On Mon, 16 Feb 2026 at 12:36, Tomasz Kamiński <[email protected]> wrote:
>
> This patch implements LWG 4491, addressing C++26 NB comments.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/mdspan (std::submdspan_extents): Rename to...
> (std::subextents): Rename of submdspan_extents.
> (std::submdspan_canonicalize_slices): Rename to...
> (std::canonical_slices):
> *
> testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc:
> Move to...
> * testsuite/23_containers/mdspan/submdspan/canonical_slices.cc:
> ...here.
> Updated calls to submdspan_canonicalize_slices.
> *
> testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc:
> Move to...
> * testsuite/23_containers/mdspan/submdspan/canonical_slices_neg.cc:
> ...here.
> Updated calls to submdspan_canonicalize_slices.
> * testsuite/23_containers/mdspan/submdspan/submdspan_extents.cc: Move
> to...
> * testsuite/23_containers/mdspan/submdspan/subextents.cc: ...here.
> Qualified and renamed calls to submdspan_extents.
> * testsuite/23_containers/mdspan/submdspan/submdspan_extents_neg.cc:
> Move to...
> * testsuite/23_containers/mdspan/submdspan/subextents_neg.cc: ...here.
> Qualified and renamed calls to submdspan_extents.
> ---
> I haven't added _GLIBCXX_RESOLVE_ISSUE comments, as it is trivial
> to check if the functions were renamed.
Also this isn't a defect in a published standard, the renaming is just
changing something that was in a C++2c draft.
I think it's more important/useful to use RESOLVE_LIB_DEFECTS comments
when what we implement is different from the published standard. But
when it's just a difference between one draft and another draft, we
can just ship the change without a comment to record it.
OK for trunk
>
> Testing on x86_64-linux. All *mdspan* test already passed in all
> supported standards.
>
> libstdc++-v3/include/std/mdspan | 8 +++----
> ...nicalize_slices.cc => canonical_slices.cc} | 24 +++++++++----------
> ..._slices_neg.cc => canonical_slices_neg.cc} | 16 ++++++-------
> .../{submdspan_extents.cc => subextents.cc} | 18 +++++++-------
> ...dspan_extents_neg.cc => subextents_neg.cc} | 6 ++---
> 5 files changed, 36 insertions(+), 36 deletions(-)
> rename
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/{submdspan_canonicalize_slices.cc
> => canonical_slices.cc} (87%)
> rename
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/{submdspan_canonicalize_slices_neg.cc
> => canonical_slices_neg.cc} (95%)
> rename
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/{submdspan_extents.cc
> => subextents.cc} (88%)
> rename
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/{submdspan_extents_neg.cc
> => subextents_neg.cc} (85%)
>
> diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
> index cedf597d3c2..0c89f8e7155 100644
> --- a/libstdc++-v3/include/std/mdspan
> +++ b/libstdc++-v3/include/std/mdspan
> @@ -3348,8 +3348,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _IndexType, size_t... _Extents, typename... _RawSlices>
> requires (sizeof...(_RawSlices) == sizeof...(_Extents))
> constexpr auto
> - submdspan_extents(const extents<_IndexType, _Extents...>& __exts,
> - _RawSlices... __raw_slices)
> + subextents(const extents<_IndexType, _Extents...>& __exts,
> + _RawSlices... __raw_slices)
> {
