1 // -*- C++ -*- 2 //===----------------------------------------------------------------------===// 3 // 4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5 // See https://llvm.org/LICENSE.txt for license information. 6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef _LIBCPP___FUNCTIONAL_IDENTITY_H 11 #define _LIBCPP___FUNCTIONAL_IDENTITY_H 12 13 #include <__config> 14 #include <__type_traits/integral_constant.h> 15 #include <__utility/forward.h> 16 17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 18 # pragma GCC system_header 19 #endif 20 21 _LIBCPP_BEGIN_NAMESPACE_STD 22 23 template <class _Tp> 24 struct __is_identity : false_type {}; 25 26 struct __identity { 27 template <class _Tp> 28 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Tp&& operator()(_Tp&& __t) const _NOEXCEPT { 29 return std::forward<_Tp>(__t); 30 } 31 32 using is_transparent = void; 33 }; 34 35 template <> 36 struct __is_identity<__identity> : true_type {}; 37 38 #if _LIBCPP_STD_VER >= 20 39 40 struct identity { 41 template<class _Tp> 42 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Tp&& operator()(_Tp&& __t) const noexcept 43 { 44 return _VSTD::forward<_Tp>(__t); 45 } 46 47 using is_transparent = void; 48 }; 49 50 template <> 51 struct __is_identity<identity> : true_type {}; 52 53 #endif // _LIBCPP_STD_VER >= 20 54 55 _LIBCPP_END_NAMESPACE_STD 56 57 #endif // _LIBCPP___FUNCTIONAL_IDENTITY_H 58