access types and dispatching subprograms

[kbrun@ibm.net]

I have some trouble with Ada95 dispatching subprograms and access types.
AFAIK, a proc. call should dispatch if all corresponding actual parameters
are of (*or pointing to*) type T'Class and if the formal parameters are
of (*or pointing to*) type T. Still, the following code sample doesn't
work.

--

package T is

   type T is tagged null record;
   type T_p is access all T;
   type TC_p is access all T'class;

   type T1 is new T with null record;
   type T1_p is access all T1;

   procedure disp(p: T_p);
   procedure disp(p: T1_p);

   procedure do_dispatch;
end T;

package body T is

   procedure disp(p: T_p) is
   begin
     Put("T_p");
   end disp;

   procedure disp(p: T1_p) is
   begin
     Put("T1_p");
   end disp;

   procedure do_dispatch is
      classp: TC_p := new T1;
   begin
      disp(classp);	-- this call won't dispatch, instead it causes
                        -- a compiler error. what's wrong?
   end do_dispatch;
end x;

--

Could someone please enlighten me on this subject?

-- Klaus A. Brunner   Austria, Europe
-- mailto:kbrun@ibm.net