A `Coin` enum in which the `Quarter` variant -also holds a `UsState` value + Let’s imagine that a friend is trying to collect all 50 state quarters. While we sort our loose change by coin type, we’ll also call out the name of the @@ -90,7 +94,7 @@ they can add it to their collection. In the match expression for this code, we add a variable called `state` to the pattern that matches values of the variant `Coin::Quarter`. When a `Coin::Quarter` matches, the `state` variable will bind to the value of that -quarter’s state. Then we can use `state` in the code for that arm, like so: +quarter’s state. Then, we can use `state` in the code for that arm, like so: ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/src/main.rs:here}} @@ -103,7 +107,12 @@ that point, the binding for `state` will be the value `UsState::Alaska`. We can then use that binding in the `println!` expression, thus getting the inner state value out of the `Coin` enum variant for `Quarter`. -### Matching with `Option` + + + + +### The `Option` `match` Pattern + In the previous section, we wanted to get the inner `T` value out of the `Some` case when using `Option`; we can also handle `Option` using `match`, as @@ -119,12 +128,13 @@ operations. This function is very easy to write, thanks to `match`, and will look like Listing 6-5. ++ ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-05/src/main.rs:here}} ``` -Listing 6-5: A function that uses a `match` expression on -an `Option` + Let’s examine the first execution of `plus_one` in more detail. When we call `plus_one(five)`, the variable `x` in the body of `plus_one` will have the @@ -165,7 +175,7 @@ consistently a user favorite. ### Matches Are Exhaustive -There’s one other aspect of `match` we need to discuss: the arms’ patterns must +There’s one other aspect of `match` we need to discuss: The arms’ patterns must cover all possibilities. Consider this version of our `plus_one` function, which has a bug and won’t compile: @@ -181,19 +191,19 @@ error: {{#include ../listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/output.txt}} ``` -Rust knows that we didn’t cover every possible case, and even knows which -pattern we forgot! Matches in Rust are *exhaustive*: we must exhaust every last +Rust knows that we didn’t cover every possible case and even knows which +pattern we forgot! Matches in Rust are _exhaustive_: We must exhaust every last possibility in order for the code to be valid. Especially in the case of `Option`, when Rust prevents us from forgetting to explicitly handle the `None` case, it protects us from assuming that we have a value when we might have null, thus making the billion-dollar mistake discussed earlier impossible. -### Catch-all Patterns and the `_` Placeholder +### Catch-All Patterns and the `_` Placeholder Using enums, we can also take special actions for a few particular values, but for all other values take one default action. Imagine we’re implementing a game -where, if you roll a 3 on a dice roll, your player doesn’t move, but instead -gets a new fancy hat. If you roll a 7, your player loses a fancy hat. For all +where, if you roll a 3 on a dice roll, your player doesn’t move but instead +gets a fancy new hat. If you roll a 7, your player loses a fancy hat. For all other values, your player moves that number of spaces on the game board. Here’s a `match` that implements that logic, with the result of the dice roll hardcoded rather than a random value, and all other logic represented by @@ -213,15 +223,16 @@ This code compiles, even though we haven’t listed all the possible values a `u8` can have, because the last pattern will match all values not specifically listed. This catch-all pattern meets the requirement that `match` must be exhaustive. Note that we have to put the catch-all arm last because the -patterns are evaluated in order. If we put the catch-all arm earlier, the other -arms would never run, so Rust will warn us if we add arms after a catch-all! +patterns are evaluated in order. If we had put the catch-all arm earlier, the +other arms would never run, so Rust will warn us if we add arms after a +catch-all! Rust also has a pattern we can use when we want a catch-all but don’t want to -*use* the value in the catch-all pattern: `_` is a special pattern that matches +_use_ the value in the catch-all pattern: `_` is a special pattern that matches any value and does not bind to that value. This tells Rust we aren’t going to use the value, so Rust won’t warn us about an unused variable. -Let’s change the rules of the game: now, if you roll anything other than a 3 or +Let’s change the rules of the game: Now, if you roll anything other than a 3 or a 7, you must roll again. We no longer need to use the catch-all value, so we can change our code to use `_` instead of the variable named `other`: @@ -246,9 +257,9 @@ that doesn’t match a pattern in an earlier arm, and we don’t want to run any code in this case. There’s more about patterns and matching that we’ll cover in [Chapter -18][ch18-00-patterns]. For now, we’re going to move on to the +19][ch19-00-patterns]. For now, we’re going to move on to the `if let` syntax, which can be useful in situations where the `match` expression is a bit wordy. [tuples]: ch03-02-data-types.html#the-tuple-type -[ch18-00-patterns]: ch18-00-patterns.html +[ch19-00-patterns]: ch19-00-patterns.html diff --git a/src/ch06-03-if-let.md b/src/ch06-03-if-let.md index c9bfbf3c7f..06b517e2ae 100644 --- a/src/ch06-03-if-let.md +++ b/src/ch06-03-if-let.md @@ -1,4 +1,4 @@ -## Concise Control Flow with `if let` +## Concise Control Flow with `if let` and `let...else` The `if let` syntax lets you combine `if` and `let` into a less verbose way to handle values that match one pattern while ignoring the rest. Consider the @@ -6,12 +6,13 @@ program in Listing 6-6 that matches on an `Option` value in the `config_max` variable but only wants to execute code if the value is the `Some` variant. ++ ```rust {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-06/src/main.rs:here}} ``` -Listing 6-6: A `match` that only cares about executing -code when the value is `Some` + If the value is `Some`, we print out the value in the `Some` variant by binding the value to the variable `max` in the pattern. We don’t want to do anything @@ -31,14 +32,14 @@ sign. It works the same way as a `match`, where the expression is given to the `match` and the pattern is its first arm. In this case, the pattern is `Some(max)`, and the `max` binds to the value inside the `Some`. We can then use `max` in the body of the `if let` block in the same way we used `max` in -the corresponding `match` arm. The code in the `if let` block isn’t run if the -value doesn’t match the pattern. +the corresponding `match` arm. The code in the `if let` block only runs if the +value matches the pattern. Using `if let` means less typing, less indentation, and less boilerplate code. -However, you lose the exhaustive checking that `match` enforces. Choosing -between `match` and `if let` depends on what you’re doing in your particular -situation and whether gaining conciseness is an appropriate trade-off for -losing exhaustive checking. +However, you lose the exhaustive checking `match` enforces that ensures that +you aren’t forgetting to handle any cases. Choosing between `match` and `if +let` depends on what you’re doing in your particular situation and whether +gaining conciseness is an appropriate trade-off for losing exhaustive checking. In other words, you can think of `if let` as syntax sugar for a `match` that runs code when the value matches one pattern and then ignores all other values. @@ -61,8 +62,72 @@ Or we could use an `if let` and `else` expression, like this: {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/src/main.rs:here}} ``` +## Staying on the “Happy Path” with `let...else` + +The common pattern is to perform some computation when a value is present and +return a default value otherwise. Continuing with our example of coins with a +`UsState` value, if we wanted to say something funny depending on how old the +state on the quarter was, we might introduce a method on `UsState` to check the +age of a state, like so: + +```rust +{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-07/src/main.rs:state}} +``` + +Then, we might use `if let` to match on the type of coin, introducing a `state` +variable within the body of the condition, as in Listing 6-7. + ++ +```rust +{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-07/src/main.rs:describe}} +``` + + + +That gets the job done, but it has pushed the work into the body of the `if +let` statement, and if the work to be done is more complicated, it might be +hard to follow exactly how the top-level branches relate. We could also take +advantage of the fact that expressions produce a value either to produce the +`state` from the `if let` or to return early, as in Listing 6-8. (You could do +something similar with a `match`, too.) + ++ +```rust +{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-08/src/main.rs:describe}} +``` + + + +This is a bit annoying to follow in its own way, though! One branch of the `if +let` produces a value, and the other one returns from the function entirely. + +To make this common pattern nicer to express, Rust has `let...else`. The +`let...else` syntax takes a pattern on the left side and an expression on the +right, very similar to `if let`, but it does not have an `if` branch, only an +`else` branch. If the pattern matches, it will bind the value from the pattern +in the outer scope. If the pattern does _not_ match, the program will flow into +the `else` arm, which must return from the function. + +In Listing 6-9, you can see how Listing 6-8 looks when using `let...else` in +place of `if let`. + ++ +```rust +{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-09/src/main.rs:describe}} +``` + + + +Notice that it stays on the “happy path” in the main body of the function this +way, without having significantly different control flow for two branches the +way the `if let` did. + If you have a situation in which your program has logic that is too verbose to -express using a `match`, remember that `if let` is in your Rust toolbox as well. +express using a `match`, remember that `if let` and `let...else` are in your +Rust toolbox as well. ## Summary @@ -73,11 +138,10 @@ data inside them, you can use `match` or `if let` to extract and use those values, depending on how many cases you need to handle. Your Rust programs can now express concepts in your domain using structs and -enums. Creating custom types to use in your API ensures type safety: the +enums. Creating custom types to use in your API ensures type safety: The compiler will make certain your functions only get values of the type each function expects. In order to provide a well-organized API to your users that is straightforward to use and only exposes exactly what your users will need, let’s now turn to Rust’s modules. - diff --git a/src/ch07-00-managing-growing-projects-with-packages-crates-and-modules.md b/src/ch07-00-managing-growing-projects-with-packages-crates-and-modules.md index 0f7abf51e3..8c6d7fb663 100644 --- a/src/ch07-00-managing-growing-projects-with-packages-crates-and-modules.md +++ b/src/ch07-00-managing-growing-projects-with-packages-crates-and-modules.md @@ -1,4 +1,8 @@ -# Managing Growing Projects with Packages, Crates, and Modules + + + + +# Packages, Crates, and Modules As you write large programs, organizing your code will become increasingly important. By grouping related functionality and separating code with distinct @@ -11,18 +15,18 @@ and then multiple files. A package can contain multiple binary crates and optionally one library crate. As a package grows, you can extract parts into separate crates that become external dependencies. This chapter covers all these techniques. For very large projects comprising a set of interrelated -packages that evolve together, Cargo provides *workspaces*, which we’ll cover -in the [“Cargo Workspaces”][workspaces] section in Chapter 14. +packages that evolve together, Cargo provides workspaces, which we’ll cover in +[“Cargo Workspaces”][workspaces] in Chapter 14. We’ll also discuss encapsulating implementation details, which lets you reuse -code at a higher level: once you’ve implemented an operation, other code can +code at a higher level: Once you’ve implemented an operation, other code can call your code via its public interface without having to know how the implementation works. The way you write code defines which parts are public for other code to use and which parts are private implementation details that you reserve the right to change. This is another way to limit the amount of detail you have to keep in your head. -A related concept is scope: the nested context in which code is written has a +A related concept is scope: The nested context in which code is written has a set of names that are defined as “in scope.” When reading, writing, and compiling code, programmers and compilers need to know whether a particular name at a particular spot refers to a variable, function, struct, enum, module, @@ -33,13 +37,13 @@ same name in the same scope; tools are available to resolve name conflicts. Rust has a number of features that allow you to manage your code’s organization, including which details are exposed, which details are private, and what names are in each scope in your programs. These features, sometimes -collectively referred to as the *module system*, include: +collectively referred to as the _module system_, include: -* **Packages:** A Cargo feature that lets you build, test, and share crates -* **Crates:** A tree of modules that produces a library or executable -* **Modules** and **use:** Let you control the organization, scope, and - privacy of paths -* **Paths:** A way of naming an item, such as a struct, function, or module +* **Packages**: A Cargo feature that lets you build, test, and share crates +* **Crates**: A tree of modules that produces a library or executable +* **Modules and use**: Let you control the organization, scope, and privacy of +paths +* **Paths**: A way of naming an item, such as a struct, function, or module In this chapter, we’ll cover all these features, discuss how they interact, and explain how to use them to manage scope. By the end, you should have a solid diff --git a/src/ch07-01-packages-and-crates.md b/src/ch07-01-packages-and-crates.md index d9a70f773b..63e6d41426 100644 --- a/src/ch07-01-packages-and-crates.md +++ b/src/ch07-01-packages-and-crates.md @@ -2,45 +2,44 @@ The first parts of the module system we’ll cover are packages and crates. -A *crate* is the smallest amount of code that the Rust compiler considers at a +A _crate_ is the smallest amount of code that the Rust compiler considers at a time. Even if you run `rustc` rather than `cargo` and pass a single source code -file (as we did all the way back in the “Writing and Running a Rust Program” -section of Chapter 1), the compiler considers that file to be a crate. Crates -can contain modules, and the modules may be defined in other files that get +file (as we did all the way back in [“Rust Program Basics”][basics] in Chapter 1), the compiler considers that file to be a crate. Crates can +contain modules, and the modules may be defined in other files that get compiled with the crate, as we’ll see in the coming sections. A crate can come in one of two forms: a binary crate or a library crate. -*Binary crates* are programs you can compile to an executable that you can run, -such as a command-line program or a server. Each must have a function called +_Binary crates_ are programs you can compile to an executable that you can run, +such as a command line program or a server. Each must have a function called `main` that defines what happens when the executable runs. All the crates we’ve created so far have been binary crates. -*Library crates* don’t have a `main` function, and they don’t compile to an +_Library crates_ don’t have a `main` function, and they don’t compile to an executable. Instead, they define functionality intended to be shared with multiple projects. For example, the `rand` crate we used in [Chapter 2][rand] provides functionality that generates random numbers. -Most of the time when Rustaceans say “crate”, they mean library crate, and they -use “crate” interchangeably with the general programming concept of a “library". +Most of the time when Rustaceans say “crate,” they mean library crate, and they +use “crate” interchangeably with the general programming concept of a “library.” -The *crate root* is a source file that the Rust compiler starts from and makes -up the root module of your crate (we’ll explain modules in depth in the -[“Defining Modules to Control Scope and Privacy”][modules] -section). +The _crate root_ is a source file that the Rust compiler starts from and makes +up the root module of your crate (we’ll explain modules in depth in [“Control +Scope and Privacy with Modules”][modules]). -A *package* is a bundle of one or more crates that provides a set of -functionality. A package contains a *Cargo.toml* file that describes how to +A _package_ is a bundle of one or more crates that provides a set of +functionality. A package contains a _Cargo.toml_ file that describes how to build those crates. Cargo is actually a package that contains the binary crate -for the command-line tool you’ve been using to build your code. The Cargo +for the command line tool you’ve been using to build your code. The Cargo package also contains a library crate that the binary crate depends on. Other projects can depend on the Cargo library crate to use the same logic the Cargo -command-line tool uses. +command line tool uses. A package can contain as many binary crates as you like, but at most only one library crate. A package must contain at least one crate, whether that’s a library or binary crate. Let’s walk through what happens when we create a package. First, we enter the -command `cargo new`: +command `cargo new my-project`: ```console $ cargo new my-project @@ -52,21 +51,22 @@ $ ls my-project/src main.rs ``` -After we run `cargo new`, we use `ls` to see what Cargo creates. In the project -directory, there’s a *Cargo.toml* file, giving us a package. There’s also a -*src* directory that contains *main.rs*. Open *Cargo.toml* in your text editor, -and note there’s no mention of *src/main.rs*. Cargo follows a convention that -*src/main.rs* is the crate root of a binary crate with the same name as the -package. Likewise, Cargo knows that if the package directory contains -*src/lib.rs*, the package contains a library crate with the same name as the -package, and *src/lib.rs* is its crate root. Cargo passes the crate root files -to `rustc` to build the library or binary. +After we run `cargo new my-project`, we use `ls` to see what Cargo creates. In +the _my-project_ directory, there’s a _Cargo.toml_ file, giving us a package. +There’s also a _src_ directory that contains _main.rs_. Open _Cargo.toml_ in +your text editor and note that there’s no mention of _src/main.rs_. Cargo +follows a convention that _src/main.rs_ is the crate root of a binary crate +with the same name as the package. Likewise, Cargo knows that if the package +directory contains _src/lib.rs_, the package contains a library crate with the +same name as the package, and _src/lib.rs_ is its crate root. Cargo passes the +crate root files to `rustc` to build the library or binary. -Here, we have a package that only contains *src/main.rs*, meaning it only -contains a binary crate named `my-project`. If a package contains *src/main.rs* -and *src/lib.rs*, it has two crates: a binary and a library, both with the same +Here, we have a package that only contains _src/main.rs_, meaning it only +contains a binary crate named `my-project`. If a package contains _src/main.rs_ +and _src/lib.rs_, it has two crates: a binary and a library, both with the same name as the package. A package can have multiple binary crates by placing files -in the *src/bin* directory: each file will be a separate binary crate. +in the _src/bin_ directory: Each file will be a separate binary crate. +[basics]: ch01-02-hello-world.html#rust-program-basics [modules]: ch07-02-defining-modules-to-control-scope-and-privacy.html [rand]: ch02-00-guessing-game-tutorial.html#generating-a-random-number diff --git a/src/ch07-02-defining-modules-to-control-scope-and-privacy.md b/src/ch07-02-defining-modules-to-control-scope-and-privacy.md index 90776dbfea..5dc3197e82 100644 --- a/src/ch07-02-defining-modules-to-control-scope-and-privacy.md +++ b/src/ch07-02-defining-modules-to-control-scope-and-privacy.md @@ -1,57 +1,58 @@ -## Defining Modules to Control Scope and Privacy + + + + +## Control Scope and Privacy with Modules In this section, we’ll talk about modules and other parts of the module system, -namely *paths* that allow you to name items; the `use` keyword that brings a +namely _paths_, which allow you to name items; the `use` keyword that brings a path into scope; and the `pub` keyword to make items public. We’ll also discuss the `as` keyword, external packages, and the glob operator. -First, we’re going to start with a list of rules for easy reference when you’re -organizing your code in the future. Then we’ll explain each of the rules in -detail. - ### Modules Cheat Sheet -Here we provide a quick reference on how modules, paths, the `use` keyword, and -the `pub` keyword work in the compiler, and how most developers organize their -code. We’ll be going through examples of each of these rules throughout this -chapter, but this is a great place to refer to as a reminder of how modules -work. +Before we get to the details of modules and paths, here we provide a quick +reference on how modules, paths, the `use` keyword, and the `pub` keyword work +in the compiler, and how most developers organize their code. We’ll be going +through examples of each of these rules throughout this chapter, but this is a +great place to refer to as a reminder of how modules work. - **Start from the crate root**: When compiling a crate, the compiler first - looks in the crate root file (usually *src/lib.rs* for a library crate or - *src/main.rs* for a binary crate) for code to compile. + looks in the crate root file (usually _src/lib.rs_ for a library crate and + _src/main.rs_ for a binary crate) for code to compile. - **Declaring modules**: In the crate root file, you can declare new modules; -say, you declare a “garden” module with `mod garden;`. The compiler will look -for the module’s code in these places: + say you declare a “garden” module with `mod garden;`. The compiler will look + for the module’s code in these places: - Inline, within curly brackets that replace the semicolon following `mod garden` - - In the file *src/garden.rs* - - In the file *src/garden/mod.rs* + - In the file _src/garden.rs_ + - In the file _src/garden/mod.rs_ - **Declaring submodules**: In any file other than the crate root, you can declare submodules. For example, you might declare `mod vegetables;` in - *src/garden.rs*. The compiler will look for the submodule’s code within the + _src/garden.rs_. The compiler will look for the submodule’s code within the directory named for the parent module in these places: - Inline, directly following `mod vegetables`, within curly brackets instead of the semicolon - - In the file *src/garden/vegetables.rs* - - In the file *src/garden/vegetables/mod.rs* + - In the file _src/garden/vegetables.rs_ + - In the file _src/garden/vegetables/mod.rs_ - **Paths to code in modules**: Once a module is part of your crate, you can refer to code in that module from anywhere else in that same crate, as long as the privacy rules allow, using the path to the code. For example, an `Asparagus` type in the garden vegetables module would be found at `crate::garden::vegetables::Asparagus`. -- **Private vs public**: Code within a module is private from its parent +- **Private vs. public**: Code within a module is private from its parent modules by default. To make a module public, declare it with `pub mod` instead of `mod`. To make items within a public module public as well, use `pub` before their declarations. - **The `use` keyword**: Within a scope, the `use` keyword creates shortcuts to items to reduce repetition of long paths. In any scope that can refer to `crate::garden::vegetables::Asparagus`, you can create a shortcut with `use - crate::garden::vegetables::Asparagus;` and from then on you only need to + crate::garden::vegetables::Asparagus;`, and from then on you only need to write `Asparagus` to make use of that type in the scope. -Here we create a binary crate named `backyard` that illustrates these rules. The -crate’s directory, also named `backyard`, contains these files and directories: +Here, we create a binary crate named `backyard` that illustrates these rules. +The crate’s directory, also named _backyard_, contains these files and +directories: ```text backyard @@ -64,24 +65,28 @@ backyard └── main.rs ``` -The crate root file in this case is *src/main.rs*, and it contains: +The crate root file in this case is _src/main.rs_, and it contains: -Filename: src/main.rs + ```rust,noplayground,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/quick-reference-example/src/main.rs}} ``` + + The `pub mod garden;` line tells the compiler to include the code it finds in -*src/garden.rs*, which is: +_src/garden.rs_, which is: -Filename: src/garden.rs + ```rust,noplayground,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/quick-reference-example/src/garden.rs}} ``` -Here, `pub mod vegetables;` means the code in *src/garden/vegetables.rs* is + + +Here, `pub mod vegetables;` means the code in _src/garden/vegetables.rs_ is included too. That code is: ```rust,noplayground,ignore @@ -92,8 +97,8 @@ Now let’s get into the details of these rules and demonstrate them in action! ### Grouping Related Code in Modules -*Modules* let us organize code within a crate for readability and easy reuse. -Modules also allow us to control the *privacy* of items, because code within a +_Modules_ let us organize code within a crate for readability and easy reuse. +Modules also allow us to control the _privacy_ of items because code within a module is private by default. Private items are internal implementation details not available for outside use. We can choose to make modules and the items within them public, which exposes them to allow external code to use and depend @@ -101,36 +106,36 @@ on them. As an example, let’s write a library crate that provides the functionality of a restaurant. We’ll define the signatures of functions but leave their bodies -empty to concentrate on the organization of the code, rather than the +empty to concentrate on the organization of the code rather than the implementation of a restaurant. -In the restaurant industry, some parts of a restaurant are referred to as -*front of house* and others as *back of house*. Front of house is where -customers are; this encompasses where the hosts seat customers, servers take -orders and payment, and bartenders make drinks. Back of house is where the -chefs and cooks work in the kitchen, dishwashers clean up, and managers do -administrative work. +In the restaurant industry, some parts of a restaurant are referred to as front +of house and others as back of house. _Front of house_ is where customers are; +this encompasses where the hosts seat customers, servers take orders and +payment, and bartenders make drinks. _Back of house_ is where the chefs and +cooks work in the kitchen, dishwashers clean up, and managers do administrative +work. To structure our crate in this way, we can organize its functions into nested modules. Create a new library named `restaurant` by running `cargo new -restaurant --lib`; then enter the code in Listing 7-1 into *src/lib.rs* to -define some modules and function signatures. Here’s the front of house section: +restaurant --lib`. Then, enter the code in Listing 7-1 into _src/lib.rs_ to +define some modules and function signatures; this code is the front of house +section. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-01/src/lib.rs}} ``` -Listing 7-1: A `front_of_house` module containing other -modules that then contain functions + We define a module with the `mod` keyword followed by the name of the module (in this case, `front_of_house`). The body of the module then goes inside curly brackets. Inside modules, we can place other modules, as in this case with the modules `hosting` and `serving`. Modules can also hold definitions for other -items, such as structs, enums, constants, traits, and—as in Listing -7-1—functions. +items, such as structs, enums, constants, traits, and as in Listing 7-1, +functions. By using modules, we can group related definitions together and name why they’re related. Programmers using this code can navigate the code based on the @@ -138,13 +143,15 @@ groups rather than having to read through all the definitions, making it easier to find the definitions relevant to them. Programmers adding new functionality to this code would know where to place the code to keep the program organized. -Earlier, we mentioned that *src/main.rs* and *src/lib.rs* are called crate -roots. The reason for their name is that the contents of either of these two +Earlier, we mentioned that _src/main.rs_ and _src/lib.rs_ are called _crate +roots_. The reason for their name is that the contents of either of these two files form a module named `crate` at the root of the crate’s module structure, -known as the *module tree*. +known as the _module tree_. Listing 7-2 shows the module tree for the structure in Listing 7-1. ++ ```text crate └── front_of_house @@ -157,16 +164,15 @@ crate └── take_payment ``` -Listing 7-2: The module tree for the code in Listing -7-1 + -This tree shows how some of the modules nest inside one another; for example, +This tree shows how some of the modules nest inside other modules; for example, `hosting` nests inside `front_of_house`. The tree also shows that some modules -are *siblings* to each other, meaning they’re defined in the same module; -`hosting` and `serving` are siblings defined within `front_of_house`. If module -A is contained inside module B, we say that module A is the *child* of module B -and that module B is the *parent* of module A. Notice that the entire module -tree is rooted under the implicit module named `crate`. +are _siblings_, meaning they’re defined in the same module; `hosting` and +`serving` are siblings defined within `front_of_house`. If module A is +contained inside module B, we say that module A is the _child_ of module B and +that module B is the _parent_ of module A. Notice that the entire module tree +is rooted under the implicit module named `crate`. The module tree might remind you of the filesystem’s directory tree on your computer; this is a very apt comparison! Just like directories in a filesystem, diff --git a/src/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md b/src/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md index c8fb3247ff..d1249fc368 100644 --- a/src/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md +++ b/src/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md @@ -6,44 +6,42 @@ know its path. A path can take two forms: -* An *absolute path* is the full path starting from a crate root; for code +- An _absolute path_ is the full path starting from a crate root; for code from an external crate, the absolute path begins with the crate name, and for code from the current crate, it starts with the literal `crate`. -* A *relative path* starts from the current module and uses `self`, `super`, or +- A _relative path_ starts from the current module and uses `self`, `super`, or an identifier in the current module. Both absolute and relative paths are followed by one or more identifiers separated by double colons (`::`). Returning to Listing 7-1, say we want to call the `add_to_waitlist` function. -This is the same as asking: what’s the path of the `add_to_waitlist` function? -Listing 7-3 contains Listing 7-1 with some of the modules and functions -removed. +This is the same as asking: What’s the path of the `add_to_waitlist` function? +Listing 7-3 contains Listing 7-1 with some of the modules and functions removed. -We’ll show two ways to call the `add_to_waitlist` function from a new function -`eat_at_restaurant` defined in the crate root. These paths are correct, but +We’ll show two ways to call the `add_to_waitlist` function from a new function, +`eat_at_restaurant`, defined in the crate root. These paths are correct, but there’s another problem remaining that will prevent this example from compiling -as-is. We’ll explain why in a bit. +as is. We’ll explain why in a bit. The `eat_at_restaurant` function is part of our library crate’s public API, so we mark it with the `pub` keyword. In the [“Exposing Paths with the `pub` Keyword”][pub] section, we’ll go into more detail about `pub`. -Filename: src/lib.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-03/src/lib.rs}} ``` -Listing 7-3: Calling the `add_to_waitlist` function using -absolute and relative paths + The first time we call the `add_to_waitlist` function in `eat_at_restaurant`, we use an absolute path. The `add_to_waitlist` function is defined in the same crate as `eat_at_restaurant`, which means we can use the `crate` keyword to start an absolute path. We then include each of the successive modules until we make our way to `add_to_waitlist`. You can imagine a filesystem with the same -structure: we’d specify the path `/front_of_house/hosting/add_to_waitlist` to +structure: We’d specify the path `/front_of_house/hosting/add_to_waitlist` to run the `add_to_waitlist` program; using the `crate` name to start from the crate root is like using `/` to start from the filesystem root in your shell. @@ -55,26 +53,28 @@ filesystem equivalent would be using the path that the path is relative. Choosing whether to use a relative or absolute path is a decision you’ll make -based on your project, and depends on whether you’re more likely to move item -definition code separately from or together with the code that uses the item. -For example, if we move the `front_of_house` module and the `eat_at_restaurant` -function into a module named `customer_experience`, we’d need to update the -absolute path to `add_to_waitlist`, but the relative path would still be valid. -However, if we moved the `eat_at_restaurant` function separately into a module -named `dining`, the absolute path to the `add_to_waitlist` call would stay the -same, but the relative path would need to be updated. Our preference in general -is to specify absolute paths because it’s more likely we’ll want to move code -definitions and item calls independently of each other. +based on your project, and it depends on whether you’re more likely to move +item definition code separately from or together with the code that uses the +item. For example, if we moved the `front_of_house` module and the +`eat_at_restaurant` function into a module named `customer_experience`, we’d +need to update the absolute path to `add_to_waitlist`, but the relative path +would still be valid. However, if we moved the `eat_at_restaurant` function +separately into a module named `dining`, the absolute path to the +`add_to_waitlist` call would stay the same, but the relative path would need to +be updated. Our preference in general is to specify absolute paths because it’s +more likely we’ll want to move code definitions and item calls independently of +each other. Let’s try to compile Listing 7-3 and find out why it won’t compile yet! The -error we get is shown in Listing 7-4. +errors we get are shown in Listing 7-4. + + ```console {{#include ../listings/ch07-managing-growing-projects/listing-07-03/output.txt}} ``` -Listing 7-4: Compiler errors from building the code in -Listing 7-3 + The error messages say that module `hosting` is private. In other words, we have the correct paths for the `hosting` module and the `add_to_waitlist` @@ -88,14 +88,14 @@ items in child modules can use the items in their ancestor modules. This is because child modules wrap and hide their implementation details, but the child modules can see the context in which they’re defined. To continue with our metaphor, think of the privacy rules as being like the back office of a -restaurant: what goes on in there is private to restaurant customers, but +restaurant: What goes on in there is private to restaurant customers, but office managers can see and do everything in the restaurant they operate. Rust chose to have the module system function this way so that hiding inner implementation details is the default. That way, you know which parts of the -inner code you can change without breaking outer code. However, Rust does give -you the option to expose inner parts of child modules’ code to outer ancestor -modules by using the `pub` keyword to make an item public. +inner code you can change without breaking the outer code. However, Rust does +give you the option to expose inner parts of child modules’ code to outer +ancestor modules by using the `pub` keyword to make an item public. ### Exposing Paths with the `pub` Keyword @@ -104,28 +104,28 @@ private. We want the `eat_at_restaurant` function in the parent module to have access to the `add_to_waitlist` function in the child module, so we mark the `hosting` module with the `pub` keyword, as shown in Listing 7-5. -Filename: src/lib.rs + ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-05/src/lib.rs}} +{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-05/src/lib.rs:here}} ``` -Listing 7-5: Declaring the `hosting` module as `pub` to -use it from `eat_at_restaurant` + + +Unfortunately, the code in Listing 7-5 still results in compiler errors, as +shown in Listing 7-6. -Unfortunately, the code in Listing 7-5 still results in an error, as shown in -Listing 7-6. + ```console {{#include ../listings/ch07-managing-growing-projects/listing-07-05/output.txt}} ``` -Listing 7-6: Compiler errors from building the code in -Listing 7-5 + What happened? Adding the `pub` keyword in front of `mod hosting` makes the module public. With this change, if we can access `front_of_house`, we can -access `hosting`. But the *contents* of `hosting` are still private; making the +access `hosting`. But the _contents_ of `hosting` are still private; making the module public doesn’t make its contents public. The `pub` keyword on a module only lets code in its ancestor modules refer to it, not access its inner code. Because modules are containers, there’s not much we can do by only making the @@ -139,19 +139,17 @@ modules. Let’s also make the `add_to_waitlist` function public by adding the `pub` keyword before its definition, as in Listing 7-7. -Filename: src/lib.rs + ```rust,noplayground,test_harness -{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-07/src/lib.rs}} +{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-07/src/lib.rs:here}} ``` -Listing 7-7: Adding the `pub` keyword to `mod hosting` -and `fn add_to_waitlist` lets us call the function from -`eat_at_restaurant` + Now the code will compile! To see why adding the `pub` keyword lets us use -these paths in `add_to_waitlist` with respect to the privacy rules, let’s look -at the absolute and the relative paths. +these paths in `eat_at_restaurant` with respect to the privacy rules, let’s +look at the absolute and the relative paths. In the absolute path, we start with `crate`, the root of our crate’s module tree. The `front_of_house` module is defined in the crate root. While @@ -160,69 +158,68 @@ defined in the same module as `front_of_house` (that is, `eat_at_restaurant` and `front_of_house` are siblings), we can refer to `front_of_house` from `eat_at_restaurant`. Next is the `hosting` module marked with `pub`. We can access the parent module of `hosting`, so we can access `hosting`. Finally, the -`add_to_waitlist` function is marked with `pub` and we can access its parent +`add_to_waitlist` function is marked with `pub`, and we can access its parent module, so this function call works! In the relative path, the logic is the same as the absolute path except for the -first step: rather than starting from the crate root, the path starts from +first step: Rather than starting from the crate root, the path starts from `front_of_house`. The `front_of_house` module is defined within the same module as `eat_at_restaurant`, so the relative path starting from the module in which `eat_at_restaurant` is defined works. Then, because `hosting` and `add_to_waitlist` are marked with `pub`, the rest of the path works, and this function call is valid! -If you plan on sharing your library crate so other projects can use your code, -your public API is your contract with users of your crate that determines how -they can interact with your code. There are many considerations around managing -changes to your public API to make it easier for people to depend on your -crate. These considerations are out of the scope of this book; if you’re -interested in this topic, see [The Rust API Guidelines][api-guidelines]. +If you plan to share your library crate so that other projects can use your +code, your public API is your contract with users of your crate that determines +how they can interact with your code. There are many considerations around +managing changes to your public API to make it easier for people to depend on +your crate. These considerations are beyond the scope of this book; if you’re +interested in this topic, see [the Rust API Guidelines][api-guidelines]. > #### Best Practices for Packages with a Binary and a Library > -> We mentioned a package can contain both a *src/main.rs* binary crate root as -> well as a *src/lib.rs* library crate root, and both crates will have the -> package name by default. Typically, packages with this pattern of containing -> both a library and a binary crate will have just enough code in the binary -> crate to start an executable that calls code with the library crate. This -> lets other projects benefit from the most functionality that the package -> provides, because the library crate’s code can be shared. +> We mentioned that a package can contain both a _src/main.rs_ binary crate +> root as well as a _src/lib.rs_ library crate root, and both crates will have +> the package name by default. Typically, packages with this pattern of +> containing both a library and a binary crate will have just enough code in the +> binary crate to start an executable that calls code defined in the library +> crate. This lets other projects benefit from the most functionality that the +> package provides because the library crate’s code can be shared. > -> The module tree should be defined in *src/lib.rs*. Then, any public items can +> The module tree should be defined in _src/lib.rs_. Then, any public items can > be used in the binary crate by starting paths with the name of the package. > The binary crate becomes a user of the library crate just like a completely -> external crate would use the library crate: it can only use the public API. -> This helps you design a good API; not only are you the author, you’re also a -> client! +> external crate would use the library crate: It can only use the public API. +> This helps you design a good API; not only are you the author, but you’re +> also a client! > > In [Chapter 12][ch12], we’ll demonstrate this organizational -> practice with a command-line program that will contain both a binary crate +> practice with a command line program that will contain both a binary crate > and a library crate. ### Starting Relative Paths with `super` We can construct relative paths that begin in the parent module, rather than the current module or the crate root, by using `super` at the start of the -path. This is like starting a filesystem path with the `..` syntax. Using -`super` allows us to reference an item that we know is in the parent module, -which can make rearranging the module tree easier when the module is closely -related to the parent, but the parent might be moved elsewhere in the module -tree someday. +path. This is like starting a filesystem path with the `..` syntax that means +to go to the parent directory. Using `super` allows us to reference an item +that we know is in the parent module, which can make rearranging the module +tree easier when the module is closely related to the parent but the parent +might be moved elsewhere in the module tree someday. Consider the code in Listing 7-8 that models the situation in which a chef fixes an incorrect order and personally brings it out to the customer. The function `fix_incorrect_order` defined in the `back_of_house` module calls the function `deliver_order` defined in the parent module by specifying the path to -`deliver_order` starting with `super`: +`deliver_order`, starting with `super`. -Filename: src/lib.rs + ```rust,noplayground,test_harness {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-08/src/lib.rs}} ``` -Listing 7-8: Calling a function using a relative path -starting with `super` + The `fix_incorrect_order` function is in the `back_of_house` module, so we can use `super` to go to the parent module of `back_of_house`, which in this case @@ -230,13 +227,13 @@ is `crate`, the root. From there, we look for `deliver_order` and find it. Success! We think the `back_of_house` module and the `deliver_order` function are likely to stay in the same relationship to each other and get moved together should we decide to reorganize the crate’s module tree. Therefore, we -used `super` so we’ll have fewer places to update code in the future if this -code gets moved to a different module. +used `super` so that we’ll have fewer places to update code in the future if +this code gets moved to a different module. ### Making Structs and Enums Public We can also use `pub` to designate structs and enums as public, but there are a -few details extra to the usage of `pub` with structs and enums. If we use `pub` +few extra details to the usage of `pub` with structs and enums. If we use `pub` before a struct definition, we make the struct public, but the struct’s fields will still be private. We can make each field public or not on a case-by-case basis. In Listing 7-9, we’ve defined a public `back_of_house::Breakfast` struct @@ -246,39 +243,37 @@ comes with a meal, but the chef decides which fruit accompanies the meal based on what’s in season and in stock. The available fruit changes quickly, so customers can’t choose the fruit or even see which fruit they’ll get. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-09/src/lib.rs}} ``` -Listing 7-9: A struct with some public fields and some -private fields + Because the `toast` field in the `back_of_house::Breakfast` struct is public, in `eat_at_restaurant` we can write and read to the `toast` field using dot notation. Notice that we can’t use the `seasonal_fruit` field in -`eat_at_restaurant` because `seasonal_fruit` is private. Try uncommenting the +`eat_at_restaurant`, because `seasonal_fruit` is private. Try uncommenting the line modifying the `seasonal_fruit` field value to see what error you get! Also, note that because `back_of_house::Breakfast` has a private field, the struct needs to provide a public associated function that constructs an instance of `Breakfast` (we’ve named it `summer` here). If `Breakfast` didn’t have such a function, we couldn’t create an instance of `Breakfast` in -`eat_at_restaurant` because we couldn’t set the value of the private +`eat_at_restaurant`, because we couldn’t set the value of the private `seasonal_fruit` field in `eat_at_restaurant`. In contrast, if we make an enum public, all of its variants are then public. We only need the `pub` before the `enum` keyword, as shown in Listing 7-10. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-10/src/lib.rs}} ``` -Listing 7-10: Designating an enum as public makes all its -variants public + Because we made the `Appetizer` enum public, we can use the `Soup` and `Salad` variants in `eat_at_restaurant`. diff --git a/src/ch07-04-bringing-paths-into-scope-with-the-use-keyword.md b/src/ch07-04-bringing-paths-into-scope-with-the-use-keyword.md index 921e5cecca..8397114f76 100644 --- a/src/ch07-04-bringing-paths-into-scope-with-the-use-keyword.md +++ b/src/ch07-04-bringing-paths-into-scope-with-the-use-keyword.md @@ -4,22 +4,21 @@ Having to write out the paths to call functions can feel inconvenient and repetitive. In Listing 7-7, whether we chose the absolute or relative path to the `add_to_waitlist` function, every time we wanted to call `add_to_waitlist` we had to specify `front_of_house` and `hosting` too. Fortunately, there’s a -way to simplify this process: we can create a shortcut to a path with the `use` -keyword once, and then use the shorter name everywhere else in the scope. +way to simplify this process: We can create a shortcut to a path with the `use` +keyword once and then use the shorter name everywhere else in the scope. In Listing 7-11, we bring the `crate::front_of_house::hosting` module into the -scope of the `eat_at_restaurant` function so we only have to specify +scope of the `eat_at_restaurant` function so that we only have to specify `hosting::add_to_waitlist` to call the `add_to_waitlist` function in `eat_at_restaurant`. -Filename: src/lib.rs + ```rust,noplayground,test_harness {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-11/src/lib.rs}} ``` -Listing 7-11: Bringing a module into scope with -`use` + Adding `use` and a path in a scope is similar to creating a symbolic link in the filesystem. By adding `use crate::front_of_house::hosting` in the crate @@ -30,16 +29,15 @@ also check privacy, like any other paths. Note that `use` only creates the shortcut for the particular scope in which the `use` occurs. Listing 7-12 moves the `eat_at_restaurant` function into a new child module named `customer`, which is then a different scope than the `use` -statement, so the function body won’t compile: +statement, so the function body won’t compile. -Filename: src/lib.rs + ```rust,noplayground,test_harness,does_not_compile,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-12/src/lib.rs}} ``` -Listing 7-12: A `use` statement only applies in the scope -it’s in + The compiler error shows that the shortcut no longer applies within the `customer` module: @@ -57,21 +55,20 @@ the shortcut in the parent module with `super::hosting` within the child In Listing 7-11, you might have wondered why we specified `use crate::front_of_house::hosting` and then called `hosting::add_to_waitlist` in -`eat_at_restaurant` rather than specifying the `use` path all the way out to +`eat_at_restaurant`, rather than specifying the `use` path all the way out to the `add_to_waitlist` function to achieve the same result, as in Listing 7-13. -Filename: src/lib.rs + ```rust,noplayground,test_harness {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-13/src/lib.rs}} ``` -Listing 7-13: Bringing the `add_to_waitlist` function -into scope with `use`, which is unidiomatic + -Although both Listing 7-11 and 7-13 accomplish the same task, Listing 7-11 is -the idiomatic way to bring a function into scope with `use`. Bringing the -function’s parent module into scope with `use` means we have to specify the +Although both Listing 7-11 and Listing 7-13 accomplish the same task, Listing +7-11 is the idiomatic way to bring a function into scope with `use`. Bringing +the function’s parent module into scope with `use` means we have to specify the parent module when calling the function. Specifying the parent module when calling the function makes it clear that the function isn’t locally defined while still minimizing repetition of the full path. The code in Listing 7-13 is @@ -82,52 +79,49 @@ it’s idiomatic to specify the full path. Listing 7-14 shows the idiomatic way to bring the standard library’s `HashMap` struct into the scope of a binary crate. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-14/src/main.rs}} ``` -Listing 7-14: Bringing `HashMap` into scope in an -idiomatic way + -There’s no strong reason behind this idiom: it’s just the convention that has +There’s no strong reason behind this idiom: It’s just the convention that has emerged, and folks have gotten used to reading and writing Rust code this way. The exception to this idiom is if we’re bringing two items with the same name into scope with `use` statements, because Rust doesn’t allow that. Listing 7-15 shows how to bring two `Result` types into scope that have the same name but -different parent modules and how to refer to them. +different parent modules, and how to refer to them. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-15/src/lib.rs:here}} ``` -Listing 7-15: Bringing two types with the same name into -the same scope requires using their parent modules. + As you can see, using the parent modules distinguishes the two `Result` types. If instead we specified `use std::fmt::Result` and `use std::io::Result`, we’d -have two `Result` types in the same scope and Rust wouldn’t know which one we +have two `Result` types in the same scope, and Rust wouldn’t know which one we meant when we used `Result`. ### Providing New Names with the `as` Keyword There’s another solution to the problem of bringing two types of the same name -into the same scope with `use`: after the path, we can specify `as` and a new -local name, or *alias*, for the type. Listing 7-16 shows another way to write +into the same scope with `use`: After the path, we can specify `as` and a new +local name, or _alias_, for the type. Listing 7-16 shows another way to write the code in Listing 7-15 by renaming one of the two `Result` types using `as`. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-16/src/lib.rs:here}} ``` -Listing 7-16: Renaming a type when it’s brought into -scope with the `as` keyword + In the second `use` statement, we chose the new name `IoResult` for the `std::io::Result` type, which won’t conflict with the `Result` from `std::fmt` @@ -136,48 +130,47 @@ considered idiomatic, so the choice is up to you! ### Re-exporting Names with `pub use` -When we bring a name into scope with the `use` keyword, the name available in -the new scope is private. To enable the code that calls our code to refer to -that name as if it had been defined in that code’s scope, we can combine `pub` -and `use`. This technique is called *re-exporting* because we’re bringing -an item into scope but also making that item available for others to bring into -their scope. +When we bring a name into scope with the `use` keyword, the name is private to +the scope into which we imported it. To enable code outside that scope to refer +to that name as if it had been defined in that scope, we can combine `pub` and +`use`. This technique is called _re-exporting_ because we’re bringing an item +into scope but also making that item available for others to bring into their +scope. Listing 7-17 shows the code in Listing 7-11 with `use` in the root module changed to `pub use`. -Filename: src/lib.rs + ```rust,noplayground,test_harness {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-17/src/lib.rs}} ``` -Listing 7-17: Making a name available for any code to use -from a new scope with `pub use` + Before this change, external code would have to call the `add_to_waitlist` function by using the path -`restaurant::front_of_house::hosting::add_to_waitlist()`. Now that this `pub +`restaurant::front_of_house::hosting::add_to_waitlist()`, which also would have +required the `front_of_house` module to be marked as `pub`. Now that this `pub use` has re-exported the `hosting` module from the root module, external code -can now use the path `restaurant::hosting::add_to_waitlist()` instead. +can use the path `restaurant::hosting::add_to_waitlist()` instead. Re-exporting is useful when the internal structure of your code is different from how programmers calling your code would think about the domain. For example, in this restaurant metaphor, the people running the restaurant think about “front of house” and “back of house.” But customers visiting a restaurant -probably won’t think about the parts of the restaurant in those terms. With -`pub use`, we can write our code with one structure but expose a different -structure. Doing so makes our library well organized for programmers working on -the library and programmers calling the library. We’ll look at another example -of `pub use` and how it affects your crate’s documentation in the [“Exporting a -Convenient Public API with `pub use`”][ch14-pub-use] section of -Chapter 14. +probably won’t think about the parts of the restaurant in those terms. With `pub +use`, we can write our code with one structure but expose a different structure. +Doing so makes our library well organized for programmers working on the library +and programmers calling the library. We’ll look at another example of `pub use` +and how it affects your crate’s documentation in [“Exporting a Convenient Public +API”][ch14-pub-use] in Chapter 14. ### Using External Packages In Chapter 2, we programmed a guessing game project that used an external package called `rand` to get random numbers. To use `rand` in our project, we -added this line to *Cargo.toml*: +added this line to _Cargo.toml_: -Filename: Cargo.toml + ```toml {{#include ../listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.toml:9:}} ``` -Adding `rand` as a dependency in *Cargo.toml* tells Cargo to download the + + +Adding `rand` as a dependency in _Cargo.toml_ tells Cargo to download the `rand` package and any dependencies from [crates.io](https://crates.io/) and make `rand` available to our project. Then, to bring `rand` definitions into the scope of our package, we added a -`use` line starting with the name of the crate, `rand`, and listed the items -we wanted to bring into scope. Recall that in the [“Generating a Random -Number”][rand] section in Chapter 2, we brought the `Rng` trait -into scope and called the `rand::thread_rng` function: +`use` line starting with the name of the crate, `rand`, and listed the items we +wanted to bring into scope. Recall that in [“Generating a Random +Number”][rand] in Chapter 2, we brought the `Rng` trait into +scope and called the `rand::thread_rng` function: ```rust,ignore {{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs:ch07-04}} @@ -207,12 +202,12 @@ into scope and called the `rand::thread_rng` function: Members of the Rust community have made many packages available at [crates.io](https://crates.io/), and pulling any of them into your package -involves these same steps: listing them in your package’s *Cargo.toml* file and +involves these same steps: listing them in your package’s _Cargo.toml_ file and using `use` to bring items from their crates into scope. Note that the standard `std` library is also a crate that’s external to our package. Because the standard library is shipped with the Rust language, we -don’t need to change *Cargo.toml* to include `std`. But we do need to refer to +don’t need to change _Cargo.toml_ to include `std`. But we do need to refer to it with `use` to bring items from there into our package’s scope. For example, with `HashMap` we would use this line: @@ -223,32 +218,37 @@ use std::collections::HashMap; This is an absolute path starting with `std`, the name of the standard library crate. -### Using Nested Paths to Clean Up Large `use` Lists + + + -If we’re using multiple items defined in the same crate or same module, -listing each item on its own line can take up a lot of vertical space in our -files. For example, these two `use` statements we had in the Guessing Game in -Listing 2-4 bring items from `std` into scope: +### Using Nested Paths to Clean Up `use` Lists -Filename: src/main.rs +If we’re using multiple items defined in the same crate or same module, listing +each item on its own line can take up a lot of vertical space in our files. For +example, these two `use` statements we had in the guessing game in Listing 2-4 +bring items from `std` into scope: + + ```rust,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/no-listing-01-use-std-unnested/src/main.rs:here}} ``` + + Instead, we can use nested paths to bring the same items into scope in one line. We do this by specifying the common part of the path, followed by two colons, and then curly brackets around a list of the parts of the paths that differ, as shown in Listing 7-18. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-18/src/main.rs:here}} ``` -Listing 7-18: Specifying a nested path to bring multiple -items with the same prefix into scope + In bigger programs, bringing many items into scope from the same crate or module using nested paths can reduce the number of separate `use` statements @@ -259,33 +259,35 @@ two `use` statements that share a subpath. For example, Listing 7-19 shows two `use` statements: one that brings `std::io` into scope and one that brings `std::io::Write` into scope. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-19/src/lib.rs}} ``` -Listing 7-19: Two `use` statements where one is a subpath -of the other + The common part of these two paths is `std::io`, and that’s the complete first path. To merge these two paths into one `use` statement, we can use `self` in the nested path, as shown in Listing 7-20. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-20/src/lib.rs}} ``` -Listing 7-20: Combining the paths in Listing 7-19 into -one `use` statement + This line brings `std::io` and `std::io::Write` into scope. -### The Glob Operator + -If we want to bring *all* public items defined in a path into scope, we can + + +### Importing Items with the Glob Operator + +If we want to bring _all_ public items defined in a path into scope, we can specify that path followed by the `*` glob operator: ```rust @@ -295,15 +297,18 @@ use std::collections::*; This `use` statement brings all public items defined in `std::collections` into the current scope. Be careful when using the glob operator! Glob can make it harder to tell what names are in scope and where a name used in your program -was defined. - -The glob operator is often used when testing to bring everything under test -into the `tests` module; we’ll talk about that in the [“How to Write -Tests”][writing-tests] section in Chapter 11. The glob operator -is also sometimes used as part of the prelude pattern: see [the standard -library documentation](../std/prelude/index.html#other-preludes) -for more information on that pattern. - -[ch14-pub-use]: ch14-02-publishing-to-crates-io.html#exporting-a-convenient-public-api-with-pub-use +was defined. Additionally, if the dependency changes its definitions, what +you’ve imported changes as well, which may lead to compiler errors when you +upgrade the dependency if the dependency adds a definition with the same name +as a definition of yours in the same scope, for example. + +The glob operator is often used when testing to bring everything under test into +the `tests` module; we’ll talk about that in [“How to Write +Tests”][writing-tests] in Chapter 11. The glob operator is also +sometimes used as part of the prelude pattern: See [the standard library +documentation](../std/prelude/index.html#other-preludes) for more +information on that pattern. + +[ch14-pub-use]: ch14-02-publishing-to-crates-io.html#exporting-a-convenient-public-api [rand]: ch02-00-guessing-game-tutorial.html#generating-a-random-number [writing-tests]: ch11-01-writing-tests.html#how-to-write-tests diff --git a/src/ch07-05-separating-modules-into-different-files.md b/src/ch07-05-separating-modules-into-different-files.md index 17e8d74526..ed3f49f7b3 100644 --- a/src/ch07-05-separating-modules-into-different-files.md +++ b/src/ch07-05-separating-modules-into-different-files.md @@ -7,74 +7,76 @@ file to make the code easier to navigate. For example, let’s start from the code in Listing 7-17 that had multiple restaurant modules. We’ll extract modules into files instead of having all the modules defined in the crate root file. In this case, the crate root file is -*src/lib.rs*, but this procedure also works with binary crates whose crate root -file is *src/main.rs*. +_src/lib.rs_, but this procedure also works with binary crates whose crate root +file is _src/main.rs_. First, we’ll extract the `front_of_house` module to its own file. Remove the code inside the curly brackets for the `front_of_house` module, leaving only -the `mod front_of_house;` declaration, so that *src/lib.rs* contains the code +the `mod front_of_house;` declaration, so that _src/lib.rs_ contains the code shown in Listing 7-21. Note that this won’t compile until we create the -*src/front_of_house.rs* file in Listing 7-22. +_src/front_of_house.rs_ file in Listing 7-22. -Filename: src/lib.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-21-and-22/src/lib.rs}} ``` -Listing 7-21: Declaring the `front_of_house` module whose -body will be in *src/front_of_house.rs* + Next, place the code that was in the curly brackets into a new file named -*src/front_of_house.rs*, as shown in Listing 7-22. The compiler knows to look +_src/front_of_house.rs_, as shown in Listing 7-22. The compiler knows to look in this file because it came across the module declaration in the crate root with the name `front_of_house`. -Filename: src/front_of_house.rs + ```rust,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-21-and-22/src/front_of_house.rs}} ``` -Listing 7-22: Definitions inside the `front_of_house` -module in *src/front_of_house.rs* + -Note that you only need to load a file using a `mod` declaration *once* in your +Note that you only need to load a file using a `mod` declaration _once_ in your module tree. Once the compiler knows the file is part of the project (and knows where in the module tree the code resides because of where you’ve put the `mod` statement), other files in your project should refer to the loaded file’s code using a path to where it was declared, as covered in the [“Paths for Referring to an Item in the Module Tree”][paths] section. In other words, -`mod` is *not* an “include” operation that you may have seen in other +`mod` is _not_ an “include” operation that you may have seen in other programming languages. Next, we’ll extract the `hosting` module to its own file. The process is a bit different because `hosting` is a child module of `front_of_house`, not of the root module. We’ll place the file for `hosting` in a new directory that will be -named for its ancestors in the module tree, in this case *src/front_of_house/*. +named for its ancestors in the module tree, in this case _src/front_of_house_. -To start moving `hosting`, we change *src/front_of_house.rs* to contain only the -declaration of the `hosting` module: +To start moving `hosting`, we change _src/front_of_house.rs_ to contain only +the declaration of the `hosting` module: -Filename: src/front_of_house.rs + ```rust,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/src/front_of_house.rs}} ``` -Then we create a *src/front_of_house* directory and a file *hosting.rs* to + + +Then, we create a _src/front_of_house_ directory and a _hosting.rs_ file to contain the definitions made in the `hosting` module: -Filename: src/front_of_house/hosting.rs + ```rust,ignore {{#rustdoc_include ../listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/src/front_of_house/hosting.rs}} ``` -If we instead put *hosting.rs* in the *src* directory, the compiler would -expect the *hosting.rs* code to be in a `hosting` module declared in the crate -root, and not declared as a child of the `front_of_house` module. The -compiler’s rules for which files to check for which modules’ code means the + + +If we instead put _hosting.rs_ in the _src_ directory, the compiler would +expect the _hosting.rs_ code to be in a `hosting` module declared in the crate +root and not declared as a child of the `front_of_house` module. The +compiler’s rules for which files to check for which modules’ code mean the directories and files more closely match the module tree. > ### Alternate File Paths @@ -84,21 +86,21 @@ directories and files more closely match the module tree. > `front_of_house` declared in the crate root, the compiler will look for the > module’s code in: > -> * *src/front_of_house.rs* (what we covered) -> * *src/front_of_house/mod.rs* (older style, still supported path) +> - _src/front_of_house.rs_ (what we covered) +> - _src/front_of_house/mod.rs_ (older style, still supported path) > > For a module named `hosting` that is a submodule of `front_of_house`, the > compiler will look for the module’s code in: > -> * *src/front_of_house/hosting.rs* (what we covered) -> * *src/front_of_house/hosting/mod.rs* (older style, still supported path) +> - _src/front_of_house/hosting.rs_ (what we covered) +> - _src/front_of_house/hosting/mod.rs_ (older style, still supported path) > -> If you use both styles for the same module, you’ll get a compiler error. Using -> a mix of both styles for different modules in the same project is allowed, but -> might be confusing for people navigating your project. +> If you use both styles for the same module, you’ll get a compiler error. +> Using a mix of both styles for different modules in the same project is +> allowed but might be confusing for people navigating your project. > -> The main downside to the style that uses files named *mod.rs* is that your -> project can end up with many files named *mod.rs*, which can get confusing +> The main downside to the style that uses files named _mod.rs_ is that your +> project can end up with many files named _mod.rs_, which can get confusing > when you have them open in your editor at the same time. We’ve moved each module’s code to a separate file, and the module tree remains @@ -107,19 +109,19 @@ modification, even though the definitions live in different files. This technique lets you move modules to new files as they grow in size. Note that the `pub use crate::front_of_house::hosting` statement in -*src/lib.rs* also hasn’t changed, nor does `use` have any impact on what files +_src/lib.rs_ also hasn’t changed, nor does `use` have any impact on what files are compiled as part of the crate. The `mod` keyword declares modules, and Rust looks in a file with the same name as the module for the code that goes into that module. ## Summary -Rust lets you split a package into multiple crates and a crate into modules -so you can refer to items defined in one module from another module. You can do -this by specifying absolute or relative paths. These paths can be brought into -scope with a `use` statement so you can use a shorter path for multiple uses of -the item in that scope. Module code is private by default, but you can make -definitions public by adding the `pub` keyword. +Rust lets you split a package into multiple crates and a crate into modules so +that you can refer to items defined in one module from another module. You can +do this by specifying absolute or relative paths. These paths can be brought +into scope with a `use` statement so that you can use a shorter path for +multiple uses of the item in that scope. Module code is private by default, but +you can make definitions public by adding the `pub` keyword. In the next chapter, we’ll look at some collection data structures in the standard library that you can use in your neatly organized code. diff --git a/src/ch08-00-common-collections.md b/src/ch08-00-common-collections.md index cf66e18854..550ee2c090 100644 --- a/src/ch08-00-common-collections.md +++ b/src/ch08-00-common-collections.md @@ -1,20 +1,20 @@ # Common Collections Rust’s standard library includes a number of very useful data structures called -*collections*. Most other data types represent one specific value, but +_collections_. Most other data types represent one specific value, but collections can contain multiple values. Unlike the built-in array and tuple -types, the data these collections point to is stored on the heap, which means -the amount of data does not need to be known at compile time and can grow or -shrink as the program runs. Each kind of collection has different capabilities -and costs, and choosing an appropriate one for your current situation is a -skill you’ll develop over time. In this chapter, we’ll discuss three -collections that are used very often in Rust programs: +types, the data that these collections point to is stored on the heap, which +means the amount of data does not need to be known at compile time and can grow +or shrink as the program runs. Each kind of collection has different +capabilities and costs, and choosing an appropriate one for your current +situation is a skill you’ll develop over time. In this chapter, we’ll discuss +three collections that are used very often in Rust programs: -* A *vector* allows you to store a variable number of values next to each other. -* A *string* is a collection of characters. We’ve mentioned the `String` type - previously, but in this chapter we’ll talk about it in depth. -* A *hash map* allows you to associate a value with a particular key. It’s a - particular implementation of the more general data structure called a *map*. +- A _vector_ allows you to store a variable number of values next to each other. +- A _string_ is a collection of characters. We’ve mentioned the `String` type + previously, but in this chapter, we’ll talk about it in depth. +- A _hash map_ allows you to associate a value with a specific key. It’s a + particular implementation of the more general data structure called a _map_. To learn about the other kinds of collections provided by the standard library, see [the documentation][collections]. diff --git a/src/ch08-01-vectors.md b/src/ch08-01-vectors.md index 85d3bcfe41..25b8f67bf7 100644 --- a/src/ch08-01-vectors.md +++ b/src/ch08-01-vectors.md @@ -1,6 +1,6 @@ ## Storing Lists of Values with Vectors -The first collection type we’ll look at is `Vec`, also known as a *vector*. +The first collection type we’ll look at is `Vec`, also known as a vector. Vectors allow you to store more than one value in a single data structure that puts all the values next to each other in memory. Vectors can only store values of the same type. They are useful when you have a list of items, such as the @@ -8,15 +8,16 @@ lines of text in a file or the prices of items in a shopping cart. ### Creating a New Vector -To create a new empty vector, we call the `Vec::new` function, as shown in +To create a new, empty vector, we call the `Vec::new` function, as shown in Listing 8-1. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-01/src/main.rs:here}} ``` -Listing 8-1: Creating a new, empty vector to hold values -of type `i32` + Note that we added a type annotation here. Because we aren’t inserting any values into this vector, Rust doesn’t know what kind of elements we intend to @@ -27,7 +28,7 @@ When we create a vector to hold a specific type, we can specify the type within angle brackets. In Listing 8-1, we’ve told Rust that the `Vec` in `v` will hold elements of the `i32` type. -More often, you’ll create a `Vec` with initial values and Rust will infer +More often, you’ll create a `Vec` with initial values, and Rust will infer the type of value you want to store, so you rarely need to do this type annotation. Rust conveniently provides the `vec!` macro, which will create a new vector that holds the values you give it. Listing 8-2 creates a new @@ -35,12 +36,13 @@ new vector that holds the values you give it. Listing 8-2 creates a new because that’s the default integer type, as we discussed in the [“Data Types”][data-types] section of Chapter 3. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-02/src/main.rs:here}} ``` -Listing 8-2: Creating a new vector containing -values + Because we’ve given initial `i32` values, Rust can infer that the type of `v` is `Vec`, and the type annotation isn’t necessary. Next, we’ll look at how @@ -51,12 +53,13 @@ to modify a vector. To create a vector and then add elements to it, we can use the `push` method, as shown in Listing 8-3. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-03/src/main.rs:here}} ``` -Listing 8-3: Using the `push` method to add values to a -vector + As with any variable, if we want to be able to change its value, we need to make it mutable using the `mut` keyword, as discussed in Chapter 3. The numbers @@ -65,19 +68,20 @@ we don’t need the `Vec` annotation. ### Reading Elements of Vectors -There are two ways to reference a value stored in a vector: via indexing or +There are two ways to reference a value stored in a vector: via indexing or by using the `get` method. In the following examples, we’ve annotated the types of the values that are returned from these functions for extra clarity. Listing 8-4 shows both methods of accessing a value in a vector, with indexing syntax and the `get` method. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-04/src/main.rs:here}} ``` -Listing 8-4: Using indexing syntax or the `get` method to -access an item in a vector + Note a few details here. We use the index value of `2` to get the third element because vectors are indexed by number, starting at zero. Using `&` and `[]` @@ -85,18 +89,19 @@ gives us a reference to the element at the index value. When we use the `get` method with the index passed as an argument, we get an `Option<&T>` that we can use with `match`. -The reason Rust provides these two ways to reference an element is so you can -choose how the program behaves when you try to use an index value outside the -range of existing elements. As an example, let’s see what happens when we have -a vector of five elements and then we try to access an element at index 100 -with each technique, as shown in Listing 8-5. +Rust provides these two ways to reference an element so that you can choose how +the program behaves when you try to use an index value outside the range of +existing elements. As an example, let’s see what happens when we have a vector +of five elements and then we try to access an element at index 100 with each +technique, as shown in Listing 8-5. + + ```rust,should_panic,panics {{#rustdoc_include ../listings/ch08-common-collections/listing-08-05/src/main.rs:here}} ``` -Listing 8-5: Attempting to access the element at index -100 in a vector containing five elements + When we run this code, the first `[]` method will cause the program to panic because it references a nonexistent element. This method is best used when you @@ -115,32 +120,31 @@ enter a valid value. That would be more user-friendly than crashing the program due to a typo! When the program has a valid reference, the borrow checker enforces the -ownership and borrowing rules (covered in Chapter 4) to ensure this reference -and any other references to the contents of the vector remain valid. Recall the -rule that states you can’t have mutable and immutable references in the same -scope. That rule applies in Listing 8-6, where we hold an immutable reference -to the first element in a vector and try to add an element to the end. This -program won’t work if we also try to refer to that element later in the -function: +ownership and borrowing rules (covered in Chapter 4) to ensure that this +reference and any other references to the contents of the vector remain valid. +Recall the rule that states you can’t have mutable and immutable references in +the same scope. That rule applies in Listing 8-6, where we hold an immutable +reference to the first element in a vector and try to add an element to the +end. This program won’t work if we also try to refer to that element later in +the function. + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch08-common-collections/listing-08-06/src/main.rs:here}} ``` -Listing 8-6: Attempting to add an element to a vector -while holding a reference to an item + Compiling this code will result in this error: - ```console {{#include ../listings/ch08-common-collections/listing-08-06/output.txt}} ``` -The code in Listing 8-6 might look like it should work: why should a reference +The code in Listing 8-6 might look like it should work: Why should a reference to the first element care about changes at the end of the vector? This error is -due to the way vectors work: because vectors put the values next to each other +due to the way vectors work: Because vectors put the values next to each other in memory, adding a new element onto the end of the vector might require allocating new memory and copying the old elements to the new space, if there isn’t enough room to put all the elements next to each other where the vector @@ -151,39 +155,40 @@ ending up in that situation. > Note: For more on the implementation details of the `Vec` type, see [“The > Rustonomicon”][nomicon]. -### Iterating over the Values in a Vector +### Iterating Over the Values in a Vector To access each element in a vector in turn, we would iterate through all of the elements rather than use indices to access one at a time. Listing 8-7 shows how to use a `for` loop to get immutable references to each element in a vector of `i32` values and print them. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-07/src/main.rs:here}} ``` -Listing 8-7: Printing each element in a vector by -iterating over the elements using a `for` loop + We can also iterate over mutable references to each element in a mutable vector in order to make changes to all the elements. The `for` loop in Listing 8-8 will add `50` to each element. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-08/src/main.rs:here}} ``` -Listing 8-8: Iterating over mutable references to -elements in a vector + To change the value that the mutable reference refers to, we have to use the `*` dereference operator to get to the value in `i` before we can use the `+=` operator. We’ll talk more about the dereference operator in the [“Following the -Pointer to the Value with the Dereference Operator”][deref] -section of Chapter 15. +Reference to the Value”][deref] section of Chapter 15. Iterating over a vector, whether immutably or mutably, is safe because of the -borrow checker's rules. If we attempted to insert or remove items in the `for` +borrow checker’s rules. If we attempted to insert or remove items in the `for` loop bodies in Listing 8-7 and Listing 8-8, we would get a compiler error similar to the one we got with the code in Listing 8-6. The reference to the vector that the `for` loop holds prevents simultaneous modification of the @@ -191,29 +196,30 @@ whole vector. ### Using an Enum to Store Multiple Types -Vectors can only store values that are the same type. This can be inconvenient; -there are definitely use cases for needing to store a list of items of -different types. Fortunately, the variants of an enum are defined under the -same enum type, so when we need one type to represent elements of different -types, we can define and use an enum! +Vectors can only store values that are of the same type. This can be +inconvenient; there are definitely use cases for needing to store a list of +items of different types. Fortunately, the variants of an enum are defined +under the same enum type, so when we need one type to represent elements of +different types, we can define and use an enum! For example, say we want to get values from a row in a spreadsheet in which some of the columns in the row contain integers, some floating-point numbers, and some strings. We can define an enum whose variants will hold the different value types, and all the enum variants will be considered the same type: that -of the enum. Then we can create a vector to hold that enum and so, ultimately, -holds different types. We’ve demonstrated this in Listing 8-9. +of the enum. Then, we can create a vector to hold that enum and so, ultimately, +hold different types. We’ve demonstrated this in Listing 8-9. + + ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-09/src/main.rs:here}} ``` -Listing 8-9: Defining an `enum` to store values of -different types in one vector + -Rust needs to know what types will be in the vector at compile time so it knows -exactly how much memory on the heap will be needed to store each element. We -must also be explicit about what types are allowed in this vector. If Rust +Rust needs to know what types will be in the vector at compile time so that it +knows exactly how much memory on the heap will be needed to store each element. +We must also be explicit about what types are allowed in this vector. If Rust allowed a vector to hold any type, there would be a chance that one or more of the types would cause errors with the operations performed on the elements of the vector. Using an enum plus a `match` expression means that Rust will ensure @@ -221,10 +227,10 @@ at compile time that every possible case is handled, as discussed in Chapter 6. If you don’t know the exhaustive set of types a program will get at runtime to store in a vector, the enum technique won’t work. Instead, you can use a trait -object, which we’ll cover in Chapter 17. +object, which we’ll cover in Chapter 18. Now that we’ve discussed some of the most common ways to use vectors, be sure -to review [the API documentation][vec-api] for all the many +to review [the API documentation][vec-api] for all of the many useful methods defined on `Vec` by the standard library. For example, in addition to `push`, a `pop` method removes and returns the last element. @@ -233,12 +239,13 @@ addition to `push`, a `pop` method removes and returns the last element. Like any other `struct`, a vector is freed when it goes out of scope, as annotated in Listing 8-10. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-10/src/main.rs:here}} ``` -Listing 8-10: Showing where the vector and its elements -are dropped + When the vector gets dropped, all of its contents are also dropped, meaning the integers it holds will be cleaned up. The borrow checker ensures that any diff --git a/src/ch08-02-strings.md b/src/ch08-02-strings.md index f38803ee3b..7e73a9073e 100644 --- a/src/ch08-02-strings.md +++ b/src/ch08-02-strings.md @@ -12,15 +12,19 @@ implemented as a collection of bytes, plus some methods to provide useful functionality when those bytes are interpreted as text. In this section, we’ll talk about the operations on `String` that every collection type has, such as creating, updating, and reading. We’ll also discuss the ways in which `String` -is different from the other collections, namely how indexing into a `String` is +is different from the other collections, namely, how indexing into a `String` is complicated by the differences between how people and computers interpret `String` data. -### What Is a String? + -We’ll first define what we mean by the term *string*. Rust has only one string + + +### Defining Strings + +We’ll first define what we mean by the term _string_. Rust has only one string type in the core language, which is the string slice `str` that is usually seen -in its borrowed form `&str`. In Chapter 4, we talked about *string slices*, +in its borrowed form, `&str`. In Chapter 4, we talked about string slices, which are references to some UTF-8 encoded string data stored elsewhere. String literals, for example, are stored in the program’s binary and are therefore string slices. @@ -36,58 +40,63 @@ are UTF-8 encoded. ### Creating a New String Many of the same operations available with `Vec` are available with `String` -as well, because `String` is actually implemented as a wrapper around a vector +as well because `String` is actually implemented as a wrapper around a vector of bytes with some extra guarantees, restrictions, and capabilities. An example of a function that works the same way with `Vec` and `String` is the `new` function to create an instance, shown in Listing 8-11. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-11/src/main.rs:here}} ``` -Listing 8-11: Creating a new, empty `String` + -This line creates a new empty string called `s`, which we can then load data -into. Often, we’ll have some initial data that we want to start the string -with. For that, we use the `to_string` method, which is available on any type +This line creates a new, empty string called `s`, into which we can then load +data. Often, we’ll have some initial data with which we want to start the +string. For that, we use the `to_string` method, which is available on any type that implements the `Display` trait, as string literals do. Listing 8-12 shows two examples. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-12/src/main.rs:here}} ``` -Listing 8-12: Using the `to_string` method to create a -`String` from a string literal + This code creates a string containing `initial contents`. We can also use the function `String::from` to create a `String` from a string -literal. The code in Listing 8-13 is equivalent to the code from Listing 8-12 +literal. The code in Listing 8-13 is equivalent to the code in Listing 8-12 that uses `to_string`. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-13/src/main.rs:here}} ``` -Listing 8-13: Using the `String::from` function to create -a `String` from a string literal + Because strings are used for so many things, we can use many different generic APIs for strings, providing us with a lot of options. Some of them can seem redundant, but they all have their place! In this case, `String::from` and -`to_string` do the same thing, so which you choose is a matter of style and +`to_string` do the same thing, so which one you choose is a matter of style and readability. Remember that strings are UTF-8 encoded, so we can include any properly encoded data in them, as shown in Listing 8-14. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-14/src/main.rs:here}} ``` -Listing 8-14: Storing greetings in different languages in -strings + All of these are valid `String` values. @@ -97,57 +106,69 @@ A `String` can grow in size and its contents can change, just like the contents of a `Vec`, if you push more data into it. In addition, you can conveniently use the `+` operator or the `format!` macro to concatenate `String` values. -#### Appending to a String with `push_str` and `push` + + + + +#### Appending with `push_str` or `push` We can grow a `String` by using the `push_str` method to append a string slice, as shown in Listing 8-15. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-15/src/main.rs:here}} ``` -Listing 8-15: Appending a string slice to a `String` -using the `push_str` method + After these two lines, `s` will contain `foobar`. The `push_str` method takes a string slice because we don’t necessarily want to take ownership of the parameter. For example, in the code in Listing 8-16, we want to be able to use `s2` after appending its contents to `s1`. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-16/src/main.rs:here}} ``` -Listing 8-16: Using a string slice after appending its -contents to a `String` + If the `push_str` method took ownership of `s2`, we wouldn’t be able to print its value on the last line. However, this code works as we’d expect! The `push` method takes a single character as a parameter and adds it to the -`String`. Listing 8-17 adds the letter “l” to a `String` using the `push` +`String`. Listing 8-17 adds the letter _l_ to a `String` using the `push` method. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-17/src/main.rs:here}} ``` -Listing 8-17: Adding one character to a `String` value -using `push` + As a result, `s` will contain `lol`. -#### Concatenation with the `+` Operator or the `format!` Macro + + + + +#### Concatenating with `+` or `format!` Often, you’ll want to combine two existing strings. One way to do so is to use the `+` operator, as shown in Listing 8-18. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-18/src/main.rs:here}} ``` -Listing 8-18: Using the `+` operator to combine two -`String` values into a new `String` value + The string `s3` will contain `Hello, world!`. The reason `s1` is no longer valid after the addition, and the reason we used a reference to `s2`, has to do @@ -159,32 +180,33 @@ this: fn add(self, s: &str) -> String { ``` -In the standard library, you'll see `add` defined using generics and associated +In the standard library, you’ll see `add` defined using generics and associated types. Here, we’ve substituted in concrete types, which is what happens when we call this method with `String` values. We’ll discuss generics in Chapter 10. -This signature gives us the clues we need to understand the tricky bits of the -`+` operator. +This signature gives us the clues we need in order to understand the tricky +bits of the `+` operator. -First, `s2` has an `&`, meaning that we’re adding a *reference* of the second +First, `s2` has an `&`, meaning that we’re adding a reference of the second string to the first string. This is because of the `s` parameter in the `add` -function: we can only add a `&str` to a `String`; we can’t add two `String` -values together. But wait—the type of `&s2` is `&String`, not `&str`, as -specified in the second parameter to `add`. So why does Listing 8-18 compile? +function: We can only add a string slice to a `String`; we can’t add two +`String` values together. But wait—the type of `&s2` is `&String`, not `&str`, +as specified in the second parameter to `add`. So, why does Listing 8-18 +compile? The reason we’re able to use `&s2` in the call to `add` is that the compiler -can *coerce* the `&String` argument into a `&str`. When we call the `add` -method, Rust uses a *deref coercion*, which here turns `&s2` into `&s2[..]`. -We’ll discuss deref coercion in more depth in Chapter 15. Because `add` does -not take ownership of the `s` parameter, `s2` will still be a valid `String` -after this operation. - -Second, we can see in the signature that `add` takes ownership of `self`, -because `self` does *not* have an `&`. This means `s1` in Listing 8-18 will be -moved into the `add` call and will no longer be valid after that. So although +can coerce the `&String` argument into a `&str`. When we call the `add` method, +Rust uses a deref coercion, which here turns `&s2` into `&s2[..]`. We’ll +discuss deref coercion in more depth in Chapter 15. Because `add` does not take +ownership of the `s` parameter, `s2` will still be a valid `String` after this +operation. + +Second, we can see in the signature that `add` takes ownership of `self` +because `self` does _not_ have an `&`. This means `s1` in Listing 8-18 will be +moved into the `add` call and will no longer be valid after that. So, although `let s3 = s1 + &s2;` looks like it will copy both strings and create a new one, this statement actually takes ownership of `s1`, appends a copy of the contents of `s2`, and then returns ownership of the result. In other words, it looks -like it’s making a lot of copies but isn’t; the implementation is more +like it’s making a lot of copies, but it isn’t; the implementation is more efficient than copying. If we need to concatenate multiple strings, the behavior of the `+` operator @@ -195,8 +217,8 @@ gets unwieldy: ``` At this point, `s` will be `tic-tac-toe`. With all of the `+` and `"` -characters, it’s difficult to see what’s going on. For more complicated string -combining, we can instead use the `format!` macro: +characters, it’s difficult to see what’s going on. For combining strings in +more complicated ways, we can instead use the `format!` macro: ```rust {{#rustdoc_include ../listings/ch08-common-collections/no-listing-02-format/src/main.rs:here}} @@ -215,12 +237,13 @@ string by referencing them by index is a valid and common operation. However, if you try to access parts of a `String` using indexing syntax in Rust, you’ll get an error. Consider the invalid code in Listing 8-19. ++ ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch08-common-collections/listing-08-19/src/main.rs:here}} ``` -Listing 8-19: Attempting to use indexing syntax with a -String + This code will result in the following error: @@ -228,9 +251,8 @@ This code will result in the following error: {{#include ../listings/ch08-common-collections/listing-08-19/output.txt}} ``` -The error and the note tell the story: Rust strings don’t support indexing. But -why not? To answer that question, we need to discuss how Rust stores strings in -memory. +The error tells the story: Rust strings don’t support indexing. But why not? To +answer that question, we need to discuss how Rust stores strings in memory. #### Internal Representation @@ -241,20 +263,21 @@ encoded UTF-8 example strings from Listing 8-14. First, this one: {{#rustdoc_include ../listings/ch08-common-collections/listing-08-14/src/main.rs:spanish}} ``` -In this case, `len` will be 4, which means the vector storing the string “Hola” -is 4 bytes long. Each of these letters takes 1 byte when encoded in UTF-8. The -following line, however, may surprise you. (Note that this string begins with -the capital Cyrillic letter Ze, not the number 3.) +In this case, `len` will be `4`, which means the vector storing the string +`"Hola"` is 4 bytes long. Each of these letters takes 1 byte when encoded in +UTF-8. The following line, however, may surprise you (note that this string +begins with the capital Cyrillic letter _Ze_, not the number 3): ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-14/src/main.rs:russian}} ``` -Asked how long the string is, you might say 12. In fact, Rust’s answer is 24: -that’s the number of bytes it takes to encode “Здравствуйте” in UTF-8, because -each Unicode scalar value in that string takes 2 bytes of storage. Therefore, -an index into the string’s bytes will not always correlate to a valid Unicode -scalar value. To demonstrate, consider this invalid Rust code: +If you were asked how long the string is, you might say 12. In fact, Rust’s +answer is 24: That’s the number of bytes it takes to encode “Здравствуйте” in +UTF-8, because each Unicode scalar value in that string takes 2 bytes of +storage. Therefore, an index into the string’s bytes will not always correlate +to a valid Unicode scalar value. To demonstrate, consider this invalid Rust +code: ```rust,ignore,does_not_compile let hello = "Здравствуйте"; @@ -267,18 +290,22 @@ seem that `answer` should in fact be `208`, but `208` is not a valid character on its own. Returning `208` is likely not what a user would want if they asked for the first letter of this string; however, that’s the only data that Rust has at byte index 0. Users generally don’t want the byte value returned, even -if the string contains only Latin letters: if `&"hello"[0]` were valid code -that returned the byte value, it would return `104`, not `h`. +if the string contains only Latin letters: If `&"hi"[0]` were valid code that +returned the byte value, it would return `104`, not `h`. The answer, then, is that to avoid returning an unexpected value and causing bugs that might not be discovered immediately, Rust doesn’t compile this code at all and prevents misunderstandings early in the development process. -#### Bytes and Scalar Values and Grapheme Clusters! Oh My! + + + + +#### Bytes, Scalar Values, and Grapheme Clusters Another point about UTF-8 is that there are actually three relevant ways to look at strings from Rust’s perspective: as bytes, scalar values, and grapheme -clusters (the closest thing to what we would call *letters*). +clusters (the closest thing to what we would call _letters_). If we look at the Hindi word “नमस्ते” written in the Devanagari script, it is stored as a vector of `u8` values that looks like this: @@ -297,7 +324,7 @@ bytes look like this: ``` There are six `char` values here, but the fourth and sixth are not letters: -they’re diacritics that don’t make sense on their own. Finally, if we look at +They’re diacritics that don’t make sense on their own. Finally, if we look at them as grapheme clusters, we’d get what a person would call the four letters that make up the Hindi word: @@ -343,15 +370,19 @@ index were accessed in a vector: {{#include ../listings/ch08-common-collections/output-only-01-not-char-boundary/output.txt}} ``` -You should use ranges to create string slices with caution, because doing so -can crash your program. +You should use caution when creating string slices with ranges, because doing +so can crash your program. + + + + -### Methods for Iterating Over Strings +### Iterating Over Strings The best way to operate on pieces of strings is to be explicit about whether you want characters or bytes. For individual Unicode scalar values, use the -`chars` method. Calling `chars` on “Зд” separates out and returns two values -of type `char`, and you can iterate over the result to access each element: +`chars` method. Calling `chars` on “Зд” separates out and returns two values of +type `char`, and you can iterate over the result to access each element: ```rust for c in "Зд".chars() { @@ -375,7 +406,7 @@ for b in "Зд".bytes() { } ``` -This code will print the four bytes that make up this string: +This code will print the 4 bytes that make up this string: ```text 208 @@ -387,18 +418,22 @@ This code will print the four bytes that make up this string: But be sure to remember that valid Unicode scalar values may be made up of more than 1 byte. -Getting grapheme clusters from strings as with the Devanagari script is +Getting grapheme clusters from strings, as with the Devanagari script, is complex, so this functionality is not provided by the standard library. Crates are available on [crates.io](https://crates.io/) if this is the functionality you need. -### Strings Are Not So Simple + + + + +### Handling the Complexities of Strings To summarize, strings are complicated. Different programming languages make different choices about how to present this complexity to the programmer. Rust has chosen to make the correct handling of `String` data the default behavior for all Rust programs, which means programmers have to put more thought into -handling UTF-8 data upfront. This trade-off exposes more of the complexity of +handling UTF-8 data up front. This trade-off exposes more of the complexity of strings than is apparent in other programming languages, but it prevents you from having to handle errors involving non-ASCII characters later in your development life cycle. diff --git a/src/ch08-03-hash-maps.md b/src/ch08-03-hash-maps.md index 6322f1324d..696216245f 100644 --- a/src/ch08-03-hash-maps.md +++ b/src/ch08-03-hash-maps.md @@ -1,11 +1,11 @@ ## Storing Keys with Associated Values in Hash Maps -The last of our common collections is the *hash map*. The type `HashMap` -stores a mapping of keys of type `K` to values of type `V` using a -*hashing function*, which determines how it places these keys and values into -memory. Many programming languages support this kind of data structure, but -they often use a different name, such as hash, map, object, hash table, -dictionary, or associative array, just to name a few. +The last of our common collections is the hash map. The type `HashMap` +stores a mapping of keys of type `K` to values of type `V` using a _hashing +function_, which determines how it places these keys and values into memory. +Many programming languages support this kind of data structure, but they often +use a different name, such as _hash_, _map_, _object_, _hash table_, +_dictionary_, or _associative array_, just to name a few. Hash maps are useful when you want to look up data not by using an index, as you can with vectors, but by using a key that can be of any type. For example, @@ -19,17 +19,18 @@ As always, check the standard library documentation for more information. ### Creating a New Hash Map -One way to create an empty hash map is using `new` and adding elements with +One way to create an empty hash map is to use `new` and to add elements with `insert`. In Listing 8-20, we’re keeping track of the scores of two teams whose -names are *Blue* and *Yellow*. The Blue team starts with 10 points, and the +names are _Blue_ and _Yellow_. The Blue team starts with 10 points, and the Yellow team starts with 50. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-20/src/main.rs:here}} ``` -Listing 8-20: Creating a new hash map and inserting some -keys and values + Note that we need to first `use` the `HashMap` from the collections portion of the standard library. Of our three common collections, this one is the least @@ -39,29 +40,30 @@ standard library; there’s no built-in macro to construct them, for example. Just like vectors, hash maps store their data on the heap. This `HashMap` has keys of type `String` and values of type `i32`. Like vectors, hash maps are -homogeneous: all of the keys must have the same type as each other, and all of -the values must have the same type. +homogeneous: All of the keys must have the same type, and all of the values +must have the same type. ### Accessing Values in a Hash Map We can get a value out of the hash map by providing its key to the `get` method, as shown in Listing 8-21. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-21/src/main.rs:here}} ``` -Listing 8-21: Accessing the score for the Blue team -stored in the hash map + Here, `score` will have the value that’s associated with the Blue team, and the result will be `10`. The `get` method returns an `Option<&V>`; if there’s no value for that key in the hash map, `get` will return `None`. This program handles the `Option` by calling `copied` to get an `Option` rather than an -`Option<&i32>`, then `unwrap_or` to set `score` to zero if `scores` doesn't +`Option<&i32>`, then `unwrap_or` to set `score` to zero if `scores` doesn’t have an entry for the key. -We can iterate over each key/value pair in a hash map in a similar manner as we +We can iterate over each key-value pair in a hash map in a similar manner as we do with vectors, using a `for` loop: ```rust @@ -75,18 +77,23 @@ Yellow: 50 Blue: 10 ``` -### Hash Maps and Ownership + + + + +### Managing Ownership in Hash Maps For types that implement the `Copy` trait, like `i32`, the values are copied into the hash map. For owned values like `String`, the values will be moved and the hash map will be the owner of those values, as demonstrated in Listing 8-22. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-22/src/main.rs:here}} ``` -Listing 8-22: Showing that keys and values are owned by -the hash map once they’re inserted + We aren’t able to use the variables `field_name` and `field_value` after they’ve been moved into the hash map with the call to `insert`. @@ -94,22 +101,21 @@ they’ve been moved into the hash map with the call to `insert`. If we insert references to values into the hash map, the values won’t be moved into the hash map. The values that the references point to must be valid for at least as long as the hash map is valid. We’ll talk more about these issues in -the [“Validating References with -Lifetimes”][validating-references-with-lifetimes] section in -Chapter 10. +[“Validating References with +Lifetimes”][validating-references-with-lifetimes] in Chapter 10. ### Updating a Hash Map Although the number of key and value pairs is growable, each unique key can -only have one value associated with it at a time (but not vice versa: for -example, both the Blue team and the Yellow team could have value 10 stored in -the `scores` hash map). +only have one value associated with it at a time (but not vice versa: For +example, both the Blue team and the Yellow team could have the value `10` +stored in the `scores` hash map). When you want to change the data in a hash map, you have to decide how to handle the case when a key already has a value assigned. You could replace the old value with the new value, completely disregarding the old value. You could keep the old value and ignore the new value, only adding the new value if the -key *doesn’t* already have a value. Or you could combine the old value and the +key _doesn’t_ already have a value. Or you could combine the old value and the new value. Let’s look at how to do each of these! #### Overwriting a Value @@ -117,54 +123,57 @@ new value. Let’s look at how to do each of these! If we insert a key and a value into a hash map and then insert that same key with a different value, the value associated with that key will be replaced. Even though the code in Listing 8-23 calls `insert` twice, the hash map will -only contain one key/value pair because we’re inserting the value for the Blue +only contain one key-value pair because we’re inserting the value for the Blue team’s key both times. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-23/src/main.rs:here}} ``` -Listing 8-23: Replacing a value stored with a particular -key + This code will print `{"Blue": 25}`. The original value of `10` has been overwritten. + #### Adding a Key and Value Only If a Key Isn’t Present It’s common to check whether a particular key already exists in the hash map -with a value then take the following actions: if the key does exist in the hash -map, the existing value should remain the way it is. If the key doesn’t exist, -insert it and a value for it. +with a value and then to take the following actions: If the key does exist in +the hash map, the existing value should remain the way it is; if the key +doesn’t exist, insert it and a value for it. Hash maps have a special API for this called `entry` that takes the key you want to check as a parameter. The return value of the `entry` method is an enum called `Entry` that represents a value that might or might not exist. Let’s say we want to check whether the key for the Yellow team has a value associated -with it. If it doesn’t, we want to insert the value 50, and the same for the +with it. If it doesn’t, we want to insert the value `50`, and the same for the Blue team. Using the `entry` API, the code looks like Listing 8-24. ++ ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-24/src/main.rs:here}} ``` -Listing 8-24: Using the `entry` method to only insert if -the key does not already have a value + The `or_insert` method on `Entry` is defined to return a mutable reference to -the value for the corresponding `Entry` key if that key exists, and if not, +the value for the corresponding `Entry` key if that key exists, and if not, it inserts the parameter as the new value for this key and returns a mutable reference to the new value. This technique is much cleaner than writing the logic ourselves and, in addition, plays more nicely with the borrow checker. Running the code in Listing 8-24 will print `{"Yellow": 50, "Blue": 10}`. The first call to `entry` will insert the key for the Yellow team with the value -50 because the Yellow team doesn’t have a value already. The second call to -`entry` will not change the hash map because the Blue team already has the -value 10. +`50` because the Yellow team doesn’t have a value already. The second call to +`entry` will not change the hash map, because the Blue team already has the +value `10`. #### Updating a Value Based on the Old Value @@ -173,23 +182,24 @@ update it based on the old value. For instance, Listing 8-25 shows code that counts how many times each word appears in some text. We use a hash map with the words as keys and increment the value to keep track of how many times we’ve seen that word. If it’s the first time we’ve seen a word, we’ll first insert -the value 0. +the value `0`. + + ```rust {{#rustdoc_include ../listings/ch08-common-collections/listing-08-25/src/main.rs:here}} ``` -Listing 8-25: Counting occurrences of words using a hash -map that stores words and counts + This code will print `{"world": 2, "hello": 1, "wonderful": 1}`. You might see -the same key/value pairs printed in a different order: recall from the -[“Accessing Values in a Hash Map”][access] section that -iterating over a hash map happens in an arbitrary order. +the same key-value pairs printed in a different order: Recall from [“Accessing +Values in a Hash Map”][access] that iterating over a hash map +happens in an arbitrary order. -The `split_whitespace` method returns an iterator over sub-slices, separated by +The `split_whitespace` method returns an iterator over subslices, separated by whitespace, of the value in `text`. The `or_insert` method returns a mutable -reference (`&mut V`) to the value for the specified key. Here we store that +reference (`&mut V`) to the value for the specified key. Here, we store that mutable reference in the `count` variable, so in order to assign to that value, we must first dereference `count` using the asterisk (`*`). The mutable reference goes out of scope at the end of the `for` loop, so all of these @@ -197,18 +207,18 @@ changes are safe and allowed by the borrowing rules. ### Hashing Functions -By default, `HashMap` uses a hashing function called *SipHash* that can provide -resistance to Denial of Service (DoS) attacks involving hash +By default, `HashMap` uses a hashing function called _SipHash_ that can provide +resistance to denial-of-service (DoS) attacks involving hash tables[^siphash]. This is not the fastest hashing algorithm available, but the trade-off for better security that comes with the drop in performance is worth it. If you profile your code and find that the default hash function is too slow for your purposes, you can switch to another function -by specifying a different hasher. A *hasher* is a type that implements the +by specifying a different hasher. A _hasher_ is a type that implements the `BuildHasher` trait. We’ll talk about traits and how to implement them in -Chapter 10. You don’t necessarily have to implement your own hasher from -scratch; [crates.io](https://crates.io/) has libraries shared by -other Rust users that provide hashers implementing many common hashing -algorithms. +[Chapter 10][traits]. You don’t necessarily have to implement +your own hasher from scratch; [crates.io](https://crates.io/) +has libraries shared by other Rust users that provide hashers implementing many +common hashing algorithms. [^siphash]: [https://en.wikipedia.org/wiki/SipHash](https://en.wikipedia.org/wiki/SipHash) @@ -218,25 +228,25 @@ Vectors, strings, and hash maps will provide a large amount of functionality necessary in programs when you need to store, access, and modify data. Here are some exercises you should now be equipped to solve: -* Given a list of integers, use a vector and return the median (when sorted, - the value in the middle position) and mode (the value that occurs most often; - a hash map will be helpful here) of the list. -* Convert strings to pig latin. The first consonant of each word is moved to - the end of the word and “ay” is added, so “first” becomes “irst-fay.” Words - that start with a vowel have “hay” added to the end instead (“apple” becomes - “apple-hay”). Keep in mind the details about UTF-8 encoding! -* Using a hash map and vectors, create a text interface to allow a user to add - employee names to a department in a company. For example, “Add Sally to - Engineering” or “Add Amir to Sales.” Then let the user retrieve a list of all - people in a department or all people in the company by department, sorted - alphabetically. +1. Given a list of integers, use a vector and return the median (when sorted, + the value in the middle position) and mode (the value that occurs most + often; a hash map will be helpful here) of the list. +1. Convert strings to Pig Latin. The first consonant of each word is moved to + the end of the word and _ay_ is added, so _first_ becomes _irst-fay_. Words + that start with a vowel have _hay_ added to the end instead (_apple_ becomes + _apple-hay_). Keep in mind the details about UTF-8 encoding! +1. Using a hash map and vectors, create a text interface to allow a user to add + employee names to a department in a company; for example, “Add Sally to + Engineering” or “Add Amir to Sales.” Then, let the user retrieve a list of + all people in a department or all people in the company by department, sorted + alphabetically. The standard library API documentation describes methods that vectors, strings, and hash maps have that will be helpful for these exercises! -We’re getting into more complex programs in which operations can fail, so, it’s +We’re getting into more complex programs in which operations can fail, so it’s a perfect time to discuss error handling. We’ll do that next! -[validating-references-with-lifetimes]: -ch10-03-lifetime-syntax.html#validating-references-with-lifetimes +[validating-references-with-lifetimes]: ch10-03-lifetime-syntax.html#validating-references-with-lifetimes [access]: #accessing-values-in-a-hash-map +[traits]: ch10-02-traits.html diff --git a/src/ch09-00-error-handling.md b/src/ch09-00-error-handling.md index 790955c591..f32061c4ff 100644 --- a/src/ch09-00-error-handling.md +++ b/src/ch09-00-error-handling.md @@ -4,13 +4,13 @@ Errors are a fact of life in software, so Rust has a number of features for handling situations in which something goes wrong. In many cases, Rust requires you to acknowledge the possibility of an error and take some action before your code will compile. This requirement makes your program more robust by ensuring -that you’ll discover errors and handle them appropriately before you’ve -deployed your code to production! +that you’ll discover errors and handle them appropriately before deploying your +code to production! -Rust groups errors into two major categories: *recoverable* and *unrecoverable* -errors. For a recoverable error, such as a *file not found* error, we most +Rust groups errors into two major categories: recoverable and unrecoverable +errors. For a _recoverable error_, such as a _file not found_ error, we most likely just want to report the problem to the user and retry the operation. -Unrecoverable errors are always symptoms of bugs, like trying to access a +_Unrecoverable errors_ are always symptoms of bugs, such as trying to access a location beyond the end of an array, and so we want to immediately stop the program. diff --git a/src/ch09-01-unrecoverable-errors-with-panic.md b/src/ch09-01-unrecoverable-errors-with-panic.md index 5675fe3e76..f74ad3206c 100644 --- a/src/ch09-01-unrecoverable-errors-with-panic.md +++ b/src/ch09-01-unrecoverable-errors-with-panic.md @@ -1,6 +1,6 @@ ## Unrecoverable Errors with `panic!` -Sometimes, bad things happen in your code, and there’s nothing you can do about +Sometimes bad things happen in your code, and there’s nothing you can do about it. In these cases, Rust has the `panic!` macro. There are two ways to cause a panic in practice: by taking an action that causes our code to panic (such as accessing an array past the end) or by explicitly calling the `panic!` macro. @@ -11,18 +11,18 @@ panic occurs to make it easier to track down the source of the panic. > ### Unwinding the Stack or Aborting in Response to a Panic > -> By default, when a panic occurs, the program starts *unwinding*, which -> means Rust walks back up the stack and cleans up the data from each function -> it encounters. However, this walking back and cleanup is a lot of work. Rust, -> therefore, allows you to choose the alternative of immediately *aborting*, +> By default, when a panic occurs, the program starts _unwinding_, which means +> Rust walks back up the stack and cleans up the data from each function it +> encounters. However, walking back and cleaning up is a lot of work. Rust +> therefore allows you to choose the alternative of immediately _aborting_, > which ends the program without cleaning up. > -> Memory that the program was using will then need to be cleaned -> up by the operating system. If in your project you need to make the resulting -> binary as small as possible, you can switch from unwinding to aborting upon a -> panic by adding `panic = 'abort'` to the appropriate `[profile]` sections in -> your *Cargo.toml* file. For example, if you want to abort on panic in release -> mode, add this: +> Memory that the program was using will then need to be cleaned up by the +> operating system. If in your project you need to make the resultant binary as +> small as possible, you can switch from unwinding to aborting upon a panic by +> adding `panic = 'abort'` to the appropriate `[profile]` sections in your +> _Cargo.toml_ file. For example, if you want to abort on panic in release mode, +> add this: > > ```toml > [profile.release] @@ -31,12 +31,14 @@ panic occurs to make it easier to track down the source of the panic. Let’s try calling `panic!` in a simple program: -Filename: src/main.rs + ```rust,should_panic,panics {{#rustdoc_include ../listings/ch09-error-handling/no-listing-01-panic/src/main.rs}} ``` + + When you run the program, you’ll see something like this: ```console @@ -45,44 +47,44 @@ When you run the program, you’ll see something like this: The call to `panic!` causes the error message contained in the last two lines. The first line shows our panic message and the place in our source code where -the panic occurred: *src/main.rs:2:5* indicates that it’s the second line, -fifth character of our *src/main.rs* file. +the panic occurred: _src/main.rs:2:5_ indicates that it’s the second line, +fifth character of our _src/main.rs_ file. In this case, the line indicated is part of our code, and if we go to that line, we see the `panic!` macro call. In other cases, the `panic!` call might be in code that our code calls, and the filename and line number reported by the error message will be someone else’s code where the `panic!` macro is -called, not the line of our code that eventually led to the `panic!` call. We -can use the backtrace of the functions the `panic!` call came from to figure -out the part of our code that is causing the problem. We’ll discuss backtraces -in more detail next. +called, not the line of our code that eventually led to the `panic!` call. + + -### Using a `panic!` Backtrace + -Let’s look at another example to see what it’s like when a `panic!` call comes -from a library because of a bug in our code instead of from our code calling -the macro directly. Listing 9-1 has some code that attempts to access an -index in a vector beyond the range of valid indexes. +We can use the backtrace of the functions the `panic!` call came from to figure +out the part of our code that is causing the problem. To understand how to use +a `panic!` backtrace, let’s look at another example and see what it’s like when +a `panic!` call comes from a library because of a bug in our code instead of +from our code calling the macro directly. Listing 9-1 has some code that +attempts to access an index in a vector beyond the range of valid indexes. -Filename: src/main.rs + ```rust,should_panic,panics {{#rustdoc_include ../listings/ch09-error-handling/listing-09-01/src/main.rs}} ``` -Listing 9-1: Attempting to access an element beyond the -end of a vector, which will cause a call to `panic!` + Here, we’re attempting to access the 100th element of our vector (which is at -index 99 because indexing starts at zero), but the vector has only 3 elements. -In this situation, Rust will panic. Using `[]` is supposed to return an -element, but if you pass an invalid index, there’s no element that Rust could -return here that would be correct. +index 99 because indexing starts at zero), but the vector has only three +elements. In this situation, Rust will panic. Using `[]` is supposed to return +an element, but if you pass an invalid index, there’s no element that Rust +could return here that would be correct. In C, attempting to read beyond the end of a data structure is undefined behavior. You might get whatever is at the location in memory that would correspond to that element in the data structure, even though the memory -doesn’t belong to that structure. This is called a *buffer overread* and can +doesn’t belong to that structure. This is called a _buffer overread_ and can lead to security vulnerabilities if an attacker is able to manipulate the index in such a way as to read data they shouldn’t be allowed to that is stored after the data structure. @@ -95,18 +97,20 @@ continue. Let’s try it and see: {{#include ../listings/ch09-error-handling/listing-09-01/output.txt}} ``` -This error points at line 4 of our `main.rs` where we attempt to access index -99. The next note line tells us that we can set the `RUST_BACKTRACE` -environment variable to get a backtrace of exactly what happened to cause the -error. A *backtrace* is a list of all the functions that have been called to -get to this point. Backtraces in Rust work as they do in other languages: the -key to reading the backtrace is to start from the top and read until you see -files you wrote. That’s the spot where the problem originated. The lines above -that spot are code that your code has called; the lines below are code that -called your code. These before-and-after lines might include core Rust code, -standard library code, or crates that you’re using. Let’s try getting a -backtrace by setting the `RUST_BACKTRACE` environment variable to any value -except 0. Listing 9-2 shows output similar to what you’ll see. +This error points at line 4 of our _main.rs_ where we attempt to access index +99 of the vector in `v`. + +The `note:` line tells us that we can set the `RUST_BACKTRACE` environment +variable to get a backtrace of exactly what happened to cause the error. A +_backtrace_ is a list of all the functions that have been called to get to this +point. Backtraces in Rust work as they do in other languages: The key to +reading the backtrace is to start from the top and read until you see files you +wrote. That’s the spot where the problem originated. The lines above that spot +are code that your code has called; the lines below are code that called your +code. These before-and-after lines might include core Rust code, standard +library code, or crates that you’re using. Let’s try to get a backtrace by +setting the `RUST_BACKTRACE` environment variable to any value except `0`. +Listing 9-2 shows output similar to what you’ll see. ++ ```console $ RUST_BACKTRACE=1 cargo run -thread 'main' panicked at 'index out of bounds: the len is 3 but the index is 99', src/main.rs:4:5 +thread 'main' panicked at src/main.rs:4:6: +index out of bounds: the len is 3 but the index is 99 stack backtrace: 0: rust_begin_unwind - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/std/src/panicking.rs:584:5 + at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/std/src/panicking.rs:692:5 1: core::panicking::panic_fmt - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core/src/panicking.rs:142:14 + at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:75:14 2: core::panicking::panic_bounds_check - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core/src/panicking.rs:84:5 + at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:273:5 3: >::index - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core/src/slice/index.rs:242:10 + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/slice/index.rs:274:10 4: core::slice::index:: for [T]>::index - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core/src/slice/index.rs:18:9 + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/slice/index.rs:16:9 5: as core::ops::index::Index>::index - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/alloc/src/vec/mod.rs:2591:9 + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:3361:9 6: panic::main - at ./src/main.rs:4:5 + at ./src/main.rs:4:6 7: core::ops::function::FnOnce::call_once - at /rustc/e092d0b6b43f2de967af0887873151bb1c0b18d3/library/core/src/ops/function.rs:248:5 + at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5 note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. ``` -Listing 9-2: The backtrace generated by a call to -`panic!` displayed when the environment variable `RUST_BACKTRACE` is set + That’s a lot of output! The exact output you see might be different depending on your operating system and Rust version. In order to get backtraces with this @@ -148,7 +154,7 @@ default when using `cargo build` or `cargo run` without the `--release` flag, as we have here. In the output in Listing 9-2, line 6 of the backtrace points to the line in our -project that’s causing the problem: line 4 of *src/main.rs*. If we don’t want +project that’s causing the problem: line 4 of _src/main.rs_. If we don’t want our program to panic, we should start our investigation at the location pointed to by the first line mentioning a file we wrote. In Listing 9-1, where we deliberately wrote code that would panic, the way to fix the panic is to not @@ -161,5 +167,4 @@ handle error conditions in the [“To `panic!` or Not to `panic!`”][to-panic-or-not-to-panic] section later in this chapter. Next, we’ll look at how to recover from an error using `Result`. -[to-panic-or-not-to-panic]: -ch09-03-to-panic-or-not-to-panic.html#to-panic-or-not-to-panic +[to-panic-or-not-to-panic]: ch09-03-to-panic-or-not-to-panic.html#to-panic-or-not-to-panic diff --git a/src/ch09-02-recoverable-errors-with-result.md b/src/ch09-02-recoverable-errors-with-result.md index 2ee006f09d..fa26509d7a 100644 --- a/src/ch09-02-recoverable-errors-with-result.md +++ b/src/ch09-02-recoverable-errors-with-result.md @@ -1,10 +1,10 @@ ## Recoverable Errors with `Result` Most errors aren’t serious enough to require the program to stop entirely. -Sometimes, when a function fails, it’s for a reason that you can easily -interpret and respond to. For example, if you try to open a file and that -operation fails because the file doesn’t exist, you might want to create the -file instead of terminating the process. +Sometimes when a function fails, it’s for a reason that you can easily interpret +and respond to. For example, if you try to open a file and that operation fails +because the file doesn’t exist, you might want to create the file instead of +terminating the process. Recall from [“Handling Potential Failure with `Result`”][handle_failure] in Chapter 2 that the `Result` enum is defined as having two @@ -17,32 +17,32 @@ enum Result { } ``` -The `T` and `E` are generic type parameters: we’ll discuss generics in more +The `T` and `E` are generic type parameters: We’ll discuss generics in more detail in Chapter 10. What you need to know right now is that `T` represents the type of the value that will be returned in a success case within the `Ok` variant, and `E` represents the type of the error that will be returned in a failure case within the `Err` variant. Because `Result` has these generic type parameters, we can use the `Result` type and the functions defined on it in -many different situations where the successful value and error value we want to +many different situations where the success value and error value we want to return may differ. Let’s call a function that returns a `Result` value because the function could -fail. In Listing 9-3 we try to open a file. +fail. In Listing 9-3, we try to open a file. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch09-error-handling/listing-09-03/src/main.rs}} ``` -Listing 9-3: Opening a file + The return type of `File::open` is a `Result`. The generic parameter `T` has been filled in by the implementation of `File::open` with the type of the success value, `std::fs::File`, which is a file handle. The type of `E` used in the error value is `std::io::Error`. This return type means the call to `File::open` might succeed and return a file handle that we can read from or -write to. The function call also might fail: for example, the file might not +write to. The function call also might fail: For example, the file might not exist, or we might not have permission to access the file. The `File::open` function needs to have a way to tell us whether it succeeded or failed and at the same time give us either the file handle or error information. This @@ -52,21 +52,20 @@ In the case where `File::open` succeeds, the value in the variable `greeting_file_result` will be an instance of `Ok` that contains a file handle. In the case where it fails, the value in `greeting_file_result` will be an instance of `Err` that contains more information about the kind of error that -happened. +occurred. We need to add to the code in Listing 9-3 to take different actions depending on the value `File::open` returns. Listing 9-4 shows one way to handle the `Result` using a basic tool, the `match` expression that we discussed in Chapter 6. -Filename: src/main.rs + ```rust,should_panic {{#rustdoc_include ../listings/ch09-error-handling/listing-09-04/src/main.rs}} ``` -Listing 9-4: Using a `match` expression to handle the -`Result` variants that might be returned + Note that, like the `Option` enum, the `Result` enum and its variants have been brought into scope by the prelude, so we don’t need to specify `Result::` @@ -79,7 +78,7 @@ writing. The other arm of the `match` handles the case where we get an `Err` value from `File::open`. In this example, we’ve chosen to call the `panic!` macro. If -there’s no file named *hello.txt* in our current directory and we run this +there’s no file named _hello.txt_ in our current directory and we run this code, we’ll see the following output from the `panic!` macro: ```console @@ -91,14 +90,14 @@ As usual, this output tells us exactly what has gone wrong. ### Matching on Different Errors The code in Listing 9-4 will `panic!` no matter why `File::open` failed. -However, we want to take different actions for different failure reasons: if +However, we want to take different actions for different failure reasons. If `File::open` failed because the file doesn’t exist, we want to create the file and return the handle to the new file. If `File::open` failed for any other reason—for example, because we didn’t have permission to open the file—we still -want the code to `panic!` in the same way as it did in Listing 9-4. For this we +want the code to `panic!` in the same way it did in Listing 9-4. For this, we add an inner `match` expression, shown in Listing 9-5. -Filename: src/main.rs + @@ -107,16 +106,15 @@ tests to fail lol --> {{#rustdoc_include ../listings/ch09-error-handling/listing-09-05/src/main.rs}} ``` -Listing 9-5: Handling different kinds of errors in -different ways + The type of the value that `File::open` returns inside the `Err` variant is `io::Error`, which is a struct provided by the standard library. This struct -has a method `kind` that we can call to get an `io::ErrorKind` value. The enum -`io::ErrorKind` is provided by the standard library and has variants +has a method, `kind`, that we can call to get an `io::ErrorKind` value. The +enum `io::ErrorKind` is provided by the standard library and has variants representing the different kinds of errors that might result from an `io` operation. The variant we want to use is `ErrorKind::NotFound`, which indicates -the file we’re trying to open doesn’t exist yet. So we match on +the file we’re trying to open doesn’t exist yet. So, we match on `greeting_file_result`, but we also have an inner match on `error.kind()`. The condition we want to check in the inner match is whether the value returned @@ -127,7 +125,7 @@ file can’t be created, a different error message is printed. The second arm of the outer `match` stays the same, so the program panics on any error besides the missing file error. -> ### Alternatives to Using `match` with `Result` +> #### Alternatives to Using `match` with `Result` > > That’s a lot of `match`! The `match` expression is very useful but also very > much a primitive. In Chapter 13, you’ll learn about closures, which are used @@ -147,10 +145,10 @@ the missing file error. > let greeting_file = File::open("hello.txt").unwrap_or_else(|error| { > if error.kind() == ErrorKind::NotFound { > File::create("hello.txt").unwrap_or_else(|error| { -> panic!("Problem creating the file: {:?}", error); +> panic!("Problem creating the file: {error:?}"); > }) > } else { -> panic!("Problem opening the file: {:?}", error); +> panic!("Problem opening the file: {error:?}"); > } > }); > } @@ -158,11 +156,15 @@ the missing file error. > > Although this code has the same behavior as Listing 9-5, it doesn’t contain > any `match` expressions and is cleaner to read. Come back to this example -> after you’ve read Chapter 13, and look up the `unwrap_or_else` method in the -> standard library documentation. Many more of these methods can clean up huge +> after you’ve read Chapter 13 and look up the `unwrap_or_else` method in the +> standard library documentation. Many more of these methods can clean up huge, > nested `match` expressions when you’re dealing with errors. -### Shortcuts for Panic on Error: `unwrap` and `expect` + + + + +#### Shortcuts for Panic on Error Using `match` works well enough, but it can be a bit verbose and doesn’t always communicate intent well. The `Result` type has many helper methods @@ -172,13 +174,15 @@ Listing 9-4. If the `Result` value is the `Ok` variant, `unwrap` will return the value inside the `Ok`. If the `Result` is the `Err` variant, `unwrap` will call the `panic!` macro for us. Here is an example of `unwrap` in action: -Filename: src/main.rs + ```rust,should_panic {{#rustdoc_include ../listings/ch09-error-handling/no-listing-04-unwrap/src/main.rs}} ``` -If we run this code without a *hello.txt* file, we’ll see an error message from + + +If we run this code without a _hello.txt_ file, we’ll see an error message from the `panic!` call that the `unwrap` method makes: ```text -thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os { -code: 2, kind: NotFound, message: "No such file or directory" }', -src/main.rs:4:49 +thread 'main' panicked at src/main.rs:4:49: +called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" } ``` Similarly, the `expect` method lets us also choose the `panic!` error message. @@ -198,12 +201,14 @@ Using `expect` instead of `unwrap` and providing good error messages can convey your intent and make tracking down the source of a panic easier. The syntax of `expect` looks like this: -Filename: src/main.rs + ```rust,should_panic {{#rustdoc_include ../listings/ch09-error-handling/no-listing-05-expect/src/main.rs}} ``` + + We use `expect` in the same way as `unwrap`: to return the file handle or call the `panic!` macro. The error message used by `expect` in its call to `panic!` will be the parameter that we pass to `expect`, rather than the default @@ -216,9 +221,8 @@ copy and paste relevant text --> ```text -thread 'main' panicked at 'hello.txt should be included in this project: Os { -code: 2, kind: NotFound, message: "No such file or directory" }', -src/main.rs:5:10 +thread 'main' panicked at src/main.rs:5:10: +hello.txt should be included in this project: Os { code: 2, kind: NotFound, message: "No such file or directory" } ``` In production-quality code, most Rustaceans choose `expect` rather than @@ -230,7 +234,7 @@ information to use in debugging. When a function’s implementation calls something that might fail, instead of handling the error within the function itself, you can return the error to the -calling code so that it can decide what to do. This is known as *propagating* +calling code so that it can decide what to do. This is known as _propagating_ the error and gives more control to the calling code, where there might be more information or logic that dictates how the error should be handled than what you have available in the context of your code. @@ -239,7 +243,7 @@ For example, Listing 9-6 shows a function that reads a username from a file. If the file doesn’t exist or can’t be read, this function will return those errors to the code that called the function. -Filename: src/main.rs + {{#include ../listings/ch09-error-handling/listing-09-06/src/main.rs:here}} ``` -Listing 9-6: A function that returns errors to the -calling code using `match` + This function can be written in a much shorter way, but we’re going to start by doing a lot of it manually in order to explore error handling; at the end, we’ll show the shorter way. Let’s look at the return type of the function first: `Result`. This means the function is returning a -value of the type `Result` where the generic parameter `T` has been -filled in with the concrete type `String`, and the generic type `E` has been +value of the type `Result`, where the generic parameter `T` has been +filled in with the concrete type `String` and the generic type `E` has been filled in with the concrete type `io::Error`. If this function succeeds without any problems, the code that calls this -function will receive an `Ok` value that holds a `String`—the username that +function will receive an `Ok` value that holds a `String`—the `username` that this function read from the file. If this function encounters any problems, the calling code will receive an `Err` value that holds an instance of `io::Error` that contains more information about what the problems were. We chose @@ -270,7 +273,7 @@ type of the error value returned from both of the operations we’re calling in this function’s body that might fail: the `File::open` function and the `read_to_string` method. -The body of the function starts by calling the `File::open` function. Then we +The body of the function starts by calling the `File::open` function. Then, we handle the `Result` value with a `match` similar to the `match` in Listing 9-4. If `File::open` succeeds, the file handle in the pattern variable `file` becomes the value in the mutable variable `username_file` and the function @@ -279,12 +282,12 @@ keyword to return early out of the function entirely and pass the error value from `File::open`, now in the pattern variable `e`, back to the calling code as this function’s error value. -So if we have a file handle in `username_file`, the function then creates a new -`String` in variable `username` and calls the `read_to_string` method on +So, if we have a file handle in `username_file`, the function then creates a +new `String` in variable `username` and calls the `read_to_string` method on the file handle in `username_file` to read the contents of the file into `username`. The `read_to_string` method also returns a `Result` because it -might fail, even though `File::open` succeeded. So we need another `match` to -handle that `Result`: if `read_to_string` succeeds, then our function has +might fail, even though `File::open` succeeded. So, we need another `match` to +handle that `Result`: If `read_to_string` succeeds, then our function has succeeded, and we return the username from the file that’s now in `username` wrapped in an `Ok`. If `read_to_string` fails, we return the error value in the same way that we returned the error value in the `match` that handled the @@ -303,13 +306,17 @@ it to handle appropriately. This pattern of propagating errors is so common in Rust that Rust provides the question mark operator `?