From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 0DEC33858415 for ; Mon, 26 Sep 2022 22:49:15 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 0DEC33858415 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1664232554; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=cXYQsWsppyH22M7EF9zYf/VZaW5JcaFs0qShQRD1uW4=; b=Vewrq2+i50Hv/jC8DPO0J63Isv9cUOXIoI8C9x2/rLbR2HUMfyakCOTu6AwYvbwQbErIsf 4o+bqN0t3B5TO5RvSThUsgdry+G18MfqmSMw12jU3D7mcmPSmdATwuiHx5Srf3P5AZ2i6K RKSz1gQFizEnsFXf2OULhJnDZmz2SUE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-594-6yj1dd9CMN25I-CXtn8d-A-1; Mon, 26 Sep 2022 18:49:11 -0400 X-MC-Unique: 6yj1dd9CMN25I-CXtn8d-A-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6E79780029D; Mon, 26 Sep 2022 22:49:10 +0000 (UTC) Received: from localhost (unknown [10.33.36.214]) by smtp.corp.redhat.com (Postfix) with ESMTP id 34FC2492B04; Mon, 26 Sep 2022 22:49:10 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [committed] libstdc++: Update std::pointer_traits to match new LWG 3545 wording Date: Mon, 26 Sep 2022 23:49:09 +0100 Message-Id: <20220926224909.2235959-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.0 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Tested powerpc64le-linux. Pushed to trunk. -- >8 -- It was pointed out in recent LWG 3545 discussion that having a constrained partial specialization of std::pointer_traits can cause ambiguities with program-defined specializations. For example, the addition to the testcase has: template requires std::derived_from; This would be ambiguous with the library's own constrained partial specialization: template requires requires { typename Ptr::element_type; } struct std::pointer_traits; Neither specialization is more specialized than the other for a type that is derived from base_type and also has an element_type member. The solution is to remove the library's partial specialization, and do the check for Ptr::element_type in the __ptr_traits_elem helper (which is what we already do for !__cpp_concepts anyway). libstdc++-v3/ChangeLog: * include/bits/ptr_traits.h (__ptr_traits_elem) [__cpp_concepts]: Also define the __ptr_traits_elem class template for the concepts case. (pointer_traits): Remove constrained partial specialization. * testsuite/20_util/pointer_traits/lwg3545.cc: Check for ambiguitiy with program-defined partial specialization. --- libstdc++-v3/include/bits/ptr_traits.h | 20 ++++++------------- .../20_util/pointer_traits/lwg3545.cc | 17 ++++++++++++++++ 2 files changed, 23 insertions(+), 14 deletions(-) diff --git a/libstdc++-v3/include/bits/ptr_traits.h b/libstdc++-v3/include/bits/ptr_traits.h index ae8810706ab..71370ff4fc9 100644 --- a/libstdc++-v3/include/bits/ptr_traits.h +++ b/libstdc++-v3/include/bits/ptr_traits.h @@ -73,25 +73,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION struct __replace_first_arg<_SomeTemplate<_Tp, _Types...>, _Up> { using type = _SomeTemplate<_Up, _Types...>; }; -#if __cpp_concepts - // When concepts are supported detection of _Ptr::element_type is done - // by a requires-clause, so __ptr_traits_elem_t only needs to do this: - template - using __ptr_traits_elem_t = typename __get_first_arg<_Ptr>::type; -#else // Detect the element type of a pointer-like type. template struct __ptr_traits_elem : __get_first_arg<_Ptr> { }; // Use _Ptr::element_type if is a valid type. +#if __cpp_concepts + template requires requires { typename _Ptr::element_type; } + struct __ptr_traits_elem<_Ptr, void> + { using type = typename _Ptr::element_type; }; +#else template struct __ptr_traits_elem<_Ptr, __void_t> { using type = typename _Ptr::element_type; }; +#endif template using __ptr_traits_elem_t = typename __ptr_traits_elem<_Ptr>::type; -#endif /// @endcond @@ -182,13 +181,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION struct pointer_traits : __ptr_traits_impl<_Ptr, __ptr_traits_elem_t<_Ptr>> { }; -#if __cpp_concepts - template requires requires { typename _Ptr::element_type; } - struct pointer_traits<_Ptr> - : __ptr_traits_impl<_Ptr, typename _Ptr::element_type> - { }; -#endif - /** * @brief Partial specialization for built-in pointers. * @headerfile memory diff --git a/libstdc++-v3/testsuite/20_util/pointer_traits/lwg3545.cc b/libstdc++-v3/testsuite/20_util/pointer_traits/lwg3545.cc index 08c3ed01b75..93c64a353bd 100644 --- a/libstdc++-v3/testsuite/20_util/pointer_traits/lwg3545.cc +++ b/libstdc++-v3/testsuite/20_util/pointer_traits/lwg3545.cc @@ -99,3 +99,20 @@ static_assert( is_same, clever_ptr>::value, "" ); static_assert( is_same, std::ptrdiff_t>::value, "" ); static_assert( is_same, clever_ptr>::value, "" ); static_assert( is_same, clever_ptr>::value, "" ); + +#ifdef __cpp_concepts +struct ptr_base { }; + +// Program-defined specialization must not be ambiguous with primary template. +template requires std::derived_from +struct std::pointer_traits

+{ + using element_type = int; + using difference_type = long; + using pointer = P; +}; + +struct Ptr : ptr_base { using element_type = int; }; + +using E = std::pointer_traits::element_type; +#endif -- 2.37.3