libcxx/include/__functional/perfect_forward.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_PERFECT_FORWARD_H
  11 #define _LIBCPP___FUNCTIONAL_PERFECT_FORWARD_H
  12
  13 #include <__config>
  14 #include <__cstddef/size_t.h>
  15 #include <__type_traits/enable_if.h>
  16 #include <__type_traits/invoke.h>
  17 #include <__type_traits/is_constructible.h>
  18 #include <__utility/declval.h>
  19 #include <__utility/forward.h>
  20 #include <__utility/integer_sequence.h>
  21 #include <__utility/move.h>
  22 #include <tuple>
  23
  24 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  25 #  pragma GCC system_header
  26 #endif
  27
  28 _LIBCPP_PUSH_MACROS
  29 #include <__undef_macros>
  30
  31 _LIBCPP_BEGIN_NAMESPACE_STD
  32
  33 #if _LIBCPP_STD_VER >= 17
  34
  35 template <class _Op, class _Indices, class... _BoundArgs>
  36 struct __perfect_forward_impl;
  37
  38 template <class _Op, size_t... _Idx, class... _BoundArgs>
  39 struct __perfect_forward_impl<_Op, index_sequence<_Idx...>, _BoundArgs...> {
  40 private:
  41   tuple<_BoundArgs...> __bound_args_;
  42
  43 public:
  44   template <class... _Args, class = enable_if_t< is_constructible_v<tuple<_BoundArgs...>, _Args&&...> >>
  45   _LIBCPP_HIDE_FROM_ABI explicit constexpr __perfect_forward_impl(_Args&&... __bound_args)
  46       : __bound_args_(std::forward<_Args>(__bound_args)...) {}
  47
  48   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl(__perfect_forward_impl const&) = default;
  49   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl(__perfect_forward_impl&&)      = default;
  50
  51   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl& operator=(__perfect_forward_impl const&) = default;
  52   _LIBCPP_HIDE_FROM_ABI __perfect_forward_impl& operator=(__perfect_forward_impl&&)      = default;
  53
  54   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs&..., _Args...>>>
  55   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) & noexcept(
  56       noexcept(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)))
  57       -> decltype(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)) {
  58     return _Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...);
  59   }
  60
  61   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs&..., _Args...>>>
  62   auto operator()(_Args&&...) & = delete;
  63
  64   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs const&..., _Args...>>>
  65   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const& noexcept(
  66       noexcept(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)))
  67       -> decltype(_Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...)) {
  68     return _Op()(std::get<_Idx>(__bound_args_)..., std::forward<_Args>(__args)...);
  69   }
  70
  71   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs const&..., _Args...>>>
  72   auto operator()(_Args&&...) const& = delete;
  73
  74   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs..., _Args...>>>
  75   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) && noexcept(
  76       noexcept(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)))
  77       -> decltype(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)) {
  78     return _Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...);
  79   }
  80
  81   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs..., _Args...>>>
  82   auto operator()(_Args&&...) && = delete;
  83
  84   template <class... _Args, class = enable_if_t<is_invocable_v<_Op, _BoundArgs const..., _Args...>>>
  85   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const&& noexcept(
  86       noexcept(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)))
  87       -> decltype(_Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...)) {
  88     return _Op()(std::get<_Idx>(std::move(__bound_args_))..., std::forward<_Args>(__args)...);
  89   }
  90
  91   template <class... _Args, class = enable_if_t<!is_invocable_v<_Op, _BoundArgs const..., _Args...>>>
  92   auto operator()(_Args&&...) const&& = delete;
  93 };
  94
  95 // __perfect_forward implements a perfect-forwarding call wrapper as explained in [func.require].
  96 template <class _Op, class... _Args>
  97 using __perfect_forward = __perfect_forward_impl<_Op, index_sequence_for<_Args...>, _Args...>;
  98
  99 #endif // _LIBCPP_STD_VER >= 17
 100
 101 _LIBCPP_END_NAMESPACE_STD
 102
 103 _LIBCPP_POP_MACROS
 104
 105 #endif // _LIBCPP___FUNCTIONAL_PERFECT_FORWARD_H