220 38670 article Path: news.gmane.org!.POSTED!not-for-mail From: m.cencora@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Three way comparison of arrays Date: Fri, 15 Jun 2018 10:05:09 -0700 (PDT) Lines: 197 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/mixed; boundary="----=_Part_8236_1239228492.1529082309693" X-Trace: blaine.gmane.org 1529082185 11488 195.159.176.226 (15 Jun 2018 17:03:05 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 15 Jun 2018 17:03:05 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD7YFUMJRYMBBRXDR7MQKGQEU6ENZHQ@isocpp.org Fri Jun 15 19:03:01 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f197.google.com ([209.85.161.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fTs7o-0002nV-K5 for gclcip-std-proposals@m.gmane.org; Fri, 15 Jun 2018 19:03:00 +0200 Original-Received: by mail-yw0-f197.google.com with SMTP id w7-v6sf7751162ywf.1 for ; Fri, 15 Jun 2018 10:05:12 -0700 (PDT) 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 :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=bM5vRuD8cX9tNvavFt8JvH2ifQ6q53nN+9um2iGJrA8=; b=Er3l/L2XksApkksc+52eCrmZVJbRk1WKhb8WXyKL4z4+a09pxQxN9IWUVOiBNV4Nst ifo5o+XkL96mFNNsk8s9lqjkbftkPL6TeKMzwtSnU41R7fcz9dqm5VaNMM7qQYeFpnKw 7TNdWO7/5+n2nxQgiPpTQLiglDze8sCznVfF5KUqq5Hy7r4qq5Nf0e3Z3mdyt9pd5nBQ yRN8MGAw9TZUVOvhOkjoQMmF9g4i29OGD7peOA+hqtSW8xNxiJPfCt7V9pQNP5E/7y8z VygH5qUbNCBvtxtZTSnHg4vbjqrP+/lvvpGskp0nH8/3BkoVrFyJH279UsAv3Hfcsije YYpw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=bM5vRuD8cX9tNvavFt8JvH2ifQ6q53nN+9um2iGJrA8=; b=aYwqnikCBWfkFKA4ek7tsV3jCf6K1Pnpyo3j+v58o0Uotfnao91OJfquOgdzPmyDD6 cPomjMADGyRhtDA6wsFQn4sj3RgS8kyTDXDx6n9vUVfVmhuq+C4V+4JG9suAyiU6SkCB /xjupQc/KiI9PejBbvsRvXWGFV/g+O0iXJvKHrGbNL0pwnEMQROiQEdFlV2QxMyb3GhA pD3f79cBAYyvi105RB1wPb2u/nfAY0hxRnA/BTrK5rMt39kvoQuc+okuOxXGcjwVeI2U wbhXymawoLGsN1J+F+R+QpUDW7JWmhoDIpj/IeLpNW6m+OiBt/9JP6etlhm9411G9RMj +ZKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version: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=bM5vRuD8cX9tNvavFt8JvH2ifQ6q53nN+9um2iGJrA8=; b=MQbKIQo+pjW43mQk/HejKjjTRlftv9n6iVrQAzMUz/GyBvfxQjwoLr9SkRJt6bu65D fD4TWkq/iO0tL1FHLHRsOFg/dbK01uIw+XHIVbjyYl02aNDgg4g1o77Rgpak4S+qvqhs ivnQ5ZM7VO9gS6hwfCheCfwaTAA9FAHCa7ihAFd11mjozNGZtpRAK4Seh5aR+iSbQhWg r5eIoUgoXdooK+9/SB+9Gm/VYw26VeeRsLOkm8AaaXxNqYtOmcUXrYt4R+XdUtiUvfKV 1dNyBb9IsPR0chN0Bz7Ku9sIE4jHw93FFqNcj7vG7DSQTs9m2CmazwxqmrRwvHuNA59z NifA== X-Gm-Message-State: APt69E2pPwqUZfn+R8U2HbB8tiaaRVrqe87rCETaVhpqQSikel6ZfyYP xxagGBT4VBMcitSjGr4zWfG/Kg== X-Google-Smtp-Source: ADUXVKI1g/mxBP8dor4YwFL6QICebwOWcwKHG0aX+/HozuCDzGrGlZ8oX8Z9d3ER48yxpdiNrO5qcw== X-Received: by 2002:a25:361e:: with SMTP id d30-v6mr724426yba.35.1529082311566; Fri, 15 Jun 2018 10:05:11 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a81:ad5f:: with SMTP id l31-v6ls1352617ywk.34.gmail; Fri, 15 Jun 2018 10:05:10 -0700 (PDT) X-Received: by 2002:a81:4b49:: with SMTP id y70-v6mr145440ywa.1.1529082310303; Fri, 15 Jun 2018 10:05:10 -0700 (PDT) In-Reply-To: X-Original-Sender: m.cencora@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:38670 Archived-At: ------=_Part_8236_1239228492.1529082309693 Content-Type: multipart/alternative; boundary="----=_Part_8237_615840004.1529082309693" ------=_Part_8237_615840004.1529082309693 