220 37551 article Path: news.gmane.org!.POSTED!not-for-mail From: Hyman Rosen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allowing std::complex's magic permission for other types Date: Wed, 28 Mar 2018 15:12:35 -0400 Lines: 80 Approved: news@gmane.org Message-ID: References: <018c02d9-7c65-4451-acc1-c49196fc7622@isocpp.org> <1e25a8ae-4752-4fc0-8c89-639cef53121c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a114b3e7e6b5c4605687dcbda" X-Trace: blaine.gmane.org 1522264257 12951 195.159.176.226 (28 Mar 2018 19:10:57 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 28 Mar 2018 19:10:57 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDKJJPVBQMKRBOWS57KQKGQEF7Y4PHQ@isocpp.org Wed Mar 28 21:10:53 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f71.google.com ([74.125.82.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1f1GTD-0003FG-Hw for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id x3sor61333wmb.33.2018.03.28.12.12.57 for (Google Transport Security); Wed, 28 Mar 2018 12:12:57 -0700 (PDT) Received-SPF: pass (google.com: domain of hyman.rosen@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.28.153.213 with SMTP id b204mr3466212wme.79.1522264376563; Wed, 28 Mar 2018 12:12:56 -0700 (PDT) Original-Received: by 10.28.55.19 with HTTP; Wed, 28 Mar 2018 12:12:35 -0700 (PDT) In-Reply-To: X-Original-Sender: hyman.rosen@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=iL1zSCUk; spf=pass (google.com: domain of hyman.rosen@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=hyman.rosen@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:37551 Archived-At: --001a114b3e7e6b5c4605687dcbda Content-Type: text/plain; charset="UTF-8" On Wed, Mar 28, 2018 at 12:38 PM, 'Edward Catmur' via ISO C++ Standard - Future Proposals wrote: > > That's [expr.eq]/2.2, which comes after 2.1 and is guarded by an > "Otherwise". > In my copy of the Draft Standard, N4700, [expr.eq]/2.1 says *If one pointer represents the address of a complete object,and another pointer represents the address * *one past thelast element of a different complete object, the result of thecomparison is unspecified.* A complete object is not a subobject of another object, therefore this clause does not apply to the array elements in question, which are perforce not complete objects. So [expr.eq]/2.2 is active, and says *Otherwise, if the pointers are both null, both point to the same function, or both represent the same **address, they compare equal.* -- 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/CAHSYqdZ9uOf3D1h4Eo61PV_jpsn6SUUzf9DhLuAwMTDrJ%3D1RMA%40mail.gmail.com. --001a114b3e7e6b5c4605687dcbda Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On W= ed, Mar 28, 2018 at 12:38 PM, 'Edward Catmur' via ISO C++ Standard = - Future Proposals <std-proposals@isocpp.org> wrote:<= blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-l= eft:1px solid rgb(204,204,204);padding-left:1ex">
That's [expr.eq]/2.2,= which comes after 2.1 and is guarded by an "Otherwise".

In my copy of the Draft Standard, N470= 0, [expr.eq]/2.1 says

If one pointer represents the address of = a complete object,
and another pointer represents the address=C2=A0<= i>one past the
last element of a different complete object, the result o= f the
comparison is unspecified.

A complete object is not a subobject of another object,= therefore this clause
does not apply to the array elements in question,= which are perforce not
complete objects.=C2=A0 So [expr.eq]/2.2 is acti= ve, and says

Otherwise, if the pointers are both null, both point to t= he same
function, or both represent the same=C2=A0address, they = compare equal.

--
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