1// Components for manipulating non-owning sequences of objects -*- C++ -*-
2
3// Copyright (C) 2019-2025 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file span
26 * This is a Standard C++ Library header.
27 */
28
29//
30// P0122 span library
31// Contributed by ThePhD
32//
33
34#ifndef _GLIBCXX_SPAN
35#define _GLIBCXX_SPAN 1
36
37#ifdef _GLIBCXX_SYSHDR
38#pragma GCC system_header
39#endif
40
41#define __glibcxx_want_span
42#define __glibcxx_want_span_initializer_list
43#include <bits/version.h>
44
45#ifdef __cpp_lib_span // C++ >= 20 && concepts
46#include <array>
47#include <cstddef>
48#include <bits/stl_iterator.h>
49#include <bits/ranges_base.h>
50#ifdef __cpp_lib_span_initializer_list
51# include <initializer_list>
52#endif
53namespace std _GLIBCXX_VISIBILITY(default)
54{
55_GLIBCXX_BEGIN_NAMESPACE_VERSION
56
57 inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
58
59 template<typename _Type, size_t _Extent>
60 class span;
61
62 namespace __detail
63 {
64 template<typename _Tp>
65 inline constexpr bool __is_span = false;
66
67 template<typename _Tp, size_t _Num>
68 inline constexpr bool __is_span<span<_Tp, _Num>> = true;
69
70 template<typename _Tp>
71 inline constexpr bool __is_std_array = false;
72
73 template<typename _Tp, size_t _Num>
74 inline constexpr bool __is_std_array<std::array<_Tp, _Num>> = true;
75
76 template<size_t _Extent>
77 class __extent_storage
78 {
79 public:
80 // Used for runtime sizes that must satisfy the precondition.
81 constexpr
82 __extent_storage([[maybe_unused]] size_t __n) noexcept
83 { __glibcxx_assert(__n == _Extent); }
84
85 // Used for constant sizes that are already known to be correct.
86 consteval
87 __extent_storage(integral_constant<size_t, _Extent>) noexcept
88 { }
89
90 // "I've made a huge mistake" - George Oscar Bluth II
91 template<size_t _Gob>
92 __extent_storage(integral_constant<size_t, _Gob>) = delete;
93
94 [[__gnu__::__always_inline__]]
95 static constexpr size_t
96 _M_extent() noexcept
97 { return _Extent; }
98 };
99
100 template<>
101 class __extent_storage<dynamic_extent>
102 {
103 public:
104 [[__gnu__::__always_inline__]]
105 constexpr
106 __extent_storage(size_t __extent) noexcept
107 : _M_extent_value(__extent)
108 { }
109
110 [[__gnu__::__always_inline__]]
111 constexpr size_t
112 _M_extent() const noexcept
113 { return this->_M_extent_value; }
114
115 private:
116 size_t _M_extent_value;
117 };
118
119 template<typename _Type> struct __span_ptr { _Type* const _M_ptr; };
120
121 } // namespace __detail
122
123 template<typename _Type, size_t _Extent = dynamic_extent>
124 class span
125 {
126 template<size_t _Offset, size_t _Count>
127 static constexpr size_t
128 _S_subspan_extent()
129 {
130 if constexpr (_Count != dynamic_extent)
131 return _Count;
132 else if constexpr (extent != dynamic_extent)
133 return _Extent - _Offset;
134 else
135 return dynamic_extent;
136 }
137
138 // _GLIBCXX_RESOLVE_LIB_DEFECTS
139 // 3255. span's array constructor is too strict
140 template<typename _Tp, size_t _ArrayExtent>
141 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
142 using __is_compatible_array = __is_array_convertible<_Type, _Tp>;
143
144 template<typename _Ref>
145 using __is_compatible_ref
146 = __is_array_convertible<_Type, remove_reference_t<_Ref>>;
147
148 // Nested type so that _Type is not an associated class of iterator.
