220 38668 article Path: news.gmane.org!.POSTED!not-for-mail From: Richard Hodges Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Three way comparison of arrays Date: Fri, 15 Jun 2018 17:51:59 +0200 Lines: 132 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="000000000000ecbf94056eb032cc" X-Trace: blaine.gmane.org 1529077809 8020 195.159.176.226 (15 Jun 2018 15:50:09 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 15 Jun 2018 15:50:09 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD4PBM7UWAHRBLGBR7MQKGQEWWWK4OI@isocpp.org Fri Jun 15 17:50:05 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io0-f198.google.com ([209.85.223.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fTqzC-0001td-3D for gclcip-std-proposals@m.gmane.org; Fri, 15 Jun 2018 17:50:02 +0200 Original-Received: by mail-io0-f198.google.com with SMTP id r10-v6sf7587438ioh.7 for ; 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[209.85.220.41]) by mx.google.com with SMTPS id m189-v6sor3438568ioa.206.2018.06.15.08.52.11 for (Google Transport Security); Fri, 15 Jun 2018 08:52:11 -0700 (PDT) Received-SPF: pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a6b:2348:: with SMTP id j69-v6mr2145147ioj.100.1529077931227; Fri, 15 Jun 2018 08:52:11 -0700 (PDT) In-Reply-To: X-Original-Sender: hodges.r@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Qh8A7NmW; spf=pass (google.com: domain of hodges.r@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=hodges.r@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE 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:38668 Archived-At: --000000000000ecbf94056eb032cc Content-Type: text/plain; charset="UTF-8" On Fri, 15 Jun 2018 at 17:34, wrote: > Hi, > > can we finally write idiomatic comparison code for arrays with three way > compare? > Wouldn't this break existing functionality? The current meaning of (a == b) when a and b are c-style arrays is to compare the addresses of the 0th element of each array - essentially testing whether a and b are the *same actual array* rather than two arrays that contain data that compares equal. Comparing two std::span will certainly work, so for generic code you may want to consider providing overloads/specialisations for span rather than c-array. http://en.cppreference.com/w/cpp/container/span/operator_cmp > > bool foo() > { > int a1[4] = { 1, 2, 3, 4 }, a2[4] = { 1, 2, 3, 4 }; > return (a1 <=> a2) == 0; > } > > I really hope so, and that would we could compare arrays of different size > too (always not equal) - useful for template code. > > Regards, > Maciej > > -- > 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 > email to std-proposals+unsubscribe@isocpp.org. > To post to this group, send email to std-proposals@isocpp.org. > To view this discussion on the web visit > https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/d50deead-c460-414b-b356-a398772b8f69%40isocpp.org > > . > -- 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 email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CALvx3hZQ4CMYBRfaQegK64d2JzLk0LS8y3u04id0Arbrgo2WKg%40mail.gmail.com. --000000000000ecbf94056eb032cc Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Fri= , 15 Jun 2018 at 17:34, <m.cencor= a@gmail.com> wrote:
Hi,

can we finally write idi= omatic comparison code for arrays with three way compare?

Wouldn't this break existing functionality? = The current meaning of (a =3D=3D b) when a and b are c-style arrays is to c= ompare the addresses of the 0th element of each array - essentially testing= whether a and b are the *same actual array* rather than two arrays that co= ntain data that compares equal.

Comparing two std::span will certainly work, so fo= r generic code you may want to consider providing overloads/specialisations= for span rather than c-array.


= =C2=A0

bool=C2=A0foo()
{
=C2=A0 =C2=A0 int a1[<= span style=3D"color:rgb(9,136,90)">4] =3D { 1, 2, 3, = 4 }, a2[4] =3D { 1, 2= , 3, 4 };
=C2=A0 =C2=A0 return (a1 <=3D> a2= ) =3D=3D 0;
}

I really hope so, and that would we could compare ar= rays of different size too (always not equal) - useful for template code.

Regards,
Maciej

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