path: root/contrib/libs/cxxsupp/libcxx/include/span

// -*- C++ -*- 
//===------------------------------ span ---------------------------------===// 
// 
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// 
//===---------------------------------------------------------------------===// 
 
#ifndef _LIBCPP_SPAN 
#define _LIBCPP_SPAN 
 
/* 
    span synopsis 
 
namespace std { 
 
// constants 
inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max(); 
 
// [views.span], class template span 
template <class ElementType, size_t Extent = dynamic_extent> 
    class span; 
 
template<class ElementType, size_t Extent> 
  inline constexpr bool ranges::enable_view<span<ElementType, Extent>> = true; 
 
template<class ElementType, size_t Extent> 
    inline constexpr bool ranges::enable_borrowed_range<span<ElementType, Extent>> = true; 
 
// [span.objectrep], views of object representation 
template <class ElementType, size_t Extent> 
    span<const byte, ((Extent == dynamic_extent) ? dynamic_extent :
        (sizeof(ElementType) * Extent))> as_bytes(span<ElementType, Extent> s) noexcept; 
 
template <class ElementType, size_t Extent> 
    span<      byte, ((Extent == dynamic_extent) ? dynamic_extent :
        (sizeof(ElementType) * Extent))> as_writable_bytes(span<ElementType, Extent> s) noexcept; 
 
 
template <class ElementType, size_t Extent = dynamic_extent> 
class span { 
public: 
    // constants and types 
    using element_type = ElementType; 
    using value_type = remove_cv_t<ElementType>; 
    using size_type = size_t; 
    using difference_type = ptrdiff_t; 
    using pointer = element_type*; 
    using const_pointer = const element_type*; 
    using reference = element_type&; 
    using const_reference = const element_type&; 
    using iterator = implementation-defined; 
    using reverse_iterator = std::reverse_iterator<iterator>; 
    static constexpr size_type extent = Extent; 
 
    // [span.cons], span constructors, copy, assignment, and destructor 
    constexpr span() noexcept; 
    template <class It> 
    constexpr explicit(Extent != dynamic_extent) span(It first, size_type count); 
    template <class It, class End> 
    constexpr explicit(Extent != dynamic_extent) span(It first, End last); 
    template <size_t N> 
        constexpr span(element_type (&arr)[N]) noexcept; 
    template <size_t N> 
        constexpr span(array<value_type, N>& arr) noexcept; 
    template <size_t N> 
        constexpr span(const array<value_type, N>& arr) noexcept; 
    template<class R> 
      constexpr explicit(Extent != dynamic_extent) span(R&& r); 
    constexpr span(const span& other) noexcept = default; 
    template <class OtherElementType, size_t OtherExtent> 
        constexpr explicit(Extent != dynamic_extent) span(const span<OtherElementType, OtherExtent>& s) noexcept; 
    ~span() noexcept = default; 
    constexpr span& operator=(const span& other) noexcept = default; 
 
    // [span.sub], span subviews 
    template <size_t Count> 
        constexpr span<element_type, Count> first() const; 
    template <size_t Count> 
        constexpr span<element_type, Count> last() const; 
    template <size_t Offset, size_t Count = dynamic_extent> 
        constexpr span<element_type, see below> subspan() const; 
 
    constexpr span<element_type, dynamic_extent> first(size_type count) const; 
    constexpr span<element_type, dynamic_extent> last(size_type count) const; 
    constexpr span<element_type, dynamic_extent> subspan(size_type offset, size_type count = dynamic_extent) const; 
 
    // [span.obs], span observers 
    constexpr size_type size() const noexcept; 
    constexpr size_type size_bytes() const noexcept; 
    constexpr bool empty() const noexcept; 
 
    // [span.elem], span element access 
    constexpr reference operator[](size_type idx) const; 
    constexpr reference front() const; 
    constexpr reference back() const; 
    constexpr pointer data() const noexcept; 
 
