220 23697 <56960730.9000403@wanadoo.fr> article Path: news.gmane.org!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Default swap/hash_value Date: Wed, 13 Jan 2016 09:13:36 +0100 Lines: 64 Approved: news@gmane.org Message-ID: <56960730.9000403@wanadoo.fr> References: <569582E5.1040108@wanadoo.fr> <4072A7C6-B09D-4847-971B-2914643B91D7@gmail.com> <569594AD.6000505@wanadoo.fr> <2170C30C-830F-47C2-8397-29DD4ED35E97@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1452672827 10419 80.91.229.3 (13 Jan 2016 08:13:47 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 13 Jan 2016 08:13:47 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBMMO3C2AKGQEEV7X3VY@isocpp.org Wed Jan 13 09:13:40 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f198.google.com ([209.85.217.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aJGYl-0003QL-46 for gclcip-std-proposals@m.gmane.org; Wed, 13 Jan 2016 09:13:39 +0100 Original-Received: by mail-lb0-f198.google.com with SMTP id dx9sf16224723lbc.3 for ; Wed, 13 Jan 2016 00:13:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-type:content-transfer-encoding :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=mitR9r4pb9WutJbKTqszHvi1srG/ljCbE4wlSy01stk=; b=csYJLwD7X02HI98l6DRrO6WJmDvLH1JOkGe9La7vPJWDWRExVmCYtl9y8sbqoFil53 NoCsp1w7L7UAqunMfSyMpbq2ADddTgPYcpJ4xblc/FlDK0+l1lI8A/NkBt2i+kKdefx4 Lr0wVEy6O1NrAIU/psneXRNw+4+ostNOTnGEAb0v7AXxoVzlsDFwyjUfDGoJmqU55eqw wpcSG+ayN0celBOKDM8TTe8Q/3e/dUZOPstPH8ZMWeKxh+wJKvVMfamCF+cnz0WSVVgG p8vmovUrAQVTWGtNnrWKIM26vYKBG5yQDuRacyQHxEgz/K9k1fMZ6Bvx+K3gt X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-type :content-transfer-encoding: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=mitR9r4pb9WutJbKTqszHvi1srG/ljCbE4wlSy01stk=; b=kPRgeXpb7TXmwU7s/e9QRbdRnag3IYuI9ZIDrLsw+TZ0h9iTiNEAdMQhgPPdXsvcva bGqkTuNGC2lguGWHMO84aFWYhIkmYyyjcHrJTpP+Hu59TCpicU2CAR+kTJgNg9PG3EQ0 hEM639uXYRZ9IC2vAZvKZSK2M/74ZqUxjT3pYYZ6C+RCx96TZViMT8vDX9t3vXWMpYx6 V7Cr2RBB+eKFCLRkjLQAkWzxYNATIHhwInXuJrDNlf5jhWpg536HT/MmAbd8I6Y/sle6 72+4ZrKy38vq3HoYXGpGUWYNEkq4Fenkcgtfhupa4226vjN X-Gm-Message-State: ALoCoQmEsutxRK/0DF+oX+NJDxnbxXHhng/UquriKcjfxRw4PWZNuZFUMbkLP4kbVb2HO1CifSeMa+x5WYqGC4W29oHHas4J1g== X-Received: by 10.112.162.101 with SMTP id xz5mr1060222lbb.20.1452672818481; Wed, 13 Jan 2016 00:13:38 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.4.74 with SMTP id 71ls781289wme.7.canary; Wed, 13 Jan 2016 00:13:37 -0800 (PST) X-Received: by 10.194.90.50 with SMTP id bt18mr144152383wjb.118.1452672817297; Wed, 13 Jan 2016 00:13:37 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp01.smtpout.orange.fr. [80.12.242.123]) by mx.google.com with ESMTPS id s140si37090138wmb.97.2016.01.13.00.13.37 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 13 Jan 2016 00:13:37 -0800 (PST) Received-SPF: neutral (google.com: 80.12.242.123 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.123; Original-Received: from new-host.home ([86.214.79.135]) by mwinf5d36 with ME id 5LDc1s00F2v9yza03LDcgP; Wed, 13 Jan 2016 09:13:37 +0100 X-ME-Helo: new-host.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Wed, 13 Jan 2016 09:13:37 +0100 X-ME-IP: 86.214.79.135 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:38.0) Gecko/20100101 Thunderbird/38.4.0 In-Reply-To: <2170C30C-830F-47C2-8397-29DD4ED35E97@gmail.com> X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.123 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr 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:23697 Archived-At: Le 13/01/2016 01:48, Howard Hinnant a =C3=A9crit : > On Jan 12, 2016, at 7:05 PM, Vicente J. Botet Escriba wrote: >> I understand your concern, and I'm taking this in account as I'm suggest= ing the generation of hash_value as defined in P0029R0. > Thanks. > >> What am I missing? >> > P0029R0 was poorly written in that it did not emphasize this capability, = even though it did include it. In contrast, this was the entire point of N= 3980. > > In P0029R0-speak, std::hash_code *is* a hash algorithm. It is just one h= ash algorithm. It is the hash algorithm supplied by the std::lib. A type = that is inspired only to operate with this single std::lib-supplied algorit= hm implements: > > std::hash_code hash_value(std::hash_code h, const Foo& foo) > > In contrast, (and still according to P0029R0), a type that wants to be ha= shable by *any* hash algorithm *instead* implements: > > template > H hash_value(H h, const Foo& foo); > > The hash algorithm now is represented by the generic template parameter H= .. > > In 3980-speak, this was spelled: > > template > void hash_append(HashAlgorithm& h, T const& t); > > But the idea was similar. > > I'll update the draft to signal that the proposed generation would need=20 to be adapted to the final composable hashing proposal and change the=20 example to make use of a template parameter H. What I'm interested in is=20 in knowing if the committee would be or not for this default definition. I've some additional concerns about the possible generation of=20 specialization of is_uniquely_represented. I would like it to be=20 generated the specialization when possible but while multiple definition=20 of hash_value could be check at link time, I believe that multiple=20 specializations of is_uniquely_represented would result in ODR, which=20 would be a showstopper. So at the end, it would be the responsibility of=20 the developer of class C to add a specialization of=20 is_uniquely_represented. What do you think about this point? Vicente --=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 https://groups.google.com/a/isocpp.org/group/std-propos= als/. .