libcxx/include/__functional/identity.h

   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>
  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 #if _LIBCPP_STD_VER > 17
  23
  24 struct identity {
  25     template<class _Tp>
  26     _LIBCPP_NODISCARD_EXT constexpr _Tp&& operator()(_Tp&& __t) const noexcept
  27     {
  28         return _VSTD::forward<_Tp>(__t);
  29     }
  30
  31     using is_transparent = void;
  32 };
  33 #endif // _LIBCPP_STD_VER > 17
  34
  35 _LIBCPP_END_NAMESPACE_STD
  36
  37 #endif // _LIBCPP___FUNCTIONAL_IDENTITY_H