Ada: packaging concepts [closed]

Answer 1

Another way to do this would be to use tagged types.

package Rectangular is
   type Instance is abstract tagged private;

   procedure Vector_Basis_r (A : in Long_Float; D : out Instance);
   procedure Set_Horz (R : in out Instance; H : Long_Float);
   function Get_Horz (R : Instance) return Long_Float;
private
   type instance is tagged null record;
end Rectangular;

with Rectangular;
package Rectangular_Method_1 is
    type Instance is new Rectangular.Instance with private;
    ...
private
    type Instance is new Rectangular.Instance with 
    record
        Horz, Vert: Long_Float;
    end record;
end Rectangular_Method_1;

(similar implementation for Rectangular_Method_2).

Then I believe you can write your code that uses it this way:

with Rectangular_Method_1;
with Rectangular_Method_2;
...
--  My_Rectangle : Rectangular_Method_1.Instance;
My_Rectangle : Rectangular_Method_2.Instance;

My_Rectangle.Set_Horiz(Whatever_Value);
...

In other words, all you'd have to change when switching between the two is the type names. Your client could even get rid of those changes by using a single subtype at the top.

subtype Rectangle_Instance is Rectangular_Method_2.Instance;

This would also give you the ability to move common code/fields up into the base class (package), which I think is sort of what you were after.