220 3070 <489b9128-09ba-48b6-a18e-965636e9a072@isocpp.org> article Path: news.gmane.org!not-for-mail From: Nikolay Ivchenkov Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: A proposal to add swap traits to the standard library Date: Tue, 12 Mar 2013 15:22:37 -0700 (PDT) Lines: 69 Approved: news@gmane.org Message-ID: <489b9128-09ba-48b6-a18e-965636e9a072@isocpp.org> References: <6c1f8dc8-faaa-4b25-aea9-5dbe95bde4d4@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1463_25037184.1363126957095" X-Trace: ger.gmane.org 1363126958 22147 80.91.229.3 (12 Mar 2013 22:22:38 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 12 Mar 2013 22:22:38 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDJK3XNWR4LRBLWV72EQKGQEWQXHNXI@isocpp.org Tue Mar 12 23:23:03 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 1UFXb3-0001Yn-8v for gclcip-std-proposals@m.gmane.org; Tue, 12 Mar 2013 23:23:01 +0100 Original-Received: by mail-vb0-f72.google.com with SMTP id ft2sf391039vbb.7 for ; Tue, 12 Mar 2013 15:22:38 -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: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=zfGq10VHQw59GtodifZFmIIx/1ZYnqjjWcVDE/XKDjM=; b=XceQx8Xcx8/4t4siz4kxP4gU0/js+jPDtWMR4ZCuF76wGwGh0sPE4Oiw47E6+kWoMC JLKHrSYyY8gYSvbgJmWwfVJkB157vt4pq0m+GNIsq7tyoOiwjcSS6p7YLP4quCUQ4Dny 1BJi5RTCnQrxAnjuELJX97QNbj4vDg+D+pE7TsFIVIueLGT5eMRnHajRRy39a3P0V56D MX+Rc/avUiFjbIJiUKLwBVKyiVPVAEgW2V+C/1gjgz5OW/wNb5TnCytcH+L9w+mgrv88 vOc08LK2scXuJsmhOhD7xAu4YVx2KHD6x2krJYleBmMxUodGf6y5P3CFPgRVCR1s3jIT ohlw== X-Received: by 10.236.131.69 with SMTP id l45mr10596548yhi.10.1363126958234; Tue, 12 Mar 2013 15:22:38 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.131.229 with SMTP id op5ls712108qeb.23.gmail; Tue, 12 Mar 2013 15:22:37 -0700 (PDT) X-Received: by 10.49.6.1 with SMTP id w1mr337384qew.24.1363126957390; Tue, 12 Mar 2013 15:22:37 -0700 (PDT) In-Reply-To: <6c1f8dc8-faaa-4b25-aea9-5dbe95bde4d4@isocpp.org> X-Original-Sender: mk.ivchenkov@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:3070 Archived-At: ------=_Part_1463_25037184.1363126957095 Content-Type: text/plain; charset=ISO-8859-1 On Wednesday, March 13, 2013 1:55:58 AM UTC+4, Nikolay Ivchenkov wrote: > > I still don't see any useful applications of such is_swappable. It doesn't > answer whether the provided argument(s) is/are swappable, even roughly. A > call to the general unconstrained version of std::swap, where both > arguments are lvalues of the same type, will be always well-formed. If you > don't want to change the declaration of std::swap, you can introduce some > constrained surrogate for it and construct the candidate set from the > surrogate and versions found by ADL: > Sorry, I didn't consider this idea properly. Such implementation isn't correct, because the general std::swap can conflict with such surrogate (e.g. we will get value false on std::string *&). Any other surrogate, that would be less specialized than the general std::swap, can potentially conflict with a user-defined template. So, I see only one viable solution: the general std::swap should be constrained. -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/?hl=en. ------=_Part_1463_25037184.1363126957095 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On Wednesday, March 13, 2013 1:55:58 AM UTC+4, Nikolay Ivchenkov wrote:I still don't see any useful appli= cations of such is_swappable. It doesn't answer whether the provided argume= nt(s) is/are swappable, even roughly. A call to the general unconstrained v= ersion of std::swap, where both arguments are lvalues of the same type, wil= l be always well-formed. If you don't want to change the declaration of std= ::swap, you can introduce some constrained surrogate for it and construct t= he candidate set from the surrogate and versions found by ADL:

Sorry, I didn't consider this idea properly. Such implementati= on isn't correct, because the general std::swap can conflict with such surr= ogate (e.g. we will get value false on std::string *&). Any other surro= gate, that would be less specialized than the general std::swap, can potent= ially conflict with a user-defined template. So, I see only one viable solu= tion: the general std::swap should be constrained.

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