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,FREEMAIL_FROM autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: 103376,6327f05d4989a68d X-Google-NewGroupId: yes X-Google-Attributes: gida07f3367d7,domainid0,public,usenet X-Google-Language: ENGLISH,UTF8 X-Received: by 10.66.82.103 with SMTP id h7mr3534545pay.11.1356364180876; Mon, 24 Dec 2012 07:49:40 -0800 (PST) Path: 6ni62194pbd.1!nntp.google.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 24 Dec 2012 09:49:40 -0600 Date: Mon, 24 Dec 2012 10:49:39 -0500 From: "Peter C. Chapin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 Newsgroups: comp.lang.ada Subject: Exception contracts for Ada? Was: Re: Press Release - Ada 2012 Language Standard Approved by ISO References: <7wrdmbre6jw9.qww9l0uzj6mg.dlg@40tude.net> <14oqoq06zhlu2.tcasif3hdyhw.dlg@40tude.net> <1drh1q1ln2dfh$.a9hwlg01fjfy.dlg@40tude.net> <50d6365d$0$6577$9b4e6d93@newsspool3.arcor-online.net> <1pbg79bz92j3t$.sz41zduivjfp.dlg@40tude.net> In-Reply-To: Message-ID: <46idnVdMEr8J5EXN4p2dnAA@giganews.com> X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-gTJ2/RyxXujpFo61tb039DnNRw8BkY/T8KjG+9FbSY7tOfcE4nqrW0NJveaqOJtdSiSFJYa2T5OvQ37!C/b1b15zEkC+dLyalZ2+QU3stWrMA+R+66Y2HBbNDCvKz67pMrvrqFHWamG8760= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 X-Original-Bytes: 4408 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: 2012-12-24T10:49:39-05:00 List-Id: On 12/24/2012 06:13 AM, Yannick Duchêne (Hibou57) wrote: > This one is fine, I see your point now. Exception contracts are a huge, HUGE topic and one that shouldn't be treated too lightly. I can understand their attraction in a language that prides itself on its suitability for robust programming. However, if exception contracts are ever added to Ada I pray to the Ada gods (the ARG?) that it is only done after an extensive review has been made of the issues related to them in other languages. One only needs to search for the topic of exception specifications in C++ and Java to find a mountain of discussion on the subject. Consider: + Should exception contracts be enforced statically or dynamically? + Should exception contracts be enforced at all or only produce warnings or logs? + What about backward compatibility with the existing code base? We don't want to force people to decorate all code with exception contracts before it will compile again with Ada 2020 (or whatever). Do we? + Should exception contracts distinguish between "impossible" exceptions that shouldn't occur in a correct program (like Constraint_Error) and "normal" exceptions that pertain to environmental problems such as invalid input data? + How should exception contracts interact with generic code? + Should exception contracts be a part of a subprogram's type? Consider access to subprogram values and their usage. + How should exception contracts interact with other static analysis techniques? For example if a subprogram has a contract that says it might raise exception E, but if static analysis can prove that a particular usage will not actually raise E, does the programmer have to declare a contract on the calling subprogram about E? One objection I've heard about exception specifications in Java is that they require programmers to either specify (or handle) exceptions that "clearly" can never actually arise at that particular program point. Now that Ada has preconditions the last point is particularly acute. The precondition on a procedure P might guarantee that a called subprogram won't raise an exception that it might nevertheless declare in its exception contract. It would be really unpleasant if the programmer had to also add an exception contract to P stating that it might raise an exception that the programmer knows the precondition will prevent! This is just a sample of some of the issues involved in the subject. There are those who have answers for all of these issues. That's great. But again I sincerely hope that if exception contracts are ever seriously considered for Ada that the matter be given the deep consideration it deserves. Peter