Re: Modular types inside records

[Jeff Carter <jrcarter@acm.org>]

"Pawe� Niewiadomski" wrote:
> generic
>     type item_type is private;
>     type mod_n_max is mod <>;
> package queues is
>     type queue is tagged private;
>     function empty (q: queue) return boolean;
>     function full (q: queue) return boolean;
>     procedure add (q: queue; item: in item_type);
>     procedure remove (q: queue; item: out item_type);
> private
>     type arr is array (natural range <>) of item_type;
>     procedure move_to_0 (var: out natural);
>     procedure move_to_last (var: out natural; values: in arr);
> 
>     type queue is tagged record
>         values: arr (0..mod_n_max'modulus-1);
>         tail: mod_n_max:=0;
>         head: mod_n_max:=1;
>     end record;
> end queues;

As you have probably found out, this won't work very well, since your
array is indexed by Natural and your index variables are Mod_N_Max. You
can put a bunch of type conversions in your code to work around this,
but it would be clearer to define

   type Arr is array (Mod_N_Max) of Item_Type;

I have no idea why you have included the procedures Move_To_0 and
Move_To_Last in the private part.

-- 
Jeff Carter
"I waggle my private parts at your aunties."
Monty Python & the Holy Grail