Skip to content

[libc++] P3029R1: Better mdspan's CTAD - std::extents #89015

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Jun 25, 2024
Merged

[libc++] P3029R1: Better mdspan's CTAD - std::extents #89015

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
9 changes: 8 additions & 1 deletion libcxx/include/__mdspan/extents.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -455,8 +455,15 @@ template <class _IndexType, size_t _Rank>
using dextents = typename __mdspan_detail::__make_dextents<_IndexType, _Rank>::type;

// Deduction guide for extents
# if _LIBCPP_STD_VER >= 26
template <class... _IndexTypes>
extents(_IndexTypes...) -> extents<size_t, size_t(((void)sizeof(_IndexTypes), dynamic_extent))...>;
requires(is_convertible_v<_IndexTypes, size_t> && ...)
Copy link
Member Author

@xiaoyang-sde xiaoyang-sde Apr 17, 2024 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

[mdspan.extents.cons]/12

Copy link
Contributor

@frederick-vs-ja frederick-vs-ja Apr 17, 2024 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Uh, this line isn't really changed by P3029R1. Looks like that it's already needed in C++23 but previously missing.

Would it be better to make only __maybe_static_ext<_IndexTypes>... and size_t(((void)sizeof(_IndexTypes), dynamic_extent))... (or the deduced extents<...>) guarded by #if? @mordante

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yes, this line is a drive-by change that applies to both C++23 and C++26.

explicit extents(_IndexTypes...) -> extents<size_t, __maybe_static_ext<_IndexTypes>...>;
# else
template <class... _IndexTypes>
requires(is_convertible_v<_IndexTypes, size_t> && ...)
explicit extents(_IndexTypes...) -> extents<size_t, size_t(((void)sizeof(_IndexTypes), dynamic_extent))...>;
# endif

namespace __mdspan_detail {

Expand Down
13 changes: 12 additions & 1 deletion libcxx/test/std/containers/views/mdspan/extents/ctad.pass.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -13,10 +13,12 @@
// explicit extents(Integrals...) -> see below;
// Constraints: (is_convertible_v<Integrals, size_t> && ...) is true.
//
// Remarks: The deduced type is dextents<size_t, sizeof...(Integrals)>.
// Remarks: The deduced type is dextents<size_t, sizeof...(Integrals)>. // until C++26
// Remarks: The deduced type is extents<size_t, maybe-static-ext<Integrals>...>. // since C++26

#include <mdspan>
#include <cassert>
#include <type_traits>

#include "../ConvertibleToIntegral.h"
#include "test_macros.h"
Expand All @@ -43,6 +45,15 @@ constexpr bool test() {
test(std::extents(1, 2u, 3, 4, 5, 6, 7, 8, 9),
std::extents<std::size_t, D, D, D, D, D, D, D, D, D>(1, 2u, 3, 4, 5, 6, 7, 8, 9));
test(std::extents(NoDefaultCtorIndex{1}, NoDefaultCtorIndex{2}), std::extents<std::size_t, D, D>(1, 2));

#if _LIBCPP_STD_VER >= 26
// P3029R1: deduction from `integral_constant`
test(std::extents(std::integral_constant<size_t, 5>{}), std::extents<std::size_t, 5>());
test(std::extents(std::integral_constant<size_t, 5>{}, 6), std::extents<std::size_t, 5, std::dynamic_extent>(6));
test(std::extents(std::integral_constant<size_t, 5>{}, 6, std::integral_constant<size_t, 7>{}),
std::extents<std::size_t, 5, std::dynamic_extent, 7>(6));
#endif

return true;
}

Expand Down
Loading