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable I don't know how could it break existing functionality, since spaceship=20 operator is a new shiny thing in C++20. Just leave the old two way array=20 comparison as it is (or even deprecate it, in order to bring it back at=20 some point later with expected behavior). Regards, Maciej W dniu pi=C4=85tek, 15 czerwca 2018 17:52:13 UTC+2 u=C5=BCytkownik Richard = Hodges=20 napisa=C5=82: > > > > On Fri, 15 Jun 2018 at 17:34, > wrote: > >> Hi, >> >> can we finally write idiomatic comparison code for arrays with three way= =20 >> compare? >> > > Wouldn't this break existing functionality? The current meaning of (a =3D= =3D=20 > b) when a and b are c-style arrays is to compare the addresses of the 0th= =20 > element of each array - essentially testing whether a and b are the *same= =20 > actual array* rather than two arrays that contain data that compares equa= l. > > Comparing two std::span will certainly work, so for generic code you may= =20 > want to consider providing overloads/specialisations for span rather than= =20 > c-array. > > http://en.cppreference.com/w/cpp/container/span/operator_cmp > > =20 > >> >> bool foo() >> { >> int a1[4] =3D { 1, 2, 3, 4 }, a2[4] =3D { 1, 2, 3, 4 }; >> return (a1 <=3D> a2) =3D=3D 0; >> } >> >> I really hope so, and that would we could compare arrays of different=20 >> size too (always not equal) - useful for template code. >> >> Regards, >> Maciej >> >> --=20 >> You received this message because you are subscribed to the Google Group= s=20 >> "ISO C++ Standard - Future Proposals" group. >> To unsubscribe from this group and stop receiving emails from it, send a= n=20 >> email to std-proposal...@isocpp.org . >> To post to this group, send email to std-pr...@isocpp.org . >> To view this discussion on the web visit=20 >> https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/d50deead-c4= 60-414b-b356-a398772b8f69%40isocpp.org=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/fb962daa-db76-4b9c-9697-7d734d327852%40isocpp.or= g. ------=_Part_8237_615840004.1529082309693 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
I don't know how could it break existing function= ality, since spaceship operator is a new shiny thing in C++20. Just leave t= he old two way array comparison as it is (or even deprecate it, in order to= bring it back at some point later with expected behavior).

<= /div>
Regards,
Maciej

W dniu pi=C4=85tek, 15 cze= rwca 2018 17:52:13 UTC+2 u=C5=BCytkownik Richard Hodges napisa=C5=82:


On Fri, 15 Jun 2018 at 17:34, <m.ce...@gmai= l.com> wrote:
Hi,

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

Wouldn't this break existing functionality? The cu= rrent meaning of (a =3D=3D b) when a and b are c-style arrays is to compare= the addresses of the 0th element of each array - essentially testing wheth= er 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 gene= ric code you may want to consider providing overloads/specialisations for s= pan rather than c-array.


=C2=A0

bool=C2= =A0foo()
{
=C2=A0 =C2=A0 int a1[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 arrays of different size too (alwa= ys not equal) - useful for template code.

Regards,
Maciej

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