220 12799 <85BDB38C-F54A-43AA-9DF7-09AB26E4E65E@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Local variables that overstay their welcome Date: Thu, 11 Sep 2014 09:35:57 +0800 Lines: 69 Approved: news@gmane.org Message-ID: <85BDB38C-F54A-43AA-9DF7-09AB26E4E65E@gmail.com> References: <778b6fbf-3b58-488c-9e51-32a05b95831e@isocpp.org> <94e564fc-f769-48d0-8a61-264f9c8f8480@isocpp.org> <66580c5b-0db4-4925-a4bd-9a5ef8f0c6c1@isocpp.org> <882aefbd-b21e-4ed3-8d08-f5cc8444f8ae@isocpp.org> 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=_9B72862E-3CA4-4C8C-9C67-3434E3CB700E" X-Trace: ger.gmane.org 1410399387 13847 80.91.229.3 (11 Sep 2014 01:36:27 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 11 Sep 2014 01:36:27 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBCXZYOQAKGQEBLO5EDA@isocpp.org Thu Sep 11 03:36:20 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pd0-f199.google.com ([209.85.192.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XRtIy-0006Zl-2E for gclcip-std-proposals@m.gmane.org; Thu, 11 Sep 2014 03:36:12 +0200 Original-Received: by mail-pd0-f199.google.com with SMTP id v10sf60896941pde.2 for ; Wed, 10 Sep 2014 18:36:10 -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=fgBSst88dQeh4NGJ2uvxRtqsG5x7kU0157J9+Dbfhz0=; b=JjtpfAq3GlAl85OaMTWtZGMMd41yOEIjNULOAXaMnzfjmZfTTEBoq4zEJ+N+BGnSv3 c4zJdWZKiaXrLJaR7AbgicrauPDzlPWUUcf/9eJVyFeVD6Kp1vMeqM1tKwO3DNTeDJdE tjXOvCmXy+HwFk+Jq+TjP7NG3bW/iVI8ylTgRcPCZBoDZ/RmdxQN0kJyDiJq0gO9ZNLz RvJ5HhnpAxFLCZH14w32bwLW1rCcpPI2AfPClV8ufhcZ2rd2Vwrilc9LUAW7HO1PgYQh U7IXYmhK8jDL6X70o3FfHcBBiRvokYvD/J2ELZVNpPqxIz2Q0LCAyHpOXbRcfK1qFbYv IOlg== X-Gm-Message-State: ALoCoQn79kcxQapGFlG+P06a3juso6kX382C2jv1jkQoWwyRzPkcd7WWIDrGLfza1VrqKKFoZI5W X-Received: by 10.66.190.67 with SMTP id go3mr27880697pac.10.1410399370758; Wed, 10 Sep 2014 18:36:10 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.117.72 with SMTP id kc8ls3505484igb.37.canary; Wed, 10 Sep 2014 18:36:10 -0700 (PDT) X-Received: by 10.66.65.195 with SMTP id z3mr57419891pas.116.1410399370025; Wed, 10 Sep 2014 18:36:10 -0700 (PDT) Original-Received: from mail-pd0-x232.google.com (mail-pd0-x232.google.com [2607:f8b0:400e:c02::232]) by mx.google.com with ESMTPS id ns9si25289591pdb.221.2014.09.10.18.36.10 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 10 Sep 2014 18:36:10 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::232 as permitted sender) client-ip=2607:f8b0:400e:c02::232; Original-Received: by mail-pd0-f178.google.com with SMTP id p10so9247089pdj.23 for ; Wed, 10 Sep 2014 18:36:09 -0700 (PDT) X-Received: by 10.66.65.133 with SMTP id x5mr68675405pas.26.1410399369902; Wed, 10 Sep 2014 18:36:09 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.59]) by mx.google.com with ESMTPSA id hp1sm15606024pbb.77.2014.09.10.18.36.08 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 10 Sep 2014 18:36:09 -0700 (PDT) In-Reply-To: <882aefbd-b21e-4ed3-8d08-f5cc8444f8ae@isocpp.org> 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:f8b0:400e:c02::232 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:12799 Archived-At: --Apple-Mail=_9B72862E-3CA4-4C8C-9C67-3434E3CB700E Content-Type: text/plain; charset=ISO-8859-1 On 2014-09-11, at 9:09 AM, Chet wrote: > Adding a "disengage and move from" method to optional is good idea. It would probably be best if the idiom for moving from an optional would disengage it, so that would be the default. Food for thought. It would be doable with an rvalue-qualified conversion function, but it would have to return by (pr)value. Returning an xvalue wouldn't give it a chance to destroy the contained object after entering the disengaged state. Alternately, std::move() could be overloaded for optional, and return a proxy object which converts to an xvalue and enters the disengaged state upon (temporary proxy) destruction. But that's dirty enough to have undesirable side-effects. -- --- 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. 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On 2014&= ndash;09–11, at 9:09 AM, Chet <chet.skolos@gmail.com> wrote:

Adding a "disengage and move from" method to optional is good ide= a.

It would probably be best i= f the idiom for moving from an optional would disengage it, so that would b= e the default.

Food for thought. 
<= br>
It would be doable with an rvalue-qualified conversion f= unction, but it would have to return by (pr)value. Returning an xvalue woul= dn’t give it a chance to destroy the contained object after entering = the disengaged state.

Alternately, std::move() cou= ld be overloaded for optional, and return a proxy object which converts to = an xvalue and enters the disengaged state upon (temporary proxy) destructio= n. But that’s dirty enough to have undesirable side-effects.

--

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