Re: Eiffel and Java

["Norman H. Cohen" <ncohen@watson.ibm.com>]

Don Harrison wrote:

> Jon, don't know why you say this. I have some vague recollection of you
> talking about Sather's separate interface and implementation *inheritance*.
> But Ada doesn't even support that, so I'm not sure what you're thinking
> of. Please explain why you make this association.

Ada DOES support separate interface and implementation inheritance:

   package Interface is
      type Interface_Type is abstract tagged ...;
      ...
   end Interface;

   package Parent_Implementation is
      type Parent_Implementation_Type is
         new Interface.Interface_Type with ...;
      ...
   end Parent_Implementation;

   package Child_Implementation is
      type Child_Implementation_Type is 
         new Interface.Interface_Type with private;
      ...
   private
      type Child_Implementation_Type is 
         new Parent_Implementation.Parent_Implementation_Type
            with ...;
   end Child_Implementation;

The declaration of Child_Implementation_Type in the visible part of the
package declares this type to be descended from Interface_Type, and this
is all that a client of the Child_Implementation package knows about the
type.  The full declaration of Child_Implementation_Type in the private
part indicates that Child_Implementation_Type implements the
Interface_Type interface by inheriting from a particular descendant of
Interface_Type, namely Parent_Implementation_Type.

-- 
Norman H. Cohen
mailto:ncohen@watson.ibm.com
http://www.research.ibm.com/people/n/ncohen