` to make this easier. -#### A Shortcut for Propagating Errors: the `?` Operator + + + + +#### The `?` Operator Shortcut Listing 9-7 shows an implementation of `read_username_from_file` that has the -same functionality as in Listing 9-6, but this implementation uses the -`?` operator. +same functionality as in Listing 9-6, but this implementation uses the `?` +operator. -Filename: src/main.rs + {{#include ../listings/ch09-error-handling/listing-09-07/src/main.rs:here}} ``` -Listing 9-7: A function that returns errors to the -calling code using the `?` operator + The `?` placed after a `Result` value is defined to work in almost the same way -as the `match` expressions we defined to handle the `Result` values in Listing -9-6. If the value of the `Result` is an `Ok`, the value inside the `Ok` will -get returned from this expression, and the program will continue. If the value -is an `Err`, the `Err` will be returned from the whole function as if we had -used the `return` keyword so the error value gets propagated to the calling -code. +as the `match` expressions that we defined to handle the `Result` values in +Listing 9-6. If the value of the `Result` is an `Ok`, the value inside the `Ok` +will get returned from this expression, and the program will continue. If the +value is an `Err`, the `Err` will be returned from the whole function as if we +had used the `return` keyword so that the error value gets propagated to the +calling code. There is a difference between what the `match` expression from Listing 9-6 does -and what the `?` operator does: error values that have the `?` operator called +and what the `?` operator does: Error values that have the `?` operator called on them go through the `from` function, defined in the `From` trait in the standard library, which is used to convert values from one type into another. When the `?` operator calls the `from` function, the error type received is @@ -357,7 +363,7 @@ The `?` operator eliminates a lot of boilerplate and makes this function’s implementation simpler. We could even shorten this code further by chaining method calls immediately after the `?`, as shown in Listing 9-8. -Filename: src/main.rs + {{#include ../listings/ch09-error-handling/listing-09-08/src/main.rs:here}} ``` -Listing 9-8: Chaining method calls after the `?` -operator + We’ve moved the creation of the new `String` in `username` to the beginning of the function; that part hasn’t changed. Instead of creating a variable @@ -381,7 +386,7 @@ this is just a different, more ergonomic way to write it. Listing 9-9 shows a way to make this even shorter using `fs::read_to_string`. -Filename: src/main.rs + {{#include ../listings/ch09-error-handling/listing-09-09/src/main.rs:here}} ``` -Listing 9-9: Using `fs::read_to_string` instead of -opening and then reading the file + Reading a file into a string is a fairly common operation, so the standard library provides the convenient `fs::read_to_string` function that opens the @@ -401,7 +405,11 @@ into that `String`, and returns it. Of course, using `fs::read_to_string` doesn’t give us the opportunity to explain all the error handling, so we did it the longer way first. -#### Where The `?` Operator Can Be Used + + + + +#### Where to Use the `?` Operator The `?` operator can only be used in functions whose return type is compatible with the value the `?` is used on. This is because the `?` operator is defined @@ -412,17 +420,16 @@ as the `match` expression we defined in Listing 9-6. In Listing 9-6, the it’s compatible with this `return`. In Listing 9-10, let’s look at the error we’ll get if we use the `?` operator -in a `main` function with a return type incompatible with the type of the value -we use `?` on: +in a `main` function with a return type that is incompatible with the type of +the value we use `?` on. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch09-error-handling/listing-09-10/src/main.rs}} ``` -Listing 9-10: Attempting to use the `?` in the `main` -function that returns `()` won’t compile + This code opens a file, which might fail. The `?` operator follows the `Result` value returned by `File::open`, but this `main` function has the return type of @@ -439,26 +446,27 @@ function that returns `Result`, `Option`, or another type that implements To fix the error, you have two choices. One choice is to change the return type of your function to be compatible with the value you’re using the `?` operator -on as long as you have no restrictions preventing that. The other technique is -to use a `match` or one of the `Result` methods to handle the `Result` in whatever way is appropriate. +on as long as you have no restrictions preventing that. The other choice is to +use a `match` or one of the `Result` methods to handle the `Result` +in whatever way is appropriate. The error message also mentioned that `?` can be used with `Option` values as well. As with using `?` on `Result`, you can only use `?` on `Option` in a function that returns an `Option`. The behavior of the `?` operator when called on an `Option` is similar to its behavior when called on a `Result`: -if the value is `None`, the `None` will be returned early from the function at +If the value is `None`, the `None` will be returned early from the function at that point. If the value is `Some`, the value inside the `Some` is the -resulting value of the expression and the function continues. Listing 9-11 has +resultant value of the expression, and the function continues. Listing 9-11 has an example of a function that finds the last character of the first line in the -given text: +given text. + + ```rust {{#rustdoc_include ../listings/ch09-error-handling/listing-09-11/src/main.rs:here}} ``` -Listing 9-11: Using the `?` operator on an `Option` -value + This function returns `Option` because it’s possible that there is a character there, but it’s also possible that there isn’t. This code takes the @@ -474,7 +482,7 @@ The `?` extracts the string slice, and we can call `chars` on that string slice to get an iterator of its characters. We’re interested in the last character in this first line, so we call `last` to return the last item in the iterator. This is an `Option` because it’s possible that the first line is the empty -string, for example if `text` starts with a blank line but has characters on +string; for example, if `text` starts with a blank line but has characters on other lines, as in `"\nhi"`. However, if there is a last character on the first line, it will be returned in the `Some` variant. The `?` operator in the middle gives us a concise way to express this logic, allowing us to implement the @@ -489,38 +497,39 @@ you can use methods like the `ok` method on `Result` or the `ok_or` method on `Option` to do the conversion explicitly. So far, all the `main` functions we’ve used return `()`. The `main` function is -special because it’s the entry and exit point of executable programs, and there -are restrictions on what its return type can be for the programs to behave as -expected. +special because it’s the entry point and exit point of an executable program, +and there are restrictions on what its return type can be for the program to +behave as expected. -Luckily, `main` can also return a `Result<(), E>`. Listing 9-12 has the -code from Listing 9-10 but we’ve changed the return type of `main` to be +Luckily, `main` can also return a `Result<(), E>`. Listing 9-12 has the code +from Listing 9-10, but we’ve changed the return type of `main` to be `Result<(), Box>` and added a return value `Ok(())` to the end. This -code will now compile: +code will now compile. + + ```rust,ignore {{#rustdoc_include ../listings/ch09-error-handling/listing-09-12/src/main.rs}} ``` -Listing 9-12: Changing `main` to return `Result<(), E>` -allows the use of the `?` operator on `Result` values - -The `Box` type is a *trait object*, which we’ll talk about in the -[“Using Trait Objects that Allow for Values of Different -Types”][trait-objects] section in Chapter 17. For now, you can -read `Box` to mean “any kind of error.” Using `?` on a `Result` -value in a `main` function with the error type `Box` is allowed, -because it allows any `Err` value to be returned early. Even though the body of -this `main` function will only ever return errors of type `std::io::Error`, by -specifying `Box`, this signature will continue to be correct even if -more code that returns other errors is added to the body of `main`. - -When a `main` function returns a `Result<(), E>`, the executable will -exit with a value of `0` if `main` returns `Ok(())` and will exit with a -nonzero value if `main` returns an `Err` value. Executables written in C return -integers when they exit: programs that exit successfully return the integer -`0`, and programs that error return some integer other than `0`. Rust also -returns integers from executables to be compatible with this convention. + + +The `Box` type is a trait object, which we’ll talk about in [“Using +Trait Objects to Abstract over Shared Behavior”][trait-objects] +in Chapter 18. For now, you can read `Box` to mean “any kind of +error.” Using `?` on a `Result` value in a `main` function with the error type +`Box` is allowed because it allows any `Err` value to be returned +early. Even though the body of this `main` function will only ever return +errors of type `std::io::Error`, by specifying `Box`, this signature +will continue to be correct even if more code that returns other errors is +added to the body of `main`. + +When a `main` function returns a `Result<(), E>`, the executable will exit with +a value of `0` if `main` returns `Ok(())` and will exit with a nonzero value if +`main` returns an `Err` value. Executables written in C return integers when +they exit: Programs that exit successfully return the integer `0`, and programs +that error return some integer other than `0`. Rust also returns integers from +executables to be compatible with this convention. The `main` function may return any types that implement [the `std::process::Termination` trait][termination], which contains @@ -533,5 +542,5 @@ let’s return to the topic of how to decide which is appropriate to use in whic cases. [handle_failure]: ch02-00-guessing-game-tutorial.html#handling-potential-failure-with-result -[trait-objects]: ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types +[trait-objects]: ch18-02-trait-objects.html#using-trait-objects-to-abstract-over-shared-behavior [termination]: ../std/process/trait.Termination.html diff --git a/src/ch09-03-to-panic-or-not-to-panic.md b/src/ch09-03-to-panic-or-not-to-panic.md index 7c77cf9331..256c367f5f 100644 --- a/src/ch09-03-to-panic-or-not-to-panic.md +++ b/src/ch09-03-to-panic-or-not-to-panic.md @@ -1,6 +1,6 @@ ## To `panic!` or Not to `panic!` -So how do you decide when you should call `panic!` and when you should return +So, how do you decide when you should call `panic!` and when you should return `Result`? When code panics, there’s no way to recover. You could call `panic!` for any error situation, whether there’s a possible way to recover or not, but then you’re making the decision that a situation is unrecoverable on behalf of @@ -19,32 +19,37 @@ some general guidelines on how to decide whether to panic in library code. ### Examples, Prototype Code, and Tests -When you’re writing an example to illustrate some concept, also including robust -error-handling code can make the example less clear. In -examples, it’s understood that a call to a method like `unwrap` that could -panic is meant as a placeholder for the way you’d want your application to -handle errors, which can differ based on what the rest of your code is doing. +When you’re writing an example to illustrate some concept, also including +robust error-handling code can make the example less clear. In examples, it’s +understood that a call to a method like `unwrap` that could panic is meant as a +placeholder for the way you’d want your application to handle errors, which can +differ based on what the rest of your code is doing. -Similarly, the `unwrap` and `expect` methods are very handy when prototyping, -before you’re ready to decide how to handle errors. They leave clear markers in -your code for when you’re ready to make your program more robust. +Similarly, the `unwrap` and `expect` methods are very handy when you’re +prototyping and you’re not yet ready to decide how to handle errors. They leave +clear markers in your code for when you’re ready to make your program more +robust. If a method call fails in a test, you’d want the whole test to fail, even if that method isn’t the functionality under test. Because `panic!` is how a test is marked as a failure, calling `unwrap` or `expect` is exactly what should happen. -### Cases in Which You Have More Information Than the Compiler + -It would also be appropriate to call `unwrap` or `expect` when you have some -other logic that ensures the `Result` will have an `Ok` value, but the logic -isn’t something the compiler understands. You’ll still have a `Result` value -that you need to handle: whatever operation you’re calling still has the -possibility of failing in general, even though it’s logically impossible in -your particular situation. If you can ensure by manually inspecting the code -that you’ll never have an `Err` variant, it’s perfectly acceptable to call -`unwrap`, and even better to document the reason you think you’ll never have an -`Err` variant in the `expect` text. Here’s an example: + + +### When You Have More Information Than the Compiler + +It would also be appropriate to call `expect` when you have some other logic +that ensures that the `Result` will have an `Ok` value, but the logic isn’t +something the compiler understands. You’ll still have a `Result` value that you +need to handle: Whatever operation you’re calling still has the possibility of +failing in general, even though it’s logically impossible in your particular +situation. If you can ensure by manually inspecting the code that you’ll never +have an `Err` variant, it’s perfectly acceptable to call `expect` and document +the reason you think you’ll never have an `Err` variant in the argument text. +Here’s an example: ```rust {{#rustdoc_include ../listings/ch09-error-handling/no-listing-08-unwrap-that-cant-fail/src/main.rs:here}} @@ -53,41 +58,41 @@ that you’ll never have an `Err` variant, it’s perfectly acceptable to call We’re creating an `IpAddr` instance by parsing a hardcoded string. We can see that `127.0.0.1` is a valid IP address, so it’s acceptable to use `expect` here. However, having a hardcoded, valid string doesn’t change the return type -of the `parse` method: we still get a `Result` value, and the compiler will +of the `parse` method: We still get a `Result` value, and the compiler will still make us handle the `Result` as if the `Err` variant is a possibility because the compiler isn’t smart enough to see that this string is always a valid IP address. If the IP address string came from a user rather than being -hardcoded into the program and therefore *did* have a possibility of failure, +hardcoded into the program and therefore _did_ have a possibility of failure, we’d definitely want to handle the `Result` in a more robust way instead. Mentioning the assumption that this IP address is hardcoded will prompt us to -change `expect` to better error handling code if in the future, we need to get +change `expect` to better error-handling code if, in the future, we need to get the IP address from some other source instead. ### Guidelines for Error Handling -It’s advisable to have your code panic when it’s possible that your code -could end up in a bad state. In this context, a *bad state* is when some -assumption, guarantee, contract, or invariant has been broken, such as when -invalid values, contradictory values, or missing values are passed to your -code—plus one or more of the following: +It’s advisable to have your code panic when it’s possible that your code could +end up in a bad state. In this context, a _bad state_ is when some assumption, +guarantee, contract, or invariant has been broken, such as when invalid values, +contradictory values, or missing values are passed to your code—plus one or +more of the following: -* The bad state is something that is unexpected, as opposed to something that +- The bad state is something that is unexpected, as opposed to something that will likely happen occasionally, like a user entering data in the wrong format. -* Your code after this point needs to rely on not being in this bad state, +- Your code after this point needs to rely on not being in this bad state, rather than checking for the problem at every step. -* There’s not a good way to encode this information in the types you use. We’ll - work through an example of what we mean in the [“Encoding States and Behavior - as Types”][encoding] section of Chapter 17. +- There’s not a good way to encode this information in the types you use. We’ll + work through an example of what we mean in [“Encoding States and Behavior as + Types”][encoding] in Chapter 18. If someone calls your code and passes in values that don’t make sense, it’s -best to return an error if you can so the user of the library can decide what -they want to do in that case. However, in cases where continuing could be +best to return an error if you can so that the user of the library can decide +what they want to do in that case. However, in cases where continuing could be insecure or harmful, the best choice might be to call `panic!` and alert the -person using your library to the bug in their code so they can fix it during -development. Similarly, `panic!` is often appropriate if you’re calling -external code that is out of your control and it returns an invalid state that -you have no way of fixing. +person using your library to the bug in their code so that they can fix it +during development. Similarly, `panic!` is often appropriate if you’re calling +external code that is out of your control and returns an invalid state that you +have no way of fixing. However, when failure is expected, it’s more appropriate to return a `Result` than to make a `panic!` call. Examples include a parser being given malformed @@ -98,15 +103,15 @@ expected possibility that the calling code must decide how to handle. When your code performs an operation that could put a user at risk if it’s called using invalid values, your code should verify the values are valid first and panic if the values aren’t valid. This is mostly for safety reasons: -attempting to operate on invalid data can expose your code to vulnerabilities. +Attempting to operate on invalid data can expose your code to vulnerabilities. This is the main reason the standard library will call `panic!` if you attempt -an out-of-bounds memory access: trying to access memory that doesn’t belong to +an out-of-bounds memory access: Trying to access memory that doesn’t belong to the current data structure is a common security problem. Functions often have -*contracts*: their behavior is only guaranteed if the inputs meet particular +_contracts_: Their behavior is only guaranteed if the inputs meet particular requirements. Panicking when the contract is violated makes sense because a -contract violation always indicates a caller-side bug and it’s not a kind of +contract violation always indicates a caller-side bug, and it’s not a kind of error you want the calling code to have to explicitly handle. In fact, there’s -no reasonable way for calling code to recover; the calling *programmers* need +no reasonable way for calling code to recover; the calling _programmers_ need to fix the code. Contracts for a function, especially when a violation will cause a panic, should be explained in the API documentation for the function. @@ -114,70 +119,77 @@ However, having lots of error checks in all of your functions would be verbose and annoying. Fortunately, you can use Rust’s type system (and thus the type checking done by the compiler) to do many of the checks for you. If your function has a particular type as a parameter, you can proceed with your code’s -logic knowing that the compiler has already ensured you have a valid value. For -example, if you have a type rather than an `Option`, your program expects to -have *something* rather than *nothing*. Your code then doesn’t have to handle -two cases for the `Some` and `None` variants: it will only have one case for -definitely having a value. Code trying to pass nothing to your function won’t -even compile, so your function doesn’t have to check for that case at runtime. -Another example is using an unsigned integer type such as `u32`, which ensures -the parameter is never negative. - -### Creating Custom Types for Validation - -Let’s take the idea of using Rust’s type system to ensure we have a valid value -one step further and look at creating a custom type for validation. Recall the -guessing game in Chapter 2 in which our code asked the user to guess a number -between 1 and 100. We never validated that the user’s guess was between those -numbers before checking it against our secret number; we only validated that -the guess was positive. In this case, the consequences were not very dire: our -output of “Too high” or “Too low” would still be correct. But it would be a -useful enhancement to guide the user toward valid guesses and have different -behavior when a user guesses a number that’s out of range versus when a user -types, for example, letters instead. +logic knowing that the compiler has already ensured that you have a valid +value. For example, if you have a type rather than an `Option`, your program +expects to have _something_ rather than _nothing_. Your code then doesn’t have +to handle two cases for the `Some` and `None` variants: It will only have one +case for definitely having a value. Code trying to pass nothing to your +function won’t even compile, so your function doesn’t have to check for that +case at runtime. Another example is using an unsigned integer type such as +`u32`, which ensures that the parameter is never negative. + + + + + +### Custom Types for Validation + +Let’s take the idea of using Rust’s type system to ensure that we have a valid +value one step further and look at creating a custom type for validation. +Recall the guessing game in Chapter 2 in which our code asked the user to guess +a number between 1 and 100. We never validated that the user’s guess was +between those numbers before checking it against our secret number; we only +validated that the guess was positive. In this case, the consequences were not +very dire: Our output of “Too high” or “Too low” would still be correct. But it +would be a useful enhancement to guide the user toward valid guesses and have +different behavior when the user guesses a number that’s out of range versus +when the user types, for example, letters instead. One way to do this would be to parse the guess as an `i32` instead of only a `u32` to allow potentially negative numbers, and then add a check for the number being in range, like so: ++ ```rust,ignore {{#rustdoc_include ../listings/ch09-error-handling/no-listing-09-guess-out-of-range/src/main.rs:here}} ``` + + The `if` expression checks whether our value is out of range, tells the user about the problem, and calls `continue` to start the next iteration of the loop and ask for another guess. After the `if` expression, we can proceed with the comparisons between `guess` and the secret number knowing that `guess` is between 1 and 100. -However, this is not an ideal solution: if it was absolutely critical that the +However, this is not an ideal solution: If it were absolutely critical that the program only operated on values between 1 and 100, and it had many functions with this requirement, having a check like this in every function would be tedious (and might impact performance). -Instead, we can make a new type and put the validations in a function to create -an instance of the type rather than repeating the validations everywhere. That -way, it’s safe for functions to use the new type in their signatures and -confidently use the values they receive. Listing 9-13 shows one way to define a -`Guess` type that will only create an instance of `Guess` if the `new` function -receives a value between 1 and 100. +Instead, we can make a new type in a dedicated module and put the validations +in a function to create an instance of the type rather than repeating the +validations everywhere. That way, it’s safe for functions to use the new type +in their signatures and confidently use the values they receive. Listing 9-13 +shows one way to define a `Guess` type that will only create an instance of +`Guess` if the `new` function receives a value between 1 and 100. - + ```rust -{{#include ../listings/ch09-error-handling/listing-09-13/src/main.rs:here}} +{{#rustdoc_include ../listings/ch09-error-handling/listing-09-13/src/guessing_game.rs}} ``` -Listing 9-13: A `Guess` type that will only continue with -values between 1 and 100 + -First, we define a struct named `Guess` that has a field named `value` that -holds an `i32`. This is where the number will be stored. +Note that this code in *src/guessing_game.rs* depends on adding a module +declaration `mod guessing_game;` in *src/lib.rs* that we haven’t shown here. +Within this new module’s file, we define a struct named `Guess` that has a +field named `value` that holds an `i32`. This is where the number will be +stored. -Then we implement an associated function named `new` on `Guess` that creates +Then, we implement an associated function named `new` on `Guess` that creates instances of `Guess` values. The `new` function is defined to have one parameter named `value` of type `i32` and to return a `Guess`. The code in the body of the `new` function tests `value` to make sure it’s between 1 and 100. @@ -193,13 +205,14 @@ to the `value` parameter and return the `Guess`. Next, we implement a method named `value` that borrows `self`, doesn’t have any other parameters, and returns an `i32`. This kind of method is sometimes called -a *getter*, because its purpose is to get some data from its fields and return +a _getter_ because its purpose is to get some data from its fields and return it. This public method is necessary because the `value` field of the `Guess` -struct is private. It’s important that the `value` field be private so code -using the `Guess` struct is not allowed to set `value` directly: code outside -the module *must* use the `Guess::new` function to create an instance of -`Guess`, thereby ensuring there’s no way for a `Guess` to have a `value` that -hasn’t been checked by the conditions in the `Guess::new` function. +struct is private. It’s important that the `value` field be private so that +code using the `Guess` struct is not allowed to set `value` directly: Code +outside the `guessing_game` module _must_ use the `Guess::new` function to +create an instance of `Guess`, thereby ensuring that there’s no way for a +`Guess` to have a `value` that hasn’t been checked by the conditions in the +`Guess::new` function. A function that has a parameter or returns only numbers between 1 and 100 could then declare in its signature that it takes or returns a `Guess` rather than an @@ -207,7 +220,7 @@ then declare in its signature that it takes or returns a `Guess` rather than an ## Summary -Rust’s error handling features are designed to help you write more robust code. +Rust’s error-handling features are designed to help you write more robust code. The `panic!` macro signals that your program is in a state it can’t handle and lets you tell the process to stop instead of trying to proceed with invalid or incorrect values. The `Result` enum uses Rust’s type system to indicate that @@ -220,4 +233,4 @@ Now that you’ve seen useful ways that the standard library uses generics with the `Option` and `Result` enums, we’ll talk about how generics work and how you can use them in your code. -[encoding]: ch17-03-oo-design-patterns.html#encoding-states-and-behavior-as-types +[encoding]: ch18-03-oo-design-patterns.html#encoding-states-and-behavior-as-types diff --git a/src/ch10-00-generics.md b/src/ch10-00-generics.md index bfe7ad3eec..7e1055fdc6 100644 --- a/src/ch10-00-generics.md +++ b/src/ch10-00-generics.md @@ -1,16 +1,16 @@ # Generic Types, Traits, and Lifetimes Every programming language has tools for effectively handling the duplication -of concepts. In Rust, one such tool is *generics*: abstract stand-ins for +of concepts. In Rust, one such tool is _generics_: abstract stand-ins for concrete types or other properties. We can express the behavior of generics or how they relate to other generics without knowing what will be in their place when compiling and running the code. Functions can take parameters of some generic type, instead of a concrete type -like `i32` or `String`, in the same way a function takes parameters with -unknown values to run the same code on multiple concrete values. In fact, we’ve -already used generics in Chapter 6 with `Option`, Chapter 8 with `Vec` -and `HashMap`, and Chapter 9 with `Result`. In this chapter, you’ll +like `i32` or `String`, in the same way they take parameters with unknown +values to run the same code on multiple concrete values. In fact, we already +used generics in Chapter 6 with `Option`, in Chapter 8 with `Vec` and +`HashMap`, and in Chapter 9 with `Result`. In this chapter, you’ll explore how to define your own types, functions, and methods with generics! First, we’ll review how to extract a function to reduce code duplication. We’ll @@ -18,83 +18,80 @@ then use the same technique to make a generic function from two functions that differ only in the types of their parameters. We’ll also explain how to use generic types in struct and enum definitions. -Then you’ll learn how to use *traits* to define behavior in a generic way. You +Then, you’ll learn how to use traits to define behavior in a generic way. You can combine traits with generic types to constrain a generic type to accept only those types that have a particular behavior, as opposed to just any type. -Finally, we’ll discuss *lifetimes*: a variety of generics that give the +Finally, we’ll discuss _lifetimes_: a variety of generics that give the compiler information about how references relate to each other. Lifetimes allow us to give the compiler enough information about borrowed values so that it can -ensure references will be valid in more situations than it could without our -help. +ensure that references will be valid in more situations than it could without +our help. ## Removing Duplication by Extracting a Function Generics allow us to replace specific types with a placeholder that represents multiple types to remove code duplication. Before diving into generics syntax, -then, let’s first look at how to remove duplication in a way that doesn’t -involve generic types by extracting a function that replaces specific values -with a placeholder that represents multiple values. Then we’ll apply the same +let’s first look at how to remove duplication in a way that doesn’t involve +generic types by extracting a function that replaces specific values with a +placeholder that represents multiple values. Then, we’ll apply the same technique to extract a generic function! By looking at how to recognize duplicated code you can extract into a function, you’ll start to recognize duplicated code that can use generics. -We begin with the short program in Listing 10-1 that finds the largest number -in a list. +We’ll begin with the short program in Listing 10-1 that finds the largest +number in a list. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/src/main.rs:here}} ``` -Listing 10-1: Finding the largest number in a list of -numbers + We store a list of integers in the variable `number_list` and place a reference to the first number in the list in a variable named `largest`. We then iterate through all the numbers in the list, and if the current number is greater than -the number stored in `largest`, replace the reference in that variable. +the number stored in `largest`, we replace the reference in that variable. However, if the current number is less than or equal to the largest number seen so far, the variable doesn’t change, and the code moves on to the next number in the list. After considering all the numbers in the list, `largest` should refer to the largest number, which in this case is 100. -We've now been tasked with finding the largest number in two different lists of +We’ve now been tasked with finding the largest number in two different lists of numbers. To do so, we can choose to duplicate the code in Listing 10-1 and use the same logic at two different places in the program, as shown in Listing 10-2. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/src/main.rs}} ``` -Listing 10-2: Code to find the largest number in *two* -lists of numbers + -Although this code works, duplicating code is tedious and error prone. We also +Although this code works, duplicating code is tedious and error-prone. We also have to remember to update the code in multiple places when we want to change it. To eliminate this duplication, we’ll create an abstraction by defining a -function that operates on any list of integers passed in a parameter. This +function that operates on any list of integers passed in as a parameter. This solution makes our code clearer and lets us express the concept of finding the largest number in a list abstractly. In Listing 10-3, we extract the code that finds the largest number into a -function named `largest`. Then we call the function to find the largest number +function named `largest`. Then, we call the function to find the largest number in the two lists from Listing 10-2. We could also use the function on any other list of `i32` values we might have in the future. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/src/main.rs:here}} ``` -Listing 10-3: Abstracted code to find the largest number -in two lists + The `largest` function has a parameter called `list`, which represents any concrete slice of `i32` values we might pass into the function. As a result, @@ -105,9 +102,9 @@ In summary, here are the steps we took to change the code from Listing 10-2 to Listing 10-3: 1. Identify duplicate code. -2. Extract the duplicate code into the body of the function and specify the +1. Extract the duplicate code into the body of the function, and specify the inputs and return values of that code in the function signature. -3. Update the two instances of duplicated code to call the function instead. +1. Update the two instances of duplicated code to call the function instead. Next, we’ll use these same steps with generics to reduce code duplication. In the same way that the function body can operate on an abstract `list` instead diff --git a/src/ch10-01-syntax.md b/src/ch10-01-syntax.md index 431dba9667..8a13a252e0 100644 --- a/src/ch10-01-syntax.md +++ b/src/ch10-01-syntax.md @@ -3,7 +3,7 @@ We use generics to create definitions for items like function signatures or structs, which we can then use with many different concrete data types. Let’s first look at how to define functions, structs, enums, and methods using -generics. Then we’ll discuss how generics affect code performance. +generics. Then, we’ll discuss how generics affect code performance. ### In Function Definitions @@ -13,17 +13,16 @@ parameters and return value. Doing so makes our code more flexible and provides more functionality to callers of our function while preventing code duplication. Continuing with our `largest` function, Listing 10-4 shows two functions that -both find the largest value in a slice. We'll then combine these into a single +both find the largest value in a slice. We’ll then combine these into a single function that uses generics. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/src/main.rs:here}} ``` -Listing 10-4: Two functions that differ only in their -names and the types in their signatures + The `largest_i32` function is the one we extracted in Listing 10-3 that finds the largest `i32` in a slice. The `largest_char` function finds the largest @@ -33,39 +32,38 @@ the duplication by introducing a generic type parameter in a single function. To parameterize the types in a new single function, we need to name the type parameter, just as we do for the value parameters to a function. You can use any identifier as a type parameter name. But we’ll use `T` because, by -convention, type parameter names in Rust are short, often just a letter, and -Rust’s type-naming convention is UpperCamelCase. Short for “type,” `T` is the +convention, type parameter names in Rust are short, often just one letter, and +Rust’s type-naming convention is UpperCamelCase. Short for _type_, `T` is the default choice of most Rust programmers. When we use a parameter in the body of the function, we have to declare the -parameter name in the signature so the compiler knows what that name means. -Similarly, when we use a type parameter name in a function signature, we have -to declare the type parameter name before we use it. To define the generic -`largest` function, place type name declarations inside angle brackets, `<>`, -between the name of the function and the parameter list, like this: +parameter name in the signature so that the compiler knows what that name +means. Similarly, when we use a type parameter name in a function signature, we +have to declare the type parameter name before we use it. To define the generic +`largest` function, we place type name declarations inside angle brackets, +`<>`, between the name of the function and the parameter list, like this: ```rust,ignore fn largest(list: &[T]) -> &T { ``` -We read this definition as: the function `largest` is generic over some type -`T`. This function has one parameter named `list`, which is a slice of values +We read this definition as “The function `largest` is generic over some type +`T`.” This function has one parameter named `list`, which is a slice of values of type `T`. The `largest` function will return a reference to a value of the same type `T`. Listing 10-5 shows the combined `largest` function definition using the generic data type in its signature. The listing also shows how we can call the function with either a slice of `i32` values or `char` values. Note that this code won’t -compile yet, but we’ll fix it later in this chapter. +compile yet. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/src/main.rs}} ``` -Listing 10-5: The `largest` function using generic type -parameters; this doesn’t yet compile + If we compile this code right now, we’ll get this error: @@ -73,16 +71,16 @@ If we compile this code right now, we’ll get this error: {{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/output.txt}} ``` -The help text mentions `std::cmp::PartialOrd`, which is a *trait*, and we’re +The help text mentions `std::cmp::PartialOrd`, which is a trait, and we’re going to talk about traits in the next section. For now, know that this error states that the body of `largest` won’t work for all possible types that `T` could be. Because we want to compare values of type `T` in the body, we can only use types whose values can be ordered. To enable comparisons, the standard library has the `std::cmp::PartialOrd` trait that you can implement on types -(see Appendix C for more on this trait). By following the help text's -suggestion, we restrict the types valid for `T` to only those that implement -`PartialOrd` and this example will compile, because the standard library -implements `PartialOrd` on both `i32` and `char`. +(see Appendix C for more on this trait). To fix Listing 10-5, we can follow the +help text’s suggestion and restrict the types valid for `T` to only those that +implement `PartialOrd`. The listing will then compile, because the standard +library implements `PartialOrd` on both `i32` and `char`. ### In Struct Definitions @@ -90,39 +88,37 @@ We can also define structs to use a generic type parameter in one or more fields using the `<>` syntax. Listing 10-6 defines a `Point` struct to hold `x` and `y` coordinate values of any type. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-06/src/main.rs}} ``` -Listing 10-6: A `Point` struct that holds `x` and `y` -values of type `T` + The syntax for using generics in struct definitions is similar to that used in function definitions. First, we declare the name of the type parameter inside -angle brackets just after the name of the struct. Then we use the generic type +angle brackets just after the name of the struct. Then, we use the generic type in the struct definition where we would otherwise specify concrete data types. Note that because we’ve used only one generic type to define `Point`, this definition says that the `Point` struct is generic over some type `T`, and -the fields `x` and `y` are *both* that same type, whatever that type may be. If +the fields `x` and `y` are _both_ that same type, whatever that type may be. If we create an instance of a `Point` that has values of different types, as in Listing 10-7, our code won’t compile. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/src/main.rs}} ``` -Listing 10-7: The fields `x` and `y` must be the same -type because both have the same generic data type `T`. + -In this example, when we assign the integer value 5 to `x`, we let the compiler -know that the generic type `T` will be an integer for this instance of -`Point`. Then when we specify 4.0 for `y`, which we’ve defined to have the -same type as `x`, we’ll get a type mismatch error like this: +In this example, when we assign the integer value `5` to `x`, we let the +compiler know that the generic type `T` will be an integer for this instance of +`Point`. Then, when we specify `4.0` for `y`, which we’ve defined to have +the same type as `x`, we’ll get a type mismatch error like this: ```console {{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/output.txt}} @@ -133,18 +129,17 @@ different types, we can use multiple generic type parameters. For example, in Listing 10-8, we change the definition of `Point` to be generic over types `T` and `U` where `x` is of type `T` and `y` is of type `U`. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-08/src/main.rs}} ``` -Listing 10-8: A `Point` generic over two types so -that `x` and `y` can be values of different types + Now all the instances of `Point` shown are allowed! You can use as many generic type parameters in a definition as you want, but using more than a few makes -your code hard to read. If you're finding you need lots of generic types in +your code hard to read. If you’re finding you need lots of generic types in your code, it could indicate that your code needs restructuring into smaller pieces. @@ -194,94 +189,90 @@ avoid duplication by using generic types instead. ### In Method Definitions We can implement methods on structs and enums (as we did in Chapter 5) and use -generic types in their definitions, too. Listing 10-9 shows the `Point` +generic types in their definitions too. Listing 10-9 shows the `Point` struct we defined in Listing 10-6 with a method named `x` implemented on it. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-09/src/main.rs}} ``` -Listing 10-9: Implementing a method named `x` on the -`Point` struct that will return a reference to the `x` field of type -`T` + Here, we’ve defined a method named `x` on `Point` that returns a reference to the data in the field `x`. -Note that we have to declare `T` just after `impl` so we can use `T` to specify -that we’re implementing methods on the type `Point`. By declaring `T` as a -generic type after `impl`, Rust can identify that the type in the angle -brackets in `Point` is a generic type rather than a concrete type. We could -have chosen a different name for this generic parameter than the generic +Note that we have to declare `T` just after `impl` so that we can use `T` to +specify that we’re implementing methods on the type `Point`. By declaring +`T` as a generic type after `impl`, Rust can identify that the type in the +angle brackets in `Point` is a generic type rather than a concrete type. We +could have chosen a different name for this generic parameter than the generic parameter declared in the struct definition, but using the same name is -conventional. Methods written within an `impl` that declares the generic type -will be defined on any instance of the type, no matter what concrete type ends -up substituting for the generic type. +conventional. If you write a method within an `impl` that declares a generic +type, that method will be defined on any instance of the type, no matter what +concrete type ends up substituting for the generic type. We can also specify constraints on generic types when defining methods on the type. We could, for example, implement methods only on `Point` instances -rather than on `Point` instances with any generic type. In Listing 10-10 we +rather than on `Point` instances with any generic type. In Listing 10-10, we use the concrete type `f32`, meaning we don’t declare any types after `impl`. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-10/src/main.rs:here}} ``` -Listing 10-10: An `impl` block that only applies to a -struct with a particular concrete type for the generic type parameter `T` + This code means the type `Point` will have a `distance_from_origin` method; other instances of `Point` where `T` is not of type `f32` will not have this method defined. The method measures how far our point is from the point at coordinates (0.0, 0.0) and uses mathematical operations that are -available only for floating point types. +available only for floating-point types. Generic type parameters in a struct definition aren’t always the same as those you use in that same struct’s method signatures. Listing 10-11 uses the generic -types `X1` and `Y1` for the `Point` struct and `X2` `Y2` for the `mixup` method -signature to make the example clearer. The method creates a new `Point` +types `X1` and `Y1` for the `Point` struct and `X2` and `Y2` for the `mixup` +method signature to make the example clearer. The method creates a new `Point` instance with the `x` value from the `self` `Point` (of type `X1`) and the `y` value from the passed-in `Point` (of type `Y2`). -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-11/src/main.rs}} ``` -Listing 10-11: A method that uses generic types different -from its struct’s definition + In `main`, we’ve defined a `Point` that has an `i32` for `x` (with value `5`) and an `f64` for `y` (with value `10.4`). The `p2` variable is a `Point` struct that has a string slice for `x` (with value `"Hello"`) and a `char` for `y` (with value `c`). Calling `mixup` on `p1` with the argument `p2` gives us `p3`, -which will have an `i32` for `x`, because `x` came from `p1`. The `p3` variable -will have a `char` for `y`, because `y` came from `p2`. The `println!` macro +which will have an `i32` for `x` because `x` came from `p1`. The `p3` variable +will have a `char` for `y` because `y` came from `p2`. The `println!` macro call will print `p3.x = 5, p3.y = c`. The purpose of this example is to demonstrate a situation in which some generic parameters are declared with `impl` and some are declared with the method definition. Here, the generic parameters `X1` and `Y1` are declared after `impl` because they go with the struct definition. The generic parameters `X2` -and `Y2` are declared after `fn mixup`, because they’re only relevant to the +and `Y2` are declared after `fn mixup` because they’re only relevant to the method. ### Performance of Code Using Generics You might be wondering whether there is a runtime cost when using generic type -parameters. The good news is that using generic types won't make your program run -any slower than it would with concrete types. +parameters. The good news is that using generic types won’t make your program +run any slower than it would with concrete types. Rust accomplishes this by performing monomorphization of the code using -generics at compile time. *Monomorphization* is the process of turning generic +generics at compile time. _Monomorphization_ is the process of turning generic code into specific code by filling in the concrete types that are used when compiled. In this process, the compiler does the opposite of the steps we used -to create the generic function in Listing 10-5: the compiler looks at all the +to create the generic function in Listing 10-5: The compiler looks at all the places where generic code is called and generates code for the concrete types the generic code is called with. @@ -295,7 +286,7 @@ let float = Some(5.0); When Rust compiles this code, it performs monomorphization. During that process, the compiler reads the values that have been used in `Option` -instances and identifies two kinds of `Option`: one is `i32` and the other +instances and identifies two kinds of `Option`: One is `i32` and the other is `f64`. As such, it expands the generic definition of `Option` into two definitions specialized to `i32` and `f64`, thereby replacing the generic definition with the specific ones. @@ -303,7 +294,7 @@ definition with the specific ones. The monomorphized version of the code looks similar to the following (the compiler uses different names than what we’re using here for illustration): -Filename: src/main.rs + ```rust enum Option_i32 { @@ -322,6 +313,8 @@ fn main() { } ``` + + The generic `Option` is replaced with the specific definitions created by the compiler. Because Rust compiles generic code into code that specifies the type in each instance, we pay no runtime cost for using generics. When the code diff --git a/src/ch10-02-traits.md b/src/ch10-02-traits.md index 3c4fb8cad1..1698cda0d3 100644 --- a/src/ch10-02-traits.md +++ b/src/ch10-02-traits.md @@ -1,11 +1,15 @@ -## Traits: Defining Shared Behavior + + + -A *trait* defines functionality a particular type has and can share with other -types. We can use traits to define shared behavior in an abstract way. We can -use *trait bounds* to specify that a generic type can be any type that has +## Defining Shared Behavior with Traits + +A _trait_ defines the functionality a particular type has and can share with +other types. We can use traits to define shared behavior in an abstract way. We +can use _trait bounds_ to specify that a generic type can be any type that has certain behavior. -> Note: Traits are similar to a feature often called *interfaces* in other +> Note: Traits are similar to a feature often called _interfaces_ in other > languages, although with some differences. ### Defining a Trait @@ -17,27 +21,27 @@ define a set of behaviors necessary to accomplish some purpose. For example, let’s say we have multiple structs that hold various kinds and amounts of text: a `NewsArticle` struct that holds a news story filed in a -particular location and a `Tweet` that can have at most 280 characters along -with metadata that indicates whether it was a new tweet, a retweet, or a reply -to another tweet. +particular location and a `SocialPost` that can have, at most, 280 characters +along with metadata that indicates whether it was a new post, a repost, or a +reply to another post. We want to make a media aggregator library crate named `aggregator` that can -display summaries of data that might be stored in a `NewsArticle` or `Tweet` -instance. To do this, we need a summary from each type, and we’ll request -that summary by calling a `summarize` method on an instance. Listing 10-12 -shows the definition of a public `Summary` trait that expresses this behavior. +display summaries of data that might be stored in a `NewsArticle` or +`SocialPost` instance. To do this, we need a summary from each type, and we’ll +request that summary by calling a `summarize` method on an instance. Listing +10-12 shows the definition of a public `Summary` trait that expresses this +behavior. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-12/src/lib.rs}} ``` -Listing 10-12: A `Summary` trait that consists of the -behavior provided by a `summarize` method + Here, we declare a trait using the `trait` keyword and then the trait’s name, -which is `Summary` in this case. We’ve also declared the trait as `pub` so that +which is `Summary` in this case. We also declare the trait as `pub` so that crates depending on this crate can make use of this trait too, as we’ll see in a few examples. Inside the curly brackets, we declare the method signatures that describe the behaviors of the types that implement this trait, which in @@ -49,8 +53,8 @@ its own custom behavior for the body of the method. The compiler will enforce that any type that has the `Summary` trait will have the method `summarize` defined with this signature exactly. -A trait can have multiple methods in its body: the method signatures are listed -one per line and each line ends in a semicolon. +A trait can have multiple methods in its body: The method signatures are listed +one per line, and each line ends in a semicolon. ### Implementing a Trait on a Type @@ -58,18 +62,17 @@ Now that we’ve defined the desired signatures of the `Summary` trait’s metho we can implement it on the types in our media aggregator. Listing 10-13 shows an implementation of the `Summary` trait on the `NewsArticle` struct that uses the headline, the author, and the location to create the return value of -`summarize`. For the `Tweet` struct, we define `summarize` as the username -followed by the entire text of the tweet, assuming that tweet content is +`summarize`. For the `SocialPost` struct, we define `summarize` as the username +followed by the entire text of the post, assuming that the post content is already limited to 280 characters. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/src/lib.rs:here}} ``` -Listing 10-13: Implementing the `Summary` trait on the -`NewsArticle` and `Tweet` types + Implementing a trait on a type is similar to implementing regular methods. The difference is that after `impl`, we put the trait name we want to implement, @@ -80,8 +83,8 @@ signature, we use curly brackets and fill in the method body with the specific behavior that we want the methods of the trait to have for the particular type. Now that the library has implemented the `Summary` trait on `NewsArticle` and -`Tweet`, users of the crate can call the trait methods on instances of -`NewsArticle` and `Tweet` in the same way we call regular methods. The only +`SocialPost`, users of the crate can call the trait methods on instances of +`NewsArticle` and `SocialPost` in the same way we call regular methods. The only difference is that the user must bring the trait into scope as well as the types. Here’s an example of how a binary crate could use our `aggregator` library crate: @@ -90,48 +93,51 @@ library crate: {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/main.rs}} ``` -This code prints `1 new tweet: horse_ebooks: of course, as you probably already +This code prints `1 new post: horse_ebooks: of course, as you probably already know, people`. Other crates that depend on the `aggregator` crate can also bring the `Summary` trait into scope to implement `Summary` on their own types. One restriction to -note is that we can implement a trait on a type only if at least one of the -trait or the type is local to our crate. For example, we can implement standard -library traits like `Display` on a custom type like `Tweet` as part of our -`aggregator` crate functionality, because the type `Tweet` is local to our +note is that we can implement a trait on a type only if either the trait or the +type, or both, are local to our crate. For example, we can implement standard +library traits like `Display` on a custom type like `SocialPost` as part of our +`aggregator` crate functionality because the type `SocialPost` is local to our `aggregator` crate. We can also implement `Summary` on `Vec` in our -`aggregator` crate, because the trait `Summary` is local to our `aggregator` +`aggregator` crate because the trait `Summary` is local to our `aggregator` crate. But we can’t implement external traits on external types. For example, we can’t implement the `Display` trait on `Vec` within our `aggregator` crate, because `Display` and `Vec` are both defined in the standard library and aren’t local to our `aggregator` crate. This restriction is part of a property -called *coherence*, and more specifically the *orphan rule*, so named because +called _coherence_, and more specifically the _orphan rule_, so named because the parent type is not present. This rule ensures that other people’s code can’t break your code and vice versa. Without the rule, two crates could implement the same trait for the same type, and Rust wouldn’t know which implementation to use. -### Default Implementations + + + + +### Using Default Implementations Sometimes it’s useful to have default behavior for some or all of the methods in a trait instead of requiring implementations for all methods on every type. Then, as we implement the trait on a particular type, we can keep or override each method’s default behavior. -In Listing 10-14 we specify a default string for the `summarize` method of the +In Listing 10-14, we specify a default string for the `summarize` method of the `Summary` trait instead of only defining the method signature, as we did in Listing 10-12. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/src/lib.rs:here}} ``` -Listing 10-14: Defining a `Summary` trait with a default -implementation of the `summarize` method + To use a default implementation to summarize instances of `NewsArticle`, we specify an empty `impl` block with `impl Summary for NewsArticle {}`. @@ -148,9 +154,10 @@ the `summarize` method on an instance of `NewsArticle`, like this: This code prints `New article available! (Read more...)`. Creating a default implementation doesn’t require us to change anything about -the implementation of `Summary` on `Tweet` in Listing 10-13. The reason is that -the syntax for overriding a default implementation is the same as the syntax -for implementing a trait method that doesn’t have a default implementation. +the implementation of `Summary` on `SocialPost` in Listing 10-13. The reason is +that the syntax for overriding a default implementation is the same as the +syntax for implementing a trait method that doesn’t have a default +implementation. Default implementations can call other methods in the same trait, even if those other methods don’t have a default implementation. In this way, a trait can @@ -172,25 +179,30 @@ when we implement the trait on a type: ``` After we define `summarize_author`, we can call `summarize` on instances of the -`Tweet` struct, and the default implementation of `summarize` will call the +`SocialPost` struct, and the default implementation of `summarize` will call the definition of `summarize_author` that we’ve provided. Because we’ve implemented `summarize_author`, the `Summary` trait has given us the behavior of the -`summarize` method without requiring us to write any more code. +`summarize` method without requiring us to write any more code. Here’s what +that looks like: ```rust,ignore {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/main.rs:here}} ``` -This code prints `1 new tweet: (Read more from @horse_ebooks...)`. +This code prints `1 new post: (Read more from @horse_ebooks...)`. Note that it isn’t possible to call the default implementation from an overriding implementation of that same method. -### Traits as Parameters + + + + +### Using Traits as Parameters Now that you know how to define and implement traits, we can explore how to use -traits to define functions that accept many different types. We'll use the -`Summary` trait we implemented on the `NewsArticle` and `Tweet` types in +traits to define functions that accept many different types. We’ll use the +`Summary` trait we implemented on the `NewsArticle` and `SocialPost` types in Listing 10-13 to define a `notify` function that calls the `summarize` method on its `item` parameter, which is of some type that implements the `Summary` trait. To do this, we use the `impl Trait` syntax, like this: @@ -203,17 +215,18 @@ Instead of a concrete type for the `item` parameter, we specify the `impl` keyword and the trait name. This parameter accepts any type that implements the specified trait. In the body of `notify`, we can call any methods on `item` that come from the `Summary` trait, such as `summarize`. We can call `notify` -and pass in any instance of `NewsArticle` or `Tweet`. Code that calls the -function with any other type, such as a `String` or an `i32`, won’t compile +and pass in any instance of `NewsArticle` or `SocialPost`. Code that calls the +function with any other type, such as a `String` or an `i32`, won’t compile, because those types don’t implement `Summary`. + #### Trait Bound Syntax The `impl Trait` syntax works for straightforward cases but is actually syntax -sugar for a longer form known as a *trait bound*; it looks like this: +sugar for a longer form known as a _trait bound_; it looks like this: ```rust,ignore pub fn notify(item: &T) { @@ -247,10 +260,14 @@ The generic type `T` specified as the type of the `item1` and `item2` parameters constrains the function such that the concrete type of the value passed as an argument for `item1` and `item2` must be the same. -#### Specifying Multiple Trait Bounds with the `+` Syntax + + + + +#### Multiple Trait Bounds with the `+` Syntax We can also specify more than one trait bound. Say we wanted `notify` to use -display formatting as well as `summarize` on `item`: we specify in the `notify` +display formatting as well as `summarize` on `item`: We specify in the `notify` definition that `item` must implement both `Display` and `Summary`. We can do so using the `+` syntax: @@ -274,7 +291,7 @@ bounds, so functions with multiple generic type parameters can contain lots of trait bound information between the function’s name and its parameter list, making the function signature hard to read. For this reason, Rust has alternate syntax for specifying trait bounds inside a `where` clause after the function -signature. So instead of writing this: +signature. So, instead of writing this: ```rust,ignore fn some_function(t: &T, u: &U) -> i32 { @@ -286,11 +303,11 @@ we can use a `where` clause, like this: {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-07-where-clause/src/lib.rs:here}} ``` -This function’s signature is less cluttered: the function name, parameter list, +This function’s signature is less cluttered: The function name, parameter list, and return type are close together, similar to a function without lots of trait bounds. -### Returning Types that Implement Traits +### Returning Types That Implement Traits We can also use the `impl Trait` syntax in the return position to return a value of some type that implements a trait, as shown here: @@ -302,7 +319,8 @@ value of some type that implements a trait, as shown here: By using `impl Summary` for the return type, we specify that the `returns_summarizable` function returns some type that implements the `Summary` trait without naming the concrete type. In this case, `returns_summarizable` -returns a `Tweet`, but the code calling this function doesn’t need to know that. +returns a `SocialPost`, but the code calling this function doesn’t need to know +that. The ability to specify a return type only by the trait it implements is especially useful in the context of closures and iterators, which we cover in @@ -312,44 +330,42 @@ specify that a function returns some type that implements the `Iterator` trait without needing to write out a very long type. However, you can only use `impl Trait` if you’re returning a single type. For -example, this code that returns either a `NewsArticle` or a `Tweet` with the -return type specified as `impl Summary` wouldn’t work: +example, this code that returns either a `NewsArticle` or a `SocialPost` with +the return type specified as `impl Summary` wouldn’t work: ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/src/lib.rs:here}} ``` -Returning either a `NewsArticle` or a `Tweet` isn’t allowed due to restrictions -around how the `impl Trait` syntax is implemented in the compiler. We’ll cover -how to write a function with this behavior in the [“Using Trait Objects That -Allow for Values of Different -Types”][using-trait-objects-that-allow-for-values-of-different-types] section of Chapter 17. +Returning either a `NewsArticle` or a `SocialPost` isn’t allowed due to +restrictions around how the `impl Trait` syntax is implemented in the compiler. +We’ll cover how to write a function with this behavior in the [“Using Trait +Objects to Abstract over Shared Behavior”][trait-objects] +section of Chapter 18. ### Using Trait Bounds to Conditionally Implement Methods By using a trait bound with an `impl` block that uses generic type parameters, we can implement methods conditionally for types that implement the specified traits. For example, the type `Pair` in Listing 10-15 always implements the -`new` function to return a new instance of `Pair` (recall from the -[“Defining Methods”][methods] section of Chapter 5 that `Self` -is a type alias for the type of the `impl` block, which in this case is -`Pair`). But in the next `impl` block, `Pair` only implements the -`cmp_display` method if its inner type `T` implements the `PartialOrd` trait -that enables comparison *and* the `Display` trait that enables printing. +`new` function to return a new instance of `Pair` (recall from the [“Method +Syntax”][methods] section of Chapter 5 that `Self` is a type +alias for the type of the `impl` block, which in this case is `Pair`). But +in the next `impl` block, `Pair` only implements the `cmp_display` method if +its inner type `T` implements the `PartialOrd` trait that enables comparison +_and_ the `Display` trait that enables printing. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-15/src/lib.rs}} ``` -Listing 10-15: Conditionally implementing methods on a -generic type depending on trait bounds + We can also conditionally implement a trait for any type that implements another trait. Implementations of a trait on any type that satisfies the trait -bounds are called *blanket implementations* and are extensively used in the +bounds are called _blanket implementations_ and are used extensively in the Rust standard library. For example, the standard library implements the `ToString` trait on any type that implements the `Display` trait. The `impl` block in the standard library looks similar to this code: @@ -377,12 +393,12 @@ reduce duplication but also specify to the compiler that we want the generic type to have particular behavior. The compiler can then use the trait bound information to check that all the concrete types used with our code provide the correct behavior. In dynamically typed languages, we would get an error at -runtime if we called a method on a type which didn’t define the method. But Rust -moves these errors to compile time so we’re forced to fix the problems before -our code is even able to run. Additionally, we don’t have to write code that -checks for behavior at runtime because we’ve already checked at compile time. -Doing so improves performance without having to give up the flexibility of -generics. - -[using-trait-objects-that-allow-for-values-of-different-types]: ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types -[methods]: ch05-03-method-syntax.html#defining-methods +runtime if we called a method on a type that didn’t define the method. But Rust +moves these errors to compile time so that we’re forced to fix the problems +before our code is even able to run. Additionally, we don’t have to write code +that checks for behavior at runtime, because we’ve already checked at compile +time. Doing so improves performance without having to give up the flexibility +of generics. + +[trait-objects]: ch18-02-trait-objects.html#using-trait-objects-to-abstract-over-shared-behavior +[methods]: ch05-03-method-syntax.html#method-syntax diff --git a/src/ch10-03-lifetime-syntax.md b/src/ch10-03-lifetime-syntax.md index 498f01f0b5..fc38d74151 100644 --- a/src/ch10-03-lifetime-syntax.md +++ b/src/ch10-03-lifetime-syntax.md @@ -6,96 +6,104 @@ references are valid as long as we need them to be. One detail we didn’t discuss in the [“References and Borrowing”][references-and-borrowing] section in Chapter 4 is -that every reference in Rust has a *lifetime*, which is the scope for which +that every reference in Rust has a lifetime, which is the scope for which that reference is valid. Most of the time, lifetimes are implicit and inferred, -just like most of the time, types are inferred. We must only annotate types -when multiple types are possible. In a similar way, we must annotate lifetimes -when the lifetimes of references could be related in a few different ways. Rust -requires us to annotate the relationships using generic lifetime parameters to -ensure the actual references used at runtime will definitely be valid. - -Annotating lifetimes is not a concept most other programming languages +just like most of the time, types are inferred. We are only required to +annotate types when multiple types are possible. In a similar way, we must +annotate lifetimes when the lifetimes of references could be related in a few +different ways. Rust requires us to annotate the relationships using generic +lifetime parameters to ensure that the actual references used at runtime will +definitely be valid. + +Annotating lifetimes is not even a concept most other programming languages have, so this is going to feel unfamiliar. Although we won’t cover lifetimes in their entirety in this chapter, we’ll discuss common ways you might encounter -lifetime syntax so you can get comfortable with the concept. +lifetime syntax so that you can get comfortable with the concept. + + + + -### Preventing Dangling References with Lifetimes +### Dangling References -The main aim of lifetimes is to prevent *dangling references*, which cause a -program to reference data other than the data it’s intended to reference. -Consider the program in Listing 10-16, which has an outer scope and an inner -scope. +The main aim of lifetimes is to prevent dangling references, which, if they +were allowed to exist, would cause a program to reference data other than the +data it’s intended to reference. Consider the program in Listing 10-16, which +has an outer scope and an inner scope. + + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/src/main.rs}} ``` -Listing 10-16: An attempt to use a reference whose value -has gone out of scope + > Note: The examples in Listings 10-16, 10-17, and 10-23 declare variables -> without giving them an initial value, so the variable name exists in the -> outer scope. At first glance, this might appear to be in conflict with Rust’s -> having no null values. However, if we try to use a variable before giving it -> a value, we’ll get a compile-time error, which shows that Rust indeed does -> not allow null values. +> without giving them an initial value, so the variable name exists in the outer +> scope. At first glance, this might appear to be in conflict with Rust having +> no null values. However, if we try to use a variable before giving it a value, +> we’ll get a compile-time error, which shows that indeed Rust does not allow +> null values. The outer scope declares a variable named `r` with no initial value, and the -inner scope declares a variable named `x` with the initial value of 5. Inside -the inner scope, we attempt to set the value of `r` as a reference to `x`. Then -the inner scope ends, and we attempt to print the value in `r`. This code won’t -compile because what the value `r` is referring to has gone out of scope before we -try to use it. Here is the error message: +inner scope declares a variable named `x` with the initial value of `5`. Inside +the inner scope, we attempt to set the value of `r` as a reference to `x`. +Then, the inner scope ends, and we attempt to print the value in `r`. This code +won’t compile, because the value that `r` is referring to has gone out of scope +before we try to use it. Here is the error message: ```console {{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/output.txt}} ``` -The variable `x` doesn’t “live long enough.” The reason is that `x` will be out -of scope when the inner scope ends on line 7. But `r` is still valid for the -outer scope; because its scope is larger, we say that it “lives longer.” If -Rust allowed this code to work, `r` would be referencing memory that was -deallocated when `x` went out of scope, and anything we tried to do with `r` -wouldn’t work correctly. So how does Rust determine that this code is invalid? -It uses a borrow checker. +The error message says that the variable `x` “does not live long enough.” The +reason is that `x` will be out of scope when the inner scope ends on line 7. +But `r` is still valid for the outer scope; because its scope is larger, we say +that it “lives longer.” If Rust allowed this code to work, `r` would be +referencing memory that was deallocated when `x` went out of scope, and +anything we tried to do with `r` wouldn’t work correctly. So, how does Rust +determine that this code is invalid? It uses a borrow checker. ### The Borrow Checker -The Rust compiler has a *borrow checker* that compares scopes to determine +The Rust compiler has a _borrow checker_ that compares scopes to determine whether all borrows are valid. Listing 10-17 shows the same code as Listing 10-16 but with annotations showing the lifetimes of the variables. ++ ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/src/main.rs}} ``` -Listing 10-17: Annotations of the lifetimes of `r` and -`x`, named `'a` and `'b`, respectively + Here, we’ve annotated the lifetime of `r` with `'a` and the lifetime of `x` with `'b`. As you can see, the inner `'b` block is much smaller than the outer `'a` lifetime block. At compile time, Rust compares the size of the two lifetimes and sees that `r` has a lifetime of `'a` but that it refers to memory with a lifetime of `'b`. The program is rejected because `'b` is shorter than -`'a`: the subject of the reference doesn’t live as long as the reference. +`'a`: The subject of the reference doesn’t live as long as the reference. -Listing 10-18 fixes the code so it doesn’t have a dangling reference and -compiles without any errors. +Listing 10-18 fixes the code so that it doesn’t have a dangling reference and +it compiles without any errors. + + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/src/main.rs}} ``` -Listing 10-18: A valid reference because the data has a -longer lifetime than the reference + Here, `x` has the lifetime `'b`, which in this case is larger than `'a`. This means `r` can reference `x` because Rust knows that the reference in `r` will always be valid while `x` is valid. Now that you know where the lifetimes of references are and how Rust analyzes -lifetimes to ensure references will always be valid, let’s explore generic -lifetimes of parameters and return values in the context of functions. +lifetimes to ensure that references will always be valid, let’s explore generic +lifetimes in function parameters and return values. ### Generic Lifetimes in Functions @@ -104,34 +112,31 @@ function will take two string slices and return a single string slice. After we’ve implemented the `longest` function, the code in Listing 10-19 should print `The longest string is abcd`. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/src/main.rs}} ``` -Listing 10-19: A `main` function that calls the `longest` -function to find the longer of two string slices + Note that we want the function to take string slices, which are references, rather than strings, because we don’t want the `longest` function to take -ownership of its parameters. Refer to the [“String Slices as -Parameters”][string-slices-as-parameters] section in Chapter 4 -for more discussion about why the parameters we use in Listing 10-19 are the -ones we want. +ownership of its parameters. Refer to [“String Slices as +Parameters”][string-slices-as-parameters] in Chapter 4 for more +discussion about why the parameters we use in Listing 10-19 are the ones we +want. If we try to implement the `longest` function as shown in Listing 10-20, it won’t compile. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/src/main.rs:here}} ``` -Listing 10-20: An implementation of the `longest` -function that returns the longer of two string slices but does not yet -compile + Instead, we get the following error that talks about lifetimes: @@ -153,7 +158,7 @@ Listings 10-17 and 10-18 to determine whether the reference we return will always be valid. The borrow checker can’t determine this either, because it doesn’t know how the lifetimes of `x` and `y` relate to the lifetime of the return value. To fix this error, we’ll add generic lifetime parameters that -define the relationship between the references so the borrow checker can +define the relationship between the references so that the borrow checker can perform its analysis. ### Lifetime Annotation Syntax @@ -164,15 +169,15 @@ other without affecting the lifetimes. Just as functions can accept any type when the signature specifies a generic type parameter, functions can accept references with any lifetime by specifying a generic lifetime parameter. -Lifetime annotations have a slightly unusual syntax: the names of lifetime +Lifetime annotations have a slightly unusual syntax: The names of lifetime parameters must start with an apostrophe (`'`) and are usually all lowercase and very short, like generic types. Most people use the name `'a` for the first lifetime annotation. We place lifetime parameter annotations after the `&` of a reference, using a space to separate the annotation from the reference’s type. -Here are some examples: a reference to an `i32` without a lifetime parameter, a +Here are some examples—a reference to an `i32` without a lifetime parameter, a reference to an `i32` that has a lifetime parameter named `'a`, and a mutable -reference to an `i32` that also has the lifetime `'a`. +reference to an `i32` that also has the lifetime `'a`: ```rust,ignore &i32 // a reference @@ -185,27 +190,29 @@ annotations are meant to tell Rust how generic lifetime parameters of multiple references relate to each other. Let’s examine how the lifetime annotations relate to each other in the context of the `longest` function. -### Lifetime Annotations in Function Signatures + + + + +### In Function Signatures To use lifetime annotations in function signatures, we need to declare the -generic *lifetime* parameters inside angle brackets between the function name -and the parameter list, just as we did with generic *type* parameters. +generic lifetime parameters inside angle brackets between the function name and +the parameter list, just as we did with generic type parameters. -We want the signature to express the following constraint: the returned -reference will be valid as long as both the parameters are valid. This is the -relationship between lifetimes of the parameters and the return value. We’ll -name the lifetime `'a` and then add it to each reference, as shown in Listing -10-21. +We want the signature to express the following constraint: The returned +reference will be valid as long as both of the parameters are valid. This is +the relationship between lifetimes of the parameters and the return value. +We’ll name the lifetime `'a` and then add it to each reference, as shown in +Listing 10-21. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/src/main.rs:here}} ``` -Listing 10-21: The `longest` function definition -specifying that all the references in the signature must have the same lifetime -`'a` + This code should compile and produce the result we want when we use it with the `main` function in Listing 10-19. @@ -249,18 +256,17 @@ Let’s look at how the lifetime annotations restrict the `longest` function by passing in references that have different concrete lifetimes. Listing 10-22 is a straightforward example. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/src/main.rs:here}} ``` -Listing 10-22: Using the `longest` function with -references to `String` values that have different concrete lifetimes + In this example, `string1` is valid until the end of the outer scope, `string2` is valid until the end of the inner scope, and `result` references something -that is valid until the end of the inner scope. Run this code, and you’ll see +that is valid until the end of the inner scope. Run this code and you’ll see that the borrow checker approves; it will compile and print `The longest string is long string is long`. @@ -268,18 +274,17 @@ Next, let’s try an example that shows that the lifetime of the reference in `result` must be the smaller lifetime of the two arguments. We’ll move the declaration of the `result` variable outside the inner scope but leave the assignment of the value to the `result` variable inside the scope with -`string2`. Then we’ll move the `println!` that uses `result` to outside the +`string2`. Then, we’ll move the `println!` that uses `result` to outside the inner scope, after the inner scope has ended. The code in Listing 10-23 will not compile. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/src/main.rs:here}} ``` -Listing 10-23: Attempting to use `result` after `string2` -has gone out of scope + When we try to compile this code, we get this error: @@ -293,7 +298,7 @@ this because we annotated the lifetimes of the function parameters and return values using the same lifetime parameter `'a`. As humans, we can look at this code and see that `string1` is longer than -`string2` and therefore `result` will contain a reference to `string1`. +`string2`, and therefore, `result` will contain a reference to `string1`. Because `string1` has not gone out of scope yet, a reference to `string1` will still be valid for the `println!` statement. However, the compiler can’t see that the reference is valid in this case. We’ve told Rust that the lifetime of @@ -304,9 +309,13 @@ disallows the code in Listing 10-23 as possibly having an invalid reference. Try designing more experiments that vary the values and lifetimes of the references passed in to the `longest` function and how the returned reference is used. Make hypotheses about whether or not your experiments will pass the -borrow checker before you compile; then check to see if you’re right! +borrow checker before you compile; then, check to see if you’re right! + + -### Thinking in Terms of Lifetimes + + +### Relationships The way in which you need to specify lifetime parameters depends on what your function is doing. For example, if we changed the implementation of the @@ -314,30 +323,34 @@ function is doing. For example, if we changed the implementation of the string slice, we wouldn’t need to specify a lifetime on the `y` parameter. The following code will compile: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/src/main.rs:here}} ``` + + We’ve specified a lifetime parameter `'a` for the parameter `x` and the return type, but not for the parameter `y`, because the lifetime of `y` does not have any relationship with the lifetime of `x` or the return value. When returning a reference from a function, the lifetime parameter for the return type needs to match the lifetime parameter for one of the parameters. If -the reference returned does *not* refer to one of the parameters, it must refer +the reference returned does _not_ refer to one of the parameters, it must refer to a value created within this function. However, this would be a dangling reference because the value will go out of scope at the end of the function. Consider this attempted implementation of the `longest` function that won’t compile: -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/src/main.rs:here}} ``` + + Here, even though we’ve specified a lifetime parameter `'a` for the return type, this implementation will fail to compile because the return value lifetime is not related to the lifetime of the parameters at all. Here is the @@ -352,7 +365,7 @@ of the `longest` function. We’re also trying to return a reference to `result` from the function. There is no way we can specify lifetime parameters that would change the dangling reference, and Rust won’t let us create a dangling reference. In this case, the best fix would be to return an owned data type -rather than a reference so the calling function is then responsible for +rather than a reference so that the calling function is then responsible for cleaning up the value. Ultimately, lifetime syntax is about connecting the lifetimes of various @@ -360,26 +373,29 @@ parameters and return values of functions. Once they’re connected, Rust has enough information to allow memory-safe operations and disallow operations that would create dangling pointers or otherwise violate memory safety. -### Lifetime Annotations in Struct Definitions + + + + +### In Struct Definitions -So far, the structs we’ve defined all hold owned types. We can define structs to -hold references, but in that case we would need to add a lifetime annotation on -every reference in the struct’s definition. Listing 10-24 has a struct named -`ImportantExcerpt` that holds a string slice. +So far, the structs we’ve defined all hold owned types. We can define structs +to hold references, but in that case, we would need to add a lifetime +annotation on every reference in the struct’s definition. Listing 10-24 has a +struct named `ImportantExcerpt` that holds a string slice. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/src/main.rs}} ``` -Listing 10-24: A struct that holds a reference, requiring -a lifetime annotation + This struct has the single field `part` that holds a string slice, which is a reference. As with generic data types, we declare the name of the generic -lifetime parameter inside angle brackets after the name of the struct so we can -use the lifetime parameter in the body of the struct definition. This +lifetime parameter inside angle brackets after the name of the struct so that +we can use the lifetime parameter in the body of the struct definition. This annotation means an instance of `ImportantExcerpt` can’t outlive the reference it holds in its `part` field. @@ -393,22 +409,20 @@ the `ImportantExcerpt` goes out of scope, so the reference in the ### Lifetime Elision You’ve learned that every reference has a lifetime and that you need to specify -lifetime parameters for functions or structs that use references. However, in -Chapter 4 we had a function in Listing 4-9, shown again in Listing 10-25, that -compiled without lifetime annotations. +lifetime parameters for functions or structs that use references. However, we +had a function in Listing 4-9, shown again in Listing 10-25, that compiled +without lifetime annotations. -Filename: src/lib.rs + ```rust {{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-25/src/main.rs:here}} ``` -Listing 10-25: A function we defined in Listing 4-9 that -compiled without lifetime annotations, even though the parameter and return -type are references + The reason this function compiles without lifetime annotations is historical: -in early versions (pre-1.0) of Rust, this code wouldn’t have compiled because +In early versions (pre-1.0) of Rust, this code wouldn’t have compiled, because every reference needed an explicit lifetime. At that time, the function signature would have been written like this: @@ -420,26 +434,26 @@ After writing a lot of Rust code, the Rust team found that Rust programmers were entering the same lifetime annotations over and over in particular situations. These situations were predictable and followed a few deterministic patterns. The developers programmed these patterns into the compiler’s code so -the borrow checker could infer the lifetimes in these situations and wouldn’t -need explicit annotations. +that the borrow checker could infer the lifetimes in these situations and +wouldn’t need explicit annotations. This piece of Rust history is relevant because it’s possible that more deterministic patterns will emerge and be added to the compiler. In the future, even fewer lifetime annotations might be required. The patterns programmed into Rust’s analysis of references are called the -*lifetime elision rules*. These aren’t rules for programmers to follow; they’re +_lifetime elision rules_. These aren’t rules for programmers to follow; they’re a set of particular cases that the compiler will consider, and if your code fits these cases, you don’t need to write the lifetimes explicitly. -The elision rules don’t provide full inference. If Rust deterministically -applies the rules but there is still ambiguity as to what lifetimes the -references have, the compiler won’t guess what the lifetime of the remaining -references should be. Instead of guessing, the compiler will give you an error -that you can resolve by adding the lifetime annotations. +The elision rules don’t provide full inference. If there is still ambiguity +about what lifetimes the references have after Rust applies the rules, the +compiler won’t guess what the lifetime of the remaining references should be. +Instead of guessing, the compiler will give you an error that you can resolve +by adding the lifetime annotations. -Lifetimes on function or method parameters are called *input lifetimes*, and -lifetimes on return values are called *output lifetimes*. +Lifetimes on function or method parameters are called _input lifetimes_, and +lifetimes on return values are called _output lifetimes_. The compiler uses three rules to figure out the lifetimes of the references when there aren’t explicit annotations. The first rule applies to input @@ -449,8 +463,8 @@ which it can’t figure out lifetimes, the compiler will stop with an error. These rules apply to `fn` definitions as well as `impl` blocks. The first rule is that the compiler assigns a lifetime parameter to each -parameter that’s a reference. In other words, a function with one parameter gets -one lifetime parameter: `fn foo<'a>(x: &'a i32)`; a function with two +parameter that’s a reference. In other words, a function with one parameter +gets one lifetime parameter: `fn foo<'a>(x: &'a i32)`; a function with two parameters gets two separate lifetime parameters: `fn foo<'a, 'b>(x: &'a i32, y: &'b i32)`; and so on. @@ -472,7 +486,7 @@ references: fn first_word(s: &str) -> &str { ``` -Then the compiler applies the first rule, which specifies that each parameter +Then, the compiler applies the first rule, which specifies that each parameter gets its own lifetime. We’ll call it `'a` as usual, so now the signature is this: @@ -499,34 +513,38 @@ no lifetime parameters when we started working with it in Listing 10-20: fn longest(x: &str, y: &str) -> &str { ``` -Let’s apply the first rule: each parameter gets its own lifetime. This time we +Let’s apply the first rule: Each parameter gets its own lifetime. This time we have two parameters instead of one, so we have two lifetimes: ```rust,ignore fn longest<'a, 'b>(x: &'a str, y: &'b str) -> &str { ``` -You can see that the second rule doesn’t apply because there is more than one +You can see that the second rule doesn’t apply, because there is more than one input lifetime. The third rule doesn’t apply either, because `longest` is a function rather than a method, so none of the parameters are `self`. After working through all three rules, we still haven’t figured out what the return type’s lifetime is. This is why we got an error trying to compile the code in -Listing 10-20: the compiler worked through the lifetime elision rules but still +Listing 10-20: The compiler worked through the lifetime elision rules but still couldn’t figure out all the lifetimes of the references in the signature. Because the third rule really only applies in method signatures, we’ll look at lifetimes in that context next to see why the third rule means we don’t have to annotate lifetimes in method signatures very often. -### Lifetime Annotations in Method Definitions + + + + +### In Method Definitions When we implement methods on a struct with lifetimes, we use the same syntax as -that of generic type parameters shown in Listing 10-11. Where we declare and -use the lifetime parameters depends on whether they’re related to the struct -fields or the method parameters and return values. +that of generic type parameters, as shown in Listing 10-11. Where we declare +and use the lifetime parameters depends on whether they’re related to the +struct fields or the method parameters and return values. Lifetime names for struct fields always need to be declared after the `impl` -keyword and then used after the struct’s name, because those lifetimes are part +keyword and then used after the struct’s name because those lifetimes are part of the struct’s type. In method signatures inside the `impl` block, references might be tied to the @@ -543,8 +561,8 @@ First, we’ll use a method named `level` whose only parameter is a reference to ``` The lifetime parameter declaration after `impl` and its use after the type name -are required, but we’re not required to annotate the lifetime of the reference -to `self` because of the first elision rule. +are required, but because of the first elision rule, we’re not required to +annotate the lifetime of the reference to `self`. Here is an example where the third lifetime elision rule applies: @@ -560,26 +578,29 @@ and all lifetimes have been accounted for. ### The Static Lifetime One special lifetime we need to discuss is `'static`, which denotes that the -affected reference *can* live for the entire duration of the program. All +affected reference _can_ live for the entire duration of the program. All string literals have the `'static` lifetime, which we can annotate as follows: ```rust let s: &'static str = "I have a static lifetime."; ``` -The text of this string is stored directly in the program’s binary, which -is always available. Therefore, the lifetime of all string literals is -`'static`. +The text of this string is stored directly in the program’s binary, which is +always available. Therefore, the lifetime of all string literals is `'static`. -You might see suggestions to use the `'static` lifetime in error messages. But +You might see suggestions in error messages to use the `'static` lifetime. But before specifying `'static` as the lifetime for a reference, think about -whether the reference you have actually lives the entire lifetime of your -program or not, and whether you want it to. Most of the time, an error message +whether or not the reference you have actually lives the entire lifetime of +your program, and whether you want it to. Most of the time, an error message suggesting the `'static` lifetime results from attempting to create a dangling reference or a mismatch of the available lifetimes. In such cases, the solution -is fixing those problems, not specifying the `'static` lifetime. +is to fix those problems, not to specify the `'static` lifetime. + + + + -## Generic Type Parameters, Trait Bounds, and Lifetimes Together +## Generic Type Parameters, Trait Bounds, and Lifetimes Let’s briefly look at the syntax of specifying generic type parameters, trait bounds, and lifetimes all in one function! @@ -609,14 +630,12 @@ that this flexible code won’t have any dangling references. And all of this analysis happens at compile time, which doesn’t affect runtime performance! Believe it or not, there is much more to learn on the topics we discussed in -this chapter: Chapter 17 discusses trait objects, which are another way to use +this chapter: Chapter 18 discusses trait objects, which are another way to use traits. There are also more complex scenarios involving lifetime annotations that you will only need in very advanced scenarios; for those, you should read the [Rust Reference][reference]. But next, you’ll learn how to write tests in -Rust so you can make sure your code is working the way it should. +Rust so that you can make sure your code is working the way it should. -[references-and-borrowing]: -ch04-02-references-and-borrowing.html#references-and-borrowing -[string-slices-as-parameters]: -ch04-03-slices.html#string-slices-as-parameters -[reference]: ../reference/index.html +[references-and-borrowing]: ch04-02-references-and-borrowing.html#references-and-borrowing +[string-slices-as-parameters]: ch04-03-slices.html#string-slices-as-parameters +[reference]: ../reference/trait-bounds.html diff --git a/src/ch11-00-testing.md b/src/ch11-00-testing.md index 7f11ec1494..110d3d28b1 100644 --- a/src/ch11-00-testing.md +++ b/src/ch11-00-testing.md @@ -1,22 +1,23 @@ # Writing Automated Tests -In his 1972 essay “The Humble Programmer,” Edsger W. Dijkstra said that -“Program testing can be a very effective way to show the presence of bugs, but -it is hopelessly inadequate for showing their absence.” That doesn’t mean we -shouldn’t try to test as much as we can! +In his 1972 essay “The Humble Programmer,” Edsger W. Dijkstra said that “program +testing can be a very effective way to show the presence of bugs, but it is +hopelessly inadequate for showing their absence.” That doesn’t mean we shouldn’t +try to test as much as we can! -Correctness in our programs is the extent to which our code does what we intend -it to do. Rust is designed with a high degree of concern about the correctness -of programs, but correctness is complex and not easy to prove. Rust’s type -system shoulders a huge part of this burden, but the type system cannot catch -everything. As such, Rust includes support for writing automated software tests. +_Correctness_ in our programs is the extent to which our code does what we +intend it to do. Rust is designed with a high degree of concern about the +correctness of programs, but correctness is complex and not easy to prove. +Rust’s type system shoulders a huge part of this burden, but the type system +cannot catch everything. As such, Rust includes support for writing automated +software tests. Say we write a function `add_two` that adds 2 to whatever number is passed to it. This function’s signature accepts an integer as a parameter and returns an integer as a result. When we implement and compile that function, Rust does all the type checking and borrow checking that you’ve learned so far to ensure that, for instance, we aren’t passing a `String` value or an invalid reference -to this function. But Rust *can’t* check that this function will do precisely +to this function. But Rust _can’t_ check that this function will do precisely what we intend, which is return the parameter plus 2 rather than, say, the parameter plus 10 or the parameter minus 50! That’s where tests come in. @@ -25,8 +26,9 @@ We can write tests that assert, for example, that when we pass `3` to the we make changes to our code to make sure any existing correct behavior has not changed. -Testing is a complex skill: although we can’t cover every detail about how to -write good tests in one chapter, we’ll discuss the mechanics of Rust’s testing -facilities. We’ll talk about the annotations and macros available to you when -writing your tests, the default behavior and options provided for running your -tests, and how to organize tests into unit tests and integration tests. +Testing is a complex skill: Although we can’t cover in one chapter every detail +about how to write good tests, in this chapter we will discuss the mechanics of +Rust’s testing facilities. We’ll talk about the annotations and macros +available to you when writing your tests, the default behavior and options +provided for running your tests, and how to organize tests into unit tests and +integration tests. diff --git a/src/ch11-01-writing-tests.md b/src/ch11-01-writing-tests.md index df09aadc84..e071b4c329 100644 --- a/src/ch11-01-writing-tests.md +++ b/src/ch11-01-writing-tests.md @@ -1,35 +1,39 @@ ## How to Write Tests -Tests are Rust functions that verify that the non-test code is functioning in +_Tests_ are Rust functions that verify that the non-test code is functioning in the expected manner. The bodies of test functions typically perform these three actions: -1. Set up any needed data or state. -2. Run the code you want to test. -3. Assert the results are what you expect. +- Set up any needed data or state. +- Run the code you want to test. +- Assert that the results are what you expect. Let’s look at the features Rust provides specifically for writing tests that take these actions, which include the `test` attribute, a few macros, and the `should_panic` attribute. -### The Anatomy of a Test Function + + + + +### Structuring Test Functions At its simplest, a test in Rust is a function that’s annotated with the `test` attribute. Attributes are metadata about pieces of Rust code; one example is the `derive` attribute we used with structs in Chapter 5. To change a function into a test function, add `#[test]` on the line before `fn`. When you run your tests with the `cargo test` command, Rust builds a test runner binary that runs -the annotated functions and reports on whether each -test function passes or fails. +the annotated functions and reports on whether each test function passes or +fails. Whenever we make a new library project with Cargo, a test module with a test function in it is automatically generated for us. This module gives you a -template for writing your tests so you don’t have to look up the exact +template for writing your tests so that you don’t have to look up the exact structure and syntax every time you start a new project. You can add as many additional test functions and as many test modules as you want! We’ll explore some aspects of how tests work by experimenting with the template -test before we actually test any code. Then we’ll write some real-world tests +test before we actually test any code. Then, we’ll write some real-world tests that call some code that we’ve written and assert that its behavior is correct. Let’s create a new library project called `adder` that will add two numbers: @@ -40,18 +44,19 @@ $ cargo new adder --lib $ cd adder ``` -The contents of the *src/lib.rs* file in your `adder` library should look like +The contents of the _src/lib.rs_ file in your `adder` library should look like Listing 11-1. -Filename: src/lib.rs + @@ -59,43 +64,46 @@ cd ../../.. {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs}} ``` -Listing 11-1: The test module and function generated -automatically by `cargo new` + + +The file starts with an example `add` function so that we have something to +test. -For now, let’s ignore the top two lines and focus on the function. Note the -`#[test]` annotation: this attribute indicates this is a test function, so the -test runner knows to treat this function as a test. We might also have non-test +For now, let’s focus solely on the `it_works` function. Note the `#[test]` +annotation: This attribute indicates this is a test function, so the test +runner knows to treat this function as a test. We might also have non-test functions in the `tests` module to help set up common scenarios or perform common operations, so we always need to indicate which functions are tests. The example function body uses the `assert_eq!` macro to assert that `result`, -which contains the result of adding 2 and 2, equals 4. This assertion serves as -an example of the format for a typical test. Let’s run it to see that this test -passes. +which contains the result of calling `add` with 2 and 2, equals 4. This +assertion serves as an example of the format for a typical test. Let’s run it +to see that this test passes. The `cargo test` command runs all tests in our project, as shown in Listing 11-2. ++ ```console {{#include ../listings/ch11-writing-automated-tests/listing-11-01/output.txt}} ``` -Listing 11-2: The output from running the automatically -generated test + Cargo compiled and ran the test. We see the line `running 1 test`. The next -line shows the name of the generated test function, called `it_works`, and that -the result of running that test is `ok`. The overall summary `test result: ok.` -means that all the tests passed, and the portion that reads `1 passed; 0 -failed` totals the number of tests that passed or failed. +line shows the name of the generated test function, called `tests::it_works`, +and that the result of running that test is `ok`. The overall summary `test +result: ok.` means that all the tests passed, and the portion that reads `1 +passed; 0 failed` totals the number of tests that passed or failed. -It’s possible to mark a test as ignored so it doesn’t run in a particular -instance; we’ll cover that in the [“Ignoring Some Tests Unless Specifically +It’s possible to mark a test as ignored so that it doesn’t run in a particular +instance; we’ll cover that in the [“Ignoring Tests Unless Specifically Requested”][ignoring] section later in this chapter. Because we haven’t done that here, the summary shows `0 ignored`. We can also pass an argument to the `cargo test` command to run only tests whose name matches a -string; this is called *filtering* and we’ll cover that in the [“Running a -Subset of Tests by Name”][subset] section. We also haven’t +string; this is called _filtering_, and we’ll cover it in the [“Running a +Subset of Tests by Name”][subset] section. Here, we haven’t filtered the tests being run, so the end of the summary shows `0 filtered out`. The `0 measured` statistic is for benchmark tests that measure performance. @@ -110,7 +118,7 @@ write documentation tests in the [“Documentation Comments as Tests”][doc-comments] section of Chapter 14. For now, we’ll ignore the `Doc-tests` output. -Let’s start to customize the test to our own needs. First change the name of +Let’s start to customize the test to our own needs. First, change the name of the `it_works` function to a different name, such as `exploration`, like so: Filename: src/lib.rs @@ -119,7 +127,7 @@ the `it_works` function to a different name, such as `exploration`, like so: {{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs}} ``` -Then run `cargo test` again. The output now shows `exploration` instead of +Then, run `cargo test` again. The output now shows `exploration` instead of `it_works`: ```console @@ -131,45 +139,54 @@ fail when something in the test function panics. Each test is run in a new thread, and when the main thread sees that a test thread has died, the test is marked as failed. In Chapter 9, we talked about how the simplest way to panic is to call the `panic!` macro. Enter the new test as a function named -`another`, so your *src/lib.rs* file looks like Listing 11-3. +`another`, so your _src/lib.rs_ file looks like Listing 11-3. -Filename: src/lib.rs + ```rust,panics,noplayground -{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs}} ``` -Listing 11-3: Adding a second test that will fail because -we call the `panic!` macro + Run the tests again using `cargo test`. The output should look like Listing 11-4, which shows that our `exploration` test passed and `another` failed. ++ ```console {{#include ../listings/ch11-writing-automated-tests/listing-11-03/output.txt}} ``` -Listing 11-4: Test results when one test passes and one -test fails + + + Instead of `ok`, the line `test tests::another` shows `FAILED`. Two new -sections appear between the individual results and the summary: the first +sections appear between the individual results and the summary: The first displays the detailed reason for each test failure. In this case, we get the -details that `another` failed because it `panicked at 'Make this test fail'` on -line 10 in the *src/lib.rs* file. The next section lists just the names of all -the failing tests, which is useful when there are lots of tests and lots of -detailed failing test output. We can use the name of a failing test to run just -that test to more easily debug it; we’ll talk more about ways to run tests in -the [“Controlling How Tests Are Run”][controlling-how-tests-are-run] section. - -The summary line displays at the end: overall, our test result is `FAILED`. We +details that `tests::another` failed because it panicked with the message `Make +this test fail` on line 17 in the _src/lib.rs_ file. The next section lists +just the names of all the failing tests, which is useful when there are lots of +tests and lots of detailed failing test output. We can use the name of a +failing test to run just that test to debug it more easily; we’ll talk more +about ways to run tests in the [“Controlling How Tests Are +Run”][controlling-how-tests-are-run] section. + +The summary line displays at the end: Overall, our test result is `FAILED`. We had one test pass and one test fail. Now that you’ve seen what the test results look like in different scenarios, let’s look at some macros other than `panic!` that are useful in tests. -### Checking Results with the `assert!` Macro + + + + +### Checking Results with `assert!` The `assert!` macro, provided by the standard library, is useful when you want to ensure that some condition in a test evaluates to `true`. We give the @@ -180,16 +197,15 @@ macro helps us check that our code is functioning in the way we intend. In Chapter 5, Listing 5-15, we used a `Rectangle` struct and a `can_hold` method, which are repeated here in Listing 11-5. Let’s put this code in the -*src/lib.rs* file, then write some tests for it using the `assert!` macro. +_src/lib.rs_ file, then write some tests for it using the `assert!` macro. -Filename: src/lib.rs + ```rust,noplayground -{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-05/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-05/src/lib.rs}} ``` -Listing 11-5: Using the `Rectangle` struct and its -`can_hold` method from Chapter 5 + The `can_hold` method returns a Boolean, which means it’s a perfect use case for the `assert!` macro. In Listing 11-6, we write a test that exercises the @@ -197,26 +213,25 @@ for the `assert!` macro. In Listing 11-6, we write a test that exercises the a height of 7 and asserting that it can hold another `Rectangle` instance that has a width of 5 and a height of 1. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-06/src/lib.rs:here}} ``` -Listing 11-6: A test for `can_hold` that checks whether a -larger rectangle can indeed hold a smaller rectangle + -Note that we’ve added a new line inside the `tests` module: `use super::*;`. -The `tests` module is a regular module that follows the usual visibility rules -we covered in Chapter 7 in the [“Paths for Referring to an Item in the Module +Note the `use super::*;` line inside the `tests` module. The `tests` module is +a regular module that follows the usual visibility rules we covered in Chapter +7 in the [“Paths for Referring to an Item in the Module Tree”][paths-for-referring-to-an-item-in-the-module-tree] section. Because the `tests` module is an inner module, we need to bring the code under test in the outer module into the scope of the inner module. We use -a glob here so anything we define in the outer module is available to this +a glob here, so anything we define in the outer module is available to this `tests` module. We’ve named our test `larger_can_hold_smaller`, and we’ve created the two -`Rectangle` instances that we need. Then we called the `assert!` macro and +`Rectangle` instances that we need. Then, we called the `assert!` macro and passed it the result of calling `larger.can_hold(&smaller)`. This expression is supposed to return `true`, so our test should pass. Let’s find out! @@ -243,8 +258,8 @@ result, our test will pass if `can_hold` returns `false`: Two tests that pass! Now let’s see what happens to our test results when we introduce a bug in our code. We’ll change the implementation of the `can_hold` -method by replacing the greater-than sign with a less-than sign when it -compares the widths: +method by replacing the greater-than sign (`>`) with a less-than sign (`<`) +when it compares the widths: ```rust,not_desired_behavior,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/src/lib.rs:here}} @@ -256,34 +271,37 @@ Running the tests now produces the following: {{#include ../listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/output.txt}} ``` -Our tests caught the bug! Because `larger.width` is 8 and `smaller.width` is -5, the comparison of the widths in `can_hold` now returns `false`: 8 is not +Our tests caught the bug! Because `larger.width` is `8` and `smaller.width` is +`5`, the comparison of the widths in `can_hold` now returns `false`: 8 is not less than 5. -### Testing Equality with the `assert_eq!` and `assert_ne!` Macros + + + + +### Testing Equality with `assert_eq!` and `assert_ne!` A common way to verify functionality is to test for equality between the result of the code under test and the value you expect the code to return. You could -do this using the `assert!` macro and passing it an expression using the `==` -operator. However, this is such a common test that the standard library +do this by using the `assert!` macro and passing it an expression using the +`==` operator. However, this is such a common test that the standard library provides a pair of macros—`assert_eq!` and `assert_ne!`—to perform this test more conveniently. These macros compare two arguments for equality or inequality, respectively. They’ll also print the two values if the assertion -fails, which makes it easier to see *why* the test failed; conversely, the +fails, which makes it easier to see _why_ the test failed; conversely, the `assert!` macro only indicates that it got a `false` value for the `==` expression, without printing the values that led to the `false` value. In Listing 11-7, we write a function named `add_two` that adds `2` to its -parameter, then we test this function using the `assert_eq!` macro. +parameter, and then we test this function using the `assert_eq!` macro. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-07/src/lib.rs}} ``` -Listing 11-7: Testing the function `add_two` using the -`assert_eq!` macro + Let’s check that it passes! @@ -291,9 +309,10 @@ Let’s check that it passes! {{#include ../listings/ch11-writing-automated-tests/listing-11-07/output.txt}} ``` -We pass `4` as the argument to `assert_eq!`, which is equal to the result of -calling `add_two(2)`. The line for this test is `test tests::it_adds_two ... -ok`, and the `ok` text indicates that our test passed! +We create a variable named `result` that holds the result of calling +`add_two(2)`. Then, we pass `result` and `4` as the arguments to the +`assert_eq!` macro. The output line for this test is `test tests::it_adds_two +... ok`, and the `ok` text indicates that our test passed! Let’s introduce a bug into our code to see what `assert_eq!` looks like when it fails. Change the implementation of the `add_two` function to instead add `3`: @@ -308,11 +327,11 @@ Run the tests again: {{#include ../listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/output.txt}} ``` -Our test caught the bug! The `it_adds_two` test failed, and the message tells -us that the assertion that fails was `` assertion failed: `(left == right)` `` -and what the `left` and `right` values are. This message helps us start -debugging: the `left` argument was `4` but the `right` argument, where we had -`add_two(2)`, was `5`. You can imagine that this would be especially helpful +Our test caught the bug! The `tests::it_adds_two` test failed, and the message +tells us that the assertion that failed was `left == right` and what the `left` +and `right` values are. This message helps us start debugging: The `left` +argument, where we had the result of calling `add_two(2)`, was `5`, but the +`right` argument was `4`. You can imagine that this would be especially helpful when we have a lot of tests going on. Note that in some languages and test frameworks, the parameters to equality @@ -320,15 +339,15 @@ assertion functions are called `expected` and `actual`, and the order in which we specify the arguments matters. However, in Rust, they’re called `left` and `right`, and the order in which we specify the value we expect and the value the code produces doesn’t matter. We could write the assertion in this test as -`assert_eq!(add_two(2), 4)`, which would result in the same failure message -that displays `` assertion failed: `(left == right)` ``. +`assert_eq!(4, result)`, which would result in the same failure message that +displays `` assertion `left == right` failed ``. The `assert_ne!` macro will pass if the two values we give it are not equal and -fail if they’re equal. This macro is most useful for cases when we’re not sure -what a value *will* be, but we know what the value definitely *shouldn’t* be. -For example, if we’re testing a function that is guaranteed to change its input -in some way, but the way in which the input is changed depends on the day of -the week that we run our tests, the best thing to assert might be that the +will fail if they are equal. This macro is most useful for cases when we’re not +sure what a value _will_ be, but we know what the value definitely _shouldn’t_ +be. For example, if we’re testing a function that is guaranteed to change its +input in some way, but the way in which the input is changed depends on the day +of the week that we run our tests, the best thing to assert might be that the output of the function is not equal to the input. Under the surface, the `assert_eq!` and `assert_ne!` macros use the operators @@ -349,13 +368,12 @@ details about these and other derivable traits. You can also add a custom message to be printed with the failure message as optional arguments to the `assert!`, `assert_eq!`, and `assert_ne!` macros. Any arguments specified after the required arguments are passed along to the -`format!` macro (discussed in Chapter 8 in the [“Concatenation with the `+` -Operator or the `format!` -Macro”][concatenation-with-the--operator-or-the-format-macro] -section), so you can pass a format string that contains `{}` placeholders and -values to go in those placeholders. Custom messages are useful for documenting -what an assertion means; when a test fails, you’ll have a better idea of what -the problem is with the code. +`format!` macro (discussed in [“Concatenating with `+` or +`format!`”][concatenating] in Chapter 8), so you can pass a format string that contains `{}` +placeholders and values to go in those placeholders. Custom messages are useful +for documenting what an assertion means; when a test fails, you’ll have a better +idea of what the problem is with the code. For example, let’s say we have a function that greets people by name and we want to test that the name we pass into the function appears in the output: @@ -421,14 +439,13 @@ inside the function doesn’t panic. Listing 11-8 shows a test that checks that the error conditions of `Guess::new` happen when we expect them to. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-08/src/lib.rs}} ``` -Listing 11-8: Testing that a condition will cause a -`panic!` + We place the `#[should_panic]` attribute after the `#[test]` attribute and before the test function it applies to. Let’s look at the result when this test @@ -464,20 +481,19 @@ consider the modified code for `Guess` in Listing 11-9 where the `new` function panics with different messages depending on whether the value is too small or too large. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-09/src/lib.rs:here}} ``` -Listing 11-9: Testing for a `panic!` with a panic message -containing a specified substring + This test will pass because the value we put in the `should_panic` attribute’s `expected` parameter is a substring of the message that the `Guess::new` function panics with. We could have specified the entire panic message that we expect, which in this case would be `Guess value must be less than or equal to -100, got 200.` What you choose to specify depends on how much of the panic +100, got 200`. What you choose to specify depends on how much of the panic message is unique or dynamic and how precise you want your test to be. In this case, a substring of the panic message is enough to ensure that the code in the test function executes the `else if value > 100` case. @@ -497,19 +513,19 @@ This time when we run the `should_panic` test, it will fail: ``` The failure message indicates that this test did indeed panic as we expected, -but the panic message did not include the expected string `'Guess value must be -less than or equal to 100'`. The panic message that we did get in this case was -`Guess value must be greater than or equal to 1, got 200.` Now we can start -figuring out where our bug is! +but the panic message did not include the expected string `less than or equal +to 100`. The panic message that we did get in this case was `Guess value must +be greater than or equal to 1, got 200`. Now we can start figuring out where +our bug is! ### Using `Result` in Tests -Our tests so far all panic when they fail. We can also write tests that use +All of our tests so far panic when they fail. We can also write tests that use `Result`! Here’s the test from Listing 11-1, rewritten to use `Result` and return an `Err` instead of panicking: ```rust,noplayground -{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs}} +{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs:here}} ``` The `it_works` function now has the `Result<(), String>` return type. In the @@ -517,12 +533,13 @@ body of the function, rather than calling the `assert_eq!` macro, we return `Ok(())` when the test passes and an `Err` with a `String` inside when the test fails. -Writing tests so they return a `Result` enables you to use the question -mark operator in the body of tests, which can be a convenient way to write -tests that should fail if any operation within them returns an `Err` variant. +Writing tests so that they return a `Result` enables you to use the +question mark operator in the body of tests, which can be a convenient way to +write tests that should fail if any operation within them returns an `Err` +variant. You can’t use the `#[should_panic]` annotation on tests that use `Result`. To assert that an operation returns an `Err` variant, *don’t* use the +E>`. To assert that an operation returns an `Err` variant, _don’t_ use the question mark operator on the `Result` value. Instead, use `assert!(value.is_err())`. @@ -530,13 +547,11 @@ Now that you know several ways to write tests, let’s look at what is happening when we run our tests and explore the different options we can use with `cargo test`. -[concatenation-with-the--operator-or-the-format-macro]: -ch08-02-strings.html#concatenation-with-the--operator-or-the-format-macro +[concatenating]: ch08-02-strings.html#concatenating-with--or-format [bench]: ../unstable-book/library-features/test.html -[ignoring]: ch11-02-running-tests.html#ignoring-some-tests-unless-specifically-requested +[ignoring]: ch11-02-running-tests.html#ignoring-tests-unless-specifically-requested [subset]: ch11-02-running-tests.html#running-a-subset-of-tests-by-name -[controlling-how-tests-are-run]: -ch11-02-running-tests.html#controlling-how-tests-are-run +[controlling-how-tests-are-run]: ch11-02-running-tests.html#controlling-how-tests-are-run [derivable-traits]: appendix-03-derivable-traits.html [doc-comments]: ch14-02-publishing-to-crates-io.html#documentation-comments-as-tests [paths-for-referring-to-an-item-in-the-module-tree]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html diff --git a/src/ch11-02-running-tests.md b/src/ch11-02-running-tests.md index 194718256c..788ff64596 100644 --- a/src/ch11-02-running-tests.md +++ b/src/ch11-02-running-tests.md @@ -1,37 +1,40 @@ ## Controlling How Tests Are Run -Just as `cargo run` compiles your code and then runs the resulting binary, -`cargo test` compiles your code in test mode and runs the resulting test +Just as `cargo run` compiles your code and then runs the resultant binary, +`cargo test` compiles your code in test mode and runs the resultant test binary. The default behavior of the binary produced by `cargo test` is to run all the tests in parallel and capture output generated during test runs, preventing the output from being displayed and making it easier to read the output related to the test results. You can, however, specify command line options to change this default behavior. -Some command line options go to `cargo test`, and some go to the resulting test +Some command line options go to `cargo test`, and some go to the resultant test binary. To separate these two types of arguments, you list the arguments that go to `cargo test` followed by the separator `--` and then the ones that go to the test binary. Running `cargo test --help` displays the options you can use with `cargo test`, and running `cargo test -- --help` displays the options you -can use after the separator. +can use after the separator. These options are also documented in [the “Tests” +section of _The `rustc` Book_][tests]. + +[tests]: https://doc.rust-lang.org/rustc/tests/index.html ### Running Tests in Parallel or Consecutively When you run multiple tests, by default they run in parallel using threads, -meaning they finish running faster and you get feedback quicker. Because the -tests are running at the same time, you must make sure your tests don’t depend -on each other or on any shared state, including a shared environment, such as -the current working directory or environment variables. +meaning they finish running more quickly and you get feedback sooner. Because +the tests are running at the same time, you must make sure your tests don’t +depend on each other or on any shared state, including a shared environment, +such as the current working directory or environment variables. For example, say each of your tests runs some code that creates a file on disk -named *test-output.txt* and writes some data to that file. Then each test reads -the data in that file and asserts that the file contains a particular value, -which is different in each test. Because the tests run at the same time, one -test might overwrite the file in the time between another test writing and -reading the file. The second test will then fail, not because the code is -incorrect but because the tests have interfered with each other while running -in parallel. One solution is to make sure each test writes to a different file; -another solution is to run the tests one at a time. +named _test-output.txt_ and writes some data to that file. Then, each test +reads the data in that file and asserts that the file contains a particular +value, which is different in each test. Because the tests run at the same time, +one test might overwrite the file in the time between when another test is +writing and reading the file. The second test will then fail, not because the +code is incorrect but because the tests have interfered with each other while +running in parallel. One solution is to make sure each test writes to a +different file; another solution is to run the tests one at a time. If you don’t want to run the tests in parallel or if you want more fine-grained control over the number of threads used, you can send the `--test-threads` flag @@ -58,14 +61,13 @@ printed to standard output with the rest of the failure message. As an example, Listing 11-10 has a silly function that prints the value of its parameter and returns 10, as well as a test that passes and a test that fails. -Filename: src/lib.rs + ```rust,panics,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-10/src/lib.rs}} ``` -Listing 11-10: Tests for a function that calls -`println!` + When we run these tests with `cargo test`, we’ll see the following output: @@ -73,13 +75,13 @@ When we run these tests with `cargo test`, we’ll see the following output: {{#include ../listings/ch11-writing-automated-tests/listing-11-10/output.txt}} ``` -Note that nowhere in this output do we see `I got the value 4`, which is what -is printed when the test that passes runs. That output has been captured. The +Note that nowhere in this output do we see `I got the value 4`, which is +printed when the test that passes runs. That output has been captured. The output from the test that failed, `I got the value 8`, appears in the section of the test summary output, which also shows the cause of the test failure. -If we want to see printed values for passing tests as well, we can tell Rust -to also show the output of successful tests with `--show-output`. +If we want to see printed values for passing tests as well, we can tell Rust to +also show the output of successful tests with `--show-output`: ```console $ cargo test -- --show-output @@ -94,7 +96,7 @@ see the following output: ### Running a Subset of Tests by Name -Sometimes, running a full test suite can take a long time. If you’re working on +Running a full test suite can sometimes take a long time. If you’re working on code in a particular area, you might want to run only the tests pertaining to that code. You can choose which tests to run by passing `cargo test` the name or names of the test(s) you want to run as an argument. @@ -102,14 +104,13 @@ or names of the test(s) you want to run as an argument. To demonstrate how to run a subset of tests, we’ll first create three tests for our `add_two` function, as shown in Listing 11-11, and choose which ones to run. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-11/src/lib.rs}} ``` -Listing 11-11: Three tests with three different -names + If we run the tests without passing any arguments, as we saw earlier, all the tests will run in parallel: @@ -148,7 +149,11 @@ named `one_hundred`. Also note that the module in which a test appears becomes part of the test’s name, so we can run all the tests in a module by filtering on the module’s name. -### Ignoring Some Tests Unless Specifically Requested + + + + +### Ignoring Tests Unless Specifically Requested Sometimes a few specific tests can be very time-consuming to execute, so you might want to exclude them during most runs of `cargo test`. Rather than @@ -159,11 +164,11 @@ here: Filename: src/lib.rs ```rust,noplayground -{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs}} +{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs:here}} ``` -After `#[test]` we add the `#[ignore]` line to the test we want to exclude. Now -when we run our tests, `it_works` runs, but `expensive_test` doesn’t: +After `#[test]`, we add the `#[ignore]` line to the test we want to exclude. +Now when we run our tests, `it_works` runs, but `expensive_test` doesn’t: ```console {{#include ../listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/output.txt}} @@ -177,7 +182,7 @@ the ignored tests, we can use `cargo test -- --ignored`: ``` By controlling which tests run, you can make sure your `cargo test` results -will be fast. When you’re at a point where it makes sense to check the results -of the `ignored` tests and you have time to wait for the results, you can run -`cargo test -- --ignored` instead. If you want to run all tests whether they’re -ignored or not, you can run `cargo test -- --include-ignored`. +will be returned quickly. When you’re at a point where it makes sense to check +the results of the `ignored` tests and you have time to wait for the results, +you can run `cargo test -- --ignored` instead. If you want to run all tests +whether they’re ignored or not, you can run `cargo test -- --include-ignored`. diff --git a/src/ch11-03-test-organization.md b/src/ch11-03-test-organization.md index 9f26546cf4..dad604f6d0 100644 --- a/src/ch11-03-test-organization.md +++ b/src/ch11-03-test-organization.md @@ -3,8 +3,8 @@ As mentioned at the start of the chapter, testing is a complex discipline, and different people use different terminology and organization. The Rust community thinks about tests in terms of two main categories: unit tests and integration -tests. *Unit tests* are small and more focused, testing one module in isolation -at a time, and can test private interfaces. *Integration tests* are entirely +tests. _Unit tests_ are small and more focused, testing one module in isolation +at a time, and can test private interfaces. _Integration tests_ are entirely external to your library and use your code in the same way any other external code would, using only the public interface and potentially exercising multiple modules per test. @@ -16,21 +16,21 @@ library are doing what you expect them to, separately and together. The purpose of unit tests is to test each unit of code in isolation from the rest of the code to quickly pinpoint where code is and isn’t working as -expected. You’ll put unit tests in the *src* directory in each file with the +expected. You’ll put unit tests in the _src_ directory in each file with the code that they’re testing. The convention is to create a module named `tests` in each file to contain the test functions and to annotate the module with `cfg(test)`. -#### The Tests Module and `#[cfg(test)]` +#### The `tests` Module and `#[cfg(test)]` -The `#[cfg(test)]` annotation on the tests module tells Rust to compile and run -the test code only when you run `cargo test`, not when you run `cargo build`. -This saves compile time when you only want to build the library and saves space -in the resulting compiled artifact because the tests are not included. You’ll -see that because integration tests go in a different directory, they don’t need -the `#[cfg(test)]` annotation. However, because unit tests go in the same files -as the code, you’ll use `#[cfg(test)]` to specify that they shouldn’t be -included in the compiled result. +The `#[cfg(test)]` annotation on the `tests` module tells Rust to compile and +run the test code only when you run `cargo test`, not when you run `cargo +build`. This saves compile time when you only want to build the library and +saves space in the resultant compiled artifact because the tests are not +included. You’ll see that because integration tests go in a different +directory, they don’t need the `#[cfg(test)]` annotation. However, because unit +tests go in the same files as the code, you’ll use `#[cfg(test)]` to specify +that they shouldn’t be included in the compiled result. Recall that when we generated the new `adder` project in the first section of this chapter, Cargo generated this code for us: @@ -41,16 +41,19 @@ this chapter, Cargo generated this code for us: {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs}} ``` -This code is the automatically generated test module. The attribute `cfg` -stands for *configuration* and tells Rust that the following item should only -be included given a certain configuration option. In this case, the -configuration option is `test`, which is provided by Rust for compiling and -running tests. By using the `cfg` attribute, Cargo compiles our test code only -if we actively run the tests with `cargo test`. This includes any helper -functions that might be within this module, in addition to the functions -annotated with `#[test]`. +On the automatically generated `tests` module, the attribute `cfg` stands for +_configuration_ and tells Rust that the following item should only be included +given a certain configuration option. In this case, the configuration option is +`test`, which is provided by Rust for compiling and running tests. By using the +`cfg` attribute, Cargo compiles our test code only if we actively run the tests +with `cargo test`. This includes any helper functions that might be within this +module, in addition to the functions annotated with `#[test]`. -#### Testing Private Functions + + + + +#### Private Function Tests There’s debate within the testing community about whether or not private functions should be tested directly, and other languages make it difficult or @@ -58,22 +61,22 @@ impossible to test private functions. Regardless of which testing ideology you adhere to, Rust’s privacy rules do allow you to test private functions. Consider the code in Listing 11-12 with the private function `internal_adder`. