220 7873 article Path: news.gmane.org!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Limited inheritance for classes Date: Wed, 20 Nov 2013 15:54:05 +0200 Lines: 58 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 X-Trace: ger.gmane.org 1384955643 27711 80.91.229.3 (20 Nov 2013 13:54:03 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 20 Nov 2013 13:54:03 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5JHI7A7ALRB7X5WKKAKGQECYLS4ZI@isocpp.org Wed Nov 20 14:54:09 2013 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 1Vj8EK-0007rf-4v for gclcip-std-proposals@m.gmane.org; Wed, 20 Nov 2013 14:54:08 +0100 Original-Received: by mail-pa0-f71.google.com with SMTP id kp14sf6953005pab.6 for ; Wed, 20 Nov 2013 05:54:06 -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: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=KBvYFM9PRog0+H3y369MNY3RFgjeR6McTNSVn3o6eRU=; b=fjxXHwkM+d67mo2vv+5OHlu1udBHXiULAQsv2sJd5vg8eD0uFof6lHfNuqSjCJ7Ovk VOb/kWDa4vKpPgqmnMQaEsyZ1a1akwdbKGCtaFfF3VGkz5WeT89iSkASsBPyQzMiI54C au7rT5keTzfTc8QeNz1Ig9HNAZa1SecMkt/HHlwpPJqke2PV6/zs8+sIRt4t9uiW9ksU 4YvVZZOfAs75RIuQOde4EVAQVJaJTuPUoOC0S/0IlJtdmitYZQkBhDG7xyLoAl8rlqpL 37tFYpZmapEe2LG0vEbxBJ4ms8Iee3gBwXqQop7+viCCL6SdGMY/bU+n73OISzpOVKg6 PHUw== X-Gm-Message-State: ALoCoQmBfTWpjdvl96/rnjd6fMP/t8+mQ0TTrgDn131nAdOD+mbVmLeBM6WU5OUfAlwbyAeDNTbb X-Received: by 10.66.188.37 with SMTP id fx5mr235291pac.45.1384955646785; Wed, 20 Nov 2013 05:54:06 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.53.3 with SMTP id x3ls58962qeo.78.gmail; Wed, 20 Nov 2013 05:54:05 -0800 (PST) X-Received: by 10.229.127.74 with SMTP id f10mr1657914qcs.16.1384955645862; Wed, 20 Nov 2013 05:54:05 -0800 (PST) Original-Received: from mail-qa0-x233.google.com (mail-qa0-x233.google.com [2607:f8b0:400d:c00::233]) by mx.google.com with ESMTPS id o9si4294636qad.116.2013.11.20.05.54.05 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 20 Nov 2013 05:54:05 -0800 (PST) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:400d:c00::233 as permitted sender) client-ip=2607:f8b0:400d:c00::233; Original-Received: by mail-qa0-f51.google.com with SMTP id o15so2885213qap.10 for ; Wed, 20 Nov 2013 05:54:05 -0800 (PST) X-Received: by 10.224.66.5 with SMTP id l5mr1487703qai.31.1384955645516; Wed, 20 Nov 2013 05:54:05 -0800 (PST) Original-Received: by 10.224.68.3 with HTTP; Wed, 20 Nov 2013 05:54:05 -0800 (PST) In-Reply-To: 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:f8b0:400d:c00::233 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:7873 Archived-At: On 20 November 2013 15:50, Dmitry Leontiev wrote: > Hello > > In my opinion, there must be a way tell compiler to not to expose parent > class to child classes. Consider the following example: > > class EventHandler { > protected: > virtual void function()=0; > }; > class EventSource { > void RegisterEventHandler(EventHandler * ev); > }; > //resides in some popular shared library > class A : private EventHandler { > A(){ > source1.RegisterEventHandler(this); > } > private: > void function(){printf("a");} > }; > //imlemented by a developer who is unaware of A internals > class B : public A, private EventHandler { > B(){ > source2.RegisterEventHandler(this); > } > private: > void function(){printf("b");} > }; > > In this example, classes A and B register event handlers for different event > sources upon creation. > However, class B steals events from A by overriding function "function" in > both EventHandlers. > There must be a convinient way for "some popular shared library" developer > to prevent overriding from child classes. > > for example > class A : private static EventHandler { ... } I can imagine at least two ways to do this with existing c++: 1) mark the overrides final in A 2) don't inherit EventHandler in A, inherit it in a subobject of A and delegate the overridden functions to non-virtual private functions of A The latter is not as convenient as it could be without programmable reflection dispatch, but it's not hugely inconvenient either. The former is rather easy. -- --- 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/. .