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_SPAN
11#define _LIBCPP_SPAN
12
13/*
14 span synopsis
15
16namespace std {
17
18// constants
19inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
20
21template<class T>
22 concept integral-constant-like = // exposition only, since C++26
23 is_integral_v<decltype(T::value)> &&
24 !is_same_v<bool, remove_const_t<decltype(T::value)>> &&
25 convertible_to<T, decltype(T::value)> &&
26 equality_comparable_with<T, decltype(T::value)> &&
27 bool_constant<T() == T::value>::value &&
28 bool_constant<static_cast<decltype(T::value)>(T()) == T::value>::value;
29
30template<class T>
31 constexpr size_t maybe-static-ext = dynamic_extent; // exposition only, since C++26
32template<integral-constant-like T>
33 constexpr size_t maybe-static-ext<T> = {T::value};
34
35// [views.span], class template span
36template <class ElementType, size_t Extent = dynamic_extent>
37 class span;
38
39template<class ElementType, size_t Extent>
40 inline constexpr bool ranges::enable_view<span<ElementType, Extent>> = true;
41
42template<class ElementType, size_t Extent>
43 inline constexpr bool ranges::enable_borrowed_range<span<ElementType, Extent>> = true;
44
45// [span.objectrep], views of object representation
46template <class ElementType, size_t Extent>
47 span<const byte, ((Extent == dynamic_extent) ? dynamic_extent :
48 (sizeof(ElementType) * Extent))> as_bytes(span<ElementType, Extent> s) noexcept;
49
50template <class ElementType, size_t Extent>
51 span< byte, ((Extent == dynamic_extent) ? dynamic_extent :
52 (sizeof(ElementType) * Extent))> as_writable_bytes(span<ElementType, Extent> s) noexcept;
53
54
55template <class ElementType, size_t Extent = dynamic_extent>
56class span {
57public:
58 // constants and types
59 using element_type = ElementType;
60 using value_type = remove_cv_t<ElementType>;
61 using size_type = size_t;
62 using difference_type = ptrdiff_t;
63 using pointer = element_type*;
64 using const_pointer = const element_type*;
65 using reference = element_type&;
66 using const_reference = const element_type&;
67 using iterator = implementation-defined;
68 using reverse_iterator = std::reverse_iterator<iterator>;
69 static constexpr size_type extent = Extent;
70
71 // [span.cons], span constructors, copy, assignment, and destructor
72 constexpr span() noexcept;
73 template <class It>
74 constexpr explicit(Extent != dynamic_extent) span(It first, size_type count);
75 template <class It, class End>
76 constexpr explicit(Extent != dynamic_extent) span(It first, End last);
77 template <size_t N>
78 constexpr span(type_identity_t<element_type> (&arr)[N]) noexcept;
79 template <size_t N>
80 constexpr span(array<value_type, N>& arr) noexcept;
81 template <size_t N>
82 constexpr span(const array<value_type, N>& arr) noexcept;
83 template<class R>
84 constexpr explicit(Extent != dynamic_extent) span(R&& r);
85 constexpr explicit(extent != dynamic_extent) span(std::initializer_list<value_type> il); // Since C++26
86 constexpr span(const span& other) noexcept = default;
87 template <class OtherElementType, size_t OtherExtent>
88 constexpr explicit(Extent != dynamic_extent) span(const span<OtherElementType, OtherExtent>& s) noexcept;
89 constexpr span& operator=(const span& other) noexcept = default;
90
91 // [span.sub], span subviews
92 template <size_t Count>
93 constexpr span<element_type, Count> first() const;
