[thirdparty/gcc.git] / libstdc++-v3 / include / std / span

// Components for manipulating non-owning sequences of objects -*- C++ -*-

// Copyright (C) 2019-2021 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file span
 *  This is a Standard C++ Library header.
 */

//
// P0122 span library
// Contributed by ThePhD
//

#ifndef _GLIBCXX_SPAN
#define _GLIBCXX_SPAN 1

#pragma GCC system_header

#if __cplusplus > 201703L

#include <array>
#include <cstddef>
#include <bits/stl_iterator.h>
#include <bits/ranges_base.h>

#if __cpp_lib_concepts
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#define __cpp_lib_span 202002L

  inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);

  template<typename _Type, size_t _Extent>
    class span;

  namespace __detail
  {
    template<typename _Tp>
      struct __is_std_span : false_type { };

    template<typename _Tp, size_t _Num>
      struct __is_std_span<span<_Tp, _Num>> : true_type { };

    template<typename _Tp>
      struct __is_std_array : false_type { };

    template<typename _Tp, size_t _Num>
      struct __is_std_array<std::array<_Tp, _Num>> : true_type { };

    template<size_t _Extent>
      class __extent_storage
      {
      public:
	constexpr
	__extent_storage(size_t) noexcept
	{ }

	static constexpr size_t
	_M_extent() noexcept
	{ return _Extent; }
      };

    template<>
      class __extent_storage<dynamic_extent>
      {
      public:
	constexpr
	__extent_storage(size_t __extent) noexcept
	: _M_extent_value(__extent)
	{ }

	constexpr size_t
	_M_extent() const noexcept
	{ return this->_M_extent_value; }

      private:
	size_t _M_extent_value;
      };
  } // namespace __detail

  template<typename _Type, size_t _Extent = dynamic_extent>
    class span
    {
      template<size_t _Offset, size_t _Count>
	static constexpr size_t
	_S_subspan_extent()
	{
	  if constexpr (_Count != dynamic_extent)
	    return _Count;
	  else if constexpr (extent != dynamic_extent)
	    return _Extent - _Offset;
	  else
	    return dynamic_extent;
	}

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 3255. span's array constructor is too strict
      template<typename _Tp, size_t _ArrayExtent>
	requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
	using __is_compatible_array = __is_array_convertible<_Type, _Tp>;

      template<typename _Ref>
	using __is_compatible_ref
	  = __is_array_convertible<_Type, remove_reference_t<_Ref>>;

    public:
      // member types
      using element_type           = _Type;
      using value_type             = remove_cv_t<_Type>;
      using size_type              = size_t;
      using difference_type        = ptrdiff_t;
      using pointer                = _Type*;
      using const_pointer          = const _Type*;
      using reference              = element_type&;
      using const_reference        = const element_type&;
      using iterator = __gnu_cxx::__normal_iterator<pointer, span>;
      using reverse_iterator       = std::reverse_iterator<iterator>;

      // member constants
      static constexpr size_t extent = _Extent;

      // constructors, copy and assignment

      constexpr
      span() noexcept
      requires ((_Extent + 1u) <= 1u)
      : _M_ptr(nullptr), _M_extent(0)
      { }

      template<contiguous_iterator _It>
	requires __is_compatible_ref<iter_reference_t<_It>>::value
	constexpr explicit(extent != dynamic_extent)
	span(_It __first, size_type __count)
	noexcept
	: _M_ptr(std::to_address(__first)), _M_extent(__count)
	{
	  if constexpr (_Extent != dynamic_extent)
	    {
	      __glibcxx_assert(__count == _Extent);
	    }
	}

      template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
	requires __is_compatible_ref<iter_reference_t<_It>>::value
	  && (!is_convertible_v<_End, size_type>)
	constexpr explicit(extent != dynamic_extent)
	span(_It __first, _End __last)
	noexcept(noexcept(__last - __first))
	: _M_ptr(std::to_address(__first)),
	  _M_extent(static_cast<size_type>(__last - __first))
	{
	  if constexpr (_Extent != dynamic_extent)
	    {
	      __glibcxx_assert((__last - __first) == _Extent);
	    }
	}

