On 21/11/19 19:56 -0500, JeanHeyd Meneide wrote:
Thank you for the review!
- I moved the concepts back into the class and changed them to
template aliases because class local concepts aren't a thing that
works.
+ They are not inline constexpr bools because that ICE's GCC
pretty hard, as you explained to me earlier, so we use ::value in some
places rather than _v
- I named the alias __is_array_convertible, to match what the intent
is, and named the template parameters very explicitly.
+ I moved it into type_traits, but I didn't change
bits/unique_ptr.h or shared_ptr yet because I'm not confident I can do
that quickly in one go.
+ (And it should probably be a different patch anyways, but it
should be in the right place when we introduce it here.)
+ template<typename _Iter>
+ using __is_compatible_iterator = __and_<
+ bool_constant<contiguous_iterator<_Iter>>,
+ is_lvalue_reference<iter_reference_t<_Iter>>,
+ is_same<iter_value_t<_Iter>, remove_cvref_t<iter_reference_t<_Iter>>>,
+ __is_array_convertible<_Type,
remove_reference_t<iter_reference_t<_Iter>>>>;
This line is too long, we stick to < 80 columns. I'm changing it to:
template<typename _Iter, typename _Ref = iter_reference_t<_Iter>>
using __is_compatible_iterator = __and_<
bool_constant<contiguous_iterator<_Iter>>,
is_lvalue_reference<iter_reference_t<_Iter>>,
is_same<iter_value_t<_Iter>, remove_cvref_t<_Ref>>,
__is_array_convertible<_Type, remove_reference_t<_Ref>>>;
public:
// member types
using value_type = remove_cv_t<_Type>;
using element_type = _Type;
- using index_type = size_t;
+ using size_type = size_t;
The comment about size_type was still there, so I'm removing that:
- // Official wording has no size_type -- why??
- // using size_type = size_t;
@@ -505,27 +426,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
span(const array<_Type, _ArrayExtent>&)
-> span<const _Type, _ArrayExtent>;
-#ifdef _GLIBCXX_P1394
-
- template<typename _ContiguousIterator, typename _Sentinel>
+ template<contiguous_iterator _ContiguousIterator, typename _Sentinel>
span(_ContiguousIterator, _Sentinel)
- -> span<remove_reference_t<
- typename iterator_traits<_ContiguousIterator>::reference>>;
+ ->
span<remove_reference_t<ranges::range_reference_t<_ContiguousIterator>>>;
This line's too long, so I'm renaming _ContiguousIterator to _Iter.
When it's a constrained parameter I think we can use less verbose
names. There's no need to use the template parameter's name to express
the (implied, unchecked) requirements on it when we constrain it with
a concept.
Since <span> is now using concepts throughout, I'm adding this around
the whole thing:
#if __cpp_lib_concepts
This also causes two new FAILs in 23_containers/span/lwg3255.cc but
that turns out to be a bug in the test, which fails now t hat you've
fixed a bug in span. I'll fix that as well.
With those changes I'm committing it to trunk, thanks!
Tested powerpc64le-linux, committed to trunk as attached.
commit b36c7ac03aab419afa177d7a5f1b1f671391e675
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Thu Dec 5 13:35:09 2019 +0000
libstdc++: Implement P1872R0 and P1394R0 for std::span
This also fixes a bug in the implementation of LWG 3255, which causes:
FAIL: 23_containers/span/lwg3255.cc (test for excess errors)
That's because the test was wrong and verified the buggy behaviour. That
will be fixed in the following commit.
2019-12-05 JeanHeyd "ThePhD" Meneide <phdoftheho...@gmail.com>
Implement P1872R0 and P1394R0 for std::span
* include/bits/range_access.h (__adl_begin, __adl_end): Remove.
(sentinel_t, range_value_t, range_reference_t)
(range_rvalue_reference_t, __forwarding_range, disable_sized_range)
(output_range, input_range, forward_range, bidirectional_range)
(random_access_range, contiguous_range, common_range): Move here from
<ranges>, to make this the "ranges lite" internal header.
