From: "Mauricio Fernández" <batsman.geo@...>
Date: 2003-04-05T00:01:07+09:00
Subject: Re: To inherit or to include? That is the question.

On Fri, Apr 04, 2003 at 10:51:02PM +0900, Jim Freeze wrote:
> I've been poking around the mailing list looking for
> some insight into using inheritance vs module include.
[...] 
> I cannot see that the two behave that differently.
> I'm sure there are some differences. Maybe someone
> can help me enumerate them.
> 
> Ideally, I would like some set of guidelines to help
> me make a choice between these two.

matz already stated that inheritance in Ruby is little more than
implementation reuse... no wonder we can mix modules and classes (no pun
intended) so easily...

So it all comes down to the following:
what's the difference between an inherited abstract base class and an
included module?

There's not really that much (if you omit syntactic issues), but here's
something I can think of now:

batsman@kodos:/tmp$ expand -t2 a.rb
module Foo; def self.bar; puts "Foo.foo" end end
class Bar; def self.bar; puts "Bar.foo" end end

class A < Bar
end

class B
  include Foo
end

A.bar
B.bar
batsman@kodos:/tmp$ ruby a.rb
Bar.foo
a.rb:13: undefined method `bar' for B:Class (NameError)

i.e. there's no relationship between singleton classes w/ include.

Another thing would be 

p B === B.new
p Bar === B.new

true
false

There must be more but I am low on caffeine today :-P

Wait for Guy Decoux's answer ;-)

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