      template<size_t _ArrayExtent>
	requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
	constexpr
	span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
	: span(static_cast<pointer>(__arr), _ArrayExtent)
	{ }

      template<typename _Tp, size_t _ArrayExtent>
	requires __is_compatible_array<_Tp, _ArrayExtent>::value
	constexpr
	span(array<_Tp, _ArrayExtent>& __arr) noexcept
	: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
	{ }

      template<typename _Tp, size_t _ArrayExtent>
	requires __is_compatible_array<const _Tp, _ArrayExtent>::value
	constexpr
	span(const array<_Tp, _ArrayExtent>& __arr) noexcept
	: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
	{ }

      template<typename _Range>
	requires ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
	  && (ranges::borrowed_range<_Range> || is_const_v<element_type>)
	  && (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
	  && (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
	  && (!is_array_v<remove_cvref_t<_Range>>)
	  && __is_compatible_ref<ranges::range_reference_t<_Range>>::value
	constexpr explicit(extent != dynamic_extent)
	span(_Range&& __range)
	noexcept(noexcept(ranges::data(__range))
		  && noexcept(ranges::size(__range)))
	: span(ranges::data(__range), ranges::size(__range))
	{
	  if constexpr (extent != dynamic_extent)
	    {
	      __glibcxx_assert(ranges::size(__range) == extent);
	    }
	}

      constexpr
      span(const span&) noexcept = default;

      template<typename _OType, size_t _OExtent>
	requires (_Extent == dynamic_extent || _OExtent == dynamic_extent
		  || _Extent == _OExtent)
	  && (__is_array_convertible<_Type, _OType>::value)
	constexpr
	explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
	span(const span<_OType, _OExtent>& __s) noexcept
	: _M_extent(__s.size()), _M_ptr(__s.data())
	{
	  if constexpr (extent != dynamic_extent)
	    {
	      __glibcxx_assert(__s.size() == extent);
	    }
	}

      ~span() noexcept = default;

      constexpr span&
      operator=(const span&) noexcept = default;

      // observers

      constexpr size_type
      size() const noexcept
      { return this->_M_extent._M_extent(); }

      constexpr size_type
      size_bytes() const noexcept
      { return this->_M_extent._M_extent() * sizeof(element_type); }

      [[nodiscard]] constexpr bool
      empty() const noexcept
      { return size() == 0; }

      // element access

      constexpr reference
      front() const noexcept
      {
	__glibcxx_assert(!empty());
	return *this->_M_ptr;
      }

      constexpr reference
      back() const noexcept
      {
	__glibcxx_assert(!empty());
	return *(this->_M_ptr + (size() - 1));
      }

      constexpr reference
      operator[](size_type __idx) const noexcept
      {
	__glibcxx_assert(__idx < size());
	return *(this->_M_ptr + __idx);
      }

      constexpr pointer
      data() const noexcept
      { return this->_M_ptr; }

      // iterator support

      constexpr iterator
      begin() const noexcept
      { return iterator(this->_M_ptr); }

      constexpr iterator
      end() const noexcept
      { return iterator(this->_M_ptr + this->size()); }

      constexpr reverse_iterator
      rbegin() const noexcept
      { return reverse_iterator(this->end()); }

      constexpr reverse_iterator
      rend() const noexcept
      { return reverse_iterator(this->begin()); }

