Skip to content

Constrain distance function using is_iterator type trait #96

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
jeremy-murphy wants to merge 16 commits into
base: develop
Choose a base branch
from
Open

Constrain distance function using is_iterator type trait #96

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
16 commits
Select commit Hold shift + click to select a range
b181c05
Constrain distance function using is_iterator type trait
jeremy-murphy May 13, 2026
668fdd0
Add enable_if include
jeremy-murphy May 13, 2026
d95f074
Fix template syntax in distance function
jeremy-murphy May 13, 2026
a312350
Fix syntax issue in distance enable_if
jeremy-murphy May 13, 2026
ec48579
Test which overload of distance is called
jeremy-murphy May 14, 2026
71d8fb2
Fix wrong spelling of std::ptrdiff_t
jeremy-murphy May 14, 2026
c9e4a8d
Move Foo struct to global scope
jeremy-murphy May 14, 2026
1ffbb8b
Merge branch 'boostorg:develop' into patch-1
jeremy-murphy May 14, 2026
66cdd2e
Andrey magic
jeremy-murphy May 14, 2026
f5ea042
Fix headers, add copyright
jeremy-murphy May 19, 2026
7f737f0
Constrain advance to iterators
jeremy-murphy May 19, 2026
fa930f2
Test contraint of advance function with int overload
jeremy-murphy May 19, 2026
1d642b2
Fix enable_if condition for advance function
jeremy-murphy May 19, 2026
c20eb82
Fix template syntax in advance constraint
jeremy-murphy May 20, 2026
5ea771c
Fix advance test
jeremy-murphy May 20, 2026
db27fad
Remove constexpr specifier
jeremy-murphy May 20, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
7 changes: 6 additions & 1 deletion include/boost/iterator/advance.hpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,11 @@
#define BOOST_ITERATOR_ADVANCE_HPP

#include <boost/config.hpp>
#include <boost/iterator/is_iterator.hpp>
#include <boost/iterator/iterator_categories.hpp>

#include <type_traits>

namespace boost {
namespace iterators {
namespace detail {
Expand Down Expand Up @@ -56,7 +59,9 @@ inline BOOST_CXX14_CONSTEXPR void advance_impl(RandomAccessIterator& it, Distanc
namespace advance_adl_barrier {

template< typename InputIterator, typename Distance >
inline BOOST_CXX14_CONSTEXPR void advance(InputIterator& it, Distance n)
inline BOOST_CXX14_CONSTEXPR
typename std::enable_if< boost::is_iterator< InputIterator >::value, void >::type
advance(InputIterator& it, Distance n)
{
detail::advance_impl(it, n, typename iterator_traversal< InputIterator >::type());
}
Expand Down
10 changes: 9 additions & 1 deletion include/boost/iterator/distance.hpp
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
// Copyright (C) 2017 Michel Morin.
// Copyright (C) 2026 Jeremy W. Murphy
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at
Expand All @@ -8,9 +9,12 @@
#define BOOST_ITERATOR_DISTANCE_HPP

#include <boost/config.hpp>
#include <boost/iterator/is_iterator.hpp>
#include <boost/iterator/iterator_categories.hpp>
#include <boost/iterator/iterator_traits.hpp>

#include <type_traits>

namespace boost {
namespace iterators {
namespace detail {
Expand Down Expand Up @@ -40,7 +44,11 @@ distance_impl(RandomAccessIterator first, RandomAccessIterator last, random_acce
namespace distance_adl_barrier {

template< typename SinglePassIterator >
inline BOOST_CXX14_CONSTEXPR typename iterator_difference< SinglePassIterator >::type
inline BOOST_CXX14_CONSTEXPR
typename std::enable_if<
boost::is_iterator< SinglePassIterator >::value,
iterator_difference< SinglePassIterator >
>::type::type
distance(SinglePassIterator first, SinglePassIterator last)
{
return detail::distance_impl(first, last, typename iterator_traversal< SinglePassIterator >::type());
Expand Down
19 changes: 19 additions & 0 deletions test/advance_test.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,18 @@ void test_advance(Iterator it_from, Iterator it_to, int n)
BOOST_TEST(it_from == it_to);
}

// Definitely not an iterator
struct Foo
{
int x = 0;

friend
void advance(Foo &value, int n)
{
value.x += 10 * n;
}
};

int main()
{
int array[3] = {1, 2, 3};
Expand Down Expand Up @@ -87,5 +99,12 @@ int main()
);
}

{
using boost::advance;
Foo bar;
advance(bar, 3);
BOOST_TEST(bar.x == 30);
}
Comment on lines +102 to +107
Copy link
Copy Markdown
Author

@jeremy-murphy jeremy-murphy May 20, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This test is not quite as convincing as the one for distance, because it still passes if I take away the constraint on advance. Any advice on how to make it fail without the change to advance?

Copy link
Copy Markdown
Author

@jeremy-murphy jeremy-murphy May 20, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I guess this question is directed at you, @Lastique.

Copy link
Copy Markdown
Member

@Lastique Lastique May 20, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Regardless of the constraint on boost::advance, the friend advance is the more preferable overload as it is not a template and the arguments don't require conversions. Make it a less preferable overload so that boost::advance is picked in overload resolution, e.g. make the second argument long or something.


return boost::report_errors();
}
14 changes: 14 additions & 0 deletions test/distance_test.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
// (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

#include <cstddef>
#include <vector>
#include <list>
#include <boost/container/slist.hpp>
Expand All @@ -19,6 +20,13 @@ void test_distance(Iterator it_from, Iterator it_to, int n)
BOOST_TEST(boost::distance(it_from, it_to) == n);
}

// Definitely not an iterator.
struct Foo
{
constexpr friend
std::ptrdiff_t distance(Foo const &, Foo const &) { return -1; }
};

int main()
{
int array[3] = {1, 2, 3};
Expand Down Expand Up @@ -80,5 +88,11 @@ int main()
);
}

{
// Make boost::distance visible since we're not actually in the boost namespace here.
using boost::distance;
auto result = distance(Foo{}, Foo{});
BOOST_TEST(result == -1);
}
return boost::report_errors();
}