220 10604 <20140510164133.GA7642@sara.home> article Path: news.gmane.org!not-for-mail From: Magnus Fromreide Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Forward declaring names Date: Sat, 10 May 2014 18:41:34 +0200 Lines: 59 Approved: news@gmane.org Message-ID: <20140510164133.GA7642@sara.home> References: <20140509221552.GA32099@sara.home> 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 1399740108 17452 80.91.229.3 (10 May 2014 16:41:48 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 10 May 2014 16:41:48 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDELLREETMBRBQFNXGNQKGQEV5OKGXQ@isocpp.org Sat May 10 18:41:41 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f71.google.com ([209.85.215.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WjALB-0002eH-Sj for gclcip-std-proposals@m.gmane.org; Sat, 10 May 2014 18:41:37 +0200 Original-Received: by mail-la0-f71.google.com with SMTP id mc6sf521077lab.6 for ; Sat, 10 May 2014 09:41:37 -0700 (PDT) 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:subject:message-id:mail-followup-to :references:mime-version:in-reply-to:user-agent: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:content-disposition; bh=qxftd4XQFR69YQzRiRT6WDtVlSlKhGudecJyUjtofSA=; b=knFQ3CQdhpEPKLBu3nBGeKKRfByMGO5BUH05In3wZq2XkFgEd+MCU/cGFvuZFTN0Yd WokAZ/JPIaQ9mWU+8B2yq4Uk9MDF/YOJL0ZZ3BZZoLfQsFcH/EjbIm3dj9pY+X4EMJM+ mZXzeNFz6wuZxjAFe91cRqWUpe3yQ6RMLrXQM72+6W0ypiRmYkZf7OHtJLZLA2HROGBu eeS432EEVVsHxz3MwX9dTutiB0qZtA5bEz1c5CqszQfzYYupbJOWbsyIQjwZ/tHCTXlo OizE+hPpq4hMqZqvhBxIOLCnwauxnu/4snEzSUieZJUqMnF4oh3A1g8yZqvvHgzrDM+X X-Gm-Message-State: ALoCoQmdOr6ZEZAD8qNf3GbuP/ZMkbUGLldJJaMS4LJ6FBBqoQZjL/uNn57VSYhYimRDMpz/8CVI X-Received: by 10.152.170.130 with SMTP id am2mr189976lac.8.1399740097414; Sat, 10 May 2014 09:41:37 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.23.41 with SMTP id j9ls78019laf.34.gmail; Sat, 10 May 2014 09:41:36 -0700 (PDT) X-Received: by 10.112.40.101 with SMTP id w5mr5023434lbk.19.1399740096333; Sat, 10 May 2014 09:41:36 -0700 (PDT) Original-Received: from mail.lysator.liu.se (mail.lysator.liu.se. [2001:6b0:17:f0a0::3]) by mx.google.com with ESMTPS id ds6si3328272lbc.222.2014.05.10.09.41.36 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Sat, 10 May 2014 09:41:36 -0700 (PDT) Received-SPF: pass (google.com: domain of magfr@lysator.liu.se designates 2001:6b0:17:f0a0::3 as permitted sender) client-ip=2001:6b0:17:f0a0::3; Original-Received: from mail.lysator.liu.se (localhost [127.0.0.1]) by mail.lysator.liu.se (Postfix) with ESMTP id DAC2540008 for ; Sat, 10 May 2014 18:41:35 +0200 (CEST) Original-Received: from sara.home (h-176-10-249-241.na.cust.bahnhof.se [176.10.249.241]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by mail.lysator.liu.se (Postfix) with ESMTPSA id C296D40003 for ; Sat, 10 May 2014 18:41:35 +0200 (CEST) Mail-Followup-To: std-proposals@isocpp.org In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-Virus-Scanned: ClamAV using ClamSMTP X-Original-Sender: magfr@lysator.liu.se X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of magfr@lysator.liu.se designates 2001:6b0:17:f0a0::3 as permitted sender) smtp.mail=magfr@lysator.liu.se 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: , Content-Disposition: inline Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:10604 Archived-At: On Sat, May 10, 2014 at 01:41:59PM +0800, David Krauss wrote: > > On 2014-05-10, at 6:15 AM, Magnus Fromreide wrote: > > > The strong typedef should introduce a new type and place it in the same > > namespace as class-names. > > Is your intent to "bite off" a piece of the strong typedef proposal and > implement it in anticipation of a more complete feature? Not really - I was edging for the ability to forward declare the strong typedef and n3741 explicitly forbids that. > > So the proposal is something along the lines of > > > > // Declare two types, say nothing of what they contain > > > > strong typedef aType; > > strong typedef aClass; > > > > // Actually define the types > > > > strong typedef int aType; // possibly allow ommitting strong here? > > class aClass { }; > > I don't think transforming a typedef-name to a class-name should be allowed; > you would need > > strong typedef class aClass_class { > ... > } aClass; Fair enough. > I suspect your problem may be solved with metaprogramming, namely a > template alias mapping from a set of tag classes ("strong typedef-names") > to a set of mapped types (which may or may not be classes) via a set of > explicit specializations ("strong typedef declarations"). If that's too > much, simply organizing the forward declarations might do. I also suspect that it could be done using template metaprogramming but that have a tendency to end up beeing more complex than the original problem. What I wanted to solve was to make it possible to say that 'aType' refers to a type, but it is not yet specified which type it is. I suppose this one could go in as an extension of n3741 but then the problem is that the proposed syntax of n3741 prevents forward declaration of typedefs. /MF -- --- 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/. .