      // subviews

      template<size_t _Count>
	constexpr span<element_type, _Count>
	first() const noexcept
	{
	  if constexpr (_Extent == dynamic_extent)
	    __glibcxx_assert(_Count <= size());
	  else
	    static_assert(_Count <= extent);
	  using _Sp = span<element_type, _Count>;
	  return _Sp{ this->data(), _Count };
	}

      constexpr span<element_type, dynamic_extent>
      first(size_type __count) const noexcept
      {
	__glibcxx_assert(__count <= size());
	return { this->data(), __count };
      }

      template<size_t _Count>
	constexpr span<element_type, _Count>
	last() const noexcept
	{
	  if constexpr (_Extent == dynamic_extent)
	    __glibcxx_assert(_Count <= size());
	  else
	    static_assert(_Count <= extent);
	  using _Sp = span<element_type, _Count>;
	  return _Sp{ this->data() + (this->size() - _Count), _Count };
	}

      constexpr span<element_type, dynamic_extent>
      last(size_type __count) const noexcept
      {
	__glibcxx_assert(__count <= size());
	return { this->data() + (this->size() - __count), __count };
      }

      template<size_t _Offset, size_t _Count = dynamic_extent>
	constexpr auto
	subspan() const noexcept
	-> span<element_type, _S_subspan_extent<_Offset, _Count>()>
	{
	  if constexpr (_Extent == dynamic_extent)
	    {
	      __glibcxx_assert(_Offset <= size());
	    }
	  else
	    static_assert(_Offset <= extent);

	  using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;

	  if constexpr (_Count == dynamic_extent)
	    return _Sp{ this->data() + _Offset, this->size() - _Offset };
	  else
	    {
	      if constexpr (_Extent == dynamic_extent)
		{
		  __glibcxx_assert(_Count <= size());
		  __glibcxx_assert(_Count <= (size() - _Offset));
		}
	      else
		{
		  static_assert(_Count <= extent);
		  static_assert(_Count <= (extent - _Offset));
		}
	      return _Sp{ this->data() + _Offset, _Count };
	    }
	}

      constexpr span<element_type, dynamic_extent>
      subspan(size_type __offset, size_type __count = dynamic_extent) const
      noexcept
      {
	__glibcxx_assert(__offset <= size());
	if (__count == dynamic_extent)
	  __count = this->size() - __offset;
	else
	  {
	    __glibcxx_assert(__count <= size());
	    __glibcxx_assert(__offset + __count <= size());
	  }
	return {this->data() + __offset, __count};
      }

    private:
      pointer _M_ptr;
      [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
    };

  // deduction guides

  template<typename _Type, size_t _ArrayExtent>
    span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;

  template<typename _Type, size_t _ArrayExtent>
    span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;

  template<typename _Type, size_t _ArrayExtent>
    span(const array<_Type, _ArrayExtent>&)
      -> span<const _Type, _ArrayExtent>;

  template<contiguous_iterator _Iter, typename _End>
    span(_Iter, _End)
      -> span<remove_reference_t<iter_reference_t<_Iter>>>;

  template<typename _Range>
    span(_Range &&)
      -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;

  template<typename _Type, size_t _Extent>
    inline
    span<const byte, _Extent == dynamic_extent
	? dynamic_extent : _Extent * sizeof(_Type)>
    as_bytes(span<_Type, _Extent> __sp) noexcept
    {
      auto data = reinterpret_cast<const byte*>(__sp.data());
      auto size = __sp.size_bytes();
      constexpr auto extent = _Extent == dynamic_extent
	? dynamic_extent : _Extent * sizeof(_Type);
      return span<const byte, extent>{data, size};
    }

  template<typename _Type, size_t _Extent>
    inline
    span<byte, _Extent == dynamic_extent
       ? dynamic_extent : _Extent * sizeof(_Type)>
    as_writable_bytes(span<_Type, _Extent> __sp) noexcept
    {
      auto data = reinterpret_cast<byte*>(__sp.data());
      auto size = __sp.size_bytes();
      constexpr auto extent = _Extent == dynamic_extent
	? dynamic_extent : _Extent * sizeof(_Type);
      return span<byte, extent>{data, size};
    }

  namespace ranges
  {
    // Opt-in to borrowed_range concept
    template<typename _ElementType, size_t _Extent>
      inline constexpr bool
	enable_borrowed_range<span<_ElementType, _Extent>> = true;

