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Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Default swap/hash_value Date: Wed, 13 Jan 2016 01:05:01 +0100 Lines: 62 Approved: news@gmane.org Message-ID: <569594AD.6000505@wanadoo.fr> References: <569582E5.1040108@wanadoo.fr> <4072A7C6-B09D-4847-971B-2914643B91D7@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 1452643523 11601 80.91.229.3 (13 Jan 2016 00:05:23 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 13 Jan 2016 00:05:23 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBLVJ222AKGQEHUI6L7A@isocpp.org Wed Jan 13 01:05:05 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f70.google.com ([209.85.215.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aJ8vv-0003UI-Ug for gclcip-std-proposals@m.gmane.org; Wed, 13 Jan 2016 01:05:03 +0100 Original-Received: by mail-lf0-f70.google.com with SMTP id b134sf153933641lfe.2 for ; Tue, 12 Jan 2016 16:05:03 -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=P+hap2VaHHv68JgAJNSUYfGBYyWUSx8ZOHi/mLTi+V4=; b=vGuqk9yGcAkDm2+J9dEkp+Yzh/l8MJmF4uYL32WgmYqMo9xSBgaaqPTovlg3qgdL44 +lYbpR3d1pwle02ckyCkYQFyoIJEySdG9uUWE26BPULtJe3IBsIfCmqUq/XDdGn8swVl W9Ix5RwS26hZUisNDyXOCHAwL/jR4c5053JQ6S6wawGHe1ZfqlaATLRVNVzdpb5FUfn9 kow01VFcEVf6bgPXRKXjsocOzImPOc/Kw0W9JeesGFRRLAF9b6iIEj5x7zjmW645/OwQ TMGSFoIwqXl9NC17nEqDKmhIhGwmV/LQc5Ftm8bf4PJKlAj7By/9K5Xr2+o+S 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=P+hap2VaHHv68JgAJNSUYfGBYyWUSx8ZOHi/mLTi+V4=; b=XN+UPyFPmMFRE3DRyIy0h2c7uEK754D3tfQRImG8zULcXG7NxD5QqYNvb5k70fwJOT MbcfL1EXJvmgtYyZtIyULUq+P20Bw5VyThJL7pde7eCM/Zi3wVwzLW+Rb9hS69Pm+t95 xUG0uzo9J/B8HfVaGNhURepIsd10wIVHSqTJsd5vveXmwGR4NFebXaYyqbX/8Us5ted0 VJ7XlR67GAQqHheQsBLCt7m2Ks5nzITCLG7Xvjn0m9yUuXti//Y6SBrRl2O8bOfysP9+ K61pqrfQbAyVeViVFf36RkJv2cxI007FSUCEM1hXNyQ9Wbh X-Gm-Message-State: ALoCoQmnshYoO/nsJfswIJsS2t9RCfgPjeQD7S9i6Nj6mAWCJHZWVfNigdbQUUhj/n25Ww1hW6s7btjL2hJA/yvW86gjjHVwcw== X-Received: by 10.112.16.34 with SMTP id c2mr2634715lbd.19.1452643503262; Tue, 12 Jan 2016 16:05:03 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.4.216 with SMTP id 207ls3530wme.35.gmail; Tue, 12 Jan 2016 16:05:02 -0800 (PST) X-Received: by 10.194.121.35 with SMTP id lh3mr141946485wjb.164.1452643502088; Tue, 12 Jan 2016 16:05:02 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp10.smtpout.orange.fr. [80.12.242.132]) by mx.google.com with ESMTPS id o123si147602wmd.53.2016.01.12.16.05.02 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 12 Jan 2016 16:05:02 -0800 (PST) Received-SPF: neutral (google.com: 80.12.242.132 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.132; Original-Received: from new-host.home ([86.214.79.135]) by mwinf5d45 with ME id 5C511s00H2v9yza03C51lq; Wed, 13 Jan 2016 01:05:01 +0100 X-ME-Helo: new-host.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Wed, 13 Jan 2016 01:05:01 +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: <4072A7C6-B09D-4847-971B-2914643B91D7@gmail.com> X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.132 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:23693 Archived-At: Le 13/01/2016 00:54, Howard Hinnant a =C3=A9crit : > On Jan 12, 2016, at 5:49 PM, Vicente J. Botet Escriba wrote: >> Hi, >> >> I've been working on a proposal (see attached document) >> >> 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 err= or-prone, and easily automated. >> >> I propose to (implicitly) supply default versions of these two operation= s, if needed. The meaning swap is to swap each member, and the meaning of h= ash_value is to combine the members using hash_combine. >> >> If the simple defaults are unsuitable for a class, a programmer can, as = ever, define more suitable ones or suppress the defaults. The proposal is t= o add the operations as an integral part of C++ (like =3D), rather than as = a library feature. >> >> The proposal follows the same approach as Default comparison as in N4475= , that is, having default generated code for these basic operations only wh= en needed and possible would makes the language simpler. >> >> >> Any comments are welcome, > > For the hash part: How does one switch to an alternate hash algorithm fo= r 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= /wg21/docs/papers/2015/p0029r0.html and http://www.open-std.org/jtc1/sc22/w= g21/docs/papers/2014/n3980.html. If the std ropes people/programs into a s= ingle hash algorithm (as it does today), then all of that code is vulnerabl= e to attack. > > Only by allowing coders to change the hash algorithm for type T with O(1)= effort can C++ ever hope to stay ahead of the arms race in software securi= ty. The C++ committee itself is too slow and cumbersome (by at least 2 ord= ers of magnitude) to supply (or even suggest) the best hashing algorithm fo= r code that must hash values from untrusted input. > > Hi Howard, I understand your concern, and I'm taking this in account as I'm=20 suggesting the generation of hash_value as defined in P0029R0. What am I=20 missing? 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/. .