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_VIEW_H
11#define _LIBCPP___RANGES_DROP_VIEW_H
12
13#include <__algorithm/min.h>
14#include <__assert>
15#include <__concepts/constructible.h>
16#include <__concepts/convertible_to.h>
17#include <__config>
18#include <__cstddef/size_t.h>
19#include <__functional/bind_back.h>
20#include <__fwd/span.h>
21#include <__fwd/string_view.h>
22#include <__iterator/concepts.h>
23#include <__iterator/distance.h>
24#include <__iterator/iterator_traits.h>
25#include <__iterator/next.h>
26#include <__ranges/access.h>
27#include <__ranges/all.h>
28#include <__ranges/concepts.h>
29#include <__ranges/empty_view.h>
30#include <__ranges/enable_borrowed_range.h>
31#include <__ranges/iota_view.h>
32#include <__ranges/non_propagating_cache.h>
33#include <__ranges/range_adaptor.h>
34#include <__ranges/repeat_view.h>
35#include <__ranges/size.h>
36#include <__ranges/subrange.h>
37#include <__ranges/view_interface.h>
38#include <__type_traits/conditional.h>
39#include <__type_traits/decay.h>
40#include <__type_traits/is_nothrow_constructible.h>
41#include <__type_traits/make_unsigned.h>
42#include <__type_traits/remove_cvref.h>
43#include <__utility/auto_cast.h>
44#include <__utility/forward.h>
45#include <__utility/move.h>
46
47#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
48# pragma GCC system_header
49#endif
50
51_LIBCPP_PUSH_MACROS
52#include <__undef_macros>
53
54_LIBCPP_BEGIN_NAMESPACE_STD
55
56#if _LIBCPP_STD_VER >= 20
57
58namespace ranges {
59template <view _View>
60class drop_view : public view_interface<drop_view<_View>> {
61 // We cache begin() whenever ranges::next is not guaranteed O(1) to provide an
62 // amortized O(1) begin() method. If this is an input_range, then we cannot cache
63 // begin because begin is not equality preserving.
64 // Note: drop_view<input-range>::begin() is still trivially amortized O(1) because
65 // one can't call begin() on it more than once.
66 static constexpr bool _UseCache = forward_range<_View> && !(random_access_range<_View> && sized_range<_View>);
67 using _Cache _LIBCPP_NODEBUG = _If<_UseCache, __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
68 _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache();
69 range_difference_t<_View> __count_ = 0;
70 _View __base_ = _View();
71
72public:
73 _LIBCPP_HIDE_FROM_ABI drop_view()
74 requires default_initializable<_View>
75 = default;
76
77 _LIBCPP_HIDE_FROM_ABI constexpr _LIBCPP_EXPLICIT_SINCE_CXX23
78 drop_view(_View __base, range_difference_t<_View> __count)
79 : __count_(__count), __base_(std::move(__base)) {
80 _LIBCPP_ASSERT_UNCATEGORIZED(__count_ >= 0, "count must be greater than or equal to zero.");
81 }
82
83 _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
84 requires copy_constructible<_View>
85 {
86 return __base_;
87 }
88 _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
89
90 _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
91 requires(!(__simple_view<_View> && random_access_range<const _View> && sized_range<const _View>))
92 {
93 if constexpr (random_access_range<_View> && sized_range<_View>) {
94 const auto __dist = std::min(ranges::distance(__base_), __count_);
95 return ranges::begin(__base_) + __dist;
96 }
97 if constexpr (_UseCache)
98 if (__cached_begin_.__has_value())
99 return *__cached_begin_;
100
101 auto __tmp = ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_));
102 if constexpr (_UseCache)
103 __cached_begin_.__emplace(__tmp);
104 return __tmp;
105 }
106
107 _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
108 requires random_access_range<const _View> && sized_range<const _View>
109 {
110 const auto __dist = std::min(ranges::distance(__base_), __count_);
111 return ranges::begin(__base_) + __dist;
112 }
113
114 _LIBCPP_HIDE_FROM_ABI constexpr auto end()
115 requires(!__simple_view<_View>)
116 {
117 return ranges::end(__base_);
118 }
119
120 _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
121 requires range<const _View>
122 {
123 return ranges::end(__base_);
124 }
125
126 _LIBCPP_HIDE_FROM_ABI static constexpr auto __size(auto& __self) {
127 const auto __s = ranges::size(__self.__base_);
128 const auto __c = static_cast<decltype(__s)>(__self.__count_);