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-12/src/lib.rs}} ``` -Listing 11-12: Testing a private function + Note that the `internal_adder` function is not marked as `pub`. Tests are just Rust code, and the `tests` module is just another module. As we discussed in -the [“Paths for Referring to an Item in the Module Tree”][paths] -section, items in child modules can use the items in their ancestor modules. In -this test, we bring all of the `test` module’s parent’s items into scope with -`use super::*`, and then the test can call `internal_adder`. If you don’t think -private functions should be tested, there’s nothing in Rust that will compel -you to do so. +[“Paths for Referring to an Item in the Module Tree”][paths], +items in child modules can use the items in their ancestor modules. In this +test, we bring all of the items belonging to the `tests` module’s parent into +scope with `use super::*`, and then the test can call `internal_adder`. If you +don’t think private functions should be tested, there’s nothing in Rust that +will compel you to do so. ### Integration Tests @@ -83,18 +86,18 @@ functions that are part of your library’s public API. Their purpose is to test whether many parts of your library work together correctly. Units of code that work correctly on their own could have problems when integrated, so test coverage of the integrated code is important as well. To create integration -tests, you first need a *tests* directory. +tests, you first need a _tests_ directory. -#### The *tests* Directory +#### The _tests_ Directory -We create a *tests* directory at the top level of our project directory, next -to *src*. Cargo knows to look for integration test files in this directory. We +We create a _tests_ directory at the top level of our project directory, next +to _src_. Cargo knows to look for integration test files in this directory. We can then make as many test files as we want, and Cargo will compile each of the files as an individual crate. Let’s create an integration test. With the code in Listing 11-12 still in the -*src/lib.rs* file, make a *tests* directory, and create a new file named -*tests/integration_test.rs*. Your directory structure should look like this: +_src/lib.rs_ file, make a _tests_ directory, and create a new file named +_tests/integration_test.rs_. Your directory structure should look like this: ```text adder @@ -106,23 +109,22 @@ adder └── integration_test.rs ``` -Enter the code in Listing 11-13 into the *tests/integration_test.rs* file: +Enter the code in Listing 11-13 into the _tests/integration_test.rs_ file. -Filename: tests/integration_test.rs + ```rust,ignore {{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-13/tests/integration_test.rs}} ``` -Listing 11-13: An integration test of a function in the -`adder` crate + -Each file in the `tests` directory is a separate crate, so we need to bring our -library into each test crate’s scope. For that reason we add `use adder` at the -top of the code, which we didn’t need in the unit tests. +Each file in the _tests_ directory is a separate crate, so we need to bring our +library into each test crate’s scope. For that reason, we add `use +adder::add_two;` at the top of the code, which we didn’t need in the unit tests. -We don’t need to annotate any code in *tests/integration_test.rs* with -`#[cfg(test)]`. Cargo treats the `tests` directory specially and compiles files +We don’t need to annotate any code in _tests/integration_test.rs_ with +`#[cfg(test)]`. Cargo treats the _tests_ directory specially and compiles files in this directory only when we run `cargo test`. Run `cargo test` now: ```console @@ -132,7 +134,7 @@ in this directory only when we run `cargo test`. Run `cargo test` now: The three sections of output include the unit tests, the integration test, and the doc tests. Note that if any test in a section fails, the following sections will not be run. For example, if a unit test fails, there won’t be any output -for integration and doc tests because those tests will only be run if all unit +for integration and doc tests, because those tests will only be run if all unit tests are passing. The first section for the unit tests is the same as we’ve been seeing: one line @@ -145,7 +147,7 @@ that integration test and a summary line for the results of the integration test just before the `Doc-tests adder` section starts. Each integration test file has its own section, so if we add more files in the -*tests* directory, there will be more integration test sections. +_tests_ directory, there will be more integration test sections. We can still run a particular integration test function by specifying the test function’s name as an argument to `cargo test`. To run all the tests in a @@ -156,24 +158,24 @@ followed by the name of the file: {{#include ../listings/ch11-writing-automated-tests/output-only-05-single-integration/output.txt}} ``` -This command runs only the tests in the *tests/integration_test.rs* file. +This command runs only the tests in the _tests/integration_test.rs_ file. #### Submodules in Integration Tests As you add more integration tests, you might want to make more files in the -*tests* directory to help organize them; for example, you can group the test +_tests_ directory to help organize them; for example, you can group the test functions by the functionality they’re testing. As mentioned earlier, each file -in the *tests* directory is compiled as its own separate crate, which is useful +in the _tests_ directory is compiled as its own separate crate, which is useful for creating separate scopes to more closely imitate the way end users will be -using your crate. However, this means files in the *tests* directory don’t -share the same behavior as files in *src* do, as you learned in Chapter 7 +using your crate. However, this means files in the _tests_ directory don’t +share the same behavior as files in _src_ do, as you learned in Chapter 7 regarding how to separate code into modules and files. -The different behavior of *tests* directory files is most noticeable when you -have a set of helper functions to use in multiple integration test files and +The different behavior of _tests_ directory files is most noticeable when you +have a set of helper functions to use in multiple integration test files, and you try to follow the steps in the [“Separating Modules into Different Files”][separating-modules-into-files] section of Chapter 7 to -extract them into a common module. For example, if we create *tests/common.rs* +extract them into a common module. For example, if we create _tests/common.rs_ and place a function named `setup` in it, we can add some code to `setup` that we want to call from multiple test functions in multiple test files: @@ -184,7 +186,7 @@ we want to call from multiple test functions in multiple test files: ``` When we run the tests again, we’ll see a new section in the test output for the -*common.rs* file, even though this file doesn’t contain any test functions nor +_common.rs_ file, even though this file doesn’t contain any test functions nor did we call the `setup` function from anywhere: ```console @@ -193,11 +195,9 @@ did we call the `setup` function from anywhere: Having `common` appear in the test results with `running 0 tests` displayed for it is not what we wanted. We just wanted to share some code with the other -integration test files. - -To avoid having `common` appear in the test output, instead of creating -*tests/common.rs*, we’ll create *tests/common/mod.rs*. The project directory -now looks like this: +integration test files. To avoid having `common` appear in the test output, +instead of creating _tests/common.rs_, we’ll create _tests/common/mod.rs_. The +project directory now looks like this: ```text ├── Cargo.lock @@ -210,18 +210,17 @@ now looks like this: └── integration_test.rs ``` -This is the older naming convention that Rust also understands that we -mentioned in the [“Alternate File Paths”][alt-paths] section of -Chapter 7. Naming the file this way tells Rust not to treat the `common` module -as an integration test file. When we move the `setup` function code into -*tests/common/mod.rs* and delete the *tests/common.rs* file, the section in the -test output will no longer appear. Files in subdirectories of the *tests* -directory don’t get compiled as separate crates or have sections in the test -output. +This is the older naming convention that Rust also understands that we mentioned +in [“Alternate File Paths”][alt-paths] in Chapter 7. Naming the +file this way tells Rust not to treat the `common` module as an integration test +file. When we move the `setup` function code into _tests/common/mod.rs_ and +delete the _tests/common.rs_ file, the section in the test output will no longer +appear. Files in subdirectories of the _tests_ directory don’t get compiled as +separate crates or have sections in the test output. -After we’ve created *tests/common/mod.rs*, we can use it from any of the +After we’ve created _tests/common/mod.rs_, we can use it from any of the integration test files as a module. Here’s an example of calling the `setup` -function from the `it_adds_two` test in *tests/integration_test.rs*: +function from the `it_adds_two` test in _tests/integration_test.rs_: Filename: tests/integration_test.rs @@ -230,30 +229,29 @@ function from the `it_adds_two` test in *tests/integration_test.rs*: ``` Note that the `mod common;` declaration is the same as the module declaration -we demonstrated in Listing 7-21. Then in the test function, we can call the +we demonstrated in Listing 7-21. Then, in the test function, we can call the `common::setup()` function. #### Integration Tests for Binary Crates -If our project is a binary crate that only contains a *src/main.rs* file and -doesn’t have a *src/lib.rs* file, we can’t create integration tests in the -*tests* directory and bring functions defined in the *src/main.rs* file into +If our project is a binary crate that only contains a _src/main.rs_ file and +doesn’t have a _src/lib.rs_ file, we can’t create integration tests in the +_tests_ directory and bring functions defined in the _src/main.rs_ file into scope with a `use` statement. Only library crates expose functions that other crates can use; binary crates are meant to be run on their own. This is one of the reasons Rust projects that provide a binary have a -straightforward *src/main.rs* file that calls logic that lives in the -*src/lib.rs* file. Using that structure, integration tests *can* test the -library crate with `use` to make the important functionality available. -If the important functionality works, the small amount of code in the -*src/main.rs* file will work as well, and that small amount of code doesn’t -need to be tested. +straightforward _src/main.rs_ file that calls logic that lives in the +_src/lib.rs_ file. Using that structure, integration tests _can_ test the +library crate with `use` to make the important functionality available. If the +important functionality works, the small amount of code in the _src/main.rs_ +file will work as well, and that small amount of code doesn’t need to be tested. ## Summary Rust’s testing features provide a way to specify how code should function to -ensure it continues to work as you expect, even as you make changes. Unit tests -exercise different parts of a library separately and can test private +ensure that it continues to work as you expect, even as you make changes. Unit +tests exercise different parts of a library separately and can test private implementation details. Integration tests check that many parts of the library work together correctly, and they use the library’s public API to test the code in the same way external code will use it. Even though Rust’s type system and @@ -264,6 +262,5 @@ Let’s combine the knowledge you learned in this chapter and in previous chapters to work on a project! [paths]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html -[separating-modules-into-files]: -ch07-05-separating-modules-into-different-files.html +[separating-modules-into-files]: ch07-05-separating-modules-into-different-files.html [alt-paths]: ch07-05-separating-modules-into-different-files.html#alternate-file-paths diff --git a/src/ch12-00-an-io-project.md b/src/ch12-00-an-io-project.md index bae99c75f7..569ce2bcb5 100644 --- a/src/ch12-00-an-io-project.md +++ b/src/ch12-00-an-io-project.md @@ -1,45 +1,47 @@ -# An I/O Project: Building a Command Line Program - -This chapter is a recap of the many skills you’ve learned so far and an -exploration of a few more standard library features. We’ll build a command line -tool that interacts with file and command line input/output to practice some of -the Rust concepts you now have under your belt. - -Rust’s speed, safety, single binary output, and cross-platform support make it -an ideal language for creating command line tools, so for our project, we’ll -make our own version of the classic command line search tool `grep` -(**g**lobally search a **r**egular **e**xpression and **p**rint). In the -simplest use case, `grep` searches a specified file for a specified string. To -do so, `grep` takes as its arguments a file path and a string. Then it reads -the file, finds lines in that file that contain the string argument, and prints -those lines. - -Along the way, we’ll show how to make our command line tool use the terminal -features that many other command line tools use. We’ll read the value of an -environment variable to allow the user to configure the behavior of our tool. -We’ll also print error messages to the standard error console stream (`stderr`) -instead of standard output (`stdout`), so, for example, the user can redirect -successful output to a file while still seeing error messages onscreen. - -One Rust community member, Andrew Gallant, has already created a fully -featured, very fast version of `grep`, called `ripgrep`. By comparison, our -version will be fairly simple, but this chapter will give you some of the -background knowledge you need to understand a real-world project such as -`ripgrep`. - -Our `grep` project will combine a number of concepts you’ve learned so far: - -* Organizing code (using what you learned about modules in [Chapter 7][ch7]) -* Using vectors and strings (collections, [Chapter 8][ch8]) -* Handling errors ([Chapter 9][ch9]) -* Using traits and lifetimes where appropriate ([Chapter 10][ch10]) -* Writing tests ([Chapter 11][ch11]) - -We’ll also briefly introduce closures, iterators, and trait objects, which -Chapters [13][ch13] and [17][ch17] will cover in -detail. +# Proyek I/O: Membangun Program Command Line + +Bab ini adalah rekap dari banyak skill yang sudah kamu pelajari sejauh ini +sekaligus eksplorasi beberapa fitur tambahan dari standard library. Kita akan +membangun sebuah **command line tool** yang berinteraksi dengan file dan +input/output terminal untuk mempraktikkan konsep Rust yang sekarang sudah kamu +kuasai. + +Kecepatan Rust, keamanannya, hasil berupa satu binary, dan dukungan lintas +platform membuat Rust jadi bahasa yang ideal untuk bikin command line tool. +Jadi, di proyek kali ini kita akan bikin versi sederhana dari tool classic +bernama `grep` (**g**lobally search a **r**egular **e**xpression and **p**rint). +Dalam penggunaan paling sederhana, `grep` akan mencari string tertentu di dalam +file tertentu. `grep` menerima dua argumen: path file dan string yang mau +dicari. Lalu tool ini membaca file tersebut, mencari baris yang mengandung +string itu, dan menampilkan baris-baris yang cocok. + +Sepanjang prosesnya, kita juga bakal belajar gimana bikin command line tool kita +terasa “profesional”, seperti tool CLI lain pada umumnya. Kita akan: + +- membaca nilai environment variable untuk mengonfigurasi perilaku tool, +- menampilkan error ke stream **stderr** (standard error), bukan `stdout`, + supaya user bisa mengalihkan output normal ke file sambil tetap melihat pesan + error di layar. + +Di komunitas Rust sendiri, sudah ada anggota bernama Andrew Gallant yang bikin +versi `grep` yang jauh lebih lengkap dan super cepat bernama **ripgrep**. +Dibandingkan itu, versi kita bakal jauh lebih sederhana. Tapi bab ini bakal +memberi kamu fondasi untuk bisa memahami proyek dunia nyata seperti `ripgrep`. + +Proyek `grep` kita bakal menggabungkan berbagai konsep yang sudah kamu pelajari: + +- Mengorganisasi kode ([Chapter 7][ch7]) +- Menggunakan vector dan string ([Chapter 8][ch8]) +- Menangani error ([Chapter 9][ch9]) +- Menggunakan traits dan lifetimes dengan tepat + ([Chapter 10][ch10]) +- Menulis test ([Chapter 11][ch11]) + +Selain itu, kita juga bakal sekilas mengenalkan closures, iterators, dan trait +objects, yang akan dibahas lebih dalam di: + +- [Chapter 13][ch13] +- [Chapter 18][ch18] [ch7]: ch07-00-managing-growing-projects-with-packages-crates-and-modules.html [ch8]: ch08-00-common-collections.html @@ -47,4 +49,4 @@ detail. [ch10]: ch10-00-generics.html [ch11]: ch11-00-testing.html [ch13]: ch13-00-functional-features.html -[ch17]: ch17-00-oop.html +[ch18]: ch18-00-oop.html diff --git a/src/ch12-01-accepting-command-line-arguments.md b/src/ch12-01-accepting-command-line-arguments.md index bb69366633..1eede992a1 100644 --- a/src/ch12-01-accepting-command-line-arguments.md +++ b/src/ch12-01-accepting-command-line-arguments.md @@ -1,8 +1,8 @@ -## Accepting Command Line Arguments +## Menerima Argumen dari Command Line -Let’s create a new project with, as always, `cargo new`. We’ll call our project -`minigrep` to distinguish it from the `grep` tool that you might already have -on your system. +Sekarang kita bikin project baru seperti biasa pakai `cargo new`. Kita kasih +nama project-nya **`minigrep`** supaya beda dari tool `grep` yang mungkin sudah +ada di sistem kamu: ```console $ cargo new minigrep @@ -10,73 +10,76 @@ $ cargo new minigrep $ cd minigrep ``` -The first task is to make `minigrep` accept its two command line arguments: the -file path and a string to search for. That is, we want to be able to run our -program with `cargo run`, two hyphens to indicate the following arguments are -for our program rather than for `cargo`, a string to search for, and a path to -a file to search in, like so: +Tugas pertama kita adalah bikin `minigrep` bisa menerima **dua argumen dari +command line**: path file dan string yang mau dicari. Jadi, kita pengin bisa +jalanin program kaya gini: kita pakai `cargo run`, lalu dua tanda minus (`--`) +buat nandain bahwa argumen setelah itu milik program kita (bukan milik Cargo), +lalu string yang mau dicari, dan path file tempat mencarinya. Contohnya: ```console -$ cargo run -- searchstring example-filename.txt +cargo run -- searchstring example-filename.txt ``` -Right now, the program generated by `cargo new` cannot process arguments we -give it. Some existing libraries on [crates.io](https://crates.io/) can help -with writing a program that accepts command line arguments, but because you’re -just learning this concept, let’s implement this capability ourselves. +Saat ini, program yang dibuat oleh `cargo new` belum bisa memproses argumen yang +kita kasih. Sebenarnya sudah ada beberapa library di +[crates.io](https://crates.io/) yang bisa bantu bikin program yang menerima +argumen command line, tapi karena kamu lagi belajar konsepnya, kita bakal bikin +fitur ini sendiri dulu. -### Reading the Argument Values +### Membaca Nilai Argumen -To enable `minigrep` to read the values of command line arguments we pass to -it, we’ll need the `std::env::args` function provided in Rust’s standard -library. This function returns an iterator of the command line arguments passed -to `minigrep`. We’ll cover iterators fully in [Chapter 13][ch13]. For now, you only need to know two details about iterators: iterators -produce a series of values, and we can call the `collect` method on an iterator -to turn it into a collection, such as a vector, that contains all the elements -the iterator produces. +Supaya `minigrep` bisa membaca nilai argumen command line yang kita kirim, kita +butuh fungsi `std::env::args` dari standard library Rust. Fungsi ini +mengembalikan **iterator** yang berisi argumen-argumen command line yang +diberikan ke `minigrep`. -The code in Listing 12-1 allows your `minigrep` program to read any command -line arguments passed to it and then collect the values into a vector. +Kita bakal membahas iterator lebih lengkap di [Chapter 13][ch13]. +Untuk sekarang, cukup tahu dua hal ini: -Filename: src/main.rs +- Iterator menghasilkan urutan nilai. +- Kita bisa memanggil `collect` pada iterator untuk mengubahnya menjadi koleksi + (misalnya `vector`) yang berisi semua elemen dari iterator tersebut. + +Kode di Listing 12-1 memungkinkan program `minigrep` kamu membaca semua argumen +command line yang diberikan dan mengumpulkannya ke dalam sebuah vector. + + ```rust {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-01/src/main.rs}} ``` -Listing 12-1: Collecting the command line arguments into -a vector and printing them + -First, we bring the `std::env` module into scope with a `use` statement so we -can use its `args` function. Notice that the `std::env::args` function is -nested in two levels of modules. As we discussed in [Chapter -7][ch7-idiomatic-use], in cases where the desired function is -nested in more than one module, we’ve chosen to bring the parent module into -scope rather than the function. By doing so, we can easily use other functions -from `std::env`. It’s also less ambiguous than adding `use std::env::args` and -then calling the function with just `args`, because `args` might easily be -mistaken for a function that’s defined in the current module. +Pertama, kita masukin module `std::env` ke dalam scope pakai `use` supaya kita +bisa pakai fungsi `args`. Perhatikan kalau `std::env::args` itu berada dua level +di dalam module. Seperti yang dibahas di +[Chapter 7][ch7-idiomatic-use], kalau fungsi yang kita butuh ada +jauh di dalam beberapa module, biasanya lebih enak masukin **parent module-nya** +aja, bukan fungsi langsung. Dengan begitu kita bisa gampang pakai fungsi lain +dari `std::env`. Selain itu, ini juga lebih jelas dibanding `use std::env::args` +lalu memanggil `args`, karena nanti `args` bisa disalahpahami seolah-olah fungsi +lokal. -> ### The `args` Function and Invalid Unicode +> ### Fungsi `args` dan Unicode Tidak Valid > -> Note that `std::env::args` will panic if any argument contains invalid -> Unicode. If your program needs to accept arguments containing invalid -> Unicode, use `std::env::args_os` instead. That function returns an iterator -> that produces `OsString` values instead of `String` values. We’ve chosen to -> use `std::env::args` here for simplicity, because `OsString` values differ -> per platform and are more complex to work with than `String` values. - -On the first line of `main`, we call `env::args`, and we immediately use -`collect` to turn the iterator into a vector containing all the values produced -by the iterator. We can use the `collect` function to create many kinds of -collections, so we explicitly annotate the type of `args` to specify that we -want a vector of strings. Although we very rarely need to annotate types in -Rust, `collect` is one function you do often need to annotate because Rust -isn’t able to infer the kind of collection you want. - -Finally, we print the vector using the debug macro. Let’s try running the code -first with no arguments and then with two arguments: +> Perlu dicatat, `std::env::args` bakal panic kalau ada argumen yang mengandung +> Unicode tidak valid. Kalau programmu harus menerima argumen yang mungkin +> berisi Unicode tidak valid, pakai `std::env::args_os` saja. Fungsi itu +> mengembalikan iterator yang menghasilkan `OsString`, bukan `String`. Di sini +> kita tetap pakai `std::env::args` biar simpel, karena `OsString` beda-beda +> tergantung platform dan lebih ribet dipakai dibanding `String`. + +Di baris pertama `main`, kita memanggil `env::args`, lalu langsung memanggil +`collect` untuk mengubah iterator-nya jadi vector yang berisi semua argumen yang +diterima. Fungsi `collect` bisa bikin banyak jenis koleksi, jadi kita perlu +kasih tahu tipenya secara eksplisit, dalam hal ini kita mau **vector of +String**. Walaupun biasanya kita jarang banget perlu tulis tipe di Rust, khusus +untuk `collect` kita memang sering butuh anotasi karena Rust nggak bisa nebak +mau jadi koleksi apa. + +Terakhir, kita print vector tersebut pakai debug macro. Sekarang coba jalankan +programnya—pertama tanpa argumen sama sekali, lalu dengan dua argumen. ```console {{#include ../listings/ch12-an-io-project/listing-12-01/output.txt}} @@ -86,50 +89,51 @@ first with no arguments and then with two arguments: {{#include ../listings/ch12-an-io-project/output-only-01-with-args/output.txt}} ``` -Notice that the first value in the vector is `"target/debug/minigrep"`, which -is the name of our binary. This matches the behavior of the arguments list in -C, letting programs use the name by which they were invoked in their execution. -It’s often convenient to have access to the program name in case you want to -print it in messages or change behavior of the program based on what command -line alias was used to invoke the program. But for the purposes of this -chapter, we’ll ignore it and save only the two arguments we need. +Perhatikan bahwa nilai pertama di dalam vector adalah `"target/debug/minigrep"`, +yaitu nama binary program kita. Ini sama seperti perilaku daftar argumen di C, +yang memungkinkan program mengetahui nama perintah yang dipakai saat program +dijalankan. Ini sering berguna kalau kamu mau menampilkan nama program di pesan +tertentu atau mengubah perilaku program berdasarkan alias command line yang +dipakai. Tapi untuk kebutuhan bab ini, kita bakal abaikan bagian itu dan fokus +hanya pada dua argumen yang kita perlukan. -### Saving the Argument Values in Variables +### Menyimpan Nilai Argumen ke dalam Variabel -The program is currently able to access the values specified as command line -arguments. Now we need to save the values of the two arguments in variables so -we can use the values throughout the rest of the program. We do that in Listing -12-2. +Sekarang program sudah bisa mengakses nilai yang dikasih lewat command line. +Langkah berikutnya, kita perlu menyimpan kedua nilai argumen itu ke dalam +variabel supaya bisa dipakai di bagian lain program. Kita lakukan itu seperti +yang ditunjukkan pada Listing 12-2. -Filename: src/main.rs + ```rust,should_panic,noplayground {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-02/src/main.rs}} ``` -Listing 12-2: Creating variables to hold the query -argument and file path argument + -As we saw when we printed the vector, the program’s name takes up the first -value in the vector at `args[0]`, so we’re starting arguments at index `1`. The -first argument `minigrep` takes is the string we’re searching for, so we put a -reference to the first argument in the variable `query`. The second argument -will be the file path, so we put a reference to the second argument in the -variable `file_path`. +Seperti yang sudah kita lihat waktu nge-print vector tadi, nama program ada di +indeks pertama (`args[0]`), jadi kita mulai baca argumen dari indeks 1. Argumen +pertama yang diterima `minigrep` adalah string yang ingin kita cari, jadi kita +simpan referensi ke argumen pertama itu ke variabel `query`. Argumen kedua +adalah path file, jadi kita simpan referensi ke argumen kedua ke variabel +`file_path`. -We temporarily print the values of these variables to prove that the code is -working as we intend. Let’s run this program again with the arguments `test` -and `sample.txt`: +Untuk sementara, kita print nilai kedua variabel ini dulu untuk memastikan kode +bekerja sesuai yang kita mau. Sekarang coba jalankan lagi programnya dengan +argumen `test` dan `sample.txt`: ```console {{#include ../listings/ch12-an-io-project/listing-12-02/output.txt}} ``` -Great, the program is working! The values of the arguments we need are being -saved into the right variables. Later we’ll add some error handling to deal -with certain potential erroneous situations, such as when the user provides no -arguments; for now, we’ll ignore that situation and work on adding file-reading -capabilities instead. +Mantap, programnya sudah jalan dengan benar! Nilai argumen yang kita butuhkan +sekarang sudah tersimpan di variabel yang tepat. Nanti kita akan tambahkan error +handling untuk menangani kemungkinan masalah, misalnya kalau user tidak +memberikan argumen sama sekali. + +Untuk sekarang, kita abaikan dulu kasus itu dan lanjut fokus ke langkah +berikutnya: menambahkan kemampuan membaca file. [ch13]: ch13-00-functional-features.html [ch7-idiomatic-use]: ch07-04-bringing-paths-into-scope-with-the-use-keyword.html#creating-idiomatic-use-paths diff --git a/src/ch12-02-reading-a-file.md b/src/ch12-02-reading-a-file.md index d8340a2a07..9e97575229 100644 --- a/src/ch12-02-reading-a-file.md +++ b/src/ch12-02-reading-a-file.md @@ -1,57 +1,58 @@ -## Reading a File +## Membaca File -Now we’ll add functionality to read the file specified in the `file_path` -argument. First, we need a sample file to test it with: we’ll use a file with a -small amount of text over multiple lines with some repeated words. Listing 12-3 -has an Emily Dickinson poem that will work well! Create a file called -*poem.txt* at the root level of your project, and enter the poem “I’m Nobody! -Who are you?” +Sekarang kita bakal nambahin fitur buat membaca file yang disebutkan di argumen +`file_path`. Pertama, kita butuh file contoh buat ngetesnya. Kita akan pakai +file berisi teks pendek dengan beberapa baris dan beberapa kata yang berulang. +Listing 12-3 berisi puisi Emily Dickinson yang pas banget buat ini! -Filename: poem.txt +Buat file bernama _**poem.txt**_ di root project kamu, lalu isi dengan puisi +**“I’m Nobody! Who are you?”** + + ```text {{#include ../listings/ch12-an-io-project/listing-12-03/poem.txt}} ``` -Listing 12-3: A poem by Emily Dickinson makes a good test -case + -With the text in place, edit *src/main.rs* and add code to read the file, as -shown in Listing 12-4. +Sekarang setelah teksnya sudah siap, edit file _**src/main.rs**_ dan tambahkan +kode untuk membaca file, seperti yang ditunjukkan pada Listing 12-4. -Filename: src/main.rs + ```rust,should_panic,noplayground {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-04/src/main.rs:here}} ``` -Listing 12-4: Reading the contents of the file specified -by the second argument + -First, we bring in a relevant part of the standard library with a `use` -statement: we need `std::fs` to handle files. +Pertama, kita masukin bagian yang relevan dari standard library pakai `use`: +kita butuh `std::fs` untuk menangani file. -In `main`, the new statement `fs::read_to_string` takes the `file_path`, opens -that file, and returns a `std::io::Result` of the file’s contents. +Di dalam `main`, perintah baru `fs::read_to_string` menerima `file_path`, +membuka file tersebut, lalu mengembalikan nilai bertipe +`std::io::Result` yang berisi isi file. -After that, we again add a temporary `println!` statement that prints the value -of `contents` after the file is read, so we can check that the program is -working so far. +Setelah itu, kita tambahkan lagi `println!` sementara untuk nge-print nilai +`contents` setelah file dibaca, supaya kita bisa cek apakah programnya sudah +jalan sesuai harapan. -Let’s run this code with any string as the first command line argument (because -we haven’t implemented the searching part yet) and the *poem.txt* file as the -second argument: +Sekarang coba jalankan programnya—isi argumen pertama dengan string apa saja +(karena fitur pencariannya belum kita implementasi), dan argumen kedua dengan +nama file **poem.txt**: ```console {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-04/output.txt}} ``` -Great! The code read and then printed the contents of the file. But the code -has a few flaws. At the moment, the `main` function has multiple -responsibilities: generally, functions are clearer and easier to maintain if -each function is responsible for only one idea. The other problem is that we’re -not handling errors as well as we could. The program is still small, so these -flaws aren’t a big problem, but as the program grows, it will be harder to fix -them cleanly. It’s good practice to begin refactoring early on when developing -a program, because it’s much easier to refactor smaller amounts of code. We’ll -do that next. +Baik! Kode tersebut berhasil membaca lalu mencetak isi file. Namun, kode ini +memiliki beberapa kekurangan. Saat ini, fungsi `main` memiliki banyak tanggung +jawab sekaligus: secara umum, fungsi akan lebih jelas dan lebih mudah dirawat +jika masing-masing hanya bertanggung jawab pada satu hal. Masalah lainnya adalah +kita belum menangani error sebaik mungkin. Program ini memang masih kecil, jadi +kekurangan tersebut belum menjadi masalah besar, tetapi ketika program +berkembang, akan lebih sulit untuk memperbaikinya dengan rapi. Merupakan praktik +yang baik untuk mulai melakukan refactoring sejak awal saat mengembangkan +program karena akan jauh lebih mudah melakukan refactor pada kode yang masih +sedikit. Kita akan melakukannya selanjutnya. diff --git a/src/ch12-03-improving-error-handling-and-modularity.md b/src/ch12-03-improving-error-handling-and-modularity.md index 87e525d122..89dd8febd9 100644 --- a/src/ch12-03-improving-error-handling-and-modularity.md +++ b/src/ch12-03-improving-error-handling-and-modularity.md @@ -1,428 +1,457 @@ -## Refactoring to Improve Modularity and Error Handling - -To improve our program, we’ll fix four problems that have to do with the -program’s structure and how it’s handling potential errors. First, our `main` -function now performs two tasks: it parses arguments and reads files. As our -program grows, the number of separate tasks the `main` function handles will -increase. As a function gains responsibilities, it becomes more difficult to -reason about, harder to test, and harder to change without breaking one of its -parts. It’s best to separate functionality so each function is responsible for -one task. - -This issue also ties into the second problem: although `query` and `file_path` -are configuration variables to our program, variables like `contents` are used -to perform the program’s logic. The longer `main` becomes, the more variables -we’ll need to bring into scope; the more variables we have in scope, the harder -it will be to keep track of the purpose of each. It’s best to group the -configuration variables into one structure to make their purpose clear. - -The third problem is that we’ve used `expect` to print an error message when -reading the file fails, but the error message just prints `Should have been -able to read the file`. Reading a file can fail in a number of ways: for -example, the file could be missing, or we might not have permission to open it. -Right now, regardless of the situation, we’d print the same error message for -everything, which wouldn’t give the user any information! - -Fourth, we use `expect` repeatedly to handle different errors, and if the user -runs our program without specifying enough arguments, they’ll get an `index out -of bounds` error from Rust that doesn’t clearly explain the problem. It would -be best if all the error-handling code were in one place so future maintainers -had only one place to consult the code if the error-handling logic needed to -change. Having all the error-handling code in one place will also ensure that -we’re printing messages that will be meaningful to our end users. - -Let’s address these four problems by refactoring our project. - -### Separation of Concerns for Binary Projects - -The organizational problem of allocating responsibility for multiple tasks to -the `main` function is common to many binary projects. As a result, the Rust -community has developed guidelines for splitting the separate concerns of a -binary program when `main` starts getting large. This process has the following -steps: - -* Split your program into a *main.rs* and a *lib.rs* and move your program’s - logic to *lib.rs*. -* As long as your command line parsing logic is small, it can remain in - *main.rs*. -* When the command line parsing logic starts getting complicated, extract it - from *main.rs* and move it to *lib.rs*. - -The responsibilities that remain in the `main` function after this process -should be limited to the following: - -* Calling the command line parsing logic with the argument values -* Setting up any other configuration -* Calling a `run` function in *lib.rs* -* Handling the error if `run` returns an error - -This pattern is about separating concerns: *main.rs* handles running the -program, and *lib.rs* handles all the logic of the task at hand. Because you -can’t test the `main` function directly, this structure lets you test all of -your program’s logic by moving it into functions in *lib.rs*. The code that -remains in *main.rs* will be small enough to verify its correctness by reading -it. Let’s rework our program by following this process. - -#### Extracting the Argument Parser - -We’ll extract the functionality for parsing arguments into a function that -`main` will call to prepare for moving the command line parsing logic to -*src/lib.rs*. Listing 12-5 shows the new start of `main` that calls a new -function `parse_config`, which we’ll define in *src/main.rs* for the moment. +## Refactoring untuk Meningkatkan Modularitas dan Penanganan Error + +Untuk meningkatkan program kita, kita akan memperbaiki empat masalah yang +berkaitan dengan struktur program dan cara program menangani kemungkinan error. +Pertama, fungsi `main` kita sekarang melakukan dua tugas: mem-parsing argumen +dan membaca file. Seiring program berkembang, jumlah tugas terpisah yang +ditangani `main` akan bertambah. Semakin banyak tanggung jawab sebuah fungsi, +semakin sulit untuk dipahami, diuji, dan diubah tanpa merusak bagian lainnya. +Akan lebih baik jika kita memisahkan fungsionalitas sehingga setiap fungsi hanya +bertanggung jawab pada satu tugas. + +Masalah ini juga berkaitan dengan masalah kedua: `query` dan `file_path` adalah +variabel konfigurasi untuk program kita, sedangkan variabel seperti `contents` +digunakan untuk menjalankan logika program. Semakin panjang fungsi `main`, +semakin banyak variabel yang harus dimasukkan ke dalam scope; semakin banyak +variabel di dalam scope, semakin sulit melacak tujuan masing-masing. Lebih baik +mengelompokkan variabel konfigurasi ke dalam satu struktur agar tujuannya lebih +jelas. + +Masalah ketiga adalah kita menggunakan `expect` untuk mencetak pesan error +ketika pembacaan file gagal, tetapi pesan error-nya hanya menampilkan +`Should have been able to read the file`. Membaca file bisa gagal karena +berbagai alasan: misalnya file tidak ada, atau kita tidak punya izin untuk +membukanya. Saat ini, apa pun penyebabnya, kita tetap mencetak pesan error yang +sama, yang tidak memberikan informasi berarti bagi pengguna! + +Keempat, kita menggunakan `expect` untuk menangani error, dan jika pengguna +menjalankan program tanpa memberikan argumen yang cukup, mereka akan mendapatkan +error `index out of bounds` dari Rust yang tidak menjelaskan masalah sebenarnya. +Akan lebih baik jika semua kode penanganan error berada di satu tempat sehingga +pengembang di masa depan hanya perlu melihat satu bagian jika logika penanganan +error perlu diubah. Mengumpulkan seluruh penanganan error di satu tempat juga +memastikan bahwa kita mencetak pesan yang benar-benar berguna bagi pengguna +akhir. + +Mari kita tangani keempat masalah ini dengan melakukan refactoring pada project +kita. -Filename: src/main.rs + + + + +### Memisahkan Tanggung Jawab dalam Proyek Biner + +Masalah organisasi berupa pembagian banyak tugas ke dalam fungsi `main` adalah +hal yang umum pada banyak proyek biner. Karena itu, banyak programmer Rust +merasa berguna untuk memisahkan berbagai tanggung jawab program biner ketika +fungsi `main` mulai membesar. Proses ini memiliki langkah-langkah berikut: + +- Pisahkan program Anda menjadi file _main.rs_ dan _lib.rs_, lalu pindahkan + logika program ke _lib.rs_. +- Selama logika parsing command line masih kecil, ia bisa tetap berada di dalam + fungsi `main`. +- Ketika logika parsing command line mulai menjadi rumit, ekstrak logika + tersebut dari fungsi `main` ke fungsi atau tipe lain. + +Tanggung jawab yang tersisa dalam fungsi `main` setelah proses ini sebaiknya +terbatas pada hal-hal berikut: + +- Memanggil logika parsing command line dengan nilai argumen +- Menyiapkan konfigurasi lain yang diperlukan +- Memanggil fungsi `run` di _lib.rs_ +- Menangani error jika `run` mengembalikan error + +Pola ini bertujuan untuk memisahkan tanggung jawab: _main.rs_ menangani eksekusi +program, dan _lib.rs_ menangani seluruh logika tugas utama. Karena Anda tidak +bisa menguji fungsi `main` secara langsung, struktur ini memungkinkan Anda +menguji seluruh logika program dengan memindahkannya keluar dari fungsi `main`. +Kode yang tersisa di dalam `main` akan cukup kecil sehingga bisa diverifikasi +kebenarannya hanya dengan membaca. Mari kita perbarui program kita dengan +mengikuti proses ini. + +#### Mengekstrak Argument Parser + +Kita akan mengekstrak fungsionalitas untuk parsing argumen ke dalam sebuah +fungsi yang akan dipanggil oleh `main`. Listing 12-5 memperlihatkan awal baru +dari fungsi `main` yang memanggil fungsi baru `parse_config`, yang akan kita +definisikan di _src/main.rs_. + + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-05/src/main.rs:here}} ``` -Listing 12-5: Extracting a `parse_config` function from -`main` - -We’re still collecting the command line arguments into a vector, but instead of -assigning the argument value at index 1 to the variable `query` and the -argument value at index 2 to the variable `file_path` within the `main` -function, we pass the whole vector to the `parse_config` function. The -`parse_config` function then holds the logic that determines which argument -goes in which variable and passes the values back to `main`. We still create -the `query` and `file_path` variables in `main`, but `main` no longer has the -responsibility of determining how the command line arguments and variables -correspond. - -This rework may seem like overkill for our small program, but we’re refactoring -in small, incremental steps. After making this change, run the program again to -verify that the argument parsing still works. It’s good to check your progress -often, to help identify the cause of problems when they occur. - -#### Grouping Configuration Values - -We can take another small step to improve the `parse_config` function further. -At the moment, we’re returning a tuple, but then we immediately break that -tuple into individual parts again. This is a sign that perhaps we don’t have -the right abstraction yet. - -Another indicator that shows there’s room for improvement is the `config` part -of `parse_config`, which implies that the two values we return are related and -are both part of one configuration value. We’re not currently conveying this -meaning in the structure of the data other than by grouping the two values into -a tuple; we’ll instead put the two values into one struct and give each of the -struct fields a meaningful name. Doing so will make it easier for future -maintainers of this code to understand how the different values relate to each -other and what their purpose is. - -Listing 12-6 shows the improvements to the `parse_config` function. + -Filename: src/main.rs +Kita masih mengumpulkan argumen baris perintah ke dalam sebuah vektor, tetapi +alih-alih langsung mengambil nilai argumen pada indeks 1 dan menyimpannya ke +variabel `query` serta nilai pada indeks 2 ke variabel `file_path` di dalam +fungsi `main`, sekarang kita meneruskan seluruh vektor tersebut ke fungsi +`parse_config`. Fungsi `parse_config` kemudian memuat logika yang menentukan +argumen mana yang masuk ke variabel mana dan mengembalikan nilai-nilainya +kembali ke `main`. Kita masih membuat variabel `query` dan `file_path` di +`main`, tetapi `main` tidak lagi bertanggung jawab untuk memetakan argumen baris +perintah ke variabel yang sesuai. + +Perubahan ini mungkin terlihat berlebihan untuk program kecil seperti ini, +tetapi kita sedang melakukan refaktor secara bertahap dan terukur. Setelah +membuat perubahan tersebut, jalankan kembali programnya untuk memastikan parsing +argumen masih bekerja dengan benar. Penting untuk sering memeriksa progres, +supaya jika ada masalah, kita bisa lebih mudah mengetahui penyebabnya. + +#### Mengelompokkan Nilai Konfigurasi + +Kita bisa mengambil satu langkah kecil lagi untuk memperbaiki fungsi +`parse_config`. Saat ini kita mengembalikan sebuah tuple, namun kemudian +langsung memecah tuple tersebut menjadi bagian-bagian terpisah kembali. Ini +merupakan tanda bahwa mungkin abstraksi kita belum tepat. + +Indikator lain adalah kata `config` pada `parse_config`, yang memberi kesan +bahwa kedua nilai yang kita kembalikan itu saling berhubungan dan merupakan +bagian dari satu nilai konfigurasi. Saat ini kita belum menyampaikan makna +tersebut dalam struktur datanya, selain hanya dengan mengelompokkannya dalam +tuple. Jadi, kita akan memasukkan kedua nilai itu ke dalam sebuah struct dan +memberikan nama field yang bermakna. Dengan begitu, akan lebih mudah bagi +pengembang lain di masa depan untuk memahami bagaimana nilai-nilai tersebut +saling terkait dan apa fungsi masing-masing. + +Listing 12-6 menunjukkan perbaikan pada fungsi `parse_config`. + + ```rust,should_panic,noplayground {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-06/src/main.rs:here}} ``` -Listing 12-6: Refactoring `parse_config` to return an -instance of a `Config` struct - -We’ve added a struct named `Config` defined to have fields named `query` and -`file_path`. The signature of `parse_config` now indicates that it returns a -`Config` value. In the body of `parse_config`, where we used to return -string slices that reference `String` values in `args`, we now define `Config` -to contain owned `String` values. The `args` variable in `main` is the owner of -the argument values and is only letting the `parse_config` function borrow -them, which means we’d violate Rust’s borrowing rules if `Config` tried to take -ownership of the values in `args`. - -There are a number of ways we could manage the `String` data; the easiest, -though somewhat inefficient, route is to call the `clone` method on the values. -This will make a full copy of the data for the `Config` instance to own, which -takes more time and memory than storing a reference to the string data. -However, cloning the data also makes our code very straightforward because we -don’t have to manage the lifetimes of the references; in this circumstance, -giving up a little performance to gain simplicity is a worthwhile trade-off. - -> ### The Trade-Offs of Using `clone` + + +Kita telah menambahkan sebuah struct bernama `Config` yang didefinisikan +memiliki field bernama `query` dan `file_path`. Tanda tangan fungsi +`parse_config` sekarang menunjukkan bahwa fungsi ini mengembalikan sebuah nilai +`Config`. Di dalam tubuh fungsi `parse_config`, di mana sebelumnya kita +mengembalikan potongan string (string slices) yang mereferensikan nilai `String` +di `args`, sekarang kita mendefinisikan `Config` untuk memiliki nilai `String` +yang memiliki kepemilikan sendiri (owned). + +Variabel `args` di `main` adalah pemilik dari nilai argumen tersebut dan hanya +meminjamkan nilainya ke fungsi `parse_config`, yang berarti kita akan melanggar +aturan peminjaman Rust jika `Config` mencoba mengambil alih kepemilikan +nilai-nilai di `args`. + +Ada beberapa cara untuk menangani data `String`; cara yang paling mudah, +walaupun agak tidak efisien, adalah memanggil metode `clone` pada nilai-nilai +tersebut. Ini akan membuat salinan penuh dari data tersebut agar instance +`Config` dapat memilikinya, yang membutuhkan lebih banyak waktu dan memori +dibandingkan hanya menyimpan referensi ke data string. Namun, melakukan clone +juga membuat kode kita jauh lebih sederhana karena kita tidak perlu mengatur +lifetime dari referensi; dalam kasus ini, mengorbankan sedikit performa demi +kesederhanaan adalah pertukaran yang sepadan. + +> ### Pertukaran Saat Menggunakan `clone` > -> There’s a tendency among many Rustaceans to avoid using `clone` to fix -> ownership problems because of its runtime cost. In -> [Chapter 13][ch13], you’ll learn how to use more efficient -> methods in this type of situation. But for now, it’s okay to copy a few -> strings to continue making progress because you’ll make these copies only -> once and your file path and query string are very small. It’s better to have -> a working program that’s a bit inefficient than to try to hyperoptimize code -> on your first pass. As you become more experienced with Rust, it’ll be -> easier to start with the most efficient solution, but for now, it’s -> perfectly acceptable to call `clone`. - -We’ve updated `main` so it places the instance of `Config` returned by -`parse_config` into a variable named `config`, and we updated the code that -previously used the separate `query` and `file_path` variables so it now uses -the fields on the `Config` struct instead. - -Now our code more clearly conveys that `query` and `file_path` are related and -that their purpose is to configure how the program will work. Any code that -uses these values knows to find them in the `config` instance in the fields -named for their purpose. - -#### Creating a Constructor for `Config` - -So far, we’ve extracted the logic responsible for parsing the command line -arguments from `main` and placed it in the `parse_config` function. Doing so -helped us to see that the `query` and `file_path` values were related and that -relationship should be conveyed in our code. We then added a `Config` struct to -name the related purpose of `query` and `file_path` and to be able to return the -values’ names as struct field names from the `parse_config` function. - -So now that the purpose of the `parse_config` function is to create a `Config` -instance, we can change `parse_config` from a plain function to a function -named `new` that is associated with the `Config` struct. Making this change -will make the code more idiomatic. We can create instances of types in the -standard library, such as `String`, by calling `String::new`. Similarly, by -changing `parse_config` into a `new` function associated with `Config`, we’ll -be able to create instances of `Config` by calling `Config::new`. Listing 12-7 -shows the changes we need to make. - -Filename: src/main.rs +> Ada kecenderungan di kalangan Rustacean untuk menghindari penggunaan `clone` +> untuk memperbaiki masalah kepemilikan karena biaya runtime-nya. Di +> [Bab 13][ch13], kamu akan mempelajari cara yang lebih efisien dalam situasi +> seperti ini. Namun untuk sekarang, tidak apa-apa menyalin beberapa string agar +> tetap bisa lanjut, karena kamu hanya akan membuat salinan ini sekali dan path +> file serta query string-mu sangat kecil. Lebih baik memiliki program yang +> bekerja meskipun sedikit tidak efisien dibandingkan mencoba terlalu +> mengoptimasi kode pada percobaan pertama. Seiring bertambahnya pengalamanmu +> dengan Rust, akan lebih mudah memulai dengan solusi paling efisien, tetapi +> untuk saat ini, menggunakan `clone` adalah hal yang sepenuhnya dapat diterima. + +Kita telah memperbarui `main` sehingga instance `Config` yang dikembalikan oleh +`parse_config` disimpan ke dalam variabel bernama `config`, dan kita memperbarui +kode yang sebelumnya menggunakan variabel terpisah `query` dan `file_path` agar +sekarang menggunakan field pada struct `Config`. + +Sekarang kode kita lebih jelas menunjukkan bahwa `query` dan `file_path` saling +berhubungan dan bahwa tujuan mereka adalah untuk mengonfigurasi bagaimana +program akan berjalan. Kode apa pun yang menggunakan nilai-nilai ini tahu bahwa +mereka dapat ditemukan di instance `config` pada field yang dinamai sesuai +fungsinya. + +#### Membuat Constructor untuk `Config` + +Sejauh ini, kita telah memisahkan logika yang bertanggung jawab untuk +mem-parsing argumen command line dari `main` dan memindahkannya ke fungsi +`parse_config`. Hal ini membantu kita melihat bahwa nilai `query` dan +`file_path` saling berhubungan, dan hubungan tersebut sebaiknya terlihat jelas +dalam kode kita. Kita kemudian menambahkan struct `Config` untuk memberi nama +tujuan yang saling terkait dari `query` dan `file_path`, serta agar kita bisa +mengembalikan nilai-nilai tersebut sebagai nama field struct dari fungsi +`parse_config`. + +Jadi sekarang, karena tujuan fungsi `parse_config` adalah membuat sebuah +instance `Config`, kita dapat mengubah `parse_config` dari fungsi biasa menjadi +fungsi bernama `new` yang terkait dengan struct `Config`. Melakukan perubahan +ini akan membuat kode lebih idiomatis. Kita bisa membuat instance dari tipe-tipe +di standard library, seperti `String`, dengan memanggil `String::new`. Dengan +cara yang sama, dengan mengubah `parse_config` menjadi fungsi `new` yang terkait +dengan `Config`, kita akan dapat membuat instance `Config` dengan memanggil +`Config::new`. Listing 12-7 menunjukkan perubahan yang perlu kita lakukan. + + ```rust,should_panic,noplayground {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-07/src/main.rs:here}} ``` -Listing 12-7: Changing `parse_config` into -`Config::new` + -We’ve updated `main` where we were calling `parse_config` to instead call -`Config::new`. We’ve changed the name of `parse_config` to `new` and moved it -within an `impl` block, which associates the `new` function with `Config`. Try -compiling this code again to make sure it works. +Kita sudah memperbarui `main` yang sebelumnya memanggil `parse_config`, agar +sekarang memanggil `Config::new`. Kita juga mengganti nama `parse_config` +menjadi `new` dan memindahkannya ke dalam blok `impl`, yang mengasosiasikan +fungsi `new` dengan `Config`. Cobalah kompilasi kode ini lagi untuk memastikan +semuanya berfungsi. -### Fixing the Error Handling +### Memperbaiki Penanganan Error -Now we’ll work on fixing our error handling. Recall that attempting to access -the values in the `args` vector at index 1 or index 2 will cause the program to -panic if the vector contains fewer than three items. Try running the program -without any arguments; it will look like this: +Sekarang kita akan memperbaiki penanganan error. Ingat bahwa mencoba mengakses +nilai dalam vektor `args` pada indeks 1 atau indeks 2 akan menyebabkan program +panic jika vektor tersebut berisi kurang dari tiga item. Cobalah menjalankan +program tanpa argumen apa pun; hasilnya akan tampak seperti ini: ```console {{#include ../listings/ch12-an-io-project/listing-12-07/output.txt}} ``` -The line `index out of bounds: the len is 1 but the index is 1` is an error -message intended for programmers. It won’t help our end users understand what -they should do instead. Let’s fix that now. +Baris `index out of bounds: the len is 1 but the index is 1` adalah pesan error +yang ditujukan untuk programmer. Pesan ini tidak akan membantu pengguna akhir +memahami apa yang seharusnya mereka lakukan. Mari kita perbaiki sekarang. -#### Improving the Error Message +#### Meningkatkan Pesan Error -In Listing 12-8, we add a check in the `new` function that will verify that the -slice is long enough before accessing index 1 and 2. If the slice isn’t long -enough, the program panics and displays a better error message. +Pada Listing 12-8, kita menambahkan pengecekan di fungsi `new` untuk memastikan +slice cukup panjang sebelum mengakses indeks 1 dan indeks 2. Jika slice tidak +cukup panjang, program akan panic dan menampilkan pesan error yang lebih jelas. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-08/src/main.rs:here}} ``` -Listing 12-8: Adding a check for the number of -arguments + -This code is similar to [the `Guess::new` function we wrote in Listing -9-13][ch9-custom-types], where we called `panic!` when the -`value` argument was out of the range of valid values. Instead of checking for -a range of values here, we’re checking that the length of `args` is at least 3 -and the rest of the function can operate under the assumption that this -condition has been met. If `args` has fewer than three items, this condition -will be true, and we call the `panic!` macro to end the program immediately. +Kode ini mirip dengan fungsi `Guess::new` yang kita tulis pada Listing 9-13, di +mana kita memanggil `panic!` ketika argumen `value` berada di luar rentang nilai +yang valid. Alih-alih memeriksa rentang nilai di sini, kita memeriksa apakah +panjang `args` setidaknya `3`, sehingga sisa fungsi bisa berasumsi bahwa kondisi +tersebut telah terpenuhi. Jika `args` memiliki kurang dari tiga item, kondisi +ini akan bernilai `true`, dan kita memanggil makro `panic!` untuk segera +menghentikan program. -With these extra few lines of code in `new`, let’s run the program without any -arguments again to see what the error looks like now: +Dengan beberapa baris tambahan di fungsi `new` ini, mari kita jalankan ulang +program tanpa argumen apa pun untuk melihat seperti apa error-nya sekarang. ```console {{#include ../listings/ch12-an-io-project/listing-12-08/output.txt}} ``` -This output is better: we now have a reasonable error message. However, we also -have extraneous information we don’t want to give to our users. Perhaps using -the technique we used in Listing 9-13 isn’t the best to use here: a call to -`panic!` is more appropriate for a programming problem than a usage problem, -[as discussed in Chapter 9][ch9-error-guidelines]. Instead, -we’ll use the other technique you learned about in Chapter 9—[returning a -`Result`][ch9-result] that indicates either success or an error. +Keluaran ini sudah lebih baik: sekarang kita punya pesan error yang masuk akal. +Namun, masih ada informasi tambahan yang tidak perlu kita berikan ke pengguna. +Mungkin teknik yang kita gunakan pada Listing 9-13 bukan yang terbaik untuk +kasus ini: pemanggilan `panic!` lebih cocok untuk masalah pemrograman daripada +masalah penggunaan program, seperti dibahas di Bab 9. Sebagai gantinya, kita +akan menggunakan teknik lain yang sudah kamu pelajari di Bab 9—mengembalikan +`Result` yang menunjukkan apakah operasi berhasil atau terjadi error. + -#### Returning a `Result` Instead of Calling `panic!` +#### Mengembalikan `Result` Alih-alih Memanggil `panic!` -We can instead return a `Result` value that will contain a `Config` instance in -the successful case and will describe the problem in the error case. We’re also -going to change the function name from `new` to `build` because many -programmers expect `new` functions to never fail. When `Config::build` is -communicating to `main`, we can use the `Result` type to signal there was a -problem. Then we can change `main` to convert an `Err` variant into a more -practical error for our users without the surrounding text about `thread -'main'` and `RUST_BACKTRACE` that a call to `panic!` causes. +Sebagai gantinya, kita bisa mengembalikan nilai `Result` yang akan berisi +instance `Config` jika berhasil, dan akan menjelaskan masalahnya jika terjadi +error. Kita juga akan mengganti nama fungsi dari `new` menjadi `build` karena +banyak programmer mengharapkan fungsi `new` **tidak pernah gagal**. Saat +`Config::build` berkomunikasi dengan `main`, kita bisa menggunakan tipe `Result` +untuk memberi sinyal bahwa ada masalah. Lalu, kita bisa mengubah `main` agar +mengonversi varian `Err` menjadi pesan error yang lebih ramah bagi pengguna, +tanpa teks tambahan seperti `thread 'main'` dan `RUST_BACKTRACE` yang muncul +ketika kita memanggil `panic!`. -Listing 12-9 shows the changes we need to make to the return value of the -function we’re now calling `Config::build` and the body of the function needed -to return a `Result`. Note that this won’t compile until we update `main` as -well, which we’ll do in the next listing. +Listing 12-9 menunjukkan perubahan yang perlu kita lakukan pada nilai kembalian +fungsi yang sekarang kita sebut `Config::build`, serta perubahan pada isi +fungsinya agar bisa mengembalikan `Result`. Perlu dicatat bahwa kode ini belum +bisa dikompilasi sampai kita memperbarui `main`, yang akan kita lakukan pada +listing berikutnya. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-09/src/main.rs:here}} ``` -Listing 12-9: Returning a `Result` from -`Config::build` + -Our `build` function returns a `Result` with a `Config` instance in the success -case and a `&'static str` in the error case. Our error values will always be -string literals that have the `'static` lifetime. +Fungsi `build` kita sekarang mengembalikan `Result` dengan `Config` pada kasus +sukses dan literal string pada kasus error. Nilai error kita selalu berupa +string literal yang punya lifetime `'static`. -We’ve made two changes in the body of the function: instead of calling `panic!` -when the user doesn’t pass enough arguments, we now return an `Err` value, and -we’ve wrapped the `Config` return value in an `Ok`. These changes make the -function conform to its new type signature. +Kita membuat dua perubahan di dalam fungsi: Alih-alih memanggil `panic!` saat +user tidak memberikan argumen yang cukup, sekarang kita mengembalikan `Err`, dan +kita membungkus nilai `Config` dalam `Ok`. Perubahan ini membuat fungsi sesuai +dengan tipe barunya. -Returning an `Err` value from `Config::build` allows the `main` function to -handle the `Result` value returned from the `build` function and exit the -process more cleanly in the error case. +Dengan mengembalikan `Err` dari `Config::build`, fungsi `main` bisa menangani +nilai `Result` tersebut dan menghentikan program dengan lebih rapi saat terjadi +error. + -#### Calling `Config::build` and Handling Errors +#### Memanggil `Config::build` dan Menangani Error -To handle the error case and print a user-friendly message, we need to update -`main` to handle the `Result` being returned by `Config::build`, as shown in -Listing 12-10. We’ll also take the responsibility of exiting the command line -tool with a nonzero error code away from `panic!` and instead implement it by -hand. A nonzero exit status is a convention to signal to the process that -called our program that the program exited with an error state. +Untuk menangani kasus error dan menampilkan pesan yang ramah bagi pengguna, kita +perlu memperbarui `main` agar menangani `Result` yang dikembalikan oleh +`Config::build`, seperti yang ditunjukkan pada Listing 12-10. Kita juga akan +mengambil alih tanggung jawab keluar dari program dengan kode error non-nol dari +`panic!` dan menerapkannya secara manual. Status keluar non-nol adalah konvensi +untuk memberi sinyal ke proses yang memanggil program bahwa program berhenti +dalam keadaan error. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-10/src/main.rs:here}} ``` -Listing 12-10: Exiting with an error code if building a -`Config` fails - -In this listing, we’ve used a method we haven’t covered in detail yet: -`unwrap_or_else`, which is defined on `Result` by the standard library. -Using `unwrap_or_else` allows us to define some custom, non-`panic!` error -handling. If the `Result` is an `Ok` value, this method’s behavior is similar -to `unwrap`: it returns the inner value `Ok` is wrapping. However, if the value -is an `Err` value, this method calls the code in the *closure*, which is an -anonymous function we define and pass as an argument to `unwrap_or_else`. We’ll -cover closures in more detail in [Chapter 13][ch13]. For now, -you just need to know that `unwrap_or_else` will pass the inner value of the -`Err`, which in this case is the static string `"not enough arguments"` that we -added in Listing 12-9, to our closure in the argument `err` that appears -between the vertical pipes. The code in the closure can then use the `err` -value when it runs. - -We’ve added a new `use` line to bring `process` from the standard library into -scope. The code in the closure that will be run in the error case is only two -lines: we print the `err` value and then call `process::exit`. The -`process::exit` function will stop the program immediately and return the -number that was passed as the exit status code. This is similar to the -`panic!`-based handling we used in Listing 12-8, but we no longer get all the -extra output. Let’s try it: + + +Dalam listing ini, kita menggunakan sebuah metode yang belum kita bahas secara +rinci: `unwrap_or_else`, yang didefinisikan pada `Result` di pustaka +standar. Menggunakan `unwrap_or_else` memungkinkan kita mendefinisikan +penanganan error kustom tanpa `panic!`. Jika `Result` bernilai `Ok`, perilaku +metode ini mirip dengan `unwrap`: ia mengembalikan nilai di dalam `Ok`. Namun, +jika bernilai `Err`, metode ini akan memanggil kode di dalam _closure_, yaitu +fungsi anonim yang kita definisikan dan berikan sebagai argumen ke +`unwrap_or_else`. + +Kita akan membahas _closure_ lebih dalam di [Bab 13], tetapi untuk saat ini +cukup pahami bahwa `unwrap_or_else` akan mengoper nilai di dalam `Err`—dalam +kasus ini string statis `"not enough arguments"` yang kita tambahkan pada +Listing 12-9—ke _closure_ melalui parameter `err` (yang berada di antara tanda +garis vertikal `|err|`). Kode di dalam _closure_ kemudian dapat menggunakan +nilai `err` tersebut saat dijalankan. + +Kita juga menambahkan baris `use` baru untuk membawa `process` dari pustaka +standar ke dalam scope. Kode dalam _closure_ yang dijalankan ketika terjadi +error hanya terdiri dari dua baris: kita mencetak nilai `err`, lalu memanggil +`process::exit`. Fungsi `process::exit` akan langsung menghentikan program dan +mengembalikan angka yang diberikan sebagai _exit status code_. Ini mirip dengan +penanganan berbasis `panic!` pada Listing 12-8, tetapi sekarang kita tidak lagi +mendapatkan keluaran tambahan yang berlebihan. Mari kita coba. ```console {{#include ../listings/ch12-an-io-project/listing-12-10/output.txt}} ``` -Great! This output is much friendlier for our users. +Keren! Keluaran ini jauh lebih ramah bagi para pengguna kita. -### Extracting Logic from `main` + -Now that we’ve finished refactoring the configuration parsing, let’s turn to -the program’s logic. As we stated in [“Separation of Concerns for Binary -Projects”](#separation-of-concerns-for-binary-projects), we’ll -extract a function named `run` that will hold all the logic currently in the -`main` function that isn’t involved with setting up configuration or handling -errors. When we’re done, `main` will be concise and easy to verify by -inspection, and we’ll be able to write tests for all the other logic. + -Listing 12-11 shows the extracted `run` function. For now, we’re just making -the small, incremental improvement of extracting the function. We’re still -defining the function in *src/main.rs*. +### Mengekstrak Logika dari `main` -Filename: src/main.rs +Sekarang setelah kita selesai melakukan refactor pada parsing konfigurasi, mari +kita beralih ke logika program. Seperti yang sudah kita bahas di bagian +[“Memisahkan Tanggung Jawab pada Proyek Binary”](#separation-of-concerns-for-binary-projects), +kita akan mengekstrak sebuah fungsi bernama `run` yang akan menampung semua +logika yang saat ini ada di fungsi `main` dan tidak berhubungan dengan +pengaturan konfigurasi atau penanganan error. Setelah selesai, fungsi `main` +akan menjadi ringkas dan mudah dicek hanya dengan melihatnya, dan kita juga bisa +menuliskan test untuk seluruh logika lainnya. + +Listing 12-11 menunjukkan peningkatan kecil dan bertahap dengan mengekstrak +fungsi `run`. + + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-11/src/main.rs:here}} ``` -Listing 12-11: Extracting a `run` function containing the -rest of the program logic + -The `run` function now contains all the remaining logic from `main`, starting -from reading the file. The `run` function takes the `Config` instance as an -argument. +Fungsi `run` sekarang berisi semua logika yang tersisa dari `main`, dimulai dari +proses membaca file. Fungsi `run` menerima instance `Config` sebagai argumennya. -#### Returning Errors from the `run` Function + -With the remaining program logic separated into the `run` function, we can -improve the error handling, as we did with `Config::build` in Listing 12-9. -Instead of allowing the program to panic by calling `expect`, the `run` -function will return a `Result` when something goes wrong. This will let -us further consolidate the logic around handling errors into `main` in a -user-friendly way. Listing 12-12 shows the changes we need to make to the -signature and body of `run`. + -Filename: src/main.rs +### Mengembalikan Error dari `run` + +Dengan sisa logika program sudah dipisahkan ke dalam fungsi `run`, sekarang kita +bisa memperbaiki penanganan error seperti yang kita lakukan pada `Config::build` +di Listing 12-9. Alih-alih membiarkan program _panic_ dengan memanggil `expect`, +fungsi `run` akan mengembalikan `Result` ketika terjadi masalah. Dengan +begitu, kita bisa memusatkan logika penanganan error di `main` agar lebih ramah +bagi pengguna. + +Listing 12-12 menunjukkan perubahan yang perlu kita lakukan pada **signature** +dan isi fungsi `run`. + + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-12/src/main.rs:here}} ``` -Listing 12-12: Changing the `run` function to return -`Result` - -We’ve made three significant changes here. First, we changed the return type of -the `run` function to `Result<(), Box>`. This function previously -returned the unit type, `()`, and we keep that as the value returned in the -`Ok` case. - -For the error type, we used the *trait object* `Box` (and we’ve -brought `std::error::Error` into scope with a `use` statement at the top). -We’ll cover trait objects in [Chapter 17][ch17]. For now, just -know that `Box` means the function will return a type that -implements the `Error` trait, but we don’t have to specify what particular type -the return value will be. This gives us flexibility to return error values that -may be of different types in different error cases. The `dyn` keyword is short -for “dynamic.” - -Second, we’ve removed the call to `expect` in favor of the `?` operator, as we -talked about in [Chapter 9][ch9-question-mark]. Rather than -`panic!` on an error, `?` will return the error value from the current function -for the caller to handle. - -Third, the `run` function now returns an `Ok` value in the success case. -We’ve declared the `run` function’s success type as `()` in the signature, -which means we need to wrap the unit type value in the `Ok` value. This -`Ok(())` syntax might look a bit strange at first, but using `()` like this is -the idiomatic way to indicate that we’re calling `run` for its side effects -only; it doesn’t return a value we need. - -When you run this code, it will compile but will display a warning: + + +Kita telah membuat tiga perubahan penting di sini. Pertama, kita mengubah tipe +nilai balik fungsi `run` menjadi `Result<(), Box>`. Sebelumnya fungsi +ini mengembalikan tipe unit `()`, dan kita tetap mempertahankannya sebagai nilai +yang dikembalikan pada kondisi `Ok`. + +Untuk tipe error-nya, kita menggunakan trait object `Box` (dan kita +memasukkan `std::error::Error` ke dalam scope dengan `use`). Kita akan membahas +trait object di **Bab 18** nanti. Untuk sekarang, cukup pahami bahwa +`Box` berarti fungsi ini akan mengembalikan tipe apa pun yang +mengimplementasikan trait `Error`, tanpa harus menentukan secara spesifik tipe +error-nya. Ini memberi fleksibilitas untuk mengembalikan berbagai jenis error +pada situasi yang berbeda. Kata kunci `dyn` sendiri merupakan singkatan dari +_dynamic_. + +Kedua, kita menghapus pemanggilan `expect` dan menggantinya dengan operator `?`, +seperti yang telah dibahas di **Bab 9**. Alih-alih memanggil `panic!` saat +terjadi error, `?` akan mengembalikan nilai error dari fungsi saat ini untuk +ditangani oleh pemanggilnya. + +Ketiga, fungsi `run` sekarang mengembalikan nilai `Ok` pada kondisi sukses. Kita +telah mendeklarasikan tipe sukses `run` sebagai `()` di tanda tangan fungsi, +jadi kita perlu membungkus nilai unit tersebut dalam `Ok`. Sintaks `Ok(())` +mungkin terlihat agak aneh pada awalnya, tetapi penggunaan `()` seperti ini +adalah cara idiomatis Rust untuk menunjukkan bahwa kita memanggil `run` hanya +untuk efek sampingnya; fungsi ini tidak mengembalikan nilai yang perlu kita +gunakan. + +Saat Anda menjalankan kode ini, program akan berhasil dikompilasi, tetapi akan +muncul sebuah peringatan: ```console {{#include ../listings/ch12-an-io-project/listing-12-12/output.txt}} ``` -Rust tells us that our code ignored the `Result` value and the `Result` value -might indicate that an error occurred. But we’re not checking to see whether or -not there was an error, and the compiler reminds us that we probably meant to -have some error-handling code here! Let’s rectify that problem now. +Rust memberi tahu kita bahwa kode kita mengabaikan nilai `Result`, padahal nilai +`Result` tersebut mungkin menunjukkan bahwa terjadi error. Namun kita tidak +memeriksa apakah terjadi error atau tidak, dan compiler mengingatkan kita bahwa +kemungkinan besar kita memang perlu menambahkan kode penanganan error di sini! +Sekarang mari kita perbaiki masalah itu. -#### Handling Errors Returned from `run` in `main` +#### Menangani Error yang Dikembalikan dari `run` di `main` -We’ll check for errors and handle them using a technique similar to one we used -with `Config::build` in Listing 12-10, but with a slight difference: +Kita akan memeriksa error dan menanganinya menggunakan teknik yang mirip dengan +yang kita gunakan pada `Config::build` di Listing 12-10, tetapi dengan sedikit +perbedaan: Filename: src/main.rs @@ -430,76 +459,80 @@ with `Config::build` in Listing 12-10, but with a slight difference: {{#rustdoc_include ../listings/ch12-an-io-project/no-listing-01-handling-errors-in-main/src/main.rs:here}} ``` -We use `if let` rather than `unwrap_or_else` to check whether `run` returns an -`Err` value and call `process::exit(1)` if it does. The `run` function doesn’t -return a value that we want to `unwrap` in the same way that `Config::build` -returns the `Config` instance. Because `run` returns `()` in the success case, -we only care about detecting an error, so we don’t need `unwrap_or_else` to -return the unwrapped value, which would only be `()`. +Kita menggunakan `if let` alih-alih `unwrap_or_else` untuk memeriksa apakah +`run` mengembalikan nilai `Err` dan memanggil `process::exit(1)` jika iya. +Fungsi `run` tidak mengembalikan nilai yang perlu kita `unwrap` seperti +`Config::build` yang mengembalikan instance `Config`. Karena `run` hanya +mengembalikan `()` pada kasus sukses, kita hanya peduli mendeteksi error saja, +jadi kita tidak membutuhkan `unwrap_or_else` untuk mengembalikan nilai yang +di-unwrap, yang sebenarnya hanya `()`. -The bodies of the `if let` and the `unwrap_or_else` functions are the same in -both cases: we print the error and exit. +Bagian isi dari `if let` dan `unwrap_or_else` pada kedua kasus tersebut sama: +kita mencetak pesan error dan keluar dari program. -### Splitting Code into a Library Crate +### Memisahkan Kode ke dalam Library Crate -Our `minigrep` project is looking good so far! Now we’ll split the -*src/main.rs* file and put some code into the *src/lib.rs* file. That way we -can test the code and have a *src/main.rs* file with fewer responsibilities. +Proyek `minigrep` kita sejauh ini sudah terlihat bagus! Sekarang kita akan +membagi file _src/main.rs_ dan memindahkan sebagian kode ke dalam _src/lib.rs_. +Dengan begitu, kita bisa menguji kode tersebut dan membuat _src/main.rs_ +memiliki tanggung jawab yang lebih sedikit. -Let’s move all the code that isn’t the `main` function from *src/main.rs* to -*src/lib.rs*: +Mari kita pindahkan kode yang bertanggung jawab untuk melakukan pencarian teks +ke dalam _src/lib.rs_, bukan di _src/main.rs_, sehingga kita (atau siapa pun +yang menggunakan library `minigrep` kita) bisa memanggil fungsi pencarian +tersebut dari konteks lain, tidak hanya dari binary `minigrep`. -* The `run` function definition -* The relevant `use` statements -* The definition of `Config` -* The `Config::build` function definition +Pertama, mari kita definisikan signature fungsi `search` di _src/lib.rs_ seperti +pada Listing 12-13, dengan body yang memanggil macro `unimplemented!`. Kita akan +menjelaskan signature-nya lebih detail setelah kita mengisi implementasinya. -The contents of *src/lib.rs* should have the signatures shown in Listing 12-13 -(we’ve omitted the bodies of the functions for brevity). Note that this won’t -compile until we modify *src/main.rs* in Listing 12-14. - -Filename: src/lib.rs + ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-13/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-13/src/lib.rs}} ``` -Listing 12-13: Moving `Config` and `run` into -*src/lib.rs* + -We’ve made liberal use of the `pub` keyword: on `Config`, on its fields and its -`build` method, and on the `run` function. We now have a library crate that has -a public API we can test! +Kita menggunakan keyword `pub` pada definisi fungsi untuk menjadikan `search` +bagian dari **public API** library crate kita. Sekarang kita punya library crate +yang bisa dipakai oleh binary crate kita, dan juga bisa kita uji! -Now we need to bring the code we moved to *src/lib.rs* into the scope of the -binary crate in *src/main.rs*, as shown in Listing 12-14. +Selanjutnya, kita perlu membawa kode yang didefinisikan di _src/lib.rs_ ke dalam +scope binary crate di _src/main.rs_ dan memanggilnya, seperti yang ditunjukkan +pada Listing 12-14. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-14/src/main.rs:here}} ``` -Listing 12-14: Using the `minigrep` library crate in -*src/main.rs* - -We add a `use minigrep::Config` line to bring the `Config` type from the -library crate into the binary crate’s scope, and we prefix the `run` function -with our crate name. Now all the functionality should be connected and should -work. Run the program with `cargo run` and make sure everything works -correctly. - -Whew! That was a lot of work, but we’ve set ourselves up for success in the -future. Now it’s much easier to handle errors, and we’ve made the code more -modular. Almost all of our work will be done in *src/lib.rs* from here on out. - -Let’s take advantage of this newfound modularity by doing something that would -have been difficult with the old code but is easy with the new code: we’ll -write some tests! + + +Kita menambahkan baris `use minigrep::search` untuk membawa fungsi `search` dari +library crate ke dalam cakupan (scope) binary crate. Lalu, di fungsi `run`, +alih-alih mencetak seluruh isi file, kita memanggil fungsi `search` dan mengoper +nilai `config.query` serta `contents` sebagai argumen. Setelah itu, `run` akan +menggunakan loop `for` untuk mencetak setiap baris hasil yang dikembalikan +`search` yang cocok dengan query. Ini juga saat yang tepat untuk menghapus +pemanggilan `println!` di fungsi `main` yang sebelumnya menampilkan query dan +path file, sehingga sekarang program hanya mencetak hasil pencarian (jika tidak +ada error). + +Perhatikan bahwa fungsi `search` akan mengumpulkan semua hasil ke dalam sebuah +vector dan mengembalikannya sebelum proses pencetakan dilakukan. Implementasi +ini bisa terasa lambat saat mencari pada file yang sangat besar karena hasil +tidak langsung dicetak ketika ditemukan; kita akan membahas kemungkinan solusi +dengan _iterators_ di Chapter 13. + +Whew! Cukup banyak kerja sejauh ini, tapi sekarang kita sudah menyiapkan +struktur program yang jauh lebih baik untuk pengembangan ke depannya. Kini +penanganan error menjadi lebih mudah dan kode jauh lebih modular. Mulai +sekarang, hampir semua pekerjaan akan dilakukan di _src/lib.rs_. + +Sekarang mari kita manfaatkan modularitas baru ini untuk melakukan sesuatu yang +sebelumnya akan sulit dilakukan, tapi sekarang jadi mudah: kita akan menulis +beberapa _test_! [ch13]: ch13-00-functional-features.html -[ch9-custom-types]: ch09-03-to-panic-or-not-to-panic.html#creating-custom-types-for-validation -[ch9-error-guidelines]: ch09-03-to-panic-or-not-to-panic.html#guidelines-for-error-handling -[ch9-result]: ch09-02-recoverable-errors-with-result.html -[ch17]: ch17-00-oop.html -[ch9-question-mark]: ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator diff --git a/src/ch12-04-testing-the-librarys-functionality.md b/src/ch12-04-testing-the-librarys-functionality.md index 129f835aa1..f998b32bda 100644 --- a/src/ch12-04-testing-the-librarys-functionality.md +++ b/src/ch12-04-testing-the-librarys-functionality.md @@ -1,244 +1,218 @@ -## Developing the Library’s Functionality with Test-Driven Development + -Now that we’ve extracted the logic into *src/lib.rs* and left the argument -collecting and error handling in *src/main.rs*, it’s much easier to write tests -for the core functionality of our code. We can call functions directly with -various arguments and check return values without having to call our binary -from the command line. + -In this section, we’ll add the searching logic to the `minigrep` program -using the test-driven development (TDD) process with the following steps: +## Nambahin Fungsionalitas pakai Test-Driven Development -1. Write a test that fails and run it to make sure it fails for the reason you - expect. -2. Write or modify just enough code to make the new test pass. -3. Refactor the code you just added or changed and make sure the tests - continue to pass. -4. Repeat from step 1! +Sekarang karena kita udah mindahin logika pencarian ke _src/lib.rs_ dan misahin +dari fungsi `main`, ngetes core logic program jadi jauh lebih gampang. Kita bisa +langsung manggil fungsi-fungsi dengan berbagai argumen dan ngecek nilai baliknya +tanpa harus jalanin binary lewat command line. -Though it’s just one of many ways to write software, TDD can help drive code -design. Writing the test before you write the code that makes the test pass -helps to maintain high test coverage throughout the process. +Di bagian ini, kita bakal nambahin logika pencarian ke program `minigrep` pakai +proses test-driven development (TDD) dengan langkah-langkah kayak gini: -We’ll test drive the implementation of the functionality that will actually do -the searching for the query string in the file contents and produce a list of -lines that match the query. We’ll add this functionality in a function called -`search`. +1. Tulis test yang gagal dan jalankan buat pastiin gagal karena alasan yang kita + ekspektasikan. +2. Tulis atau ubah kode secukupnya aja supaya test baru itu lulus. +3. Refactor kode yang baru kamu tambahin atau ubah, dan pastiin test masih tetap + lulus. +4. Ulangi lagi dari langkah 1! -### Writing a Failing Test +Walaupun ini cuma salah satu cara nulis software, TDD bisa bantu ngarahin desain +kode. Nulis test sebelum nulis kode yang bikin testnya lulus juga bantu ngejaga +coverage test tetap tinggi selama proses development. -Because we don’t need them anymore, let’s remove the `println!` statements from -*src/lib.rs* and *src/main.rs* that we used to check the program’s behavior. -Then, in *src/lib.rs*, add a `tests` module with a test function, as we did in -[Chapter 11][ch11-anatomy]. The test function specifies the -behavior we want the `search` function to have: it will take a query and the -text to search, and it will return only the lines from the text that contain -the query. Listing 12-15 shows this test, which won’t compile yet. +Kita bakal bikin implementasi fungsi yang beneran ngelakuin pencarian query di +isi file dan ngasilin daftar baris yang cocok sama query. Kita bakal nambahin +fungsionalitas ini di sebuah fungsi bernama `search`. -Filename: src/lib.rs +### Nulis Test yang Gagal Dulu + +Di _src/lib.rs_, kita bakal nambahin module `tests` dengan sebuah fungsi test, +sama kayak yang udah kita lakukan di [Chapter 11][ch11-anatomy]. +Fungsi test ini bakal ngejelasin perilaku yang kita pengen dari fungsi `search`: +dia bakal nerima query dan teks yang mau dicariin, lalu balikannya cuma baris +yang mengandung query itu aja. Listing 12-15 nunjukin testnya. + + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-15/src/lib.rs:here}} ``` -Listing 12-15: Creating a failing test for the `search` -function we wish we had + -This test searches for the string `"duct"`. The text we’re searching is three -lines, only one of which contains `"duct"` (Note that the backslash after the -opening double quote tells Rust not to put a newline character at the beginning -of the contents of this string literal). We assert that the value returned from -the `search` function contains only the line we expect. +Test ini nyari string `"duct"`. Teks yang kita cari terdiri dari tiga baris, dan +cuma satu baris yang ngandung `"duct"` (perhatikan backslash setelah tanda kutip +buka buat ngasih tau Rust supaya gak nambah karakter newline di awal string +literal ini). Kita ngasih assert kalau nilai balik dari fungsi `search` harus +cuma berisi baris yang kita ekspektasikan. -We aren’t yet able to run this test and watch it fail because the test doesn’t -even compile: the `search` function doesn’t exist yet! In accordance with TDD -principles, we’ll add just enough code to get the test to compile and run by -adding a definition of the `search` function that always returns an empty -vector, as shown in Listing 12-16. Then the test should compile and fail -because an empty vector doesn’t match a vector containing the line `"safe, -fast, productive."` +Kalau sekarang kita jalanin test ini, jelas bakal gagal karena macro +`unimplemented!` bakal panic dengan pesan “not implemented”. Sesuai prinsip TDD, +kita bakal ambil langkah kecil dulu: tambahin kode secukupnya supaya fungsi ini +gak panic lagi saat dipanggil, misalnya dengan bikin `search` selalu nge-return +vector kosong dulu, kayak di Listing 12-16. Setelah itu testnya bakal bisa +dikompilasi tapi gagal, karena vector kosong jelas gak sama dengan vector yang +isinya baris `"safe, fast, productive."`. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-16/src/lib.rs:here}} ``` -Listing 12-16: Defining just enough of the `search` -function so our test will compile + -Notice that we need to define an explicit lifetime `'a` in the signature of -`search` and use that lifetime with the `contents` argument and the return -value. Recall in [Chapter 10][ch10-lifetimes] that the lifetime -parameters specify which argument lifetime is connected to the lifetime of the -return value. In this case, we indicate that the returned vector should contain -string slices that reference slices of the argument `contents` (rather than the -argument `query`). +Sekarang kita bahas kenapa kita perlu nentuin lifetime eksplisit `'a` di +signature fungsi `search` dan pakai lifetime itu buat argumen `contents` dan +nilai baliknya. Ingat lagi di [Chapter 10][ch10-lifetimes] kalau +parameter lifetime itu nunjukin argumen mana yang lifetimenya nyambung ke return +value. Di kasus ini, kita ngasih tau kalau vector yang dikembalikan bakal berisi +string slice yang mereferensikan slice dari argumen `contents` (bukan dari +`query`). -In other words, we tell Rust that the data returned by the `search` function -will live as long as the data passed into the `search` function in the -`contents` argument. This is important! The data referenced *by* a slice needs -to be valid for the reference to be valid; if the compiler assumes we’re making -string slices of `query` rather than `contents`, it will do its safety checking -incorrectly. +Dengan kata lain, kita ngasih tau Rust kalau data yang dikembalikan fungsi +`search` bakal hidup selama data yang dikirim lewat argumen `contents` masih +valid. Ini penting banget! Data yang direferensikan sama slice harus valid +supaya referensinya valid. Kalau compiler malah nganggep kita bikin slice dari +`query` bukan dari `contents`, pengecekan keamanannya jadi salah. -If we forget the lifetime annotations and try to compile this function, we’ll -get this error: +Kalau kita lupa nulis lifetime ini dan langsung coba kompilasi, kita bakal dapet +error kayak gini: ```console {{#include ../listings/ch12-an-io-project/output-only-02-missing-lifetimes/output.txt}} ``` -Rust can’t possibly know which of the two arguments we need, so we need to tell -it explicitly. Because `contents` is the argument that contains all of our text -and we want to return the parts of that text that match, we know `contents` is -the argument that should be connected to the return value using the lifetime -syntax. - -Other programming languages don’t require you to connect arguments to return -values in the signature, but this practice will get easier over time. You might -want to compare this example with the [“Validating References with -Lifetimes”][validating-references-with-lifetimes] section in -Chapter 10. - -Now let’s run the test: - -```console -{{#include ../listings/ch12-an-io-project/listing-12-16/output.txt}} -``` +Rust gak tau parameter mana yang lifetimenya harus dipakai buat output, jadi +kita harus jelasin eksplisit. Perhatikan juga kalau pesan bantuannya nyaranin +pakai lifetime yang sama buat semua parameter dan output, tapi itu salah! Karena +`contents` adalah parameter yang nyimpen semua teks yang kita cari, dan yang mau +kita balikin itu bagian dari teks tersebut, berarti cuma `contents` yang harus +dikaitin sama return value lewat syntax lifetime. -Great, the test fails, exactly as we expected. Let’s get the test to pass! +Bahasa pemrograman lain mungkin gak maksa kamu ngaitin argumen dengan return +value di signature kayak gini, tapi lama-lama kamu bakal kebiasa. Kamu mungkin +mau bandingin contoh ini sama bagian +[“Validating References with Lifetimes”][validating-references-with-lifetimes] +di Chapter 10. -### Writing Code to Pass the Test +### Nulis Kode Biar Testnya Lulus -Currently, our test is failing because we always return an empty vector. To fix -that and implement `search`, our program needs to follow these steps: +Sekarang test kita gagal karena kita selalu balikkin vector kosong. Buat benerin +dan ngelakuin implementasi `search`, program kita perlu ngelakuin +langkah-langkah ini: -* Iterate through each line of the contents. -* Check whether the line contains our query string. -* If it does, add it to the list of values we’re returning. -* If it doesn’t, do nothing. -* Return the list of results that match. +1. Iterasi setiap baris dari `contents`. +2. Cek apakah baris tersebut mengandung query string. +3. Kalau iya, masukin barisnya ke list hasil yang mau kita return. +4. Kalau enggak, ya di-skip aja. +5. Balikin daftar hasil yang cocok. -Let’s work through each step, starting with iterating through lines. +Yuk kita kerjain step-step ini satu-satu, mulai dari looping tiap baris dulu. -#### Iterating Through Lines with the `lines` Method +#### Iterasi Baris Pakai Method `lines` -Rust has a helpful method to handle line-by-line iteration of strings, -conveniently named `lines`, that works as shown in Listing 12-17. Note this -won’t compile yet. +Rust punya method handy buat nge-handle iterasi string per baris, namanya +`lines`, dan cara kerjanya kayak di Listing 12-17. Tapi ini masih belum bisa +dikompilasi ya. -Filename: src/lib.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-17/src/lib.rs:here}} ``` -Listing 12-17: Iterating through each line in `contents` - + -The `lines` method returns an iterator. We’ll talk about iterators in depth in -[Chapter 13][ch13-iterators], but recall that you saw this way -of using an iterator in [Listing 3-5][ch3-iter], where we used a -`for` loop with an iterator to run some code on each item in a collection. +Method `lines` bakal balikin iterator. Kita bakal bahas iterators lebih dalam di +[Chapter 13][ch13-iterators]. Tapi inget, kamu udah pernah lihat +cara pake iterator kayak gini di [Listing 3-5][ch3-iter], waktu +kita pake loop `for` bareng iterator buat ngejalanin kode ke setiap item di +suatu koleksi. -#### Searching Each Line for the Query +#### Nyari Query di Setiap Baris -Next, we’ll check whether the current line contains our query string. -Fortunately, strings have a helpful method named `contains` that does this for -us! Add a call to the `contains` method in the `search` function, as shown in -Listing 12-18. Note this still won’t compile yet. +Selanjutnya kita bakal ngecek apakah baris saat ini mengandung query string +kita. Untungnya, string punya method berguna bernama `contains` buat bantu kita! +Tambahin aja pemanggilan `contains` ke fungsi `search`, kayak di Listing 12-18. +Tapi ini juga masih belum bisa dikompilasi. -Filename: src/lib.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-18/src/lib.rs:here}} ``` -Listing 12-18: Adding functionality to see whether the -line contains the string in `query` + -At the moment, we’re building up functionality. To get it to compile, we need -to return a value from the body as we indicated we would in the function -signature. +Sekarang kita lagi dalam proses ngebangun fungsionalitasnya pelan-pelan. Supaya +bisa dikompilasi, kita perlu balikin nilai sesuai yang udah kita definisiin di +function signature. -#### Storing Matching Lines +#### Nyimpen Baris yang Cocok -To finish this function, we need a way to store the matching lines that we want -to return. For that, we can make a mutable vector before the `for` loop and -call the `push` method to store a `line` in the vector. After the `for` loop, -we return the vector, as shown in Listing 12-19. +Biar fungsi ini kelar, kita butuh cara buat nyimpen baris-baris yang cocok dan +bakal kita balikin nanti. Untuk itu, kita bisa bikin vector mutable sebelum +`for` loop dan manggil method `push` buat masukin `line` ke vector. Setelah +`for` loop selesai, tinggal return vectornya. Kayak di Listing 12-19. -Filename: src/lib.rs + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-19/src/lib.rs:here}} ``` -Listing 12-19: Storing the lines that match so we can -return them + -Now the `search` function should return only the lines that contain `query`, -and our test should pass. Let’s run the test: +Sekarang fungsi `search` harusnya cuma bakal balikin baris yang mengandung +`query`, dan test kita harusnya lulus. Yuk coba jalanin testnya: ```console {{#include ../listings/ch12-an-io-project/listing-12-19/output.txt}} ``` -Our test passed, so we know it works! - -At this point, we could consider opportunities for refactoring the -implementation of the search function while keeping the tests passing to -maintain the same functionality. The code in the search function isn’t too bad, -but it doesn’t take advantage of some useful features of iterators. We’ll -return to this example in [Chapter 13][ch13-iterators], where -we’ll explore iterators in detail, and look at how to improve it. - -#### Using the `search` Function in the `run` Function - -Now that the `search` function is working and tested, we need to call `search` -from our `run` function. We need to pass the `config.query` value and the -`contents` that `run` reads from the file to the `search` function. Then `run` -will print each line returned from `search`: - -Filename: src/lib.rs - -```rust,ignore -{{#rustdoc_include ../listings/ch12-an-io-project/no-listing-02-using-search-in-run/src/lib.rs:here}} -``` +Mantap! Testnya lulus, berarti udah jalan sesuai harapan. -We’re still using a `for` loop to return each line from `search` and print it. +Sampai di titik ini, kita bisa mulai kepikiran buat refactor implementasi +`search` sambil tetep pastiin testnya lulus supaya perilakunya tetap sama. Kode +di fungsi search sebenernya udah oke, tapi masih belum manfaatin fitur-fitur +keren dari iterator. Kita bakal balik lagi ke contoh ini di +[Chapter 13][ch13-iterators] buat bahas iterator lebih dalam dan +ngeliat cara ningkatinnya. -Now the entire program should work! Let’s try it out, first with a word that -should return exactly one line from the Emily Dickinson poem, “frog”: +Sekarang seluruh programnya harusnya udah bekerja! Yuk kita cobain, pertama +pakai kata yang harusnya cuma match satu baris dari puisi Emily Dickinson: +_frog_. ```console {{#include ../listings/ch12-an-io-project/no-listing-02-using-search-in-run/output.txt}} ``` -Cool! Now let’s try a word that will match multiple lines, like “body”: +Keren! Sekarang coba kata yang match ke beberapa baris, misalnya _body_: ```console {{#include ../listings/ch12-an-io-project/output-only-03-multiple-matches/output.txt}} ``` -And finally, let’s make sure that we don’t get any lines when we search for a -word that isn’t anywhere in the poem, such as “monomorphization”: +Dan terakhir, pastiin gak ada hasil yang keluar kalau kita cari kata yang gak +ada sama sekali di puisinya, misalnya _monomorphization_: ```console {{#include ../listings/ch12-an-io-project/output-only-04-no-matches/output.txt}} ``` -Excellent! We’ve built our own mini version of a classic tool and learned a lot -about how to structure applications. We’ve also learned a bit about file input -and output, lifetimes, testing, and command line parsing. +Cakep! Kita berhasil bikin versi mini dari tool klasik dan belajar banyak +tentang cara nge-structure aplikasi. Kita juga udah belajar sedikit soal input +output file, lifetimes, testing, dan parsing command line. -To round out this project, we’ll briefly demonstrate how to work with -environment variables and how to print to standard error, both of which are -useful when you’re writing command line programs. +Buat nutupin project ini, kita bakal sekilas nunjukin cara kerja environment +variable dan cara nge-print ke standard error, dua hal yang berguna banget kalau +kamu bikin program command line. -[validating-references-with-lifetimes]: -ch10-03-lifetime-syntax.html#validating-references-with-lifetimes +[validating-references-with-lifetimes]: ch10-03-lifetime-syntax.html#validating-references-with-lifetimes [ch11-anatomy]: ch11-01-writing-tests.html#the-anatomy-of-a-test-function [ch10-lifetimes]: ch10-03-lifetime-syntax.html [ch3-iter]: ch03-05-control-flow.html#looping-through-a-collection-with-for diff --git a/src/ch12-05-working-with-environment-variables.md b/src/ch12-05-working-with-environment-variables.md index 4e6b40fb3b..565b3cfbd2 100644 --- a/src/ch12-05-working-with-environment-variables.md +++ b/src/ch12-05-working-with-environment-variables.md @@ -1,186 +1,170 @@ -## Working with Environment Variables +## Bekerja dengan Environment Variable -We’ll improve `minigrep` by adding an extra feature: an option for -case-insensitive searching that the user can turn on via an environment -variable. We could make this feature a command line option and require that -users enter it each time they want it to apply, but by instead making it an -environment variable, we allow our users to set the environment variable once -and have all their searches be case insensitive in that terminal session. +Kita bakal ningkatin binary `minigrep` dengan nambahin fitur baru: opsi +pencarian yang **gak peka huruf besar–kecil (case-insensitive)** yang bisa +diaktifin user lewat environment variable. Sebenernya kita bisa aja bikin fitur +ini jadi opsi command line, tapi itu bakal maksa user buat terus ngetik opsinya +setiap kali mau dipake. Dengan dijadiin environment variable, user cukup set +sekali aja dan semua pencarian di session terminal itu bakal otomatis jadi +case-insensitive. -### Writing a Failing Test for the Case-Insensitive `search` Function + -We first add a new `search_case_insensitive` function that will be called when -the environment variable has a value. We’ll continue to follow the TDD process, -so the first step is again to write a failing test. We’ll add a new test for -the new `search_case_insensitive` function and rename our old test from -`one_result` to `case_sensitive` to clarify the differences between the two -tests, as shown in Listing 12-20. + -Filename: src/lib.rs +### Nulis Test yang Gagal Buat Case-Insensitive Search + +Pertama, kita bakal nambahin fungsi baru `search_case_insensitive` ke library +`minigrep` yang bakal dipanggil kalau environment variable punya nilai. Kita +tetap lanjut pake proses TDD, jadi langkah pertama masih sama: bikin test yang +gagal dulu. Kita bakal nambahin test baru buat fungsi `search_case_insensitive`, +dan ganti nama test lama dari `one_result` jadi `case_sensitive` biar perbedaan +dua test ini makin jelas, kayak di Listing 12-20. + + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-20/src/lib.rs:here}} ``` -Listing 12-20: Adding a new failing test for the -case-insensitive function we’re about to add + -Note that we’ve edited the old test’s `contents` too. We’ve added a new line -with the text `"Duct tape."` using a capital D that shouldn’t match the query -`"duct"` when we’re searching in a case-sensitive manner. Changing the old test -in this way helps ensure that we don’t accidentally break the case-sensitive -search functionality that we’ve already implemented. This test should pass now -and should continue to pass as we work on the case-insensitive search. +Perhatiin kalau kita juga ngedit `contents` di test lama. Kita nambah satu baris +`"Duct tape."` dengan huruf _D_ kapital yang **gak seharusnya ke-detect** pas +pencarian case-sensitive `"duct"`. Perubahan ini buat mastiin kita gak tanpa +sengaja ngerusak fitur case-sensitive yang udah jadi. Test lama ini harusnya +tetap lulus sekarang dan harus tetap lulus selama kita ngerjain fitur +case-insensitive. -The new test for the case-*insensitive* search uses `"rUsT"` as its query. In -the `search_case_insensitive` function we’re about to add, the query `"rUsT"` -should match the line containing `"Rust:"` with a capital R and match the line -`"Trust me."` even though both have different casing from the query. This is -our failing test, and it will fail to compile because we haven’t yet defined -the `search_case_insensitive` function. Feel free to add a skeleton -implementation that always returns an empty vector, similar to the way we did -for the `search` function in Listing 12-16 to see the test compile and fail. +Test baru buat pencarian case-_insensitive_ pake query `"rUsT"`. Di fungsi +`search_case_insensitive` yang bakal kita tambahin, query `"rUsT"` harusnya +cocok sama baris `"Rust:"` yang huruf depannya kapital, dan juga cocok sama +`"Trust me."` walaupun casing-nya beda. Ini test gagal kita, dan sekarang bakal +gagal compile karena fungsi `search_case_insensitive` belum ada. Kalau mau, +bikin aja skeleton function yang cuma return vector kosong dulu, sama kayak +waktu kita bikin `search` di Listing 12-16, biar testnya bisa compile dan gagal +normal. -### Implementing the `search_case_insensitive` Function +### Implementasi Fungsi `search_case_insensitive` -The `search_case_insensitive` function, shown in Listing 12-21, will be almost -the same as the `search` function. The only difference is that we’ll lowercase -the `query` and each `line` so whatever the case of the input arguments, -they’ll be the same case when we check whether the line contains the query. +Fungsi `search_case_insensitive`, kayak di Listing 12-21, bakal hampir sama +kayak `search`. Bedanya cuma satu: kita bakal **lowercase** `query` dan tiap +`line` biar perbandingannya gak peduli huruf besar kecil. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-21/src/lib.rs:here}} ``` -Listing 12-21: Defining the `search_case_insensitive` -function to lowercase the query and the line before comparing them + -First, we lowercase the `query` string and store it in a shadowed variable with -the same name. Calling `to_lowercase` on the query is necessary so no -matter whether the user’s query is `"rust"`, `"RUST"`, `"Rust"`, or `"rUsT"`, -we’ll treat the query as if it were `"rust"` and be insensitive to the case. -While `to_lowercase` will handle basic Unicode, it won’t be 100% accurate. If -we were writing a real application, we’d want to do a bit more work here, but -this section is about environment variables, not Unicode, so we’ll leave it at -that here. +Pertama, kita lowercase string `query` dan simpen ke variabel baru dengan nama +yang sama (shadowing variabel lama). `to_lowercase` dipanggil supaya mau +query-nya `"rust"`, `"RUST"`, `"Rust"`, atau `"rUsT"`, semuanya bakal +diperlakuin sama. -Note that `query` is now a `String` rather than a string slice, because calling -`to_lowercase` creates new data rather than referencing existing data. Say the -query is `"rUsT"`, as an example: that string slice doesn’t contain a lowercase -`u` or `t` for us to use, so we have to allocate a new `String` containing -`"rust"`. When we pass `query` as an argument to the `contains` method now, we -need to add an ampersand because the signature of `contains` is defined to take -a string slice. +Walaupun `to_lowercase` udah ngedukung Unicode basic, tapi emang gak 100% akurat +sih. Kalau ini aplikasi beneran, mungkin butuh effort lebih. Tapi karena fokus +bagian ini environment variable, bukan Unicode, kita santai aja dulu. -Next, we add a call to `to_lowercase` on each `line` to lowercase all -characters. Now that we’ve converted `line` and `query` to lowercase, we’ll -find matches no matter what the case of the query is. +Yang perlu dicatat: Sekarang `query` jadi `String`, bukan string slice lagi, +karena `to_lowercase` bikin data baru, bukan referensi data lama. Misal query +`"rUsT"`, string aslinya gak punya huruf `u` dan `t` lowercase, jadi kita harus +bikin `String` baru `"rust"`. Dan karena `contains` butuh string slice, kita +kasih `&query`. -Let’s see if this implementation passes the tests: +Selanjutnya kita juga panggil `to_lowercase` ke tiap `line` biar semuanya +lowercase juga. Karena sekarang `line` dan `query` udah sama-sama lowercase, +pencarian jadi benar-benar case-insensitive. + +Coba cek testnya: ```console {{#include ../listings/ch12-an-io-project/listing-12-21/output.txt}} ``` -Great! They passed. Now, let’s call the new `search_case_insensitive` function -from the `run` function. First, we’ll add a configuration option to the -`Config` struct to switch between case-sensitive and case-insensitive search. -Adding this field will cause compiler errors because we aren’t initializing -this field anywhere yet: +Mantap, lulus semua + +Sekarang kita panggil fungsi `search_case_insensitive` dari `run`. Pertama, kita +nambah opsi konfigurasi ke struct `Config` buat nge-switch antara mode +case-sensitive dan case-insensitive. Tapi nambah field ini bakal bikin compiler +error dulu karena belum diinisialisasi: -Filename: src/lib.rs +Filename: src/main.rs ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-22/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-22/src/main.rs:here}} ``` -We added the `ignore_case` field that holds a Boolean. Next, we need the `run` -function to check the `ignore_case` field’s value and use that to decide -whether to call the `search` function or the `search_case_insensitive` -function, as shown in Listing 12-22. This still won’t compile yet. +Kita nambah field `ignore_case` bertipe Boolean. Selanjutnya, fungsi `run` harus +ngecek nilai `ignore_case` dan mutusin apakah mau manggil `search` atau +`search_case_insensitive`, kayak di Listing 12-22. Ini juga masih belum compile. -Filename: src/lib.rs + ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-22/src/lib.rs:there}} +{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-22/src/main.rs:there}} ``` -Listing 12-22: Calling either `search` or -`search_case_insensitive` based on the value in `config.ignore_case` + -Finally, we need to check for the environment variable. The functions for -working with environment variables are in the `env` module in the standard -library, so we bring that module into scope at the top of *src/lib.rs*. Then -we’ll use the `var` function from the `env` module to check to see if any value -has been set for an environment variable named `IGNORE_CASE`, as shown in -Listing 12-23. +Terakhir, kita perlu ngecek environment variable. Fungsi buat kerja sama +environment variable ada di module `env` di standard library, dan dia udah +di-import di bagian atas _src/main.rs_. Kita bakal pake fungsi `var` buat ngecek +apakah environment variable `IGNORE_CASE` punya nilai, kayak di Listing 12-23. -Filename: src/lib.rs + -```rust,noplayground -{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-23/src/lib.rs:here}} +```rust,ignore,noplayground +{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-23/src/main.rs:here}} ``` -Listing 12-23: Checking for any value in an environment -variable named `IGNORE_CASE` + + +Di sini kita bikin variabel baru `ignore_case`. Nilainya diambil dari +`env::var("IGNORE_CASE")`. Fungsi `env::var` balikannya `Result`: -Here, we create a new variable `ignore_case`. To set its value, we call the -`env::var` function and pass it the name of the `IGNORE_CASE` environment -variable. The `env::var` function returns a `Result` that will be the -successful `Ok` variant that contains the value of the environment variable if -the environment variable is set to any value. It will return the `Err` variant -if the environment variable is not set. +- `Ok(value)` kalau environment variablenya ada dan punya nilai apa pun +- `Err` kalau environment variablenya gak ada -We’re using the `is_ok` method on the `Result` to check whether the environment -variable is set, which means the program should do a case-insensitive search. -If the `IGNORE_CASE` environment variable isn’t set to anything, `is_ok` will -return false and the program will perform a case-sensitive search. We don’t -care about the *value* of the environment variable, just whether it’s set or -unset, so we’re checking `is_ok` rather than using `unwrap`, `expect`, or any -of the other methods we’ve seen on `Result`. +Kita pake `is_ok` buat ngecek apakah variabel environment diset. Kalau +`IGNORE_CASE` diset → pencarian case-insensitive. Kalau gak diset → tetap +case-sensitive. -We pass the value in the `ignore_case` variable to the `Config` instance so the -`run` function can read that value and decide whether to call -`search_case_insensitive` or `search`, as we implemented in Listing 12-22. +Kita gak peduli nilai environment variablenya apa, yang penting ada atau enggak, +jadi `is_ok` udah cukup. Nilai `ignore_case` ini kita lempar ke `Config`, biar +`run` bisa baca dan mutusin mau pake fungsi yang mana. -Let’s give it a try! First, we’ll run our program without the environment -variable set and with the query `to`, which should match any line that contains -the word “to” in all lowercase: +Sekarang kita coba! Pertama jalankan program TANPA environment variable, pakai +query `to`, yang cuma harus match huruf kecil. ```console {{#include ../listings/ch12-an-io-project/listing-12-23/output.txt}} ``` -Looks like that still works! Now, let’s run the program with `IGNORE_CASE` -set to `1` but with the same query `to`. +Masih jalan + +Sekarang kita jalanin lagi tapi dengan `IGNORE_CASE=1` ```console -$ IGNORE_CASE=1 cargo run -- to poem.txt +IGNORE_CASE=1 cargo run -- to poem.txt ``` -If you’re using PowerShell, you will need to set the environment variable and -run the program as separate commands: +Kalau kamu pake PowerShell, caranya beda dikit: ```console PS> $Env:IGNORE_CASE=1; cargo run -- to poem.txt ``` -This will make `IGNORE_CASE` persist for the remainder of your shell -session. It can be unset with the `Remove-Item` cmdlet: +Ini bikin `IGNORE_CASE` tetap aktif sampai session shell selesai. Buat +ngehapusnya: ```console PS> Remove-Item Env:IGNORE_CASE ``` -We should get lines that contain “to” that might have uppercase letters: - - +Sekarang hasilnya harusnya juga match huruf kapital: ```console Are you nobody, too? @@ -189,18 +173,16 @@ To tell your name the livelong day To an admiring bog! ``` -Excellent, we also got lines containing “To”! Our `minigrep` program can now do -case-insensitive searching controlled by an environment variable. Now you know -how to manage options set using either command line arguments or environment -variables. - -Some programs allow arguments *and* environment variables for the same -configuration. In those cases, the programs decide that one or the other takes -precedence. For another exercise on your own, try controlling case sensitivity -through either a command line argument or an environment variable. Decide -whether the command line argument or the environment variable should take -precedence if the program is run with one set to case sensitive and one set to -ignore case. - -The `std::env` module contains many more useful features for dealing with -environment variables: check out its documentation to see what is available. +Gas, berhasil Sekarang `minigrep` bisa pencarian case-insensitive yang +dikontrol environment variable. Jadi sekarang kamu tau gimana caranya ngatur +opsi lewat argumen command line maupun environment variable. + +Beberapa program malah nge-dukung dua-duanya sekaligus, dan biasanya salah +satunya punya prioritas lebih. Kalau mau latihan tambahan, coba bikin: + +- case sensitivity bisa dikontrol via command line argument +- atau environment variable +- lalu tentuin mana yang lebih prioritas kalau dua-duanya dipakai + +Module `std::env` masih punya banyak fitur lain buat kerja dengan environment +variable. Silakan cek dokumentasinya kalau penasaran! diff --git a/src/ch12-06-writing-to-stderr-instead-of-stdout.md b/src/ch12-06-writing-to-stderr-instead-of-stdout.md index d017fa3245..91f4eaf7c7 100644 --- a/src/ch12-06-writing-to-stderr-instead-of-stdout.md +++ b/src/ch12-06-writing-to-stderr-instead-of-stdout.md @@ -1,88 +1,88 @@ -## Writing Error Messages to Standard Error Instead of Standard Output + -At the moment, we’re writing all of our output to the terminal using the -`println!` macro. In most terminals, there are two kinds of output: *standard -output* (`stdout`) for general information and *standard error* (`stderr`) for -error messages. This distinction enables users to choose to direct the -successful output of a program to a file but still print error messages to the -screen. + -The `println!` macro is only capable of printing to standard output, so we -have to use something else to print to standard error. +## Ngeredirect Error ke Standard Error -### Checking Where Errors Are Written +Sekarang ini, kita masih nge-print semua output ke terminal pakai macro +`println!`. Di kebanyakan terminal, sebenarnya ada dua jenis output: _standard +output_ (`stdout`) buat info biasa dan _standard error_ (`stderr`) buat pesan +error. Pemisahan ini bikin user bisa ngirim hasil sukses program ke file, tapi +pesan errornya tetap muncul di layar. -First, let’s observe how the content printed by `minigrep` is currently being -written to standard output, including any error messages we want to write to -standard error instead. We’ll do that by redirecting the standard output stream -to a file while intentionally causing an error. We won’t redirect the standard -error stream, so any content sent to standard error will continue to display on -the screen. +Masalahnya, `println!` cuma bisa nge-print ke standard output, jadi kita perlu +cara lain buat nge-print ke standard error. -Command line programs are expected to send error messages to the standard error -stream so we can still see error messages on the screen even if we redirect the -standard output stream to a file. Our program is not currently well-behaved: -we’re about to see that it saves the error message output to a file instead! +### Ngecek Error Sekarang Lagi Dicetak ke Mana -To demonstrate this behavior, we’ll run the program with `>` and the file path, -*output.txt*, that we want to redirect the standard output stream to. We won’t -pass any arguments, which should cause an error: +Pertama, kita cek dulu sebenernya konten yang diprint `minigrep` sekarang itu +keluar ke standard output semua, termasuk error yang sebenernya pengen kita +arahin ke standard error. Kita bakal ngetes ini dengan nge-redirect output +standard ke file sambil sengaja bikin error. Kita gak bakal nge-redirect +standard error, jadi kalau ada sesuatu dikirim ke standard error, itu tetap +bakal muncul di layar. + +Program command line yang “sopan” itu harusnya ngirim error ke standard error +biar kita masih bisa lihat error di layar meskipun standard output lagi +di-redirect ke file. Tapi program kita sekarang belum sopan nih: kita bakal +lihat kalau dia malah nyimpen pesan error ke file! + +Buat nunjukin ini, kita jalanin program pakai tanda `>` dan nama file, +_output.txt_, buat tujuan redirect standard output. Kita gak bakal masukin +argumen apa pun, jadi pasti muncul error: ```console $ cargo run > output.txt ``` -The `>` syntax tells the shell to write the contents of standard output to -*output.txt* instead of the screen. We didn’t see the error message we were -expecting printed to the screen, so that means it must have ended up in the -file. This is what *output.txt* contains: +Sintaks `>` ngasih tau shell buat nulis isi standard output ke _output.txt_ +bukannya ke layar. Kita gak lihat pesan error yang seharusnya muncul di layar, +berarti kemungkinan besar malah masuk ke file. Ini isi file _output.txt_: ```text Problem parsing arguments: not enough arguments ``` -Yup, our error message is being printed to standard output. It’s much more -useful for error messages like this to be printed to standard error so only -data from a successful run ends up in the file. We’ll change that. +Yap, error kita lagi-lagi dicetak ke standard output. Jauh lebih berguna kalau +pesan error kayak gini diprint ke standard error, jadi yang masuk file cuma +output sukses aja. Yuk kita benerin. -### Printing Errors to Standard Error +### Nge-print Error ke Standard Error -We’ll use the code in Listing 12-24 to change how error messages are printed. -Because of the refactoring we did earlier in this chapter, all the code that -prints error messages is in one function, `main`. The standard library provides -the `eprintln!` macro that prints to the standard error stream, so let’s change -the two places we were calling `println!` to print errors to use `eprintln!` -instead. +Kita bakal pakai kode di Listing 12-24 buat ngubah cara nge-print error. +Untungnya, karena refactoring yang udah kita lakukan sebelumnya, semua kode yang +nge-print error sekarang ada cuma di satu fungsi: `main`. Standard library udah +nyediain macro `eprintln!` yang nge-print ke standard error, jadi kita tinggal +ganti dua pemanggilan `println!` yang dipakai buat error jadi `eprintln!`. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-24/src/main.rs:here}} ``` -Listing 12-24: Writing error messages to standard error -instead of standard output using `eprintln!` + -Let’s now run the program again in the same way, without any arguments and -redirecting standard output with `>`: +Sekarang kita jalanin program lagi dengan cara yang sama: tanpa argumen dan +tetap nge-redirect standard output pakai `>`: ```console $ cargo run > output.txt Problem parsing arguments: not enough arguments ``` -Now we see the error onscreen and *output.txt* contains nothing, which is the -behavior we expect of command line programs. +Sekarang errornya muncul di layar dan _output.txt_ kosong. Ini behavior yang +memang diharapkan dari program command line. -Let’s run the program again with arguments that don’t cause an error but still -redirect standard output to a file, like so: +Sekarang kita coba lagi, tapi kali ini pakai argumen yang valid dan tetap +redirect standard output ke file: ```console $ cargo run -- to poem.txt > output.txt ``` -We won’t see any output to the terminal, and *output.txt* will contain our -results: +Kita gak bakal lihat output apa pun di terminal, dan isi _output.txt_ bakal +jadi: Filename: output.txt @@ -91,18 +91,23 @@ Are you nobody, too? How dreary to be somebody! ``` -This demonstrates that we’re now using standard output for successful output -and standard error for error output as appropriate. +Ini nunjukin kalau sekarang kita udah bener: standard output dipakai buat hasil +yang sukses, dan standard error khusus buat pesan error. + +## Ringkasan + +Di chapter ini kita nge-recap beberapa konsep besar yang udah kamu pelajari +sejauh ini dan ngebahas gimana caranya ngelakuin operasi I/O umum di Rust. +Dengan pakai argumen command line, file, environment variable, dan macro +`eprintln!` buat nge-print error, sekarang kamu udah siap bikin aplikasi command +line sendiri. -## Summary +Digabung sama konsep-konsep di chapter sebelumnya, sekarang kode kamu: -This chapter recapped some of the major concepts you’ve learned so far and -covered how to perform common I/O operations in Rust. By using command line -arguments, files, environment variables, and the `eprintln!` macro for printing -errors, you’re now prepared to write command line applications. Combined with -the concepts in previous chapters, your code will be well organized, store data -effectively in the appropriate data structures, handle errors nicely, and be -well tested. +- lebih rapi dan terorganisir, +- bisa nyimpen data dengan struktur yang tepat, +- punya error handling yang oke, +- dan tentu aja, udah bisa dites dengan baik. -Next, we’ll explore some Rust features that were influenced by functional -languages: closures and iterators. +Selanjutnya, kita bakal eksplor fitur Rust yang terinspirasi dari bahasa +functional: closures dan iterators. diff --git a/src/ch13-00-functional-features.md b/src/ch13-00-functional-features.md index 7011cb9f4a..2ed6770a98 100644 --- a/src/ch13-00-functional-features.md +++ b/src/ch13-00-functional-features.md @@ -1,7 +1,7 @@ # Functional Language Features: Iterators and Closures Rust’s design has taken inspiration from many existing languages and -techniques, and one significant influence is *functional programming*. +techniques, and one significant influence is _functional programming_. Programming in a functional style often includes using functions as values by passing them in arguments, returning them from other functions, assigning them to variables for later execution, and so forth. @@ -12,13 +12,13 @@ features in many languages often referred to as functional. More specifically, we’ll cover: -* *Closures*, a function-like construct you can store in a variable -* *Iterators*, a way of processing a series of elements -* How to use closures and iterators to improve the I/O project in Chapter 12 -* The performance of closures and iterators (Spoiler alert: they’re faster than +- _Closures_, a function-like construct you can store in a variable +- _Iterators_, a way of processing a series of elements +- How to use closures and iterators to improve the I/O project in Chapter 12 +- The performance of closures and iterators (spoiler alert: They’re faster than you might think!) We’ve already covered some other Rust features, such as pattern matching and enums, that are also influenced by the functional style. Because mastering -closures and iterators is an important part of writing idiomatic, fast Rust +closures and iterators is an important part of writing fast, idiomatic, Rust code, we’ll devote this entire chapter to them. diff --git a/src/ch13-01-closures.md b/src/ch13-01-closures.md index f1ae324354..ecda1acff5 100644 --- a/src/ch13-01-closures.md +++ b/src/ch13-01-closures.md @@ -1,7 +1,9 @@ - + + + -## Closures: Anonymous Functions that Capture Their Environment +## Closures Rust’s closures are anonymous functions you can save in a variable or pass as arguments to other functions. You can create the closure in one place and then @@ -11,15 +13,17 @@ We’ll demonstrate how these closure features allow for code reuse and behavior customization. + + -### Capturing the Environment with Closures +### Capturing the Environment We’ll first examine how we can use closures to capture values from the environment they’re defined in for later use. Here’s the scenario: Every so -often, our t-shirt company gives away an exclusive, limited-edition shirt to +often, our T-shirt company gives away an exclusive, limited-edition shirt to someone on our mailing list as a promotion. People on the mailing list can optionally add their favorite color to their profile. If the person chosen for a free shirt has their favorite color set, they get that color shirt. If the @@ -31,24 +35,24 @@ enum called `ShirtColor` that has the variants `Red` and `Blue` (limiting the number of colors available for simplicity). We represent the company’s inventory with an `Inventory` struct that has a field named `shirts` that contains a `Vec` representing the shirt colors currently in stock. -The method `giveaway` defined on `Inventory` gets the optional shirt -color preference of the free shirt winner, and returns the shirt color the -person will get. This setup is shown in Listing 13-1: +The method `giveaway` defined on `Inventory` gets the optional shirt color +preference of the free-shirt winner, and it returns the shirt color the +person will get. This setup is shown in Listing 13-1. -Filename: src/main.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch13-functional-features/listing-13-01/src/main.rs}} ``` -Listing 13-1: Shirt company giveaway situation + The `store` defined in `main` has two blue shirts and one red shirt remaining to distribute for this limited-edition promotion. We call the `giveaway` method for a user with a preference for a red shirt and a user without any preference. Again, this code could be implemented in many ways, and here, to focus on -closures, we’ve stuck to concepts you’ve already learned except for the body of +closures, we’ve stuck to concepts you’ve already learned, except for the body of the `giveaway` method that uses a closure. In the `giveaway` method, we get the user preference as a parameter of type `Option` and call the `unwrap_or_else` method on `user_preference`. The [`unwrap_or_else` method on @@ -62,12 +66,12 @@ the closure. We specify the closure expression `|| self.most_stocked()` as the argument to `unwrap_or_else`. This is a closure that takes no parameters itself (if the -closure had parameters, they would appear between the two vertical bars). The +closure had parameters, they would appear between the two vertical pipes). The body of the closure calls `self.most_stocked()`. We’re defining the closure here, and the implementation of `unwrap_or_else` will evaluate the closure later if the result is needed. -Running this code prints: +Running this code prints the following: ```console {{#include ../listings/ch13-functional-features/listing-13-01/output.txt}} @@ -81,7 +85,11 @@ immutable reference to the `self` `Inventory` instance and passes it with the code we specify to the `unwrap_or_else` method. Functions, on the other hand, are not able to capture their environment in this way. -### Closure Type Inference and Annotation + + + + +### Inferring and Annotating Closure Types There are more differences between functions and closures. Closures don’t usually require you to annotate the types of the parameters or the return value @@ -89,8 +97,8 @@ like `fn` functions do. Type annotations are required on functions because the types are part of an explicit interface exposed to your users. Defining this interface rigidly is important for ensuring that everyone agrees on what types of values a function uses and returns. Closures, on the other hand, aren’t used -in an exposed interface like this: they’re stored in variables and used without -naming them and exposing them to users of our library. +in an exposed interface like this: They’re stored in variables, and they’re +used without naming them and exposing them to users of our library. Closures are typically short and relevant only within a narrow context rather than in any arbitrary scenario. Within these limited contexts, the compiler can @@ -103,19 +111,18 @@ explicitness and clarity at the cost of being more verbose than is strictly necessary. Annotating the types for a closure would look like the definition shown in Listing 13-2. In this example, we’re defining a closure and storing it in a variable rather than defining the closure in the spot we pass it as an -argument as we did in Listing 13-1. +argument, as we did in Listing 13-1. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-02/src/main.rs:here}} ``` -Listing 13-2: Adding optional type annotations of the -parameter and return value types in the closure + With type annotations added, the syntax of closures looks more similar to the -syntax of functions. Here we define a function that adds 1 to its parameter and +syntax of functions. Here, we define a function that adds 1 to its parameter and a closure that has the same behavior, for comparison. We’ve added some spaces to line up the relevant parts. This illustrates how closure syntax is similar to function syntax except for the use of pipes and the amount of syntax that is @@ -128,7 +135,7 @@ let add_one_v3 = |x| { x + 1 }; let add_one_v4 = |x| x + 1 ; ``` -The first line shows a function definition, and the second line shows a fully +The first line shows a function definition and the second line shows a fully annotated closure definition. In the third line, we remove the type annotations from the closure definition. In the fourth line, we remove the brackets, which are optional because the closure body has only one expression. These are all @@ -147,14 +154,13 @@ Because there are no type annotations, we can call the closure with any type, which we’ve done here with `String` the first time. If we then try to call `example_closure` with an integer, we’ll get an error. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch13-functional-features/listing-13-03/src/main.rs:here}} ``` -Listing 13-3: Attempting to call a closure whose types -are inferred with two different types + The compiler gives us this error: @@ -177,16 +183,15 @@ captured values. In Listing 13-4, we define a closure that captures an immutable reference to the vector named `list` because it only needs an immutable reference to print -the value: +the value. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-04/src/main.rs}} ``` -Listing 13-4: Defining and calling a closure that -captures an immutable reference + This example also illustrates that a variable can bind to a closure definition, and we can later call the closure by using the variable name and parentheses as @@ -202,16 +207,15 @@ is called. This code compiles, runs, and prints: ``` Next, in Listing 13-5, we change the closure body so that it adds an element to -the `list` vector. The closure now captures a mutable reference: +the `list` vector. The closure now captures a mutable reference. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-05/src/main.rs}} ``` -Listing 13-5: Defining and calling a closure that -captures a mutable reference + This code compiles, runs, and prints: @@ -220,10 +224,10 @@ This code compiles, runs, and prints: ``` Note that there’s no longer a `println!` between the definition and the call of -the `borrows_mutably` closure: when `borrows_mutably` is defined, it captures a +the `borrows_mutably` closure: When `borrows_mutably` is defined, it captures a mutable reference to `list`. We don’t use the closure again after the closure is called, so the mutable borrow ends. Between the closure definition and the -closure call, an immutable borrow to print isn’t allowed because no other +closure call, an immutable borrow to print isn’t allowed, because no other borrows are allowed when there’s a mutable borrow. Try adding a `println!` there to see what error message you get! @@ -236,16 +240,15 @@ the data so that it’s owned by the new thread. We’ll discuss threads and why you would want to use them in detail in Chapter 16 when we talk about concurrency, but for now, let’s briefly explore spawning a new thread using a closure that needs the `move` keyword. Listing 13-6 shows Listing 13-4 modified -to print the vector in a new thread rather than in the main thread: +to print the vector in a new thread rather than in the main thread. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-06/src/main.rs}} ``` -Listing 13-6: Using `move` to force the closure for the -thread to take ownership of `list` + We spawn a new thread, giving the thread a closure to run as an argument. The closure body prints out the list. In Listing 13-4, the closure only captured @@ -253,30 +256,34 @@ closure body prints out the list. In Listing 13-4, the closure only captured to `list` needed to print it. In this example, even though the closure body still only needs an immutable reference, we need to specify that `list` should be moved into the closure by putting the `move` keyword at the beginning of the -closure definition. The new thread might finish before the rest of the main -thread finishes, or the main thread might finish first. If the main thread -maintained ownership of `list` but ended before the new thread did and dropped +closure definition. If the main thread performed more operations before calling +`join` on the new thread, the new thread might finish before the rest of the +main thread finishes, or the main thread might finish first. If the main thread +maintained ownership of `list` but ended before the new thread and drops `list`, the immutable reference in the thread would be invalid. Therefore, the compiler requires that `list` be moved into the closure given to the new thread -so the reference will be valid. Try removing the `move` keyword or using `list` -in the main thread after the closure is defined to see what compiler errors you -get! +so that the reference will be valid. Try removing the `move` keyword or using +`list` in the main thread after the closure is defined to see what compiler +errors you get! + + -### Moving Captured Values Out of Closures and the `Fn` Traits +### Moving Captured Values Out of Closures Once a closure has captured a reference or captured ownership of a value from the environment where the closure is defined (thus affecting what, if anything, -is moved *into* the closure), the code in the body of the closure defines what +is moved _into_ the closure), the code in the body of the closure defines what happens to the references or values when the closure is evaluated later (thus -affecting what, if anything, is moved *out of* the closure). A closure body can -do any of the following: move a captured value out of the closure, mutate the -captured value, neither move nor mutate the value, or capture nothing from the -environment to begin with. +affecting what, if anything, is moved _out of_ the closure). + +A closure body can do any of the following: Move a captured value out of the +closure, mutate the captured value, neither move nor mutate the value, or +capture nothing from the environment to begin with. The way a closure captures and handles values from the environment affects which traits the closure implements, and traits are how functions and structs @@ -284,18 +291,17 @@ can specify what kinds of closures they can use. Closures will automatically implement one, two, or all three of these `Fn` traits, in an additive fashion, depending on how the closure’s body handles the values: -1. `FnOnce` applies to closures that can be called once. All closures implement - at least this trait, because all closures can be called. A closure that - moves captured values out of its body will only implement `FnOnce` and none - of the other `Fn` traits, because it can only be called once. -2. `FnMut` applies to closures that don’t move captured values out of their - body, but that might mutate the captured values. These closures can be - called more than once. -3. `Fn` applies to closures that don’t move captured values out of their body - and that don’t mutate captured values, as well as closures that capture - nothing from their environment. These closures can be called more than once - without mutating their environment, which is important in cases such as - calling a closure multiple times concurrently. +* `FnOnce` applies to closures that can be called once. All closures implement + at least this trait because all closures can be called. A closure that moves + captured values out of its body will only implement `FnOnce` and none of the + other `Fn` traits because it can only be called once. +* `FnMut` applies to closures that don’t move captured values out of their body + but might mutate the captured values. These closures can be called more than + once. +* `Fn` applies to closures that don’t move captured values out of their body + and don’t mutate captured values, as well as closures that capture nothing + from their environment. These closures can be called more than once without + mutating their environment, which is important in cases such as calling a closure multiple times concurrently. Let’s look at the definition of the `unwrap_or_else` method on `Option` that we used in Listing 13-1: @@ -316,7 +322,7 @@ impl Option { Recall that `T` is the generic type representing the type of the value in the `Some` variant of an `Option`. That type `T` is also the return type of the -`unwrap_or_else` function: code that calls `unwrap_or_else` on an +`unwrap_or_else` function: Code that calls `unwrap_or_else` on an `Option`, for example, will get a `String`. Next, notice that the `unwrap_or_else` function has the additional generic type @@ -326,36 +332,36 @@ the closure we provide when calling `unwrap_or_else`. The trait bound specified on the generic type `F` is `FnOnce() -> T`, which means `F` must be able to be called once, take no arguments, and return a `T`. Using `FnOnce` in the trait bound expresses the constraint that -`unwrap_or_else` is only going to call `f` at most one time. In the body of +`unwrap_or_else` will not call `f` more than once. In the body of `unwrap_or_else`, we can see that if the `Option` is `Some`, `f` won’t be called. If the `Option` is `None`, `f` will be called once. Because all -closures implement `FnOnce`, `unwrap_or_else` accepts the most different kinds -of closures and is as flexible as it can be. - -> Note: Functions can implement all three of the `Fn` traits too. If what we -> want to do doesn’t require capturing a value from the environment, we can use -> the name of a function rather than a closure where we need something that -> implements one of the `Fn` traits. For example, on an `Option>` value, -> we could call `unwrap_or_else(Vec::new)` to get a new, empty vector if the -> value is `None`. - -Now let’s look at the standard library method `sort_by_key` defined on slices, +closures implement `FnOnce`, `unwrap_or_else` accepts all three kinds of +closures and is as flexible as it can be. + +> Note: If what we want to do doesn’t require capturing a value from the +> environment, we can use the name of a function rather than a closure where we +> need something that implements one of the `Fn` traits. For example, on an +> `Option>` value, we could call `unwrap_or_else(Vec::new)` to get a +> new, empty vector if the value is `None`. The compiler automatically +> implements whichever of the `Fn` traits is applicable for a function +> definition. + +Now let’s look at the standard library method `sort_by_key`, defined on slices, to see how that differs from `unwrap_or_else` and why `sort_by_key` uses `FnMut` instead of `FnOnce` for the trait bound. The closure gets one argument in the form of a reference to the current item in the slice being considered, -and returns a value of type `K` that can be ordered. This function is useful +and it returns a value of type `K` that can be ordered. This function is useful when you want to sort a slice by a particular attribute of each item. In -Listing 13-7, we have a list of `Rectangle` instances and we use `sort_by_key` -to order them by their `width` attribute from low to high: +Listing 13-7, we have a list of `Rectangle` instances, and we use `sort_by_key` +to order them by their `width` attribute from low to high. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-07/src/main.rs}} ``` -Listing 13-7: Using `sort_by_key` to order rectangles by -width + This code prints: @@ -365,29 +371,28 @@ This code prints: The reason `sort_by_key` is defined to take an `FnMut` closure is that it calls the closure multiple times: once for each item in the slice. The closure `|r| -r.width` doesn’t capture, mutate, or move out anything from its environment, so +r.width` doesn’t capture, mutate, or move anything out from its environment, so it meets the trait bound requirements. In contrast, Listing 13-8 shows an example of a closure that implements just the `FnOnce` trait, because it moves a value out of the environment. The -compiler won’t let us use this closure with `sort_by_key`: +compiler won’t let us use this closure with `sort_by_key`. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch13-functional-features/listing-13-08/src/main.rs}} ``` -Listing 13-8: Attempting to use an `FnOnce` closure with -`sort_by_key` + -This is a contrived, convoluted way (that doesn’t work) to try and count the -number of times `sort_by_key` gets called when sorting `list`. This code +This is a contrived, convoluted way (that doesn’t work) to try to count the +number of times `sort_by_key` calls the closure when sorting `list`. This code attempts to do this counting by pushing `value`—a `String` from the closure’s -environment—into the `sort_operations` vector. The closure captures `value` +environment—into the `sort_operations` vector. The closure captures `value` and then moves `value` out of the closure by transferring ownership of `value` to the `sort_operations` vector. This closure can be called once; trying to call -it a second time wouldn’t work because `value` would no longer be in the +it a second time wouldn’t work, because `value` would no longer be in the environment to be pushed into `sort_operations` again! Therefore, this closure only implements `FnOnce`. When we try to compile this code, we get this error that `value` can’t be moved out of the closure because the closure must @@ -399,21 +404,19 @@ implement `FnMut`: The error points to the line in the closure body that moves `value` out of the environment. To fix this, we need to change the closure body so that it doesn’t -move values out of the environment. To count the number of times `sort_by_key` -is called, keeping a counter in the environment and incrementing its value in -the closure body is a more straightforward way to calculate that. The closure -in Listing 13-9 works with `sort_by_key` because it is only capturing a mutable -reference to the `num_sort_operations` counter and can therefore be called more -than once: +move values out of the environment. Keeping a counter in the environment and +incrementing its value in the closure body is a more straightforward way to +count the number of times the closure is called. The closure in Listing 13-9 +works with `sort_by_key` because it is only capturing a mutable reference to the +`num_sort_operations` counter and can therefore be called more than once. