[self-interest] prioritized multiple inheritance?

[Jecel Assumpcao Jr.]

Michael Kusber wrote on Tue, 22 Jun 2010 01:44:05 -0700 (PDT)

> I'm new to Self, so sorry for maybe a stupid question. 
> I have read "Parents are shared parts of objects: inheritance and
> encapsulation in SELF" by Chambers, Ungar, Chang, and Hölzle and there is
> spoken about prioritized multiple inheritance by using the amount of "*"s
> after the slots name. 

That was implemented in Self 1.0, but removed in Self 3.0 (after these
papers were written).

> I tried to use this in the 4.4 Beta and get the error message that there
> must not be more than one * for a parent slot. 
> Did I made a mistake? Is prioritized inheritance implemented in an earlier
> release? 

You have to try Self 1 or 2 (not easy since you would need an old Sun
machine) to be able to use these features. The reason why they were
removed was that programmers often guessed wrong what method would be
found be the lookup algorithm, though in theory it wasn't that
complicated. The consequences of removing the tie-breaker-rule and
parent priorities were:

1) inheritance could no longer be used to break up large objects into
namespaces, which was needed for the first UI. So a scheme of
"annotations" was created instead which was used not only for name
spaces (the outliner objects in UI2 depend on them) but also for other
meta information needed by different tools (like the transporter, which
could export objects from a running system to be loaded into another
system).

2) privacy was eliminated. The syntax remained and the UI2 reflected it
(by showing slot names in bold or not) but the virtual machine ignore it
and treated all slots exactly the same. The idea was to later "do it
right", which was done in the Us experimental programming language.

3) mixins continued to work well, but other than that multiple
inheritance wasn't used as much.

-- Jecel