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_TAKE_VIEW_H
11#define _LIBCPP___RANGES_TAKE_VIEW_H
12
13#include <__algorithm/min.h>
14#include <__algorithm/ranges_min.h>
15#include <__assert>
16#include <__concepts/constructible.h>
17#include <__concepts/convertible_to.h>
18#include <__config>
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/counted_iterator.h>
24#include <__iterator/default_sentinel.h>
25#include <__iterator/distance.h>
26#include <__iterator/iterator_traits.h>
27#include <__ranges/access.h>
28#include <__ranges/all.h>
29#include <__ranges/concepts.h>
30#include <__ranges/empty_view.h>
31#include <__ranges/enable_borrowed_range.h>
32#include <__ranges/iota_view.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/decay.h>
39#include <__type_traits/is_nothrow_constructible.h>
40#include <__type_traits/maybe_const.h>
41#include <__type_traits/remove_cvref.h>
42#include <__utility/auto_cast.h>
43#include <__utility/forward.h>
44#include <__utility/move.h>
45
46#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
47# pragma GCC system_header
48#endif
49
50_LIBCPP_PUSH_MACROS
51#include <__undef_macros>
52
53_LIBCPP_BEGIN_NAMESPACE_STD
54
55#if _LIBCPP_STD_VER >= 20
56
57namespace ranges {
58
59template <view _View>
60class take_view : public view_interface<take_view<_View>> {
61 _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
62 range_difference_t<_View> __count_ = 0;
63
64 template <bool>
65 class __sentinel;
66
67public:
68 _LIBCPP_HIDE_FROM_ABI take_view()
69 requires default_initializable<_View>
70 = default;
71
72 _LIBCPP_HIDE_FROM_ABI constexpr _LIBCPP_EXPLICIT_SINCE_CXX23
73 take_view(_View __base, range_difference_t<_View> __count)
74 : __base_(std::move(__base)), __count_(__count) {
75 _LIBCPP_ASSERT_UNCATEGORIZED(__count >= 0, "count has to be greater than or equal to zero");
76 }
77
78 _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
79 requires copy_constructible<_View>
80 {
81 return __base_;
82 }
83
84 _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
85
86 _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
87 requires(!__simple_view<_View>)
88 {
89 if constexpr (sized_range<_View>) {
90 if constexpr (random_access_range<_View>) {
91 return ranges::begin(__base_);
92 } else {
93 using _DifferenceT = range_difference_t<_View>;
94 auto __size = size();
95 return counted_iterator(ranges::begin(__base_), static_cast<_DifferenceT>(__size));
96 }
97 } else {
98 return counted_iterator(ranges::begin(__base_), __count_);
99 }
100 }
101
102 _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
103 requires range<const _View>
104 {
105 if constexpr (sized_range<const _View>) {
106 if constexpr (random_access_range<const _View>) {
107 return ranges::begin(__base_);
108 } else {
109 using _DifferenceT = range_difference_t<const _View>;
110 auto __size = size();
111 return counted_iterator(ranges::begin(__base_), static_cast<_DifferenceT>(__size));
112 }
113 } else {
114 return counted_iterator(ranges::begin(__base_), __count_);
115 }
116 }
117
118 _LIBCPP_HIDE_FROM_ABI constexpr auto end()
119 requires(!__simple_view<_View>)
120 {
121 if constexpr (sized_range<_View>) {
122 if constexpr (random_access_range<_View>) {
123 return ranges::begin(__base_) + size();
124 } else {
125 return default_sentinel;
126 }
127 } else {
128 return __sentinel<false>{ranges::end(__base_)};
129 }
130 }
131
132 _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
133 requires range<const _View>
134 {
135 if constexpr (sized_range<const _View>) {
136 if constexpr (random_access_range<const _View>) {
137 return ranges::begin(__base_) + size();
138 } else {
139 return default_sentinel;
140 }
141 } else {
142 return __sentinel<true>{ranges::end(__base_)};
143 }
144 }
145
146 _LIBCPP_HIDE_FROM_ABI constexpr auto size()
147 requires sized_range<_View>
148 {
149 auto __n = ranges::size(__base_);
150 return ranges::min(__n, static_cast<decltype(__n)>(__count_));
151 }
152
153 _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
