On Mon, Jul 14, 2025 at 10:58 PM Jonathan Wakely <jwak...@redhat.com> wrote:
> 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.
> ---
>
> Tested powerpc64le-linux, pushed to trunk.
>
Only tangentially related, but it looks like we are adding more and more
use cases for having a conditional = delete(expr),
than can be followed by body.
>
> libstdc++-v3/include/bits/stl_pair.h | 2 ++
> libstdc++-v3/include/bits/unique_ptr.h | 2 ++
> libstdc++-v3/include/std/array | 2 ++
> libstdc++-v3/include/std/optional | 2 ++
> libstdc++-v3/include/std/tuple | 4 +++-
> libstdc++-v3/include/std/variant | 2 ++
> .../23_containers/array/tuple_interface/get_neg.cc | 6 +++---
> 7 files changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/stl_pair.h
> b/libstdc++-v3/include/bits/stl_pair.h
> index 8c57712b4617..393f6a016196 100644
> --- a/libstdc++-v3/include/bits/stl_pair.h
> +++ b/libstdc++-v3/include/bits/stl_pair.h
> @@ -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
> diff --git a/libstdc++-v3/include/bits/unique_ptr.h
> b/libstdc++-v3/include/bits/unique_ptr.h
> index 6ae46a93800c..d76ad63ba7bf 100644
> --- a/libstdc++-v3/include/bits/unique_ptr.h
> +++ b/libstdc++-v3/include/bits/unique_ptr.h
> @@ -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>&,
> diff --git a/libstdc++-v3/include/std/array
> b/libstdc++-v3/include/std/array
> index fdcf0b073762..12f010921db1 100644
> --- a/libstdc++-v3/include/std/array
> +++ b/libstdc++-v3/include/std/array
> @@ -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;
> diff --git a/libstdc++-v3/include/std/optional
> b/libstdc++-v3/include/std/optional
> index cc7af5bbd7d2..e5051d72c828 100644
> --- a/libstdc++-v3/include/std/optional
> +++ b/libstdc++-v3/include/std/optional
> @@ -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;
> diff --git a/libstdc++-v3/include/std/tuple
> b/libstdc++-v3/include/std/tuple
> index b39ce710984c..2e6499eab22d 100644
> --- a/libstdc++-v3/include/std/tuple
> +++ b/libstdc++-v3/include/std/tuple
> @@ -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
> diff --git a/libstdc++-v3/include/std/variant
> b/libstdc++-v3/include/std/variant
> index ec46ff1dabb5..2f44f9700283 100644
> --- a/libstdc++-v3/include/std/variant
> +++ b/libstdc++-v3/include/std/variant
> @@ -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> && ...))>
> diff --git
> a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
> b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
> index 25511e79941d..e1e9ce9bdac1 100644
> --- a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
> +++ b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
> @@ -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 }
> --
> 2.50.1
>
>
