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llvm/libcxx/include/span
Michael Schellenberger Costa ab9f11168f [libcxx][span] Implement solution to LWG-3255 
This implements the relaxed requirements on the std::array constructors of span,
where the type only needs to be convertible to the element type of the span.

Note that the previous tests were not sufficient, as the const array<T, n> constructor
was only tested for compile time and the array<T, N> only during runtime.

Restructure the tests so that we can test conversions as well as both constructors.

Differential Revision: https://reviews.llvm.org/D75706
2020-05-14 10:50:44 -04:00

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// -*- 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;
// [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;
namespace std {
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;
constexpr explicit(Extent != dynamic_extent) span(pointer ptr, size_type count);
constexpr explicit(Extent != dynamic_extent) 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 explicit(Extent != dynamic_extent) span(Container& cont);
template <class Container>
constexpr explicit(Extent != dynamic_extent) span(const Container& cont);
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 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 <__config>
#include <array> // for array
#include <cstddef> // for byte
#include <iterator> // for iterators
#include <type_traits> // for remove_cv, etc
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif
_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_span_impl : public false_type {};
template <class _Tp, size_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, 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 &;
using iterator = __wrap_iter<pointer>;
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;
_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)"); }
_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()} {}
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)");
}
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 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 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 &;
using iterator = __wrap_iter<pointer>;
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;
_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))} {}
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} {}
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)} {}
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()); }
_LIBCPP_INLINE_VISIBILITY constexpr void swap(span &__other) noexcept
{
pointer __p = __data;
__data = __other.__data;
__other.__data = __p;
size_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_writable_bytes() const noexcept
{ return {reinterpret_cast<byte *>(data()), size_bytes()}; }
private:
pointer __data;
size_type __size;
};
// 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(); }
template <class _Tp, size_t _Extent>
_LIBCPP_INLINE_VISIBILITY
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>;
#endif // _LIBCPP_STD_VER > 17
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP_SPAN
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