From: Joel VanderWerf <vjoel@...>
Date: 2005-07-28T06:13:52+09:00
Subject: Re: What's so special about operators, built-in classes and modules?

Pit Capitain wrote:
> twifkak@comcast.net schrieb:
> 
>>> Then you will have complex network of classes instead of simple
>>> tree structure, sharing code with modules.
>>
>>
>> How does a complex network of classes differ from a complex network
>> of mixins? The main difference that I see is, as Ara pointed out,
>> #is_a?. But I could be missing something. I usually am.
> 
> 
> For me, the main difference between modules and classes is that classes
> "define" state (instance variables), not only behaviour (methods). One
> classic problem with multiple inheritence is the so called diamond:

Actually, wouldn't it make more sense to say that neither classes nor
modules define state, but rather that methods do?

classirb(main):001:0> class A; attr_accessor :x; end
=> nil
irb(main):002:0> a = A.new
=> #<A:0xb7d85bb0>
irb(main):003:0> a.x = 6
=> 6
irb(main):004:0> a
=> #<A:0xb7d85bb0 @x=6>
                  ^^^^
irb(main):005:0> module M; attr_accessor :y; end
=> nil
irb(main):006:0> class A; include M; end
=> A
irb(main):007:0> a
=> #<A:0xb7d85bb0 @x=6>
irb(main):008:0> a.y = 8
=> 8
irb(main):009:0> a
=> #<A:0xb7d85bb0 @y=8, @x=6>
                  ^^^^