* include/std/ranges: Move basic aliases and concepts to
<bits/range_access.h>.
* include/std/span: Use concepts and ranges:: calls instead of
enable_if and friends.
* include/std/type_traits: Add __is_array_convertible trait.
diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index de074460c16..c94e965afb4 100644
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/libstdc++-v3/include/bits/range_access.h
@@ -336,19 +336,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
ssize(const _Tp (&)[_Num]) noexcept
{ return _Num; }
- // "why are these in namespace std:: and not __gnu_cxx:: ?"
- // because if we don't put them here it's impossible to
- // have implicit ADL with "using std::begin/end/size/data;".
- template <typename _Container>
- constexpr auto
- __adl_begin(_Container& __cont) noexcept(noexcept(begin(__cont)))
- { return begin(__cont); }
-
- template <typename _Container>
- constexpr auto
- __adl_data(_Container& __cont) noexcept(noexcept(data(__cont)))
- { return data(__cont); }
-
#ifdef __cpp_lib_concepts
namespace ranges
{
@@ -869,11 +856,71 @@ namespace ranges
template<typename _Tp>
concept range = __detail::__range_impl<_Tp&>;
+ template<range _Range>
+ using sentinel_t = decltype(ranges::end(std::declval<_Range&>()));
+
+ template<range _Range>
+ using iterator_t = decltype(ranges::begin(std::declval<_Range&>()));
+
+ template<range _Range>
+ using range_value_t = iter_value_t<iterator_t<_Range>>;
+
+ template<range _Range>
+ using range_reference_t = iter_reference_t<iterator_t<_Range>>;
+
+ template<range _Range>
+ using range_rvalue_reference_t
+ = iter_rvalue_reference_t<iterator_t<_Range>>;
+
+ template<range _Range>
+ using range_difference_t = iter_difference_t<iterator_t<_Range>>;
+
+ namespace __detail
+ {
+ template<typename _Tp>
+ concept __forwarding_range = range<_Tp> && __range_impl<_Tp>;
+ } // namespace __detail
+
/// [range.sized] The sized_range concept.
template<typename _Tp>
concept sized_range = range<_Tp>
&& requires(_Tp& __t) { ranges::size(__t); };
+ template<typename>
+ inline constexpr bool disable_sized_range = false;
+
+ // [range.refinements]
+ template<typename _Range, typename _Tp>
+ concept output_range
+ = range<_Range> && output_iterator<iterator_t<_Range>, _Tp>;
+
+ template<typename _Tp>
+ concept input_range = range<_Tp> && input_iterator<iterator_t<_Tp>>;
+
+ template<typename _Tp>
+ concept forward_range
+ = input_range<_Tp> && forward_iterator<iterator_t<_Tp>>;
+
+ template<typename _Tp>
+ concept bidirectional_range
+ = forward_range<_Tp> && bidirectional_iterator<iterator_t<_Tp>>;
+
+ template<typename _Tp>
+ concept random_access_range
+ = bidirectional_range<_Tp> && random_access_iterator<iterator_t<_Tp>>;
+
+ template<typename _Tp>
+ concept contiguous_range
+ = random_access_range<_Tp> && contiguous_iterator<iterator_t<_Tp>>
+ && requires(_Tp& __t)
+ {
+ { ranges::data(__t) } -> same_as<add_pointer_t<range_reference_t<_Tp>>>;
+ };
+
+ template<typename _Tp>
+ concept common_range
+ = range<_Tp> && same_as<iterator_t<_Tp>, sentinel_t<_Tp>>;
+
// [range.iter.ops] range iterator operations
template<input_or_output_iterator _It>
@@ -1008,12 +1055,6 @@ namespace ranges
}
}
- template<range _Range>
- using iterator_t = decltype(ranges::begin(std::declval<_Range&>()));
-
- template<range _Range>
- using range_difference_t = iter_difference_t<iterator_t<_Range>>;
-
template<range _Range>
constexpr range_difference_t<_Range>
distance(_Range&& __r)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 333d110b67e..e1bf6eec5d0 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -56,64 +56,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace ranges
{
// [range.range] The range concept.
