220 16283 <101e95f6-67fd-4884-9ab3-d51a1565df6a@isocpp.org> article Path: news.gmane.org!not-for-mail From: Markus Grech Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Pointers to members of unknown class Date: Mon, 16 Feb 2015 07:05:15 -0800 (PST) Lines: 127 Approved: news@gmane.org Message-ID: <101e95f6-67fd-4884-9ab3-d51a1565df6a@isocpp.org> References: <9b03a820-0ac5-4931-9825-b2fc9ef893f9@isocpp.org> <885c1fbd-8701-4f70-b7ad-89ee9104f42d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_449_1604886013.1424099115171" X-Trace: ger.gmane.org 1424099124 29597 80.91.229.3 (16 Feb 2015 15:05:24 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 16 Feb 2015 15:05:24 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC44PYFDYAGRBK4ORCTQKGQEEODDWJY@isocpp.org Mon Feb 16 16:05:24 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pd0-f200.google.com ([209.85.192.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YNNEh-00066F-C5 for gclcip-std-proposals@m.gmane.org; Mon, 16 Feb 2015 16:05:23 +0100 Original-Received: by pdev10 with SMTP id v10sf252316188pde.3 for ; Mon, 16 Feb 2015 07:05:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=9muoOO2l7+OwLsEbaZKNHs4NlqixoKPB00ir/THdbXQ=; b=ZFLal7rt6wLSVoCWEmohYbrYC9pQ9RYLB41125XL9v33DbdEmpLt1f9AV0JX0F6+vZ xhUv0ftrX1F1NICaoRbsjq3pwkVwuco6U4yAw5kMB8+xyx0ixZpku78IKeGUGTqcSAdf zsBhl1AaIAPeEfPiESEW1nJf1TND2BjkA5fJvq1770RIdwQ5+UVHzj1OrggmY+QwXI3H sXRRPoDusXpm5YlhpvJE3IsVuT53iz/DvLFGfUugY4r0VxK22J8/Dr4OUSVfyBZa4rvI TnJIeaaxFUrYp1GLCzEtH0SRTDXl5rdQYpYYj93zQI8PiEQnTq+gzCc+8a6+v2u4N8wE Vz3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type:x-original-sender:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=9muoOO2l7+OwLsEbaZKNHs4NlqixoKPB00ir/THdbXQ=; b=lb2RQR1qBUibWNsyegyVToBk3Yu3yxjYEpX+4hMm7nI2bmSH6xopb0Ldlr0EWEK+2Q aSuIJ3/1t8QGN8UvTrwDZ9Ueb5kbmPrPqmBGIyg0M908D6rws5nE1xvewEXD1N91HNsV 5dWcZlwhvGRnkdn/lf8GTKbOOw5yvECD0s52UBTw73qjfvDRnd/JCQm72OOy9D11KoYz p/+58V8j1c1+MCNGNFjiQTHdZGg5FS/mVsQt7KfJOYrdZH5dXSrIufxL6V6rkugWM0UG 8DsJVHtlZFGnl5CBTUO72qN3yno3zwHjMrIT96j6jnMuRDfpHx5pb0Y8tNp+crajpIzb BCfA== X-Gm-Message-State: ALoCoQmfWIvxzwcCgc+OSqmza1O52h9jUYhUGBfoSa84ac6KkYjSiPNJ7QBINpwtpzagp5Jm5v+z X-Received: by 10.66.194.163 with SMTP id hx3mr20171977pac.18.1424099116314; Mon, 16 Feb 2015 07:05:16 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.91.2 with SMTP id y2ls2534036qgd.53.gmail; Mon, 16 Feb 2015 07:05:15 -0800 (PST) X-Received: by 10.140.101.150 with SMTP id u22mr256428qge.5.1424099115455; Mon, 16 Feb 2015 07:05:15 -0800 (PST) In-Reply-To: X-Original-Sender: markus.grech@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:16283 Archived-At: ------=_Part_449_1604886013.1424099115171 Content-Type: multipart/alternative; boundary="----=_Part_450_924614171.1424099115171" ------=_Part_450_924614171.1424099115171 Content-Type: text/plain; charset=UTF-8 On Monday, February 16, 2015 at 3:58:57 PM UTC+1, Scott Prager wrote: > > > > On Monday, February 16, 2015 at 5:58:52 AM UTC-5, Markus Grech wrote: >> >> I have updated the proposal, feedback would be very appreciated. >> >> https://docs.google.com/document/d/1B4zWiym1twufigKA4RSXYR5xU4g32EJ8XNl_bzFtX08/edit?usp=sharing >> > > One possible use-case that I don't see in this proposal: > > struct X { int mem; }; > struct Y { int mem; }; > > > int void::* p = X::mem; > auto xp = static_cast(p); // (1) > auto yp = static_cast(p); // (2) > > > Obviously, *(1) *should be valid, and you describe such a round trip in > the proposal, but what about *(2)*? > Certainly not valid, but I don't see anything prohibiting it. > This would certainly not have any portably meaningful result, as described by the second open question. It is however not easily possible to get a compiletime-error in general. A compiler could possibly emit a warning here however. -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_450_924614171.1424099115171 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Monday, February 16, 2015 at 3:58:57 PM UTC+1, = Scott Prager wrote:


On Monday, February 16, 2015 at 5:58:52 AM UTC-5, Markus Grec= h wrote:

One possible use-case that I don't see in this proposal:

struct X { = int mem= ; };
struct= Y { int mem;<= span style=3D"color:#000"> };


int void::* p = =3D X::mem;
auto xp =3D static_cast<= int X::*>(p= );  // (1)
auto yp <= /span>=3D static_cast= <int= Y::*>(p); =  // (2)


Obviously, (1) should be valid, and = you describe such a round trip in the proposal, but what about (2)?<= /div>
Certainly not valid, but I don't see anything prohibiting it.
This would certainly not have any portably meanin= gful result, as described by the second open question. It is however not ea= sily possible to get a compiletime-error in general. A compiler could possi= bly emit a warning here however. 

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