idiom/empty-struct: add empty struct

README.md

@@ -101,6 +101,7 @@ A curated collection of idiomatic design & application patterns for Go language.
 
 | Pattern | Description | Status |
 |:-------:|:----------- |:------:|
+| [Empty Struct](/idiom/empty-struct.md) | Uses a struct with no fields to clarify intent and reduce memory usage | ✔ |
 | [Functional Options](/idiom/functional-options.md) | Allows creating clean APIs with sane defaults and idiomatic overrides | ✔ |
 
 ## Anti-Patterns

idiom/empty-struct.md

@@ -0,0 +1,84 @@
+# Empty Struct
+The empty struct is a struct type with no fields.
+It has a couple of interesting properties.
+
+- Its size is zero bytes, so values of this type occupy no storage
+- It is often used when no data needs to be stored, but the type itself conveys intent
+
+## Implementation
+### Zero Size
+```go
+package main
+
+import (
+	"fmt"
+	"unsafe"
+)
+
+var i int16
+var c complex128
+var s struct{}
+
+func main() {
+	fmt.Println(unsafe.Sizeof(i)) // 2 bytes
+	fmt.Println(unsafe.Sizeof(c)) // 16 bytes
+	fmt.Println(unsafe.Sizeof(s)) // 0 bytes
+}
+```
+
+
+### Signal-only Channel
+```go
+package main
+
+func main() {
+    done := make(chan struct{})
+
+    go func() {
+        // do work...
+        close(done)
+    }()
+
+    <-done
+}
+```
+
+### Set
+```go
+type S map[string]struct{}
+
+func (s S) Add(key string) {
+    s[key] = struct{}{}
+}
+
+func (s S) Has(key string) bool {
+    _, ok := s[key]
+    return ok
+}
+```
+
+## Usage
+### Signal-only Channel
+```go
+done := make(chan struct{})
+
+go func() {
+    close(done)
+}()
+
+<-done // blocks until goroutine signals completion
+```
+
+### Set
+```go
+s := make(S)
+s.Add("go")
+s.Add("patterns")
+
+fmt.Println(s.Has("go"))    // true
+fmt.Println(s.Has("rust"))  // false
+```
+
+## Rules of Thumb
+- Prefer `chan struct{}` over `chan bool` when no data needs to be sent
+- Prefer `map[K]struct{}` over `map[K]bool` when implementing a set