Implement <span>. Reviewed as https://reviews.llvm.org/D49338
llvm-svn: 337804
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 8a0794b722bd42d12c58295c69b659e79c73a903
diff --git a/include/CMakeLists.txt b/include/CMakeLists.txt
index e44ff3e..c60e61e 100644
--- a/include/CMakeLists.txt
+++ b/include/CMakeLists.txt
@@ -128,6 +128,7 @@
set
setjmp.h
shared_mutex
+ span
sstream
stack
stdbool.h
diff --git a/include/module.modulemap b/include/module.modulemap
index 70f82a7..e17c3a2 100644
--- a/include/module.modulemap
+++ b/include/module.modulemap
@@ -559,6 +559,10 @@
header "experimental/set"
export *
}
+ module span {
+ header "span"
+ export *
+ }
module string {
header "experimental/string"
export *
diff --git a/include/span b/include/span
new file mode 100644
index 0000000..b1a13dd
--- /dev/null
+++ b/include/span
@@ -0,0 +1,606 @@
+// -*- C++ -*-
+//===------------------------------ span ---------------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_SPAN
+#define _LIBCPP_SPAN
+
+/*
+ span synopsis
+
+namespace std {
+
+// constants
+inline constexpr ptrdiff_t dynamic_extent = -1;
+
+// [views.span], class template span
+template <class ElementType, ptrdiff_t Extent = dynamic_extent>
+ class span;
+
+// [span.comparison], span comparison operators
+template <class T, ptrdiff_t X, class U, ptrdiff_t Y>
+ constexpr bool operator==(span<T, X> l, span<U, Y> r);
+template <class T, ptrdiff_t X, class U, ptrdiff_t Y>
+ constexpr bool operator!=(span<T, X> l, span<U, Y> r);
+template <class T, ptrdiff_t X, class U, ptrdiff_t Y>
+ constexpr bool operator<(span<T, X> l, span<U, Y> r);
+template <class T, ptrdiff_t X, class U, ptrdiff_t Y>
+ constexpr bool operator<=(span<T, X> l, span<U, Y> r);
+template <class T, ptrdiff_t X, class U, ptrdiff_t Y>
+ constexpr bool operator>(span<T, X> l, span<U, Y> r);
+template <class T, ptrdiff_t X, class U, ptrdiff_t Y>
+ constexpr bool operator>=(span<T, X> l, span<U, Y> r);
+
+// [span.objectrep], views of object representation
+template <class ElementType, ptrdiff_t Extent>
+ span<const byte, ((Extent == dynamic_extent) ? dynamic_extent :
+ (static_cast<ptrdiff_t>(sizeof(ElementType)) * Extent))> as_bytes(span<ElementType, Extent> s) noexcept;
+
+template <class ElementType, ptrdiff_t Extent>
+ span< byte, ((Extent == dynamic_extent) ? dynamic_extent :
+ (static_cast<ptrdiff_t>(sizeof(ElementType)) * Extent))> as_writable_bytes(span<ElementType, Extent> s) noexcept;
+
+
+namespace std {
+template <class ElementType, ptrdiff_t Extent = dynamic_extent>
+class span {
+public:
+ // constants and types
+ using element_type = ElementType;
+ using value_type = remove_cv_t<ElementType>;
+ using index_type = ptrdiff_t;
+ using difference_type = ptrdiff_t;
+ using pointer = element_type*;
+ using reference = element_type&;
+ using iterator = implementation-defined;
+ using const_iterator = implementation-defined;
+ using reverse_iterator = std::reverse_iterator<iterator>;
+ using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+ static constexpr index_type extent = Extent;
+
+ // [span.cons], span constructors, copy, assignment, and destructor
+ constexpr span() noexcept;
+ constexpr span(pointer ptr, index_type count);
+ constexpr span(pointer firstElem, pointer lastElem);
+ 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 Container>
+ constexpr span(Container& cont);
+ template <class Container>
+ constexpr span(const Container& cont);
+ constexpr span(const span& other) noexcept = default;
+ template <class OtherElementType, ptrdiff_t OtherExtent>
+ constexpr span(const span<OtherElementType, OtherExtent>& s) noexcept;
+ ~span() noexcept = default;
+ constexpr span& operator=(const span& other) noexcept = default;
+
+ // [span.sub], span subviews
+ template <ptrdiff_t Count>
+ constexpr span<element_type, Count> first() const;
+ template <ptrdiff_t Count>
+ constexpr span<element_type, Count> last() const;
+ template <ptrdiff_t Offset, ptrdiff_t Count = dynamic_extent>
+ constexpr span<element_type, see below> subspan() const;
+
+ constexpr span<element_type, dynamic_extent> first(index_type count) const;
