220 15647 article Path: news.gmane.org!not-for-mail From: "Arthur O'Dwyer" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: RFC: Adding Symmetry Between shared_ptr and weak_ptr Date: Tue, 13 Jan 2015 16:02:06 -0800 Lines: 107 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=089e0102f2123a34d2050c9173f6 X-Trace: ger.gmane.org 1421193732 31267 80.91.229.3 (14 Jan 2015 00:02:12 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 14 Jan 2015 00:02:12 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDLZJYWNDQIP7Y6WUUCRUBHGMDLNU@isocpp.org Wed Jan 14 01:02:08 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f69.google.com ([209.85.215.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YBBPU-0008VS-91 for gclcip-std-proposals@m.gmane.org; Wed, 14 Jan 2015 01:02:08 +0100 Original-Received: by mail-la0-f69.google.com with SMTP id gd6sf3215211lab.0 for ; Tue, 13 Jan 2015 16:02:07 -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:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=NwmhTZVkofIpBUCXl7D+BB00zL8AlQqBZOhO5uFuOAM=; b=aALJDB+iA+faQ4FadvSyZgU7VwsYJvBvouX09ZohGMSqroj0HgphgUCp8Mq7e0GrNp N7FULFNjf2eLfPpHqF7MYm2AZhYnNRD45yzcr8asVOt7Vk1H+NsViRSMsiAbblKruMgW NEA8LBkosGSHMufbuAxHL8n6rT5ikxl1ESOYLNuIW90L4HXvm2HueDBB5QRmb8CkYwk6 Ix/CmXp4CT4ZofJ+NQwtsTJTPdvzeRhXhTsZICdKtM68fnkiepFhQ3T8JoI75CW6FGQS 2tDzglc4X1wn/k7jKnW/OW1xJQ9mjgnieOo2HCbGQJwYg6A6XlkskG9BFG+T3dLgeJXC J/LQ== X-Gm-Message-State: ALoCoQn7gYKeNHMpeeOSNiIkYlnC0n5ni6aP/dPdiUQIhUFbCZZ1Ep6W599cMn7JkEQzJ9ifRnfU X-Received: by 10.152.37.193 with SMTP id a1mr118713lak.3.1421193727664; Tue, 13 Jan 2015 16:02:07 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.20.37 with SMTP id k5ls120152wie.40.gmail; Tue, 13 Jan 2015 16:02:06 -0800 (PST) X-Received: by 10.194.185.243 with SMTP id ff19mr1687140wjc.126.1421193726837; Tue, 13 Jan 2015 16:02:06 -0800 (PST) Original-Received: from mail-wg0-x22c.google.com (mail-wg0-x22c.google.com. [2a00:1450:400c:c00::22c]) by mx.google.com with ESMTPS id js4si44585093wjc.159.2015.01.13.16.02.06 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 13 Jan 2015 16:02:06 -0800 (PST) Received-SPF: pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c00::22c as permitted sender) client-ip=2a00:1450:400c:c00::22c; Original-Received: by mail-wg0-f44.google.com with SMTP id y19so5975156wgg.3 for ; Tue, 13 Jan 2015 16:02:06 -0800 (PST) X-Received: by 10.194.108.162 with SMTP id hl2mr1677377wjb.134.1421193726536; Tue, 13 Jan 2015 16:02:06 -0800 (PST) Original-Received: by 10.217.2.18 with HTTP; Tue, 13 Jan 2015 16:02:06 -0800 (PST) In-Reply-To: X-Original-Sender: arthur.j.odwyer@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c00::22c as permitted sender) smtp.mail=arthur.j.odwyer@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:15647 Archived-At: --089e0102f2123a34d2050c9173f6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Tue, Jan 13, 2015 at 3:24 PM, wrote: > On Saturday, January 10, 2015 at 2:01:54 PM UTC-5, Arthur O'Dwyer wrote: > >> I've got a rough draft of a proposal for the next meeting in May, and >> would like to hear anyone's feedback on the format and content before th= en. >> >> https://quuxplusone.github.io/draft/Nweak_ptr_proposal.html >> > > Just one minor quibble. I don't see the use case for the weak_ptr overload > that takes a pointer and a weak_ptr. The pointer should always be some > kind of sub-object of an object pointed to by a shared_ptr, such as a dat= a > member or container element. For you to have this pointer and know that = it > is still valid, you should still have access to the shared_ptr owning it. > Therefore, you should be able to construct your new weak_ptr from the > pointer and the shared_ptr. > I'm not convinced that your analysis is correct in all possible use-cases. (Maybe we only have a weak_ptr at this point in the program, and we don't wish to lock it unnecessarily, and for some reason we *can* compute the appropriate raw pointer without evaluating the weak_ptr.) However, you're right in that shared_ptr(weak_ptr const&, T*) doesn't exist, so I'm not adding any symmetry via this particular overload. I'm mulling it over. =E2=80=93Arthur --=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/. --089e0102f2123a34d2050c9173f6 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Tue, Jan 13, 2015 at 3:24 PM, <jgottman6@gmail.com<= /a>> wrote:=C2=A0
On Saturday, January 10, 2015 = at 2:01:54 PM UTC-5, Arthur O'Dwyer wrote:
=
I've got a rough draft of a proposal for the next= meeting in May, and would like to hear anyone's feedback on the format= and content before then.

https://quuxpl= usone.github.io/draft/Nweak_ptr_proposal.html
=
=C2=A0
Just one minor quibble.=C2=A0 I don't se= e the use case for the weak_ptr overload that takes a pointer and a weak_pt= r.=C2=A0 The pointer should always be some kind of sub-object of an object = pointed to by a shared_ptr, such as a data member or container element.=C2= =A0 For you to have this pointer and know that it is still valid, you shoul= d still have access to the shared_ptr owning it.=C2=A0 Therefore, you shoul= d be able to construct your new weak_ptr from the pointer and the shared_pt= r.

I'm not convinced that your an= alysis is correct in all possible use-cases. (Maybe we only have a weak_ptr= at this point in the program, and we don't wish to lock it unnecessari= ly, and for some reason we *can* compute the appropriate raw pointer withou= t evaluating the weak_ptr.)

However, you're ri= ght in that shared_ptr(weak_ptr<Y>= ; const&, T*) doesn't exist, so I'm not adding any symme= try via this particular overload. I'm mulling it over.

=E2=80=93Arthur

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