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-09/src/main.rs}} ``` -Listing 13-9: Using an `FnMut` closure with `sort_by_key` -is allowed + The `Fn` traits are important when defining or using functions or types that make use of closures. In the next section, we’ll discuss iterators. Many diff --git a/src/ch13-02-iterators.md b/src/ch13-02-iterators.md index 030ebf48eb..99f2625947 100644 --- a/src/ch13-02-iterators.md +++ b/src/ch13-02-iterators.md @@ -5,34 +5,38 @@ turn. An iterator is responsible for the logic of iterating over each item and determining when the sequence has finished. When you use iterators, you don’t have to reimplement that logic yourself. -In Rust, iterators are *lazy*, meaning they have no effect until you call +In Rust, iterators are _lazy_, meaning they have no effect until you call methods that consume the iterator to use it up. For example, the code in Listing 13-10 creates an iterator over the items in the vector `v1` by calling the `iter` method defined on `Vec`. This code by itself doesn’t do anything useful. ++ ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-10/src/main.rs:here}} ``` -Listing 13-10: Creating an iterator + The iterator is stored in the `v1_iter` variable. Once we’ve created an -iterator, we can use it in a variety of ways. In Listing 3-5 in Chapter 3, we -iterated over an array using a `for` loop to execute some code on each of its -items. Under the hood this implicitly created and then consumed an iterator, -but we glossed over how exactly that works until now. +iterator, we can use it in a variety of ways. In Listing 3-5, we iterated over +an array using a `for` loop to execute some code on each of its items. Under +the hood, this implicitly created and then consumed an iterator, but we glossed +over how exactly that works until now. In the example in Listing 13-11, we separate the creation of the iterator from the use of the iterator in the `for` loop. When the `for` loop is called using the iterator in `v1_iter`, each element in the iterator is used in one iteration of the loop, which prints out each value. ++ ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-11/src/main.rs:here}} ``` -Listing 13-11: Using an iterator in a `for` loop + In languages that don’t have iterators provided by their standard libraries, you would likely write this same functionality by starting a variable at index @@ -40,7 +44,7 @@ you would likely write this same functionality by starting a variable at index incrementing the variable value in a loop until it reached the total number of items in the vector. -Iterators handle all that logic for you, cutting down on repetitive code you +Iterators handle all of that logic for you, cutting down on repetitive code you could potentially mess up. Iterators give you more flexibility to use the same logic with many different kinds of sequences, not just data structures you can index into, like vectors. Let’s examine how iterators do that. @@ -60,36 +64,35 @@ pub trait Iterator { } ``` -Notice this definition uses some new syntax: `type Item` and `Self::Item`, -which are defining an *associated type* with this trait. We’ll talk about -associated types in depth in Chapter 19. For now, all you need to know is that +Notice that this definition uses some new syntax: `type Item` and `Self::Item`, +which are defining an associated type with this trait. We’ll talk about +associated types in depth in Chapter 20. For now, all you need to know is that this code says implementing the `Iterator` trait requires that you also define an `Item` type, and this `Item` type is used in the return type of the `next` method. In other words, the `Item` type will be the type returned from the iterator. The `Iterator` trait only requires implementors to define one method: the -`next` method, which returns one item of the iterator at a time wrapped in -`Some` and, when iteration is over, returns `None`. +`next` method, which returns one item of the iterator at a time, wrapped in +`Some`, and, when iteration is over, returns `None`. We can call the `next` method on iterators directly; Listing 13-12 demonstrates what values are returned from repeated calls to `next` on the iterator created from the vector. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch13-functional-features/listing-13-12/src/lib.rs:here}} ``` -Listing 13-12: Calling the `next` method on an -iterator + -Note that we needed to make `v1_iter` mutable: calling the `next` method on an +Note that we needed to make `v1_iter` mutable: Calling the `next` method on an iterator changes internal state that the iterator uses to keep track of where -it is in the sequence. In other words, this code *consumes*, or uses up, the +it is in the sequence. In other words, this code _consumes_, or uses up, the iterator. Each call to `next` eats up an item from the iterator. We didn’t need -to make `v1_iter` mutable when we used a `for` loop because the loop took +to make `v1_iter` mutable when we used a `for` loop, because the loop took ownership of `v1_iter` and made it mutable behind the scenes. Also note that the values we get from the calls to `next` are immutable @@ -99,7 +102,7 @@ ownership of `v1` and returns owned values, we can call `into_iter` instead of `iter`. Similarly, if we want to iterate over mutable references, we can call `iter_mut` instead of `iter`. -### Methods that Consume the Iterator +### Methods That Consume the Iterator The `Iterator` trait has a number of different methods with default implementations provided by the standard library; you can find out about these @@ -108,45 +111,43 @@ trait. Some of these methods call the `next` method in their definition, which is why you’re required to implement the `next` method when implementing the `Iterator` trait. -Methods that call `next` are called *consuming adaptors*, because calling them +Methods that call `next` are called _consuming adapters_ because calling them uses up the iterator. One example is the `sum` method, which takes ownership of the iterator and iterates through the items by repeatedly calling `next`, thus consuming the iterator. As it iterates through, it adds each item to a running total and returns the total when iteration is complete. Listing 13-13 has a -test illustrating a use of the `sum` method: +test illustrating a use of the `sum` method. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch13-functional-features/listing-13-13/src/lib.rs:here}} ``` -Listing 13-13: Calling the `sum` method to get the total -of all items in the iterator + -We aren’t allowed to use `v1_iter` after the call to `sum` because `sum` takes +We aren’t allowed to use `v1_iter` after the call to `sum`, because `sum` takes ownership of the iterator we call it on. -### Methods that Produce Other Iterators +### Methods That Produce Other Iterators -*Iterator adaptors* are methods defined on the `Iterator` trait that don’t +_Iterator adapters_ are methods defined on the `Iterator` trait that don’t consume the iterator. Instead, they produce different iterators by changing some aspect of the original iterator. -Listing 13-14 shows an example of calling the iterator adaptor method `map`, +Listing 13-14 shows an example of calling the iterator adapter method `map`, which takes a closure to call on each item as the items are iterated through. The `map` method returns a new iterator that produces the modified items. The closure here creates a new iterator in which each item from the vector will be -incremented by 1: +incremented by 1. -Filename: src/main.rs + ```rust,not_desired_behavior {{#rustdoc_include ../listings/ch13-functional-features/listing-13-14/src/main.rs:here}} ``` -Listing 13-14: Calling the iterator adaptor `map` to -create a new iterator + However, this code produces a warning: @@ -155,38 +156,39 @@ However, this code produces a warning: ``` The code in Listing 13-14 doesn’t do anything; the closure we’ve specified -never gets called. The warning reminds us why: iterator adaptors are lazy, and +never gets called. The warning reminds us why: Iterator adapters are lazy, and we need to consume the iterator here. To fix this warning and consume the iterator, we’ll use the `collect` method, -which we used in Chapter 12 with `env::args` in Listing 12-1. This method -consumes the iterator and collects the resulting values into a collection data -type. +which we used with `env::args` in Listing 12-1. This method consumes the +iterator and collects the resultant values into a collection data type. In Listing 13-15, we collect the results of iterating over the iterator that’s returned from the call to `map` into a vector. This vector will end up -containing each item from the original vector incremented by 1. +containing each item from the original vector, incremented by 1. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch13-functional-features/listing-13-15/src/main.rs:here}} ``` -Listing 13-15: Calling the `map` method to create a new -iterator and then calling the `collect` method to consume the new iterator and -create a vector + Because `map` takes a closure, we can specify any operation we want to perform on each item. This is a great example of how closures let you customize some behavior while reusing the iteration behavior that the `Iterator` trait provides. -You can chain multiple calls to iterator adaptors to perform complex actions in +You can chain multiple calls to iterator adapters to perform complex actions in a readable way. But because all iterators are lazy, you have to call one of the -consuming adaptor methods to get results from calls to iterator adaptors. +consuming adapter methods to get results from calls to iterator adapters. + + + + -### Using Closures that Capture Their Environment +### Closures That Capture Their Environment Many iterator adapters take closures as arguments, and commonly the closures we’ll specify as arguments to iterator adapters will be closures that capture @@ -201,28 +203,27 @@ In Listing 13-16, we use `filter` with a closure that captures the `shoe_size` variable from its environment to iterate over a collection of `Shoe` struct instances. It will return only shoes that are the specified size. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch13-functional-features/listing-13-16/src/lib.rs}} ``` -Listing 13-16: Using the `filter` method with a closure -that captures `shoe_size` + The `shoes_in_size` function takes ownership of a vector of shoes and a shoe size as parameters. It returns a vector containing only shoes of the specified size. -In the body of `shoes_in_size`, we call `into_iter` to create an iterator -that takes ownership of the vector. Then we call `filter` to adapt that -iterator into a new iterator that only contains elements for which the closure -returns `true`. +In the body of `shoes_in_size`, we call `into_iter` to create an iterator that +takes ownership of the vector. Then, we call `filter` to adapt that iterator +into a new iterator that only contains elements for which the closure returns +`true`. The closure captures the `shoe_size` parameter from the environment and compares the value with each shoe’s size, keeping only shoes of the size specified. Finally, calling `collect` gathers the values returned by the adapted iterator into a vector that’s returned by the function. -The test shows that when we call `shoes_in_size`, we get back only shoes -that have the same size as the value we specified. +The test shows that when we call `shoes_in_size`, we get back only shoes that +have the same size as the value we specified. diff --git a/src/ch13-03-improving-our-io-project.md b/src/ch13-03-improving-our-io-project.md index 42a5be89d2..6bfeb97705 100644 --- a/src/ch13-03-improving-our-io-project.md +++ b/src/ch13-03-improving-our-io-project.md @@ -11,16 +11,15 @@ In Listing 12-6, we added code that took a slice of `String` values and created an instance of the `Config` struct by indexing into the slice and cloning the values, allowing the `Config` struct to own those values. In Listing 13-17, we’ve reproduced the implementation of the `Config::build` function as it was -in Listing 12-23: +in Listing 12-23. -Filename: src/lib.rs + ```rust,ignore -{{#rustdoc_include ../listings/ch13-functional-features/listing-12-23-reproduced/src/lib.rs:ch13}} +{{#rustdoc_include ../listings/ch13-functional-features/listing-12-23-reproduced/src/main.rs:ch13}} ``` -Listing 13-17: Reproduction of the `Config::build` -function from Listing 12-23 + At the time, we said not to worry about the inefficient `clone` calls because we would remove them in the future. Well, that time is now! @@ -28,7 +27,8 @@ we would remove them in the future. Well, that time is now! We needed `clone` here because we have a slice with `String` elements in the parameter `args`, but the `build` function doesn’t own `args`. To return ownership of a `Config` instance, we had to clone the values from the `query` -and `file_path` fields of `Config` so the `Config` instance can own its values. +and `file_path` fields of `Config` so that the `Config` instance can own its +values. With our new knowledge about iterators, we can change the `build` function to take ownership of an iterator as its argument instead of borrowing a slice. @@ -42,7 +42,7 @@ operations that borrow, we can move the `String` values from the iterator into #### Using the Returned Iterator Directly -Open your I/O project’s *src/main.rs* file, which should look like this: +Open your I/O project’s _src/main.rs_ file, which should look like this: Filename: src/main.rs @@ -54,125 +54,140 @@ We’ll first change the start of the `main` function that we had in Listing 12-24 to the code in Listing 13-18, which this time uses an iterator. This won’t compile until we update `Config::build` as well. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch13-functional-features/listing-13-18/src/main.rs:here}} ``` -Listing 13-18: Passing the return value of `env::args` to -`Config::build` + The `env::args` function returns an iterator! Rather than collecting the iterator values into a vector and then passing a slice to `Config::build`, now we’re passing ownership of the iterator returned from `env::args` to `Config::build` directly. -Next, we need to update the definition of `Config::build`. In your I/O -project’s *src/lib.rs* file, let’s change the signature of `Config::build` to -look like Listing 13-19. This still won’t compile because we need to update the -function body. +Next, we need to update the definition of `Config::build`. Let’s change the +signature of `Config::build` to look like Listing 13-19. This still won’t +compile, because we need to update the function body. -Filename: src/lib.rs + ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch13-functional-features/listing-13-19/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch13-functional-features/listing-13-19/src/main.rs:here}} ``` -Listing 13-19: Updating the signature of `Config::build` -to expect an iterator + The standard library documentation for the `env::args` function shows that the type of the iterator it returns is `std::env::Args`, and that type implements the `Iterator` trait and returns `String` values. -We’ve updated the signature of the `Config::build` function so the parameter -`args` has a generic type with the trait bounds `impl Iterator` -instead of `&[String]`. This usage of the `impl Trait` syntax we discussed in -the [“Traits as Parameters”][impl-trait] section of Chapter 10 -means that `args` can be any type that implements the `Iterator` type and -returns `String` items. +We’ve updated the signature of the `Config::build` function so that the +parameter `args` has a generic type with the trait bounds `impl Iterator` instead of `&[String]`. This usage of the `impl Trait` syntax we +discussed in the [“Using Traits as Parameters”][impl-trait] +section of Chapter 10 means that `args` can be any type that implements the +`Iterator` trait and returns `String` items. Because we’re taking ownership of `args` and we’ll be mutating `args` by iterating over it, we can add the `mut` keyword into the specification of the `args` parameter to make it mutable. -#### Using `Iterator` Trait Methods Instead of Indexing + + + + +#### Using `Iterator` Trait Methods Next, we’ll fix the body of `Config::build`. Because `args` implements the `Iterator` trait, we know we can call the `next` method on it! Listing 13-20 -updates the code from Listing 12-23 to use the `next` method: +updates the code from Listing 12-23 to use the `next` method. -Filename: src/lib.rs + -```rust,noplayground -{{#rustdoc_include ../listings/ch13-functional-features/listing-13-20/src/lib.rs:here}} +```rust,ignore,noplayground +{{#rustdoc_include ../listings/ch13-functional-features/listing-13-20/src/main.rs:here}} ``` -Listing 13-20: Changing the body of `Config::build` to use -iterator methods + Remember that the first value in the return value of `env::args` is the name of the program. We want to ignore that and get to the next value, so first we call -`next` and do nothing with the return value. Second, we call `next` to get the -value we want to put in the `query` field of `Config`. If `next` returns a +`next` and do nothing with the return value. Then, we call `next` to get the +value we want to put in the `query` field of `Config`. If `next` returns `Some`, we use a `match` to extract the value. If it returns `None`, it means -not enough arguments were given and we return early with an `Err` value. We do +not enough arguments were given, and we return early with an `Err` value. We do the same thing for the `file_path` value. -### Making Code Clearer with Iterator Adaptors + + + + +### Clarifying Code with Iterator Adapters We can also take advantage of iterators in the `search` function in our I/O -project, which is reproduced here in Listing 13-21 as it was in Listing 12-19: +project, which is reproduced here in Listing 13-21 as it was in Listing 12-19. -Filename: src/lib.rs + ```rust,ignore {{#rustdoc_include ../listings/ch12-an-io-project/listing-12-19/src/lib.rs:ch13}} ``` -Listing 13-21: The implementation of the `search` -function from Listing 12-19 + -We can write this code in a more concise way using iterator adaptor methods. +We can write this code in a more concise way using iterator adapter methods. Doing so also lets us avoid having a mutable intermediate `results` vector. The functional programming style prefers to minimize the amount of mutable state to make code clearer. Removing the mutable state might enable a future enhancement -to make searching happen in parallel, because we wouldn’t have to manage -concurrent access to the `results` vector. Listing 13-22 shows this change: +to make searching happen in parallel because we wouldn’t have to manage +concurrent access to the `results` vector. Listing 13-22 shows this change. -Filename: src/lib.rs + ```rust,ignore {{#rustdoc_include ../listings/ch13-functional-features/listing-13-22/src/lib.rs:here}} ``` -Listing 13-22: Using iterator adaptor methods in the -implementation of the `search` function + Recall that the purpose of the `search` function is to return all lines in `contents` that contain the `query`. Similar to the `filter` example in Listing -13-16, this code uses the `filter` adaptor to keep only the lines that -`line.contains(query)` returns `true` for. We then collect the matching lines -into another vector with `collect`. Much simpler! Feel free to make the same -change to use iterator methods in the `search_case_insensitive` function as -well. +13-16, this code uses the `filter` adapter to keep only the lines for which +`line.contains(query)` returns `true`. We then collect the matching lines into +another vector with `collect`. Much simpler! Feel free to make the same change +to use iterator methods in the `search_case_insensitive` function as well. + +For a further improvement, return an iterator from the `search` function by +removing the call to `collect` and changing the return type to `impl +Iterator` so that the function becomes an iterator adapter. +Note that you’ll also need to update the tests! Search through a large file +using your `minigrep` tool before and after making this change to observe the +difference in behavior. Before this change, the program won’t print any results +until it has collected all of the results, but after the change, the results +will be printed as each matching line is found because the `for` loop in the +`run` function is able to take advantage of the laziness of the iterator. + + + + -### Choosing Between Loops or Iterators +### Choosing Between Loops and Iterators The next logical question is which style you should choose in your own code and why: the original implementation in Listing 13-21 or the version using -iterators in Listing 13-22. Most Rust programmers prefer to use the iterator -style. It’s a bit tougher to get the hang of at first, but once you get a feel -for the various iterator adaptors and what they do, iterators can be easier to -understand. Instead of fiddling with the various bits of looping and building -new vectors, the code focuses on the high-level objective of the loop. This -abstracts away some of the commonplace code so it’s easier to see the concepts -that are unique to this code, such as the filtering condition each element in -the iterator must pass. +iterators in Listing 13-22 (assuming we’re collecting all the results before +returning them rather than returning the iterator). Most Rust programmers +prefer to use the iterator style. It’s a bit tougher to get the hang of at +first, but once you get a feel for the various iterator adapters and what they +do, iterators can be easier to understand. Instead of fiddling with the various +bits of looping and building new vectors, the code focuses on the high-level +objective of the loop. This abstracts away some of the commonplace code so that +it’s easier to see the concepts that are unique to this code, such as the +filtering condition each element in the iterator must pass. But are the two implementations truly equivalent? The intuitive assumption -might be that the more low-level loop will be faster. Let’s talk about -performance. +might be that the lower-level loop will be faster. Let’s talk about performance. [impl-trait]: ch10-02-traits.html#traits-as-parameters diff --git a/src/ch13-04-performance.md b/src/ch13-04-performance.md index 5d09bf2940..cdc2f98fd4 100644 --- a/src/ch13-04-performance.md +++ b/src/ch13-04-performance.md @@ -1,12 +1,16 @@ -## Comparing Performance: Loops vs. Iterators + + + + +## Performance in Loops vs. Iterators To determine whether to use loops or iterators, you need to know which implementation is faster: the version of the `search` function with an explicit `for` loop or the version with iterators. -We ran a benchmark by loading the entire contents of *The Adventures of -Sherlock Holmes* by Sir Arthur Conan Doyle into a `String` and looking for the -word *the* in the contents. Here are the results of the benchmark on the +We ran a benchmark by loading the entire contents of _The Adventures of +Sherlock Holmes_ by Sir Arthur Conan Doyle into a `String` and looking for the +word _the_ in the contents. Here are the results of the benchmark on the version of `search` using the `for` loop and the version using iterators: ```text @@ -14,72 +18,31 @@ test bench_search_for ... bench: 19,620,300 ns/iter (+/- 915,700) test bench_search_iter ... bench: 19,234,900 ns/iter (+/- 657,200) ``` -The iterator version was slightly faster! We won’t explain the benchmark code -here, because the point is not to prove that the two versions are equivalent -but to get a general sense of how these two implementations compare -performance-wise. +The two implementations have similar performance! We won’t explain the +benchmark code here because the point is not to prove that the two versions +are equivalent but to get a general sense of how these two implementations +compare performance-wise. For a more comprehensive benchmark, you should check using various texts of various sizes as the `contents`, different words and words of different lengths as the `query`, and all kinds of other variations. The point is this: -iterators, although a high-level abstraction, get compiled down to roughly the +Iterators, although a high-level abstraction, get compiled down to roughly the same code as if you’d written the lower-level code yourself. Iterators are one -of Rust’s *zero-cost abstractions*, by which we mean using the abstraction +of Rust’s _zero-cost abstractions_, by which we mean that using the abstraction imposes no additional runtime overhead. This is analogous to how Bjarne Stroustrup, the original designer and implementor of C++, defines -*zero-overhead* in “Foundations of C++” (2012): +zero-overhead in his 2012 ETAPS keynote presentation “Foundations of C++”: > In general, C++ implementations obey the zero-overhead principle: What you > don’t use, you don’t pay for. And further: What you do use, you couldn’t hand > code any better. -As another example, the following code is taken from an audio decoder. The -decoding algorithm uses the linear prediction mathematical operation to -estimate future values based on a linear function of the previous samples. This -code uses an iterator chain to do some math on three variables in scope: a -`buffer` slice of data, an array of 12 `coefficients`, and an amount by which -to shift data in `qlp_shift`. We’ve declared the variables within this example -but not given them any values; although this code doesn’t have much meaning -outside of its context, it’s still a concise, real-world example of how Rust -translates high-level ideas to low-level code. - -```rust,ignore -let buffer: &mut [i32]; -let coefficients: [i64; 12]; -let qlp_shift: i16; - -for i in 12..buffer.len() { - let prediction = coefficients.iter() - .zip(&buffer[i - 12..i]) - .map(|(&c, &s)| c * s as i64) - .sum::() >> qlp_shift; - let delta = buffer[i]; - buffer[i] = prediction as i32 + delta; -} -``` - -To calculate the value of `prediction`, this code iterates through each of the -12 values in `coefficients` and uses the `zip` method to pair the coefficient -values with the previous 12 values in `buffer`. Then, for each pair, we -multiply the values together, sum all the results, and shift the bits in the -sum `qlp_shift` bits to the right. - -Calculations in applications like audio decoders often prioritize performance -most highly. Here, we’re creating an iterator, using two adaptors, and then -consuming the value. What assembly code would this Rust code compile to? Well, -as of this writing, it compiles down to the same assembly you’d write by hand. -There’s no loop at all corresponding to the iteration over the values in -`coefficients`: Rust knows that there are 12 iterations, so it “unrolls” the -loop. *Unrolling* is an optimization that removes the overhead of the loop -controlling code and instead generates repetitive code for each iteration of -the loop. - -All of the coefficients get stored in registers, which means accessing the -values is very fast. There are no bounds checks on the array access at runtime. -All these optimizations that Rust is able to apply make the resulting code -extremely efficient. Now that you know this, you can use iterators and closures -without fear! They make code seem like it’s higher level but don’t impose a -runtime performance penalty for doing so. +In many cases, Rust code using iterators compiles to the same assembly you’d +write by hand. Optimizations such as loop unrolling and eliminating bounds +checking on array access apply and make the resultant code extremely efficient. +Now that you know this, you can use iterators and closures without fear! They +make code seem like it’s higher level but don’t impose a runtime performance +penalty for doing so. ## Summary diff --git a/src/ch14-00-more-about-cargo.md b/src/ch14-00-more-about-cargo.md index 8f8b8e51c7..59408b8e9a 100644 --- a/src/ch14-00-more-about-cargo.md +++ b/src/ch14-00-more-about-cargo.md @@ -1,15 +1,14 @@ # More About Cargo and Crates.io -So far we’ve used only the most basic features of Cargo to build, run, and test -our code, but it can do a lot more. In this chapter, we’ll discuss some of its -other, more advanced features to show you how to do the following: +So far, we’ve used only the most basic features of Cargo to build, run, and +test our code, but it can do a lot more. In this chapter, we’ll discuss some of +its other, more advanced features to show you how to do the following: -* Customize your build through release profiles -* Publish libraries on [crates.io](https://crates.io/) -* Organize large projects with workspaces -* Install binaries from [crates.io](https://crates.io/) -* Extend Cargo using custom commands +- Customize your build through release profiles. +- Publish libraries on [crates.io](https://crates.io/). +- Organize large projects with workspaces. +- Install binaries from [crates.io](https://crates.io/). +- Extend Cargo using custom commands. Cargo can do even more than the functionality we cover in this chapter, so for -a full explanation of all its features, see [its -documentation](https://doc.rust-lang.org/cargo/). +a full explanation of all its features, see [its documentation](https://doc.rust-lang.org/cargo/). diff --git a/src/ch14-01-release-profiles.md b/src/ch14-01-release-profiles.md index 44391ae611..4bbb2d390a 100644 --- a/src/ch14-01-release-profiles.md +++ b/src/ch14-01-release-profiles.md @@ -1,12 +1,12 @@ ## Customizing Builds with Release Profiles -In Rust, *release profiles* are predefined and customizable profiles with +In Rust, _release profiles_ are predefined, customizable profiles with different configurations that allow a programmer to have more control over various options for compiling code. Each profile is configured independently of the others. Cargo has two main profiles: the `dev` profile Cargo uses when you run `cargo -build` and the `release` profile Cargo uses when you run `cargo build +build`, and the `release` profile Cargo uses when you run `cargo build --release`. The `dev` profile is defined with good defaults for development, and the `release` profile has good defaults for release builds. @@ -21,15 +21,15 @@ and ensure output below is accurate ```console $ cargo build - Finished dev [unoptimized + debuginfo] target(s) in 0.0s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s $ cargo build --release - Finished release [optimized] target(s) in 0.0s + Finished `release` profile [optimized] target(s) in 0.32s ``` The `dev` and `release` are these different profiles used by the compiler. Cargo has default settings for each of the profiles that apply when you haven't -explicitly added any `[profile.*]` sections in the project’s *Cargo.toml* file. +explicitly added any `[profile.*]` sections in the project’s _Cargo.toml_ file. By adding `[profile.*]` sections for any profile you want to customize, you override any subset of the default settings. For example, here are the default values for the `opt-level` setting for the `dev` and `release` profiles: @@ -47,7 +47,7 @@ opt-level = 3 The `opt-level` setting controls the number of optimizations Rust will apply to your code, with a range of 0 to 3. Applying more optimizations extends compiling time, so if you’re in development and compiling your code often, -you’ll want fewer optimizations to compile faster even if the resulting code +you’ll want fewer optimizations to compile faster even if the resultant code runs slower. The default `opt-level` for `dev` is therefore `0`. When you’re ready to release your code, it’s best to spend more time compiling. You’ll only compile in release mode once, but you’ll run the compiled program many times, @@ -55,8 +55,8 @@ so release mode trades longer compile time for code that runs faster. That is why the default `opt-level` for the `release` profile is `3`. You can override a default setting by adding a different value for it in -*Cargo.toml*. For example, if we want to use optimization level 1 in the -development profile, we can add these two lines to our project’s *Cargo.toml* +_Cargo.toml_. For example, if we want to use optimization level 1 in the +development profile, we can add these two lines to our project’s _Cargo.toml_ file: Filename: Cargo.toml diff --git a/src/ch14-02-publishing-to-crates-io.md b/src/ch14-02-publishing-to-crates-io.md index c5b1ac7fc3..2af90dc9a1 100644 --- a/src/ch14-02-publishing-to-crates-io.md +++ b/src/ch14-02-publishing-to-crates-io.md @@ -16,41 +16,40 @@ Accurately documenting your packages will help other users know how and when to use them, so it’s worth investing the time to write documentation. In Chapter 3, we discussed how to comment Rust code using two slashes, `//`. Rust also has a particular kind of comment for documentation, known conveniently as a -*documentation comment*, that will generate HTML documentation. The HTML +_documentation comment_, that will generate HTML documentation. The HTML displays the contents of documentation comments for public API items intended -for programmers interested in knowing how to *use* your crate as opposed to how -your crate is *implemented*. +for programmers interested in knowing how to _use_ your crate as opposed to how +your crate is _implemented_. Documentation comments use three slashes, `///`, instead of two and support Markdown notation for formatting the text. Place documentation comments just before the item they’re documenting. Listing 14-1 shows documentation comments for an `add_one` function in a crate named `my_crate`. -Filename: src/lib.rs + ```rust,ignore {{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-01/src/lib.rs}} ``` -Listing 14-1: A documentation comment for a -function + Here, we give a description of what the `add_one` function does, start a section with the heading `Examples`, and then provide code that demonstrates how to use the `add_one` function. We can generate the HTML documentation from this documentation comment by running `cargo doc`. This command runs the `rustdoc` tool distributed with Rust and puts the generated HTML documentation -in the *target/doc* directory. +in the _target/doc_ directory. For convenience, running `cargo doc --open` will build the HTML for your current crate’s documentation (as well as the documentation for all of your crate’s dependencies) and open the result in a web browser. Navigate to the `add_one` function and you’ll see how the text in the documentation comments is -rendered, as shown in Figure 14-1: +rendered, as shown in Figure 14-1. Rendered HTML documentation for the `add_one` function of `my_crate` -Figure 14-1: HTML documentation for the `add_one` +Figure 14-1: The HTML documentation for the `add_one` function #### Commonly Used Sections @@ -59,15 +58,15 @@ We used the `# Examples` Markdown heading in Listing 14-1 to create a section in the HTML with the title “Examples.” Here are some other sections that crate authors commonly use in their documentation: -* **Panics**: The scenarios in which the function being documented could - panic. Callers of the function who don’t want their programs to panic should - make sure they don’t call the function in these situations. -* **Errors**: If the function returns a `Result`, describing the kinds of +- **Panics**: These are the scenarios in which the function being documented + could panic. Callers of the function who don’t want their programs to panic + should make sure they don’t call the function in these situations. +- **Errors**: If the function returns a `Result`, describing the kinds of errors that might occur and what conditions might cause those errors to be - returned can be helpful to callers so they can write code to handle the + returned can be helpful to callers so that they can write code to handle the different kinds of errors in different ways. -* **Safety**: If the function is `unsafe` to call (we discuss unsafety in - Chapter 19), there should be a section explaining why the function is unsafe +- **Safety**: If the function is `unsafe` to call (we discuss unsafety in + Chapter 20), there should be a section explaining why the function is unsafe and covering the invariants that the function expects callers to uphold. Most documentation comments don’t need all of these sections, but this is a @@ -77,12 +76,12 @@ interested in knowing about. #### Documentation Comments as Tests Adding example code blocks in your documentation comments can help demonstrate -how to use your library, and doing so has an additional bonus: running `cargo -test` will run the code examples in your documentation as tests! Nothing is -better than documentation with examples. But nothing is worse than examples -that don’t work because the code has changed since the documentation was -written. If we run `cargo test` with the documentation for the `add_one` -function from Listing 14-1, we will see a section in the test results like this: +how to use your library and has an additional bonus: Running `cargo test` will +run the code examples in your documentation as tests! Nothing is better than +documentation with examples. But nothing is worse than examples that don’t work +because the code has changed since the documentation was written. If we run +`cargo test` with the documentation for the `add_one` function from Listing +14-1, we will see a section in the test results that looks like this: -#### Commenting Contained Items + -The style of doc comment `//!` adds documentation to the item that contains the -comments rather than to the items following the comments. We typically use -these doc comments inside the crate root file (*src/lib.rs* by convention) or -inside a module to document the crate or the module as a whole. +#### Contained Item Comments + +The style of doc comment `//!` adds documentation to the item that *contains* +the comments rather than to the items *following* the comments. We typically +use these doc comments inside the crate root file (_src/lib.rs_ by convention) +or inside a module to document the crate or the module as a whole. For example, to add documentation that describes the purpose of the `my_crate` crate that contains the `add_one` function, we add documentation comments that -start with `//!` to the beginning of the *src/lib.rs* file, as shown in Listing -14-2: +start with `//!` to the beginning of the _src/lib.rs_ file, as shown in Listing +14-2. -Filename: src/lib.rs + ```rust,ignore {{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-02/src/lib.rs:here}} ``` -Listing 14-2: Documentation for the `my_crate` crate as a -whole + Notice there isn’t any code after the last line that begins with `//!`. Because we started the comments with `//!` instead of `///`, we’re documenting the item that contains this comment rather than an item that follows this comment. In -this case, that item is the *src/lib.rs* file, which is the crate root. These +this case, that item is the _src/lib.rs_ file, which is the crate root. These comments describe the entire crate. -When we run `cargo doc --open`, these comments will display on the front -page of the documentation for `my_crate` above the list of public items in the -crate, as shown in Figure 14-2: +When we run `cargo doc --open`, these comments will display on the front page +of the documentation for `my_crate` above the list of public items in the +crate, as shown in Figure 14-2. + +Documentation comments within items are useful for describing crates and +modules especially. Use them to explain the overall purpose of the container to +help your users understand the crate’s organization. Rendered HTML documentation with a comment for the crate as a whole -Figure 14-2: Rendered documentation for `my_crate`, +Figure 14-2: The rendered documentation for `my_crate`, including the comment describing the crate as a whole -Documentation comments within items are useful for describing crates and -modules especially. Use them to explain the overall purpose of the container to -help your users understand the crate’s organization. + -### Exporting a Convenient Public API with `pub use` + + +### Exporting a Convenient Public API The structure of your public API is a major consideration when publishing a crate. People who use your crate are less familiar with the structure than you @@ -151,42 +157,41 @@ are and might have difficulty finding the pieces they want to use if your crate has a large module hierarchy. In Chapter 7, we covered how to make items public using the `pub` keyword, and -bring items into a scope with the `use` keyword. However, the structure that -makes sense to you while you’re developing a crate might not be very convenient -for your users. You might want to organize your structs in a hierarchy -containing multiple levels, but then people who want to use a type you’ve -defined deep in the hierarchy might have trouble finding out that type exists. -They might also be annoyed at having to enter `use` -`my_crate::some_module::another_module::UsefulType;` rather than `use` -`my_crate::UsefulType;`. - -The good news is that if the structure *isn’t* convenient for others to use +how to bring items into a scope with the `use` keyword. However, the structure +that makes sense to you while you’re developing a crate might not be very +convenient for your users. You might want to organize your structs in a +hierarchy containing multiple levels, but then people who want to use a type +you’ve defined deep in the hierarchy might have trouble finding out that type +exists. They might also be annoyed at having to enter `use +my_crate::some_module::another_module::UsefulType;` rather than `use +my_crate::UsefulType;`. + +The good news is that if the structure _isn’t_ convenient for others to use from another library, you don’t have to rearrange your internal organization: -instead, you can re-export items to make a public structure that’s different -from your private structure by using `pub use`. Re-exporting takes a public +Instead, you can re-export items to make a public structure that’s different +from your private structure by using `pub use`. *Re-exporting* takes a public item in one location and makes it public in another location, as if it were defined in the other location instead. For example, say we made a library named `art` for modeling artistic concepts. Within this library are two modules: a `kinds` module containing two enums named `PrimaryColor` and `SecondaryColor` and a `utils` module containing a -function named `mix`, as shown in Listing 14-3: +function named `mix`, as shown in Listing 14-3. -Filename: src/lib.rs + ```rust,noplayground,test_harness {{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-03/src/lib.rs:here}} ``` -Listing 14-3: An `art` library with items organized into -`kinds` and `utils` modules + Figure 14-3 shows what the front page of the documentation for this crate -generated by `cargo doc` would look like: +generated by `cargo doc` would look like. Rendered documentation for the `art` crate that lists the `kinds` and `utils` modules -Figure 14-3: Front page of the documentation for `art` +Figure 14-3: The front page of the documentation for `art` that lists the `kinds` and `utils` modules Note that the `PrimaryColor` and `SecondaryColor` types aren’t listed on the @@ -196,16 +201,15 @@ see them. Another crate that depends on this library would need `use` statements that bring the items from `art` into scope, specifying the module structure that’s currently defined. Listing 14-4 shows an example of a crate that uses the -`PrimaryColor` and `mix` items from the `art` crate: +`PrimaryColor` and `mix` items from the `art` crate. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-04/src/main.rs}} ``` -Listing 14-4: A crate using the `art` crate’s items with -its internal structure exported + The author of the code in Listing 14-4, which uses the `art` crate, had to figure out that `PrimaryColor` is in the `kinds` module and `mix` is in the @@ -218,16 +222,15 @@ module names in the `use` statements. To remove the internal organization from the public API, we can modify the `art` crate code in Listing 14-3 to add `pub use` statements to re-export the -items at the top level, as shown in Listing 14-5: +items at the top level, as shown in Listing 14-5. -Filename: src/lib.rs + ```rust,ignore {{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-05/src/lib.rs:here}} ``` -Listing 14-5: Adding `pub use` statements to re-export -items + The API documentation that `cargo doc` generates for this crate will now list and link re-exports on the front page, as shown in Figure 14-4, making the @@ -240,16 +243,15 @@ that lists the re-exports The `art` crate users can still see and use the internal structure from Listing 14-3 as demonstrated in Listing 14-4, or they can use the more convenient -structure in Listing 14-5, as shown in Listing 14-6: +structure in Listing 14-5, as shown in Listing 14-6. -Filename: src/main.rs + ```rust,ignore {{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-06/src/main.rs:here}} ``` -Listing 14-6: A program using the re-exported items from -the `art` crate + In cases where there are many nested modules, re-exporting the types at the top level with `pub use` can make a significant difference in the experience of @@ -257,12 +259,12 @@ people who use the crate. Another common use of `pub use` is to re-export definitions of a dependency in the current crate to make that crate's definitions part of your crate’s public API. -Creating a useful public API structure is more of an art than a science, and -you can iterate to find the API that works best for your users. Choosing `pub -use` gives you flexibility in how you structure your crate internally and -decouples that internal structure from what you present to your users. Look at -some of the code of crates you’ve installed to see if their internal structure -differs from their public API. +Creating a useful public API structure is more an art than a science, and you +can iterate to find the API that works best for your users. Choosing `pub use` +gives you flexibility in how you structure your crate internally and decouples +that internal structure from what you present to your users. Look at some of +the code of crates you’ve installed to see if their internal structure differs +from their public API. ### Setting Up a Crates.io Account @@ -273,22 +275,23 @@ in via a GitHub account. (The GitHub account is currently a requirement, but the site might support other ways of creating an account in the future.) Once you’re logged in, visit your account settings at [https://crates.io/me/](https://crates.io/me/) and retrieve your -API key. Then run the `cargo login` command with your API key, like this: +API key. Then, run the `cargo login` command and paste your API key when prompted, like this: ```console -$ cargo login abcdefghijklmnopqrstuvwxyz012345 +$ cargo login +abcdefghijklmnopqrstuvwxyz012345 ``` This command will inform Cargo of your API token and store it locally in -*~/.cargo/credentials*. Note that this token is a *secret*: do not share it -with anyone else. If you do share it with anyone for any reason, you should +_~/.cargo/credentials.toml_. Note that this token is a secret: Do not share +it with anyone else. If you do share it with anyone for any reason, you should revoke it and generate a new token on [crates.io](https://crates.io/). ### Adding Metadata to a New Crate Let’s say you have a crate you want to publish. Before publishing, you’ll need -to add some metadata in the `[package]` section of the crate’s *Cargo.toml* +to add some metadata in the `[package]` section of the crate’s _Cargo.toml_ file. Your crate will need a unique name. While you’re working on a crate locally, @@ -297,7 +300,7 @@ you can name a crate whatever you’d like. However, crate names on first-served basis. Once a crate name is taken, no one else can publish a crate with that name. Before attempting to publish a crate, search for the name you want to use. If the name has been used, you will need to find another name and -edit the `name` field in the *Cargo.toml* file under the `[package]` section to +edit the `name` field in the _Cargo.toml_ file under the `[package]` section to use the new name for publishing, like so: Filename: Cargo.toml @@ -311,7 +314,8 @@ Even if you’ve chosen a unique name, when you run `cargo publish` to publish the crate at this point, you’ll get a warning and then an error: @@ -325,17 +329,17 @@ See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for error: failed to publish to registry at https://crates.io Caused by: - the remote server responded with an error: missing or empty metadata fields: description, license. Please see https://doc.rust-lang.org/cargo/reference/manifest.html for how to upload metadata + the remote server responded with an error (status 400 Bad Request): missing or empty metadata fields: description, license. Please see https://doc.rust-lang.org/cargo/reference/manifest.html for more information on configuring these fields ``` -This errors because you’re missing some crucial information: a description and -license are required so people will know what your crate does and under what -terms they can use it. In *Cargo.toml*, add a description that's just a -sentence or two, because it will appear with your crate in search results. For -the `license` field, you need to give a *license identifier value*. The [Linux -Foundation’s Software Package Data Exchange (SPDX)][spdx] lists the identifiers -you can use for this value. For example, to specify that you’ve licensed your -crate using the MIT License, add the `MIT` identifier: +This results in an error because you’re missing some crucial information: A +description and license are required so that people will know what your crate +does and under what terms they can use it. In _Cargo.toml_, add a description +that's just a sentence or two, because it will appear with your crate in search +results. For the `license` field, you need to give a _license identifier +value_. The [Linux Foundation’s Software Package Data Exchange (SPDX)][spdx] +lists the identifiers you can use for this value. For example, to specify that +you’ve licensed your crate using the MIT License, add the `MIT` identifier: Filename: Cargo.toml @@ -357,7 +361,7 @@ demonstrates that you can also specify multiple license identifiers separated by `OR` to have multiple licenses for your project. With a unique name, the version, your description, and a license added, the -*Cargo.toml* file for a project that is ready to publish might look like this: +_Cargo.toml_ file for a project that is ready to publish might look like this: Filename: Cargo.toml @@ -365,7 +369,7 @@ With a unique name, the version, your description, and a license added, the [package] name = "guessing_game" version = "0.1.0" -edition = "2021" +edition = "2024" description = "A fun game where you guess what number the computer has chosen." license = "MIT OR Apache-2.0" @@ -373,8 +377,8 @@ license = "MIT OR Apache-2.0" ``` [Cargo’s documentation](https://doc.rust-lang.org/cargo/) describes other -metadata you can specify to ensure others can discover and use your crate more -easily. +metadata you can specify to ensure that others can discover and use your crate +more easily. ### Publishing to Crates.io @@ -383,10 +387,10 @@ your crate, and specified the required metadata, you’re ready to publish! Publishing a crate uploads a specific version to [crates.io](https://crates.io/) for others to use. -Be careful, because a publish is *permanent*. The version can never be -overwritten, and the code cannot be deleted. One major goal of -[crates.io](https://crates.io/) is to act as a permanent archive -of code so that builds of all projects that depend on crates from +Be careful, because a publish is _permanent_. The version can never be +overwritten, and the code cannot be deleted except in certain circumstances. +One major goal of Crates.io is to act as a permanent archive of code so that +builds of all projects that depend on crates from [crates.io](https://crates.io/) will continue to work. Allowing version deletions would make fulfilling that goal impossible. However, there is no limit to the number of crate versions you can publish. @@ -403,11 +407,17 @@ copy just the relevant lines below $ cargo publish Updating crates.io index Packaging guessing_game v0.1.0 (file:///projects/guessing_game) + Packaged 6 files, 1.2KiB (895.0B compressed) Verifying guessing_game v0.1.0 (file:///projects/guessing_game) Compiling guessing_game v0.1.0 (file:///projects/guessing_game/target/package/guessing_game-0.1.0) - Finished dev [unoptimized + debuginfo] target(s) in 0.19s + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.19s Uploading guessing_game v0.1.0 (file:///projects/guessing_game) + Uploaded guessing_game v0.1.0 to registry `crates-io` +note: waiting for `guessing_game v0.1.0` to be available at registry +`crates-io`. +You may press ctrl-c to skip waiting; the crate should be available shortly. + Published guessing_game v0.1.0 at registry `crates-io` ``` Congratulations! You’ve now shared your code with the Rust community, and @@ -416,31 +426,33 @@ anyone can easily add your crate as a dependency of their project. ### Publishing a New Version of an Existing Crate When you’ve made changes to your crate and are ready to release a new version, -you change the `version` value specified in your *Cargo.toml* file and +you change the `version` value specified in your _Cargo.toml_ file and republish. Use the [Semantic Versioning rules][semver] to decide what an -appropriate next version number is based on the kinds of changes you’ve made. -Then run `cargo publish` to upload the new version. +appropriate next version number is, based on the kinds of changes you’ve made. +Then, run `cargo publish` to upload the new version. + + - + -### Deprecating Versions from Crates.io with `cargo yank` +### Deprecating Versions from Crates.io Although you can’t remove previous versions of a crate, you can prevent any future projects from adding them as a new dependency. This is useful when a crate version is broken for one reason or another. In such situations, Cargo -supports *yanking* a crate version. +supports yanking a crate version. -Yanking a version prevents new projects from depending on that version while +_Yanking_ a version prevents new projects from depending on that version while allowing all existing projects that depend on it to continue. Essentially, a -yank means that all projects with a *Cargo.lock* will not break, and any future -*Cargo.lock* files generated will not use the yanked version. +yank means that all projects with a _Cargo.lock_ will not break, and any future +_Cargo.lock_ files generated will not use the yanked version. To yank a version of a crate, in the directory of the crate that you’ve previously published, run `cargo yank` and specify which version you want to -yank. For example, if we've published a crate named `guessing_game` version -1.0.1 and we want to yank it, in the project directory for `guessing_game` we'd -run: +yank. For example, if we’ve published a crate named `guessing_game` version +1.0.1 and we want to yank it, then we’d run the following in the project +directory for `guessing_game`: -#### Depending on an External Package in a Workspace + -Notice that the workspace has only one *Cargo.lock* file at the top level, -rather than having a *Cargo.lock* in each crate’s directory. This ensures that +### Depending on an External Package + +Notice that the workspace has only one _Cargo.lock_ file at the top level, +rather than having a _Cargo.lock_ in each crate’s directory. This ensures that all crates are using the same version of all dependencies. If we add the `rand` -package to the *adder/Cargo.toml* and *add_one/Cargo.toml* files, Cargo will +package to the _adder/Cargo.toml_ and _add_one/Cargo.toml_ files, Cargo will resolve both of those to one version of `rand` and record that in the one -*Cargo.lock*. Making all crates in the workspace use the same dependencies +_Cargo.lock_. Making all crates in the workspace use the same dependencies means the crates will always be compatible with each other. Let’s add the -`rand` crate to the `[dependencies]` section in the *add_one/Cargo.toml* file -so we can use the `rand` crate in the `add_one` crate: +`rand` crate to the `[dependencies]` section in the _add_one/Cargo.toml_ file +so that we can use the `rand` crate in the `add_one` crate: , each crate in the workspace +will need to be published separately. Like `cargo test`, we can publish a +particular crate in our workspace by using the `-p` flag and specifying the +name of the crate we want to publish. For additional practice, add an `add_two` crate to this workspace in a similar way as the `add_one` crate! -As your project grows, consider using a workspace: it’s easier to understand -smaller, individual components than one big blob of code. Furthermore, keeping -the crates in a workspace can make coordination between crates easier if they -are often changed at the same time. +As your project grows, consider using a workspace: It enables you to work with +smaller, easier-to-understand components than one big blob of code. +Furthermore, keeping the crates in a workspace can make coordination between +crates easier if they are often changed at the same time. diff --git a/src/ch14-04-installing-binaries.md b/src/ch14-04-installing-binaries.md index fd821f3a0e..40fc633e6c 100644 --- a/src/ch14-04-installing-binaries.md +++ b/src/ch14-04-installing-binaries.md @@ -1,4 +1,5 @@ - + + ## Installing Binaries with `cargo install` @@ -7,18 +8,18 @@ The `cargo install` command allows you to install and use binary crates locally. This isn’t intended to replace system packages; it’s meant to be a convenient way for Rust developers to install tools that others have shared on [crates.io](https://crates.io/). Note that you can only install -packages that have binary targets. A *binary target* is the runnable program -that is created if the crate has a *src/main.rs* file or another file specified +packages that have binary targets. A _binary target_ is the runnable program +that is created if the crate has a _src/main.rs_ file or another file specified as a binary, as opposed to a library target that isn’t runnable on its own but is suitable for including within other programs. Usually, crates have -information in the *README* file about whether a crate is a library, has a +information in the README file about whether a crate is a library, has a binary target, or both. All binaries installed with `cargo install` are stored in the installation -root’s *bin* folder. If you installed Rust using *rustup.rs* and don’t have any +root’s _bin_ folder. If you installed Rust using _rustup.rs_ and don’t have any custom configurations, this directory will be *$HOME/.cargo/bin*. Ensure that -directory is in your `$PATH` to be able to run programs you’ve installed with -`cargo install`. +this directory is in your `$PATH` to be able to run programs you’ve installed +with `cargo install`. For example, in Chapter 12 we mentioned that there’s a Rust implementation of the `grep` tool called `ripgrep` for searching files. To install `ripgrep`, we @@ -31,17 +32,17 @@ cargo install something you don't have, copy relevant output below ```console $ cargo install ripgrep Updating crates.io index - Downloaded ripgrep v13.0.0 - Downloaded 1 crate (243.3 KB) in 0.88s - Installing ripgrep v13.0.0 + Downloaded ripgrep v14.1.1 + Downloaded 1 crate (213.6 KB) in 0.40s + Installing ripgrep v14.1.1 --snip-- - Compiling ripgrep v13.0.0 - Finished release [optimized + debuginfo] target(s) in 3m 10s + Compiling grep v0.3.2 + Finished `release` profile [optimized + debuginfo] target(s) in 6.73s Installing ~/.cargo/bin/rg - Installed package `ripgrep v13.0.0` (executable `rg`) + Installed package `ripgrep v14.1.1` (executable `rg`) ``` The second-to-last line of the output shows the location and the name of the installed binary, which in the case of `ripgrep` is `rg`. As long as the installation directory is in your `$PATH`, as mentioned previously, you can -then run `rg --help` and start using a faster, rustier tool for searching files! +then run `rg --help` and start using a faster, Rustier tool for searching files! diff --git a/src/ch14-05-extending-cargo.md b/src/ch14-05-extending-cargo.md index bd228714ae..b351d7fff7 100644 --- a/src/ch14-05-extending-cargo.md +++ b/src/ch14-05-extending-cargo.md @@ -1,11 +1,11 @@ ## Extending Cargo with Custom Commands -Cargo is designed so you can extend it with new subcommands without having to -modify Cargo. If a binary in your `$PATH` is named `cargo-something`, you can -run it as if it was a Cargo subcommand by running `cargo something`. Custom +Cargo is designed so that you can extend it with new subcommands without having +to modify it. If a binary in your `$PATH` is named `cargo-something`, you can +run it as if it were a Cargo subcommand by running `cargo something`. Custom commands like this are also listed when you run `cargo --list`. Being able to use `cargo install` to install extensions and then run them just like the -built-in Cargo tools is a super convenient benefit of Cargo’s design! +built-in Cargo tools is a super-convenient benefit of Cargo’s design! ## Summary diff --git a/src/ch15-00-smart-pointers.md b/src/ch15-00-smart-pointers.md index 9ecdcc8350..8e0c0e89d8 100644 --- a/src/ch15-00-smart-pointers.md +++ b/src/ch15-00-smart-pointers.md @@ -1,53 +1,46 @@ # Smart Pointers -A *pointer* is a general concept for a variable that contains an address in +A pointer is a general concept for a variable that contains an address in memory. This address refers to, or “points at,” some other data. The most common kind of pointer in Rust is a reference, which you learned about in Chapter 4. References are indicated by the `&` symbol and borrow the value they point to. They don’t have any special capabilities other than referring to -data, and have no overhead. +data, and they have no overhead. -*Smart pointers*, on the other hand, are data structures that act like a +_Smart pointers_, on the other hand, are data structures that act like a pointer but also have additional metadata and capabilities. The concept of -smart pointers isn’t unique to Rust: smart pointers originated in C++ and exist +smart pointers isn’t unique to Rust: Smart pointers originated in C++ and exist in other languages as well. Rust has a variety of smart pointers defined in the standard library that provide functionality beyond that provided by references. To explore the general concept, we’ll look at a couple of different examples of -smart pointers, including a *reference counting* smart pointer type. This +smart pointers, including a _reference counting_ smart pointer type. This pointer enables you to allow data to have multiple owners by keeping track of the number of owners and, when no owners remain, cleaning up the data. -Rust, with its concept of ownership and borrowing, has an additional difference -between references and smart pointers: while references only borrow data, in -many cases, smart pointers *own* the data they point to. - -Though we didn’t call them as such at the time, we’ve already encountered a few -smart pointers in this book, including `String` and `Vec` in Chapter 8. Both -these types count as smart pointers because they own some memory and allow you -to manipulate it. They also have metadata and extra capabilities or guarantees. -`String`, for example, stores its capacity as metadata and has the extra -ability to ensure its data will always be valid UTF-8. +In Rust, with its concept of ownership and borrowing, there is an additional +difference between references and smart pointers: While references only borrow +data, in many cases smart pointers _own_ the data they point to. Smart pointers are usually implemented using structs. Unlike an ordinary struct, smart pointers implement the `Deref` and `Drop` traits. The `Deref` trait allows an instance of the smart pointer struct to behave like a reference -so you can write your code to work with either references or smart pointers. -The `Drop` trait allows you to customize the code that’s run when an instance -of the smart pointer goes out of scope. In this chapter, we’ll discuss both -traits and demonstrate why they’re important to smart pointers. +so that you can write your code to work with either references or smart +pointers. The `Drop` trait allows you to customize the code that’s run when an +instance of the smart pointer goes out of scope. In this chapter, we’ll discuss +both of these traits and demonstrate why they’re important to smart pointers. Given that the smart pointer pattern is a general design pattern used frequently in Rust, this chapter won’t cover every existing smart pointer. Many libraries have their own smart pointers, and you can even write your own. We’ll cover the most common smart pointers in the standard library: -* `Box` for allocating values on the heap -* `Rc`, a reference counting type that enables multiple ownership -* `Ref` and `RefMut`, accessed through `RefCell`, a type that enforces +- `Box`, for allocating values on the heap +- `Rc`, a reference counting type that enables multiple ownership +- `Ref` and `RefMut`, accessed through `RefCell`, a type that enforces the borrowing rules at runtime instead of compile time -In addition, we’ll cover the *interior mutability* pattern where an immutable +In addition, we’ll cover the _interior mutability_ pattern where an immutable type exposes an API for mutating an interior value. We’ll also discuss -*reference cycles*: how they can leak memory and how to prevent them. +reference cycles: how they can leak memory and how to prevent them. Let’s dive in! diff --git a/src/ch15-01-box.md b/src/ch15-01-box.md index 8380625527..723d2c9364 100644 --- a/src/ch15-01-box.md +++ b/src/ch15-01-box.md @@ -1,52 +1,54 @@ ## Using `Box` to Point to Data on the Heap -The most straightforward smart pointer is a *box*, whose type is written -`Box`. Boxes allow you to store data on the heap rather than the stack. What -remains on the stack is the pointer to the heap data. Refer to Chapter 4 to -review the difference between the stack and the heap. +The most straightforward smart pointer is a box, whose type is written +`Box`. _Boxes_ allow you to store data on the heap rather than the stack. +What remains on the stack is the pointer to the heap data. Refer to Chapter 4 +to review the difference between the stack and the heap. Boxes don’t have performance overhead, other than storing their data on the heap instead of on the stack. But they don’t have many extra capabilities either. You’ll use them most often in these situations: -* When you have a type whose size can’t be known at compile time and you want +- When you have a type whose size can’t be known at compile time, and you want to use a value of that type in a context that requires an exact size -* When you have a large amount of data and you want to transfer ownership but - ensure the data won’t be copied when you do so -* When you want to own a value and you care only that it’s a type that +- When you have a large amount of data, and you want to transfer ownership but + ensure that the data won’t be copied when you do so +- When you want to own a value, and you care only that it’s a type that implements a particular trait rather than being of a specific type -We’ll demonstrate the first situation in the [“Enabling Recursive Types with -Boxes”](#enabling-recursive-types-with-boxes) section. In the -second case, transferring ownership of a large amount of data can take a long -time because the data is copied around on the stack. To improve performance in -this situation, we can store the large amount of data on the heap in a box. -Then, only the small amount of pointer data is copied around on the stack, -while the data it references stays in one place on the heap. The third case is -known as a *trait object*, and Chapter 17 devotes an entire section, [“Using -Trait Objects That Allow for Values of Different Types,”][trait-objects] just to that topic. So what you learn here you’ll apply again in -Chapter 17! +We’ll demonstrate the first situation in [“Enabling Recursive Types with +Boxes”](#enabling-recursive-types-with-boxes). In the second +case, transferring ownership of a large amount of data can take a long time +because the data is copied around on the stack. To improve performance in this +situation, we can store the large amount of data on the heap in a box. Then, +only the small amount of pointer data is copied around on the stack, while the +data it references stays in one place on the heap. The third case is known as a +_trait object_, and [“Using Trait Objects to Abstract over Shared +Behavior”][trait-objects] in Chapter 18 is devoted to that +topic. So, what you learn here you’ll apply again in that section! -### Using a `Box` to Store Data on the Heap + + + + +### Storing Data on the Heap Before we discuss the heap storage use case for `Box`, we’ll cover the syntax and how to interact with values stored within a `Box`. -Listing 15-1 shows how to use a box to store an `i32` value on the heap: +Listing 15-1 shows how to use a box to store an `i32` value on the heap. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-01/src/main.rs}} ``` -Listing 15-1: Storing an `i32` value on the heap using a -box + We define the variable `b` to have the value of a `Box` that points to the value `5`, which is allocated on the heap. This program will print `b = 5`; in -this case, we can access the data in the box similar to how we would if this +this case, we can access the data in the box similarly to how we would if this data were on the stack. Just like any owned value, when a box goes out of scope, as `b` does at the end of `main`, it will be deallocated. The deallocation happens both for the box (stored on the stack) and the data it @@ -56,64 +58,67 @@ Putting a single value on the heap isn’t very useful, so you won’t use boxes themselves in this way very often. Having values like a single `i32` on the stack, where they’re stored by default, is more appropriate in the majority of situations. Let’s look at a case where boxes allow us to define types that we -wouldn’t be allowed to if we didn’t have boxes. +wouldn’t be allowed to define if we didn’t have boxes. ### Enabling Recursive Types with Boxes -A value of *recursive type* can have another value of the same type as part of -itself. Recursive types pose an issue because at compile time Rust needs to -know how much space a type takes up. However, the nesting of values of -recursive types could theoretically continue infinitely, so Rust can’t know how -much space the value needs. Because boxes have a known size, we can enable -recursive types by inserting a box in the recursive type definition. +A value of a _recursive type_ can have another value of the same type as part of +itself. Recursive types pose an issue because Rust needs to know at compile time +how much space a type takes up. However, the nesting of values of recursive +types could theoretically continue infinitely, so Rust can’t know how much space +the value needs. Because boxes have a known size, we can enable recursive types +by inserting a box in the recursive type definition. -As an example of a recursive type, let’s explore the *cons list*. This is a data +As an example of a recursive type, let’s explore the cons list. This is a data type commonly found in functional programming languages. The cons list type we’ll define is straightforward except for the recursion; therefore, the -concepts in the example we’ll work with will be useful any time you get into +concepts in the example we’ll work with will be useful anytime you get into more complex situations involving recursive types. -#### More Information About the Cons List + + + + +#### Understanding the Cons List -A *cons list* is a data structure that comes from the Lisp programming language -and its dialects and is made up of nested pairs, and is the Lisp version of a -linked list. Its name comes from the `cons` function (short for “construct -function”) in Lisp that constructs a new pair from its two arguments. By +A _cons list_ is a data structure that comes from the Lisp programming language +and its dialects, is made up of nested pairs, and is the Lisp version of a +linked list. Its name comes from the `cons` function (short for _construct +function_) in Lisp that constructs a new pair from its two arguments. By calling `cons` on a pair consisting of a value and another pair, we can construct cons lists made up of recursive pairs. For example, here’s a pseudocode representation of a cons list containing the -list 1, 2, 3 with each pair in parentheses: +list `1, 2, 3` with each pair in parentheses: ```text (1, (2, (3, Nil))) ``` Each item in a cons list contains two elements: the value of the current item -and the next item. The last item in the list contains only a value called `Nil` -without a next item. A cons list is produced by recursively calling the `cons` -function. The canonical name to denote the base case of the recursion is `Nil`. -Note that this is not the same as the “null” or “nil” concept in Chapter 6, -which is an invalid or absent value. +and of the next item. The last item in the list contains only a value called +`Nil` without a next item. A cons list is produced by recursively calling the +`cons` function. The canonical name to denote the base case of the recursion is +`Nil`. Note that this is not the same as the “null” or “nil” concept discussed +in Chapter 6, which is an invalid or absent value. The cons list isn’t a commonly used data structure in Rust. Most of the time when you have a list of items in Rust, `Vec` is a better choice to use. -Other, more complex recursive data types *are* useful in various situations, +Other, more complex recursive data types _are_ useful in various situations, but by starting with the cons list in this chapter, we can explore how boxes let us define a recursive data type without much distraction. Listing 15-2 contains an enum definition for a cons list. Note that this code -won’t compile yet because the `List` type doesn’t have a known size, which +won’t compile yet, because the `List` type doesn’t have a known size, which we’ll demonstrate. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-02/src/main.rs:here}} ``` -Listing 15-2: The first attempt at defining an enum to -represent a cons list data structure of `i32` values + > Note: We’re implementing a cons list that holds only `i32` values for the > purposes of this example. We could have implemented it using generics, as we @@ -121,16 +126,15 @@ represent a cons list data structure of `i32` values > any type. Using the `List` type to store the list `1, 2, 3` would look like the code in -Listing 15-3: +Listing 15-3. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-03/src/main.rs:here}} ``` -Listing 15-3: Using the `List` enum to store the list `1, -2, 3` + The first `Cons` value holds `1` and another `List` value. This `List` value is another `Cons` value that holds `2` and another `List` value. This `List` value @@ -138,17 +142,18 @@ is one more `Cons` value that holds `3` and a `List` value, which is finally `Nil`, the non-recursive variant that signals the end of the list. If we try to compile the code in Listing 15-3, we get the error shown in -Listing 15-4: +Listing 15-4. + + ```console {{#include ../listings/ch15-smart-pointers/listing-15-03/output.txt}} ``` -Listing 15-4: The error we get when attempting to define -a recursive enum + The error shows this type “has infinite size.” The reason is that we’ve defined -`List` with a variant that is recursive: it holds another value of itself +`List` with a variant that is recursive: It holds another value of itself directly. As a result, Rust can’t figure out how much space it needs to store a `List` value. Let’s break down why we get this error. First, we’ll look at how Rust decides how much space it needs to store a value of a non-recursive type. @@ -178,12 +183,16 @@ type needs, the compiler looks at the variants, starting with the `Cons` variant. The `Cons` variant holds a value of type `i32` and a value of type `List`, and this process continues infinitely, as shown in Figure 15-1. -An infinite Cons list +An infinite Cons list: a rectangle labeled 'Cons' split into two smaller rectangles. The first smaller rectangle holds the label 'i32', and the second smaller rectangle holds the label 'Cons' and a smaller version of the outer 'Cons' rectangle. The 'Cons' rectangles continue to hold smaller and smaller versions of themselves until the smallest comfortably sized rectangle holds an infinity symbol, indicating that this repetition goes on forever. Figure 15-1: An infinite `List` consisting of infinite `Cons` variants -#### Using `Box` to Get a Recursive Type with a Known Size + + + + +#### Getting a Recursive Type with a Known Size Because Rust can’t figure out how much space to allocate for recursively defined types, the compiler gives an error with this helpful suggestion: @@ -193,18 +202,18 @@ after doing automatic regeneration, look at listings/ch15-smart-pointers/listing --> ```text -help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to make `List` representable +help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle | 2 | Cons(i32, Box), | ++++ + ``` -In this suggestion, “indirection” means that instead of storing a value +In this suggestion, _indirection_ means that instead of storing a value directly, we should change the data structure to store the value indirectly by storing a pointer to the value instead. Because a `Box` is a pointer, Rust always knows how much space a `Box` -needs: a pointer’s size doesn’t change based on the amount of data it’s +needs: A pointer’s size doesn’t change based on the amount of data it’s pointing to. This means we can put a `Box` inside the `Cons` variant instead of another `List` value directly. The `Box` will point to the next `List` value that will be on the heap rather than inside the `Cons` variant. @@ -213,28 +222,27 @@ this implementation is now more like placing the items next to one another rather than inside one another. We can change the definition of the `List` enum in Listing 15-2 and the usage -of the `List` in Listing 15-3 to the code in Listing 15-5, which will compile: +of the `List` in Listing 15-3 to the code in Listing 15-5, which will compile. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-05/src/main.rs}} ``` -Listing 15-5: Definition of `List` that uses `Box` in -order to have a known size + -The `Cons` variant needs the size of an `i32` plus the space to store the -box’s pointer data. The `Nil` variant stores no values, so it needs less space -than the `Cons` variant. We now know that any `List` value will take up the -size of an `i32` plus the size of a box’s pointer data. By using a box, we’ve -broken the infinite, recursive chain, so the compiler can figure out the size -it needs to store a `List` value. Figure 15-2 shows what the `Cons` variant -looks like now. +The `Cons` variant needs the size of an `i32` plus the space to store the box’s +pointer data. The `Nil` variant stores no values, so it needs less space on the +stack than the `Cons` variant. We now know that any `List` value will take up +the size of an `i32` plus the size of a box’s pointer data. By using a box, +we’ve broken the infinite, recursive chain, so the compiler can figure out the +size it needs to store a `List` value. Figure 15-2 shows what the `Cons` +variant looks like now. -A finite Cons list +A rectangle labeled 'Cons' split into two smaller rectangles. The first smaller rectangle holds the label 'i32', and the second smaller rectangle holds the label 'Box' with one inner rectangle that contains the label 'usize', representing the finite size of the box's pointer. -Figure 15-2: A `List` that is not infinitely sized +Figure 15-2: A `List` that is not infinitely sized, because `Cons` holds a `Box` Boxes provide only the indirection and heap allocation; they don’t have any @@ -242,7 +250,7 @@ other special capabilities, like those we’ll see with the other smart pointer types. They also don’t have the performance overhead that these special capabilities incur, so they can be useful in cases like the cons list where the indirection is the only feature we need. We’ll look at more use cases for boxes -in Chapter 17, too. +in Chapter 18. The `Box` type is a smart pointer because it implements the `Deref` trait, which allows `Box` values to be treated like references. When a `Box` @@ -252,4 +260,4 @@ even more important to the functionality provided by the other smart pointer types we’ll discuss in the rest of this chapter. Let’s explore these two traits in more detail. -[trait-objects]: ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types +[trait-objects]: ch18-02-trait-objects.html#using-trait-objects-to-abstract-over-shared-behavior diff --git a/src/ch15-02-deref.md b/src/ch15-02-deref.md index 23c9fe8bfc..7a8339602a 100644 --- a/src/ch15-02-deref.md +++ b/src/ch15-02-deref.md @@ -1,49 +1,50 @@ -## Treating Smart Pointers Like Regular References with the `Deref` Trait + + + + + +## Treating Smart Pointers Like Regular References Implementing the `Deref` trait allows you to customize the behavior of the -*dereference operator* `*` (not to be confused with the multiplication or glob +_dereference operator_ `*` (not to be confused with the multiplication or glob operator). By implementing `Deref` in such a way that a smart pointer can be treated like a regular reference, you can write code that operates on references and use that code with smart pointers too. Let’s first look at how the dereference operator works with regular references. -Then we’ll try to define a custom type that behaves like `Box`, and see why +Then, we’ll try to define a custom type that behaves like `Box` and see why the dereference operator doesn’t work like a reference on our newly defined type. We’ll explore how implementing the `Deref` trait makes it possible for -smart pointers to work in ways similar to references. Then we’ll look at -Rust’s *deref coercion* feature and how it lets us work with either references -or smart pointers. +smart pointers to work in ways similar to references. Then, we’ll look at +Rust’s deref coercion feature and how it lets us work with either references or +smart pointers. -> Note: there’s one big difference between the `MyBox` type we’re about to -> build and the real `Box`: our version will not store its data on the heap. -> We are focusing this example on `Deref`, so where the data is actually stored -> is less important than the pointer-like behavior. + - + -### Following the Pointer to the Value +### Following the Reference to the Value A regular reference is a type of pointer, and one way to think of a pointer is as an arrow to a value stored somewhere else. In Listing 15-6, we create a reference to an `i32` value and then use the dereference operator to follow the -reference to the value: +reference to the value. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-06/src/main.rs}} ``` -Listing 15-6: Using the dereference operator to follow a -reference to an `i32` value + The variable `x` holds an `i32` value `5`. We set `y` equal to a reference to `x`. We can assert that `x` is equal to `5`. However, if we want to make an assertion about the value in `y`, we have to use `*y` to follow the reference -to the value it’s pointing to (hence *dereference*) so the compiler can compare -the actual value. Once we dereference `y`, we have access to the integer value -`y` is pointing to that we can compare with `5`. +to the value it’s pointing to (hence, _dereference_) so that the compiler can +compare the actual value. Once we dereference `y`, we have access to the +integer value `y` is pointing to that we can compare with `5`. If we tried to write `assert_eq!(5, y);` instead, we would get this compilation error: @@ -61,64 +62,66 @@ to the value it’s pointing to. We can rewrite the code in Listing 15-6 to use a `Box` instead of a reference; the dereference operator used on the `Box` in Listing 15-7 functions in the same way as the dereference operator used on the reference in -Listing 15-6: +Listing 15-6. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-07/src/main.rs}} ``` -Listing 15-7: Using the dereference operator on a -`Box` + The main difference between Listing 15-7 and Listing 15-6 is that here we set -`y` to be an instance of a `Box` pointing to a copied value of `x` rather -than a reference pointing to the value of `x`. In the last assertion, we can -use the dereference operator to follow the pointer of the `Box` in the same -way that we did when `y` was a reference. Next, we’ll explore what is special -about `Box` that enables us to use the dereference operator by defining our -own type. +`y` to be an instance of a box pointing to a copied value of `x` rather than a +reference pointing to the value of `x`. In the last assertion, we can use the +dereference operator to follow the box’s pointer in the same way that we did +when `y` was a reference. Next, we’ll explore what is special about `Box` +that enables us to use the dereference operator by defining our own box type. ### Defining Our Own Smart Pointer -Let’s build a smart pointer similar to the `Box` type provided by the -standard library to experience how smart pointers behave differently from -references by default. Then we’ll look at how to add the ability to use the +Let’s build a wrapper type similar to the `Box` type provided by the +standard library to experience how smart pointer types behave differently from +references by default. Then, we’ll look at how to add the ability to use the dereference operator. +> Note: There’s one big difference between the `MyBox` type we’re about to +> build and the real `Box`: Our version will not store its data on the heap. +> We are focusing this example on `Deref`, so where the data is actually stored +> is less important than the pointer-like behavior. + The `Box` type is ultimately defined as a tuple struct with one element, so Listing 15-8 defines a `MyBox` type in the same way. We’ll also define a `new` function to match the `new` function defined on `Box`. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-08/src/main.rs:here}} ``` -Listing 15-8: Defining a `MyBox` type + -We define a struct named `MyBox` and declare a generic parameter `T`, because -we want our type to hold values of any type. The `MyBox` type is a tuple struct +We define a struct named `MyBox` and declare a generic parameter `T` because we +want our type to hold values of any type. The `MyBox` type is a tuple struct with one element of type `T`. The `MyBox::new` function takes one parameter of type `T` and returns a `MyBox` instance that holds the value passed in. Let’s try adding the `main` function in Listing 15-7 to Listing 15-8 and changing it to use the `MyBox` type we’ve defined instead of `Box`. The -code in Listing 15-9 won’t compile because Rust doesn’t know how to dereference -`MyBox`. +code in Listing 15-9 won’t compile, because Rust doesn’t know how to +dereference `MyBox`. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-09/src/main.rs:here}} ``` -Listing 15-9: Attempting to use `MyBox` in the same -way we used references and `Box` + -Here’s the resulting compilation error: +Here’s the resultant compilation error: ```console {{#include ../listings/ch15-smart-pointers/listing-15-09/output.txt}} @@ -128,38 +131,42 @@ Our `MyBox` type can’t be dereferenced because we haven’t implemented tha ability on our type. To enable dereferencing with the `*` operator, we implement the `Deref` trait. -### Treating a Type Like a Reference by Implementing the `Deref` Trait + -As discussed in the [“Implementing a Trait on a Type”][impl-trait] section of Chapter 10, to implement a trait, we need to provide -implementations for the trait’s required methods. The `Deref` trait, provided -by the standard library, requires us to implement one method named `deref` that -borrows `self` and returns a reference to the inner data. Listing 15-10 -contains an implementation of `Deref` to add to the definition of `MyBox`: + -Filename: src/main.rs +### Implementing the `Deref` Trait + +As discussed in [“Implementing a Trait on a Type”][impl-trait] in +Chapter 10, to implement a trait we need to provide implementations for the +trait’s required methods. The `Deref` trait, provided by the standard library, +requires us to implement one method named `deref` that borrows `self` and +returns a reference to the inner data. Listing 15-10 contains an implementation +of `Deref` to add to the definition of `MyBox`. + + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-10/src/main.rs:here}} ``` -Listing 15-10: Implementing `Deref` on `MyBox` + -The `type Target = T;` syntax defines an associated type for the `Deref` -trait to use. Associated types are a slightly different way of declaring a -generic parameter, but you don’t need to worry about them for now; we’ll cover -them in more detail in Chapter 19. +The `type Target = T;` syntax defines an associated type for the `Deref` trait +to use. Associated types are a slightly different way of declaring a generic +parameter, but you don’t need to worry about them for now; we’ll cover them in +more detail in Chapter 20. -We fill in the body of the `deref` method with `&self.0` so `deref` returns a -reference to the value we want to access with the `*` operator; recall from the -[“Using Tuple Structs without Named Fields to Create Different -Types”][tuple-structs] section of Chapter 5 that `.0` accesses -the first value in a tuple struct. The `main` function in Listing 15-9 that -calls `*` on the `MyBox` value now compiles, and the assertions pass! +We fill in the body of the `deref` method with `&self.0` so that `deref` +returns a reference to the value we want to access with the `*` operator; +recall from [“Creating Different Types with Tuple Structs”][tuple-structs] in Chapter 5 that `.0` accesses the first value in a tuple struct. +The `main` function in Listing 15-9 that calls `*` on the `MyBox` value now +compiles, and the assertions pass! Without the `Deref` trait, the compiler can only dereference `&` references. The `deref` method gives the compiler the ability to take a value of any type -that implements `Deref` and call the `deref` method to get a `&` reference that +that implements `Deref` and call the `deref` method to get a reference that it knows how to dereference. When we entered `*y` in Listing 15-9, behind the scenes Rust actually ran this @@ -170,14 +177,14 @@ code: ``` Rust substitutes the `*` operator with a call to the `deref` method and then a -plain dereference so we don’t have to think about whether or not we need to -call the `deref` method. This Rust feature lets us write code that functions +plain dereference so that we don’t have to think about whether or not we need +to call the `deref` method. This Rust feature lets us write code that functions identically whether we have a regular reference or a type that implements `Deref`. The reason the `deref` method returns a reference to a value, and that the plain dereference outside the parentheses in `*(y.deref())` is still necessary, -is to do with the ownership system. If the `deref` method returned the value +has to do with the ownership system. If the `deref` method returned the value directly instead of a reference to the value, the value would be moved out of `self`. We don’t want to take ownership of the inner value inside `MyBox` in this case or in most cases where we use the dereference operator. @@ -188,13 +195,18 @@ Because the substitution of the `*` operator does not recurse infinitely, we end up with data of type `i32`, which matches the `5` in `assert_eq!` in Listing 15-9. -### Implicit Deref Coercions with Functions and Methods + + + + -*Deref coercion* converts a reference to a type that implements the `Deref` +### Using Deref Coercion in Functions and Methods + +_Deref coercion_ converts a reference to a type that implements the `Deref` trait into a reference to another type. For example, deref coercion can convert `&String` to `&str` because `String` implements the `Deref` trait such that it returns `&str`. Deref coercion is a convenience Rust performs on arguments to -functions and methods, and works only on types that implement the `Deref` +functions and methods, and it works only on types that implement the `Deref` trait. It happens automatically when we pass a reference to a particular type’s value as an argument to a function or method that doesn’t match the parameter type in the function or method definition. A sequence of calls to the `deref` @@ -208,29 +220,27 @@ can work for either references or smart pointers. To see deref coercion in action, let’s use the `MyBox` type we defined in Listing 15-8 as well as the implementation of `Deref` that we added in Listing 15-10. Listing 15-11 shows the definition of a function that has a string slice -parameter: +parameter. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-11/src/main.rs:here}} ``` -Listing 15-11: A `hello` function that has the parameter -`name` of type `&str` + We can call the `hello` function with a string slice as an argument, such as -`hello("Rust");` for example. Deref coercion makes it possible to call `hello` -with a reference to a value of type `MyBox`, as shown in Listing 15-12: +`hello("Rust");`, for example. Deref coercion makes it possible to call `hello` +with a reference to a value of type `MyBox`, as shown in Listing 15-12. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-12/src/main.rs:here}} ``` -Listing 15-12: Calling `hello` with a reference to a -`MyBox` value, which works because of deref coercion + Here we’re calling the `hello` function with the argument `&m`, which is a reference to a `MyBox` value. Because we implemented the `Deref` trait @@ -244,16 +254,15 @@ If Rust didn’t implement deref coercion, we would have to write the code in Listing 15-13 instead of the code in Listing 15-12 to call `hello` with a value of type `&MyBox`. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-13/src/main.rs:here}} ``` -Listing 15-13: The code we would have to write if Rust -didn’t have deref coercion + -The `(*m)` dereferences the `MyBox` into a `String`. Then the `&` and +The `(*m)` dereferences the `MyBox` into a `String`. Then, the `&` and `[..]` take a string slice of the `String` that is equal to the whole string to match the signature of `hello`. This code without deref coercions is harder to read, write, and understand with all of these symbols involved. Deref coercion @@ -265,7 +274,11 @@ match the parameter’s type. The number of times that `Deref::deref` needs to b inserted is resolved at compile time, so there is no runtime penalty for taking advantage of deref coercion! -### How Deref Coercion Interacts with Mutability + + + + +### Handling Deref Coercion with Mutable References Similar to how you use the `Deref` trait to override the `*` operator on immutable references, you can use the `DerefMut` trait to override the `*` @@ -274,17 +287,17 @@ operator on mutable references. Rust does deref coercion when it finds types and trait implementations in three cases: -* From `&T` to `&U` when `T: Deref` -* From `&mut T` to `&mut U` when `T: DerefMut` -* From `&mut T` to `&U` when `T: Deref` +1. From `&T` to `&U` when `T: Deref` +2. From `&mut T` to `&mut U` when `T: DerefMut` +3. From `&mut T` to `&U` when `T: Deref` -The first two cases are the same as each other except that the second -implements mutability. The first case states that if you have a `&T`, and `T` -implements `Deref` to some type `U`, you can get a `&U` transparently. The -second case states that the same deref coercion happens for mutable references. +The first two cases are the same except that the second implements mutability. +The first case states that if you have a `&T`, and `T` implements `Deref` to +some type `U`, you can get a `&U` transparently. The second case states that +the same deref coercion happens for mutable references. The third case is trickier: Rust will also coerce a mutable reference to an -immutable one. But the reverse is *not* possible: immutable references will +immutable one. But the reverse is _not_ possible: Immutable references will never coerce to mutable references. Because of the borrowing rules, if you have a mutable reference, that mutable reference must be the only reference to that data (otherwise, the program wouldn’t compile). Converting one mutable @@ -296,4 +309,4 @@ assumption that converting an immutable reference to a mutable reference is possible. [impl-trait]: ch10-02-traits.html#implementing-a-trait-on-a-type -[tuple-structs]: ch05-01-defining-structs.html#using-tuple-structs-without-named-fields-to-create-different-types +[tuple-structs]: ch05-01-defining-structs.html#creating-different-types-with-tuple-structs diff --git a/src/ch15-03-drop.md b/src/ch15-03-drop.md index 05ab86873b..58b244b77b 100644 --- a/src/ch15-03-drop.md +++ b/src/ch15-03-drop.md @@ -7,15 +7,15 @@ be used to release resources like files or network connections. We’re introducing `Drop` in the context of smart pointers because the functionality of the `Drop` trait is almost always used when implementing a -smart pointer. For example, when a `Box` is dropped it will deallocate the +smart pointer. For example, when a `Box` is dropped, it will deallocate the space on the heap that the box points to. In some languages, for some types, the programmer must call code to free memory or resources every time they finish using an instance of those types. Examples -include file handles, sockets, or locks. If they forget, the system might -become overloaded and crash. In Rust, you can specify that a particular bit of -code be run whenever a value goes out of scope, and the compiler will insert -this code automatically. As a result, you don’t need to be careful about +include file handles, sockets, and locks. If the programmer forgets, the system +might become overloaded and crash. In Rust, you can specify that a particular +bit of code be run whenever a value goes out of scope, and the compiler will +insert this code automatically. As a result, you don’t need to be careful about placing cleanup code everywhere in a program that an instance of a particular type is finished with—you still won’t leak resources! @@ -26,22 +26,21 @@ let’s implement `drop` with `println!` statements for now. Listing 15-14 shows a `CustomSmartPointer` struct whose only custom functionality is that it will print `Dropping CustomSmartPointer!` when the -instance goes out of scope, to show when Rust runs the `drop` function. +instance goes out of scope, to show when Rust runs the `drop` method. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-14/src/main.rs}} ``` -Listing 15-14: A `CustomSmartPointer` struct that -implements the `Drop` trait where we would put our cleanup code + The `Drop` trait is included in the prelude, so we don’t need to bring it into scope. We implement the `Drop` trait on `CustomSmartPointer` and provide an implementation for the `drop` method that calls `println!`. The body of the -`drop` function is where you would place any logic that you wanted to run when -an instance of your type goes out of scope. We’re printing some text here to +`drop` method is where you would place any logic that you wanted to run when an +instance of your type goes out of scope. We’re printing some text here to demonstrate visually when Rust will call `drop`. In `main`, we create two instances of `CustomSmartPointer` and then print @@ -63,30 +62,30 @@ give you a visual guide to how the `drop` method works; usually you would specify the cleanup code that your type needs to run rather than a print message. -### Dropping a Value Early with `std::mem::drop` + + + Unfortunately, it’s not straightforward to disable the automatic `drop` functionality. Disabling `drop` isn’t usually necessary; the whole point of the `Drop` trait is that it’s taken care of automatically. Occasionally, however, you might want to clean up a value early. One example is when using smart -pointers that manage locks: you might want to force the `drop` method that +pointers that manage locks: You might want to force the `drop` method that releases the lock so that other code in the same scope can acquire the lock. -Rust doesn’t let you call the `Drop` trait’s `drop` method manually; instead +Rust doesn’t let you call the `Drop` trait’s `drop` method manually; instead, you have to call the `std::mem::drop` function provided by the standard library if you want to force a value to be dropped before the end of its scope. -If we try to call the `Drop` trait’s `drop` method manually by modifying the -`main` function from Listing 15-14, as shown in Listing 15-15, we’ll get a -compiler error: +Trying to call the `Drop` trait’s `drop` method manually by modifying the +`main` function from Listing 15-14 won’t work, as shown in Listing 15-15. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-15/src/main.rs:here}} ``` -Listing 15-15: Attempting to call the `drop` method from -the `Drop` trait manually to clean up early + When we try to compile this code, we’ll get this error: @@ -95,33 +94,31 @@ When we try to compile this code, we’ll get this error: ``` This error message states that we’re not allowed to explicitly call `drop`. The -error message uses the term *destructor*, which is the general programming term -for a function that cleans up an instance. A *destructor* is analogous to a -*constructor*, which creates an instance. The `drop` function in Rust is one +error message uses the term _destructor_, which is the general programming term +for a function that cleans up an instance. A _destructor_ is analogous to a +_constructor_, which creates an instance. The `drop` function in Rust is one particular destructor. -Rust doesn’t let us call `drop` explicitly because Rust would still +Rust doesn’t let us call `drop` explicitly, because Rust would still automatically call `drop` on the value at the end of `main`. This would cause a -*double free* error because Rust would be trying to clean up the same value -twice. +double free error because Rust would be trying to clean up the same value twice. We can’t disable the automatic insertion of `drop` when a value goes out of scope, and we can’t call the `drop` method explicitly. So, if we need to force a value to be cleaned up early, we use the `std::mem::drop` function. The `std::mem::drop` function is different from the `drop` method in the `Drop` -trait. We call it by passing as an argument the value we want to force drop. +trait. We call it by passing as an argument the value we want to force-drop. The function is in the prelude, so we can modify `main` in Listing 15-15 to -call the `drop` function, as shown in Listing 15-16: +call the `drop` function, as shown in Listing 15-16. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-16/src/main.rs:here}} ``` -Listing 15-16: Calling `std::mem::drop` to explicitly -drop a value before it goes out of scope + Running this code will print the following: @@ -129,18 +126,18 @@ Running this code will print the following: {{#include ../listings/ch15-smart-pointers/listing-15-16/output.txt}} ``` -The text ```Dropping CustomSmartPointer with data `some data`!``` is printed -between the `CustomSmartPointer created.` and `CustomSmartPointer dropped -before the end of main.` text, showing that the `drop` method code is called to -drop `c` at that point. +The text ``Dropping CustomSmartPointer with data `some data`!`` is printed +between the `CustomSmartPointer created` and `CustomSmartPointer dropped before +the end of main` text, showing that the `drop` method code is called to drop +`c` at that point. You can use code specified in a `Drop` trait implementation in many ways to -make cleanup convenient and safe: for instance, you could use it to create your +make cleanup convenient and safe: For instance, you could use it to create your own memory allocator! With the `Drop` trait and Rust’s ownership system, you -don’t have to remember to clean up because Rust does it automatically. +don’t have to remember to clean up, because Rust does it automatically. You also don’t have to worry about problems resulting from accidentally -cleaning up values still in use: the ownership system that makes sure +cleaning up values still in use: The ownership system that makes sure references are always valid also ensures that `drop` gets called only once when the value is no longer being used. diff --git a/src/ch15-04-rc.md b/src/ch15-04-rc.md index 87a42eb1a5..9b5f7f86eb 100644 --- a/src/ch15-04-rc.md +++ b/src/ch15-04-rc.md @@ -1,6 +1,6 @@ -## `Rc`, the Reference Counted Smart Pointer +## `Rc`, the Reference-Counted Smart Pointer -In the majority of cases, ownership is clear: you know exactly which variable +In the majority of cases, ownership is clear: You know exactly which variable owns a given value. However, there are cases when a single value might have multiple owners. For example, in graph data structures, multiple edges might point to the same node, and that node is conceptually owned by all of the edges @@ -8,7 +8,7 @@ that point to it. A node shouldn’t be cleaned up unless it doesn’t have any edges pointing to it and so has no owners. You have to enable multiple ownership explicitly by using the Rust type -`Rc`, which is an abbreviation for *reference counting*. The `Rc` type +`Rc`, which is an abbreviation for _reference counting_. The `Rc` type keeps track of the number of references to a value to determine whether or not the value is still in use. If there are zero references to a value, the value can be cleaned up without any references becoming invalid. @@ -17,7 +17,7 @@ Imagine `Rc` as a TV in a family room. When one person enters to watch TV, they turn it on. Others can come into the room and watch the TV. When the last person leaves the room, they turn off the TV because it’s no longer being used. If someone turns off the TV while others are still watching it, there would be -uproar from the remaining TV watchers! +an uproar from the remaining TV watchers! We use the `Rc` type when we want to allocate some data on the heap for multiple parts of our program to read and we can’t determine at compile time @@ -29,33 +29,41 @@ Note that `Rc` is only for use in single-threaded scenarios. When we discuss concurrency in Chapter 16, we’ll cover how to do reference counting in multithreaded programs. -### Using `Rc` to Share Data + + + + +### Sharing Data Let’s return to our cons list example in Listing 15-5. Recall that we defined it using `Box`. This time, we’ll create two lists that both share ownership -of a third list. Conceptually, this looks similar to Figure 15-3: +of a third list. Conceptually, this looks similar to Figure 15-3. -Two lists that share ownership of a third list +A linked list with the label 'a' pointing to three elements. The first element contains the integer 5 and points to the second element. Th +e second element contains the integer 10 and points to the third element. The third element contains the value 'Nil' that signifies the end of the l +ist; it does not point anywhere. A linked list with the label 'b' points to an element that contains the integer 3 and points to the first element o +f list 'a'. A linked list with the label 'c' points to an element that contains the integer 4 and also points to the first element of list 'a' so th +at the tails of lists 'b' and 'c' are both list 'a'. Figure 15-3: Two lists, `b` and `c`, sharing ownership of a third list, `a` -We’ll create list `a` that contains 5 and then 10. Then we’ll make two more -lists: `b` that starts with 3 and `c` that starts with 4. Both `b` and `c` -lists will then continue on to the first `a` list containing 5 and 10. In other -words, both lists will share the first list containing 5 and 10. +We’ll create list `a` that contains `5` and then `10`. Then, we’ll make two +more lists: `b` that starts with `3` and `c` that starts with `4`. Both the `b` +and `c` lists will then continue on to the first `a` list containing `5` and +`10`. In other words, both lists will share the first list containing `5` and +`10`. Trying to implement this scenario using our definition of `List` with `Box` -won’t work, as shown in Listing 15-17: +won’t work, as shown in Listing 15-17. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-17/src/main.rs}} ``` -Listing 15-17: Demonstrating we’re not allowed to have -two lists using `Box` that try to share ownership of a third list + When we compile this code, we get this error: @@ -84,18 +92,17 @@ we call `Rc::clone`, the reference count to the data within the `Rc` will increase, and the data won’t be cleaned up unless there are zero references to it. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-18/src/main.rs}} ``` -Listing 15-18: A definition of `List` that uses -`Rc` + We need to add a `use` statement to bring `Rc` into scope because it’s not -in the prelude. In `main`, we create the list holding 5 and 10 and store it in -a new `Rc` in `a`. Then when we create `b` and `c`, we call the +in the prelude. In `main`, we create the list holding `5` and `10` and store it +in a new `Rc` in `a`. Then, when we create `b` and `c`, we call the `Rc::clone` function and pass a reference to the `Rc` in `a` as an argument. @@ -110,28 +117,33 @@ increase the reference count. When looking for performance problems in the code, we only need to consider the deep-copy clones and can disregard calls to `Rc::clone`. -### Cloning an `Rc` Increases the Reference Count + + + + +### Cloning to Increase the Reference Count -Let’s change our working example in Listing 15-18 so we can see the reference -counts changing as we create and drop references to the `Rc` in `a`. +Let’s change our working example in Listing 15-18 so that we can see the +reference counts changing as we create and drop references to the `Rc` in +`a`. -In Listing 15-19, we’ll change `main` so it has an inner scope around list `c`; -then we can see how the reference count changes when `c` goes out of scope. +In Listing 15-19, we’ll change `main` so that it has an inner scope around list +`c`; then, we can see how the reference count changes when `c` goes out of +scope. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-19/src/main.rs:here}} ``` -Listing 15-19: Printing the reference count + At each point in the program where the reference count changes, we print the reference count, which we get by calling the `Rc::strong_count` function. This function is named `strong_count` rather than `count` because the `Rc` type -also has a `weak_count`; we’ll see what `weak_count` is used for in the -[“Preventing Reference Cycles: Turning an `Rc` into a -`Weak`”][preventing-ref-cycles] section. +also has a `weak_count`; we’ll see what `weak_count` is used for in [“Preventing +Reference Cycles Using `Weak`”][preventing-ref-cycles]. This code prints the following: @@ -139,15 +151,15 @@ This code prints the following: {{#include ../listings/ch15-smart-pointers/listing-15-19/output.txt}} ``` -We can see that the `Rc` in `a` has an initial reference count of 1; then -each time we call `clone`, the count goes up by 1. When `c` goes out of scope, -the count goes down by 1. We don’t have to call a function to decrease the -reference count like we have to call `Rc::clone` to increase the reference -count: the implementation of the `Drop` trait decreases the reference count +We can see that the `Rc` in `a` has an initial reference count of 1; +then, each time we call `clone`, the count goes up by 1. When `c` goes out of +scope, the count goes down by 1. We don’t have to call a function to decrease +the reference count like we have to call `Rc::clone` to increase the reference +count: The implementation of the `Drop` trait decreases the reference count automatically when an `Rc` value goes out of scope. What we can’t see in this example is that when `b` and then `a` go out of scope -at the end of `main`, the count is then 0, and the `Rc` is cleaned up +at the end of `main`, the count is 0, and the `Rc` is cleaned up completely. Using `Rc` allows a single value to have multiple owners, and the count ensures that the value remains valid as long as any of the owners still exist. @@ -155,7 +167,7 @@ still exist. Via immutable references, `Rc` allows you to share data between multiple parts of your program for reading only. If `Rc` allowed you to have multiple mutable references too, you might violate one of the borrowing rules discussed -in Chapter 4: multiple mutable borrows to the same place can cause data races +in Chapter 4: Multiple mutable borrows to the same place can cause data races and inconsistencies. But being able to mutate data is very useful! In the next section, we’ll discuss the interior mutability pattern and the `RefCell` type that you can use in conjunction with an `Rc` to work with this diff --git a/src/ch15-05-interior-mutability.md b/src/ch15-05-interior-mutability.md index 7b5e825d7e..2bc04a770c 100644 --- a/src/ch15-05-interior-mutability.md +++ b/src/ch15-05-interior-mutability.md @@ -1,12 +1,12 @@ ## `RefCell` and the Interior Mutability Pattern -*Interior mutability* is a design pattern in Rust that allows you to mutate +_Interior mutability_ is a design pattern in Rust that allows you to mutate data even when there are immutable references to that data; normally, this action is disallowed by the borrowing rules. To mutate data, the pattern uses `unsafe` code inside a data structure to bend Rust’s usual rules that govern mutation and borrowing. Unsafe code indicates to the compiler that we’re checking the rules manually instead of relying on the compiler to check them -for us; we will discuss unsafe code more in Chapter 19. +for us; we will discuss unsafe code more in Chapter 20. We can use types that use the interior mutability pattern only when we can ensure that the borrowing rules will be followed at runtime, even though the @@ -16,18 +16,22 @@ safe API, and the outer type is still immutable. Let’s explore this concept by looking at the `RefCell` type that follows the interior mutability pattern. -### Enforcing Borrowing Rules at Runtime with `RefCell` + + + + +### Enforcing Borrowing Rules at Runtime Unlike `Rc`, the `RefCell` type represents single ownership over the data it holds. So, what makes `RefCell` different from a type like `Box`? Recall the borrowing rules you learned in Chapter 4: -* At any given time, you can have *either* (but not both) one mutable reference - or any number of immutable references. -* References must always be valid. +- At any given time, you can have _either_ one mutable reference or any number + of immutable references (but not both). +- References must always be valid. With references and `Box`, the borrowing rules’ invariants are enforced at -compile time. With `RefCell`, these invariants are enforced *at runtime*. +compile time. With `RefCell`, these invariants are enforced _at runtime_. With references, if you break these rules, you’ll get a compiler error. With `RefCell`, if you break these rules, your program will panic and exit. @@ -41,14 +45,14 @@ The advantage of checking the borrowing rules at runtime instead is that certain memory-safe scenarios are then allowed, where they would’ve been disallowed by the compile-time checks. Static analysis, like the Rust compiler, is inherently conservative. Some properties of code are impossible to detect by -analyzing the code: the most famous example is the Halting Problem, which is +analyzing the code: The most famous example is the Halting Problem, which is beyond the scope of this book but is an interesting topic to research. Because some analysis is impossible, if the Rust compiler can’t be sure the code complies with the ownership rules, it might reject a correct program; in this way, it’s conservative. If Rust accepted an incorrect program, users -wouldn’t be able to trust in the guarantees Rust makes. However, if Rust -rejects a correct program, the programmer will be inconvenienced, but nothing +wouldn’t be able to trust the guarantees Rust makes. However, if Rust rejects a +correct program, the programmer will be inconvenienced, but nothing catastrophic can occur. The `RefCell` type is useful when you’re sure your code follows the borrowing rules but the compiler is unable to understand and guarantee that. @@ -60,20 +64,24 @@ multithreaded program in Chapter 16. Here is a recap of the reasons to choose `Box`, `Rc`, or `RefCell`: -* `Rc` enables multiple owners of the same data; `Box` and `RefCell` +- `Rc` enables multiple owners of the same data; `Box` and `RefCell` have single owners. -* `Box` allows immutable or mutable borrows checked at compile time; `Rc` +- `Box` allows immutable or mutable borrows checked at compile time; `Rc` allows only immutable borrows checked at compile time; `RefCell` allows immutable or mutable borrows checked at runtime. -* Because `RefCell` allows mutable borrows checked at runtime, you can +- Because `RefCell` allows mutable borrows checked at runtime, you can mutate the value inside the `RefCell` even when the `RefCell` is immutable. -Mutating the value inside an immutable value is the *interior mutability* +Mutating the value inside an immutable value is the interior mutability pattern. Let’s look at a situation in which interior mutability is useful and examine how it’s possible. -### Interior Mutability: A Mutable Borrow to an Immutable Value + + + + +### Using Interior Mutability A consequence of the borrowing rules is that when you have an immutable value, you can’t borrow it mutably. For example, this code won’t compile: @@ -92,7 +100,7 @@ However, there are situations in which it would be useful for a value to mutate itself in its methods but appear immutable to other code. Code outside the value’s methods would not be able to mutate the value. Using `RefCell` is one way to get the ability to have interior mutability, but `RefCell` -doesn’t get around the borrowing rules completely: the borrow checker in the +doesn’t get around the borrowing rules completely: The borrow checker in the compiler allows this interior mutability, and the borrowing rules are checked at runtime instead. If you violate the rules, you’ll get a `panic!` instead of a compiler error. @@ -100,23 +108,27 @@ a compiler error. Let’s work through a practical example where we can use `RefCell` to mutate an immutable value and see why that is useful. -#### A Use Case for Interior Mutability: Mock Objects + + + + +#### Testing with Mock Objects Sometimes during testing a programmer will use a type in place of another type, -in order to observe particular behavior and assert it’s implemented correctly. -This placeholder type is called a *test double*. Think of it in the sense of a -“stunt double” in filmmaking, where a person steps in and substitutes for an -actor to do a particular tricky scene. Test doubles stand in for other types -when we’re running tests. *Mock objects* are specific types of test doubles -that record what happens during a test so you can assert that the correct -actions took place. +in order to observe particular behavior and assert that it’s implemented +correctly. This placeholder type is called a _test double_. Think of it in the +sense of a stunt double in filmmaking, where a person steps in and substitutes +for an actor to do a particularly tricky scene. Test doubles stand in for other +types when we’re running tests. _Mock objects_ are specific types of test +doubles that record what happens during a test so that you can assert that the +correct actions took place. Rust doesn’t have objects in the same sense as other languages have objects, and Rust doesn’t have mock object functionality built into the standard library as some other languages do. However, you can definitely create a struct that will serve the same purposes as a mock object. -Here’s the scenario we’ll test: we’ll create a library that tracks a value +Here’s the scenario we’ll test: We’ll create a library that tracks a value against a maximum value and sends messages based on how close to the maximum value the current value is. This library could be used to keep track of a user’s quota for the number of API calls they’re allowed to make, for example. @@ -124,19 +136,18 @@ user’s quota for the number of API calls they’re allowed to make, for exampl Our library will only provide the functionality of tracking how close to the maximum a value is and what the messages should be at what times. Applications that use our library will be expected to provide the mechanism for sending the -messages: the application could put a message in the application, send an -email, send a text message, or something else. The library doesn’t need to know -that detail. All it needs is something that implements a trait we’ll provide -called `Messenger`. Listing 15-20 shows the library code: +messages: The application could show the message to the user directly, send an +email, send a text message, or do something else. The library doesn’t need to +know that detail. All it needs is something that implements a trait we’ll +provide, called `Messenger`. Listing 15-20 shows the library code. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-20/src/lib.rs}} ``` -Listing 15-20: A library to keep track of how close a -value is to a maximum value and warn when the value is at certain levels + One important part of this code is that the `Messenger` trait has one method called `send` that takes an immutable reference to `self` and the text of the @@ -146,30 +157,29 @@ is that we want to test the behavior of the `set_value` method on the `LimitTracker`. We can change what we pass in for the `value` parameter, but `set_value` doesn’t return anything for us to make assertions on. We want to be able to say that if we create a `LimitTracker` with something that implements -the `Messenger` trait and a particular value for `max`, when we pass different -numbers for `value`, the messenger is told to send the appropriate messages. +the `Messenger` trait and a particular value for `max`, the messenger is told +to send the appropriate messages when we pass different numbers for `value`. We need a mock object that, instead of sending an email or text message when we call `send`, will only keep track of the messages it’s told to send. We can create a new instance of the mock object, create a `LimitTracker` that uses the mock object, call the `set_value` method on `LimitTracker`, and then check that the mock object has the messages we expect. Listing 15-21 shows an attempt to -implement a mock object to do just that, but the borrow checker won’t allow it: +implement a mock object to do just that, but the borrow checker won’t allow it. -Filename: src/lib.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-21/src/lib.rs:here}} ``` -Listing 15-21: An attempt to implement a `MockMessenger` -that isn’t allowed by the borrow checker + This test code defines a `MockMessenger` struct that has a `sent_messages` field with a `Vec` of `String` values to keep track of the messages it’s told to send. We also define an associated function `new` to make it convenient to create new `MockMessenger` values that start with an empty list of messages. We -then implement the `Messenger` trait for `MockMessenger` so we can give a +then implement the `Messenger` trait for `MockMessenger` so that we can give a `MockMessenger` to a `LimitTracker`. In the definition of the `send` method, we take the message passed in as a parameter and store it in the `MockMessenger` list of `sent_messages`. @@ -177,11 +187,11 @@ list of `sent_messages`. In the test, we’re testing what happens when the `LimitTracker` is told to set `value` to something that is more than 75 percent of the `max` value. First, we create a new `MockMessenger`, which will start with an empty list of messages. -Then we create a new `LimitTracker` and give it a reference to the new -`MockMessenger` and a `max` value of 100. We call the `set_value` method on the -`LimitTracker` with a value of 80, which is more than 75 percent of 100. Then -we assert that the list of messages that the `MockMessenger` is keeping track -of should now have one message in it. +Then, we create a new `LimitTracker` and give it a reference to the new +`MockMessenger` and a `max` value of `100`. We call the `set_value` method on +the `LimitTracker` with a value of `80`, which is more than 75 percent of 100. +Then, we assert that the list of messages that the `MockMessenger` is keeping +track of should now have one message in it. However, there’s one problem with this test, as shown here: @@ -191,23 +201,23 @@ However, there’s one problem with this test, as shown here: We can’t modify the `MockMessenger` to keep track of the messages, because the `send` method takes an immutable reference to `self`. We also can’t take the -suggestion from the error text to use `&mut self` instead, because then the -signature of `send` wouldn’t match the signature in the `Messenger` trait -definition (feel free to try and see what error message you get). +suggestion from the error text to use `&mut self` in both the `impl` method and +the trait definition. We do not want to change the `Messenger` trait solely for +the sake of testing. Instead, we need to find a way to make our test code work +correctly with our existing design. This is a situation in which interior mutability can help! We’ll store the -`sent_messages` within a `RefCell`, and then the `send` method will be -able to modify `sent_messages` to store the messages we’ve seen. Listing 15-22 -shows what that looks like: +`sent_messages` within a `RefCell`, and then the `send` method will be able +to modify `sent_messages` to store the messages we’ve seen. Listing 15-22 shows +what that looks like. -Filename: src/lib.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-22/src/lib.rs:here}} ``` -Listing 15-22: Using `RefCell` to mutate an inner -value while the outer value is considered immutable + The `sent_messages` field is now of type `RefCell>` instead of `Vec`. In the `new` function, we create a new `RefCell>` @@ -217,16 +227,20 @@ For the implementation of the `send` method, the first parameter is still an immutable borrow of `self`, which matches the trait definition. We call `borrow_mut` on the `RefCell>` in `self.sent_messages` to get a mutable reference to the value inside the `RefCell>`, which is the -vector. Then we can call `push` on the mutable reference to the vector to keep +vector. Then, we can call `push` on the mutable reference to the vector to keep track of the messages sent during the test. -The last change we have to make is in the assertion: to see how many items are +The last change we have to make is in the assertion: To see how many items are in the inner vector, we call `borrow` on the `RefCell>` to get an immutable reference to the vector. Now that you’ve seen how to use `RefCell`, let’s dig into how it works! -#### Keeping Track of Borrows at Runtime with `RefCell` + + + + +#### Tracking Borrows at Runtime When creating immutable and mutable references, we use the `&` and `&mut` syntax, respectively. With `RefCell`, we use the `borrow` and `borrow_mut` @@ -238,7 +252,7 @@ can treat them like regular references. The `RefCell` keeps track of how many `Ref` and `RefMut` smart pointers are currently active. Every time we call `borrow`, the `RefCell` increases its count of how many immutable borrows are active. When a `Ref` -value goes out of scope, the count of immutable borrows goes down by one. Just +value goes out of scope, the count of immutable borrows goes down by 1. Just like the compile-time borrowing rules, `RefCell` lets us have many immutable borrows or one mutable borrow at any point in time. @@ -249,18 +263,17 @@ Listing 15-22. We’re deliberately trying to create two mutable borrows active for the same scope to illustrate that `RefCell` prevents us from doing this at runtime. -Filename: src/lib.rs + ```rust,ignore,panics {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-23/src/lib.rs:here}} ``` -Listing 15-23: Creating two mutable references in the -same scope to see that `RefCell` will panic + We create a variable `one_borrow` for the `RefMut` smart pointer returned -from `borrow_mut`. Then we create another mutable borrow in the same way in the -variable `two_borrow`. This makes two mutable references in the same scope, +from `borrow_mut`. Then, we create another mutable borrow in the same way in +the variable `two_borrow`. This makes two mutable references in the same scope, which isn’t allowed. When we run the tests for our library, the code in Listing 15-23 will compile without any errors, but the test will fail: @@ -283,50 +296,54 @@ in a context where only immutable values are allowed. You can use `RefCell` despite its trade-offs to get more functionality than regular references provide. -### Having Multiple Owners of Mutable Data by Combining `Rc` and `RefCell` + + + + + +### Allowing Multiple Owners of Mutable Data A common way to use `RefCell` is in combination with `Rc`. Recall that `Rc` lets you have multiple owners of some data, but it only gives immutable access to that data. If you have an `Rc` that holds a `RefCell`, you can -get a value that can have multiple owners *and* that you can mutate! +get a value that can have multiple owners _and_ that you can mutate! For example, recall the cons list example in Listing 15-18 where we used `Rc` to allow multiple lists to share ownership of another list. Because `Rc` holds only immutable values, we can’t change any of the values in the -list once we’ve created them. Let’s add in `RefCell` to gain the ability to +list once we’ve created them. Let’s add in `RefCell` for its ability to change the values in the lists. Listing 15-24 shows that by using a `RefCell` in the `Cons` definition, we can modify the value stored in all -the lists: +the lists. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-24/src/main.rs}} ``` -Listing 15-24: Using `Rc>` to create a -`List` that we can mutate + We create a value that is an instance of `Rc>` and store it in a -variable named `value` so we can access it directly later. Then we create a -`List` in `a` with a `Cons` variant that holds `value`. We need to clone -`value` so both `a` and `value` have ownership of the inner `5` value rather -than transferring ownership from `value` to `a` or having `a` borrow from -`value`. +variable named `value` so that we can access it directly later. Then, we create +a `List` in `a` with a `Cons` variant that holds `value`. We need to clone +`value` so that both `a` and `value` have ownership of the inner `5` value +rather than transferring ownership from `value` to `a` or having `a` borrow +from `value`. -We wrap the list `a` in an `Rc` so when we create lists `b` and `c`, they -can both refer to `a`, which is what we did in Listing 15-18. +We wrap the list `a` in an `Rc` so that when we create lists `b` and `c`, +they can both refer to `a`, which is what we did in Listing 15-18. After we’ve created the lists in `a`, `b`, and `c`, we want to add 10 to the value in `value`. We do this by calling `borrow_mut` on `value`, which uses the -automatic dereferencing feature we discussed in Chapter 5 (see the section -[“Where’s the `->` Operator?”][wheres-the---operator]) to -dereference the `Rc` to the inner `RefCell` value. The `borrow_mut` -method returns a `RefMut` smart pointer, and we use the dereference operator -on it and change the inner value. +automatic dereferencing feature we discussed in [“Where’s the `->` +Operator?”][wheres-the---operator] in Chapter 5 to dereference +the `Rc` to the inner `RefCell` value. The `borrow_mut` method returns a +`RefMut` smart pointer, and we use the dereference operator on it and change +the inner value. When we print `a`, `b`, and `c`, we can see that they all have the modified -value of 15 rather than 5: +value of `15` rather than `5`: ```console {{#include ../listings/ch15-smart-pointers/listing-15-24/output.txt}} @@ -334,11 +351,11 @@ value of 15 rather than 5: This technique is pretty neat! By using `RefCell`, we have an outwardly immutable `List` value. But we can use the methods on `RefCell` that provide -access to its interior mutability so we can modify our data when we need to. -The runtime checks of the borrowing rules protect us from data races, and it’s -sometimes worth trading a bit of speed for this flexibility in our data +access to its interior mutability so that we can modify our data when we need +to. The runtime checks of the borrowing rules protect us from data races, and +it’s sometimes worth trading a bit of speed for this flexibility in our data structures. Note that `RefCell` does not work for multithreaded code! -`Mutex` is the thread-safe version of `RefCell` and we’ll discuss +`Mutex` is the thread-safe version of `RefCell`, and we’ll discuss `Mutex` in Chapter 16. [wheres-the---operator]: ch05-03-method-syntax.html#wheres-the---operator diff --git a/src/ch15-06-reference-cycles.md b/src/ch15-06-reference-cycles.md index beb2bc2169..1c11b02a4d 100644 --- a/src/ch15-06-reference-cycles.md +++ b/src/ch15-06-reference-cycles.md @@ -1,10 +1,10 @@ ## Reference Cycles Can Leak Memory Rust’s memory safety guarantees make it difficult, but not impossible, to -accidentally create memory that is never cleaned up (known as a *memory leak*). +accidentally create memory that is never cleaned up (known as a _memory leak_). Preventing memory leaks entirely is not one of Rust’s guarantees, meaning memory leaks are memory safe in Rust. We can see that Rust allows memory leaks -by using `Rc` and `RefCell`: it’s possible to create references where +by using `Rc` and `RefCell`: It’s possible to create references where items refer to each other in a cycle. This creates memory leaks because the reference count of each item in the cycle will never reach 0, and the values will never be dropped. @@ -13,16 +13,15 @@ will never be dropped. Let’s look at how a reference cycle might happen and how to prevent it, starting with the definition of the `List` enum and a `tail` method in Listing -15-25: +15-25. -Filename: src/main.rs + ```rust -{{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-25/src/main.rs}} +{{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-25/src/main.rs:here}} ``` -Listing 15-25: A cons list definition that holds a -`RefCell` so we can modify what a `Cons` variant is referring to + We’re using another variation of the `List` definition from Listing 15-5. The second element in the `Cons` variant is now `RefCell>`, meaning that @@ -33,29 +32,28 @@ second item if we have a `Cons` variant. In Listing 15-26, we’re adding a `main` function that uses the definitions in Listing 15-25. This code creates a list in `a` and a list in `b` that points to -the list in `a`. Then it modifies the list in `a` to point to `b`, creating a +the list in `a`. Then, it modifies the list in `a` to point to `b`, creating a reference cycle. There are `println!` statements along the way to show what the reference counts are at various points in this process. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-26/src/main.rs:here}} ``` -Listing 15-26: Creating a reference cycle of two `List` -values pointing to each other + We create an `Rc` instance holding a `List` value in the variable `a` with an initial list of `5, Nil`. We then create an `Rc` instance holding -another `List` value in the variable `b` that contains the value 10 and points -to the list in `a`. +another `List` value in the variable `b` that contains the value `10` and +points to the list in `a`. -We modify `a` so it points to `b` instead of `Nil`, creating a cycle. We do -that by using the `tail` method to get a reference to the `RefCell>` -in `a`, which we put in the variable `link`. Then we use the `borrow_mut` -method on the `RefCell>` to change the value inside from an `Rc` -that holds a `Nil` value to the `Rc` in `b`. +We modify `a` so that it points to `b` instead of `Nil`, creating a cycle. We +do that by using the `tail` method to get a reference to the +`RefCell>` in `a`, which we put in the variable `link`. Then, we use +the `borrow_mut` method on the `RefCell>` to change the value inside +from an `Rc` that holds a `Nil` value to the `Rc` in `b`. When we run this code, keeping the last `println!` commented out for the moment, we’ll get this output: @@ -64,18 +62,18 @@ moment, we’ll get this output: {{#include ../listings/ch15-smart-pointers/listing-15-26/output.txt}} ``` -The reference count of the `Rc` instances in both `a` and `b` are 2 after +The reference count of the `Rc` instances in both `a` and `b` is 2 after we change the list in `a` to point to `b`. At the end of `main`, Rust drops the -variable `b`, which decreases the reference count of the `b` `Rc` instance -from 2 to 1. The memory that `Rc` has on the heap won’t be dropped at -this point, because its reference count is 1, not 0. Then Rust drops `a`, which -decreases the reference count of the `a` `Rc` instance from 2 to 1 as -well. This instance’s memory can’t be dropped either, because the other +variable `b`, which decreases the reference count of the `b` `Rc` +instance from 2 to 1. The memory that `Rc` has on the heap won’t be +dropped at this point because its reference count is 1, not 0. Then, Rust drops +`a`, which decreases the reference count of the `a` `Rc` instance from 2 +to 1 as well. This instance’s memory can’t be dropped either, because the other `Rc` instance still refers to it. The memory allocated to the list will -remain uncollected forever. To visualize this reference cycle, we’ve created a -diagram in Figure 15-4. +remain uncollected forever. To visualize this reference cycle, we’ve created +the diagram in Figure 15-4. -Reference cycle of lists +A rectangle labeled 'a' that points to a rectangle containing the integer 5. A rectangle labeled 'b' that points to a rectangle containing the integer 10. The rectangle containing 5 points to the rectangle containing 10, and the rectangle containing 10 points back to the rectangle containing 5, creating a cycle. Figure 15-4: A reference cycle of lists `a` and `b` pointing to each other @@ -84,11 +82,11 @@ If you uncomment the last `println!