+ constexpr span<element_type, dynamic_extent> last(index_type count) const;
+ constexpr span<element_type, dynamic_extent> subspan(index_type offset, index_type count = dynamic_extent) const;
+
+ // [span.obs], span observers
+ constexpr index_type size() const noexcept;
+ constexpr index_type size_bytes() const noexcept;
+ constexpr bool empty() const noexcept;
+
+ // [span.elem], span element access
+ constexpr reference operator[](index_type idx) const;
+ constexpr reference operator()(index_type idx) const;
+ constexpr pointer data() const noexcept;
+
+ // [span.iterators], span iterator support
+ constexpr iterator begin() const noexcept;
+ constexpr iterator end() const noexcept;
+ constexpr const_iterator cbegin() const noexcept;
+ constexpr const_iterator cend() const noexcept;
+ constexpr reverse_iterator rbegin() const noexcept;
+ constexpr reverse_iterator rend() const noexcept;
+ constexpr const_reverse_iterator crbegin() const noexcept;
+ constexpr const_reverse_iterator crend() const noexcept;
+
+private:
+ pointer data_; // exposition only
+ index_type size_; // exposition only
+};
+
+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 Container>
+ span(Container&) -> span<typename Container::value_type>;
+
+template<class Container>
+ span(const Container&) -> span<const typename Container::value_type>;
+
+} // namespace std
+
+*/
+
+#include <cstddef> // for ptrdiff_t
+#include <iterator> // for iterators
+#include <array> // for array
+#include <type_traits> // for remove_cv, etc
+#include <cstddef> // for byte
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER > 17
+
+inline constexpr ptrdiff_t dynamic_extent = -1;
+template <typename _Tp, ptrdiff_t _Extent = dynamic_extent> class span;
+
+
+template <class _Tp>
+struct __is_span_impl : public false_type {};
+
+template <class _Tp, ptrdiff_t _Extent>
+struct __is_span_impl<span<_Tp, _Extent>> : public true_type {};
+
+template <class _Tp>
+struct __is_span : public __is_span_impl<remove_cv_t<_Tp>> {};
+
+template <class _Tp>
+struct __is_std_array_impl : public false_type {};
+
+template <class _Tp, size_t _Sz>
+struct __is_std_array_impl<array<_Tp, _Sz>> : public true_type {};
+
+template <class _Tp>
+struct __is_std_array : public __is_std_array_impl<remove_cv_t<_Tp>> {};
+
+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
+ typename enable_if<!__is_span<_Tp>::value, nullptr_t>::type,
+ // is not a specialization of array
+ typename enable_if<!__is_std_array<_Tp>::value, nullptr_t>::type,
+ // is_array_v<Container> is false,
+ typename enable_if<!is_array_v<_Tp>, nullptr_t>::type,
+ // 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(*)[]
+ typename enable_if<
+ is_convertible_v<remove_pointer_t<decltype(data(declval<_Tp &>()))>(*)[],
+ _ElementType(*)[]>,
+ nullptr_t>::type
+ >>
+ : public true_type {};
+
+
+template <typename _Tp, ptrdiff_t _Extent>
+class _LIBCPP_TEMPLATE_VIS span {
+public:
+// constants and types
+ using element_type = _Tp;
+ using value_type = remove_cv_t<_Tp>;
+ using index_type = ptrdiff_t;
+ using difference_type = ptrdiff_t;
+ using pointer = _Tp *;
+ using const_pointer = const _Tp *; // not in standard
+ using reference = _Tp &;
+ using const_reference = const _Tp &; // not in standard
+ using iterator = __wrap_iter<pointer>;
+ using const_iterator = __wrap_iter<const_pointer>;
+ using reverse_iterator = _VSTD::reverse_iterator<iterator>;
+ using const_reverse_iterator = _VSTD::reverse_iterator<const_iterator>;
+
+ static constexpr index_type extent = _Extent;
+ static_assert (_Extent >= 0, "Can't have a span with an extent < 0");
+
+// [span.cons], span constructors, copy, assignment, and destructor
+ _LIBCPP_INLINE_VISIBILITY constexpr span() noexcept : __data{nullptr}
+ { static_assert(_Extent == 0, "Can't default construct a statically sized span with size > 0"); }
+
+ constexpr span (const span&) noexcept = default;
+ constexpr span& operator=(const span&) noexcept = default;
+
+ _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __ptr, index_type __count) : __data{__ptr}
