{"id":2229617,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2229617/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260428144100.672367-1-tkaminsk@redhat.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null},"msgid":"<20260428144100.672367-1-tkaminsk@redhat.com>","date":"2026-04-28T14:40:33","name":"libstdc++: Make pointer_traits::pointer_to constexpr for main template.","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"c260cbfb92b18a84da5affb1f7945a5a646ce03b","submitter":{"id":90409,"url":"http://patchwork.ozlabs.org/api/1.1/people/90409/?format=json","name":"Tomasz Kaminski","email":"tkaminsk@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260428144100.672367-1-tkaminsk@redhat.com/mbox/","series":[{"id":501870,"url":"http://patchwork.ozlabs.org/api/1.1/series/501870/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=501870","date":"2026-04-28T14:40:33","name":"libstdc++: Make pointer_traits::pointer_to constexpr for main template.","version":1,"mbox":"http://patchwork.ozlabs.org/series/501870/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2229617/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2229617/checks/","tags":{},"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=ATVgxLOw;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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charset=\"US-ASCII\"; x-default=true","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"This resolves LWG3454, \"pointer_traits::pointer_to should be constexpr\",\naccepted in Kona 2025.\n\nThe change is applied since C++20, i.e. standard in which pointer_to\nwas made constexpr for T* specialization.\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/bits/ptr_traits.h (__ptr_traits_ptr_to::pointer_to):\n\tDefine as constexpr since C++20.\n\t* testsuite/20_util/pointer_traits/pointer_to_constexpr.cc:\n\tNew test for custom pointer-like type.\n---\nTested on x86_64-linux locally. OK for trunk?\n\n libstdc++-v3/include/bits/ptr_traits.h | 4 +++-\n .../20_util/pointer_traits/pointer_to_constexpr.cc | 14 ++++++++++++++\n 2 files changed, 17 insertions(+), 1 deletion(-)","diff":"diff --git a/libstdc++-v3/include/bits/ptr_traits.h b/libstdc++-v3/include/bits/ptr_traits.h\nindex df83e0cad1d..c1dc76509ce 100644\n--- a/libstdc++-v3/include/bits/ptr_traits.h\n+++ b/libstdc++-v3/include/bits/ptr_traits.h\n@@ -97,13 +97,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n using pointer = _Ptr;\n using element_type = _Elt;\n \n+ // _GLIBCXX_RESOLVE_LIB_DEFECTS\n+ // 3454. pointer_traits::pointer_to should be constexpr\n /**\n * @brief Obtain a pointer to an object\n * @param __r A reference to an object of type `element_type`\n * @return `pointer::pointer_to(__r)`\n * @pre `pointer::pointer_to(__r)` is a valid expression.\n */\n- static pointer\n+ static _GLIBCXX20_CONSTEXPR pointer\n pointer_to(element_type& __r)\n #if __cpp_lib_concepts\n requires requires {\ndiff --git a/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to_constexpr.cc b/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to_constexpr.cc\nindex cfd35f899c4..929d004fd4a 100644\n--- a/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to_constexpr.cc\n+++ b/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to_constexpr.cc\n@@ -24,3 +24,17 @@ static_assert( std::pointer_traits::pointer_to(i) == &i );\n \n struct X { } x;\n static_assert( std::pointer_traits::pointer_to(x) == &x );\n+\n+template\n+struct Ptr\n+{\n+ T* value;\n+\n+ constexpr static Ptr\n+ pointer_to(T& t) { return Ptr{&t}; }\n+\n+ friend bool operator==(Ptr, Ptr) = default;\n+};\n+\n+static_assert( std::pointer_traits>::pointer_to(i) == Ptr{&i} );\n+static_assert( std::pointer_traits>::pointer_to(x) == Ptr{&x} );\n","prefixes":[]}