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 
58 namespace ranges {
59 
60 template <view _View>
61 class 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 
68 public:
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 
162 template <view _View>
163 template <bool _Const>
164 class 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 
173 public:
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 
195 template <class _Range>
196 take_view(_Range&&, range_difference_t<_Range>) -> take_view<views::all_t<_Range>>;
197 
198 template <class _Tp>
199 inline constexpr bool enable_borrowed_range<take_view<_Tp>> = enable_borrowed_range<_Tp>;
200 
201 namespace views {
202 namespace __take {
203 
204 template <class _Tp>
205 inline constexpr bool __is_empty_view = false;
206 
207 template <class _Tp>
208 inline constexpr bool __is_empty_view<empty_view<_Tp>> = true;
209 
210 template <class _Tp>
211 inline constexpr bool __is_passthrough_specialization = false;
212 
213 template <class _Tp, size_t _Extent>
214 inline constexpr bool __is_passthrough_specialization<span<_Tp, _Extent>> = true;
215 
216 template <class _CharT, class _Traits>
217 inline constexpr bool __is_passthrough_specialization<basic_string_view<_CharT, _Traits>> = true;
218 
219 template <class _Iter, class _Sent, subrange_kind _Kind>
220 inline constexpr bool __is_passthrough_specialization<subrange<_Iter, _Sent, _Kind>> = true;
221 
222 template <class _Tp>
223 inline constexpr bool __is_iota_specialization = false;
224 
225 template <class _Np, class _Bound>
226 inline constexpr bool __is_iota_specialization<iota_view<_Np, _Bound>> = true;
227 
228 template <class _Tp>
229 struct __passthrough_type;
230 
231 template <class _Tp, size_t _Extent>
232 struct __passthrough_type<span<_Tp, _Extent>> {
233   using type = span<_Tp>;
234 };
235 
236 template <class _CharT, class _Traits>
237 struct __passthrough_type<basic_string_view<_CharT, _Traits>> {
238   using type = basic_string_view<_CharT, _Traits>;
239 };
240 
241 template <class _Iter, class _Sent, subrange_kind _Kind>
242   requires requires { typename subrange<_Iter>; }
243 struct __passthrough_type<subrange<_Iter, _Sent, _Kind>> {
244   using type = subrange<_Iter>;
245 };
246 
247 template <class _Tp>
248 using __passthrough_type_t = typename __passthrough_type<_Tp>::type;
249 
250 struct __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 
356 inline namespace __cpo {
357 inline 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