+ { (void)__count; _LIBCPP_ASSERT(_Extent == __count, "size mismatch in span's constructor (ptr, len)"); }
+ _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __f, pointer __l) : __data{__f}
+ { (void)__l; _LIBCPP_ASSERT(_Extent == distance(__f, __l), "size mismatch in span's constructor (ptr, ptr)"); }
+
+ _LIBCPP_INLINE_VISIBILITY constexpr span(element_type (&__arr)[_Extent]) noexcept : __data{__arr} {}
+ _LIBCPP_INLINE_VISIBILITY constexpr span( array<value_type, _Extent>& __arr) noexcept : __data{__arr.data()} {}
+ _LIBCPP_INLINE_VISIBILITY constexpr span(const array<value_type, _Extent>& __arr) noexcept : __data{__arr.data()} {}
+
+ template <class _Container>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr 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 (container))"); }
+
+ template <class _Container>
+ inline _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)}
+ { _LIBCPP_ASSERT(_Extent == _VSTD::size(__c), "size mismatch in span's constructor (const container)"); }
+
+ template <class _OtherElementType>
+ inline _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>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr 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 <ptrdiff_t _Count>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, _Count> first() const noexcept
+ {
+ static_assert(_Count >= 0, "Count must be >= 0 in span::first()");
+ static_assert(_Count <= _Extent, "Count out of range in span::first()");
+ return {data(), _Count};
+ }
+
+ template <ptrdiff_t _Count>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, _Count> last() const noexcept
+ {
+ static_assert(_Count >= 0, "Count must be >= 0 in span::last()");
+ static_assert(_Count <= _Extent, "Count out of range in span::last()");
+ return {data() + size() - _Count, _Count};
+ }
+
+ _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, dynamic_extent> first(index_type __count) const noexcept
+ {
+ _LIBCPP_ASSERT(__count >= 0 && __count <= size(), "Count out of range in span::first(count)");
+ return {data(), __count};
+ }
+
+ _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, dynamic_extent> last(index_type __count) const noexcept
+ {
+ _LIBCPP_ASSERT(__count >= 0 && __count <= size(), "Count out of range in span::last(count)");
+ return {data() + size() - __count, __count};
+ }
+
+ template <ptrdiff_t _Offset, ptrdiff_t _Count = dynamic_extent>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr auto subspan() const noexcept
+ -> span<element_type, _Count != dynamic_extent ? _Count : _Extent - _Offset>
+ {
+ _LIBCPP_ASSERT(_Offset >= 0 && _Offset <= size(), "Offset out of range in span::subspan()");
+ return {data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
+ }
+
+
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, dynamic_extent>
+ subspan(index_type __offset, index_type __count = dynamic_extent) const noexcept
+ {
+ _LIBCPP_ASSERT( __offset >= 0 && __offset <= size(), "Offset out of range in span::subspan(offset, count)");
+ _LIBCPP_ASSERT((__count >= 0 && __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(__offset + __count <= size(), "count + offset out of range in span::subspan(offset, count)");
+ return {data() + __offset, __count};
+ }
+
+ _LIBCPP_INLINE_VISIBILITY constexpr index_type size() const noexcept { return _Extent; }
+ _LIBCPP_INLINE_VISIBILITY constexpr index_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[](index_type __idx) const noexcept
+ {
+ _LIBCPP_ASSERT(__idx >= 0 && __idx < size(), "span<T,N>[] index out of bounds");
+ return __data[__idx];
+ }
+
+ _LIBCPP_INLINE_VISIBILITY constexpr reference operator()(index_type __idx) const noexcept
+ {
+ _LIBCPP_ASSERT(__idx >= 0 && __idx < size(), "span<T,N>() index out of bounds");
+ return __data[__idx];
+ }
+
+ _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 const_iterator cbegin() const noexcept { return const_iterator(data()); }
+ _LIBCPP_INLINE_VISIBILITY constexpr const_iterator cend() const noexcept { return const_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 constexpr const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator(cend()); }
