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=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Ada 2012 Constraints (WRT an Ada IR) Date: Wed, 7 Dec 2016 11:20:07 +0100 Organization: Aioe.org NNTP Server Message-ID: References: <92ed75e9-baae-455c-9e34-53348dc6eaef@googlegroups.com> <03847fd7-5699-48de-bb3c-ef5512398f26@googlegroups.com> <3ef819e8-55f7-4ef7-9f37-77e6abc33f98@googlegroups.com> <47366b42-c0a3-41bf-a44a-5241c109d60f@googlegroups.com> NNTP-Posting-Host: vZYCW951TbFitc4GdEwQJg.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:32651 Date: 2016-12-07T11:20:07+01:00 List-Id: On 07/12/2016 00:15, Randy Brukardt wrote: > "Dmitry A. Kazakov" wrote in message > news:o24phv$1ou6$1@gioia.aioe.org... >> On 2016-12-05 23:12, Randy Brukardt wrote: > ... >>> Until you compare to the alternative, which is a subprogram body that >>> gives the wrong answer without detection. As I said in another message, a >>> visible bug is much better than an invisible bug. >> >> The alternative is a contract to raise exception. So there is no bug >> anymore, just well-defined behavior. > > All contracts raise an exception (I'm pretty sure Assertion_Error is an > exception :-). They don't raise, it was sloppy language. A correct statement would be that the contract requires the behavior to propagate exception. In that sense, namely when you willing to include it into the contract, Assertion_Error is not a violation of, but a fulfillment of. > Moreover, most contracts (at least the ones I'd write) raise specific > exceptions (not Assertion_Error). Indeed, this is a far better way to define > something that raises an exception than an English comment. (Which is the > only other alternative for the specification - and its the specification > that matters, not the body.) As I said in another post it is a bad idea. The list exceptions, their names, must tell the reader when they are to propagate. You could specify the exact condition in a few very limited cases. In a real life scenario you cannot specify the Boolean expression guarding Disk_Error. Moreover, in most cases that would be an over-specification. My point is that either you don't need the expression or else it must/can be statically provable and thus become a proper pre-/post-condition with no exceptions involved. -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de