And some further simplifications and improvements to the constructor
constraints for std::span.
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.
Tested x86_64-linux, committed to trunk.
commit cf9248752de63a49bde062eb00681ae1c6d1a546
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Mon Sep 9 10:56:54 2019 +0100
Improve constraints for std::span constructors
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.
diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index c5744145590..bc137d7396e 100644
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/libstdc++-v3/include/bits/range_access.h
@@ -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
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index 95d778b104b..1a0d61c1947 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -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)
