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 {
  31 public:
  32     // types
  33     typedef _Tp type;
  34 private:
  35     type* __f_;
  36
  37     static void __fun(_Tp&) _NOEXCEPT;
  38     static void __fun(_Tp&&) = delete;
  39
  40 public:
  41     template <class _Up, class = __enable_if_t<!__is_same_uncvref<_Up, reference_wrapper>::value, decltype(__fun(std::declval<_Up>())) > >
  42     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  43     reference_wrapper(_Up&& __u) _NOEXCEPT_(noexcept(__fun(std::declval<_Up>()))) {
  44         type& __f = static_cast<_Up&&>(__u);
  45         __f_ = _VSTD::addressof(__f);
  46     }
  47
  48     // access
  49     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  50     operator type&() const _NOEXCEPT {return *__f_;}
  51     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  52     type& get() const _NOEXCEPT {return *__f_;}
  53
  54     // invoke
  55     template <class... _ArgTypes>
  56     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  57     typename __invoke_of<type&, _ArgTypes...>::type
  58     operator() (_ArgTypes&&... __args) const
  59 #if _LIBCPP_STD_VER >= 17
  60         // Since is_nothrow_invocable requires C++17 LWG3764 is not backported
  61         // to earlier versions.
  62         noexcept(is_nothrow_invocable_v<_Tp&, _ArgTypes...>)
  63 #endif
  64     {
  65         return std::__invoke(get(), std::forward<_ArgTypes>(__args)...);
  66     }
  67 };
  68
  69 #if _LIBCPP_STD_VER >= 17
  70 template <class _Tp>
  71 reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
  72 #endif
  73
  74 template <class _Tp>
  75 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  76 reference_wrapper<_Tp>
  77 ref(_Tp& __t) _NOEXCEPT
  78 {
  79     return reference_wrapper<_Tp>(__t);
  80 }
  81
  82 template <class _Tp>
  83 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  84 reference_wrapper<_Tp>
  85 ref(reference_wrapper<_Tp> __t) _NOEXCEPT
  86 {
  87     return __t;
  88 }
  89
  90 template <class _Tp>
  91 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
  92 reference_wrapper<const _Tp>
  93 cref(const _Tp& __t) _NOEXCEPT
  94 {
  95     return reference_wrapper<const _Tp>(__t);
  96 }
  97
  98 template <class _Tp>
  99 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 100 reference_wrapper<const _Tp>
 101 cref(reference_wrapper<_Tp> __t) _NOEXCEPT
 102 {
 103     return __t;
 104 }
 105
 106 template <class _Tp> void ref(const _Tp&&) = delete;
 107 template <class _Tp> void cref(const _Tp&&) = delete;
 108
 109 _LIBCPP_END_NAMESPACE_STD
 110
 111 #endif // _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H