libcxx/include/__functional/unwrap_ref.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___FUNCTIONAL_UNWRAP_REF_H
  10 #define _LIBCPP___FUNCTIONAL_UNWRAP_REF_H
  11
  12 #include <__config>
  13
  14 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  15 #pragma GCC system_header
  16 #endif
  17
  18 _LIBCPP_BEGIN_NAMESPACE_STD
  19
  20 template <class _Tp>
  21 struct __unwrap_reference { typedef _LIBCPP_NODEBUG _Tp type; };
  22
  23 template <class _Tp>
  24 class reference_wrapper;
  25
  26 template <class _Tp>
  27 struct __unwrap_reference<reference_wrapper<_Tp> > { typedef _LIBCPP_NODEBUG _Tp& type; };
  28
  29 template <class _Tp>
  30 struct decay;
  31
  32 #if _LIBCPP_STD_VER > 17
  33 template <class _Tp>
  34 struct unwrap_reference : __unwrap_reference<_Tp> { };
  35
  36 template <class _Tp>
  37 using unwrap_reference_t = typename unwrap_reference<_Tp>::type;
  38
  39 template <class _Tp>
  40 struct unwrap_ref_decay : unwrap_reference<typename decay<_Tp>::type> { };
  41
  42 template <class _Tp>
  43 using unwrap_ref_decay_t = typename unwrap_ref_decay<_Tp>::type;
  44 #endif // > C++17
  45
  46 template <class _Tp>
  47 struct __unwrap_ref_decay
  48 #if _LIBCPP_STD_VER > 17
  49     : unwrap_ref_decay<_Tp>
  50 #else
  51     : __unwrap_reference<typename decay<_Tp>::type>
  52 #endif
  53 { };
  54
  55 _LIBCPP_END_NAMESPACE_STD
  56
  57 #endif // _LIBCPP___FUNCTIONAL_UNWRAP_REF_H