libcxx/include/__ranges/take_view.h

   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> class __sentinel;
  66
  67 public:
  68   _LIBCPP_HIDE_FROM_ABI
  69   take_view() requires default_initializable<_View> = default;
  70
  71   _LIBCPP_HIDE_FROM_ABI
  72   constexpr _LIBCPP_EXPLICIT_SINCE_CXX23 take_view(_View __base, range_difference_t<_View> __count)
  73       : __base_(std::move(__base)), __count_(__count) {
  74     _LIBCPP_ASSERT_UNCATEGORIZED(__count >= 0, "count has to be greater than or equal to zero");
  75   }
  76
  77   _LIBCPP_HIDE_FROM_ABI
  78   constexpr _View base() const& requires copy_constructible<_View> { return __base_; }
  79
  80   _LIBCPP_HIDE_FROM_ABI
  81   constexpr _View base() && { return std::move(__base_); }
  82
  83   _LIBCPP_HIDE_FROM_ABI
  84   constexpr auto begin() requires (!__simple_view<_View>) {
  85     if constexpr (sized_range<_View>) {
  86       if constexpr (random_access_range<_View>) {
  87         return ranges::begin(__base_);
  88       } else {
  89         using _DifferenceT = range_difference_t<_View>;
  90         auto __size = size();
  91         return counted_iterator(ranges::begin(__base_), static_cast<_DifferenceT>(__size));
  92       }
  93     } else {
  94       return counted_iterator(ranges::begin(__base_), __count_);
  95     }
  96   }
  97
  98   _LIBCPP_HIDE_FROM_ABI
  99   constexpr auto begin() const requires range<const _View> {
 100     if constexpr (sized_range<const _View>) {
 101       if constexpr (random_access_range<const _View>) {
 102         return ranges::begin(__base_);
 103       } else {
 104         using _DifferenceT = range_difference_t<const _View>;
 105         auto __size = size();
 106         return counted_iterator(ranges::begin(__base_), static_cast<_DifferenceT>(__size));
 107       }
 108     } else {
 109       return counted_iterator(ranges::begin(__base_), __count_);
 110     }
 111   }
 112
 113   _LIBCPP_HIDE_FROM_ABI
 114   constexpr auto end() requires (!__simple_view<_View>) {
 115     if constexpr (sized_range<_View>) {
 116       if constexpr (random_access_range<_View>) {
 117         return ranges::begin(__base_) + size();
 118       } else {
 119         return default_sentinel;
 120       }
 121     } else {
 122       return __sentinel<false>{ranges::end(__base_)};
 123     }
 124   }
 125
 126   _LIBCPP_HIDE_FROM_ABI
 127   constexpr auto end() const requires range<const _View> {
 128     if constexpr (sized_range<const _View>) {
 129       if constexpr (random_access_range<const _View>) {
 130         return ranges::begin(__base_) + size();
 131       } else {
 132         return default_sentinel;
 133       }
 134     } else {
 135       return __sentinel<true>{ranges::end(__base_)};
 136     }
 137   }
 138
 139   _LIBCPP_HIDE_FROM_ABI
 140   constexpr auto size() requires sized_range<_View> {
 141     auto __n = ranges::size(__base_);
 142     return ranges::min(__n, static_cast<decltype(__n)>(__count_));
 143   }
 144
 145   _LIBCPP_HIDE_FROM_ABI
 146   constexpr auto size() const requires sized_range<const _View> {
 147     auto __n = ranges::size(__base_);
 148     return ranges::min(__n, static_cast<decltype(__n)>(__count_));
 149   }
 150 };
 151
 152 template<view _View>
 153 template<bool _Const>
 154 class take_view<_View>::__sentinel {
 155   using _Base = __maybe_const<_Const, _View>;
 156   template<bool _OtherConst>
 157   using _Iter = counted_iterator<iterator_t<__maybe_const<_OtherConst, _View>>>;
 158   _LIBCPP_NO_UNIQUE_ADDRESS sentinel_t<_Base> __end_ = sentinel_t<_Base>();
 159
 160   template<bool>
 161   friend class take_view<_View>::__sentinel;
 162
 163 public:
 164   _LIBCPP_HIDE_FROM_ABI
 165   __sentinel() = default;
 166
 167   _LIBCPP_HIDE_FROM_ABI
 168   constexpr explicit __sentinel(sentinel_t<_Base> __end) : __end_(std::move(__end)) {}
 169
 170   _LIBCPP_HIDE_FROM_ABI
 171   constexpr __sentinel(__sentinel<!_Const> __s)
 172     requires _Const && convertible_to<sentinel_t<_View>, sentinel_t<_Base>>
 173     : __end_(std::move(__s.__end_)) {}
 174
 175   _LIBCPP_HIDE_FROM_ABI
 176   constexpr sentinel_t<_Base> base() const { return __end_; }
 177
 178   _LIBCPP_HIDE_FROM_ABI
 179   friend constexpr bool operator==(const _Iter<_Const>& __lhs, const __sentinel& __rhs) {
 180     return __lhs.count() == 0 || __lhs.base() == __rhs.__end_;
 181   }
 182
