span revision 360784 
1// -*- C++ -*-
2//===------------------------------ span ---------------------------------===//
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
21// [views.span], class template span
22template <class ElementType, size_t Extent = dynamic_extent>
23    class span;
24
25// [span.objectrep], views of object representation
26template <class ElementType, size_t Extent>
27    span<const byte, ((Extent == dynamic_extent) ? dynamic_extent :
28        (sizeof(ElementType) * Extent))> as_bytes(span<ElementType, Extent> s) noexcept;
29
30template <class ElementType, size_t Extent>
31    span<      byte, ((Extent == dynamic_extent) ? dynamic_extent :
32        (sizeof(ElementType) * Extent))> as_writable_bytes(span<ElementType, Extent> s) noexcept;
33
34
35namespace std {
36template <class ElementType, size_t Extent = dynamic_extent>
37class span {
38public:
39    // constants and types
40    using element_type = ElementType;
41    using value_type = remove_cv_t<ElementType>;
42    using size_type = size_t;
43    using difference_type = ptrdiff_t;
44    using pointer = element_type*;
45    using const_pointer = const element_type*;
46    using reference = element_type&;
47    using const_reference = const element_type&;
48    using iterator = implementation-defined;
49    using const_iterator = implementation-defined;
50    using reverse_iterator = std::reverse_iterator<iterator>;
51    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
52    static constexpr size_type extent = Extent;
53
54    // [span.cons], span constructors, copy, assignment, and destructor
55    constexpr span() noexcept;
56    constexpr span(pointer ptr, size_type count);
57    constexpr span(pointer firstElem, pointer lastElem);
58    template <size_t N>
59        constexpr span(element_type (&arr)[N]) noexcept;
60    template <size_t N>
61        constexpr span(array<value_type, N>& arr) noexcept;
62    template <size_t N>
63        constexpr span(const array<value_type, N>& arr) noexcept;
64    template <class Container>
65        constexpr span(Container& cont);
66    template <class Container>
67        constexpr span(const Container& cont);
68    constexpr span(const span& other) noexcept = default;
69    template <class OtherElementType, size_t OtherExtent>
70        constexpr span(const span<OtherElementType, OtherExtent>& s) noexcept;
71    ~span() noexcept = default;
72    constexpr span& operator=(const span& other) noexcept = default;
73
74    // [span.sub], span subviews
75    template <size_t Count>
76        constexpr span<element_type, Count> first() const;
77    template <size_t Count>
78        constexpr span<element_type, Count> last() const;
79    template <size_t Offset, size_t Count = dynamic_extent>
80        constexpr span<element_type, see below> subspan() const;
81
82    constexpr span<element_type, dynamic_extent> first(size_type count) const;
83    constexpr span<element_type, dynamic_extent> last(size_type count) const;
84    constexpr span<element_type, dynamic_extent> subspan(size_type offset, size_type count = dynamic_extent) const;
85
86    // [span.obs], span observers
87    constexpr size_type size() const noexcept;
88    constexpr size_type size_bytes() const noexcept;
89    constexpr bool empty() const noexcept;
90
91    // [span.elem], span element access
92    constexpr reference operator[](size_type idx) const;
93    constexpr reference front() const;
94    constexpr reference back() const;
95    constexpr pointer data() const noexcept;
96
97    // [span.iterators], span iterator support
98    constexpr iterator begin() const noexcept;
99    constexpr iterator end() const noexcept;
100    constexpr const_iterator cbegin() const noexcept;
101    constexpr const_iterator cend() const noexcept;
102    constexpr reverse_iterator rbegin() const noexcept;
103    constexpr reverse_iterator rend() const noexcept;
104    constexpr const_reverse_iterator crbegin() const noexcept;
105    constexpr const_reverse_iterator crend() const noexcept;
106
107private:
108    pointer data_;    // exposition only
109    size_type size_;  // exposition only
110};
111
