220 28004 <997FEFE7601FB061.100935c7-c671-4405-9c66-74522255c54e@mail.outlook.com> article Path: news.gmane.org!.POSTED!not-for-mail From: jsphadetula@gmail.com 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: Sun, 28 Aug 2016 09:58:56 +0000 (UTC) Lines: 226 Approved: news@gmane.org Message-ID: <997FEFE7601FB061.100935c7-c671-4405-9c66-74522255c54e@mail.outlook.com> References: <16f4f27a-daf4-4eff-8408-73aadc99e0c5@isocpp.org> <52303ad8-6485-49e6-b797-da61d270627e@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_3662_706498864.1472378336052" X-Trace: blaine.gmane.org 1472378343 5270 195.159.176.226 (28 Aug 2016 09:59:03 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 28 Aug 2016 09:59:03 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCF6REN4VUERBYXLRK7AKGQENJRENQI@isocpp.org Sun Aug 28 11:58:58 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f69.google.com ([209.85.214.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bdwrh-0000yv-RX for gclcip-std-proposals@m.gmane.org; Sun, 28 Aug 2016 11:58:58 +0200 Original-Received: by mail-it0-f69.google.com with SMTP id x131sf69338950ite.0 for ; Sun, 28 Aug 2016 02:58:59 -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:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=kCdvc2DyQ+KoZ0cYV1wHuuzgG1QMtB2EO6F5Ma08gpg=; b=q283beTGpz9GPMwCP7jBonhVl2CTFuSJSEK4Nr0NsYUwBD0QXTDu5wCiakIB1QwTNU 58SC09wAYYCQ3E6UvnhyZxYmWuiagzEUOGIZogx9xaeMY/gQmnyrpbevwF/jEIIRvCde YhpJyFYw57/8XVMGaISExi6shyX2x5W4ufUpS5xVpXzbI7+R49LzGYyHEGPummLo0Hdt 7JFL1dCtvW48jkRPcGbklr34GVq4me4anDdz60XZoKXn7g0ieiKpLvPVS5YkXtiFiAEU xEP3dj+UKJeLbZ3iAbvHfNTtXSqtV6Mp1Qr6P38+UxhwTpNwOj9S5kn4x3j77aaUoCaL LV9A== 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 :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=kCdvc2DyQ+KoZ0cYV1wHuuzgG1QMtB2EO6F5Ma08gpg=; b=TDK4Ey0hYANQHAJGIjlmW5wEUrtBVY87B6ng3Fm46twBcCNcEJRT+QKy7+ReA0USFI fTgJ2ZN4JEKKG5FOkkuNQ1dcYD7Ozs/gaPDEfJd1uMxuzCkmT9L61iQv/oG8P/vKQAJS nvEDAbl7zkUl3rHe8N/WZNG6SkYJfj/Pgb0lVq+NmQN2wYhlni/JsKPFsuh9cTZrkdg8 /il6GugJlNGMYeco4jIiWdWZTTRohsreSuag7L+4bCb/Z03AyBeHHR24pziq8/vkbAKI Ji+m7heIk/MWceg16pbnlNSHRJ/5AboKRwyPknyygU8UZYMdyqv8FnH09KEBbRw9c7Ca yGNg== X-Gm-Message-State: AE9vXwNtMpYuxd5phjhARw3HtDAJFm/X3osixq5JTUq1+XzlbXmiDS22BsCS8OAgYc5/2w== X-Received: by 10.157.22.234 with SMTP id s39mr2035636ots.26.1472378338571; Sun, 28 Aug 2016 02:58:58 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.238.5 with SMTP id b5ls2876231iti.3.gmail; Sun, 28 Aug 2016 02:58:57 -0700 (PDT) X-Received: by 10.98.23.134 with SMTP id 128mr22066777pfx.96.1472378337859; Sun, 28 Aug 2016 02:58:57 -0700 (PDT) Original-Received: from mail-pa0-x22b.google.com (mail-pa0-x22b.google.com. [2607:f8b0:400e:c03::22b]) by mx.google.com with ESMTPS id x184si32544182pfb.210.2016.08.28.02.58.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Aug 2016 02:58:57 -0700 (PDT) Received-SPF: pass (google.com: domain of jsphadetula@gmail.com designates 2607:f8b0:400e:c03::22b as permitted sender) client-ip=2607:f8b0:400e:c03::22b; Original-Received: by mail-pa0-x22b.google.com with SMTP id cy9so19381015pac.0 for ; Sun, 28 Aug 2016 02:58:57 -0700 (PDT) X-Received: by 10.66.134.165 with SMTP id pl5mr154166pab.98.1472378337530; Sun, 28 Aug 2016 02:58:57 -0700 (PDT) Original-Received: from mail.outlook.com (ec2-50-112-144-222.us-west-2.compute.amazonaws.com. [50.112.144.222]) by smtp.gmail.com with ESMTPSA id n13sm40995337pfj.16.2016.08.28.02.58.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Aug 2016 02:58:56 -0700 (PDT) In-Reply-To: X-Mailer: Outlook for iOS and Android X-Original-Sender: jsphadetula@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of jsphadetula@gmail.com designates 2607:f8b0:400e:c03::22b as permitted sender) smtp.mailfrom=jsphadetula@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:28004 Archived-At: ------=_Part_3662_706498864.1472378336052 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable varName; what if =C2=A0is explicitly applied on the intended last use o= f varName after which any reference to varName will be treated as compile t= ime error=20 in summary make =C2=A0end the scope of varName even before the= end of the current scope Get Outlook for Android On Sun, Aug 28, 2016 at 9:06 AM +0100, "D. B." wrote: On Sat, Aug 27, 2016 at 11:48 PM, Nicol Bolas wrote: Hmm. At first, I didn't like the idea of it being merely a hint to the opti= mizer. When a destructor gets called is an observable side-effect for any c= ode where we would care to use such a thing. So it should be something you = could rely on. After thinking about it for a bit however, making it a hint does solve a nu= mber of issues. Heh, I thought I was just inferring what you meant, but instead I came up w= ith a new idea. That was unexpectedly useful! The rest of what you said is = a good (probably better than I could've written) outline of what I was thin= king. So thanks! Although: =C2=A0That said, I wonder how likely this is, given that by my understandin= g, we're far into GC territory. But as a non-binding hint to the compiler t= hat wouldn't affect semantics of well-formed programs, maybe it's not that = outlandish at all... we have several of those already. But it would affect the semantics of well-formed programs. See my tuple exa= mple above; if `T t` had been annotated with the attribute, then it would m= ake use of `tpl` without the use of `t` undefined behavior. That's part of = the promise you make when you use [[eager-destruct]] or whatever we call it= .. It's no different from [[noreturn]] in that regard; if such a function ever= actually returns, you provoke UB. Not sure if this was an imprecise choice of words on my part. But what I re= ally meant was precisely what you said: the new behaviour could not suddenly wreck any current, working, compliant = programs - since it'd be an opt-in attribute, and if one deliberately added said attribute but also stashed a reference to an= object for which it was declared they would not, the program might compile= , but it's on the programmer's head if=C2=A0 the optimisation process bites= them, as doing so would be UB. --=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/CACGiwhF_PGSqbfROx5tvxDBj0nsTpao3kOKqSGzpsKmTDwT= jTQ%40mail.gmail.com. --=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/997FEFE7601FB061.100935c7-c671-4405-9c66-7452225= 5c54e%40mail.outlook.com. ------=_Part_3662_706498864.1472378336052 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


