From: Paul Brannan <pbrannan@...>
Date: 2002-10-16T23:12:49+09:00
Subject: Re: Interfaces in Ruby

On Wed, Oct 16, 2002 at 01:30:04PM +0900, Chris Gehlker wrote:
> 
> On Tuesday, October 15, 2002, at 09:02 PM, Edward Wilson wrote:
> 
> > Is there a way to write/inforce interfaces in Ruby like one can using
> > Abstract Classes in C++ or Interfaces in Java?
> >
> > If not, how has everyone been approaching this?
> >
> I don't think C++ abstract classes are that similar to Java interfaces. 

Not having used Java interfaces extensively, I can't speak about their
subtleties, but Java interfaces and C++ abstract classes are used for
similar functions.  Both are used to say "this class implements this set
of functions."  This is particularly important in C++, since, through
the magic of virtual functions, it allows me to write a single function
that can accept objects of many different types, without using
templates.  This is less useful in Ruby, since an object always retains
its type when I pass it as a parameter to a method (whereas in C++ I
only have a reference to the base class).

> I don't see the need for interfaces in a language with mix-ins.

This doesn't make sense to me.  I see interfaces and mixins as
orthogonal concepts; interfaces are used to specify a contract, while
mixins are used to provide additional methods to a class.

> When I want something like a C++ abstract class, I use a class
> cluster. Maybe that's just my ObjC background showing.

What is a "class cluster"?  Can you provide an example?

Paul