FreeChainXenon/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Improve constraints for std::span constructors

Browse source 
This patch simplifies the constraints on the constructors from arrays by
removing the redundant checks that element_type and value_type are
convertible to element_type. The incorrect uses of __adl_data in those
constructors are removed as well (they should use std::data not
std::ranges::data, and the former doesn't use ADL).

The range/container constructors are now constrained to exclude all
specializations of std::span, not just the current instantiation. The
range constructor now also checks s subset of the contiguous_range
requirements.

All relevant constructor constraints now use the _Require helper in
order to short circuit and avoid unnecessary instantiations after the
first failed constraint.

A new constructor supports initialization from different specializations
of std::span<OtherType, OtherExtent>, as specified in the C++20 draft.

	* include/bits/range_access.h (__adl_to_address): Remove.
	* include/std/span (__is_base_derived_safe_convertible_v): Replace
	with span::__is_compatible.
	(__is_std_array_v): Replace with __is_std_array class template and
	partial specializations.
	(__is_std_array, __is_std_span): New class templates and partial
	specializations.
	(span::__is_compatible): New alias template for SFINAE constraints.
	(span::span(element_type (&)[N])): Remove redundant constraints. Do
	not use __adl_data to obtain a pointer.
	(span::span(array<value_type, N>&)): Likewise.
	(span::span(const array<value_type, N>&)): Likewise.
	[_GLIBCXX_P1394] (span::iter_reference_t, span::iterator_t)
	(span::iter_value_t, span::derived_from): New alias templates for
	SFINAE constraints, until the equivalents are supported in <concepts>
	and <iterator>.
	[_GLIBCXX_P1394] (span::__is_compatible_iterator): New alias template
	for SFINAE constraints.
	[_GLIBCXX_P1394] (span::is_compatible_range): New class template for
	SFINAE constraints.
	[_GLIBCXX_P1394] (span::span(Range&&)): Improve constraints.
	[_GLIBCXX_P1394] (span::span(ContiguousIterator, Sentinel)): Likewise.
	Use std::to_address instead of __adl_to_address.
	[_GLIBCXX_P1394] (span::span(ContiguousIterator, size_type)): Likewise.
	[!_GLIBCXX_P1394] (span::__is_compatible_container): New alias
	template for SFINAE constraints.
	[!_GLIBCXX_P1394] (span::span(Container&))
	(span::span(const Container&)): Improve constraints.
	[!_GLIBCXX_P1394] (span::span(pointer, size_type))
	(span::span(pointer, pointer)): Remove redundant cast of pointer.
	(span(const span<OType, OExtent>&)): New constructor.

From-SVN: r275513
This commit is contained in:
Jonathan Wakely 2019-09-09 12:12:38 +01:00 • committed by Jonathan Wakely
parent ca47c3987c
commit 27dada7d06
3 changed files with 156 additions and 101 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

34
libstdc++-v3/ChangeLog
View file

@ -1,3 +1,37 @@
2019-09-09 Jonathan Wakely <jwakely@redhat.com>
* include/bits/range_access.h (__adl_to_address): Remove.
* include/std/span (__is_base_derived_safe_convertible_v): Replace
with span::__is_compatible.
(__is_std_array_v): Replace with __is_std_array class template and
partial specializations.
(__is_std_array, __is_std_span): New class templates and partial
specializations.
(span::__is_compatible): New alias template for SFINAE constraints.
(span::span(element_type (&)[N])): Remove redundant constraints. Do
not use __adl_data to obtain a pointer.
(span::span(array<value_type, N>&)): Likewise.
(span::span(const array<value_type, N>&)): Likewise.
[_GLIBCXX_P1394] (span::iter_reference_t, span::iterator_t)
(span::iter_value_t, span::derived_from): New alias templates for
SFINAE constraints, until the equivalents are supported in <concepts>
and <iterator>.
[_GLIBCXX_P1394] (span::__is_compatible_iterator): New alias template
for SFINAE constraints.
[_GLIBCXX_P1394] (span::is_compatible_range): New class template for
SFINAE constraints.
[_GLIBCXX_P1394] (span::span(Range&&)): Improve constraints.
[_GLIBCXX_P1394] (span::span(ContiguousIterator, Sentinel)): Likewise.
Use std::to_address instead of __adl_to_address.
[_GLIBCXX_P1394] (span::span(ContiguousIterator, size_type)): Likewise.
[!_GLIBCXX_P1394] (span::__is_compatible_container): New alias
template for SFINAE constraints.
[!_GLIBCXX_P1394] (span::span(Container&))
(span::span(const Container&)): Improve constraints.
[!_GLIBCXX_P1394] (span::span(pointer, size_type))
(span::span(pointer, pointer)): Remove redundant cast of pointer.
(span(const span<OType, OExtent>&)): New constructor.
2019-09-06 Jonathan Wakely <jwakely@redhat.com>
* include/bits/range_access.h (ssize): Define for C++20.