- // Defined in <bits/range_iterator.h>
- // template<typename> concept range;
-
- template<range _Range>
- using sentinel_t = decltype(ranges::end(std::declval<_Range&>()));
-
- template<range _Range>
- using range_value_t = iter_value_t<iterator_t<_Range>>;
-
- template<range _Range>
- using range_reference_t = iter_reference_t<iterator_t<_Range>>;
-
- template<range _Range>
- using range_rvalue_reference_t
- = iter_rvalue_reference_t<iterator_t<_Range>>;
-
- namespace __detail
- {
- template<typename _Tp>
- concept __forwarding_range = range<_Tp> && __range_impl<_Tp>;
- } // namespace __detail
-
// [range.sized] The sized_range concept.
- // Defined in <bits/range_iterator.h>
- // template<typename> concept sized_range;
+ // Defined in <bits/range_access.h>
// [range.refinements]
-
- template<typename _Range, typename _Tp>
- concept output_range
- = range<_Range> && output_iterator<iterator_t<_Range>, _Tp>;
-
- template<typename _Tp>
- concept input_range = range<_Tp> && input_iterator<iterator_t<_Tp>>;
-
- template<typename _Tp>
- concept forward_range
- = input_range<_Tp> && forward_iterator<iterator_t<_Tp>>;
-
- template<typename _Tp>
- concept bidirectional_range
- = forward_range<_Tp> && bidirectional_iterator<iterator_t<_Tp>>;
-
- template<typename _Tp>
- concept random_access_range
- = bidirectional_range<_Tp> && random_access_iterator<iterator_t<_Tp>>;
-
- template<typename _Tp>
- concept contiguous_range
- = random_access_range<_Tp> && contiguous_iterator<iterator_t<_Tp>>
- && requires(_Tp& __t)
- {
- { ranges::data(__t) } -> same_as<add_pointer_t<range_reference_t<_Tp>>>;
- };
-
- template<typename _Tp>
- concept common_range
- = range<_Tp> && same_as<iterator_t<_Tp>, sentinel_t<_Tp>>;
+ // Defined in <bits/range_access.h>
struct view_base { };
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index fcec22a6c57..c71f8bc3f89 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -45,6 +45,7 @@
#include <bits/stl_iterator.h>
#include <bits/range_access.h>
+#if __cpp_lib_concepts
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -104,7 +105,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
private:
size_t _M_extent_value;
};
-
} // namespace __detail
template<typename _Type, size_t _Extent = dynamic_extent>
@@ -122,21 +122,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return dynamic_extent;
}
- template<typename _Tp>
- using __is_compatible = is_convertible<_Tp(*)[], _Type(*)[]>;
-
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3255. span's array constructor is too strict
- template<typename _Tp, size_t _ArrayExtent,
- typename = enable_if_t<_Extent == dynamic_extent
- || _ArrayExtent == _Extent>>
- using __is_compatible_array = __is_compatible<_Tp>;
+ template<typename _Tp, size_t _ArrayExtent>
+ using __is_compatible_array = __and_<
+ bool_constant<(_Extent == dynamic_extent || _ArrayExtent == _Extent)>,
+ __is_array_convertible<_Type, _Tp>>;
+
+ template<typename _Iter, typename _Ref = iter_reference_t<_Iter>>
+ using __is_compatible_iterator = __and_<
+ bool_constant<contiguous_iterator<_Iter>>,
+ is_lvalue_reference<iter_reference_t<_Iter>>,
+ is_same<iter_value_t<_Iter>, remove_cvref_t<_Ref>>,
+ __is_array_convertible<_Type, remove_reference_t<_Ref>>>;
+
+ template<typename _Range>
+ using __is_compatible_range
+ = __is_compatible_iterator<ranges::iterator_t<_Range>>;
public:
// member types
using value_type = remove_cv_t<_Type>;
using element_type = _Type;
- using index_type = size_t;
+ using size_type = size_t;
using reference = element_type&;
using const_reference = const element_type&;
using pointer = _Type*;
@@ -148,168 +156,80 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
using difference_type = ptrdiff_t;
- // Official wording has no size_type -- why??
