True confessions RE:Multiple Inheritance

[Michael.P.Card@lmco.com]

I thought everyone might enjoy the following post which appeared on
comp.lang.eiffel this evening:

Ingo Pakleppa (ingop@cts.com) wrote RE: absence of MI in Java:

>Where is the problem? A book is loanable - but being loanable is not an
>intrinsic feature of the book, when you are talking about real-life
>books (this may be different if you are developing a library check-out
>application, where loanable is the primary information of interest). So
>just derive BOOK from PUBLICATION, implement the LOANABLE interface, and
>contains a LOANABLEOBJECT member. All you have to actually implement,
>you just have to provide the member functions that forward all calls to
>the embedded LOANABLEOBJECT.
>
>In my almost ten years of C++ programming, I have used multiple
>inheritance maybe 10 times at the most, and 80% of that was for mix-in
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>classes such as making objects collectable - where interfaces are
>actually better than MI.
>
>So - when I started Java, I thought I was going to miss MI, but by now
>find that I don't really need it in the first place.

The reason I thought this worthy of mention is that I have seen Ada
bashed for not suppporting MI. The use of generics/tagged types for
mixin inheritance has been described as a poor substitute for "the
real thing", and the advocates for some other languages often crow
about their support of "true MI." I have also seen many posts comp-
laining about the complexity of using "true MI" on the newsgroups of
these languages, however.

We have done a lot of work here with Ada 95 and I believe we are really
pushing the limits of the language as we attempt to build a real-time
object database management engine in Ada. I have been continually
impressed by the work done by the Ada 95 team. On our program, we do
not have a need for "true MI", so the fact that Ada doesn't have it
has never bothered us. Posts like the one I quoted here lead me to
believe that the Ada 95 team did the right thing when they omitted it.

- Mike

---------------
Michael P. Card
Lockheed Martin Ocean, Radar and Sensor Systems Division
Syracuse, NY 13221
voice: (315)-456-3022  FAX: (315)-456-2414  e-mail:card@syr.lmco.com

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