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libstdc++: Add comments to deleted std::swap overloads for LWG 2766

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We pre-emptively implemented part of LWG 2766, which still hasn't been
approved. Add comments to the deleted swap overloads saying why they're
there, because the standard doesn't require them.

libstdc++-v3/ChangeLog:

	* include/bits/stl_pair.h (swap): Add comment to deleted
	overload.
	* include/bits/unique_ptr.h (swap): Likewise.
	* include/std/array (swap): Likewise.
	* include/std/optional (swap): Likewise.
	* include/std/tuple (swap): Likewise.
	* include/std/variant (swap): Likewise.
	* testsuite/23_containers/array/tuple_interface/get_neg.cc:
	Adjust dg-error line numbers.
This commit is contained in:
Jonathan Wakely
2025-07-13 15:34:15 +01:00
committed by Jonathan Wakely
parent d8680bac95
commit 9840a1db02
7 changed files with 16 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
libstdc++-v3/include/bits/stl_pair.h
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@@ -1132,6 +1132,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif // C++23
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2766. Swapping non-swappable types
template<typename _T1, typename _T2>
typename enable_if<!__and_<__is_swappable<_T1>,
__is_swappable<_T2>>::value>::type

2
libstdc++-v3/include/bits/unique_ptr.h
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@@ -832,6 +832,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ __x.swap(__y); }
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2766. Swapping non-swappable types
template<typename _Tp, typename _Dp>
typename enable_if<!__is_swappable<_Dp>::value>::type
swap(unique_ptr<_Tp, _Dp>&,

2
libstdc++-v3/include/std/array
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@@ -381,6 +381,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ __one.swap(__two); }
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2766. Swapping non-swappable types
template<typename _Tp, std::size_t _Nm>
__enable_if_t<!__array_traits<_Tp, _Nm>::_Is_swappable::value>
swap(array<_Tp, _Nm>&, array<_Tp, _Nm>&) = delete;

2
libstdc++-v3/include/std/optional
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@@ -1740,6 +1740,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
noexcept(noexcept(__lhs.swap(__rhs)))
{ __lhs.swap(__rhs); }
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2766. Swapping non-swappable types
template<typename _Tp>
enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
swap(optional<_Tp>&, optional<_Tp>&) = delete;

4
libstdc++-v3/include/std/tuple
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@@ -2835,6 +2835,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ __x.swap(__y); }
#if __cpp_lib_ranges_zip // >= C++23
/// Exchange the values of two const tuples (if const elements can be swapped)
template<typename... _Elements>
requires (is_swappable_v<const _Elements> && ...)
constexpr void
@@ -2844,7 +2845,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif // C++23
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
/// Exchange the values of two const tuples (if const elements can be swapped)
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2766. Swapping non-swappable types
template<typename... _Elements>
_GLIBCXX20_CONSTEXPR
typename enable_if<!__and_<__is_swappable<_Elements>...>::value>::type

2
libstdc++-v3/include/std/variant
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@@ -1387,6 +1387,8 @@ namespace __detail::__variant
noexcept(noexcept(__lhs.swap(__rhs)))
{ __lhs.swap(__rhs); }
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2766. Swapping non-swappable types
template<typename... _Types>
enable_if_t<!((is_move_constructible_v<_Types> && ...)
&& (is_swappable_v<_Types> && ...))>

6
libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
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@@ -26,6 +26,6 @@ int n1 = std::get<1>(a);
int n2 = std::get<1>(std::move(a));
int n3 = std::get<1>(ca);
// { dg-error "static assertion failed" "" { target *-*-* } 394 }
// { dg-error "static assertion failed" "" { target *-*-* } 403 }
// { dg-error "static assertion failed" "" { target *-*-* } 412 }
// { dg-error "static assertion failed" "" { target *-*-* } 396 }
// { dg-error "static assertion failed" "" { target *-*-* } 405 }
// { dg-error "static assertion failed" "" { target *-*-* } 414 }