220 5121 article Path: news.gmane.org!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: constexpr data member Date: Wed, 19 Jun 2013 12:18:15 -0700 Lines: 48 Approved: news@gmane.org Message-ID: References: <300a19dd-8a82-4788-9802-45170480b30a@isocpp.org> <63d90b03-5605-476d-b40b-7ebcee0d3354@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 1371669497 29303 80.91.229.3 (19 Jun 2013 19:18:17 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 19 Jun 2013 19:18:17 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDVNBJG4YAIBB54HRCHAKGQEFVM4RRI@isocpp.org Wed Jun 19 21:18:17 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-gh0-f199.google.com ([209.85.160.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UpNtZ-0000FZ-4p for gclcip-std-proposals@m.gmane.org; Wed, 19 Jun 2013 21:18:17 +0200 Original-Received: by mail-gh0-f199.google.com with SMTP id g14sf4618745ghb.10 for ; Wed, 19 Jun 2013 12:18:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-beenthere: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:x-google-group-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=y41ncTwjQEjjVEeReqOUhm6ibBqzXNSQqEJq+lMQrX8=; b=n1wSsM56006dsRl9LP1+6zlsVeboOFVs444jcmJHzOKSS1aE5C0ftPiQHobkJAbuxd 1bUR7LSyRCEztM3h10M7RSEURd5g6OuOLFeAt/2h01U41A99NniH8xSXZmHbbbYP3sl4 M+DldXDcOndscEtFS/A3zN7C4m7q6EbEFc33AdWLetUMHpkmvSBgSSIyOOVTJ52fIvsv cYl6aQD3rMD4doR+Y2cTrUMDKl7derDPrtkQt7btPegLnPTdVHdKmLw0ZLSwgVbdrAZE Q8Rk3rSY5JNz7ZS0cWVPmkilY317pT/HiEjiApNevg+xDkpsuivpl3vTVjT8REva1GkN mcyw== X-Received: by 10.236.15.73 with SMTP id e49mr2314485yhe.15.1371669496307; Wed, 19 Jun 2013 12:18:16 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.88.99 with SMTP id bf3ls385306qeb.78.gmail; Wed, 19 Jun 2013 12:18:15 -0700 (PDT) X-Received: by 10.58.249.236 with SMTP id yx12mr1435163vec.25.1371669495701; Wed, 19 Jun 2013 12:18:15 -0700 (PDT) Original-Received: from mail-vc0-f182.google.com (mail-vc0-f182.google.com [209.85.220.182]) by mx.google.com with ESMTPS id tq4si6897383vdc.27.2013.06.19.12.18.15 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 19 Jun 2013 12:18:15 -0700 (PDT) Received-SPF: pass (google.com: domain of metafoo@gmail.com designates 209.85.220.182 as permitted sender) client-ip=209.85.220.182; Original-Received: by mail-vc0-f182.google.com with SMTP id id13so4145531vcb.13 for ; Wed, 19 Jun 2013 12:18:15 -0700 (PDT) X-Received: by 10.52.69.177 with SMTP id f17mr1221509vdu.48.1371669495311; Wed, 19 Jun 2013 12:18:15 -0700 (PDT) Original-Sender: metafoo@gmail.com Original-Received: by 10.58.206.110 with HTTP; Wed, 19 Jun 2013 12:18:15 -0700 (PDT) In-Reply-To: X-Original-Sender: richard@metafoo.co.uk X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of metafoo@gmail.com designates 209.85.220.182 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:5121 Archived-At: On Wed, Jun 19, 2013 at 11:43 AM, Zhihao Yuan wrote: > On Wed, Jun 19, 2013 at 1:06 PM, Jonathan Wakely wrote: >> Does it enable new features not currently available? No it would just save >> some typing. > > I mentioned we can allow it in local class. But yea, the major > physical difference is all about saving typing. C++ has a history of making one keyword imply another in various contexts. In my experience, it makes the language more complex, and harder to read and reason about. (For an example of that, try to summarize the rules on when a variable has external linkage.) >> Your proposal to change the meaning of constexpr on >> a member variable does not imply anything about linkage, but makes the >> member static. That's inconsistent with *everything* else. > > I prefer not to be limited by the specific behaviors, but think > it like a designer. The design purpose of `constexpr` is to > define *real* constant, which has no storage. constexpr is not limited to that purpose. It is also used to require static initialization for a constant variable, for instance, and it certainly doesn't prohibit taking the address of the variable, or binding a reference to it, or calling a member function on it, all of which require storage. >> Does it make the langue easier to teach? > > Yes! So that we can teach "constexpr variables are just constant, > don't spent your time on figuring out *what* exactly they are". If you need to say "don't try to understand this", that does not suggest it is easy to teach. Right now, we have a simple rule that class members are instance-specific if they are not 'static', and are not instance-specific if they are 'static'. Adding a 'constexpr' special case seems to make that rule more complex. -- --- 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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