` and run the program, Rust will try to print this cycle with `a` pointing to `b` pointing to `a` and so forth until it overflows the stack. -Compared to a real-world program, the consequences of creating a reference cycle -in this example aren’t very dire: right after we create the reference cycle, -the program ends. However, if a more complex program allocated lots of memory -in a cycle and held onto it for a long time, the program would use more memory -than it needed and might overwhelm the system, causing it to run out of +Compared to a real-world program, the consequences of creating a reference +cycle in this example aren’t very dire: Right after we create the reference +cycle, the program ends. However, if a more complex program allocated lots of +memory in a cycle and held onto it for a long time, the program would use more +memory than it needed and might overwhelm the system, causing it to run out of available memory. Creating reference cycles is not easily done, but it’s not impossible either. @@ -109,17 +107,22 @@ Let’s look at an example using graphs made up of parent nodes and child nodes to see when non-ownership relationships are an appropriate way to prevent reference cycles. -### Preventing Reference Cycles: Turning an `Rc` into a `Weak` + + + + +### Preventing Reference Cycles Using `Weak` So far, we’ve demonstrated that calling `Rc::clone` increases the `strong_count` of an `Rc` instance, and an `Rc` instance is only cleaned -up if its `strong_count` is 0. You can also create a *weak reference* to the +up if its `strong_count` is 0. You can also create a weak reference to the value within an `Rc` instance by calling `Rc::downgrade` and passing a -reference to the `Rc`. Strong references are how you can share ownership of -an `Rc` instance. Weak references don’t express an ownership relationship, -and their count doesn’t affect when an `Rc` instance is cleaned up. They -won’t cause a reference cycle because any cycle involving some weak references -will be broken once the strong reference count of values involved is 0. +reference to the `Rc`. *Strong references* are how you can share ownership +of an `Rc` instance. *Weak references* don’t express an ownership +relationship, and their count doesn’t affect when an `Rc` instance is +cleaned up. They won’t cause a reference cycle, because any cycle involving +some weak references will be broken once the strong reference count of values +involved is 0. When you call `Rc::downgrade`, you get a smart pointer of type `Weak`. Instead of increasing the `strong_count` in the `Rc` instance by 1, calling @@ -129,7 +132,7 @@ Instead of increasing the `strong_count` in the `Rc` instance by 1, calling `Rc` instance to be cleaned up. Because the value that `Weak` references might have been dropped, to do -anything with the value that a `Weak` is pointing to, you must make sure the +anything with the value that a `Weak` is pointing to you must make sure the value still exists. Do this by calling the `upgrade` method on a `Weak` instance, which will return an `Option>`. You’ll get a result of `Some` if the `Rc` value has not been dropped yet and a result of `None` if the @@ -138,14 +141,18 @@ Rust will ensure that the `Some` case and the `None` case are handled, and there won’t be an invalid pointer. As an example, rather than using a list whose items know only about the next -item, we’ll create a tree whose items know about their children items *and* -their parent items. +item, we’ll create a tree whose items know about their child items _and_ their +parent items. + + -#### Creating a Tree Data Structure: a `Node` with Child Nodes + + +#### Creating a Tree Data Structure To start, we’ll build a tree with nodes that know about their child nodes. We’ll create a struct named `Node` that holds its own `i32` value as well as -references to its children `Node` values: +references to its child `Node` values: Filename: src/main.rs @@ -154,23 +161,22 @@ references to its children `Node` values: ``` We want a `Node` to own its children, and we want to share that ownership with -variables so we can access each `Node` in the tree directly. To do this, we -define the `Vec` items to be values of type `Rc`. We also want to +variables so that we can access each `Node` in the tree directly. To do this, +we define the `Vec` items to be values of type `Rc`. We also want to modify which nodes are children of another node, so we have a `RefCell` in `children` around the `Vec>`. Next, we’ll use our struct definition and create one `Node` instance named -`leaf` with the value 3 and no children, and another instance named `branch` -with the value 5 and `leaf` as one of its children, as shown in Listing 15-27: +`leaf` with the value `3` and no children, and another instance named `branch` +with the value `5` and `leaf` as one of its children, as shown in Listing 15-27. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-27/src/main.rs:there}} ``` -Listing 15-27: Creating a `leaf` node with no children -and a `branch` node with `leaf` as one of its children + We clone the `Rc` in `leaf` and store that in `branch`, meaning the `Node` in `leaf` now has two owners: `leaf` and `branch`. We can get from @@ -189,11 +195,11 @@ create a reference cycle with `leaf.parent` pointing to `branch` and values to never be 0. Thinking about the relationships another way, a parent node should own its -children: if a parent node is dropped, its child nodes should be dropped as -well. However, a child should not own its parent: if we drop a child node, the +children: If a parent node is dropped, its child nodes should be dropped as +well. However, a child should not own its parent: If we drop a child node, the parent should still exist. This is a case for weak references! -So instead of `Rc`, we’ll make the type of `parent` use `Weak`, +So, instead of `Rc`, we’ll make the type of `parent` use `Weak`, specifically a `RefCell>`. Now our `Node` struct definition looks like this: @@ -203,18 +209,17 @@ like this: {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-28/src/main.rs:here}} ``` -A node will be able to refer to its parent node but doesn’t own its parent. -In Listing 15-28, we update `main` to use this new definition so the `leaf` -node will have a way to refer to its parent, `branch`: +A node will be able to refer to its parent node but doesn’t own its parent. In +Listing 15-28, we update `main` to use this new definition so that the `leaf` +node will have a way to refer to its parent, `branch`. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-28/src/main.rs:there}} ``` -Listing 15-28: A `leaf` node with a weak reference to its -parent node `branch` + Creating the `leaf` node looks similar to Listing 15-27 with the exception of the `parent` field: `leaf` starts out without a parent, so we create a new, @@ -229,16 +234,15 @@ leaf parent = None ``` When we create the `branch` node, it will also have a new `Weak` -reference in the `parent` field, because `branch` doesn’t have a parent node. -We still have `leaf` as one of the children of `branch`. Once we have the -`Node` instance in `branch`, we can modify `leaf` to give it a `Weak` -reference to its parent. We use the `borrow_mut` method on the -`RefCell>` in the `parent` field of `leaf`, and then we use the -`Rc::downgrade` function to create a `Weak` reference to `branch` from -the `Rc` in `branch.` +reference in the `parent` field because `branch` doesn’t have a parent node. We +still have `leaf` as one of the children of `branch`. Once we have the `Node` +instance in `branch`, we can modify `leaf` to give it a `Weak` reference +to its parent. We use the `borrow_mut` method on the `RefCell>` in +the `parent` field of `leaf`, and then we use the `Rc::downgrade` function to +create a `Weak` reference to `branch` from the `Rc` in `branch`. When we print the parent of `leaf` again, this time we’ll get a `Some` variant -holding `branch`: now `leaf` can access its parent! When we print `leaf`, we +holding `branch`: Now `leaf` can access its parent! When we print `leaf`, we also avoid the cycle that eventually ended in a stack overflow like we had in Listing 15-26; the `Weak` references are printed as `(Weak)`: @@ -258,24 +262,23 @@ Let’s look at how the `strong_count` and `weak_count` values of the `Rc` instances change by creating a new inner scope and moving the creation of `branch` into that scope. By doing so, we can see what happens when `branch` is created and then dropped when it goes out of scope. The modifications are shown -in Listing 15-29: +in Listing 15-29. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-29/src/main.rs:here}} ``` -Listing 15-29: Creating `branch` in an inner scope and -examining strong and weak reference counts + After `leaf` is created, its `Rc` has a strong count of 1 and a weak count of 0. In the inner scope, we create `branch` and associate it with `leaf`, at which point when we print the counts, the `Rc` in `branch` will have a strong count of 1 and a weak count of 1 (for `leaf.parent` pointing to `branch` with a `Weak`). When we print the counts in `leaf`, we’ll see -it will have a strong count of 2, because `branch` now has a clone of the -`Rc` of `leaf` stored in `branch.children`, but will still have a weak +it will have a strong count of 2 because `branch` now has a clone of the +`Rc` of `leaf` stored in `branch.children` but will still have a weak count of 0. When the inner scope ends, `branch` goes out of scope and the strong count of @@ -285,7 +288,7 @@ don’t get any memory leaks! If we try to access the parent of `leaf` after the end of the scope, we’ll get `None` again. At the end of the program, the `Rc` in `leaf` has a strong -count of 1 and a weak count of 0, because the variable `leaf` is now the only +count of 1 and a weak count of 0 because the variable `leaf` is now the only reference to the `Rc` again. All of the logic that manages the counts and value dropping is built into @@ -301,7 +304,7 @@ This chapter covered how to use smart pointers to make different guarantees and trade-offs from those Rust makes by default with regular references. The `Box` type has a known size and points to data allocated on the heap. The `Rc` type keeps track of the number of references to data on the heap so -that data can have multiple owners. The `RefCell` type with its interior +that the data can have multiple owners. The `RefCell` type with its interior mutability gives us a type that we can use when we need an immutable type but need to change an inner value of that type; it also enforces the borrowing rules at runtime instead of at compile time. diff --git a/src/ch16-00-concurrency.md b/src/ch16-00-concurrency.md index 410f3e40da..95b1562f1d 100644 --- a/src/ch16-00-concurrency.md +++ b/src/ch16-00-concurrency.md @@ -1,38 +1,38 @@ # Fearless Concurrency Handling concurrent programming safely and efficiently is another of Rust’s -major goals. *Concurrent programming*, where different parts of a program -execute independently, and *parallel programming*, where different parts of a -program execute at the same time, are becoming increasingly important as more +major goals. _Concurrent programming_, in which different parts of a program +execute independently, and _parallel programming_, in which different parts of +a program execute at the same time, are becoming increasingly important as more computers take advantage of their multiple processors. Historically, -programming in these contexts has been difficult and error prone: Rust hopes to +programming in these contexts has been difficult and error-prone. Rust hopes to change that. Initially, the Rust team thought that ensuring memory safety and preventing concurrency problems were two separate challenges to be solved with different methods. Over time, the team discovered that the ownership and type systems are -a powerful set of tools to help manage memory safety *and* concurrency +a powerful set of tools to help manage memory safety _and_ concurrency problems! By leveraging ownership and type checking, many concurrency errors are compile-time errors in Rust rather than runtime errors. Therefore, rather than making you spend lots of time trying to reproduce the exact circumstances under which a runtime concurrency bug occurs, incorrect code will refuse to compile and present an error explaining the problem. As a result, you can fix your code while you’re working on it rather than potentially after it has been -shipped to production. We’ve nicknamed this aspect of Rust *fearless* -*concurrency*. Fearless concurrency allows you to write code that is free of +shipped to production. We’ve nicknamed this aspect of Rust _fearless +concurrency_. Fearless concurrency allows you to write code that is free of subtle bugs and is easy to refactor without introducing new bugs. > Note: For simplicity’s sake, we’ll refer to many of the problems as -> *concurrent* rather than being more precise by saying *concurrent and/or -> parallel*. If this book were about concurrency and/or parallelism, we’d be -> more specific. For this chapter, please mentally substitute *concurrent -> and/or parallel* whenever we use *concurrent*. +> _concurrent_ rather than being more precise by saying _concurrent and/or +> parallel_. For this chapter, please mentally substitute _concurrent and/or +> parallel_ whenever we use _concurrent_. In the next chapter, where the +> distinction matters more, we’ll be more specific. Many languages are dogmatic about the solutions they offer for handling concurrent problems. For example, Erlang has elegant functionality for message-passing concurrency but has only obscure ways to share state between threads. Supporting only a subset of possible solutions is a reasonable -strategy for higher-level languages, because a higher-level language promises +strategy for higher-level languages because a higher-level language promises benefits from giving up some control to gain abstractions. However, lower-level languages are expected to provide the solution with the best performance in any given situation and have fewer abstractions over the hardware. Therefore, Rust @@ -41,9 +41,9 @@ for your situation and requirements. Here are the topics we’ll cover in this chapter: -* How to create threads to run multiple pieces of code at the same time -* *Message-passing* concurrency, where channels send messages between threads -* *Shared-state* concurrency, where multiple threads have access to some piece +- How to create threads to run multiple pieces of code at the same time +- _Message-passing_ concurrency, where channels send messages between threads +- _Shared-state_ concurrency, where multiple threads have access to some piece of data -* The `Sync` and `Send` traits, which extend Rust’s concurrency guarantees to +- The `Sync` and `Send` traits, which extend Rust’s concurrency guarantees to user-defined types as well as types provided by the standard library diff --git a/src/ch16-01-threads.md b/src/ch16-01-threads.md index cfdd0c7066..6a1e3d4063 100644 --- a/src/ch16-01-threads.md +++ b/src/ch16-01-threads.md @@ -1,10 +1,10 @@ ## Using Threads to Run Code Simultaneously In most current operating systems, an executed program’s code is run in a -*process*, and the operating system will manage multiple processes at once. +_process_, and the operating system will manage multiple processes at once. Within a program, you can also have independent parts that run simultaneously. -The features that run these independent parts are called *threads*. For -example, a web server could have multiple threads so that it could respond to +The features that run these independent parts are called _threads_. For +example, a web server could have multiple threads so that it can respond to more than one request at the same time. Splitting the computation in your program into multiple threads to run multiple @@ -13,11 +13,11 @@ Because threads can run simultaneously, there’s no inherent guarantee about th order in which parts of your code on different threads will run. This can lead to problems, such as: -* Race conditions, where threads are accessing data or resources in an +- Race conditions, in which threads are accessing data or resources in an inconsistent order -* Deadlocks, where two threads are waiting for each other, preventing both +- Deadlocks, in which two threads are waiting for each other, preventing both threads from continuing -* Bugs that happen only in certain situations and are hard to reproduce and fix +- Bugs that only happen in certain situations and are hard to reproduce and fix reliably Rust attempts to mitigate the negative effects of using threads, but @@ -26,27 +26,27 @@ a code structure that is different from that in programs running in a single thread. Programming languages implement threads in a few different ways, and many -operating systems provide an API the language can call for creating new -threads. The Rust standard library uses a *1:1* model of thread implementation, -whereby a program uses one operating system thread per one language thread. -There are crates that implement other models of threading that make different -tradeoffs to the 1:1 model. +operating systems provide an API the programming language can call for creating +new threads. The Rust standard library uses a _1:1_ model of thread +implementation, whereby a program uses one operating system thread per one +language thread. There are crates that implement other models of threading that +make different trade-offs to the 1:1 model. (Rust’s async system, which we will +see in the next chapter, provides another approach to concurrency as well.) ### Creating a New Thread with `spawn` To create a new thread, we call the `thread::spawn` function and pass it a closure (we talked about closures in Chapter 13) containing the code we want to run in the new thread. The example in Listing 16-1 prints some text from a main -thread and other text from a new thread: +thread and other text from a new thread. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-01/src/main.rs}} ``` -Listing 16-1: Creating a new thread to print one thing -while the main thread prints something else + Note that when the main thread of a Rust program completes, all spawned threads are shut down, whether or not they have finished running. The output from this @@ -71,41 +71,45 @@ hi number 5 from the spawned thread! The calls to `thread::sleep` force a thread to stop its execution for a short duration, allowing a different thread to run. The threads will probably take -turns, but that isn’t guaranteed: it depends on how your operating system +turns, but that isn’t guaranteed: It depends on how your operating system schedules the threads. In this run, the main thread printed first, even though the print statement from the spawned thread appears first in the code. And even -though we told the spawned thread to print until `i` is 9, it only got to 5 +though we told the spawned thread to print until `i` is `9`, it only got to `5` before the main thread shut down. If you run this code and only see output from the main thread, or don’t see any overlap, try increasing the numbers in the ranges to create more opportunities for the operating system to switch between the threads. -### Waiting for All Threads to Finish Using `join` Handles + + + + +### Waiting for All Threads to Finish The code in Listing 16-1 not only stops the spawned thread prematurely most of the time due to the main thread ending, but because there is no guarantee on the order in which threads run, we also can’t guarantee that the spawned thread will get to run at all! -We can fix the problem of the spawned thread not running or ending prematurely -by saving the return value of `thread::spawn` in a variable. The return type of -`thread::spawn` is `JoinHandle`. A `JoinHandle` is an owned value that, when we -call the `join` method on it, will wait for its thread to finish. Listing 16-2 -shows how to use the `JoinHandle` of the thread we created in Listing 16-1 and -call `join` to make sure the spawned thread finishes before `main` exits: +We can fix the problem of the spawned thread not running or of it ending +prematurely by saving the return value of `thread::spawn` in a variable. The +return type of `thread::spawn` is `JoinHandle`. A `JoinHandle` is an +owned value that, when we call the `join` method on it, will wait for its +thread to finish. Listing 16-2 shows how to use the `JoinHandle` of the +thread we created in Listing 16-1 and how to call `join` to make sure the +spawned thread finishes before `main` exits. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-02/src/main.rs}} ``` -Listing 16-2: Saving a `JoinHandle` from `thread::spawn` -to guarantee the thread is run to completion + Calling `join` on the handle blocks the thread currently running until the -thread represented by the handle terminates. *Blocking* a thread means that +thread represented by the handle terminates. _Blocking_ a thread means that thread is prevented from performing work or exiting. Because we’ve put the call to `join` after the main thread’s `for` loop, running Listing 16-2 should produce output similar to this: @@ -136,12 +140,14 @@ call to `handle.join()` and does not end until the spawned thread is finished. But let’s see what happens when we instead move `handle.join()` before the `for` loop in `main`, like this: -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/no-listing-01-join-too-early/src/main.rs}} ``` + + The main thread will wait for the spawned thread to finish and then run its `for` loop, so the output won’t be interleaved anymore, as shown here: @@ -170,28 +176,27 @@ threads run at the same time. ### Using `move` Closures with Threads -We'll often use the `move` keyword with closures passed to `thread::spawn` +We’ll often use the `move` keyword with closures passed to `thread::spawn` because the closure will then take ownership of the values it uses from the environment, thus transferring ownership of those values from one thread to -another. In the [“Capturing References or Moving Ownership”][capture] section of Chapter 13, we discussed `move` in the context of closures. Now, -we’ll concentrate more on the interaction between `move` and `thread::spawn`. +another. In [“Capturing References or Moving Ownership”][capture] in Chapter 13, we discussed `move` in the context of closures. Now we’ll +concentrate more on the interaction between `move` and `thread::spawn`. Notice in Listing 16-1 that the closure we pass to `thread::spawn` takes no -arguments: we’re not using any data from the main thread in the spawned +arguments: We’re not using any data from the main thread in the spawned thread’s code. To use data from the main thread in the spawned thread, the spawned thread’s closure must capture the values it needs. Listing 16-3 shows an attempt to create a vector in the main thread and use it in the spawned -thread. However, this won’t yet work, as you’ll see in a moment. +thread. However, this won’t work yet, as you’ll see in a moment. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-03/src/main.rs}} ``` -Listing 16-3: Attempting to use a vector created by the -main thread in another thread + The closure uses `v`, so it will capture `v` and make it part of the closure’s environment. Because `thread::spawn` runs this closure in a new thread, we @@ -202,27 +207,26 @@ example, we get the following error: {{#include ../listings/ch16-fearless-concurrency/listing-16-03/output.txt}} ``` -Rust *infers* how to capture `v`, and because `println!` only needs a reference +Rust _infers_ how to capture `v`, and because `println!` only needs a reference to `v`, the closure tries to borrow `v`. However, there’s a problem: Rust can’t -tell how long the spawned thread will run, so it doesn’t know if the reference -to `v` will always be valid. +tell how long the spawned thread will run, so it doesn’t know whether the +reference to `v` will always be valid. Listing 16-4 provides a scenario that’s more likely to have a reference to `v` -that won’t be valid: +that won’t be valid. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-04/src/main.rs}} ``` -Listing 16-4: A thread with a closure that attempts to -capture a reference to `v` from a main thread that drops `v` + -If Rust allowed us to run this code, there’s a possibility the spawned thread -would be immediately put in the background without running at all. The spawned -thread has a reference to `v` inside, but the main thread immediately drops -`v`, using the `drop` function we discussed in Chapter 15. Then, when the +If Rust allowed us to run this code, there’s a possibility that the spawned +thread would be immediately put in the background without running at all. The +spawned thread has a reference to `v` inside, but the main thread immediately +drops `v`, using the `drop` function we discussed in Chapter 15. Then, when the spawned thread starts to execute, `v` is no longer valid, so a reference to it is also invalid. Oh no! @@ -243,16 +247,15 @@ help: to force the closure to take ownership of `v` (and any other referenced va By adding the `move` keyword before the closure, we force the closure to take ownership of the values it’s using rather than allowing Rust to infer that it should borrow the values. The modification to Listing 16-3 shown in Listing -16-5 will compile and run as we intend: +16-5 will compile and run as we intend. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-05/src/main.rs}} ``` -Listing 16-5: Using the `move` keyword to force a closure -to take ownership of the values it uses + We might be tempted to try the same thing to fix the code in Listing 16-4 where the main thread called `drop` by using a `move` closure. However, this fix will @@ -269,13 +272,13 @@ Rust’s ownership rules have saved us again! We got an error from the code in Listing 16-3 because Rust was being conservative and only borrowing `v` for the thread, which meant the main thread could theoretically invalidate the spawned thread’s reference. By telling Rust to move ownership of `v` to the spawned -thread, we’re guaranteeing Rust that the main thread won’t use `v` anymore. If -we change Listing 16-4 in the same way, we’re then violating the ownership +thread, we’re guaranteeing to Rust that the main thread won’t use `v` anymore. +If we change Listing 16-4 in the same way, we’re then violating the ownership rules when we try to use `v` in the main thread. The `move` keyword overrides Rust’s conservative default of borrowing; it doesn’t let us violate the ownership rules. -With a basic understanding of threads and the thread API, let’s look at what we -can *do* with threads. +Now that we’ve covered what threads are and the methods supplied by the thread +API, let’s look at some situations in which we can use threads. [capture]: ch13-01-closures.html#capturing-references-or-moving-ownership diff --git a/src/ch16-02-message-passing.md b/src/ch16-02-message-passing.md index e2f0b63c14..75bb15724b 100644 --- a/src/ch16-02-message-passing.md +++ b/src/ch16-02-message-passing.md @@ -1,13 +1,16 @@ -## Using Message Passing to Transfer Data Between Threads + -One increasingly popular approach to ensuring safe concurrency is *message -passing*, where threads or actors communicate by sending each other messages -containing data. Here’s the idea in a slogan from [the Go language -documentation](https://golang.org/doc/effective_go.html#concurrency): + + +## Transfer Data Between Threads with Message Passing + +One increasingly popular approach to ensuring safe concurrency is message +passing, where threads or actors communicate by sending each other messages +containing data. Here’s the idea in a slogan from [the Go language documentation](https://golang.org/doc/effective_go.html#concurrency): “Do not communicate by sharing memory; instead, share memory by communicating.” -To accomplish message-sending concurrency, Rust's standard library provides an -implementation of *channels*. A channel is a general programming concept by +To accomplish message-sending concurrency, Rust’s standard library provides an +implementation of channels. A _channel_ is a general programming concept by which data is sent from one thread to another. You can imagine a channel in programming as being like a directional channel of @@ -15,91 +18,90 @@ water, such as a stream or a river. If you put something like a rubber duck into a river, it will travel downstream to the end of the waterway. A channel has two halves: a transmitter and a receiver. The transmitter half is -the upstream location where you put rubber ducks into the river, and the +the upstream location where you put the rubber duck into the river, and the receiver half is where the rubber duck ends up downstream. One part of your code calls methods on the transmitter with the data you want to send, and another part checks the receiving end for arriving messages. A channel is said -to be *closed* if either the transmitter or receiver half is dropped. +to be _closed_ if either the transmitter or receiver half is dropped. Here, we’ll work up to a program that has one thread to generate values and send them down a channel, and another thread that will receive the values and print them out. We’ll be sending simple values between threads using a channel to illustrate the feature. Once you’re familiar with the technique, you could -use channels for any threads that need to communicate between each other, such -as a chat system or a system where many threads perform parts of a calculation -and send the parts to one thread that aggregates the results. +use channels for any threads that need to communicate with each other, such as +a chat system or a system where many threads perform parts of a calculation and +send the parts to one thread that aggregates the results. First, in Listing 16-6, we’ll create a channel but not do anything with it. Note that this won’t compile yet because Rust can’t tell what type of values we want to send over the channel. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-06/src/main.rs}} ``` -Listing 16-6: Creating a channel and assigning the two -halves to `tx` and `rx` + We create a new channel using the `mpsc::channel` function; `mpsc` stands for -*multiple producer, single consumer*. In short, the way Rust’s standard library -implements channels means a channel can have multiple *sending* ends that -produce values but only one *receiving* end that consumes those values. Imagine -multiple streams flowing together into one big river: everything sent down any +_multiple producer, single consumer_. In short, the way Rust’s standard library +implements channels means a channel can have multiple _sending_ ends that +produce values but only one _receiving_ end that consumes those values. Imagine +multiple streams flowing together into one big river: Everything sent down any of the streams will end up in one river at the end. We’ll start with a single producer for now, but we’ll add multiple producers when we get this example working. The `mpsc::channel` function returns a tuple, the first element of which is the -sending end--the transmitter--and the second element is the receiving end--the -receiver. The abbreviations `tx` and `rx` are traditionally used in many fields -for *transmitter* and *receiver* respectively, so we name our variables as such -to indicate each end. We’re using a `let` statement with a pattern that -destructures the tuples; we’ll discuss the use of patterns in `let` statements -and destructuring in Chapter 18. For now, know that using a `let` statement -this way is a convenient approach to extract the pieces of the tuple returned -by `mpsc::channel`. +sending end—the transmitter—and the second element of which is the receiving +end—the receiver. The abbreviations `tx` and `rx` are traditionally used in +many fields for _transmitter_ and _receiver_, respectively, so we name our +variables as such to indicate each end. We’re using a `let` statement with a +pattern that destructures the tuples; we’ll discuss the use of patterns in +`let` statements and destructuring in Chapter 19. For now, know that using a +`let` statement in this way is a convenient approach to extract the pieces of +the tuple returned by `mpsc::channel`. Let’s move the transmitting end into a spawned thread and have it send one -string so the spawned thread is communicating with the main thread, as shown in -Listing 16-7. This is like putting a rubber duck in the river upstream or -sending a chat message from one thread to another. +string so that the spawned thread is communicating with the main thread, as +shown in Listing 16-7. This is like putting a rubber duck in the river upstream +or sending a chat message from one thread to another. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-07/src/main.rs}} ``` -Listing 16-7: Moving `tx` to a spawned thread and sending -“hi” + Again, we’re using `thread::spawn` to create a new thread and then using `move` -to move `tx` into the closure so the spawned thread owns `tx`. The spawned +to move `tx` into the closure so that the spawned thread owns `tx`. The spawned thread needs to own the transmitter to be able to send messages through the -channel. The transmitter has a `send` method that takes the value we want to -send. The `send` method returns a `Result` type, so if the receiver has -already been dropped and there’s nowhere to send a value, the send operation -will return an error. In this example, we’re calling `unwrap` to panic in case -of an error. But in a real application, we would handle it properly: return to +channel. + +The transmitter has a `send` method that takes the value we want to send. The +`send` method returns a `Result` type, so if the receiver has already +been dropped and there’s nowhere to send a value, the send operation will +return an error. In this example, we’re calling `unwrap` to panic in case of an +error. But in a real application, we would handle it properly: Return to Chapter 9 to review strategies for proper error handling. In Listing 16-8, we’ll get the value from the receiver in the main thread. This is like retrieving the rubber duck from the water at the end of the river or receiving a chat message. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-08/src/main.rs}} ``` -Listing 16-8: Receiving the value “hi” in the main thread -and printing it + The receiver has two useful methods: `recv` and `try_recv`. We’re using `recv`, -short for *receive*, which will block the main thread’s execution and wait +short for _receive_, which will block the main thread’s execution and wait until a value is sent down the channel. Once a value is sent, `recv` will return it in a `Result`. When the transmitter closes, `recv` will return an error to signal that no more values will be coming. @@ -107,7 +109,7 @@ an error to signal that no more values will be coming. The `try_recv` method doesn’t block, but will instead return a `Result` immediately: an `Ok` value holding a message if one is available and an `Err` value if there aren’t any messages this time. Using `try_recv` is useful if -this thread has other work to do while waiting for messages: we could write a +this thread has other work to do while waiting for messages: We could write a loop that calls `try_recv` every so often, handles a message if one is available, and otherwise does other work for a little while until checking again. @@ -129,27 +131,30 @@ Got: hi Perfect! -### Channels and Ownership Transference + + + + +### Transferring Ownership Through Channels The ownership rules play a vital role in message sending because they help you write safe, concurrent code. Preventing errors in concurrent programming is the advantage of thinking about ownership throughout your Rust programs. Let’s do an experiment to show how channels and ownership work together to prevent -problems: we’ll try to use a `val` value in the spawned thread *after* we’ve +problems: We’ll try to use a `val` value in the spawned thread _after_ we’ve sent it down the channel. Try compiling the code in Listing 16-9 to see why -this code isn’t allowed: +this code isn’t allowed. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-09/src/main.rs}} ``` -Listing 16-9: Attempting to use `val` after we’ve sent it -down the channel + Here, we try to print `val` after we’ve sent it down the channel via `tx.send`. -Allowing this would be a bad idea: once the value has been sent to another +Allowing this would be a bad idea: Once the value has been sent to another thread, that thread could modify or drop it before we try to use the value again. Potentially, the other thread’s modifications could cause errors or unexpected results due to inconsistent or nonexistent data. However, Rust gives @@ -159,39 +164,43 @@ us an error if we try to compile the code in Listing 16-9: {{#include ../listings/ch16-fearless-concurrency/listing-16-09/output.txt}} ``` -Our concurrency mistake has caused a compile time error. The `send` function -takes ownership of its parameter, and when the value is moved, the receiver +Our concurrency mistake has caused a compile-time error. The `send` function +takes ownership of its parameter, and when the value is moved the receiver takes ownership of it. This stops us from accidentally using the value again after sending it; the ownership system checks that everything is okay. -### Sending Multiple Values and Seeing the Receiver Waiting + + + + +### Sending Multiple Values The code in Listing 16-8 compiled and ran, but it didn’t clearly show us that -two separate threads were talking to each other over the channel. In Listing -16-10 we’ve made some modifications that will prove the code in Listing 16-8 is -running concurrently: the spawned thread will now send multiple messages and -pause for a second between each message. +two separate threads were talking to each other over the channel. + +In Listing 16-10, we’ve made some modifications that will prove the code in +Listing 16-8 is running concurrently: The spawned thread will now send multiple +messages and pause for a second between each message. -Filename: src/main.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-10/src/main.rs}} ``` -Listing 16-10: Sending multiple messages and pausing -between each + This time, the spawned thread has a vector of strings that we want to send to the main thread. We iterate over them, sending each individually, and pause between each by calling the `thread::sleep` function with a `Duration` value of -1 second. +one second. In the main thread, we’re not calling the `recv` function explicitly anymore: -instead, we’re treating `rx` as an iterator. For each value received, we’re +Instead, we’re treating `rx` as an iterator. For each value received, we’re printing it. When the channel is closed, iteration will end. When running the code in Listing 16-10, you should see the following output -with a 1-second pause in between each line: +with a one-second pause in between each line: + + + +### Creating Multiple Producers -Earlier we mentioned that `mpsc` was an acronym for *multiple producer, -single consumer*. Let’s put `mpsc` to use and expand the code in Listing 16-10 -to create multiple threads that all send values to the same receiver. We can do -so by cloning the transmitter, as shown in Listing 16-11: +Earlier we mentioned that `mpsc` was an acronym for _multiple producer, single +consumer_. Let’s put `mpsc` to use and expand the code in Listing 16-10 to +create multiple threads that all send values to the same receiver. We can do so +by cloning the transmitter, as shown in Listing 16-11. -Filename: src/main.rs + ```rust,noplayground {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-11/src/main.rs:here}} ``` -Listing 16-11: Sending multiple messages from multiple -producers + This time, before we create the first spawned thread, we call `clone` on the transmitter. This will give us a new transmitter we can pass to the first diff --git a/src/ch16-03-shared-state.md b/src/ch16-03-shared-state.md index 918d162cf5..621f74b408 100644 --- a/src/ch16-03-shared-state.md +++ b/src/ch16-03-shared-state.md @@ -1,16 +1,16 @@ ## Shared-State Concurrency -Message passing is a fine way of handling concurrency, but it’s not the only -one. Another method would be for multiple threads to access the same shared -data. Consider this part of the slogan from the Go language documentation -again: “do not communicate by sharing memory.” +Message passing is a fine way to handle concurrency, but it’s not the only way. +Another method would be for multiple threads to access the same shared data. +Consider this part of the slogan from the Go language documentation again: “Do +not communicate by sharing memory.” What would communicating by sharing memory look like? In addition, why would message-passing enthusiasts caution not to use memory sharing? -In a way, channels in any programming language are similar to single ownership, +In a way, channels in any programming language are similar to single ownership because once you transfer a value down a channel, you should no longer use that -value. Shared memory concurrency is like multiple ownership: multiple threads +value. Shared-memory concurrency is like multiple ownership: Multiple threads can access the same memory location at the same time. As you saw in Chapter 15, where smart pointers made multiple ownership possible, multiple ownership can add complexity because these different owners need managing. Rust’s type system @@ -18,21 +18,25 @@ and ownership rules greatly assist in getting this management correct. For an example, let’s look at mutexes, one of the more common concurrency primitives for shared memory. -### Using Mutexes to Allow Access to Data from One Thread at a Time + -*Mutex* is an abbreviation for *mutual exclusion*, as in, a mutex allows only + + +### Controlling Access with Mutexes + +_Mutex_ is an abbreviation for _mutual exclusion_, as in a mutex allows only one thread to access some data at any given time. To access the data in a mutex, a thread must first signal that it wants access by asking to acquire the -mutex’s *lock*. The lock is a data structure that is part of the mutex that +mutex’s lock. The _lock_ is a data structure that is part of the mutex that keeps track of who currently has exclusive access to the data. Therefore, the -mutex is described as *guarding* the data it holds via the locking system. +mutex is described as _guarding_ the data it holds via the locking system. Mutexes have a reputation for being difficult to use because you have to remember two rules: -* You must attempt to acquire the lock before using the data. -* When you’re done with the data that the mutex guards, you must unlock the - data so other threads can acquire the lock. +1. You must attempt to acquire the lock before using the data. +2. When you’re done with the data that the mutex guards, you must unlock the + data so that other threads can acquire the lock. For a real-world metaphor for a mutex, imagine a panel discussion at a conference with only one microphone. Before a panelist can speak, they have to @@ -50,21 +54,20 @@ system and ownership rules, you can’t get locking and unlocking wrong. #### The API of `Mutex` As an example of how to use a mutex, let’s start by using a mutex in a -single-threaded context, as shown in Listing 16-12: +single-threaded context, as shown in Listing 16-12. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-12/src/main.rs}} ``` -Listing 16-12: Exploring the API of `Mutex` in a -single-threaded context for simplicity + As with many types, we create a `Mutex` using the associated function `new`. To access the data inside the mutex, we use the `lock` method to acquire the -lock. This call will block the current thread so it can’t do any work until -it’s our turn to have the lock. +lock. This call will block the current thread so that it can’t do any work +until it’s our turn to have the lock. The call to `lock` would fail if another thread holding the lock panicked. In that case, no one would ever be able to get the lock, so we’ve chosen to @@ -73,39 +76,40 @@ that case, no one would ever be able to get the lock, so we’ve chosen to After we’ve acquired the lock, we can treat the return value, named `num` in this case, as a mutable reference to the data inside. The type system ensures that we acquire a lock before using the value in `m`. The type of `m` is -`Mutex`, not `i32`, so we *must* call `lock` to be able to use the `i32` +`Mutex`, not `i32`, so we _must_ call `lock` to be able to use the `i32` value. We can’t forget; the type system won’t let us access the inner `i32` otherwise. -As you might suspect, `Mutex` is a smart pointer. More accurately, the call -to `lock` *returns* a smart pointer called `MutexGuard`, wrapped in a -`LockResult` that we handled with the call to `unwrap`. The `MutexGuard` smart -pointer implements `Deref` to point at our inner data; the smart pointer also -has a `Drop` implementation that releases the lock automatically when a -`MutexGuard` goes out of scope, which happens at the end of the inner scope. As -a result, we don’t risk forgetting to release the lock and blocking the mutex -from being used by other threads, because the lock release happens -automatically. +The call to `lock` returns a type called `MutexGuard`, wrapped in a +`LockResult` that we handled with the call to `unwrap`. The `MutexGuard` type +implements `Deref` to point at our inner data; the type also has a `Drop` +implementation that releases the lock automatically when a `MutexGuard` goes +out of scope, which happens at the end of the inner scope. As a result, we +don’t risk forgetting to release the lock and blocking the mutex from being +used by other threads because the lock release happens automatically. After dropping the lock, we can print the mutex value and see that we were able -to change the inner `i32` to 6. +to change the inner `i32` to `6`. + + -#### Sharing a `Mutex` Between Multiple Threads + -Now, let’s try to share a value between multiple threads using `Mutex`. -We’ll spin up 10 threads and have them each increment a counter value by 1, so -the counter goes from 0 to 10. The next example in Listing 16-13 will have -a compiler error, and we’ll use that error to learn more about using -`Mutex` and how Rust helps us use it correctly. +#### Shared Access to `Mutex` -Filename: src/main.rs +Now let’s try to share a value between multiple threads using `Mutex`. We’ll +spin up 10 threads and have them each increment a counter value by 1, so the +counter goes from 0 to 10. The example in Listing 16-13 will have a compiler +error, and we’ll use that error to learn more about using `Mutex` and how +Rust helps us use it correctly. + + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-13/src/main.rs}} ``` -Listing 16-13: Ten threads each increment a counter -guarded by a `Mutex` + We create a `counter` variable to hold an `i32` inside a `Mutex`, as we did in Listing 16-12. Next, we create 10 threads by iterating over a range of @@ -113,7 +117,7 @@ numbers. We use `thread::spawn` and give all the threads the same closure: one that moves the counter into the thread, acquires a lock on the `Mutex` by calling the `lock` method, and then adds 1 to the value in the mutex. When a thread finishes running its closure, `num` will go out of scope and release the -lock so another thread can acquire it. +lock so that another thread can acquire it. In the main thread, we collect all the join handles. Then, as we did in Listing 16-2, we call `join` on each handle to make sure all the threads finish. At @@ -127,28 +131,27 @@ We hinted that this example wouldn’t compile. Now let’s find out why! ``` The error message states that the `counter` value was moved in the previous -iteration of the loop. Rust is telling us that we can’t move the ownership -of lock `counter` into multiple threads. Let’s fix the compiler error with a +iteration of the loop. Rust is telling us that we can’t move the ownership of +lock `counter` into multiple threads. Let’s fix the compiler error with the multiple-ownership method we discussed in Chapter 15. #### Multiple Ownership with Multiple Threads -In Chapter 15, we gave a value multiple owners by using the smart pointer -`Rc` to create a reference counted value. Let’s do the same here and see +In Chapter 15, we gave a value to multiple owners by using the smart pointer +`Rc` to create a reference-counted value. Let’s do the same here and see what happens. We’ll wrap the `Mutex` in `Rc` in Listing 16-14 and clone the `Rc` before moving ownership to the thread. -Filename: src/main.rs + ```rust,ignore,does_not_compile {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-14/src/main.rs}} ``` -Listing 16-14: Attempting to use `Rc` to allow -multiple threads to own the `Mutex` + Once again, we compile and get... different errors! The compiler is teaching us -a lot. +a lot: ```console {{#include ../listings/ch16-fearless-concurrency/listing-16-14/output.txt}} @@ -156,9 +159,9 @@ a lot. Wow, that error message is very wordy! Here’s the important part to focus on: `` `Rc>` cannot be sent between threads safely ``. The compiler is -also telling us the reason why: ``the trait `Send` is not implemented for -`Rc>` ``. We’ll talk about `Send` in the next section: it’s one of -the traits that ensures the types we use with threads are meant for use in +also telling us the reason why: `` the trait `Send` is not implemented for +`Rc>` ``. We’ll talk about `Send` in the next section: It’s one of +the traits that ensures that the types we use with threads are meant for use in concurrent situations. Unfortunately, `Rc` is not safe to share across threads. When `Rc` @@ -167,15 +170,15 @@ subtracts from the count when each clone is dropped. But it doesn’t use any concurrency primitives to make sure that changes to the count can’t be interrupted by another thread. This could lead to wrong counts—subtle bugs that could in turn lead to memory leaks or a value being dropped before we’re done -with it. What we need is a type exactly like `Rc` but one that makes changes -to the reference count in a thread-safe way. +with it. What we need is a type that is exactly like `Rc`, but that makes +changes to the reference count in a thread-safe way. #### Atomic Reference Counting with `Arc` -Fortunately, `Arc` *is* a type like `Rc` that is safe to use in -concurrent situations. The *a* stands for *atomic*, meaning it’s an *atomically -reference counted* type. Atomics are an additional kind of concurrency -primitive that we won’t cover in detail here: see the standard library +Fortunately, `Arc` _is_ a type like `Rc` that is safe to use in +concurrent situations. The _a_ stands for _atomic_, meaning it’s an _atomically +reference-counted_ type. Atomics are an additional kind of concurrency +primitive that we won’t cover in detail here: See the standard library documentation for [`std::sync::atomic`][atomic] for more details. At this point, you just need to know that atomics work like primitive types but are safe to share across threads. @@ -189,16 +192,15 @@ guarantees atomics provide. Let’s return to our example: `Arc` and `Rc` have the same API, so we fix our program by changing the `use` line, the call to `new`, and the call to -`clone`. The code in Listing 16-15 will finally compile and run: +`clone`. The code in Listing 16-15 will finally compile and run. -Filename: src/main.rs + ```rust {{#rustdoc_include ../listings/ch16-fearless-concurrency/listing-16-15/src/main.rs}} ``` -Listing 16-15: Using an `Arc` to wrap the `Mutex` -to be able to share ownership across multiple threads + This code will print the following: @@ -221,24 +223,28 @@ Note that if you are doing simple numerical operations, there are types simpler than `Mutex` types provided by the [`std::sync::atomic` module of the standard library][atomic]. These types provide safe, concurrent, atomic access to primitive types. We chose to use `Mutex` with a primitive -type for this example so we could concentrate on how `Mutex` works. +type for this example so that we could concentrate on how `Mutex` works. + + + + -### Similarities Between `RefCell`/`Rc` and `Mutex`/`Arc` +### Comparing `RefCell`/`Rc` and `Mutex`/`Arc` -You might have noticed that `counter` is immutable but we could get a mutable -reference to the value inside it; this means `Mutex` provides interior -mutability, as the `Cell` family does. In the same way we used `RefCell` in -Chapter 15 to allow us to mutate contents inside an `Rc`, we use `Mutex` -to mutate contents inside an `Arc`. +You might have noticed that `counter` is immutable but that we could get a +mutable reference to the value inside it; this means `Mutex` provides +interior mutability, as the `Cell` family does. In the same way we used +`RefCell` in Chapter 15 to allow us to mutate contents inside an `Rc`, we +use `Mutex` to mutate contents inside an `Arc`. Another detail to note is that Rust can’t protect you from all kinds of logic -errors when you use `Mutex`. Recall in Chapter 15 that using `Rc` came +errors when you use `Mutex`. Recall from Chapter 15 that using `Rc` came with the risk of creating reference cycles, where two `Rc` values refer to each other, causing memory leaks. Similarly, `Mutex` comes with the risk of -creating *deadlocks*. These occur when an operation needs to lock two resources +creating _deadlocks_. These occur when an operation needs to lock two resources and two threads have each acquired one of the locks, causing them to wait for each other forever. If you’re interested in deadlocks, try creating a Rust -program that has a deadlock; then research deadlock mitigation strategies for +program that has a deadlock; then, research deadlock mitigation strategies for mutexes in any language and have a go at implementing them in Rust. The standard library API documentation for `Mutex` and `MutexGuard` offers useful information. diff --git a/src/ch16-04-extensible-concurrency-sync-and-send.md b/src/ch16-04-extensible-concurrency-sync-and-send.md index 4586b8d2c4..a866b6174f 100644 --- a/src/ch16-04-extensible-concurrency-sync-and-send.md +++ b/src/ch16-04-extensible-concurrency-sync-and-send.md @@ -1,60 +1,75 @@ -## Extensible Concurrency with the `Sync` and `Send` Traits + -Interestingly, the Rust language has *very* few concurrency features. Almost -every concurrency feature we’ve talked about so far in this chapter has been -part of the standard library, not the language. Your options for handling -concurrency are not limited to the language or the standard library; you can -write your own concurrency features or use those written by others. + + -However, two concurrency concepts are embedded in the language: the -`std::marker` traits `Sync` and `Send`. +## Extensible Concurrency with `Send` and `Sync` -### Allowing Transference of Ownership Between Threads with `Send` +Interestingly, almost every concurrency feature we’ve talked about so far in +this chapter has been part of the standard library, not the language. Your +options for handling concurrency are not limited to the language or the +standard library; you can write your own concurrency features or use those +written by others. + +However, among the key concurrency concepts that are embedded in the language +rather than the standard library are the `std::marker` traits `Send` and `Sync`. + + + + + +### Transferring Ownership Between Threads The `Send` marker trait indicates that ownership of values of the type implementing `Send` can be transferred between threads. Almost every Rust type -is `Send`, but there are some exceptions, including `Rc`: this cannot be -`Send` because if you cloned an `Rc` value and tried to transfer ownership -of the clone to another thread, both threads might update the reference count -at the same time. For this reason, `Rc` is implemented for use in -single-threaded situations where you don’t want to pay the thread-safe -performance penalty. +implements `Send`, but there are some exceptions, including `Rc`: This +cannot implement `Send` because if you cloned an `Rc` value and tried to +transfer ownership of the clone to another thread, both threads might update +the reference count at the same time. For this reason, `Rc` is implemented +for use in single-threaded situations where you don’t want to pay the +thread-safe performance penalty. Therefore, Rust’s type system and trait bounds ensure that you can never accidentally send an `Rc` value across threads unsafely. When we tried to do -this in Listing 16-14, we got the error `the trait Send is not implemented for -Rc>`. When we switched to `Arc`, which is `Send`, the code -compiled. +this in Listing 16-14, we got the error `` the trait `Send` is not implemented +for `Rc>` ``. When we switched to `Arc`, which does implement +`Send`, the code compiled. Any type composed entirely of `Send` types is automatically marked as `Send` as well. Almost all primitive types are `Send`, aside from raw pointers, which -we’ll discuss in Chapter 19. +we’ll discuss in Chapter 20. -### Allowing Access from Multiple Threads with `Sync` + + + + +### Accessing from Multiple Threads The `Sync` marker trait indicates that it is safe for the type implementing -`Sync` to be referenced from multiple threads. In other words, any type `T` is -`Sync` if `&T` (an immutable reference to `T`) is `Send`, meaning the reference -can be sent safely to another thread. Similar to `Send`, primitive types are -`Sync`, and types composed entirely of types that are `Sync` are also `Sync`. - -The smart pointer `Rc` is also not `Sync` for the same reasons that it’s not -`Send`. The `RefCell` type (which we talked about in Chapter 15) and the -family of related `Cell` types are not `Sync`. The implementation of borrow -checking that `RefCell` does at runtime is not thread-safe. The smart -pointer `Mutex` is `Sync` and can be used to share access with multiple -threads as you saw in the [“Sharing a `Mutex` Between Multiple -Threads”][sharing-a-mutext-between-multiple-threads] section. +`Sync` to be referenced from multiple threads. In other words, any type `T` +implements `Sync` if `&T` (an immutable reference to `T`) implements `Send`, +meaning the reference can be sent safely to another thread. Similar to `Send`, +primitive types all implement `Sync`, and types composed entirely of types that +implement `Sync` also implement `Sync`. + +The smart pointer `Rc` also doesn’t implement `Sync` for the same reasons +that it doesn’t implement `Send`. The `RefCell` type (which we talked about +in Chapter 15) and the family of related `Cell` types don’t implement +`Sync`. The implementation of borrow checking that `RefCell` does at runtime +is not thread-safe. The smart pointer `Mutex` implements `Sync` and can be +used to share access with multiple threads, as you saw in [“Shared Access to +`Mutex`”][shared-access]. ### Implementing `Send` and `Sync` Manually Is Unsafe -Because types that are made up of `Send` and `Sync` traits are automatically -also `Send` and `Sync`, we don’t have to implement those traits manually. As -marker traits, they don’t even have any methods to implement. They’re just -useful for enforcing invariants related to concurrency. +Because types composed entirely of other types that implement the `Send` and +`Sync` traits also automatically implement `Send` and `Sync`, we don’t have to +implement those traits manually. As marker traits, they don’t even have any +methods to implement. They’re just useful for enforcing invariants related to +concurrency. Manually implementing these traits involves implementing unsafe Rust code. -We’ll talk about using unsafe Rust code in Chapter 19; for now, the important +We’ll talk about using unsafe Rust code in Chapter 20; for now, the important information is that building new concurrent types not made up of `Send` and `Sync` parts requires careful thought to uphold the safety guarantees. [“The Rustonomicon”][nomicon] has more information about these guarantees and how to @@ -62,9 +77,10 @@ uphold them. ## Summary -This isn’t the last you’ll see of concurrency in this book: the project in -Chapter 20 will use the concepts in this chapter in a more realistic situation -than the smaller examples discussed here. +This isn’t the last you’ll see of concurrency in this book: The next chapter +focuses on async programming, and the project in Chapter 21 will use the +concepts in this chapter in a more realistic situation than the smaller +examples discussed here. As mentioned earlier, because very little of how Rust handles concurrency is part of the language, many concurrency solutions are implemented as crates. @@ -79,12 +95,7 @@ code using these solutions won’t end up with data races or invalid references. Once you get your code to compile, you can rest assured that it will happily run on multiple threads without the kinds of hard-to-track-down bugs common in other languages. Concurrent programming is no longer a concept to be afraid of: -go forth and make your programs concurrent, fearlessly! - -Next, we’ll talk about idiomatic ways to model problems and structure solutions -as your Rust programs get bigger. In addition, we’ll discuss how Rust’s idioms -relate to those you might be familiar with from object-oriented programming. +Go forth and make your programs concurrent, fearlessly! -[sharing-a-mutext-between-multiple-threads]: -ch16-03-shared-state.html#sharing-a-mutext-between-multiple-threads +[shared-access]: ch16-03-shared-state.html#shared-access-to-mutext [nomicon]: ../nomicon/index.html diff --git a/src/ch17-00-async-await.md b/src/ch17-00-async-await.md new file mode 100644 index 0000000000..8564b1e41d --- /dev/null +++ b/src/ch17-00-async-await.md @@ -0,0 +1,167 @@ +# Fundamentals of Asynchronous Programming: Async, Await, Futures, and Streams + +Many operations we ask the computer to do can take a while to finish. It would +be nice if we could do something else while we’re waiting for those +long-running processes to complete. Modern computers offer two techniques for +working on more than one operation at a time: parallelism and concurrency. Our +programs’ logic, however, is written in a mostly linear fashion. We’d like to +be able to specify the operations a program should perform and points at which +a function could pause and some other part of the program could run instead, +without needing to specify up front exactly the order and manner in which each +bit of code should run. _Asynchronous programming_ is an abstraction that lets +us express our code in terms of potential pausing points and eventual results +that takes care of the details of coordination for us. + +This chapter builds on Chapter 16’s use of threads for parallelism and +concurrency by introducing an alternative approach to writing code: Rust’s +futures, streams, and the `async` and `await` syntax that let us express how +operations could be asynchronous, and the third-party crates that implement +asynchronous runtimes: code that manages and coordinates the execution of +asynchronous operations. + +Let’s consider an example. Say you’re exporting a video you’ve created of a +family celebration, an operation that could take anywhere from minutes to +hours. The video export will use as much CPU and GPU power as it can. If you +had only one CPU core and your operating system didn’t pause that export until +it completed—that is, if it executed the export _synchronously_—you couldn’t do +anything else on your computer while that task was running. That would be a +pretty frustrating experience. Fortunately, your computer’s operating system +can, and does, invisibly interrupt the export often enough to let you get other +work done simultaneously. + +Now say you’re downloading a video shared by someone else, which can also take +a while but does not take up as much CPU time. In this case, the CPU has to +wait for data to arrive from the network. While you can start reading the data +once it starts to arrive, it might take some time for all of it to show up. +Even once the data is all present, if the video is quite large, it could take +at least a second or two to load it all. That might not sound like much, but +it’s a very long time for a modern processor, which can perform billions of +operations every second. Again, your operating system will invisibly interrupt +your program to allow the CPU to perform other work while waiting for the +network call to finish. + +The video export is an example of a _CPU-bound_ or _compute-bound_ operation. +It’s limited by the computer’s potential data processing speed within the CPU +or GPU, and how much of that speed it can dedicate to the operation. The video +download is an example of an _I/O-bound_ operation, because it’s limited by the +speed of the computer’s _input and output_; it can only go as fast as the data +can be sent across the network. + +In both of these examples, the operating system’s invisible interrupts provide +a form of concurrency. That concurrency happens only at the level of the entire +program, though: the operating system interrupts one program to let other +programs get work done. In many cases, because we understand our programs at a +much more granular level than the operating system does, we can spot +opportunities for concurrency that the operating system can’t see. + +For example, if we’re building a tool to manage file downloads, we should be +able to write our program so that starting one download won’t lock up the UI, +and users should be able to start multiple downloads at the same time. Many +operating system APIs for interacting with the network are _blocking_, though; +that is, they block the program’s progress until the data they’re processing is +completely ready. + +> Note: This is how _most_ function calls work, if you think about it. However, +> the term _blocking_ is usually reserved for function calls that interact with +> files, the network, or other resources on the computer, because those are the +> cases where an individual program would benefit from the operation being +> _non_-blocking. + +We could avoid blocking our main thread by spawning a dedicated thread to +download each file. However, the overhead of the system resources used by those +threads would eventually become a problem. It would be preferable if the call +didn’t block in the first place, and instead we could define a number of tasks +that we’d like our program to complete and allow the runtime to choose the best +order and manner in which to run them. + +That is exactly what Rust’s _async_ (short for _asynchronous_) abstraction +gives us. In this chapter, you’ll learn all about async as we cover the +following topics: + +- How to use Rust’s `async` and `await` syntax and execute asynchronous + functions with a runtime +- How to use the async model to solve some of the same challenges we looked at + in Chapter 16 +- How multithreading and async provide complementary solutions that you can + combine in many cases + +Before we see how async works in practice, though, we need to take a short +detour to discuss the differences between parallelism and concurrency. + +## Parallelism and Concurrency + +We’ve treated parallelism and concurrency as mostly interchangeable so far. Now +we need to distinguish between them more precisely, because the differences +will show up as we start working. + +Consider the different ways a team could split up work on a software project. +You could assign a single member multiple tasks, assign each member one task, +or use a mix of the two approaches. + +When an individual works on several different tasks before any of them is +complete, this is _concurrency_. One way to implement concurrency is similar to +having two different projects checked out on your computer, and when you get +bored or stuck on one project, you switch to the other. You’re just one person, +so you can’t make progress on both tasks at the exact same time, but you can +multitask, making progress on one at a time by switching between them (see +Figure 17-1). + +
+ +A diagram with stacked boxes labeled Task A and Task B, with diamonds in them representing subtasks. Arrows point from A1 to B1, B1 to A2, A2 to B2, B2 to A3, A3 to A4, and A4 to B3. The arrows between the subtasks cross the boxes between Task A and Task B. + +
Figure 17-1: A concurrent workflow, switching between Task A and Task B
+ +
+ +When the team splits up a group of tasks by having each member take one task +and work on it alone, this is _parallelism_. Each person on the team can make +progress at the exact same time (see Figure 17-2). + +
+ +A diagram with stacked boxes labeled Task A and Task B, with diamonds in them representing subtasks. Arrows point from A1 to A2, A2 to A3, A3 to A4, B1 to B2, and B2 to B3. No arrows cross between the boxes for Task A and Task B. + +
Figure 17-2: A parallel workflow, where work happens on Task A and Task B independently
+ +
+ +In both of these workflows, you might have to coordinate between different +tasks. Maybe you thought the task assigned to one person was totally +independent from everyone else’s work, but it actually requires another person +on the team to finish their task first. Some of the work could be done in +parallel, but some of it was actually _serial_: it could only happen in a +series, one task after the other, as in Figure 17-3. + +
+ +A diagram with stacked boxes labeled Task A and Task B, with diamonds in them representing subtasks. In Task A, arrows point from A1 to A2, from A2 to a pair of thick vertical lines like a “pause” symbol, and from that symbol to A3. In task B, arrows point from B1 to B2, from B2 to B3, from B3 to A3, and from B3 to B4. + +
Figure 17-3: A partially parallel workflow, where work happens on Task A and Task B independently until Task A3 is blocked on the results of Task B3.
+ +
+ +Likewise, you might realize that one of your own tasks depends on another of +your tasks. Now your concurrent work has also become serial. + +Parallelism and concurrency can intersect with each other, too. If you learn +that a colleague is stuck until you finish one of your tasks, you’ll probably +focus all your efforts on that task to “unblock” your colleague. You and your +coworker are no longer able to work in parallel, and you’re also no longer able +to work concurrently on your own tasks. + +The same basic dynamics come into play with software and hardware. On a machine +with a single CPU core, the CPU can perform only one operation at a time, but +it can still work concurrently. Using tools such as threads, processes, and +async, the computer can pause one activity and switch to others before +eventually cycling back to that first activity again. On a machine with +multiple CPU cores, it can also do work in parallel. One core can be performing +one task while another core performs a completely unrelated one, and those +operations actually happen at the same time. + +Running async code in Rust usually happens concurrently. Depending on the +hardware, the operating system, and the async runtime we are using (more on +async runtimes shortly), that concurrency may also use parallelism under the +hood. + +Now, let’s dive into how async programming in Rust actually works. diff --git a/src/ch17-01-futures-and-syntax.md b/src/ch17-01-futures-and-syntax.md new file mode 100644 index 0000000000..4ac55c467a --- /dev/null +++ b/src/ch17-01-futures-and-syntax.md @@ -0,0 +1,405 @@ +## Futures and the Async Syntax + +The key elements of asynchronous programming in Rust are _futures_ and Rust’s +`async` and `await` keywords. + +A _future_ is a value that may not be ready now but will become ready at some +point in the future. (This same concept shows up in many languages, sometimes +under other names such as _task_ or _promise_.) Rust provides a `Future` trait +as a building block so that different async operations can be implemented with +different data structures but with a common interface. In Rust, futures are +types that implement the `Future` trait. Each future holds its own information +about the progress that has been made and what “ready” means. + +You can apply the `async` keyword to blocks and functions to specify that they +can be interrupted and resumed. Within an async block or async function, you +can use the `await` keyword to _await a future_ (that is, wait for it to become +ready). Any point where you await a future within an async block or function is +a potential spot for that block or function to pause and resume. The process of +checking with a future to see if its value is available yet is called _polling_. + +Some other languages, such as C# and JavaScript, also use `async` and `await` +keywords for async programming. If you’re familiar with those languages, you +may notice some significant differences in how Rust handles the syntax. That’s +for good reason, as we’ll see! + +When writing async Rust, we use the `async` and `await` keywords most of the +time. Rust compiles them into equivalent code using the `Future` trait, much as +it compiles `for` loops into equivalent code using the `Iterator` trait. +Because Rust provides the `Future` trait, though, you can also implement it for +your own data types when you need to. Many of the functions we’ll see +throughout this chapter return types with their own implementations of +`Future`. We’ll return to the definition of the trait at the end of the chapter +and dig into more of how it works, but this is enough detail to keep us moving +forward. + +This may all feel a bit abstract, so let’s write our first async program: a +little web scraper. We’ll pass in two URLs from the command line, fetch both of +them concurrently, and return the result of whichever one finishes first. This +example will have a fair bit of new syntax, but don’t worry—we’ll explain +everything you need to know as we go. + +## Our First Async Program + +To keep the focus of this chapter on learning async rather than juggling parts +of the ecosystem, we’ve created the `trpl` crate (`trpl` is short for “The Rust +Programming Language”). It re-exports all the types, traits, and functions +you’ll need, primarily from the [`futures`][futures-crate] and +[`tokio`][tokio] crates. The `futures` crate is an official home +for Rust experimentation for async code, and it’s actually where the `Future` +trait was originally designed. Tokio is the most widely used async runtime in +Rust today, especially for web applications. There are other great runtimes out +there, and they may be more suitable for your purposes. We use the `tokio` +crate under the hood for `trpl` because it’s well tested and widely used. + +In some cases, `trpl` also renames or wraps the original APIs to keep you +focused on the details relevant to this chapter. If you want to understand what +the crate does, we encourage you to check out [its source code][crate-source]. +You’ll be able to see what crate each re-export comes from, and we’ve left +extensive comments explaining what the crate does. + +Create a new binary project named `hello-async` and add the `trpl` crate as a +dependency: + +```console +$ cargo new hello-async +$ cd hello-async +$ cargo add trpl +``` + +Now we can use the various pieces provided by `trpl` to write our first async +program. We’ll build a little command line tool that fetches two web pages, +pulls the `` element from each, and prints out the title of whichever +page finishes that whole process first. + +### Defining the page_title Function + +Let’s start by writing a function that takes one page URL as a parameter, makes +a request to it, and returns the text of the `<title>` element (see Listing +17-1). + +<Listing number="17-1" file-name="src/main.rs" caption="Defining an async function to get the title element from an HTML page"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-01/src/main.rs:all}} +``` + +</Listing> + +First, we define a function named `page_title` and mark it with the `async` +keyword. Then we use the `trpl::get` function to fetch whatever URL is passed +in and add the `await` keyword to await the response. To get the text of the +`response`, we call its `text` method and once again await it with the `await` +keyword. Both of these steps are asynchronous. For the `get` function, we have +to wait for the server to send back the first part of its response, which will +include HTTP headers, cookies, and so on and can be delivered separately from +the response body. Especially if the body is very large, it can take some time +for it all to arrive. Because we have to wait for the _entirety_ of the +response to arrive, the `text` method is also async. + +We have to explicitly await both of these futures, because futures in Rust are +_lazy_: they don’t do anything until you ask them to with the `await` keyword. +(In fact, Rust will show a compiler warning if you don’t use a future.) This +might remind you of the discussion of iterators in the [“Processing a Series of +Items with Iterators”][iterators-lazy]<!-- ignore --> section in Chapter 13. +Iterators do nothing unless you call their `next` method—whether directly or by +using `for` loops or methods such as `map` that use `next` under the hood. +Likewise, futures do nothing unless you explicitly ask them to. This laziness +allows Rust to avoid running async code until it’s actually needed. + +> Note: This is different from the behavior we saw when using `thread::spawn` +> in the [“Creating a New Thread with spawn”][thread-spawn]<!-- ignore --> +> section in Chapter 16, where the closure we passed to another thread started +> running immediately. It’s also different from how many other languages +> approach async. But it’s important for Rust to be able to provide its +> performance guarantees, just as it is with iterators. + +Once we have `response_text`, we can parse it into an instance of the `Html` +type using `Html::parse`. Instead of a raw string, we now have a data type we +can use to work with the HTML as a richer data structure. In particular, we can +use the `select_first` method to find the first instance of a given CSS +selector. By passing the string `"title"`, we’ll get the first `<title>` +element in the document, if there is one. Because there may not be any matching +element, `select_first` returns an `Option<ElementRef>`. Finally, we use the +`Option::map` method, which lets us work with the item in the `Option` if it’s +present, and do nothing if it isn’t. (We could also use a `match` expression +here, but `map` is more idiomatic.) In the body of the function we supply to +`map`, we call `inner_html` on the `title` to get its content, which is a +`String`. When all is said and done, we have an `Option<String>`. + +Notice that Rust’s `await` keyword goes _after_ the expression you’re awaiting, +not before it. That is, it’s a _postfix_ keyword. This may differ from what +you’re used to if you’ve used `async` in other languages, but in Rust it makes +chains of methods much nicer to work with. As a result, we could change the +body of `page_title` to chain the `trpl::get` and `text` function calls +together with `await` between them, as shown in Listing 17-2. + +<Listing number="17-2" file-name="src/main.rs" caption="Chaining with the `await` keyword"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-02/src/main.rs:chaining}} +``` + +</Listing> + +With that, we have successfully written our first async function! Before we add +some code in `main` to call it, let’s talk a little more about what we’ve +written and what it means. + +When Rust sees a _block_ marked with the `async` keyword, it compiles it into a +unique, anonymous data type that implements the `Future` trait. When Rust sees +a _function_ marked with `async`, it compiles it into a non-async function +whose body is an async block. An async function’s return type is the type of +the anonymous data type the compiler creates for that async block. + +Thus, writing `async fn` is equivalent to writing a function that returns a +_future_ of the return type. To the compiler, a function definition such as the +`async fn page_title` in Listing 17-1 is roughly equivalent to a non-async +function defined like this: + +```rust +# extern crate trpl; // required for mdbook test +use std::future::Future; +use trpl::Html; + +fn page_title(url: &str) -> impl Future<Output = Option<String>> { + async move { + let text = trpl::get(url).await.text().await; + Html::parse(&text) + .select_first("title") + .map(|title| title.inner_html()) + } +} +``` + +Let’s walk through each part of the transformed version: + +- It uses the `impl Trait` syntax we discussed back in Chapter 10 in the + [“Traits as Parameters”][impl-trait]<!-- ignore --> section. +- The returned value implements the `Future` trait with an associated type of + `Output`. Notice that the `Output` type is `Option<String>`, which is the + same as the original return type from the `async fn` version of `page_title`. +- All of the code called in the body of the original function is wrapped in + an `async move` block. Remember that blocks are expressions. This whole block + is the expression returned from the function. +- This async block produces a value with the type `Option<String>`, as just + described. That value matches the `Output` type in the return type. This is + just like other blocks you have seen. +- The new function body is an `async move` block because of how it uses the + `url` parameter. (We’ll talk much more about `async` versus `async move` + later in the chapter.) + +Now we can call `page_title` in `main`. + +<!-- Old headings. Do not remove or links may break. --> + +<a id ="determining-a-single-pages-title"></a> + +### Executing an Async Function with a Runtime + +To start, we’ll get the title for a single page, shown in Listing 17-3. +Unfortunately, this code doesn’t compile yet. + +<Listing number="17-3" file-name="src/main.rs" caption="Calling the `page_title` function from `main` with a user-supplied argument"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch17-async-await/listing-17-03/src/main.rs:main}} +``` + +</Listing> + +We follow the same pattern we used to get command line arguments in the +[“Accepting Command Line Arguments”][cli-args]<!-- ignore --> section in +Chapter 12. Then we pass the URL argument to `page_title` and await the result. +Because the value produced by the future is an `Option<String>`, we use a +`match` expression to print different messages to account for whether the page +had a `<title>`. + +The only place we can use the `await` keyword is in async functions or blocks, +and Rust won’t let us mark the special `main` function as `async`. + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-03 +cargo build +copy just the compiler error +--> + +```text +error[E0752]: `main` function is not allowed to be `async` + --> src/main.rs:6:1 + | +6 | async fn main() { + | ^^^^^^^^^^^^^^^ `main` function is not allowed to be `async` +``` + +The reason `main` can’t be marked `async` is that async code needs a _runtime_: +a Rust crate that manages the details of executing asynchronous code. A +program’s `main` function can _initialize_ a runtime, but it’s not a runtime +_itself_. (We’ll see more about why this is the case in a bit.) Every Rust +program that executes async code has at least one place where it sets up a +runtime that executes the futures. + +Most languages that support async bundle a runtime, but Rust does not. Instead, +there are many different async runtimes available, each of which makes different +tradeoffs suitable to the use case it targets. For example, a high-throughput +web server with many CPU cores and a large amount of RAM has very different +needs than a microcontroller with a single core, a small amount of RAM, and no +heap allocation ability. The crates that provide those runtimes also often +supply async versions of common functionality such as file or network I/O. + +Here, and throughout the rest of this chapter, we’ll use the `block_on` +function from the `trpl` crate, which takes a future as an argument and blocks +the current thread until this future runs to completion. Behind the scenes, +calling `block_on` sets up a runtime using the `tokio` crate that’s used to run +the future passed in (the `trpl` crate’s `block_on` behavior is similar to +other runtime crates’ `block_on` functions). Once the future completes, +`block_on` returns whatever value the future produced. + +We could pass the future returned by `page_title` directly to `block_on` and, +once it completed, we could match on the resulting `Option<String>` as we tried +to do in Listing 17-3. However, for most of the examples in the chapter (and +most async code in the real world), we’ll be doing more than just one async +function call, so instead we’ll pass an `async` block and explicitly await the +result of the `page_title` call, as in Listing 17-4. + +<Listing number="17-4" caption="Awaiting an async block with `trpl::block_on`" file-name="src/main.rs"> + +<!-- should_panic,noplayground because mdbook test does not pass args --> + +```rust,should_panic,noplayground +{{#rustdoc_include ../listings/ch17-async-await/listing-17-04/src/main.rs:run}} +``` + +</Listing> + +When we run this code, we get the behavior we expected initially: + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-04 +cargo build # skip all the build noise +cargo run -- "https://www.rust-lang.org" +# copy the output here +--> + +```console +$ cargo run -- "https://www.rust-lang.org" + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s + Running `target/debug/async_await 'https://www.rust-lang.org'` +The title for https://www.rust-lang.org was + Rust Programming Language +``` + +Phew—we finally have some working async code! But before we add the code to +race two sites against each other, let’s briefly turn our attention back to how +futures work. + +Each _await point_—that is, every place where the code uses the `await` +keyword—represents a place where control is handed back to the runtime. To make +that work, Rust needs to keep track of the state involved in the async block so +that the runtime could kick off some other work and then come back when it’s +ready to try advancing the first one again. This is an invisible state machine, +as if you’d written an enum like this to save the current state at each await +point: + +```rust +{{#rustdoc_include ../listings/ch17-async-await/no-listing-state-machine/src/lib.rs:enum}} +``` + +Writing the code to transition between each state by hand would be tedious and +error-prone, however, especially when you need to add more functionality and +more states to the code later. Fortunately, the Rust compiler creates and +manages the state machine data structures for async code automatically. The +normal borrowing and ownership rules around data structures all still apply, +and happily, the compiler also handles checking those for us and provides +useful error messages. We’ll work through a few of those later in the chapter. + +Ultimately, something has to execute this state machine, and that something is +a runtime. (This is why you may come across mentions of _executors_ when +looking into runtimes: an executor is the part of a runtime responsible for +executing the async code.) + +Now you can see why the compiler stopped us from making `main` itself an async +function back in Listing 17-3. If `main` were an async function, something else +would need to manage the state machine for whatever future `main` returned, but +`main` is the starting point for the program! Instead, we called the +`trpl::block_on` function in `main` to set up a runtime and run the future +returned by the `async` block until it’s done. + +> Note: Some runtimes provide macros so you _can_ write an async `main` +> function. Those macros rewrite `async fn main() { ... }` to be a normal `fn +> main`, which does the same thing we did by hand in Listing 17-4: call a +> function that runs a future to completion the way `trpl::block_on` does. + +Now let’s put these pieces together and see how we can write concurrent code. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="racing-our-two-urls-against-each-other"></a> + +### Racing Two URLs Against Each Other Concurrently + +In Listing 17-5, we call `page_title` with two different URLs passed in from the +command line and race them by selecting whichever future finishes first. + +<Listing number="17-5" caption="Calling `page_title` for two URLs to see which returns first" file-name="src/main.rs"> + +<!-- should_panic,noplayground because mdbook does not pass args --> + +```rust,should_panic,noplayground +{{#rustdoc_include ../listings/ch17-async-await/listing-17-05/src/main.rs:all}} +``` + +</Listing> + +We begin by calling `page_title` for each of the user-supplied URLs. We save +the resulting futures as `title_fut_1` and `title_fut_2`. Remember, these don’t +do anything yet, because futures are lazy and we haven’t yet awaited them. Then +we pass the futures to `trpl::select`, which returns a value to indicate which +of the futures passed to it finishes first. + +> Note: Under the hood, `trpl::select` is built on a more general `select` +> function defined in the `futures` crate. The `futures` crate’s `select` +> function can do a lot of things that the `trpl::select` function can’t, but +> it also has some additional complexity that we can skip over for now. + +Either future can legitimately “win,” so it doesn’t make sense to return a +`Result`. Instead, `trpl::select` returns a type we haven’t seen before, +`trpl::Either`. The `Either` type is somewhat similar to a `Result` in that it +has two cases. Unlike `Result`, though, there is no notion of success or +failure baked into `Either`. Instead, it uses `Left` and `Right` to indicate +“one or the other”: + +```rust +enum Either<A, B> { + Left(A), + Right(B), +} +``` + +The `select` function returns `Left` with that future’s output if the first +argument wins, and `Right` with the second future argument’s output if _that_ +one wins. This matches the order the arguments appear in when calling the +function: the first argument is to the left of the second argument. + +We also update `page_title` to return the same URL passed in. That way, if the +page that returns first does not have a `<title>` we can resolve, we can still +print a meaningful message. With that information available, we wrap up by +updating our `println!` output to indicate both which URL finished first and +what, if any, the `<title>` is for the web page at that URL. + +You have built a small working web scraper now! Pick a couple URLs and run the +command line tool. You may discover that some sites are consistently faster +than others, while in other cases the faster site varies from run to run. More +importantly, you’ve learned the basics of working with futures, so now we can +dig deeper into what we can do with async. + +[impl-trait]: ch10-02-traits.html#traits-as-parameters +[iterators-lazy]: ch13-02-iterators.html +[thread-spawn]: ch16-01-threads.html#creating-a-new-thread-with-spawn +[cli-args]: ch12-01-accepting-command-line-arguments.html + +<!-- TODO: map source link version to version of Rust? --> + +[crate-source]: https://github.com/rust-lang/book/tree/main/packages/trpl +[futures-crate]: https://crates.io/crates/futures +[tokio]: https://tokio.rs diff --git a/src/ch17-02-concurrency-with-async.md b/src/ch17-02-concurrency-with-async.md new file mode 100644 index 0000000000..783053702a --- /dev/null +++ b/src/ch17-02-concurrency-with-async.md @@ -0,0 +1,421 @@ +<!-- Old headings. Do not remove or links may break. --> + +<a id="concurrency-with-async"></a> + +## Applying Concurrency with Async + +In this section, we’ll apply async to some of the same concurrency challenges +we tackled with threads in Chapter 16. Because we already talked about a lot of +the key ideas there, in this section we’ll focus on what’s different between +threads and futures. + +In many cases, the APIs for working with concurrency using async are very +similar to those for using threads. In other cases, they end up being quite +different. Even when the APIs _look_ similar between threads and async, they +often have different behavior—and they nearly always have different performance +characteristics. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="counting"></a> + +### Creating a New Task with `spawn_task` + +The first operation we tackled in the [“Creating a New Thread with +`spawn`”][thread-spawn]<!-- ignore --> section in Chapter 16 was counting up on +two separate threads. Let’s do the same using async. The `trpl` crate supplies +a `spawn_task` function that looks very similar to the `thread::spawn` API, and +a `sleep` function that is an async version of the `thread::sleep` API. We can +use these together to implement the counting example, as shown in Listing 17-6. + +<Listing number="17-6" caption="Creating a new task to print one thing while the main task prints something else" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-06/src/main.rs:all}} +``` + +</Listing> + +As our starting point, we set up our `main` function with `trpl::block_on` so +that our top-level function can be async. + +> Note: From this point forward in the chapter, every example will include this +> exact same wrapping code with `trpl::block_on` in `main`, so we’ll often skip it +> just as we do with `main`. Remember to include it in your code! + +Then we write two loops within that block, each containing a `trpl::sleep` +call, which waits for half a second (500 milliseconds) before sending the next +message. We put one loop in the body of a `trpl::spawn_task` and the other in a +top-level `for` loop. We also add an `await` after the `sleep` calls. + +This code behaves similarly to the thread-based implementation—including the +fact that you may see the messages appear in a different order in your own +terminal when you run it: + +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> + +```text +hi number 1 from the second task! +hi number 1 from the first task! +hi number 2 from the first task! +hi number 2 from the second task! +hi number 3 from the first task! +hi number 3 from the second task! +hi number 4 from the first task! +hi number 4 from the second task! +hi number 5 from the first task! +``` + +This version stops as soon as the `for` loop in the body of the main async +block finishes, because the task spawned by `spawn_task` is shut down when the +`main` function ends. If you want it to run all the way to the task’s +completion, you will need to use a join handle to wait for the first task to +complete. With threads, we used the `join` method to “block” until the thread +was done running. In Listing 17-7, we can use `await` to do the same thing, +because the task handle itself is a future. Its `Output` type is a `Result`, so +we also unwrap it after awaiting it. + +<Listing number="17-7" caption="Using `await` with a join handle to run a task to completion" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-07/src/main.rs:handle}} +``` + +</Listing> + +This updated version runs until _both_ loops finish: + +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> + +```text +hi number 1 from the second task! +hi number 1 from the first task! +hi number 2 from the first task! +hi number 2 from the second task! +hi number 3 from the first task! +hi number 3 from the second task! +hi number 4 from the first task! +hi number 4 from the second task! +hi number 5 from the first task! +hi number 6 from the first task! +hi number 7 from the first task! +hi number 8 from the first task! +hi number 9 from the first task! +``` + +So far, it looks like async and threads give us similar outcomes, just with +different syntax: using `await` instead of calling `join` on the join handle, +and awaiting the `sleep` calls. + +The bigger difference is that we didn’t need to spawn another operating system +thread to do this. In fact, we don’t even need to spawn a task here. Because +async blocks compile to anonymous futures, we can put each loop in an async +block and have the runtime run them both to completion using the `trpl::join` +function. + +In the [“Waiting for All Threads to Finish”][join-handles]<!-- ignore --> +section in Chapter 16, we showed how to use the `join` method on the +`JoinHandle` type returned when you call `std::thread::spawn`. The `trpl::join` +function is similar, but for futures. When you give it two futures, it produces +a single new future whose output is a tuple containing the output of each +future you passed in once they _both_ complete. Thus, in Listing 17-8, we use +`trpl::join` to wait for both `fut1` and `fut2` to finish. We do _not_ await +`fut1` and `fut2` but instead the new future produced by `trpl::join`. We +ignore the output, because it’s just a tuple containing two unit values. + +<Listing number="17-8" caption="Using `trpl::join` to await two anonymous futures" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-08/src/main.rs:join}} +``` + +</Listing> + +When we run this, we see both futures run to completion: + +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> + +```text +hi number 1 from the first task! +hi number 1 from the second task! +hi number 2 from the first task! +hi number 2 from the second task! +hi number 3 from the first task! +hi number 3 from the second task! +hi number 4 from the first task! +hi number 4 from the second task! +hi number 5 from the first task! +hi number 6 from the first task! +hi number 7 from the first task! +hi number 8 from the first task! +hi number 9 from the first task! +``` + +Now, you’ll see the exact same order every time, which is very different from +what we saw with threads and with `trpl::spawn_task` in Listing 17-7. That is +because the `trpl::join` function is _fair_, meaning it checks each future +equally often, alternating between them, and never lets one race ahead if the +other is ready. With threads, the operating system decides which thread to +check and how long to let it run. With async Rust, the runtime decides which +task to check. (In practice, the details get complicated because an async +runtime might use operating system threads under the hood as part of how it +manages concurrency, so guaranteeing fairness can be more work for a +runtime—but it’s still possible!) Runtimes don’t have to guarantee fairness for +any given operation, and they often offer different APIs to let you choose +whether or not you want fairness. + +Try some of these variations on awaiting the futures and see what they do: + +- Remove the async block from around either or both of the loops. +- Await each async block immediately after defining it. +- Wrap only the first loop in an async block, and await the resulting future + after the body of second loop. + +For an extra challenge, see if you can figure out what the output will be in +each case _before_ running the code! + +<!-- Old headings. Do not remove or links may break. --> + +<a id="message-passing"></a> +<a id="counting-up-on-two-tasks-using-message-passing"></a> + +### Sending Data Between Two Tasks Using Message Passing + +Sharing data between futures will also be familiar: we’ll use message passing +again, but this time with async versions of the types and functions. We’ll take +a slightly different path than we did in the [“Transfer Data Between Threads +with Message Passing”][message-passing-threads]<!-- ignore --> section in +Chapter 16 to illustrate some of the key differences between thread-based and +futures-based concurrency. In Listing 17-9, we’ll begin with just a single +async block—_not_ spawning a separate task as we spawned a separate thread. + +<Listing number="17-9" caption="Creating an async channel and assigning the two halves to `tx` and `rx`" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-09/src/main.rs:channel}} +``` + +</Listing> + +Here, we use `trpl::channel`, an async version of the multiple-producer, +single-consumer channel API we used with threads back in Chapter 16. The async +version of the API is only a little different from the thread-based version: it +uses a mutable rather than an immutable receiver `rx`, and its `recv` method +produces a future we need to await rather than producing the value directly. +Now we can send messages from the sender to the receiver. Notice that we don’t +have to spawn a separate thread or even a task; we merely need to await the +`rx.recv` call. + +The synchronous `Receiver::recv` method in `std::mpsc::channel` blocks until it +receives a message. The `trpl::Receiver::recv` method does not, because it is +async. Instead of blocking, it hands control back to the runtime until either a +message is received or the send side of the channel closes. By contrast, we +don’t await the `send` call, because it doesn’t block. It doesn’t need to, +because the channel we’re sending it into is unbounded. + +> Note: Because all of this async code runs in an async block in a +> `trpl::block_on` call, everything within it can avoid blocking. However, the +> code _outside_ it will block on the `block_on` function returning. That’s the +> whole point of the `trpl::block_on` function: it lets you _choose_ where to +> block on some set of async code, and thus where to transition between sync +> and async code. + +Notice two things about this example. First, the message will arrive right +away. Second, although we use a future here, there’s no concurrency yet. +Everything in the listing happens in sequence, just as it would if there were +no futures involved. + +Let’s address the first part by sending a series of messages and sleeping in +between them, as shown in Listing 17-10. + +<!-- We cannot test this one because it never stops! --> + +<Listing number="17-10" caption="Sending and receiving multiple messages over the async channel and sleeping with an `await` between each message" file-name="src/main.rs"> + +```rust,ignore +{{#rustdoc_include ../listings/ch17-async-await/listing-17-10/src/main.rs:many-messages}} +``` + +</Listing> + +In addition to sending the messages, we need to receive them. In this case, +because we know how many messages are coming in, we could do that manually by +calling `rx.recv().await` four times. In the real world, though, we’ll generally +be waiting on some _unknown_ number of messages, so we need to keep waiting +until we determine that there are no more messages. + +In Listing 16-10, we used a `for` loop to process all the items received from a +synchronous channel. Rust doesn’t yet have a way to use a `for` loop with an +_asynchronously produced_ series of items, however, so we need to use a loop we +haven’t seen before: the `while let` conditional loop. This is the loop version +of the `if let` construct we saw back in the [“Concise Control Flow with `if +let` and `let...else`”][if-let]<!-- ignore --> section in Chapter 6. The loop +will continue executing as long as the pattern it specifies continues to match +the value. + +The `rx.recv` call produces a future, which we await. The runtime will pause +the future until it is ready. Once a message arrives, the future will resolve +to `Some(message)` as many times as a message arrives. When the channel closes, +regardless of whether _any_ messages have arrived, the future will instead +resolve to `None` to indicate that there are no more values and thus we should +stop polling—that is, stop awaiting. + +The `while let` loop pulls all of this together. If the result of calling +`rx.recv().await` is `Some(message)`, we get access to the message and we can +use it in the loop body, just as we could with `if let`. If the result is +`None`, the loop ends. Every time the loop completes, it hits the await point +again, so the runtime pauses it again until another message arrives. + +The code now successfully sends and receives all of the messages. +Unfortunately, there are still a couple of problems. For one thing, the +messages do not arrive at half-second intervals. They arrive all at once, 2 +seconds (2,000 milliseconds) after we start the program. For another, this +program also never exits! Instead, it waits forever for new messages. You will +need to shut it down using <kbd>ctrl</kbd>-<kbd>C</kbd>. + +#### Code Within One Async Block Executes Linearly + +Let’s start by examining why the messages come in all at once after the full +delay, rather than coming in with delays between each one. Within a given async +block, the order in which `await` keywords appear in the code is also the order +in which they’re executed when the program runs. + +There’s only one async block in Listing 17-10, so everything in it runs +linearly. There’s still no concurrency. All the `tx.send` calls happen, +interspersed with all of the `trpl::sleep` calls and their associated await +points. Only then does the `while let` loop get to go through any of the +`await` points on the `recv` calls. + +To get the behavior we want, where the sleep delay happens between each +message, we need to put the `tx` and `rx` operations in their own async blocks, +as shown in Listing 17-11. Then the runtime can execute each of them separately +using `trpl::join`, just as in Listing 17-8. Once again, we await the result of +calling `trpl::join`, not the individual futures. If we awaited the individual +futures in sequence, we would just end up back in a sequential flow—exactly +what we’re trying _not_ to do. + +<!-- We cannot test this one because it never stops! --> + +<Listing number="17-11" caption="Separating `send` and `recv` into their own `async` blocks and awaiting the futures for those blocks" file-name="src/main.rs"> + +```rust,ignore +{{#rustdoc_include ../listings/ch17-async-await/listing-17-11/src/main.rs:futures}} +``` + +</Listing> + +With the updated code in Listing 17-11, the messages get printed at +500-millisecond intervals, rather than all in a rush after 2 seconds. + +#### Moving Ownership Into an Async Block + +The program still never exits, though, because of the way the `while let` loop +interacts with `trpl::join`: + +- The future returned from `trpl::join` completes only once _both_ futures + passed to it have completed. +- The `tx_fut` future completes once it finishes sleeping after sending the last + message in `vals`. +- The `rx_fut` future won’t complete until the `while let` loop ends. +- The `while let` loop won’t end until awaiting `rx.recv` produces `None`. +- Awaiting `rx.recv` will return `None` only once the other end of the channel + is closed. +- The channel will close only if we call `rx.close` or when the sender side, + `tx`, is dropped. +- We don’t call `rx.close` anywhere, and `tx` won’t be dropped until the + outermost async block passed to `trpl::block_on` ends. +- The block can’t end because it is blocked on `trpl::join` completing, which + takes us back to the top of this list. + +Right now, the async block where we send the messages only _borrows_ `tx` +because sending a message doesn’t require ownership, but if we could _move_ +`tx` into that async block, it would be dropped once that block ends. In the +[“Capturing References or Moving Ownership”][capture-or-move]<!-- ignore --> +section in Chapter 13, you learned how to use the `move` keyword with closures, +and, as discussed in the [“Using `move` Closures with +Threads”][move-threads]<!-- ignore --> section in Chapter 16, we often need to +move data into closures when working with threads. The same basic dynamics +apply to async blocks, so the `move` keyword works with async blocks just as it +does with closures. + +In Listing 17-12, we change the block used to send messages from `async` to +`async move`. + +<Listing number="17-12" caption="A revision of the code from Listing 17-11 that correctly shuts down when complete" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-12/src/main.rs:with-move}} +``` + +</Listing> + +When we run _this_ version of the code, it shuts down gracefully after the last +message is sent and received. Next, let’s see what would need to change to send +data from more than one future. + +#### Joining a Number of Futures with the `join!` Macro + +This async channel is also a multiple-producer channel, so we can call `clone` +on `tx` if we want to send messages from multiple futures, as shown in Listing +17-13. + +<Listing number="17-13" caption="Using multiple producers with async blocks" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-13/src/main.rs:here}} +``` + +</Listing> + +First, we clone `tx`, creating `tx1` outside the first async block. We move +`tx1` into that block just as we did before with `tx`. Then, later, we move the +original `tx` into a _new_ async block, where we send more messages on a +slightly slower delay. We happen to put this new async block after the async +block for receiving messages, but it could go before it just as well. The key is +the order in which the futures are awaited, not in which they’re created. + +Both of the async blocks for sending messages need to be `async move` blocks so +that both `tx` and `tx1` get dropped when those blocks finish. Otherwise, we’ll +end up back in the same infinite loop we started out in. + +Finally, we switch from `trpl::join` to `trpl::join!` to handle the additional +future: the `join!` macro awaits an arbitrary number of futures where we know +the number of futures at compile time. We’ll discuss awaiting a collection of +an unknown number of futures later in this chapter. + +Now we see all the messages from both sending futures, and because the sending +futures use slightly different delays after sending, the messages are also +received at those different intervals: + +<!-- Not extracting output because changes to this output aren't significant; +the changes are likely to be due to the threads running differently rather than +changes in the compiler --> + +```text +received 'hi' +received 'more' +received 'from' +received 'the' +received 'messages' +received 'future' +received 'for' +received 'you' +``` + +We’ve explored how to use message passing to send data between futures, how +code within an async block runs sequentially, how to move ownership into an +async block, and how to join multiple futures. Next, let’s discuss how and why +to tell the runtime it can switch to another task. + +[thread-spawn]: ch16-01-threads.html#creating-a-new-thread-with-spawn +[join-handles]: ch16-01-threads.html#waiting-for-all-threads-to-finish +[message-passing-threads]: ch16-02-message-passing.html +[if-let]: ch06-03-if-let.html +[capture-or-move]: ch13-01-closures.html#capturing-references-or-moving-ownership +[move-threads]: ch16-01-threads.html#using-move-closures-with-threads diff --git a/src/ch17-03-more-futures.md b/src/ch17-03-more-futures.md new file mode 100644 index 0000000000..893385d585 --- /dev/null +++ b/src/ch17-03-more-futures.md @@ -0,0 +1,249 @@ + +<!-- Old headings. Do not remove or links may break. --> + +<a id="yielding"></a> + +### Yielding Control to the Runtime + +Recall from the [“Our First Async Program”][async-program]<!-- ignore --> +section that at each await point, Rust gives a runtime a chance to pause the +task and switch to another one if the future being awaited isn’t ready. The +inverse is also true: Rust _only_ pauses async blocks and hands control back to +a runtime at an await point. Everything between await points is synchronous. + +That means if you do a bunch of work in an async block without an await point, +that future will block any other futures from making progress. You may sometimes +hear this referred to as one future _starving_ other futures. In some cases, +that may not be a big deal. However, if you are doing some kind of expensive +setup or long-running work, or if you have a future that will keep doing some +particular task indefinitely, you’ll need to think about when and where to hand +control back to the runtime. + +Let’s simulate a long-running operation to illustrate the starvation problem, +then explore how to solve it. Listing 17-14 introduces a `slow` function. + +<Listing number="17-14" caption="Using `thread::sleep` to simulate slow operations" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-14/src/main.rs:slow}} +``` + +</Listing> + +This code uses `std::thread::sleep` instead of `trpl::sleep` so that calling +`slow` will block the current thread for some number of milliseconds. We can +use `slow` to stand in for real-world operations that are both long-running and +blocking. + +In Listing 17-15, we use `slow` to emulate doing this kind of CPU-bound work in +a pair of futures. + +<Listing number="17-15" caption="Calling the `slow` function to simulate slow operations" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-15/src/main.rs:slow-futures}} +``` + +</Listing> + +Each future hands control back to the runtime only _after_ carrying out a bunch +of slow operations. If you run this code, you will see this output: + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-15/ +cargo run +copy just the output +--> + +```text +'a' started. +'a' ran for 30ms +'a' ran for 10ms +'a' ran for 20ms +'b' started. +'b' ran for 75ms +'b' ran for 10ms +'b' ran for 15ms +'b' ran for 350ms +'a' finished. +``` + +As with Listing 17-5 where we used `trpl::select` to race futures fetching two +URLs, `select` still finishes as soon as `a` is done. There’s no interleaving +between the calls to `slow` in the two futures, though. The `a` future does all +of its work until the `trpl::sleep` call is awaited, then the `b` future does +all of its work until its own `trpl::sleep` call is awaited, and finally the +`a` future completes. To allow both futures to make progress between their slow +tasks, we need await points so we can hand control back to the runtime. That +means we need something we can await! + +We can already see this kind of handoff happening in Listing 17-15: if we +removed the `trpl::sleep` at the end of the `a` future, it would complete +without the `b` future running _at all_. Let’s try using the `trpl::sleep` +function as a starting point for letting operations switch off making progress, +as shown in Listing 17-16. + +<Listing number="17-16" caption="Using `trpl::sleep` to let operations switch off making progress" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-16/src/main.rs:here}} +``` + +</Listing> + +We’ve added `trpl::sleep` calls with await points between each call to `slow`. +Now the two futures’ work is interleaved: + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-16 +cargo run +copy just the output +--> + +```text +'a' started. +'a' ran for 30ms +'b' started. +'b' ran for 75ms +'a' ran for 10ms +'b' ran for 10ms +'a' ran for 20ms +'b' ran for 15ms +'a' finished. +``` + +The `a` future still runs for a bit before handing off control to `b`, because +it calls `slow` before ever calling `trpl::sleep`, but after that the futures +swap back and forth each time one of them hits an await point. In this case, we +have done that after every call to `slow`, but we could break up the work in +whatever way makes the most sense to us. + +We don’t really want to _sleep_ here, though: we want to make progress as fast +as we can. We just need to hand back control to the runtime. We can do that +directly, using the `trpl::yield_now` function. In Listing 17-17, we replace +all those `trpl::sleep` calls with `trpl::yield_now`. + +<Listing number="17-17" caption="Using `yield_now` to let operations switch off making progress" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-17/src/main.rs:yields}} +``` + +</Listing> + +This code is both clearer about the actual intent and can be significantly +faster than using `sleep`, because timers such as the one used by `sleep` often +have limits on how granular they can be. The version of `sleep` we are using, +for example, will always sleep for at least a millisecond, even if we pass it a +`Duration` of one nanosecond. Again, modern computers are _fast_: they can do a +lot in one millisecond! + +This means that async can be useful even for compute-bound tasks, depending on +what else your program is doing, because it provides a useful tool for +structuring the relationships between different parts of the program (but at a +cost of the overhead of the async state machine). This is a form of +_cooperative multitasking_, where each future has the power to determine when +it hands over control via await points. Each future therefore also has the +responsibility to avoid blocking for too long. In some Rust-based embedded +operating systems, this is the _only_ kind of multitasking! + +In real-world code, you won’t usually be alternating function calls with await +points on every single line, of course. While yielding control in this way is +relatively inexpensive, it’s not free. In many cases, trying to break up a +compute-bound task might make it significantly slower, so sometimes it’s better +for _overall_ performance to let an operation block briefly. Always +measure to see what your code’s actual performance bottlenecks are. The +underlying dynamic is important to keep in mind, though, if you _are_ seeing a +lot of work happening in serial that you expected to happen concurrently! + +### Building Our Own Async Abstractions + +We can also compose futures together to create new patterns. For example, we can +build a `timeout` function with async building blocks we already have. When +we’re done, the result will be another building block we could use to create +still more async abstractions. + +Listing 17-18 shows how we would expect this `timeout` to work with a slow +future. + +<Listing number="17-18" caption="Using our imagined `timeout` to run a slow operation with a time limit" file-name="src/main.rs"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch17-async-await/listing-17-18/src/main.rs:here}} +``` + +</Listing> + +Let’s implement this! To begin, let’s think about the API for `timeout`: + +- It needs to be an async function itself so we can await it. +- Its first parameter should be a future to run. We can make it generic to allow + it to work with any future. +- Its second parameter will be the maximum time to wait. If we use a `Duration`, + that will make it easy to pass along to `trpl::sleep`. +- It should return a `Result`. If the future completes successfully, the + `Result` will be `Ok` with the value produced by the future. If the timeout + elapses first, the `Result` will be `Err` with the duration that the timeout + waited for. + +Listing 17-19 shows this declaration. + +<!-- This is not tested because it intentionally does not compile. --> + +<Listing number="17-19" caption="Defining the signature of `timeout`" file-name="src/main.rs"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch17-async-await/listing-17-19/src/main.rs:declaration}} +``` + +</Listing> + +That satisfies our goals for the types. Now let’s think about the _behavior_ we +need: we want to race the future passed in against the duration. We can use +`trpl::sleep` to make a timer future from the duration, and use `trpl::select` +to run that timer with the future the caller passes in. + +In Listing 17-20, we implement `timeout` by matching on the result of awaiting +`trpl::select`. + +<Listing number="17-20" caption="Defining `timeout` with `select` and `sleep`" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-20/src/main.rs:implementation}} +``` + +</Listing> + +The implementation of `trpl::select` is not fair: it always polls arguments in +the order in which they are passed (other `select` implementations will +randomly choose which argument to poll first). Thus, we pass `future_to_try` to +`select` first so it gets a chance to complete even if `max_time` is a very +short duration. If `future_to_try` finishes first, `select` will return `Left` +with the output from `future_to_try`. If `timer` finishes first, `select` will +return `Right` with the timer’s output of `()`. + +If the `future_to_try` succeeds and we get a `Left(output)`, we return +`Ok(output)`. If the sleep timer elapses instead and we get a `Right(())`, we +ignore the `()` with `_` and return `Err(max_time)` instead. + +With that, we have a working `timeout` built out of two other async helpers. If +we run our code, it will print the failure mode after the timeout: + +```text +Failed after 2 seconds +``` + +Because futures compose with other futures, you can build really powerful tools +using smaller async building blocks. For example, you can use this same +approach to combine timeouts with retries, and in turn use those with +operations such as network calls (such as those in Listing 17-5). + +In practice, you’ll usually work directly with `async` and `await`, and +secondarily with functions such as `select` and macros such as the `join!` +macro to control how the outermost futures are executed. + +We’ve now seen a number of ways to work with multiple futures at the same time. +Up next, we’ll look at how we can work with multiple futures in a sequence over +time with _streams_. + +[async-program]: ch17-01-futures-and-syntax.html#our-first-async-program diff --git a/src/ch17-04-streams.md b/src/ch17-04-streams.md new file mode 100644 index 0000000000..b7cb2f543f --- /dev/null +++ b/src/ch17-04-streams.md @@ -0,0 +1,112 @@ +<!-- Old headings. Do not remove or links may break. --> + +<a id="streams"></a> + +## Streams: Futures in Sequence + +Recall how we used the receiver for our async channel earlier in this chapter +in the [“Message Passing”][17-02-messages]<!-- ignore --> section. The async +`recv` method produces a sequence of items over time. This is an instance of a +much more general pattern known as a _stream_. Many concepts are naturally +represented as streams: items becoming available in a queue, chunks of data +being pulled incrementally from the filesystem when the full data set is too +large for the computer’s memory, or data arriving over the network over time. +Because streams are futures, we can use them with any other kind of future and +combine them in interesting ways. For example, we can batch up events to avoid +triggering too many network calls, set timeouts on sequences of long-running +operations, or throttle user interface events to avoid doing needless work. + +We saw a sequence of items back in Chapter 13, when we looked at the Iterator +trait in [“The Iterator Trait and the `next` Method”][iterator-trait]<!-- +ignore --> section, but there are two differences between iterators and the +async channel receiver. The first difference is time: iterators are +synchronous, while the channel receiver is asynchronous. The second difference +is the API. When working directly with `Iterator`, we call its synchronous +`next` method. With the `trpl::Receiver` stream in particular, we called an +asynchronous `recv` method instead. Otherwise, these APIs feel very similar, +and that similarity isn’t a coincidence. A stream is like an asynchronous form +of iteration. Whereas the `trpl::Receiver` specifically waits to receive +messages, though, the general-purpose stream API is much broader: it provides +the next item the way `Iterator` does, but asynchronously. + +The similarity between iterators and streams in Rust means we can actually +create a stream from any iterator. As with an iterator, we can work with a +stream by calling its `next` method and then awaiting the output, as in Listing +17-21, which won’t compile yet. + +<Listing number="17-21" caption="Creating a stream from an iterator and printing its values" file-name="src/main.rs"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch17-async-await/listing-17-21/src/main.rs:stream}} +``` + +</Listing> + +We start with an array of numbers, which we convert to an iterator and then +call `map` on to double all the values. Then we convert the iterator into a +stream using the `trpl::stream_from_iter` function. Next, we loop over the +items in the stream as they arrive with the `while let` loop. + +Unfortunately, when we try to run the code, it doesn’t compile but instead +reports that there’s no `next` method available: + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-21 +cargo build +copy only the error output +--> + +```text +error[E0599]: no method named `next` found for struct `tokio_stream::iter::Iter` in the current scope + --> src/main.rs:10:40 + | +10 | while let Some(value) = stream.next().await { + | ^^^^ + | + = help: items from traits can only be used if the trait is in scope +help: the following traits which provide `next` are implemented but not in scope; perhaps you want to import one of them + | +1 + use crate::trpl::StreamExt; + | +1 + use futures_util::stream::stream::StreamExt; + | +1 + use std::iter::Iterator; + | +1 + use std::str::pattern::Searcher; + | +help: there is a method `try_next` with a similar name + | +10 | while let Some(value) = stream.try_next().await { + | ~~~~~~~~ +``` + +As this output explains, the reason for the compiler error is that we need the +right trait in scope to be able to use the `next` method. Given our discussion +so far, you might reasonably expect that trait to be `Stream`, but it’s +actually `StreamExt`. Short for _extension_, `Ext` is a common pattern in the +Rust community for extending one trait with another. + +The `Stream` trait defines a low-level interface that effectively combines the +`Iterator` and `Future` traits. `StreamExt` supplies a higher-level set of APIs +on top of `Stream`, including the `next` method as well as other utility +methods similar to those provided by the `Iterator` trait. `Stream` and +`StreamExt` are not yet part of Rust’s standard library, but most ecosystem +crates use similar definitions. + +The fix to the compiler error is to add a `use` statement for +`trpl::StreamExt`, as in Listing 17-22. + +<Listing number="17-22" caption="Successfully using an iterator as the basis for a stream" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-22/src/main.rs:all}} +``` + +</Listing> + +With all those pieces put together, this code works the way we want! What’s +more, now that we have `StreamExt` in scope, we can use all of its utility +methods, just as with iterators. + +[17-02-messages]: ch17-02-concurrency-with-async.html#message-passing +[iterator-trait]: ch13-02-iterators.html#the-iterator-trait-and-the-next-method diff --git a/src/ch17-05-traits-for-async.md b/src/ch17-05-traits-for-async.md new file mode 100644 index 0000000000..4b502ceafe --- /dev/null +++ b/src/ch17-05-traits-for-async.md @@ -0,0 +1,542 @@ +<!-- Old headings. Do not remove or links may break. --> + +<a id="digging-into-the-traits-for-async"></a> + +## A Closer Look at the Traits for Async + +Throughout the chapter, we’ve used the `Future`, `Stream`, and `StreamExt` +traits in various ways. So far, though, we’ve avoided getting too far into the +details of how they work or how they fit together, which is fine most of the +time for your day-to-day Rust work. Sometimes, though, you’ll encounter +situations where you’ll need to understand a few more of these traits’ details, +along with the `Pin` type and the `Unpin` trait. In this section, we’ll dig in +just enough to help in those scenarios, still leaving the _really_ deep dive +for other documentation. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="future"></a> + +### The `Future` Trait + +Let’s start by taking a closer look at how the `Future` trait works. Here’s how +Rust defines it: + +```rust +use std::pin::Pin; +use std::task::{Context, Poll}; + +pub trait Future { + type Output; + + fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>; +} +``` + +That trait definition includes a bunch of new types and also some syntax we +haven’t seen before, so let’s walk through the definition piece by piece. + +First, `Future`’s associated type `Output` says what the future resolves to. +This is analogous to the `Item` associated type for the `Iterator` trait. +Second, `Future` has the `poll` method, which takes a special `Pin` reference +for its `self` parameter and a mutable reference to a `Context` type, and +returns a `Poll<Self::Output>`. We’ll talk more about `Pin` and `Context` in a +moment. For now, let’s focus on what the method returns, the `Poll` type: + +```rust +pub enum Poll<T> { + Ready(T), + Pending, +} +``` + +This `Poll` type is similar to an `Option`. It has one variant that has a value, +`Ready(T)`, and one that does not, `Pending`. `Poll` means something quite +different from `Option`, though! The `Pending` variant indicates that the future +still has work to do, so the caller will need to check again later. The `Ready` +variant indicates that the `Future` has finished its work and the `T` value is +available. + +> Note: It’s rare to need to call `poll` directly, but if you do need to, keep +> in mind that with most futures, the caller should not call `poll` again after +> the future has returned `Ready`. Many futures will panic if polled again after +> becoming ready. Futures that are safe to poll again will say so explicitly in +> their documentation. This is similar to how `Iterator::next` behaves. + +When you see code that uses `await`, Rust compiles it under the hood to code +that calls `poll`. If you look back at Listing 17-4, where we printed out the +page title for a single URL once it resolved, Rust compiles it into something +kind of (although not exactly) like this: + +```rust,ignore +match page_title(url).poll() { + Ready(page_title) => match page_title { + Some(title) => println!("The title for {url} was {title}"), + None => println!("{url} had no title"), + } + Pending => { + // But what goes here? + } +} +``` + +What should we do when the future is still `Pending`? We need some way to try +again, and again, and again, until the future is finally ready. In other words, +we need a loop: + +```rust,ignore +let mut page_title_fut = page_title(url); +loop { + match page_title_fut.poll() { + Ready(value) => match page_title { + Some(title) => println!("The title for {url} was {title}"), + None => println!("{url} had no title"), + } + Pending => { + // continue + } + } +} +``` + +If Rust compiled it to exactly that code, though, every `await` would be +blocking—exactly the opposite of what we were going for! Instead, Rust ensures +that the loop can hand off control to something that can pause work on this +future to work on other futures and then check this one again later. As we’ve +seen, that something is an async runtime, and this scheduling and coordination +work is one of its main jobs. + +In the [“Sending Data Between Two Tasks Using Message +Passing”][message-passing]<!-- ignore --> section, we described waiting on +`rx.recv`. The `recv` call returns a future, and awaiting the future polls it. +We noted that a runtime will pause the future until it’s ready with either +`Some(message)` or `None` when the channel closes. With our deeper +understanding of the `Future` trait, and specifically `Future::poll`, we can +see how that works. The runtime knows the future isn’t ready when it returns +`Poll::Pending`. Conversely, the runtime knows the future _is_ ready and +advances it when `poll` returns `Poll::Ready(Some(message))` or +`Poll::Ready(None)`. + +The exact details of how a runtime does that are beyond the scope of this book, +but the key is to see the basic mechanics of futures: a runtime _polls_ each +future it is responsible for, putting the future back to sleep when it is not +yet ready. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="pinning-and-the-pin-and-unpin-traits"></a> +<a id="the-pin-and-unpin-traits"></a> + +### The `Pin` Type and the `Unpin` Trait + +Back in Listing 17-13, we used the `trpl::join!` macro to await three +futures. However, it’s common to have a collection such as a vector containing +some number futures that won’t be known until runtime. Let’s change Listing +17-13 to the code in Listing 17-23 that puts the three futures into a vector +and calls the `trpl::join_all` function instead, which won’t compile yet. + +<Listing number="17-23" caption="Awaiting futures in a collection" file-name="src/main.rs"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch17-async-await/listing-17-23/src/main.rs:here}} +``` + +</Listing> + +We put each future within a `Box` to make them into _trait objects_, just as +we did in the “Returning Errors from `run`” section in Chapter 12. (We’ll cover +trait objects in detail in Chapter 18.) Using trait objects lets us treat each +of the anonymous futures produced by these types as the same type, because all +of them implement the `Future` trait. + +This might be surprising. After all, none of the async blocks returns anything, +so each one produces a `Future<Output = ()>`. Remember that `Future` is a +trait, though, and that the compiler creates a unique enum for each async +block, even when they have identical output types. Just as you can’t put two +different handwritten structs in a `Vec`, you can’t mix compiler-generated +enums. + +Then we pass the collection of futures to the `trpl::join_all` function and +await the result. However, this doesn’t compile; here’s the relevant part of +the error messages. + +<!-- manual-regeneration +cd listings/ch17-async-await/listing-17-23 +cargo build +copy *only* the final `error` block from the errors +--> + +```text +error[E0277]: `dyn Future<Output = ()>` cannot be unpinned + --> src/main.rs:48:33 + | +48 | trpl::join_all(futures).await; + | ^^^^^ the trait `Unpin` is not implemented for `dyn Future<Output = ()>` + | + = note: consider using the `pin!` macro + consider using `Box::pin` if you need to access the pinned value outside of the current scope + = note: required for `Box<dyn Future<Output = ()>>` to implement `Future` +note: required by a bound in `futures_util::future::join_all::JoinAll` + --> file:///home/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/futures-util-0.3.30/src/future/join_all.rs:29:8 + | +27 | pub struct JoinAll<F> + | ------- required by a bound in this struct +28 | where +29 | F: Future, + | ^^^^^^ required by this bound in `JoinAll` +``` + +The note in this error message tells us that we should use the `pin!` macro to +_pin_ the values, which means putting them inside the `Pin` type that +guarantees the values won’t be moved in memory. The error message says pinning +is required because `dyn Future<Output = ()>` needs to implement the `Unpin` +trait and it currently does not. + +The `trpl::join_all` function returns a struct called `JoinAll`. That struct is +generic over a type `F`, which is constrained to implement the `Future` trait. +Directly awaiting a future with `await` pins the future implicitly. That’s why +we don’t need to use `pin!` everywhere we want to await futures. + +However, we’re not directly awaiting a future here. Instead, we construct a new +future, JoinAll, by passing a collection of futures to the `join_all` function. +The signature for `join_all` requires that the types of the items in the +collection all implement the `Future` trait, and `Box<T>` implements `Future` +only if the `T` it wraps is a future that implements the `Unpin` trait. + +That’s a lot to absorb! To really understand it, let’s dive a little further +into how the `Future` trait actually works, in particular around pinning. Look +again at the definition of the `Future` trait: + +```rust +use std::pin::Pin; +use std::task::{Context, Poll}; + +pub trait Future { + type Output; + + // Required method + fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>; +} +``` + +The `cx` parameter and its `Context` type are the key to how a runtime actually +knows when to check any given future while still being lazy. Again, the details +of how that works are beyond the scope of this chapter, and you generally only +need to think about this when writing a custom `Future` implementation. We’ll +focus instead on the type for `self`, as this is the first time we’ve seen a +method where `self` has a type annotation. A type annotation for `self` works +like type annotations for other function parameters but with two key +differences: + +- It tells Rust what type `self` must be for the method to be called. +- It can’t be just any type. It’s restricted to the type on which the method is + implemented, a reference or smart pointer to that type, or a `Pin` wrapping a + reference to that type. + +We’ll see more on this syntax in [Chapter 18][ch-18]<!-- ignore -->. For now, +it’s enough to know that if we want to poll a future to check whether it is +`Pending` or `Ready(Output)`, we need a `Pin`-wrapped mutable reference to the +type. + +`Pin` is a wrapper for pointer-like types such as `&`, `&mut`, `Box`, and `Rc`. +(Technically, `Pin` works with types that implement the `Deref` or `DerefMut` +traits, but this is effectively equivalent to working only with references and +smart pointers.) `Pin` is not a pointer itself and doesn’t have any behavior of +its own like `Rc` and `Arc` do with reference counting; it’s purely a tool the +compiler can use to enforce constraints on pointer usage. + +Recalling that `await` is implemented in terms of calls to `poll` starts to +explain the error message we saw earlier, but that was in terms of `Unpin`, not +`Pin`. So how exactly does `Pin` relate to `Unpin`, and why does `Future` need +`self` to be in a `Pin` type to call `poll`? + +Remember from earlier in this chapter that a series of await points in a future +get compiled into a state machine, and the compiler makes sure that state +machine follows all of Rust’s normal rules around safety, including borrowing +and ownership. To make that work, Rust looks at what data is needed between one +await point and either the next await point or the end of the async block. It +then creates a corresponding variant in the compiled state machine. Each +variant gets the access it needs to the data that will be used in that section +of the source code, whether by taking ownership of that data or by getting a +mutable or immutable reference to it. + +So far, so good: if we get anything wrong about the ownership or references in +a given async block, the borrow checker will tell us. When we want to move +around the future that corresponds to that block—like moving it into a `Vec` to +pass to `join_all`—things get trickier. + +When we move a future—whether by pushing it into a data structure to use as an +iterator with `join_all` or by returning it from a function—that actually means +moving the state machine Rust creates for us. And unlike most other types in +Rust, the futures Rust creates for async blocks can end up with references to +themselves in the fields of any given variant, as shown in the simplified illustration in Figure 17-4. + +<figure> + +<img alt="A single-column, three-row table representing a future, fut1, which has data values 0 and 1 in the first two rows and an arrow pointing from the third row back to the second row, representing an internal reference within the future." src="img/trpl17-04.svg" class="center" /> + +<figcaption>Figure 17-4: A self-referential data type</figcaption> + +</figure> + +By default, though, any object that has a reference to itself is unsafe to move, +because references always point to the actual memory address of whatever they +refer to (see Figure 17-5). If you move the data structure itself, those +internal references will be left pointing to the old location. However, that +memory location is now invalid. For one thing, its value will not be updated +when you make changes to the data structure. For another—more important—thing, +the computer is now free to reuse that memory for other purposes! You could end +up reading completely unrelated data later. + +<figure> + +<img alt="Two tables, depicting two futures, fut1 and fut2, each of which has one column and three rows, representing the result of having moved a future out of fut1 into fut2. The first, fut1, is grayed out, with a question mark in each index, representing unknown memory. The second, fut2, has 0 and 1 in the first and second rows and an arrow pointing from its third row back to the second row of fut1, representing a pointer that is referencing the old location in memory of the future before it was moved." src="img/trpl17-05.svg" class="center" /> + +<figcaption>Figure 17-5: The unsafe result of moving a self-referential data type</figcaption> + +</figure> + +Theoretically, the Rust compiler could try to update every reference to an +object whenever it gets moved, but that could add a lot of performance overhead, +especially if a whole web of references needs updating. If we could instead make +sure the data structure in question _doesn’t move in memory_, we wouldn’t have +to update any references. This is exactly what Rust’s borrow checker is for: +in safe code, it prevents you from moving any item with an active reference to +it. + +`Pin` builds on that to give us the exact guarantee we need. When we _pin_ a +value by wrapping a pointer to that value in `Pin`, it can no longer move. Thus, +if you have `Pin<Box<SomeType>>`, you actually pin the `SomeType` value, _not_ +the `Box` pointer. Figure 17-6 illustrates this process. + +<figure> + +<img alt="Three boxes laid out side by side. The first is labeled “Pin”, the second “b1”, and the third “pinned”. Within “pinned” is a table labeled “fut”, with a single column; it represents a future with cells for each part of the data structure. Its first cell has the value “0”, its second cell has an arrow coming out of it and pointing to the fourth and final cell, which has the value “1” in it, and the third cell has dashed lines and an ellipsis to indicate there may be other parts to the data structure. All together, the “fut” table represents a future which is self-referential. An arrow leaves the box labeled “Pin”, goes through the box labeled “b1” and terminates inside the “pinned” box at the “fut” table." src="img/trpl17-06.svg" class="center" /> + +<figcaption>Figure 17-6: Pinning a `Box` that points to a self-referential future type</figcaption> + +</figure> + +In fact, the `Box` pointer can still move around freely. Remember: we care about +making sure the data ultimately being referenced stays in place. If a pointer +moves around, _but the data it points to_ is in the same place, as in Figure +17-7, there’s no potential problem. (As an independent exercise, look at the docs +for the types as well as the `std::pin` module and try to work out how you’d do +this with a `Pin` wrapping a `Box`.) The key is that the self-referential type +itself cannot move, because it is still pinned. + +<figure> + +<img alt="Four boxes laid out in three rough columns, identical to the previous diagram with a change to the second column. Now there are two boxes in the second column, labeled “b1” and “b2”, “b1” is grayed out, and the arrow from “Pin” goes through “b2” instead of “b1”, indicating that the pointer has moved from “b1” to “b2”, but the data in “pinned” has not moved." src="img/trpl17-07.svg" class="center" /> + +<figcaption>Figure 17-7: Moving a `Box` which points to a self-referential future type</figcaption> + +</figure> + +However, most types are perfectly safe to move around, even if they happen to be +behind a `Pin` pointer. We only need to think about pinning when items have +internal references. Primitive values such as numbers and Booleans are safe +because they obviously don’t have any internal references. +Neither do most types you normally work with in Rust. You can move around +a `Vec`, for example, without worrying. Given what we have seen so far, if +you have a `Pin<Vec<String>>`, you’d have to do everything via the safe but +restrictive APIs provided by `Pin`, even though a `Vec<String>` is always safe +to move if there are no other references to it. We need a way to tell the +compiler that it’s fine to move items around in cases like this—and that’s +where `Unpin` comes into play. + +`Unpin` is a marker trait, similar to the `Send` and `Sync` traits we saw in +Chapter 16, and thus has no functionality of its own. Marker traits exist only +to tell the compiler it’s safe to use the type implementing a given trait in a +particular context. `Unpin` informs the compiler that a given type does _not_ +need to uphold any guarantees about whether the value in question can be safely +moved. + +<!