+ _LIBCPP_INLINE_VISIBILITY constexpr const_reverse_iterator crend() const noexcept { return const_reverse_iterator(cbegin()); }
+
+ _LIBCPP_INLINE_VISIBILITY constexpr void swap(span &__other) noexcept
+ {
+ pointer __p = __data;
+ __data = __other.__data;
+ __other.__data = __p;
+ }
+
+ _LIBCPP_INLINE_VISIBILITY span<const byte, _Extent * sizeof(element_type)> __as_bytes() const noexcept
+ { return {reinterpret_cast<const byte *>(data()), size_bytes()}; }
+
+ _LIBCPP_INLINE_VISIBILITY span<byte, _Extent * sizeof(element_type)> __as_writeable_bytes() const noexcept
+ { return {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 index_type = ptrdiff_t;
+ using difference_type = ptrdiff_t;
+ using pointer = _Tp *;
+ using const_pointer = const _Tp *; // not in standard
+ using reference = _Tp &;
+ using const_reference = const _Tp &; // not in standard
+ using iterator = __wrap_iter<pointer>;
+ using const_iterator = __wrap_iter<const_pointer>;
+ using reverse_iterator = _VSTD::reverse_iterator<iterator>;
+ using const_reverse_iterator = _VSTD::reverse_iterator<const_iterator>;
+
+ static constexpr index_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;
+
+ _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __ptr, index_type __count) : __data{__ptr}, __size{__count} {}
+ _LIBCPP_INLINE_VISIBILITY constexpr span(pointer __f, pointer __l) : __data{__f}, __size{distance(__f, __l)} {}
+
+ template <size_t _Sz>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span(element_type (&__arr)[_Sz]) noexcept : __data{__arr}, __size{_Sz} {}
+
+ template <size_t _Sz>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span(array<value_type, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
+
+ template <size_t _Sz>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span(const array<value_type, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
+
+ template <class _Container>
+ inline _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{(index_type) _VSTD::size(__c)} {}
+
+ template <class _Container>
+ inline _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{(index_type) _VSTD::size(__c)} {}
+
+
+ template <class _OtherElementType, ptrdiff_t _OtherExtent>
+ inline _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 <ptrdiff_t _Count>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, _Count> first() const noexcept
+ {
+ static_assert(_Count >= 0);
+ _LIBCPP_ASSERT(_Count <= size(), "Count out of range in span::first()");
+ return {data(), _Count};
+ }
+
+ template <ptrdiff_t _Count>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, _Count> last() const noexcept
+ {
+ static_assert(_Count >= 0);
+ _LIBCPP_ASSERT(_Count <= size(), "Count out of range in span::last()");
+ return {data() + size() - _Count, _Count};
+ }
+
+ _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, dynamic_extent> first(index_type __count) const noexcept
+ {
+ _LIBCPP_ASSERT(__count >= 0 && __count <= size(), "Count out of range in span::first(count)");
+ return {data(), __count};
+ }
+
+ _LIBCPP_INLINE_VISIBILITY
+ constexpr span<element_type, dynamic_extent> last (index_type __count) const noexcept
+ {
+ _LIBCPP_ASSERT(__count >= 0 && __count <= size(), "Count out of range in span::last(count)");
+ return {data() + size() - __count, __count};
+ }
+
+ template <ptrdiff_t _Offset, ptrdiff_t _Count = dynamic_extent>
+ inline _LIBCPP_INLINE_VISIBILITY
+ constexpr span<_Tp, dynamic_extent> subspan() const noexcept
+ {
+ _LIBCPP_ASSERT(_Offset >= 0 && _Offset <= size(), "Offset out of range in span::subspan()");
+ _LIBCPP_ASSERT(_Count == dynamic_extent || _Offset + _Count <= size(), "Count out of range in span::subspan()");
+ return {data() + _Offset, _Count == dynamic_extent ? size() - _Offset : _Count};
+ }
+
+ constexpr span<element_type, dynamic_extent>
+ inline _LIBCPP_INLINE_VISIBILITY
+ subspan(index_type __offset, index_type __count = dynamic_extent) const noexcept
+ {
+ _LIBCPP_ASSERT( __offset >= 0 && __offset <= size(), "Offset out of range in span::subspan(offset, count)");
