220 23691 <4072A7C6-B09D-4847-971B-2914643B91D7@gmail.com> article Path: news.gmane.org!not-for-mail From: Howard Hinnant Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Default swap/hash_value Date: Tue, 12 Jan 2016 18:54:44 -0500 Lines: 56 Approved: news@gmane.org Message-ID: <4072A7C6-B09D-4847-971B-2914643B91D7@gmail.com> References: <569582E5.1040108@wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 9.2 \(3112\)) Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1452642897 3333 80.91.229.3 (12 Jan 2016 23:54:57 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 12 Jan 2016 23:54:57 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCK2HM4L6YERBRVE222AKGQEFKHL4GA@isocpp.org Wed Jan 13 00:54:49 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f200.google.com ([209.85.214.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aJ8m0-0005WE-PP for gclcip-std-proposals@m.gmane.org; Wed, 13 Jan 2016 00:54:48 +0100 Original-Received: by mail-ob0-f200.google.com with SMTP id k5sf62459686obo.3 for ; Tue, 12 Jan 2016 15:54:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=content-type:mime-version:subject:from:in-reply-to:date :content-transfer-encoding:message-id:references: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=Ey2bdfLALmfsvdjLosa+ZM6VbBsgc7Niglt2DYbTITI=; b=yMY2VJrLTl/syWSYJJMZgO92g6f8s4lhx2rCxf/m7auzYzyVE3NIyBI2eozpJ6BH6a mN9M6Q57XpKE+Y7FzvqBPtrtr3DkLNZu8RwVP+9IPttJ/OBtSCbsjTf0HYR9xUdzc39C +FyyzUgDI+mW7GirS/ioniCJT4mqX4ysr1BU4RfxbcWGehOSgU6WIr4a3QY9FVjXS9JS PTSZsCX+7+OXqC2Sp5ORs8zNJOOv20qxu7y8b9hwJqCccksA8QtJ1JFiULZ+vxtuQglf 3S/SCoo/hefR5oB0x/gUl8MuUI8kS2wWCCCuCZE5u7HA/cmKOfWaqATBaGGof324QWwN X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:content-type:mime-version:subject:from :in-reply-to:date:content-transfer-encoding:message-id:references: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=Ey2bdfLALmfsvdjLosa+ZM6VbBsgc7Niglt2DYbTITI=; b=ExSMwwpDFdnpS5IVH2RJr0Rq3vJAFkx34JPtDeL4P7cJzAaVDawjAKTyOWoSV/FhYH EZfZa4da8wZHHLFyKJXJOAPOKxNpFuH2tnwxQ4SwZ9o36wlDw4/OH8COk+aBgrpUlhoq 3wlJP8h5pdekz5xFWSNHw/p3PSkosleBH+MG2Pa+KEEZFDaqQUPa/ahpLJ/0h2e5kXy0 mzQiJonBbH5sY47+ZqGbpXEQlQXJKjRh20oPPzD7bQ/uF7gGu3vNjkdUxMZRB8n2aAvn +9/6OSe6NDTxYs4vptW+wecWpMbOZhZKzWXxk5neviBMCrzm7OqnYw/9c7vc6WoYPmZ/ X-Gm-Message-State: ALoCoQnUg+P4+GfHcXSFlHi6vriFsQL6CHfWUJrT7UmRXbC+LP4ph63w2EJ55RWHNH+Nb5GtHDkfuoqW0Di59AX0cH2q0laviA== X-Received: by 10.182.142.8 with SMTP id rs8mr97366669obb.33.1452642887852; Tue, 12 Jan 2016 15:54:47 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.98.173 with SMTP id o42ls15727672qge.95.gmail; Tue, 12 Jan 2016 15:54:46 -0800 (PST) X-Received: by 10.55.21.143 with SMTP id 15mr29774183qkv.74.1452642886380; Tue, 12 Jan 2016 15:54:46 -0800 (PST) Original-Received: from mail-qg0-x233.google.com (mail-qg0-x233.google.com. [2607:f8b0:400d:c04::233]) by mx.google.com with ESMTPS id g13si2260833qhc.69.2016.01.12.15.54.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Jan 2016 15:54:46 -0800 (PST) Received-SPF: pass (google.com: domain of howard.hinnant@gmail.com designates 2607:f8b0:400d:c04::233 as permitted sender) client-ip=2607:f8b0:400d:c04::233; Original-Received: by mail-qg0-x233.google.com with SMTP id b35so312489985qge.0 for ; Tue, 12 Jan 2016 15:54:46 -0800 (PST) X-Received: by 10.140.105.198 with SMTP id c64mr15393700qgf.94.1452642886256; Tue, 12 Jan 2016 15:54:46 -0800 (PST) Original-Received: from [10.0.1.2] (cpe-104-229-168-124.twcny.res.rr.com. [104.229.168.124]) by smtp.gmail.com with ESMTPSA id s90sm3790464qgs.13.2016.01.12.15.54.45 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 12 Jan 2016 15:54:45 -0800 (PST) In-Reply-To: <569582E5.1040108@wanadoo.fr> X-Mailer: Apple Mail (2.3112) X-Original-Sender: howard.hinnant@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of howard.hinnant@gmail.com designates 2607:f8b0:400d:c04::233 as permitted sender) smtp.mailfrom=howard.hinnant@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-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:23691 Archived-At: On Jan 12, 2016, at 5:49 PM, Vicente J. Botet Escriba wrote: >=20 > Hi,=20 >=20 > I've been working on a proposal (see attached document) >=20 > Default swap/hash_value > Defining swap and hash_value P0029R0 as well as comparison operators, as = proposed in N4475, for simple classes is tedious, repetitive, slightly erro= r-prone, and easily automated.=20 >=20 > I propose to (implicitly) supply default versions of these two operations= , if needed. The meaning swap is to swap each member, and the meaning of ha= sh_value is to combine the members using hash_combine.=20 >=20 > If the simple defaults are unsuitable for a class, a programmer can, as e= ver, define more suitable ones or suppress the defaults. The proposal is to= add the operations as an integral part of C++ (like =3D), rather than as a= library feature.=20 >=20 > The proposal follows the same approach as Default comparison as in N4475,= that is, having default generated code for these basic operations only whe= n needed and possible would makes the language simpler.=20 >=20 >=20 > Any comments are welcome, For the hash part: How does one switch to an alternate hash algorithm for = type T without having to revisit the code for every base and member of T? = This is the most important part of both http://www.open-std.org/jtc1/sc22/w= g21/docs/papers/2015/p0029r0.html and http://www.open-std.org/jtc1/sc22/wg2= 1/docs/papers/2014/n3980.html. If the std ropes people/programs into a sin= gle hash algorithm (as it does today), then all of that code is vulnerable = to attack. Only by allowing coders to change the hash algorithm for type T with O(1) e= ffort can C++ ever hope to stay ahead of the arms race in software security= .. The C++ committee itself is too slow and cumbersome (by at least 2 order= s of magnitude) to supply (or even suggest) the best hashing algorithm for = code that must hash values from untrusted input. Howard --=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/. .