Re: Zoo question

[rgilbert@unconfigured.xvnews.domain (Bob Gilbert)]

In article <3211C9C6.41C67EA6@escmail.orl.mmc.com>, Ted Dennison <dennison@escmail.orl.mmc.com> writes:
> Bob Gilbert wrote:
> > 
> > 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
> > 
> > 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
> 
> This didn't sound right to me, so its LRM time...
> 
> 3.5.4 -
> the type declaration is equivalent to -
> 
>    type integer_type is new predefined_integer_type;
>    subtype Animal_ID is integer_type range 1..5;
> 
> where integer_type is an ananoymous base type, snd predefined_integer_type
> can be any predefined integer type the compiler wants, as long as it 
> includes 1 and 5.
> 
> Thus the base type is NOT integer.

I guess I should have said that the base type of Animal_ID is *equivalent* to
or derived from type integer, at least as far as the constraints are concerned.

> However, the base type's range may well be the same as integer's.

As I would expect it to be.

> 3.5.5(8) -
> 
>  Animal_ID'SUCC(Next_Animal) 
> 
> returns a value in the range of the BASE type of Animal_ID, which is the
> range of whatever predefined type the compiler picked above. However, 
> when this value is assigned back into Next_Animal, it is subject to a
> constraint check on the 1..5 range. The constraint check doesn't HAVE to
> happen, but it could.

That's what I said (I think).  The attribute 'Succ is not constrained to
the specified range 1 .. 5, but I think I would expect a constraint check
to raise an exception when making the assignment back to Next_Animal.

-Bob