Re: Processing array subsections, a newbie question.

["Peter C. Chapin" <pcc482719@gmail.com>]

Phil Thornley wrote:

> I don't think the state machine will make any difference, but you
> certainly can't exit an enclosing loop when in a case arm - you have
> to move the exit(s) to after the 'end case'.
> 
> This is not usually too much of a problem, but in your code it forces
> the exit to come after the increment (assuming that this has to stay
> in the case arm).

Yes that could be a problem for me. On the other hand *most* of the cases do
the increment. With a little thought I might be able to make them all do the
increment... and then factor that out of the case.

> As you suggest elsewhere in this thread, it is a good idea to have
> subtype constraints as tight as possible.  In the situation you
> describe I would define a type (to replace your use of Natural) that
> has one extra value at the end (for the Index_Fst variable).  Then
> define the array index as a subtype that excludes that extra value.
> This should allow the increment to stay in the case arm, with the exit
> following after the case.

That sounds like what I've got at the moment. Maybe I'll just end up sticking
with that and see how it plays out.

> (BTW, if you haven't tried it yet, you will find that using
> unconstrained arrays creates additional work when doing run-time
> checks as the VCs generated by any reference to an array element use
> the limits for that array object, not just the array index subtype).

I'll keep that in mind. I could probably defined a constrained array type
instead. In my situation the array sizes should only vary between about 20
and 40 elements. I could probably just define the array to have 40 elements
(or whatever I actually need... I'll have to check). My state machine just
returns once it is satisfied so it will ignore the extra "junk" if there is
any. I think that would be okay.

Thanks for your input.

Peter