    // Opt-in to view concept
    template<typename _ElementType, size_t _Extent>
      inline constexpr bool
	enable_view<span<_ElementType, _Extent>>
	  = _Extent == 0 || _Extent == dynamic_extent;
  }
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // concepts
#endif // C++20
#endif // _GLIBCXX_SPAN
Commit	Line	Data
95e9a761 JM	1	// Components for manipulating non-owning sequences of objects -- C++ --
95e9a761 JM	2
99dee823	3	// Copyright (C) 2019-2021 Free Software Foundation, Inc.
95e9a761 JM	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	#pragma GCC system_header
	38
	39	#if __cplusplus > 201703L
	40
95e9a761	41	#include <array>
0f7cd5e5	42	#include <cstddef>
95e9a761	43	#include <bits/stl_iterator.h>
160061ac	44	#include <bits/ranges_base.h>
95e9a761	45
a7922ddf	46	#if __cpp_lib_concepts
95e9a761 JM	47	namespace std _GLIBCXX_VISIBILITY(default)
	48	{
	49	_GLIBCXX_BEGIN_NAMESPACE_VERSION
	50
9b8e2dea	51	#define __cpp_lib_span 202002L
95e9a761 JM	52
	53	inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
	54
27dada7d JW	55	template<typename _Type, size_t _Extent>
	56	class span;
	57
95e9a761 JM	58	namespace __detail
95e9a761 JM	59	{
27dada7d JW	60	template<typename _Tp>
	61	struct __is_std_span : false_type { };
	62
	63	template<typename _Tp, size_t _Num>
	64	struct __is_std_span<span<_Tp, _Num>> : true_type { };
95e9a761 JM	65
95e9a761 JM	66	template<typename _Tp>
27dada7d	67	struct __is_std_array : false_type { };
95e9a761 JM	68
95e9a761 JM	69	template<typename _Tp, size_t _Num>
6db08247	70	struct __is_std_array<std::array<_Tp, _Num>> : true_type { };
95e9a761 JM	71
	72	template<size_t _Extent>
	73	class __extent_storage
	74	{
	75	public:
95e9a761 JM	76	constexpr
	77	__extent_storage(size_t) noexcept
	78	{ }
	79
	80	static constexpr size_t
	81	_M_extent() noexcept
	82	{ return _Extent; }
	83	};
	84
	85	template<>
b5c433ce	86	class __extent_storage<dynamic_extent>
95e9a761 JM	87	{
95e9a761 JM	88	public:
95e9a761 JM	89	constexpr
	90	__extent_storage(size_t __extent) noexcept
	91	: _M_extent_value(__extent)
	92	{ }
	93
	94	constexpr size_t
	95	_M_extent() const noexcept
	96	{ return this->_M_extent_value; }
	97
	98	private:
	99	size_t _M_extent_value;
	100	};
95e9a761 JM	101	} // namespace __detail
	102
	103	template<typename _Type, size_t _Extent = dynamic_extent>
b5c433ce	104	class span
95e9a761	105	{
b5c433ce JW	106	template<size_t _Offset, size_t _Count>
	107	static constexpr size_t
	108	_S_subspan_extent()
	109	{
	110	if constexpr (_Count != dynamic_extent)
	111	return _Count;
	112	else if constexpr (extent != dynamic_extent)
	113	return _Extent - _Offset;
	114	else
	115	return dynamic_extent;
	116	}
	117
582c57a1 JW	118	// _GLIBCXX_RESOLVE_LIB_DEFECTS
582c57a1 JW	119	// 3255. span's array constructor is too strict
a7922ddf	120	template<typename _Tp, size_t _ArrayExtent>
d6c9e372 JW	121	requires (_Extent == dynamic_extent \|\| _ArrayExtent == _Extent)
d6c9e372 JW	122	using __is_compatible_array = __is_array_convertible<_Type, _Tp>;
a7922ddf	123