7
libstdc++-v3/include/bits/range_access.h
View file

@ -396,13 +396,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr auto
__adl_empty(_Container& __cont) noexcept(noexcept(empty(__cont)))
{ return empty(__cont); }
#if defined(_GLIBCXX_P1394) && _GLIBCXX_P1394
template <typename _Container>
constexpr auto
__adl_to_address(_Container& __cont) noexcept(noexcept(to_address(__cont)))
{ return to_address(__cont); }
#endif // P1394 and new contiguous_iterator requirements [iterator.concept.contiguous]
#endif // C++20
_GLIBCXX_END_NAMESPACE_VERSION

216
libstdc++-v3/include/std/span
View file

@ -53,24 +53,27 @@ _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 _Element, typename _ToElement>
static constexpr inline bool __is_base_derived_safe_convertible_v
= is_convertible_v<_Element (*)[], _ToElement (*)[]>;
template<typename _Tp>
inline constexpr bool __is_std_array_v = false;
struct __is_std_span : false_type { };
template<typename _Tp, size_t _Num>
inline constexpr bool
__is_std_array_v<_GLIBCXX_STD_C::array<_Tp, _Num>> = true;
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<_GLIBCXX_STD_C::array<_Tp, _Num>> : true_type { };
#ifdef _GLIBCXX_DEBUG
template<typename _Tp, size_t _Num>
inline constexpr bool
__is_std_array_v<std::__debug::array<_Tp, _Num>> = true;
#endif // debug/array
struct __is_std_array<__debug::array<_Tp, _Num>> : true_type { };
#endif
template<size_t _Extent>
class __extent_storage
@ -119,6 +122,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return dynamic_extent;
}
template<typename _Tp>
using __is_compatible = is_convertible<_Tp(*)[], _Type(*)[]>;
public:
// member types
using value_type = remove_cv_t<_Type>;
@ -154,41 +160,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
span(const span&) noexcept = default;
template<size_t _ArrayExtent,
enable_if_t<
(_Extent == dynamic_extent || _ArrayExtent == _Extent)
&& __detail::__is_base_derived_safe_convertible_v<
remove_pointer_t<decltype(::std::__adl_data(
::std::declval<element_type (&)[_ArrayExtent]>()))>,
element_type>>* = nullptr>
constexpr span(element_type (&__arr)[_ArrayExtent])
noexcept(noexcept(::std::__adl_data(__arr)))
: span(::std::__adl_data(__arr), _ArrayExtent)
enable_if_t<_Extent == dynamic_extent || _ArrayExtent == _Extent>*
= nullptr>
constexpr
span(element_type (&__arr)[_ArrayExtent]) noexcept
: span(static_cast<pointer>(__arr), _ArrayExtent)
{ }
template<size_t _ArrayExtent,
enable_if_t<
(_Extent == dynamic_extent || _ArrayExtent == _Extent)
&& __detail::__is_base_derived_safe_convertible_v<
remove_pointer_t<decltype(::std::__adl_data(
::std::declval<const array<value_type, _ArrayExtent>&>()))>,
element_type>>* = nullptr>
enable_if_t<_Extent == dynamic_extent || _ArrayExtent == _Extent>*
= nullptr>
constexpr
span(array<value_type, _ArrayExtent>& __arr)
noexcept(noexcept(::std::__adl_data(__arr)))
: span(::std::__adl_data(__arr), _ArrayExtent)
span(array<value_type, _ArrayExtent>& __arr) noexcept
: span(__arr.data(), _ArrayExtent)
{ }
template<size_t _ArrayExtent,
enable_if_t<
(_Extent == dynamic_extent || _ArrayExtent == _Extent)
&& __detail::__is_base_derived_safe_convertible_v<
remove_pointer_t<decltype(::std::__adl_data(
::std::declval<const array<value_type, _ArrayExtent>&>()))>,
element_type>>* = nullptr>
enable_if_t<_Extent == dynamic_extent || _ArrayExtent == _Extent>*
= nullptr>
constexpr
span(const array<value_type, _ArrayExtent>& __arr)
noexcept(noexcept(::std::__adl_data(__arr)))
: span(::std::__adl_data(__arr), _ArrayExtent)
span(const array<value_type, _ArrayExtent>& __arr) noexcept
: span(__arr.data(), _ArrayExtent)
{ }