112template<class T, size_t N>
113    span(T (&)[N]) -> span<T, N>;
114
115template<class T, size_t N>
116    span(array<T, N>&) -> span<T, N>;
117
118template<class T, size_t N>
119    span(const array<T, N>&) -> span<const T, N>;
120
121template<class Container>
122    span(Container&) -> span<typename Container::value_type>;
123
124template<class Container>
125    span(const Container&) -> span<const typename Container::value_type>;
126
127} // namespace std
128
129*/
130
131#include <__config>
132#include <cstddef>      // for ptrdiff_t
133#include <iterator>     // for iterators
134#include <array>        // for array
135#include <type_traits>  // for remove_cv, etc
136#include <cstddef>      // for byte
137
138#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
139#pragma GCC system_header
140#endif
141
142_LIBCPP_BEGIN_NAMESPACE_STD
143
144#if _LIBCPP_STD_VER > 17
145
146inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
147template <typename _Tp, size_t _Extent = dynamic_extent> class span;
148
149
150template <class _Tp>
151struct __is_span_impl : public false_type {};
152
153template <class _Tp, size_t _Extent>
154struct __is_span_impl<span<_Tp, _Extent>> : public true_type {};
155
156template <class _Tp>
157struct __is_span : public __is_span_impl<remove_cv_t<_Tp>> {};
158
159template <class _Tp>
160struct __is_std_array_impl : public false_type {};
161
162template <class _Tp, size_t _Sz>
163struct __is_std_array_impl<array<_Tp, _Sz>> : public true_type {};
164
165template <class _Tp>
166struct __is_std_array : public __is_std_array_impl<remove_cv_t<_Tp>> {};
167
168template <class _Tp, class _ElementType, class = void>
169struct __is_span_compatible_container : public false_type {};
170
171template <class _Tp, class _ElementType>
172struct __is_span_compatible_container<_Tp, _ElementType,
173        void_t<
174        // is not a specialization of span
175            typename enable_if<!__is_span<_Tp>::value, nullptr_t>::type,
176        // is not a specialization of array
177            typename enable_if<!__is_std_array<_Tp>::value, nullptr_t>::type,
178        // is_array_v<Container> is false,
179            typename enable_if<!is_array_v<_Tp>, nullptr_t>::type,
180        // data(cont) and size(cont) are well formed
181            decltype(data(declval<_Tp>())),
182            decltype(size(declval<_Tp>())),
183        // remove_pointer_t<decltype(data(cont))>(*)[] is convertible to ElementType(*)[]
184            typename enable_if<
185                is_convertible_v<remove_pointer_t<decltype(data(declval<_Tp &>()))>(*)[],
186                                 _ElementType(*)[]>,
187                nullptr_t>::type
188        >>
189    : public true_type {};
190
191
192template <typename _Tp, size_t _Extent>
193class _LIBCPP_TEMPLATE_VIS span {
194public:
195//  constants and types
196    using element_type           = _Tp;
197    using value_type             = remove_cv_t<_Tp>;
198    using size_type              = size_t;
199    using difference_type        = ptrdiff_t;
200    using pointer                = _Tp *;
201    using const_pointer          = const _Tp *;
202    using reference              = _Tp &;
203    using const_reference        = const _Tp &;
204    using iterator               =  __wrap_iter<pointer>;
205    using const_iterator         =  __wrap_iter<const_pointer>;
206    using reverse_iterator       = _VSTD::reverse_iterator<iterator>;
207    using const_reverse_iterator = _VSTD::reverse_iterator<const_iterator>;
208
209    static constexpr size_type extent = _Extent;
210
211// [span.cons], span constructors, copy, assignment, and destructor
212    _LIBCPP_INLINE_VISIBILITY constexpr span() noexcept : __data{nullptr}
213    { static_assert(_Extent == 0, "Can't default construct a statically sized span with size > 0"); }
214
215    constexpr span           (const span&) noexcept = default;
216    constexpr span& operator=(const span&) noexcept = default;
217
218    _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __ptr, size_type __count) : __data{__ptr}
219        { (void)__count; _LIBCPP_ASSERT(_Extent == __count, "size mismatch in span's constructor (ptr, len)"); }
