The problems with MI are basically the same as manual memory management:  
(a) to easy to shoot yourself and anyone near you and (b) hinders 
composability/encapsulation.

The problem is, if you have multiple inheritance then from now on people 
probably need to know what classes any class they inherit from inherit from 
themselves, since you may be introducing the same base classes from 
different hierarchies points.

There are ways to deal with it of course, but for me it is a red flag that 
maybe I am walking down the wrong road when I see such things.  Especially 
when an "interfaces with default implementations" seems to work so well.


>From: Matthew Fulmer <tapplek at gmail.com>
>Reply-To: The general-purpose Squeak developers 
>list<squeak-dev at lists.squeakfoundation.org>
>To: The general-purpose Squeak developers 
>list<squeak-dev at lists.squeakfoundation.org>
>Subject: Re: election details *PLEASE READ*
>Date: Thu, 1 Mar 2007 00:32:32 -0700
>
>On Fri, Feb 23, 2007 at 10:35:35PM -0800, Andreas Raab wrote:
> > Early on I thought the same way (and this was why we started thinking
> > down that road when Nathanael interned with us). However, in practice it
> > seems like Traits are mostly being used as a thinly veiled version of MI
> > with all the same problems. You have correctly pointed out that Java
> > interfaces are "nothing but abstract virtual base classes in C++" -
> > which coincidentally, was the only way that MI ever worked in C++, which
> > itself has two dozen ways of doing MI wrong and exactly ONE to do it
> > right (abstract virtual base classes). Java choose a stand on that and
> > it worked (which is pretty impressive given that it was the first
> > language that used interface to that extent). Traits seem to reintroduce
> > a number of ways of using MI wrongly (at least that's the feeling that I
> > get when I look at the practical example) and that's why I prefer
> > interfaces.
>
>Forgive me, but I am not familiar with "All the problems
>Multiple Inheritance got wrong". I will be testing out how
>Multiple Inheritance works in Squeak, since I have made it my
>top priority to get ThingLab [1] working in a recent Squeak
>system. ThingLab adds multiple inheritance [2] and a constraint
>solver to Smalltalk, and both have at least a good theoretical
>reason to be there, but I cannot test the implementation yet,
>since such a change currently breaks squeak. Multiple
>Inheritance has at least a solid theory; I have not had much
>experience with an implementation.
>
>[1] http://wiki.squeak.org/squeak/607
>     Links to ThingLab papers and code.
>
>[2] http://www.2share.com/thinglab/ThingLab%20-%20Chapter%203.html
>     Chapter 3 of the ThingLab paper. Section 2 contains a
>     defense of ThingLab's multiple inheritance.
>
>--
>Matthew Fulmer -- http://mtfulmer.wordpress.com/
>Help improve Squeak Documentation: http://wiki.squeak.org/squeak/808
>

_________________________________________________________________
With tax season right around the corner, make sure to follow these few 
simple tips. 
http://articles.moneycentral.msn.com/Taxes/PreparationTips/PreparationTips.aspx?icid=HMFebtagline