220 8368 <14C8EC03-2834-45DA-B6D1-64178D13A88F@gmail.com> article Path: news.gmane.org!not-for-mail From: Howard Hinnant Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Obtaining a non-const iterators from a const_iterator and a non-const reference to the container Date: Thu, 2 Jan 2014 10:51:11 -0500 Lines: 37 Approved: news@gmane.org Message-ID: <14C8EC03-2834-45DA-B6D1-64178D13A88F@gmail.com> References: <68deff4f-5f1d-440e-b6cd-1e5077a3ff96@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 6.6 \(1510\)) Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1388677880 26829 80.91.229.3 (2 Jan 2014 15:51:20 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 2 Jan 2014 15:51:20 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCK2HM4L6YERB44VS2LAKGQEYUJ3IYQ@isocpp.org Thu Jan 02 16:51:23 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yh0-f69.google.com ([209.85.213.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VykYG-0005fF-Ps for gclcip-std-proposals@m.gmane.org; Thu, 02 Jan 2014 16:51:17 +0100 Original-Received: by mail-yh0-f69.google.com with SMTP id a41sf17983799yho.4 for ; Thu, 02 Jan 2014 07:51:15 -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:subject:from:in-reply-to:date :message-id:references: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:content-transfer-encoding; bh=PvKzBNCjuEAquwZp+P6ISGqEnRawgIiShiEHGSETBK4=; b=lwFrGx/U0NHsAWOMdu/6banFlCZpVPOA72qbQarpmB417DQDi0wen1hT7guYrLDkl5 qQGYoECU+AIsGxxCS10p2bWwBxYM9dlyNXCcRvmMp0AIVdnr7tMClBfJEptYeBugsKfd SVVsAZP/XfOGGndcQy2frH3G5bb6PNLSZQ+N97wBdZfbGPcZQc2JiWawM+VJEjh0f/1F QfPcInURDrc22fQGu8EWPizNH0V4TfUuIeY4ls98FAkG5ZUM2rM8Upm2YpZLTWRwhN+O TXElltvqWdl+hKAzWmbHya920rUo7+riAmF2UHJsiRuRRtPZSJbAwg4Ubck6omEDJOd9 O9JQ== X-Gm-Message-State: ALoCoQmdQ1eZrgHgHQxFxMxbSxw2hLUhlmILurlh/wgnbR+8g5Ar2U3iOaVsNyxhTc2YrFeyX6mQ X-Received: by 10.58.54.97 with SMTP id i1mr1494976vep.40.1388677875730; Thu, 02 Jan 2014 07:51:15 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.60.37 with SMTP id e5ls4527743qer.84.gmail; Thu, 02 Jan 2014 07:51:15 -0800 (PST) X-Received: by 10.49.116.78 with SMTP id ju14mr141548107qeb.57.1388677875176; Thu, 02 Jan 2014 07:51:15 -0800 (PST) Original-Received: from mail-ig0-x232.google.com (mail-ig0-x232.google.com [2607:f8b0:4001:c05::232]) by mx.google.com with ESMTPS id hi9si24130108qcb.73.2014.01.02.07.51.15 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 02 Jan 2014 07:51:15 -0800 (PST) Received-SPF: pass (google.com: domain of howard.hinnant@gmail.com designates 2607:f8b0:4001:c05::232 as permitted sender) client-ip=2607:f8b0:4001:c05::232; Original-Received: by mail-ig0-f178.google.com with SMTP id ut6so33912178igb.5 for ; Thu, 02 Jan 2014 07:51:14 -0800 (PST) X-Received: by 10.42.227.195 with SMTP id jb3mr59633804icb.27.1388677874641; Thu, 02 Jan 2014 07:51:14 -0800 (PST) Original-Received: from [10.0.1.4] (cpe-24-59-186-27.twcny.res.rr.com. [24.59.186.27]) by mx.google.com with ESMTPSA id f5sm72203307igc.4.2014.01.02.07.51.13 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 02 Jan 2014 07:51:13 -0800 (PST) In-Reply-To: <68deff4f-5f1d-440e-b6cd-1e5077a3ff96@isocpp.org> X-Mailer: Apple Mail (2.1510) X-Original-Sender: howard.hinnant@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of howard.hinnant@gmail.com designates 2607:f8b0:4001:c05::232 as permitted sender) smtp.mail=howard.hinnant@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:8368 Archived-At: On Jan 1, 2014, at 11:19 PM, Xavi Gratal wrote: > Given a const_iterator ci to an element of a container c, it is already p= ossible to obtain a non-const iterator with: >=20 > auto i=3Dstd::advance(c.begin(),std::distance(c.cbegin(),ci); >=20 > However, this is extremely inefficient for non-random-access containers. = I would like to add some mechanism to the standard containers so that given= a non-const reference to the container and a const_iterator, it is possibl= e to obtain a non-const iterator in constant time. > This would be useful in a scenario where an algorithm takes a const refer= ence to a container and finds some interesting element inside, returning a = const_iterator to it. Then, as long as you have a non-const reference to th= e container, you should be able to modify the element you found. It is alre= ady possible to erase it using a const_iterator. >=20 > Is there any reason why such a facility doesn't exist for the standard co= ntainers? It does exist, and it is efficient: auto i =3D c.erase(ci, ci); Howard --=20 ---=20 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 e= mail 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-proposa= ls/. .