libcxx/include/__functional/reference_wrapper.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_REFERENCE_WRAPPER_H
  11 #define _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H
  12
  13 #include <__config>
  14 #include <__functional/invoke.h>
  15 #include <__functional/weak_result_type.h>
  16 #include <__memory/addressof.h>
  17 #include <__type_traits/enable_if.h>
  18 #include <__type_traits/remove_cvref.h>
  19 #include <__utility/declval.h>
  20 #include <__utility/forward.h>
  21
  22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  23 #  pragma GCC system_header
  24 #endif
  25
  26 _LIBCPP_BEGIN_NAMESPACE_STD
  27
  28 template <class _Tp>
  29 class _LIBCPP_TEMPLATE_VIS reference_wrapper : public __weak_result_type<_Tp> {
  30 public:
  31   // types
  32   typedef _Tp type;
  33
  34 private:
  35   type* __f_;
  36
  37   static void __fun(_Tp&) _NOEXCEPT;
  38   static void __fun(_Tp&&) = delete;
  39
  40 public:
  41   template <
  42       class _Up,
  43       class = __enable_if_t<!__is_same_uncvref<_Up, reference_wrapper>::value, decltype(__fun(std::declval<_Up>())) > >
  44   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper(_Up&& __u)
  45       _NOEXCEPT_(noexcept(__fun(std::declval<_Up>()))) {
  46     type& __f = static_cast<_Up&&>(__u);
  47     __f_      = std::addressof(__f);
  48   }
  49
  50   // access
  51   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 operator type&() const _NOEXCEPT { return *__f_; }
  52   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 type& get() const _NOEXCEPT { return *__f_; }
  53
  54   // invoke
  55   template <class... _ArgTypes>
  56   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 typename __invoke_of<type&, _ArgTypes...>::type
  57   operator()(_ArgTypes&&... __args) const
  58 #if _LIBCPP_STD_VER >= 17
  59       // Since is_nothrow_invocable requires C++17 LWG3764 is not backported
  60       // to earlier versions.
  61       noexcept(is_nothrow_invocable_v<_Tp&, _ArgTypes...>)
  62 #endif
  63   {
  64     return std::__invoke(get(), std::forward<_ArgTypes>(__args)...);
  65   }
  66 };
  67
  68 #if _LIBCPP_STD_VER >= 17
  69 template <class _Tp>
  70 reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
  71 #endif
  72
  73 template <class _Tp>
  74 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<_Tp> ref(_Tp& __t) _NOEXCEPT {
  75   return reference_wrapper<_Tp>(__t);
  76 }
  77
  78 template <class _Tp>
  79 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<_Tp>
  80 ref(reference_wrapper<_Tp> __t) _NOEXCEPT {
  81   return __t;
  82 }
  83
  84 template <class _Tp>
  85 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<const _Tp> cref(const _Tp& __t) _NOEXCEPT {
  86   return reference_wrapper<const _Tp>(__t);
  87 }
  88
  89 template <class _Tp>
  90 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<const _Tp>
  91 cref(reference_wrapper<_Tp> __t) _NOEXCEPT {
  92   return __t;
  93 }
  94
  95 template <class _Tp>
  96 void ref(const _Tp&&) = delete;
  97 template <class _Tp>
  98 void cref(const _Tp&&) = delete;
  99
 100 _LIBCPP_END_NAMESPACE_STD
 101
 102 #endif // _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H