Re: How to?: Re-dispatching within an inherited method

["David C. Hoos, Sr." <david.c.hoos.sr@ada95.com>]

Anthony E. Glover wrote in message <37AF0ADE.3D80FEB3@hiwaay.net>...
>Is it possible to re-dispatch a method call within an inherited method?
>For example:
>
>package A defines a type widget that has methods widget_size and
run_widget.
>package B defines a type bigwidget that has an overriding method for
>widget_size, but
>inherits the run_widget method without modification.
>Within package A, run_widget makes a call to widget_size.  Is it
>possbile to force
>a re-dispatch such that the appropriate widget_size method gets called
based
>on the object passed into run_widget?
>
Yes.  You need to type convert the actual parameter in the call to
Widget'Class to make the call a dispatching call.  See RM 95 3.9.2 (1, 5).

As in the example:

with Ada.Text_IO;
package body A is

   procedure Run_Widget (The_Widget : Widget'Class) is
   begin
      Ada.Text_IO.Put_Line
        ("in Run_Widget (The_Widget : Widget): Size =" &
         Positive'Image (Widget_Size (Widget'Class (The_Widget))));
   end Run_Widget;

   function Widget_Size (The_Widget : Widget) return Positive is
   begin
      return 1;
   end Widget_Size;

end A;


package A is
   type Widget is tagged null record;
   procedure Run_Widget (The_Widget : Widget'Class);
   function Widget_Size (The_Widget : Widget) return Positive;
end A;

package body B is
   function Widget_Size (The_Widget : BigWidget) return Positive is
   begin
      return 10;
   end Widget_Size;
end B;

with A;
package B is
   type BigWidget is new A.Widget with null record;
   function Widget_Size (The_Widget : BigWidget) return Positive;
end B;

with A;
with B;
procedure Glover is

   The_Widget : A.Widget;
   The_BigWidget : B.BigWidget;

begin

   A.Run_Widget (The_Widget);
   A.Run_Widget (The_BigWidget);

end Glover;