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 <__type_traits/is_move_constructible.h>
  21 #include <__utility/forward.h>
  22
  23 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  24 #  pragma GCC system_header
  25 #endif
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 #if _LIBCPP_STD_VER >= 20
  30
  31 struct __bind_front_op {
  32   template <class... _Args>
  33   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Args&&... __args) const
  34       noexcept(noexcept(std::invoke(std::forward<_Args>(__args)...)))
  35           -> decltype(std::invoke(std::forward<_Args>(__args)...)) {
  36     return std::invoke(std::forward<_Args>(__args)...);
  37   }
  38 };
  39
  40 template <class _Fn, class... _BoundArgs>
  41 struct __bind_front_t : __perfect_forward<__bind_front_op, _Fn, _BoundArgs...> {
  42   using __perfect_forward<__bind_front_op, _Fn, _BoundArgs...>::__perfect_forward;
  43 };
  44
  45 template <class _Fn, class... _Args>
  46   requires is_constructible_v<decay_t<_Fn>, _Fn> && is_move_constructible_v<decay_t<_Fn>> &&
  47            (is_constructible_v<decay_t<_Args>, _Args> && ...) && (is_move_constructible_v<decay_t<_Args>> && ...)
  48 _LIBCPP_HIDE_FROM_ABI constexpr auto bind_front(_Fn&& __f, _Args&&... __args) {
  49   return __bind_front_t<decay_t<_Fn>, decay_t<_Args>...>(std::forward<_Fn>(__f), std::forward<_Args>(__args)...);
  50 }
  51
  52 #endif // _LIBCPP_STD_VER >= 20
  53
  54 _LIBCPP_END_NAMESPACE_STD
  55
  56 #endif // _LIBCPP___FUNCTIONAL_BIND_FRONT_H