220 14492 article Path: news.gmane.org!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Range-based if Date: Tue, 11 Nov 2014 16:34:21 -0500 Lines: 44 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=UTF-8 X-Trace: ger.gmane.org 1415741690 10051 80.91.229.3 (11 Nov 2014 21:34:50 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 11 Nov 2014 21:34:50 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCO5FYHBU4ERB3MBRKRQKGQEJRXFILI@isocpp.org Tue Nov 11 22:34:40 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ee0-f71.google.com ([74.125.83.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XoJ5D-00035m-3Z for gclcip-std-proposals@m.gmane.org; Tue, 11 Nov 2014 22:34:39 +0100 Original-Received: by mail-ee0-f71.google.com with SMTP id e51sf7334759eek.6 for ; Tue, 11 Nov 2014 13:34:38 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:user-agent:in-reply-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=v6aUXV9gCxAfX340eK/M6hsEvzLRi1GSuvDU5aaMXNE=; b=k4S2CNdQdX/mCdUhblo/JSVLoLGJWFj07WEvhLoOPaPMLi2RDaym75TP2qVHxUbqMY mpCW+gploE+0wdpJc5NGu8Qf+f0tMShWVVrGhTUB0uEFcZG4X81nvb8beDgxrmV2O78L W3MCmJDPaHFfNYDoUSLQMW5A10RwGh0RHCqpLB3OzGT4XGVOdwt2ad5wiWvOrCsrrU7E kvo8VRf2kjKk+RdAYCoUFJioma1h8aIG3XlItjDDUtq1bTf8LrJQpvALpjUupY8RutiN mxBPLth/Sv/OaDRxJn61tMnFfhKCbBOdDN4JI2JrGBZohgMcQyLMRWoPysuI5GVvE3kl 94QA== X-Gm-Message-State: ALoCoQn6vCwLn8ZyWLJ0sUHp4+Lty9s0xDgqG5dff6Aq0JYdaeejBbgXarKZO14JJKjD6hx283/C X-Received: by 10.152.27.38 with SMTP id q6mr1043954lag.5.1415741678717; Tue, 11 Nov 2014 13:34:38 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.29.135 with SMTP id k7ls543767lah.78.gmail; Tue, 11 Nov 2014 13:34:36 -0800 (PST) X-Received: by 10.152.115.131 with SMTP id jo3mr38360390lab.20.1415741676845; Tue, 11 Nov 2014 13:34:36 -0800 (PST) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id o3si32924862lag.29.2014.11.11.13.34.36 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 11 Nov 2014 13:34:36 -0800 (PST) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1XoJ58-00033q-N5 for std-proposals@isocpp.org; Tue, 11 Nov 2014 22:34:34 +0100 Original-Received: from cpe-67-240-43-113.nycap.res.rr.com ([67.240.43.113]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 11 Nov 2014 22:34:34 +0100 Original-Received: from mw_triad by cpe-67-240-43-113.nycap.res.rr.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 11 Nov 2014 22:34:34 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 35 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: cpe-67-240-43-113.nycap.res.rr.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 In-Reply-To: X-Original-Sender: mw_triad@users.sourceforge.net X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mail=gclcip-std-proposals@m.gmane.org 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:14492 Archived-At: On 2014-11-11 16:12, Brent Friedman wrote: > I've noted in our codebase that we lean heavily on the convenience of > range-based for even when it's not perhaps the best way to express an idea. > > //do something to the first item > for (auto& Item : range) > { > DoSomething(Item); > break; > } auto first_or_null(auto range) -> decltype(&range.begin()) { auto begin = range.begin(); auto end = range.end(); return (begin == end ? nullptr : &(*begin)); } if (auto item = first_or_null(range)) Basically you want that, right? :-) I'm not sure if that actually works, and it requires an additional dereference when you go to use 'item', but OTOH it wouldn't require a language change... That said, how often can you not write: if (!range.empty()) DoSomething(*range.begin()); ....? -- Matthew -- --- 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/. .