On Mon, 18 May 2026, 09:02 Tomasz Kamiński, <[email protected]> wrote:
> This is specified as const in the standard, and required to be
> const-callable
> per layout mapping requirement. This made calls to is_exhaustive on mdspan
> with such layout ill-formed.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/mdspan (layout_left_padded::is_exhaustive)
> (layout_righ_padded::is_exhaustive): Mark as const.
> * testsuite/23_containers/mdspan/layouts/mapping.cc: Test noexcept
> and
> const-invocability for is_exhaustive, is_strided, and is_unique.
> * testsuite/23_containers/mdspan/layouts/padded.cc: Test
> is_exhaustive on
> const mapping..
> * testsuite/23_containers/mdspan/layouts/stride.cc: Likewise.
> * testsuite/23_containers/mdspan/mdspan.cc: Checks
> const-invocability
> for is_exhaustive, is_strided, is_unique.
> ---
> This patch fixes both padded layouts mappings. Expands test to check
> const-invocability for all layouts.
>
> Testing on x86_64-linux. *mdspan* test already passed.
> OK for trunk. I would like to backport that to 16 (mdspan::is_exhaustive
> calls
> are ill-formed), any objections?
>
OK for trunk and 16
> libstdc++-v3/include/std/mdspan | 4 ++--
> .../testsuite/23_containers/mdspan/layouts/mapping.cc | 8 ++++++++
> .../testsuite/23_containers/mdspan/layouts/padded.cc | 9 +++++----
> .../testsuite/23_containers/mdspan/layouts/stride.cc | 2 +-
> libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc | 6 +++---
> 5 files changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/mdspan
> b/libstdc++-v3/include/std/mdspan
> index 5938bf09a94..adc1c0c6421 100644
> --- a/libstdc++-v3/include/std/mdspan
> +++ b/libstdc++-v3/include/std/mdspan
> @@ -2621,7 +2621,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { return _PaddedStorage::_M_is_always_exhaustive(); }
>
> constexpr bool
> - is_exhaustive() noexcept
> + is_exhaustive() const noexcept
> { return _M_storage._M_is_exhaustive(); }
>
> static constexpr bool
> @@ -2794,7 +2794,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { return _PaddedStorage::_M_is_always_exhaustive(); }
>
> constexpr bool
> - is_exhaustive() noexcept
> + is_exhaustive() const noexcept
> { return _M_storage._M_is_exhaustive(); }
>
> static constexpr bool
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> index 17cfac54113..28aa69eca77 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc
> @@ -44,6 +44,14 @@ template<typename Layout, typename Extents>
> static_assert(M::is_always_strided() && M::is_strided());
> if constexpr (has_static_is_exhaustive<M>)
> static_assert(M::is_always_exhaustive() && M::is_exhaustive());
> +
> + static_assert(noexcept(M::is_always_unique()));
> + static_assert(noexcept(M::is_always_strided()));
> + static_assert(noexcept(M::is_always_exhaustive()));
> + static_assert(noexcept(std::declval<const M>().is_unique()));
> + static_assert(noexcept(std::declval<const M>().is_strided()));
> + static_assert(noexcept(std::declval<const M>().is_exhaustive()));
> +
> return true;
> }
>
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/padded.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/padded.cc
> index 1b6e063d12d..30e52c10d1c 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/padded.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/padded.cc
> @@ -509,7 +509,7 @@ template<template<size_t> typename Layout>
> {
> auto exts = std::extents<int>{};
>
> - auto check = [](auto m)
> + auto check = [](const auto m)
> {
> static_assert(m.is_always_exhaustive());
> VERIFY(m.is_exhaustive());
> @@ -529,9 +529,10 @@ constexpr void
> {
> auto check = [](auto exts)
> {
> - auto m = typename PaddedLayout::mapping(exts);
> + const auto m = typename PaddedLayout::mapping(exts);
> static_assert(m.is_always_exhaustive());
> - VERIFY(m.is_exhaustive());
> + VERIFY(m.is_exhaustive());
> + VERIFY(std::as_const(m).is_exhaustive());
> };
>
> check(std::extents(4));
> @@ -554,7 +555,7 @@ template<template<size_t> typename Layout>
> auto ctrue = std::cw<true>;
> auto cfalse= std::cw<false>;
>
> - auto check = [](auto m, auto static_expected, auto runtime_expected)
> + auto check = [](const auto m, auto static_expected, auto
> runtime_expected)
> {
> static_assert(m.is_always_exhaustive() == static_expected);
> VERIFY(m.is_exhaustive() == runtime_expected);
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> index 8d2fad2936f..94deea33e1c 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/stride.cc
> @@ -278,7 +278,7 @@ template<typename Extents, typename Strides>
> constexpr void
> test_is_exhaustive(Extents extents, Strides strides, bool expected)
> {
> - std::layout_stride::mapping<Extents> m(extents, strides);
> + const std::layout_stride::mapping<Extents> m(extents, strides);
> VERIFY(m.is_exhaustive() == expected);
>
> bool always_exhaustive = extents.rank() == 0 ||
> m.required_span_size() == 0;
> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> index 62ff7201cce..a2e244df3c5 100644
> --- a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
> @@ -720,9 +720,9 @@ template<typename Layout, bool Expected>
> static_assert(noexcept(MDSpan::is_always_exhaustive()) == Expected);
> static_assert(noexcept(MDSpan::is_always_strided()) == Expected);
>
> - static_assert(noexcept(std::declval<MDSpan>().is_unique()) ==
> Expected);
> - static_assert(noexcept(std::declval<MDSpan>().is_exhaustive()) ==
> Expected);
> - static_assert(noexcept(std::declval<MDSpan>().is_strided()) ==
> Expected);
> + static_assert(noexcept(std::declval<const MDSpan>().is_unique()) ==
> Expected);
> + static_assert(noexcept(std::declval<const MDSpan>().is_exhaustive())
> == Expected);
> + static_assert(noexcept(std::declval<const MDSpan>().is_strided()) ==
> Expected);
> }
>
> int
> --
> 2.54.0
>
>