129 return __s < __c ? 0 : __s - __c;
130 }
131
132 _LIBCPP_HIDE_FROM_ABI constexpr auto size()
133 requires sized_range<_View>
134 {
135 return __size(*this);
136 }
137
138 _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
139 requires sized_range<const _View>
140 {
141 return __size(*this);
142 }
143};
144
145template <class _Range>
146drop_view(_Range&&, range_difference_t<_Range>) -> drop_view<views::all_t<_Range>>;
147
148template <class _Tp>
149inline constexpr bool enable_borrowed_range<drop_view<_Tp>> = enable_borrowed_range<_Tp>;
150
151namespace views {
152namespace __drop {
153
154template <class _Tp>
155inline constexpr bool __is_empty_view = false;
156
157template <class _Tp>
158inline constexpr bool __is_empty_view<empty_view<_Tp>> = true;
159
160template <class _Tp>
161inline constexpr bool __is_passthrough_specialization = false;
162
163template <class _Tp, size_t _Extent>
164inline constexpr bool __is_passthrough_specialization<span<_Tp, _Extent>> = true;
165
166template <class _CharT, class _Traits>
167inline constexpr bool __is_passthrough_specialization<basic_string_view<_CharT, _Traits>> = true;
168
169template <class _Np, class _Bound>
170inline constexpr bool __is_passthrough_specialization<iota_view<_Np, _Bound>> = true;
171
172template <class _Iter, class _Sent, subrange_kind _Kind>
173inline constexpr bool __is_passthrough_specialization<subrange<_Iter, _Sent, _Kind>> =
174 !subrange<_Iter, _Sent, _Kind>::_StoreSize;
175
176template <class _Tp>
177inline constexpr bool __is_subrange_specialization_with_store_size = false;
178
179template <class _Iter, class _Sent, subrange_kind _Kind>
180inline constexpr bool __is_subrange_specialization_with_store_size<subrange<_Iter, _Sent, _Kind>> =
181 subrange<_Iter, _Sent, _Kind>::_StoreSize;
182
183template <class _Tp>
184struct __passthrough_type;
185
186template <class _Tp, size_t _Extent>
187struct __passthrough_type<span<_Tp, _Extent>> {
188 using type _LIBCPP_NODEBUG = span<_Tp>;
189};
190
191template <class _CharT, class _Traits>
192struct __passthrough_type<basic_string_view<_CharT, _Traits>> {
193 using type _LIBCPP_NODEBUG = basic_string_view<_CharT, _Traits>;
194};
195
196template <class _Np, class _Bound>
197struct __passthrough_type<iota_view<_Np, _Bound>> {
198 using type _LIBCPP_NODEBUG = iota_view<_Np, _Bound>;
199};
200
201template <class _Iter, class _Sent, subrange_kind _Kind>
202struct __passthrough_type<subrange<_Iter, _Sent, _Kind>> {
203 using type _LIBCPP_NODEBUG = subrange<_Iter, _Sent, _Kind>;
204};
205
206template <class _Tp>
207using __passthrough_type_t _LIBCPP_NODEBUG = typename __passthrough_type<_Tp>::type;
208
209struct __fn {
210 // [range.drop.overview]: the `empty_view` case.
211 template <class _Range, convertible_to<range_difference_t<_Range>> _Np>
212 requires __is_empty_view<remove_cvref_t<_Range>>
213 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&&) const
214 noexcept(noexcept(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))))
215 -> decltype(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))) {
216 return _LIBCPP_AUTO_CAST(std::forward<_Range>(__range));
217 }
218
219 // [range.drop.overview]: the `span | basic_string_view | iota_view | subrange (StoreSize == false)` case.
220 template <class _Range,
221 convertible_to<range_difference_t<_Range>> _Np,
222 class _RawRange = remove_cvref_t<_Range>,
223 class _Dist = range_difference_t<_Range>>
224 requires(!__is_empty_view<_RawRange> && random_access_range<_RawRange> && sized_range<_RawRange> &&
225 __is_passthrough_specialization<_RawRange>)
226 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __rng, _Np&& __n) const
227 noexcept(noexcept(__passthrough_type_t<_RawRange>(
228 ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)), ranges::end(__rng))))
229 -> decltype(__passthrough_type_t<_RawRange>(
230 // Note: deliberately not forwarding `__rng` to guard against double moves.
231 ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)),
232 ranges::end(__rng))) {
233 return __passthrough_type_t<_RawRange>(
234 ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)), ranges::end(__rng));
235 }
236
237 // [range.drop.overview]: the `subrange (StoreSize == true)` case.