    // [span.iterators], span iterator support 
    constexpr iterator begin() const noexcept; 
    constexpr iterator end() const noexcept; 
    constexpr reverse_iterator rbegin() const noexcept; 
    constexpr reverse_iterator rend() const noexcept; 
 
private: 
    pointer data_;    // exposition only
    size_type size_;  // exposition only 
}; 
 
template<class It, class EndOrSize> 
    span(It, EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>>; 
 
template<class T, size_t N> 
    span(T (&)[N]) -> span<T, N>; 

template<class T, size_t N> 
    span(array<T, N>&) -> span<T, N>; 
 
template<class T, size_t N> 
    span(const array<T, N>&) -> span<const T, N>; 
 
template<class R> 
    span(R&&) -> span<remove_reference_t<ranges::range_reference_t<R>>>; 
 
} // namespace std 
 
*/ 
 
#include <__config> 
#include <__debug> 
#include <__iterator/concepts.h> 
#include <__iterator/wrap_iter.h> 
#include <__ranges/concepts.h> 
#include <__ranges/data.h> 
#include <__ranges/enable_borrowed_range.h> 
#include <__ranges/enable_view.h> 
#include <__ranges/size.h> 
#include <array>        // for array 
#include <cstddef>      // for byte 
#include <iterator>     // for iterators 
#include <limits> 
#include <type_traits>  // for remove_cv, etc 
#include <version> 
 
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 
#pragma GCC system_header 
#endif 
 
_LIBCPP_PUSH_MACROS 
#include <__undef_macros> 
 
_LIBCPP_BEGIN_NAMESPACE_STD 
 
#if _LIBCPP_STD_VER > 17 
 
inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max(); 
template <typename _Tp, size_t _Extent = dynamic_extent> class span; 
 
 
template <class _Tp> 
struct __is_std_array : false_type {}; 
 
template <class _Tp, size_t _Sz> 
struct __is_std_array<array<_Tp, _Sz>> : true_type {}; 
 
template <class _Tp> 
struct __is_std_span : false_type {}; 
 
template <class _Tp, size_t _Sz> 
struct __is_std_span<span<_Tp, _Sz>> : true_type {}; 
 
#if !defined(_LIBCPP_HAS_NO_RANGES) 
template <class _Range, class _ElementType> 
concept __span_compatible_range = 
  ranges::contiguous_range<_Range> && 
  ranges::sized_range<_Range> && 
  (ranges::borrowed_range<_Range> || is_const_v<_ElementType>) && 
  !__is_std_span<remove_cvref_t<_Range>>::value  && 
  !__is_std_array<remove_cvref_t<_Range>>::value && 
  !is_array_v<remove_cvref_t<_Range>> && 
  is_convertible_v<remove_reference_t<ranges::range_reference_t<_Range>>(*)[], _ElementType(*)[]>; 
#else 
template <class _Tp, class _ElementType, class = void> 
struct __is_span_compatible_container : public false_type {}; 
 
template <class _Tp, class _ElementType> 
struct __is_span_compatible_container<_Tp, _ElementType, 
        void_t< 
        // is not a specialization of span 
            enable_if_t<!__is_std_span<_Tp>::value, nullptr_t>, 
        // is not a specialization of array 
            enable_if_t<!__is_std_array<_Tp>::value, nullptr_t>, 
        // is_array_v<Container> is false, 
            enable_if_t<!is_array_v<_Tp>, nullptr_t>, 
        // data(cont) and size(cont) are well formed 
            decltype(data(declval<_Tp>())), 
            decltype(size(declval<_Tp>())), 
        // remove_pointer_t<decltype(data(cont))>(*)[] is convertible to ElementType(*)[] 
            enable_if_t< 
                is_convertible_v<remove_pointer_t<decltype(data(declval<_Tp &>()))>(*)[],
                                 _ElementType(*)[]>,
                nullptr_t> 
        >> 
    : public true_type {}; 
#endif 
 
template <typename _Tp, size_t _Extent> 
class _LIBCPP_TEMPLATE_VIS span { 
public: 
//  constants and types 
    using element_type           = _Tp; 
    using value_type             = remove_cv_t<_Tp>; 
    using size_type              = size_t; 
    using difference_type        = ptrdiff_t; 
    using pointer                = _Tp *; 
    using const_pointer          = const _Tp *; 
    using reference              = _Tp &; 
    using const_reference        = const _Tp &; 
#if (_LIBCPP_DEBUG_LEVEL == 2) || defined(_LIBCPP_ABI_SPAN_POINTER_ITERATORS) 
    using iterator               = pointer; 
#else 
    using iterator               = __wrap_iter<pointer>; 
#endif 
    using reverse_iterator       = _VSTD::reverse_iterator<iterator>; 
 
    static constexpr size_type extent = _Extent; 
 
