220 14516 article Path: news.gmane.org!not-for-mail From: Brent Friedman Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Range-based if Date: Wed, 12 Nov 2014 20:31:35 -0600 Lines: 110 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: multipart/alternative; boundary=001a11352dfcaa83040507b44ffd X-Trace: ger.gmane.org 1415845904 11965 80.91.229.3 (13 Nov 2014 02:31:44 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 13 Nov 2014 02:31:44 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCHLPXGUXMJBBB5QSCRQKGQEQJ374VI@isocpp.org Thu Nov 13 03:31:38 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f72.google.com ([209.85.218.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XokC9-0001qK-4x for gclcip-std-proposals@m.gmane.org; Thu, 13 Nov 2014 03:31:37 +0100 Original-Received: by mail-oi0-f72.google.com with SMTP id u20sf59593921oif.11 for ; Wed, 12 Nov 2014 18:31:36 -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=JM2VKKzi4+pSrvwI9g+hVN+PjT/IR8vda9XNieIvA+w=; b=fl9BFXBMgSr4Gy8zepWLG5DJQ49wdeOubrpIGLGZue6YR7YHWCQlxBIAqoObFN/ppj fQk6AeKKY2nXyjKwAedovhjTh5xCeJE03jtkk+KsL4vKvfNjT4WVgjf1M//6a/tag6Vw czYGSdOJ0nvCAr8PeGNM/i2OZ9MUGbUO/+Kk5yDfx7K8o9ijc4qispmmHCHD2jJsRHcL PtpQYh9GYGmaazDGq7JvUOtQk1NmM3lcp0FzT2vs2u6cjWMNgnd7vJfnj2pE5uP9qpp9 +PMEV5GLlyMO8lziTLT5hSe0K8JqyES3mYthNkRRmgzUdj/ctm8mNlXQunPG4jg9Y6pP YR+A== X-Gm-Message-State: ALoCoQkvzIqmaNbL39X9Fc5iBvXAsdYjaAvlxtV8YJ8MnwYgIwntDsbSOf96oxXzsW6xpn0RkA7k X-Received: by 10.182.128.71 with SMTP id nm7mr41689860obb.22.1415845896475; Wed, 12 Nov 2014 18:31:36 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.106.13 with SMTP id gq13ls1155858obb.27.gmail; Wed, 12 Nov 2014 18:31:35 -0800 (PST) X-Received: by 10.60.94.73 with SMTP id da9mr41980923oeb.10.1415845895753; Wed, 12 Nov 2014 18:31:35 -0800 (PST) Original-Received: from mail-oi0-x22a.google.com (mail-oi0-x22a.google.com. [2607:f8b0:4003:c06::22a]) by mx.google.com with ESMTPS id e2si500376oia.140.2014.11.12.18.31.35 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 12 Nov 2014 18:31:35 -0800 (PST) Received-SPF: pass (google.com: domain of fourthgeek@gmail.com designates 2607:f8b0:4003:c06::22a as permitted sender) client-ip=2607:f8b0:4003:c06::22a; Original-Received: by mail-oi0-f42.google.com with SMTP id v63so459483oia.1 for ; Wed, 12 Nov 2014 18:31:35 -0800 (PST) X-Received: by 10.202.197.199 with SMTP id v190mr39542687oif.2.1415845895630; Wed, 12 Nov 2014 18:31:35 -0800 (PST) Original-Received: by 10.202.232.77 with HTTP; Wed, 12 Nov 2014 18:31:35 -0800 (PST) In-Reply-To: X-Original-Sender: fourthgeek@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of fourthgeek@gmail.com designates 2607:f8b0:4003:c06::22a as permitted sender) smtp.mail=fourthgeek@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:14516 Archived-At: --001a11352dfcaa83040507b44ffd Content-Type: text/plain; charset=UTF-8 > It doesn't assume that the iterators are pointers, if that's what you mean. It assumes that it is possible to convert from nullptr_t to decltype(&range.begin()). It also assumes that this value constructed from nullptr necessarily represents an invalid value (converts to false) for that iterator type. On Wed, Nov 12, 2014 at 7:43 PM, Benjamin Lindley wrote: > > > On Tuesday, November 11, 2014 8:39:34 PM UTC-6, Brent Friedman wrote: >> >> > auto first_or_null(auto range) -> decltype(&range.begin()) >> >> This assumes pointers, which while addressing some use cases it isn't >> sufficient for the general case. >> >> > What case does it not handle? And what exactly do you mean by "This > assumes pointers"? It doesn't assume that the iterators are pointers, if > that's what you mean. > > -- > > --- > 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/. > -- --- 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/. --001a11352dfcaa83040507b44ffd Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
>=C2=A0It doesn't assume that the iterators are pointers, if that&= #39;s what you mean.
It assumes that it is possible to convert from nullptr_t t= o=C2=A0d= ecltype(&range.begin()). It also assumes that this value constructed fr= om nullptr necessarily represents an invalid value (converts to false) for = that iterator type.

On Wed, Nov 12, 2014 at 7:43 PM, Benjamin Lindley <benjameslindley@gmail.com> wrote:


On Tuesday, Novembe= r 11, 2014 8:39:34 PM UTC-6, Brent Friedman wrote:
>=C2=A0auto first_or_null(auto range) -> decltype(&a= mp;range.begin())

This assumes pointers, which wh= ile addressing some use cases it isn't sufficient for the general case.=


What case does it n= ot handle? And what exactly do you mean by "This assumes pointers"= ;? It doesn't assume that the iterators are pointers, if that's wha= t you mean.

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