// NOTE: when the time comes, and P1394 -
@ -199,18 +191,49 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// and keep the crappy #else block
// and then cry that NB comments failed C++20...
// but maybe for C++23?
#if defined(_GLIBCXX_P1394) && _GLIBCXX_P1394
template<typename _Range,
enable_if_t<
(_Extent == dynamic_extent)
&& !is_same_v<remove_cvref_t<_Range>, span>
&& !__detail::__is_std_array_v<remove_cvref_t<_Range>>
&& !is_array_v<remove_cvref_t<_Range>>
&& __detail::__is_base_derived_safe_convertible_v<
remove_pointer_t<decltype(
::std::__adl_data(::std::declval<_Range&>())
+ ::std::__adl_size(::std::declval<_Range&>()))>,
element_type>>* = nullptr>
#ifdef _GLIBCXX_P1394
private:
// FIXME: use std::iter_reference_t
template<typename _Iterator>
using iter_reference_t = decltype(*std::declval<_Iterator&>());
// FIXME: use std::ranges::iterator_t
// N.B. constraint is needed to prevent a cycle when __adl_begin finds
// begin(span) which does overload resolution on span(Range&&).
template<typename _Rng,
typename _Rng2 = remove_cvref_t<_Rng>,
typename = enable_if_t<!__detail::__is_std_span<_Rng2>::value>>
using iterator_t = decltype(std::__adl_begin(std::declval<_Rng&>()));
// FIXME: use std::iter_value_t
template<typename _Iter>
using iter_value_t = typename iterator_traits<_Iter>::value_type;
// FIXME: use std::derived_from concept
template<typename _Derived, typename _Base>
using derived_from
= __and_<is_base_of<_Base, _Derived>,
is_convertible<const volatile _Derived*, const volatile _Base*>>;
// FIXME: require contiguous_iterator<_Iterator>
template<typename _Iter,
typename _Ref = iter_reference_t<_Iter>,
typename _Traits = iterator_traits<_Iter>,
typename _Tag = typename _Traits::iterator_category>
using __is_compatible_iterator
= __and_<derived_from<_Tag, random_access_iterator_tag>,
is_lvalue_reference<_Ref>,
is_same<iter_value_t<_Iter>, remove_cvref_t<_Ref>>,
__is_compatible<remove_reference_t<_Ref>>>;
template<typename _Range>
using __is_compatible_range
= __is_compatible_iterator<iterator_t<_Range>>;
public:
template<typename _Range, typename = _Require<
bool_constant<_Extent == dynamic_extent>,
__not_<__detail::__is_std_span<remove_cvref_t<_Range>>>,
__not_<__detail::__is_std_array<remove_cvref_t<_Range>>>,
__not_<is_array<remove_reference_t<_Range>>>,
__is_compatible_range<_Range>>,
typename = decltype(std::__adl_data(std::declval<_Range&>()))>
constexpr
span(_Range&& __range)
noexcept(noexcept(::std::__adl_data(__range))
@ -218,72 +241,77 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: span(::std::__adl_data(__range), ::std::__adl_size(__range))
{ }
template<typename _ContiguousIterator, typename _Sentinel,
enable_if_t<!is_convertible_v<_Sentinel, index_type>
&& __detail::__is_base_derived_safe_convertible_v<
remove_reference_t<typename
iterator_traits<_ContiguousIterator>::reference>,
element_type>>* = nullptr>
template<typename _ContiguousIterator, typename _Sentinel, typename
= _Require<__not_<is_convertible<_Sentinel, index_type>>,
__is_compatible_iterator<_ContiguousIterator>>>
constexpr
span(_ContiguousIterator __first, _Sentinel __last)
: span(::std::move(__first), static_cast<index_type>(__last - __first))
{ }
: _M_extent(static_cast<index_type>(__last - __first)),
_M_ptr(std::to_address(__first))
{
if (_Extent != dynamic_extent)
__glibcxx_assert((__last - __first) == _Extent);
}
template<typename _ContiguousIterator>
template<typename _ContiguousIterator, typename
= _Require<__is_compatible_iterator<_ContiguousIterator>>>
constexpr
span(_ContiguousIterator __first, index_type __count)
