On Tue, 23 Jan 2024, 23:53 Patrick Palka, <ppa...@redhat.com> wrote:
> This is consistent with std::tuple's __const_assignable member function,
> and will be reused when implementing the new pair::operator= overloads
> from P2165R4.
>
OK
> libstdc++-v3/ChangeLog:
>
> * include/bits/stl_pair.h (pair::_S_const_assignable): Define,
> factored out from ...
> (pair::operator=): ... the constraints of the const overloads.
> ---
> libstdc++-v3/include/bits/stl_pair.h | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/stl_pair.h
> b/libstdc++-v3/include/bits/stl_pair.h
> index acd0c7b58f9..b81b479ad43 100644
> --- a/libstdc++-v3/include/bits/stl_pair.h
> +++ b/libstdc++-v3/include/bits/stl_pair.h
> @@ -404,6 +404,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> return false;
> }
>
> + template<typename _U1, typename _U2>
> + static constexpr bool
> + _S_const_assignable()
> + {
> + if constexpr (is_assignable_v<const _T1&, _U1>)
> + return is_assignable_v<const _T2&, _U2>;
> + return false;
> + }
> +
> template<typename _U1, typename _U2>
> static constexpr bool
> _S_nothrow_assignable()
> @@ -468,8 +477,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> /// Copy assignment operator (const)
> constexpr const pair&
> operator=(const pair& __p) const
> - requires is_copy_assignable_v<const first_type>
> - && is_copy_assignable_v<const second_type>
> + requires (_S_const_assignable<const first_type&, const
> second_type&>())
> {
> first = __p.first;
> second = __p.second;
> @@ -479,8 +487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> /// Move assignment operator (const)
> constexpr const pair&
> operator=(pair&& __p) const
> - requires is_assignable_v<const first_type&, first_type>
> - && is_assignable_v<const second_type&, second_type>
> + requires (_S_const_assignable<first_type, second_type>())
> {
> first = std::forward<first_type>(__p.first);
> second = std::forward<second_type>(__p.second);
> @@ -491,8 +498,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _U1, typename _U2>
> constexpr const pair&
> operator=(const pair<_U1, _U2>& __p) const
> - requires is_assignable_v<const first_type&, const _U1&>
> - && is_assignable_v<const second_type&, const _U2&>
> + requires (_S_const_assignable<const _U1&, const _U2&>())
> {
> first = __p.first;
> second = __p.second;
> @@ -503,8 +509,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _U1, typename _U2>
> constexpr const pair&
> operator=(pair<_U1, _U2>&& __p) const
> - requires is_assignable_v<const first_type&, _U1>
> - && is_assignable_v<const second_type&, _U2>
> + requires (_S_const_assignable<_U1, _U2>())
> {
> first = std::forward<_U1>(__p.first);
> second = std::forward<_U2>(__p.second);
> --
> 2.43.0.386.ge02ecfcc53
>
>
