220 18015 <53EE4B7E-4B59-4464-B02B-57DEE89A86A1@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: First draft: Non-copyable call wrapper, std::unique_function Date: Wed, 20 May 2015 09:53:42 +0800 Lines: 109 Approved: news@gmane.org Message-ID: <53EE4B7E-4B59-4464-B02B-57DEE89A86A1@gmail.com> References: <59ED9069-2650-44E2-B00E-0E56ED37B83D@gmail.com> <27a788e7-4912-4a58-8201-79138ddf15a3@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_9AA3278A-698B-488F-BA75-CF628664B6CA" X-Trace: ger.gmane.org 1432086834 26836 80.91.229.3 (20 May 2015 01:53:54 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 20 May 2015 01:53:54 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBL6S56VAKGQE5XYXUVY@isocpp.org Wed May 20 03:53:53 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f199.google.com ([209.85.214.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YutCj-00076y-CA for gclcip-std-proposals@m.gmane.org; Wed, 20 May 2015 03:53:53 +0200 Original-Received: by obbkp3 with SMTP id kp3sf47813858obb.0 for ; Tue, 19 May 2015 18:53:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:content-type:message-id:mime-version :subject:date:references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=3aKX4eVcES2lczdq3dvyPIf/5ya3cDu4eZ8iwAl7GEk=; b=Ssvzb4owOpsMCRJCu1Q+RYD8/ypJPbhYCJYQV/ggyyN7U8eMtpsOmlmrYYukNGEoIZ YVwNRkaWkiUYlyEXP3luJTJQ85Q5nX2WvNNl8S74BWffGwQd0skKm/jEJVzbmXp7TEQl DYsShseHH9uEqlF2XZaEtYqp+SSQub7wSzNlZvlEUWnriYnT5v5I9o06MZQ2GHfvlob2 pvK2vN9LFG9offofKJllGLtB2i3rgKsRxc8UdidYQiJfQRi00ojfwVUQqLcEAfFARcTy /QuSFFe4v7mkozkUrRzo2CbtDZbwXaEFyBdYlDjfufhW/J+UWodoOk//TigipDJFY1/7 sDvA== X-Gm-Message-State: ALoCoQlbKOPxvX355LQrI1kgnEOm4bICJ0YMuubj9y/KYlHsvdrBcMKP9zMEGvyugvCmPqxSeM5F X-Received: by 10.50.128.231 with SMTP id nr7mr29303335igb.11.1432086832197; Tue, 19 May 2015 18:53:52 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.18.39 with SMTP id t7ls248713obd.85.gmail; Tue, 19 May 2015 18:53:51 -0700 (PDT) X-Received: by 10.60.175.72 with SMTP id by8mr27240802oec.35.1432086831355; Tue, 19 May 2015 18:53:51 -0700 (PDT) Original-Received: from mail-oi0-x22a.google.com (mail-oi0-x22a.google.com. [2607:f8b0:4003:c06::22a]) by mx.google.com with ESMTPS id gu7si9680983obb.95.2015.05.19.18.53.51 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 19 May 2015 18:53:51 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:4003:c06::22a as permitted sender) client-ip=2607:f8b0:4003:c06::22a; Original-Received: by oihb9 with SMTP id b9so25236377oih.3 for ; Tue, 19 May 2015 18:53:51 -0700 (PDT) X-Received: by 10.202.220.135 with SMTP id t129mr17665494oig.115.1432086830825; Tue, 19 May 2015 18:53:50 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.44.91]) by mx.google.com with ESMTPSA id y19sm9296312oie.13.2015.05.19.18.53.47 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 19 May 2015 18:53:49 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.2098) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:4003:c06::22a as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@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:18015 Archived-At: --Apple-Mail=_9AA3278A-698B-488F-BA75-CF628664B6CA Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2015=E2=80=9305=E2=80=9320, at 1:52 AM, 'Matt Calabrese' via ISO C++ S= tandard - Future Proposals > wrote: >=20 > On Tue, May 19, 2015 at 10:49 AM, Nevin Liber > wrote: > Also, consider making unique_function(unique_function&&) noexcept. >=20 > +1 for noexcept, and it should be able to avoid calling the move construc= tor when in remote storage (forcing remote storage if the underlying object= has a move constructor that can throw) That=E2=80=99s an idea. I don=E2=80=99t know if it=E2=80=99s worth it, but = I=E2=80=99ll add it as a note. The idea would apply to std::function just as well. The main problem is that most explicitly-defined move constructors in pract= ice aren=E2=80=99t noexcept, just because people forget. On the other hand,= most classes with an explicitly-defined move constructor (or composed from= something with one) are big enough that the in-wrapper storage optimizatio= n won=E2=80=99t apply anyway. Also, another corner case: the move constructor will allocate memory when t= he source has a non-POCMA (allocator_traits::propagate_on_container_move_as= signment) allocator. I=E2=80=99m not really seeing an exception-safety guar= antee being feasible. --=20 ---=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --Apple-Mail=_9AA3278A-698B-488F-BA75-CF628664B6CA Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2015=E2=80=9305=E2=80=9320, at= 1:52 AM, 'Matt Calabrese' via ISO C++ Standard - Future Proposals <std-proposals@isocpp.org= > wrote:

On Tue, May 19, 2015 at 10:49 AM, Nevin Liber <nevin@eviloverlord.com> wrote:
Also, consider making unique= _function(unique_function&&) noexcept.

+1 for noexcep= t, and it should be able to avoid calling the move constructor when in remo= te storage (forcing remote storage if the underlying object has a move cons= tructor that can throw)

That=E2=80=99s an idea. I don=E2=80=99t know if= it=E2=80=99s worth it, but I=E2=80=99ll add it as a note.

The idea would apply to std::function just as well.

The main problem is that most e= xplicitly-defined move constructors in practice aren=E2=80=99t noexcept, just because people forget. On the= other hand, most classes with an explicitly-defined move constructor (or c= omposed from something with one) are big enough that the in-wrapper storage= optimization won=E2=80=99t apply anyway.

Also, another corner case: the move constructor wi= ll allocate memory when the source has a non-POCMA (allocator_traits::propagate_on_container_move_assignment)= allocator. I=E2=80=99m not really seeing an exception-safety guarantee bei= ng feasible.

--

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