d6c9e372 JW	124	template<typename _Ref>
	125	using __is_compatible_ref
	126	= __is_array_convertible<_Type, remove_reference_t<_Ref>>;
582c57a1	127
95e9a761 JM	128	public:
95e9a761 JM	129	// member types
95e9a761	130	using element_type = _Type;
f09f3242	131	using value_type = remove_cv_t<_Type>;
a7922ddf	132	using size_type = size_t;
f09f3242	133	using difference_type = ptrdiff_t;
95e9a761 JM	134	using pointer = _Type*;
95e9a761 JM	135	using const_pointer = const _Type*;
f09f3242 JW	136	using reference = element_type&;
	137	using const_reference = const element_type&;
	138	using iterator = __gnu_cxx::__normal_iterator<pointer, span>;
95e9a761	139	using reverse_iterator = std::reverse_iterator<iterator>;
95e9a761 JM	140
95e9a761 JM	141	// member constants
f09f3242	142	static constexpr size_t extent = _Extent;
95e9a761	143
f09f3242	144	// constructors, copy and assignment
95e9a761	145
a7922ddf JTM	146	constexpr
	147	span() noexcept
	148	requires ((_Extent + 1u) <= 1u)
0f7cd5e5	149	: _M_ptr(nullptr), _M_extent(0)
a7922ddf	150	{ }
95e9a761	151
f09f3242	152	template<contiguous_iterator _It>
d6c9e372	153	requires __is_compatible_ref<iter_reference_t<_It>>::value
9b8e2dea	154	constexpr explicit(extent != dynamic_extent)
f09f3242 JW	155	span(_It __first, size_type __count)
f09f3242 JW	156	noexcept
0f7cd5e5	157	: _M_ptr(std::to_address(__first)), _M_extent(__count)
9b8e2dea JW	158	{
	159	if constexpr (_Extent != dynamic_extent)
	160	{
	161	__glibcxx_assert(__count == _Extent);
	162	}
	163	}
f09f3242 JW	164
f09f3242 JW	165	template<contiguous_iterator _It, sized_sentinel_for<_It> _End>
d6c9e372 JW	166	requires __is_compatible_ref<iter_reference_t<_It>>::value
d6c9e372 JW	167	&& (!is_convertible_v<_End, size_type>)
9b8e2dea	168	constexpr explicit(extent != dynamic_extent)
f09f3242 JW	169	span(_It __first, _End __last)
f09f3242 JW	170	noexcept(noexcept(__last - __first))
0f7cd5e5 JW	171	: _M_ptr(std::to_address(__first)),
0f7cd5e5 JW	172	_M_extent(static_cast<size_type>(__last - __first))
f09f3242	173	{
9b8e2dea JW	174	if constexpr (_Extent != dynamic_extent)
	175	{
	176	__glibcxx_assert((__last - __first) == _Extent);
	177	}
f09f3242	178	}
95e9a761	179
66ae31eb JW	180	template<size_t _ArrayExtent>
66ae31eb JW	181	requires (_Extent == dynamic_extent \|\| _ArrayExtent == _Extent)
27dada7d	182	constexpr
66ae31eb	183	span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
27dada7d	184	: span(static_cast<pointer>(__arr), _ArrayExtent)
95e9a761 JM	185	{ }
95e9a761 JM	186
a7922ddf	187	template<typename _Tp, size_t _ArrayExtent>
d6c9e372	188	requires __is_compatible_array<_Tp, _ArrayExtent>::value
95e9a761	189	constexpr
582c57a1 JW	190	span(array<_Tp, _ArrayExtent>& __arr) noexcept
582c57a1 JW	191	: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
95e9a761 JM	192	{ }
95e9a761 JM	193
a7922ddf	194	template<typename _Tp, size_t _ArrayExtent>
d6c9e372	195	requires __is_compatible_array<const _Tp, _ArrayExtent>::value
95e9a761	196	constexpr
582c57a1 JW	197	span(const array<_Tp, _ArrayExtent>& __arr) noexcept
