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#include <cstddef>
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 {
59
60template <view _View>
61class take_view : public view_interface<take_view<_View>> {
62  _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
63  range_difference_t<_View> __count_      = 0;
64
65  template <bool>
66  class __sentinel;
67
68public:
69  _LIBCPP_HIDE_FROM_ABI take_view()
70    requires default_initializable<_View>
71  = default;
72
73  _LIBCPP_HIDE_FROM_ABI constexpr _LIBCPP_EXPLICIT_SINCE_CXX23
74  take_view(_View __base, range_difference_t<_View> __count)
75      : __base_(std::move(__base)), __count_(__count) {
76    _LIBCPP_ASSERT_UNCATEGORIZED(__count >= 0, "count has to be greater than or equal to zero");
77  }
78
79  _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
80    requires copy_constructible<_View>
81  {
82    return __base_;
83  }
84
85  _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
86
87  _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
88    requires(!__simple_view<_View>)
89  {
90    if constexpr (sized_range<_View>) {
91      if constexpr (random_access_range<_View>) {
92        return ranges::begin(__base_);
93      } else {
94        using _DifferenceT = range_difference_t<_View>;
95        auto __size        = size();
96        return counted_iterator(ranges::begin(__base_), static_cast<_DifferenceT>(__size));
97      }
98    } else {
99      return counted_iterator(ranges::begin(__base_), __count_);
100    }
101  }
102
103  _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
104    requires range<const _View>
105  {
106    if constexpr (sized_range<const _View>) {
107      if constexpr (random_access_range<const _View>) {
108        return ranges::begin(__base_);
109      } else {
110        using _DifferenceT = range_difference_t<const _View>;
111        auto __size        = size();
112        return counted_iterator(ranges::begin(__base_), static_cast<_DifferenceT>(__size));
113      }
114    } else {
115      return counted_iterator(ranges::begin(__base_), __count_);
116    }
117  }
118
119  _LIBCPP_HIDE_FROM_ABI constexpr auto end()
120    requires(!__simple_view<_View>)
121  {
122    if constexpr (sized_range<_View>) {
123      if constexpr (random_access_range<_View>) {
124        return ranges::begin(__base_) + size();
125      } else {
126        return default_sentinel;
127      }
128    } else {
129      return __sentinel<false>{ranges::end(__base_)};
130    }
131  }
132
133  _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
134    requires range<const _View>
135  {
136    if constexpr (sized_range<const _View>) {
137      if constexpr (random_access_range<const _View>) {
138        return ranges::begin(__base_) + size();
139      } else {
140        return default_sentinel;
141      }
142    } else {
143      return __sentinel<true>{ranges::end(__base_)};
144    }
145  }
146
147  _LIBCPP_HIDE_FROM_ABI constexpr auto size()
148    requires sized_range<_View>
149  {
150    auto __n = ranges::size(__base_);
151    return ranges::min(__n, static_cast<decltype(__n)>(__count_));
152  }
153
154  _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
155    requires sized_range<const _View>
156  {
157    auto __n = ranges::size(__base_);
158    return ranges::min(__n, static_cast<decltype(__n)>(__count_));
159  }
160};
161
162template <view _View>
163template <bool _Const>
164class take_view<_View>::__sentinel {
165  using _Base = __maybe_const<_Const, _View>;
166  template <bool _OtherConst>
167  using _Iter                                        = counted_iterator<iterator_t<__maybe_const<_OtherConst, _View>>>;
168  _LIBCPP_NO_UNIQUE_ADDRESS sentinel_t<_Base> __end_ = sentinel_t<_Base>();
169
170  template <bool>
171  friend class take_view<_View>::__sentinel;
172
173public:
174  _LIBCPP_HIDE_FROM_ABI __sentinel() = default;
175
176  _LIBCPP_HIDE_FROM_ABI constexpr explicit __sentinel(sentinel_t<_Base> __end) : __end_(std::move(__end)) {}
177
178  _LIBCPP_HIDE_FROM_ABI constexpr __sentinel(__sentinel<!_Const> __s)
179    requires _Const && convertible_to<sentinel_t<_View>, sentinel_t<_Base>>