// [span.cons], span constructors, copy, assignment, and destructor
    template <size_t _Sz = _Extent, enable_if_t<_Sz == 0, nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY constexpr span() noexcept : __data{nullptr} {} 
 
    constexpr span           (const span&) noexcept = default; 
    constexpr span& operator=(const span&) noexcept = default; 
 
#if !defined(_LIBCPP_HAS_NO_RANGES) 
    template <class _It, 
              enable_if_t<contiguous_iterator<_It> && 
                              is_convertible_v<remove_reference_t<iter_reference_t<_It>>(*)[], element_type (*)[]>, 
                          nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr explicit span(_It __first, size_type __count) 
        : __data{_VSTD::to_address(__first)} { 
      (void)__count; 
      _LIBCPP_ASSERT(_Extent == __count, "size mismatch in span's constructor (iterator, len)"); 
    } 
 
    template < 
        class _It, class _End, 
        enable_if_t<is_convertible_v<remove_reference_t<iter_reference_t<_It> > (*)[], element_type (*)[]> && 
                        contiguous_iterator<_It> && sized_sentinel_for<_End, _It> && !is_convertible_v<_End, size_t>, 
                    nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr explicit span(_It __first, _End __last) : __data{_VSTD::to_address(__first)} { 
      (void)__last; 
      _LIBCPP_ASSERT((__last - __first >= 0), "invalid range in span's constructor (iterator, sentinel)"); 
      _LIBCPP_ASSERT(__last - __first == _Extent, 
                     "invalid range in span's constructor (iterator, sentinel): last - first != extent"); 
    } 
#else 
    _LIBCPP_INLINE_VISIBILITY constexpr explicit span(pointer __ptr, size_type __count) : __data{__ptr} 
        { (void)__count; _LIBCPP_ASSERT(_Extent == __count, "size mismatch in span's constructor (ptr, len)"); } 
    _LIBCPP_INLINE_VISIBILITY constexpr explicit span(pointer __f, pointer __l) : __data{__f} 
        { (void)__l;     _LIBCPP_ASSERT(_Extent == distance(__f, __l), "size mismatch in span's constructor (ptr, ptr)"); } 
#endif 
 
    _LIBCPP_INLINE_VISIBILITY constexpr span(element_type (&__arr)[_Extent])          noexcept : __data{__arr} {} 
 
    template <class _OtherElementType, 
              enable_if_t<is_convertible_v<_OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(array<_OtherElementType, _Extent>& __arr) noexcept : __data{__arr.data()} {} 
 
    template <class _OtherElementType, 
              enable_if_t<is_convertible_v<const _OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(const array<_OtherElementType, _Extent>& __arr) noexcept : __data{__arr.data()} {} 
 
#if !defined(_LIBCPP_HAS_NO_RANGES) 
    template <__span_compatible_range<element_type> _Range> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr explicit span(_Range&& __r) : __data{ranges::data(__r)} { 
      _LIBCPP_ASSERT(ranges::size(__r) == _Extent, "size mismatch in span's constructor (range)"); 
    } 
#else 
    template <class _Container> 
    _LIBCPP_INLINE_VISIBILITY 
        constexpr explicit span(      _Container& __c, 
            enable_if_t<__is_span_compatible_container<_Container, _Tp>::value, nullptr_t> = nullptr) 
        : __data{_VSTD::data(__c)} { 
            _LIBCPP_ASSERT(_Extent == _VSTD::size(__c), "size mismatch in span's constructor (range)"); 
        } 
 
