220 37552 article Path: news.gmane.org!.POSTED!not-for-mail From: "'Edward Catmur' via ISO C++ Standard - Future Proposals" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allowing std::complex's magic permission for other types Date: Wed, 28 Mar 2018 19:17:20 +0000 Lines: 135 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="f403045f1c6acbd85c05687ddb4f" X-Trace: blaine.gmane.org 1522264533 1163 195.159.176.226 (28 Mar 2018 19:15:33 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 28 Mar 2018 19:15:33 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDZLZTXF7UJBBTGU57KQKGQESSJMTVQ@isocpp.org Wed Mar 28 21:15:29 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f69.google.com ([74.125.82.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1f1GXd-00008t-Hv for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id k17sor2252839wre.28.2018.03.28.12.17.31 for (Google Transport Security); Wed, 28 Mar 2018 12:17:31 -0700 (PDT) Received-SPF: pass (google.com: domain of ecatmur@googlemail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.223.161.145 with SMTP id u17mr4216006wru.61.1522264651321; Wed, 28 Mar 2018 12:17:31 -0700 (PDT) In-Reply-To: X-Original-Sender: ecatmur@googlemail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@googlemail.com header.s=20161025 header.b=GIgWAs7u; spf=pass (google.com: domain of ecatmur@googlemail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=ecatmur@googlemail.com; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=googlemail.com X-Original-From: Edward Catmur 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:37552 Archived-At: --f403045f1c6acbd85c05687ddb4f Content-Type: text/plain; charset="UTF-8" On Wed, 28 Mar 2018, 20:13 Hyman Rosen, wrote: > 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.* > > -- > Oh, I missed that. Thanks for the correction. I agree that in this case the pointers are required to compare equal. You received this message because you are subscribed to a topic in the > Google Groups "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this topic, visit > https://groups.google.com/a/isocpp.org/d/topic/std-proposals/HpRRF7RWzTY/unsubscribe > . > To unsubscribe from this group and all its topics, 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 > > . > -- 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/CAJnLdOb2-CwDFtfdFDFX3OxnL%2B3Qv2%3DDtk0noy54nZX3kZOpMA%40mail.gmail.com. --f403045f1c6acbd85c05687ddb4f Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


= On Wed, 28 Mar 2018, 20:13 Hyman Rosen, <hyman.rosen@gmail.com> wrote:
On Wed, Mar 28, 2018 at 12:38 PM, 'Edward Catmur' via ISO= C++ Standard - Future Proposals <std-proposals@= isocpp.org> wrote:
That's [expr.eq]/2.2, which comes after 2.1 and is guarded by a= n "Otherwise".

In my= copy of the Draft Standard, N4700, [expr.eq]/2.1 says

<= /div>
=
If one p= ointer represents the address of a complete object,
and another pointer = represents the address=C2=A0one past the
last element of a differ= ent complete object, the result of 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 active, and says

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

--

Oh, I missed that. Thanks for the correction. I agree that in this case = the pointers are required to compare equal.=C2=A0

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