[{"id":3680377,"web_url":"http://patchwork.ozlabs.org/comment/3680377/","msgid":"","list_archive_url":null,"date":"2026-04-22T09:28:43","subject":"Re: [PATCH] libstdc++: Accept data_handle_type by value in mdspan\n deduction guide.","submitter":{"id":48004,"url":"http://patchwork.ozlabs.org/api/people/48004/","name":"Jonathan Wakely","email":"jwakely@redhat.com"},"content":"On Wed, 22 Apr 2026 at 08:35, Tomasz Kamiński wrote:\n>\n> This makes the deduction guide accepting data_handle_type, mapping\n> and accessor consistent with corresponding constructor.\n> Resolves LWG4511.\n>\n> libstdc++-v3/ChangeLog:\n>\n> * include/std/mdspan (mdspan): Remove reference from\n> _AccessorType::data_handle_type parameteter of deduction\n> guide.\n> * testsuite/23_containers/mdspan/mdspan.cc: New test.\n> ---\n> Testing on x86_64-linux locally. All *mdspan* test passed in C++23,C++26\n> mode and with modules. OK for trunk when all test passes?\n\nOK, thanks\n\n\n>\n> libstdc++-v3/include/std/mdspan | 4 +++-\n> .../testsuite/23_containers/mdspan/mdspan.cc | 19 +++++++++++++++++++\n> 2 files changed, 22 insertions(+), 1 deletion(-)\n>\n> diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan\n> index f30c5e83d16..fae4ce0baa2 100644\n> --- a/libstdc++-v3/include/std/mdspan\n> +++ b/libstdc++-v3/include/std/mdspan\n> @@ -3267,8 +3267,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n> -> mdspan<_ElementType, typename _MappingType::extents_type,\n> typename _MappingType::layout_type>;\n>\n> + // _GLIBCXX_RESOLVE_LIB_DEFECTS\n> + // 4511. Inconsistency between the deduction guide of std::mdspan taking...\n> template\n> - mdspan(const typename _AccessorType::data_handle_type&, const _MappingType&,\n> + mdspan(typename _AccessorType::data_handle_type, const _MappingType&,\n> const _AccessorType&)\n> -> mdspan typename _MappingType::extents_type,\n> diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc\n> index 270b3f18daa..62ff7201cce 100644\n> --- a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc\n> +++ b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc\n> @@ -404,6 +404,24 @@ template\n> return true;\n> }\n>\n> +void\n> +test_from_volatile_ptr_and_accessor()\n> +{\n> + constexpr size_t n = 3*5*7;\n> + std::array storage{};\n> + double* volatile vptr = storage.data();\n> + using Extents = std::extents;\n> +\n> + auto exts = Extents{};\n> + auto m = std::layout_left::mapping(exts);\n> + auto a = std::default_accessor{};\n> + auto md = std::mdspan(vptr, m, a);\n> +\n> + assert_deduced_typedefs(md);\n> + VERIFY(md.data_handle() == storage.data());\n> + VERIFY(md.mapping() == m);\n> +}\n> +\n> template bool NothrowAssignable = true>\n> class OpaqueAccessor\n> @@ -757,6 +775,7 @@ main()\n> test_from_int_like();\n> test_from_int_like();\n>\n> + test_from_volatile_ptr_and_accessor();\n> test_from_opaque_accessor();\n> test_from_base_class_accessor();\n> test_from_mapping_like();\n> --\n> 2.53.0\n>","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=SKCb7oxP;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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