220 11785 <3EF9F5C2-EF9D-4DC5-9F53-82CA1155D4DF@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: N4078: Rvalue reference overloads for value() method returns object by value Date: Thu, 10 Jul 2014 14:22:42 +0800 Lines: 86 Approved: news@gmane.org Message-ID: <3EF9F5C2-EF9D-4DC5-9F53-82CA1155D4DF@gmail.com> References: <4DA018C3-2327-4F55-B7F8-7988EC7B789A@gmail.com> <1a858a77-310b-4591-aaf5-960c40d9f5fc@isocpp.org> <66AF41C1-CB37-4311-98EA-D47DBC6068DC@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_624E72F2-A725-4634-BC33-269A15A4996B" X-Trace: ger.gmane.org 1404973377 27320 80.91.229.3 (10 Jul 2014 06:22:57 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 10 Jul 2014 06:22:57 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBNXC7COQKGQE6Q4HQ2A@isocpp.org Thu Jul 10 08:22:49 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qc0-f200.google.com ([209.85.216.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1X57km-0003OD-5Y for gclcip-std-proposals@m.gmane.org; Thu, 10 Jul 2014 08:22:48 +0200 Original-Received: by mail-qc0-f200.google.com with SMTP id x13sf1796880qcv.7 for ; Wed, 09 Jul 2014 23:22:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:message-id:mime-version:subject:date :references:to: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=6j2y9QxNCktLP79Fl592QNrdUeOlTm0Hlk5rUHluv3M=; b=AU5e0XKb3Zb5fFLiMCNWuOIA2AZVdglF4SwMPyr0GxOl0/G5KkyEDohrbJrV2rjSB3 BH0Ivz2FT5UgGtHYc58p1DQeh+GzxO6tZYXHCJI3pJ8MJwSanhLwM95SWskU85/lWmXj QVMnovxyPa8lpXSWujRM9yiJ7ozs1GpeczTmz61Rg2AYJ3h/rTKLqHTPdgp+vbU+BoMr 5uJQMRa+W859vzizcq1bbABnqT7DsF9IJ9PbWI/U8rueux/NjQjcy7NHhbeyHUYujsqE bM+F7NFIuBzlWnLm1pucPy3LA2hiJLgDYZTXaJpkItOrucLxeDskFHwgzngzHOo02+bD Ozhw== X-Gm-Message-State: ALoCoQkfgSSosRnKieb5uWlROLK0w4+lOYTXb1qI4PMxUI1Hzi+pgahuHhnXGydzZX4s8enRsNs4 X-Received: by 10.236.204.38 with SMTP id g26mr19367817yho.43.1404973367101; Wed, 09 Jul 2014 23:22:47 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.117.7 with SMTP id ka7ls3735igb.32.gmail; Wed, 09 Jul 2014 23:22:46 -0700 (PDT) X-Received: by 10.43.133.201 with SMTP id hz9mr75130icc.95.1404973366461; Wed, 09 Jul 2014 23:22:46 -0700 (PDT) Original-Received: from mail-ig0-x22e.google.com (mail-ig0-x22e.google.com [2607:f8b0:4001:c05::22e]) by mx.google.com with ESMTPS id dy8si22872061icc.71.2014.07.09.23.22.46 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 09 Jul 2014 23:22:46 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:4001:c05::22e as permitted sender) client-ip=2607:f8b0:4001:c05::22e; Original-Received: by mail-ig0-f174.google.com with SMTP id c1so2728742igq.13 for ; Wed, 09 Jul 2014 23:22:46 -0700 (PDT) X-Received: by 10.50.126.7 with SMTP id mu7mr19471430igb.20.1404973366314; Wed, 09 Jul 2014 23:22:46 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.63]) by mx.google.com with ESMTPSA id jf5sm22409916igb.2.2014.07.09.23.22.44 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 09 Jul 2014 23:22:45 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.1878.6) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:4001:c05::22e as permitted sender) smtp.mail=potswa@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:11785 Archived-At: --Apple-Mail=_624E72F2-A725-4634-BC33-269A15A4996B Content-Type: text/plain; charset=ISO-8859-1 On 2014-07-10, at 2:17 PM, Ville Voutilainen wrote: >> Returning by rvalue reference may be tempting, but that is the semantic of >> move(). It does not transfer ownership, it only provides the caller with a >> handle to accept ownership. Returning an rvalue reference is something only >> special functions should do. > > I have no idea where this guideline popped out of. Which part? Name three functions that return an rvalue reference. There's move(), forward(), and ??? . >> Then perhaps we need more cases for copy elision. Sneaky rvalue reference >> hacks will only provide surprises and make user code more brittle. If there >> must be an rvalue reference overload, it should be named move_value() to >> indicate the different semantic. > > > That would be equally detrimental to users who want to forward. So, call it forward_value() with appropriate semantics. It's equally a bad idea to bind a named reference to move() or forward(). -- --- 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/. --Apple-Mail=_624E72F2-A725-4634-BC33-269A15A4996B Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
On 2014&= ndash;07–10, at 2:17 PM, Ville Voutilainen <ville.voutilainen@gmail.com> wrote:
Returning by rvalue r= eference may be tempting, but that is the semantic of
move(). It does no= t transfer ownership, it only provides the caller with a
handle to accep= t ownership. Returning an rvalue reference is something only
special fun= ctions should do.

I have no idea where this guideline p= opped out of.

Which part? Name th= ree functions that return an rvalue reference. There’s move(), forwar= d(), and ??? .

Then perhaps we need more cases for copy elision. Sneaky rvalue reference<= br>hacks will only provide surprises and make user code more brittle. If th= ere
must be an rvalue reference overload, it should be named move_value(= ) to
indicate the different semantic.


That would= be equally detrimental to users who want to forward.

So, call it forward_value() with appropriate semantics. It’s equally a bad idea to bind a nam= ed reference to move() or forward().

--

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