make_projected.h revision 1.1.1.1 
1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___ALGORITHM_MAKE_PROJECTED_H
10#define _LIBCPP___ALGORITHM_MAKE_PROJECTED_H
11
12#include <__concepts/same_as.h>
13#include <__config>
14#include <__functional/identity.h>
15#include <__functional/invoke.h>
16#include <__type_traits/decay.h>
17#include <__type_traits/enable_if.h>
18#include <__type_traits/integral_constant.h>
19#include <__type_traits/is_member_pointer.h>
20#include <__type_traits/is_same.h>
21#include <__utility/declval.h>
22#include <__utility/forward.h>
23
24#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
25#  pragma GCC system_header
26#endif
27
28_LIBCPP_BEGIN_NAMESPACE_STD
29
30template <class _Pred, class _Proj>
31struct _ProjectedPred {
32  _Pred& __pred; // Can be a unary or a binary predicate.
33  _Proj& __proj;
34
35  _LIBCPP_CONSTEXPR _ProjectedPred(_Pred& __pred_arg, _Proj& __proj_arg) : __pred(__pred_arg), __proj(__proj_arg) {}
36
37  template <class _Tp>
38  typename __invoke_of<_Pred&,
39                       decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_Tp>()))
40  >::type
41  _LIBCPP_CONSTEXPR operator()(_Tp&& __v) const {
42    return std::__invoke(__pred, std::__invoke(__proj, std::forward<_Tp>(__v)));
43  }
44
45  template <class _T1, class _T2>
46  typename __invoke_of<_Pred&,
47                       decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T1>())),
48                       decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T2>()))
49  >::type
50  _LIBCPP_CONSTEXPR operator()(_T1&& __lhs, _T2&& __rhs) const {
51    return std::__invoke(__pred,
52                      std::__invoke(__proj, std::forward<_T1>(__lhs)),
53                      std::__invoke(__proj, std::forward<_T2>(__rhs)));
54  }
55
56};
57
58template <class _Pred, class _Proj, class = void>
59struct __can_use_pristine_comp : false_type {};
60
61template <class _Pred, class _Proj>
62struct __can_use_pristine_comp<_Pred, _Proj, __enable_if_t<
63    !is_member_pointer<typename decay<_Pred>::type>::value && (
64#if _LIBCPP_STD_VER > 17
65      is_same<typename decay<_Proj>::type, identity>::value ||
66#endif
67      is_same<typename decay<_Proj>::type, __identity>::value
68    )
69> > : true_type {};
70
71template <class _Pred, class _Proj>
72_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static
73__enable_if_t<
74    !__can_use_pristine_comp<_Pred, _Proj>::value,
75    _ProjectedPred<_Pred, _Proj>
76>
77__make_projected(_Pred& __pred, _Proj& __proj) {
78  return _ProjectedPred<_Pred, _Proj>(__pred, __proj);
79}
80
81// Avoid creating the functor and just use the pristine comparator -- for certain algorithms, this would enable
82// optimizations that rely on the type of the comparator. Additionally, this results in less layers of indirection in
83// the call stack when the comparator is invoked, even in an unoptimized build.
84template <class _Pred, class _Proj>
85_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static
86__enable_if_t<
87    __can_use_pristine_comp<_Pred, _Proj>::value,
88    _Pred&
89>
90__make_projected(_Pred& __pred, _Proj&) {
91  return __pred;
92}
93
94_LIBCPP_END_NAMESPACE_STD
95
96#if _LIBCPP_STD_VER > 17
97
98_LIBCPP_BEGIN_NAMESPACE_STD
99
100namespace ranges {
101
102template <class _Comp, class _Proj1, class _Proj2>
103_LIBCPP_HIDE_FROM_ABI constexpr static
104decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
105  if constexpr (same_as<decay_t<_Proj1>, identity> && same_as<decay_t<_Proj2>, identity> &&
106                !is_member_pointer_v<decay_t<_Comp>>) {
107    // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
108    // optimizations that rely on the type of the comparator.
109    return __comp;
110
111  } else {
112    return [&](auto&& __lhs, auto&& __rhs) {
113      return std::invoke(__comp,
114                        std::invoke(__proj1, std::forward<decltype(__lhs)>(__lhs)),
115                        std::invoke(__proj2, std::forward<decltype(__rhs)>(__rhs)));
116    };
117  }
118}
119
120} // namespace ranges
121
122_LIBCPP_END_NAMESPACE_STD
123
124#endif // _LIBCPP_STD_VER > 17
125
126#endif // _LIBCPP___ALGORITHM_MAKE_PROJECTED_H
127