180      : __end_(std::move(__s.__end_)) {}
181
182  _LIBCPP_HIDE_FROM_ABI constexpr sentinel_t<_Base> base() const { return __end_; }
183
184  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const _Iter<_Const>& __lhs, const __sentinel& __rhs) {
185    return __lhs.count() == 0 || __lhs.base() == __rhs.__end_;
186  }
187
188  template <bool _OtherConst = !_Const>
189    requires sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
190  _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const _Iter<_OtherConst>& __lhs, const __sentinel& __rhs) {
191    return __lhs.count() == 0 || __lhs.base() == __rhs.__end_;
192  }
193};
194
195template <class _Range>
196take_view(_Range&&, range_difference_t<_Range>) -> take_view<views::all_t<_Range>>;
197
198template <class _Tp>
199inline constexpr bool enable_borrowed_range<take_view<_Tp>> = enable_borrowed_range<_Tp>;
200
201namespace views {
202namespace __take {
203
204template <class _Tp>
205inline constexpr bool __is_empty_view = false;
206
207template <class _Tp>
208inline constexpr bool __is_empty_view<empty_view<_Tp>> = true;
209
210template <class _Tp>
211inline constexpr bool __is_passthrough_specialization = false;
212
213template <class _Tp, size_t _Extent>
214inline constexpr bool __is_passthrough_specialization<span<_Tp, _Extent>> = true;
215
216template <class _CharT, class _Traits>
217inline constexpr bool __is_passthrough_specialization<basic_string_view<_CharT, _Traits>> = true;
218
219template <class _Iter, class _Sent, subrange_kind _Kind>
220inline constexpr bool __is_passthrough_specialization<subrange<_Iter, _Sent, _Kind>> = true;
221
222template <class _Tp>
223inline constexpr bool __is_iota_specialization = false;
224
225template <class _Np, class _Bound>
226inline constexpr bool __is_iota_specialization<iota_view<_Np, _Bound>> = true;
227
228template <class _Tp>
229struct __passthrough_type;
230
231template <class _Tp, size_t _Extent>
232struct __passthrough_type<span<_Tp, _Extent>> {
233  using type = span<_Tp>;
234};
235
236template <class _CharT, class _Traits>
237struct __passthrough_type<basic_string_view<_CharT, _Traits>> {
238  using type = basic_string_view<_CharT, _Traits>;
239};
240
241template <class _Iter, class _Sent, subrange_kind _Kind>
242  requires requires { typename subrange<_Iter>; }
243struct __passthrough_type<subrange<_Iter, _Sent, _Kind>> {
244  using type = subrange<_Iter>;
245};
246
247template <class _Tp>
248using __passthrough_type_t = typename __passthrough_type<_Tp>::type;
249
250struct __fn {
251  // [range.take.overview]: the `empty_view` case.
252  template <class _Range, convertible_to<range_difference_t<_Range>> _Np>
253    requires __is_empty_view<remove_cvref_t<_Range>>
254  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&&) const
255      noexcept(noexcept(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))))
256          -> decltype(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))) {
257    return _LIBCPP_AUTO_CAST(std::forward<_Range>(__range));
258  }
259
260  // [range.take.overview]: the `span | basic_string_view | subrange` case.
261  template <class _Range,
262            convertible_to<range_difference_t<_Range>> _Np,
263            class _RawRange = remove_cvref_t<_Range>,
264            class _Dist     = range_difference_t<_Range>>
265    requires(!__is_empty_view<_RawRange> && random_access_range<_RawRange> && sized_range<_RawRange> &&
266             __is_passthrough_specialization<_RawRange>)
267  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto
268  operator()(_Range&& __rng, _Np&& __n) const noexcept(noexcept(__passthrough_type_t<_RawRange>(
269      ranges::begin(__rng), ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))))
270      -> decltype(__passthrough_type_t<_RawRange>(
271          // Note: deliberately not forwarding `__rng` to guard against double moves.
272          ranges::begin(__rng),
273          ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))) {
274    return __passthrough_type_t<_RawRange>(
275        ranges::begin(__rng), ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)));
276  }
277
278  // [range.take.overview]: the `iota_view` case.
