220 13310 article Path: news.gmane.org!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Tighten rules for virtual override keyword combination Date: Mon, 29 Sep 2014 15:05:53 +0300 Lines: 56 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1411992373 10394 80.91.229.3 (29 Sep 2014 12:06:13 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 29 Sep 2014 12:06:13 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5JHI7A7ALRBIUWUWQQKGQE4IEV7EQ@isocpp.org Mon Sep 29 14:06:07 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f70.google.com ([209.85.218.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XYZiF-0000fk-JU for gclcip-std-proposals@m.gmane.org; Mon, 29 Sep 2014 14:05:55 +0200 Original-Received: by mail-oi0-f70.google.com with SMTP id u20sf96116835oif.1 for ; Mon, 29 Sep 2014 05:05:54 -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:in-reply-to:references:date :message-id:subject:from: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=LoNkU5gWSdJ2pNFJADPv8zh5AZ7zgOQvCNZEi2MCrO8=; b=m3AXjczNm3sSiEn0m3Zdrf3gYF5NPi8NgcQFW8PkP5e/FIGh2FFndZ/ox+5dJkfoLc THmhjedSlA+A9oQw8+XYE7/igxK0FqGyeszTFgud5lwMbu4xTm4FE9bvSLdYyo/zlZcG 24VDLnH98IpdZ5MHZKiO6QFzs/w2kQzcnvZhLQ1XtQ142/hAbi/HSoD8Z43dmN6nT89E dIPuLxWxfi4jZQH1Ub+Yizb1DszFuPEmiG+KadYQ3tiRaG3t3PYMqBSC0b0yBzoM1qEX gx8RUtzUv1QxrPAktNLv0qU1cawTObsalLdq9QMl7jloEg8lQW2pxk46hvcx25uW/hmg SzBA== X-Gm-Message-State: ALoCoQnLEP9CNRWjrT6NMGI4Eo2xz65fRCLsMkVU0790GYpjteHKAh7iNawOdqNe8nFJ35aebJ2Z X-Received: by 10.182.51.161 with SMTP id l1mr4914861obo.13.1411992354685; Mon, 29 Sep 2014 05:05:54 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.79.161 with SMTP id k1ls2139152igx.20.gmail; Mon, 29 Sep 2014 05:05:53 -0700 (PDT) X-Received: by 10.50.61.243 with SMTP id t19mr13306993igr.20.1411992353972; Mon, 29 Sep 2014 05:05:53 -0700 (PDT) Original-Received: from mail-ie0-x22e.google.com (mail-ie0-x22e.google.com [2607:f8b0:4001:c03::22e]) by mx.google.com with ESMTPS id lk10si14674480icc.82.2014.09.29.05.05.53 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 29 Sep 2014 05:05:53 -0700 (PDT) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:4001:c03::22e as permitted sender) client-ip=2607:f8b0:4001:c03::22e; Original-Received: by mail-ie0-f174.google.com with SMTP id tr6so1259615ieb.33 for ; Mon, 29 Sep 2014 05:05:53 -0700 (PDT) X-Received: by 10.50.122.5 with SMTP id lo5mr34333235igb.25.1411992353757; Mon, 29 Sep 2014 05:05:53 -0700 (PDT) Original-Received: by 10.42.44.8 with HTTP; Mon, 29 Sep 2014 05:05:53 -0700 (PDT) In-Reply-To: X-Original-Sender: ville.voutilainen@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:4001:c03::22e as permitted sender) smtp.mail=ville.voutilainen@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:13310 Archived-At: On 29 September 2014 11:57, David Krauss wrote: > > 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? It's not possible to make all hiding cases ill-formed, but at least we can = make the ones with identical signatures ill-formed. > If the implementation is specially written around it, then it can avoid g= enerating a vtable entry, and then the standard can start to reflect that p= ractice too. Ideally, avoiding any implication of virtual behavior or polym= orphism. Maybe? > Otherwise, might as well introduce a specific feature with no baggage or = overhead. These cases are nowhere near common enough to mandate a specific feature. >>> If the same pattern is used with CRTP instead of virtual dispatch, you = would have the same usage scenario, and the user would certainly have acces= s to the derived class, but the vtable would represent a high, likely prohi= bitive cost for an unused feature. >> A likely prohibitive cost? Premature optimization, much? > Mangled names of highly templated classes are a major cause of bloat. The= re was some discussion of Perhaps you should decide which of those things is your concern, the vtbl or mangled names. > Throwing polymorphism into big templates isn't done lightly. Yeah, that's why I prefer measuring before spouting nonsense about a "likely prohibitive cost". --=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/. .