149 struct __iter_tag;
150
151 template<size_t _Nm>
152 static inline constexpr integral_constant<size_t, _Nm> __v{};
153
154 public:
155 // member types
156 using element_type = _Type;
157 using value_type = remove_cv_t<_Type>;
158 using size_type = size_t;
159 using difference_type = ptrdiff_t;
160 using pointer = _Type*;
161 using const_pointer = const _Type*;
162 using reference = element_type&;
163 using const_reference = const element_type&;
164 using iterator = __gnu_cxx::__normal_iterator<pointer, __iter_tag>;
165 using reverse_iterator = std::reverse_iterator<iterator>;
166#if __cplusplus > 202002L
167 using const_iterator = std::const_iterator<iterator>;
168 using const_reverse_iterator = std::const_iterator<reverse_iterator>;
169#endif
170
171 // member constants
172 static constexpr size_t extent = _Extent;
173
174 // constructors, copy and assignment
175
176 constexpr
177 span() noexcept
178 requires (_Extent == dynamic_extent || _Extent == 0)
179 : _M_ptr(nullptr), _M_extent(__v<0>)
180 { }
181
182 template<contiguous_iterator _It>
183 requires __is_compatible_ref<iter_reference_t<_It>>::value
184 constexpr explicit(extent != dynamic_extent)
185 span(_It __first, size_type __count)
186 noexcept
187 : _M_ptr(std::to_address(__first)), _M_extent(__count)
188 { __glibcxx_requires_valid_range(__first, __first + __count); }
189
190 template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
191 requires __is_compatible_ref<iter_reference_t<_It>>::value
192 && (!is_convertible_v<_End, size_type>)
193 constexpr explicit(extent != dynamic_extent)
194 span(_It __first, _End __last)
195 noexcept(noexcept(__last - __first))
196 : _M_ptr(std::to_address(__first)),
197 _M_extent(static_cast<size_type>(__last - __first))
198 { __glibcxx_requires_valid_range(__first, __last); }
199
200 template<size_t _ArrayExtent>
201 requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
202 constexpr
203 span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
204 : _M_ptr(__arr), _M_extent(__v<_ArrayExtent>)
205 { }
206
207 template<typename _Tp, size_t _ArrayExtent>
208 requires __is_compatible_array<_Tp, _ArrayExtent>::value
209 constexpr
210 span(array<_Tp, _ArrayExtent>& __arr) noexcept
211 : _M_ptr(__arr.data()), _M_extent(__v<_ArrayExtent>)
212 { }
213
214 template<typename _Tp, size_t _ArrayExtent>
215 requires __is_compatible_array<const _Tp, _ArrayExtent>::value
216 constexpr
217 span(const array<_Tp, _ArrayExtent>& __arr) noexcept
218 : _M_ptr(__arr.data()), _M_extent(__v<_ArrayExtent>)
219 { }
220
221 template<typename _Range>
222 requires (!__detail::__is_span<remove_cvref_t<_Range>>)
223 && (!__detail::__is_std_array<remove_cvref_t<_Range>>)
224 && (!is_array_v<remove_cvref_t<_Range>>)
225 && ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
226 && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
227 && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
228 constexpr explicit(extent != dynamic_extent)
229 span(_Range&& __range)
230 noexcept(noexcept(ranges::data(__range))
231 && noexcept(ranges::size(__range)))
232 : _M_ptr(ranges::data(__range)), _M_extent(ranges::size(__range))
233 { }
234
235#if __cpp_lib_span_initializer_list >= 202311L // >= C++26
236#pragma GCC diagnostic push
237#pragma GCC diagnostic ignored "-Winit-list-lifetime"
238 constexpr
239 explicit(extent != dynamic_extent)
240 span(initializer_list<value_type> __il)
241 requires (is_const_v<_Type>)
242 : _M_ptr(__il.begin()), _M_extent(__il.size())
243 { }
244#pragma GCC diagnostic pop
245#endif
246
247 constexpr
248 span(const span&) noexcept = default;
249
250 template<typename _OType, size_t _OExtent>
251 requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
252 || _Extent == _OExtent)
253 && (__is_array_convertible<_Type, _OType>::value)
254 constexpr