-- + The inline `<code>` in the next block is to allow the inline `<em>` inside it, + matching what NoStarch does style-wise, and emphasizing within the text here + that it is something distinct from a normal type. +--> + +Just as with `Send` and `Sync`, the compiler implements `Unpin` automatically +for all types where it can prove it is safe. A special case, again similar to +`Send` and `Sync`, is where `Unpin` is _not_ implemented for a type. The +notation for this is <code>impl !Unpin for <em>SomeType</em></code>, where +<code><em>SomeType</em></code> is the name of a type that _does_ need to uphold +those guarantees to be safe whenever a pointer to that type is used in a `Pin`. + +In other words, there are two things to keep in mind about the relationship +between `Pin` and `Unpin`. First, `Unpin` is the “normal” case, and `!Unpin` is +the special case. Second, whether a type implements `Unpin` or `!Unpin` _only_ +matters when you’re using a pinned pointer to that type like <code>Pin<&mut +<em>SomeType</em>></code>. + +To make that concrete, think about a `String`: it has a length and the Unicode +characters that make it up. We can wrap a `String` in `Pin`, as seen in Figure +17-8. However, `String` automatically implements `Unpin`, as do most other types +in Rust. + +<figure> + +<img alt="A box labeled “Pin” on the left with an arrow going from it to a box labeled “String” on the right. The “String” box contains the data 5usize, representing the length of the string, and the letters “h”, “e”, “l”, “l”, and “o” representing the characters of the string “hello” stored in this String instance. A dotted rectangle surrounds the “String” box and its label, but not the “Pin” box." src="img/trpl17-08.svg" class="center" /> + +<figcaption>Figure 17-8: Pinning a `String`; the dotted line indicates that the `String` implements the `Unpin` trait and thus is not pinned</figcaption> + +</figure> + +As a result, we can do things that would be illegal if `String` implemented +`!Unpin` instead, such as replacing one string with another at the exact same +location in memory as in Figure 17-9. This doesn’t violate the `Pin` contract, +because `String` has no internal references that make it unsafe to move around. +That is precisely why it implements `Unpin` rather than `!Unpin`. + +<figure> + +<img alt="The same “hello” string data from the previous example, now labeled “s1” and grayed out. The “Pin” box from the previous example now points to a different String instance, one that is labeled “s2”, is valid, has a length of 7usize, and contains the characters of the string “goodbye”. s2 is surrounded by a dotted rectangle because it, too, implements the Unpin trait." src="img/trpl17-09.svg" class="center" /> + +<figcaption>Figure 17-9: Replacing the `String` with an entirely different `String` in memory</figcaption> + +</figure> + +Now we know enough to understand the errors reported for that `join_all` call +from back in Listing 17-23. We originally tried to move the futures produced by +async blocks into a `Vec<Box<dyn Future<Output = ()>>>`, but as we’ve seen, +those futures may have internal references, so they don’t automatically +implement `Unpin`. Once we pin them, we can pass the resulting `Pin` type into +the `Vec`, confident that the underlying data in the futures will _not_ be +moved. Listing 17-24 shows how to fix the code by calling the `pin!` macro +where each of the three futures are defined and adjusting the trait object type. + +<Listing number="17-24" caption="Pinning the futures to enable moving them into the vector"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-24/src/main.rs:here}} +``` + +</Listing> + +This example now compiles and runs, and we could add or remove futures from the +vector at runtime and join them all. + +`Pin` and `Unpin` are mostly important for building lower-level libraries, or +when you’re building a runtime itself, rather than for day-to-day Rust code. +When you see these traits in error messages, though, now you’ll have a better +idea of how to fix your code! + +> Note: This combination of `Pin` and `Unpin` makes it possible to safely +> implement a whole class of complex types in Rust that would otherwise prove +> challenging because they’re self-referential. Types that require `Pin` show up +> most commonly in async Rust today, but every once in a while, you might see +> them in other contexts, too. +> +> The specifics of how `Pin` and `Unpin` work, and the rules they’re required +> to uphold, are covered extensively in the API documentation for `std::pin`, so +> if you’re interested in learning more, that’s a great place to start. +> +> If you want to understand how things work under the hood in even more detail, +> see Chapters [2][under-the-hood]<!-- ignore --> and +> [4][pinning]<!-- ignore --> of +> [_Asynchronous Programming in Rust_][async-book]. + +### The `Stream` Trait + +Now that you have a deeper grasp on the `Future`, `Pin`, and `Unpin` traits, we +can turn our attention to the `Stream` trait. As you learned earlier in the +chapter, streams are similar to asynchronous iterators. Unlike `Iterator` and +`Future`, however, `Stream` has no definition in the standard library as of +this writing, but there _is_ a very common definition from the `futures` crate +used throughout the ecosystem. + +Let’s review the definitions of the `Iterator` and `Future` traits before +looking at how a `Stream` trait might merge them together. From `Iterator`, we +have the idea of a sequence: its `next` method provides an +`Option<Self::Item>`. From `Future`, we have the idea of readiness over time: +its `poll` method provides a `Poll<Self::Output>`. To represent a sequence of +items that become ready over time, we define a `Stream` trait that puts those +features together: + +```rust +use std::pin::Pin; +use std::task::{Context, Poll}; + +trait Stream { + type Item; + + fn poll_next( + self: Pin<&mut Self>, + cx: &mut Context<'_> + ) -> Poll<Option<Self::Item>>; +} +``` + +The `Stream` trait defines an associated type called `Item` for the type of the +items produced by the stream. This is similar to `Iterator`, where there may be +zero to many items, and unlike `Future`, where there is always a single +`Output`, even if it’s the unit type `()`. + +`Stream` also defines a method to get those items. We call it `poll_next`, to +make it clear that it polls in the same way `Future::poll` does and produces a +sequence of items in the same way `Iterator::next` does. Its return type +combines `Poll` with `Option`. The outer type is `Poll`, because it has to be +checked for readiness, just as a future does. The inner type is `Option`, +because it needs to signal whether there are more messages, just as an iterator +does. + +Something very similar to this definition will likely end up as part of Rust’s +standard library. In the meantime, it’s part of the toolkit of most runtimes, +so you can rely on it, and everything we cover next should generally apply! + +In the examples we saw in the [“Streams: Futures in Sequence”][streams]<!-- +ignore --> section, though, we didn’t use `poll_next` _or_ `Stream`, but +instead used `next` and `StreamExt`. We _could_ work directly in terms of the +`poll_next` API by hand-writing our own `Stream` state machines, of course, +just as we _could_ work with futures directly via their `poll` method. Using +`await` is much nicer, though, and the `StreamExt` trait supplies the `next` +method so we can do just that: + +```rust +{{#rustdoc_include ../listings/ch17-async-await/no-listing-stream-ext/src/lib.rs:here}} +``` + +<!-- +TODO: update this if/when tokio/etc. update their MSRV and switch to using async functions +in traits, since the lack thereof is the reason they do not yet have this. +--> + +> Note: The actual definition we used earlier in the chapter looks slightly +> different than this, because it supports versions of Rust that did not yet +> support using async functions in traits. As a result, it looks like this: +> +> ```rust,ignore +> fn next(&mut self) -> Next<'_, Self> where Self: Unpin; +> ``` +> +> That `Next` type is a `struct` that implements `Future` and allows us to name +> the lifetime of the reference to `self` with `Next<'_, Self>`, so that `await` +> can work with this method. + +The `StreamExt` trait is also the home of all the interesting methods available +to use with streams. `StreamExt` is automatically implemented for every type +that implements `Stream`, but these traits are defined separately to enable the +community to iterate on convenience APIs without affecting the foundational +trait. + +In the version of `StreamExt` used in the `trpl` crate, the trait not only +defines the `next` method but also supplies a default implementation of `next` +that correctly handles the details of calling `Stream::poll_next`. This means +that even when you need to write your own streaming data type, you _only_ have +to implement `Stream`, and then anyone who uses your data type can use +`StreamExt` and its methods with it automatically. + +That’s all we’re going to cover for the lower-level details on these traits. To +wrap up, let’s consider how futures (including streams), tasks, and threads all +fit together! + +[message-passing]: ch17-02-concurrency-with-async.md#sending-data-between-two-tasks-using-message-passing +[ch-18]: ch18-00-oop.html +[async-book]: https://rust-lang.github.io/async-book/ +[under-the-hood]: https://rust-lang.github.io/async-book/02_execution/01_chapter.html +[pinning]: https://rust-lang.github.io/async-book/04_pinning/01_chapter.html +[first-async]: ch17-01-futures-and-syntax.html#our-first-async-program +[any-number-futures]: ch17-03-more-futures.html#working-with-any-number-of-futures +[streams]: ch17-04-streams.html diff --git a/src/ch17-06-futures-tasks-threads.md b/src/ch17-06-futures-tasks-threads.md new file mode 100644 index 0000000000..b78902a38e --- /dev/null +++ b/src/ch17-06-futures-tasks-threads.md @@ -0,0 +1,105 @@ +## Putting It All Together: Futures, Tasks, and Threads + +As we saw in [Chapter 16][ch16]<!-- ignore -->, threads provide one approach to +concurrency. We’ve seen another approach in this chapter: using async with +futures and streams. If you’re wondering when to choose one method over the other, +the answer is: it depends! And in many cases, the choice isn’t threads _or_ +async but rather threads _and_ async. + +Many operating systems have supplied threading-based concurrency models for +decades now, and many programming languages support them as a result. However, +these models are not without their tradeoffs. On many operating systems, they +use a fair bit of memory for each thread. Threads are also only an option when +your operating system and hardware support them. Unlike mainstream desktop and +mobile computers, some embedded systems don’t have an OS at all, so they also +don’t have threads. + +The async model provides a different—and ultimately complementary—set of +tradeoffs. In the async model, concurrent operations don’t require their own +threads. Instead, they can run on tasks, as when we used `trpl::spawn_task` to +kick off work from a synchronous function in the streams section. A task is +similar to a thread, but instead of being managed by the operating system, it’s +managed by library-level code: the runtime. + +There’s a reason the APIs for spawning threads and spawning tasks are so +similar. Threads act as a boundary for sets of synchronous operations; +concurrency is possible _between_ threads. Tasks act as a boundary for sets of +_asynchronous_ operations; concurrency is possible both _between_ and _within_ +tasks, because a task can switch between futures in its body. Finally, futures +are Rust’s most granular unit of concurrency, and each future may represent a +tree of other futures. The runtime—specifically, its executor—manages tasks, +and tasks manage futures. In that regard, tasks are similar to lightweight, +runtime-managed threads with added capabilities that come from being managed by +a runtime instead of by the operating system. + +This doesn’t mean that async tasks are always better than threads (or vice +versa). Concurrency with threads is in some ways a simpler programming model +than concurrency with `async`. That can be a strength or a weakness. Threads are +somewhat “fire and forget”; they have no native equivalent to a future, so they +simply run to completion without being interrupted except by the operating +system itself. + +And it turns out that threads and tasks often work +very well together, because tasks can (at least in some runtimes) be moved +around between threads. In fact, under the hood, the runtime we’ve been +using—including the `spawn_blocking` and `spawn_task` functions—is multithreaded +by default! Many runtimes use an approach called _work stealing_ to +transparently move tasks around between threads, based on how the threads are +currently being utilized, to improve the system’s overall performance. That +approach actually requires threads _and_ tasks, and therefore futures. + +When thinking about which method to use when, consider these rules of thumb: + +- If the work is _very parallelizable_ (that is, CPU-bound), such as processing + a bunch of data where each part can be processed separately, threads are a + better choice. +- If the work is _very concurrent_ (that is, I/O-bound), such as handling + messages from a bunch of different sources that may come in at different + intervals or different rates, async is a better choice. + +And if you need both parallelism and concurrency, you don’t have to choose +between threads and async. You can use them together freely, letting each +play the part it’s best at. For example, Listing 17-25 shows a fairly common +example of this kind of mix in real-world Rust code. + +<Listing number="17-25" caption="Sending messages with blocking code in a thread and awaiting the messages in an async block" file-name="src/main.rs"> + +```rust +{{#rustdoc_include ../listings/ch17-async-await/listing-17-25/src/main.rs:all}} +``` + +</Listing> + +We begin by creating an async channel, then spawning a thread that takes +ownership of the sender side of the channel using the `move` keyword. Within +the thread, we send the numbers 1 through 10, sleeping for a second between +each. Finally, we run a future created with an async block passed to +`trpl::block_on` just as we have throughout the chapter. In that future, we +await those messages, just as in the other message-passing examples we have +seen. + +To return to the scenario we opened the chapter with, imagine running a set of +video encoding tasks using a dedicated thread (because video encoding is +compute-bound) but notifying the UI that those operations are done with an +async channel. There are countless examples of these kinds of combinations in +real-world use cases. + +## Summary + +This isn’t the last you’ll see of concurrency in this book. The project in +[Chapter 21][ch21]<!-- ignore --> will apply these concepts in a more realistic +situation than the simpler examples discussed here and compare problem-solving +with threading versus tasks and futures more directly. + +No matter which of these approaches you choose, Rust gives you the tools you +need to write safe, fast, concurrent code—whether for a high-throughput web +server or an embedded operating system. + +Next, we’ll talk about idiomatic ways to model problems and structure solutions +as your Rust programs get bigger. In addition, we’ll discuss how Rust’s idioms +relate to those you might be familiar with from object-oriented programming. + +[ch16]: http://localhost:3000/ch16-00-concurrency.html +[combining-futures]: ch17-03-more-futures.html#building-our-own-async-abstractions +[streams]: ch17-04-streams.html#composing-streams +[ch21]: ch21-00-final-project-a-web-server.html diff --git a/src/ch17-00-oop.md b/src/ch18-00-oop.md similarity index 70% rename from src/ch17-00-oop.md rename to src/ch18-00-oop.md index e20f6583f3..b55c0cf0f3 100644 --- a/src/ch17-00-oop.md +++ b/src/ch18-00-oop.md @@ -1,13 +1,17 @@ -# Object-Oriented Programming Features of Rust +# Object-Oriented Programming Features + +<!-- Old headings. Do not remove or links may break. --> + +<a id="object-oriented-programming-features-of-rust"></a> Object-oriented programming (OOP) is a way of modeling programs. Objects as a programmatic concept were introduced in the programming language Simula in the 1960s. Those objects influenced Alan Kay’s programming architecture in which objects pass messages to each other. To describe this architecture, he coined -the term *object-oriented programming* in 1967. Many competing definitions -describe what OOP is, and by some of these definitions Rust is object-oriented, +the term _object-oriented programming_ in 1967. Many competing definitions +describe what OOP is, and by some of these definitions Rust is object oriented but by others it is not. In this chapter, we’ll explore certain characteristics -that are commonly considered object-oriented and how those characteristics +that are commonly considered object oriented and how those characteristics translate to idiomatic Rust. We’ll then show you how to implement an object-oriented design pattern in Rust and discuss the trade-offs of doing so versus implementing a solution using some of Rust’s strengths instead. diff --git a/src/ch18-01-all-the-places-for-patterns.md b/src/ch18-01-all-the-places-for-patterns.md deleted file mode 100644 index 58f5af573b..0000000000 --- a/src/ch18-01-all-the-places-for-patterns.md +++ /dev/null @@ -1,250 +0,0 @@ -## All the Places Patterns Can Be Used - -Patterns pop up in a number of places in Rust, and you’ve been using them a lot -without realizing it! This section discusses all the places where patterns are -valid. - -### `match` Arms - -As discussed in Chapter 6, we use patterns in the arms of `match` expressions. -Formally, `match` expressions are defined as the keyword `match`, a value to -match on, and one or more match arms that consist of a pattern and an -expression to run if the value matches that arm’s pattern, like this: - -```text -match VALUE { - PATTERN => EXPRESSION, - PATTERN => EXPRESSION, - PATTERN => EXPRESSION, -} -``` - -For example, here's the `match` expression from Listing 6-5 that matches on an -`Option<i32>` value in the variable `x`: - -```rust,ignore -match x { - None => None, - Some(i) => Some(i + 1), -} -``` - -The patterns in this `match` expression are the `None` and `Some(i)` on the -left of each arrow. - -One requirement for `match` expressions is that they need to be *exhaustive* in -the sense that all possibilities for the value in the `match` expression must -be accounted for. One way to ensure you’ve covered every possibility is to have -a catchall pattern for the last arm: for example, a variable name matching any -value can never fail and thus covers every remaining case. - -The particular pattern `_` will match anything, but it never binds to a -variable, so it’s often used in the last match arm. The `_` pattern can be -useful when you want to ignore any value not specified, for example. We’ll -cover the `_` pattern in more detail in the [“Ignoring Values in a -Pattern”][ignoring-values-in-a-pattern]<!-- ignore --> section later in this -chapter. - -### Conditional `if let` Expressions - -In Chapter 6 we discussed how to use `if let` expressions mainly as a shorter -way to write the equivalent of a `match` that only matches one case. -Optionally, `if let` can have a corresponding `else` containing code to run if -the pattern in the `if let` doesn’t match. - -Listing 18-1 shows that it’s also possible to mix and match `if let`, `else -if`, and `else if let` expressions. Doing so gives us more flexibility than a -`match` expression in which we can express only one value to compare with the -patterns. Also, Rust doesn't require that the conditions in a series of `if -let`, `else if`, `else if let` arms relate to each other. - -The code in Listing 18-1 determines what color to make your background based on -a series of checks for several conditions. For this example, we’ve created -variables with hardcoded values that a real program might receive from user -input. - -<span class="filename">Filename: src/main.rs</span> - -```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-01/src/main.rs}} -``` - -<span class="caption">Listing 18-1: Mixing `if let`, `else if`, `else if let`, -and `else`</span> - -If the user specifies a favorite color, that color is used as the background. -If no favorite color is specified and today is Tuesday, the background color is -green. Otherwise, if the user specifies their age as a string and we can parse -it as a number successfully, the color is either purple or orange depending on -the value of the number. If none of these conditions apply, the background -color is blue. - -This conditional structure lets us support complex requirements. With the -hardcoded values we have here, this example will print `Using purple as the -background color`. - -You can see that `if let` can also introduce shadowed variables in the same way -that `match` arms can: the line `if let Ok(age) = age` introduces a new -shadowed `age` variable that contains the value inside the `Ok` variant. This -means we need to place the `if age > 30` condition within that block: we can’t -combine these two conditions into `if let Ok(age) = age && age > 30`. The -shadowed `age` we want to compare to 30 isn’t valid until the new scope starts -with the curly bracket. - -The downside of using `if let` expressions is that the compiler doesn’t check -for exhaustiveness, whereas with `match` expressions it does. If we omitted the -last `else` block and therefore missed handling some cases, the compiler would -not alert us to the possible logic bug. - -### `while let` Conditional Loops - -Similar in construction to `if let`, the `while let` conditional loop allows a -`while` loop to run for as long as a pattern continues to match. In Listing -18-2 we code a `while let` loop that uses a vector as a stack and prints the -values in the vector in the opposite order in which they were pushed. - -```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-02/src/main.rs:here}} -``` - -<span class="caption">Listing 18-2: Using a `while let` loop to print values -for as long as `stack.pop()` returns `Some`</span> - -This example prints 3, 2, and then 1. The `pop` method takes the last element -out of the vector and returns `Some(value)`. If the vector is empty, `pop` -returns `None`. The `while` loop continues running the code in its block as -long as `pop` returns `Some`. When `pop` returns `None`, the loop stops. We can -use `while let` to pop every element off our stack. - -### `for` Loops - -In a `for` loop, the value that directly follows the keyword `for` is a -pattern. For example, in `for x in y` the `x` is the pattern. Listing 18-3 -demonstrates how to use a pattern in a `for` loop to destructure, or break -apart, a tuple as part of the `for` loop. - -```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-03/src/main.rs:here}} -``` - -<span class="caption">Listing 18-3: Using a pattern in a `for` loop to -destructure a tuple</span> - -The code in Listing 18-3 will print the following: - -```console -{{#include ../listings/ch18-patterns-and-matching/listing-18-03/output.txt}} -``` - -We adapt an iterator using the `enumerate` method so it produces a value and -the index for that value, placed into a tuple. The first value produced is the -tuple `(0, 'a')`. When this value is matched to the pattern `(index, value)`, -`index` will be `0` and `value` will be `'a'`, printing the first line of the -output. - -### `let` Statements - -Prior to this chapter, we had only explicitly discussed using patterns with -`match` and `if let`, but in fact, we’ve used patterns in other places as well, -including in `let` statements. For example, consider this straightforward -variable assignment with `let`: - -```rust -let x = 5; -``` - -Every time you've used a `let` statement like this you've been using patterns, -although you might not have realized it! More formally, a `let` statement looks -like this: - -```text -let PATTERN = EXPRESSION; -``` - -In statements like `let x = 5;` with a variable name in the `PATTERN` slot, the -variable name is just a particularly simple form of a pattern. Rust compares -the expression against the pattern and assigns any names it finds. So in the -`let x = 5;` example, `x` is a pattern that means “bind what matches here to -the variable `x`.” Because the name `x` is the whole pattern, this pattern -effectively means “bind everything to the variable `x`, whatever the value is.” - -To see the pattern matching aspect of `let` more clearly, consider Listing -18-4, which uses a pattern with `let` to destructure a tuple. - -```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-04/src/main.rs:here}} -``` - -<span class="caption">Listing 18-4: Using a pattern to destructure a tuple and -create three variables at once</span> - -Here, we match a tuple against a pattern. Rust compares the value `(1, 2, 3)` -to the pattern `(x, y, z)` and sees that the value matches the pattern, so Rust -binds `1` to `x`, `2` to `y`, and `3` to `z`. You can think of this tuple -pattern as nesting three individual variable patterns inside it. - -If the number of elements in the pattern doesn’t match the number of elements -in the tuple, the overall type won’t match and we’ll get a compiler error. For -example, Listing 18-5 shows an attempt to destructure a tuple with three -elements into two variables, which won’t work. - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-05/src/main.rs:here}} -``` - -<span class="caption">Listing 18-5: Incorrectly constructing a pattern whose -variables don’t match the number of elements in the tuple</span> - -Attempting to compile this code results in this type error: - -```console -{{#include ../listings/ch18-patterns-and-matching/listing-18-05/output.txt}} -``` - -To fix the error, we could ignore one or more of the values in the tuple using -`_` or `..`, as you’ll see in the [“Ignoring Values in a -Pattern”][ignoring-values-in-a-pattern]<!-- ignore --> section. If the problem -is that we have too many variables in the pattern, the solution is to make the -types match by removing variables so the number of variables equals the number -of elements in the tuple. - -### Function Parameters - -Function parameters can also be patterns. The code in Listing 18-6, which -declares a function named `foo` that takes one parameter named `x` of type -`i32`, should by now look familiar. - -```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-06/src/main.rs:here}} -``` - -<span class="caption">Listing 18-6: A function signature uses patterns in the -parameters</span> - -The `x` part is a pattern! As we did with `let`, we could match a tuple in a -function’s arguments to the pattern. Listing 18-7 splits the values in a tuple -as we pass it to a function. - -<span class="filename">Filename: src/main.rs</span> - -```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-07/src/main.rs}} -``` - -<span class="caption">Listing 18-7: A function with parameters that destructure -a tuple</span> - -This code prints `Current location: (3, 5)`. The values `&(3, 5)` match the -pattern `&(x, y)`, so `x` is the value `3` and `y` is the value `5`. - -We can also use patterns in closure parameter lists in the same way as in -function parameter lists, because closures are similar to functions, as -discussed in Chapter 13. - -At this point, you’ve seen several ways of using patterns, but patterns don’t -work the same in every place we can use them. In some places, the patterns must -be irrefutable; in other circumstances, they can be refutable. We’ll discuss -these two concepts next. - -[ignoring-values-in-a-pattern]: -ch18-03-pattern-syntax.html#ignoring-values-in-a-pattern diff --git a/src/ch17-01-what-is-oo.md b/src/ch18-01-what-is-oo.md similarity index 61% rename from src/ch17-01-what-is-oo.md rename to src/ch18-01-what-is-oo.md index a47afebd93..482c7fd756 100644 --- a/src/ch17-01-what-is-oo.md +++ b/src/ch18-01-what-is-oo.md @@ -1,32 +1,32 @@ ## Characteristics of Object-Oriented Languages There is no consensus in the programming community about what features a -language must have to be considered object-oriented. Rust is influenced by many +language must have to be considered object oriented. Rust is influenced by many programming paradigms, including OOP; for example, we explored the features that came from functional programming in Chapter 13. Arguably, OOP languages -share certain common characteristics, namely objects, encapsulation, and +share certain common characteristics—namely, objects, encapsulation, and inheritance. Let’s look at what each of those characteristics means and whether Rust supports it. ### Objects Contain Data and Behavior -The book *Design Patterns: Elements of Reusable Object-Oriented Software* by -Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (Addison-Wesley -Professional, 1994), colloquially referred to as *The Gang of Four* book, is a -catalog of object-oriented design patterns. It defines OOP this way: +The book _Design Patterns: Elements of Reusable Object-Oriented Software_ by +Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (Addison-Wesley, +1994), colloquially referred to as _The Gang of Four_ book, is a catalog of +object-oriented design patterns. It defines OOP in this way: -> Object-oriented programs are made up of objects. An *object* packages both +> Object-oriented programs are made up of objects. An **object** packages both > data and the procedures that operate on that data. The procedures are -> typically called *methods* or *operations*. +> typically called **methods** or **operations**. -Using this definition, Rust is object-oriented: structs and enums have data, +Using this definition, Rust is object oriented: Structs and enums have data, and `impl` blocks provide methods on structs and enums. Even though structs and -enums with methods aren’t *called* objects, they provide the same +enums with methods aren’t _called_ objects, they provide the same functionality, according to the Gang of Four’s definition of objects. -### Encapsulation that Hides Implementation Details +### Encapsulation That Hides Implementation Details -Another aspect commonly associated with OOP is the idea of *encapsulation*, +Another aspect commonly associated with OOP is the idea of _encapsulation_, which means that the implementation details of an object aren’t accessible to code using that object. Therefore, the only way to interact with an object is through its public API; code using the object shouldn’t be able to reach into @@ -34,48 +34,45 @@ the object’s internals and change data or behavior directly. This enables the programmer to change and refactor an object’s internals without needing to change the code that uses the object. -We discussed how to control encapsulation in Chapter 7: we can use the `pub` +We discussed how to control encapsulation in Chapter 7: We can use the `pub` keyword to decide which modules, types, functions, and methods in our code should be public, and by default everything else is private. For example, we can define a struct `AveragedCollection` that has a field containing a vector of `i32` values. The struct can also have a field that contains the average of -the values in the vector, meaning the average doesn’t have to be computed -on demand whenever anyone needs it. In other words, `AveragedCollection` will -cache the calculated average for us. Listing 17-1 has the definition of the -`AveragedCollection` struct: +the values in the vector, meaning the average doesn’t have to be computed on +demand whenever anyone needs it. In other words, `AveragedCollection` will +cache the calculated average for us. Listing 18-1 has the definition of the +`AveragedCollection` struct. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-1" file-name="src/lib.rs" caption="An `AveragedCollection` struct that maintains a list of integers and the average of the items in the collection"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-01/src/lib.rs}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-01/src/lib.rs}} ``` -<span class="caption">Listing 17-1: An `AveragedCollection` struct that -maintains a list of integers and the average of the items in the -collection</span> +</Listing> The struct is marked `pub` so that other code can use it, but the fields within the struct remain private. This is important in this case because we want to ensure that whenever a value is added or removed from the list, the average is also updated. We do this by implementing `add`, `remove`, and `average` methods -on the struct, as shown in Listing 17-2: +on the struct, as shown in Listing 18-2. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-2" file-name="src/lib.rs" caption="Implementations of the public methods `add`, `remove`, and `average` on `AveragedCollection`"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-02/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-02/src/lib.rs:here}} ``` -<span class="caption">Listing 17-2: Implementations of the public methods -`add`, `remove`, and `average` on `AveragedCollection`</span> +</Listing> The public methods `add`, `remove`, and `average` are the only ways to access -or modify data in an instance of `AveragedCollection`. When an item is added -to `list` using the `add` method or removed using the `remove` method, the +or modify data in an instance of `AveragedCollection`. When an item is added to +`list` using the `add` method or removed using the `remove` method, the implementations of each call the private `update_average` method that handles updating the `average` field as well. -We leave the `list` and `average` fields private so there is no way for +We leave the `list` and `average` fields private so that there is no way for external code to add or remove items to or from the `list` field directly; otherwise, the `average` field might become out of sync when the `list` changes. The `average` method returns the value in the `average` field, @@ -85,24 +82,24 @@ Because we’ve encapsulated the implementation details of the struct `AveragedCollection`, we can easily change aspects, such as the data structure, in the future. For instance, we could use a `HashSet<i32>` instead of a `Vec<i32>` for the `list` field. As long as the signatures of the `add`, -`remove`, and `average` public methods stay the same, code using +`remove`, and `average` public methods stayed the same, code using `AveragedCollection` wouldn’t need to change. If we made `list` public instead, this wouldn’t necessarily be the case: `HashSet<i32>` and `Vec<i32>` have different methods for adding and removing items, so the external code would likely have to change if it were modifying `list` directly. -If encapsulation is a required aspect for a language to be considered -object-oriented, then Rust meets that requirement. The option to use `pub` or -not for different parts of code enables encapsulation of implementation details. +If encapsulation is a required aspect for a language to be considered object +oriented, then Rust meets that requirement. The option to use `pub` or not for +different parts of code enables encapsulation of implementation details. ### Inheritance as a Type System and as Code Sharing -*Inheritance* is a mechanism whereby an object can inherit elements from +_Inheritance_ is a mechanism whereby an object can inherit elements from another object’s definition, thus gaining the parent object’s data and behavior without you having to define them again. -If a language must have inheritance to be an object-oriented language, then -Rust is not one. There is no way to define a struct that inherits the parent +If a language must have inheritance to be object oriented, then Rust is not +such a language. There is no way to define a struct that inherits the parent struct’s fields and method implementations without using a macro. However, if you’re used to having inheritance in your programming toolbox, you @@ -110,7 +107,7 @@ can use other solutions in Rust, depending on your reason for reaching for inheritance in the first place. You would choose inheritance for two main reasons. One is for reuse of code: -you can implement particular behavior for one type, and inheritance enables you +You can implement particular behavior for one type, and inheritance enables you to reuse that implementation for a different type. You can do this in a limited way in Rust code using default trait method implementations, which you saw in Listing 10-14 when we added a default implementation of the `summarize` method @@ -124,29 +121,29 @@ implementation of a method inherited from a parent class. The other reason to use inheritance relates to the type system: to enable a child type to be used in the same places as the parent type. This is also -called *polymorphism*, which means that you can substitute multiple objects for +called _polymorphism_, which means that you can substitute multiple objects for each other at runtime if they share certain characteristics. > ### Polymorphism > > To many people, polymorphism is synonymous with inheritance. But it’s -> actually a more general concept that refers to code that can work with data -> of multiple types. For inheritance, those types are generally subclasses. +> actually a more general concept that refers to code that can work with data of +> multiple types. For inheritance, those types are generally subclasses. > > Rust instead uses generics to abstract over different possible types and > trait bounds to impose constraints on what those types must provide. This is -> sometimes called *bounded parametric polymorphism*. - -Inheritance has recently fallen out of favor as a programming design solution -in many programming languages because it’s often at risk of sharing more code -than necessary. Subclasses shouldn’t always share all characteristics of their -parent class but will do so with inheritance. This can make a program’s design -less flexible. It also introduces the possibility of calling methods on -subclasses that don’t make sense or that cause errors because the methods don’t -apply to the subclass. In addition, some languages will only allow single -inheritance (meaning a subclass can only inherit from one class), further -restricting the flexibility of a program’s design. +> sometimes called _bounded parametric polymorphism_. + +Rust has chosen a different set of trade-offs by not offering inheritance. +Inheritance is often at risk of sharing more code than necessary. Subclasses +shouldn’t always share all characteristics of their parent class but will do so +with inheritance. This can make a program’s design less flexible. It also +introduces the possibility of calling methods on subclasses that don’t make +sense or that cause errors because the methods don’t apply to the subclass. In +addition, some languages will only allow _single inheritance_ (meaning a +subclass can only inherit from one class), further restricting the flexibility +of a program’s design. For these reasons, Rust takes the different approach of using trait objects -instead of inheritance. Let’s look at how trait objects enable polymorphism in -Rust. +instead of inheritance to achieve polymorphism at runtime. Let’s look at how +trait objects work. diff --git a/src/ch17-02-trait-objects.md b/src/ch18-02-trait-objects.md similarity index 51% rename from src/ch17-02-trait-objects.md rename to src/ch18-02-trait-objects.md index 2d3fea24a1..aee4e1e142 100644 --- a/src/ch17-02-trait-objects.md +++ b/src/ch18-02-trait-objects.md @@ -1,4 +1,8 @@ -## Using Trait Objects That Allow for Values of Different Types +<!-- Old headings. Do not remove or links may break. --> + +<a id="using-trait-objects-that-allow-for-values-of-different-types"></a> + +## Using Trait Objects to Abstract over Shared Behavior In Chapter 8, we mentioned that one limitation of vectors is that they can store elements of only one type. We created a workaround in Listing 8-9 where @@ -15,17 +19,16 @@ through a list of items, calling a `draw` method on each one to draw it to the screen—a common technique for GUI tools. We’ll create a library crate called `gui` that contains the structure of a GUI library. This crate might include some types for people to use, such as `Button` or `TextField`. In addition, -`gui` users will want to create their own types that can be drawn: for -instance, one programmer might add an `Image` and another might add a +`gui` users will want to create their own types that can be drawn: For +instance, one programmer might add an `Image`, and another might add a `SelectBox`. -We won’t implement a fully fledged GUI library for this example but will show -how the pieces would fit together. At the time of writing the library, we can’t -know and define all the types other programmers might want to create. But we do -know that `gui` needs to keep track of many values of different types, and it -needs to call a `draw` method on each of these differently typed values. It -doesn’t need to know exactly what will happen when we call the `draw` method, -just that the value will have that method available for us to call. +At the time of writing the library, we can’t know and define all the types +other programmers might want to create. But we do know that `gui` needs to keep +track of many values of different types, and it needs to call a `draw` method +on each of these differently typed values. It doesn’t need to know exactly what +will happen when we call the `draw` method, just that the value will have that +method available for us to call. To do this in a language with inheritance, we might define a class named `Component` that has a method named `draw` on it. The other classes, such as @@ -34,89 +37,83 @@ inherit the `draw` method. They could each override the `draw` method to define their custom behavior, but the framework could treat all of the types as if they were `Component` instances and call `draw` on them. But because Rust doesn’t have inheritance, we need another way to structure the `gui` library to -allow users to extend it with new types. +allow users to create new types compatible with the library. ### Defining a Trait for Common Behavior -To implement the behavior we want `gui` to have, we’ll define a trait named -`Draw` that will have one method named `draw`. Then we can define a vector that -takes a *trait object*. A trait object points to both an instance of a type -implementing our specified trait and a table used to look up trait methods on -that type at runtime. We create a trait object by specifying some sort of -pointer, such as a `&` reference or a `Box<T>` smart pointer, then the `dyn` -keyword, and then specifying the relevant trait. (We’ll talk about the reason -trait objects must use a pointer in Chapter 19 in the section [“Dynamically -Sized Types and the `Sized` Trait.”][dynamically-sized]<!-- ignore -->) We can -use trait objects in place of a generic or concrete type. Wherever we use a -trait object, Rust’s type system will ensure at compile time that any value -used in that context will implement the trait object’s trait. Consequently, we -don’t need to know all the possible types at compile time. +To implement the behavior that we want `gui` to have, we’ll define a trait +named `Draw` that will have one method named `draw`. Then, we can define a +vector that takes a trait object. A _trait object_ points to both an instance +of a type implementing our specified trait and a table used to look up trait +methods on that type at runtime. We create a trait object by specifying some +sort of pointer, such as a reference or a `Box<T>` smart pointer, then the +`dyn` keyword, and then specifying the relevant trait. (We’ll talk about the +reason trait objects must use a pointer in [“Dynamically Sized Types and the +`Sized` Trait”][dynamically-sized]<!-- ignore --> in Chapter 20.) We can use +trait objects in place of a generic or concrete type. Wherever we use a trait +object, Rust’s type system will ensure at compile time that any value used in +that context will implement the trait object’s trait. Consequently, we don’t +need to know all the possible types at compile time. We’ve mentioned that, in Rust, we refrain from calling structs and enums “objects” to distinguish them from other languages’ objects. In a struct or enum, the data in the struct fields and the behavior in `impl` blocks are separated, whereas in other languages, the data and behavior combined into one -concept is often labeled an object. However, trait objects *are* more like -objects in other languages in the sense that they combine data and behavior. -But trait objects differ from traditional objects in that we can’t add data to -a trait object. Trait objects aren’t as generally useful as objects in other -languages: their specific purpose is to allow abstraction across common -behavior. +concept is often labeled an object. Trait objects differ from objects in other +languages in that we can’t add data to a trait object. Trait objects aren’t as +generally useful as objects in other languages: Their specific purpose is to +allow abstraction across common behavior. -Listing 17-3 shows how to define a trait named `Draw` with one method named -`draw`: +Listing 18-3 shows how to define a trait named `Draw` with one method named +`draw`. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-3" file-name="src/lib.rs" caption="Definition of the `Draw` trait"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-03/src/lib.rs}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-03/src/lib.rs}} ``` -<span class="caption">Listing 17-3: Definition of the `Draw` trait</span> +</Listing> This syntax should look familiar from our discussions on how to define traits -in Chapter 10. Next comes some new syntax: Listing 17-4 defines a struct named +in Chapter 10. Next comes some new syntax: Listing 18-4 defines a struct named `Screen` that holds a vector named `components`. This vector is of type -`Box<dyn Draw>`, which is a trait object; it’s a stand-in for any type inside -a `Box` that implements the `Draw` trait. +`Box<dyn Draw>`, which is a trait object; it’s a stand-in for any type inside a +`Box` that implements the `Draw` trait. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-4" file-name="src/lib.rs" caption="Definition of the `Screen` struct with a `components` field holding a vector of trait objects that implement the `Draw` trait"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-04/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-04/src/lib.rs:here}} ``` -<span class="caption">Listing 17-4: Definition of the `Screen` struct with a -`components` field holding a vector of trait objects that implement the `Draw` -trait</span> +</Listing> On the `Screen` struct, we’ll define a method named `run` that will call the -`draw` method on each of its `components`, as shown in Listing 17-5: +`draw` method on each of its `components`, as shown in Listing 18-5. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-5" file-name="src/lib.rs" caption="A `run` method on `Screen` that calls the `draw` method on each component"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-05/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-05/src/lib.rs:here}} ``` -<span class="caption">Listing 17-5: A `run` method on `Screen` that calls the -`draw` method on each component</span> +</Listing> This works differently from defining a struct that uses a generic type -parameter with trait bounds. A generic type parameter can only be substituted -with one concrete type at a time, whereas trait objects allow for multiple +parameter with trait bounds. A generic type parameter can be substituted with +only one concrete type at a time, whereas trait objects allow for multiple concrete types to fill in for the trait object at runtime. For example, we -could have defined the `Screen` struct using a generic type and a trait bound -as in Listing 17-6: +could have defined the `Screen` struct using a generic type and a trait bound, +as in Listing 18-6. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-6" file-name="src/lib.rs" caption="An alternate implementation of the `Screen` struct and its `run` method using generics and trait bounds"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-06/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-06/src/lib.rs:here}} ``` -<span class="caption">Listing 17-6: An alternate implementation of the `Screen` -struct and its `run` method using generics and trait bounds</span> +</Listing> This restricts us to a `Screen` instance that has a list of components all of type `Button` or all of type `TextField`. If you’ll only ever have homogeneous @@ -134,16 +131,15 @@ Now we’ll add some types that implement the `Draw` trait. We’ll provide the `Button` type. Again, actually implementing a GUI library is beyond the scope of this book, so the `draw` method won’t have any useful implementation in its body. To imagine what the implementation might look like, a `Button` struct -might have fields for `width`, `height`, and `label`, as shown in Listing 17-7: +might have fields for `width`, `height`, and `label`, as shown in Listing 18-7. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-7" file-name="src/lib.rs" caption="A `Button` struct that implements the `Draw` trait"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-07/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-07/src/lib.rs:here}} ``` -<span class="caption">Listing 17-7: A `Button` struct that implements the -`Draw` trait</span> +</Listing> The `width`, `height`, and `label` fields on `Button` will differ from the fields on other components; for example, a `TextField` type might have those @@ -156,32 +152,30 @@ happens when a user clicks the button. These kinds of methods won’t apply to types like `TextField`. If someone using our library decides to implement a `SelectBox` struct that has -`width`, `height`, and `options` fields, they implement the `Draw` trait on the -`SelectBox` type as well, as shown in Listing 17-8: +`width`, `height`, and `options` fields, they would implement the `Draw` trait +on the `SelectBox` type as well, as shown in Listing 18-8. -<span class="filename">Filename: src/main.rs</span> +<Listing number="18-8" file-name="src/main.rs" caption="Another crate using `gui` and implementing the `Draw` trait on a `SelectBox` struct"> ```rust,ignore -{{#rustdoc_include ../listings/ch17-oop/listing-17-08/src/main.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-08/src/main.rs:here}} ``` -<span class="caption">Listing 17-8: Another crate using `gui` and implementing -the `Draw` trait on a `SelectBox` struct</span> +</Listing> Our library’s user can now write their `main` function to create a `Screen` instance. To the `Screen` instance, they can add a `SelectBox` and a `Button` by putting each in a `Box<T>` to become a trait object. They can then call the `run` method on the `Screen` instance, which will call `draw` on each of the -components. Listing 17-9 shows this implementation: +components. Listing 18-9 shows this implementation. -<span class="filename">Filename: src/main.rs</span> +<Listing number="18-9" file-name="src/main.rs" caption="Using trait objects to store values of different types that implement the same trait"> ```rust,ignore -{{#rustdoc_include ../listings/ch17-oop/listing-17-09/src/main.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-09/src/main.rs:here}} ``` -<span class="caption">Listing 17-9: Using trait objects to store values of -different types that implement the same trait</span> +</Listing> When we wrote the library, we didn’t know that someone might add the `SelectBox` type, but our `Screen` implementation was able to operate on the @@ -189,10 +183,10 @@ new type and draw it because `SelectBox` implements the `Draw` trait, which means it implements the `draw` method. This concept—of being concerned only with the messages a value responds to -rather than the value’s concrete type—is similar to the concept of *duck -typing* in dynamically typed languages: if it walks like a duck and quacks -like a duck, then it must be a duck! In the implementation of `run` on `Screen` -in Listing 17-5, `run` doesn’t need to know what the concrete type of each +rather than the value’s concrete type—is similar to the concept of _duck +typing_ in dynamically typed languages: If it walks like a duck and quacks like +a duck, then it must be a duck! In the implementation of `run` on `Screen` in +Listing 18-5, `run` doesn’t need to know what the concrete type of each component is. It doesn’t check whether a component is an instance of a `Button` or a `SelectBox`, it just calls the `draw` method on the component. By specifying `Box<dyn Draw>` as the type of the values in the `components` @@ -205,52 +199,57 @@ value implements a particular method at runtime or worry about getting errors if a value doesn’t implement a method but we call it anyway. Rust won’t compile our code if the values don’t implement the traits that the trait objects need. -For example, Listing 17-10 shows what happens if we try to create a `Screen` -with a `String` as a component: +For example, Listing 18-10 shows what happens if we try to create a `Screen` +with a `String` as a component. -<span class="filename">Filename: src/main.rs</span> +<Listing number="18-10" file-name="src/main.rs" caption="Attempting to use a type that doesn’t implement the trait object’s trait"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch17-oop/listing-17-10/src/main.rs}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-10/src/main.rs}} ``` -<span class="caption">Listing 17-10: Attempting to use a type that doesn’t -implement the trait object’s trait</span> +</Listing> We’ll get this error because `String` doesn’t implement the `Draw` trait: ```console -{{#include ../listings/ch17-oop/listing-17-10/output.txt}} +{{#include ../listings/ch18-oop/listing-18-10/output.txt}} ``` -This error lets us know that either we’re passing something to `Screen` we -didn’t mean to pass and so should pass a different type or we should implement +This error lets us know that either we’re passing something to `Screen` that we +didn’t mean to pass and so should pass a different type, or we should implement `Draw` on `String` so that `Screen` is able to call `draw` on it. -### Trait Objects Perform Dynamic Dispatch +<!-- Old headings. Do not remove or links may break. --> + +<a id="trait-objects-perform-dynamic-dispatch"></a> + +### Performing Dynamic Dispatch -Recall in the [“Performance of Code Using -Generics”][performance-of-code-using-generics]<!-- ignore --> section in -Chapter 10 our discussion on the monomorphization process performed by the -compiler when we use trait bounds on generics: the compiler generates -nongeneric implementations of functions and methods for each concrete type that -we use in place of a generic type parameter. The code that results from -monomorphization is doing *static dispatch*, which is when the compiler knows -what method you’re calling at compile time. This is opposed to *dynamic -dispatch*, which is when the compiler can’t tell at compile time which method -you’re calling. In dynamic dispatch cases, the compiler emits code that at -runtime will figure out which method to call. +Recall in [“Performance of Code Using +Generics”][performance-of-code-using-generics]<!-- ignore --> in Chapter 10 our +discussion on the monomorphization process performed on generics by the +compiler: The compiler generates nongeneric implementations of functions and +methods for each concrete type that we use in place of a generic type +parameter. The code that results from monomorphization is doing _static +dispatch_, which is when the compiler knows what method you’re calling at +compile time. This is opposed to _dynamic dispatch_, which is when the compiler +can’t tell at compile time which method you’re calling. In dynamic dispatch +cases, the compiler emits code that at runtime will know which method to call. When we use trait objects, Rust must use dynamic dispatch. The compiler doesn’t know all the types that might be used with the code that’s using trait objects, so it doesn’t know which method implemented on which type to call. Instead, at runtime, Rust uses the pointers inside the trait object to know which method to -call. This lookup incurs a runtime cost that doesn’t occur with static -dispatch. Dynamic dispatch also prevents the compiler from choosing to inline a -method’s code, which in turn prevents some optimizations. However, we did get -extra flexibility in the code that we wrote in Listing 17-5 and were able to -support in Listing 17-9, so it’s a trade-off to consider. - -[performance-of-code-using-generics]: -ch10-01-syntax.html#performance-of-code-using-generics -[dynamically-sized]: ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait +call. This lookup incurs a runtime cost that doesn’t occur with static dispatch. +Dynamic dispatch also prevents the compiler from choosing to inline a method’s +code, which in turn prevents some optimizations, and Rust has some rules about +where you can and cannot use dynamic dispatch, called _dyn compatibility_. Those +rules are beyond the scope of this discussion, but you can read more about them +[in the reference][dyn-compatibility]<!-- ignore -->. However, we did get extra +flexibility in the code that we wrote in Listing 18-5 and were able to support +in Listing 18-9, so it’s a trade-off to consider. + +[performance-of-code-using-generics]: ch10-01-syntax.html#performance-of-code-using-generics +[dynamically-sized]: ch20-03-advanced-types.html#dynamically-sized-types-and-the-sized-trait +[dyn-compatibility]: https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility diff --git a/src/ch17-03-oo-design-patterns.md b/src/ch18-03-oo-design-patterns.md similarity index 59% rename from src/ch17-03-oo-design-patterns.md rename to src/ch18-03-oo-design-patterns.md index 13503ef02b..e6e5943861 100644 --- a/src/ch17-03-oo-design-patterns.md +++ b/src/ch18-03-oo-design-patterns.md @@ -1,13 +1,13 @@ ## Implementing an Object-Oriented Design Pattern -The *state pattern* is an object-oriented design pattern. The crux of the +The _state pattern_ is an object-oriented design pattern. The crux of the pattern is that we define a set of states a value can have internally. The -states are represented by a set of *state objects*, and the value’s behavior +states are represented by a set of _state objects_, and the value’s behavior changes based on its state. We’re going to work through an example of a blog post struct that has a field to hold its state, which will be a state object -from the set "draft", "review", or "published". +from the set “draft,” “review,” or “published.” -The state objects share functionality: in Rust, of course, we use structs and +The state objects share functionality: In Rust, of course, we use structs and traits rather than objects and inheritance. Each state object is responsible for its own behavior and for governing when it should change into another state. The value that holds a state object knows nothing about the different @@ -20,34 +20,48 @@ update the code inside one of the state objects to change its rules or perhaps add more state objects. First, we’re going to implement the state pattern in a more traditional -object-oriented way, then we’ll use an approach that’s a bit more natural in -Rust. Let’s dig in to incrementally implementing a blog post workflow using the +object-oriented way. Then, we’ll use an approach that’s a bit more natural in +Rust. Let’s dig in to incrementally implement a blog post workflow using the state pattern. The final functionality will look like this: 1. A blog post starts as an empty draft. -2. When the draft is done, a review of the post is requested. -3. When the post is approved, it gets published. -4. Only published blog posts return content to print, so unapproved posts can’t - accidentally be published. +1. When the draft is done, a review of the post is requested. +1. When the post is approved, it gets published. +1. Only published blog posts return content to print so that unapproved posts + can’t accidentally be published. Any other changes attempted on a post should have no effect. For example, if we try to approve a draft blog post before we’ve requested a review, the post should remain an unpublished draft. -Listing 17-11 shows this workflow in code form: this is an example usage of the +<!-- Old headings. Do not remove or links may break. --> + +<a id="a-traditional-object-oriented-attempt"></a> + +### Attempting Traditional Object-Oriented Style + +There are infinite ways to structure code to solve the same problem, each with +different trade-offs. This section’s implementation is more of a traditional +object-oriented style, which is possible to write in Rust, but doesn’t take +advantage of some of Rust’s strengths. Later, we’ll demonstrate a different +solution that still uses the object-oriented design pattern but is structured +in a way that might look less familiar to programmers with object-oriented +experience. We’ll compare the two solutions to experience the trade-offs of +designing Rust code differently than code in other languages. + +Listing 18-11 shows this workflow in code form: This is an example usage of the API we’ll implement in a library crate named `blog`. This won’t compile yet because we haven’t implemented the `blog` crate. -<span class="filename">Filename: src/main.rs</span> +<Listing number="18-11" file-name="src/main.rs" caption="Code that demonstrates the desired behavior we want our `blog` crate to have"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch17-oop/listing-17-11/src/main.rs:all}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-11/src/main.rs:all}} ``` -<span class="caption">Listing 17-11: Code that demonstrates the desired -behavior we want our `blog` crate to have</span> +</Listing> We want to allow the user to create a new draft blog post with `Post::new`. We want to allow text to be added to the blog post. If we try to get the post’s @@ -65,34 +79,36 @@ be returned when `content` is called. Notice that the only type we’re interacting with from the crate is the `Post` type. This type will use the state pattern and will hold a value that will be one of three state objects representing the various states a post can be -in—draft, waiting for review, or published. Changing from one state to another -will be managed internally within the `Post` type. The states change in -response to the methods called by our library’s users on the `Post` instance, -but they don’t have to manage the state changes directly. Also, users can’t -make a mistake with the states, like publishing a post before it’s reviewed. +in—draft, review, or published. Changing from one state to another will be +managed internally within the `Post` type. The states change in response to the +methods called by our library’s users on the `Post` instance, but they don’t +have to manage the state changes directly. Also, users can’t make a mistake +with the states, such as publishing a post before it’s reviewed. -### Defining `Post` and Creating a New Instance in the Draft State +<!-- Old headings. Do not remove or links may break. --> + +<a id="defining-post-and-creating-a-new-instance-in-the-draft-state"></a> + +#### Defining `Post` and Creating a New Instance Let’s get started on the implementation of the library! We know we need a public `Post` struct that holds some content, so we’ll start with the definition of the struct and an associated public `new` function to create an -instance of `Post`, as shown in Listing 17-12. We’ll also make a private +instance of `Post`, as shown in Listing 18-12. We’ll also make a private `State` trait that will define the behavior that all state objects for a `Post` must have. -Then `Post` will hold a trait object of `Box<dyn State>` inside an `Option<T>` +Then, `Post` will hold a trait object of `Box<dyn State>` inside an `Option<T>` in a private field named `state` to hold the state object. You’ll see why the `Option<T>` is necessary in a bit. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-12" file-name="src/lib.rs" caption="Definition of a `Post` struct and a `new` function that creates a new `Post` instance, a `State` trait, and a `Draft` struct"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-12/src/lib.rs}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-12/src/lib.rs}} ``` -<span class="caption">Listing 17-12: Definition of a `Post` struct and a `new` -function that creates a new `Post` instance, a `State` trait, and a `Draft` -struct</span> +</Listing> The `State` trait defines the behavior shared by different post states. The state objects are `Draft`, `PendingReview`, and `Published`, and they will all @@ -101,32 +117,31 @@ we’ll start by defining just the `Draft` state because that is the state we want a post to start in. When we create a new `Post`, we set its `state` field to a `Some` value that -holds a `Box`. This `Box` points to a new instance of the `Draft` struct. -This ensures whenever we create a new instance of `Post`, it will start out as +holds a `Box`. This `Box` points to a new instance of the `Draft` struct. This +ensures that whenever we create a new instance of `Post`, it will start out as a draft. Because the `state` field of `Post` is private, there is no way to create a `Post` in any other state! In the `Post::new` function, we set the `content` field to a new, empty `String`. -### Storing the Text of the Post Content +#### Storing the Text of the Post Content -We saw in Listing 17-11 that we want to be able to call a method named +We saw in Listing 18-11 that we want to be able to call a method named `add_text` and pass it a `&str` that is then added as the text content of the blog post. We implement this as a method, rather than exposing the `content` field as `pub`, so that later we can implement a method that will control how the `content` field’s data is read. The `add_text` method is pretty -straightforward, so let’s add the implementation in Listing 17-13 to the `impl -Post` block: +straightforward, so let’s add the implementation in Listing 18-13 to the `impl +Post` block. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-13" file-name="src/lib.rs" caption="Implementing the `add_text` method to add text to a post’s `content`"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-13/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-13/src/lib.rs:here}} ``` -<span class="caption">Listing 17-13: Implementing the `add_text` method to add -text to a post’s `content`</span> +</Listing> -The `add_text` method takes a mutable reference to `self`, because we’re +The `add_text` method takes a mutable reference to `self` because we’re changing the `Post` instance that we’re calling `add_text` on. We then call `push_str` on the `String` in `content` and pass the `text` argument to add to the saved `content`. This behavior doesn’t depend on the state the post is in, @@ -134,45 +149,53 @@ so it’s not part of the state pattern. The `add_text` method doesn’t interac with the `state` field at all, but it is part of the behavior we want to support. -### Ensuring the Content of a Draft Post Is Empty +<!-- Old headings. Do not remove or links may break. --> + +<a id="ensuring-the-content-of-a-draft-post-is-empty"></a> + +#### Ensuring That the Content of a Draft Post Is Empty Even after we’ve called `add_text` and added some content to our post, we still want the `content` method to return an empty string slice because the post is -still in the draft state, as shown on line 7 of Listing 17-11. For now, let’s -implement the `content` method with the simplest thing that will fulfill this -requirement: always returning an empty string slice. We’ll change this later -once we implement the ability to change a post’s state so it can be published. -So far, posts can only be in the draft state, so the post content should always -be empty. Listing 17-14 shows this placeholder implementation: +still in the draft state, as shown by the first `assert_eq!` in Listing 18-11. +For now, let’s implement the `content` method with the simplest thing that will +fulfill this requirement: always returning an empty string slice. We’ll change +this later once we implement the ability to change a post’s state so that it +can be published. So far, posts can only be in the draft state, so the post +content should always be empty. Listing 18-14 shows this placeholder +implementation. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-14" file-name="src/lib.rs" caption="Adding a placeholder implementation for the `content` method on `Post` that always returns an empty string slice"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-14/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-14/src/lib.rs:here}} ``` -<span class="caption">Listing 17-14: Adding a placeholder implementation for -the `content` method on `Post` that always returns an empty string slice</span> +</Listing> -With this added `content` method, everything in Listing 17-11 up to line 7 -works as intended. +With this added `content` method, everything in Listing 18-11 through the first +`assert_eq!` works as intended. -### Requesting a Review of the Post Changes Its State +<!-- Old headings. Do not remove or links may break. --> + +<a id="requesting-a-review-of-the-post-changes-its-state"></a> +<a id="requesting-a-review-changes-the-posts-state"></a> + +#### Requesting a Review, Which Changes the Post’s State Next, we need to add functionality to request a review of a post, which should -change its state from `Draft` to `PendingReview`. Listing 17-15 shows this code: +change its state from `Draft` to `PendingReview`. Listing 18-15 shows this code. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-15" file-name="src/lib.rs" caption="Implementing `request_review` methods on `Post` and the `State` trait"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-15/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-15/src/lib.rs:here}} ``` -<span class="caption">Listing 17-15: Implementing `request_review` methods on -`Post` and the `State` trait</span> +</Listing> We give `Post` a public method named `request_review` that will take a mutable -reference to `self`. Then we call an internal `request_review` method on the +reference to `self`. Then, we call an internal `request_review` method on the current state of `Post`, and this second `request_review` method consumes the current state and returns a new state. @@ -181,55 +204,56 @@ implement the trait will now need to implement the `request_review` method. Note that rather than having `self`, `&self`, or `&mut self` as the first parameter of the method, we have `self: Box<Self>`. This syntax means the method is only valid when called on a `Box` holding the type. This syntax takes -ownership of `Box<Self>`, invalidating the old state so the state value of the -`Post` can transform into a new state. +ownership of `Box<Self>`, invalidating the old state so that the state value of +the `Post` can transform into a new state. To consume the old state, the `request_review` method needs to take ownership of the state value. This is where the `Option` in the `state` field of `Post` -comes in: we call the `take` method to take the `Some` value out of the `state` -field and leave a `None` in its place, because Rust doesn’t let us have +comes in: We call the `take` method to take the `Some` value out of the `state` +field and leave a `None` in its place because Rust doesn’t let us have unpopulated fields in structs. This lets us move the `state` value out of -`Post` rather than borrowing it. Then we’ll set the post’s `state` value to the -result of this operation. +`Post` rather than borrowing it. Then, we’ll set the post’s `state` value to +the result of this operation. We need to set `state` to `None` temporarily rather than setting it directly with code like `self.state = self.state.request_review();` to get ownership of -the `state` value. This ensures `Post` can’t use the old `state` value after -we’ve transformed it into a new state. +the `state` value. This ensures that `Post` can’t use the old `state` value +after we’ve transformed it into a new state. The `request_review` method on `Draft` returns a new, boxed instance of a new `PendingReview` struct, which represents the state when a post is waiting for a review. The `PendingReview` struct also implements the `request_review` method -but doesn’t do any transformations. Rather, it returns itself, because when we +but doesn’t do any transformations. Rather, it returns itself because when we request a review on a post already in the `PendingReview` state, it should stay in the `PendingReview` state. -Now we can start seeing the advantages of the state pattern: the +Now we can start seeing the advantages of the state pattern: The `request_review` method on `Post` is the same no matter its `state` value. Each state is responsible for its own rules. We’ll leave the `content` method on `Post` as is, returning an empty string slice. We can now have a `Post` in the `PendingReview` state as well as in the `Draft` state, but we want the same behavior in the `PendingReview` state. -Listing 17-11 now works up to line 10! +Listing 18-11 now works up to the second `assert_eq!` call! <!-- Old headings. Do not remove or links may break. --> + <a id="adding-the-approve-method-that-changes-the-behavior-of-content"></a> +<a id="adding-approve-to-change-the-behavior-of-content"></a> -### Adding `approve` to Change the Behavior of `content` +#### Adding `approve` to Change `content`'s Behavior -The `approve` method will be similar to the `request_review` method: it will +The `approve` method will be similar to the `request_review` method: It will set `state` to the value that the current state says it should have when that -state is approved, as shown in Listing 17-16: +state is approved, as shown in Listing 18-16. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-16" file-name="src/lib.rs" caption="Implementing the `approve` method on `Post` and the `State` trait"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-16/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-16/src/lib.rs:here}} ``` -<span class="caption">Listing 17-16: Implementing the `approve` method on -`Post` and the `State` trait</span> +</Listing> We add the `approve` method to the `State` trait and add a new struct that implements `State`, the `Published` state. @@ -239,110 +263,113 @@ Similar to the way `request_review` on `PendingReview` works, if we call the return `self`. When we call `approve` on `PendingReview`, it returns a new, boxed instance of the `Published` struct. The `Published` struct implements the `State` trait, and for both the `request_review` method and the `approve` -method, it returns itself, because the post should stay in the `Published` -state in those cases. +method, it returns itself because the post should stay in the `Published` state +in those cases. Now we need to update the `content` method on `Post`. We want the value returned from `content` to depend on the current state of the `Post`, so we’re going to have the `Post` delegate to a `content` method defined on its `state`, -as shown in Listing 17-17: +as shown in Listing 18-17. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-17" file-name="src/lib.rs" caption="Updating the `content` method on `Post` to delegate to a `content` method on `State`"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch17-oop/listing-17-17/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-17/src/lib.rs:here}} ``` -<span class="caption">Listing 17-17: Updating the `content` method on `Post` to -delegate to a `content` method on `State`</span> +</Listing> -Because the goal is to keep all these rules inside the structs that implement -`State`, we call a `content` method on the value in `state` and pass the post -instance (that is, `self`) as an argument. Then we return the value that’s -returned from using the `content` method on the `state` value. +Because the goal is to keep all of these rules inside the structs that +implement `State`, we call a `content` method on the value in `state` and pass +the post instance (that is, `self`) as an argument. Then, we return the value +that’s returned from using the `content` method on the `state` value. We call the `as_ref` method on the `Option` because we want a reference to the -value inside the `Option` rather than ownership of the value. Because `state` -is an `Option<Box<dyn State>>`, when we call `as_ref`, an `Option<&Box<dyn +value inside the `Option` rather than ownership of the value. Because `state` is +an `Option<Box<dyn State>>`, when we call `as_ref`, an `Option<&Box<dyn State>>` is returned. If we didn’t call `as_ref`, we would get an error because we can’t move `state` out of the borrowed `&self` of the function parameter. -We then call the `unwrap` method, which we know will never panic, because we +We then call the `unwrap` method, which we know will never panic because we know the methods on `Post` ensure that `state` will always contain a `Some` value when those methods are done. This is one of the cases we talked about in -the [“Cases In Which You Have More Information Than the +the [“When You Have More Information Than the Compiler”][more-info-than-rustc]<!-- ignore --> section of Chapter 9 when we know that a `None` value is never possible, even though the compiler isn’t able to understand that. At this point, when we call `content` on the `&Box<dyn State>`, deref coercion -will take effect on the `&` and the `Box` so the `content` method will +will take effect on the `&` and the `Box` so that the `content` method will ultimately be called on the type that implements the `State` trait. That means we need to add `content` to the `State` trait definition, and that is where we’ll put the logic for what content to return depending on which state we -have, as shown in Listing 17-18: +have, as shown in Listing 18-18. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-18" file-name="src/lib.rs" caption="Adding the `content` method to the `State` trait"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-18/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-18/src/lib.rs:here}} ``` -<span class="caption">Listing 17-18: Adding the `content` method to the `State` -trait</span> +</Listing> We add a default implementation for the `content` method that returns an empty string slice. That means we don’t need to implement `content` on the `Draft` and `PendingReview` structs. The `Published` struct will override the `content` -method and return the value in `post.content`. +method and return the value in `post.content`. While convenient, having the +`content` method on `State` determine the content of the `Post` is blurring +the lines between the responsibility of `State` and the responsibility of +`Post`. Note that we need lifetime annotations on this method, as we discussed in Chapter 10. We’re taking a reference to a `post` as an argument and returning a reference to part of that `post`, so the lifetime of the returned reference is related to the lifetime of the `post` argument. -And we’re done—all of Listing 17-11 now works! We’ve implemented the state +And we’re done—all of Listing 18-11 now works! We’ve implemented the state pattern with the rules of the blog post workflow. The logic related to the rules lives in the state objects rather than being scattered throughout `Post`. -> #### Why Not An Enum? +> ### Why Not An Enum? > -> You may have been wondering why we didn’t use an `enum` with the different -> possible post states as variants. That’s certainly a possible solution, try -> it and compare the end results to see which you prefer! One disadvantage of -> using an enum is every place that checks the value of the enum will need a -> `match` expression or similar to handle every possible variant. This could -> get more repetitive than this trait object solution. +> You may have been wondering why we didn’t use an enum with the different +> possible post states as variants. That’s certainly a possible solution; try it +> and compare the end results to see which you prefer! One disadvantage of using +> an enum is that every place that checks the value of the enum will need a +> `match` expression or similar to handle every possible variant. This could get +> more repetitive than this trait object solution. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="trade-offs-of-the-state-pattern"></a> -### Trade-offs of the State Pattern +#### Evaluating the State Pattern We’ve shown that Rust is capable of implementing the object-oriented state pattern to encapsulate the different kinds of behavior a post should have in -each state. The methods on `Post` know nothing about the various behaviors. The -way we organized the code, we have to look in only one place to know the -different ways a published post can behave: the implementation of the `State` -trait on the `Published` struct. +each state. The methods on `Post` know nothing about the various behaviors. +Because of the way we organized the code, we have to look in only one place to +know the different ways a published post can behave: the implementation of the +`State` trait on the `Published` struct. If we were to create an alternative implementation that didn’t use the state pattern, we might instead use `match` expressions in the methods on `Post` or even in the `main` code that checks the state of the post and changes behavior in those places. That would mean we would have to look in several places to -understand all the implications of a post being in the published state! This -would only increase the more states we added: each of those `match` expressions -would need another arm. +understand all the implications of a post being in the published state. With the state pattern, the `Post` methods and the places we use `Post` don’t need `match` expressions, and to add a new state, we would only need to add a -new struct and implement the trait methods on that one struct. +new struct and implement the trait methods on that one struct in one location. The implementation using the state pattern is easy to extend to add more functionality. To see the simplicity of maintaining code that uses the state pattern, try a few of these suggestions: -* Add a `reject` method that changes the post’s state from `PendingReview` back +- Add a `reject` method that changes the post’s state from `PendingReview` back to `Draft`. -* Require two calls to `approve` before the state can be changed to `Published`. -* Allow users to add text content only when a post is in the `Draft` state. +- Require two calls to `approve` before the state can be changed to `Published`. +- Allow users to add text content only when a post is in the `Draft` state. Hint: have the state object responsible for what might change about the content but not responsible for modifying the `Post`. @@ -356,57 +383,61 @@ another design pattern. Another downside is that we’ve duplicated some logic. To eliminate some of the duplication, we might try to make default implementations for the -`request_review` and `approve` methods on the `State` trait that return `self`; -however, this would violate object safety, because the trait doesn’t know what -the concrete `self` will be exactly. We want to be able to use `State` as a -trait object, so we need its methods to be object safe. +`request_review` and `approve` methods on the `State` trait that return `self`. +However, this wouldn’t work: When using `State` as a trait object, the trait +doesn’t know what the concrete `self` will be exactly, so the return type isn’t +known at compile time. (This is one of the dyn compatibility rules mentioned +earlier.) Other duplication includes the similar implementations of the `request_review` -and `approve` methods on `Post`. Both methods delegate to the implementation of -the same method on the value in the `state` field of `Option` and set the new -value of the `state` field to the result. If we had a lot of methods on `Post` -that followed this pattern, we might consider defining a macro to eliminate the -repetition (see the [“Macros”][macros]<!-- ignore --> section in Chapter 19). +and `approve` methods on `Post`. Both methods use `Option::take` with the +`state` field of `Post`, and if `state` is `Some`, they delegate to the wrapped +value’s implementation of the same method and set the new value of the `state` +field to the result. If we had a lot of methods on `Post` that followed this +pattern, we might consider defining a macro to eliminate the repetition (see +the [“Macros”][macros]<!-- ignore --> section in Chapter 20). By implementing the state pattern exactly as it’s defined for object-oriented languages, we’re not taking as full advantage of Rust’s strengths as we could. Let’s look at some changes we can make to the `blog` crate that can make -invalid states and transitions into compile time errors. +invalid states and transitions into compile-time errors. -#### Encoding States and Behavior as Types +### Encoding States and Behavior as Types We’ll show you how to rethink the state pattern to get a different set of trade-offs. Rather than encapsulating the states and transitions completely so -outside code has no knowledge of them, we’ll encode the states into different -types. Consequently, Rust’s type checking system will prevent attempts to use -draft posts where only published posts are allowed by issuing a compiler error. +that outside code has no knowledge of them, we’ll encode the states into +different types. Consequently, Rust’s type-checking system will prevent +attempts to use draft posts where only published posts are allowed by issuing a +compiler error. -Let’s consider the first part of `main` in Listing 17-11: +Let’s consider the first part of `main` in Listing 18-11: -<span class="filename">Filename: src/main.rs</span> +<Listing file-name="src/main.rs"> ```rust,ignore -{{#rustdoc_include ../listings/ch17-oop/listing-17-11/src/main.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-11/src/main.rs:here}} ``` +</Listing> + We still enable the creation of new posts in the draft state using `Post::new` and the ability to add text to the post’s content. But instead of having a `content` method on a draft post that returns an empty string, we’ll make it so -draft posts don’t have the `content` method at all. That way, if we try to get -a draft post’s content, we’ll get a compiler error telling us the method +that draft posts don’t have the `content` method at all. That way, if we try to +get a draft post’s content, we’ll get a compiler error telling us the method doesn’t exist. As a result, it will be impossible for us to accidentally -display draft post content in production, because that code won’t even compile. -Listing 17-19 shows the definition of a `Post` struct and a `DraftPost` struct, -as well as methods on each: +display draft post content in production because that code won’t even compile. +Listing 18-19 shows the definition of a `Post` struct and a `DraftPost` struct, +as well as methods on each. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-19" file-name="src/lib.rs" caption="A `Post` with a `content` method and a `DraftPost` without a `content` method"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-19/src/lib.rs}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-19/src/lib.rs}} ``` -<span class="caption">Listing 17-19: A `Post` with a `content` method and a -`DraftPost` without a `content` method</span> +</Listing> Both the `Post` and `DraftPost` structs have a private `content` field that stores the blog post text. The structs no longer have the `state` field because @@ -415,35 +446,35 @@ struct will represent a published post, and it has a `content` method that returns the `content`. We still have a `Post::new` function, but instead of returning an instance of -`Post`, it returns an instance of `DraftPost`. Because `content` is private -and there aren’t any functions that return `Post`, it’s not possible to create -an instance of `Post` right now. +`Post`, it returns an instance of `DraftPost`. Because `content` is private and +there aren’t any functions that return `Post`, it’s not possible to create an +instance of `Post` right now. The `DraftPost` struct has an `add_text` method, so we can add text to `content` as before, but note that `DraftPost` does not have a `content` method -defined! So now the program ensures all posts start as draft posts, and draft -posts don’t have their content available for display. Any attempt to get around -these constraints will result in a compiler error. +defined! So now the program ensures that all posts start as draft posts, and +draft posts don’t have their content available for display. Any attempt to get +around these constraints will result in a compiler error. + +<!-- Old headings. Do not remove or links may break. --> -#### Implementing Transitions as Transformations into Different Types +<a id="implementing-transitions-as-transformations-into-different-types"></a> -So how do we get a published post? We want to enforce the rule that a draft +So, how do we get a published post? We want to enforce the rule that a draft post has to be reviewed and approved before it can be published. A post in the pending review state should still not display any content. Let’s implement these constraints by adding another struct, `PendingReviewPost`, defining the -`request_review` method on `DraftPost` to return a `PendingReviewPost`, and +`request_review` method on `DraftPost` to return a `PendingReviewPost` and defining an `approve` method on `PendingReviewPost` to return a `Post`, as -shown in Listing 17-20: +shown in Listing 18-20. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="18-20" file-name="src/lib.rs" caption="A `PendingReviewPost` that gets created by calling `request_review` on `DraftPost` and an `approve` method that turns a `PendingReviewPost` into a published `Post`"> ```rust,noplayground -{{#rustdoc_include ../listings/ch17-oop/listing-17-20/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-20/src/lib.rs:here}} ``` -<span class="caption">Listing 17-20: A `PendingReviewPost` that gets created by -calling `request_review` on `DraftPost` and an `approve` method that turns a -`PendingReviewPost` into a published `Post`</span> +</Listing> The `request_review` and `approve` methods take ownership of `self`, thus consuming the `DraftPost` and `PendingReviewPost` instances and transforming @@ -461,29 +492,28 @@ But we also have to make some small changes to `main`. The `request_review` and `approve` methods return new instances rather than modifying the struct they’re called on, so we need to add more `let post =` shadowing assignments to save the returned instances. We also can’t have the assertions about the draft and -pending review posts’ contents be empty strings, nor do we need them: we can’t +pending review posts’ contents be empty strings, nor do we need them: We can’t compile code that tries to use the content of posts in those states any longer. -The updated code in `main` is shown in Listing 17-21: +The updated code in `main` is shown in Listing 18-21. -<span class="filename">Filename: src/main.rs</span> +<Listing number="18-21" file-name="src/main.rs" caption="Modifications to `main` to use the new implementation of the blog post workflow"> ```rust,ignore -{{#rustdoc_include ../listings/ch17-oop/listing-17-21/src/main.rs}} +{{#rustdoc_include ../listings/ch18-oop/listing-18-21/src/main.rs}} ``` -<span class="caption">Listing 17-21: Modifications to `main` to use the new -implementation of the blog post workflow</span> +</Listing> The changes we needed to make to `main` to reassign `post` mean that this implementation doesn’t quite follow the object-oriented state pattern anymore: -the transformations between the states are no longer encapsulated entirely +The transformations between the states are no longer encapsulated entirely within the `Post` implementation. However, our gain is that invalid states are now impossible because of the type system and the type checking that happens at compile time! This ensures that certain bugs, such as display of the content of an unpublished post, will be discovered before they make it to production. Try the tasks suggested at the start of this section on the `blog` crate as it -is after Listing 17-21 to see what you think about the design of this version +is after Listing 18-21 to see what you think about the design of this version of the code. Note that some of the tasks might be completed already in this design. @@ -498,14 +528,14 @@ object-oriented languages don’t have. ## Summary -No matter whether or not you think Rust is an object-oriented language after +Regardless of whether you think Rust is an object-oriented language after reading this chapter, you now know that you can use trait objects to get some object-oriented features in Rust. Dynamic dispatch can give your code some flexibility in exchange for a bit of runtime performance. You can use this flexibility to implement object-oriented patterns that can help your code’s maintainability. Rust also has other features, like ownership, that object-oriented languages don’t have. An object-oriented pattern won’t always -be the best way to take advantage of Rust’s strengths, but is an available +be the best way to take advantage of Rust’s strengths, but it is an available option. Next, we’ll look at patterns, which are another of Rust’s features that enable @@ -513,4 +543,4 @@ lots of flexibility. We’ve looked at them briefly throughout the book but haven’t seen their full capability yet. Let’s go! [more-info-than-rustc]: ch09-03-to-panic-or-not-to-panic.html#cases-in-which-you-have-more-information-than-the-compiler -[macros]: ch19-06-macros.html#macros +[macros]: ch20-05-macros.html#macros diff --git a/src/ch18-00-patterns.md b/src/ch19-00-patterns.md similarity index 87% rename from src/ch18-00-patterns.md rename to src/ch19-00-patterns.md index dc9290e331..ad6976ca77 100644 --- a/src/ch18-00-patterns.md +++ b/src/ch19-00-patterns.md @@ -1,15 +1,15 @@ # Patterns and Matching -*Patterns* are a special syntax in Rust for matching against the structure of +Patterns are a special syntax in Rust for matching against the structure of types, both complex and simple. Using patterns in conjunction with `match` expressions and other constructs gives you more control over a program’s control flow. A pattern consists of some combination of the following: -* Literals -* Destructured arrays, enums, structs, or tuples -* Variables -* Wildcards -* Placeholders +- Literals +- Destructured arrays, enums, structs, or tuples +- Variables +- Wildcards +- Placeholders Some example patterns include `x`, `(a, 3)`, and `Some(Color::Red)`. In the contexts in which patterns are valid, these components describe the shape of diff --git a/src/ch19-01-all-the-places-for-patterns.md b/src/ch19-01-all-the-places-for-patterns.md new file mode 100644 index 0000000000..1a6d21eb54 --- /dev/null +++ b/src/ch19-01-all-the-places-for-patterns.md @@ -0,0 +1,266 @@ +## All the Places Patterns Can Be Used + +Patterns pop up in a number of places in Rust, and you’ve been using them a lot +without realizing it! This section discusses all the places where patterns are +valid. + +### `match` Arms + +As discussed in Chapter 6, we use patterns in the arms of `match` expressions. +Formally, `match` expressions are defined as the keyword `match`, a value to +match on, and one or more match arms that consist of a pattern and an +expression to run if the value matches that arm’s pattern, like this: + +<!-- + Manually formatted rather than using Markdown intentionally: Markdown does not + support italicizing code in the body of a block like this! +--> + +<pre><code>match <em>VALUE</em> { + <em>PATTERN</em> => <em>EXPRESSION</em>, + <em>PATTERN</em> => <em>EXPRESSION</em>, + <em>PATTERN</em> => <em>EXPRESSION</em>, +}</code></pre> + +For example, here’s the `match` expression from Listing 6-5 that matches on an +`Option<i32>` value in the variable `x`: + +```rust,ignore +match x { + None => None, + Some(i) => Some(i + 1), +} +``` + +The patterns in this `match` expression are the `None` and `Some(i)` to the +left of each arrow. + +One requirement for `match` expressions is that they need to be exhaustive in +the sense that all possibilities for the value in the `match` expression must +be accounted for. One way to ensure that you’ve covered every possibility is to +have a catch-all pattern for the last arm: For example, a variable name +matching any value can never fail and thus covers every remaining case. + +The particular pattern `_` will match anything, but it never binds to a +variable, so it’s often used in the last match arm. The `_` pattern can be +useful when you want to ignore any value not specified, for example. We’ll +cover the `_` pattern in more detail in [“Ignoring Values in a +Pattern”][ignoring-values-in-a-pattern]<!-- ignore --> later in this chapter. + +### `let` Statements + +Prior to this chapter, we had only explicitly discussed using patterns with +`match` and `if let`, but in fact, we’ve used patterns in other places as well, +including in `let` statements. For example, consider this straightforward +variable assignment with `let`: + +```rust +let x = 5; +``` + +Every time you’ve used a `let` statement like this you’ve been using patterns, +although you might not have realized it! More formally, a `let` statement looks +like this: + +<!-- + Manually formatted rather than using Markdown intentionally: Markdown does not + support italicizing code in the body of a block like this! +--> + +<pre> +<code>let <em>PATTERN</em> = <em>EXPRESSION</em>;</code> +</pre> + +In statements like `let x = 5;` with a variable name in the PATTERN slot, the +variable name is just a particularly simple form of a pattern. Rust compares +the expression against the pattern and assigns any names it finds. So, in the +`let x = 5;` example, `x` is a pattern that means “bind what matches here to +the variable `x`.” Because the name `x` is the whole pattern, this pattern +effectively means “bind everything to the variable `x`, whatever the value is.” + +To see the pattern-matching aspect of `let` more clearly, consider Listing +19-1, which uses a pattern with `let` to destructure a tuple. + + +<Listing number="19-1" caption="Using a pattern to destructure a tuple and create three variables at once"> + +```rust +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-01/src/main.rs:here}} +``` + +</Listing> + +Here, we match a tuple against a pattern. Rust compares the value `(1, 2, 3)` +to the pattern `(x, y, z)` and sees that the value matches the pattern—that is, +it sees that the number of elements is the same in both—so Rust binds `1` to +`x`, `2` to `y`, and `3` to `z`. You can think of this tuple pattern as nesting +three individual variable patterns inside it. + +If the number of elements in the pattern doesn’t match the number of elements +in the tuple, the overall type won’t match and we’ll get a compiler error. For +example, Listing 19-2 shows an attempt to destructure a tuple with three +elements into two variables, which won’t work. + +<Listing number="19-2" caption="Incorrectly constructing a pattern whose variables don’t match the number of elements in the tuple"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-02/src/main.rs:here}} +``` + +</Listing> + +Attempting to compile this code results in this type error: + +```console +{{#include ../listings/ch19-patterns-and-matching/listing-19-02/output.txt}} +``` + +To fix the error, we could ignore one or more of the values in the tuple using +`_` or `..`, as you’ll see in the [“Ignoring Values in a +Pattern”][ignoring-values-in-a-pattern]<!-- ignore --> section. If the problem +is that we have too many variables in the pattern, the solution is to make the +types match by removing variables so that the number of variables equals the +number of elements in the tuple. + +### Conditional `if let` Expressions + +In Chapter 6, we discussed how to use `if let` expressions mainly as a shorter +way to write the equivalent of a `match` that only matches one case. +Optionally, `if let` can have a corresponding `else` containing code to run if +the pattern in the `if let` doesn’t match. + +Listing 19-3 shows that it’s also possible to mix and match `if let`, `else +if`, and `else if let` expressions. Doing so gives us more flexibility than a +`match` expression in which we can express only one value to compare with the +patterns. Also, Rust doesn’t require that the conditions in a series of `if +let`, `else if`, and `else if let` arms relate to each other. + +The code in Listing 19-3 determines what color to make your background based on +a series of checks for several conditions. For this example, we’ve created +variables with hardcoded values that a real program might receive from user +input. + +<Listing number="19-3" file-name="src/main.rs" caption="Mixing `if let`, `else if`, `else if let`, and `else`"> + +```rust +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-03/src/main.rs}} +``` + +</Listing> + +If the user specifies a favorite color, that color is used as the background. +If no favorite color is specified and today is Tuesday, the background color is +green. Otherwise, if the user specifies their age as a string and we can parse +it as a number successfully, the color is either purple or orange depending on +the value of the number. If none of these conditions apply, the background +color is blue. + +This conditional structure lets us support complex requirements. With the +hardcoded values we have here, this example will print `Using purple as the +background color`. + +You can see that `if let` can also introduce new variables that shadow existing +variables in the same way that `match` arms can: The line `if let Ok(age) = age` +introduces a new `age` variable that contains the value inside the `Ok` variant, +shadowing the existing `age` variable. This means we need to place the `if age > +30` condition within that block: We can’t combine these two conditions into `if +let Ok(age) = age && age > 30`. The new `age` we want to compare to 30 isn’t +valid until the new scope starts with the curly bracket. + +The downside of using `if let` expressions is that the compiler doesn’t check +for exhaustiveness, whereas with `match` expressions it does. If we omitted the +last `else` block and therefore missed handling some cases, the compiler would +not alert us to the possible logic bug. + +### `while let` Conditional Loops + +Similar in construction to `if let`, the `while let` conditional loop allows a +`while` loop to run for as long as a pattern continues to match. In Listing +19-4, we show a `while let` loop that waits on messages sent between threads, +but in this case checking a `Result` instead of an `Option`. + +<Listing number="19-4" caption="Using a `while let` loop to print values for as long as `rx.recv()` returns `Ok`"> + +```rust +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-04/src/main.rs:here}} +``` + +</Listing> + +This example prints `1`, `2`, and then `3`. The `recv` method takes the first +message out of the receiver side of the channel and returns an `Ok(value)`. When +we first saw `recv` back in Chapter 16, we unwrapped the error directly, or +we interacted with it as an iterator using a `for` loop. As Listing 19-4 shows, +though, we can also use `while let`, because the `recv` method returns an `Ok` +each time a message arrives, as long as the sender exists, and then produces an +`Err` once the sender side disconnects. + +### `for` Loops + +In a `for` loop, the value that directly follows the keyword `for` is a +pattern. For example, in `for x in y`, the `x` is the pattern. Listing 19-5 +demonstrates how to use a pattern in a `for` loop to destructure, or break +apart, a tuple as part of the `for` loop. + + +<Listing number="19-5" caption="Using a pattern in a `for` loop to destructure a tuple"> + +```rust +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-05/src/main.rs:here}} +``` + +</Listing> + +The code in Listing 19-5 will print the following: + + +```console +{{#include ../listings/ch19-patterns-and-matching/listing-19-05/output.txt}} +``` + +We adapt an iterator using the `enumerate` method so that it produces a value +and the index for that value, placed into a tuple. The first value produced is +the tuple `(0, 'a')`. When this value is matched to the pattern `(index, +value)`, index will be `0` and value will be `'a'`, printing the first line of +the output. + + +### Function Parameters + +Function parameters can also be patterns. The code in Listing 19-6, which +declares a function named `foo` that takes one parameter named `x` of type +`i32`, should by now look familiar. + +<Listing number="19-6" caption="A function signature using patterns in the parameters"> + +```rust +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-06/src/main.rs:here}} +``` + +</Listing> + +The `x` part is a pattern! As we did with `let`, we could match a tuple in a +function’s arguments to the pattern. Listing 19-7 splits the values in a tuple +as we pass it to a function. + +<Listing number="19-7" file-name="src/main.rs" caption="A function with parameters that destructure a tuple"> + +```rust +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-07/src/main.rs}} +``` + +</Listing> + +This code prints `Current location: (3, 5)`. The values `&(3, 5)` match the +pattern `&(x, y)`, so `x` is the value `3` and `y` is the value `5`. + +We can also use patterns in closure parameter lists in the same way as in +function parameter lists because closures are similar to functions, as +discussed in Chapter 13. + +At this point, you’ve seen several ways to use patterns, but patterns don’t +work the same in every place we can use them. In some places, the patterns must +be irrefutable; in other circumstances, they can be refutable. We’ll discuss +these two concepts next. + +[ignoring-values-in-a-pattern]: ch19-03-pattern-syntax.html#ignoring-values-in-a-pattern diff --git a/src/ch19-01-unsafe-rust.md b/src/ch19-01-unsafe-rust.md deleted file mode 100644 index 6ff229dd37..0000000000 --- a/src/ch19-01-unsafe-rust.md +++ /dev/null @@ -1,460 +0,0 @@ -## Unsafe Rust - -All the code we’ve discussed so far has had Rust’s memory safety guarantees -enforced at compile time. However, Rust has a second language hidden inside it -that doesn’t enforce these memory safety guarantees: it’s called *unsafe Rust* -and works just like regular Rust, but gives us extra superpowers. - -Unsafe Rust exists because, by nature, static analysis is conservative. When -the compiler tries to determine whether or not code upholds the guarantees, -it’s better for it to reject some valid programs than to accept some invalid -programs. Although the code *might* be okay, if the Rust compiler doesn’t have -enough information to be confident, it will reject the code. In these cases, -you can use unsafe code to tell the compiler, “Trust me, I know what I’m -doing.” Be warned, however, that you use unsafe Rust at your own risk: if you -use unsafe code incorrectly, problems can occur due to memory unsafety, such as -null pointer dereferencing. - -Another reason Rust has an unsafe alter ego is that the underlying computer -hardware is inherently unsafe. If Rust didn’t let you do unsafe operations, you -couldn’t do certain tasks. Rust needs to allow you to do low-level systems -programming, such as directly interacting with the operating system or even -writing your own operating system. Working with low-level systems programming -is one of the goals of the language. Let’s explore what we can do with unsafe -Rust and how to do it. - -### Unsafe Superpowers - -To switch to unsafe Rust, use the `unsafe` keyword and then start a new block -that holds the unsafe code. You can take five actions in unsafe Rust that you -can’t in safe Rust, which we call *unsafe superpowers*. Those superpowers -include the ability to: - -* Dereference a raw pointer -* Call an unsafe function or method -* Access or modify a mutable static variable -* Implement an unsafe trait -* Access fields of `union`s - -It’s important to understand that `unsafe` doesn’t turn off the borrow checker -or disable any other of Rust’s safety checks: if you use a reference in unsafe -code, it will still be checked. The `unsafe` keyword only gives you access to -these five features that are then not checked by the compiler for memory -safety. You’ll still get some degree of safety inside of an unsafe block. - -In addition, `unsafe` does not mean the code inside the block is necessarily -dangerous or that it will definitely have memory safety problems: the intent is -that as the programmer, you’ll ensure the code inside an `unsafe` block will -access memory in a valid way. - -People are fallible, and mistakes will happen, but by requiring these five -unsafe operations to be inside blocks annotated with `unsafe` you’ll know that -any errors related to memory safety must be within an `unsafe` block. Keep -`unsafe` blocks small; you’ll be thankful later when you investigate memory -bugs. - -To isolate unsafe code as much as possible, it’s best to enclose unsafe code -within a safe abstraction and provide a safe API, which we’ll discuss later in -the chapter when we examine unsafe functions and methods. Parts of the standard -library are implemented as safe abstractions over unsafe code that has been -audited. Wrapping unsafe code in a safe abstraction prevents uses of `unsafe` -from leaking out into all the places that you or your users might want to use -the functionality implemented with `unsafe` code, because using a safe -abstraction is safe. - -Let’s look at each of the five unsafe superpowers in turn. We’ll also look at -some abstractions that provide a safe interface to unsafe code. - -### Dereferencing a Raw Pointer - -In Chapter 4, in the [“Dangling References”][dangling-references]<!-- ignore ---> section, we mentioned that the compiler ensures references are always -valid. Unsafe Rust has two new types called *raw pointers* that are similar to -references. As with references, raw pointers can be immutable or mutable and -are written as `*const T` and `*mut T`, respectively. The asterisk isn’t the -dereference operator; it’s part of the type name. In the context of raw -pointers, *immutable* means that the pointer can’t be directly assigned to -after being dereferenced. - -Different from references and smart pointers, raw pointers: - -* Are allowed to ignore the borrowing rules by having both immutable and - mutable pointers or multiple mutable pointers to the same location -* Aren’t guaranteed to point to valid memory -* Are allowed to be null -* Don’t implement any automatic cleanup - -By opting out of having Rust enforce these guarantees, you can give up -guaranteed safety in exchange for greater performance or the ability to -interface with another language or hardware where Rust’s guarantees don’t apply. - -Listing 19-1 shows how to create an immutable and a mutable raw pointer from -references. - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-01/src/main.rs:here}} -``` - -<span class="caption">Listing 19-1: Creating raw pointers from references</span> - -Notice that we don’t include the `unsafe` keyword in this code. We can create -raw pointers in safe code; we just can’t dereference raw pointers outside an -unsafe block, as you’ll see in a bit. - -We’ve created raw pointers by using `as` to cast an immutable and a mutable -reference into their corresponding raw pointer types. Because we created them -directly from references guaranteed to be valid, we know these particular raw -pointers are valid, but we can’t make that assumption about just any raw -pointer. - -To demonstrate this, next we’ll create a raw pointer whose validity we can’t be -so certain of. Listing 19-2 shows how to create a raw pointer to an arbitrary -location in memory. Trying to use arbitrary memory is undefined: there might be -data at that address or there might not, the compiler might optimize the code -so there is no memory access, or the program might error with a segmentation -fault. Usually, there is no good reason to write code like this, but it is -possible. - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-02/src/main.rs:here}} -``` - -<span class="caption">Listing 19-2: Creating a raw pointer to an arbitrary -memory address</span> - -Recall that we can create raw pointers in safe code, but we can’t *dereference* -raw pointers and read the data being pointed to. In Listing 19-3, we use the -dereference operator `*` on a raw pointer that requires an `unsafe` block. - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-03/src/main.rs:here}} -``` - -<span class="caption">Listing 19-3: Dereferencing raw pointers within an -`unsafe` block</span> - -Creating a pointer does no harm; it’s only when we try to access the value that -it points at that we might end up dealing with an invalid value. - -Note also that in Listing 19-1 and 19-3, we created `*const i32` and `*mut i32` -raw pointers that both pointed to the same memory location, where `num` is -stored. If we instead tried to create an immutable and a mutable reference to -`num`, the code would not have compiled because Rust’s ownership rules don’t -allow a mutable reference at the same time as any immutable references. With -raw pointers, we can create a mutable pointer and an immutable pointer to the -same location and change data through the mutable pointer, potentially creating -a data race. Be careful! - -With all of these dangers, why would you ever use raw pointers? One major use -case is when interfacing with C code, as you’ll see in the next section, -[“Calling an Unsafe Function or -Method.”](#calling-an-unsafe-function-or-method)<!-- ignore --> Another case is -when building up safe abstractions that the borrow checker doesn’t understand. -We’ll introduce unsafe functions and then look at an example of a safe -abstraction that uses unsafe code. - -### Calling an Unsafe Function or Method - -The second type of operation you can perform in an unsafe block is calling -unsafe functions. Unsafe functions and methods look exactly like regular -functions and methods, but they have an extra `unsafe` before the rest of the -definition. The `unsafe` keyword in this context indicates the function has -requirements we need to uphold when we call this function, because Rust can’t -guarantee we’ve met these requirements. By calling an unsafe function within an -`unsafe` block, we’re saying that we’ve read this function’s documentation and -take responsibility for upholding the function’s contracts. - -Here is an unsafe function named `dangerous` that doesn’t do anything in its -body: - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-01-unsafe-fn/src/main.rs:here}} -``` - -We must call the `dangerous` function within a separate `unsafe` block. If we -try to call `dangerous` without the `unsafe` block, we’ll get an error: - -```console -{{#include ../listings/ch19-advanced-features/output-only-01-missing-unsafe/output.txt}} -``` - -With the `unsafe` block, we’re asserting to Rust that we’ve read the function’s -documentation, we understand how to use it properly, and we’ve verified that -we’re fulfilling the contract of the function. - -Bodies of unsafe functions are effectively `unsafe` blocks, so to perform other -unsafe operations within an unsafe function, we don’t need to add another -`unsafe` block. - -#### Creating a Safe Abstraction over Unsafe Code - -Just because a function contains unsafe code doesn’t mean we need to mark the -entire function as unsafe. In fact, wrapping unsafe code in a safe function is -a common abstraction. As an example, let’s study the `split_at_mut` function -from the standard library, which requires some unsafe code. We’ll explore how -we might implement it. This safe method is defined on mutable slices: it takes -one slice and makes it two by splitting the slice at the index given as an -argument. Listing 19-4 shows how to use `split_at_mut`. - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-04/src/main.rs:here}} -``` - -<span class="caption">Listing 19-4: Using the safe `split_at_mut` -function</span> - -We can’t implement this function using only safe Rust. An attempt might look -something like Listing 19-5, which won’t compile. For simplicity, we’ll -implement `split_at_mut` as a function rather than a method and only for slices -of `i32` values rather than for a generic type `T`. - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-05/src/main.rs:here}} -``` - -<span class="caption">Listing 19-5: An attempted implementation of -`split_at_mut` using only safe Rust</span> - -This function first gets the total length of the slice. Then it asserts that -the index given as a parameter is within the slice by checking whether it’s -less than or equal to the length. The assertion means that if we pass an index -that is greater than the length to split the slice at, the function will panic -before it attempts to use that index. - -Then we return two mutable slices in a tuple: one from the start of the -original slice to the `mid` index and another from `mid` to the end of the -slice. - -When we try to compile the code in Listing 19-5, we’ll get an error. - -```console -{{#include ../listings/ch19-advanced-features/listing-19-05/output.txt}} -``` - -Rust’s borrow checker can’t understand that we’re borrowing different parts of -the slice; it only knows that we’re borrowing from the same slice twice. -Borrowing different parts of a slice is fundamentally okay because the two -slices aren’t overlapping, but Rust isn’t smart enough to know this. When we -know code is okay, but Rust doesn’t, it’s time to reach for unsafe code. - -Listing 19-6 shows how to use an `unsafe` block, a raw pointer, and some calls -to unsafe functions to make the implementation of `split_at_mut` work. - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-06/src/main.rs:here}} -``` - -<span class="caption">Listing 19-6: Using unsafe code in the implementation of -the `split_at_mut` function</span> - -Recall from [“The Slice Type”][the-slice-type]<!-- ignore --> section in -Chapter 4 that slices are a pointer to some data and the length of the slice. -We use the `len` method to get the length of a slice and the `as_mut_ptr` -method to access the raw pointer of a slice. In this case, because we have a -mutable slice to `i32` values, `as_mut_ptr` returns a raw pointer with the type -`*mut i32`, which we’ve stored in the variable `ptr`. - -We keep the assertion that the `mid` index is within the slice. Then we get to -the unsafe code: the `slice::from_raw_parts_mut` function takes a raw pointer -and a length, and it creates a slice. We use this function to create a slice -that starts from `ptr` and is `mid` items long. Then we call the `add` -method on `ptr` with `mid` as an argument to get a raw pointer that starts at -`mid`, and we create a slice using that pointer and the remaining number of -items after `mid` as the length. - -The function `slice::from_raw_parts_mut` is unsafe because it takes a raw -pointer and must trust that this pointer is valid. The `add` method on raw -pointers is also unsafe, because it must trust that the offset location is also -a valid pointer. Therefore, we had to put an `unsafe` block around our calls to -`slice::from_raw_parts_mut` and `add` so we could call them. By looking at -the code and by adding the assertion that `mid` must be less than or equal to -`len`, we can tell that all the raw pointers used within the `unsafe` block -will be valid pointers to data within the slice. This is an acceptable and -appropriate use of `unsafe`. - -Note that we don’t need to mark the resulting `split_at_mut` function as -`unsafe`, and we can call this function from safe Rust. We’ve created a safe -abstraction to the unsafe code with an implementation of the function that uses -`unsafe` code in a safe way, because it creates only valid pointers from the -data this function has access to. - -In contrast, the use of `slice::from_raw_parts_mut` in Listing 19-7 would -likely crash when the slice is used. This code takes an arbitrary memory -location and creates a slice 10,000 items long. - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-07/src/main.rs:here}} -``` - -<span class="caption">Listing 19-7: Creating a slice from an arbitrary memory -location</span> - -We don’t own the memory at this arbitrary location, and there is no guarantee -that the slice this code creates contains valid `i32` values. Attempting to use -`values` as though it’s a valid slice results in undefined behavior. - -#### Using `extern` Functions to Call External Code - -Sometimes, your Rust code might need to interact with code written in another -language. For this, Rust has the keyword `extern` that facilitates the creation -and use of a *Foreign Function Interface (FFI)*. An FFI is a way for a -programming language to define functions and enable a different (foreign) -programming language to call those functions. - -Listing 19-8 demonstrates how to set up an integration with the `abs` function -from the C standard library. Functions declared within `extern` blocks are -always unsafe to call from Rust code. The reason is that other languages don’t -enforce Rust’s rules and guarantees, and Rust can’t check them, so -responsibility falls on the programmer to ensure safety. - -<span class="filename">Filename: src/main.rs</span> - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-08/src/main.rs}} -``` - -<span class="caption">Listing 19-8: Declaring and calling an `extern` function -defined in another language</span> - -Within the `extern "C"` block, we list the names and signatures of external -functions from another language we want to call. The `"C"` part defines which -*application binary interface (ABI)* the external function uses: the ABI -defines how to call the function at the assembly level. The `"C"` ABI is the -most common and follows the C programming language’s ABI. - -> #### Calling Rust Functions from Other Languages -> -> We can also use `extern` to create an interface that allows other languages -> to call Rust functions. Instead of creating a whole `extern` block, we add -> the `extern` keyword and specify the ABI to use just before the `fn` keyword -> for the relevant function. We also need to add a `#[no_mangle]` annotation to -> tell the Rust compiler not to mangle the name of this function. *Mangling* is -> when a compiler changes the name we’ve given a function to a different name -> that contains more information for other parts of the compilation process to -> consume but is less human readable. Every programming language compiler -> mangles names slightly differently, so for a Rust function to be nameable by -> other languages, we must disable the Rust compiler’s name mangling. -> -> In the following example, we make the `call_from_c` function accessible from -> C code, after it’s compiled to a shared library and linked from C: -> -> ```rust -> #[no_mangle] -> pub extern "C" fn call_from_c() { -> println!("Just called a Rust function from C!"); -> } -> ``` -> -> This usage of `extern` does not require `unsafe`. - -### Accessing or Modifying a Mutable Static Variable - -In this book, we’ve not yet talked about *global variables*, which Rust does -support but can be problematic with Rust’s ownership rules. If two threads are -accessing the same mutable global variable, it can cause a data race. - -In Rust, global variables are called *static* variables. Listing 19-9 shows an -example declaration and use of a static variable with a string slice as a -value. - -<span class="filename">Filename: src/main.rs</span> - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-09/src/main.rs}} -``` - -<span class="caption">Listing 19-9: Defining and using an immutable static -variable</span> - -Static variables are similar to constants, which we discussed in the -[“Differences Between Variables and -Constants”][differences-between-variables-and-constants]<!-- ignore --> section -in Chapter 3. The names of static variables are in `SCREAMING_SNAKE_CASE` by -convention. Static variables can only store references with the `'static` -lifetime, which means the Rust compiler can figure out the lifetime and we -aren’t required to annotate it explicitly. Accessing an immutable static -variable is safe. - -A subtle difference between constants and immutable static variables is that -values in a static variable have a fixed address in memory. Using the value -will always access the same data. Constants, on the other hand, are allowed to -duplicate their data whenever they’re used. Another difference is that static -variables can be mutable. Accessing and modifying mutable static variables is -*unsafe*. Listing 19-10 shows how to declare, access, and modify a mutable -static variable named `COUNTER`. - -<span class="filename">Filename: src/main.rs</span> - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-10/src/main.rs}} -``` - -<span class="caption">Listing 19-10: Reading from or writing to a mutable -static variable is unsafe</span> - -As with regular variables, we specify mutability using the `mut` keyword. Any -code that reads or writes from `COUNTER` must be within an `unsafe` block. This -code compiles and prints `COUNTER: 3` as we would expect because it’s single -threaded. Having multiple threads access `COUNTER` would likely result in data -races. - -With mutable data that is globally accessible, it’s difficult to ensure there -are no data races, which is why Rust considers mutable static variables to be -unsafe. Where possible, it’s preferable to use the concurrency techniques and -thread-safe smart pointers we discussed in Chapter 16 so the compiler checks -that data accessed from different threads is done safely. - -### Implementing an Unsafe Trait - -We can use `unsafe` to implement an unsafe trait. A trait is unsafe when at -least one of its methods has some invariant that the compiler can’t verify. We -declare that a trait is `unsafe` by adding the `unsafe` keyword before `trait` -and marking the implementation of the trait as `unsafe` too, as shown in -Listing 19-11. - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-11/src/main.rs}} -``` - -<span class="caption">Listing 19-11: Defining and implementing an unsafe -trait</span> - -By using `unsafe impl`, we’re promising that we’ll uphold the invariants that -the compiler can’t verify. - -As an example, recall the `Sync` and `Send` marker traits we discussed in the -[“Extensible Concurrency with the `Sync` and `Send` -Traits”][extensible-concurrency-with-the-sync-and-send-traits]<!-- ignore --> -section in Chapter 16: the compiler implements these traits automatically if -our types are composed entirely of `Send` and `Sync` types. If we implement a -type that contains a type that is not `Send` or `Sync`, such as raw pointers, -and we want to mark that type as `Send` or `Sync`, we must use `unsafe`. Rust -can’t verify that our type upholds the guarantees that it can be safely sent -across threads or accessed from multiple threads; therefore, we need to do -those checks manually and indicate as such with `unsafe`. - -### Accessing Fields of a Union - -The final action that works only with `unsafe` is accessing fields of a -*union*. A `union` is similar to a `struct`, but only one declared field is -used in a particular instance at one time. Unions are primarily used to -interface with unions in C code. Accessing union fields is unsafe because Rust -can’t guarantee the type of the data currently being stored in the union -instance. You can learn more about unions in [the Rust Reference][reference]. - -### When to Use Unsafe Code - -Using `unsafe` to take one of the five actions (superpowers) just discussed -isn’t wrong or even frowned upon. But it is trickier to get `unsafe` code -correct because the compiler can’t help uphold memory safety. When you have a -reason to use `unsafe` code, you can do so, and having the explicit `unsafe` -annotation makes it easier to track down the source of problems when they occur. - -[dangling-references]: -ch04-02-references-and-borrowing.html#dangling-references -[differences-between-variables-and-constants]: -ch03-01-variables-and-mutability.html#constants -[extensible-concurrency-with-the-sync-and-send-traits]: -ch16-04-extensible-concurrency-sync-and-send.html#extensible-concurrency-with-the-sync-and-send-traits -[the-slice-type]: ch04-03-slices.html#the-slice-type -[reference]: ../reference/items/unions.html diff --git a/src/ch18-02-refutability.md b/src/ch19-02-refutability.md similarity index 53% rename from src/ch18-02-refutability.md rename to src/ch19-02-refutability.md index be3c31765c..4117d3fbe7 100644 --- a/src/ch18-02-refutability.md +++ b/src/ch19-02-refutability.md @@ -1,82 +1,85 @@ ## Refutability: Whether a Pattern Might Fail to Match Patterns come in two forms: refutable and irrefutable. Patterns that will match -for any possible value passed are *irrefutable*. An example would be `x` in the +for any possible value passed are _irrefutable_. An example would be `x` in the statement `let x = 5;` because `x` matches anything and therefore cannot fail to match. Patterns that can fail to match for some possible value are -*refutable*. An example would be `Some(x)` in the expression `if let Some(x) = +_refutable_. An example would be `Some(x)` in the expression `if let Some(x) = a_value` because if the value in the `a_value` variable is `None` rather than `Some`, the `Some(x)` pattern will not match. Function parameters, `let` statements, and `for` loops can only accept -irrefutable patterns, because the program cannot do anything meaningful when -values don’t match. The `if let` and `while let` expressions accept -refutable and irrefutable patterns, but the compiler warns against -irrefutable patterns because by definition they’re intended to handle possible -failure: the functionality of a conditional is in its ability to perform -differently depending on success or failure. +irrefutable patterns because the program cannot do anything meaningful when +values don’t match. The `if let` and `while let` expressions and the +`let...else` statement accept refutable and irrefutable patterns, but the +compiler warns against irrefutable patterns because, by definition, they’re +intended to handle possible failure: The functionality of a conditional is in +its ability to perform differently depending on success or failure. In general, you shouldn’t have to worry about the distinction between refutable and irrefutable patterns; however, you do need to be familiar with the concept -of refutability so you can respond when you see it in an error message. In +of refutability so that you can respond when you see it in an error message. In those cases, you’ll need to change either the pattern or the construct you’re using the pattern with, depending on the intended behavior of the code. Let’s look at an example of what happens when we try to use a refutable pattern -where Rust requires an irrefutable pattern and vice versa. Listing 18-8 shows a -`let` statement, but for the pattern we’ve specified `Some(x)`, a refutable +where Rust requires an irrefutable pattern and vice versa. Listing 19-8 shows a +`let` statement, but for the pattern, we’ve specified `Some(x)`, a refutable pattern. As you might expect, this code will not compile. +<Listing number="19-8" caption="Attempting to use a refutable pattern with `let`"> + ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-08/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-08/src/main.rs:here}} ``` -<span class="caption">Listing 18-8: Attempting to use a refutable pattern with -`let`</span> +</Listing> -If `some_option_value` was a `None` value, it would fail to match the pattern +If `some_option_value` were a `None` value, it would fail to match the pattern `Some(x)`, meaning the pattern is refutable. However, the `let` statement can only accept an irrefutable pattern because there is nothing valid the code can do with a `None` value. At compile time, Rust will complain that we’ve tried to use a refutable pattern where an irrefutable pattern is required: ```console -{{#include ../listings/ch18-patterns-and-matching/listing-18-08/output.txt}} +{{#include ../listings/ch19-patterns-and-matching/listing-19-08/output.txt}} ``` Because we didn’t cover (and couldn’t cover!) every valid value with the pattern `Some(x)`, Rust rightfully produces a compiler error. If we have a refutable pattern where an irrefutable pattern is needed, we can -fix it by changing the code that uses the pattern: instead of using `let`, we -can use `if let`. Then if the pattern doesn’t match, the code will just skip -the code in the curly brackets, giving it a way to continue validly. Listing -18-9 shows how to fix the code in Listing 18-8. +fix it by changing the code that uses the pattern: Instead of using `let`, we +can use `let...else`. Then, if the pattern doesn’t match, the code in the curly +brackets will handle the value. Listing 19-9 shows how to fix the code in +Listing 19-8. + +<Listing number="19-9" caption="Using `let...else` and a block with refutable patterns instead of `let`"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-09/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-09/src/main.rs:here}} ``` -<span class="caption">Listing 18-9: Using `if let` and a block with refutable -patterns instead of `let`</span> +</Listing> We’ve given the code an out! This code is perfectly valid, although it means we -cannot use an irrefutable pattern without receiving an error. If we give `if -let` a pattern that will always match, such as `x`, as shown in Listing 18-10, -the compiler will give a warning. +cannot use an irrefutable pattern without receiving a warning. If we give +`let...else` a pattern that will always match, such as `x`, as shown in Listing +19-10, the compiler will give a warning. + +<Listing number="19-10" caption="Attempting to use an irrefutable pattern with `let...else`"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-10/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-10/src/main.rs:here}} ``` -<span class="caption">Listing 18-10: Attempting to use an irrefutable pattern -with `if let`</span> +</Listing> -Rust complains that it doesn’t make sense to use `if let` with an irrefutable -pattern: +Rust complains that it doesn’t make sense to use `let...else` with an +irrefutable pattern: ```console -{{#include ../listings/ch18-patterns-and-matching/listing-18-10/output.txt}} +{{#include ../listings/ch19-patterns-and-matching/listing-19-10/output.txt}} ``` For this reason, match arms must use refutable patterns, except for the last diff --git a/src/ch18-03-pattern-syntax.md b/src/ch19-03-pattern-syntax.md similarity index 54% rename from src/ch18-03-pattern-syntax.md rename to src/ch19-03-pattern-syntax.md index aeaa766ff3..92a3cc4086 100644 --- a/src/ch18-03-pattern-syntax.md +++ b/src/ch19-03-pattern-syntax.md @@ -1,7 +1,7 @@ ## Pattern Syntax -In this section, we gather all the syntax valid in patterns and discuss why and -when you might want to use each one. +In this section, we gather all the syntax that is valid in patterns and discuss +why and when you might want to use each one. ### Matching Literals @@ -9,34 +9,33 @@ As you saw in Chapter 6, you can match patterns against literals directly. The following code gives some examples: ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/no-listing-01-literals/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/no-listing-01-literals/src/main.rs:here}} ``` -This code prints `one` because the value in `x` is 1. This syntax is useful +This code prints `one` because the value in `x` is `1`. This syntax is useful when you want your code to take an action if it gets a particular concrete value. ### Matching Named Variables Named variables are irrefutable patterns that match any value, and we’ve used -them many times in the book. However, there is a complication when you use -named variables in `match` expressions. Because `match` starts a new scope, -variables declared as part of a pattern inside the `match` expression will -shadow those with the same name outside the `match` construct, as is the case -with all variables. In Listing 18-11, we declare a variable named `x` with the -value `Some(5)` and a variable `y` with the value `10`. We then create a -`match` expression on the value `x`. Look at the patterns in the match arms and -`println!` at the end, and try to figure out what the code will print before -running this code or reading further. - -<span class="filename">Filename: src/main.rs</span> +them many times in this book. However, there is a complication when you use +named variables in `match`, `if let`, or `while let` expressions. Because each +of these kinds of expressions starts a new scope, variables declared as part of +a pattern inside these expressions will shadow those with the same name outside +the constructs, as is the case with all variables. In Listing 19-11, we declare +a variable named `x` with the value `Some(5)` and a variable `y` with the value +`10`. We then create a `match` expression on the value `x`. Look at the +patterns in the match arms and `println!` at the end, and try to figure out +what the code will print before running this code or reading further. + +<Listing number="19-11" file-name="src/main.rs" caption="A `match` expression with an arm that introduces a new variable which shadows an existing variable `y`"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-11/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-11/src/main.rs:here}} ``` -<span class="caption">Listing 18-11: A `match` expression with an arm that -introduces a shadowed variable `y`</span> +</Listing> Let’s walk through what happens when the `match` expression runs. The pattern in the first match arm doesn’t match the defined value of `x`, so the code @@ -45,7 +44,7 @@ continues. The pattern in the second match arm introduces a new variable named `y` that will match any value inside a `Some` value. Because we’re in a new scope inside the `match` expression, this is a new `y` variable, not the `y` we declared at -the beginning with the value 10. This new `y` binding will match any value +the beginning with the value `10`. This new `y` binding will match any value inside a `Some`, which is what we have in `x`. Therefore, this new `y` binds to the inner value of the `Some` in `x`. That value is `5`, so the expression for that arm executes and prints `Matched, y = 5`. @@ -54,28 +53,32 @@ If `x` had been a `None` value instead of `Some(5)`, the patterns in the first two arms wouldn’t have matched, so the value would have matched to the underscore. We didn’t introduce the `x` variable in the pattern of the underscore arm, so the `x` in the expression is still the outer `x` that hasn’t -been shadowed. In this hypothetical case, the `match` would print `Default -case, x = None`. +been shadowed. In this hypothetical case, the `match` would print `Default case, +x = None`. When the `match` expression is done, its scope ends, and so does the scope of the inner `y`. The last `println!