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 = _VSTD::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
42