220    _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __f, pointer __l) : __data{__f}
221        { (void)__l;     _LIBCPP_ASSERT(_Extent == distance(__f, __l), "size mismatch in span's constructor (ptr, ptr)"); }
222
223    _LIBCPP_INLINE_VISIBILITY constexpr span(element_type (&__arr)[_Extent])          noexcept : __data{__arr} {}
224    _LIBCPP_INLINE_VISIBILITY constexpr span(      array<value_type, _Extent>& __arr) noexcept : __data{__arr.data()} {}
225    _LIBCPP_INLINE_VISIBILITY constexpr span(const array<value_type, _Extent>& __arr) noexcept : __data{__arr.data()} {}
226
227    template <class _OtherElementType>
228    _LIBCPP_INLINE_VISIBILITY
229        constexpr span(const span<_OtherElementType, _Extent>& __other,
230                       enable_if_t<
231                          is_convertible_v<_OtherElementType(*)[], element_type (*)[]>,
232                          nullptr_t> = nullptr)
233        : __data{__other.data()} {}
234
235    template <class _OtherElementType>
236    _LIBCPP_INLINE_VISIBILITY
237        constexpr span(const span<_OtherElementType, dynamic_extent>& __other,
238                       enable_if_t<
239                          is_convertible_v<_OtherElementType(*)[], element_type (*)[]>,
240                          nullptr_t> = nullptr) noexcept
241        : __data{__other.data()} { _LIBCPP_ASSERT(_Extent == __other.size(), "size mismatch in span's constructor (other span)"); }
242
243
244//  ~span() noexcept = default;
245
246    template <size_t _Count>
247    _LIBCPP_INLINE_VISIBILITY
248    constexpr span<element_type, _Count> first() const noexcept
249    {
250        static_assert(_Count <= _Extent, "Count out of range in span::first()");
251        return {data(), _Count};
252    }
253
254    template <size_t _Count>
255    _LIBCPP_INLINE_VISIBILITY
256    constexpr span<element_type, _Count> last() const noexcept
257    {
258        static_assert(_Count <= _Extent, "Count out of range in span::last()");
259        return {data() + size() - _Count, _Count};
260    }
261
262    _LIBCPP_INLINE_VISIBILITY
263    constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept
264    {
265        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::first(count)");
266        return {data(), __count};
267    }
268
269    _LIBCPP_INLINE_VISIBILITY
270    constexpr span<element_type, dynamic_extent> last(size_type __count) const noexcept
271    {
272        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::last(count)");
273        return {data() + size() - __count, __count};
274    }
275
276    template <size_t _Offset, size_t _Count = dynamic_extent>
277    _LIBCPP_INLINE_VISIBILITY
278    constexpr auto subspan() const noexcept
279        -> span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset>
280    {
281        static_assert(_Offset <= _Extent, "Offset out of range in span::subspan()");
282        return {data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
283    }
284
285
286    _LIBCPP_INLINE_VISIBILITY
287    constexpr span<element_type, dynamic_extent>
288       subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept
289    {
290        _LIBCPP_ASSERT(__offset <= size(), "Offset out of range in span::subspan(offset, count)");
291        _LIBCPP_ASSERT(__count  <= size() || __count == dynamic_extent, "Count out of range in span::subspan(offset, count)");
292        if (__count == dynamic_extent)
293            return {data() + __offset, size() - __offset};
294        _LIBCPP_ASSERT(__offset <= size() - __count, "count + offset out of range in span::subspan(offset, count)");
295        return {data() + __offset, __count};
296    }
297
298    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()       const noexcept { return _Extent; }
299    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes() const noexcept { return _Extent * sizeof(element_type); }
300    _LIBCPP_INLINE_VISIBILITY constexpr bool empty()           const noexcept { return _Extent == 0; }
301
302    _LIBCPP_INLINE_VISIBILITY constexpr reference operator[](size_type __idx) const noexcept
303    {