    template <class _Container> 
    _LIBCPP_INLINE_VISIBILITY 
        constexpr explicit span(const _Container& __c, 
            enable_if_t<__is_span_compatible_container<const _Container, _Tp>::value, nullptr_t> = nullptr) 
        : __data{_VSTD::data(__c)} { 
            _LIBCPP_ASSERT(_Extent == _VSTD::size(__c), "size mismatch in span's constructor (range)"); 
        } 
#endif 
 
    template <class _OtherElementType> 
    _LIBCPP_INLINE_VISIBILITY 
        constexpr span(const span<_OtherElementType, _Extent>& __other, 
                       enable_if_t< 
                          is_convertible_v<_OtherElementType(*)[], element_type (*)[]>, 
                          nullptr_t> = nullptr) 
        : __data{__other.data()} {} 
 
    template <class _OtherElementType> 
    _LIBCPP_INLINE_VISIBILITY 
        constexpr explicit span(const span<_OtherElementType, dynamic_extent>& __other, 
                       enable_if_t< 
                          is_convertible_v<_OtherElementType(*)[], element_type (*)[]>, 
                          nullptr_t> = nullptr) noexcept 
        : __data{__other.data()} { _LIBCPP_ASSERT(_Extent == __other.size(), "size mismatch in span's constructor (other span)"); } 
 
 
//  ~span() noexcept = default; 
 
    template <size_t _Count> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, _Count> first() const noexcept
    { 
        static_assert(_Count <= _Extent, "Count out of range in span::first()"); 
        return span<element_type, _Count>{data(), _Count}; 
    } 
 
    template <size_t _Count> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, _Count> last() const noexcept
    { 
        static_assert(_Count <= _Extent, "Count out of range in span::last()"); 
        return span<element_type, _Count>{data() + size() - _Count, _Count}; 
    } 

    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept 
    { 
        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::first(count)"); 
        return {data(), __count}; 
    } 
 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, dynamic_extent> last(size_type __count) const noexcept 
    { 
        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::last(count)"); 
        return {data() + size() - __count, __count}; 
    } 
 
    template <size_t _Offset, size_t _Count = dynamic_extent> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr auto subspan() const noexcept
        -> span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset> 
    { 
        static_assert(_Offset <= _Extent, "Offset out of range in span::subspan()"); 
        static_assert(_Count == dynamic_extent || _Count <= _Extent - _Offset, "Offset + count out of range in span::subspan()"); 
 
        using _ReturnType = span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset>; 
        return _ReturnType{data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count}; 
    } 
 
 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, dynamic_extent> 
       subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept 
    {
        _LIBCPP_ASSERT(__offset <= size(), "Offset out of range in span::subspan(offset, count)"); 
        _LIBCPP_ASSERT(__count  <= size() || __count == dynamic_extent, "Count out of range in span::subspan(offset, count)"); 
        if (__count == dynamic_extent) 
            return {data() + __offset, size() - __offset}; 
        _LIBCPP_ASSERT(__count <= size() - __offset, "Offset + count out of range in span::subspan(offset, count)"); 
        return {data() + __offset, __count}; 
    } 
 
    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()       const noexcept { return _Extent; } 
    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes() const noexcept { return _Extent * sizeof(element_type); } 
    _LIBCPP_INLINE_VISIBILITY constexpr bool empty()           const noexcept { return _Extent == 0; }
 
    _LIBCPP_INLINE_VISIBILITY constexpr reference operator[](size_type __idx) const noexcept 
    { 
        _LIBCPP_ASSERT(__idx < size(), "span<T,N>[] index out of bounds"); 
        return __data[__idx];
    }
 
    _LIBCPP_INLINE_VISIBILITY constexpr reference front() const noexcept 
    { 
        _LIBCPP_ASSERT(!empty(), "span<T, N>::front() on empty span"); 
        return __data[0]; 
    }
 
    _LIBCPP_INLINE_VISIBILITY constexpr reference back() const noexcept 
    { 
        _LIBCPP_ASSERT(!empty(), "span<T, N>::back() on empty span"); 
        return __data[size()-1]; 
    } 
 