+ _LIBCPP_ASSERT((__count >= 0 && __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(__offset + __count <= size(), "Offset + count out of range in span::subspan(offset, count)");
+ return {data() + __offset, __count};
+ }
+
+ _LIBCPP_INLINE_VISIBILITY constexpr index_type size() const noexcept { return __size; }
+ _LIBCPP_INLINE_VISIBILITY constexpr index_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[](index_type __idx) const noexcept
+ {
+ _LIBCPP_ASSERT(__idx >= 0 && __idx < size(), "span<T>[] index out of bounds");
+ return __data[__idx];
+ }
+
+ _LIBCPP_INLINE_VISIBILITY constexpr reference operator()(index_type __idx) const noexcept
+ {
+ _LIBCPP_ASSERT(__idx >= 0 && __idx < size(), "span<T>() index out of bounds");
+ return __data[__idx];
+ }
+
+ _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 const_iterator cbegin() const noexcept { return const_iterator(data()); }
+ _LIBCPP_INLINE_VISIBILITY constexpr const_iterator cend() const noexcept { return const_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 constexpr const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator(cend()); }
+ _LIBCPP_INLINE_VISIBILITY constexpr const_reverse_iterator crend() const noexcept { return const_reverse_iterator(cbegin()); }
+
+ _LIBCPP_INLINE_VISIBILITY constexpr void swap(span &__other) noexcept
+ {
+ pointer __p = __data;
+ __data = __other.__data;
+ __other.__data = __p;
+
+ index_type __sz = __size;
+ __size = __other.__size;
+ __other.__size = __sz;
+ }
+
+ _LIBCPP_INLINE_VISIBILITY span<const byte, dynamic_extent> __as_bytes() const noexcept
+ { return {reinterpret_cast<const byte *>(data()), size_bytes()}; }
+
+ _LIBCPP_INLINE_VISIBILITY span<byte, dynamic_extent> __as_writeable_bytes() const noexcept
+ { return {reinterpret_cast<byte *>(data()), size_bytes()}; }
+
+private:
+ pointer __data;
+ index_type __size;
+};
+
+template <class _Tp1, ptrdiff_t _Extent1, class _Tp2, ptrdiff_t _Extent2>
+ constexpr bool
+ operator==(const span<_Tp1, _Extent1>& __lhs, const span<_Tp2, _Extent2>& __rhs)
+ { return equal(__lhs.begin(), __lhs.end(), __rhs.begin(), __rhs.end()); }
+
+template <class _Tp1, ptrdiff_t _Extent1, class _Tp2, ptrdiff_t _Extent2>
+ constexpr bool
+ operator!=(const span<_Tp1, _Extent1>& __lhs, const span<_Tp2, _Extent2>& __rhs)
+ { return !(__rhs == __lhs); }
+
+template <class _Tp1, ptrdiff_t _Extent1, class _Tp2, ptrdiff_t _Extent2>
+ constexpr bool
+ operator< (const span<_Tp1, _Extent1>& __lhs, const span<_Tp2, _Extent2>& __rhs)
+ { return lexicographical_compare (__lhs.begin(), __lhs.end(), __rhs.begin(), __rhs.end()); }
+
+template <class _Tp1, ptrdiff_t _Extent1, class _Tp2, ptrdiff_t _Extent2>
+ constexpr bool
+ operator<=(const span<_Tp1, _Extent1>& __lhs, const span<_Tp2, _Extent2>& __rhs)
+ { return !(__rhs < __lhs); }
+
+template <class _Tp1, ptrdiff_t _Extent1, class _Tp2, ptrdiff_t _Extent2>
+ constexpr bool
+ operator> (const span<_Tp1, _Extent1>& __lhs, const span<_Tp2, _Extent2>& __rhs)
+ { return __rhs < __lhs; }
+
+template <class _Tp1, ptrdiff_t _Extent1, class _Tp2, ptrdiff_t _Extent2>
+ constexpr bool
+ operator>=(const span<_Tp1, _Extent1>& __lhs, const span<_Tp2, _Extent2>& __rhs)
+ { return !(__lhs < __rhs); }
+
+// as_bytes & as_writeable_bytes
+template <class _Tp, ptrdiff_t _Extent>
+ auto as_bytes(span<_Tp, _Extent> __s) noexcept
+ -> decltype(__s.__as_bytes())
+ { return __s.__as_bytes(); }
+
+template <class _Tp, ptrdiff_t _Extent>
+ auto as_writeable_bytes(span<_Tp, _Extent> __s) noexcept
+ -> typename enable_if<!is_const_v<_Tp>, decltype(__s.__as_writeable_bytes())>::type
+ { return __s.__as_writeable_bytes(); }
+
+template <class _Tp, ptrdiff_t _Extent>
+ constexpr void swap(span<_Tp, _Extent> &__lhs, span<_Tp, _Extent> &__rhs) noexcept
+ { __lhs.swap(__rhs); }
+
+
+// Deduction guides
+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>;
+
+template<class _Container>
+ span(_Container&) -> span<typename _Container::value_type>;
+
+template<class _Container>
+ span(const _Container&) -> span<const typename _Container::value_type>;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_SPAN