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=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,74a56083ffbe573d X-Google-Attributes: gid103376,public From: kst@thomsoft.com (Keith Thompson) Subject: Re: Zoo question Date: 1996/08/15 Message-ID: #1/1 X-Deja-AN: 174294105 sender: news@thomsoft.com (USENET News Admin @flash) x-nntp-posting-host: pulsar references: <320F16B6.6944@lmtas.lmco.com> <3210A142.2781E494@escmail.orl.mmc.com> organization: Thomson Software Products, San Diego, CA, USA newsgroups: comp.lang.ada originator: kst@pulsar Date: 1996-08-15T00:00:00+00:00 List-Id: In <3210A142.2781E494@escmail.orl.mmc.com> Ted Dennison writes: > Ken Garlington wrote: > > > > Here's a little brain teaser we received recently. Assuming no typos or > > other obvious syntax errors, will the Fill procedure work in Ada 83? > > OK. I'll bite. It looks like it would probably perform as advertised, with > no optimization set on the compiler. The following constraint check code - > > > > > Get_Next_Animal: begin -- look carefully at this code! > > Next_Animal := Animal_ID'Succ(Next_Animal); > > exception > > when others => Next_Animal := Animal_ID'First; > > end Get_Next_Animal; > > isn't guaranteed to work (assuming "work" means raise an execption within > this block when Animal_ID'Succ(Next_Animal) > Animal_ID'last). I believe it *is* guaranteed (by the language) to work. In both Ada 83 and Ada 95, the Animal_ID'Succ attribute is a function that takes a value of type Animal_ID'Base and returns a value of type Animal_ID'Base. Since Animal_ID'Base will almost certainly have bounds greater than 1..5, Animal_ID'Succ(5) will return 6, without raising an exception. However, attempting to assign the resulting value to Next_Animal *must* raise Constraint_Error, since Next_Animal is of subtype Animal_ID and is constrained to the range 1..5. I can imagine a compiler implementer mistakenly thinking that the Succ attribute returns a value of the prefix subtype, and optimizing out the check. If this is what you're seeing, it's clearly a compiler bug. Incidentally, this worked as expected (i.e., properly raised Constraint_Error) on every Ada 83 and Ada 95 compiler I tried. -- Keith Thompson (The_Other_Keith) kst@thomsoft.com <*> TeleSoft^H^H^H^H^H^H^H^H Alsys^H^H^H^H^H Thomson Software Products 10251 Vista Sorrento Parkway, Suite 300, San Diego, CA, USA, 92121-2718 "As the most participatory form of mass speech yet developed, the Internet deserves the highest protection from government intrusion." -- ACLU v. Reno