220 36411 article Path: news.gmane.org!.POSTED!not-for-mail From: Antony Polukhin Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Sub-objects and their copy ellision Date: Thu, 28 Dec 2017 11:02:32 +0300 Lines: 80 Approved: news@gmane.org Message-ID: References: <1c6eff77-d71f-4dd7-8c13-f609460a03f0@isocpp.org> <3ec0bd22-b228-4026-bb49-aec5102918c7@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="f403045e9f503551d0056161f054" X-Trace: blaine.gmane.org 1514448037 17248 195.159.176.226 (28 Dec 2017 08:00:37 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 28 Dec 2017 08:00:37 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDR7DZXHY4MRBGOKSLJAKGQETNIFHZI@isocpp.org Thu Dec 28 09:00:32 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f69.google.com ([209.85.215.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eUT7A-00049y-Ha for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id a80sor5234903lfb.15.2017.12.28.00.02.33 for (Google Transport Security); Thu, 28 Dec 2017 00:02:33 -0800 (PST) Received-SPF: pass (google.com: domain of antoshkka@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.25.202.83 with SMTP id h19mr6330762lfj.97.1514448153299; Thu, 28 Dec 2017 00:02:33 -0800 (PST) Original-Received: by 10.25.215.210 with HTTP; Thu, 28 Dec 2017 00:02:32 -0800 (PST) In-Reply-To: X-Original-Sender: antoshkka@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=WTggP5jc; spf=pass (google.com: domain of antoshkka@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=antoshkka@gmail.com; dmarc=pass (p=NONE sp=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-Spam-Checked-In-Group: std-proposals@isocpp.org 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:36411 Archived-At: --f403045e9f503551d0056161f054 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable 2017-12-27 1:33 GMT+03:00 David Krauss : > Hi Antony, > > This looks more like lifetime extension than copy elision. If the copy is > elided, then the complete object cannot be destroyed until the subobject > is. Quickly scanning through your =E2=80=9Cultimate=E2=80=9D paper, I don= =E2=80=99t see this issue > mentioned. > > Since C++98 we already have a rule for lifetime extension when using a > return value subobject to initialize a scoped reference. So, does this > feature not already exist with the syntax of declaring a reference? Also, > the behavior is required, not optional. > That's different. The paper is mostly about removing copy/move+destructor from the assembly or intermediate-representation. This does not extend the lifetime of the objects as you see them in C++ code. --=20 Best regards, Antony Polukhin --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/CAKqmYPbnrh-dDTA7HAGuGZkgphtPRr6AYCXtuTUWesEBzbC= UNQ%40mail.gmail.com. --f403045e9f503551d0056161f054 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

= 2017-12-27 1:33 GMT+03:00 David Krauss <potswa@gmail.com>:
Hi Antony,

This looks more like lifeti= me extension than copy elision. If the copy is elided, then the complete ob= ject cannot be destroyed until the subobject is. Quickly scanning through y= our =E2=80=9Cultimate=E2=80=9D paper, I don=E2=80=99t see this issue mentio= ned.

Since C++98 we already have a rule for lifeti= me extension when using a return value subobject to initialize a scoped ref= erence. So, does this feature not already exist with the syntax of declarin= g a reference? Also, the behavior is required, not optional.

That's different. The p= aper is mostly about removing copy/move+destructor from the assembly or int= ermediate-representation. This does not extend the lifetime of the objects = as you see them in C++ code.

--
Best regards,
Antony Polukhin

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