220 27916 <5c7c5507-698d-460c-bed2-88adb07ebc07@isocpp.org> 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 12:17:46 -0700 (PDT) Lines: 83 Approved: news@gmane.org Message-ID: <5c7c5507-698d-460c-bed2-88adb07ebc07@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_73_941638373.1472066266965" X-Trace: blaine.gmane.org 1472066274 31753 195.159.176.226 (24 Aug 2016 19:17:54 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 24 Aug 2016 19:17:54 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBXHF666QKGQEI6PRVEA@isocpp.org Wed Aug 24 21:17:50 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pa0-f69.google.com ([209.85.220.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bcdgK-0007dA-EP for gclcip-std-proposals@m.gmane.org; Wed, 24 Aug 2016 21:17:48 +0200 Original-Received: by mail-pa0-f69.google.com with SMTP id ag5sf42570235pad.2 for ; Wed, 24 Aug 2016 12:17:49 -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=NbLNcgcYGILmXLnnuuWeitjXaiD0Nl7wKSgnE/+XnD4=; b=C6sZZfBuwbC5SeI1/iMCg/Es8+rRH6HSSNbd4VCARsjnkyFf39hrIXnplUYJ2cJVW8 1/u6yFQFaaFsXNSp6wwcP35MB46PKIiEzDZNJJqgeKiBo8FakQu7RQZ8QTAulvdjz41V 4OsjFiZtZdEUyLDlVIT7kUNjgWwyZAYD/H0tQVbusafakn38mN0+ogdIlg7RwMf3nfKb vV/0kGNd5JeGNenUUTY3593xM4rIsFwUp35ApehHpNzbIrHRU0ADwpyelMUS5aszPVGb feyTrkB9K5kSmDEOaAIPtaTyFrvctZoV6rakhOjkFNxaoyNtpaqp3X6b8T39fRsqLSps bKFA== 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=NbLNcgcYGILmXLnnuuWeitjXaiD0Nl7wKSgnE/+XnD4=; b=xhs+2Nu1VVuAk+nfP+P4WLDDzIXjVBM+1wvpwEhJtBYHDRt8a4xflcQkzqwQABBc+V 9RRTom3m5WqYYneDsbwYqSdFX5AGRRbVFEc9A9dRXBeigO6Ycv+D6QyIYZWTvIOLsMd4 +XDHbjh0RuPWNlnCmigzMada4de7A8B6GfO60f2Ik7HTKezn5xO/vHVjPPbKNQOrJ4Dw LFAx4QNvATnlybbU1vVpi0CYqdFFtdelRN5vRgkEkx5PeQBkEfg840iWiDSmflubBnaS 0DaeVdBWTLVeIy9+XJO7QzpldiyrBazIm4jSsE8G6dNIFdmoYb/P4eDmkP6ACIS2g/PI iYrw== 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=NbLNcgcYGILmXLnnuuWeitjXaiD0Nl7wKSgnE/+XnD4=; b=e8BZ2j7tQ4ZEyHw3d7BVFxDBZB99/9qE5Vp4SlNFcJEI8w0YMom1n7Be4VOIu/eazk RyzG5fn9JIYgz655w5Zai/1qogVOkwt5yfwqXMIUdyDsFWDTWz9hCLMDTA5up1eHQFBk 4rpxtGfqXHGj/9cKqxsujoGJthREWah3GJ6C9xHEYTJlmz1Dd9MN/wT8s+WrYjwZk/yE rgC4okFRv5/ZUPIfRnRL2Lt4X+8JuDSTuHHhP9n6Q2H5mGu9yAQVDFCEboYnNpGvajyw sYvtHWBCNYQHLtu8t9QhQkSsu0W+PY9/ktdXjnTFY8hTOP6G5toGchpxjGmQVNPXiT/+ TXcg== X-Gm-Message-State: AE9vXwN/bYga0+0kdhg6hpvv0rtyfuG1JUgK0rVr3J/AuJempTEh+SXzKfKI0HxZVfARHQ== X-Received: by 10.98.20.196 with SMTP id 187mr3221619pfu.0.1472066268890; Wed, 24 Aug 2016 12:17:48 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.47.205 with SMTP id j196ls1272206itj.17.gmail; Wed, 24 Aug 2016 12:17:47 -0700 (PDT) X-Received: by 10.36.36.10 with SMTP id f10mr51023ita.7.1472066267966; Wed, 24 Aug 2016 12:17:47 -0700 (PDT) In-Reply-To: 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:27916 Archived-At: ------=_Part_73_941638373.1472066266965 Content-Type: multipart/alternative; boundary="----=_Part_74_110875447.1472066266965" ------=_Part_74_110875447.1472066266965 Content-Type: text/plain; charset=UTF-8 On Wednesday, August 24, 2016 at 3:10:04 PM UTC-4, Pablo Oliva wrote: > > I don't quite get why simply calling the normal destructor for the object > wouldn't achieve the optimization goals you pretend. > Because that would provoke UB. If you explicitly call the destructor for an automatic object, the system will still call the destructor at the end of scope. Unless you reconstructed the object in that memory beforehand, you will get UB. What you seem to be suggesting is that we can signal the complier that an > object should be destroyed as soon as possible. This seems to be more of a > quality of implementation issue on the compiler's side than something that > needs to be standardized. And it doesn't need a different destructor. > The destructor for a non-trivially destructible automatic object is called at the end of scope, and will be called in the reverse order of construction. As such, the side-effects *cannot* happen before the end of scope. So there's no QOI here; the standard does not permit a non-trivially destructible automatic object to be destroyed before the end of scope or out-of-order. -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/5c7c5507-698d-460c-bed2-88adb07ebc07%40isocpp.org. ------=_Part_74_110875447.1472066266965 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Wednesday, August 24, 2016 at 3:10:04 PM UTC-4, Pablo O= liva wrote:
I = don't quite get why simply calling the normal destructor for the object= wouldn't achieve the optimization goals you pretend.

Because that would provoke UB. If you explicitly call the destruc= tor for an automatic object, the system will still call the destructor at t= he end of scope. Unless you reconstructed the object in that memory beforeh= and, you will get UB.

What you seem to be suggesting is th= at we can signal the complier that an object should be destroyed as soon as= possible. This seems to be more of a quality of implementation issue on th= e compiler's side than something that needs to be standardized. And it = doesn't need a different destructor.

T= he destructor for a non-trivially destructible automatic object is called a= t the end of scope, and will be called in the reverse order of construction= .. As such, the side-effects cannot happen before the end of scope. S= o there's no QOI here; the standard does not permit a non-trivially des= tructible automatic object to be destroyed before the end of scope or out-o= f-order.

--
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/5c7c5507-698d-460c-bed2-88adb07ebc07= %40isocpp.org.
------=_Part_74_110875447.1472066266965-- ------=_Part_73_941638373.1472066266965-- .