<some_syntax> varName;

what if <some_syntax> is explicitly applied on t= he intended last use of varName after which any reference to varName will b= e treated as compile time error

in summary make <some_syntax> end the scope of v= arName even before the end of the current scope

Get Outlook for Android




On Sun, Aug 28, 2016 at 9:06 AM +0100, "D. B." <= span dir=3D"ltr"><= db0451@gmail.com> wrote:

On S= at, Aug 27, 2016 at 11:48 PM, Nicol Bolas <jmckesson@gmail.com> wrote:

Hmm. At first, I didn't like the idea of it being mer= ely a hint to the optimizer. When a destructor gets called is an observable= side-effect for any code where we would care to use such a thing. So it sh= ould be something you could rely on.

After thinking about it for a b= it however, making it a hint does solve a number of issues.
=

Heh, I thought I was just inferring what y= ou meant, but instead I came up with a new idea. That was unexpectedly usef= ul! The rest of what you said is a good (probably better than I could've wr= itten) outline of what I was thinking. So thanks! Although:

 
T= hat said, I wonder how likely this is, given that by my understanding, we'r= e far into GC territory. But as a non-binding hint to the compiler that wou= ldn't affect semantics of well-formed programs, maybe it's not that outland= ish at all... we have several of those already.

But it would affect the semantics of well-formed programs. See m= y tuple example above; if `T t` had been annotated with the attribute, then= it would make use of `tpl` without the use of `t` undefined behavior. That= 's part of the promise you make when you use [[eager-destruct]] or whatever= we call it.

It's no different from [[noreturn]] in that regard; if = such a function ever actually returns, you provoke UB.

Not sure if this was an imprecise choice of words = on my part. But what I really meant was precisely what you said:
    the new behaviour could not suddenly wreck any current, working, co= mpliant programs - since it'd be an opt-in attribute, and
    =
  • if one deliberately added said attribute but also stashed a refe= rence to an object for which it was declared they would not, the program mi= ght compile, but it's on the programmer's head if  the optimisation pr= ocess bites them, as doing so would be UB.


=

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