[{"id":3682069,"web_url":"http://patchwork.ozlabs.org/comment/3682069/","msgid":"","list_archive_url":null,"date":"2026-04-24T15:03:07","subject":"Re: [PATCH] libstdc++: Disallow duration of cv-qualified types and\n references.","submitter":{"id":48004,"url":"http://patchwork.ozlabs.org/api/people/48004/","name":"Jonathan Wakely","email":"jwakely@redhat.com"},"content":"On Fri, 24 Apr 2026 at 15:59, Tomasz Kamiński wrote:\n>\n> This implements LWG 4481, \"Disallow chrono::duration\",\n> which was approved in Croydon 2026.\n>\n> libstdc++-v3/ChangeLog:\n>\n> * include/bits/chrono.h: Add static_assert requiring cv-unqualified\n> non-reference type.\n> * testsuite/20_util/duration/io.cc: Remove test for duration\n> with const rep.\n> * testsuite/20_util/duration/requirements/typedefs_neg4.cc:\n> New test.\n> ---\n> Testing on x86_64-linux. All *duration* tests passed in all standard modes.\n> OK for trunk when all test passes?\n>\n> libstdc++-v3/include/bits/chrono.h | 4 ++++\n> libstdc++-v3/testsuite/20_util/duration/io.cc | 14 --------------\n> .../20_util/duration/requirements/typedefs_neg4.cc | 11 +++++++++++\n> 3 files changed, 15 insertions(+), 14 deletions(-)\n> create mode 100644 libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg4.cc\n>\n> diff --git a/libstdc++-v3/include/bits/chrono.h b/libstdc++-v3/include/bits/chrono.h\n> index fd91505c16f..d639cfaa485 100644\n> --- a/libstdc++-v3/include/bits/chrono.h\n> +++ b/libstdc++-v3/include/bits/chrono.h\n> @@ -514,6 +514,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n> template\n> class duration\n> {\n> + // _GLIBCXX_RESOLVE_LIB_DEFECTS\n> + // 4481. Disallow chrono::duration\n> + static_assert(is_same<_Rep, __remove_cvref_t<_Rep>>::value,\n> + \"rep should be cv-unqualified object type\");\n> static_assert(!__is_duration<_Rep>::value,\n> \"rep cannot be a std::chrono::duration\");\n> static_assert(__is_ratio<_Period>::value,\n> diff --git a/libstdc++-v3/testsuite/20_util/duration/io.cc b/libstdc++-v3/testsuite/20_util/duration/io.cc\n> index 6ada4fcfa84..463d9feb21f 100644\n> --- a/libstdc++-v3/testsuite/20_util/duration/io.cc\n> +++ b/libstdc++-v3/testsuite/20_util/duration/io.cc\n> @@ -38,13 +38,6 @@ test01()\n> ss << duration(126) << ' ';\n> ss << duration(127) << ' ';\n> VERIFY( ss.str() == \"121s 122s 123s 124s 125s 126s 127s \" );\n> -\n> - ss.str(\"\");\n> - ss << std::hex << std::uppercase << duration(0x1A) << ' ';\n> - ss << std::hex << std::uppercase << duration(0x2A) << ' ';\n> - ss << std::hex << std::uppercase << duration(0x3A) << ' ';\n\nThis line isn't a cv-qualified type. Is it redundant with other checks above?\nWe could just remove the 'const' from these lines.\n\n> - ss << std::scientific << duration(4.5) << ' ';\n> - VERIFY( ss.str() == \"1As 2As 3As 4.500000E+00s \" );\n> }\n>\n> void\n> @@ -77,13 +70,6 @@ test02()\n> ss << duration(126) << ' ';\n> ss << duration(127) << ' ';\n> VERIFY( ss.str() == L\"121s 122s 123s 124s 125s 126s 127s \" );\n> -\n> - ss.str(L\"\");\n> - ss << std::hex << std::uppercase << duration(0x1A) << ' ';\n> - ss << std::hex << std::uppercase << duration(0x2A) << ' ';\n> - ss << std::hex << std::uppercase << duration(0x3A) << ' ';\n> - ss << std::scientific << duration(4.5) << ' ';\n> - VERIFY( ss.str() == L\"1As 2As 3As 4.500000E+00s \" );\n> #endif\n> }\n>\n> diff --git a/libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg4.cc b/libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg4.cc\n> new file mode 100644\n> index 00000000000..52a5d92cc8b\n> --- /dev/null\n> +++ b/libstdc++-v3/testsuite/20_util/duration/requirements/typedefs_neg4.cc\n> @@ -0,0 +1,11 @@\n> +// { dg-do compile { target c++11 } }\n> +\n> +#include \n> +\n> +const int i = 10;\n> +// Check if rep is a cv-unqualifed object type\n> +std::chrono::duration d1(i); // { dg-error \"required from here\" }\n> +std::chrono::duration d2(i); // { dg-error \"required from here\" }\n> +std::chrono::duration d3(i); // { dg-error \"required from here\" }\n> +\n> +// { dg-error \"rep should be cv-unqualified object type\" \"\" { target *-*-* } 0 }\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=dU0GEfM9;\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; 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=dU0GEfM9","sourceware.org; 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