255 explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
256 span(const span<_OType, _OExtent>& __s) noexcept
257 : _M_ptr(__s.data()), _M_extent(__s.size())
258 { }
259
260 constexpr span&
261 operator=(const span&) noexcept = default;
262
263 // observers
264
265 [[nodiscard]]
266 constexpr size_type
267 size() const noexcept
268 { return this->_M_extent._M_extent(); }
269
270 [[nodiscard]]
271 constexpr size_type
272 size_bytes() const noexcept
273 { return this->_M_extent._M_extent() * sizeof(element_type); }
274
275 [[nodiscard]]
276 constexpr bool
277 empty() const noexcept
278 { return size() == 0; }
279
280 // element access
281
282 [[nodiscard]]
283 constexpr reference
284 front() const noexcept
285 {
286 __glibcxx_assert(!empty());
287 return *this->_M_ptr;
288 }
289
290 [[nodiscard]]
291 constexpr reference
292 back() const noexcept
293 {
294 __glibcxx_assert(!empty());
295 return *(this->_M_ptr + (size() - 1));
296 }
297
298 [[nodiscard]]
299 constexpr reference
300 operator[](size_type __idx) const noexcept
301 {
302 __glibcxx_assert(__idx < size());
303 return *(this->_M_ptr + __idx);
304 }
305
306#if __cpp_lib_span >= 202311L // >= C++26
307 [[nodiscard]]
308 constexpr reference
309 at(size_type __idx) const
310 {
311 if (__idx >= size())
312 __throw_out_of_range_fmt(__N("span::at(%zu) out-of-range for span "
313 "of size %zu"), __idx, this->size());
314 return *(this->_M_ptr + __idx);
315 }
316#endif
317
318 [[nodiscard]]
319 constexpr pointer
320 data() const noexcept
321 { return this->_M_ptr; }
322
323 // iterator support
324
325 [[nodiscard]]
326 constexpr iterator
327 begin() const noexcept
328 { return iterator(this->_M_ptr); }
329
330 [[nodiscard]]
331 constexpr iterator
332 end() const noexcept
333 { return iterator(this->_M_ptr + this->size()); }
334
335 [[nodiscard]]
336 constexpr reverse_iterator
337 rbegin() const noexcept
338 { return reverse_iterator(this->end()); }
339
340 [[nodiscard]]
341 constexpr reverse_iterator
342 rend() const noexcept
343 { return reverse_iterator(this->begin()); }
344
345#if __cplusplus > 202002L
346 [[nodiscard]]
347 constexpr const_iterator
348 cbegin() const noexcept
349 { return begin(); }
350
351 [[nodiscard]]
352 constexpr const_iterator
353 cend() const noexcept
354 { return end(); }
355
356 [[nodiscard]]
357 constexpr const_reverse_iterator
358 crbegin() const noexcept
359 { return rbegin(); }
360
361 [[nodiscard]]
362 constexpr const_reverse_iterator
363 crend() const noexcept
364 { return rend(); }
365#endif
366
367 // subviews
368
369 template<size_t _Count>
370 [[nodiscard]]
371 constexpr span<element_type, _Count>
372 first() const noexcept
373 {
374 if constexpr (_Extent == dynamic_extent)
375 __glibcxx_assert(_Count <= size());
376 else
377 static_assert(_Count <= extent);
378 using _Sp = span<element_type, _Count>;
379 return _Sp(_SizedPtr{this->data()});
380 }
381
382 [[nodiscard]]
383 constexpr span<element_type, dynamic_extent>
384 first(size_type __count) const noexcept
385 {
386 __glibcxx_assert(__count <= size());
387 return span<element_type>(this->data(), __count);
388 }
389
390 template<size_t _Count>
391 [[nodiscard]]
392 constexpr span<element_type, _Count>
393 last() const noexcept
394 {
395 if constexpr (_Extent == dynamic_extent)
396 __glibcxx_assert(_Count <= size());
397 else
398 static_assert(_Count <= extent);
399 using _Sp = span<element_type, _Count>;
400 return _Sp(_SizedPtr{this->data() + (this->size() - _Count)});
401 }
402
403 [[nodiscard]]
404 constexpr span<element_type, dynamic_extent>
405 last(size_type __count) const noexcept
406 {
407 __glibcxx_assert(__count <= size());
408 return span<element_type>(this->data() + (this->size() - __count),
409 __count);
410 }
411
412 template<size_t _Offset, size_t _Count = dynamic_extent>
413 [[nodiscard]]
414 constexpr auto
415 subspan() const noexcept