> auto __impl = [&__exts](auto... __slices)
> {
> @@ -3362,8 +3362,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _IndexType, size_t... _Extents, typename... _RawSlices>
> requires (sizeof...(_Extents) == sizeof...(_RawSlices))
> constexpr auto
> - submdspan_canonicalize_slices(const extents<_IndexType, _Extents...>&
> __exts,
> - _RawSlices... __raw_slices)
> + canonical_slices(const extents<_IndexType, _Extents...>& __exts,
> + _RawSlices... __raw_slices)
> {
> auto __impl = [&__exts](auto... __slices)
> {
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/canonical_slices.cc
> similarity index 87%
> rename from
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc
> rename to
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/canonical_slices.cc
> index 077bafc2a9b..5ca123eee50 100644
> ---
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc
> +++
> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/canonical_slices.cc
> @@ -13,11 +13,11 @@ template<typename Extents, typename CInt>
> {
> using IndexType = typename Extents::index_type;
> auto ci_expected = std::cw<IndexType{ci_raw.value}>;
> - auto [ci] = std::submdspan_canonicalize_slices(exts, ci_raw);
> + auto [ci] = std::canonical_slices(exts, ci_raw);
> static_assert(std::same_as<decltype(ci), decltype(ci_expected)>);
> VERIFY(std::cmp_equal(ci.value, ci_raw.value));
>
> - auto [i] = std::submdspan_canonicalize_slices(exts, ci_raw.value);
> + auto [i] = std::canonical_slices(exts, ci_raw.value);
> static_assert(std::same_as<decltype(i), IndexType>);
> VERIFY(std::cmp_equal(i, ci_raw.value));
> return true;
> @@ -62,25 +62,25 @@ template<template<typename, typename> typename Pair>
> auto c1 = std::cw<IndexType{1}>;
>
> auto raw_cc = Pair{cbegin, cend};
> - auto [cc] = std::submdspan_canonicalize_slices(exts, raw_cc);
> + auto [cc] = std::canonical_slices(exts, raw_cc);
> assert_same(cc.offset, coffset);
> assert_same(cc.extent, cextent);
> assert_same(cc.stride, c1);
>
> auto raw_cd = Pair{cbegin, cend.value};
> - auto [cd] = std::submdspan_canonicalize_slices(exts, raw_cd);
> + auto [cd] = std::canonical_slices(exts, raw_cd);
> assert_same(cd.offset, coffset);
> assert_same(cd.extent, cextent.value);
> assert_same(cd.stride, c1);
>
> auto raw_dc = Pair{cbegin.value, cend};
> - auto [dc] = std::submdspan_canonicalize_slices(exts, raw_dc);
> + auto [dc] = std::canonical_slices(exts, raw_dc);
> assert_same(dc.offset, coffset.value);
> assert_same(dc.extent, cextent.value);
> assert_same(dc.stride, c1);
>
> auto raw_dd = Pair{cbegin.value, cend.value};
> - auto [dd] = std::submdspan_canonicalize_slices(exts, raw_dd);
> + auto [dd] = std::canonical_slices(exts, raw_dd);
> assert_same(dd.offset, coffset.value);
> assert_same(dd.extent, cextent.value);
> assert_same(dd.stride, c1);
> @@ -128,25 +128,25 @@ test_strided_slice(auto exts, auto co, auto ce, auto cs)
> auto cstride = std::cw<IndexType{cs.value}>;
>
> auto raw_ccc = std::strided_slice{co, ce, cs};
> - auto [ccc] = std::submdspan_canonicalize_slices(exts, raw_ccc);
> + auto [ccc] = std::canonical_slices(exts, raw_ccc);
> assert_same(ccc.offset, coffset);
> assert_same(ccc.extent, cextent);
> assert_same(ccc.stride, cstride);
>
> auto raw_dcc = std::strided_slice{co.value, ce, cs};