582c57a1 JW	198	: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
95e9a761 JM	199	{ }
95e9a761 JM	200
d6c9e372	201	template<typename _Range>
9b8e2dea	202	requires ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
15411a64	203	&& (ranges::borrowed_range<_Range> \|\| is_const_v<element_type>)
a7922ddf JTM	204	&& (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
a7922ddf JTM	205	&& (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
d6c9e372 JW	206	&& (!is_array_v<remove_cvref_t<_Range>>)
d6c9e372 JW	207	&& __is_compatible_ref<ranges::range_reference_t<_Range>>::value
9b8e2dea	208	constexpr explicit(extent != dynamic_extent)
95e9a761	209	span(_Range&& __range)
a7922ddf JTM	210	noexcept(noexcept(ranges::data(__range))
	211	&& noexcept(ranges::size(__range)))
	212	: span(ranges::data(__range), ranges::size(__range))
9b8e2dea JW	213	{
	214	if constexpr (extent != dynamic_extent)
	215	{
	216	__glibcxx_assert(ranges::size(__range) == extent);
	217	}
	218	}
95e9a761	219
f09f3242 JW	220	constexpr
f09f3242 JW	221	span(const span&) noexcept = default;
27dada7d	222
a7922ddf	223	template<typename _OType, size_t _OExtent>
9b8e2dea JW	224	requires (_Extent == dynamic_extent \|\| _OExtent == dynamic_extent
9b8e2dea JW	225	\|\| _Extent == _OExtent)
a7922ddf	226	&& (__is_array_convertible<_Type, _OType>::value)
27dada7d	227	constexpr
9b8e2dea	228	explicit(extent != dynamic_extent && _OExtent == dynamic_extent)
27dada7d JW	229	span(const span<_OType, _OExtent>& __s) noexcept
27dada7d JW	230	: _M_extent(__s.size()), _M_ptr(__s.data())
9b8e2dea JW	231	{
	232	if constexpr (extent != dynamic_extent)
	233	{
	234	__glibcxx_assert(__s.size() == extent);
	235	}
	236	}
27dada7d	237
f09f3242	238	~span() noexcept = default;
95e9a761 JM	239
	240	constexpr span&
	241	operator=(const span&) noexcept = default;
	242
b5c433ce JW	243	// observers
b5c433ce JW	244
a7922ddf	245	constexpr size_type
b5c433ce JW	246	size() const noexcept
	247	{ return this->_M_extent._M_extent(); }
	248
a7922ddf	249	constexpr size_type
b5c433ce JW	250	size_bytes() const noexcept
	251	{ return this->_M_extent._M_extent() * sizeof(element_type); }
	252
	253	[[nodiscard]] constexpr bool
	254	empty() const noexcept
	255	{ return size() == 0; }
	256
	257	// element access
95e9a761 JM	258
	259	constexpr reference
	260	front() const noexcept
b5c433ce	261	{
b5c433ce JW	262	__glibcxx_assert(!empty());
	263	return *this->_M_ptr;
	264	}
95e9a761 JM	265
	266	constexpr reference
	267	back() const noexcept
	268	{
b5c433ce JW	269	__glibcxx_assert(!empty());
b5c433ce JW	270	return *(this->_M_ptr + (size() - 1));
95e9a761 JM	271	}
	272
	273	constexpr reference
a7922ddf	274	operator[](size_type __idx) const noexcept
b5c433ce	275	{
b5c433ce JW	276	__glibcxx_assert(__idx < size());
	277	return *(this->_M_ptr + __idx);
	278	}
95e9a761 JM	279
	280	constexpr pointer
	281	data() const noexcept
	282	{ return this->_M_ptr; }
	283
b5c433ce	284	// iterator support
95e9a761	285
95e9a761 JM	286	constexpr iterator
	287	begin() const noexcept
