Re: OOP & Packages in Ada

[tmoran@bix.com (Tom Moran)]

Is this what you want:
package parent is
  type mammal is tagged null record;
  procedure eat(x : in out mammal);
end parent;

with ada.text_io;
package body parent is
  procedure eat(x : in out mammal) is
  begin ada.text_io.put_line("eat");end eat;
end parent;

with parent;
package child is
  type dog is new parent.mammal with null record;
  procedure bark(x : in out dog);
end child;

with ada.text_io;
package body child is
  procedure bark(x : in out dog) is
  begin ada.text_io.put_line("bark");end bark;
end child;

with child;
procedure user is
  rover : child.dog;
begin
  child.bark(rover);
  child.eat(rover);
end user;
    Note that primitive operations are inherited by child and appear
to user as if child declared them.  This isn't so for other things -
other types, constants, variables, etc.  For instance, if we add
  epitome : mammals;
to the spec of parent, this does not produce a child.epitome (clearly
such a beast would be expected to be different anyway).  If user
wanted to refer to the epitome of mammals, he would "with parent" and
reference parent.epitome.  (Not good naming here, sorry.)  
  The primitive operations supplied by a child may replace or
supplement, or both, those supplied by the parent.