220 9786 article Path: news.gmane.org!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: pointer to member of class C of type reference to T Date: Thu, 13 Mar 2014 14:39:15 -0700 Lines: 85 Approved: news@gmane.org Message-ID: References: <7b18f21a-cae0-4a26-89be-87f8aec094ad@isocpp.org> <251bafb5-8d28-44b1-8691-e69a4a767106@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=047d7b3a946aee372f04f483c853 X-Trace: ger.gmane.org 1394746751 21399 80.91.229.3 (13 Mar 2014 21:39:11 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 13 Mar 2014 21:39:11 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDVNBJG4YAIBBBGLRCMQKGQEFYBNF2I@isocpp.org Thu Mar 13 22:39:19 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yh0-f71.google.com ([209.85.213.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WODLS-0002DC-2p for gclcip-std-proposals@m.gmane.org; Thu, 13 Mar 2014 22:39:18 +0100 Original-Received: by mail-yh0-f71.google.com with SMTP id a41sf3844550yho.6 for ; Thu, 13 Mar 2014 14:39:17 -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:sender: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; bh=VSbPtaeiRj721NIB8jm3zCN/jBVYwhYplmHFtC5aklw=; b=aiFooNCYhIeN7VApE+9ZdNaI3u2GnW6UdPEOImQc38JVIKGDsMIR37Gnomf96QyoPi KeaoA3aQyXnmbHKSbnx7z1Ev9COzyPKJ7e5s302eT07SQVzPNgE+AFkfmqRPLKePR2lR WTG/WeSUBFGikGMsmnGDsk/FTdkBKnk49PcpKITLjGVPSvEhNYoojD1tBZ8CN7GHsOa+ DZVTDdoRcuVAjbTwRj8e1dXaXOXrXrozZuANDDBIXJ3pFGDjVUbx+4YozaCFh6xHXFEC VHgvtngECAH5h2rTkEv9BXoqjh0dWrkofDyjnhhU0uJiehF7vIP7y8Oeub1P+BXKG8m9 SRKw== X-Gm-Message-State: ALoCoQlttyYtQXnFsZAJAViQlryZhN4sfsmqP2ZMm5LJ1jGXHLXIibbbIhWvyDz5PHLhL3V9yuk+ X-Received: by 10.58.112.1 with SMTP id im1mr1508065veb.33.1394746756979; Thu, 13 Mar 2014 14:39:16 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.94.41 with SMTP id f38ls458019qge.55.gmail; Thu, 13 Mar 2014 14:39:16 -0700 (PDT) X-Received: by 10.221.61.210 with SMTP id wx18mr3233546vcb.27.1394746756153; Thu, 13 Mar 2014 14:39:16 -0700 (PDT) Original-Received: from mail-ve0-x22b.google.com (mail-ve0-x22b.google.com [2607:f8b0:400c:c01::22b]) by mx.google.com with ESMTPS id u5si1330725vdo.56.2014.03.13.14.39.15 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 13 Mar 2014 14:39:16 -0700 (PDT) Received-SPF: pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c01::22b as permitted sender) client-ip=2607:f8b0:400c:c01::22b; Original-Received: by mail-ve0-f171.google.com with SMTP id cz12so1814831veb.30 for ; Thu, 13 Mar 2014 14:39:15 -0700 (PDT) X-Received: by 10.220.164.80 with SMTP id d16mr3162944vcy.15.1394746755788; Thu, 13 Mar 2014 14:39:15 -0700 (PDT) Original-Sender: metafoo@gmail.com Original-Received: by 10.58.218.131 with HTTP; Thu, 13 Mar 2014 14:39:15 -0700 (PDT) In-Reply-To: <251bafb5-8d28-44b1-8691-e69a4a767106@isocpp.org> X-Original-Sender: richard@metafoo.co.uk X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c01::22b as permitted sender) smtp.mail=metafoo@gmail.com; dkim=pass header.i=@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:9786 Archived-At: --047d7b3a946aee372f04f483c853 Content-Type: text/plain; charset=ISO-8859-1 On Thu, Mar 13, 2014 at 2:17 PM, Cleiton Santoia wrote: > We got the same problem on N3951 as Tiago Macieira pointed and remains the > doubt why "int& X::*" not allowed ? I think i should have a const > somewhere, since you cannot reassign the refererence. But other than that > references are pointer in disguise. > No, they aren't (no matter how any particular implementation chooses to represent them). A reference isn't required to occupy storage or have an address (see 8.3.2/4). For instance, given: int n; struct X { X() {} int &r = n; }; .... an implementation could choose to not allocate any storage for the 'r' member in X, and instead rewrite all uses of it to directly reference ::n. That said, as far as I'm aware no implementation does anything remotely like this for class members of reference type, and in practice this extension seems feasible (even though it weakens the conceptual model for references). -- --- 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. 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On T= hu, Mar 13, 2014 at 2:17 PM, Cleiton Santoia <cleitonsantoia@gmail= ..com> wrote:
We got the same proble= m on N3951 as Tiago Macieira pointed and remains the doubt why "int&am= p; X::*" not allowed ? I think i should have a const somewhere, since = you cannot reassign the refererence. But other than that references are poi= nter in disguise.

No, they aren't (no matter how a= ny particular implementation chooses to represent them). A reference isn= 9;t required to occupy storage or have an address (see 8.3.2/4). For instan= ce, given:

=A0 int n;
=A0 struct X {
=A0 =A0 X= () {}
=A0 =A0 int &r =3D n;
=A0 };

... an implementation could choose to not allocate any storage for= the 'r' member in X, and instead rewrite all uses of it to directl= y reference ::n.

That said, as far as I'm aware no implementation do= es anything remotely like this for class members of reference type, and in = practice this extension seems feasible (even though it weakens the conceptu= al model for references).

--

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