From: Mauricio Fernandez <mfp@...>
Date: 2007-10-09T06:20:02+09:00
Subject: Re: The Case for Multiple-Inheritance

On Tue, Oct 09, 2007 at 02:00:05AM +0900, Rick DeNatale wrote:
[...]
> In Java/C++ inheritance is primarily a means of expressing type
> relationships, and secondarily a means of sharing implementation.
> Because of the statically typed nature of these languages, related
> types HAVE to be related by inheritance.
[...] 
> In a statically typed language the coupling of type specification with
> implementation leads to a particular set of pressures on the design of
> both the language and programs in that language which are different
> from the pressures on Ruby and it's programs.  

This is getting OT, but I just wanted to clarify that not all the languages
with a statically typed OO system confound subclassing and subtyping the way
C++ and Java do. In OCaml, for instance, two unrelated classes can represent
the same type, and a class might not be a subtype of its parent(s). 
In fact, you can get what amounts to a sort of duck-typing, with the
guarantee that there will never be a "NoMethodError".

If in Ruby you have

  def foo(x); x.bar end

in OCaml

  let foo x = x#bar

and the foo function will work on any object with a 'bar' method, regardless
of the class (there are also "immediate objects"). The existence of that
method is checked statically.

-- 
Mauricio Fernandez  -   http://eigenclass.org