span
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// Components for manipulating non-owning sequences of objects -*- C++ -*-
// Copyright (C) 2019-2025 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
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#define __glibcxx_want_span
#define __glibcxx_want_span_initializer_list
#include <bits/version.h>
#ifdef __cpp_lib_span // C++ >= 20 && concepts
#include <array>
#include <cstddef>
#include <bits/stl_iterator.h>
#include <bits/ranges_base.h>
#ifdef __cpp_lib_span_initializer_list
# include <initializer_list>
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
template<typename _Type, size_t _Extent>
class span;
namespace __detail
{
template<typename _Tp>
inline constexpr bool __is_span = false;
template<typename _Tp, size_t _Num>
inline constexpr bool __is_span<span<_Tp, _Num>> = true;
template<typename _Tp>
inline constexpr bool __is_std_array = false;
template<typename _Tp, size_t _Num>
inline constexpr bool __is_std_array<std::array<_Tp, _Num>> = true;
template<size_t _Extent>
class __extent_storage
{
public:
// Used for runtime sizes that must satisfy the precondition.
constexpr
__extent_storage([[maybe_unused]] size_t __n) noexcept
{ __glibcxx_assert(__n == _Extent); }
// Used for constant sizes that are already known to be correct.
consteval
__extent_storage(integral_constant<size_t, _Extent>) noexcept
{ }
// "I've made a huge mistake" - George Oscar Bluth II
template<size_t _Gob>
__extent_storage(integral_constant<size_t, _Gob>) = delete;
[[__gnu__::__always_inline__]]
static constexpr size_t
_M_extent() noexcept
{ return _Extent; }
};
template<>
class __extent_storage<dynamic_extent>
{
public:
[[__gnu__::__always_inline__]]
constexpr
__extent_storage(size_t __extent) noexcept
: _M_extent_value(__extent)
{ }
[[__gnu__::__always_inline__]]
constexpr size_t
_M_extent() const noexcept
{ return this->_M_extent_value; }
private:
size_t _M_extent_value;
};
template<typename _Type> struct __span_ptr { _Type* const _M_ptr; };
} // 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>>;
// Nested type so that _Type is not an associated class of iterator.
struct __iter_tag;
template<size_t _Nm>
static inline constexpr integral_constant<size_t, _Nm> __v{};
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, __iter_tag>;
using reverse_iterator = std::reverse_iterator<iterator>;
#if __cplusplus > 202002L
using const_iterator = std::const_iterator<iterator>;
using const_reverse_iterator = std::const_iterator<reverse_iterator>;
#endif
// member constants
static constexpr size_t extent = _Extent;
// constructors, copy and assignment
constexpr
span() noexcept
requires (_Extent == dynamic_extent || _Extent == 0)
: _M_ptr(nullptr), _M_extent(__v<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)
{ __glibcxx_requires_valid_range(__first, __first + __count); }
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))
{ __glibcxx_requires_valid_range(__first, __last); }
template<size_t _ArrayExtent>
requires (_Extent == dynamic_extent || _ArrayExtent == _Extent)
constexpr
span(type_identity_t<element_type> (&__arr)[_ArrayExtent]) noexcept
: _M_ptr(__arr), _M_extent(__v<_ArrayExtent>)
{ }
template<typename _Tp, size_t _ArrayExtent>
requires __is_compatible_array<_Tp, _ArrayExtent>::value
constexpr
span(array<_Tp, _ArrayExtent>& __arr) noexcept
: _M_ptr(__arr.data()), _M_extent(__v<_ArrayExtent>)
{ }
template<typename _Tp, size_t _ArrayExtent>
requires __is_compatible_array<const _Tp, _ArrayExtent>::value
constexpr
span(const array<_Tp, _ArrayExtent>& __arr) noexcept
: _M_ptr(__arr.data()), _M_extent(__v<_ArrayExtent>)
{ }
template<typename _Range>
requires (!__detail::__is_span<remove_cvref_t<_Range>>)
&& (!__detail::__is_std_array<remove_cvref_t<_Range>>)
&& (!is_array_v<remove_cvref_t<_Range>>)
&& ranges::contiguous_range<_Range> && ranges::sized_range<_Range>
&& (ranges::borrowed_range<_Range> || is_const_v<element_type>)
&& __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)))
: _M_ptr(ranges::data(__range)), _M_extent(ranges::size(__range))
{ }
#if __cpp_lib_span_initializer_list >= 202311L // >= C++26
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Winit-list-lifetime"
constexpr
explicit(extent != dynamic_extent)
span(initializer_list<value_type> __il)
requires (is_const_v<_Type>)
: _M_ptr(__il.begin()), _M_extent(__il.size())
{ }
#pragma GCC diagnostic pop
#endif
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_ptr(__s.data()), _M_extent(__s.size())
{ }
constexpr span&
operator=(const span&) noexcept = default;
// observers
[[nodiscard]]
constexpr size_type
size() const noexcept
{ return this->_M_extent._M_extent(); }
[[nodiscard]]
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
[[nodiscard]]
constexpr reference
front() const noexcept
{
__glibcxx_assert(!empty());
return *this->_M_ptr;
}
[[nodiscard]]
constexpr reference
back() const noexcept
{
__glibcxx_assert(!empty());
return *(this->_M_ptr + (size() - 1));
}
[[nodiscard]]
constexpr reference
operator[](size_type __idx) const noexcept
{
__glibcxx_assert(__idx < size());
return *(this->_M_ptr + __idx);
}
#if __cpp_lib_span >= 202311L // >= C++26
[[nodiscard]]
constexpr reference
at(size_type __idx) const
{
if (__idx >= size())
__throw_out_of_range_fmt(__N("span::at(%zu) out-of-range for span "
"of size %zu"), __idx, this->size());
return *(this->_M_ptr + __idx);
}
#endif
[[nodiscard]]
constexpr pointer
data() const noexcept
