On Mon, May 26, 2025 at 4:22 PM Luc Grosheintz <luc.groshei...@gmail.com>
wrote:
> [mdspan.layout.left.cons] of N4950 states that this ctor is not
> noexcept. Since, all other ctors of layout_left, layout_right or
> layout_stride are noexcept, the choice was made, based on
> [res.on.exception.handling], to make this ctor noexcept.
>
> Two other major implementations of the STL make the same choice.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/mdspan: Strengthen the exception
> guarantees of layout_left::mapping(layout_stride::mapping).
> * testsuite/23_containers/mdspan/layouts/ctors.cc:
> Simplify tests to reflect the change.
>
> Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
> ---
>
LGTM.
> libstdc++-v3/include/std/mdspan | 6 +++-
> .../23_containers/mdspan/layouts/ctors.cc | 33 ++++++++-----------
> 2 files changed, 19 insertions(+), 20 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/mdspan
> b/libstdc++-v3/include/std/mdspan
> index 33ad5070a37..2a7f0452cd7 100644
> --- a/libstdc++-v3/include/std/mdspan
> +++ b/libstdc++-v3/include/std/mdspan
> @@ -561,10 +561,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> : mapping(__other.extents(), __mdspan::__internal_ctor{})
> { }
>
> + // [mdspan.layout.left.cons] of N4950 states that this ctor is not
> + // noexcept. Since, all other ctors of layout_left, layout_right or
> + // layout_stride are noexcept, the choice was made, based on
> + // [res.on.exception.handling], to make this ctor noexcept.
> template<typename _OExtents>
> requires (is_constructible_v<extents_type, _OExtents>)
> constexpr explicit(extents_type::rank() > 0)
> - mapping(const layout_stride::mapping<_OExtents>& __other)
> + mapping(const layout_stride::mapping<_OExtents>& __other) noexcept
> : mapping(__other.extents(), __mdspan::__internal_ctor{})
> { __glibcxx_assert(*this == __other); }
>
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/ctors.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/ctors.cc
> index 2507eeaf7a1..6f813e9877b 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/ctors.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/ctors.cc
> @@ -362,30 +362,24 @@ namespace from_stride
>
> template<typename Layout, typename Extents, typename OExtents>
> constexpr void
> - verify_convertible(OExtents oexts)
> + verify_nothrow_convertible(OExtents oexts)
> {
> using Mapping = typename Layout::mapping<Extents>;
> using OMapping = std::layout_stride::mapping<OExtents>;
>
> constexpr auto other = OMapping(oexts,
> strides(Mapping(Extents(oexts))));
> - if constexpr (std::is_same_v<Layout, std::layout_right>)
> - ::verify_nothrow_convertible<Mapping>(other);
> - else
> - ::verify_convertible<Mapping>(other);
> + ::verify_nothrow_convertible<Mapping>(other);
> }
>
> template<typename Layout, typename Extents, typename OExtents>
> constexpr void
> - verify_constructible(OExtents oexts)
> + verify_nothrow_constructible(OExtents oexts)
> {
> using Mapping = typename Layout::mapping<Extents>;
> using OMapping = std::layout_stride::mapping<OExtents>;
>
> constexpr auto other = OMapping(oexts,
> strides(Mapping(Extents(oexts))));
> - if constexpr (std::is_same_v<Layout, std::layout_right>)
> - ::verify_nothrow_constructible<Mapping>(other);
> - else
> - ::verify_constructible<Mapping>(other);
> + ::verify_nothrow_constructible<Mapping>(other);
> }
>
> template<typename Layout>
> @@ -404,31 +398,32 @@ namespace from_stride
> typename Layout::mapping<std::extents<int, 2>>,
> std::layout_stride::mapping<std::extents<int, 1>>>();
>
> - verify_convertible<Layout, std::extents<int>>(std::extents<int>{});
> + verify_nothrow_convertible<Layout, std::extents<int>>(
> + std::extents<int>{});
>
> - verify_convertible<Layout, std::extents<unsigned int>>(
> + verify_nothrow_convertible<Layout, std::extents<unsigned int>>(
> std::extents<int>{});
>
> // Rank == 0 doesn't check IndexType for convertibility.
> - verify_convertible<Layout, std::extents<int>>(
> + verify_nothrow_convertible<Layout, std::extents<int>>(
> std::extents<unsigned int>{});
>
> - verify_constructible<Layout, std::extents<int, 3>>(
> + verify_nothrow_constructible<Layout, std::extents<int, 3>>(
> std::extents<int, 3>{});
>
> - verify_constructible<Layout, std::extents<unsigned int, 3>>(
> + verify_nothrow_constructible<Layout, std::extents<unsigned int, 3>>(
> std::extents<int, 3>{});
>
> - verify_constructible<Layout, std::extents<int, 3>>(
> + verify_nothrow_constructible<Layout, std::extents<int, 3>>(
> std::extents<unsigned int, 3>{});
>
> - verify_constructible<Layout, std::extents<int, 3, 5>>(
> + verify_nothrow_constructible<Layout, std::extents<int, 3, 5>>(
> std::extents<int, 3, 5>{});
>
> - verify_constructible<Layout, std::extents<unsigned int, 3, 5>>(
> + verify_nothrow_constructible<Layout, std::extents<unsigned int, 3,
> 5>>(
> std::extents<int, 3, 5>{});
>
> - verify_constructible<Layout, std::extents<int, 3, 5>>(
> + verify_nothrow_constructible<Layout, std::extents<int, 3, 5>>(
> std::extents<unsigned int, 3, 5>{});
> return true;
> }
> --
> 2.49.0
>
>
