220 16363 <4118260.ahajs63pV4@tjmaciei-mobl4> article Path: news.gmane.org!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Pointers to members of unknown class Date: Tue, 17 Feb 2015 23:34:10 -0800 Lines: 48 Approved: news@gmane.org Message-ID: <4118260.ahajs63pV4@tjmaciei-mobl4> References: <9b03a820-0ac5-4931-9825-b2fc9ef893f9@isocpp.org> <3195225.rb5WNQZqGk@tjmaciei-mobl4> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: ger.gmane.org 1424244892 15325 80.91.229.3 (18 Feb 2015 07:34:52 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 18 Feb 2015 07:34:52 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBFEBSGTQKGQETHLQSXQ@isocpp.org Wed Feb 18 08:34:46 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f199.google.com ([209.85.217.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YNz9h-0006nf-QD for gclcip-std-proposals@m.gmane.org; Wed, 18 Feb 2015 08:34:45 +0100 Original-Received: by lbvp9 with SMTP id p9sf6240032lbv.1 for ; Tue, 17 Feb 2015 23:34:45 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:subject:date:message-id:user-agent :in-reply-to:references:mime-version:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=rEaS1QyLnImb4+s0df/Vf0aaz/x2c+JIwKK3cB+CO0A=; b=FhRHcfMgavsfJp0EV6aYDSlGkiExOw4PdSMfouKXN+i+EK/gie8wtQmlKlB7C60NrI 5wCAaZWATeY+gbnDQMq3oTOx2ZQ3vxCRg4KO3vzNELBEf4qVP2IBZIc8arG3hiMSWInt yg9yvUITQY94HIYFxfwZA5saG8PsummYw7cBF+Hh9klULXpI6c3kJpH7DNw2emvWp8zB gMPoPJl2qS3KVQFJImwicztJKmxQVFozLdScMj5nT7KmnaqeeG5a2QOqEvZlhHL9znly 45jbPLe2h3icLGu5Mdg6B/ngwoEwhFoyycIKX8NBGMfZIhcz4uAxXJ8cc+AdPOwkFqdk E8Mg== X-Gm-Message-State: ALoCoQnUkUJF8XrkyybFffLjxDXPDL5XcfJn0Zw1nobHzHB4JgALwTVbFxo/nxwVHfM5QtCj3Q/I X-Received: by 10.180.12.146 with SMTP id y18mr125344wib.6.1424244885340; Tue, 17 Feb 2015 23:34:45 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.84.72 with SMTP id w8ls550145wiy.4.canary; Tue, 17 Feb 2015 23:34:44 -0800 (PST) X-Received: by 10.180.107.71 with SMTP id ha7mr109621wib.23.1424244884327; Tue, 17 Feb 2015 23:34:44 -0800 (PST) Original-Received: from gondolin.macieira.info (gondolin.macieira.info. [2a01:4f8:d13:f81:21c:14ff:fe01:12a3]) by mx.google.com with ESMTP id ff5si33543300wib.42.2015.02.17.23.34.43 for ; Tue, 17 Feb 2015 23:34:43 -0800 (PST) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) client-ip=2a01:4f8:d13:f81:21c:14ff:fe01:12a3; Original-Received: from tjmaciei-mobl4.localnet (jfdmzpr06-ext.jf.intel.com [134.134.137.75]) by gondolin.macieira.info (Postfix) with ESMTPSA id C9E1511BB01 for ; Tue, 17 Feb 2015 23:34:42 -0800 (PST) User-Agent: KMail/4.14.4 (Linux/3.11.10-25-desktop; KDE/4.14.4; x86_64; ; ) In-Reply-To: X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) smtp.mail=thiago@macieira.org 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:16363 Archived-At: On Tuesday 17 February 2015 15:33:01 Richard Smith wrote: > > > > If MSVC has broken ABI *every* *single* release in the past 15 years, why > > hasn't it fixed the above issue, when there is a clear solution works for > > everyone and, moreover, is available via compile switch (the /vmg option) > > https://msdn.microsoft.com/en-us/library/yad46a6z.aspx > > > > The /vmg option makes pointers-to-members quite large (3-4 pointers) > because it gives a "most general" representation for all > pointers-to-members. MSVC's "most general" representation supports (as an > extension) things that the standard does not require, such as converting a > pointer-to-member of a *virtual* base class to a pointer-to-member of a > derived class, and thus cannot be as compact as that of the Itanium C++ > ABI. MSVC can't simply switch to a strict, standard-conforming, smaller > pointer-to-member representation without breaking existing code that uses > its extension. I'm not asking to drop the extension. I'm asking that they fix their non- conforming behaviour. They could introduce a default that is as big as the Itanium C++ ABI does and provide the even-larger version when necessary. Or they could use the large one everywhere. > I don't know if that's the reason they've not done anything about this, but > it seems like a possible explanation. You can *almost* get a small and > correct pointer-to-member representation by using the /vmm switch, but > their compiler emits spurious errors if you then take the address of a > member of a class that uses virtual inheritance. So what they need is a "/vmm" that applies to everything except virtual inheritance, leaving the 3-4 pointer version for classes with virtuals. Since that is an extension anyway, it doesn't need to support incomplete classes. -- Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center PGP/GPG: 0x6EF45358; fingerprint: E067 918B B660 DBD1 105C 966C 33F5 F005 6EF4 5358 -- --- 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. 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