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 <__fwd/functional.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
24template <class _Tp>
25struct __is_identity : false_type {};
26
27struct __identity {
28  template <class _Tp>
29  [[__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
36template <>
37struct __is_identity<__identity> : true_type {};
38template <>
39struct __is_identity<reference_wrapper<__identity> > : true_type {};
40template <>
41struct __is_identity<reference_wrapper<const __identity> > : true_type {};
42
43#if _LIBCPP_STD_VER >= 20
44
45struct identity {
46  template <class _Tp>
47  [[nodiscard]] _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
54template <>
55struct __is_identity<identity> : true_type {};
56template <>
57struct __is_identity<reference_wrapper<identity> > : true_type {};
58template <>
59struct __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