From: Kent Dahl <kentda@...>
Date: 2002-06-14T22:13:07+09:00
Subject: Re: referring to variables in the scope outside the def

k wrote:
> 
> When defining a singleton method, I want to refer to variables in the scope
> outside the def. Is it possible to do something like the following?
> 
> class C
>   def initialize
>     @child = Object.new
>     s = self
>     def @child.parent
>       s # Wrong. But how do I refer to the instance of C?
>     end
>   end
>   attr_reader :child
> end
> 
> c = C.new
> c == c.child.parent # Should be true.
> 
> Any hints? I think I'm missing a vital piece of magic here. Or maybe I'm
> expecting too much Lisp-ness.

Probably the latter. A method doesn't have access to the surrounding
scope as such. I suggest feeding it into an attribute in the child
object. Quick stab:

<CODE>
class C
  def initialize
    @child = Object.new
    s = self
    # feed the variable into it
    @child.instance_eval {
      @parent_C = s
    }
    # define the method for retrieving it
    def @child.parent
      @parent_C 
    end
  end
  attr_reader :child
end

c = C.new
puts c == c.child.parent # Is now true
</CODE>

HTH

-- 
(\[ Kent Dahl ]/)_    _~_    __[ http://www.stud.ntnu.no/~kentda/ ]___/~
 ))\_student_/((  \__d L b__/  NTNU - graduate engineering - 4. year  )
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