220 27918 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Specifier to cause the destructor to be called at last use instead of end of scope Date: Wed, 24 Aug 2016 12:21:23 -0700 (PDT) Lines: 117 Approved: news@gmane.org Message-ID: References: <466EEE26-C7BA-4CD7-A8A5-B86EB179D8F3@googlemail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_660_328973787.1472066483544" X-Trace: blaine.gmane.org 1472066490 4520 195.159.176.226 (24 Aug 2016 19:21:30 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 24 Aug 2016 19:21:30 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBNHH666QKGQE6L3GWZY@isocpp.org Wed Aug 24 21:21:26 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f197.google.com ([209.85.217.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bcdjo-0000k8-Qj for gclcip-std-proposals@m.gmane.org; Wed, 24 Aug 2016 21:21:24 +0200 Original-Received: by mail-ua0-f197.google.com with SMTP id m60sf50778926uam.3 for ; Wed, 24 Aug 2016 12:21:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=RTr5BE0c/B6hBSaQFKBd+9Rx3ZhzDHhxkldyzEsHk3c=; b=TS3VDEmJx9XEfVNDlzSlGgphTkuGsQu7U6VO8hnmWlMY4thVTZYLmFlq5U8S2Bd+TR wt6dwPijgTfY8Xc+KYTYo7kusZ2LhyuRDVmXW5CeZsloVxXFAT1iiXSBWuEcxP4cTTD+ R9BuCURdDG6df8XqPCbb6xOwsn8qNj5yGWmhTDNV4QQrVe51wbZLOClppejJyPow+vAV k8l6TZi6+GEClu3nqoF5/t9A7gRNBEoBzjrBNG3AKnXZhhDGRrRwe5b9MdbjMR1flSr1 cQbSznP9f6+x2jKv6KXEF8CcinLino9YfM9jI0vYVQGVfOrcrB1PYwViuxQC6oegPPoz nkyQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=RTr5BE0c/B6hBSaQFKBd+9Rx3ZhzDHhxkldyzEsHk3c=; b=AplQN8/MHeI0/Ht6mlIh9tppextCn5E+20o9YIzlsDRpCRneVfDuddhkfTfm8081IR Z98hy2wvsMQrYgp5Ta0dstQMOfWPKBSCSAwQtDhjIxeJHQuaKNv2fXJFmWLMBzN5lbqH Io6pTWF9iBGQ4HrBmV085D4oqH0zG2Qg2T2k1fp9ym9WrcHxzGljNg9HH6zpVkoV3ziG ubTLqlLk9sVlU9AszWakxOYaUO2+F/jVwp6D7IRmzTw99so6hrSKmnkzOZAvm2137fKY 00NJ12SeCr/IKpChLLJxveExu/WqIlTvkdt+pDrz9LqASXODvBl+1YoEA+WxiSWdZxVy QnYw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=RTr5BE0c/B6hBSaQFKBd+9Rx3ZhzDHhxkldyzEsHk3c=; b=DJezVJDmILgF1ETqnv7Jjib3UQxhHk9YlWq3PVILp34rA1Zc/o7u0m+ANqFuSwWqPE NHdLoZspdHlmpI2KKf7jvQvmzWTsvD9nQ8lvjfXdUpuE3R9cScChbJ/T2tyWpZ73Pzl7 yDTF6WPYossZOP5wPzpCtUiWvHOZItBm8o4aaY9/KbSYSRVLLl/45l+gdfunKr0ykbnL 9wg+hQ/BW40CrwhRD7czLvefWpwr8DF/el/3WaOfqFi0qkHlFKYuaOp/7RvR7bQ17ImJ Gvb7jjc4YM4/dGi422e07MF1GAWSOcFvlS0EBjCPbMSVYMCC5sN3oSvBEQRiZf2Ewx2e OAvw== X-Gm-Message-State: AE9vXwMTaqqOh/Dl5dJ87hWX6Q733PnrfBtxUhFDq2GRly3Y6UxvuYfU3E4OyllsEvOCMg== X-Received: by 10.13.234.205 with SMTP id t196mr3294391ywe.20.1472066485312; Wed, 24 Aug 2016 12:21:25 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.46.156 with SMTP id u28ls6039654iou.14.gmail; Wed, 24 Aug 2016 12:21:24 -0700 (PDT) X-Received: by 10.36.120.140 with SMTP id p134mr792635itc.10.1472066484442; Wed, 24 Aug 2016 12:21:24 -0700 (PDT) In-Reply-To: <466EEE26-C7BA-4CD7-A8A5-B86EB179D8F3@googlemail.com> X-Original-Sender: jmckesson@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:27918 Archived-At: ------=_Part_660_328973787.1472066483544 Content-Type: multipart/alternative; boundary="----=_Part_661_69617179.1472066483544" ------=_Part_661_69617179.1472066483544 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Wednesday, August 24, 2016 at 3:16:52 PM UTC-4, Bernd L=C3=B6rwald wrote= : > > > > Am 24.08.2016 um 21:01 schrieb Ville Voutilainen >:=20 > >=20 > >> Limiting the scope with extra braces or by putting the operations in a= =20 > >> subroutine also often isn't a desirable workaround. Note that compiler= s=20 > have=20 > >=20 > > ..because..?=20 > > It might sometimes be difficult to express the lifetimes as short as=20 > possible:=20 > > resource a; // begin minimum lifetime a=20 > resource b; // begin minimum lifetime b=20 > last_use (a); // end minimum lifetime a=20 > long_task (b);=20 > last_use (b); //end minimum lifetime b=20 > // end current lifetime b=20 > // end current lifetime a=20 > =20 > And how do you know that `b` isn't using `a`? That's the point of Ville's= =20 "Define 'last use'." question. You cannot just look at code and know that= =20 `a` is finished being used when the locally visible code stops using it. Destruction of automatic objects in the reverse order of their construction= =20 is a guarantee that the standard should not arbitrarily discard. --=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/a54b7cf2-6c83-48d5-aeb6-4c179cef1520%40isocpp.or= g. ------=_Part_661_69617179.1472066483544 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Wednesday, August 24, 2016 at 3:16:52 PM UTC-4, Bernd L= =C3=B6rwald wrote:

> Am 24.08.2016 um 21:01 schrieb Ville Voutilainen <ville.vo...@gmail.= com>:
>=20
>> Limiting the scope with extra braces or by putting the operati= ons in a
>> subroutine also often isn't a desirable workaround. Note t= hat compilers have
>=20
> ..because..?

It might sometimes be difficult to express the lifetimes as short as po= ssible:

=C2=A0 resource a; // begin minimum lifetime a
=C2=A0 resource b; // begin minimum lifetime b
=C2=A0 last_use (a); // end minimum lifetime a
=C2=A0 long_task (b);
=C2=A0 last_use (b); //end minimum lifetime b
=C2=A0 // end current lifetime b
=C2=A0 // end current lifetime a
=C2=A0=20

And how do you know that `b` isn't using `a`?= That's the point of=20 Ville's "Define 'last use'." question. You cannot jus= t look at code and=20 know that `a` is finished being used when the locally visible code stops us= ing it.

Destruction of automatic objects in the reverse order of the= ir construction is a guarantee that the standard should not arbitrarily dis= card.

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/a54b7cf2-6c83-48d5-aeb6-4c179cef1520= %40isocpp.org.
------=_Part_661_69617179.1472066483544-- ------=_Part_660_328973787.1472066483544-- .