` produces `at the end: x = Some(5), y = 10`. To create a `match` expression that compares the values of the outer `x` and -`y`, rather than introducing a shadowed variable, we would need to use a match -guard conditional instead. We’ll talk about match guards later in the [“Extra -Conditionals with Match Guards”](#extra-conditionals-with-match-guards)<!-- -ignore --> section. +`y`, rather than introducing a new variable that shadows the existing `y` +variable, we would need to use a match guard conditional instead. We’ll talk +about match guards later in the [“Adding Conditionals with Match +Guards”](#adding-conditionals-with-match-guards)<!-- ignore --> section. -### Multiple Patterns +<!-- Old headings. Do not remove or links may break. --> +<a id="multiple-patterns"></a> + +### Matching Multiple Patterns In `match` expressions, you can match multiple patterns using the `|` syntax, -which is the pattern *or* operator. For example, in the following code we match -the value of `x` against the match arms, the first of which has an *or* option, +which is the pattern _or_ operator. For example, in the following code, we match +the value of `x` against the match arms, the first of which has an _or_ option, meaning if the value of `x` matches either of the values in that arm, that arm’s code will run: + ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/no-listing-02-multiple-patterns/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/no-listing-02-multiple-patterns/src/main.rs:here}} ``` This code prints `one or two`. @@ -87,14 +90,14 @@ following code, when a pattern matches any of the values within the given range, that arm will execute: ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/no-listing-03-ranges/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/no-listing-03-ranges/src/main.rs:here}} ``` -If `x` is 1, 2, 3, 4, or 5, the first arm will match. This syntax is more -convenient for multiple match values than using the `|` operator to express the -same idea; if we were to use `|` we would have to specify `1 | 2 | 3 | 4 | 5`. -Specifying a range is much shorter, especially if we want to match, say, any -number between 1 and 1,000! +If `x` is `1`, `2`, `3`, `4`, or `5`, the first arm will match. This syntax is +more convenient for multiple match values than using the `|` operator to +express the same idea; if we were to use `|`, we would have to specify `1 | 2 | +3 | 4 | 5`. Specifying a range is much shorter, especially if we want to match, +say, any number between 1 and 1,000! The compiler checks that the range isn’t empty at compile time, and because the only types for which Rust can tell if a range is empty or not are `char` and @@ -103,7 +106,7 @@ numeric values, ranges are only allowed with numeric or `char` values. Here is an example using ranges of `char` values: ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/no-listing-04-ranges-of-char/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/no-listing-04-ranges-of-char/src/main.rs:here}} ``` Rust can tell that `'c'` is within the first pattern’s range and prints `early @@ -114,19 +117,22 @@ ASCII letter`. We can also use patterns to destructure structs, enums, and tuples to use different parts of these values. Let’s walk through each value. -#### Destructuring Structs +<!-- Old headings. Do not remove or links may break. --> + +<a id="destructuring-structs"></a> + +#### Structs -Listing 18-12 shows a `Point` struct with two fields, `x` and `y`, that we can +Listing 19-12 shows a `Point` struct with two fields, `x` and `y`, that we can break apart using a pattern with a `let` statement. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-12" file-name="src/main.rs" caption="Destructuring a struct’s fields into separate variables"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-12/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-12/src/main.rs}} ``` -<span class="caption">Listing 18-12: Destructuring a struct’s fields into -separate variables</span> +</Listing> This code creates the variables `a` and `b` that match the values of the `x` and `y` fields of the `p` struct. This example shows that the names of the @@ -135,19 +141,18 @@ However, it’s common to match the variable names to the field names to make it easier to remember which variables came from which fields. Because of this common usage, and because writing `let Point { x: x, y: y } = p;` contains a lot of duplication, Rust has a shorthand for patterns that match struct fields: -you only need to list the name of the struct field, and the variables created -from the pattern will have the same names. Listing 18-13 behaves in the same -way as the code in Listing 18-12, but the variables created in the `let` +You only need to list the name of the struct field, and the variables created +from the pattern will have the same names. Listing 19-13 behaves in the same +way as the code in Listing 19-12, but the variables created in the `let` pattern are `x` and `y` instead of `a` and `b`. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-13" file-name="src/main.rs" caption="Destructuring struct fields using struct field shorthand"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-13/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-13/src/main.rs}} ``` -<span class="caption">Listing 18-13: Destructuring struct fields using struct -field shorthand</span> +</Listing> This code creates the variables `x` and `y` that match the `x` and `y` fields of the `p` variable. The outcome is that the variables `x` and `y` contain the @@ -158,18 +163,17 @@ rather than creating variables for all the fields. Doing so allows us to test some of the fields for particular values while creating variables to destructure the other fields. -In Listing 18-14, we have a `match` expression that separates `Point` values +In Listing 19-14, we have a `match` expression that separates `Point` values into three cases: points that lie directly on the `x` axis (which is true when -`y = 0`), on the `y` axis (`x = 0`), or neither. +`y = 0`), on the `y` axis (`x = 0`), or on neither axis. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-14" file-name="src/main.rs" caption="Destructuring and matching literal values in one pattern"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-14/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-14/src/main.rs:here}} ``` -<span class="caption">Listing 18-14: Destructuring and matching literal values -in one pattern</span> +</Listing> The first arm will match any point that lies on the `x` axis by specifying that the `y` field matches if its value matches the literal `0`. The pattern still @@ -181,30 +185,33 @@ value of the `y` field. The third arm doesn’t specify any literals, so it matches any other `Point` and creates variables for both the `x` and `y` fields. In this example, the value `p` matches the second arm by virtue of `x` -containing a 0, so this code will print `On the y axis at 7`. +containing a `0`, so this code will print `On the y axis at 7`. Remember that a `match` expression stops checking arms once it has found the -first matching pattern, so even though `Point { x: 0, y: 0}` is on the `x` axis +first matching pattern, so even though `Point { x: 0, y: 0 }` is on the `x` axis and the `y` axis, this code would only print `On the x axis at 0`. -#### Destructuring Enums +<!-- Old headings. Do not remove or links may break. --> -We've destructured enums in this book (for example, Listing 6-5 in Chapter 6), -but haven’t yet explicitly discussed that the pattern to destructure an enum +<a id="destructuring-enums"></a> + +#### Enums + +We’ve destructured enums in this book (for example, Listing 6-5 in Chapter 6), +but we haven’t yet explicitly discussed that the pattern to destructure an enum corresponds to the way the data stored within the enum is defined. As an -example, in Listing 18-15 we use the `Message` enum from Listing 6-2 and write +example, in Listing 19-15, we use the `Message` enum from Listing 6-2 and write a `match` with patterns that will destructure each inner value. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-15" file-name="src/main.rs" caption="Destructuring enum variants that hold different kinds of values"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-15/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-15/src/main.rs}} ``` -<span class="caption">Listing 18-15: Destructuring enum variants that hold -different kinds of values</span> +</Listing> -This code will print `Change the color to red 0, green 160, and blue 255`. Try +This code will print `Change color to red 0, green 160, and blue 255`. Try changing the value of `msg` to see the code from the other arms run. For enum variants without any data, like `Message::Quit`, we can’t destructure @@ -213,9 +220,9 @@ and no variables are in that pattern. For struct-like enum variants, such as `Message::Move`, we can use a pattern similar to the pattern we specify to match structs. After the variant name, we -place curly brackets and then list the fields with variables so we break apart -the pieces to use in the code for this arm. Here we use the shorthand form as -we did in Listing 18-13. +place curly brackets and then list the fields with variables so that we break +apart the pieces to use in the code for this arm. Here we use the shorthand +form as we did in Listing 19-13. For tuple-like enum variants, like `Message::Write` that holds a tuple with one element and `Message::ChangeColor` that holds a tuple with three elements, the @@ -223,38 +230,48 @@ pattern is similar to the pattern we specify to match tuples. The number of variables in the pattern must match the number of elements in the variant we’re matching. -#### Destructuring Nested Structs and Enums +<!-- Old headings. Do not remove or links may break. --> + +<a id="destructuring-nested-structs-and-enums"></a> + +#### Nested Structs and Enums So far, our examples have all been matching structs or enums one level deep, but matching can work on nested items too! For example, we can refactor the -code in Listing 18-15 to support RGB and HSV colors in the `ChangeColor` -message, as shown in Listing 18-16. +code in Listing 19-15 to support RGB and HSV colors in the `ChangeColor` +message, as shown in Listing 19-16. + +<Listing number="19-16" caption="Matching on nested enums"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-16/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-16/src/main.rs}} ``` -<span class="caption">Listing 18-16: Matching on nested enums</span> +</Listing> The pattern of the first arm in the `match` expression matches a -`Message::ChangeColor` enum variant that contains a `Color::Rgb` variant; then +`Message::ChangeColor` enum variant that contains a `Color::Rgb` variant; then, the pattern binds to the three inner `i32` values. The pattern of the second arm also matches a `Message::ChangeColor` enum variant, but the inner enum matches `Color::Hsv` instead. We can specify these complex conditions in one `match` expression, even though two enums are involved. -#### Destructuring Structs and Tuples +<!-- Old headings. Do not remove or links may break. --> + +<a id="destructuring-structs-and-tuples"></a> + +#### Structs and Tuples We can mix, match, and nest destructuring patterns in even more complex ways. The following example shows a complicated destructure where we nest structs and tuples inside a tuple and destructure all the primitive values out: ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/no-listing-05-destructuring-structs-and-tuples/src/main.rs:here}} ``` -This code lets us break complex types into their component parts so we can use -the values we’re interested in separately. +This code lets us break complex types into their component parts so that we can +use the values we’re interested in separately. Destructuring with patterns is a convenient way to use pieces of values, such as the value from each field in a struct, separately from each other. @@ -262,55 +279,63 @@ as the value from each field in a struct, separately from each other. ### Ignoring Values in a Pattern You’ve seen that it’s sometimes useful to ignore values in a pattern, such as -in the last arm of a `match`, to get a catchall that doesn’t actually do +in the last arm of a `match`, to get a catch-all that doesn’t actually do anything but does account for all remaining possible values. There are a few ways to ignore entire values or parts of values in a pattern: using the `_` pattern (which you’ve seen), using the `_` pattern within another pattern, using a name that starts with an underscore, or using `..` to ignore remaining parts of a value. Let’s explore how and why to use each of these patterns. -#### Ignoring an Entire Value with `_` +<!-- Old headings. Do not remove or links may break. --> + +<a id="ignoring-an-entire-value-with-_"></a> + +#### An Entire Value with `_` We’ve used the underscore as a wildcard pattern that will match any value but not bind to the value. This is especially useful as the last arm in a `match` expression, but we can also use it in any pattern, including function -parameters, as shown in Listing 18-17. +parameters, as shown in Listing 19-17. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-17" file-name="src/main.rs" caption="Using `_` in a function signature"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-17/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-17/src/main.rs}} ``` -<span class="caption">Listing 18-17: Using `_` in a function signature</span> +</Listing> This code will completely ignore the value `3` passed as the first argument, and will print `This code only uses the y parameter: 4`. In most cases when you no longer need a particular function parameter, you -would change the signature so it doesn’t include the unused parameter. Ignoring -a function parameter can be especially useful in cases when, for example, -you're implementing a trait when you need a certain type signature but the -function body in your implementation doesn’t need one of the parameters. You -then avoid getting a compiler warning about unused function parameters, as you -would if you used a name instead. +would change the signature so that it doesn’t include the unused parameter. +Ignoring a function parameter can be especially useful in cases when, for +example, you’re implementing a trait when you need a certain type signature but +the function body in your implementation doesn’t need one of the parameters. +You then avoid getting a compiler warning about unused function parameters, as +you would if you used a name instead. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="ignoring-parts-of-a-value-with-a-nested-_"></a> -#### Ignoring Parts of a Value with a Nested `_` +#### Parts of a Value with a Nested `_` We can also use `_` inside another pattern to ignore just part of a value, for example, when we want to test for only part of a value but have no use for the -other parts in the corresponding code we want to run. Listing 18-18 shows code +other parts in the corresponding code we want to run. Listing 19-18 shows code responsible for managing a setting’s value. The business requirements are that the user should not be allowed to overwrite an existing customization of a setting but can unset the setting and give it a value if it is currently unset. +<Listing number="19-18" caption="Using an underscore within patterns that match `Some` variants when we don’t need to use the value inside the `Some`"> + ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-18/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-18/src/main.rs:here}} ``` -<span class="caption">Listing 18-18: Using an underscore within patterns that -match `Some` variants when we don’t need to use the value inside the -`Some`</span> +</Listing> This code will print `Can't overwrite an existing customized value` and then `setting is Some(5)`. In the first match arm, we don’t need to match on or use @@ -319,126 +344,134 @@ when `setting_value` and `new_setting_value` are the `Some` variant. In that case, we print the reason for not changing `setting_value`, and it doesn’t get changed. -In all other cases (if either `setting_value` or `new_setting_value` are -`None`) expressed by the `_` pattern in the second arm, we want to allow +In all other cases (if either `setting_value` or `new_setting_value` is `None`) +expressed by the `_` pattern in the second arm, we want to allow `new_setting_value` to become `setting_value`. We can also use underscores in multiple places within one pattern to ignore -particular values. Listing 18-19 shows an example of ignoring the second and +particular values. Listing 19-19 shows an example of ignoring the second and fourth values in a tuple of five items. +<Listing number="19-19" caption="Ignoring multiple parts of a tuple"> + ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-19/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-19/src/main.rs:here}} ``` -<span class="caption">Listing 18-19: Ignoring multiple parts of a tuple</span> +</Listing> + +This code will print `Some numbers: 2, 8, 32`, and the values `4` and `16` will +be ignored. + +<!-- Old headings. Do not remove or links may break. --> -This code will print `Some numbers: 2, 8, 32`, and the values 4 and 16 will be -ignored. +<a id="ignoring-an-unused-variable-by-starting-its-name-with-_"></a> -#### Ignoring an Unused Variable by Starting Its Name with `_` +#### An Unused Variable by Starting Its Name with `_` If you create a variable but don’t use it anywhere, Rust will usually issue a warning because an unused variable could be a bug. However, sometimes it’s useful to be able to create a variable you won’t use yet, such as when you’re prototyping or just starting a project. In this situation, you can tell Rust not to warn you about the unused variable by starting the name of the variable -with an underscore. In Listing 18-20, we create two unused variables, but when +with an underscore. In Listing 19-20, we create two unused variables, but when we compile this code, we should only get a warning about one of them. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-20" file-name="src/main.rs" caption="Starting a variable name with an underscore to avoid getting unused variable warnings"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-20/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-20/src/main.rs}} ``` -<span class="caption">Listing 18-20: Starting a variable name with an -underscore to avoid getting unused variable warnings</span> +</Listing> -Here we get a warning about not using the variable `y`, but we don’t get a +Here, we get a warning about not using the variable `y`, but we don’t get a warning about not using `_x`. Note that there is a subtle difference between using only `_` and using a name that starts with an underscore. The syntax `_x` still binds the value to the variable, whereas `_` doesn’t bind at all. To show a case where this -distinction matters, Listing 18-21 will provide us with an error. +distinction matters, Listing 19-21 will provide us with an error. + +<Listing number="19-21" caption="An unused variable starting with an underscore still binds the value, which might take ownership of the value."> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-21/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-21/src/main.rs:here}} ``` -<span class="caption">Listing 18-21: An unused variable starting with an -underscore still binds the value, which might take ownership of the value</span> +</Listing> We’ll receive an error because the `s` value will still be moved into `_s`, which prevents us from using `s` again. However, using the underscore by itself -doesn’t ever bind to the value. Listing 18-22 will compile without any errors +doesn’t ever bind to the value. Listing 19-22 will compile without any errors because `s` doesn’t get moved into `_`. +<Listing number="19-22" caption="Using an underscore does not bind the value."> + ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-22/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-22/src/main.rs:here}} ``` -<span class="caption">Listing 18-22: Using an underscore does not bind the -value</span> +</Listing> This code works just fine because we never bind `s` to anything; it isn’t moved. -#### Ignoring Remaining Parts of a Value with `..` +<a id="ignoring-remaining-parts-of-a-value-with-"></a> + +#### Remaining Parts of a Value with `..` With values that have many parts, we can use the `..` syntax to use specific parts and ignore the rest, avoiding the need to list underscores for each ignored value. The `..` pattern ignores any parts of a value that we haven’t -explicitly matched in the rest of the pattern. In Listing 18-23, we have a +explicitly matched in the rest of the pattern. In Listing 19-23, we have a `Point` struct that holds a coordinate in three-dimensional space. In the `match` expression, we want to operate only on the `x` coordinate and ignore the values in the `y` and `z` fields. +<Listing number="19-23" caption="Ignoring all fields of a `Point` except for `x` by using `..`"> + ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-23/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-23/src/main.rs:here}} ``` -<span class="caption">Listing 18-23: Ignoring all fields of a `Point` except -for `x` by using `..`</span> +</Listing> We list the `x` value and then just include the `..` pattern. This is quicker than having to list `y: _` and `z: _`, particularly when we’re working with structs that have lots of fields in situations where only one or two fields are relevant. -The syntax `..` will expand to as many values as it needs to be. Listing 18-24 +The syntax `..` will expand to as many values as it needs to be. Listing 19-24 shows how to use `..` with a tuple. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-24" file-name="src/main.rs" caption="Matching only the first and last values in a tuple and ignoring all other values"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-24/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-24/src/main.rs}} ``` -<span class="caption">Listing 18-24: Matching only the first and last values in -a tuple and ignoring all other values</span> +</Listing> -In this code, the first and last value are matched with `first` and `last`. The -`..` will match and ignore everything in the middle. +In this code, the first and last values are matched with `first` and `last`. +The `..` will match and ignore everything in the middle. However, using `..` must be unambiguous. If it is unclear which values are intended for matching and which should be ignored, Rust will give us an error. -Listing 18-25 shows an example of using `..` ambiguously, so it will not +Listing 19-25 shows an example of using `..` ambiguously, so it will not compile. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-25" file-name="src/main.rs" caption="An attempt to use `..` in an ambiguous way"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-25/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-25/src/main.rs}} ``` -<span class="caption">Listing 18-25: An attempt to use `..` in an ambiguous -way</span> +</Listing> When we compile this example, we get this error: ```console -{{#include ../listings/ch18-patterns-and-matching/listing-18-25/output.txt}} +{{#include ../listings/ch19-patterns-and-matching/listing-19-25/output.txt}} ``` It’s impossible for Rust to determine how many values in the tuple to ignore @@ -449,52 +482,59 @@ ignore thereafter. This code could mean that we want to ignore `2`, bind The variable name `second` doesn’t mean anything special to Rust, so we get a compiler error because using `..` in two places like this is ambiguous. -### Extra Conditionals with Match Guards +<!-- Old headings. Do not remove or links may break. --> -A *match guard* is an additional `if` condition, specified after the pattern in +<a id="extra-conditionals-with-match-guards"></a> + +### Adding Conditionals with Match Guards + +A _match guard_ is an additional `if` condition, specified after the pattern in a `match` arm, that must also match for that arm to be chosen. Match guards are -useful for expressing more complex ideas than a pattern alone allows. +useful for expressing more complex ideas than a pattern alone allows. Note, +however, that they are only available in `match` expressions, not `if let` or +`while let` expressions. -The condition can use variables created in the pattern. Listing 18-26 shows a +The condition can use variables created in the pattern. Listing 19-26 shows a `match` where the first arm has the pattern `Some(x)` and also has a match -guard of `if x % 2 == 0` (which will be true if the number is even). +guard of `if x % 2 == 0` (which will be `true` if the number is even). + +<Listing number="19-26" caption="Adding a match guard to a pattern"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-26/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-26/src/main.rs:here}} ``` -<span class="caption">Listing 18-26: Adding a match guard to a pattern</span> +</Listing> This example will print `The number 4 is even`. When `num` is compared to the -pattern in the first arm, it matches, because `Some(4)` matches `Some(x)`. Then +pattern in the first arm, it matches because `Some(4)` matches `Some(x)`. Then, the match guard checks whether the remainder of dividing `x` by 2 is equal to 0, and because it is, the first arm is selected. If `num` had been `Some(5)` instead, the match guard in the first arm would -have been false because the remainder of 5 divided by 2 is 1, which is not +have been `false` because the remainder of 5 divided by 2 is 1, which is not equal to 0. Rust would then go to the second arm, which would match because the second arm doesn’t have a match guard and therefore matches any `Some` variant. There is no way to express the `if x % 2 == 0` condition within a pattern, so the match guard gives us the ability to express this logic. The downside of -this additional expressiveness is that the compiler doesn't try to check for +this additional expressiveness is that the compiler doesn’t try to check for exhaustiveness when match guard expressions are involved. -In Listing 18-11, we mentioned that we could use match guards to solve our -pattern-shadowing problem. Recall that we created a new variable inside the -pattern in the `match` expression instead of using the variable outside the -`match`. That new variable meant we couldn’t test against the value of the -outer variable. Listing 18-27 shows how we can use a match guard to fix this -problem. +When discussing Listing 19-11, we mentioned that we could use match guards to +solve our pattern-shadowing problem. Recall that we created a new variable +inside the pattern in the `match` expression instead of using the variable +outside the `match`. That new variable meant we couldn’t test against the value +of the outer variable. Listing 19-27 shows how we can use a match guard to fix +this problem. -<span class="filename">Filename: src/main.rs</span> +<Listing number="19-27" file-name="src/main.rs" caption="Using a match guard to test for equality with an outer variable"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-27/src/main.rs}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-27/src/main.rs}} ``` -<span class="caption">Listing 18-27: Using a match guard to test for equality -with an outer variable</span> +</Listing> This code will now print `Default case, x = Some(5)`. The pattern in the second match arm doesn’t introduce a new variable `y` that would shadow the outer `y`, @@ -503,33 +543,34 @@ pattern as `Some(y)`, which would have shadowed the outer `y`, we specify `Some(n)`. This creates a new variable `n` that doesn’t shadow anything because there is no `n` variable outside the `match`. -The match guard `if n == y` is not a pattern and therefore doesn’t introduce -new variables. This `y` *is* the outer `y` rather than a new shadowed `y`, and +The match guard `if n == y` is not a pattern and therefore doesn’t introduce new +variables. This `y` _is_ the outer `y` rather than a new `y` shadowing it, and we can look for a value that has the same value as the outer `y` by comparing `n` to `y`. -You can also use the *or* operator `|` in a match guard to specify multiple +You can also use the _or_ operator `|` in a match guard to specify multiple patterns; the match guard condition will apply to all the patterns. Listing -18-28 shows the precedence when combining a pattern that uses `|` with a match +19-28 shows the precedence when combining a pattern that uses `|` with a match guard. The important part of this example is that the `if y` match guard -applies to `4`, `5`, *and* `6`, even though it might look like `if y` only +applies to `4`, `5`, _and_ `6`, even though it might look like `if y` only applies to `6`. +<Listing number="19-28" caption="Combining multiple patterns with a match guard"> + ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-28/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-28/src/main.rs:here}} ``` -<span class="caption">Listing 18-28: Combining multiple patterns with a match -guard</span> +</Listing> The match condition states that the arm only matches if the value of `x` is -equal to `4`, `5`, or `6` *and* if `y` is `true`. When this code runs, the +equal to `4`, `5`, or `6` _and_ if `y` is `true`. When this code runs, the pattern of the first arm matches because `x` is `4`, but the match guard `if y` -is false, so the first arm is not chosen. The code moves on to the second arm, -which does match, and this program prints `no`. The reason is that the `if` -condition applies to the whole pattern `4 | 5 | 6`, not only to the last value -`6`. In other words, the precedence of a match guard in relation to a pattern -behaves like this: +is `false`, so the first arm is not chosen. The code moves on to the second +arm, which does match, and this program prints `no`. The reason is that the +`if` condition applies to the whole pattern `4 | 5 | 6`, not just to the last +value `6`. In other words, the precedence of a match guard in relation to a +pattern behaves like this: ```text (4 | 5 | 6) if y => ... @@ -541,53 +582,57 @@ rather than this: 4 | 5 | (6 if y) => ... ``` -After running the code, the precedence behavior is evident: if the match guard +After running the code, the precedence behavior is evident: If the match guard were applied only to the final value in the list of values specified using the -`|` operator, the arm would have matched and the program would have printed +`|` operator, the arm would have matched, and the program would have printed `yes`. -### `@` Bindings +<!-- Old headings. Do not remove or links may break. --> + +<a id="-bindings"></a> + +### Using `@` Bindings + +The _at_ operator `@` lets us create a variable that holds a value at the same +time we’re testing that value for a pattern match. In Listing 19-29, we want to +test that a `Message::Hello` `id` field is within the range `3..=7`. We also +want to bind the value to the variable `id` so that we can use it in the code +associated with the arm. -The *at* operator `@` lets us create a variable that holds a value at the same -time as we’re testing that value for a pattern match. In Listing 18-29, we want -to test that a `Message::Hello` `id` field is within the range `3..=7`. We also -want to bind the value to the variable `id_variable` so we can use it in the -code associated with the arm. We could name this variable `id`, the same as the -field, but for this example we’ll use a different name. +<Listing number="19-29" caption="Using `@` to bind to a value in a pattern while also testing it"> ```rust -{{#rustdoc_include ../listings/ch18-patterns-and-matching/listing-18-29/src/main.rs:here}} +{{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-29/src/main.rs:here}} ``` -<span class="caption">Listing 18-29: Using `@` to bind to a value in a pattern -while also testing it</span> +</Listing> -This example will print `Found an id in range: 5`. By specifying `id_variable -@` before the range `3..=7`, we’re capturing whatever value matched the range -while also testing that the value matched the range pattern. +This example will print `Found an id in range: 5`. By specifying `id @` before +the range `3..=7`, we’re capturing whatever value matched the range in a +variable named `id` while also testing that the value matched the range pattern. In the second arm, where we only have a range specified in the pattern, the code associated with the arm doesn’t have a variable that contains the actual value of the `id` field. The `id` field’s value could have been 10, 11, or 12, but the code that goes with that pattern doesn’t know which it is. The pattern code -isn’t able to use the value from the `id` field, because we haven’t saved the +isn’t able to use the value from the `id` field because we haven’t saved the `id` value in a variable. In the last arm, where we’ve specified a variable without a range, we do have the value available to use in the arm’s code in a variable named `id`. The reason is that we’ve used the struct field shorthand syntax. But we haven’t applied any test to the value in the `id` field in this arm, as we did with the -first two arms: any value would match this pattern. +first two arms: Any value would match this pattern. Using `@` lets us test a value and save it in a variable within one pattern. ## Summary Rust’s patterns are very useful in distinguishing between different kinds of -data. When used in `match` expressions, Rust ensures your patterns cover every -possible value, or your program won’t compile. Patterns in `let` statements and -function parameters make those constructs more useful, enabling the -destructuring of values into smaller parts at the same time as assigning to +data. When used in `match` expressions, Rust ensures that your patterns cover +every possible value, or your program won’t compile. Patterns in `let` +statements and function parameters make those constructs more useful, enabling +the destructuring of values into smaller parts and assigning those parts to variables. We can create simple or complex patterns to suit our needs. Next, for the penultimate chapter of the book, we’ll look at some advanced diff --git a/src/ch19-05-advanced-functions-and-closures.md b/src/ch19-05-advanced-functions-and-closures.md deleted file mode 100644 index 88c46847d5..0000000000 --- a/src/ch19-05-advanced-functions-and-closures.md +++ /dev/null @@ -1,130 +0,0 @@ -## Advanced Functions and Closures - -This section explores some advanced features related to functions and closures, -including function pointers and returning closures. - -### Function Pointers - -We’ve talked about how to pass closures to functions; you can also pass regular -functions to functions! This technique is useful when you want to pass a -function you’ve already defined rather than defining a new closure. Functions -coerce to the type `fn` (with a lowercase f), not to be confused with the `Fn` -closure trait. The `fn` type is called a *function pointer*. Passing functions -with function pointers will allow you to use functions as arguments to other -functions. - -The syntax for specifying that a parameter is a function pointer is similar to -that of closures, as shown in Listing 19-27, where we’ve defined a function -`add_one` that adds one to its parameter. The function `do_twice` takes two -parameters: a function pointer to any function that takes an `i32` parameter -and returns an `i32`, and one `i32` value. The `do_twice` function calls the -function `f` twice, passing it the `arg` value, then adds the two function call -results together. The `main` function calls `do_twice` with the arguments -`add_one` and `5`. - -<span class="filename">Filename: src/main.rs</span> - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-27/src/main.rs}} -``` - -<span class="caption">Listing 19-27: Using the `fn` type to accept a function -pointer as an argument</span> - -This code prints `The answer is: 12`. We specify that the parameter `f` in -`do_twice` is an `fn` that takes one parameter of type `i32` and returns an -`i32`. We can then call `f` in the body of `do_twice`. In `main`, we can pass -the function name `add_one` as the first argument to `do_twice`. - -Unlike closures, `fn` is a type rather than a trait, so we specify `fn` as the -parameter type directly rather than declaring a generic type parameter with one -of the `Fn` traits as a trait bound. - -Function pointers implement all three of the closure traits (`Fn`, `FnMut`, and -`FnOnce`), meaning you can always pass a function pointer as an argument for a -function that expects a closure. It’s best to write functions using a generic -type and one of the closure traits so your functions can accept either -functions or closures. - -That said, one example of where you would want to only accept `fn` and not -closures is when interfacing with external code that doesn’t have closures: C -functions can accept functions as arguments, but C doesn’t have closures. - -As an example of where you could use either a closure defined inline or a named -function, let’s look at a use of the `map` method provided by the `Iterator` -trait in the standard library. To use the `map` function to turn a vector of -numbers into a vector of strings, we could use a closure, like this: - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-15-map-closure/src/main.rs:here}} -``` - -Or we could name a function as the argument to `map` instead of the closure, -like this: - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-16-map-function/src/main.rs:here}} -``` - -Note that we must use the fully qualified syntax that we talked about earlier -in the [“Advanced Traits”][advanced-traits]<!-- ignore --> section because -there are multiple functions available named `to_string`. Here, we’re using the -`to_string` function defined in the `ToString` trait, which the standard -library has implemented for any type that implements `Display`. - -Recall from the [“Enum values”][enum-values]<!-- ignore --> section of Chapter -6 that the name of each enum variant that we define also becomes an initializer -function. We can use these initializer functions as function pointers that -implement the closure traits, which means we can specify the initializer -functions as arguments for methods that take closures, like so: - -```rust -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-17-map-initializer/src/main.rs:here}} -``` - -Here we create `Status::Value` instances using each `u32` value in the range -that `map` is called on by using the initializer function of `Status::Value`. -Some people prefer this style, and some people prefer to use closures. They -compile to the same code, so use whichever style is clearer to you. - -### Returning Closures - -Closures are represented by traits, which means you can’t return closures -directly. In most cases where you might want to return a trait, you can instead -use the concrete type that implements the trait as the return value of the -function. However, you can’t do that with closures because they don’t have a -concrete type that is returnable; you’re not allowed to use the function -pointer `fn` as a return type, for example. - -The following code tries to return a closure directly, but it won’t compile: - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-18-returns-closure/src/lib.rs}} -``` - -The compiler error is as follows: - -```console -{{#include ../listings/ch19-advanced-features/no-listing-18-returns-closure/output.txt}} -``` - -The error references the `Sized` trait again! Rust doesn’t know how much space -it will need to store the closure. We saw a solution to this problem earlier. -We can use a trait object: - -```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-19-returns-closure-trait-object/src/lib.rs}} -``` - -This code will compile just fine. For more about trait objects, refer to the -section [“Using Trait Objects That Allow for Values of Different -Types”][using-trait-objects-that-allow-for-values-of-different-types]<!-- -ignore --> in Chapter 17. - -Next, let’s look at macros! - -[advanced-traits]: -ch19-03-advanced-traits.html#advanced-traits -[enum-values]: ch06-01-defining-an-enum.html#enum-values -[using-trait-objects-that-allow-for-values-of-different-types]: -ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types diff --git a/src/ch19-00-advanced-features.md b/src/ch20-00-advanced-features.md similarity index 65% rename from src/ch19-00-advanced-features.md rename to src/ch20-00-advanced-features.md index a0db41fde4..6754bce3f1 100644 --- a/src/ch19-00-advanced-features.md +++ b/src/ch20-00-advanced-features.md @@ -1,8 +1,8 @@ # Advanced Features By now, you’ve learned the most commonly used parts of the Rust programming -language. Before we do one more project in Chapter 20, we’ll look at a few -aspects of the language you might run into every once in a while, but may not +language. Before we do one more project, in Chapter 21, we’ll look at a few +aspects of the language you might run into every once in a while but may not use every day. You can use this chapter as a reference for when you encounter any unknowns. The features covered here are useful in very specific situations. Although you might not reach for them often, we want to make sure you have a @@ -10,13 +10,13 @@ grasp of all the features Rust has to offer. In this chapter, we’ll cover: -* Unsafe Rust: how to opt out of some of Rust’s guarantees and take +- Unsafe Rust: How to opt out of some of Rust’s guarantees and take responsibility for manually upholding those guarantees -* Advanced traits: associated types, default type parameters, fully qualified +- Advanced traits: Associated types, default type parameters, fully qualified syntax, supertraits, and the newtype pattern in relation to traits -* Advanced types: more about the newtype pattern, type aliases, the never type, +- Advanced types: More about the newtype pattern, type aliases, the never type, and dynamically sized types -* Advanced functions and closures: function pointers and returning closures -* Macros: ways to define code that defines more code at compile time +- Advanced functions and closures: Function pointers and returning closures +- Macros: Ways to define code that defines more code at compile time It’s a panoply of Rust features with something for everyone! Let’s dive in! diff --git a/src/ch20-00-final-project-a-web-server.md b/src/ch20-00-final-project-a-web-server.md deleted file mode 100644 index 1004eaf3f1..0000000000 --- a/src/ch20-00-final-project-a-web-server.md +++ /dev/null @@ -1,33 +0,0 @@ -# Final Project: Building a Multithreaded Web Server - -It’s been a long journey, but we’ve reached the end of the book. In this -chapter, we’ll build one more project together to demonstrate some of the -concepts we covered in the final chapters, as well as recap some earlier -lessons. - -For our final project, we’ll make a web server that says “hello” and looks like -Figure 20-1 in a web browser. - -![hello from rust](img/trpl20-01.png) - -<span class="caption">Figure 20-1: Our final shared project</span> - -Here is our plan for building the web server: - -1. Learn a bit about TCP and HTTP. -2. Listen for TCP connections on a socket. -3. Parse a small number of HTTP requests. -4. Create a proper HTTP response. -5. Improve the throughput of our server with a thread pool. - -Before we get started, we should mention one detail: the method we’ll use won’t -be the best way to build a web server with Rust. Community members have -published a number of production-ready crates available on -[crates.io](https://crates.io/) that provide more complete web server and -thread pool implementations than we’ll build. However, our intention in this -chapter is to help you learn, not to take the easy route. Because Rust is a -systems programming language, we can choose the level of abstraction we want to -work with and can go to a lower level than is possible or practical in other -languages. We’ll therefore write the basic HTTP server and thread pool manually -so you can learn the general ideas and techniques behind the crates you might -use in the future. diff --git a/src/ch20-01-single-threaded.md b/src/ch20-01-single-threaded.md deleted file mode 100644 index 993239a981..0000000000 --- a/src/ch20-01-single-threaded.md +++ /dev/null @@ -1,460 +0,0 @@ -## Building a Single-Threaded Web Server - -We’ll start by getting a single-threaded web server working. Before we begin, -let’s look at a quick overview of the protocols involved in building web -servers. The details of these protocols are beyond the scope of this book, but -a brief overview will give you the information you need. - -The two main protocols involved in web servers are *Hypertext Transfer -Protocol* *(HTTP)* and *Transmission Control Protocol* *(TCP)*. Both protocols -are *request-response* protocols, meaning a *client* initiates requests and a -*server* listens to the requests and provides a response to the client. The -contents of those requests and responses are defined by the protocols. - -TCP is the lower-level protocol that describes the details of how information -gets from one server to another but doesn’t specify what that information is. -HTTP builds on top of TCP by defining the contents of the requests and -responses. It’s technically possible to use HTTP with other protocols, but in -the vast majority of cases, HTTP sends its data over TCP. We’ll work with the -raw bytes of TCP and HTTP requests and responses. - -### Listening to the TCP Connection - -Our web server needs to listen to a TCP connection, so that’s the first part -we’ll work on. The standard library offers a `std::net` module that lets us do -this. Let’s make a new project in the usual fashion: - -```console -$ cargo new hello - Created binary (application) `hello` project -$ cd hello -``` - -Now enter the code in Listing 20-1 in *src/main.rs* to start. This code will -listen at the local address `127.0.0.1:7878` for incoming TCP streams. When it -gets an incoming stream, it will print `Connection established!`. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-01/src/main.rs}} -``` - -<span class="caption">Listing 20-1: Listening for incoming streams and printing -a message when we receive a stream</span> - -Using `TcpListener`, we can listen for TCP connections at the address -`127.0.0.1:7878`. In the address, the section before the colon is an IP address -representing your computer (this is the same on every computer and doesn’t -represent the authors’ computer specifically), and `7878` is the port. We’ve -chosen this port for two reasons: HTTP isn’t normally accepted on this port so -our server is unlikely to conflict with any other web server you might have -running on your machine, and 7878 is *rust* typed on a telephone. - -The `bind` function in this scenario works like the `new` function in that it -will return a new `TcpListener` instance. The function is called `bind` -because, in networking, connecting to a port to listen to is known as “binding -to a port.” - -The `bind` function returns a `Result<T, E>`, which indicates that it’s -possible for binding to fail. For example, connecting to port 80 requires -administrator privileges (nonadministrators can listen only on ports higher -than 1023), so if we tried to connect to port 80 without being an -administrator, binding wouldn’t work. Binding also wouldn’t work, for example, -if we ran two instances of our program and so had two programs listening to the -same port. Because we’re writing a basic server just for learning purposes, we -won’t worry about handling these kinds of errors; instead, we use `unwrap` to -stop the program if errors happen. - -The `incoming` method on `TcpListener` returns an iterator that gives us a -sequence of streams (more specifically, streams of type `TcpStream`). A single -*stream* represents an open connection between the client and the server. A -*connection* is the name for the full request and response process in which a -client connects to the server, the server generates a response, and the server -closes the connection. As such, we will read from the `TcpStream` to see what -the client sent and then write our response to the stream to send data back to -the client. Overall, this `for` loop will process each connection in turn and -produce a series of streams for us to handle. - -For now, our handling of the stream consists of calling `unwrap` to terminate -our program if the stream has any errors; if there aren’t any errors, the -program prints a message. We’ll add more functionality for the success case in -the next listing. The reason we might receive errors from the `incoming` method -when a client connects to the server is that we’re not actually iterating over -connections. Instead, we’re iterating over *connection attempts*. The -connection might not be successful for a number of reasons, many of them -operating system specific. For example, many operating systems have a limit to -the number of simultaneous open connections they can support; new connection -attempts beyond that number will produce an error until some of the open -connections are closed. - -Let’s try running this code! Invoke `cargo run` in the terminal and then load -*127.0.0.1:7878* in a web browser. The browser should show an error message -like “Connection reset,” because the server isn’t currently sending back any -data. But when you look at your terminal, you should see several messages that -were printed when the browser connected to the server! - -```text - Running `target/debug/hello` -Connection established! -Connection established! -Connection established! -``` - -Sometimes, you’ll see multiple messages printed for one browser request; the -reason might be that the browser is making a request for the page as well as a -request for other resources, like the *favicon.ico* icon that appears in the -browser tab. - -It could also be that the browser is trying to connect to the server multiple -times because the server isn’t responding with any data. When `stream` goes out -of scope and is dropped at the end of the loop, the connection is closed as -part of the `drop` implementation. Browsers sometimes deal with closed -connections by retrying, because the problem might be temporary. The important -factor is that we’ve successfully gotten a handle to a TCP connection! - -Remember to stop the program by pressing <span class="keystroke">ctrl-c</span> -when you’re done running a particular version of the code. Then restart the -program by invoking the `cargo run` command after you’ve made each set of code -changes to make sure you’re running the newest code. - -### Reading the Request - -Let’s implement the functionality to read the request from the browser! To -separate the concerns of first getting a connection and then taking some action -with the connection, we’ll start a new function for processing connections. In -this new `handle_connection` function, we’ll read data from the TCP stream and -print it so we can see the data being sent from the browser. Change the code to -look like Listing 20-2. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-02/src/main.rs}} -``` - -<span class="caption">Listing 20-2: Reading from the `TcpStream` and printing -the data</span> - -We bring `std::io::prelude` and `std::io::BufReader` into scope to get access -to traits and types that let us read from and write to the stream. In the `for` -loop in the `main` function, instead of printing a message that says we made a -connection, we now call the new `handle_connection` function and pass the -`stream` to it. - -In the `handle_connection` function, we create a new `BufReader` instance that -wraps a mutable reference to the `stream`. `BufReader` adds buffering by -managing calls to the `std::io::Read` trait methods for us. - -We create a variable named `http_request` to collect the lines of the request -the browser sends to our server. We indicate that we want to collect these -lines in a vector by adding the `Vec<_>` type annotation. - -`BufReader` implements the `std::io::BufRead` trait, which provides the `lines` -method. The `lines` method returns an iterator of `Result<String, -std::io::Error>` by splitting the stream of data whenever it sees a newline -byte. To get each `String`, we map and `unwrap` each `Result`. The `Result` -might be an error if the data isn’t valid UTF-8 or if there was a problem -reading from the stream. Again, a production program should handle these errors -more gracefully, but we’re choosing to stop the program in the error case for -simplicity. - -The browser signals the end of an HTTP request by sending two newline -characters in a row, so to get one request from the stream, we take lines until -we get a line that is the empty string. Once we’ve collected the lines into the -vector, we’re printing them out using pretty debug formatting so we can take a -look at the instructions the web browser is sending to our server. - -Let’s try this code! Start the program and make a request in a web browser -again. Note that we’ll still get an error page in the browser, but our -program’s output in the terminal will now look similar to this: - -```console -$ cargo run - Compiling hello v0.1.0 (file:///projects/hello) - Finished dev [unoptimized + debuginfo] target(s) in 0.42s - Running `target/debug/hello` -Request: [ - "GET / HTTP/1.1", - "Host: 127.0.0.1:7878", - "User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:99.0) Gecko/20100101 Firefox/99.0", - "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8", - "Accept-Language: en-US,en;q=0.5", - "Accept-Encoding: gzip, deflate, br", - "DNT: 1", - "Connection: keep-alive", - "Upgrade-Insecure-Requests: 1", - "Sec-Fetch-Dest: document", - "Sec-Fetch-Mode: navigate", - "Sec-Fetch-Site: none", - "Sec-Fetch-User: ?1", - "Cache-Control: max-age=0", -] -``` - -Depending on your browser, you might get slightly different output. Now that -we’re printing the request data, we can see why we get multiple connections -from one browser request by looking at the path after `GET` in the first line -of the request. If the repeated connections are all requesting */*, we know the -browser is trying to fetch */* repeatedly because it’s not getting a response -from our program. - -Let’s break down this request data to understand what the browser is asking of -our program. - -### A Closer Look at an HTTP Request - -HTTP is a text-based protocol, and a request takes this format: - -```text -Method Request-URI HTTP-Version CRLF -headers CRLF -message-body -``` - -The first line is the *request line* that holds information about what the -client is requesting. The first part of the request line indicates the *method* -being used, such as `GET` or `POST`, which describes how the client is making -this request. Our client used a `GET` request, which means it is asking for -information. - -The next part of the request line is */*, which indicates the *Uniform Resource -Identifier* *(URI)* the client is requesting: a URI is almost, but not quite, -the same as a *Uniform Resource Locator* *(URL)*. The difference between URIs -and URLs isn’t important for our purposes in this chapter, but the HTTP spec -uses the term URI, so we can just mentally substitute URL for URI here. - -The last part is the HTTP version the client uses, and then the request line -ends in a *CRLF sequence*. (CRLF stands for *carriage return* and *line feed*, -which are terms from the typewriter days!) The CRLF sequence can also be -written as `\r\n`, where `\r` is a carriage return and `\n` is a line feed. The -CRLF sequence separates the request line from the rest of the request data. -Note that when the CRLF is printed, we see a new line start rather than `\r\n`. - -Looking at the request line data we received from running our program so far, -we see that `GET` is the method, */* is the request URI, and `HTTP/1.1` is the -version. - -After the request line, the remaining lines starting from `Host:` onward are -headers. `GET` requests have no body. - -Try making a request from a different browser or asking for a different -address, such as *127.0.0.1:7878/test*, to see how the request data changes. - -Now that we know what the browser is asking for, let’s send back some data! - -### Writing a Response - -We’re going to implement sending data in response to a client request. -Responses have the following format: - -```text -HTTP-Version Status-Code Reason-Phrase CRLF -headers CRLF -message-body -``` - -The first line is a *status line* that contains the HTTP version used in the -response, a numeric status code that summarizes the result of the request, and -a reason phrase that provides a text description of the status code. After the -CRLF sequence are any headers, another CRLF sequence, and the body of the -response. - -Here is an example response that uses HTTP version 1.1, has a status code of -200, an OK reason phrase, no headers, and no body: - -```text -HTTP/1.1 200 OK\r\n\r\n -``` - -The status code 200 is the standard success response. The text is a tiny -successful HTTP response. Let’s write this to the stream as our response to a -successful request! From the `handle_connection` function, remove the -`println!` that was printing the request data and replace it with the code in -Listing 20-3. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-03/src/main.rs:here}} -``` - -<span class="caption">Listing 20-3: Writing a tiny successful HTTP response to -the stream</span> - -The first new line defines the `response` variable that holds the success -message’s data. Then we call `as_bytes` on our `response` to convert the string -data to bytes. The `write_all` method on `stream` takes a `&[u8]` and sends -those bytes directly down the connection. Because the `write_all` operation -could fail, we use `unwrap` on any error result as before. Again, in a real -application you would add error handling here. - -With these changes, let’s run our code and make a request. We’re no longer -printing any data to the terminal, so we won’t see any output other than the -output from Cargo. When you load *127.0.0.1:7878* in a web browser, you should -get a blank page instead of an error. You’ve just hand-coded receiving an HTTP -request and sending a response! - -### Returning Real HTML - -Let’s implement the functionality for returning more than a blank page. Create -the new file *hello.html* in the root of your project directory, not in the -*src* directory. You can input any HTML you want; Listing 20-4 shows one -possibility. - -<span class="filename">Filename: hello.html</span> - -```html -{{#include ../listings/ch20-web-server/listing-20-05/hello.html}} -``` - -<span class="caption">Listing 20-4: A sample HTML file to return in a -response</span> - -This is a minimal HTML5 document with a heading and some text. To return this -from the server when a request is received, we’ll modify `handle_connection` as -shown in Listing 20-5 to read the HTML file, add it to the response as a body, -and send it. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-05/src/main.rs:here}} -``` - -<span class="caption">Listing 20-5: Sending the contents of *hello.html* as the -body of the response</span> - -We’ve added `fs` to the `use` statement to bring the standard library’s -filesystem module into scope. The code for reading the contents of a file to a -string should look familiar; we used it in Chapter 12 when we read the contents -of a file for our I/O project in Listing 12-4. - -Next, we use `format!` to add the file’s contents as the body of the success -response. To ensure a valid HTTP response, we add the `Content-Length` header -which is set to the size of our response body, in this case the size of -`hello.html`. - -Run this code with `cargo run` and load *127.0.0.1:7878* in your browser; you -should see your HTML rendered! - -Currently, we’re ignoring the request data in `http_request` and just sending -back the contents of the HTML file unconditionally. That means if you try -requesting *127.0.0.1:7878/something-else* in your browser, you’ll still get -back this same HTML response. At the moment, our server is very limited and -does not do what most web servers do. We want to customize our responses -depending on the request and only send back the HTML file for a well-formed -request to */*. - -### Validating the Request and Selectively Responding - -Right now, our web server will return the HTML in the file no matter what the -client requested. Let’s add functionality to check that the browser is -requesting */* before returning the HTML file and return an error if the -browser requests anything else. For this we need to modify `handle_connection`, -as shown in Listing 20-6. This new code checks the content of the request -received against what we know a request for */* looks like and adds `if` and -`else` blocks to treat requests differently. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-06/src/main.rs:here}} -``` - -<span class="caption">Listing 20-6: Handling requests to */* differently from -other requests</span> - -We’re only going to be looking at the first line of the HTTP request, so rather -than reading the entire request into a vector, we’re calling `next` to get the -first item from the iterator. The first `unwrap` takes care of the `Option` and -stops the program if the iterator has no items. The second `unwrap` handles the -`Result` and has the same effect as the `unwrap` that was in the `map` added in -Listing 20-2. - -Next, we check the `request_line` to see if it equals the request line of a GET -request to the */* path. If it does, the `if` block returns the contents of our -HTML file. - -If the `request_line` does *not* equal the GET request to the */* path, it -means we’ve received some other request. We’ll add code to the `else` block in -a moment to respond to all other requests. - -Run this code now and request *127.0.0.1:7878*; you should get the HTML in -*hello.html*. If you make any other request, such as -*127.0.0.1:7878/something-else*, you’ll get a connection error like those you -saw when running the code in Listing 20-1 and Listing 20-2. - -Now let’s add the code in Listing 20-7 to the `else` block to return a response -with the status code 404, which signals that the content for the request was -not found. We’ll also return some HTML for a page to render in the browser -indicating the response to the end user. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-07/src/main.rs:here}} -``` - -<span class="caption">Listing 20-7: Responding with status code 404 and an -error page if anything other than */* was requested</span> - -Here, our response has a status line with status code 404 and the reason phrase -`NOT FOUND`. The body of the response will be the HTML in the file *404.html*. -You’ll need to create a *404.html* file next to *hello.html* for the error -page; again feel free to use any HTML you want or use the example HTML in -Listing 20-8. - -<span class="filename">Filename: 404.html</span> - -```html -{{#include ../listings/ch20-web-server/listing-20-07/404.html}} -``` - -<span class="caption">Listing 20-8: Sample content for the page to send back -with any 404 response</span> - -With these changes, run your server again. Requesting *127.0.0.1:7878* should -return the contents of *hello.html*, and any other request, like -*127.0.0.1:7878/foo*, should return the error HTML from *404.html*. - -### A Touch of Refactoring - -At the moment the `if` and `else` blocks have a lot of repetition: they’re both -reading files and writing the contents of the files to the stream. The only -differences are the status line and the filename. Let’s make the code more -concise by pulling out those differences into separate `if` and `else` lines -that will assign the values of the status line and the filename to variables; -we can then use those variables unconditionally in the code to read the file -and write the response. Listing 20-9 shows the resulting code after replacing -the large `if` and `else` blocks. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-09/src/main.rs:here}} -``` - -<span class="caption">Listing 20-9: Refactoring the `if` and `else` blocks to -contain only the code that differs between the two cases</span> - -Now the `if` and `else` blocks only return the appropriate values for the -status line and filename in a tuple; we then use destructuring to assign these -two values to `status_line` and `filename` using a pattern in the `let` -statement, as discussed in Chapter 18. - -The previously duplicated code is now outside the `if` and `else` blocks and -uses the `status_line` and `filename` variables. This makes it easier to see -the difference between the two cases, and it means we have only one place to -update the code if we want to change how the file reading and response writing -work. The behavior of the code in Listing 20-9 will be the same as that in -Listing 20-8. - -Awesome! We now have a simple web server in approximately 40 lines of Rust code -that responds to one request with a page of content and responds to all other -requests with a 404 response. - -Currently, our server runs in a single thread, meaning it can only serve one -request at a time. Let’s examine how that can be a problem by simulating some -slow requests. Then we’ll fix it so our server can handle multiple requests at -once. diff --git a/src/ch20-01-unsafe-rust.md b/src/ch20-01-unsafe-rust.md new file mode 100644 index 0000000000..12f9fb6f27 --- /dev/null +++ b/src/ch20-01-unsafe-rust.md @@ -0,0 +1,572 @@ +## Unsafe Rust + +All the code we’ve discussed so far has had Rust’s memory safety guarantees +enforced at compile time. However, Rust has a second language hidden inside it +that doesn’t enforce these memory safety guarantees: It’s called _unsafe Rust_ +and works just like regular Rust but gives us extra superpowers. + +Unsafe Rust exists because, by nature, static analysis is conservative. When +the compiler tries to determine whether or not code upholds the guarantees, +it’s better for it to reject some valid programs than to accept some invalid +programs. Although the code _might_ be okay, if the Rust compiler doesn’t have +enough information to be confident, it will reject the code. In these cases, +you can use unsafe code to tell the compiler, “Trust me, I know what I’m +doing.” Be warned, however, that you use unsafe Rust at your own risk: If you +use unsafe code incorrectly, problems can occur due to memory unsafety, such as +null pointer dereferencing. + +Another reason Rust has an unsafe alter ego is that the underlying computer +hardware is inherently unsafe. If Rust didn’t let you do unsafe operations, you +couldn’t do certain tasks. Rust needs to allow you to do low-level systems +programming, such as directly interacting with the operating system or even +writing your own operating system. Working with low-level systems programming +is one of the goals of the language. Let’s explore what we can do with unsafe +Rust and how to do it. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="unsafe-superpowers"></a> + +### Performing Unsafe Superpowers + +To switch to unsafe Rust, use the `unsafe` keyword and then start a new block +that holds the unsafe code. You can take five actions in unsafe Rust that you +can’t in safe Rust, which we call _unsafe superpowers_. Those superpowers +include the ability to: + +1. Dereference a raw pointer. +1. Call an unsafe function or method. +1. Access or modify a mutable static variable. +1. Implement an unsafe trait. +1. Access fields of `union`s. + +It’s important to understand that `unsafe` doesn’t turn off the borrow checker +or disable any of Rust’s other safety checks: If you use a reference in unsafe +code, it will still be checked. The `unsafe` keyword only gives you access to +these five features that are then not checked by the compiler for memory +safety. You’ll still get some degree of safety inside an unsafe block. + +In addition, `unsafe` does not mean the code inside the block is necessarily +dangerous or that it will definitely have memory safety problems: The intent is +that as the programmer, you’ll ensure that the code inside an `unsafe` block +will access memory in a valid way. + +People are fallible and mistakes will happen, but by requiring these five +unsafe operations to be inside blocks annotated with `unsafe`, you’ll know that +any errors related to memory safety must be within an `unsafe` block. Keep +`unsafe` blocks small; you’ll be thankful later when you investigate memory +bugs. + +To isolate unsafe code as much as possible, it’s best to enclose such code +within a safe abstraction and provide a safe API, which we’ll discuss later in +the chapter when we examine unsafe functions and methods. Parts of the standard +library are implemented as safe abstractions over unsafe code that has been +audited. Wrapping unsafe code in a safe abstraction prevents uses of `unsafe` +from leaking out into all the places that you or your users might want to use +the functionality implemented with `unsafe` code, because using a safe +abstraction is safe. + +Let’s look at each of the five unsafe superpowers in turn. We’ll also look at +some abstractions that provide a safe interface to unsafe code. + +### Dereferencing a Raw Pointer + +In Chapter 4, in the [“Dangling References”][dangling-references]<!-- ignore +--> section, we mentioned that the compiler ensures that references are always +valid. Unsafe Rust has two new types called _raw pointers_ that are similar to +references. As with references, raw pointers can be immutable or mutable and +are written as `*const T` and `*mut T`, respectively. The asterisk isn’t the +dereference operator; it’s part of the type name. In the context of raw +pointers, _immutable_ means that the pointer can’t be directly assigned to +after being dereferenced. + +Different from references and smart pointers, raw pointers: + +- Are allowed to ignore the borrowing rules by having both immutable and + mutable pointers or multiple mutable pointers to the same location +- Aren’t guaranteed to point to valid memory +- Are allowed to be null +- Don’t implement any automatic cleanup + +By opting out of having Rust enforce these guarantees, you can give up +guaranteed safety in exchange for greater performance or the ability to +interface with another language or hardware where Rust’s guarantees don’t apply. + +Listing 20-1 shows how to create an immutable and a mutable raw pointer. + +<Listing number="20-1" caption="Creating raw pointers with the raw borrow operators"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-01/src/main.rs:here}} +``` + +</Listing> + +Notice that we don’t include the `unsafe` keyword in this code. We can create +raw pointers in safe code; we just can’t dereference raw pointers outside an +unsafe block, as you’ll see in a bit. + +We’ve created raw pointers by using the raw borrow operators: `&raw const num` +creates a `*const i32` immutable raw pointer, and `&raw mut num` creates a `*mut +i32` mutable raw pointer. Because we created them directly from a local +variable, we know these particular raw pointers are valid, but we can’t make +that assumption about just any raw pointer. + +To demonstrate this, next we’ll create a raw pointer whose validity we can’t be +so certain of, using the keyword `as` to cast a value instead of using the raw +borrow operator. Listing 20-2 shows how to create a raw pointer to an arbitrary +location in memory. Trying to use arbitrary memory is undefined: There might be +data at that address or there might not, the compiler might optimize the code +so that there is no memory access, or the program might terminate with a +segmentation fault. Usually, there is no good reason to write code like this, +especially in cases where you can use a raw borrow operator instead, but it is +possible. + +<Listing number="20-2" caption="Creating a raw pointer to an arbitrary memory address"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-02/src/main.rs:here}} +``` + +</Listing> + +Recall that we can create raw pointers in safe code, but we can’t dereference +raw pointers and read the data being pointed to. In Listing 20-3, we use the +dereference operator `*` on a raw pointer that requires an `unsafe` block. + +<Listing number="20-3" caption="Dereferencing raw pointers within an `unsafe` block"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-03/src/main.rs:here}} +``` + +</Listing> + +Creating a pointer does no harm; it’s only when we try to access the value that +it points at that we might end up dealing with an invalid value. + +Note also that in Listings 20-1 and 20-3, we created `*const i32` and `*mut +i32` raw pointers that both pointed to the same memory location, where `num` is +stored. If we instead tried to create an immutable and a mutable reference to +`num`, the code would not have compiled because Rust’s ownership rules don’t +allow a mutable reference at the same time as any immutable references. With +raw pointers, we can create a mutable pointer and an immutable pointer to the +same location and change data through the mutable pointer, potentially creating +a data race. Be careful! + +With all of these dangers, why would you ever use raw pointers? One major use +case is when interfacing with C code, as you’ll see in the next section. +Another case is when building up safe abstractions that the borrow checker +doesn’t understand. We’ll introduce unsafe functions and then look at an +example of a safe abstraction that uses unsafe code. + +### Calling an Unsafe Function or Method + +The second type of operation you can perform in an unsafe block is calling +unsafe functions. Unsafe functions and methods look exactly like regular +functions and methods, but they have an extra `unsafe` before the rest of the +definition. The `unsafe` keyword in this context indicates the function has +requirements we need to uphold when we call this function, because Rust can’t +guarantee we’ve met these requirements. By calling an unsafe function within an +`unsafe` block, we’re saying that we’ve read this function’s documentation and +we take responsibility for upholding the function’s contracts. + +Here is an unsafe function named `dangerous` that doesn’t do anything in its +body: + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-01-unsafe-fn/src/main.rs:here}} +``` + +We must call the `dangerous` function within a separate `unsafe` block. If we +try to call `dangerous` without the `unsafe` block, we’ll get an error: + +```console +{{#include ../listings/ch20-advanced-features/output-only-01-missing-unsafe/output.txt}} +``` + +With the `unsafe` block, we’re asserting to Rust that we’ve read the function’s +documentation, we understand how to use it properly, and we’ve verified that +we’re fulfilling the contract of the function. + +To perform unsafe operations in the body of an `unsafe` function, you still +need to use an `unsafe` block, just as within a regular function, and the +compiler will warn you if you forget. This helps us keep `unsafe` blocks as +small as possible, as unsafe operations may not be needed across the whole +function body. + +#### Creating a Safe Abstraction over Unsafe Code + +Just because a function contains unsafe code doesn’t mean we need to mark the +entire function as unsafe. In fact, wrapping unsafe code in a safe function is +a common abstraction. As an example, let’s study the `split_at_mut` function +from the standard library, which requires some unsafe code. We’ll explore how +we might implement it. This safe method is defined on mutable slices: It takes +one slice and makes it two by splitting the slice at the index given as an +argument. Listing 20-4 shows how to use `split_at_mut`. + +<Listing number="20-4" caption="Using the safe `split_at_mut` function"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-04/src/main.rs:here}} +``` + +</Listing> + +We can’t implement this function using only safe Rust. An attempt might look +something like Listing 20-5, which won’t compile. For simplicity, we’ll +implement `split_at_mut` as a function rather than a method and only for slices +of `i32` values rather than for a generic type `T`. + +<Listing number="20-5" caption="An attempted implementation of `split_at_mut` using only safe Rust"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-05/src/main.rs:here}} +``` + +</Listing> + +This function first gets the total length of the slice. Then, it asserts that +the index given as a parameter is within the slice by checking whether it’s +less than or equal to the length. The assertion means that if we pass an index +that is greater than the length to split the slice at, the function will panic +before it attempts to use that index. + +Then, we return two mutable slices in a tuple: one from the start of the +original slice to the `mid` index and another from `mid` to the end of the +slice. + +When we try to compile the code in Listing 20-5, we’ll get an error: + +```console +{{#include ../listings/ch20-advanced-features/listing-20-05/output.txt}} +``` + +Rust’s borrow checker can’t understand that we’re borrowing different parts of +the slice; it only knows that we’re borrowing from the same slice twice. +Borrowing different parts of a slice is fundamentally okay because the two +slices aren’t overlapping, but Rust isn’t smart enough to know this. When we +know code is okay, but Rust doesn’t, it’s time to reach for unsafe code. + +Listing 20-6 shows how to use an `unsafe` block, a raw pointer, and some calls +to unsafe functions to make the implementation of `split_at_mut` work. + +<Listing number="20-6" caption="Using unsafe code in the implementation of the `split_at_mut` function"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-06/src/main.rs:here}} +``` + +</Listing> + +Recall from [“The Slice Type”][the-slice-type]<!-- ignore --> section in +Chapter 4 that a slice is a pointer to some data and the length of the slice. +We use the `len` method to get the length of a slice and the `as_mut_ptr` +method to access the raw pointer of a slice. In this case, because we have a +mutable slice to `i32` values, `as_mut_ptr` returns a raw pointer with the type +`*mut i32`, which we’ve stored in the variable `ptr`. + +We keep the assertion that the `mid` index is within the slice. Then, we get to +the unsafe code: The `slice::from_raw_parts_mut` function takes a raw pointer +and a length, and it creates a slice. We use this function to create a slice +that starts from `ptr` and is `mid` items long. Then, we call the `add` method +on `ptr` with `mid` as an argument to get a raw pointer that starts at `mid`, +and we create a slice using that pointer and the remaining number of items +after `mid` as the length. + +The function `slice::from_raw_parts_mut` is unsafe because it takes a raw +pointer and must trust that this pointer is valid. The `add` method on raw +pointers is also unsafe because it must trust that the offset location is also +a valid pointer. Therefore, we had to put an `unsafe` block around our calls to +`slice::from_raw_parts_mut` and `add` so that we could call them. By looking at +the code and by adding the assertion that `mid` must be less than or equal to +`len`, we can tell that all the raw pointers used within the `unsafe` block +will be valid pointers to data within the slice. This is an acceptable and +appropriate use of `unsafe`. + +Note that we don’t need to mark the resultant `split_at_mut` function as +`unsafe`, and we can call this function from safe Rust. We’ve created a safe +abstraction to the unsafe code with an implementation of the function that uses +`unsafe` code in a safe way, because it creates only valid pointers from the +data this function has access to. + +In contrast, the use of `slice::from_raw_parts_mut` in Listing 20-7 would +likely crash when the slice is used. This code takes an arbitrary memory +location and creates a slice 10,000 items long. + +<Listing number="20-7" caption="Creating a slice from an arbitrary memory location"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-07/src/main.rs:here}} +``` + +</Listing> + +We don’t own the memory at this arbitrary location, and there is no guarantee +that the slice this code creates contains valid `i32` values. Attempting to use +`values` as though it’s a valid slice results in undefined behavior. + +#### Using `extern` Functions to Call External Code + +Sometimes your Rust code might need to interact with code written in another +language. For this, Rust has the keyword `extern` that facilitates the creation +and use of a _Foreign Function Interface (FFI)_, which is a way for a +programming language to define functions and enable a different (foreign) +programming language to call those functions. + +Listing 20-8 demonstrates how to set up an integration with the `abs` function +from the C standard library. Functions declared within `extern` blocks are +generally unsafe to call from Rust code, so `extern` blocks must also be marked +`unsafe`. The reason is that other languages don’t enforce Rust’s rules and +guarantees, and Rust can’t check them, so responsibility falls on the +programmer to ensure safety. + +<Listing number="20-8" file-name="src/main.rs" caption="Declaring and calling an `extern` function defined in another language"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-08/src/main.rs}} +``` + +</Listing> + +Within the `unsafe extern "C"` block, we list the names and signatures of +external functions from another language we want to call. The `"C"` part +defines which _application binary interface (ABI)_ the external function uses: +The ABI defines how to call the function at the assembly level. The `"C"` ABI +is the most common and follows the C programming language’s ABI. Information +about all the ABIs Rust supports is available in [the Rust Reference][ABI]. + +Every item declared within an `unsafe extern` block is implicitly unsafe. +However, some FFI functions *are* safe to call. For example, the `abs` function +from C’s standard library does not have any memory safety considerations, and we +know it can be called with any `i32`. In cases like this, we can use the `safe` +keyword to say that this specific function is safe to call even though it is in +an `unsafe extern` block. Once we make that change, calling it no longer +requires an `unsafe` block, as shown in Listing 20-9. + +<Listing number="20-9" file-name="src/main.rs" caption="Explicitly marking a function as `safe` within an `unsafe extern` block and calling it safely"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-09/src/main.rs}} +``` + +</Listing> + +Marking a function as `safe` does not inherently make it safe! Instead, it is +like a promise you are making to Rust that it is safe. It is still your +responsibility to make sure that promise is kept! + +#### Calling Rust Functions from Other Languages + +We can also use `extern` to create an interface that allows other languages to +call Rust functions. Instead of creating a whole `extern` block, we add the +`extern` keyword and specify the ABI to use just before the `fn` keyword for +the relevant function. We also need to add an `#[unsafe(no_mangle)]` annotation +to tell the Rust compiler not to mangle the name of this function. _Mangling_ +is when a compiler changes the name we’ve given a function to a different name +that contains more information for other parts of the compilation process to +consume but is less human readable. Every programming language compiler mangles +names slightly differently, so for a Rust function to be nameable by other +languages, we must disable the Rust compiler’s name mangling. This is unsafe +because there might be name collisions across libraries without the built-in +mangling, so it is our responsibility to make sure the name we choose is safe +to export without mangling. + +In the following example, we make the `call_from_c` function accessible from C +code, after it’s compiled to a shared library and linked from C: + +``` +#[unsafe(no_mangle)] +pub extern "C" fn call_from_c() { + println!("Just called a Rust function from C!"); +} +``` + +This usage of `extern` requires `unsafe` only in the attribute, not on the +`extern` block. + +### Accessing or Modifying a Mutable Static Variable + +In this book, we’ve not yet talked about global variables, which Rust does +support but which can be problematic with Rust’s ownership rules. If two +threads are accessing the same mutable global variable, it can cause a data +race. + +In Rust, global variables are called _static_ variables. Listing 20-10 shows an +example declaration and use of a static variable with a string slice as a +value. + +<Listing number="20-10" file-name="src/main.rs" caption="Defining and using an immutable static variable"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-10/src/main.rs}} +``` + +</Listing> + +Static variables are similar to constants, which we discussed in the +[“Declaring Constants”][constants]<!-- ignore --> section in Chapter 3. The +names of static variables are in `SCREAMING_SNAKE_CASE` by convention. Static +variables can only store references with the `'static` lifetime, which means +the Rust compiler can figure out the lifetime and we aren’t required to +annotate it explicitly. Accessing an immutable static variable is safe. + +A subtle difference between constants and immutable static variables is that +values in a static variable have a fixed address in memory. Using the value +will always access the same data. Constants, on the other hand, are allowed to +duplicate their data whenever they’re used. Another difference is that static +variables can be mutable. Accessing and modifying mutable static variables is +_unsafe_. Listing 20-11 shows how to declare, access, and modify a mutable +static variable named `COUNTER`. + +<Listing number="20-11" file-name="src/main.rs" caption="Reading from or writing to a mutable static variable is unsafe."> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-11/src/main.rs}} +``` + +</Listing> + +As with regular variables, we specify mutability using the `mut` keyword. Any +code that reads or writes from `COUNTER` must be within an `unsafe` block. The +code in Listing 20-11 compiles and prints `COUNTER: 3` as we would expect +because it’s single threaded. Having multiple threads access `COUNTER` would +likely result in data races, so it is undefined behavior. Therefore, we need to +mark the entire function as `unsafe` and document the safety limitation so that +anyone calling the function knows what they are and are not allowed to do +safely. + +Whenever we write an unsafe function, it is idiomatic to write a comment +starting with `SAFETY` and explaining what the caller needs to do to call the +function safely. Likewise, whenever we perform an unsafe operation, it is +idiomatic to write a comment starting with `SAFETY` to explain how the safety +rules are upheld. + +Additionally, the compiler will deny by default any attempt to create +references to a mutable static variable through a compiler lint. You must +either explicitly opt out of that lint’s protections by adding an +`#[allow(static_mut_refs)]` annotation or access the mutable static variable +via a raw pointer created with one of the raw borrow operators. That includes +cases where the reference is created invisibly, as when it is used in the +`println!` in this code listing. Requiring references to static mutable +variables to be created via raw pointers helps make the safety requirements for +using them more obvious. + +With mutable data that is globally accessible, it’s difficult to ensure that +there are no data races, which is why Rust considers mutable static variables +to be unsafe. Where possible, it’s preferable to use the concurrency techniques +and thread-safe smart pointers we discussed in Chapter 16 so that the compiler +checks that data access from different threads is done safely. + +### Implementing an Unsafe Trait + +We can use `unsafe` to implement an unsafe trait. A trait is unsafe when at +least one of its methods has some invariant that the compiler can’t verify. We +declare that a trait is `unsafe` by adding the `unsafe` keyword before `trait` +and marking the implementation of the trait as `unsafe` too, as shown in +Listing 20-12. + +<Listing number="20-12" caption="Defining and implementing an unsafe trait"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-12/src/main.rs:here}} +``` + +</Listing> + +By using `unsafe impl`, we’re promising that we’ll uphold the invariants that +the compiler can’t verify. + +As an example, recall the `Send` and `Sync` marker traits we discussed in the +[“Extensible Concurrency with `Send` and `Sync`”][send-and-sync]<!-- ignore --> +section in Chapter 16: The compiler implements these traits automatically if +our types are composed entirely of other types that implement `Send` and +`Sync`. If we implement a type that contains a type that does not implement +`Send` or `Sync`, such as raw pointers, and we want to mark that type as `Send` +or `Sync`, we must use `unsafe`. Rust can’t verify that our type upholds the +guarantees that it can be safely sent across threads or accessed from multiple +threads; therefore, we need to do those checks manually and indicate as such +with `unsafe`. + +### Accessing Fields of a Union + +The final action that works only with `unsafe` is accessing fields of a union. +A *union* is similar to a `struct`, but only one declared field is used in a +particular instance at one time. Unions are primarily used to interface with +unions in C code. Accessing union fields is unsafe because Rust can’t guarantee +the type of the data currently being stored in the union instance. You can +learn more about unions in [the Rust Reference][unions]. + +### Using Miri to Check Unsafe Code + +When writing unsafe code, you might want to check that what you have written +actually is safe and correct. One of the best ways to do that is to use Miri, +an official Rust tool for detecting undefined behavior. Whereas the borrow +checker is a _static_ tool that works at compile time, Miri is a _dynamic_ +tool that works at runtime. It checks your code by running your program, or +its test suite, and detecting when you violate the rules it understands about +how Rust should work. + +Using Miri requires a nightly build of Rust (which we talk about more in +[Appendix G: How Rust is Made and “Nightly Rust”][nightly]<!-- ignore -->). You +can install both a nightly version of Rust and the Miri tool by typing `rustup ++nightly component add miri`. This does not change what version of Rust your +project uses; it only adds the tool to your system so you can use it when you +want to. You can run Miri on a project by typing `cargo +nightly miri run` or +`cargo +nightly miri test`. + +For an example of how helpful this can be, consider what happens when we run it +against Listing 20-7. + +```console +{{#include ../listings/ch20-advanced-features/listing-20-07/output.txt}} +``` + +Miri correctly warns us that we’re casting an integer to a pointer, which might +be a problem, but Miri can’t determine whether a problem exists because it +doesn’t know how the pointer originated. Then, Miri returns an error where +Listing 20-7 has undefined behavior because we have a dangling pointer. Thanks +to Miri, we now know there is a risk of undefined behavior, and we can think +about how to make the code safe. In some cases, Miri can even make +recommendations about how to fix errors. + +Miri doesn’t catch everything you might get wrong when writing unsafe code. +Miri is a dynamic analysis tool, so it only catches problems with code that +actually gets run. That means you will need to use it in conjunction with good +testing techniques to increase your confidence about the unsafe code you have +written. Miri also does not cover every possible way your code can be unsound. + +Put another way: If Miri _does_ catch a problem, you know there’s a bug, but +just because Miri _doesn’t_ catch a bug doesn’t mean there isn’t a problem. It +can catch a lot, though. Try running it on the other examples of unsafe code in +this chapter and see what it says! + +You can learn more about Miri at [its GitHub repository][miri]. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="when-to-use-unsafe-code"></a> + +### Using Unsafe Code Correctly + +Using `unsafe` to use one of the five superpowers just discussed isn’t wrong or +even frowned upon, but it is trickier to get `unsafe` code correct because the +compiler can’t help uphold memory safety. When you have a reason to use +`unsafe` code, you can do so, and having the explicit `unsafe` annotation makes +it easier to track down the source of problems when they occur. Whenever you +write unsafe code, you can use Miri to help you be more confident that the code +you have written upholds Rust’s rules. + +For a much deeper exploration of how to work effectively with unsafe Rust, read +Rust’s official guide for `unsafe`, [The Rustonomicon][nomicon]. + +[dangling-references]: ch04-02-references-and-borrowing.html#dangling-references +[ABI]: ../reference/items/external-blocks.html#abi +[constants]: ch03-01-variables-and-mutability.html#declaring-constants +[send-and-sync]: ch16-04-extensible-concurrency-sync-and-send.html +[the-slice-type]: ch04-03-slices.html#the-slice-type +[unions]: ../reference/items/unions.html +[miri]: https://github.com/rust-lang/miri +[editions]: appendix-05-editions.html +[nightly]: appendix-07-nightly-rust.html +[nomicon]: https://doc.rust-lang.org/nomicon/ diff --git a/src/ch19-03-advanced-traits.md b/src/ch20-02-advanced-traits.md similarity index 55% rename from src/ch19-03-advanced-traits.md rename to src/ch20-02-advanced-traits.md index 6fd3e09f49..a16d5c8347 100644 --- a/src/ch19-03-advanced-traits.md +++ b/src/ch20-02-advanced-traits.md @@ -1,13 +1,18 @@ ## Advanced Traits -We first covered traits in the [“Traits: Defining Shared -Behavior”][traits-defining-shared-behavior]<!-- ignore --> section of Chapter -10, but we didn’t discuss the more advanced details. Now that you know more -about Rust, we can get into the nitty-gritty. +We first covered traits in the [“Defining Shared Behavior with +Traits”][traits]<!-- ignore --> section in Chapter 10, but we didn’t discuss +the more advanced details. Now that you know more about Rust, we can get into +the nitty-gritty. -### Specifying Placeholder Types in Trait Definitions with Associated Types +<!-- Old headings. Do not remove or links may break. --> -*Associated types* connect a type placeholder with a trait such that the trait +<a id="specifying-placeholder-types-in-trait-definitions-with-associated-types"></a> +<a id="associated-types"></a> + +### Defining Traits with Associated Types + +_Associated types_ connect a type placeholder with a trait such that the trait method definitions can use these placeholder types in their signatures. The implementor of a trait will specify the concrete type to be used instead of the placeholder type for the particular implementation. That way, we can define a @@ -15,7 +20,7 @@ trait that uses some types without needing to know exactly what those types are until the trait is implemented. We’ve described most of the advanced features in this chapter as being rarely -needed. Associated types are somewhere in the middle: they’re used more rarely +needed. Associated types are somewhere in the middle: They’re used more rarely than features explained in the rest of the book but more commonly than many of the other features discussed in this chapter. @@ -23,14 +28,15 @@ One example of a trait with an associated type is the `Iterator` trait that the standard library provides. The associated type is named `Item` and stands in for the type of the values the type implementing the `Iterator` trait is iterating over. The definition of the `Iterator` trait is as shown in Listing -19-12. +20-13. + +<Listing number="20-13" caption="The definition of the `Iterator` trait that has an associated type `Item`"> ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-12/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-13/src/lib.rs}} ``` -<span class="caption">Listing 19-12: The definition of the `Iterator` trait -that has an associated type `Item`</span> +</Listing> The type `Item` is a placeholder, and the `next` method’s definition shows that it will return values of type `Option<Self::Item>`. Implementors of the @@ -43,23 +49,26 @@ handle. To examine the difference between the two concepts, we’ll look at an implementation of the `Iterator` trait on a type named `Counter` that specifies the `Item` type is `u32`: -<span class="filename">Filename: src/lib.rs</span> +<Listing file-name="src/lib.rs"> ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-22-iterator-on-counter/src/lib.rs:ch19}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-22-iterator-on-counter/src/lib.rs:ch19}} ``` -This syntax seems comparable to that of generics. So why not just define the -`Iterator` trait with generics, as shown in Listing 19-13? +</Listing> + +This syntax seems comparable to that of generics. So, why not just define the +`Iterator` trait with generics, as shown in Listing 20-14? + +<Listing number="20-14" caption="A hypothetical definition of the `Iterator` trait using generics"> ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-13/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-14/src/lib.rs}} ``` -<span class="caption">Listing 19-13: A hypothetical definition of the -`Iterator` trait using generics</span> +</Listing> -The difference is that when using generics, as in Listing 19-13, we must +The difference is that when using generics, as in Listing 20-14, we must annotate the types in each implementation; because we can also implement `Iterator<String> for Counter` or any other type, we could have multiple implementations of `Iterator` for `Counter`. In other words, when a trait has a @@ -68,44 +77,47 @@ the concrete types of the generic type parameters each time. When we use the `next` method on `Counter`, we would have to provide type annotations to indicate which implementation of `Iterator` we want to use. -With associated types, we don’t need to annotate types because we can’t -implement a trait on a type multiple times. In Listing 19-12 with the -definition that uses associated types, we can only choose what the type of -`Item` will be once, because there can only be one `impl Iterator for Counter`. -We don’t have to specify that we want an iterator of `u32` values everywhere -that we call `next` on `Counter`. +With associated types, we don’t need to annotate types, because we can’t +implement a trait on a type multiple times. In Listing 20-13 with the +definition that uses associated types, we can choose what the type of `Item` +will be only once because there can be only one `impl Iterator for Counter`. We +don’t have to specify that we want an iterator of `u32` values everywhere we +call `next` on `Counter`. -Associated types also become part of the trait’s contract: implementors of the +Associated types also become part of the trait’s contract: Implementors of the trait must provide a type to stand in for the associated type placeholder. Associated types often have a name that describes how the type will be used, -and documenting the associated type in the API documentation is good practice. +and documenting the associated type in the API documentation is a good practice. + +<!-- Old headings. Do not remove or links may break. --> -### Default Generic Type Parameters and Operator Overloading +<a id="default-generic-type-parameters-and-operator-overloading"></a> + +### Using Default Generic Parameters and Operator Overloading When we use generic type parameters, we can specify a default concrete type for the generic type. This eliminates the need for implementors of the trait to specify a concrete type if the default type works. You specify a default type when declaring a generic type with the `<PlaceholderType=ConcreteType>` syntax. -A great example of a situation where this technique is useful is with *operator -overloading*, in which you customize the behavior of an operator (such as `+`) +A great example of a situation where this technique is useful is with _operator +overloading_, in which you customize the behavior of an operator (such as `+`) in particular situations. Rust doesn’t allow you to create your own operators or overload arbitrary operators. But you can overload the operations and corresponding traits listed in `std::ops` by implementing the traits associated with the operator. For -example, in Listing 19-14 we overload the `+` operator to add two `Point` +example, in Listing 20-15, we overload the `+` operator to add two `Point` instances together. We do this by implementing the `Add` trait on a `Point` -struct: +struct. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-15" file-name="src/main.rs" caption="Implementing the `Add` trait to overload the `+` operator for `Point` instances"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-14/src/main.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-15/src/main.rs}} ``` -<span class="caption">Listing 19-14: Implementing the `Add` trait to overload -the `+` operator for `Point` instances</span> +</Listing> The `add` method adds the `x` values of two `Point` instances and the `y` values of two `Point` instances to create a new `Point`. The `Add` trait has an @@ -124,8 +136,8 @@ trait Add<Rhs=Self> { ``` This code should look generally familiar: a trait with one method and an -associated type. The new part is `Rhs=Self`: this syntax is called *default -type parameters*. The `Rhs` generic type parameter (short for “right hand +associated type. The new part is `Rhs=Self`: This syntax is called _default +type parameters_. The `Rhs` generic type parameter (short for “right-hand side”) defines the type of the `rhs` parameter in the `add` method. If we don’t specify a concrete type for `Rhs` when we implement the `Add` trait, the type of `Rhs` will default to `Self`, which will be the type we’re implementing @@ -138,42 +150,46 @@ default. We have two structs, `Millimeters` and `Meters`, holding values in different units. This thin wrapping of an existing type in another struct is known as the -*newtype pattern*, which we describe in more detail in the [“Using the Newtype -Pattern to Implement External Traits on External Types”][newtype]<!-- ignore ---> section. We want to add values in millimeters to values in meters and have -the implementation of `Add` do the conversion correctly. We can implement `Add` -for `Millimeters` with `Meters` as the `Rhs`, as shown in Listing 19-15. +_newtype pattern_, which we describe in more detail in the [“Implementing +External Traits with the Newtype Pattern”][newtype]<!-- ignore --> section. We +want to add values in millimeters to values in meters and have the +implementation of `Add` do the conversion correctly. We can implement `Add` for +`Millimeters` with `Meters` as the `Rhs`, as shown in Listing 20-16. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="20-16" file-name="src/lib.rs" caption="Implementing the `Add` trait on `Millimeters` to add `Millimeters` and `Meters`"> ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-15/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-16/src/lib.rs}} ``` -<span class="caption">Listing 19-15: Implementing the `Add` trait on -`Millimeters` to add `Millimeters` to `Meters`</span> +</Listing> To add `Millimeters` and `Meters`, we specify `impl Add<Meters>` to set the value of the `Rhs` type parameter instead of using the default of `Self`. You’ll use default type parameters in two main ways: -* To extend a type without breaking existing code -* To allow customization in specific cases most users won’t need +1. To extend a type without breaking existing code +2. To allow customization in specific cases most users won’t need The standard library’s `Add` trait is an example of the second purpose: -usually, you’ll add two like types, but the `Add` trait provides the ability to +Usually, you’ll add two like types, but the `Add` trait provides the ability to customize beyond that. Using a default type parameter in the `Add` trait definition means you don’t have to specify the extra parameter most of the time. In other words, a bit of implementation boilerplate isn’t needed, making it easier to use the trait. -The first purpose is similar to the second but in reverse: if you want to add a +The first purpose is similar to the second but in reverse: If you want to add a type parameter to an existing trait, you can give it a default to allow extension of the functionality of the trait without breaking the existing implementation code. -### Fully Qualified Syntax for Disambiguation: Calling Methods with the Same Name +<!-- Old headings. Do not remove or links may break. --> + +<a id="fully-qualified-syntax-for-disambiguation-calling-methods-with-the-same-name"></a> +<a id="disambiguating-between-methods-with-the-same-name"></a> + +### Disambiguating Between Identically Named Methods Nothing in Rust prevents a trait from having a method with the same name as another trait’s method, nor does Rust prevent you from implementing both traits @@ -181,83 +197,77 @@ on one type. It’s also possible to implement a method directly on the type wit the same name as methods from traits. When calling methods with the same name, you’ll need to tell Rust which one you -want to use. Consider the code in Listing 19-16 where we’ve defined two traits, +want to use. Consider the code in Listing 20-17 where we’ve defined two traits, `Pilot` and `Wizard`, that both have a method called `fly`. We then implement both traits on a type `Human` that already has a method named `fly` implemented on it. Each `fly` method does something different. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-17" file-name="src/main.rs" caption="Two traits are defined to have a `fly` method and are implemented on the `Human` type, and a `fly` method is implemented on `Human` directly."> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-16/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-17/src/main.rs:here}} ``` -<span class="caption">Listing 19-16: Two traits are defined to have a `fly` -method and are implemented on the `Human` type, and a `fly` method is -implemented on `Human` directly</span> +</Listing> When we call `fly` on an instance of `Human`, the compiler defaults to calling -the method that is directly implemented on the type, as shown in Listing 19-17. +the method that is directly implemented on the type, as shown in Listing 20-18. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-18" file-name="src/main.rs" caption="Calling `fly` on an instance of `Human`"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-17/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-18/src/main.rs:here}} ``` -<span class="caption">Listing 19-17: Calling `fly` on an instance of -`Human`</span> +</Listing> Running this code will print `*waving arms furiously*`, showing that Rust called the `fly` method implemented on `Human` directly. To call the `fly` methods from either the `Pilot` trait or the `Wizard` trait, we need to use more explicit syntax to specify which `fly` method we mean. -Listing 19-18 demonstrates this syntax. +Listing 20-19 demonstrates this syntax. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-19" file-name="src/main.rs" caption="Specifying which trait’s `fly` method we want to call"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-18/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-19/src/main.rs:here}} ``` -<span class="caption">Listing 19-18: Specifying which trait’s `fly` method we -want to call</span> +</Listing> Specifying the trait name before the method name clarifies to Rust which implementation of `fly` we want to call. We could also write `Human::fly(&person)`, which is equivalent to the `person.fly()` that we used -in Listing 19-18, but this is a bit longer to write if we don’t need to +in Listing 20-19, but this is a bit longer to write if we don’t need to disambiguate. Running this code prints the following: ```console -{{#include ../listings/ch19-advanced-features/listing-19-18/output.txt}} +{{#include ../listings/ch20-advanced-features/listing-20-19/output.txt}} ``` -Because the `fly` method takes a `self` parameter, if we had two *types* that -both implement one *trait*, Rust could figure out which implementation of a +Because the `fly` method takes a `self` parameter, if we had two _types_ that +both implement one _trait_, Rust could figure out which implementation of a trait to use based on the type of `self`. However, associated functions that are not methods don’t have a `self` parameter. When there are multiple types or traits that define non-method -functions with the same function name, Rust doesn't always know which type you -mean unless you use *fully qualified syntax*. For example, in Listing 19-19 we -create a trait for an animal shelter that wants to name all baby dogs *Spot*. -We make an `Animal` trait with an associated non-method function `baby_name`. -The `Animal` trait is implemented for the struct `Dog`, on which we also -provide an associated non-method function `baby_name` directly. +functions with the same function name, Rust doesn’t always know which type you +mean unless you use fully qualified syntax. For example, in Listing 20-20, we +create a trait for an animal shelter that wants to name all baby dogs Spot. We +make an `Animal` trait with an associated non-method function `baby_name`. The +`Animal` trait is implemented for the struct `Dog`, on which we also provide an +associated non-method function `baby_name` directly. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-20" file-name="src/main.rs" caption="A trait with an associated function and a type with an associated function of the same name that also implements the trait"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-19/src/main.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-20/src/main.rs}} ``` -<span class="caption">Listing 19-19: A trait with an associated function and a -type with an associated function of the same name that also implements the -trait</span> +</Listing> We implement the code for naming all puppies Spot in the `baby_name` associated function that is defined on `Dog`. The `Dog` type also implements the trait @@ -269,47 +279,43 @@ In `main`, we call the `Dog::baby_name` function, which calls the associated function defined on `Dog` directly. This code prints the following: ```console -{{#include ../listings/ch19-advanced-features/listing-19-19/output.txt}} +{{#include ../listings/ch20-advanced-features/listing-20-20/output.txt}} ``` This output isn’t what we wanted. We want to call the `baby_name` function that -is part of the `Animal` trait that we implemented on `Dog` so the code prints -`A baby dog is called a puppy`. The technique of specifying the trait name that -we used in Listing 19-18 doesn’t help here; if we change `main` to the code in -Listing 19-20, we’ll get a compilation error. +is part of the `Animal` trait that we implemented on `Dog` so that the code +prints `A baby dog is called a puppy`. The technique of specifying the trait +name that we used in Listing 20-19 doesn’t help here; if we change `main` to +the code in Listing 20-21, we’ll get a compilation error. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-21" file-name="src/main.rs" caption="Attempting to call the `baby_name` function from the `Animal` trait, but Rust doesn’t know which implementation to use"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-20/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-21/src/main.rs:here}} ``` -<span class="caption">Listing 19-20: Attempting to call the `baby_name` -function from the `Animal` trait, but Rust doesn’t know which implementation to -use</span> +</Listing> Because `Animal::baby_name` doesn’t have a `self` parameter, and there could be other types that implement the `Animal` trait, Rust can’t figure out which implementation of `Animal::baby_name` we want. We’ll get this compiler error: ```console -{{#include ../listings/ch19-advanced-features/listing-19-20/output.txt}} +{{#include ../listings/ch20-advanced-features/listing-20-21/output.txt}} ``` To disambiguate and tell Rust that we want to use the implementation of `Animal` for `Dog` as opposed to the implementation of `Animal` for some other -type, we need to use fully qualified syntax. Listing 19-21 demonstrates how to +type, we need to use fully qualified syntax. Listing 20-22 demonstrates how to use fully qualified syntax. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-22" file-name="src/main.rs" caption="Using fully qualified syntax to specify that we want to call the `baby_name` function from the `Animal` trait as implemented on `Dog`"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-21/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-22/src/main.rs:here}} ``` -<span class="caption">Listing 19-21: Using fully qualified syntax to specify -that we want to call the `baby_name` function from the `Animal` trait as -implemented on `Dog`</span> +</Listing> We’re providing Rust with a type annotation within the angle brackets, which indicates we want to call the `baby_name` method from the `Animal` trait as @@ -317,7 +323,7 @@ implemented on `Dog` by saying that we want to treat the `Dog` type as an `Animal` for this function call. This code will now print what we want: ```console -{{#include ../listings/ch19-advanced-features/listing-19-21/output.txt}} +{{#include ../listings/ch20-advanced-features/listing-20-22/output.txt}} ``` In general, fully qualified syntax is defined as follows: @@ -327,23 +333,27 @@ In general, fully qualified syntax is defined as follows: ``` For associated functions that aren’t methods, there would not be a `receiver`: -there would only be the list of other arguments. You could use fully qualified +There would only be the list of other arguments. You could use fully qualified syntax everywhere that you call functions or methods. However, you’re allowed to omit any part of this syntax that Rust can figure out from other information in the program. You only need to use this more verbose syntax in cases where there are multiple implementations that use the same name and Rust needs help to identify which implementation you want to call. -### Using Supertraits to Require One Trait’s Functionality Within Another Trait +<!-- Old headings. Do not remove or links may break. --> + +<a id="using-supertraits-to-require-one-traits-functionality-within-another-trait"></a> -Sometimes, you might write a trait definition that depends on another trait: -for a type to implement the first trait, you want to require that type to also +### Using Supertraits + +Sometimes you might write a trait definition that depends on another trait: For +a type to implement the first trait, you want to require that type to also implement the second trait. You would do this so that your trait definition can make use of the associated items of the second trait. The trait your trait -definition is relying on is called a *supertrait* of your trait. +definition is relying on is called a _supertrait_ of your trait. For example, let’s say we want to make an `OutlinePrint` trait with an -`outline_print` method that will print a given value formatted so that it's +`outline_print` method that will print a given value formatted so that it’s framed in asterisks. That is, given a `Point` struct that implements the standard library trait `Display` to result in `(x, y)`, when we call `outline_print` on a `Point` instance that has `1` for `x` and `3` for `y`, it @@ -362,17 +372,16 @@ In the implementation of the `outline_print` method, we want to use the `OutlinePrint` trait will work only for types that also implement `Display` and provide the functionality that `OutlinePrint` needs. We can do that in the trait definition by specifying `OutlinePrint: Display`. This technique is -similar to adding a trait bound to the trait. Listing 19-22 shows an +similar to adding a trait bound to the trait. Listing 20-23 shows an implementation of the `OutlinePrint` trait. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-23" file-name="src/main.rs" caption="Implementing the `OutlinePrint` trait that requires the functionality from `Display`"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-22/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-23/src/main.rs:here}} ``` -<span class="caption">Listing 19-22: Implementing the `OutlinePrint` trait that -requires the functionality from `Display`</span> +</Listing> Because we’ve specified that `OutlinePrint` requires the `Display` trait, we can use the `to_string` function that is automatically implemented for any type @@ -384,85 +393,90 @@ the current scope. Let’s see what happens when we try to implement `OutlinePrint` on a type that doesn’t implement `Display`, such as the `Point` struct: -<span class="filename">Filename: src/main.rs</span> +<Listing file-name="src/main.rs"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/src/main.rs:here}} ``` +</Listing> + We get an error saying that `Display` is required but not implemented: ```console -{{#include ../listings/ch19-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt}} +{{#include ../listings/ch20-advanced-features/no-listing-02-impl-outlineprint-for-point/output.txt}} ``` To fix this, we implement `Display` on `Point` and satisfy the constraint that `OutlinePrint` requires, like so: -<span class="filename">Filename: src/main.rs</span> +<Listing file-name="src/main.rs"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-03-impl-display-for-point/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-03-impl-display-for-point/src/main.rs:here}} ``` -Then implementing the `OutlinePrint` trait on `Point` will compile +</Listing> + +Then, implementing the `OutlinePrint` trait on `Point` will compile successfully, and we can call `outline_print` on a `Point` instance to display it within an outline of asterisks. -### Using the Newtype Pattern to Implement External Traits on External Types - -In Chapter 10 in the [“Implementing a Trait on a -Type”][implementing-a-trait-on-a-type]<!-- ignore --> section, we mentioned the -orphan rule that states we’re only allowed to implement a trait on a type if -either the trait or the type are local to our crate. It’s possible to get -around this restriction using the *newtype pattern*, which involves creating a -new type in a tuple struct. (We covered tuple structs in the [“Using Tuple -Structs without Named Fields to Create Different Types”][tuple-structs]<!-- -ignore --> section of Chapter 5.) The tuple struct will have one field and be a -thin wrapper around the type we want to implement a trait for. Then the wrapper -type is local to our crate, and we can implement the trait on the wrapper. -*Newtype* is a term that originates from the Haskell programming language. -There is no runtime performance penalty for using this pattern, and the wrapper -type is elided at compile time. +<!-- Old headings. Do not remove or links may break. --> + +<a id="using-the-newtype-pattern-to-implement-external-traits-on-external-types"></a> +<a id="using-the-newtype-pattern-to-implement-external-traits"></a> + +### Implementing External Traits with the Newtype Pattern + +In the [“Implementing a Trait on a Type”][implementing-a-trait-on-a-type]<!-- +ignore --> section in Chapter 10, we mentioned the orphan rule that states +we’re only allowed to implement a trait on a type if either the trait or the +type, or both, are local to our crate. It’s possible to get around this +restriction using the newtype pattern, which involves creating a new type in a +tuple struct. (We covered tuple structs in the [“Creating Different Types with +Tuple Structs”][tuple-structs]<!-- ignore --> section in Chapter 5.) The tuple +struct will have one field and be a thin wrapper around the type for which we +want to implement a trait. Then, the wrapper type is local to our crate, and we +can implement the trait on the wrapper. _Newtype_ is a term that originates +from the Haskell programming language. There is no runtime performance penalty +for using this pattern, and the wrapper type is elided at compile time. As an example, let’s say we want to implement `Display` on `Vec<T>`, which the orphan rule prevents us from doing directly because the `Display` trait and the `Vec<T>` type are defined outside our crate. We can make a `Wrapper` struct -that holds an instance of `Vec<T>`; then we can implement `Display` on -`Wrapper` and use the `Vec<T>` value, as shown in Listing 19-23. +that holds an instance of `Vec<T>`; then, we can implement `Display` on +`Wrapper` and use the `Vec<T>` value, as shown in Listing 20-24. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-24" file-name="src/main.rs" caption="Creating a `Wrapper` type around `Vec<String>` to implement `Display`"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-23/src/main.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-24/src/main.rs}} ``` -<span class="caption">Listing 19-23: Creating a `Wrapper` type around -`Vec<String>` to implement `Display`</span> +</Listing> -The implementation of `Display` uses `self.0` to access the inner `Vec<T>`, +The implementation of `Display` uses `self.0` to access the inner `Vec<T>` because `Wrapper` is a tuple struct and `Vec<T>` is the item at index 0 in the -tuple. Then we can use the functionality of the `Display` type on `Wrapper`. +tuple. Then, we can use the functionality of the `Display` trait on `Wrapper`. The downside of using this technique is that `Wrapper` is a new type, so it doesn’t have the methods of the value it’s holding. We would have to implement all the methods of `Vec<T>` directly on `Wrapper` such that the methods delegate to `self.0`, which would allow us to treat `Wrapper` exactly like a `Vec<T>`. If we wanted the new type to have every method the inner type has, -implementing the `Deref` trait (discussed in Chapter 15 in the [“Treating Smart -Pointers Like Regular References with the `Deref` -Trait”][smart-pointer-deref]<!-- ignore --> section) on the `Wrapper` to return -the inner type would be a solution. If we don’t want the `Wrapper` type to have -all the methods of the inner type—for example, to restrict the `Wrapper` type’s +implementing the `Deref` trait on the `Wrapper` to return the inner type would +be a solution (we discussed implementing the `Deref` trait in the [“Treating +Smart Pointers Like Regular References”][smart-pointer-deref]<!-- ignore --> +section in Chapter 15). If we didn’t want the `Wrapper` type to have all the +methods of the inner type—for example, to restrict the `Wrapper` type’s behavior—we would have to implement just the methods we do want manually. This newtype pattern is also useful even when traits are not involved. Let’s switch focus and look at some advanced ways to interact with Rust’s type system. -[newtype]: ch19-03-advanced-traits.html#using-the-newtype-pattern-to-implement-external-traits-on-external-types -[implementing-a-trait-on-a-type]: -ch10-02-traits.html#implementing-a-trait-on-a-type -[traits-defining-shared-behavior]: -ch10-02-traits.html#traits-defining-shared-behavior -[smart-pointer-deref]: ch15-02-deref.html#treating-smart-pointers-like-regular-references-with-the-deref-trait -[tuple-structs]: ch05-01-defining-structs.html#using-tuple-structs-without-named-fields-to-create-different-types +[newtype]: ch20-02-advanced-traits.html#implementing-external-traits-with-the-newtype-pattern +[implementing-a-trait-on-a-type]: ch10-02-traits.html#implementing-a-trait-on-a-type +[traits]: ch10-02-traits.html +[smart-pointer-deref]: ch15-02-deref.html#treating-smart-pointers-like-regular-references +[tuple-structs]: ch05-01-defining-structs.html#creating-different-types-with-tuple-structs diff --git a/src/ch20-02-multithreaded.md b/src/ch20-02-multithreaded.md deleted file mode 100644 index 5a4a50ac01..0000000000 --- a/src/ch20-02-multithreaded.md +++ /dev/null @@ -1,698 +0,0 @@ -## Turning Our Single-Threaded Server into a Multithreaded Server - -Right now, the server will process each request in turn, meaning it won’t -process a second connection until the first is finished processing. If the -server received more and more requests, this serial execution would be less and -less optimal. If the server receives a request that takes a long time to -process, subsequent requests will have to wait until the long request is -finished, even if the new requests can be processed quickly. We’ll need to fix -this, but first, we’ll look at the problem in action. - -### Simulating a Slow Request in the Current Server Implementation - -We’ll look at how a slow-processing request can affect other requests made to -our current server implementation. Listing 20-10 implements handling a request -to */sleep* with a simulated slow response that will cause the server to sleep -for 5 seconds before responding. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-10/src/main.rs:here}} -``` - -<span class="caption">Listing 20-10: Simulating a slow request by sleeping for -5 seconds</span> - -We switched from `if` to `match` now that we have three cases. We need to -explicitly match on a slice of `request_line` to pattern match against the -string literal values; `match` doesn’t do automatic referencing and -dereferencing like the equality method does. - -The first arm is the same as the `if` block from Listing 20-9. The second arm -matches a request to */sleep*. When that request is received, the server will -sleep for 5 seconds before rendering the successful HTML page. The third arm is -the same as the `else` block from Listing 20-9. - -You can see how primitive our server is: real libraries would handle the -recognition of multiple requests in a much less verbose way! - -Start the server using `cargo run`. Then open two browser windows: one for -*http://127.0.0.1:7878/* and the other for *http://127.0.0.1:7878/sleep*. If -you enter the */* URI a few times, as before, you’ll see it respond quickly. -But if you enter */sleep* and then load */*, you’ll see that */* waits until -`sleep` has slept for its full 5 seconds before loading. - -There are multiple techniques we could use to avoid requests backing up behind -a slow request; the one we’ll implement is a thread pool. - -### Improving Throughput with a Thread Pool - -A *thread pool* is a group of spawned threads that are waiting and ready to -handle a task. When the program receives a new task, it assigns one of the -threads in the pool to the task, and that thread will process the task. The -remaining threads in the pool are available to handle any other tasks that come -in while the first thread is processing. When the first thread is done -processing its task, it’s returned to the pool of idle threads, ready to handle -a new task. A thread pool allows you to process connections concurrently, -increasing the throughput of your server. - -We’ll limit the number of threads in the pool to a small number to protect us -from Denial of Service (DoS) attacks; if we had our program create a new thread -for each request as it came in, someone making 10 million requests to our -server could create havoc by using up all our server’s resources and grinding -the processing of requests to a halt. - -Rather than spawning unlimited threads, then, we’ll have a fixed number of -threads waiting in the pool. Requests that come in are sent to the pool for -processing. The pool will maintain a queue of incoming requests. Each of the -threads in the pool will pop off a request from this queue, handle the request, -and then ask the queue for another request. With this design, we can process up -to `N` requests concurrently, where `N` is the number of threads. If each -thread is responding to a long-running request, subsequent requests can still -back up in the queue, but we’ve increased the number of long-running requests -we can handle before reaching that point. - -This technique is just one of many ways to improve the throughput of a web -server. Other options you might explore are the *fork/join model*, the -*single-threaded async I/O model*, or the *multi-threaded async I/O model*. If -you’re interested in this topic, you can read more about other solutions and -try to implement them; with a low-level language like Rust, all of these -options are possible. - -Before we begin implementing a thread pool, let’s talk about what using the -pool should look like. When you’re trying to design code, writing the client -interface first can help guide your design. Write the API of the code so it’s -structured in the way you want to call it; then implement the functionality -within that structure rather than implementing the functionality and then -designing the public API. - -Similar to how we used test-driven development in the project in Chapter 12, -we’ll use compiler-driven development here. We’ll write the code that calls the -functions we want, and then we’ll look at errors from the compiler to determine -what we should change next to get the code to work. Before we do that, however, -we’ll explore the technique we’re not going to use as a starting point. - -<!-- Old headings. Do not remove or links may break. --> -<a id="code-structure-if-we-could-spawn-a-thread-for-each-request"></a> - -#### Spawning a Thread for Each Request - -First, let’s explore how our code might look if it did create a new thread for -every connection. As mentioned earlier, this isn’t our final plan due to the -problems with potentially spawning an unlimited number of threads, but it is a -starting point to get a working multithreaded server first. Then we’ll add the -thread pool as an improvement, and contrasting the two solutions will be -easier. Listing 20-11 shows the changes to make to `main` to spawn a new thread -to handle each stream within the `for` loop. - -<span class="filename">Filename: src/main.rs</span> - -```rust,no_run -{{#rustdoc_include ../listings/ch20-web-server/listing-20-11/src/main.rs:here}} -``` - -<span class="caption">Listing 20-11: Spawning a new thread for each -stream</span> - -As you learned in Chapter 16, `thread::spawn` will create a new thread and then -run the code in the closure in the new thread. If you run this code and load -*/sleep* in your browser, then */* in two more browser tabs, you’ll indeed see -that the requests to */* don’t have to wait for */sleep* to finish. However, as -we mentioned, this will eventually overwhelm the system because you’d be making -new threads without any limit. - -<!-- Old headings. Do not remove or links may break. --> -<a id="creating-a-similar-interface-for-a-finite-number-of-threads"></a> - -#### Creating a Finite Number of Threads - -We want our thread pool to work in a similar, familiar way so switching from -threads to a thread pool doesn’t require large changes to the code that uses -our API. Listing 20-12 shows the hypothetical interface for a `ThreadPool` -struct we want to use instead of `thread::spawn`. - -<span class="filename">Filename: src/main.rs</span> - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch20-web-server/listing-20-12/src/main.rs:here}} -``` - -<span class="caption">Listing 20-12: Our ideal `ThreadPool` interface</span> - -We use `ThreadPool::new` to create a new thread pool with a configurable number -of threads, in this case four. Then, in the `for` loop, `pool.execute` has a -similar interface as `thread::spawn` in that it takes a closure the pool should -run for each stream. We need to implement `pool.execute` so it takes the -closure and gives it to a thread in the pool to run. This code won’t yet -compile, but we’ll try so the compiler can guide us in how to fix it. - -<!-- Old headings. Do not remove or links may break. --> -<a id="building-the-threadpool-struct-using-compiler-driven-development"></a> - -#### Building `ThreadPool` Using Compiler Driven Development - -Make the changes in Listing 20-12 to *src/main.rs*, and then let’s use the -compiler errors from `cargo check` to drive our development. Here is the first -error we get: - -```console -{{#include ../listings/ch20-web-server/listing-20-12/output.txt}} -``` - -Great! This error tells us we need a `ThreadPool` type or module, so we’ll -build one now. Our `ThreadPool` implementation will be independent of the kind -of work our web server is doing. So, let’s switch the `hello` crate from a -binary crate to a library crate to hold our `ThreadPool` implementation. After -we change to a library crate, we could also use the separate thread pool -library for any work we want to do using a thread pool, not just for serving -web requests. - -Create a *src/lib.rs* that contains the following, which is the simplest -definition of a `ThreadPool` struct that we can have for now: - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/no-listing-01-define-threadpool-struct/src/lib.rs}} -``` - -Then edit *main.rs* file to bring `ThreadPool` into scope from the library -crate by adding the following code to the top of *src/main.rs*: - -<span class="filename">Filename: src/main.rs</span> - -```rust,ignore -{{#rustdoc_include ../listings/ch20-web-server/no-listing-01-define-threadpool-struct/src/main.rs:here}} -``` - -This code still won’t work, but let’s check it again to get the next error that -we need to address: - -```console -{{#include ../listings/ch20-web-server/no-listing-01-define-threadpool-struct/output.txt}} -``` - -This error indicates that next we need to create an associated function named -`new` for `ThreadPool`. We also know that `new` needs to have one parameter -that can accept `4` as an argument and should return a `ThreadPool` instance. -Let’s implement the simplest `new` function that will have those -characteristics: - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/no-listing-02-impl-threadpool-new/src/lib.rs}} -``` - -We chose `usize` as the type of the `size` parameter, because we know that a -negative number of threads doesn’t make any sense. We also know we’ll use this -4 as the number of elements in a collection of threads, which is what the -`usize` type is for, as discussed in the [“Integer Types”][integer-types]<!-- -ignore --> section of Chapter 3. - -Let’s check the code again: - -```console -{{#include ../listings/ch20-web-server/no-listing-02-impl-threadpool-new/output.txt}} -``` - -Now the error occurs because we don’t have an `execute` method on `ThreadPool`. -Recall from the [“Creating a Finite Number of -Threads”](#creating-a-finite-number-of-threads)<!-- ignore --> section that we -decided our thread pool should have an interface similar to `thread::spawn`. In -addition, we’ll implement the `execute` function so it takes the closure it’s -given and gives it to an idle thread in the pool to run. - -We’ll define the `execute` method on `ThreadPool` to take a closure as a -parameter. Recall from the [“Moving Captured Values Out of the Closure and the -`Fn` Traits”][fn-traits]<!-- ignore --> section in Chapter 13 that we can take -closures as parameters with three different traits: `Fn`, `FnMut`, and -`FnOnce`. We need to decide which kind of closure to use here. We know we’ll -end up doing something similar to the standard library `thread::spawn` -implementation, so we can look at what bounds the signature of `thread::spawn` -has on its parameter. The documentation shows us the following: - -```rust,ignore -pub fn spawn<F, T>(f: F) -> JoinHandle<T> - where - F: FnOnce() -> T, - F: Send + 'static, - T: Send + 'static, -``` - -The `F` type parameter is the one we’re concerned with here; the `T` type -parameter is related to the return value, and we’re not concerned with that. We -can see that `spawn` uses `FnOnce` as the trait bound on `F`. This is probably -what we want as well, because we’ll eventually pass the argument we get in -`execute` to `spawn`. We can be further confident that `FnOnce` is the trait we -want to use because the thread for running a request will only execute that -request’s closure one time, which matches the `Once` in `FnOnce`. - -The `F` type parameter also has the trait bound `Send` and the lifetime bound -`'static`, which are useful in our situation: we need `Send` to transfer the -closure from one thread to another and `'static` because we don’t know how long -the thread will take to execute. Let’s create an `execute` method on -`ThreadPool` that will take a generic parameter of type `F` with these bounds: - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/no-listing-03-define-execute/src/lib.rs:here}} -``` - -We still use the `()` after `FnOnce` because this `FnOnce` represents a closure -that takes no parameters and returns the unit type `()`. Just like function -definitions, the return type can be omitted from the signature, but even if we -have no parameters, we still need the parentheses. - -Again, this is the simplest implementation of the `execute` method: it does -nothing, but we’re trying only to make our code compile. Let’s check it again: - -```console -{{#include ../listings/ch20-web-server/no-listing-03-define-execute/output.txt}} -``` - -It compiles! But note that if you try `cargo run` and make a request in the -browser, you’ll see the errors in the browser that we saw at the beginning of -the chapter. Our library isn’t actually calling the closure passed to `execute` -yet! - -> Note: A saying you might hear about languages with strict compilers, such as -> Haskell and Rust, is “if the code compiles, it works.” But this saying is not -> universally true. Our project compiles, but it does absolutely nothing! If we -> were building a real, complete project, this would be a good time to start -> writing unit tests to check that the code compiles *and* has the behavior we -> want. - -#### Validating the Number of Threads in `new` - -We aren’t doing anything with the parameters to `new` and `execute`. Let’s -implement the bodies of these functions with the behavior we want. To start, -let’s think about `new`. Earlier we chose an unsigned type for the `size` -parameter, because a pool with a negative number of threads makes no sense. -However, a pool with zero threads also makes no sense, yet zero is a perfectly -valid `usize`. We’ll add code to check that `size` is greater than zero before -we return a `ThreadPool` instance and have the program panic if it receives a -zero by using the `assert!` macro, as shown in Listing 20-13. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/listing-20-13/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-13: Implementing `ThreadPool::new` to panic if -`size` is zero</span> - -We’ve also added some documentation for our `ThreadPool` with doc comments. -Note that we followed good documentation practices by adding a section that -calls out the situations in which our function can panic, as discussed in -Chapter 14. Try running `cargo doc --open` and clicking the `ThreadPool` struct -to see what the generated docs for `new` look like! - -Instead of adding the `assert!