noexcept(noexcept(::std::__adl_to_address(__first)))
: _M_extent(__count), _M_ptr(::std::__adl_to_address(__first))
noexcept(noexcept(std::to_address(__first)))
: _M_extent(__count), _M_ptr(std::to_address(__first))
{ __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }
#else
private:
template<typename _Container,
enable_if_t<
(_Extent == dynamic_extent)
&& !is_same_v<remove_cvref_t<_Container>, span>
&& !__detail::__is_std_array_v<remove_cvref_t<_Container>>
&& !is_array_v<remove_cvref_t<_Container>>
&& __detail::__is_base_derived_safe_convertible_v<
remove_pointer_t<decltype(
::std::__adl_data(::std::declval<_Container&>())
+ ::std::__adl_size(::std::declval<_Container&>()))>,
element_type>>* = nullptr>
typename _DataT = decltype(std::data(std::declval<_Container&>())),
typename _SizeT = decltype(std::size(std::declval<_Container&>()))>
using __is_compatible_container
= __is_compatible<remove_pointer_t<_DataT>>;
public:
template<typename _Container, typename = _Require<
bool_constant<_Extent == dynamic_extent>,
__not_<__detail::__is_std_span<_Container>>,
__not_<__detail::__is_std_array<_Container>>,
__not_<is_array<_Container>>,
__is_compatible_container<_Container>>>
constexpr
span(_Container& __range)
noexcept(noexcept(::std::__adl_data(__range))
&& noexcept(::std::__adl_size(__range)))
: span(::std::__adl_data(__range), ::std::__adl_size(__range))
span(_Container& __cont)
noexcept(noexcept(std::data(__cont)) && noexcept(std::size(__cont)))
: _M_extent(std::size(__cont)), _M_ptr(std::data(__cont))
{ }
template<typename _Container,
enable_if_t<
(_Extent == dynamic_extent)
&& !is_same_v<remove_cvref_t<_Container>, span>
&& !__detail::__is_std_array_v<remove_cvref_t<_Container>>
&& !is_array_v<remove_cvref_t<_Container>>
&& __detail::__is_base_derived_safe_convertible_v<
remove_pointer_t<decltype(
::std::__adl_data(::std::declval<_Container&>())
+ ::std::__adl_size(::std::declval<_Container&>()))>,
element_type>>* = nullptr>
constexpr span(const _Container& __range)
noexcept(noexcept(::std::__adl_data(__range))
&& noexcept(::std::__adl_size(__range)))
: span(::std::__adl_data(__range), ::std::__adl_size(__range))
template<typename _Container, typename = _Require<
bool_constant<_Extent == dynamic_extent>,
__not_<__detail::__is_std_span<_Container>>,
__not_<__detail::__is_std_array<_Container>>,
__not_<is_array<_Container>>,
__is_compatible_container<const _Container>>>
constexpr
span(const _Container& __cont)
noexcept(noexcept(std::data(__cont)) && noexcept(std::size(__cont)))
: _M_extent(std::size(__cont)), _M_ptr(std::data(__cont))
{ }
constexpr
span(pointer __first, index_type __count) noexcept
: _M_extent(__count), _M_ptr(static_cast<pointer>(__first))
: _M_extent(__count), _M_ptr(__first)
{ __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }
constexpr
span(pointer __first, pointer __last) noexcept
: span(::std::move(__first), static_cast<index_type>(__last - __first))
: span(__first, static_cast<index_type>(__last - __first))
{ }
#endif // P1394
template<typename _OType, size_t _OExtent, typename = _Require<
__bool_constant<_Extent == dynamic_extent || _Extent == _OExtent>,
is_convertible<_OType(*)[], _Type(*)[]>>>
constexpr
span(const span<_OType, _OExtent>& __s) noexcept
: _M_extent(__s.size()), _M_ptr(__s.data())
{ }
// assignment
constexpr span&
@ -474,7 +502,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
span(const array<_Type, _ArrayExtent>&)
-> span<const _Type, _ArrayExtent>;
#if defined(_GLIBCXX_P1394) && _GLIBCXX_P1394
#ifdef _GLIBCXX_P1394
template<typename _ContiguousIterator, typename _Sentinel>
span(_ContiguousIterator, _Sentinel)