94 template <size_t Count>
95 constexpr span<element_type, Count> last() const;
96 template <size_t Offset, size_t Count = dynamic_extent>
97 constexpr span<element_type, see below> subspan() const;
98
99 constexpr span<element_type, dynamic_extent> first(size_type count) const;
100 constexpr span<element_type, dynamic_extent> last(size_type count) const;
101 constexpr span<element_type, dynamic_extent> subspan(size_type offset, size_type count = dynamic_extent) const;
102
103 // [span.obs], span observers
104 constexpr size_type size() const noexcept;
105 constexpr size_type size_bytes() const noexcept;
106 [[nodiscard]] constexpr bool empty() const noexcept;
107
108 // [span.elem], span element access
109 constexpr reference operator[](size_type idx) const;
110 constexpr reference at(size_type idx) const; // since C++26
111 constexpr reference front() const;
112 constexpr reference back() const;
113 constexpr pointer data() const noexcept;
114
115 // [span.iterators], span iterator support
116 constexpr iterator begin() const noexcept;
117 constexpr iterator end() const noexcept;
118 constexpr reverse_iterator rbegin() const noexcept;
119 constexpr reverse_iterator rend() const noexcept;
120
121private:
122 pointer data_; // exposition only
123 size_type size_; // exposition only
124};
125
126template<class It, class EndOrSize>
127 span(It, EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>>; // until C++26
128template<class It, class EndOrSize>
129 span(It, EndOrSize) -> span<remove_reference_t<iter_reference_t<It>>, maybe-static-ext<EndOrSize>>; // since C++26
130
131template<class T, size_t N>
132 span(T (&)[N]) -> span<T, N>;
133
134template<class T, size_t N>
135 span(array<T, N>&) -> span<T, N>;
136
137template<class T, size_t N>
138 span(const array<T, N>&) -> span<const T, N>;
139
140template<class R>
141 span(R&&) -> span<remove_reference_t<ranges::range_reference_t<R>>>;
142
143} // namespace std
144
145*/
146
147#include <__assert>
148#include <__concepts/convertible_to.h>
149#include <__concepts/equality_comparable.h>
150#include <__config>
151#include <__fwd/array.h>
152#include <__fwd/span.h>
153#include <__iterator/bounded_iter.h>
154#include <__iterator/concepts.h>
155#include <__iterator/iterator_traits.h>
156#include <__iterator/reverse_iterator.h>
157#include <__iterator/wrap_iter.h>
158#include <__memory/pointer_traits.h>
159#include <__ranges/concepts.h>
160#include <__ranges/data.h>
161#include <__ranges/enable_borrowed_range.h>
162#include <__ranges/enable_view.h>
163#include <__ranges/size.h>
164#include <__type_traits/integral_constant.h>
165#include <__type_traits/is_array.h>
166#include <__type_traits/is_const.h>
167#include <__type_traits/is_convertible.h>
168#include <__type_traits/is_integral.h>
169#include <__type_traits/is_same.h>
170#include <__type_traits/remove_const.h>
171#include <__type_traits/remove_cv.h>
172#include <__type_traits/remove_cvref.h>
173#include <__type_traits/remove_reference.h>
174#include <__type_traits/type_identity.h>
175#include <__utility/forward.h>
176#include <cstddef> // for byte
177#include <initializer_list>
178#include <stdexcept>
179#include <version>
180
181// standard-mandated includes
182
183// [iterator.range]
184#include <__iterator/access.h>
185#include <__iterator/data.h>
186#include <__iterator/empty.h>
187#include <__iterator/reverse_access.h>
