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