Re: cross linking packages

[ncohen@watson.ibm.com (Norman H. Cohen)]

In article <CzzAMz.K9F@inter.NL.net>, rburema@inter.NL.net (Rene Burema)
writes: 

|> I have a problem specifing a seemingly simple problem in Ada. Anybody
|> want to help?
|>
|> The problem is as follows: 
|>
|> -------------------- package A -----------------------
|> package A;
|> type tA is private;
|> procedure giveB(x: in tA,y: out tB);
|> end A;
|> -------------------- package B -----------------------
|> package B;
|> type tB is private;
|> procedure giveA(x: in tB,y: out tA);
|> end B;
|> ---------------
|> where tA could be a reference to a  Doctor giving the reference to
|> a Patient (tB) and vice versa.
|>
|> I need a with statement for B and A respectively. The Ada gnat compiler
|> however stumbles into a circular dependency. How can I solve this without
|> placing the two types tA and tB in a single package.

package Parents is
   type tA_Parent is abstract tagged null record;
   type tB_Parent is abstract tagged null record;
end Parents;

with Parents;
package A is
   type tA is new tA_Parent with private;
   procedure giveB(x: in tA_Parent'Class; y: out tB_Parent'Class);
private
   type tA is new tA_Parent with ...;
end A;

with Parents;
package B is
   type tB is new tB_Parent with private;
   procedure giveA (x: in tB_Parent'Class; y: out tA_Parent'Class);
private
   type tB is new tB_Parent with ...;
end B;

--
Norman H. Cohen    ncohen@watson.ibm.com