libcxx/include/__functional/compose.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___FUNCTIONAL_COMPOSE_H
#define _LIBCPP___FUNCTIONAL_COMPOSE_H

#include <__config>
#include <__functional/invoke.h>
#include <__functional/perfect_forward.h>
#include <__type_traits/decay.h>
#include <__utility/forward.h>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

#if _LIBCPP_STD_VER >= 20

_LIBCPP_BEGIN_NAMESPACE_STD

struct __compose_op {
  template <class _Fn1, class _Fn2, class... _Args>
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Fn1&& __f1, _Fn2&& __f2, _Args&&... __args) const noexcept(noexcept(
      std::invoke(std::forward<_Fn1>(__f1), std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...))))
      -> decltype(std::invoke(std::forward<_Fn1>(__f1),
                              std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...))) {
    return std::invoke(std::forward<_Fn1>(__f1), std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...));
  }
};

template <class _Fn1, class _Fn2>
struct __compose_t : __perfect_forward<__compose_op, _Fn1, _Fn2> {
  using __perfect_forward<__compose_op, _Fn1, _Fn2>::__perfect_forward;
};

template <class _Fn1, class _Fn2>
_LIBCPP_HIDE_FROM_ABI constexpr auto __compose(_Fn1&& __f1, _Fn2&& __f2) noexcept(
    noexcept(__compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2))))
    -> decltype(__compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2))) {
  return __compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2));
}

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_STD_VER >= 20

#endif // _LIBCPP___FUNCTIONAL_COMPOSE_H