    _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data; } 
 
// [span.iter], span iterator support 
    _LIBCPP_INLINE_VISIBILITY constexpr iterator                 begin() const noexcept { return iterator(data()); } 
    _LIBCPP_INLINE_VISIBILITY constexpr iterator                   end() const noexcept { return iterator(data() + size()); } 
    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); } 
    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); } 
 
    _LIBCPP_INLINE_VISIBILITY span<const byte, _Extent * sizeof(element_type)> __as_bytes() const noexcept 
    { return span<const byte, _Extent * sizeof(element_type)>{reinterpret_cast<const byte *>(data()), size_bytes()}; } 
 
    _LIBCPP_INLINE_VISIBILITY span<byte, _Extent * sizeof(element_type)> __as_writable_bytes() const noexcept 
    { return span<byte, _Extent * sizeof(element_type)>{reinterpret_cast<byte *>(data()), size_bytes()}; } 
 
private: 
    pointer    __data; 
 
}; 
 
 
template <typename _Tp> 
class _LIBCPP_TEMPLATE_VIS span<_Tp, dynamic_extent> { 
private: 
 
public: 
//  constants and types 
    using element_type           = _Tp; 
    using value_type             = remove_cv_t<_Tp>; 
    using size_type              = size_t; 
    using difference_type        = ptrdiff_t; 
    using pointer                = _Tp *; 
    using const_pointer          = const _Tp *; 
    using reference              = _Tp &; 
    using const_reference        = const _Tp &; 
#if (_LIBCPP_DEBUG_LEVEL == 2) || defined(_LIBCPP_ABI_SPAN_POINTER_ITERATORS) 
    using iterator               = pointer; 
#else 
    using iterator               = __wrap_iter<pointer>; 
#endif 
    using reverse_iterator       = _VSTD::reverse_iterator<iterator>; 
 
    static constexpr size_type extent = dynamic_extent; 
 
// [span.cons], span constructors, copy, assignment, and destructor
    _LIBCPP_INLINE_VISIBILITY constexpr span() noexcept : __data{nullptr}, __size{0} {} 
 
    constexpr span           (const span&) noexcept = default; 
    constexpr span& operator=(const span&) noexcept = default; 
 
#if !defined(_LIBCPP_HAS_NO_RANGES) 
    template <class _It, 
              enable_if_t<contiguous_iterator<_It> && 
                              is_convertible_v<remove_reference_t<iter_reference_t<_It> > (*)[], element_type (*)[]>, 
                          nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(_It __first, size_type __count) 
        : __data{_VSTD::to_address(__first)}, __size{__count} {} 
 
    template < 
        class _It, class _End, 
        enable_if_t<is_convertible_v<remove_reference_t<iter_reference_t<_It> > (*)[], element_type (*)[]> && 
                        contiguous_iterator<_It> && sized_sentinel_for<_End, _It> && !is_convertible_v<_End, size_t>, 
                    nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(_It __first, _End __last) 
        : __data(_VSTD::to_address(__first)), __size(__last - __first) {} 
#else 
    _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __ptr, size_type __count) : __data{__ptr}, __size{__count} {} 
    _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __f, pointer __l) : __data{__f}, __size{static_cast<size_t>(distance(__f, __l))} {} 
#endif 
 
    template <size_t _Sz> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(element_type (&__arr)[_Sz])          noexcept : __data{__arr}, __size{_Sz} {}
 
    template <class _OtherElementType, size_t _Sz, 
              enable_if_t<is_convertible_v<_OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(array<_OtherElementType, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}

    template <class _OtherElementType, size_t _Sz, 
              enable_if_t<is_convertible_v<const _OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(const array<_OtherElementType, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
 
