libcxx/include/__functional/bind_front.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_BIND_FRONT_H
  11 #define _LIBCPP___FUNCTIONAL_BIND_FRONT_H
  12
  13 #include <__config>
  14 #include <__functional/invoke.h>
  15 #include <__functional/perfect_forward.h>
  16 #include <__type_traits/conjunction.h>
  17 #include <__type_traits/decay.h>
  18 #include <__type_traits/enable_if.h>
  19 #include <__type_traits/is_constructible.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 #if _LIBCPP_STD_VER >= 20
  29
  30 struct __bind_front_op {
  31   template <class... _Args>
  32   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const noexcept(
  33       noexcept(std::invoke(std::forward<_Args>(__args)...))) -> decltype(std::invoke(std::forward<_Args>(__args)...)) {
  34     return std::invoke(std::forward<_Args>(__args)...);
  35   }
  36 };
  37
  38 template <class _Fn, class... _BoundArgs>
  39 struct __bind_front_t : __perfect_forward<__bind_front_op, _Fn, _BoundArgs...> {
  40   using __perfect_forward<__bind_front_op, _Fn, _BoundArgs...>::__perfect_forward;
  41 };
  42
  43 template <class _Fn, class... _Args>
  44   requires is_constructible_v<decay_t<_Fn>, _Fn> && is_move_constructible_v<decay_t<_Fn>> &&
  45            (is_constructible_v<decay_t<_Args>, _Args> && ...) && (is_move_constructible_v<decay_t<_Args>> && ...)
  46 _LIBCPP_HIDE_FROM_ABI constexpr auto bind_front(_Fn&& __f, _Args&&... __args) {
  47   return __bind_front_t<decay_t<_Fn>, decay_t<_Args>...>(std::forward<_Fn>(__f), std::forward<_Args>(__args)...);
  48 }
  49
  50 #endif // _LIBCPP_STD_VER >= 20
  51
  52 _LIBCPP_END_NAMESPACE_STD
  53
  54 #endif // _LIBCPP___FUNCTIONAL_BIND_FRONT_H