154 requires sized_range<const _View>
155 {
156 auto __n = ranges::size(__base_);
157 return ranges::min(__n, static_cast<decltype(__n)>(__count_));
158 }
159};
160
161template <view _View>
162template <bool _Const>
163class take_view<_View>::__sentinel {
164 using _Base _LIBCPP_NODEBUG = __maybe_const<_Const, _View>;
165 template <bool _OtherConst>
166 using _Iter _LIBCPP_NODEBUG = counted_iterator<iterator_t<__maybe_const<_OtherConst, _View>>>;
167 _LIBCPP_NO_UNIQUE_ADDRESS sentinel_t<_Base> __end_ = sentinel_t<_Base>();
168
169 template <bool>
170 friend class take_view<_View>::__sentinel;
171
172public:
173 _LIBCPP_HIDE_FROM_ABI __sentinel() = default;
174
175 _LIBCPP_HIDE_FROM_ABI constexpr explicit __sentinel(sentinel_t<_Base> __end) : __end_(std::move(__end)) {}
176
177 _LIBCPP_HIDE_FROM_ABI constexpr __sentinel(__sentinel<!_Const> __s)
178 requires _Const && convertible_to<sentinel_t<_View>, sentinel_t<_Base>>
179 : __end_(std::move(__s.__end_)) {}
180
181 _LIBCPP_HIDE_FROM_ABI constexpr sentinel_t<_Base> base() const { return __end_; }
182
183 _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const _Iter<_Const>& __lhs, const __sentinel& __rhs) {
184 return __lhs.count() == 0 || __lhs.base() == __rhs.__end_;
185 }
186
187 template <bool _OtherConst = !_Const>
188 requires sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
189 _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const _Iter<_OtherConst>& __lhs, const __sentinel& __rhs) {
190 return __lhs.count() == 0 || __lhs.base() == __rhs.__end_;
191 }
192};
193
194template <class _Range>
195take_view(_Range&&, range_difference_t<_Range>) -> take_view<views::all_t<_Range>>;
196
197template <class _Tp>
198inline constexpr bool enable_borrowed_range<take_view<_Tp>> = enable_borrowed_range<_Tp>;
199
200namespace views {
201namespace __take {
202
203template <class _Tp>
204inline constexpr bool __is_empty_view = false;
205
206template <class _Tp>
207inline constexpr bool __is_empty_view<empty_view<_Tp>> = true;
208
209template <class _Tp>
210inline constexpr bool __is_passthrough_specialization = false;
211
212template <class _Tp, size_t _Extent>
213inline constexpr bool __is_passthrough_specialization<span<_Tp, _Extent>> = true;
214
215template <class _CharT, class _Traits>
216inline constexpr bool __is_passthrough_specialization<basic_string_view<_CharT, _Traits>> = true;
217
218template <class _Iter, class _Sent, subrange_kind _Kind>
219inline constexpr bool __is_passthrough_specialization<subrange<_Iter, _Sent, _Kind>> = true;
220
221template <class _Tp>
222inline constexpr bool __is_iota_specialization = false;
223
224template <class _Np, class _Bound>
225inline constexpr bool __is_iota_specialization<iota_view<_Np, _Bound>> = true;
226
227template <class _Tp>
228struct __passthrough_type;
229
230template <class _Tp, size_t _Extent>
231struct __passthrough_type<span<_Tp, _Extent>> {
232 using type _LIBCPP_NODEBUG = span<_Tp>;
233};
234
235template <class _CharT, class _Traits>
236struct __passthrough_type<basic_string_view<_CharT, _Traits>> {
237 using type _LIBCPP_NODEBUG = basic_string_view<_CharT, _Traits>;
238};
239
240template <class _Iter, class _Sent, subrange_kind _Kind>
241 requires requires { typename subrange<_Iter>; }
242struct __passthrough_type<subrange<_Iter, _Sent, _Kind>> {
243 using type _LIBCPP_NODEBUG = subrange<_Iter>;
244};
245
246template <class _Tp>
247using __passthrough_type_t _LIBCPP_NODEBUG = typename __passthrough_type<_Tp>::type;
248
249struct __fn {
250 // [range.take.overview]: the `empty_view` case.
251 template <class _Range, convertible_to<range_difference_t<_Range>> _Np>
252 requires __is_empty_view<remove_cvref_t<_Range>>
253 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&&) const
254 noexcept(noexcept(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))))
255 -> decltype(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))) {
256 return _LIBCPP_AUTO_CAST(std::forward<_Range>(__range));
257 }
258
259 // [range.take.overview]: the `span | basic_string_view | subrange` case.