304        _LIBCPP_ASSERT(__idx >= 0 && __idx < size(), "span<T,N>[] index out of bounds");
305        return __data[__idx];
306    }
307
308    _LIBCPP_INLINE_VISIBILITY constexpr reference front() const noexcept
309    {
310        static_assert(_Extent > 0, "span<T,N>[].front() on empty span");
311        return __data[0];
312    }
313
314    _LIBCPP_INLINE_VISIBILITY constexpr reference back() const noexcept
315    {
316        static_assert(_Extent > 0, "span<T,N>[].back() on empty span");
317        return __data[size()-1];
318    }
319
320    _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data; }
321
322// [span.iter], span iterator support
323    _LIBCPP_INLINE_VISIBILITY constexpr iterator                 begin() const noexcept { return iterator(data()); }
324    _LIBCPP_INLINE_VISIBILITY constexpr iterator                   end() const noexcept { return iterator(data() + size()); }
325    _LIBCPP_INLINE_VISIBILITY constexpr const_iterator          cbegin() const noexcept { return const_iterator(data()); }
326    _LIBCPP_INLINE_VISIBILITY constexpr const_iterator            cend() const noexcept { return const_iterator(data() + size()); }
327    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); }
328    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); }
329    _LIBCPP_INLINE_VISIBILITY constexpr const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator(cend()); }
330    _LIBCPP_INLINE_VISIBILITY constexpr const_reverse_iterator   crend() const noexcept { return const_reverse_iterator(cbegin()); }
331
332    _LIBCPP_INLINE_VISIBILITY constexpr void swap(span &__other) noexcept
333    {
334        pointer __p = __data;
335        __data = __other.__data;
336        __other.__data = __p;
337    }
338
339    _LIBCPP_INLINE_VISIBILITY span<const byte, _Extent * sizeof(element_type)> __as_bytes() const noexcept
340    { return {reinterpret_cast<const byte *>(data()), size_bytes()}; }
341
342    _LIBCPP_INLINE_VISIBILITY span<byte, _Extent * sizeof(element_type)> __as_writable_bytes() const noexcept
343    { return {reinterpret_cast<byte *>(data()), size_bytes()}; }
344
345private:
346    pointer    __data;
347
348};
349
350
351template <typename _Tp>
352class _LIBCPP_TEMPLATE_VIS span<_Tp, dynamic_extent> {
353private:
354
355public:
356//  constants and types
357    using element_type           = _Tp;
358    using value_type             = remove_cv_t<_Tp>;
359    using size_type              = size_t;
360    using difference_type        = ptrdiff_t;
361    using pointer                = _Tp *;
362    using const_pointer          = const _Tp *;
363    using reference              = _Tp &;
364    using const_reference        = const _Tp &;
365    using iterator               =  __wrap_iter<pointer>;
366    using const_iterator         =  __wrap_iter<const_pointer>;
367    using reverse_iterator       = _VSTD::reverse_iterator<iterator>;
368    using const_reverse_iterator = _VSTD::reverse_iterator<const_iterator>;
369
370    static constexpr size_type extent = dynamic_extent;
371
372// [span.cons], span constructors, copy, assignment, and destructor
373    _LIBCPP_INLINE_VISIBILITY constexpr span() noexcept : __data{nullptr}, __size{0} {}
374
375    constexpr span           (const span&) noexcept = default;
376    constexpr span& operator=(const span&) noexcept = default;
377
378    _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __ptr, size_type __count) : __data{__ptr}, __size{__count} {}
379    _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __f, pointer __l) : __data{__f}, __size{static_cast<size_t>(distance(__f, __l))} {}
380
381    template <size_t _Sz>
382    _LIBCPP_INLINE_VISIBILITY
383    constexpr span(element_type (&__arr)[_Sz])          noexcept : __data{__arr}, __size{_Sz} {}
384
385    template <size_t _Sz>
386    _LIBCPP_INLINE_VISIBILITY
387    constexpr span(array<value_type, _Sz>& __arr)       noexcept : __data{__arr.data()}, __size{_Sz} {}
388
389    template <size_t _Sz>
390    _LIBCPP_INLINE_VISIBILITY
391    constexpr span(const array<value_type, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
392
393    template <class _Container>
394    _LIBCPP_INLINE_VISIBILITY