238 template <class _Range,
239 convertible_to<range_difference_t<_Range>> _Np,
240 class _RawRange = remove_cvref_t<_Range>,
241 class _Dist = range_difference_t<_Range>>
242 requires(!__is_empty_view<_RawRange> && random_access_range<_RawRange> && sized_range<_RawRange> &&
243 __is_subrange_specialization_with_store_size<_RawRange>)
244 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __rng, _Np&& __n) const noexcept(noexcept(
245 _RawRange(ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)),
246 ranges::end(__rng),
247 std::__to_unsigned_like(ranges::distance(__rng) -
248 std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))))))
249 -> decltype(_RawRange(
250 // Note: deliberately not forwarding `__rng` to guard against double moves.
251 ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)),
252 ranges::end(__rng),
253 std::__to_unsigned_like(ranges::distance(__rng) -
254 std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))))) {
255 // Introducing local variables avoids calculating `min` and `distance` twice (at the cost of diverging from the
256 // expression used in the `noexcept` clause and the return statement).
257 auto __dist = ranges::distance(__rng);
258 auto __clamped = std::min<_Dist>(__dist, std::forward<_Np>(__n));
259 return _RawRange(ranges::begin(__rng) + __clamped, ranges::end(__rng), std::__to_unsigned_like(__dist - __clamped));
260 }
261 // clang-format off
262#if _LIBCPP_STD_VER >= 23
263 // [range.drop.overview]: the `repeat_view` "_RawRange models sized_range" case.
264 template <class _Range,
265 convertible_to<range_difference_t<_Range>> _Np,
266 class _RawRange = remove_cvref_t<_Range>,
267 class _Dist = range_difference_t<_Range>>
268 requires (__is_repeat_specialization<_RawRange> && sized_range<_RawRange>)
269 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
270 noexcept(noexcept(views::repeat(*__range.__value_, ranges::distance(__range) - std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n)))))
271 -> decltype( views::repeat(*__range.__value_, ranges::distance(__range) - std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))))
272 { return views::repeat(*__range.__value_, ranges::distance(__range) - std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))); }
273
274 // [range.drop.overview]: the `repeat_view` "otherwise" case.
275 template <class _Range,
276 convertible_to<range_difference_t<_Range>> _Np,
277 class _RawRange = remove_cvref_t<_Range>,
278 class _Dist = range_difference_t<_Range>>
279 requires (__is_repeat_specialization<_RawRange> && !sized_range<_RawRange>)
280 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
281 constexpr auto operator()(_Range&& __range, _Np&&) const
282 noexcept(noexcept(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))))
283 -> decltype( _LIBCPP_AUTO_CAST(std::forward<_Range>(__range)))
284 { return _LIBCPP_AUTO_CAST(std::forward<_Range>(__range)); }
285#endif
286 // clang-format on
287
288 // [range.drop.overview]: the "otherwise" case.
289 template <class _Range, convertible_to<range_difference_t<_Range>> _Np, class _RawRange = remove_cvref_t<_Range>>
290 // Note: without specifically excluding the other cases, GCC sees this overload as ambiguous with the other
291 // overloads.
292 requires(!(__is_empty_view<_RawRange> ||
293# if _LIBCPP_STD_VER >= 23
294 __is_repeat_specialization<_RawRange> ||
295# endif
296 (__is_subrange_specialization_with_store_size<_RawRange> && sized_range<_RawRange> &&
297 random_access_range<_RawRange>) ||
298 (__is_passthrough_specialization<_RawRange> && sized_range<_RawRange> &&
299 random_access_range<_RawRange>)))
300 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
301 noexcept(noexcept(drop_view(std::forward<_Range>(__range), std::forward<_Np>(__n))))
302 -> decltype(drop_view(std::forward<_Range>(__range), std::forward<_Np>(__n))) {
303 return drop_view(std::forward<_Range>(__range), std::forward<_Np>(__n));
304 }
305
306 template <class _Np>
307 requires constructible_from<decay_t<_Np>, _Np>
308 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Np&& __n) const
309 noexcept(is_nothrow_constructible_v<decay_t<_Np>, _Np>) {
310 return __pipeable(std::__bind_back(*this, std::forward<_Np>(__n)));
311 }
312};
313
314} // namespace __drop
315
316inline namespace __cpo {
317inline constexpr auto drop = __drop::__fn{};
318} // namespace __cpo
319} // namespace views
320
321} // namespace ranges
322
323#endif // _LIBCPP_STD_VER >= 20
324
325_LIBCPP_END_NAMESPACE_STD
326
327_LIBCPP_POP_MACROS
328
329#endif // _LIBCPP___RANGES_DROP_VIEW_H
330