Polymorphism

[slos <new.stephane.los@gmail.com>]

Hello,

Please consider the following simple case :

package Object is
   
   type Instance is abstract tagged private;
   
   function Distance (O : Instance'Class) return Float;
   
   function Weight (O : Instance'Class; Coef : Float) return Float;
   --  returns Area * Coef
   
   function Area (O : Instance) return Float is abstract;
   
private
   
   type Instance is abstract tagged
      record
         X_Coord : Float;
         Y_Coord : Float;
      end record;
   
end Object;

with Object; use Object;

package Circle is

   type Instance is new Object.Instance with private;

private

   type Instance is new Object.Instance with
      record
         Radius : Float;
      end record;

   overriding
   function Area (C : Instance) return Float;

end Circle;

I'd like function Object.Area to stay private but the compiler doesn't see it like that and complains if I try to move it in the private part.

In other words, I'd like to not expose internals to clients of the package.

Any hint to achieve that ?

Thanks in advance.

BR,
Stéphane