libcxx/include/__functional/compose.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_COMPOSE_H
  11 #define _LIBCPP___FUNCTIONAL_COMPOSE_H
  12
  13 #include <__config>
  14 #include <__functional/invoke.h>
  15 #include <__functional/perfect_forward.h>
  16 #include <__type_traits/decay.h>
  17 #include <__utility/forward.h>
  18
  19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  20 #  pragma GCC system_header
  21 #endif
  22
  23 _LIBCPP_BEGIN_NAMESPACE_STD
  24
  25 #if _LIBCPP_STD_VER >= 20
  26
  27 struct __compose_op {
  28   template <class _Fn1, class _Fn2, class... _Args>
  29   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Fn1&& __f1, _Fn2&& __f2, _Args&&... __args) const noexcept(noexcept(
  30       std::invoke(std::forward<_Fn1>(__f1), std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...))))
  31       -> decltype(std::invoke(std::forward<_Fn1>(__f1),
  32                               std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...))) {
  33     return std::invoke(std::forward<_Fn1>(__f1), std::invoke(std::forward<_Fn2>(__f2), std::forward<_Args>(__args)...));
  34   }
  35 };
  36
  37 template <class _Fn1, class _Fn2>
  38 struct __compose_t : __perfect_forward<__compose_op, _Fn1, _Fn2> {
  39   using __perfect_forward<__compose_op, _Fn1, _Fn2>::__perfect_forward;
  40 };
  41
  42 template <class _Fn1, class _Fn2>
  43 _LIBCPP_HIDE_FROM_ABI constexpr auto __compose(_Fn1&& __f1, _Fn2&& __f2) noexcept(
  44     noexcept(__compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2))))
  45     -> decltype(__compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2))) {
  46   return __compose_t<decay_t<_Fn1>, decay_t<_Fn2>>(std::forward<_Fn1>(__f1), std::forward<_Fn2>(__f2));
  47 }
  48
  49 #endif // _LIBCPP_STD_VER >= 20
  50
  51 _LIBCPP_END_NAMESPACE_STD
  52
  53 #endif // _LIBCPP___FUNCTIONAL_COMPOSE_H