220 15965 article Path: news.gmane.org!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: const T* operator->() const Date: Mon, 2 Feb 2015 16:39:47 +0200 Lines: 69 Approved: news@gmane.org Message-ID: References: <56a7727d-9839-45c9-be72-a6ecb61f38c9@isocpp.org> 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 1422888001 7446 80.91.229.3 (2 Feb 2015 14:40:01 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 2 Feb 2015 14:40:01 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5JHI7A7ALRBNEYX2TAKGQEHDRUXIA@isocpp.org Mon Feb 02 15:40:01 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pa0-f70.google.com ([209.85.220.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YIIAS-0001m0-0J for gclcip-std-proposals@m.gmane.org; Mon, 02 Feb 2015 15:40:00 +0100 Original-Received: by mail-pa0-f70.google.com with SMTP id eu11sf458461123pac.1 for ; Mon, 02 Feb 2015 06:39:48 -0800 (PST) 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: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=GXbnxDev1d8t7MyY4bfCWKHvxNhyKhMKOf1Ho42xR7M=; b=ePGStjeMZgToDwgJK/3i85L6oobw/2eQNPZd8264HwHX+k3fLrH7RqrPYPf+rNQSjt JeG6S1YiG0wqyd/Fdhx0PILHOW9PBCVpEhPRlkQfKtIJaK7Z4IAU+b5bCHnQdVKiOw+y BBrG2vyOiwfD9JNOskiKyMf8253s0DAn6yBGaJI7BefrzxFIQd50AYeV1pYTdySCDJid f9Qp6duReXQQM3fqy3mNT7rvRIJp91Mnxh11aR4t9Ikzmxppkne+y3Ny4Nu5M3sIlARp Acs0fbHRzrXE7a5LJQgiGS9O+GYo4qhf/VetXuBrsZN229YDU4pAuV+8FlbLQf59rz5T T/vg== X-Gm-Message-State: ALoCoQnhzVTNNTC5jhCNcA26RNQt2L14IE003dKSHQXqca/iCMGkZhPLdBjBreocKfp9fRKbHvbO X-Received: by 10.66.149.170 with SMTP id ub10mr17356676pab.15.1422887988935; Mon, 02 Feb 2015 06:39:48 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.148.85 with SMTP id w82ls1905699iod.100.gmail; Mon, 02 Feb 2015 06:39:47 -0800 (PST) X-Received: by 10.107.158.146 with SMTP id h140mr22431529ioe.27.1422887987923; Mon, 02 Feb 2015 06:39:47 -0800 (PST) Original-Received: from mail-ig0-x22b.google.com (mail-ig0-x22b.google.com. [2607:f8b0:4001:c05::22b]) by mx.google.com with ESMTPS id bs1si7569645icb.34.2015.02.02.06.39.47 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Feb 2015 06:39:47 -0800 (PST) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:4001:c05::22b as permitted sender) client-ip=2607:f8b0:4001:c05::22b; Original-Received: by mail-ig0-f171.google.com with SMTP id h15so2354751igd.4 for ; Mon, 02 Feb 2015 06:39:47 -0800 (PST) X-Received: by 10.107.36.70 with SMTP id k67mr19997915iok.30.1422887987827; Mon, 02 Feb 2015 06:39:47 -0800 (PST) Original-Received: by 10.36.0.4 with HTTP; Mon, 2 Feb 2015 06:39:47 -0800 (PST) In-Reply-To: <56a7727d-9839-45c9-be72-a6ecb61f38c9@isocpp.org> 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:c05::22b 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:15965 Archived-At: On 2 February 2015 at 16:27, mobiphil wrote: > Problem: compiler does not paste const operator -> when used to refer to a > const method > Proposal: well, fix it > > Context: Thought a trivial solution for cow, but does not work. The idea was > to have a Cow wrapper template around the classes used in my system. The > protocol would be: if a non const method is called on the object then a copy > is made (if necessary), otherwise just call the method. The idea was to play > with pair of const and nonconst operator-> > > So, in the example below, I thought for a moment that when writing > a->constFunc() for non const object the const "->" operator would be chosen > by the compiler as constFunc() is const, but had to conclude that it is not > the case. > > What is your opinion? Was my expectation completely wrong. If was not wrong, > could this make subject of a proposal? > > thanks for your feedback > > #include > > template > class Cow { > private: > T* ptr; > public: > > T* operator->() { > printf("-> called\n") ; > } > const T* operator->() const { > printf("const -> called\n") ; > } > }; > > class A { > public: > void func() {}; > void constFunc() const {}; > }; > > > int main() > { > Cow a = Cow(); > a->constFunc(); /* as constFunc is const, would expect the operator-> > const to be used*/ > > const Cow ca = Cow(); > ca->constFunc(); /* well, this one uses the const operator -> */ > } Your expectation is wrong. What the result of an operator-> is used to access doesn't affect the overload resolution of operator-> itself, so the first case with a non-const Cow will use the non-const Cow::operator->. -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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