188#include <__iterator/size.h>
189
190#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
191# pragma GCC system_header
192#endif
193
194_LIBCPP_PUSH_MACROS
195#include <__undef_macros>
196
197_LIBCPP_BEGIN_NAMESPACE_STD
198
199#if _LIBCPP_STD_VER >= 20
200
201template <class _Tp>
202struct __is_std_span : false_type {};
203
204template <class _Tp, size_t _Sz>
205struct __is_std_span<span<_Tp, _Sz>> : true_type {};
206
207template <class _Range, class _ElementType>
208concept __span_compatible_range =
209 !__is_std_span<remove_cvref_t<_Range>>::value && //
210 ranges::contiguous_range<_Range> && //
211 ranges::sized_range<_Range> && //
212 (ranges::borrowed_range<_Range> || is_const_v<_ElementType>) && //
213 !__is_std_array<remove_cvref_t<_Range>>::value && //
214 !is_array_v<remove_cvref_t<_Range>> && //
215 is_convertible_v<remove_reference_t<ranges::range_reference_t<_Range>> (*)[], _ElementType (*)[]>;
216
217template <class _From, class _To>
218concept __span_array_convertible = is_convertible_v<_From (*)[], _To (*)[]>;
219
220template <class _It, class _Tp>
221concept __span_compatible_iterator =
222 contiguous_iterator<_It> && __span_array_convertible<remove_reference_t<iter_reference_t<_It>>, _Tp>;
223
224template <class _Sentinel, class _It>
225concept __span_compatible_sentinel_for = sized_sentinel_for<_Sentinel, _It> && !is_convertible_v<_Sentinel, size_t>;
226
227template <typename _Tp, size_t _Extent>
228class _LIBCPP_TEMPLATE_VIS span {
229public:
230 // constants and types
231 using element_type = _Tp;
232 using value_type = remove_cv_t<_Tp>;
233 using size_type = size_t;
234 using difference_type = ptrdiff_t;
235 using pointer = _Tp*;
236 using const_pointer = const _Tp*;
237 using reference = _Tp&;
238 using const_reference = const _Tp&;
239# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
240 using iterator = __bounded_iter<pointer>;
241# else
242 using iterator = __wrap_iter<pointer>;
243# endif
244 using reverse_iterator = std::reverse_iterator<iterator>;
245
246 static constexpr size_type extent = _Extent;
247
248 // [span.cons], span constructors, copy, assignment, and destructor
249 template <size_t _Sz = _Extent>
250 requires(_Sz == 0)
251 _LIBCPP_HIDE_FROM_ABI constexpr span() noexcept : __data_{nullptr} {}
252
253# if _LIBCPP_STD_VER >= 26
254 _LIBCPP_HIDE_FROM_ABI constexpr explicit span(std::initializer_list<value_type> __il)
255 requires is_const_v<element_type>
256 : __data_{__il.begin()} {
257 _LIBCPP_ASSERT_VALID_INPUT_RANGE(
258 _Extent == __il.size(), "Size mismatch in span's constructor _Extent != __il.size().");
259 }
260# endif
261
262 constexpr span(const span&) noexcept = default;
263 constexpr span& operator=(const span&) noexcept = default;
264
265 template <__span_compatible_iterator<element_type> _It>
266 _LIBCPP_HIDE_FROM_ABI constexpr explicit span(_It __first, size_type __count) : __data_{std::to_address(__first)} {
267 (void)__count;
268 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Extent == __count, "size mismatch in span's constructor (iterator, len)");
269 }
270
271 template <__span_compatible_iterator<element_type> _It, __span_compatible_sentinel_for<_It> _End>
272 _LIBCPP_HIDE_FROM_ABI constexpr explicit span(_It __first, _End __last) : __data_{std::to_address(__first)} {
273 // [span.cons]/10
274 // Throws: When and what last - first throws.
