Dispatching with a child for a parameter? (was: Freezing question)

[Ted Dennison <dennison@telepath.com>]

In article <379347D8.A902583C@averstar.com>,
  Tucker Taft <stt@averstar.com> wrote:
> Ted Dennison wrote:
> > Ahhh. I bet that's it. Does that mean that in the example above,
Apple
> > will inherit *none* of Fruit's operations, since none of them were
> > declared before Apple?
>
> Correct.  See 7.3.1(7).


Ahhh. OK. So I'll ask the next question (with the topic appropriately
renamed:

How would one implement a hierarchy where one object has dispatching
operations that take a specific one of its chilren types as parameters?
I'm running out of ideas.

eg:

   type Widget is abstract tagged private;
   type Container is abstract new Widget with private;

   procedure Add
      (Child  : in out Widget;
       Parent : in out Container'Class
      );

Won't quite work because Add won't be inherited by any Containers unless
it is placed before the declaration of Container. But if I move it
between the two declarations, it won't compile because Container won't
have been declared yet.

--
T.E.D.


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