- // using size_type = size_t;
// member constants
static inline constexpr size_t extent = _Extent;
// constructors
- template<bool _DefaultConstructible = (_Extent + 1u) <= 1u,
- enable_if_t<_DefaultConstructible>* = nullptr>
- constexpr
- span() noexcept : _M_extent(0), _M_ptr(nullptr)
- { }
+ constexpr
+ span() noexcept
+ requires ((_Extent + 1u) <= 1u)
+ : _M_extent(0), _M_ptr(nullptr)
+ { }
constexpr
span(const span&) noexcept = default;
- template<typename _Tp, size_t _ArrayExtent,
- typename = _Require<__is_compatible_array<_Tp, _ArrayExtent>>>
+ template<typename _Tp, size_t _ArrayExtent>
+ requires (__is_compatible_array<_Tp, _ArrayExtent>::value)
constexpr
span(_Tp (&__arr)[_ArrayExtent]) noexcept
: span(static_cast<pointer>(__arr), _ArrayExtent)
{ }
- template<typename _Tp, size_t _ArrayExtent,
- typename = _Require<__is_compatible_array<_Tp, _ArrayExtent>>>
+ template<typename _Tp, size_t _ArrayExtent>
+ requires (__is_compatible_array<_Tp, _ArrayExtent>::value)
constexpr
span(array<_Tp, _ArrayExtent>& __arr) noexcept
: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
{ }
- template<typename _Tp, size_t _ArrayExtent,
- typename = _Require<__is_compatible_array<_Tp, _ArrayExtent>>>
+ template<typename _Tp, size_t _ArrayExtent>
+ requires (__is_compatible_array<const _Tp, _ArrayExtent>::value)
constexpr
span(const array<_Tp, _ArrayExtent>& __arr) noexcept
: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
{ }
- // NOTE: when the time comes, and P1394 -
- // range constructors for std::span - ships in
- // the standard, delete the #else block and remove
- // the conditional
- // if the paper fails, delete #if block
- // and keep the crappy #else block
- // and then cry that NB comments failed C++20...
- // but maybe for C++23?
-#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&>()))>
+ template<ranges::contiguous_range _Range>
+ requires (_Extent == dynamic_extent)
+ && (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
+ && (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
+ && (!is_array_v<remove_reference_t<_Range>>)
+ && (__is_compatible_range<_Range>::value)
constexpr
span(_Range&& __range)
- noexcept(noexcept(::std::__adl_data(__range))
- && noexcept(::std::__adl_size(__range)))
- : span(::std::__adl_data(__range), ::std::__adl_size(__range))
+ noexcept(noexcept(ranges::data(__range))
+ && noexcept(ranges::size(__range)))
+ : span(ranges::data(__range), ranges::size(__range))
{ }
- template<typename _ContiguousIterator, typename _Sentinel, typename
- = _Require<__not_<is_convertible<_Sentinel, index_type>>,
- __is_compatible_iterator<_ContiguousIterator>>>
+ template<contiguous_iterator _ContiguousIterator,
+ sized_sentinel_for<_ContiguousIterator> _Sentinel>
+ requires (__is_compatible_iterator<_ContiguousIterator>::value)
+ && (!is_convertible_v<_Sentinel, size_type>)
constexpr
span(_ContiguousIterator __first, _Sentinel __last)
- : _M_extent(static_cast<index_type>(__last - __first)),
+ : _M_extent(static_cast<size_type>(__last - __first)),
_M_ptr(std::to_address(__first))
{
if (_Extent != dynamic_extent)
__glibcxx_assert((__last - __first) == _Extent);
}
- template<typename _ContiguousIterator, typename
- = _Require<__is_compatible_iterator<_ContiguousIterator>>>
+ template<contiguous_iterator _ContiguousIterator>
+ requires (__is_compatible_iterator<_ContiguousIterator>::value)
constexpr
- span(_ContiguousIterator __first, index_type __count)
+ span(_ContiguousIterator __first, size_type __count)
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,
- 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<remove_cv_t<_Container>>>,
- __not_<__detail::__is_std_array<remove_cv_t<_Container>>>,
- __not_<is_array<_Container>>,
- __is_compatible_container<_Container>>>
- constexpr
- 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, typename = _Require<
