From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A21D3C2D0E2 for ; Tue, 22 Sep 2020 10:01:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47FAD23A1E for ; Tue, 22 Sep 2020 10:01:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ehQHH5lE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726547AbgIVKBN (ORCPT ); Tue, 22 Sep 2020 06:01:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:54844 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726353AbgIVKBN (ORCPT ); Tue, 22 Sep 2020 06:01:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1600768871; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=TilmuF3NABOtIHa4EkAnwA7L+b+pAv6qVaPXaLjKBSY=; b=ehQHH5lEkUdxrUkV+WNBuWVJSoKxLt+abhZLFhvDfgr3uCkwyF/woLB6NnjQD11yuWH28C aBb0+2XaaW1Qseg+wcZsBKAQ5ERRkMpYBwDoIJVuyWj4+itMPicpMpyfG815nuOIq10JIJ z61mqgx4xJH85GdbUJUC/8ftDAM+968= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-10-yKz6bfK1Mui8iIiKYPM4Ag-1; Tue, 22 Sep 2020 06:01:07 -0400 X-MC-Unique: yKz6bfK1Mui8iIiKYPM4Ag-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 806E21007465; Tue, 22 Sep 2020 10:01:06 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-114-108.ams2.redhat.com [10.36.114.108]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3891D5577B; Tue, 22 Sep 2020 10:01:03 +0000 (UTC) From: Florian Weimer To: Jonathan Wakely Cc: Alejandro Colomar , Ville Voutilainen , gcc@gcc.gnu.org, libstdc++ , Libc-alpha , LKML , libc-coord@lists.openwall.com Subject: Re: Expose 'array_length()' macro in References: <946e9377-0558-3adf-3eb9-38c507afe2d0@gmail.com> <874knr8qyl.fsf@oldenburg2.str.redhat.com> <875z875si2.fsf@oldenburg2.str.redhat.com> <20200921140100.GA449323@redhat.com> <20200921220443.GP6061@redhat.com> <34bae433-f67e-877d-f871-928cb55d2a87@gmail.com> <20200922094020.GS6061@redhat.com> Date: Tue, 22 Sep 2020 12:01:02 +0200 In-Reply-To: <20200922094020.GS6061@redhat.com> (Jonathan Wakely's message of "Tue, 22 Sep 2020 10:40:20 +0100") Message-ID: <87k0wmyvtt.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Jonathan Wakely: > I don't see much point in using std::size here. If you're going to > provide the alternative implementation for when std::size isn't > defined, why not just use it always? > > template > #if __cplusplus >= 201103L > constexpr > #endif > inline std::size_t > __array_length(const _Tp(&)[_Num]) __THROW > { > return _Num; > } > > This only requires , not . I agree that this is an advantage. But the version without constexpr is not sufficient because __array_length does not produce a constant expression. I've seen something like this used instead: template char (&___array_length(const _Tp(&)[_Num]))[_Num]; #define __array_length(v) (sizeof(___array_length(v))) If the function type is too cute, a helper struct could be used instead. Thanks, Florian -- Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn, Commercial register: Amtsgericht Muenchen, HRB 153243, Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill