libcxx/include/__algorithm/make_projected.h

//===----------------------------------------------------------------------===//
//
// 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___ALGORITHM_MAKE_PROJECTED_H
#define _LIBCPP___ALGORITHM_MAKE_PROJECTED_H

#include <__config>
#include <__functional/identity.h>
#include <__functional/invoke.h>
#include <__type_traits/decay.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/invoke.h>
#include <__type_traits/is_member_pointer.h>
#include <__utility/declval.h>
#include <__utility/forward.h>

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

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Pred, class _Proj>
struct _ProjectedPred {
  _Pred& __pred; // Can be a unary or a binary predicate.
  _Proj& __proj;

  _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI _ProjectedPred(_Pred& __pred_arg, _Proj& __proj_arg)
      : __pred(__pred_arg), __proj(__proj_arg) {}

  template <class _Tp>
  __invoke_result_t<_Pred&, decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_Tp>()))> _LIBCPP_CONSTEXPR
  _LIBCPP_HIDE_FROM_ABI
  operator()(_Tp&& __v) const {
    return std::__invoke(__pred, std::__invoke(__proj, std::forward<_Tp>(__v)));
  }

  template <class _T1, class _T2>
  __invoke_result_t<_Pred&,
                    decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T1>())),
                    decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T2>()))> _LIBCPP_CONSTEXPR
  _LIBCPP_HIDE_FROM_ABI
  operator()(_T1&& __lhs, _T2&& __rhs) const {
    return std::__invoke(
        __pred, std::__invoke(__proj, std::forward<_T1>(__lhs)), std::__invoke(__proj, std::forward<_T2>(__rhs)));
  }
};

template <
    class _Pred,
    class _Proj,
    __enable_if_t<!(!is_member_pointer<__decay_t<_Pred> >::value && __is_identity<__decay_t<_Proj> >::value), int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ProjectedPred<_Pred, _Proj> __make_projected(_Pred& __pred, _Proj& __proj) {
  return _ProjectedPred<_Pred, _Proj>(__pred, __proj);
}

// Avoid creating the functor and just use the pristine comparator -- for certain algorithms, this would enable
// optimizations that rely on the type of the comparator. Additionally, this results in less layers of indirection in
// the call stack when the comparator is invoked, even in an unoptimized build.
template <
    class _Pred,
    class _Proj,
    __enable_if_t<!is_member_pointer<__decay_t<_Pred> >::value && __is_identity<__decay_t<_Proj> >::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Pred& __make_projected(_Pred& __pred, _Proj&) {
  return __pred;
}

_LIBCPP_END_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 20

_LIBCPP_BEGIN_NAMESPACE_STD

namespace ranges {

template <class _Comp, class _Proj1, class _Proj2>
_LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
  if constexpr (__is_identity<decay_t<_Proj1>>::value && __is_identity<decay_t<_Proj2>>::value &&
                !is_member_pointer_v<decay_t<_Comp>>) {
    // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
    // optimizations that rely on the type of the comparator.
    return __comp;

  } else {
    return [&](auto&& __lhs, auto&& __rhs) -> bool {
      return std::invoke(__comp,
                         std::invoke(__proj1, std::forward<decltype(__lhs)>(__lhs)),
                         std::invoke(__proj2, std::forward<decltype(__rhs)>(__rhs)));
    };
  }
}

} // namespace ranges

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_STD_VER >= 20

#endif // _LIBCPP___ALGORITHM_MAKE_PROJECTED_H