From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: 103376,7d83a6223f4f2443 X-Google-Attributes: gid103376,domainid0,public,usenet X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!postnews.google.com!f3g2000yqf.googlegroups.com!not-for-mail From: Ludovic Brenta Newsgroups: comp.lang.ada Subject: Re: Run-time accessibility checks Date: Sun, 7 Dec 2008 06:56:49 -0800 (PST) Organization: http://groups.google.com Message-ID: <877dccaf-67d2-47ba-951d-2546ab500f75@f3g2000yqf.googlegroups.com> References: <68719e0e-af31-488a-b45c-f8db93fb70d2@v13g2000yqm.googlegroups.com> NNTP-Posting-Host: 94.108.199.211 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Trace: posting.google.com 1228661809 3488 127.0.0.1 (7 Dec 2008 14:56:49 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Sun, 7 Dec 2008 14:56:49 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: f3g2000yqf.googlegroups.com; posting-host=94.108.199.211; posting-account=pcLQNgkAAAD9TrXkhkIgiY6-MDtJjIlC User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.8.1.17) Gecko/20080829 Iceape/1.1.12 (Debian-1.1.12-1),gzip(gfe),gzip(gfe) Xref: g2news2.google.com comp.lang.ada:3887 Date: 2008-12-07T06:56:49-08:00 List-Id: On Dec 7, 9:44 am, "Dmitry A. Kazakov" wrote: > On Sat, 6 Dec 2008 09:10:49 -0800 (PST), Ludovic Brenta wrote: > > Dmitry A. Kazakov wrote: > >> It is absolutely unacceptable to me that a correct > >> program might fail at run-time because of accessibility checks. > > > I differ here; to me, a program that fails an accessibility check at > > run time is incorrect. > > Ah, I used to think this way too. But then I realized that this form of > constraint is not a semantic one. Comparing to the constraint range 1..10, > accessibility constraint is an implementation detail. It has no semantic > meaning. When you assign a value outside the range that is semantically > incorrect. When you assign a pointer that potentially might become > dangling, that has no semantic meaning. The pointer is not yet dangling. > The program correctness depends on whether it will become dangling. My definition of correctness is a bit more demanding. I want to be *certain* that the pointer *cannot* become dangling, *ever*, especially in the face of software maintenance where the program changes. That's what accessibility checks give me, and I am grateful for their existence and I will design my programs so as not to fail accessibility checks. -- Ludovic Brenta.