Containers: The REALLY difficult stuff...

[Peter Froehlich <pfroehli@ics.uci.edu>]

Hi there!

Don't get me wrong, the discussion has been interesting up to now, but all
those topics have been "solved in my mind" for some time now. What is
really scaring the **** out of me design-wise is another problem:

   How can we separate abstract and concrete structure in a general way?

Let me give one example of what I mean: Consider a "Set" abstraction. It
can be defined (informally) as having elementary operations "Insert",
"Remove", "In" and "Empty", as well as "higher-order" operations "Union",
"Difference", and so on.

Now these can of course be implemented in various ways, eg. by using a
"java.util.Vector" like class, by a linked list, by various trees, etc. The
problem is how we combine "abstract" behaviour with a "concrete"
implementation. I would like to be able to do the following:

   VAR s: Set; l: List;
   ...
   BEGIN
     NEW (s); NEW (l);
     s.UseImplementation (l);
     ...

So how do we do that? I have that strange feeling that this is next to
unsolvable with the Oberon-2 context in which we are operating...

By(T)e...        /  Department of Information and Computer Science  \
        Peter... \ University of California - Irvine, CA 92697-3425 /