220 23707 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: Default swap/hash_value Date: Wed, 13 Jan 2016 23:47:12 -0800 (PST) Lines: 149 Approved: news@gmane.org Message-ID: References: <569582E5.1040108@wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_204_1714295254.1452757632758" X-Trace: ger.gmane.org 1452757641 30657 80.91.229.3 (14 Jan 2016 07:47:21 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 14 Jan 2016 07:47:21 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDT2DGOJ34DBBAVF3W2AKGQESKCSOWA@isocpp.org Thu Jan 14 08:47:17 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f197.google.com ([209.85.192.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aJccm-0005zS-Bd for gclcip-std-proposals@m.gmane.org; Thu, 14 Jan 2016 08:47:16 +0100 Original-Received: by mail-pf0-f197.google.com with SMTP id 65sf406726888pfd.1 for ; Wed, 13 Jan 2016 23:47:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=J70lTTb9r16HQAiV1m8jtJxylwa9CuHaPnLtK8Wagcs=; b=XJ7YjKF66MYEu7P4ejynchPNMKQFzhMEQhqzISqa07RxOX6kBQsG7l2nGPr2xhelZj KKHnSnDqiOYXJEbGBfVlFc9JZeLzzYulbAm3drysFB4rS7MY109PATqTqNRByIIGWkzu g5XdDeVBU3MAU7O0aksWBAue9vTmHlTKPlV5uTOoRcbpYKImhhvoWr03om9jzmq5dkV1 wGWZJ/ouEVuci1btsaxQaZxnNgGA68Q88/UV3g6cfaYu3p+bnIgKQCUMEh9nP6rsAyv0 gweEvfjPi7onF9vE8WfwjMJM+5Puf+9rPQz5FepKO3rJTILaihu4aD9X5uSGNvURXsaE 4etQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=J70lTTb9r16HQAiV1m8jtJxylwa9CuHaPnLtK8Wagcs=; b=tCEiohXXYj90WdcHJ1M9jpYfrf6OJryw4ud5emKgJWyy83uOi5IVd6tN3d9E5RTqrk YFP0K7GDpOlnyYNbErheaeZUKz1Be/78sCzq0ZIiEtxYfYBbbRYufXLsx7LMI8qDugx8 ufXHl1gDdf10+foqv+tpgWCN1MDuNkdw7PQXph9/S+4+PwV6gYmxfCMWn42Cfv/cGPvY qqudrNM7TVCYFUSEHpDqF2q/HZtexGE6A7ql0N50KLGKtTyBAvEwasqBKNsfrLqf4LL6 tK7QL2/V6a8ujHJ8a08NXRSh1+TC6OYr0RHiPS/Dc4iwSaRCb/48opT4RA4SA/SNXoHu Qwdg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=J70lTTb9r16HQAiV1m8jtJxylwa9CuHaPnLtK8Wagcs=; b=GXOhlcDFsSV30muIS9fIa+pFZGgi31yA7TL+riDD3GKdnq56li1OWs+cInRlOL+y86 o1MIFEtGAgwlEwOlleqozsIISfvHw8jf3SyoUMsinYa4FuejexDF7RscsJPI4MDFytvG irVPObGHU70nsqiRJ2vDI1ifGCkcD+e9kcAnEEMerUB40GwPBhj8kTrWU8rpSC2jehJo U7+yy6q+EJ4xHe0aROIaCbINFip4FNz6WYjZPvRrXhXDYIYzxvNEMkxl2hn3POdRRVc3 JrQcs9qhVUC6ebhML3G6lL63o3gWP7Ck9UV07K15a9z/uNJ5n4eR2LPbHBaFWEL1iJi4 uIAQ== X-Gm-Message-State: ALoCoQmpfySgvEKeogopVNi+BVNwqmKgNqgnP33HGcubrx7elYahSk0wC9vGP7nzKkwzfWMUrnfu7uvBJffQL7bzS7Q6kSqkig== X-Received: by 10.66.144.138 with SMTP id sm10mr2347574pab.4.1452757635164; Wed, 13 Jan 2016 23:47:15 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.129.70 with SMTP id nu6ls1474473igb.0.canary; Wed, 13 Jan 2016 23:47:14 -0800 (PST) X-Received: by 10.50.108.20 with SMTP id hg20mr101741igb.5.1452757633991; Wed, 13 Jan 2016 23:47:13 -0800 (PST) In-Reply-To: <569582E5.1040108@wanadoo.fr> X-Original-Sender: akrzemi1@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:23707 Archived-At: ------=_Part_204_1714295254.1452757632758 Content-Type: multipart/alternative; boundary="----=_Part_205_948825230.1452757632758" ------=_Part_205_948825230.1452757632758 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable W dniu wtorek, 12 stycznia 2016 23:49:14 UTC+1 u=C5=BCytkownik Vicente J. B= otet=20 Escriba napisa=C5=82: > > Default swap/hash_value=20 > > Defining swap and hash_value P0029R0=20 > as= =20 > well as comparison operators, as proposed in N4475=20 > , for= =20 > simple classes is tedious, repetitive, slightly error-prone, and easily= =20 > automated.=20 > > Any comments are welcome, > Hi Vicente, My intuition tells me that it would be beneficial to make it two separate= =20 proposals. I expect that swap and hash have different constraints, would=20 rise different concerns, different discussions, and perhaps different=20 outcomes as to whether include them or not. I can see that Howard only=20 commented on the hash part. I, in contrast, will only comment on the swap= =20 part. I would add to the rationale for swap. Additional benefit for a default=20 member-wise swap (rather than relying on the move-based) (apart from=20 performance) is that the former can sometimes offer a better noexcept=20 guarantee. E.g., for std::vector, swap can be always guaranteed to be=20 noexcept, whereas its move operations throw. Regards, &rzej --=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/. ------=_Part_205_948825230.1452757632758 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

W dniu wtorek, 12 stycznia 2016 23:49:14 UTC+1 u=C5=BCytkownik Vice= nte J. Botet Escriba napisa=C5=82:

Default=C2=A0swap/hash_value

Defining=C2=A0swap= =C2=A0and=C2=A0hash_value=C2=A0P0029R0=C2=A0as well as comparison operators, as proposed in=C2=A0N4475, for simple classes is tedious, r= epetitive, slightly error-prone, and easily automated.

Any comments are welcome,

Hi = Vicente,
My intuition tells me that it would be beneficial to make it tw= o separate proposals. I expect that swap and hash have different constraint= s, would rise different concerns, different discussions, and perhaps differ= ent outcomes as to whether include them or not. I can see that Howard only = commented on the hash part. I, in contrast, will only comment on the swap p= art.

I would add to the rationale for swap. Additional benefit for a= default member-wise swap (rather than relying on the move-based) (apart fr= om performance) is that the former can sometimes offer a better noexcept gu= arantee. E.g., for std::vector, swap can be always guaranteed to be noexcep= t, whereas its move operations throw.

Regards,
&rzej

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