` macro as we’ve done here, we could change `new` -into `build` and return a `Result` like we did with `Config::build` in the I/O -project in Listing 12-9. But we’ve decided in this case that trying to create a -thread pool without any threads should be an unrecoverable error. If you’re -feeling ambitious, try to write a function named `build` with the following -signature to compare with the `new` function: - -```rust,ignore -pub fn build(size: usize) -> Result<ThreadPool, PoolCreationError> { -``` - -#### Creating Space to Store the Threads - -Now that we have a way to know we have a valid number of threads to store in -the pool, we can create those threads and store them in the `ThreadPool` struct -before returning the struct. But how do we “store” a thread? Let’s take another -look at the `thread::spawn` signature: - -```rust,ignore -pub fn spawn<F, T>(f: F) -> JoinHandle<T> - where - F: FnOnce() -> T, - F: Send + 'static, - T: Send + 'static, -``` - -The `spawn` function returns a `JoinHandle<T>`, where `T` is the type that the -closure returns. Let’s try using `JoinHandle` too and see what happens. In our -case, the closures we’re passing to the thread pool will handle the connection -and not return anything, so `T` will be the unit type `()`. - -The code in Listing 20-14 will compile but doesn’t create any threads yet. -We’ve changed the definition of `ThreadPool` to hold a vector of -`thread::JoinHandle<()>` instances, initialized the vector with a capacity of -`size`, set up a `for` loop that will run some code to create the threads, and -returned a `ThreadPool` instance containing them. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,ignore,not_desired_behavior -{{#rustdoc_include ../listings/ch20-web-server/listing-20-14/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-14: Creating a vector for `ThreadPool` to hold -the threads</span> - -We’ve brought `std::thread` into scope in the library crate, because we’re -using `thread::JoinHandle` as the type of the items in the vector in -`ThreadPool`. - -Once a valid size is received, our `ThreadPool` creates a new vector that can -hold `size` items. The `with_capacity` function performs the same task as -`Vec::new` but with an important difference: it preallocates space in the -vector. Because we know we need to store `size` elements in the vector, doing -this allocation up front is slightly more efficient than using `Vec::new`, -which resizes itself as elements are inserted. - -When you run `cargo check` again, it should succeed. - -#### A `Worker` Struct Responsible for Sending Code from the `ThreadPool` to a Thread - -We left a comment in the `for` loop in Listing 20-14 regarding the creation of -threads. Here, we’ll look at how we actually create threads. The standard -library provides `thread::spawn` as a way to create threads, and -`thread::spawn` expects to get some code the thread should run as soon as the -thread is created. However, in our case, we want to create the threads and have -them *wait* for code that we’ll send later. The standard library’s -implementation of threads doesn’t include any way to do that; we have to -implement it manually. - -We’ll implement this behavior by introducing a new data structure between the -`ThreadPool` and the threads that will manage this new behavior. We’ll call -this data structure *Worker*, which is a common term in pooling -implementations. The Worker picks up code that needs to be run and runs the -code in the Worker’s thread. Think of people working in the kitchen at a -restaurant: the workers wait until orders come in from customers, and then -they’re responsible for taking those orders and fulfilling them. - -Instead of storing a vector of `JoinHandle<()>` instances in the thread pool, -we’ll store instances of the `Worker` struct. Each `Worker` will store a single -`JoinHandle<()>` instance. Then we’ll implement a method on `Worker` that will -take a closure of code to run and send it to the already running thread for -execution. We’ll also give each worker an `id` so we can distinguish between -the different workers in the pool when logging or debugging. - -Here is the new process that will happen when we create a `ThreadPool`. We’ll -implement the code that sends the closure to the thread after we have `Worker` -set up in this way: - -1. Define a `Worker` struct that holds an `id` and a `JoinHandle<()>`. -2. Change `ThreadPool` to hold a vector of `Worker` instances. -3. Define a `Worker::new` function that takes an `id` number and returns a - `Worker` instance that holds the `id` and a thread spawned with an empty - closure. -4. In `ThreadPool::new`, use the `for` loop counter to generate an `id`, create - a new `Worker` with that `id`, and store the worker in the vector. - -If you’re up for a challenge, try implementing these changes on your own before -looking at the code in Listing 20-15. - -Ready? Here is Listing 20-15 with one way to make the preceding modifications. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/listing-20-15/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-15: Modifying `ThreadPool` to hold `Worker` -instances instead of holding threads directly</span> - -We’ve changed the name of the field on `ThreadPool` from `threads` to `workers` -because it’s now holding `Worker` instances instead of `JoinHandle<()>` -instances. We use the counter in the `for` loop as an argument to -`Worker::new`, and we store each new `Worker` in the vector named `workers`. - -External code (like our server in *src/main.rs*) doesn’t need to know the -implementation details regarding using a `Worker` struct within `ThreadPool`, -so we make the `Worker` struct and its `new` function private. The -`Worker::new` function uses the `id` we give it and stores a `JoinHandle<()>` -instance that is created by spawning a new thread using an empty closure. - -> Note: If the operating system can’t create a thread because there aren’t -> enough system resources, `thread::spawn` will panic. That will cause our -> whole server to panic, even though the creation of some threads might -> succeed. For simplicity’s sake, this behavior is fine, but in a production -> thread pool implementation, you’d likely want to use -> [`std::thread::Builder`][builder]<!-- ignore --> and its -> [`spawn`][builder-spawn]<!-- ignore --> method that returns `Result` instead. - -This code will compile and will store the number of `Worker` instances we -specified as an argument to `ThreadPool::new`. But we’re *still* not processing -the closure that we get in `execute`. Let’s look at how to do that next. - -#### Sending Requests to Threads via Channels - -The next problem we’ll tackle is that the closures given to `thread::spawn` do -absolutely nothing. Currently, we get the closure we want to execute in the -`execute` method. But we need to give `thread::spawn` a closure to run when we -create each `Worker` during the creation of the `ThreadPool`. - -We want the `Worker` structs that we just created to fetch the code to run from -a queue held in the `ThreadPool` and send that code to its thread to run. - -The channels we learned about in Chapter 16—a simple way to communicate between -two threads—would be perfect for this use case. We’ll use a channel to function -as the queue of jobs, and `execute` will send a job from the `ThreadPool` to -the `Worker` instances, which will send the job to its thread. Here is the plan: - -1. The `ThreadPool` will create a channel and hold on to the sender. -2. Each `Worker` will hold on to the receiver. -3. We’ll create a new `Job` struct that will hold the closures we want to send - down the channel. -4. The `execute` method will send the job it wants to execute through the - sender. -5. In its thread, the `Worker` will loop over its receiver and execute the - closures of any jobs it receives. - -Let’s start by creating a channel in `ThreadPool::new` and holding the sender -in the `ThreadPool` instance, as shown in Listing 20-16. The `Job` struct -doesn’t hold anything for now but will be the type of item we’re sending down -the channel. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/listing-20-16/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-16: Modifying `ThreadPool` to store the -sender of a channel that transmits `Job` instances</span> - -In `ThreadPool::new`, we create our new channel and have the pool hold the -sender. This will successfully compile. - -Let’s try passing a receiver of the channel into each worker as the thread pool -creates the channel. We know we want to use the receiver in the thread that the -workers spawn, so we’ll reference the `receiver` parameter in the closure. The -code in Listing 20-17 won’t quite compile yet. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch20-web-server/listing-20-17/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-17: Passing the receiver to the workers</span> - -We’ve made some small and straightforward changes: we pass the receiver into -`Worker::new`, and then we use it inside the closure. - -When we try to check this code, we get this error: - -```console -{{#include ../listings/ch20-web-server/listing-20-17/output.txt}} -``` - -The code is trying to pass `receiver` to multiple `Worker` instances. This -won’t work, as you’ll recall from Chapter 16: the channel implementation that -Rust provides is multiple *producer*, single *consumer*. This means we can’t -just clone the consuming end of the channel to fix this code. We also don’t -want to send a message multiple times to multiple consumers; we want one list -of messages with multiple workers such that each message gets processed once. - -Additionally, taking a job off the channel queue involves mutating the -`receiver`, so the threads need a safe way to share and modify `receiver`; -otherwise, we might get race conditions (as covered in Chapter 16). - -Recall the thread-safe smart pointers discussed in Chapter 16: to share -ownership across multiple threads and allow the threads to mutate the value, we -need to use `Arc<Mutex<T>>`. The `Arc` type will let multiple workers own the -receiver, and `Mutex` will ensure that only one worker gets a job from the -receiver at a time. Listing 20-18 shows the changes we need to make. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/listing-20-18/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-18: Sharing the receiver among the workers -using `Arc` and `Mutex`</span> - -In `ThreadPool::new`, we put the receiver in an `Arc` and a `Mutex`. For each -new worker, we clone the `Arc` to bump the reference count so the workers can -share ownership of the receiver. - -With these changes, the code compiles! We’re getting there! - -#### Implementing the `execute` Method - -Let’s finally implement the `execute` method on `ThreadPool`. We’ll also change -`Job` from a struct to a type alias for a trait object that holds the type of -closure that `execute` receives. As discussed in the [“Creating Type Synonyms -with Type Aliases”][creating-type-synonyms-with-type-aliases]<!-- ignore --> -section of Chapter 19, type aliases allow us to make long types shorter for -ease of use. Look at Listing 20-19. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/listing-20-19/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-19: Creating a `Job` type alias for a `Box` -that holds each closure and then sending the job down the channel</span> - -After creating a new `Job` instance using the closure we get in `execute`, we -send that job down the sending end of the channel. We’re calling `unwrap` on -`send` for the case that sending fails. This might happen if, for example, we -stop all our threads from executing, meaning the receiving end has stopped -receiving new messages. At the moment, we can’t stop our threads from -executing: our threads continue executing as long as the pool exists. The -reason we use `unwrap` is that we know the failure case won’t happen, but the -compiler doesn’t know that. - -But we’re not quite done yet! In the worker, our closure being passed to -`thread::spawn` still only *references* the receiving end of the channel. -Instead, we need the closure to loop forever, asking the receiving end of the -channel for a job and running the job when it gets one. Let’s make the change -shown in Listing 20-20 to `Worker::new`. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/listing-20-20/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-20: Receiving and executing the jobs in the -worker’s thread</span> - -Here, we first call `lock` on the `receiver` to acquire the mutex, and then we -call `unwrap` to panic on any errors. Acquiring a lock might fail if the mutex -is in a *poisoned* state, which can happen if some other thread panicked while -holding the lock rather than releasing the lock. In this situation, calling -`unwrap` to have this thread panic is the correct action to take. Feel free to -change this `unwrap` to an `expect` with an error message that is meaningful to -you. - -If we get the lock on the mutex, we call `recv` to receive a `Job` from the -channel. A final `unwrap` moves past any errors here as well, which might occur -if the thread holding the sender has shut down, similar to how the `send` -method returns `Err` if the receiver shuts down. - -The call to `recv` blocks, so if there is no job yet, the current thread will -wait until a job becomes available. The `Mutex<T>` ensures that only one -`Worker` thread at a time is trying to request a job. - -Our thread pool is now in a working state! Give it a `cargo run` and make some -requests: - -<!-- manual-regeneration -cd listings/ch20-web-server/listing-20-20 -cargo run -make some requests to 127.0.0.1:7878 -Can't automate because the output depends on making requests ---> - -```console -$ cargo run - Compiling hello v0.1.0 (file:///projects/hello) -warning: field is never read: `workers` - --> src/lib.rs:7:5 - | -7 | workers: Vec<Worker>, - | ^^^^^^^^^^^^^^^^^^^^ - | - = note: `#[warn(dead_code)]` on by default - -warning: field is never read: `id` - --> src/lib.rs:48:5 - | -48 | id: usize, - | ^^^^^^^^^ - -warning: field is never read: `thread` - --> src/lib.rs:49:5 - | -49 | thread: thread::JoinHandle<()>, - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -warning: `hello` (lib) generated 3 warnings - Finished dev [unoptimized + debuginfo] target(s) in 1.40s - Running `target/debug/hello` -Worker 0 got a job; executing. -Worker 2 got a job; executing. -Worker 1 got a job; executing. -Worker 3 got a job; executing. -Worker 0 got a job; executing. -Worker 2 got a job; executing. -Worker 1 got a job; executing. -Worker 3 got a job; executing. -Worker 0 got a job; executing. -Worker 2 got a job; executing. -``` - -Success! We now have a thread pool that executes connections asynchronously. -There are never more than four threads created, so our system won’t get -overloaded if the server receives a lot of requests. If we make a request to -*/sleep*, the server will be able to serve other requests by having another -thread run them. - -> Note: if you open */sleep* in multiple browser windows simultaneously, they -> might load one at a time in 5 second intervals. Some web browsers execute -> multiple instances of the same request sequentially for caching reasons. This -> limitation is not caused by our web server. - -After learning about the `while let` loop in Chapter 18, you might be wondering -why we didn’t write the worker thread code as shown in Listing 20-21. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,ignore,not_desired_behavior -{{#rustdoc_include ../listings/ch20-web-server/listing-20-21/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-21: An alternative implementation of -`Worker::new` using `while let`</span> - -This code compiles and runs but doesn’t result in the desired threading -behavior: a slow request will still cause other requests to wait to be -processed. The reason is somewhat subtle: the `Mutex` struct has no public -`unlock` method because the ownership of the lock is based on the lifetime of -the `MutexGuard<T>` within the `LockResult<MutexGuard<T>>` that the `lock` -method returns. At compile time, the borrow checker can then enforce the rule -that a resource guarded by a `Mutex` cannot be accessed unless we hold the -lock. However, this implementation can also result in the lock being held -longer than intended if we aren’t mindful of the lifetime of the -`MutexGuard<T>`. - -The code in Listing 20-20 that uses `let job = -receiver.lock().unwrap().recv().unwrap();` works because with `let`, any -temporary values used in the expression on the right hand side of the equals -sign are immediately dropped when the `let` statement ends. However, `while -let` (and `if let` and `match`) does not drop temporary values until the end of -the associated block. In Listing 20-21, the lock remains held for the duration -of the call to `job()`, meaning other workers cannot receive jobs. - -[creating-type-synonyms-with-type-aliases]: -ch19-04-advanced-types.html#creating-type-synonyms-with-type-aliases -[integer-types]: ch03-02-data-types.html#integer-types -[fn-traits]: -ch13-01-closures.html#moving-captured-values-out-of-the-closure-and-the-fn-traits -[builder]: ../std/thread/struct.Builder.html -[builder-spawn]: ../std/thread/struct.Builder.html#method.spawn diff --git a/src/ch19-04-advanced-types.md b/src/ch20-03-advanced-types.md similarity index 57% rename from src/ch19-04-advanced-types.md rename to src/ch20-03-advanced-types.md index 2dfed23cca..02e418f36b 100644 --- a/src/ch19-04-advanced-types.md +++ b/src/ch20-03-advanced-types.md @@ -2,27 +2,28 @@ The Rust type system has some features that we’ve so far mentioned but haven’t yet discussed. We’ll start by discussing newtypes in general as we examine why -newtypes are useful as types. Then we’ll move on to type aliases, a feature +they are useful as types. Then, we’ll move on to type aliases, a feature similar to newtypes but with slightly different semantics. We’ll also discuss the `!` type and dynamically sized types. -### Using the Newtype Pattern for Type Safety and Abstraction +<!-- Old headings. Do not remove or links may break. --> -> Note: This section assumes you’ve read the earlier section [“Using the -> Newtype Pattern to Implement External Traits on External -> Types.”][using-the-newtype-pattern]<!-- ignore --> +<a id="using-the-newtype-pattern-for-type-safety-and-abstraction"></a> -The newtype pattern is also useful for tasks beyond those we’ve discussed so -far, including statically enforcing that values are never confused and -indicating the units of a value. You saw an example of using newtypes to -indicate units in Listing 19-15: recall that the `Millimeters` and `Meters` -structs wrapped `u32` values in a newtype. If we wrote a function with a -parameter of type `Millimeters`, we couldn’t compile a program that -accidentally tried to call that function with a value of type `Meters` or a -plain `u32`. +### Type Safety and Abstraction with the Newtype Pattern + +This section assumes you’ve read the earlier section [“Implementing External +Traits with the Newtype Pattern”][newtype]<!-- ignore -->. The newtype pattern +is also useful for tasks beyond those we’ve discussed so far, including +statically enforcing that values are never confused and indicating the units of +a value. You saw an example of using newtypes to indicate units in Listing +20-16: Recall that the `Millimeters` and `Meters` structs wrapped `u32` values +in a newtype. If we wrote a function with a parameter of type `Millimeters`, we +wouldn’t be able to compile a program that accidentally tried to call that +function with a value of type `Meters` or a plain `u32`. We can also use the newtype pattern to abstract away some implementation -details of a type: the new type can expose a public API that is different from +details of a type: The new type can expose a public API that is different from the API of the private inner type. Newtypes can also hide internal implementation. For example, we could provide a @@ -34,30 +35,34 @@ internally. The newtype pattern is a lightweight way to achieve encapsulation to hide implementation details, which we discussed in the [“Encapsulation that Hides Implementation Details”][encapsulation-that-hides-implementation-details]<!-- ignore --> -section of Chapter 17. +section in Chapter 18. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="creating-type-synonyms-with-type-aliases"></a> -### Creating Type Synonyms with Type Aliases +### Type Synonyms and Type Aliases -Rust provides the ability to declare a *type alias* to give an existing type +Rust provides the ability to declare a _type alias_ to give an existing type another name. For this we use the `type` keyword. For example, we can create the alias `Kilometers` to `i32` like so: ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-04-kilometers-alias/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-04-kilometers-alias/src/main.rs:here}} ``` -Now, the alias `Kilometers` is a *synonym* for `i32`; unlike the `Millimeters` -and `Meters` types we created in Listing 19-15, `Kilometers` is not a separate, +Now the alias `Kilometers` is a _synonym_ for `i32`; unlike the `Millimeters` +and `Meters` types we created in Listing 20-16, `Kilometers` is not a separate, new type. Values that have the type `Kilometers` will be treated the same as values of type `i32`: ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-04-kilometers-alias/src/main.rs:there}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-04-kilometers-alias/src/main.rs:there}} ``` Because `Kilometers` and `i32` are the same type, we can add values of both -types and we can pass `Kilometers` values to functions that take `i32` -parameters. However, using this method, we don’t get the type checking benefits +types and can pass `Kilometers` values to functions that take `i32` +parameters. However, using this method, we don’t get the type-checking benefits that we get from the newtype pattern discussed earlier. In other words, if we mix up `Kilometers` and `i32` values somewhere, the compiler will not give us an error. @@ -70,28 +75,31 @@ Box<dyn Fn() + Send + 'static> ``` Writing this lengthy type in function signatures and as type annotations all -over the code can be tiresome and error prone. Imagine having a project full of -code like that in Listing 19-24. +over the code can be tiresome and error-prone. Imagine having a project full of +code like that in Listing 20-25. + +<Listing number="20-25" caption="Using a long type in many places"> ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-24/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-25/src/main.rs:here}} ``` -<span class="caption">Listing 19-24: Using a long type in many places</span> +</Listing> A type alias makes this code more manageable by reducing the repetition. In -Listing 19-25, we’ve introduced an alias named `Thunk` for the verbose type and +Listing 20-26, we’ve introduced an alias named `Thunk` for the verbose type and can replace all uses of the type with the shorter alias `Thunk`. +<Listing number="20-26" caption="Introducing a type alias, `Thunk`, to reduce repetition"> + ```rust -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-25/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-26/src/main.rs:here}} ``` -<span class="caption">Listing 19-25: Introducing a type alias `Thunk` to reduce -repetition</span> +</Listing> This code is much easier to read and write! Choosing a meaningful name for a -type alias can help communicate your intent as well (*thunk* is a word for code +type alias can help communicate your intent as well (_thunk_ is a word for code to be evaluated at a later time, so it’s an appropriate name for a closure that gets stored). @@ -104,14 +112,14 @@ possible I/O errors. Many of the functions in `std::io` will be returning the `Write` trait: ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-05-write-trait/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-05-write-trait/src/lib.rs}} ``` The `Result<..., Error>` is repeated a lot. As such, `std::io` has this type alias declaration: ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-06-result-alias/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-06-result-alias/src/lib.rs:here}} ``` Because this declaration is in the `std::io` module, we can use the fully @@ -120,53 +128,54 @@ filled in as `std::io::Error`. The `Write` trait function signatures end up looking like this: ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-06-result-alias/src/lib.rs:there}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-06-result-alias/src/lib.rs:there}} ``` -The type alias helps in two ways: it makes code easier to write *and* it gives +The type alias helps in two ways: It makes code easier to write _and_ it gives us a consistent interface across all of `std::io`. Because it’s an alias, it’s just another `Result<T, E>`, which means we can use any methods that work on `Result<T, E>` with it, as well as special syntax like the `?` operator. -### The Never Type that Never Returns +### The Never Type That Never Returns Rust has a special type named `!` that’s known in type theory lingo as the -*empty type* because it has no values. We prefer to call it the *never type* +_empty type_ because it has no values. We prefer to call it the _never type_ because it stands in the place of the return type when a function will never return. Here is an example: ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-07-never-type/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-07-never-type/src/lib.rs:here}} ``` This code is read as “the function `bar` returns never.” Functions that return -never are called *diverging functions*. We can’t create values of the type `!` +never are called _diverging functions_. We can’t create values of the type `!`, so `bar` can never possibly return. But what use is a type you can never create values for? Recall the code from -Listing 2-5, part of the number guessing game; we’ve reproduced a bit of it -here in Listing 19-26. +Listing 2-5, part of the number-guessing game; we’ve reproduced a bit of it +here in Listing 20-27. + +<Listing number="20-27" caption="A `match` with an arm that ends in `continue`"> ```rust,ignore {{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-05/src/main.rs:ch19}} ``` -<span class="caption">Listing 19-26: A `match` with an arm that ends in -`continue`</span> +</Listing> -At the time, we skipped over some details in this code. In Chapter 6 in [“The -`match` Control Flow Operator”][the-match-control-flow-operator]<!-- ignore --> -section, we discussed that `match` arms must all return the same type. So, for -example, the following code doesn’t work: +At the time, we skipped over some details in this code. In [“The `match` +Control Flow Construct”][the-match-control-flow-construct]<!-- ignore --> +section in Chapter 6, we discussed that `match` arms must all return the same +type. So, for example, the following code doesn’t work: ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-08-match-arms-different-types/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-08-match-arms-different-types/src/main.rs:here}} ``` -The type of `guess` in this code would have to be an integer *and* a string, -and Rust requires that `guess` have only one type. So what does `continue` +The type of `guess` in this code would have to be an integer _and_ a string, +and Rust requires that `guess` have only one type. So, what does `continue` return? How were we allowed to return a `u32` from one arm and have another arm -that ends with `continue` in Listing 19-26? +that ends with `continue` in Listing 20-27? As you might have guessed, `continue` has a `!` value. That is, when Rust computes the type of `guess`, it looks at both match arms, the former with a @@ -184,19 +193,19 @@ function that we call on `Option<T>` values to produce a value or panic with this definition: ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-09-unwrap-definition/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-09-unwrap-definition/src/lib.rs:here}} ``` -In this code, the same thing happens as in the `match` in Listing 19-26: Rust +In this code, the same thing happens as in the `match` in Listing 20-27: Rust sees that `val` has the type `T` and `panic!` has the type `!`, so the result of the overall `match` expression is `T`. This code works because `panic!` doesn’t produce a value; it ends the program. In the `None` case, we won’t be returning a value from `unwrap`, so this code is valid. -One final expression that has the type `!` is a `loop`: +One final expression that has the type `!` is a loop: ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-10-loop-returns-never/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-10-loop-returns-never/src/main.rs:here}} ``` Here, the loop never ends, so `!` is the value of the expression. However, this @@ -207,18 +216,19 @@ when it got to the `break`. Rust needs to know certain details about its types, such as how much space to allocate for a value of a particular type. This leaves one corner of its type -system a little confusing at first: the concept of *dynamically sized types*. -Sometimes referred to as *DSTs* or *unsized types*, these types let us write +system a little confusing at first: the concept of _dynamically sized types_. +Sometimes referred to as _DSTs_ or _unsized types_, these types let us write code using values whose size we can know only at runtime. Let’s dig into the details of a dynamically sized type called `str`, which we’ve been using throughout the book. That’s right, not `&str`, but `str` on -its own, is a DST. We can’t know how long the string is until runtime, meaning -we can’t create a variable of type `str`, nor can we take an argument of type -`str`. Consider the following code, which does not work: +its own, is a DST. In many cases, such as when storing text entered by a user, +we can’t know how long the string is until runtime. That means we can’t create +a variable of type `str`, nor can we take an argument of type `str`. Consider +the following code, which does not work: ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-11-cant-create-str/src/main.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-11-cant-create-str/src/main.rs:here}} ``` Rust needs to know how much memory to allocate for any value of a particular @@ -228,29 +238,28 @@ same amount of space. But they have different lengths: `s1` needs 12 bytes of storage and `s2` needs 15. This is why it’s not possible to create a variable holding a dynamically sized type. -So what do we do? In this case, you already know the answer: we make the types -of `s1` and `s2` a `&str` rather than a `str`. Recall from the [“String -Slices”][string-slices]<!-- ignore --> section of Chapter 4 that the slice data -structure just stores the starting position and the length of the slice. So -although a `&T` is a single value that stores the memory address of where the -`T` is located, a `&str` is *two* values: the address of the `str` and its -length. As such, we can know the size of a `&str` value at compile time: it’s -twice the length of a `usize`. That is, we always know the size of a `&str`, no -matter how long the string it refers to is. In general, this is the way in -which dynamically sized types are used in Rust: they have an extra bit of -metadata that stores the size of the dynamic information. The golden rule of -dynamically sized types is that we must always put values of dynamically sized -types behind a pointer of some kind. +So, what do we do? In this case, you already know the answer: We make the type +of `s1` and `s2` string slice (`&str`) rather than `str`. Recall from the +[“String Slices”][string-slices]<!-- ignore --> section in Chapter 4 that the +slice data structure only stores the starting position and the length of the +slice. So, although `&T` is a single value that stores the memory address of +where the `T` is located, a string slice is _two_ values: the address of the +`str` and its length. As such, we can know the size of a string slice value at +compile time: It’s twice the length of a `usize`. That is, we always know the +size of a string slice, no matter how long the string it refers to is. In +general, this is the way in which dynamically sized types are used in Rust: +They have an extra bit of metadata that stores the size of the dynamic +information. The golden rule of dynamically sized types is that we must always +put values of dynamically sized types behind a pointer of some kind. We can combine `str` with all kinds of pointers: for example, `Box<str>` or `Rc<str>`. In fact, you’ve seen this before but with a different dynamically sized type: traits. Every trait is a dynamically sized type we can refer to by -using the name of the trait. In Chapter 17 in the [“Using Trait Objects That -Allow for Values of Different -Types”][using-trait-objects-that-allow-for-values-of-different-types]<!-- -ignore --> section, we mentioned that to use traits as trait objects, we must -put them behind a pointer, such as `&dyn Trait` or `Box<dyn Trait>` (`Rc<dyn -Trait>` would work too). +using the name of the trait. In the [“Using Trait Objects to Abstract over +Shared Behavior”][using-trait-objects-to-abstract-over-shared-behavior]<!-- +ignore --> section in Chapter 18, we mentioned that to use traits as trait +objects, we must put them behind a pointer, such as `&dyn Trait` or `Box<dyn +Trait>` (`Rc<dyn Trait>` would work too). To work with DSTs, Rust provides the `Sized` trait to determine whether or not a type’s size is known at compile time. This trait is automatically implemented @@ -259,13 +268,13 @@ implicitly adds a bound on `Sized` to every generic function. That is, a generic function definition like this: ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-12-generic-fn-definition/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-12-generic-fn-definition/src/lib.rs}} ``` is actually treated as though we had written this: ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-13-generic-implicit-sized-bound/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-13-generic-implicit-sized-bound/src/lib.rs}} ``` By default, generic functions will work only on types that have a known size at @@ -273,10 +282,10 @@ compile time. However, you can use the following special syntax to relax this restriction: ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-14-generic-maybe-sized/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/no-listing-14-generic-maybe-sized/src/lib.rs}} ``` -A trait bound on `?Sized` means “`T` may or may not be `Sized`” and this +A trait bound on `?Sized` means “`T` may or may not be `Sized`,” and this notation overrides the default that generic types must have a known size at compile time. The `?Trait` syntax with this meaning is only available for `Sized`, not any other traits. @@ -287,11 +296,8 @@ pointer. In this case, we’ve chosen a reference. Next, we’ll talk about functions and closures! -[encapsulation-that-hides-implementation-details]: -ch17-01-what-is-oo.html#encapsulation-that-hides-implementation-details +[encapsulation-that-hides-implementation-details]: ch18-01-what-is-oo.html#encapsulation-that-hides-implementation-details [string-slices]: ch04-03-slices.html#string-slices -[the-match-control-flow-operator]: -ch06-02-match.html#the-match-control-flow-operator -[using-trait-objects-that-allow-for-values-of-different-types]: -ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types -[using-the-newtype-pattern]: ch19-03-advanced-traits.html#using-the-newtype-pattern-to-implement-external-traits-on-external-types +[the-match-control-flow-construct]: ch06-02-match.html#the-match-control-flow-construct +[using-trait-objects-to-abstract-over-shared-behavior]: ch18-02-trait-objects.html#using-trait-objects-to-abstract-over-shared-behavior +[newtype]: ch20-02-advanced-traits.html#implementing-external-traits-with-the-newtype-pattern diff --git a/src/ch20-03-graceful-shutdown-and-cleanup.md b/src/ch20-03-graceful-shutdown-and-cleanup.md deleted file mode 100644 index a28c79e5ad..0000000000 --- a/src/ch20-03-graceful-shutdown-and-cleanup.md +++ /dev/null @@ -1,245 +0,0 @@ -## Graceful Shutdown and Cleanup - -The code in Listing 20-20 is responding to requests asynchronously through the -use of a thread pool, as we intended. We get some warnings about the `workers`, -`id`, and `thread` fields that we’re not using in a direct way that reminds us -we’re not cleaning up anything. When we use the less elegant <span -class="keystroke">ctrl-c</span> method to halt the main thread, all other -threads are stopped immediately as well, even if they’re in the middle of -serving a request. - -Next, then, we’ll implement the `Drop` trait to call `join` on each of the -threads in the pool so they can finish the requests they’re working on before -closing. Then we’ll implement a way to tell the threads they should stop -accepting new requests and shut down. To see this code in action, we’ll modify -our server to accept only two requests before gracefully shutting down its -thread pool. - -### Implementing the `Drop` Trait on `ThreadPool` - -Let’s start with implementing `Drop` on our thread pool. When the pool is -dropped, our threads should all join to make sure they finish their work. -Listing 20-22 shows a first attempt at a `Drop` implementation; this code won’t -quite work yet. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch20-web-server/listing-20-22/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-22: Joining each thread when the thread pool -goes out of scope</span> - -First, we loop through each of the thread pool `workers`. We use `&mut` for -this because `self` is a mutable reference, and we also need to be able to -mutate `worker`. For each worker, we print a message saying that this -particular worker is shutting down, and then we call `join` on that worker’s -thread. If the call to `join` fails, we use `unwrap` to make Rust panic and go -into an ungraceful shutdown. - -Here is the error we get when we compile this code: - -```console -{{#include ../listings/ch20-web-server/listing-20-22/output.txt}} -``` - -The error tells us we can’t call `join` because we only have a mutable borrow -of each `worker` and `join` takes ownership of its argument. To solve this -issue, we need to move the thread out of the `Worker` instance that owns -`thread` so `join` can consume the thread. We did this in Listing 17-15: if -`Worker` holds an `Option<thread::JoinHandle<()>>` instead, we can call the -`take` method on the `Option` to move the value out of the `Some` variant and -leave a `None` variant in its place. In other words, a `Worker` that is running -will have a `Some` variant in `thread`, and when we want to clean up a -`Worker`, we’ll replace `Some` with `None` so the `Worker` doesn’t have a -thread to run. - -So we know we want to update the definition of `Worker` like this: - -<span class="filename">Filename: src/lib.rs</span> - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch20-web-server/no-listing-04-update-worker-definition/src/lib.rs:here}} -``` - -Now let’s lean on the compiler to find the other places that need to change. -Checking this code, we get two errors: - -```console -{{#include ../listings/ch20-web-server/no-listing-04-update-worker-definition/output.txt}} -``` - -Let’s address the second error, which points to the code at the end of -`Worker::new`; we need to wrap the `thread` value in `Some` when we create a -new `Worker`. Make the following changes to fix this error: - -<span class="filename">Filename: src/lib.rs</span> - -```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch20-web-server/no-listing-05-fix-worker-new/src/lib.rs:here}} -``` - -The first error is in our `Drop` implementation. We mentioned earlier that we -intended to call `take` on the `Option` value to move `thread` out of `worker`. -The following changes will do so: - -<span class="filename">Filename: src/lib.rs</span> - -```rust,ignore,not_desired_behavior -{{#rustdoc_include ../listings/ch20-web-server/no-listing-06-fix-threadpool-drop/src/lib.rs:here}} -``` - -As discussed in Chapter 17, the `take` method on `Option` takes the `Some` -variant out and leaves `None` in its place. We’re using `if let` to destructure -the `Some` and get the thread; then we call `join` on the thread. If a worker’s -thread is already `None`, we know that worker has already had its thread -cleaned up, so nothing happens in that case. - -### Signaling to the Threads to Stop Listening for Jobs - -With all the changes we’ve made, our code compiles without any warnings. -However, the bad news is this code doesn’t function the way we want it to yet. -The key is the logic in the closures run by the threads of the `Worker` -instances: at the moment, we call `join`, but that won’t shut down the threads -because they `loop` forever looking for jobs. If we try to drop our -`ThreadPool` with our current implementation of `drop`, the main thread will -block forever waiting for the first thread to finish. - -To fix this problem, we’ll need a change in the `ThreadPool` `drop` -implementation and then a change in the `Worker` loop. - -First, we’ll change the `ThreadPool` `drop` implementation to explicitly drop -the `sender` before waiting for the threads to finish. Listing 20-23 shows the -changes to `ThreadPool` to explicitly drop `sender`. We use the same `Option` -and `take` technique as we did with the thread to be able to move `sender` out -of `ThreadPool`: - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground,not_desired_behavior -{{#rustdoc_include ../listings/ch20-web-server/listing-20-23/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-23: Explicitly drop `sender` before joining -the worker threads</span> - -Dropping `sender` closes the channel, which indicates no more messages will be -sent. When that happens, all the calls to `recv` that the workers do in the -infinite loop will return an error. In Listing 20-24, we change the `Worker` -loop to gracefully exit the loop in that case, which means the threads will -finish when the `ThreadPool` `drop` implementation calls `join` on them. - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/listing-20-24/src/lib.rs:here}} -``` - -<span class="caption">Listing 20-24: Explicitly break out of the loop when -`recv` returns an error</span> - -To see this code in action, let’s modify `main` to accept only two requests -before gracefully shutting down the server, as shown in Listing 20-25. - -<span class="filename">Filename: src/main.rs</span> - -```rust,ignore -{{#rustdoc_include ../listings/ch20-web-server/listing-20-25/src/main.rs:here}} -``` - -<span class="caption">Listing 20-25: Shut down the server after serving two -requests by exiting the loop</span> - -You wouldn’t want a real-world web server to shut down after serving only two -requests. This code just demonstrates that the graceful shutdown and cleanup is -in working order. - -The `take` method is defined in the `Iterator` trait and limits the iteration -to the first two items at most. The `ThreadPool` will go out of scope at the -end of `main`, and the `drop` implementation will run. - -Start the server with `cargo run`, and make three requests. The third request -should error, and in your terminal you should see output similar to this: - -<!-- manual-regeneration -cd listings/ch20-web-server/listing-20-25 -cargo run -curl http://127.0.0.1:7878 -curl http://127.0.0.1:7878 -curl http://127.0.0.1:7878 -third request will error because server will have shut down -copy output below -Can't automate because the output depends on making requests ---> - -```console -$ cargo run - Compiling hello v0.1.0 (file:///projects/hello) - Finished dev [unoptimized + debuginfo] target(s) in 1.0s - Running `target/debug/hello` -Worker 0 got a job; executing. -Shutting down. -Shutting down worker 0 -Worker 3 got a job; executing. -Worker 1 disconnected; shutting down. -Worker 2 disconnected; shutting down. -Worker 3 disconnected; shutting down. -Worker 0 disconnected; shutting down. -Shutting down worker 1 -Shutting down worker 2 -Shutting down worker 3 -``` - -You might see a different ordering of workers and messages printed. We can see -how this code works from the messages: workers 0 and 3 got the first two -requests. The server stopped accepting connections after the second connection, -and the `Drop` implementation on `ThreadPool` starts executing before worker 3 -even starts its job. Dropping the `sender` disconnects all the workers and -tells them to shut down. The workers each print a message when they disconnect, -and then the thread pool calls `join` to wait for each worker thread to finish. - -Notice one interesting aspect of this particular execution: the `ThreadPool` -dropped the `sender`, and before any worker received an error, we tried to join -worker 0. Worker 0 had not yet gotten an error from `recv`, so the main thread -blocked waiting for worker 0 to finish. In the meantime, worker 3 received a -job and then all threads received an error. When worker 0 finished, the main -thread waited for the rest of the workers to finish. At that point, they had -all exited their loops and stopped. - -Congrats! We’ve now completed our project; we have a basic web server that uses -a thread pool to respond asynchronously. We’re able to perform a graceful -shutdown of the server, which cleans up all the threads in the pool. - -Here’s the full code for reference: - -<span class="filename">Filename: src/main.rs</span> - -```rust,ignore -{{#rustdoc_include ../listings/ch20-web-server/no-listing-07-final-code/src/main.rs}} -``` - -<span class="filename">Filename: src/lib.rs</span> - -```rust,noplayground -{{#rustdoc_include ../listings/ch20-web-server/no-listing-07-final-code/src/lib.rs}} -``` - -We could do more here! If you want to continue enhancing this project, here are -some ideas: - -* Add more documentation to `ThreadPool` and its public methods. -* Add tests of the library’s functionality. -* Change calls to `unwrap` to more robust error handling. -* Use `ThreadPool` to perform some task other than serving web requests. -* Find a thread pool crate on [crates.io](https://crates.io/) and implement a - similar web server using the crate instead. Then compare its API and - robustness to the thread pool we implemented. - -## Summary - -Well done! You’ve made it to the end of the book! We want to thank you for -joining us on this tour of Rust. You’re now ready to implement your own Rust -projects and help with other peoples’ projects. Keep in mind that there is a -welcoming community of other Rustaceans who would love to help you with any -challenges you encounter on your Rust journey. diff --git a/src/ch20-04-advanced-functions-and-closures.md b/src/ch20-04-advanced-functions-and-closures.md new file mode 100644 index 0000000000..72aa6a25b2 --- /dev/null +++ b/src/ch20-04-advanced-functions-and-closures.md @@ -0,0 +1,178 @@ +## Advanced Functions and Closures + +This section explores some advanced features related to functions and closures, +including function pointers and returning closures. + +### Function Pointers + +We’ve talked about how to pass closures to functions; you can also pass regular +functions to functions! This technique is useful when you want to pass a +function you’ve already defined rather than defining a new closure. Functions +coerce to the type `fn` (with a lowercase _f_), not to be confused with the +`Fn` closure trait. The `fn` type is called a _function pointer_. Passing +functions with function pointers will allow you to use functions as arguments +to other functions. + +The syntax for specifying that a parameter is a function pointer is similar to +that of closures, as shown in Listing 20-28, where we’ve defined a function +`add_one` that adds 1 to its parameter. The function `do_twice` takes two +parameters: a function pointer to any function that takes an `i32` parameter +and returns an `i32`, and one `i32` value. The `do_twice` function calls the +function `f` twice, passing it the `arg` value, then adds the two function call +results together. The `main` function calls `do_twice` with the arguments +`add_one` and `5`. + +<Listing number="20-28" file-name="src/main.rs" caption="Using the `fn` type to accept a function pointer as an argument"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-28/src/main.rs}} +``` + +</Listing> + +This code prints `The answer is: 12`. We specify that the parameter `f` in +`do_twice` is an `fn` that takes one parameter of type `i32` and returns an +`i32`. We can then call `f` in the body of `do_twice`. In `main`, we can pass +the function name `add_one` as the first argument to `do_twice`. + +Unlike closures, `fn` is a type rather than a trait, so we specify `fn` as the +parameter type directly rather than declaring a generic type parameter with one +of the `Fn` traits as a trait bound. + +Function pointers implement all three of the closure traits (`Fn`, `FnMut`, and +`FnOnce`), meaning you can always pass a function pointer as an argument for a +function that expects a closure. It’s best to write functions using a generic +type and one of the closure traits so that your functions can accept either +functions or closures. + +That said, one example of where you would want to only accept `fn` and not +closures is when interfacing with external code that doesn’t have closures: C +functions can accept functions as arguments, but C doesn’t have closures. + +As an example of where you could use either a closure defined inline or a named +function, let’s look at a use of the `map` method provided by the `Iterator` +trait in the standard library. To use the `map` method to turn a vector of +numbers into a vector of strings, we could use a closure, as in Listing 20-29. + +<Listing number="20-29" caption="Using a closure with the `map` method to convert numbers to strings"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-29/src/main.rs:here}} +``` + +</Listing> + +Or we could name a function as the argument to `map` instead of the closure. +Listing 20-30 shows what this would look like. + +<Listing number="20-30" caption="Using the `String::to_string` function with the `map` method to convert numbers to strings"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-30/src/main.rs:here}} +``` + +</Listing> + +Note that we must use the fully qualified syntax that we talked about in the +[“Advanced Traits”][advanced-traits]<!-- ignore --> section because there are +multiple functions available named `to_string`. + +Here, we’re using the `to_string` function defined in the `ToString` trait, +which the standard library has implemented for any type that implements +`Display`. + +Recall from the [“Enum Values”][enum-values]<!-- ignore --> section in Chapter +6 that the name of each enum variant that we define also becomes an initializer +function. We can use these initializer functions as function pointers that +implement the closure traits, which means we can specify the initializer +functions as arguments for methods that take closures, as seen in Listing 20-31. + +<Listing number="20-31" caption="Using an enum initializer with the `map` method to create a `Status` instance from numbers"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-31/src/main.rs:here}} +``` + +</Listing> + +Here, we create `Status::Value` instances using each `u32` value in the range +that `map` is called on by using the initializer function of `Status::Value`. +Some people prefer this style and some people prefer to use closures. They +compile to the same code, so use whichever style is clearer to you. + +### Returning Closures + +Closures are represented by traits, which means you can’t return closures +directly. In most cases where you might want to return a trait, you can instead +use the concrete type that implements the trait as the return value of the +function. However, you can’t usually do that with closures because they don’t +have a concrete type that is returnable; you’re not allowed to use the function +pointer `fn` as a return type if the closure captures any values from its +scope, for example. + +Instead, you will normally use the `impl Trait` syntax we learned about in +Chapter 10. You can return any function type, using `Fn`, `FnOnce`, and `FnMut`. +For example, the code in Listing 20-32 will compile just fine. + +<Listing number="20-32" caption="Returning a closure from a function using the `impl Trait` syntax"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-32/src/lib.rs}} +``` + +</Listing> + +However, as we noted in the [“Inferring and Annotating Closure +Types”][closure-types]<!-- ignore --> section in Chapter 13, each closure is +also its own distinct type. If you need to work with multiple functions that +have the same signature but different implementations, you will need to use a +trait object for them. Consider what happens if you write code like that shown +in Listing 20-33. + +<Listing file-name="src/main.rs" number="20-33" caption="Creating a `Vec<T>` of closures defined by functions that return `impl Fn` types"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-33/src/main.rs}} +``` + +</Listing> + +Here we have two functions, `returns_closure` and `returns_initialized_closure`, +which both return `impl Fn(i32) -> i32`. Notice that the closures that they +return are different, even though they implement the same type. If we try to +compile this, Rust lets us know that it won’t work: + +```text +{{#include ../listings/ch20-advanced-features/listing-20-33/output.txt}} +``` + +The error message tells us that whenever we return an `impl Trait`, Rust +creates a unique _opaque type_, a type where we cannot see into the details of +what Rust constructs for us, nor can we guess the type Rust will generate to +write ourselves. So, even though these functions return closures that implement +the same trait, `Fn(i32) -> i32`, the opaque types Rust generates for each are +distinct. (This is similar to how Rust produces different concrete types for +distinct async blocks even when they have the same output type, as we saw in +[“The `Pin` Type and the `Unpin` Trait”][future-types]<!-- ignore --> in +Chapter 17.) We have seen a solution to this problem a few times now: We can +use a trait object, as in Listing 20-34. + +<Listing number="20-34" caption="Creating a `Vec<T>` of closures defined by functions that return `Box<dyn Fn>` so that they have the same type"> + +```rust +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-34/src/main.rs:here}} +``` + +</Listing> + +This code will compile just fine. For more about trait objects, refer to the +section [“Using Trait Objects To Abstract over Shared +Behavior”][trait-objects]<!-- ignore --> in Chapter 18. + +Next, let’s look at macros! + +[advanced-traits]: ch20-02-advanced-traits.html#advanced-traits +[enum-values]: ch06-01-defining-an-enum.html#enum-values +[closure-types]: ch13-01-closures.html#closure-type-inference-and-annotation +[future-types]: ch17-03-more-futures.html +[trait-objects]: ch18-02-trait-objects.html diff --git a/src/ch19-06-macros.md b/src/ch20-05-macros.md similarity index 68% rename from src/ch19-06-macros.md rename to src/ch20-05-macros.md index 7731869eae..6d2e48f5a2 100644 --- a/src/ch19-06-macros.md +++ b/src/ch20-05-macros.md @@ -1,14 +1,14 @@ ## Macros We’ve used macros like `println!` throughout this book, but we haven’t fully -explored what a macro is and how it works. The term *macro* refers to a family -of features in Rust: *declarative* macros with `macro_rules!` and three kinds -of *procedural* macros: +explored what a macro is and how it works. The term _macro_ refers to a family +of features in Rust—declarative macros with `macro_rules!` and three kinds of +procedural macros: -* Custom `#[derive]` macros that specify code added with the `derive` attribute +- Custom `#[derive]` macros that specify code added with the `derive` attribute used on structs and enums -* Attribute-like macros that define custom attributes usable on any item -* Function-like macros that look like function calls but operate on the tokens +- Attribute-like macros that define custom attributes usable on any item +- Function-like macros that look like function calls but operate on the tokens specified as their argument We’ll talk about each of these in turn, but first, let’s look at why we even @@ -17,18 +17,18 @@ need macros when we already have functions. ### The Difference Between Macros and Functions Fundamentally, macros are a way of writing code that writes other code, which -is known as *metaprogramming*. In Appendix C, we discuss the `derive` +is known as _metaprogramming_. In Appendix C, we discuss the `derive` attribute, which generates an implementation of various traits for you. We’ve also used the `println!` and `vec!` macros throughout the book. All of these -macros *expand* to produce more code than the code you’ve written manually. +macros _expand_ to produce more code than the code you’ve written manually. Metaprogramming is useful for reducing the amount of code you have to write and maintain, which is also one of the roles of functions. However, macros have -some additional powers that functions don’t. +some additional powers that functions don’t have. A function signature must declare the number and type of parameters the function has. Macros, on the other hand, can take a variable number of -parameters: we can call `println!("hello")` with one argument or +parameters: We can call `println!("hello")` with one argument or `println!("hello {}", name)` with two arguments. Also, macros are expanded before the compiler interprets the meaning of the code, so a macro can, for example, implement a trait on a given type. A function can’t, because it gets @@ -41,19 +41,23 @@ generally more difficult to read, understand, and maintain than function definitions. Another important difference between macros and functions is that you must -define macros or bring them into scope *before* you call them in a file, as +define macros or bring them into scope _before_ you call them in a file, as opposed to functions you can define anywhere and call anywhere. -### Declarative Macros with `macro_rules!` for General Metaprogramming +<!-- Old headings. Do not remove or links may break. --> -The most widely used form of macros in Rust is the *declarative macro*. These +<a id="declarative-macros-with-macro_rules-for-general-metaprogramming"></a> + +### Declarative Macros for General Metaprogramming + +The most widely used form of macros in Rust is the _declarative macro_. These are also sometimes referred to as “macros by example,” “`macro_rules!` macros,” or just plain “macros.” At their core, declarative macros allow you to write something similar to a Rust `match` expression. As discussed in Chapter 6, `match` expressions are control structures that take an expression, compare the -resulting value of the expression to patterns, and then run the code associated +resultant value of the expression to patterns, and then run the code associated with the matching pattern. Macros also compare a value to patterns that are -associated with particular code: in this situation, the value is the literal +associated with particular code: In this situation, the value is the literal Rust source code passed to the macro; the patterns are compared with the structure of that source code; and the code associated with each pattern, when matched, replaces the code passed to the macro. This all happens during @@ -73,27 +77,26 @@ We could also use the `vec!` macro to make a vector of two integers or a vector of five string slices. We wouldn’t be able to use a function to do the same because we wouldn’t know the number or type of values up front. -Listing 19-28 shows a slightly simplified definition of the `vec!` macro. +Listing 20-35 shows a slightly simplified definition of the `vec!` macro. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="20-35" file-name="src/lib.rs" caption="A simplified version of the `vec!` macro definition"> ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-28/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-35/src/lib.rs}} ``` -<span class="caption">Listing 19-28: A simplified version of the `vec!` macro -definition</span> +</Listing> > Note: The actual definition of the `vec!` macro in the standard library -> includes code to preallocate the correct amount of memory up front. That code -> is an optimization that we don’t include here to make the example simpler. +> includes code to pre-allocate the correct amount of memory up front. That code +> is an optimization that we don’t include here, to make the example simpler. The `#[macro_export]` annotation indicates that this macro should be made available whenever the crate in which the macro is defined is brought into scope. Without this annotation, the macro can’t be brought into scope. We then start the macro definition with `macro_rules!` and the name of the -macro we’re defining *without* the exclamation mark. The name, in this case +macro we’re defining _without_ the exclamation mark. The name, in this case `vec`, is followed by curly brackets denoting the body of the macro definition. The structure in the `vec!` body is similar to the structure of a `match` @@ -104,10 +107,10 @@ is the only pattern in this macro, there is only one valid way to match; any other pattern will result in an error. More complex macros will have more than one arm. -Valid pattern syntax in macro definitions is different than the pattern syntax -covered in Chapter 18 because macro patterns are matched against Rust code +Valid pattern syntax in macro definitions is different from the pattern syntax +covered in Chapter 19 because macro patterns are matched against Rust code structure rather than values. Let’s walk through what the pattern pieces in -Listing 19-28 mean; for the full macro pattern syntax, see the [Rust +Listing 20-29 mean; for the full macro pattern syntax, see the [Rust Reference][ref]. First, we use a set of parentheses to encompass the whole pattern. We use a @@ -119,8 +122,9 @@ for use in the replacement code. Within `$()` is `$x:expr`, which matches any Rust expression and gives the expression the name `$x`. The comma following `$()` indicates that a literal comma separator character -could optionally appear after the code that matches the code in `$()`. The `*` -specifies that the pattern matches zero or more of whatever precedes the `*`. +must appear between each instance of the code that matches the code in `$()`. +The `*` specifies that the pattern matches zero or more of whatever precedes +the `*`. When we call this macro with `vec![1, 2, 3];`, the `$x` pattern matches three times with the three expressions `1`, `2`, and `3`. @@ -151,65 +155,67 @@ Daniel Keep and continued by Lukas Wirth. ### Procedural Macros for Generating Code from Attributes -The second form of macros is the *procedural macro*, which acts more like a -function (and is a type of procedure). Procedural macros accept some code as an -input, operate on that code, and produce some code as an output rather than +The second form of macros is the procedural macro, which acts more like a +function (and is a type of procedure). _Procedural macros_ accept some code as +an input, operate on that code, and produce some code as an output rather than matching against patterns and replacing the code with other code as declarative -macros do. The three kinds of procedural macros are custom derive, +macros do. The three kinds of procedural macros are custom `derive`, attribute-like, and function-like, and all work in a similar fashion. When creating procedural macros, the definitions must reside in their own crate with a special crate type. This is for complex technical reasons that we hope -to eliminate in the future. In Listing 19-29, we show how to define a +to eliminate in the future. In Listing 20-36, we show how to define a procedural macro, where `some_attribute` is a placeholder for using a specific macro variety. -<span class="filename">Filename: src/lib.rs</span> +<Listing number="20-36" file-name="src/lib.rs" caption="An example of defining a procedural macro"> ```rust,ignore -use proc_macro; +use proc_macro::TokenStream; #[some_attribute] pub fn some_name(input: TokenStream) -> TokenStream { } ``` -<span class="caption">Listing 19-29: An example of defining a procedural -macro</span> +</Listing> The function that defines a procedural macro takes a `TokenStream` as an input and produces a `TokenStream` as an output. The `TokenStream` type is defined by the `proc_macro` crate that is included with Rust and represents a sequence of -tokens. This is the core of the macro: the source code that the macro is +tokens. This is the core of the macro: The source code that the macro is operating on makes up the input `TokenStream`, and the code the macro produces is the output `TokenStream`. The function also has an attribute attached to it that specifies which kind of procedural macro we’re creating. We can have multiple kinds of procedural macros in the same crate. Let’s look at the different kinds of procedural macros. We’ll start with a -custom derive macro and then explain the small dissimilarities that make the +custom `derive` macro and then explain the small dissimilarities that make the other forms different. -### How to Write a Custom `derive` Macro +<!-- Old headings. Do not remove or links may break. --> + +<a id="how-to-write-a-custom-derive-macro"></a> + +### Custom `derive` Macros Let’s create a crate named `hello_macro` that defines a trait named `HelloMacro` with one associated function named `hello_macro`. Rather than making our users implement the `HelloMacro` trait for each of their types, -we’ll provide a procedural macro so users can annotate their type with +we’ll provide a procedural macro so that users can annotate their type with `#[derive(HelloMacro)]` to get a default implementation of the `hello_macro` function. The default implementation will print `Hello, Macro! My name is TypeName!` where `TypeName` is the name of the type on which this trait has been defined. In other words, we’ll write a crate that enables another -programmer to write code like Listing 19-30 using our crate. +programmer to write code like Listing 20-37 using our crate. -<span class="filename">Filename: src/main.rs</span> +<Listing number="20-37" file-name="src/main.rs" caption="The code a user of our crate will be able to write when using our procedural macro"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-30/src/main.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-37/src/main.rs}} ``` -<span class="caption">Listing 19-30: The code a user of our crate will be able -to write when using our procedural macro</span> +</Listing> This code will print `Hello, Macro! My name is Pancakes!` when we’re done. The first step is to make a new library crate, like this: @@ -218,21 +224,28 @@ first step is to make a new library crate, like this: $ cargo new hello_macro --lib ``` -Next, we’ll define the `HelloMacro` trait and its associated function: +Next, in Listing 20-38, we’ll define the `HelloMacro` trait and its associated +function. -<span class="filename">Filename: src/lib.rs</span> +<Listing file-name="src/lib.rs" number="20-38" caption="A simple trait that we will use with the `derive` macro"> ```rust,noplayground -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/hello_macro/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-38/hello_macro/src/lib.rs}} ``` +</Listing> + We have a trait and its function. At this point, our crate user could implement -the trait to achieve the desired functionality, like so: +the trait to achieve the desired functionality, as in Listing 20-39. + +<Listing number="20-39" file-name="src/main.rs" caption="How it would look if users wrote a manual implementation of the `HelloMacro` trait"> ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/no-listing-20-impl-hellomacro-for-pancakes/pancakes/src/main.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-39/pancakes/src/main.rs}} ``` +</Listing> + However, they would need to write the implementation block for each type they wanted to use with `hello_macro`; we want to spare them from having to do this work. @@ -245,7 +258,7 @@ name at runtime. We need a macro to generate code at compile time. The next step is to define the procedural macro. At the time of this writing, procedural macros need to be in their own crate. Eventually, this restriction might be lifted. The convention for structuring crates and macro crates is as -follows: for a crate named `foo`, a custom derive procedural macro crate is +follows: For a crate named `foo`, a custom `derive` procedural macro crate is called `foo_derive`. Let’s start a new crate called `hello_macro_derive` inside our `hello_macro` project: @@ -267,45 +280,47 @@ possible for programmers to use `hello_macro` even if they don’t want the We need to declare the `hello_macro_derive` crate as a procedural macro crate. We’ll also need functionality from the `syn` and `quote` crates, as you’ll see in a moment, so we need to add them as dependencies. Add the following to the -*Cargo.toml* file for `hello_macro_derive`: +_Cargo.toml_ file for `hello_macro_derive`: -<span class="filename">Filename: hello_macro_derive/Cargo.toml</span> +<Listing file-name="hello_macro_derive/Cargo.toml"> ```toml -{{#include ../listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/Cargo.toml:6:12}} +{{#include ../listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/Cargo.toml:6:12}} ``` -To start defining the procedural macro, place the code in Listing 19-31 into -your *src/lib.rs* file for the `hello_macro_derive` crate. Note that this code +</Listing> + +To start defining the procedural macro, place the code in Listing 20-40 into +your _src/lib.rs_ file for the `hello_macro_derive` crate. Note that this code won’t compile until we add a definition for the `impl_hello_macro` function. -<span class="filename">Filename: hello_macro_derive/src/lib.rs</span> +<Listing number="20-40" file-name="hello_macro_derive/src/lib.rs" caption="Code that most procedural macro crates will require in order to process Rust code"> ```rust,ignore,does_not_compile -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-31/hello_macro/hello_macro_derive/src/lib.rs}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-40/hello_macro/hello_macro_derive/src/lib.rs}} ``` -<span class="caption">Listing 19-31: Code that most procedural macro crates -will require in order to process Rust code</span> +</Listing> Notice that we’ve split the code into the `hello_macro_derive` function, which is responsible for parsing the `TokenStream`, and the `impl_hello_macro` -function, which is responsible for transforming the syntax tree: this makes +function, which is responsible for transforming the syntax tree: This makes writing a procedural macro more convenient. The code in the outer function (`hello_macro_derive` in this case) will be the same for almost every procedural macro crate you see or create. The code you specify in the body of the inner function (`impl_hello_macro` in this case) will be different depending on your procedural macro’s purpose. -We’ve introduced three new crates: `proc_macro`, [`syn`], and [`quote`]. The -`proc_macro` crate comes with Rust, so we didn’t need to add that to the -dependencies in *Cargo.toml*. The `proc_macro` crate is the compiler’s API that -allows us to read and manipulate Rust code from our code. +We’ve introduced three new crates: `proc_macro`, [`syn`][syn]<!-- ignore -->, +and [`quote`][quote]<!-- ignore -->. The `proc_macro` crate comes with Rust, +so we didn’t need to add that to the dependencies in _Cargo.toml_. The +`proc_macro` crate is the compiler’s API that allows us to read and manipulate +Rust code from our code. The `syn` crate parses Rust code from a string into a data structure that we can perform operations on. The `quote` crate turns `syn` data structures back into Rust code. These crates make it much simpler to parse any sort of Rust -code we might want to handle: writing a full parser for Rust code is no simple +code we might want to handle: Writing a full parser for Rust code is no simple task. The `hello_macro_derive` function will be called when a user of our library @@ -318,8 +333,10 @@ The `hello_macro_derive` function first converts the `input` from a `TokenStream` to a data structure that we can then interpret and perform operations on. This is where `syn` comes into play. The `parse` function in `syn` takes a `TokenStream` and returns a `DeriveInput` struct representing the -parsed Rust code. Listing 19-32 shows the relevant parts of the `DeriveInput` -struct we get from parsing the `struct Pancakes;` string: +parsed Rust code. Listing 20-41 shows the relevant parts of the `DeriveInput` +struct we get from parsing the `struct Pancakes;` string. + +<Listing number="20-41" caption="The `DeriveInput` instance we get when parsing the code that has the macro’s attribute in Listing 20-37"> ```rust,ignore DeriveInput { @@ -341,17 +358,16 @@ DeriveInput { } ``` -<span class="caption">Listing 19-32: The `DeriveInput` instance we get when -parsing the code that has the macro’s attribute in Listing 19-30</span> +</Listing> The fields of this struct show that the Rust code we’ve parsed is a unit struct -with the `ident` (identifier, meaning the name) of `Pancakes`. There are more +with the `ident` (_identifier_, meaning the name) of `Pancakes`. There are more fields on this struct for describing all sorts of Rust code; check the [`syn` documentation for `DeriveInput`][syn-docs] for more information. Soon we’ll define the `impl_hello_macro` function, which is where we’ll build the new Rust code we want to include. But before we do, note that the output -for our derive macro is also a `TokenStream`. The returned `TokenStream` is +for our `derive` macro is also a `TokenStream`. The returned `TokenStream` is added to the code that our crate users write, so when they compile their crate, they’ll get the extra functionality that we provide in the modified `TokenStream`. @@ -366,32 +382,31 @@ about what went wrong by using `panic!` or `expect`. Now that we have the code to turn the annotated Rust code from a `TokenStream` into a `DeriveInput` instance, let’s generate the code that implements the -`HelloMacro` trait on the annotated type, as shown in Listing 19-33. +`HelloMacro` trait on the annotated type, as shown in Listing 20-42. -<span class="filename">Filename: hello_macro_derive/src/lib.rs</span> +<Listing number="20-42" file-name="hello_macro_derive/src/lib.rs" caption="Implementing the `HelloMacro` trait using the parsed Rust code"> ```rust,ignore -{{#rustdoc_include ../listings/ch19-advanced-features/listing-19-33/hello_macro/hello_macro_derive/src/lib.rs:here}} +{{#rustdoc_include ../listings/ch20-advanced-features/listing-20-42/hello_macro/hello_macro_derive/src/lib.rs:here}} ``` -<span class="caption">Listing 19-33: Implementing the `HelloMacro` trait using -the parsed Rust code</span> +</Listing> We get an `Ident` struct instance containing the name (identifier) of the -annotated type using `ast.ident`. The struct in Listing 19-32 shows that when -we run the `impl_hello_macro` function on the code in Listing 19-30, the +annotated type using `ast.ident`. The struct in Listing 20-41 shows that when +we run the `impl_hello_macro` function on the code in Listing 20-37, the `ident` we get will have the `ident` field with a value of `"Pancakes"`. Thus, -the `name` variable in Listing 19-33 will contain an `Ident` struct instance +the `name` variable in Listing 20-42 will contain an `Ident` struct instance that, when printed, will be the string `"Pancakes"`, the name of the struct in -Listing 19-30. +Listing 20-37. The `quote!` macro lets us define the Rust code that we want to return. The -compiler expects something different to the direct result of the `quote!` +compiler expects something different from the direct result of the `quote!` macro’s execution, so we need to convert it to a `TokenStream`. We do this by calling the `into` method, which consumes this intermediate representation and returns a value of the required `TokenStream` type. -The `quote!` macro also provides some very cool templating mechanics: we can +The `quote!` macro also provides some very cool templating mechanics: We can enter `#name`, and `quote!` will replace it with the value in the variable `name`. You can even do some repetition similar to the way regular macros work. Check out [the `quote` crate’s docs][quote-docs] for a thorough introduction. @@ -404,41 +419,43 @@ the name of the annotated type. The `stringify!` macro used here is built into Rust. It takes a Rust expression, such as `1 + 2`, and at compile time turns the expression into a -string literal, such as `"1 + 2"`. This is different than `format!` or -`println!`, macros which evaluate the expression and then turn the result into -a `String`. There is a possibility that the `#name` input might be an -expression to print literally, so we use `stringify!`. Using `stringify!` also -saves an allocation by converting `#name` to a string literal at compile time. +string literal, such as `"1 + 2"`. This is different from `format!` or +`println!`, which are macros that evaluate the expression and then turn the +result into a `String`. There is a possibility that the `#name` input might be +an expression to print literally, so we use `stringify!`. Using `stringify!` +also saves an allocation by converting `#name` to a string literal at compile +time. At this point, `cargo build` should complete successfully in both `hello_macro` and `hello_macro_derive`. Let’s hook up these crates to the code in Listing -19-30 to see the procedural macro in action! Create a new binary project in -your *projects* directory using `cargo new pancakes`. We need to add +20-37 to see the procedural macro in action! Create a new binary project in +your _projects_ directory using `cargo new pancakes`. We need to add `hello_macro` and `hello_macro_derive` as dependencies in the `pancakes` -crate’s *Cargo.toml*. If you’re publishing your versions of `hello_macro` and -`hello_macro_derive` to [crates.io](https://crates.io/), they would be regular -dependencies; if not, you can specify them as `path` dependencies as follows: +crate’s _Cargo.toml_. If you’re publishing your versions of `hello_macro` and +`hello_macro_derive` to [crates.io](https://crates.io/)<!-- ignore -->, they +would be regular dependencies; if not, you can specify them as `path` +dependencies as follows: ```toml -{{#include ../listings/ch19-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml:7:9}} +{{#include ../listings/ch20-advanced-features/no-listing-21-pancakes/pancakes/Cargo.toml:6:8}} ``` -Put the code in Listing 19-30 into *src/main.rs*, and run `cargo run`: it -should print `Hello, Macro! My name is Pancakes!` The implementation of the +Put the code in Listing 20-37 into _src/main.rs_, and run `cargo run`: It +should print `Hello, Macro! My name is Pancakes!`. The implementation of the `HelloMacro` trait from the procedural macro was included without the `pancakes` crate needing to implement it; the `#[derive(HelloMacro)]` added the trait implementation. Next, let’s explore how the other kinds of procedural macros differ from custom -derive macros. +`derive` macros. -### Attribute-like macros +### Attribute-Like Macros -Attribute-like macros are similar to custom derive macros, but instead of +Attribute-like macros are similar to custom `derive` macros, but instead of generating code for the `derive` attribute, they allow you to create new attributes. They’re also more flexible: `derive` only works for structs and enums; attributes can be applied to other items as well, such as functions. -Here’s an example of using an attribute-like macro: say you have an attribute +Here’s an example of using an attribute-like macro. Say you have an attribute named `route` that annotates functions when using a web application framework: ```rust,ignore @@ -459,21 +476,21 @@ contents of the attribute: the `GET, "/"` part. The second is the body of the item the attribute is attached to: in this case, `fn index() {}` and the rest of the function’s body. -Other than that, attribute-like macros work the same way as custom derive -macros: you create a crate with the `proc-macro` crate type and implement a +Other than that, attribute-like macros work the same way as custom `derive` +macros: You create a crate with the `proc-macro` crate type and implement a function that generates the code you want! -### Function-like macros +### Function-Like Macros Function-like macros define macros that look like function calls. Similarly to `macro_rules!` macros, they’re more flexible than functions; for example, they -can take an unknown number of arguments. However, `macro_rules!` macros can be -defined only using the match-like syntax we discussed in the section -[“Declarative Macros with `macro_rules!` for General -Metaprogramming”][decl]<!-- ignore --> earlier. Function-like macros take a -`TokenStream` parameter and their definition manipulates that `TokenStream` -using Rust code as the other two types of procedural macros do. An example of a -function-like macro is an `sql!` macro that might be called like so: +can take an unknown number of arguments. However, `macro_rules!` macros can +only be defined using the match-like syntax we discussed in the [“Declarative +Macros for General Metaprogramming”][decl]<!-- ignore --> section earlier. +Function-like macros take a `TokenStream` parameter, and their definition +manipulates that `TokenStream` using Rust code as the other two types of +procedural macros do. An example of a function-like macro is an `sql!` macro +that might be called like so: ```rust,ignore let sql = sql!(SELECT * FROM posts WHERE id=1); @@ -488,7 +505,7 @@ syntactically correct, which is much more complex processing than a pub fn sql(input: TokenStream) -> TokenStream { ``` -This definition is similar to the custom derive macro’s signature: we receive +This definition is similar to the custom `derive` macro’s signature: We receive the tokens that are inside the parentheses and return the code we wanted to generate. @@ -497,7 +514,7 @@ generate. Whew! Now you have some Rust features in your toolbox that you likely won’t use often, but you’ll know they’re available in very particular circumstances. We’ve introduced several complex topics so that when you encounter them in -error message suggestions or in other peoples’ code, you’ll be able to +error message suggestions or in other people’s code, you’ll be able to recognize these concepts and syntax. Use this chapter as a reference to guide you to solutions. @@ -506,8 +523,8 @@ and do one more project! [ref]: ../reference/macros-by-example.html [tlborm]: https://veykril.github.io/tlborm/ -[`syn`]: https://crates.io/crates/syn -[`quote`]: https://crates.io/crates/quote -[syn-docs]: https://docs.rs/syn/1.0/syn/struct.DeriveInput.html +[syn]: https://crates.io/crates/syn +[quote]: https://crates.io/crates/quote +[syn-docs]: https://docs.rs/syn/2.0/syn/struct.DeriveInput.html [quote-docs]: https://docs.rs/quote [decl]: #declarative-macros-with-macro_rules-for-general-metaprogramming diff --git a/src/ch21-00-final-project-a-web-server.md b/src/ch21-00-final-project-a-web-server.md new file mode 100644 index 0000000000..fc14225d16 --- /dev/null +++ b/src/ch21-00-final-project-a-web-server.md @@ -0,0 +1,42 @@ +# Proyek Final: Membangun Web Server Multithreaded + +Perjalanan kita panjang banget, tapi akhirnya sampai juga di akhir buku ini. Di +chapter ini, kita bakal bikin satu project terakhir bareng-bareng buat nunjukin +beberapa konsep yang udah kita pelajari di chapter akhir, sekaligus ngerecap +materi sebelumnya juga. + +Buat project penutup ini, kita bakal bikin web server yang bakal nampilin +“Hello!” dan tampilannya bakal mirip kayak Gambar 21-1 di browser. + +Ini rencana kita buat bikin web servernya: + +1. Belajar dikit tentang TCP dan HTTP. +2. Dengerin koneksi TCP di sebuah socket. +3. Parsing beberapa request HTTP sederhana. +4. Bikin response HTTP yang proper. +5. Ningkatin performa server pakai thread pool. + +<img alt="Screenshot of a web browser visiting the address 127.0.0.1:8080 displaying a webpage with the text content “Hello! Hi from Rust”" src="img/trpl21-01.png" class="center" style="width: 50%;" /> + +<span class="caption">Gambar 21-1: Proyek terakhir kita bareng-bareng</span> + +Sebelum mulai, ada dua hal penting yang perlu disebutin dulu. Pertama, cara yang +bakal kita pake ini **bukan** cara terbaik buat bikin web server di Rust. +Komunitas Rust udah bikin banyak crate siap pakai yang bisa kamu temuin di +[crates.io](https://crates.io/), dan crate- crate itu punya implementasi web +server dan thread pool yang jauh lebih matang dibanding apa yang bakal kita +bikin di sini. Tapi tujuan chapter ini bukan “cara tercepat bikin web server”, +melainkan biar kamu **belajar konsepnya**. Karena Rust itu bahasa sistem, kita +punya kebebasan memilih level abstraksi yang kita mau, bahkan bisa turun ke +level yang lebih “rendah” dibanding bahasa lain. + +Kedua, di sini kita **gak bakal pakai async/await dulu**. Bikin thread pool aja +udah cukup menantang, apalagi kalau ditambah bikin async runtime sendiri! Tapi +nanti kita tetap bakal bahas dikit gimana async/await bisa relevan sama +masalah-masalah yang kita bahas di chapter ini. Pada akhirnya, kayak yang udah +disebut di Chapter 17, banyak async runtime juga sebenernya pakai thread pool +buat ngatur pekerjaannya. + +Jadi kita bakal nulis HTTP server dasar dan thread pool-nya secara manual biar +kamu beneran paham konsep dan teknik dasarnya, yang nantinya bakal kepake banget +kalau kamu mau pake crate siap pakai di masa depan. diff --git a/src/ch21-01-single-threaded.md b/src/ch21-01-single-threaded.md new file mode 100644 index 0000000000..0406928148 --- /dev/null +++ b/src/ch21-01-single-threaded.md @@ -0,0 +1,308 @@ +## Membangun Web Server Single-Threaded + +Kita bakal mulai dulu dengan bikin web server yang jalan pake **single thread**. +Sebelum mulai, kita lihat dulu gambaran singkat tentang protokol yang terlibat +saat bikin web server. Detail lengkap soal protokol ini sebenernya di luar fokus +buku ini, tapi gambaran singkatnya udah cukup kok buat kebutuhan kita. + +Dua protokol utama yang dipake web server adalah **Hypertext Transfer Protocol +(HTTP)** dan **Transmission Control Protocol (TCP)**. Dua-duanya adalah protokol +tipe _request-response_, artinya **client** bakal ngirim request dan **server** +bakal dengerin lalu ngasih response balik. Isi request dan response itu diatur +sama protokolnya. + +TCP itu protokol level bawah yang ngatur gimana data dikirim dari satu server ke +server lain, tapi dia gak nentuin isi datanya itu apa. HTTP dibangun di atas TCP +buat ngatur isi request dan response-nya. Secara teknis HTTP bisa jalan di atas +protokol lain, tapi hampir semua kasus HTTP dikirim lewat TCP. Di sini kita +bakal kerja langsung sama raw bytes request dan response HTTP dan TCP. + +### Ngedengerin Koneksi TCP + +Web server kita harus bisa dengerin koneksi TCP, jadi ini hal pertama yang bakal +kita kerjain. Standard library Rust punya module `std::net` yang bisa bantu +kita. Bikin project baru kayak biasa: + +```console +$ cargo new hello + Created binary (application) `hello` project +$ cd hello +``` + +Sekarang masukin kode Listing 21-1 ke _src/main.rs_. Kode ini bakal dengerin +alamat lokal `127.0.0.1:7878` buat nerima TCP stream baru. Kalau ada koneksi +masuk, dia bakal nge-print `Connection established!`. + +<Listing number="21-1" file-name="src/main.rs" caption="Ngedengerin incoming stream dan nge-print pesan kalau ada stream masuk"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-01/src/main.rs}} +``` + +</Listing> + +Dengan `TcpListener`, kita bisa dengerin koneksi TCP di alamat `127.0.0.1:7878`. +Bagian sebelum titik dua itu IP address komputer kamu (ini sama di semua +komputer, bukan khusus penulis ya), dan `7878` itu portnya. Kita pilih port ini +karena: + +- HTTP biasanya gak jalan di port ini, jadi kecil kemungkinan bentrok dengan + server lain +- dan “7878” kalau diketik di keypad telepon bacaannya mirip “rust” + +Fungsi `bind` di sini mirip kayak `new`, yang balikannya instance `TcpListener` +baru. Disebut `bind` karena di dunia networking, proses ngiket ke port buat +dengerin koneksi itu disebut “binding to a port”. + +`bind` balikin `Result<T, E>` karena bisa aja gagal, misalnya kalau kita jalanin +dua instance program ini sekaligus di port yang sama. Karena ini cuma server +buat belajar, kita gak ribet handle errornya — cukup `unwrap` aja biar program +stop kalau error. + +Method `incoming` di `TcpListener` balikin iterator berisi stream TCP +(`TcpStream`). Satu _stream_ itu satu koneksi aktif antara client dan server. +“Connection” itu keseluruhan proses request–response: client connect, server +balas, lalu server tutup koneksi. Jadi kita bakal baca dari `TcpStream` buat +lihat apa yang dikirim client, lalu nulis response ke stream buat dibalikin ke +client. Loop `for` bakal proses tiap koneksi satu-satu. + +Untuk sekarang, kita cuma `unwrap` stream biar program berhenti kalau error; +kalau aman, kita print pesan. Nanti bagian suksesnya bakal kita tambahin. Kenapa +bisa error? Karena yang kita iterasi sebenernya “usaha koneksi”, bukan selalu +koneksi yang berhasil. OS punya batas maksimal koneksi, kalau lewat batas bisa +gagal. + +Ayo coba jalanin! Jalankan `cargo run`, terus buka _127.0.0.1:7878_ di browser. +Browser bakal nunjukin error kayak “Connection reset” karena server belum +ngirimin apa-apa. Tapi di terminal kamu harusnya kelihatan ini: + +```text + Running `target/debug/hello` +Connection established! +Connection established! +Connection established! +``` + +Kadang satu request bisa bikin beberapa pesan muncul. Bisa karena browser juga +minta resource lain kayak _favicon.ico_. Bisa juga browser nyoba connect ulang +karena server gak ngasih response. Kalau `stream` drop (keluar scope), koneksi +ditutup, browser bisa nyoba lagi otomatis. + +Beberapa browser juga sengaja buka banyak koneksi kosong dulu biar nanti kalau +ada request beneran bisa lebih cepat. Server kita bakal tetap lihat koneksinya, +walaupun belum ada requestnya. + +Intinya, kita udah sukses dapet koneksi TCP + +Jangan lupa stop pakai <kbd>ctrl</kbd>-<kbd>C</kbd> kalau mau berhenti, dan +setiap abis ngedit kode, jalankan ulang `cargo run`. + +### Ngebaca Request + +Sekarang kita siap baca request dari browser! Biar rapi, kita bikin fungsi baru +buat handle koneksi. Di fungsi baru `handle_connection`, kita bakal baca data +dari stream lalu print buat lihat apa yang dikirim browser. Ubah kodenya jadi +kayak Listing 21-2. + +<Listing number="21-2" file-name="src/main.rs" caption="Membaca `TcpStream` dan nge-print datanya"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-02/src/main.rs}} +``` + +</Listing> + +Kita import `BufReader` dan trait I/O supaya bisa baca tulis stream. Di loop +`main`, sekarang kita panggil `handle_connection` sambil passing `stream`. + +Di `handle_connection`, kita bungkus stream pake `BufReader` biar bacanya lebih +efisien. Kita bikin variabel `http_request` buat nampung semua baris request. +`lines()` bakal balikin iterator `Result<String, Error>`, jadi kita `map` dan +`unwrap` biar dapet `String`. + +Browser nandain request selesai dengan dua newline kosong berturut-turut, jadi +kita ambil line sampai ketemu string kosong. Setelah terkumpul, kita print pake +pretty debug supaya gampang dibaca. + +Coba jalanin lagi, buka browser ke alamat tadi. Browser masih error, tapi di +terminal sekarang bakal kelihatan request HTTP lengkapnya. + +Sekarang kita udah tau browser ngirim apa. Saatnya balas + +### Ngeliat Lebih Deket HTTP Request + +HTTP itu protokol berbasis teks, format requestnya: + +```text +Method Request-URI HTTP-Version CRLF +headers CRLF +message-body +``` + +Baris pertama adalah **request line**. + +- bagian pertama: method (`GET`, `POST`, dll) +- bagian kedua: URI yang diminta (contohnya `/`) +- bagian terakhir: versi HTTP + +CRLF (`\r\n`) adalah pemisah antar bagian. + +Di output kita kelihatan: + +- method → `GET` +- path → `/` +- versi → `HTTP/1.1` + +Sisanya adalah header. `GET` biasanya gak punya body. + +Coba request alamat lain misalnya _127.0.0.1:7878/test_ biar lihat perbedaan +requestnya. + +Sekarang kita udah paham apa yang diminta browser, waktunya balas balik! + +### Nulis Response + +Response HTTP formatnya kayak gini: + +```text +HTTP-Version Status-Code Reason-Phrase CRLF +headers CRLF +message-body +``` + +Contoh response super simpel: + +```text +HTTP/1.1 200 OK\r\n\r\n +``` + +Ini berarti: + +- sukses +- gak ada header +- gak ada body + +Sekarang kita tulis response ini ke stream. Ganti `println!` sebelumnya dengan +kode di Listing 21-3. + +<Listing number="21-3" file-name="src/main.rs" caption="Nulis HTTP response sederhana ke stream"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-03/src/main.rs:here}} +``` + +</Listing> + +Kita simpan response di variabel `response`, ubah jadi bytes pakai `as_bytes`, +lalu kirim ke stream. Kalau gagal, `unwrap` bakal berhentiin program. + +Sekarang coba jalanin dan buka browser lagi. Kamu bakal dapat halaman kosong — +tapi sekarang server kita udah bener-bener balas request + +### Balikin HTML Beneran + +Sekarang kita balikin halaman HTML beneran. Bikin file baru _hello.html_ di root +project (bukan di _src_). Isi bebas, contohnya kayak Listing 21-4. + +<Listing number="21-4" file-name="hello.html" caption="Contoh HTML yang bakal dikirim sebagai response"> + +```html +{{#include ../listings/ch21-web-server/listing-21-05/hello.html}} +``` + +</Listing> + +Sekarang ubah `handle_connection` jadi kayak Listing 21-5 supaya: + +- baca file HTML +- masukin ke response body +- kirim ke client + +<Listing number="21-5" file-name="src/main.rs" caption="Ngirim isi *hello.html* sebagai body response"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-05/src/main.rs:here}} +``` + +</Listing> + +Sekarang jalankan `cargo run`, buka browser ke _127.0.0.1:7878_, dan halaman +HTML kamu bakal muncul + +Saat ini kita masih ngabaikan isi request dan selalu balikin file yang sama, +walaupun user akses path lain. Jadi server kita masih “ polos banget”. + +### Validasi Request & Respon Selektif + +Sekarang kita bikin server cuma balikin HTML kalau request-nya ke `/`. Kalau +selain itu, kita balikin error. Edit `handle_connection` kayak Listing 21-6. + +<Listing number="21-6" file-name="src/main.rs" caption="Ngebedain request ke */* sama selain itu"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-06/src/main.rs:here}} +``` + +</Listing> + +Kita cuma baca baris pertama request, cek apakah sama dengan GET `/`. Kalau iya +→ balikin html. Kalau enggak → nanti kita isi else-nya. + +Kalau sekarang kamu request: + +- `/` → dapet HTML +- selain itu → error koneksi + +Sekarang lanjut, kita tambahin response 404 kayak Listing 21-7. + +<Listing number="21-7" file-name="src/main.rs" caption="Balikin 404 + halaman error kalau bukan */*"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-07/src/main.rs:here}} +``` + +</Listing> + +Bikin file _404.html_ juga (contohnya Listing 21-8). + +<Listing number="21-8" file-name="404.html" caption="Contoh halaman error buat response 404"> + +```html +{{#include ../listings/ch21-web-server/listing-21-07/404.html}} +``` + +</Listing> + +Sekarang: + +- buka `/` → dapet hello.html +- buka `/apa-aja` → dapet halaman 404 + +### Sedikit Refactoring + +Sekarang `if` dan `else` kita agak banyak duplikasi: dua-duanya masih baca file +dan kirim stream. Bedanya cuma status dan nama file. + +Mari kita ringkas kayak Listing 21-9. + +<Listing number="21-9" file-name="src/main.rs" caption="Ngerapihin kode biar lebih clean dan gak duplikatif"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-09/src/main.rs:here}} +``` + +</Listing> + +Sekarang lebih clean, gampang dibaca, dan gampang di-maintain. + +Keren! Sekarang kita punya web server sederhana, sekitar 40 baris Rust: + +- bisa nerima koneksi +- baca request +- balikin halaman normal +- balikin halaman 404 kalau salah path + +Tapi sekarang servernya masih **single-threaded**, artinya cuma bisa handle satu +request dalam satu waktu. Di bagian selanjutnya kita bakal lihat kenapa ini +masalah kalau ada request lambat, dan gimana cara bikin servernya bisa handle +banyak request sekaligus. diff --git a/src/ch21-02-multithreaded.md b/src/ch21-02-multithreaded.md new file mode 100644 index 0000000000..d2bc81a80f --- /dev/null +++ b/src/ch21-02-multithreaded.md @@ -0,0 +1,380 @@ +<!-- Old headings. Do not remove or links may break. --> + +<a id="turning-our-single-threaded-server-into-a-multithreaded-server"></a> +<a id="from-single-threaded-to-multithreaded-server"></a> + +## Dari Server Single-Threaded ke Multithreaded + +Sekarang server kita masih ngeproses request **satu per satu**. Artinya, server +gak bakal proses koneksi kedua sebelum koneksi pertama selesai. Kalau server +dapet makin banyak request, eksekusi model _serial_ kayak gini makin gak ideal. +Kalau ada satu request yang prosesnya lama, request-request berikutnya harus +nunggu sampai yang lama selesai, bahkan kalau request barunya sebenernya bisa +diproses cepat. Kita bakal benerin ini, tapi sebelumnya kita lihat dulu +masalahnya secara langsung. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="simulating-a-slow-request-in-the-current-server-implementation"></a> + +### Simulasi Request yang Lambat + +Kita bakal lihat gimana satu request lambat bisa ngeganggu request lain di +server kita sekarang. Listing 21-10 nambahin handler buat request ke _/sleep_ +yang bakal nyimulasikan respons lambat dengan **delay 5 detik** sebelum +ngerespon. + +<Listing number="21-10" file-name="src/main.rs" caption="Ngesimulasikan request lambat dengan `sleep` selama lima detik"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-10/src/main.rs:here}} +``` + +</Listing> + +Sekarang kita ganti dari `if` ke `match` karena udah ada tiga kondisi. Kita +harus match langsung ke _slice_ dari `request_line` buat bandingin dengan +literal string; `match` gak otomatis melakukan referencing/dereferencing kayak +pengecekan `==`. + +Arm pertama sama kayak blok `if` di Listing 21-9. Arm kedua buat request ke +_/sleep_. Kalau dapet request ini, server bakal tidur 5 detik dulu baru kirim +HTML sukses. Arm ketiga sama kayak blok `else` di Listing 21-9. + +Di sini keliatan banget server kita masih sangat sederhana—library beneran tentu +punya cara lebih rapi buat handle banyak route + +Sekarang jalanin server pakai `cargo run`. Buka dua tab browser: + +- _[http://127.0.0.1:7878](http://127.0.0.1:7878)_ +- _[http://127.0.0.1:7878/sleep](http://127.0.0.1:7878/sleep)_ + +Kalau buka `/` beberapa kali, responsnya bakal cepat. Tapi kalau buka `/sleep`, +lalu coba buka `/`, kamu bakal lihat kalau `/` **ikut nunggu** 5 detik sampai +`/sleep` selesai dulu. + +Ada banyak cara buat ngatasi antrean request kayak gini, termasuk pakai async +kayak di Chapter 17, tapi di sini kita bakal pakai **thread pool**. + +### Ningkatin Throughput dengan Thread Pool + +**Thread pool** itu kumpulan thread yang udah dibuat duluan dan siap kerja. +Ketika ada task masuk, salah satu thread di pool bakal ditugasin ngerjain. +Thread lain tetap standby buat task berikutnya. Kalau tugas selesai, thread +balik lagi ke pool. + +Dengan ini server bisa proses beberapa koneksi sekaligus, jadi throughput +meningkat. + +Kita bakal batasi jumlah thread biar aman dari DoS attack. Kalau tiap request +bikin thread baru tanpa batas, orang iseng tinggal spam 10 juta request dan +server kamu tamat + +Jadi: + +- kita punya jumlah thread tetap +- request masuk dimasukin ke queue +- tiap thread ambil job dari queue +- kerjain +- balik ngantri lagi + +Dengan ini kita bisa handle sampai **N request paralel** (di mana N = jumlah +thread). Kalau semuanya lagi sibuk ngerjain task lama, request baru tetap +ngantri, tapi pool kita jauh lebih kuat dibanding satu thread doang. + +Ini cuma satu dari banyak teknik buat naikin performa server. Kamu juga bisa +explore: + +- fork/join +- async I/O single-threaded +- async I/O multithreaded + +Karena Rust itu low-level friendly, semua itu memungkinkan. + +Sebelum implementasi thread pool, kita pikirin dulu **seharusnya API-nya seperti +apa**. Kayak biasa, kita tulis dulu “cara pakainya”, baru bangun +implementasinya. + +Kali ini kita pakai gaya **compiler-driven development**: tulis dulu kode yang +kita pengen, biarin compiler marah, terus kita perbaiki berdasarkan errornya + +Tapi sebelum itu, kita lihat dulu pendekatan naive sebagai titik awal. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="code-structure-if-we-could-spawn-a-thread-for-each-request"></a> + +#### Bikin Thread Baru untuk Tiap Request + +Pertama bayangin kalau tiap koneksi kita bikin thread baru. Ini bukan solusi +akhir karena jelas bakal bahaya, tapi ini titik awal buat bikin server +multithreaded. + +Listing 21-11 nunjukin perubahan di `main`. + +<Listing number="21-11" file-name="src/main.rs" caption="Bikin thread baru buat tiap stream"> + +```rust,no_run +{{#rustdoc_include ../listings/ch21-web-server/listing-21-11/src/main.rs:here}} +``` + +</Listing> + +Kayak yang kamu pelajari di Chapter 16, `thread::spawn` bakal bikin thread baru +dan ngejalanin closure di dalamnya. + +Kalau kamu coba jalanin ini, buka `/sleep`, terus buka `/` di tab lain, kamu +bakal lihat sekarang `/` **gak ikut nunggu lagi**. + +Tapi ya balik lagi: kalau request jutaan, thread jutaan juga… system kamu bisa +langsung KO. + +Dan ya, ini juga kasus pas banget di mana **async/await** bersinar Tapi sekarang +kita fokus ke thread pool dulu. + +<!-- Old headings. Do not remove or links may break. --> + +<a id="creating-a-similar-interface-for-a-finite-number-of-threads"></a> + +#### Bikin Jumlah Thread yang Terbatas + +Kita pengen API thread pool tetap mirip biar gampang migrasinya. + +Listing 21-12 nunjukin API idealnya: + +<Listing number="21-12" file-name="src/main.rs" caption="Interface `ThreadPool` yang kita pengen"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch21-web-server/listing-21-12/src/main.rs:here}} +``` + +</Listing> + +Kita bikin: + +```rust +let pool = ThreadPool::new(4); +``` + +Lalu pakai: + +```rust +pool.execute(|| { + handle_connection(stream); +}); +``` + +Mirip `thread::spawn`, tapi jumlah thread fix. + +Kodenya belum bisa compile—dan emang sengaja. Kita biarin compiler jadi mentor +kita + +<!-- Old headings. Do not remove or links may break. --> + +<a id="building-the-threadpool-struct-using-compiler-driven-development"></a> + +#### Ngebangun `ThreadPool` dengan Compiler-Driven Development + +Masukin kode Listing 21-12, jalanin `cargo check`. + +Error pertama: + +```console +{{#include ../listings/ch21-web-server/listing-21-12/output.txt}} +``` + +Compiler bilang: “Bro, `ThreadPool` gak ada tuh” + +Oke, kita bikin library dulu. + +Bikin _src/lib.rs_: + +<Listing file-name="src/lib.rs"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/no-listing-01-define-threadpool-struct/src/lib.rs}} +``` + +</Listing> + +Import ke main: + +<Listing file-name="src/main.rs"> + +```rust,ignore +{{#rustdoc_include ../listings/ch21-web-server/no-listing-01-define-threadpool-struct/src/main.rs:here}} +``` + +Cek lagi, error berikutnya bilang: “`new` gak ada” + +Kita tambahin: + +<Listing file-name="src/lib.rs"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/no-listing-02-impl-threadpool-new/src/lib.rs}} +``` + +</Listing> + +Kenapa `usize`? Karena jumlah thread gak mungkin negatif, dan dipakai buat +ukuran koleksi. + +Cek lagi, sekarang error: “`execute` gak ada” + +Kita definisikan dulu skeleton-nya: + +<Listing file-name="src/lib.rs"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/no-listing-03-define-execute/src/lib.rs:here}} +``` + +</Listing> + +Kita pakai `FnOnce + Send + 'static` biar closure aman dipindahin antar thread. + +Dan yea, akhirnya compile Walau… servernya masih gak ngapa-ngapain + +> Jadi, “Kalau Rust compile berarti pasti jalan” itu gak selalu benar ya + +#### Validasi Jumlah Thread di `new` + +Pool dengan 0 thread itu konyol, jadi kita proteksi: + +<Listing number="21-13" file-name="src/lib.rs" caption="`ThreadPool::new` panic kalau size = 0"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/listing-21-13/src/lib.rs:here}} +``` + +</Listing> + +#### Nyediain Tempat Buat Nyimpen Thread + +Kita butuh nyimpen thread. `thread::spawn` balikin `JoinHandle`, jadi kita +simpen itu. + +Listing 21-14: + +<Listing number="21-14" file-name="src/lib.rs" caption="Bikin vector buat nyimpen thread"> + +```rust,ignore,not_desired_behavior +{{#rustdoc_include ../listings/ch21-web-server/listing-21-14/src/lib.rs:here}} +``` + +</Listing> + +Sekarang compile lagi. Masih aman. + +<a id ="a-worker-struct-responsible-for-sending-code-from-the-threadpool-to-a-thread"></a> + +#### Ngirim Kode dari `ThreadPool` ke Thread + +Masalah: `thread::spawn` butuh closure langsung. Tapi kita pengen thread standby +dulu, nunggu job dikirim nantinya. + +Solusinya: kita bikin struct **Worker**. + +Worker itu kayak pegawai restoran: nunggu order, kalau ada → kerjain. + +Plan: + +1. bikin `Worker` +2. `ThreadPool` sekarang nyimpen `Vec<Worker>` +3. tiap worker punya thread sendiri +4. kita kasih id buat debugging + +Listing 21-15: + +<Listing number="21-15" file-name="src/lib.rs" caption="`ThreadPool` sekarang nyimpen `Worker` bukan langsung thread"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/listing-21-15/src/lib.rs:here}} +``` + +</Listing> + +Sekarang worker udah ada, tapi belum ngejalanin job. + +#### Ngirim Job ke Thread Lewat Channel + +Di sini kita pakai **channel** (Chapter 16). + +Flow-nya: + +1. pool punya sender +2. worker punya receiver +3. `execute()` kirim job +4. worker terima job +5. worker jalanin job + +Listing 21-16: + +<Listing number="21-16" file-name="src/lib.rs" caption="ThreadPool nyimpen sender channel `Job`"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/listing-21-16/src/lib.rs:here}} +``` + +</Listing> + +Kita coba oper receiver ke tiap worker (Listing 21-17), tapi error karena +channel cuma boleh 1 consumer. + +Jadi: pakai `Arc<Mutex<T>>` + +Listing 21-18: + +<Listing number="21-18" file-name="src/lib.rs" caption="Share receiver pakai Arc + Mutex"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/listing-21-18/src/lib.rs:here}} +``` + +</Listing> + +Compile + +#### Implementasi `execute` + +Sekarang bikin Job sebagai trait object: + +Listing 21-19: + +<Listing number="21-19" file-name="src/lib.rs" caption="Bikin alias `Job` dan kirim lewat channel"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/listing-21-19/src/lib.rs:here}} +``` + +</Listing> + +Sekarang worker harus jalanin job: + +Listing 21-20: + +<Listing number="21-20" file-name="src/lib.rs" caption="Worker nerima dan ngejalanin job"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/listing-21-20/src/lib.rs:here}} +``` + +</Listing> + +Dan… Thread pool kita resmi jalan + +Coba `cargo run` terus spam request. + +Outputnya bakal keliatan worker ngerjain job bergantian. + +Catatan penting: Kalau kamu penasaran versi `while let` (21-21), itu kelihatan +keren tapi salah perilaku. Karena Mutex lock-nya kepegang terlalu lama. + +Sekarang: + +- thread pool jalan +- maksimal cuma 4 thread +- request lambat gak ganggu request lain + +Server kita udah jauh lebih “dewasa” diff --git a/src/ch21-03-graceful-shutdown-and-cleanup.md b/src/ch21-03-graceful-shutdown-and-cleanup.md new file mode 100644 index 0000000000..6fc9e1d40e --- /dev/null +++ b/src/ch21-03-graceful-shutdown-and-cleanup.md @@ -0,0 +1,210 @@ +## Shutdown Santai & Cleanup yang Rapi + +Kode di Listing 21-20 sekarang sudah bener-bener nge-handle request secara async +pakai thread pool seperti yang kita pengen. Tapi kita masih dapet warning soal +field `workers`, `id`, dan `thread` yang gak dipakai langsung—ini jadi reminder +kalau kita sebenernya belum beresin proses cleanup. Kalau kita ngehentikan main +thread pakai cara barbar <kbd>ctrl</kbd>-<kbd>C</kbd>, semua thread lain +langsung ikut mati juga, bahkan kalau mereka lagi ngerjain request. + +Selanjutnya, kita bakal implement `Drop` trait buat manggil `join` di tiap +thread di pool, supaya mereka bisa selesain request yang lagi dikerjain sebelum +ditutup. Habis itu, kita bakal bikin mekanisme buat ngasih sinyal ke thread +kalau mereka harus berhenti nerima request baru dan shutdown. Biar keliatan +efeknya, nanti kita ubah server kita supaya cuma nerima dua request sebelum +shutdown dengan cara yang “baik-baik”. + +Perlu diperhatiin juga: semua yang kita lakukan di sini **gak ngubah bagian kode +yang ngejalanin closure**. Jadi kalaupun thread pool ini dipakai buat async +runtime, bagian ini bakal tetap sama aja. + +### Implementasi `Drop` Trait di `ThreadPool` + +Kita mulai dengan implement `Drop` buat thread pool. Waktu pool di-drop, semua +threadnya harus di-`join` biar bisa beresin kerjaannya dulu. Listing 21-22 +nunjukin percobaan pertama implementasi `Drop`. Tapi kode ini belum bakal jalan +sempurna. + +<Listing number="21-22" file-name="src/lib.rs" caption="Nge-join tiap thread waktu thread pool keluar scope"> + +```rust,ignore,does_not_compile +{{#rustdoc_include ../listings/ch21-web-server/listing-21-22/src/lib.rs:here}} +``` + +</Listing> + +Pertama, kita loop ke semua `workers` di thread pool. Kita pakai `&mut` karena +`self` itu reference mutable, dan kita juga bakal perlu mutate tiap `worker`. +Buat tiap `worker`, kita print pesan kalau `Worker` itu lagi shutdown, terus +kita panggil `join` di thread punya dia. Kalau `join` gagal, kita `unwrap` biar +langsung panic aja dan shutdown gak elegan. + +Ini error yang muncul pas kita compile: + +```console +{{#include ../listings/ch21-web-server/listing-21-22/output.txt}} +``` + +Error-nya bilang kita gak bisa manggil `join` karena kita cuma punya mutable +borrow ke tiap `worker`, sedangkan `join` butuh ownership. Jadi kita harus +mindahin thread keluar dari `Worker`, supaya bisa dikonsumsi sama `join`. + +Satu cara adalah kayak yang kita lakuin di Listing 18-15. Kalau `Worker` nyimpen +`Option<thread::JoinHandle<()>>`, kita bisa `take` nilainya keluar dari `Some` +dan ninggalin `None`. Jadi selama `Worker` masih jalan, dia punya `Some`, dan +waktu dibersihin, kita ubah jadi `None` supaya dia udah gak punya thread lagi. + +Tapi masalahnya, ini cuma kepake pas drop aja. Di luar itu, kita jadi ribet +harus selalu nge-handle `Option` tiap kali akses `worker.thread`. Rust emang +sering pakai `Option`, tapi kalau cuma buat “ngakalin” kasus kayak gini, lebih +baik cari solusi lain biar kode tetap clean dan minim error. + +Untungnya, ada alternatif yang lebih cakep: method `Vec::drain`. Method ini +nerima range, hapus item di range itu, dan balikin iterator item yang dihapus. +Kalau kita pakai `..`, berarti hapus semua. + +Jadi kita update implementasi `drop` di `ThreadPool` jadi kayak gini: + +<Listing file-name="src/lib.rs"> + +```rust +{{#rustdoc_include ../listings/ch21-web-server/no-listing-04-update-drop-definition/src/lib.rs:here}} +``` + +</Listing> + +Ini nge-fix error compiler tanpa perlu ubah kode lain. Tapi note penting: karena +`drop` bisa kepanggil pas program lagi panic, `unwrap` di dalamnya juga bisa +panic dan bikin “double panic”, yang bikin program langsung crash total dan +berhenti cleanup. Buat contoh buku ini masih oke lah, tapi di production jelas +gak direkomendasiin. + +### Ngasih Sinyal ke Thread Biar Berhenti Dengerin Job + +Dengan semua perubahan tadi, kode kita sekarang bisa compile tanpa warning. +Masalahnya, masih belum sesuai yang kita mau. Intinya ada di logic closure yang +jalan di thread `Worker`: saat ini, walaupun kita panggil `join`, threadnya gak +bakal berhenti karena mereka `loop` selamanya nunggu job. Kalau kita drop +`ThreadPool` sekarang, main thread bakal nge-freeze selamanya nunggu thread +pertama selesai. + +Buat benerin, kita harus ubah implementasi `drop` di `ThreadPool`, lalu ubah +loop di `Worker`. + +Pertama, kita ubah implementasi `drop` biar `sender` di-drop dulu sebelum nunggu +thread selesai. Listing 21-23 nunjukin perubahan buat nge-drop `sender`. Beda +sama thread tadi, di sini kita **butuh** `Option` biar bisa mindahin `sender` +keluar dari `ThreadPool` pakai `Option::take`. + +<Listing number="21-23" file-name="src/lib.rs" caption="Nge-drop `sender` dulu sebelum nge-join thread `Worker`"> + +```rust,noplayground,not_desired_behavior +{{#rustdoc_include ../listings/ch21-web-server/listing-21-23/src/lib.rs:here}} +``` + +</Listing> + +Waktu `sender` di-drop, channel otomatis ketutup, yang artinya gak bakal ada +pesan baru dikirim. Setelah itu, semua `recv` di loop `Worker` bakal balikin +error. Di Listing 21-24, kita ubah loop `Worker` biar keluar dengan santai kalau +`recv` error. Dengan begitu, thread selesai, dan `drop` bisa manggil `join` +tanpa ke-lock selamanya. + +<Listing number="21-24" file-name="src/lib.rs" caption="Keluar dari loop kalau `recv` balikin error"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/listing-21-24/src/lib.rs:here}} +``` + +</Listing> + +Biar kelihatan jelas efeknya, kita ubah `main` supaya server cuma nerima dua +request sebelum shutdown santai, kayak di Listing 21-25. + +<Listing number="21-25" file-name="src/main.rs" caption="Shutdown server setelah serve dua request dengan keluar dari loop"> + +```rust,ignore +{{#rustdoc_include ../listings/ch21-web-server/listing-21-25/src/main.rs:here}} +``` + +</Listing> + +Jelas di dunia nyata server gak mungkin cuma nerima dua request doang Ini +cuma buat ngebuktiin kalau graceful shutdown kita udah berfungsi. + +Method `take` adalah bagian dari `Iterator`, dan dia ngebatesin iterasi ke dua +item pertama aja. Begitu `main` selesai, `ThreadPool` keluar scope dan `drop` +jalan. + +Coba jalanin: + +```console +$ cargo run + Compiling hello v0.1.0 (file:///projects/hello) + Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.41s + Running `target/debug/hello` +Worker 0 got a job; executing. +Shutting down. +Shutting down worker 0 +Worker 3 got a job; executing. +Worker 1 disconnected; shutting down. +Worker 2 disconnected; shutting down. +Worker 3 disconnected; shutting down. +Worker 0 disconnected; shutting down. +Shutting down worker 1 +Shutting down worker 2 +Shutting down worker 3 +``` + +Urutan ID `Worker` mungkin beda di kamu, tapi alurnya sama: `Worker` 0 dan 3 +dapet dua request pertama. Server berhenti nerima koneksi setelah request kedua, +dan `Drop` mulai jalan bahkan sebelum `Worker 3` mulai kerja. Waktu `sender` +di-drop, semua `Worker` disconnect dan shutdown. Mereka print pesan disconnect, +terus thread pool `join` mereka satu-satu. + +Menariknya di eksekusi ini: ThreadPool nge-drop `sender`, lalu sebelum `Worker` +dapet error dari `recv`, kita udah coba `join Worker 0`. Karena dia belum error, +main thread nunggu. Sementara itu `Worker 3` lanjut kerja dan thread lain dapet +error dan keluar. Begitu `Worker 0` selesai, sisanya udah pada kelar duluan. + +Mantap! Sekarang kita udah selesai projectnya: + +- web server basic +- support thread pool +- async-style handling +- bisa graceful shutdown +- semua thread ke-cleanup dengan baik + +Ini full kode finalnya: + +<Listing file-name="src/main.rs"> + +```rust,ignore +{{#rustdoc_include ../listings/ch21-web-server/no-listing-07-final-code/src/main.rs}} +``` + +</Listing> + +<Listing file-name="src/lib.rs"> + +```rust,noplayground +{{#rustdoc_include ../listings/ch21-web-server/no-listing-07-final-code/src/lib.rs}} +``` + +</Listing> + +Kalau mau lanjut improve, ini ide-idenya: + +- Tambahin dokumentasi ke `ThreadPool` dan method-methodnya. +- Tambahin testing. +- Ganti semua `unwrap` jadi error handling yang lebih proper. +- Pakai `ThreadPool` buat tugas selain web server. +- Coba bandingin dengan thread pool crate dari [crates.io](https://crates.io/), + bikin web server yang sama, lalu bandingin API dan robustness-nya. + +## Ringkasan + +Keren banget! Kamu udah sampai akhir buku Makasih udah nemenin perjalanan +Rust ini. Sekarang kamu udah siap bikin project Rust sendiri atau contribute ke +project orang lain. Jangan lupa, komunitas Rust itu ramah banget dan selalu siap +bantu kalau kamu nemu masalah di perjalanan Rust kamu diff --git a/src/foreword.md b/src/foreword.md index 2265e27142..706e4ab8e4 100644 --- a/src/foreword.md +++ b/src/foreword.md @@ -1,41 +1,47 @@ # Foreword -It wasn’t always so clear, but the Rust programming language is fundamentally -about *empowerment*: no matter what kind of code you are writing now, Rust -empowers you to reach farther, to program with confidence in a wider variety of -domains than you did before. +The Rust programming language has come a long way in a few short years, from +its creation and incubation by a small and nascent community of enthusiasts, to +becoming one of the most loved and in-demand programming languages in the +world. Looking back, it was inevitable that the power and promise of Rust would +turn heads and gain a foothold in systems programming. What was not inevitable +was the global growth in interest and innovation that permeated through open +source communities and catalyzed wide-scale adoption across industries. -Take, for example, “systems-level” work that deals with low-level details of -memory management, data representation, and concurrency. Traditionally, this -realm of programming is seen as arcane, accessible only to a select few who -have devoted the necessary years learning to avoid its infamous pitfalls. And -even those who practice it do so with caution, lest their code be open to -exploits, crashes, or corruption. +At this point in time, it is easy to point to the wonderful features that Rust +has to offer to explain this explosion in interest and adoption. Who doesn’t +want memory safety, *and* fast performance, *and* a friendly compiler, *and* +great tooling, among a host of other wonderful features? The Rust language you +see today combines years of research in systems programming with the practical +wisdom of a vibrant and passionate community. This language was designed with +purpose and crafted with care, offering developers a tool that makes it easier +to write safe, fast, and reliable code. -Rust breaks down these barriers by eliminating the old pitfalls and providing a -friendly, polished set of tools to help you along the way. Programmers who need -to “dip down” into lower-level control can do so with Rust, without taking on -the customary risk of crashes or security holes, and without having to learn -the fine points of a fickle toolchain. Better yet, the language is designed to -guide you naturally towards reliable code that is efficient in terms of speed -and memory usage. +But what makes Rust truly special is its roots in empowering you, the user, to +achieve your goals. This is a language that wants you to succeed, and the +principle of empowerment runs through the core of the community that builds, +maintains, and advocates for this language. Since the previous edition of this +definitive text, Rust has further developed into a truly global and trusted +language. The Rust Project is now robustly supported by the Rust Foundation, +which also invests in key initiatives to ensure that Rust is secure, stable, +and sustainable. -Programmers who are already working with low-level code can use Rust to raise -their ambitions. For example, introducing parallelism in Rust is a relatively -low-risk operation: the compiler will catch the classical mistakes for you. And -you can tackle more aggressive optimizations in your code with the confidence -that you won’t accidentally introduce crashes or vulnerabilities. +This edition of *The Rust Programming Language* is a comprehensive update, +reflecting the language’s evolution over the years and providing valuable new +information. But it is not just a guide to syntax and libraries—it’s an +invitation to join a community that values quality, performance, and thoughtful +design. Whether you’re a seasoned developer looking to explore Rust for the +first time or an experienced Rustacean looking to refine your skills, this +edition offers something for everyone. -But Rust isn’t limited to low-level systems programming. It’s expressive and -ergonomic enough to make CLI apps, web servers, and many other kinds of code -quite pleasant to write — you’ll find simple examples of both later in the -book. Working with Rust allows you to build skills that transfer from one -domain to another; you can learn Rust by writing a web app, then apply those -same skills to target your Raspberry Pi. +The Rust journey has been one of collaboration, learning, and iteration. The +growth of the language and its ecosystem is a direct reflection of the vibrant, +diverse community behind it. The contributions of thousands of developers, from +core language designers to casual contributors, are what make Rust such a +unique and powerful tool. By picking up this book, you’re not just learning a +new programming language—you’re joining a movement to make software better, +safer, and more enjoyable to work with. -This book fully embraces the potential of Rust to empower its users. It’s a -friendly and approachable text intended to help you level up not just your -knowledge of Rust, but also your reach and confidence as a programmer in -general. So dive in, get ready to learn—and welcome to the Rust community! +Welcome to the Rust community! -— Nicholas Matsakis and Aaron Turon +- Bec Rumbul, Executive Director of the Rust Foundation diff --git a/src/img/trpl04-05.svg b/src/img/trpl04-05.svg index b4bf2ebee8..f3c6e8a82b 100644 --- a/src/img/trpl04-05.svg +++ b/src/img/trpl04-05.svg @@ -1,87 +1,95 @@ <?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> -<!-- Generated by graphviz version 2.40.1 (20161225.0304) +<!-- Generated by graphviz version 12.1.2 (20240928.0832) --> -<!-- Title: %3 Pages: 1 --> +<!-- Pages: 1 --> <svg - viewBox="0.00 0.00 1500.00 650.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> -<g id="graph0" class="graph" transform="scale(4.1667 4.1667) rotate(0) translate(4 152)"> -<title>%3 - - - -table0 - -s - -name - -value - -ptr - - - - -table1 - -s1 - -name - -value - -ptr - - -len - -5 - -capacity - -5 + viewBox="0.00 0.00 1038.00 1342.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> + + + +cluster_heap - - -table0:c->table1:borrowee - - + + +s + +s + +name + +value + +ptr + + +len + +4 + +capacity + +4 - + -table2 - -index - -value - -0 - -h - -1 - -e - -2 - -l - -3 - -l - -4 - -o +ahoy + +index + +value + +0 + +a + +1 + +h + +2 + +o + +3 + +y - + -table1:c->table2:pointee - - +s:c->ahoy:pointee + + + + + +hello + + +index + +value + +0 + +h + +1 + +e + +2 + +l + +3 + +l + +4 + +o diff --git a/src/img/trpl04-06.svg b/src/img/trpl04-06.svg index e64415fe43..b4bf2ebee8 100644 --- a/src/img/trpl04-06.svg +++ b/src/img/trpl04-06.svg @@ -5,111 +5,83 @@ --> - + viewBox="0.00 0.00 1500.00 650.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> + %3 - + table0 - -world - -name - -value - -ptr - - -len - -5 + +s + +name + +value + +ptr + - - -table4 - -index - -value - -0 - -h - -1 - -e - -2 - -l - -3 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a/src/img/trpl14-01.png b/src/img/trpl14-01.png index d7deaaf952..bcd5491ff1 100644 Binary files a/src/img/trpl14-01.png and b/src/img/trpl14-01.png differ diff --git a/src/img/trpl14-02.png b/src/img/trpl14-02.png index 121801b763..5a102722d9 100644 Binary files a/src/img/trpl14-02.png and b/src/img/trpl14-02.png differ diff --git a/src/img/trpl14-03.png b/src/img/trpl14-03.png index cf5a15c41a..31850a72e0 100644 Binary files a/src/img/trpl14-03.png and b/src/img/trpl14-03.png differ diff --git a/src/img/trpl14-04.png b/src/img/trpl14-04.png index dc1caaba9c..718d47b6ba 100644 Binary files a/src/img/trpl14-04.png and b/src/img/trpl14-04.png differ diff --git a/src/img/trpl17-01.svg b/src/img/trpl17-01.svg new file mode 100644 index 0000000000..483bf7216d --- /dev/null +++ b/src/img/trpl17-01.svg @@ -0,0 +1,110 @@ + + + + + + + + +cluster_task_a + +Task A + + +cluster_task_b + +Task B + + + +A1 + +A1 + + + +A2 + +A2 + + + + +B1 + +B1 + + + +A1->B1 + + + + + +A3 + +A3 + + + + +B2 + +B2 + + + +A2->B2 + + + + + +A4 + +A4 + + + + +A3->A4 + + + + + + + + +B3 + +B3 + + + +A4->B3 + + + + + + + +B1->A2 + + + + + + +B2->A3 + + + + + + diff --git a/src/img/trpl17-02.svg b/src/img/trpl17-02.svg new file mode 100644 index 0000000000..5c32a1a262 --- /dev/null +++ b/src/img/trpl17-02.svg @@ -0,0 +1,96 @@ + + + + + + + + +cluster_ColleagueB + +Task B + + +cluster_ColleagueA + +Task A + + + +B1 + +B1 + + + +B2 + +B2 + + + +B1->B2 + + + + + +B3 + +B3 + + + +B2->B3 + + + + + + + +A1 + +A1 + + + +A2 + +A2 + + + +A1->A2 + + + + + +A3 + +A3 + + + +A2->A3 + + + + + +A4 + +A4 + + + +A3->A4 + + + + + diff --git a/src/img/trpl17-03.svg b/src/img/trpl17-03.svg new file mode 100644 index 0000000000..ad105a5830 --- /dev/null +++ b/src/img/trpl17-03.svg @@ -0,0 +1,110 @@ + + + + + + + + +cluster_ColleagueB + +Task A + + +cluster_ColleagueA + +Task B + + + +A1 + +A1 + + + +A2 + +A2 + + + +A1->A2 + + + + + + +A2->A0_1:c + + + + + + +A3 + +A3 + + + +A0_1->A3 + + + + + + + +B1 + +B1 + + + +B2 + +B2 + + + +B1->B2 + + + + + +B3 + +B3 + + + +B2->B3 + + + + + +B3->A3 + + + + + +B4 + +B4 + + + +B3->B4 + + + + + diff --git a/src/img/trpl17-04.svg b/src/img/trpl17-04.svg new file mode 100644 index 0000000000..fed6c36040 --- /dev/null +++ b/src/img/trpl17-04.svg @@ -0,0 +1,30 @@ + + + + + + + + + +fut1 + +fut1 + +0 + +1 + +   + + + +fut1:c->fut1:target + + + + + diff --git a/src/img/trpl17-05.svg b/src/img/trpl17-05.svg new file mode 100644 index 0000000000..e3472baa7c --- /dev/null +++ b/src/img/trpl17-05.svg @@ -0,0 +1,46 @@ + + + + + + + + +%3 + + + +fut1 + + +fut1 + +? + +? + +? + + + +fut2 + +fut2 + +0 + +1 + + + + + +fut2:c->fut1:c + + + + + diff --git a/src/img/trpl17-06.svg b/src/img/trpl17-06.svg new file mode 100644 index 0000000000..443bb568dc --- /dev/null +++ b/src/img/trpl17-06.svg @@ -0,0 +1,69 @@ + + + + + + + + +cluster_box + + +cluster_box_internal + +b1 + + +cluster_deref + +pinned + + + +pinned_box + +Pin + + + + + +pin + + + + +pinned_box:c->pin + + + + +box + +fut + +0 + + + +... + +1 + + + +pin->box:target + + + + + +box:c->box:internal + + + + + diff --git a/src/img/trpl17-07.svg b/src/img/trpl17-07.svg new file mode 100644 index 0000000000..712e3006f6 --- /dev/null +++ b/src/img/trpl17-07.svg @@ -0,0 +1,86 @@ + + + + + + + + +cluster_not_fut + + +cluster_boxes + + +cluster_box_1 + + +cluster_box_2_internal + +b1 + + +cluster_box_2 + + +cluster_box_2_internal + +b2 + + +cluster_target + +pinned + + + +pin + +Pin + + + + + + + +box2 + + + + +pin:c->box2 + + + + + +fut + +fut + +0 + + + +... + +1 + + + +box2->fut:target + + + + + +fut:c->fut:internal + + + + + diff --git a/src/img/trpl17-08.svg b/src/img/trpl17-08.svg new file mode 100644 index 0000000000..b2275ac19f --- /dev/null +++ b/src/img/trpl17-08.svg @@ -0,0 +1,57 @@ + + + + + + + + +cluster_deref + +String + + + +pinned_box + +Pin + + + + + +pin + + + + +pinned_box:c->pin + + + + +fut + +5usize + +h + +e + +l + +l + +o + + + +pin->fut:target + + + + + diff --git a/src/img/trpl17-09.svg b/src/img/trpl17-09.svg new file mode 100644 index 0000000000..997d9b82e1 --- /dev/null +++ b/src/img/trpl17-09.svg @@ -0,0 +1,85 @@ + + + + + + + + +cluster_both + + +cluster_deref + +String + + + +pinned_box + +Pin + + + + + +pin + + + + +pinned_box:c->pin + + + + +string1 + + +s1 + +5usize + +h + +e + +l + +l + +o + + + +string2 + +s2 + +7usize + +g + +o + +o + +d + +b + +y + +e + + + +pin->string2:target + + + + + diff --git a/src/img/trpl20-01.png b/src/img/trpl21-01.png similarity index 100% rename from src/img/trpl20-01.png rename to src/img/trpl21-01.png diff --git a/src/title-page.md b/src/title-page.md index 5f7a7a680a..099ab8d643 100644 --- a/src/title-page.md +++ b/src/title-page.md @@ -1,14 +1,18 @@ # The Rust Programming Language -*by Steve Klabnik and Carol Nichols, with contributions from the Rust Community* +_by Steve Klabnik, Carol Nichols, and Chris Krycho, with contributions from the +Rust Community_ -This version of the text assumes you’re using Rust 1.67.1 (released 2023-02-09) -or later. See the [“Installation” section of Chapter 1][install] -to install or update Rust. +This version of the text assumes you’re using Rust 1.90.0 (released 2025-09-18) +or later with `edition = "2024"` in the *Cargo.toml* file of all projects to +configure them to use Rust 2024 Edition idioms. See the [“Installation” section +of Chapter 1][install] for instructions on installing or +updating Rust, and see [Appendix E][appendix-e] for information +on editions. The HTML format is available online at [https://doc.rust-lang.org/stable/book/](https://doc.rust-lang.org/stable/book/) -and offline with installations of Rust made with `rustup`; run `rustup docs +and offline with installations of Rust made with `rustup`; run `rustup doc --book` to open. Several community [translations] are also available. @@ -17,8 +21,8 @@ This text is available in [paperback and ebook format from No Starch Press][nsprust]. [install]: ch01-01-installation.html -[editions]: appendix-05-editions.html -[nsprust]: https://nostarch.com/rust-programming-language-2nd-edition +[appendix-e]: appendix-05-editions.html +[nsprust]: https://nostarch.com/rust-programming-language-3rd-edition [translations]: appendix-06-translation.html > **🚨 Want a more interactive learning experience? Try out a different version diff --git a/style-guide.md b/style-guide.md index 56677811f4..04dc805ca5 100644 --- a/style-guide.md +++ b/style-guide.md @@ -2,33 +2,33 @@ ## Prose -* Prefer title case for chapter/section headings, ex: `## Generating a Secret +- Prefer title case for chapter/section headings, ex: `## Generating a Secret Number` rather than `## Generating a secret number`. -* Prefer italics over single quotes when calling out a term, ex: `is an +- Prefer italics over single quotes when calling out a term, ex: `is an *associated function* of` rather than `is an ‘associated function’ of`. -* When talking about a method in prose, DO NOT include the parentheses, ex: +- When talking about a method in prose, DO NOT include the parentheses, ex: `read_line` rather than `read_line()`. -* Hard wrap at 80 chars -* Prefer not mixing code and not-code in one word, ex: ``Remember when we wrote +- Hard wrap at 80 chars +- Prefer not mixing code and not-code in one word, ex: ``Remember when we wrote `use std::io`?`` rather than ``Remember when we `use`d `std::io`?`` ## Code -* Add the file name before markdown blocks to make it clear which file we're +- Add the file name before markdown blocks to make it clear which file we're talking about, when applicable. -* When making changes to code, make it clear which parts of the code changed +- When making changes to code, make it clear which parts of the code changed and which stayed the same... not sure how to do this yet -* Split up long lines as appropriate to keep them under 80 chars if possible -* Use `bash` syntax highlighting for command line output code blocks +- Split up long lines as appropriate to keep them under 80 chars if possible +- Use `bash` syntax highlighting for command line output code blocks ## Links Once all the scripts are done: -* If a link shouldn't be printed, mark it to be ignored - * This includes all "Chapter XX" intra-book links, which *should* be links +- If a link shouldn't be printed, mark it to be ignored + - This includes all "Chapter XX" intra-book links, which _should_ be links for the HTML version -* Make intra-book links and stdlib API doc links relative so they work whether +- Make intra-book links and stdlib API doc links relative so they work whether the book is read offline or on docs.rust-lang.org -* Use markdown links and keep in mind that they will be changed into `text at +- Use markdown links and keep in mind that they will be changed into `text at *url*` in print, so word them in a way that it reads well in that format diff --git a/theme/2018-edition.css b/theme/2018-edition.css index b1dcf93641..2276ccbe3e 100644 --- a/theme/2018-edition.css +++ b/theme/2018-edition.css @@ -1,9 +1,9 @@ span.caption { - font-size: .8em; - font-weight: 600; + font-size: 0.8em; + font-weight: 600; } span.caption code { - font-size: 0.875em; - font-weight: 400; + font-size: 0.875em; + font-weight: 400; } diff --git a/theme/listing.css b/theme/listing.css new file mode 100644 index 0000000000..40ae35a5fb --- /dev/null +++ b/theme/listing.css @@ -0,0 +1,8 @@ +figure.listing { + margin: 0; +} + +.listing figcaption { + font-size: 0.8em; + font-weight: 600; +} diff --git a/theme/semantic-notes.css b/theme/semantic-notes.css new file mode 100644 index 0000000000..b6852a0994 --- /dev/null +++ b/theme/semantic-notes.css @@ -0,0 +1,13 @@ +/* + This is copied directly from the styles for blockquotes, because notes were + historically rendered *as* blockquotes. This keeps the presentation of them + identical while updating the presentation. +*/ +.note { + margin: 20px 0; + padding: 0 20px; + color: var(--fg); + background-color: var(--quote-bg); + border-block-start: 0.1em solid var(--quote-border); + border-block-end: 0.1em solid var(--quote-border); +} diff --git a/tools/doc-to-md.sh b/tools/doc-to-md.sh index 8c802a71fa..2b25f3d69f 100755 --- a/tools/doc-to-md.sh +++ b/tools/doc-to-md.sh @@ -22,7 +22,10 @@ directory, so all fixes need to be made in `/src/`. unzip -o "tmp/$filename.docx" -d "tmp/$filename" # Convert to markdown with XSL. xsltproc tools/docx-to-md.xsl "tmp/$filename/word/document.xml" | \ - # Hard wrap at 80 chars at word bourdaries. + # Remove all non-breaking spaces, which NoStarch adds for inline references + # to listings, chapters, etc., but which we don’t care about in the source. + sed "s: : :g" | \ + # Hard wrap at 80 chars at word boundaries. fold -w 80 -s | \ # Remove trailing whitespace and append to the file in the `nostarch` dir for comparison. sed -e "s/ *$//" >> "nostarch/$filename.md" diff --git a/tools/docx-to-md.xsl b/tools/docx-to-md.xsl index 8deec85c92..ca4873348e 100644 --- a/tools/docx-to-md.xsl +++ b/tools/docx-to-md.xsl @@ -25,8 +25,16 @@ + + + + + + + + @@ -130,13 +138,13 @@ - + Filename: - + @@ -223,22 +231,26 @@ - : - + + + + + - + Listing - - + : - + > @@ -249,11 +261,11 @@ > - + > - + > @@ -304,7 +316,11 @@ - : - + + + + + @@ -345,17 +361,17 @@ Unmatched: - + - + ` - + ` @@ -387,19 +403,19 @@ Unmatched: - + - + * - + * @@ -432,8 +448,8 @@ Unmatched: - - + + <sup> diff --git a/tools/generate-preview.sh b/tools/generate-preview.sh new file mode 100755 index 0000000000..a5d9022b9e --- /dev/null +++ b/tools/generate-preview.sh @@ -0,0 +1,6 @@ +#!/usr/bin/env bash + +mdbook build +cp ./tools/preview-robots.txt ./book/robots.txt +ghp-import -m "rebuild GitHub Pages from generated-book" book +git push origin gh-pages diff --git a/tools/nostarch.sh b/tools/nostarch.sh index eec0ac5ea1..7d9c735a80 100755 --- a/tools/nostarch.sh +++ b/tools/nostarch.sh @@ -9,10 +9,12 @@ rm -rf tmp/*.md rm -rf tmp/markdown # Render the book as Markdown to include all the code listings -MDBOOK_OUTPUT__MARKDOWN=1 mdbook build -d tmp +MDBOOK_OUTPUT__MARKDOWN='{}' mdbook build nostarch # Get all the Markdown files -find tmp/markdown -name "${1:-\"\"}*.md" -print0 | \ +# TODO: what was this doing and why?!? +# find tmp/markdown -name "${1:-\"\"}*.md" -print0 | \ +find tmp/markdown -name "*.md" -print0 | \ # Extract just the filename so we can reuse it easily. xargs -0 basename | \ # Remove all links followed by ```, then @@ -21,7 +23,8 @@ while IFS= read -r filename; do < "tmp/markdown/$filename" ./target/release/remove_links \ | ./target/release/link2print \ | ./target/release/remove_markup \ - | ./target/release/remove_hidden_lines > "tmp/$filename" + | ./target/release/remove_hidden_lines \ + | ./target/release/cleanup_blockquotes > "tmp/$filename" done # Concatenate the files into the `nostarch` dir. ./target/release/concat_chapters tmp nostarch diff --git a/tools/preview-robots.txt b/tools/preview-robots.txt new file mode 100644 index 0000000000..1f53798bb4 --- /dev/null +++ b/tools/preview-robots.txt @@ -0,0 +1,2 @@ +User-agent: * +Disallow: / diff --git a/tools/update-editions.sh b/tools/update-editions.sh index bd52bc9c81..c356beb9c3 100755 --- a/tools/update-editions.sh +++ b/tools/update-editions.sh @@ -2,7 +2,18 @@ set -eu -OLD_EDITION=2018 -NEW_EDITION=2021 +# So that we can do this in a single pass, check *here* if there are any “dirty” +# files from Git, and bail if so. +git diff --quiet || { echo "Git working directory is not clean"; exit 1; } -find listings/** -name "Cargo.toml" -exec sed -i '' "s/edition = \"$OLD_EDITION\"/edition = \"$NEW_EDITION\"/g" '{}' \; +OLD_EDITION=2021 +NEW_EDITION=2024 + +# Start by preparing all listings for the edition. +find listings -name "Cargo.toml" -exec cargo fix --allow-dirty --edition --manifest-path '{}' \; + +# Update the edition itself +find listings -name "Cargo.toml" -exec sed -i '' "s/edition = \"$OLD_EDITION\"/edition = \"$NEW_EDITION\"/g" '{}' \; + +# Update all id +find listings -name "Cargo.toml" -exec cargo fix --allow-dirty --edition-idioms --manifest-path {} \; diff --git a/tools/update-rustc.sh b/tools/update-rustc.sh index 45a0ce4f67..7ee40a0e9e 100755 --- a/tools/update-rustc.sh +++ b/tools/update-rustc.sh @@ -2,6 +2,17 @@ set -eu +# Build book `trpl` crate dependency in the location where the listings will go +# looking for it so they can compile correctly. +echo 'Building book dependencies in tmp/packages...' +mkdir -p tmp/packages +cp -r packages/trpl tmp/packages/trpl +cd tmp/packages/trpl + # hide the output; if it fails, debug then. +cargo clean > /dev/null 2>&1 +cargo build > /dev/null 2>&1 +cd - > /dev/null + # Build the book before making any changes for comparison of the output. echo 'Building book into tmp/book-before before updating...' mdbook build -d tmp/book-before @@ -39,14 +50,14 @@ find -s listings -name output.txt -print0 | while IFS= read -r -d '' f; do # Save the previous compile time; we're going to keep it to minimize diff # churn - compile_time=$(sed -E -ne 's/.*Finished (dev|test) \[unoptimized \+ debuginfo] target\(s\) in ([0-9.]*).*/\2/p' "${full_output_path}") + compile_time=$(sed -E -ne "s/.*Finished \`(dev|test)\` profile \[unoptimized \+ debuginfo] target\(s\) in ([0-9.]*).*/\2/p" "${full_output_path}") # Save the hash from the first test binary; we're going to keep it to # minimize diff churn test_binary_hash=$(sed -E -ne 's@.*Running [^[:space:]]+( [^[:space:]\(\)]+)? \(target/debug/deps/[^-]*-([^\s]*)\)@\2@p' "${full_output_path}" | head -n 1) # Act like this is the first time this listing has been built - cargo clean + cargo clean > /dev/null 2>&1 # Run the command in the existing output file cargo_command=$(sed -ne 's/$ \(.*\)/\1/p' "${full_output_path}") @@ -63,9 +74,22 @@ find -s listings -name output.txt -print0 | while IFS= read -r -d '' f; do # instead of a path to the computer of whoever is running this sed -i '' -E -e 's@(Compiling|Checking) ([^\)]*) v0.1.0 (.*)@\1 \2 v0.1.0 (file:///projects/\2)@' "${full_output_path}" + # Likewise, use a "default" installation directory for rustup's install + # location so the version of the source is not a path on the computer of + # whoever is doing the update. This does two substitutions: + # + # - Replaces the path up to `.rustup/toolchains` with `file:///home`, while + # preserving leading spaces and the `-->`. + # - Replaces the version-and-architecture-triple with just the version, so + # e.g. `1.82-aarch64-apple-darwin` becomes `1.82`. + sed -i '' -E -e 's@^([[:space:]]*-->[[:space:]]+).*(\.rustup/toolchains/[[:digit:]]+\.[[:digit:]]+)([^/]*)@\1file:///home/\2@' "${full_output_path}" + + # Similarly, replace Miri paths + sed -i '' -E -e "s@Running \`(.*)\.rustup/toolchains/nightly([^/]*)/bin/cargo-miri runner target/miri/([^/]*)/debug/([^/]*)@Running \`file:///home/.rustup/toolchains/nightly/bin/cargo-miri runner target/miri/debug/\4@" "${full_output_path}" + # Restore the previous compile time, if there is one if [ -n "${compile_time}" ]; then - sed -i '' -E -e "s/Finished (dev|test) \[unoptimized \+ debuginfo] target\(s\) in [0-9.]*/Finished \1 [unoptimized + debuginfo] target(s) in ${compile_time}/" "${full_output_path}" + sed -i '' -E -e "s/Finished \`(dev|test)\` profile \[unoptimized \+ debuginfo] target\(s\) in [0-9.]*/Finished \`\1\` profile [unoptimized + debuginfo] target(s) in ${compile_time}/" "${full_output_path}" fi # Restore the previous test binary hash, if there is one @@ -77,7 +101,7 @@ find -s listings -name output.txt -print0 | while IFS= read -r -d '' f; do fi # Clean again - cargo clean + cargo clean > /dev/null 2>&1 cd - > /dev/null done