275 [[maybe_unused]] auto __dist = __last - __first;
276 _LIBCPP_ASSERT_VALID_INPUT_RANGE(__dist >= 0, "invalid range in span's constructor (iterator, sentinel)");
277 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
278 __dist == _Extent, "invalid range in span's constructor (iterator, sentinel): last - first != extent");
279 }
280
281 _LIBCPP_HIDE_FROM_ABI constexpr span(type_identity_t<element_type> (&__arr)[_Extent]) noexcept : __data_{__arr} {}
282
283 template <__span_array_convertible<element_type> _OtherElementType>
284 _LIBCPP_HIDE_FROM_ABI constexpr span(array<_OtherElementType, _Extent>& __arr) noexcept : __data_{__arr.data()} {}
285
286 template <class _OtherElementType>
287 requires __span_array_convertible<const _OtherElementType, element_type>
288 _LIBCPP_HIDE_FROM_ABI constexpr span(const array<_OtherElementType, _Extent>& __arr) noexcept
289 : __data_{__arr.data()} {}
290
291 template <__span_compatible_range<element_type> _Range>
292 _LIBCPP_HIDE_FROM_ABI constexpr explicit span(_Range&& __r) : __data_{ranges::data(__r)} {
293 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(ranges::size(__r) == _Extent, "size mismatch in span's constructor (range)");
294 }
295
296 template <__span_array_convertible<element_type> _OtherElementType>
297 _LIBCPP_HIDE_FROM_ABI constexpr span(const span<_OtherElementType, _Extent>& __other) noexcept
298 : __data_{__other.data()} {}
299
300 template <__span_array_convertible<element_type> _OtherElementType>
301 _LIBCPP_HIDE_FROM_ABI constexpr explicit span(const span<_OtherElementType, dynamic_extent>& __other) noexcept
302 : __data_{__other.data()} {
303 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Extent == __other.size(), "size mismatch in span's constructor (other span)");
304 }
305
306 template <size_t _Count>
307 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> first() const noexcept {
308 static_assert(_Count <= _Extent, "span<T, N>::first<Count>(): Count out of range");
309 return span<element_type, _Count>{data(), _Count};
310 }
311
312 template <size_t _Count>
313 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> last() const noexcept {
314 static_assert(_Count <= _Extent, "span<T, N>::last<Count>(): Count out of range");
315 return span<element_type, _Count>{data() + size() - _Count, _Count};
316 }
317
318 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept {
319 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T, N>::first(count): count out of range");
320 return {data(), __count};
321 }
322
323 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> last(size_type __count) const noexcept {
324 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T, N>::last(count): count out of range");
325 return {data() + size() - __count, __count};
326 }
327
328 template <size_t _Offset, size_t _Count = dynamic_extent>
329 _LIBCPP_HIDE_FROM_ABI constexpr auto
330 subspan() const noexcept -> span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset> {
331 static_assert(_Offset <= _Extent, "span<T, N>::subspan<Offset, Count>(): Offset out of range");
332 static_assert(_Count == dynamic_extent || _Count <= _Extent - _Offset,
333 "span<T, N>::subspan<Offset, Count>(): Offset + Count out of range");
334
335 using _ReturnType = span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset>;
336 return _ReturnType{data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
337 }
338
339 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent>
340 subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept {
341 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__offset <= size(), "span<T, N>::subspan(offset, count): offset out of range");
342 if (__count == dynamic_extent)
343 return {data() + __offset, size() - __offset};
344 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
345 __count <= size() - __offset, "span<T, N>::subspan(offset, count): offset + count out of range");
346 return {data() + __offset, __count};
347 }
348
349 _LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept { return _Extent; }
