220 3097 <19425b1d-6f18-4532-85aa-2bb58aab5d11@isocpp.org> article Path: news.gmane.org!not-for-mail From: =?UTF-8?Q?Andrzej_Krzemie=C5=84ski?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: A proposal to add swap traits to the standard library Date: Fri, 15 Mar 2013 00:59:24 -0700 (PDT) Lines: 135 Approved: news@gmane.org Message-ID: <19425b1d-6f18-4532-85aa-2bb58aab5d11@isocpp.org> References: <6c1f8dc8-faaa-4b25-aea9-5dbe95bde4d4@isocpp.org> <489b9128-09ba-48b6-a18e-965636e9a072@isocpp.org> <5142390A.2040507@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_974_10406188.1363334364028" X-Trace: ger.gmane.org 1363334365 2697 80.91.229.3 (15 Mar 2013 07:59:25 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 15 Mar 2013 07:59:25 +0000 (UTC) Cc: "Andrew C. Morrow" To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDT2DGOJ34DBBXFJROFAKGQEJ6EQQLA@isocpp.org Fri Mar 15 08:59:50 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vb0-f72.google.com ([209.85.212.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UGPYK-00005o-7E for gclcip-std-proposals@m.gmane.org; Fri, 15 Mar 2013 08:59:48 +0100 Original-Received: by mail-vb0-f72.google.com with SMTP id ft2sf4133616vbb.11 for ; Fri, 15 Mar 2013 00:59:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:x-beenthere:x-received:date:from:to:cc:message-id :in-reply-to:references:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-google-group-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=N7fJtZR8LQX/OqkdCCVZ1EijJzXD68RlDMLvuxL2Wmg=; b=ODslsAELD/LU98QxPJgkiiCU8md1PAF63mNVh5s8ccpLDM8KSs/Lob1TyYwhey0qQ7 rjfJdJ5gbpVtEbLuNaw3uqS5QU8Z98Eu2Mfwq+cFl2e2Q2RkZx0ow1JI0TeVhxA0Szdl t4IGCNM4v7MirbRX/Ev+t4qPDxlPo7eF3T/7ggGLr7hQHCFVHQte/YPUA6ZXe/qIAXm5 W1s/OXmMxe3HsZVyjmtJdDNfW7L9gPjjGGQKK6UVwPteM3SO/kXnc5nmiErEbVkgtY0j 0RiPXMMWCleBNc2F3K+VerY1kY0fyW4kyGLXcSLV88wq643qU2GAzGXKYH8v08wUOj2l /zUQ== X-Received: by 10.224.185.79 with SMTP id cn15mr2518043qab.4.1363334364768; Fri, 15 Mar 2013 00:59:24 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.12.34 with SMTP id v2ls287103qeb.76.gmail; Fri, 15 Mar 2013 00:59:24 -0700 (PDT) X-Received: by 10.49.106.131 with SMTP id gu3mr487594qeb.36.1363334364352; Fri, 15 Mar 2013 00:59:24 -0700 (PDT) In-Reply-To: <5142390A.2040507@gmail.com> X-Original-Sender: akrzemi1@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:3097 Archived-At: ------=_Part_974_10406188.1363334364028 Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable W dniu czwartek, 14 marca 2013 21:54:34 UTC+1 u=BFytkownik Mikael Kilpel=E4= inen=20 napisa=B3: > > 14.3.2013 20:50, Andrew C. Morrow kirjoitti:=20 > >=20 > > Any suggestions about how to repair this proposal given the problems=20 > > with is_swappable?=20 > >=20 > > Not really. Sorry.=20 > > I was experimenting with a version that has swap(...) that hides the=20 > std::swap to see if there is anything that matches via=20 > ADL and if not, use qualified std::swap and some more constraints. This= =20 > works in normal cases fine, but=20 > of course there is this small gap between the template std::swap and the= =20 > swap(...) where the adl version might match=20 > and hence you get wrong results again (you cannot hide the std::swap=20 > with same signature as it is as it gets pulled in by adl anyhow=20 > and it is ambigious, like Nikolay already noted).=20 > > So I can only conclude, since you need the is_swappable for the main=20 > purpose, namely is_swappale_nothrow. Keep it there, explain=20 > the current problems with it and mention that something should probably= =20 > be done about it (ie. constrain swap or ..) and let committee give=20 > feedback.=20 > And make sure that the nothrow version is the main purpose of this=20 > proposal.=20 > > Of course we should continue thinking how to solve this but...=20 > Mikael=20 > Sorry, if my suggestion is dumb (I am not entirely following the details),= =20 but it looked like you have a problem with implementing the proposed traits= =20 within the C++ language, rather than with the proposal itself. Did you=20 consider proposing a requirement that is not implementable within C++ but= =20 could be provided by the vendors by some intrinsics or compiler magic (much= =20 like other traits)? Regards, &rzej =20 --=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/?hl=3Den. ------=_Part_974_10406188.1363334364028 Content-Type: text/html; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable

W dniu czwartek, 14 marca 2013 21:54:34 UTC+1 u=BFytkownik Mikael K= ilpel=E4inen napisa=B3:
14.3.20= 13 20:50, Andrew C. Morrow kirjoitti:
>
> Any suggestions about how to repair this proposal given the proble= ms=20
> with is_swappable?
>

Not really. Sorry.

I was experimenting with a version that has swap(...) that hides the=20
std::swap to see if there is anything that matches via
ADL and if not, use qualified std::swap and some more constraints. This= =20
works in normal cases fine, but
of course there is this small gap between the template std::swap and th= e=20
swap(...) where the adl version might match
and hence you get wrong results again (you cannot hide the std::swap=20
with same signature as it is as it gets pulled in by adl anyhow
and it is ambigious, like Nikolay already noted).

So I can only conclude, since you need the is_swappable for the main=20
purpose, namely is_swappale_nothrow. Keep it there, explain
the current problems with it and mention that something should probably= =20
be done about it (ie. constrain swap or ..) and let committee give feed= back.
And make sure that the nothrow version is the main purpose of this prop= osal.

Of course we should continue thinking how to solve this but...
Mikael

Sorry, if my suggestion is dumb (I am not entirel= y following the details), but it looked like you have a problem with implem= enting the proposed traits within the C++ language, rather than with the pr= oposal itself. Did you consider proposing a requirement that is not impleme= ntable within C++ but could be provided by the vendors by some intrinsics o= r compiler magic (much like other traits)?

Regards,
&rzej &nb= sp;

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