279  // clang-format off
280  template <class _Range,
281            convertible_to<range_difference_t<_Range>> _Np,
282            class _RawRange = remove_cvref_t<_Range>,
283            class _Dist     = range_difference_t<_Range>>
284    requires (!__is_empty_view<_RawRange> &&
285              random_access_range<_RawRange> &&
286              sized_range<_RawRange> &&
287              __is_iota_specialization<_RawRange>)
288  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
289  constexpr auto operator()(_Range&& __rng, _Np&& __n) const
290    noexcept(noexcept(ranges::iota_view(
291                              *ranges::begin(__rng),
292                              *(ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))
293                              )))
294    -> decltype(      ranges::iota_view(
295                              // Note: deliberately not forwarding `__rng` to guard against double moves.
296                              *ranges::begin(__rng),
297                              *(ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))
298                              ))
299    { return          ranges::iota_view(
300                              *ranges::begin(__rng),
301                              *(ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n)))
302                              ); }
303
304#if _LIBCPP_STD_VER >= 23
305  // [range.take.overview]: the `repeat_view` "_RawRange models sized_range" case.
306  template <class _Range,
307            convertible_to<range_difference_t<_Range>> _Np,
308            class _RawRange = remove_cvref_t<_Range>,
309            class _Dist     = range_difference_t<_Range>>
310    requires(__is_repeat_specialization<_RawRange> && sized_range<_RawRange>)
311  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
312    noexcept(noexcept(views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n)))))
313    -> decltype(      views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))))
314    { return          views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))); }
315
316  // [range.take.overview]: the `repeat_view` "otherwise" case.
317  template <class _Range,
318            convertible_to<range_difference_t<_Range>> _Np,
319            class _RawRange = remove_cvref_t<_Range>,
320            class _Dist     = range_difference_t<_Range>>
321    requires(__is_repeat_specialization<_RawRange> && !sized_range<_RawRange>)
322  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
323    noexcept(noexcept(views::repeat(*__range.__value_, static_cast<_Dist>(__n))))
324    -> decltype(      views::repeat(*__range.__value_, static_cast<_Dist>(__n)))
325    { return          views::repeat(*__range.__value_, static_cast<_Dist>(__n)); }
326#endif
327  // clang-format on
328
329  // [range.take.overview]: the "otherwise" case.
330  template <class _Range, convertible_to<range_difference_t<_Range>> _Np, class _RawRange = remove_cvref_t<_Range>>
331  // Note: without specifically excluding the other cases, GCC sees this overload as ambiguous with the other
332  // overloads.
333    requires(!(__is_empty_view<_RawRange> ||
334#  if _LIBCPP_STD_VER >= 23
335               __is_repeat_specialization<_RawRange> ||
336#  endif
337               (__is_iota_specialization<_RawRange> && sized_range<_RawRange> && random_access_range<_RawRange>) ||
338               (__is_passthrough_specialization<_RawRange> && sized_range<_RawRange> &&
339                random_access_range<_RawRange>)))
340  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
341      noexcept(noexcept(take_view(std::forward<_Range>(__range), std::forward<_Np>(__n))))
342          -> decltype(take_view(std::forward<_Range>(__range), std::forward<_Np>(__n))) {
343    return take_view(std::forward<_Range>(__range), std::forward<_Np>(__n));
344  }
345
346  template <class _Np>
347    requires constructible_from<decay_t<_Np>, _Np>
348  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Np&& __n) const
349      noexcept(is_nothrow_constructible_v<decay_t<_Np>, _Np>) {
350    return __range_adaptor_closure_t(std::__bind_back(*this, std::forward<_Np>(__n)));
351  }
352};
353
354} // namespace __take
355
356inline namespace __cpo {
357inline constexpr auto take = __take::__fn{};
358} // namespace __cpo
359} // namespace views
360
361} // namespace ranges
362
363#endif // _LIBCPP_STD_VER >= 20
364
365_LIBCPP_END_NAMESPACE_STD
366
367_LIBCPP_POP_MACROS
368
369#endif // _LIBCPP___RANGES_TAKE_VIEW_H
370