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___ALGORITHM_FOLD_H
11 #define _LIBCPP___ALGORITHM_FOLD_H
12 
13 #include <__concepts/assignable.h>
14 #include <__concepts/convertible_to.h>
15 #include <__concepts/invocable.h>
16 #include <__concepts/movable.h>
17 #include <__config>
18 #include <__functional/invoke.h>
19 #include <__functional/reference_wrapper.h>
20 #include <__iterator/concepts.h>
21 #include <__iterator/iterator_traits.h>
22 #include <__iterator/next.h>
23 #include <__ranges/access.h>
24 #include <__ranges/concepts.h>
25 #include <__ranges/dangling.h>
26 #include <__type_traits/decay.h>
27 #include <__type_traits/invoke.h>
28 #include <__utility/forward.h>
29 #include <__utility/move.h>
30 
31 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
32 #  pragma GCC system_header
33 #endif
34 
35 _LIBCPP_PUSH_MACROS
36 #include <__undef_macros>
37 
38 _LIBCPP_BEGIN_NAMESPACE_STD
39 
40 #if _LIBCPP_STD_VER >= 23
41 
42 namespace ranges {
43 template <class _Ip, class _Tp>
44 struct in_value_result {
45   _LIBCPP_NO_UNIQUE_ADDRESS _Ip in;
46   _LIBCPP_NO_UNIQUE_ADDRESS _Tp value;
47 
48   template <class _I2, class _T2>
49     requires convertible_to<const _Ip&, _I2> && convertible_to<const _Tp&, _T2>
50   _LIBCPP_HIDE_FROM_ABI constexpr operator in_value_result<_I2, _T2>() const& {
51     return {in, value};
52   }
53 
54   template <class _I2, class _T2>
55     requires convertible_to<_Ip, _I2> && convertible_to<_Tp, _T2>
56   _LIBCPP_HIDE_FROM_ABI constexpr operator in_value_result<_I2, _T2>() && {
57     return {std::move(in), std::move(value)};
58   }
59 };
60 
61 template <class _Ip, class _Tp>
62 using fold_left_with_iter_result = in_value_result<_Ip, _Tp>;
63 
64 template <class _Fp, class _Tp, class _Ip, class _Rp, class _Up = decay_t<_Rp>>
65 concept __indirectly_binary_left_foldable_impl =
66     convertible_to<_Rp, _Up> &&                    //
67     movable<_Tp> &&                                //
68     movable<_Up> &&                                //
69     convertible_to<_Tp, _Up> &&                    //
70     invocable<_Fp&, _Up, iter_reference_t<_Ip>> && //
71     assignable_from<_Up&, invoke_result_t<_Fp&, _Up, iter_reference_t<_Ip>>>;
72 
73 template <class _Fp, class _Tp, class _Ip>
74 concept __indirectly_binary_left_foldable =
75     copy_constructible<_Fp> &&                     //
76     invocable<_Fp&, _Tp, iter_reference_t<_Ip>> && //
77     __indirectly_binary_left_foldable_impl<_Fp, _Tp, _Ip, invoke_result_t<_Fp&, _Tp, iter_reference_t<_Ip>>>;
78 
79 struct __fold_left_with_iter {
80   template <input_iterator _Ip, sentinel_for<_Ip> _Sp, class _Tp, __indirectly_binary_left_foldable<_Tp, _Ip> _Fp>
81   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI static constexpr auto
operator__fold_left_with_iter82   operator()(_Ip __first, _Sp __last, _Tp __init, _Fp __f) {
83     using _Up = decay_t<invoke_result_t<_Fp&, _Tp, iter_reference_t<_Ip>>>;
84 
85     if (__first == __last) {
86       return fold_left_with_iter_result<_Ip, _Up>{std::move(__first), _Up(std::move(__init))};
87     }
88 
89     _Up __result = std::invoke(__f, std::move(__init), *__first);
90     for (++__first; __first != __last; ++__first) {
91       __result = std::invoke(__f, std::move(__result), *__first);
92     }
93 
94     return fold_left_with_iter_result<_Ip, _Up>{std::move(__first), std::move(__result)};
95   }
96 
97   template <input_range _Rp, class _Tp, __indirectly_binary_left_foldable<_Tp, iterator_t<_Rp>> _Fp>
operator__fold_left_with_iter98   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI static constexpr auto operator()(_Rp&& __r, _Tp __init, _Fp __f) {
99     auto __result = operator()(ranges::begin(__r), ranges::end(__r), std::move(__init), std::ref(__f));
100 
101     using _Up = decay_t<invoke_result_t<_Fp&, _Tp, range_reference_t<_Rp>>>;
102     return fold_left_with_iter_result<borrowed_iterator_t<_Rp>, _Up>{std::move(__result.in), std::move(__result.value)};
103   }
104 };
105 
106 inline constexpr auto fold_left_with_iter = __fold_left_with_iter();
107 
108 struct __fold_left {
109   template <input_iterator _Ip, sentinel_for<_Ip> _Sp, class _Tp, __indirectly_binary_left_foldable<_Tp, _Ip> _Fp>
110   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI static constexpr auto
operator__fold_left111   operator()(_Ip __first, _Sp __last, _Tp __init, _Fp __f) {
112     return fold_left_with_iter(std::move(__first), std::move(__last), std::move(__init), std::ref(__f)).value;
113   }
114 
115   template <input_range _Rp, class _Tp, __indirectly_binary_left_foldable<_Tp, iterator_t<_Rp>> _Fp>
operator__fold_left116   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI static constexpr auto operator()(_Rp&& __r, _Tp __init, _Fp __f) {
117     return fold_left_with_iter(ranges::begin(__r), ranges::end(__r), std::move(__init), std::ref(__f)).value;
118   }
119 };
120 
121 inline constexpr auto fold_left = __fold_left();
122 } // namespace ranges
123 
124 #endif // _LIBCPP_STD_VER >= 23
125 
126 _LIBCPP_END_NAMESPACE_STD
127 
128 _LIBCPP_POP_MACROS
129 
130 #endif // _LIBCPP___ALGORITHM_FOLD_H
131