220 13304 article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Tighten rules for virtual override keyword combination Date: Mon, 29 Sep 2014 16:57:48 +0800 Lines: 47 Approved: news@gmane.org Message-ID: References: <19267205-7e26-4c12-b9b4-f26ab2f99eb7@isocpp.org> <803262EF-88B4-40B0-AC9B-7C7356CDE56A@gmail.com> <54274B57.6040007@gmail.com> <8DC1AED8-83B6-453A-A93A-EAB6AF942968@gmail.com> <39638C85-5546-444B-A7AA-F873947777B4@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1411981087 22261 80.91.229.3 (29 Sep 2014 08:58:07 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 29 Sep 2014 08:58:07 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBFV6USQQKGQE4HD6IHQ@isocpp.org Mon Sep 29 10:58:00 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f198.google.com ([209.85.223.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XYWmN-0004D2-UQ for gclcip-std-proposals@m.gmane.org; Mon, 29 Sep 2014 10:58:00 +0200 Original-Received: by mail-ie0-f198.google.com with SMTP id tp5sf27954325ieb.1 for ; Mon, 29 Sep 2014 01:57:59 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date :message-id:references:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type:content-transfer-encoding; bh=1xxpVFeN98jj4K6IAvlLI/5KO19z6CcO2jz8013ZLBA=; b=CmJzTp5BcWJfV8wvCkATE3Xjxhn4HiMKJsSu6YtY0v2gl6RAU5aDphVLGrGK2PlQUe NJOaeoBZJedo1PJyGCtmes6oX6H1W2+0zTIx7l3ghYXnzppKUAPGXHg6L5fV+BYMEewg N1oX4cYqv3BuEsF/s06YY4DcjstJkR3KQNwJ24+nzzE55LDNsa3biLVOUu6B67rv/PRR F9IuM4wKN7DyGlGAyjDpXtRK5IPhs8ta1CUNfJMs7GYdBqMbWmAMfXnKiSHDaB/xAXRZ 03hw/dLnIyoLrHbf+cW3MdMkEaP9OOGZtik3xVqoGVCSa2wMh6j+VUcIB1fwAQwrtrLo /QfQ== X-Gm-Message-State: ALoCoQkJZZaGdTUe74e0FZAAevbIVJxBQhbHmkwsaH3PXD7nqPi86l7qpaMHVxvfCSw4XSvfqeY2 X-Received: by 10.182.230.133 with SMTP id sy5mr34144065obc.22.1411981079012; Mon, 29 Sep 2014 01:57:59 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.134.6 with SMTP id pg6ls2044101igb.37.gmail; Mon, 29 Sep 2014 01:57:58 -0700 (PDT) X-Received: by 10.68.69.109 with SMTP id d13mr53559490pbu.40.1411981078467; Mon, 29 Sep 2014 01:57:58 -0700 (PDT) Original-Received: from mail-pd0-x233.google.com (mail-pd0-x233.google.com [2607:f8b0:400e:c02::233]) by mx.google.com with ESMTPS id gg3si22061724pbc.4.2014.09.29.01.57.58 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 29 Sep 2014 01:57:58 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::233 as permitted sender) client-ip=2607:f8b0:400e:c02::233; Original-Received: by mail-pd0-f179.google.com with SMTP id r10so2265205pdi.38 for ; Mon, 29 Sep 2014 01:57:58 -0700 (PDT) X-Received: by 10.68.134.130 with SMTP id pk2mr57670970pbb.133.1411981078340; Mon, 29 Sep 2014 01:57:58 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.43]) by mx.google.com with ESMTPSA id iq3sm11656958pbb.71.2014.09.29.01.57.55 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 29 Sep 2014 01:57:57 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.1878.6) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::233 as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.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:13304 Archived-At: On 2014-09-29, at 3:12 PM, Ville Voutilainen = wrote: > Compilers do issue warnings for such cases, doing more of that > "serious idiot-proofing", > so apparently it has been deemed necessary enough to bother writing > book chapters > about it and implement implementation support for diagnosing it. Parts > of the hiding > cases can be made actually ill-formed by doing what I described. Not sure I follow. The whole intent is to make the hiding case ill-formed, = no? If the implementation is specially written around it, then it can avoid gen= erating a vtable entry, and then the standard can start to reflect that pra= ctice too. Ideally, avoiding any implication of virtual behavior or polymor= phism. Maybe? Otherwise, might as well introduce a specific feature with no baggage or ov= erhead. >> If the same pattern is used with CRTP instead of virtual dispatch, you w= ould have the same usage scenario, and the user would certainly have access= to the derived class, but the vtable would represent a high, likely prohib= itive cost for an unused feature. >=20 > A likely prohibitive cost? Premature optimization, much? Mangled names of highly templated classes are a major cause of bloat. There= was some discussion of this in the recent "type list indexing" thread, see= K-Ballo's messages. My replies to him reference another earlier thread. Throwing polymorphism into big templates isn't done lightly. --=20 ---=20 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 e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. .