 183   template<bool _OtherConst = !_Const>
 184     requires sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
 185   _LIBCPP_HIDE_FROM_ABI
 186   friend constexpr bool operator==(const _Iter<_Const>& __lhs, const __sentinel& __rhs) {
 187     return __lhs.count() == 0 || __lhs.base() == __rhs.__end_;
 188   }
 189 };
 190
 191 template<class _Range>
 192 take_view(_Range&&, range_difference_t<_Range>) -> take_view<views::all_t<_Range>>;
 193
 194 template<class _Tp>
 195 inline constexpr bool enable_borrowed_range<take_view<_Tp>> = enable_borrowed_range<_Tp>;
 196
 197 namespace views {
 198 namespace __take {
 199
 200 template <class _Tp>
 201 inline constexpr bool __is_empty_view = false;
 202
 203 template <class _Tp>
 204 inline constexpr bool __is_empty_view<empty_view<_Tp>> = true;
 205
 206 template <class _Tp>
 207 inline constexpr bool __is_passthrough_specialization = false;
 208
 209 template <class _Tp, size_t _Extent>
 210 inline constexpr bool __is_passthrough_specialization<span<_Tp, _Extent>> = true;
 211
 212 template <class _CharT, class _Traits>
 213 inline constexpr bool __is_passthrough_specialization<basic_string_view<_CharT, _Traits>> = true;
 214
 215 template <class _Iter, class _Sent, subrange_kind _Kind>
 216 inline constexpr bool __is_passthrough_specialization<subrange<_Iter, _Sent, _Kind>> = true;
 217
 218 template <class _Tp>
 219 inline constexpr bool __is_iota_specialization = false;
 220
 221 template <class _Np, class _Bound>
 222 inline constexpr bool __is_iota_specialization<iota_view<_Np, _Bound>> = true;
 223
 224 template <class _Tp>
 225 struct __passthrough_type;
 226
 227 template <class _Tp, size_t _Extent>
 228 struct __passthrough_type<span<_Tp, _Extent>> {
 229   using type = span<_Tp>;
 230 };
 231
 232 template <class _CharT, class _Traits>
 233 struct __passthrough_type<basic_string_view<_CharT, _Traits>> {
 234   using type = basic_string_view<_CharT, _Traits>;
 235 };
 236
 237 template <class _Iter, class _Sent, subrange_kind _Kind>
 238   requires requires{typename subrange<_Iter>;}
 239 struct __passthrough_type<subrange<_Iter, _Sent, _Kind>> {
 240   using type = subrange<_Iter>;
 241 };
 242
 243 template <class _Tp>
 244 using __passthrough_type_t = typename __passthrough_type<_Tp>::type;
 245
 246 struct __fn {
 247   // [range.take.overview]: the `empty_view` case.
 248   template <class _Range, convertible_to<range_difference_t<_Range>> _Np>
 249     requires __is_empty_view<remove_cvref_t<_Range>>
 250   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
 251   constexpr auto operator()(_Range&& __range, _Np&&) const
 252     noexcept(noexcept(_LIBCPP_AUTO_CAST(std::forward<_Range>(__range))))
 253     -> decltype(      _LIBCPP_AUTO_CAST(std::forward<_Range>(__range)))
 254     { return          _LIBCPP_AUTO_CAST(std::forward<_Range>(__range)); }
 255
 256   // [range.take.overview]: the `span | basic_string_view | subrange` case.
 257   template <class _Range,
 258             convertible_to<range_difference_t<_Range>> _Np,
 259             class _RawRange = remove_cvref_t<_Range>,
 260             class _Dist = range_difference_t<_Range>>
 261     requires (!__is_empty_view<_RawRange> &&
 262               random_access_range<_RawRange> &&
 263               sized_range<_RawRange> &&
 264               __is_passthrough_specialization<_RawRange>)
 265   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
 266   constexpr auto operator()(_Range&& __rng, _Np&& __n) const
 267     noexcept(noexcept(__passthrough_type_t<_RawRange>(
 268                               ranges::begin(__rng),
 269                               ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))
 270                               )))
 271     -> decltype(      __passthrough_type_t<_RawRange>(
 272                               // Note: deliberately not forwarding `__rng` to guard against double moves.
 273                               ranges::begin(__rng),
 274                               ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))
 275                               ))
 276     { return          __passthrough_type_t<_RawRange>(
 277                               ranges::begin(__rng),
 278                               ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))
 279                               ); }
 280
 281   // [range.take.overview]: the `iota_view` case.