350 _LIBCPP_HIDE_FROM_ABI constexpr size_type size_bytes() const noexcept { return _Extent * sizeof(element_type); }
351 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty() const noexcept { return _Extent == 0; }
352
353 _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](size_type __idx) const noexcept {
354 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__idx < size(), "span<T, N>::operator[](index): index out of range");
355 return __data_[__idx];
356 }
357
358# if _LIBCPP_STD_VER >= 26
359 _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __index) const {
360 if (__index >= size())
361 std::__throw_out_of_range("span");
362 return __data_[__index];
363 }
364# endif
365
366 _LIBCPP_HIDE_FROM_ABI constexpr reference front() const noexcept {
367 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T, N>::front() on empty span");
368 return __data_[0];
369 }
370
371 _LIBCPP_HIDE_FROM_ABI constexpr reference back() const noexcept {
372 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T, N>::back() on empty span");
373 return __data_[size() - 1];
374 }
375
376 _LIBCPP_HIDE_FROM_ABI constexpr pointer data() const noexcept { return __data_; }
377
378 // [span.iter], span iterator support
379 _LIBCPP_HIDE_FROM_ABI constexpr iterator begin() const noexcept {
380# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
381 return std::__make_bounded_iter(data(), data(), data() + size());
382# else
383 return iterator(data());
384# endif
385 }
386 _LIBCPP_HIDE_FROM_ABI constexpr iterator end() const noexcept {
387# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
388 return std::__make_bounded_iter(data() + size(), data(), data() + size());
389# else
390 return iterator(data() + size());
391# endif
392 }
393 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator(end()); }
394 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rend() const noexcept { return reverse_iterator(begin()); }
395
396 _LIBCPP_HIDE_FROM_ABI span<const byte, _Extent * sizeof(element_type)> __as_bytes() const noexcept {
397 return span<const byte, _Extent * sizeof(element_type)>{reinterpret_cast<const byte*>(data()), size_bytes()};
398 }
399
400 _LIBCPP_HIDE_FROM_ABI span<byte, _Extent * sizeof(element_type)> __as_writable_bytes() const noexcept {
401 return span<byte, _Extent * sizeof(element_type)>{reinterpret_cast<byte*>(data()), size_bytes()};
402 }
403
404private:
405 pointer __data_;
406};
407
408template <typename _Tp>
409class _LIBCPP_TEMPLATE_VIS span<_Tp, dynamic_extent> {
410public:
411 // constants and types
412 using element_type = _Tp;
413 using value_type = remove_cv_t<_Tp>;
414 using size_type = size_t;
415 using difference_type = ptrdiff_t;
416 using pointer = _Tp*;
417 using const_pointer = const _Tp*;
418 using reference = _Tp&;
419 using const_reference = const _Tp&;
420# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
421 using iterator = __bounded_iter<pointer>;
422# else
423 using iterator = __wrap_iter<pointer>;
424# endif
425 using reverse_iterator = std::reverse_iterator<iterator>;
426
427 static constexpr size_type extent = dynamic_extent;
428
429 // [span.cons], span constructors, copy, assignment, and destructor
430 _LIBCPP_HIDE_FROM_ABI constexpr span() noexcept : __data_{nullptr}, __size_{0} {}
431
432# if _LIBCPP_STD_VER >= 26
433 _LIBCPP_HIDE_FROM_ABI constexpr span(std::initializer_list<value_type> __il)
434 requires is_const_v<element_type>
435 : __data_{__il.begin()}, __size_{__il.size()} {}
436# endif
437
438 constexpr span(const span&) noexcept = default;
439 constexpr span& operator=(const span&) noexcept = default;
440
441 template <__span_compatible_iterator<element_type> _It>
442 _LIBCPP_HIDE_FROM_ABI constexpr span(_It __first, size_type __count)
443 : __data_{std::to_address(__first)}, __size_{__count} {}
444
445 template <__span_compatible_iterator<element_type> _It, __span_compatible_sentinel_for<_It> _End>
446 _LIBCPP_HIDE_FROM_ABI constexpr span(_It __first, _End __last)
447 : __data_(std::to_address(__first)), __size_(__last - __first) {
