deallocating class wide types

[alfonso acosta <alfonso_acosta_mail@yahoo.es>]

hi:

I provide a simplified example of my problem:

package spec:
----------------------------------------------------------------
package My_Class is

type My_Class is abstract tagged null record;
type My_Class_Access is access all My_Class'Class;
procedure Destroy (Object: in out My_Class_Access);

end My_Class;
----------------------------------------------------------------

first body approach:
----------------------------------------------------------------
with Ada.Unchecked_Deallocation;
package body My_Class is
procedure Free is
    new Ada.Unchecked_Deallocation(Name => My_Class_Access,
				  Object => My_Class'Class);

procedure Destroy (Object: in out My_Class_Access) renames Free;

end My_Class;
----------------------------------------------------------------

I get:
my_class.adb:7:59: subprogram used in renaming_as_body cannot be intrinsic

second approach:
----------------------------------------------------------------
with Ada.Unchecked_Deallocation;
package body My_Class is
procedure Free is
    new Ada.Unchecked_Deallocation(Name => My_Class_Access,
				  Object => My_Class'Class);

procedure Destroy (Object: in out My_Class_Access) is
begin
    Free(My_Class_Access);
end Destroy;

end My_Class;
------------------------------------------------------------------

I get:
my_class.adb:9:09: Invalid use of subtype mark in expression or call

Can someone tell me what Im doing wrong?
And, should Destroy work with any type which extends My_Class?

Thanks in advance:

Alfonso Acosta