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 <__functional/reference_wrapper.h> 15 #include <__type_traits/integral_constant.h> 16 #include <__utility/forward.h> 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 template <class _Tp> 25 struct __is_identity : false_type {}; 26 27 struct __identity { 28 template <class _Tp> 29 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Tp&& operator()(_Tp&& __t) const _NOEXCEPT { 30 return std::forward<_Tp>(__t); 31 } 32 33 using is_transparent = void; 34 }; 35 36 template <> 37 struct __is_identity<__identity> : true_type {}; 38 template <> 39 struct __is_identity<reference_wrapper<__identity> > : true_type {}; 40 template <> 41 struct __is_identity<reference_wrapper<const __identity> > : true_type {}; 42 43 #if _LIBCPP_STD_VER >= 20 44 45 struct identity { 46 template <class _Tp> 47 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Tp&& operator()(_Tp&& __t) const noexcept { 48 return std::forward<_Tp>(__t); 49 } 50 51 using is_transparent = void; 52 }; 53 54 template <> 55 struct __is_identity<identity> : true_type {}; 56 template <> 57 struct __is_identity<reference_wrapper<identity> > : true_type {}; 58 template <> 59 struct __is_identity<reference_wrapper<const identity> > : true_type {}; 60 61 #endif // _LIBCPP_STD_VER >= 20 62 63 _LIBCPP_END_NAMESPACE_STD 64 65 #endif // _LIBCPP___FUNCTIONAL_IDENTITY_H 66