> - auto [dcc] = std::submdspan_canonicalize_slices(exts, raw_dcc);
> + auto [dcc] = std::canonical_slices(exts, raw_dcc);
> assert_same(dcc.offset, coffset.value);
> assert_same(dcc.extent, cextent);
> assert_same(dcc.stride, cstride);
>
> auto raw_cdc = std::strided_slice{co, ce.value, cs};
> - auto [cdc] = std::submdspan_canonicalize_slices(exts, raw_cdc);
> + auto [cdc] = std::canonical_slices(exts, raw_cdc);
> assert_same(cdc.offset, coffset);
> assert_same(cdc.extent, cextent.value);
> assert_same(cdc.stride, cstride);
>
> auto raw_ccd = std::strided_slice{co, ce, cs.value};
> - auto [ccd] = std::submdspan_canonicalize_slices(exts, raw_ccd);
> + auto [ccd] = std::canonical_slices(exts, raw_ccd);
> assert_same(ccd.offset, coffset);
> assert_same(ccd.extent, cextent);
> assert_same(ccd.stride, cstride.value);
> @@ -174,11 +174,11 @@ test_strided_slice_zero_extent(auto exts, auto cs)
> using IndexType = typename decltype(exts)::index_type;
> auto c0 = std::cw<uint8_t{0}>;
> auto raw_ccc = std::strided_slice{c0, c0, cs};
> - auto [ccc] = std::submdspan_canonicalize_slices(exts, raw_ccc);
> + auto [ccc] = std::canonical_slices(exts, raw_ccc);
> assert_same(ccc.stride, std::cw<IndexType{1}>);
>
> auto raw_ccd = std::strided_slice{c0, c0, cs.value};
> - auto [ccd] = std::submdspan_canonicalize_slices(exts, raw_ccd);
> + auto [ccd] = std::canonical_slices(exts, raw_ccd);
> assert_same(ccd.stride, std::cw<IndexType{1}>);
> return true;
> }
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc
>
> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/canonical_slices_neg.cc
> similarity index 95%
> rename from
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc
> rename to
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/canonical_slices_neg.cc
> index 94bca183aa3..6dbfd5e8a1b 100644
> ---
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc
> +++
> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/canonical_slices_neg.cc
> @@ -17,7 +17,7 @@ constexpr bool
> test_rank_mismatch()
> {
> auto exts = std::extents(1);
> - std::submdspan_canonicalize_slices(exts, 0, 0); // { dg-error "no
> matching" }
> + std::canonical_slices(exts, 0, 0); // { dg-error "no matching" }
> return true;
> }
>
> @@ -25,7 +25,7 @@ template<typename Int, typename Extents>
> constexpr bool
> test_under1(Int i1, Extents exts)
> {
> - auto [s1] = std::submdspan_canonicalize_slices(exts, i1);
> + auto [s1] = std::canonical_slices(exts, i1);
> return true;
> }
>
> @@ -43,7 +43,7 @@ template<typename Int, typename Extents>
> constexpr bool
> test_over1(Int i1, Extents exts)
> {
> - auto [s1] = std::submdspan_canonicalize_slices(exts, i1);
> + auto [s1] = std::canonical_slices(exts, i1);
> return true;
> }
>
> @@ -65,7 +65,7 @@ template<typename Offset, typename Extent, typename Stride,
> typename Extents>
> constexpr bool
> test_under2(Offset o, Extent e, Stride s, Extents exts)
> {
> - std::submdspan_canonicalize_slices(exts, std::strided_slice{o, e, s});
> + std::canonical_slices(exts, std::strided_slice{o, e, s});
> return true;
> }
>
> @@ -105,7 +105,7 @@ template<typename Offset, typename Extent, typename
> Stride, typename Extents>
> constexpr bool
> test_over2(Offset o, Extent e, Stride s, Extents exts)
