220 4082 article Path: news.gmane.org!not-for-mail From: Lawrence Crowl Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: A cleaner way to define nested class/structure Date: Mon, 29 Apr 2013 11:57:53 -0700 Lines: 79 Approved: news@gmane.org Message-ID: References: <27175469-a158-4bc1-9f30-66e3a647e931@isocpp.org> 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 1367261877 12802 80.91.229.3 (29 Apr 2013 18:57:57 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 29 Apr 2013 18:57:57 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCY3D77DYUDBBM4F7OFQKGQEXGXAIPA@isocpp.org Mon Apr 29 20:57:58 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oa0-f69.google.com ([209.85.219.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UWtGv-0002qV-Gq for gclcip-std-proposals@m.gmane.org; Mon, 29 Apr 2013 20:57:57 +0200 Original-Received: by mail-oa0-f69.google.com with SMTP id l20sf41367649oag.4 for ; Mon, 29 Apr 2013 11:57:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlers.com; s=googlers; h=x-received:x-beenthere:x-received:received-spf:mime-version :x-received:in-reply-to:references:date:message-id:subject:from:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-google-group-id:list-post :list-help:list-archive:list-subscribe:list-unsubscribe:content-type; bh=yEdxAilQITyO9uPLMCbAlYQ4FMFVCfwyNzoNQRi//0w=; b=C11aLjCVna0XpO9nkV38FsfA1XEVcFj5/XHUNO/eDtWLtXw6ubwTeHcqD68poJHT72 XUuwVNJTqmw7AXjx4IniXUhPpXK6kh+ZxDoXyQvRWodjaIhTob7QQXkkPnF9VtyA3TxG 7smIpU5lz29KztTEhGmWVXZ/4dVw6RW6bb0KA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-received:x-beenthere:x-received:received-spf:mime-version :x-received:in-reply-to:references:date:message-id:subject:from:to :x-gm-message-state:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-google-group-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=yEdxAilQITyO9uPLMCbAlYQ4FMFVCfwyNzoNQRi//0w=; b=hsOUFvQykULfvkAm3TjeJy8QcGMFi+YDKuGIO2pCAIHEvybkCIulNLamyYJcNCABR+ wkFz39udiAonW39fz51z6PN3aZ0P5+HcSO+BEK6529w5jryAkqo4SPYLaZd91XZKGHKE fCkhH+6bUgH0WYEN61/3noU1u89QYHmMCq2WbDhYcQ9/7AhgvkdIUyE01+qu1DBpHfan Bujw4zmDFbquLeVExKFCHxLDyRNnPdEpDyvvjVA+wxDrsEf53IGNQuWfzHH3/oYD1jj2 qrqoRkclEh8vbABiZ8JclHCRDSH7x1o X-Received: by 10.43.113.131 with SMTP id ew3mr42353052icc.24.1367261876258; Mon, 29 Apr 2013 11:57:56 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.154.102 with SMTP id vn6ls430072igb.23.canary; Mon, 29 Apr 2013 11:57:54 -0700 (PDT) X-Received: by 10.42.95.195 with SMTP id g3mr29421118icn.14.1367261874211; Mon, 29 Apr 2013 11:57:54 -0700 (PDT) Original-Received: from mail-ie0-x22e.google.com (mail-ie0-x22e.google.com [2607:f8b0:4001:c03::22e]) by mx.google.com with ESMTPS id dd9si12541602igc.7.2013.04.29.11.57.54 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 29 Apr 2013 11:57:54 -0700 (PDT) Received-SPF: pass (google.com: domain of crowl@google.com designates 2607:f8b0:4001:c03::22e as permitted sender) client-ip=2607:f8b0:4001:c03::22e; Original-Received: by mail-ie0-f174.google.com with SMTP id 10so7647516ied.5 for ; Mon, 29 Apr 2013 11:57:54 -0700 (PDT) X-Received: by 10.50.171.73 with SMTP id as9mr1700397igc.23.1367261873997; Mon, 29 Apr 2013 11:57:53 -0700 (PDT) Original-Received: by 10.231.110.80 with HTTP; Mon, 29 Apr 2013 11:57:53 -0700 (PDT) In-Reply-To: <27175469-a158-4bc1-9f30-66e3a647e931@isocpp.org> X-Gm-Message-State: ALoCoQnlO/PaS2UGdJ/poebw1kKoUCLv3K5kwYMwAAT4cNegbyRh143Q4YBJNq//3zQwQIH2XhOv0l0ddzwv9rsi6Ya2bxyQ+J/ovEyEdys35n+1+fN8UcpUoa1o2VGfjwAvanRNgx0dtuH+Ek/21X8C+dphBdTTgfUbnSz6M8nIiPwgM9IyiBXyUCvRO4l0CMzjFib35KTY X-Original-Sender: crowl@googlers.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of crowl@google.com designates 2607:f8b0:4001:c03::22e as permitted sender) smtp.mail=crowl@google.com; dkim=pass header.i=@googlers.com; dmarc=pass (p=NONE dis=none) d=googlers.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:4082 Archived-At: On 4/29/13, Hariharan Subramanian wrote: > Problem: > > class Outer { > class Inner1; > class Inner2; > > Inner1 inner1; > Inner2 *inner2; > }; > > class Outer::Inner1 { > int i1; > }; > > class Outer::Inner2 { > int i2; > }; > > The code above results in compilation error because the class Inner1 is not > > defined before the declaration of the object inner1. Inner2 obviously has > no problem.Defining the nested classes within the Outer class hampers > readability. > > Solution: > > class Outer; //Declare the Outer class > > class Outer::Inner1 { //Define the Inner1 class > int i1; > }; > > class Outer { //If this class is not defined in the same > compilation unit then it should result in an error because Inner1 is > defined as a nested class but the nesting class is undefined. > class Inner1; //If this is absent then it should result in compilation > error > class Inner2; > > Inner1 inner1; > Inner2 *inner2; > }; > > class Outer::Inner2 { > int i2; > }; > > This solution honours the C++ convention that the class must be defined > before creating an object of its type. This certainly improves readability. Why isn't the following solution sufficient? class Outer { class Inner1 { int i1; }; class Inner2; Inner1 inner1; Inner2 *inner2; }; class Outer::Inner2 { int i2; }; -- Lawrence Crowl -- --- 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/?hl=en. .