On 7/17/25 09:07, Luc Grosheintz wrote:
This commit implements the C++26 feature std::dims, sets the feature
testing macro to 202403 and adds tests.
libstdc++-v3/ChangeLog:
* include/bits/version.def (mdspan): Set value for C++26.
* include/bits/version.h: Regenerate.
* include/std/mdspan (dims): Add.
* testsuite/23_containers/mdspan/extents/misc.cc: Add tests.
* testsuite/23_containers/mdspan/version.cc: Update test.
Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
---
libstdc++-v3/include/bits/version.def | 4 ++++
libstdc++-v3/include/bits/version.h | 7 ++++++-
libstdc++-v3/include/std/mdspan | 5 +++++
.../testsuite/23_containers/mdspan/extents/misc.cc | 7 +++++++
libstdc++-v3/testsuite/23_containers/mdspan/version.cc | 6 ++++--
5 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/libstdc++-v3/include/bits/version.def
b/libstdc++-v3/include/bits/version.def
index cf0672b4822..f645bb3ed3b 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -1007,6 +1007,10 @@ ftms = {
ftms = {
name = mdspan;
+ values = {
+ v = 202403;
+ cxxmin = 26;
+ };
values = {
v = 202207;
cxxmin = 23;
diff --git a/libstdc++-v3/include/bits/version.h
b/libstdc++-v3/include/bits/version.h
index c01ddf14dd5..fbdc9b65acf 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -1125,7 +1125,12 @@
#undef __glibcxx_want_span
#if !defined(__cpp_lib_mdspan)
-# if (__cplusplus >= 202100L)
+# if (__cplusplus > 202302L)
+# define __glibcxx_mdspan 202403L
+# if defined(__glibcxx_want_all) || defined(__glibcxx_want_mdspan)
+# define __cpp_lib_mdspan 202403L
+# endif
+# elif (__cplusplus >= 202100L)
# define __glibcxx_mdspan 202207L
# if defined(__glibcxx_want_all) || defined(__glibcxx_want_mdspan)
# define __cpp_lib_mdspan 202207L
diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index b34116a85e6..ffbd1d9d542 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -412,6 +412,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using dextents = decltype(__mdspan::__build_dextents_type<_IndexType>(
make_index_sequence<_Rank>()));
+#if __glibcxx_mdspan >= 202403L
+ template<size_t _Rank, typename _IndexType = size_t>
+ using dims = dextents<_IndexType, _Rank>;
+#endif
+
template<typename... _Integrals>
requires (is_convertible_v<_Integrals, size_t> && ...)
explicit extents(_Integrals...) ->
diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
b/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
index bca8901685d..933a77aab79 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
@@ -159,6 +159,13 @@ static_assert(std::extents<int, 1, dyn>::static_extent(1)
== dyn);
static_assert(std::extents<int, dyn, dyn>::static_extent(0) == dyn);
static_assert(std::extents<int, dyn, dyn>::static_extent(1) == dyn);
+// dims
+#if __glibcxx_mdspan >= 202403L
+static_assert(std::is_same_v<std::dims<0>, std::dextents<size_t, 0>>);
+static_assert(std::is_same_v<std::dims<3>, std::dextents<size_t, 3>>);
+static_assert(std::is_same_v<std::dims<3, int>, std::dextents<int, 3>>);
+#endif
+
// extent
template<typename Extent>
constexpr void
diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/version.cc
b/libstdc++-v3/testsuite/23_containers/mdspan/version.cc
index 106ee4010ee..aa3767bd2c5 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/version.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/version.cc
@@ -3,7 +3,9 @@
#ifndef __cpp_lib_mdspan
#error "Feature test macro __cpp_lib_mdspan is missing for <mdspan>"
-#if __cpp_lib_mdspan < 202207
-#error "Feature test macro __cpp_lib_mdspan has the wrong value"
+#if __cplusplus <= 202302L && __cpp_lib_mdspan != 202207L
+#error "Feature test macro __cpp_lib_mdspan has the wrong value for C++23"
+#elif __cplusplus > 202302L && __cpp_lib_mdspan != 202403L
+#error "Feature test macro __cpp_lib_mdspan has the wrong value for C++26"
I think this test is and was ineffective, because it would first check
if __cpp_lib_mdspan is defined. If it wasn't defined it would error out. Then,
in the same branch it would pointlessly check if the undefined __cpp_lib_mdspan
had a particular value.
#endif
#endif
