v1/__concepts/assignable.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef _LIBCPP___CONCEPTS_ASSIGNABLE_H
0010 #define _LIBCPP___CONCEPTS_ASSIGNABLE_H
0011
0012 #include <__concepts/common_reference_with.h>
0013 #include <__concepts/same_as.h>
0014 #include <__config>
0015 #include <__type_traits/is_reference.h>
0016 #include <__type_traits/make_const_lvalue_ref.h>
0017 #include <__utility/forward.h>
0018
0019 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0020 #  pragma GCC system_header
0021 #endif
0022
0023 _LIBCPP_BEGIN_NAMESPACE_STD
0024
0025 #if _LIBCPP_STD_VER >= 20
0026
0027 // [concept.assignable]
0028
0029 template <class _Lhs, class _Rhs>
0030 concept assignable_from =
0031     is_lvalue_reference_v<_Lhs> &&
0032     common_reference_with<__make_const_lvalue_ref<_Lhs>, __make_const_lvalue_ref<_Rhs>> &&
0033     requires(_Lhs __lhs, _Rhs&& __rhs) {
0034       { __lhs = std::forward<_Rhs>(__rhs) } -> same_as<_Lhs>;
0035     };
0036
0037 #endif // _LIBCPP_STD_VER >= 20
0038
0039 _LIBCPP_END_NAMESPACE_STD
0040
0041 #endif // _LIBCPP___CONCEPTS_ASSIGNABLE_H