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From: rgilbert@unconfigured.xvnews.domain (Bob Gilbert)
Subject: Re: Zoo question
Date: 1996/08/14
Message-ID: <4usdkl$fg6@zeus.orl.mmc.com>#1/1
X-Deja-AN: 174139217
references: <320F16B6.6944@lmtas.lmco.com>
organization: The unconfigured xvnews people
reply-to: rgilbert@unconfigured.xvnews.domain
newsgroups: comp.lang.ada
Date: 1996-08-14T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <320F16B6.6944@lmtas.lmco.com>, Ken Garlington <garlingtonke@lmtas.lmco.com> writes:
> 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?
> 
> package Zoo is
> 
>   type Animal_ID is range 1 .. 5; -- yes, an enumeration type might be
>  	                                -- better, but it spoils the example!

{snip}

>       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;

I assume that the tricky part is that the attribute 'Succ operates
on the base type of Animal_ID, which is of type integer, and does not
consider the constraint 1 .. 5 (although the attributes 'First and
'Last do).  That is if Next_Animal := 5, then Animal_ID'succ(Next_Animal)
would not raise an exception but would return the value 6.  However, 
I would expect an exception to occur when attempting to assign the 
result back to Next_Animal, so the code would probably produce the 
expected result (or perhaps not?).

Of course using an enumeration type for Animal_ID would avoid the
confusion.

Is this any different for Ada 95?

-Bob