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Date: 12 Dec 91 15:34:11 GMT
From: elroy.jpl.nasa.gov!swrinde!cs.utexas.edu!asuvax!ennews!enuxha.eas.asu.edu
!koehnema@ames.arc.nasa.gov  (Harry Koehnemann)
Subject: OO in Ada (wasRe: Invoking Inherited Routines in Ada9x)
Message-ID: <1991Dec12.153411.4361@ennews.eas.asu.edu>
List-Id: <comp.lang.ada>

In article <1991Dec11.155758.6327@software.org> blakemor@software.org (Alex Bla
kemore) writes:
>
>Ada's solution seems similar to C++'s in that the subclass must
>name the superclass to invoke the parent method (using OO speak)
>I assume you find that brittle because it makes it difficult
>to rearrange the inheritance hierarchy ? perhaps to add a new 
>intermediate level.

Further, it makes the user of a method be responsible for implementation
knowledge.  This sits a little funny with me in terms of encapsulation.
I want an ADT to provide me operations.  I shouldn't by my responsibilty
to know (in fact, I shouldn't be allowed to know) that a certain operation
is actually being provided by a particular parent 'class' (or package).

Furthermore, this mechanism also allows any other 'class' to declare
operations on a type that they are not even providing.  It's a more powerful
mechanism, but seems to sit a little funny with traditional OO concepts.
We lose that 'textual closeness' we have with a class construct.

This may be the wrong group to ask this question, but does anyone know
of papers/talks/...  that contrast languages that use type extensions
to support inheritance with those that use a class construct?  It seems
feasible to take a few OO problems and implement them with classes and
type extensions and see which one works cleaner and for which types of
problems.  Has anyone done this?  (now, if only I hadn't already picked
out a thesis topic...)
--
Harry Koehnemann
koehnema@enuxha.eas.asu.edu