220 31758 article Path: news.gmane.org!.POSTED!not-for-mail From: Avi Kivity Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow constexpr static data members in a literal type. Date: Sun, 26 Mar 2017 17:50:36 +0300 Organization: ScyllaDB Lines: 46 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed X-Trace: blaine.gmane.org 1490539845 28020 195.159.176.226 (26 Mar 2017 14:50:45 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 26 Mar 2017 14:50:45 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDHJFOWD7YCRBP5K37DAKGQEMVHHUMY@isocpp.org Sun Mar 26 16:50:40 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wr0-f200.google.com ([209.85.128.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cs9V3-0006Aa-E7 for gclcip-std-proposals@m.gmane.org; Sun, 26 Mar 2017 16:50:33 +0200 Original-Received: by mail-wr0-f200.google.com with SMTP id r71sf17557002wrb.17 for ; Sun, 26 Mar 2017 07:50:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:organization:message-id:date:user-agent :mime-version:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=CqZQ3DRbGKktpnvyBp1UYVhuss6b0uNTlVUB296TQmA=; b=kZN2i21FkQ7zAhkys0t0vDzcff/c563m15b2lUgNOraYpo16dTXbP5b4HFUufvHw8A wm6iZYA11aToMpPGkt27JNjEyZTAwx8gwVCxxoUV9A/AWAKoJA9kZbGGplLGKE198ZG1 7jD1IZie3zHEZXxnr86pMazb7e18mnk4E0XUsIUUWLZBh91lt7EHZNm7aH9RP3B/bI9b HscioX4ZV0ntxJ1MuyfEvO/inGH7UCatg0OMaR/oTc8CKa4Dr8gUWynNn0hB4LU+aTfu ypbAE/UH1RSh8e0hwfBNMAv5V2yqwFJ9FI4vnLz2XolZFvwgyUWr1WZCFil2KQkDbr/7 I4IA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:organization :message-id:date:user-agent:mime-version:in-reply-to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=CqZQ3DRbGKktpnvyBp1UYVhuss6b0uNTlVUB296TQmA=; b=CZ3CXjRtRRsuL4d57ub3Mobur14pfMcw74UK0ZO+V6w0htU2O9LKxo4O3IeAOGoiI1 /o+1/0d76rY2UeQWuGz6YqLGDikLlXw23GsbV5HP5EIUl4HjBm4u0D3Zx4if9rSdgf7l d3q+K4BVW/sujQNg7h0idIUd+xsKyqms5mb8x4oI9o5jzG/olomYQFHPD35m5dCzlXQr W552LiGrUr8Je3TpssgnOy3WMuErrqxowI8Hg6ZOzqzpAO7xc7eivl+dy4nkOuPVXyGB fJz65nJ4f35+bkEPgDT+T4mF0H+SDpxUH534w5XnBNvOOSV8s3vmetJggJgb2QuyvIoY D8Rg= X-Gm-Message-State: AFeK/H0MtIz+Zh6SD9oSlBSn96iwGhNpbYNnDQf77s/qlVWawnqaWp7MrZayBOWOUAMs7A== X-Received: by 10.28.91.19 with SMTP id p19mr218432wmb.16.1490539839693; Sun, 26 Mar 2017 07:50:39 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.199.3 with SMTP id x3ls965861wmf.16.canary-gmail; Sun, 26 Mar 2017 07:50:38 -0700 (PDT) X-Received: by 10.28.225.69 with SMTP id y66mr588354wmg.84.1490539838761; Sun, 26 Mar 2017 07:50:38 -0700 (PDT) Original-Received: from mail-wr0-x235.google.com (mail-wr0-x235.google.com. [2a00:1450:400c:c0c::235]) by mx.google.com with ESMTPS id r69si10796596wmd.71.2017.03.26.07.50.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 26 Mar 2017 07:50:38 -0700 (PDT) Received-SPF: pass (google.com: domain of avi@scylladb.com designates 2a00:1450:400c:c0c::235 as permitted sender) client-ip=2a00:1450:400c:c0c::235; Original-Received: by mail-wr0-x235.google.com with SMTP id w43so11223128wrb.0 for ; Sun, 26 Mar 2017 07:50:38 -0700 (PDT) X-Received: by 10.223.134.98 with SMTP id 31mr17970708wrw.69.1490539838463; Sun, 26 Mar 2017 07:50:38 -0700 (PDT) Original-Received: from avi.cloudius-systems.com ([37.142.229.250]) by smtp.gmail.com with ESMTPSA id a10sm10234894wra.17.2017.03.26.07.50.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 26 Mar 2017 07:50:38 -0700 (PDT) In-Reply-To: X-Original-Sender: avi@scylladb.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@scylladb-com.20150623.gappssmtp.com; spf=pass (google.com: domain of avi@scylladb.com designates 2a00:1450:400c:c0c::235 as permitted sender) smtp.mailfrom=avi@scylladb.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:31758 Archived-At: On 03/26/2017 05:35 PM, Ville Voutilainen wrote: > On 26 March 2017 at 17:30, Avi Kivity wrote: >> Consider this type-safe bool class: >> >> >> template >> >> class bool_class { >> >> bool _value; >> >> public: >> >> explicit constexpr bool_class(bool v) noexcept : _value(v) {} >> >> // more emulation of bool >> >> static constexpr bool_class yes = bool_class{true}; >> >> static constexpr bool_class no = bool_class{true}; >> >> }; >> >> >> Compilation fails, I believe rightly, on clang, because by the time yes and >> no are parsed, bool_class is an incomplete type, and therefore not a literal >> type. It could be worked around by making yes and no functions. >> >> Should we make this legal? It seems reasonable for types to offer constants >> scoped under their own name, and if they are literal types, that these >> constants can be constexpr. > > This is US 24 in > http://open-std.org/JTC1/SC22/WG21/docs/papers/2016/p0488r0.pdf. The > comment was rejected > for C++17 due to lack of a proper proposal and the timing. > Thanks. I hope to see this corrected in the future. -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/f8590f49-fb6f-ee08-7fd6-a4b160066143%40scylladb.com. .