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From: ncohen@watson.ibm.com (Norman H. Cohen)
Newsgroups: comp.lang.ada
Subject: Re: cross linking packages
Date: 29 Nov 1994 18:28:47 GMT
Organization: IBM T.J. Watson Research Center
Distribution: world
Message-ID: <3bfrsv$1e2o@watnews1.watson.ibm.com>
References: <CzzAMz.K9F@inter.NL.net>
Reply-To: ncohen@watson.ibm.com
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Date: 1994-11-29T18:28:47+00:00
List-Id: <comp.lang.ada>

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