448 _LIBCPP_ASSERT_VALID_INPUT_RANGE(__last - __first >= 0, "invalid range in span's constructor (iterator, sentinel)");
449 }
450
451 template <size_t _Sz>
452 _LIBCPP_HIDE_FROM_ABI constexpr span(type_identity_t<element_type> (&__arr)[_Sz]) noexcept
453 : __data_{__arr}, __size_{_Sz} {}
454
455 template <__span_array_convertible<element_type> _OtherElementType, size_t _Sz>
456 _LIBCPP_HIDE_FROM_ABI constexpr span(array<_OtherElementType, _Sz>& __arr) noexcept
457 : __data_{__arr.data()}, __size_{_Sz} {}
458
459 template <class _OtherElementType, size_t _Sz>
460 requires __span_array_convertible<const _OtherElementType, element_type>
461 _LIBCPP_HIDE_FROM_ABI constexpr span(const array<_OtherElementType, _Sz>& __arr) noexcept
462 : __data_{__arr.data()}, __size_{_Sz} {}
463
464 template <__span_compatible_range<element_type> _Range>
465 _LIBCPP_HIDE_FROM_ABI constexpr span(_Range&& __r) : __data_(ranges::data(__r)), __size_{ranges::size(__r)} {}
466
467 template <__span_array_convertible<element_type> _OtherElementType, size_t _OtherExtent>
468 _LIBCPP_HIDE_FROM_ABI constexpr span(const span<_OtherElementType, _OtherExtent>& __other) noexcept
469 : __data_{__other.data()}, __size_{__other.size()} {}
470
471 template <size_t _Count>
472 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> first() const noexcept {
473 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Count <= size(), "span<T>::first<Count>(): Count out of range");
474 return span<element_type, _Count>{data(), _Count};
475 }
476
477 template <size_t _Count>
478 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> last() const noexcept {
479 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Count <= size(), "span<T>::last<Count>(): Count out of range");
480 return span<element_type, _Count>{data() + size() - _Count, _Count};
481 }
482
483 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept {
484 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T>::first(count): count out of range");
485 return {data(), __count};
486 }
487
488 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, dynamic_extent> last(size_type __count) const noexcept {
489 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__count <= size(), "span<T>::last(count): count out of range");
490 return {data() + size() - __count, __count};
491 }
492
493 template <size_t _Offset, size_t _Count = dynamic_extent>
494 _LIBCPP_HIDE_FROM_ABI constexpr span<element_type, _Count> subspan() const noexcept {
495 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Offset <= size(), "span<T>::subspan<Offset, Count>(): Offset out of range");
496 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(_Count == dynamic_extent || _Count <= size() - _Offset,
497 "span<T>::subspan<Offset, Count>(): Offset + Count out of range");
498 return span<element_type, _Count>{data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
499 }
500
501 constexpr span<element_type, dynamic_extent> _LIBCPP_HIDE_FROM_ABI
502 subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept {
503 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__offset <= size(), "span<T>::subspan(offset, count): offset out of range");
504 if (__count == dynamic_extent)
505 return {data() + __offset, size() - __offset};
506 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
507 __count <= size() - __offset, "span<T>::subspan(offset, count): offset + count out of range");
508 return {data() + __offset, __count};
509 }
510
511 _LIBCPP_HIDE_FROM_ABI constexpr size_type size() const noexcept { return __size_; }
512 _LIBCPP_HIDE_FROM_ABI constexpr size_type size_bytes() const noexcept { return __size_ * sizeof(element_type); }
513 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty() const noexcept { return __size_ == 0; }
514
515 _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](size_type __idx) const noexcept {
516 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__idx < size(), "span<T>::operator[](index): index out of range");
517 return __data_[__idx];
518 }
519
520# if _LIBCPP_STD_VER >= 26
521 _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __index) const {