	288	{ return iterator(this->_M_ptr); }
	289
95e9a761 JM	290	constexpr iterator
	291	end() const noexcept
	292	{ return iterator(this->_M_ptr + this->size()); }
	293
95e9a761 JM	294	constexpr reverse_iterator
	295	rbegin() const noexcept
	296	{ return reverse_iterator(this->end()); }
	297
95e9a761 JM	298	constexpr reverse_iterator
	299	rend() const noexcept
	300	{ return reverse_iterator(this->begin()); }
	301
b5c433ce JW	302	// subviews
b5c433ce JW	303
95e9a761 JM	304	template<size_t _Count>
95e9a761 JM	305	constexpr span<element_type, _Count>
b5c433ce	306	first() const noexcept
95e9a761	307	{
b5c433ce JW	308	if constexpr (_Extent == dynamic_extent)
	309	__glibcxx_assert(_Count <= size());
	310	else
	311	static_assert(_Count <= extent);
9b8e2dea JW	312	using _Sp = span<element_type, _Count>;
9b8e2dea JW	313	return _Sp{ this->data(), _Count };
95e9a761 JM	314	}
	315
	316	constexpr span<element_type, dynamic_extent>
a7922ddf	317	first(size_type __count) const noexcept
95e9a761	318	{
b5c433ce	319	__glibcxx_assert(__count <= size());
95e9a761 JM	320	return { this->data(), __count };
	321	}
	322
	323	template<size_t _Count>
	324	constexpr span<element_type, _Count>
b5c433ce	325	last() const noexcept
95e9a761	326	{
b5c433ce JW	327	if constexpr (_Extent == dynamic_extent)
	328	__glibcxx_assert(_Count <= size());
	329	else
	330	static_assert(_Count <= extent);
9b8e2dea JW	331	using _Sp = span<element_type, _Count>;
9b8e2dea JW	332	return _Sp{ this->data() + (this->size() - _Count), _Count };
95e9a761 JM	333	}
	334
	335	constexpr span<element_type, dynamic_extent>
a7922ddf	336	last(size_type __count) const noexcept
95e9a761	337	{
b5c433ce JW	338	__glibcxx_assert(__count <= size());
b5c433ce JW	339	return { this->data() + (this->size() - __count), __count };
95e9a761 JM	340	}
	341
	342	template<size_t _Offset, size_t _Count = dynamic_extent>
	343	constexpr auto
b5c433ce JW	344	subspan() const noexcept
b5c433ce JW	345	-> span<element_type, _S_subspan_extent<_Offset, _Count>()>
95e9a761	346	{
b5c433ce	347	if constexpr (_Extent == dynamic_extent)
9b8e2dea JW	348	{
	349	__glibcxx_assert(_Offset <= size());
	350	}
b5c433ce JW	351	else
	352	static_assert(_Offset <= extent);
	353
9b8e2dea JW	354	using _Sp = span<element_type, _S_subspan_extent<_Offset, _Count>()>;
9b8e2dea JW	355
b5c433ce	356	if constexpr (_Count == dynamic_extent)
9b8e2dea	357	return _Sp{ this->data() + _Offset, this->size() - _Offset };
b5c433ce	358	else
95e9a761	359	{
b5c433ce JW	360	if constexpr (_Extent == dynamic_extent)
	361	{
	362	__glibcxx_assert(_Count <= size());
	363	__glibcxx_assert(_Count <= (size() - _Offset));
	364	}
	365	else
	366	{
	367	static_assert(_Count <= extent);
	368	static_assert(_Count <= (extent - _Offset));
	369	}
9b8e2dea	370	return _Sp{ this->data() + _Offset, _Count };
95e9a761	371	}
95e9a761 JM	372	}
	373
	374	constexpr span<element_type, dynamic_extent>
a7922ddf	375	subspan(size_type __offset, size_type __count = dynamic_extent) const
b5c433ce	376	noexcept
95e9a761	377	{
b5c433ce JW	378	__glibcxx_assert(__offset <= size());
