220 26367 article Path: news.gmane.org!not-for-mail From: Farid Mehrabi Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Swapping with volatile lvalues Date: Tue, 21 Jun 2016 23:06:55 +0430 Lines: 171 Approved: news@gmane.org Message-ID: References: <81998cb5-722e-49a1-be98-7ca1e219b72a@isocpp.org> <9608d5c4-e60f-449e-9078-f27fed1f79fd@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=94eb2c06c64250b9b30535ce1db5 X-Trace: ger.gmane.org 1466534260 15125 80.91.229.3 (21 Jun 2016 18:37:40 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 21 Jun 2016 18:37:40 +0000 (UTC) To: std-proposals Original-X-From: std-proposals+bncBC27JR6ERAOBB34SU25QKGQE7QKUQIY@isocpp.org Tue Jun 21 20:37:39 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f70.google.com ([209.85.215.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bFQYK-0008TB-MF for gclcip-std-proposals@m.gmane.org; Tue, 21 Jun 2016 20:37:36 +0200 Original-Received: by mail-lf0-f70.google.com with SMTP id a2sf19536377lfe.0 for ; Tue, 21 Jun 2016 11:37:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :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=4l9fQ0N53L3JY+GXZjJGJLwRhBOwuly694FVvKwxsOM=; b=lH9bta7668pMOLwHxPiv7Js07to8f00pBIJfYn718pR1S3EXKERigccMfwmJBAhjYe 7s/IicDloPp+Uqog9ApOSYkxVpd1cqPxjHg3bz2x48xQFT5zCS9ug3oyKZKbfID0hFLD m6O5NPNVYZo2HR19RlIPwpqmi0zIxBWMGTEgNmUNfL4lEwmyUmnRAV6ipN/SOGM5MEVx xgLlFpzRphoS7EnmrnZBA29QGFA851PX75bw8Wf6UY07TI3TQBITdkxJrwsE/7zns51S KB+v4Vzv7dI9iKAkAq9hcfqsoR92ZdBjjPuCZML0Nw9jmaYQZm9QhxhBDpHrfFYd5M0G ms3w== 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:from:date :message-id:subject:to: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=4l9fQ0N53L3JY+GXZjJGJLwRhBOwuly694FVvKwxsOM=; b=UPKB6UqzGL1op6jQEsIOYE4okMGVXjcWgIW84VsgOsdNAqXwfiqH6ontQ4FwVIIucM s9KNoYA8r/PuqUqbCsdiyvm5NzNJZFUYWhOYqMmgd4Q/ICWq7uPcuVAlstsaHrGD6inh cdDRpgWzk2Q/GLCZi0MfEo3CflbZkw2jXAxgz30kPdzOEfhScHNxdD3jxscBoNKCm3Fa UjNhSc7IDdowxawyc9s1M8GJqbtj4v3j7Qdd23KnhacgtgBidf+rgXSo2WIsm84XEVOU Fg/Oh4+CxAt/bvoJthNamBojQ8VeDLzDzgjdRI8G6eVQEvzq4Q8GEtFOOADWQMNaLrje 00ng== X-Gm-Message-State: ALyK8tK7KpPvvG/dxYS4fVJMPv/E1kwavwDffDNaRhqBS/gGQasgQN/cT6zmcinvTu9lTw== X-Received: by 10.157.42.106 with SMTP id t97mr24896564ota.0.1466534256028; Tue, 21 Jun 2016 11:37:36 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.18.181 with SMTP id g50ls3984513otg.36.gmail; Tue, 21 Jun 2016 11:37:35 -0700 (PDT) X-Received: by 10.200.42.43 with SMTP id k40mr30894279qtk.98.1466534255092; Tue, 21 Jun 2016 11:37:35 -0700 (PDT) Original-Received: from mail-qk0-x229.google.com (mail-qk0-x229.google.com. [2607:f8b0:400d:c09::229]) by mx.google.com with ESMTPS id v65si1037569qkh.228.2016.06.21.11.37.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 Jun 2016 11:37:35 -0700 (PDT) Received-SPF: pass (google.com: domain of farid.mehrabi@gmail.com designates 2607:f8b0:400d:c09::229 as permitted sender) client-ip=2607:f8b0:400d:c09::229; Original-Received: by mail-qk0-x229.google.com with SMTP id t127so33610524qkf.1 for ; Tue, 21 Jun 2016 11:37:35 -0700 (PDT) X-Received: by 10.55.181.1 with SMTP id e1mr28937791qkf.99.1466534254916; Tue, 21 Jun 2016 11:37:34 -0700 (PDT) Original-Received: by 10.55.141.131 with HTTP; Tue, 21 Jun 2016 11:36:55 -0700 (PDT) In-Reply-To: X-Original-Sender: farid.mehrabi@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of farid.mehrabi@gmail.com designates 2607:f8b0:400d:c09::229 as permitted sender) smtp.mailfrom=farid.mehrabi@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-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:26367 Archived-At: --94eb2c06c64250b9b30535ce1db5 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Whenever I face volatile, the atomic bells start to ring in my ears. Should swapping a volatile object mean atomic exchange, for non-trivial types we might get in trouble, but for in-built integrals I would rather use std::atomic_exchange. Otherwise (if atomicity is not a concern), a cv-cast followed by conventional swap can do. regards, FM. 2016-06-21 14:48 GMT+04:30 Daniel Kr=C3=BCgler : > 2016-06-21 12:12 GMT+02:00 FrankHB1989 : > > Call of std::exchange can work, but it seems not so ideal. > > This is a misunderstanding of my possibly ambiguous response. I didn't > mean to use std::exchange, but instead I was trying to suggest that if > you were considering to reuse an existing name it should better be > exchange instead of swap. > > > The return type > > of std::exchange is template parameter type T, so when T is a volatile > type, > > lvalue-to-rvalue conversion would be performed, and there are likely mo= re > > side effects than needed. > > I also don't think using the volatile lvalue return value (which is not > the > > case for std::exchange) a good idea. Discarded-value expressions can > work in > > such cases, but is seems to be strange and too error-prone. So perhaps > the > > return type of the call should be void. > > Regarding with Swappable requriements and symmetry... how about > providing 2 > > overloading? > > I still feel uneasy about it, especially when trying to make a > consistent sense with your suggested overloads (even assuming that > both overloads would be provided) and the Swappable post-conditions. > But again, I haven't thought carefully through it. > > - Daniel > > -- > 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/CAGNvRgCYLyw= vtFSO65-NKpeycpT4cPnw0SjvQPhE_DRL98UO7g%40mail.gmail.com > . > --=20 how am I supposed to end the twisted road of your hair in such a dark night?? unless the candle of your face does shed some light upon my way!!! --=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/CALDL7dFth8B%3DXvDL4pAb_jy%3DQAKJ_J6VWs-8vMxnmsO= xz%3DR-DA%40mail.gmail.com. --94eb2c06c64250b9b30535ce1db5 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Whenever I face vo= latile, the atomic bells start to ring in my ears. Should swapping a volati= le object mean atomic exchange, for non-trivial types we might get in troub= le, but for in-built integrals I would rather use std::atomic_exchange.
Otherwise (if atomicity is not a = concern), a cv-cast followed by conventional swap can do.

