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