	379	if (__count == dynamic_extent)
	380	__count = this->size() - __offset;
	381	else
	382	{
	383	__glibcxx_assert(__count <= size());
	384	__glibcxx_assert(__offset + __count <= size());
	385	}
	386	return {this->data() + __offset, __count};
95e9a761 JM	387	}
95e9a761 JM	388
95e9a761 JM	389	private:
95e9a761 JM	390	pointer _M_ptr;
0f7cd5e5	391	[[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
95e9a761 JM	392	};
	393
	394	// deduction guides
389cd88c	395
95e9a761	396	template<typename _Type, size_t _ArrayExtent>
b5c433ce	397	span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;
95e9a761 JM	398
95e9a761 JM	399	template<typename _Type, size_t _ArrayExtent>
b5c433ce	400	span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;
95e9a761 JM	401
	402	template<typename _Type, size_t _ArrayExtent>
	403	span(const array<_Type, _ArrayExtent>&)
b5c433ce	404	-> span<const _Type, _ArrayExtent>;
95e9a761	405
f09f3242 JW	406	template<contiguous_iterator _Iter, typename _End>
f09f3242 JW	407	span(_Iter, _End)
389cd88c	408	-> span<remove_reference_t<iter_reference_t<_Iter>>>;
95e9a761 JM	409
	410	template<typename _Range>
	411	span(_Range &&)
a7922ddf	412	-> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
95e9a761 JM	413
95e9a761 JM	414	template<typename _Type, size_t _Extent>
b5c433ce	415	inline
95e9a761 JM	416	span<const byte, _Extent == dynamic_extent
95e9a761 JM	417	? dynamic_extent : _Extent * sizeof(_Type)>
b5c433ce	418	as_bytes(span<_Type, _Extent> __sp) noexcept
95e9a761	419	{
9b8e2dea JW	420	auto data = reinterpret_cast<const byte*>(__sp.data());
	421	auto size = __sp.size_bytes();
	422	constexpr auto extent = _Extent == dynamic_extent
	423	? dynamic_extent : _Extent * sizeof(_Type);
	424	return span<const byte, extent>{data, size};
95e9a761 JM	425	}
	426
	427	template<typename _Type, size_t _Extent>
b5c433ce	428	inline
95e9a761 JM	429	span<byte, _Extent == dynamic_extent
	430	? dynamic_extent : _Extent * sizeof(_Type)>
	431	as_writable_bytes(span<_Type, _Extent> __sp) noexcept
	432	{
9b8e2dea JW	433	auto data = reinterpret_cast<byte*>(__sp.data());
	434	auto size = __sp.size_bytes();
	435	constexpr auto extent = _Extent == dynamic_extent
	436	? dynamic_extent : _Extent * sizeof(_Type);
	437	return span<byte, extent>{data, size};
95e9a761 JM	438	}
95e9a761 JM	439
b5b2e387 JW	440	namespace ranges
b5b2e387 JW	441	{
15411a64	442	// Opt-in to borrowed_range concept
b5b2e387 JW	443	template<typename _ElementType, size_t _Extent>
b5b2e387 JW	444	inline constexpr bool
15411a64	445	enable_borrowed_range<span<_ElementType, _Extent>> = true;
3841739c JW	446
	447	// Opt-in to view concept
	448	template<typename _ElementType, size_t _Extent>
	449	inline constexpr bool
	450	enable_view<span<_ElementType, _Extent>>
	451	= _Extent == 0 \|\| _Extent == dynamic_extent;
b5b2e387	452	}
95e9a761 JM	453	_GLIBCXX_END_NAMESPACE_VERSION
95e9a761 JM	454	} // namespace std
a7922ddf	455	#endif // concepts
95e9a761 JM	456	#endif // C++20
95e9a761 JM	457	#endif // _GLIBCXX_SPAN