220 13240 <8DC1AED8-83B6-453A-A93A-EAB6AF942968@gmail.com> 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: Sun, 28 Sep 2014 14:07:32 +0800 Lines: 111 Approved: news@gmane.org Message-ID: <8DC1AED8-83B6-453A-A93A-EAB6AF942968@gmail.com> References: <19267205-7e26-4c12-b9b4-f26ab2f99eb7@isocpp.org> <803262EF-88B4-40B0-AC9B-7C7356CDE56A@gmail.com> <54274B57.6040007@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: multipart/alternative; boundary="Apple-Mail=_87C2A59F-4EE5-4F60-8FA2-DEC6E1CD7A2E" X-Trace: ger.gmane.org 1411884480 13644 80.91.229.3 (28 Sep 2014 06:08:00 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 28 Sep 2014 06:08:00 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBMWLT2QQKGQEY5F2P5A@isocpp.org Sun Sep 28 08:07:49 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pa0-f71.google.com ([209.85.220.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XY7e9-0001m1-0q for gclcip-std-proposals@m.gmane.org; Sun, 28 Sep 2014 08:07:49 +0200 Original-Received: by mail-pa0-f71.google.com with SMTP id rd3sf12779788pab.10 for ; Sat, 27 Sep 2014 23:07:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:message-id:mime-version:subject:date :references:to:in-reply-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; bh=EcEeVyOey8uIeZaDm9EgtY2Iyb0RjbtfQTL9jgZj21w=; b=MdcFK9teFn62OKe3kBt7N8hNoMeWmKjQcbMFsEGmHEe8flhI9c29vh1e7amFiIoT5T ZH3LoJBLD850QDLCdDlvFeL/Wc8tPYM6B7INEzkISzLVFPLhLN3mhlNMOmPmp5Bu40UC YrEENXKPiZo5J/F9TkoLeiy/krrT3mCAQpW+ODbd9eA11DGzi2IgGjMMcdID/+QnJnIc wKNnLbi9CMQVX3Fw0Szdl9s5Dg+SI+7ldSJxU5MEEgQAVTPx4Qp0RPr87oOsaFmX95T7 wYBqplfsUmu9w5xv3aG48FYkEp5WThGAWXw/OLacDF451pUNbWrK0qkZusnTrAF+z4Hu fYYw== X-Gm-Message-State: ALoCoQk6ORiVg2Q65QZ79VefiAR0uT4A645Czxv8dG7dJo8HXcHk9SkvXLy5aoTR1Uu6quluLYuW X-Received: by 10.66.66.196 with SMTP id h4mr26184112pat.18.1411884467195; Sat, 27 Sep 2014 23:07:47 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.23.8 with SMTP id i8ls1460430igf.34.canary; Sat, 27 Sep 2014 23:07:46 -0700 (PDT) X-Received: by 10.70.16.2 with SMTP id b2mr62348408pdd.36.1411884466611; Sat, 27 Sep 2014 23:07:46 -0700 (PDT) Original-Received: from mail-pd0-x22c.google.com (mail-pd0-x22c.google.com [2607:f8b0:400e:c02::22c]) by mx.google.com with ESMTPS id pq1si17027756pac.109.2014.09.27.23.07.46 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 27 Sep 2014 23:07:46 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::22c as permitted sender) client-ip=2607:f8b0:400e:c02::22c; Original-Received: by mail-pd0-f172.google.com with SMTP id g10so3420047pdj.31 for ; Sat, 27 Sep 2014 23:07:46 -0700 (PDT) X-Received: by 10.66.159.8 with SMTP id wy8mr47345516pab.17.1411884466424; Sat, 27 Sep 2014 23:07:46 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.39]) by mx.google.com with ESMTPSA id hs8sm8944522pbc.35.2014.09.27.23.07.44 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sat, 27 Sep 2014 23:07:45 -0700 (PDT) In-Reply-To: <54274B57.6040007@gmail.com> 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::22c 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:13240 Archived-At: --Apple-Mail=_87C2A59F-4EE5-4F60-8FA2-DEC6E1CD7A2E Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1 On 2014-09-28, at 7:42 AM, germinolegrand wrote: > - when i see virtual, i know it's the base definition I proposed a while ago on this list to define !override (or not override) t= o provide a base definition, and !final (or not final) as a less obtuse syn= onym for =3D 0, which would not preclude =3D default for destructors. There= was little interest. C++ does not currently have a way to declare base definitions, so every der= ived class is at the mercy of its bases and even their inaccessible members= .. On 2014-09-28, at 1:50 PM, 'Geoffrey Romer' via ISO C++ Standard - Future P= roposals wrote: > Note that in the case of 'final', the presence or absence of 'virtual' ma= kes an important semantic difference: without the 'virtual', it behaves lik= e 'override', so you get an error if it doesn't override a virtual method i= n the base class. Adding 'virtual' suppresses that error, which is almost n= ever what you want. This makes "use exactly one of the three" a pretty good= rule of thumb. I wonder why implementations don't warn on a non-override final definition,= and why override isn't implicit in final in the first place. It's too late= to change now, but where's the use case? It has the effect of reserving a = name from derived classes, I suppose, but such a thing doesn't belong in th= e vtable at all. --=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/. --Apple-Mail=_87C2A59F-4EE5-4F60-8FA2-DEC6E1CD7A2E Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
On 2014&= ndash;09–28, at 7:42 AM, germinolegrand <germinolegrand@gmail.com> wrote:

- when i see virtual, i kno= w it's the base definition
=
I proposed a while ago on this list to define !override (or not override) to prov= ide a base definition, and !final (or not final) as a less obtuse synonym for =3D 0, which would not preclude =3D default for destructors. There was little interest.

C++ does not currently have a way to declare base defi= nitions, so every derived class is at the mercy of its bases and even their= inaccessible members.


On 2014= –09–28, at 1:50 PM, 'Geoffrey Romer' via ISO C++ Standard - Fut= ure Proposals <std-proposals= @isocpp.org> wrote:

Note that in the case of 'final', the presence or ab= sence of 'virtual' makes an important semantic difference: without the 'vir= tual', it behaves like 'override', so you get an error if it doesn't overri= de a virtual method in the base class. Adding 'virtual' suppresses that err= or, which is almost never what you want. This makes "use exactly one of the= three" a pretty good rule of thumb.

I wonder why implementations don&rs= quo;t warn on a non-override final definition= , and why override isn’t implicit in final in the first place. It’s too late t= o change now, but where’s the use case? It has the effect of reservin= g a name from derived classes, I suppose, but such a thing doesn’t be= long in the vtable at all.

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