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___RANGES_DROP_WHILE_VIEW_H
11 #define _LIBCPP___RANGES_DROP_WHILE_VIEW_H
12 
13 #include <__algorithm/ranges_find_if_not.h>
14 #include <__assert>
15 #include <__concepts/constructible.h>
16 #include <__config>
17 #include <__functional/bind_back.h>
18 #include <__functional/reference_wrapper.h>
19 #include <__iterator/concepts.h>
20 #include <__ranges/access.h>
21 #include <__ranges/all.h>
22 #include <__ranges/concepts.h>
23 #include <__ranges/copyable_box.h>
24 #include <__ranges/enable_borrowed_range.h>
25 #include <__ranges/non_propagating_cache.h>
26 #include <__ranges/range_adaptor.h>
27 #include <__ranges/view_interface.h>
28 #include <__type_traits/conditional.h>
29 #include <__type_traits/decay.h>
30 #include <__type_traits/is_nothrow_constructible.h>
31 #include <__type_traits/is_object.h>
32 #include <__utility/forward.h>
33 #include <__utility/in_place.h>
34 #include <__utility/move.h>
35 
36 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
37 #  pragma GCC system_header
38 #endif
39 
40 _LIBCPP_BEGIN_NAMESPACE_STD
41 
42 #if _LIBCPP_STD_VER >= 20
43 
44 namespace ranges {
45 
46 template <view _View, class _Pred>
47   requires input_range<_View> && is_object_v<_Pred> && indirect_unary_predicate<const _Pred, iterator_t<_View>>
48 class drop_while_view : public view_interface<drop_while_view<_View, _Pred>> {
49 public:
50   _LIBCPP_HIDE_FROM_ABI drop_while_view()
51     requires default_initializable<_View> && default_initializable<_Pred>
52   = default;
53 
54   _LIBCPP_HIDE_FROM_ABI constexpr drop_while_view(_View __base, _Pred __pred)
55       : __base_(std::move(__base)), __pred_(std::in_place, std::move(__pred)) {}
56 
57   _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
58     requires copy_constructible<_View>
59   {
60     return __base_;
61   }
62 
63   _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
64 
65   _LIBCPP_HIDE_FROM_ABI constexpr const _Pred& pred() const { return *__pred_; }
66 
67   _LIBCPP_HIDE_FROM_ABI constexpr auto begin() {
68     _LIBCPP_ASSERT(__pred_.__has_value(),
69                    "drop_while_view needs to have a non-empty predicate before calling begin() -- did a previous "
70                    "assignment to this drop_while_view fail?");
71     if constexpr (_UseCache) {
72       if (!__cached_begin_.__has_value()) {
73         __cached_begin_.__emplace(ranges::find_if_not(__base_, std::cref(*__pred_)));
74       }
75       return *__cached_begin_;
76     } else {
77       return ranges::find_if_not(__base_, std::cref(*__pred_));
78     }
79   }
80 
81   _LIBCPP_HIDE_FROM_ABI constexpr auto end() { return ranges::end(__base_); }
82 
83 private:
84   _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
85   _LIBCPP_NO_UNIQUE_ADDRESS __copyable_box<_Pred> __pred_;
86 
87   static constexpr bool _UseCache = forward_range<_View>;
88   using _Cache                    = _If<_UseCache, __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
89   _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache();
90 };
91 
92 template <class _View, class _Pred>
93 inline constexpr bool enable_borrowed_range<drop_while_view<_View, _Pred>> = enable_borrowed_range<_View>;
94 
95 template <class _Range, class _Pred>
96 drop_while_view(_Range&&, _Pred) -> drop_while_view<views::all_t<_Range>, _Pred>;
97 
98 namespace views {
99 namespace __drop_while {
100 
101 struct __fn {
102   template <class _Range, class _Pred>
103   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Pred&& __pred) const
104       noexcept(noexcept(/**/ drop_while_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred))))
105           -> decltype(/*--*/ drop_while_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred))) {
106     return /*-------------*/ drop_while_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred));
107   }
108 
109   template <class _Pred>
110     requires constructible_from<decay_t<_Pred>, _Pred>
111   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Pred&& __pred) const
112       noexcept(is_nothrow_constructible_v<decay_t<_Pred>, _Pred>) {
113     return __range_adaptor_closure_t(std::__bind_back(*this, std::forward<_Pred>(__pred)));
114   }
115 };
116 
117 } // namespace __drop_while
118 
119 inline namespace __cpo {
120 inline constexpr auto drop_while = __drop_while::__fn{};
121 } // namespace __cpo
122 } // namespace views
123 } // namespace ranges
124 
125 #endif // _LIBCPP_STD_VER >= 20
126 
127 _LIBCPP_END_NAMESPACE_STD
128 
129 #endif // _LIBCPP___RANGES_DROP_WHILE_VIEW_H
130