395        constexpr span(      _Container& __c,
396            enable_if_t<__is_span_compatible_container<_Container, _Tp>::value, nullptr_t> = nullptr)
397        : __data{_VSTD::data(__c)}, __size{(size_type) _VSTD::size(__c)} {}
398
399    template <class _Container>
400    _LIBCPP_INLINE_VISIBILITY
401        constexpr span(const _Container& __c,
402            enable_if_t<__is_span_compatible_container<const _Container, _Tp>::value, nullptr_t> = nullptr)
403        : __data{_VSTD::data(__c)}, __size{(size_type) _VSTD::size(__c)} {}
404
405
406    template <class _OtherElementType, size_t _OtherExtent>
407    _LIBCPP_INLINE_VISIBILITY
408        constexpr span(const span<_OtherElementType, _OtherExtent>& __other,
409                       enable_if_t<
410                          is_convertible_v<_OtherElementType(*)[], element_type (*)[]>,
411                          nullptr_t> = nullptr) noexcept
412        : __data{__other.data()}, __size{__other.size()} {}
413
414//    ~span() noexcept = default;
415
416    template <size_t _Count>
417    _LIBCPP_INLINE_VISIBILITY
418    constexpr span<element_type, _Count> first() const noexcept
419    {
420        _LIBCPP_ASSERT(_Count <= size(), "Count out of range in span::first()");
421        return {data(), _Count};
422    }
423
424    template <size_t _Count>
425    _LIBCPP_INLINE_VISIBILITY
426    constexpr span<element_type, _Count> last() const noexcept
427    {
428        _LIBCPP_ASSERT(_Count <= size(), "Count out of range in span::last()");
429        return {data() + size() - _Count, _Count};
430    }
431
432    _LIBCPP_INLINE_VISIBILITY
433    constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept
434    {
435        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::first(count)");
436        return {data(), __count};
437    }
438
439    _LIBCPP_INLINE_VISIBILITY
440    constexpr span<element_type, dynamic_extent> last (size_type __count) const noexcept
441    {
442        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::last(count)");
443        return {data() + size() - __count, __count};
444    }
445
446    template <size_t _Offset, size_t _Count = dynamic_extent>
447    _LIBCPP_INLINE_VISIBILITY
448    constexpr span<_Tp, dynamic_extent> subspan() const noexcept
449    {
450        _LIBCPP_ASSERT(_Offset <= size(), "Offset out of range in span::subspan()");
451        _LIBCPP_ASSERT(_Count == dynamic_extent || _Offset + _Count <= size(), "Count out of range in span::subspan()");
452        return {data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
453    }
454
455    constexpr span<element_type, dynamic_extent>
456    _LIBCPP_INLINE_VISIBILITY
457    subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept
458    {
459        _LIBCPP_ASSERT(__offset <= size(), "Offset out of range in span::subspan(offset, count)");
460        _LIBCPP_ASSERT(__count  <= size() || __count == dynamic_extent, "count out of range in span::subspan(offset, count)");
461        if (__count == dynamic_extent)
462            return {data() + __offset, size() - __offset};
463        _LIBCPP_ASSERT(__offset <= size() - __count, "Offset + count out of range in span::subspan(offset, count)");
464        return {data() + __offset, __count};
465    }
466
467    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()       const noexcept { return __size; }
468    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes() const noexcept { return __size * sizeof(element_type); }
469    _LIBCPP_INLINE_VISIBILITY constexpr bool empty()           const noexcept { return __size == 0; }
470
471    _LIBCPP_INLINE_VISIBILITY constexpr reference operator[](size_type __idx) const noexcept
472    {
473        _LIBCPP_ASSERT(__idx >= 0 && __idx < size(), "span<T>[] index out of bounds");
474        return __data[__idx];
475    }
476
477    _LIBCPP_INLINE_VISIBILITY constexpr reference front() const noexcept
478    {
479        _LIBCPP_ASSERT(!empty(), "span<T>[].front() on empty span");
480        return __data[0];
481    }
482
483    _LIBCPP_INLINE_VISIBILITY constexpr reference back() const noexcept
484    {