#if !defined(_LIBCPP_HAS_NO_RANGES) 
    template <__span_compatible_range<element_type> _Range> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span(_Range&& __r) : __data(ranges::data(__r)), __size{ranges::size(__r)} {} 
#else 
    template <class _Container> 
    _LIBCPP_INLINE_VISIBILITY 
        constexpr span(      _Container& __c, 
            enable_if_t<__is_span_compatible_container<_Container, _Tp>::value, nullptr_t> = nullptr) 
        : __data{_VSTD::data(__c)}, __size{(size_type) _VSTD::size(__c)} {} 
 
    template <class _Container> 
    _LIBCPP_INLINE_VISIBILITY 
        constexpr span(const _Container& __c, 
            enable_if_t<__is_span_compatible_container<const _Container, _Tp>::value, nullptr_t> = nullptr) 
        : __data{_VSTD::data(__c)}, __size{(size_type) _VSTD::size(__c)} {} 
#  endif 
 
    template <class _OtherElementType, size_t _OtherExtent> 
    _LIBCPP_INLINE_VISIBILITY 
        constexpr span(const span<_OtherElementType, _OtherExtent>& __other, 
                       enable_if_t< 
                          is_convertible_v<_OtherElementType(*)[], element_type (*)[]>, 
                          nullptr_t> = nullptr) noexcept 
        : __data{__other.data()}, __size{__other.size()} {} 
 
//    ~span() noexcept = default; 
 
    template <size_t _Count> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, _Count> first() const noexcept 
    { 
        _LIBCPP_ASSERT(_Count <= size(), "Count out of range in span::first()"); 
        return span<element_type, _Count>{data(), _Count}; 
    } 
 
    template <size_t _Count> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, _Count> last() const noexcept 
    { 
        _LIBCPP_ASSERT(_Count <= size(), "Count out of range in span::last()"); 
        return span<element_type, _Count>{data() + size() - _Count, _Count}; 
    } 
 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, dynamic_extent> first(size_type __count) const noexcept 
    { 
        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::first(count)"); 
        return {data(), __count}; 
    } 

    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, dynamic_extent> last (size_type __count) const noexcept 
    { 
        _LIBCPP_ASSERT(__count <= size(), "Count out of range in span::last(count)"); 
        return {data() + size() - __count, __count}; 
    } 
 
    template <size_t _Offset, size_t _Count = dynamic_extent> 
    _LIBCPP_INLINE_VISIBILITY 
    constexpr span<element_type, _Count> subspan() const noexcept 
    { 
        _LIBCPP_ASSERT(_Offset <= size(), "Offset out of range in span::subspan()"); 
        _LIBCPP_ASSERT(_Count == dynamic_extent || _Count <= size() - _Offset, "Offset + count out of range in span::subspan()"); 
        return span<element_type, _Count>{data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count}; 
    } 
 
    constexpr span<element_type, dynamic_extent> 
    _LIBCPP_INLINE_VISIBILITY 
    subspan(size_type __offset, size_type __count = dynamic_extent) const noexcept
    {
        _LIBCPP_ASSERT(__offset <= size(), "Offset out of range in span::subspan(offset, count)"); 
        _LIBCPP_ASSERT(__count  <= size() || __count == dynamic_extent, "count out of range in span::subspan(offset, count)"); 
        if (__count == dynamic_extent) 
            return {data() + __offset, size() - __offset}; 
        _LIBCPP_ASSERT(__count <= size() - __offset, "Offset + count out of range in span::subspan(offset, count)"); 
        return {data() + __offset, __count}; 
    } 
 
    _LIBCPP_INLINE_VISIBILITY constexpr size_type size()       const noexcept { return __size; } 
    _LIBCPP_INLINE_VISIBILITY constexpr size_type size_bytes() const noexcept { return __size * sizeof(element_type); } 
    _LIBCPP_INLINE_VISIBILITY constexpr bool empty()           const noexcept { return __size == 0; }
 
    _LIBCPP_INLINE_VISIBILITY constexpr reference operator[](size_type __idx) const noexcept 
    { 
        _LIBCPP_ASSERT(__idx < size(), "span<T>[] index out of bounds"); 
        return __data[__idx];
    }
 
    _LIBCPP_INLINE_VISIBILITY constexpr reference front() const noexcept 
    { 
        _LIBCPP_ASSERT(!empty(), "span<T>[].front() on empty span"); 
        return __data[0]; 
    }
 