- bool_constant<_Extent == dynamic_extent>,
- __not_<__detail::__is_std_span<remove_cv_t<_Container>>>,
- __not_<__detail::__is_std_array<remove_cv_t<_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(__first)
- { __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }
-
- constexpr
- span(pointer __first, pointer __last) noexcept
- : 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(*)[]>>>
+ template<typename _OType, size_t _OExtent>
+ requires (_Extent == dynamic_extent || _Extent == _OExtent)
+ && (__is_array_convertible<_Type, _OType>::value)
constexpr
span(const span<_OType, _OExtent>& __s) noexcept
: _M_extent(__s.size()), _M_ptr(__s.data())
@@ -322,11 +242,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// observers
- constexpr index_type
+ constexpr size_type
size() const noexcept
{ return this->_M_extent._M_extent(); }
- constexpr index_type
+ constexpr size_type
size_bytes() const noexcept
{ return this->_M_extent._M_extent() * sizeof(element_type); }
@@ -353,7 +273,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
constexpr reference
- operator[](index_type __idx) const noexcept
+ operator[](size_type __idx) const noexcept
{
static_assert(extent != 0);
__glibcxx_assert(__idx < size());
@@ -412,7 +332,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
constexpr span<element_type, dynamic_extent>
- first(index_type __count) const noexcept
+ first(size_type __count) const noexcept
{
__glibcxx_assert(__count <= size());
return { this->data(), __count };
@@ -430,7 +350,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
constexpr span<element_type, dynamic_extent>
- last(index_type __count) const noexcept
+ last(size_type __count) const noexcept
{
__glibcxx_assert(__count <= size());
return { this->data() + (this->size() - __count), __count };
@@ -465,7 +385,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
constexpr span<element_type, dynamic_extent>
- subspan(index_type __offset, index_type __count = dynamic_extent) const
+ subspan(size_type __offset, size_type __count = dynamic_extent) const
noexcept
{
__glibcxx_assert(__offset <= size());
@@ -505,27 +425,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
span(const array<_Type, _ArrayExtent>&)
-> span<const _Type, _ArrayExtent>;
-#ifdef _GLIBCXX_P1394
-
- template<typename _ContiguousIterator, typename _Sentinel>
- span(_ContiguousIterator, _Sentinel)
- -> span<remove_reference_t<
- typename iterator_traits<_ContiguousIterator>::reference>>;
+ template<contiguous_iterator _Iter, typename _Sentinel>
+ span(_Iter, _Sentinel)
+ -> span<remove_reference_t<ranges::range_reference_t<_Iter>>>;
template<typename _Range>
span(_Range &&)
- -> span<remove_reference_t<typename iterator_traits<
- decltype(std::__adl_begin(::std::declval<_Range&>()))>::reference>>;
-
-#else
-
- template<typename _Container>
- span(_Container&) -> span<typename _Container::value_type>;
-
- template<typename _Container>
- span(const _Container&) -> span<const typename _Container::value_type>;
-
-#endif // P1394
+ -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;
template<typename _Type, size_t _Extent>
inline
@@ -574,6 +480,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
-
+#endif // concepts
#endif // C++20
#endif // _GLIBCXX_SPAN
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 8e787a994c3..28981d84e76 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1475,6 +1475,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
};
#pragma GCC diagnostic pop
+ // helper trait for unique_ptr<T[]>, shared_ptr<T[]>, and span<T, N>
+ template<typename _ToElementType, typename _FromElementType>
+ using __is_array_convertible
+ = is_convertible<_FromElementType(*)[], _ToElementType(*)[]>;
+
// is_nothrow_convertible for C++11
template<typename _From, typename _To>
struct __is_nothrow_convertible