{ return this->_M_ptr; }
// iterator support
[[nodiscard]]
constexpr iterator
begin() const noexcept
{ return iterator(this->_M_ptr); }
[[nodiscard]]
constexpr iterator
end() const noexcept
{ return iterator(this->_M_ptr + this->size()); }
[[nodiscard]]
constexpr reverse_iterator
rbegin() const noexcept
{ return reverse_iterator(this->end()); }
[[nodiscard]]
constexpr reverse_iterator
rend() const noexcept
{ return reverse_iterator(this->begin()); }
#if __cplusplus > 202002L
[[nodiscard]]
constexpr const_iterator
cbegin() const noexcept
{ return begin(); }
[[nodiscard]]
constexpr const_iterator
cend() const noexcept
{ return end(); }
[[nodiscard]]
constexpr const_reverse_iterator
crbegin() const noexcept
{ return rbegin(); }
[[nodiscard]]
constexpr const_reverse_iterator
crend() const noexcept
{ return rend(); }
#endif
// subviews
template<size_t _Count>
[[nodiscard]]
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(_SizedPtr{this->data()});
}
[[nodiscard]]
constexpr span<element_type, dynamic_extent>
first(size_type __count) const noexcept
{
__glibcxx_assert(__count <= size());
return span<element_type>(this->data(), __count);
}
template<size_t _Count>
[[nodiscard]]
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(_SizedPtr{this->data() + (this->size() - _Count)});
}
[[nodiscard]]
constexpr span<element_type, dynamic_extent>
last(size_type __count) const noexcept
{
__glibcxx_assert(__count <= size());
return span<element_type>(this->data() + (this->size() - __count),
__count);
}
template<size_t _Offset, size_t _Count = dynamic_extent>
[[nodiscard]]
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(_SizedPtr{this->data() + _Offset});
}
}
[[nodiscard]]
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 span<element_type>(this->data() + __offset, __count);
}
private:
template<typename, size_t> friend class span;
// Tag type for pointer that has known extent.
using _SizedPtr = __detail::__span_ptr<_Type>;
// Private constructor with an implied extent.
[[__gnu__::__always_inline__]]
constexpr explicit
span(_SizedPtr __ptr) noexcept
requires (extent != dynamic_extent)
: _M_ptr(__ptr._M_ptr), _M_extent(__v<extent>)
{ }
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<ranges::contiguous_range _Range>
span(_Range &&)
-> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
template<typename _Type, size_t _Extent>
[[nodiscard]]
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>
requires (!is_const_v<_Type>)
inline
span<byte, _Extent == dynamic_extent
? dynamic_extent : _Extent * sizeof(_Type)>
as_writable_bytes [[nodiscard]] (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>> = true;
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // __cpp_lib_span
#endif // _GLIBCXX_SPAN
initializer_list
array
cstddef
ranges_base.h
version.h
std::to_address
constexpr _Tp * to_address(_Tp *__ptr) noexcept
Obtain address referenced by a pointer to an object.
Definition ptr_traits.h:232
std::end
_Tp * end(valarray< _Tp > &__va) noexcept
Return an iterator pointing to one past the last element of the valarray.
Definition valarray:1251
std::begin
_Tp * begin(valarray< _Tp > &__va) noexcept
Return an iterator pointing to the first element of the valarray.
Definition valarray:1229
std
ISO C++ entities toplevel namespace is std.
std::rbegin
constexpr auto rbegin(_Container &__cont) noexcept(noexcept(__cont.rbegin())) -> decltype(__cont.rbegin())
Return a reverse iterator pointing to the last element of the container.
Definition range_access.h:156
std::cend
constexpr auto cend(const _Container &__cont) noexcept(noexcept(std::end(__cont))) -> decltype(std::end(__cont))
Return an iterator pointing to one past the last element of the const container.
Definition range_access.h:144
std::empty
constexpr auto empty(const _Container &__cont) noexcept(noexcept(__cont.empty())) -> decltype(__cont.empty())
Return whether a container is empty.
Definition range_access.h:294
std::crbegin
constexpr auto crbegin(const _Container &__cont) noexcept(noexcept(std::rbegin(__cont))) -> decltype(std::rbegin(__cont))
Return a reverse iterator pointing to the last element of the const container.
Definition range_access.h:248
std::size
constexpr auto size(const _Container &__cont) noexcept(noexcept(__cont.size())) -> decltype(__cont.size())
Return the size of a container.
Definition range_access.h:274
std::data
constexpr auto data(_Container &__cont) noexcept(noexcept(__cont.data())) -> decltype(__cont.data())
Return the data pointer of a container.
Definition range_access.h:324
std::cbegin
constexpr auto cbegin(const _Container &__cont) noexcept(noexcept(std::begin(__cont))) -> decltype(std::begin(__cont))
Return an iterator pointing to the first element of the const container.
Definition range_access.h:132
std::rend
constexpr auto rend(_Container &__cont) noexcept(noexcept(__cont.rend())) -> decltype(__cont.rend())
Return a reverse iterator pointing one past the first element of the container.
Definition range_access.h:180
std::crend
constexpr auto crend(const _Container &__cont) noexcept(noexcept(std::rend(__cont))) -> decltype(std::rend(__cont))
Return a reverse iterator pointing one past the first element of the const container.
Definition range_access.h:260
std::__detail
Implementation details not part of the namespace std interface.
std::array
A standard container for storing a fixed size sequence of elements.
Definition array:103
std::extent
extent
Definition type_traits:1509
stl_iterator.h