522 if (__index >= size())
523 std::__throw_out_of_range("span");
524 return __data_[__index];
525 }
526# endif
527
528 _LIBCPP_HIDE_FROM_ABI constexpr reference front() const noexcept {
529 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T>::front() on empty span");
530 return __data_[0];
531 }
532
533 _LIBCPP_HIDE_FROM_ABI constexpr reference back() const noexcept {
534 _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T>::back() on empty span");
535 return __data_[size() - 1];
536 }
537
538 _LIBCPP_HIDE_FROM_ABI constexpr pointer data() const noexcept { return __data_; }
539
540 // [span.iter], span iterator support
541 _LIBCPP_HIDE_FROM_ABI constexpr iterator begin() const noexcept {
542# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
543 return std::__make_bounded_iter(data(), data(), data() + size());
544# else
545 return iterator(data());
546# endif
547 }
548 _LIBCPP_HIDE_FROM_ABI constexpr iterator end() const noexcept {
549# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
550 return std::__make_bounded_iter(data() + size(), data(), data() + size());
551# else
552 return iterator(data() + size());
553# endif
554 }
555 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator(end()); }
556 _LIBCPP_HIDE_FROM_ABI constexpr reverse_iterator rend() const noexcept { return reverse_iterator(begin()); }
557
558 _LIBCPP_HIDE_FROM_ABI span<const byte, dynamic_extent> __as_bytes() const noexcept {
559 return {reinterpret_cast<const byte*>(data()), size_bytes()};
560 }
561
562 _LIBCPP_HIDE_FROM_ABI span<byte, dynamic_extent> __as_writable_bytes() const noexcept {
563 return {reinterpret_cast<byte*>(data()), size_bytes()};
564 }
565
566private:
567 pointer __data_;
568 size_type __size_;
569};
570
571template <class _Tp, size_t _Extent>
572inline constexpr bool ranges::enable_borrowed_range<span<_Tp, _Extent> > = true;
573
574template <class _ElementType, size_t _Extent>
575inline constexpr bool ranges::enable_view<span<_ElementType, _Extent>> = true;
576
577// as_bytes & as_writable_bytes
578template <class _Tp, size_t _Extent>
579_LIBCPP_HIDE_FROM_ABI auto as_bytes(span<_Tp, _Extent> __s) noexcept {
580 return __s.__as_bytes();
581}
582
583template <class _Tp, size_t _Extent>
584 requires(!is_const_v<_Tp>)
585_LIBCPP_HIDE_FROM_ABI auto as_writable_bytes(span<_Tp, _Extent> __s) noexcept {
586 return __s.__as_writable_bytes();
587}
588
589# if _LIBCPP_STD_VER >= 26
590template <class _Tp>
591concept __integral_constant_like =
592 is_integral_v<decltype(_Tp::value)> && !is_same_v<bool, remove_const_t<decltype(_Tp::value)>> &&
593 convertible_to<_Tp, decltype(_Tp::value)> && equality_comparable_with<_Tp, decltype(_Tp::value)> &&
594 bool_constant<_Tp() == _Tp::value>::value &&
595 bool_constant<static_cast<decltype(_Tp::value)>(_Tp()) == _Tp::value>::value;
596
597template <class _Tp>
598inline constexpr size_t __maybe_static_ext = dynamic_extent;
599
600template <__integral_constant_like _Tp>
601inline constexpr size_t __maybe_static_ext<_Tp> = {_Tp::value};
602
603template <contiguous_iterator _It, class _EndOrSize>
604span(_It, _EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>, __maybe_static_ext<_EndOrSize>>;
605# else
606template <contiguous_iterator _It, class _EndOrSize>
607span(_It, _EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>>;
608# endif
609
610template <class _Tp, size_t _Sz>
611span(_Tp (&)[_Sz]) -> span<_Tp, _Sz>;
612
613template <class _Tp, size_t _Sz>
614span(array<_Tp, _Sz>&) -> span<_Tp, _Sz>;
615
616template <class _Tp, size_t _Sz>
617span(const array<_Tp, _Sz>&) -> span<const _Tp, _Sz>;
618
619template <ranges::contiguous_range _Range>
620span(_Range&&) -> span<remove_reference_t<ranges::range_reference_t<_Range>>>;
621
622#endif // _LIBCPP_STD_VER >= 20
623
624_LIBCPP_END_NAMESPACE_STD
625
626_LIBCPP_POP_MACROS
627
628#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
629# include <array>
630# include <concepts>
631# include <functional>
632# include <iterator>
633# include <type_traits>
634#endif
635
636#endif // _LIBCPP_SPAN
637