Re: Private Children

[Richard D Riehle <laoXhai@ix.netcom.com>]

In article <dale-2206991424480001@192.168.0.2>,
	dale@cs.rmit.edu.au (Dale Stanbrough) wrote:

>Richard D Riehle wrote:
>
>         package P.Hidden_Level.Public_Level is
>          -- code deleted

>         package body P.Hidden_Level.Public_Level is
            -- code deleted
>
>It's still a bit ordinary though. The services offered in the
>public level can't rely on abstractions advertised in the private
>section, which I see as the major failure of this model.

I see it differently -- not as a failure but as an opportunity
for powerful design of abstractions.  It might be the case that
we want to make some specifications available for type derivation
with a hierarchy of types, T'Class, as an implementation detail,
but hide those implementation details from the final user of 
some public class.  I wonder if this is one way for an Ada designer 
to differentiate implementation inheritance from interface inheritance. 

The type exported from the public package will be a pure interface,
a contract with some client.  The abstractions in the parent packages,
those with no public specifications, can safely focus on implementation
inheritance without the risk that the client will inadvertantly enter the
hierarchy at the wrong place.  

Richard Riehle
richard@adaworks.com
http://www.adaworks.com