protocols, inheritance and polymorphism

[Steven Bethard]

Donn Cave wrote:
> I don't have any beef with multiple inheritance, in fact the
> notion of "mix-in" classes might have some potential to be the
> basis for a more sound approach to OO.

The people that have a beef with multiple inheritance have it because 
multiple inheritance can sometimes break encapsulation by forcing the 
designer of a class to be aware of changes in the inheritance chain far 
above its parents (even when no methods/attributes are added by the 
change).  A classic reference:

Snyder, Alan. "Encapsulation and Inheritance in Object-Oriented 
Programming Languages"
http://www-plan.cs.colorado.edu/diwan/class-papers/snyder.pdf

Python tries to combat some of these problems with a good method 
resolution order:

http://www.python.org/2.3/mro.html

I don't make enough use of multiple inheritance to ever have run into 
these kinds of problems, but the literature in this area is enormous...

Steve