libcxx/include/__concepts/assignable.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___CONCEPTS_ASSIGNABLE_H
  10 #define _LIBCPP___CONCEPTS_ASSIGNABLE_H
  11
  12 #include <__concepts/common_reference_with.h>
  13 #include <__concepts/same_as.h>
  14 #include <__config>
  15 #include <__type_traits/is_reference.h>
  16 #include <__type_traits/make_const_lvalue_ref.h>
  17 #include <__utility/forward.h>
  18
  19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  20 #  pragma GCC system_header
  21 #endif
  22
  23 _LIBCPP_BEGIN_NAMESPACE_STD
  24
  25 #if _LIBCPP_STD_VER >= 20
  26
  27 // [concept.assignable]
  28
  29 template <class _Lhs, class _Rhs>
  30 concept assignable_from =
  31     is_lvalue_reference_v<_Lhs> &&
  32     common_reference_with<__make_const_lvalue_ref<_Lhs>, __make_const_lvalue_ref<_Rhs>> &&
  33     requires(_Lhs __lhs, _Rhs&& __rhs) {
  34       { __lhs = std::forward<_Rhs>(__rhs) } -> same_as<_Lhs>;
  35     };
  36
  37 #endif // _LIBCPP_STD_VER >= 20
  38
  39 _LIBCPP_END_NAMESPACE_STD
  40
  41 #endif // _LIBCPP___CONCEPTS_ASSIGNABLE_H