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