From: Ittay Dror <ittay.dror@...>
Date: 2008-10-22T18:38:54+09:00
Subject: Re: extending object with another object

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Brian Candler wrote:

> 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?
>   
I want just to get the methods defined in the second object, something like
object.extend(as_module(other_object))

where 'as_module' is some method that returns a module representing the 
class hierarchy (with singletons) of the other object.

class A
  def initialize(name)
     @name = name
  end
  def hi
     puts @name
  end
end

class B
  def initialize(name)
     @name = name
  end
end

a = A.new('a')
b = B.new('b')
b.object_extend(a)
b.hi  #=> 'b'

Ittay


> 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.
>   

-- 
Ittay Dror <ittayd@tikalk.com>
Tikal <http://www.tikalk.com>
Tikal Project <http://tikal.sourceforge.net>


-- 
--
Ittay Dror <ittay.dror@gmail.com>


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