220 38671 <9c6a84e4-66a2-4a25-8372-c7a6c7b8de25@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Barry Revzin Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Three way comparison of arrays Date: Fri, 15 Jun 2018 10:45:12 -0700 (PDT) Lines: 108 Approved: news@gmane.org Message-ID: <9c6a84e4-66a2-4a25-8372-c7a6c7b8de25@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_8245_117857566.1529084712130" X-Trace: blaine.gmane.org 1529084588 27036 195.159.176.226 (15 Jun 2018 17:43:08 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 15 Jun 2018 17:43:08 +0000 (UTC) Cc: m.cencora@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCJJTG7CS4ARBKPWR7MQKGQE7A2LOHA@isocpp.org Fri Jun 15 19:43:04 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f198.google.com ([209.85.213.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fTskZ-0006v3-RK for gclcip-std-proposals@m.gmane.org; Fri, 15 Jun 2018 19:43:03 +0200 Original-Received: by mail-yb0-f198.google.com with SMTP id x134-v6sf7360549ybg.2 for ; Fri, 15 Jun 2018 10:45:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc: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=FIdZEm7OjbZEDnx0/R+ICwKYIWAS2UmGTEsWex4p0Wo=; b=Zb0/woqKxrMuhBxgk1xtT+glXeqsbOWe5an04pR0EBM+tT0oghd01YLus2WzX88XSX HgBNs/DEQ0ySIS9TVrReVqG5Q9/RVJwpoS6S2lMu2b8w0bFzvP1ZrgJ1gvil247DZW6j dWD4L50EbtH6/DyNbCPOHHBySLHq8WRSIOAz6hGtjx48BXZeR0MSCi2kyHIyWTlkeXF3 WyXYtVE5GaZKqrA6MogDvxRWON91AGB8AynKRcJCYAjydnh0HHXAAtMuC98AQIC57n6S OWBzwXhOS03AEH2lO4YxB2Y88GhmmqZenUEyXHeYFUXbgElXc8ely64tTz0B31KLEcgC f7dg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc: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=FIdZEm7OjbZEDnx0/R+ICwKYIWAS2UmGTEsWex4p0Wo=; b=lw2u8ED5KnlxbtZ4/qFcWdRRvSOXXRr/Np66R+rgX9dWGnlE1mXpu8KIRrSVYqzyVs 5Rbmqi8PKPBaAEa/jodKKCkyRqZ05Qg5GAQRxJ1BBhxcCX15wBvjS1Ad9XaInuPyB6Qa k4NS4uq5xWv3mmg+rIVemELfNJAxGgrLdOK6b0KR5RAWkQREbO0RXSvdtPilHtS//luQ Y9B84/Lm6HwgXQesRn84lmSI6Oab7qMLK+3sdhjVRc+BnU4EHRCaGAi1MwCCTUJuk6Fy ITct4Z0Y3lfiWCOedm2ofSUD3ctSLycBu7V/32v9too73tDoYVFBPfZh6/6N6YAkYIHf DCkQ== 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:cc: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=FIdZEm7OjbZEDnx0/R+ICwKYIWAS2UmGTEsWex4p0Wo=; b=qxuzpp8Goo3iKMwFtltfRnxl40dqeRAEUz/v5QK9dDQR+GE33VISsYvv05csVovqn/ kXmh8TjKyG9fmQkLNN5gTxEpdwWKHSbQFfAqx62PJnFvBcQKiJ9AVMYXYtvIi1UcODSK GG9baMjL8uKRcAi5NO8snH8Rn29Qhl3p5TQ1k1AUMPz/7OcI0CWg+HezkPFVLtFNhTgY YhiZLtRIuM4SKQdZo2Qaugi5lXwmlxafxts2mibquaa7wzS2cnSwqcOYE0ru9gTk/g88 JOpZU6iVqOUUySyWE2FIs1zYfHmcq5d13x4TGiPX/ApW77IcLVwkuAyf84LNgqYE1v1r lCIQ== X-Gm-Message-State: APt69E2myePEP/YOB7ckrJU33b4LPX01Eu715d3BD+WjavZNGcL8wIyj 6P1vy+hoHuH0EXAinVxdRWiqvQ== X-Google-Smtp-Source: ADUXVKKnVeUmBQG2jzPeaELaPL/qnYTyzG1rZNhyQ2We8cMy7wGksWkCfxjQLVcUWsYiFBrvLAwyJA== X-Received: by 2002:a81:5ed4:: with SMTP id s203-v6mr737522ywb.73.1529084714342; Fri, 15 Jun 2018 10:45:14 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a81:4c89:: with SMTP id z131-v6ls1510502ywa.14.gmail; Fri, 15 Jun 2018 10:45:13 -0700 (PDT) X-Received: by 2002:a81:7a10:: with SMTP id v16-v6mr113024ywc.3.1529084713006; Fri, 15 Jun 2018 10:45:13 -0700 (PDT) In-Reply-To: X-Original-Sender: Barry.Revzin@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:38671 Archived-At: ------=_Part_8245_117857566.1529084712130 Content-Type: multipart/alternative; boundary="----=_Part_8246_1425871839.1529084712130" ------=_Part_8246_1425871839.1529084712130 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Friday, June 15, 2018 at 10:34:10 AM UTC-5, m.ce...@gmail.com wrote: > > Hi, > > can we finally write idiomatic comparison code for arrays with three way= =20 > compare? > > bool foo() > { > int a1[4] =3D { 1, 2, 3, 4 }, a2[4] =3D { 1, 2, 3, 4 }; > return (a1 <=3D> a2) =3D=3D 0; > } > > > No. This is explicitly rejected by design. Quoting=20 from http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0515r3.pdf: For arrays, we don=E2=80=99t provide comparison if the array is not copyabl= e in the=20 > language, to keep copying and comparison consistent. Note that for two=20 > arrays, arr1<=3D>arr2 is ill-formed because the array-to-pointer conversi= on=20 > is not applied > Additionally, in Rapperswil, the two-way comparisons between arrays (i.e.= =20 a1 =3D=3D a2) were deprecated. So now at least they both consistently will = not=20 work.=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/9c6a84e4-66a2-4a25-8372-c7a6c7b8de25%40isocpp.or= g. ------=_Part_8246_1425871839.1529084712130 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Friday, June 15, 2018 at 10:34:10 AM UTC-5, m.c= e...@gmail.com wrote:
Hi,

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

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;
}


<= /div>

No. This is explicitly re= jected by design. Quoting from=C2=A0=C2=A0http://www.open-std.org/jtc1/sc22= /wg21/docs/papers/2017/p0515r3.pdf:

For arrays, we don=E2=80=99t provi= de comparison if the array is not copyable in the language, to keep copying and comparison consistent. Note that for two arrays, arr1<=3D>arr2 is= ill-formed because the array-to-pointer conversion is not applied

Additionally,= in Rapperswil, the two-way comparisons between arrays (i.e. a1 =3D=3D a2) = were deprecated. So now at least they both consistently will not work.=C2= =A0

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