> {
> - std::submdspan_canonicalize_slices(exts, std::strided_slice{o, e, s});
> + std::canonical_slices(exts, std::strided_slice{o, e, s});
> return true;
> }
>
> @@ -157,7 +157,7 @@ test_overflow1(auto o, auto e)
> {
> auto exts = std::extents<uint8_t, dyn>{255};
> auto slice = std::strided_slice{o, e, 1};
> - std::submdspan_canonicalize_slices(exts, slice);
> + std::canonical_slices(exts, slice);
> return true;
> }
>
> @@ -171,7 +171,7 @@ test_overflow2(auto b, auto e)
> {
> auto exts = std::extents<uint8_t, dyn>{255};
> auto slice = std::pair{b, e};
> - std::submdspan_canonicalize_slices(exts, slice);
> + std::canonical_slices(exts, slice);
> return true;
> }
>
> @@ -192,7 +192,7 @@ test_invalid(auto e, auto s)
> {
> auto exts = std::extents(5);
> auto slice = std::strided_slice(0, e, s);
> - std::submdspan_canonicalize_slices(exts, slice);
> + std::canonical_slices(exts, slice);
> return true;
> }
>
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/subextents.cc
> similarity index 88%
> rename from
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents.cc
> rename to libstdc++-v3/testsuite/23_containers/mdspan/submdspan/subextents.cc
> index 841910a77c8..ae77d3d96a8 100644
> ---
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/subextents.cc
> @@ -11,7 +11,7 @@ constexpr bool
> test_from_full_extent()
> {
> auto exts = std::extents<int, 3, dyn, 7>{};
> - auto sub_exts = submdspan_extents(exts, 1, all, all);
> + auto sub_exts = std::subextents(exts, 1, all, all);
> VERIFY(sub_exts.rank() == 2);
> VERIFY(sub_exts.static_extent(0) == dyn);
> VERIFY(sub_exts.extent(0) == exts.extent(1));
> @@ -27,7 +27,7 @@ template<template<typename, typename> typename Pair,
> template<int> typename Cw>
> auto s0 = Cw<1>{};
> auto s1 = Pair{Cw<1>{}, Cw<2>{}};
> auto s2 = Pair{Cw<1>{}, 4};
> - auto sub_exts = submdspan_extents(exts, s0, s1, s2);
> + auto sub_exts = std::subextents(exts, s0, s1, s2);
> VERIFY(sub_exts.rank() == 2);
> VERIFY(sub_exts.static_extent(0) == size_t(get<1>(s1) - get<0>(s1)));
> VERIFY(sub_exts.static_extent(1) == dyn);
> @@ -50,7 +50,7 @@ template<typename Int>
> test_from_int_like_as_scalar()
> {
> auto exts = std::extents<int, 3, 5>{};
> - auto sub_exts = submdspan_extents(exts, Int(1), std::tuple{1, 3});
> + auto sub_exts = std::subextents(exts, Int(1), std::tuple{1, 3});
> VERIFY(sub_exts.rank() == 1);
> VERIFY(sub_exts.static_extent(0) == dyn);
> VERIFY(sub_exts.extent(0) == 2);
> @@ -61,7 +61,7 @@ template<template<int> typename Cw>
> test_from_const_int()
> {
> auto exts = std::extents<int, 3, 5>{};
> - auto sub_exts = submdspan_extents(exts, Cw<1>{}, std::tuple{1, 3});
> + auto sub_exts = std::subextents(exts, Cw<1>{}, std::tuple{1, 3});
> VERIFY(sub_exts.rank() == 1);
> VERIFY(sub_exts.static_extent(0) == dyn);
> VERIFY(sub_exts.extent(0) == 2);
> @@ -73,7 +73,7 @@ template<typename Int>
> test_from_int_like_in_tuple()
> {
> auto exts = std::extents<int, 3, 5>{};
> - auto sub_exts = submdspan_extents(exts, Int(1), std::tuple{Int(1),
> Int(3)});
> + auto sub_exts = std::subextents(exts, Int(1), std::tuple{Int(1),
> Int(3)});
> VERIFY(sub_exts.rank() == 1);
> VERIFY(sub_exts.static_extent(0) == dyn);
> VERIFY(sub_exts.extent(0) == 2);
