220 3654 article Path: news.gmane.org!not-for-mail From: =?UTF-8?Q?R=C3=B3bert_D=C3=A1vid?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: N3573: Why heterogenous extensions to unordered containers will not work Date: Tue, 9 Apr 2013 06:11:14 -0700 (PDT) Lines: 95 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_5299_1564840.1365513074550" X-Trace: ger.gmane.org 1365513076 11224 80.91.229.3 (9 Apr 2013 13:11:16 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 9 Apr 2013 13:11:16 +0000 (UTC) Cc: jgottman6@gmail.com To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDMKHJ4B6MARB45GSCFQKGQEJPM2N3A@isocpp.org Tue Apr 09 15:11:20 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vb0-f69.google.com ([209.85.212.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UPYKS-0002Vg-RB for gclcip-std-proposals@m.gmane.org; Tue, 09 Apr 2013 15:11:17 +0200 Original-Received: by mail-vb0-f69.google.com with SMTP id p12sf9221438vbe.8 for ; Tue, 09 Apr 2013 06:11:16 -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:cc: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=N4Tf49eH9c08rLXWULW9wVRMhMgcP4OzaATBBPDYNI4=; b=ec+E4fqTVKJKb9r5UckZBUS6FqPpkiuNDQRj3c2AZFmZxDyrCFHOlst2nVCkh65VDq GYqvsvOjctPWeAc/GES7oHrdBQ+O0Au8YFqWvxJ+9/eP/TEtagySNj/s99uZXomWBnQA Kw6YwgJ8i94CrkOMFuMspyT+UuMUXwHnjks/GMsi9JhJIH0gwPQmeiBpsJ+QcSLjYD9X CohrGRES33b0LmxzRH7CDIxGRQwbzfBklIt7vnWfFP72Nwo0+h9Wh966srzpdXtC77GP xgwZhCep1MKJEu5C8IQj+j9G5jy5sp5/RtlBSsVjBmF577ROIChIrwnEjzR7qm670NOh TUiA== X-Received: by 10.236.174.6 with SMTP id w6mr278078yhl.25.1365513075984; Tue, 09 Apr 2013 06:11:15 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.118.70 with SMTP id kk6ls1580512qeb.9.gmail; Tue, 09 Apr 2013 06:11:14 -0700 (PDT) X-Received: by 10.49.120.105 with SMTP id lb9mr2045673qeb.17.1365513074888; Tue, 09 Apr 2013 06:11:14 -0700 (PDT) In-Reply-To: X-Original-Sender: lrdxgm@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:3654 Archived-At: ------=_Part_5299_1564840.1365513074550 Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable 2013. =E1prilis 9., kedd 2:36:46 UTC+2 id=F5pontban jgot...@gmail.com a=20 k=F6vetkez=F5t =EDrta: > > While this would be useful, there is too much chance of two types being= =20 > equality-comparable but having incompatible hashes. For example, under g= cc=20 > 8.0,=20 > std::hash(-1L) =3D=3D 18446744073709551615 > and > std::hash(-1.0) =3D=3D 11078049357879903929 > > > If a =3D=3D b, then I would expect that hash(a) =3D=3D hash(b). If a langua= ge does=20 not exhibit this, then there is something wrong - from a user's perspective= =20 hashing is useless if it produces different results for equal values...=20 Implementer's perspective is a different question.. Regards, Robert PS: What is gcc 8.0? --=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 http://groups.google.com/a/isocpp.org/group/std-proposa= ls/?hl=3Den. ------=_Part_5299_1564840.1365513074550 Content-Type: text/html; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable

2013. =E1prilis 9., kedd 2:36:46 UTC+2 id=F5pontban jgot...@gmail.c= om a k=F6vetkez=F5t =EDrta:
Whi= le this would be useful, there is too much chance of two types being equali= ty-comparable but having incompatible hashes.  For example, under gcc = 8.0,
std::= hash<long&g= t;(-1L<= /span>) =3D=3D 18446744073709551615
and
std::hash<double>(-1.0= ) =3D= =3D 110= 78049357879903929
=



If a =3D=3D b, then I would expect that= hash(a) =3D=3D hash(b). If a language does not exhibit this, then there is= something wrong - from a user's perspective hashing is useless if it produ= ces different results for equal values... Implementer's perspective is a di= fferent question..

Regards, Robert

PS: What is gcc 8.0?

--
 
---
You received this message because you are subscribed to the Google Groups &= quot;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 http://groups.google.com/a/isocpp.org/group/std-pro= posals/?hl=3Den.
 
 
------=_Part_5299_1564840.1365513074550-- .