[{"id":3682564,"web_url":"http://patchwork.ozlabs.org/comment/3682564/","msgid":"","list_archive_url":null,"date":"2026-04-27T08:59:45","subject":"Re: [PATCH] libstdc++: Fix up std::is_scalar for std::meta::info\n [PR125024]","submitter":{"id":48004,"url":"http://patchwork.ozlabs.org/api/people/48004/","name":"Jonathan Wakely","email":"jwakely@redhat.com"},"content":"On Mon, 27 Apr 2026 at 09:05, Jakub Jelinek wrote:\n>\n> Hi!\n>\n> https://eel.is/c++draft/basic.types.general#9.sentence-1 says that\n> std::meta::info and its cv-qualified versions are scalar types too\n> (and in https://eel.is/c++draft/basic.fundamental#19.sentence-1\n> that they are fundamental types too).\n> Now, on the reflection side, eval_is_scalar_type is handled\n> in the compiler and uses SCALAR_TYPE_P (type) which includes\n> REFLECTION_TYPE_P check and eval_is_fundamental_type includes that\n> explicitly too.\n> std::is_fundamental uses\n> template\n> struct is_fundamental\n> : public __or_, is_void<_Tp>,\n> is_null_pointer<_Tp>\n> #if __cpp_impl_reflection >= 202506L\n> , is_reflection<_Tp>\n> #endif\n> >::type\n> { };\n> but for std::is_scalar we apparently forgot to include is_reflection.\n>\n> The following patch fixes that.\n>\n> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/16.2?\n\nOK for both.\n\nis_scalar is one of the more expensive traits and it would be good to\nhave a builtin for it some day.\n\n>\n> 2026-04-26 Jakub Jelinek \n>\n> PR libstdc++/125024\n> * include/std/type_traits (std::is_scalar): For\n> __cpp_impl_reflection >= 202506L handle is_reflection types as\n> scalar.\n> * testsuite/20_util/is_scalar/reflection.cc: New test.\n>\n> --- libstdc++-v3/include/std/type_traits.jj 2026-04-09 18:09:11.002020134 +0200\n> +++ libstdc++-v3/include/std/type_traits 2026-04-26 19:20:37.109205308 +0200\n> @@ -871,7 +871,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n> template\n> struct is_scalar\n> : public __or_, is_enum<_Tp>, is_pointer<_Tp>,\n> - is_member_pointer<_Tp>, is_null_pointer<_Tp>>::type\n> + is_member_pointer<_Tp>, is_null_pointer<_Tp>\n> +#if __cpp_impl_reflection >= 202506L\n> + , is_reflection<_Tp>\n> +#endif\n> + >::type\n> { };\n>\n> /// is_compound\n> --- libstdc++-v3/testsuite/20_util/is_scalar/reflection.cc.jj 2026-04-26 20:30:15.661943601 +0200\n> +++ libstdc++-v3/testsuite/20_util/is_scalar/reflection.cc 2026-04-26 20:49:40.107965736 +0200\n> @@ -0,0 +1,13 @@\n> +// { dg-do compile { target c++26 } }\n> +// { dg-additional-options \"-freflection\" }\n> +\n> +#include \n> +#include \n> +\n> +void test01()\n> +{\n> + using std::is_scalar;\n> + using namespace __gnu_test;\n> +\n> + static_assert(test_category(true), \"\");\n> +}\n>\n> Jakub\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=QR3L+wk7;\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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Mon, 27 Apr 2026\n 02:00:01 -0700 (PDT)"],"MIME-Version":"1.0","References":"","In-Reply-To":"","From":"Jonathan Wakely ","Date":"Mon, 27 Apr 2026 09:59:45 +0100","X-Gm-Features":"AQROBzD7cWwxunL8JsoXcexV4RcIUvnLXcCMb9kP7LsVe3YuronOy1ENF7qcDMo","Message-ID":"\n ","Subject":"Re: [PATCH] libstdc++: Fix up std::is_scalar for std::meta::info\n [PR125024]","To":"Jakub Jelinek ","Cc":"gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"558LTI4Pnzo98-N5pAugFgEZwZ255JelsNP2-exGZ90_1777280402","X-Mimecast-Originator":"redhat.com","Content-Type":"text/plain; charset=\"UTF-8\"","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"}},{"id":3682667,"web_url":"http://patchwork.ozlabs.org/comment/3682667/","msgid":"","list_archive_url":null,"date":"2026-04-27T12:08:54","subject":"Re: [PATCH] libstdc++: Fix up std::is_scalar for std::meta::info\n [PR125024]","submitter":{"id":671,"url":"http://patchwork.ozlabs.org/api/people/671/","name":"Jakub Jelinek","email":"jakub@redhat.com"},"content":"On Mon, Apr 27, 2026 at 09:59:45AM +0100, Jonathan Wakely wrote:\n> is_scalar is one of the more expensive traits and it would be good to\n> have a builtin for it some day.\n\nGuess that is doable, but the question is if you are ok with losing\ncontrol on the library side what exactly is integral/arithmetic type and\nwhat is not (e.g. whether __int128 is or is not integral, arithmetic etc.\ntype).\nWhat other traits you'd like to change to using builtin versions (and is\n__builtin_is_WHATEVER ok for that)?\nis_integral/is_arithmetic/is_scalar/is_fundamental? Something else?\n\n\tJakub","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=YDOVxoT3;\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; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.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=YDOVxoT3","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; spf=pass smtp.mailfrom=redhat.com","server2.sourceware.org;\n arc=none smtp.remote-ip=170.10.129.124"],"Received":["from vm01.sourceware.org (vm01.sourceware.org\n [IPv6:2620:52:6:3111::32])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g42Rt73gvz1xvV\n\tfor ; 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