    _LIBCPP_INLINE_VISIBILITY constexpr reference back() const noexcept 
    { 
        _LIBCPP_ASSERT(!empty(), "span<T>[].back() on empty span"); 
        return __data[size()-1]; 
    } 
 
 
    _LIBCPP_INLINE_VISIBILITY constexpr pointer data()                         const noexcept { return __data; } 
 
// [span.iter], span iterator support 
    _LIBCPP_INLINE_VISIBILITY constexpr iterator                 begin() const noexcept { return iterator(data()); } 
    _LIBCPP_INLINE_VISIBILITY constexpr iterator                   end() const noexcept { return iterator(data() + size()); } 
    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator        rbegin() const noexcept { return reverse_iterator(end()); } 
    _LIBCPP_INLINE_VISIBILITY constexpr reverse_iterator          rend() const noexcept { return reverse_iterator(begin()); } 
 
    inline _LIBCPP_INLINE_VISIBILITY span<const byte, dynamic_extent> __as_bytes() const noexcept;
 
    inline _LIBCPP_INLINE_VISIBILITY span<byte, dynamic_extent> __as_writable_bytes() const noexcept;
 
private: 
    pointer   __data;
    size_type __size; 
}; 
 
template<typename _Tp>
inline _LIBCPP_INLINE_VISIBILITY span<const byte, dynamic_extent> span<_Tp, dynamic_extent>::__as_bytes() const noexcept
{ return {reinterpret_cast<const byte *>(data()), size_bytes()}; }

template<typename _Tp>
inline _LIBCPP_INLINE_VISIBILITY span<byte, dynamic_extent> span<_Tp, dynamic_extent>::__as_writable_bytes() const noexcept
{ return {reinterpret_cast<byte *>(data()), size_bytes()}; }

#if !defined(_LIBCPP_HAS_NO_RANGES) 
template <class _Tp, size_t _Extent> 
inline constexpr bool ranges::enable_borrowed_range<span<_Tp, _Extent> > = true; 
 
template <class _ElementType, size_t _Extent> 
inline constexpr bool ranges::enable_view<span<_ElementType, _Extent>> = true; 
#endif // !defined(_LIBCPP_HAS_NO_RANGES) 
 
//  as_bytes & as_writable_bytes 
template <class _Tp, size_t _Extent> 
_LIBCPP_INLINE_VISIBILITY 
auto as_bytes(span<_Tp, _Extent> __s) noexcept 
-> decltype(__s.__as_bytes()) 
{ return    __s.__as_bytes(); }
 
template <class _Tp, size_t _Extent> 
_LIBCPP_INLINE_VISIBILITY 
auto as_writable_bytes(span<_Tp, _Extent> __s) noexcept 
-> enable_if_t<!is_const_v<_Tp>, decltype(__s.__as_writable_bytes())> 
{ return __s.__as_writable_bytes(); } 
 
#if !defined(_LIBCPP_HAS_NO_RANGES) 
//  Deduction guides 
template<contiguous_iterator _It, class _EndOrSize> 
    span(_It, _EndOrSize) -> span<remove_reference_t<iter_reference_t<_It>>>; 
#endif 
 
template<class _Tp, size_t _Sz> 
    span(_Tp (&)[_Sz]) -> span<_Tp, _Sz>; 

template<class _Tp, size_t _Sz> 
    span(array<_Tp, _Sz>&) -> span<_Tp, _Sz>; 
 
template<class _Tp, size_t _Sz> 
    span(const array<_Tp, _Sz>&) -> span<const _Tp, _Sz>; 
 
#if !defined(_LIBCPP_HAS_NO_RANGES) 
template<ranges::contiguous_range _Range> 
    span(_Range&&) -> span<remove_reference_t<ranges::range_reference_t<_Range>>>; 
#endif 
 
#endif // _LIBCPP_STD_VER > 17 
 
_LIBCPP_END_NAMESPACE_STD 
 
_LIBCPP_POP_MACROS 
 
#endif // _LIBCPP_SPAN