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
29template <class _Lhs, class _Rhs>
30concept 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