220 37528 article Path: news.gmane.org!.POSTED!not-for-mail From: Viacheslav Usov Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allowing std::complex's magic permission for other types Date: Wed, 28 Mar 2018 16:19:46 +0200 Lines: 59 Approved: news@gmane.org Message-ID: References: <018c02d9-7c65-4451-acc1-c49196fc7622@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="089e08256408018a0f056879b30e" X-Trace: blaine.gmane.org 1522246666 21889 195.159.176.226 (28 Mar 2018 14:17:46 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 28 Mar 2018 14:17:46 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBDU6VRPKW4BBBBGJ53KQKGQEQJOOAQA@isocpp.org Wed Mar 28 16:17:42 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f71.google.com ([74.125.83.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1f1BtV-0005ZJ-UH for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id w2sor1100264pgt.26.2018.03.28.07.19.47 for (Google Transport Security); Wed, 28 Mar 2018 07:19:47 -0700 (PDT) Received-SPF: pass (google.com: domain of via.usov@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.101.74.141 with SMTP id b13mr890434pgu.308.1522246787105; Wed, 28 Mar 2018 07:19:47 -0700 (PDT) Original-Received: by 10.236.175.138 with HTTP; Wed, 28 Mar 2018 07:19:46 -0700 (PDT) In-Reply-To: <018c02d9-7c65-4451-acc1-c49196fc7622@isocpp.org> X-Original-Sender: via.usov@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Lh+gJ6Mj; spf=pass (google.com: domain of via.usov@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=via.usov@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:37528 Archived-At: --089e08256408018a0f056879b30e Content-Type: text/plain; charset="UTF-8" On Wed, Mar 28, 2018 at 3:24 PM, Edward Catmur wrote: > No, you need magic to perform aliasing between any kind of array types. [expr.add]/4 does not permit aliasing, so any array arithmetic must remain within the bounds of an array that actually exists. Let's tackle a simpler question first. Suppose: int foo[5][2]; auto bar = reinterpret_cast(&foo[0][0]); Are you saying that bar[2] is not well-defined? Cheers, V. -- 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/CAA7YVg1Tt-hwYej80qK_Cr2RxvBtP3aM%2BEZ7gqC4RKz6z9aGPw%40mail.gmail.com. --089e08256408018a0f056879b30e Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On W= ed, Mar 28, 2018 at 3:24 PM, Edward Catmur <ed@catmur.co.uk> w= rote:

> No, you need magic to perform aliasing be= tween any kind of array types. [expr.add]/4 does not permit aliasing, so an= y array arithmetic must remain within the bounds of an array that actually = exists.

Let's tackle a simpler question first.= Suppose:

int foo[5][2];
auto bar =3D re= interpret_cast<int*>(&foo[0][0]);

Are yo= u saying that bar[2] is not well-defined?

Cheers,<= /div>
V.

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