485        _LIBCPP_ASSERT(!empty(), "span<T>[].back() on empty span");
486        return __data[size()-1];
487    }
488
489
490    _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data; }
491
492// [span.iter], span iterator support
493    _LIBCPP_INLINE_VISIBILITY constexpr iterator                 begin() const noexcept { return iterator(data()); }
494    _LIBCPP_INLINE_VISIBILITY constexpr iterator                   end() const noexcept { return iterator(data() + size()); }
495    _LIBCPP_INLINE_VISIBILITY constexpr const_iterator          cbegin() const noexcept { return const_iterator(data()); }
496    _LIBCPP_INLINE_VISIBILITY constexpr const_iterator            cend() const noexcept { return const_iterator(data() + size()); }
497    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); }
498    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); }
499    _LIBCPP_INLINE_VISIBILITY constexpr const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator(cend()); }
500    _LIBCPP_INLINE_VISIBILITY constexpr const_reverse_iterator   crend() const noexcept { return const_reverse_iterator(cbegin()); }
501
502    _LIBCPP_INLINE_VISIBILITY constexpr void swap(span &__other) noexcept
503    {
504        pointer __p = __data;
505        __data = __other.__data;
506        __other.__data = __p;
507
508        size_type __sz = __size;
509        __size = __other.__size;
510        __other.__size = __sz;
511    }
512
513    _LIBCPP_INLINE_VISIBILITY span<const byte, dynamic_extent> __as_bytes() const noexcept
514    { return {reinterpret_cast<const byte *>(data()), size_bytes()}; }
515
516    _LIBCPP_INLINE_VISIBILITY span<byte, dynamic_extent> __as_writable_bytes() const noexcept
517    { return {reinterpret_cast<byte *>(data()), size_bytes()}; }
518
519private:
520    pointer   __data;
521    size_type __size;
522};
523
524//  tuple interface
525template <class _Tp, size_t _Size>
526struct _LIBCPP_TEMPLATE_VIS tuple_size<span<_Tp, _Size>>
527    : public integral_constant<size_t, _Size> {};
528
529template <class _Tp>
530struct _LIBCPP_TEMPLATE_VIS tuple_size<span<_Tp, dynamic_extent>>; // declared but not defined
531
532
533template <size_t _Ip, class _Tp, size_t _Size>
534struct _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, span<_Tp, _Size>>
535{
536    static_assert( dynamic_extent != _Size, "std::tuple_element<> not supported for std::span<T, dynamic_extent>");
537    static_assert(_Ip < _Size, "Index out of bounds in std::tuple_element<> (std::span)");
538    typedef _Tp type;
539};
540
541template <size_t _Ip, class _Tp, size_t _Size>
542_LIBCPP_INLINE_VISIBILITY constexpr
543_Tp&
544get(span<_Tp, _Size> __s) noexcept
545{
546    static_assert( dynamic_extent != _Size, "std::get<> not supported for std::span<T, dynamic_extent>");
547    static_assert(_Ip < _Size, "Index out of bounds in std::get<> (std::span)");
548    return __s[_Ip];
549}
550
551
552//  as_bytes & as_writable_bytes
553template <class _Tp, size_t _Extent>
554_LIBCPP_INLINE_VISIBILITY
555auto as_bytes(span<_Tp, _Extent> __s) noexcept
556-> decltype(__s.__as_bytes())
557{ return    __s.__as_bytes(); }
558
559template <class _Tp, size_t _Extent>
560_LIBCPP_INLINE_VISIBILITY
561auto as_writable_bytes(span<_Tp, _Extent> __s) noexcept
562-> enable_if_t<!is_const_v<_Tp>, decltype(__s.__as_writable_bytes())>
563{ return __s.__as_writable_bytes(); }
564
565template <class _Tp, size_t _Extent>
566_LIBCPP_INLINE_VISIBILITY
567constexpr void swap(span<_Tp, _Extent> &__lhs, span<_Tp, _Extent> &__rhs) noexcept
568{ __lhs.swap(__rhs); }
569
570
571//  Deduction guides
572template<class _Tp, size_t _Sz>
573    span(_Tp (&)[_Sz]) -> span<_Tp, _Sz>;
574
575template<class _Tp, size_t _Sz>
576    span(array<_Tp, _Sz>&) -> span<_Tp, _Sz>;
577
578template<class _Tp, size_t _Sz>
579    span(const array<_Tp, _Sz>&) -> span<const _Tp, _Sz>;
580
581template<class _Container>
582    span(_Container&) -> span<typename _Container::value_type>;
583
584template<class _Container>
585    span(const _Container&) -> span<const typename _Container::value_type>;
586
587#endif // _LIBCPP_STD_VER > 17
588
589_LIBCPP_END_NAMESPACE_STD
590
591#endif // _LIBCPP_SPAN
592