Re: Deallocating list of polymorphic objects?

[Matthew Heaney <matthewjheaney@earthlink.net>]

"Michael Rohan" <mrohan@ACM.ORG> writes:

> I would like to construct a list of polymorphic objects that,
> as part of the list's finalization, deallocates the objects on
> the list.  Basically, I have a vector of pointers to Object'Class.
> The objects are added to the list via procedures defined for
> the list, e.g., append an integer, append a floating point.
> These append procedures allocate objects derived from the
> base Object type for the type being appended, e.g.,
> Integer_Object, which is private to the list package.


Here's one way to do it:

--STX
with Ada.Containers.Indefinite_Vectors;
pragma Elaborate_All (Ada.Containers.Indefinite_Vectors);

package Lists is

   type List_Type is tagged limited private;

   procedure Append (L : in out List_Type; I : Integer);
   procedure Append (L : in out List_Type; F : Float);

private

   type Object is interface;
   procedure Print (O : Object) is abstract;

   package List_Vectors is
      new Ada.Containers.Indefinite_Vectors (Natural, Object'Class);

   type List_Type is tagged limited record
      V : List_Vectors.Vector;
   end record;


   type Integer_Object is new Object with record
      I : Integer;
   end record;

   procedure Print (O : Integer_Object);

   type Float_Object is new Object with record
      F : Float;
   end record;

   procedure Print (O : Float_Object);

end Lists;


package body Lists is

   procedure Append (L : in out List_Type; I : Integer) is
   begin
      L.V.Append (Integer_Object'(I => I));
   end;

   procedure Append (L : in out List_Type; F : Float) is
   begin
      L.V.Append (Float_Object'(F => F));
   end;

   procedure Print (O : Integer_Object) is
   begin
      null;
   end;

   procedure Print (O : Float_Object) is
   begin
      null;
   end;

end Lists;