260 template <class _Range,
261 convertible_to<range_difference_t<_Range>> _Np,
262 class _RawRange = remove_cvref_t<_Range>,
263 class _Dist = range_difference_t<_Range>>
264 requires(!__is_empty_view<_RawRange> && random_access_range<_RawRange> && sized_range<_RawRange> &&
265 __is_passthrough_specialization<_RawRange>)
266 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto
267 operator()(_Range&& __rng, _Np&& __n) const noexcept(noexcept(__passthrough_type_t<_RawRange>(
268 ranges::begin(__rng), ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))))
269 -> decltype(__passthrough_type_t<_RawRange>(
270 // Note: deliberately not forwarding `__rng` to guard against double moves.
271 ranges::begin(__rng),
272 ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))) {
273 return __passthrough_type_t<_RawRange>(
274 ranges::begin(__rng), ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)));
275 }
276
277 // [range.take.overview]: the `iota_view` case.
278 // clang-format off
279 template <class _Range,
280 convertible_to<range_difference_t<_Range>> _Np,
281 class _RawRange = remove_cvref_t<_Range>,
282 class _Dist = range_difference_t<_Range>>
283 requires (!__is_empty_view<_RawRange> &&
284 random_access_range<_RawRange> &&
285 sized_range<_RawRange> &&
286 __is_iota_specialization<_RawRange>)
287 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
288 constexpr auto operator()(_Range&& __rng, _Np&& __n) const
289 noexcept(noexcept(ranges::iota_view(
290 *ranges::begin(__rng),
291 *(ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))
292 )))
293 -> decltype( ranges::iota_view(
294 // Note: deliberately not forwarding `__rng` to guard against double moves.
295 *ranges::begin(__rng),
296 *(ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))
297 ))
298 { return ranges::iota_view(
299 *ranges::begin(__rng),
300 *(ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))
301 ); }
302
303#if _LIBCPP_STD_VER >= 23
304 // [range.take.overview]: the `repeat_view` "_RawRange models sized_range" case.
305 template <class _Range,
306 convertible_to<range_difference_t<_Range>> _Np,
307 class _RawRange = remove_cvref_t<_Range>,
308 class _Dist = range_difference_t<_Range>>
309 requires(__is_repeat_specialization<_RawRange> && sized_range<_RawRange>)
310 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
311 noexcept(noexcept(views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n)))))
312 -> decltype( views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))))
313 { return views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))); }
314
315 // [range.take.overview]: the `repeat_view` "otherwise" case.
316 template <class _Range,
317 convertible_to<range_difference_t<_Range>> _Np,
318 class _RawRange = remove_cvref_t<_Range>,
319 class _Dist = range_difference_t<_Range>>
320 requires(__is_repeat_specialization<_RawRange> && !sized_range<_RawRange>)
321 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
322 noexcept(noexcept(views::repeat(*__range.__value_, static_cast<_Dist>(__n))))
323 -> decltype( views::repeat(*__range.__value_, static_cast<_Dist>(__n)))
324 { return views::repeat(*__range.__value_, static_cast<_Dist>(__n)); }
325#endif
326 // clang-format on
327
328 // [range.take.overview]: the "otherwise" case.
329 template <class _Range, convertible_to<range_difference_t<_Range>> _Np, class _RawRange = remove_cvref_t<_Range>>
330 // Note: without specifically excluding the other cases, GCC sees this overload as ambiguous with the other
331 // overloads.
332 requires(!(__is_empty_view<_RawRange> ||
333# if _LIBCPP_STD_VER >= 23
334 __is_repeat_specialization<_RawRange> ||
335# endif
336 (__is_iota_specialization<_RawRange> && sized_range<_RawRange> && random_access_range<_RawRange>) ||
337 (__is_passthrough_specialization<_RawRange> && sized_range<_RawRange> &&
338 random_access_range<_RawRange>)))
339 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
340 noexcept(noexcept(take_view(std::forward<_Range>(__range), std::forward<_Np>(__n))))
341 -> decltype(take_view(std::forward<_Range>(__range), std::forward<_Np>(__n))) {
342 return take_view(std::forward<_Range>(__range), std::forward<_Np>(__n));
343 }
344
345 template <class _Np>
346 requires constructible_from<decay_t<_Np>, _Np>
347 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Np&& __n) const
348 noexcept(is_nothrow_constructible_v<decay_t<_Np>, _Np>) {
349 return __pipeable(std::__bind_back(*this, std::forward<_Np>(__n)));
350 }
351};
352
353} // namespace __take
354
355inline namespace __cpo {
356inline constexpr auto take = __take::__fn{};
357} // namespace __cpo
358} // namespace views
359
360} // namespace ranges
361
362#endif // _LIBCPP_STD_VER >= 20
363
364_LIBCPP_END_NAMESPACE_STD
365
366_LIBCPP_POP_MACROS
367
368#endif // _LIBCPP___RANGES_TAKE_VIEW_H
369