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 <__utility/forward.h>
16 #include <type_traits>
17 
18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19 #  pragma GCC system_header
20 #endif
21 
22 _LIBCPP_BEGIN_NAMESPACE_STD
23 
24 #if _LIBCPP_STD_VER > 17
25 
26 // [concept.assignable]
27 
28 template<class _Lhs, class _Rhs>
29 concept assignable_from =
30   is_lvalue_reference_v<_Lhs> &&
31   common_reference_with<__make_const_lvalue_ref<_Lhs>, __make_const_lvalue_ref<_Rhs>> &&
32   requires (_Lhs __lhs, _Rhs&& __rhs) {
33     { __lhs = _VSTD::forward<_Rhs>(__rhs) } -> same_as<_Lhs>;
34   };
35 
36 #endif // _LIBCPP_STD_VER > 17
37 
38 _LIBCPP_END_NAMESPACE_STD
39 
40 #endif // _LIBCPP___CONCEPTS_ASSIGNABLE_H
41