> @@ -89,7 +89,7 @@ template<template<int> typename Cw>
> auto s0 = 1;
> auto s1 = std::strided_slice{0, 0, 0};
> auto s2 = std::strided_slice{1, Cw<0>{}, 0};
> - auto sub_exts = submdspan_extents(exts, s0, s1, s2);
> + auto sub_exts = std::subextents(exts, s0, s1, s2);
> VERIFY(sub_exts.rank() == 2);
> VERIFY(sub_exts.static_extent(0) == dyn);
> VERIFY(sub_exts.extent(0) == 0);
> @@ -100,7 +100,7 @@ template<template<int> typename Cw>
> auto s0 = 1;
> auto s1 = std::strided_slice{0, 2, Cw<1>{}};
> auto s2 = std::strided_slice{1, Cw<2>{}, 1};
> - auto sub_exts = submdspan_extents(exts, s0, s1, s2);
> + auto sub_exts = std::subextents(exts, s0, s1, s2);
> VERIFY(sub_exts.rank() == 2);
> VERIFY(sub_exts.static_extent(0) == dyn);
> VERIFY(sub_exts.extent(0) == 2);
> @@ -113,7 +113,7 @@ template<template<int> typename Cw>
> auto s0 = 1;
> auto s1 = std::strided_slice{1, Cw<4>{}, 2};
> auto s2 = std::strided_slice{1, Cw<10>{}, Cw<3>{}};
> - auto sub_exts = submdspan_extents(exts, s0, s1, s2);
> + auto sub_exts = std::subextents(exts, s0, s1, s2);
> VERIFY(sub_exts.rank() == 2);
> VERIFY(sub_exts.static_extent(0) == dyn);
> VERIFY(sub_exts.extent(0) == 2);
> @@ -125,7 +125,7 @@ template<template<int> typename Cw>
> auto s0 = std::strided_slice(0, 3, 2);
> auto s1 = std::strided_slice(1, 4, 2);
> auto s2 = std::strided_slice(0, 7, 3);
> - auto sub_exts = submdspan_extents(exts, s0, s1, s2);
> + auto sub_exts = std::subextents(exts, s0, s1, s2);
> VERIFY(sub_exts.rank() == 3);
> VERIFY(sub_exts.extent(0) == 2);
> VERIFY(sub_exts.extent(1) == 2);
> diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents_neg.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/subextents_neg.cc
> similarity index 85%
> rename from
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents_neg.cc
> rename to
> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/subextents_neg.cc
> index cf27c0c7e4d..c81a1383e3c 100644
> ---
> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents_neg.cc
> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/subextents_neg.cc
> @@ -10,7 +10,7 @@ constexpr bool
> test_unrelated_stride_type()
> {
> auto exts = std::extents(3, 5, 7);
> - auto sub_exts = submdspan_extents(exts, 1, NotASlice{}, 2); // { dg-error
> "required from" }
> + auto sub_exts = subextents(exts, 1, NotASlice{}, 2); // { dg-error
> "required from" }
> return true;
> }
> static_assert(test_unrelated_stride_type());
> @@ -20,7 +20,7 @@ test_invalid_stride_zero()
> {
> auto exts = std::extents(3, 5, 7);
> auto s = std::strided_slice{0, 1, 0};
> - auto sub_exts = submdspan_extents(exts, 1, s, 2); // { dg-error
> "expansion of" }
> + auto sub_exts = std::subextents(exts, 1, s, 2); // { dg-error "expansion
> of" }
> return true;
> }
> static_assert(test_invalid_stride_zero());
> @@ -30,7 +30,7 @@ constexpr bool
> test_out_of_bounds(const Slice& slice)
> {
> auto exts = std::extents<uint16_t, 3, 5, 7>{};
> - auto sub_exts = submdspan_extents(exts, 1, slice, 2); // { dg-error
> "expansion of" }
> + auto sub_exts = std::subextents(exts, 1, slice, 2); // { dg-error
> "expansion of" }
> return true;
> }
> static_assert(test_out_of_bounds(std::strided_slice{0, 6, 1})); // {
> dg-error "expansion of" }
> --
> 2.53.0
>