 282   template <class _Range,
 283             convertible_to<range_difference_t<_Range>> _Np,
 284             class _RawRange = remove_cvref_t<_Range>,
 285             class _Dist = range_difference_t<_Range>>
 286     requires (!__is_empty_view<_RawRange> &&
 287               random_access_range<_RawRange> &&
 288               sized_range<_RawRange> &&
 289               __is_iota_specialization<_RawRange>)
 290   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
 291   constexpr auto operator()(_Range&& __rng, _Np&& __n) const
 292     noexcept(noexcept(ranges::iota_view(
 293                               *ranges::begin(__rng),
 294                               *ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))
 295                               )))
 296     -> decltype(      ranges::iota_view(
 297                               // Note: deliberately not forwarding `__rng` to guard against double moves.
 298                               *ranges::begin(__rng),
 299                               *ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))
 300                               ))
 301     { return          ranges::iota_view(
 302                               *ranges::begin(__rng),
 303                               *ranges::begin(__rng) + std::min<_Dist>(ranges::distance(__rng), std::forward<_Np>(__n))
 304                               ); }
 305 // clang-format off
 306 #if _LIBCPP_STD_VER >= 23
 307   // [range.take.overview]: the `repeat_view` "_RawRange models sized_range" case.
 308   template <class _Range,
 309             convertible_to<range_difference_t<_Range>> _Np,
 310             class _RawRange = remove_cvref_t<_Range>,
 311             class _Dist     = range_difference_t<_Range>>
 312     requires(__is_repeat_specialization<_RawRange> && sized_range<_RawRange>)
 313   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
 314     noexcept(noexcept(views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n)))))
 315     -> decltype(      views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))))
 316     { return          views::repeat(*__range.__value_, std::min<_Dist>(ranges::distance(__range), std::forward<_Np>(__n))); }
 317
 318   // [range.take.overview]: the `repeat_view` "otherwise" case.
 319   template <class _Range,
 320             convertible_to<range_difference_t<_Range>> _Np,
 321             class _RawRange = remove_cvref_t<_Range>,
 322             class _Dist     = range_difference_t<_Range>>
 323     requires(__is_repeat_specialization<_RawRange> && !sized_range<_RawRange>)
 324   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Np&& __n) const
 325     noexcept(noexcept(views::repeat(*__range.__value_, static_cast<_Dist>(__n))))
 326     -> decltype(      views::repeat(*__range.__value_, static_cast<_Dist>(__n)))
 327     { return          views::repeat(*__range.__value_, static_cast<_Dist>(__n)); }
 328 #endif
 329 // clang-format on
 330
 331   // [range.take.overview]: the "otherwise" case.
 332   template <class _Range, convertible_to<range_difference_t<_Range>> _Np,
 333             class _RawRange = remove_cvref_t<_Range>>
 334     // Note: without specifically excluding the other cases, GCC sees this overload as ambiguous with the other
 335     // overloads.
 336     requires (!(__is_empty_view<_RawRange> ||
 337 #if _LIBCPP_STD_VER >= 23
 338                 __is_repeat_specialization<_RawRange> ||
 339 #endif
 340                (__is_iota_specialization<_RawRange> &&
 341                 sized_range<_RawRange> &&
 342                 random_access_range<_RawRange>) ||
 343                (__is_passthrough_specialization<_RawRange> &&
 344                 sized_range<_RawRange> &&
 345                 random_access_range<_RawRange>)
 346              ))
 347   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
 348   constexpr auto operator()(_Range&& __range, _Np&& __n) const
 349     noexcept(noexcept(take_view(std::forward<_Range>(__range), std::forward<_Np>(__n))))
 350     -> decltype(      take_view(std::forward<_Range>(__range), std::forward<_Np>(__n)))
 351     { return          take_view(std::forward<_Range>(__range), std::forward<_Np>(__n)); }
 352
 353   template <class _Np>
 354     requires constructible_from<decay_t<_Np>, _Np>
 355   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
 356   constexpr auto operator()(_Np&& __n) const
 357     noexcept(is_nothrow_constructible_v<decay_t<_Np>, _Np>)
 358   { return __range_adaptor_closure_t(std::__bind_back(*this, std::forward<_Np>(__n))); }
 359 };
 360
 361 } // namespace __take
 362
 363 inline namespace __cpo {
 364   inline constexpr auto take = __take::__fn{};
 365 } // namespace __cpo
 366 } // namespace views
 367
 368 } // namespace ranges
 369
 370 #endif // _LIBCPP_STD_VER >= 20
 371
 372 _LIBCPP_END_NAMESPACE_STD
 373
 374 _LIBCPP_POP_MACROS
 375
 376 #endif // _LIBCPP___RANGES_TAKE_VIEW_H