416 -> span<element_type, _S_subspan_extent<_Offset, _Count>()>
417 {
418 if constexpr (_Extent == dynamic_extent)
419 {
420 __glibcxx_assert(_Offset <= size());
421 }
422 else
423 static_assert(_Offset <= extent);
424
425 using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
426
427 if constexpr (_Count == dynamic_extent)
428 return _Sp(this->data() + _Offset, this->size() - _Offset);
429 else
430 {
431 if constexpr (_Extent == dynamic_extent)
432 {
433 __glibcxx_assert(_Count <= size());
434 __glibcxx_assert(_Count <= (size() - _Offset));
435 }
436 else
437 {
438 static_assert(_Count <= extent);
439 static_assert(_Count <= (extent - _Offset));
440 }
441 return _Sp(_SizedPtr{this->data() + _Offset});
442 }
443 }
444
445 [[nodiscard]]
446 constexpr span<element_type, dynamic_extent>
447 subspan(size_type __offset, size_type __count = dynamic_extent) const
448 noexcept
449 {
450 __glibcxx_assert(__offset <= size());
451 if (__count == dynamic_extent)
452 __count = this->size() - __offset;
453 else
454 {
455 __glibcxx_assert(__count <= size());
456 __glibcxx_assert(__offset + __count <= size());
457 }
458 return span<element_type>(this->data() + __offset, __count);
459 }
460
461 private:
462 template<typename, size_t> friend class span;
463
464 // Tag type for pointer that has known extent.
465 using _SizedPtr = __detail::__span_ptr<_Type>;
466
467 // Private constructor with an implied extent.
468 [[__gnu__::__always_inline__]]
469 constexpr explicit
470 span(_SizedPtr __ptr) noexcept
471 requires (extent != dynamic_extent)
472 : _M_ptr(__ptr._M_ptr), _M_extent(__v<extent>)
473 { }
474
475 pointer _M_ptr;
476 [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
477 };
478
479 // deduction guides
480
481 template<typename _Type, size_t _ArrayExtent>
482 span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
483
484 template<typename _Type, size_t _ArrayExtent>
485 span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
486
487 template<typename _Type, size_t _ArrayExtent>
488 span(const array<_Type, _ArrayExtent>&)
489 -> span<const _Type, _ArrayExtent>;
490
491 template<contiguous_iterator _Iter, typename _End>
492 span(_Iter, _End)
493 -> span<remove_reference_t<iter_reference_t<_Iter>>>;
494
495 template<ranges::contiguous_range _Range>
496 span(_Range &&)
497 -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
498
499 template<typename _Type, size_t _Extent>
500 [[nodiscard]]
501 inline
502 span<const byte, _Extent == dynamic_extent
503 ? dynamic_extent : _Extent * sizeof(_Type)>
504 as_bytes(span<_Type, _Extent> __sp) noexcept
505 {
506 auto data = reinterpret_cast<const byte*>(__sp.data());
507 auto size = __sp.size_bytes();
508 constexpr auto extent = _Extent == dynamic_extent
509 ? dynamic_extent : _Extent * sizeof(_Type);
510 return span<const byte, extent>{data, size};
511 }
512
513 template<typename _Type, size_t _Extent>
514 requires (!is_const_v<_Type>)
515 inline
516 span<byte, _Extent == dynamic_extent
517 ? dynamic_extent : _Extent * sizeof(_Type)>
518 as_writable_bytes [[nodiscard]] (span<_Type, _Extent> __sp) noexcept
519 {
520 auto data = reinterpret_cast<byte*>(__sp.data());
521 auto size = __sp.size_bytes();
522 constexpr auto extent = _Extent == dynamic_extent
523 ? dynamic_extent : _Extent * sizeof(_Type);
524 return span<byte, extent>{data, size};
525 }
526
527 namespace ranges
528 {
529 // Opt-in to borrowed_range concept
530 template<typename _ElementType, size_t _Extent>
531 inline constexpr bool
532 enable_borrowed_range<span<_ElementType, _Extent>> = true;
533
534 // Opt-in to view concept
535 template<typename _ElementType, size_t _Extent>
536 inline constexpr bool
537 enable_view<span<_ElementType, _Extent>> = true;
538 }
539_GLIBCXX_END_NAMESPACE_VERSION
540} // namespace std
541#endif // __cpp_lib_span
542#endif // _GLIBCXX_SPAN
543