From: Brian Candler <b.candler@...>
Date: 2008-10-22T17:20:22+09:00
Subject: Re: extending object with another object

Ittay Dror wrote:
> How is it possible to extend an object using another object?

It depends exactly on what you're trying to achieve.

You have two separate objects, both with their own sets of methods *and* 
their own sets of instance variables. In what way do you want to 
"extend" the first with the second? What happens to instance variables 
belonging to the second object?

Now, if you simply want a call to method X on object A to be forwarded 
to object B (in which context it would use object B's instance 
variables), then look at delegate.rb, or you can synthesise this pattern 
yourself using method_missing

class A
  def hello
    puts "hello"
  end
end

class B
  def bye
    puts "bye"
  end
end

a = A.new
b = B.new

# This is a rough implementation of SimpleDelegator
def a.other=(x)
  @other=x
end
def a.method_missing(*args)
  @other.send(*args)
end

a.other = b
a.hello
a.bye

The important thing here is that when methods are delegated to the other 
object, they will be in the context of that object and hence have access 
to that object's instance variables. Put simply, that object will 
"work".

In cases where the methods by themselves make sense, then generally 
you'd stick those methods into a Module so that both a and b could make 
use of them.

class A
  include MyStuff
end
...
b = B.new
b.extend MyStuff

But clearly you know about this already.
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