regards,
FM.
=

= 2016-06-21 14:48 GMT+04:30 Daniel Kr=C3=BCgler <daniel.kruegler@gm= ail.com>:
2016-06-21 12:12 GMT+02:00 FrankHB1989 <frankhb1989@gmail.com>:
> Call of std::exchange can work, but it seems not so ideal.

This is a misunderstanding of my possibly ambiguous response. I didn= 't
mean to use std::exchange, but instead I was trying to suggest that if
you were considering to reuse an existing name it should better be
exchange instead of swap.

> The return type
> of std::exchange is template parameter type T, so when T is a volatile= type,
> lvalue-to-rvalue conversion would be performed, and there are likely m= ore
> side effects than needed.
> I also don't think using the volatile lvalue return value (which i= s not the
> case for std::exchange) a good idea. Discarded-value expressions can w= ork in
> such cases, but is seems to be strange and too error-prone. So perhaps= the
> return type of the call should be void.
> Regarding with Swappable requriements and symmetry... how about provid= ing 2
> overloading?

I still feel uneasy about it, especially when trying to make a
consistent sense with your suggested overloads (even assuming that
both overloads would be provided) and the Swappable post-conditions.
But again, I haven't thought carefully through it.

- Daniel

--
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-propo= sals+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/CAGNvRgCYLyw= vtFSO65-NKpeycpT4cPnw0SjvQPhE_DRL98UO7g%40mail.gmail.com.



--
how am I supposed to end the twisted road of=C2=A0 your= hair in such a dark night??
unless the candle of your face does shed so= me light upon my way!!!

--
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/CALDL7dFth8= B%3DXvDL4pAb_jy%3DQAKJ_J6VWs-8vMxnmsOxz%3DR-DA%40mail.gmail.com.
--94eb2c06c64250b9b30535ce1db5-- .