xref: /freebsd/contrib/llvm-project/libcxx/include/__functional/identity.h (revision 1b10e191f341111fad7be32ead11484dfd09b800)
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 <__utility/forward.h>
15 
16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17 #  pragma GCC system_header
18 #endif
19 
20 _LIBCPP_BEGIN_NAMESPACE_STD
21 
22 struct __identity {
23   template <class _Tp>
24   _LIBCPP_NODISCARD _LIBCPP_CONSTEXPR _Tp&& operator()(_Tp&& __t) const _NOEXCEPT {
25     return std::forward<_Tp>(__t);
26   }
27 
28   using is_transparent = void;
29 };
30 
31 #if _LIBCPP_STD_VER > 17
32 
33 struct identity {
34     template<class _Tp>
35     _LIBCPP_NODISCARD_EXT constexpr _Tp&& operator()(_Tp&& __t) const noexcept
36     {
37         return _VSTD::forward<_Tp>(__t);
38     }
39 
40     using is_transparent = void;
41 };
42 #endif // _LIBCPP_STD_VER > 17
43 
44 _LIBCPP_END_NAMESPACE_STD
45 
46 #endif // _LIBCPP___FUNCTIONAL_IDENTITY_H
47