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 
30 template <class _Pred, class _Proj>
31 struct _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 
58 template <class _Pred, class _Proj, class = void>
59 struct __can_use_pristine_comp : false_type {};
60 
61 template <class _Pred, class _Proj>
62 struct __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 
71 template <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.
84 template <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 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
97 
98 _LIBCPP_BEGIN_NAMESPACE_STD
99 
100 namespace ranges {
101 
102 template <class _Comp, class _Proj1, class _Proj2>
103 _LIBCPP_HIDE_FROM_ABI constexpr static
104 decltype(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 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
125 
126 #endif // _LIBCPP___ALGORITHM_MAKE_PROJECTED_H
127