From: Lyle Johnson <lyle@...>
Date: 2003-01-24T08:45:37+09:00
Subject: Re: contained_by method (challange)

Tom Sawyer wrote:

> okay, after all this time i finally figured out exactly what i am after.

Congratulations; so few people reach that point in their life ;)

> i would like all my objects to have a #contained_by method that returns a 
> reference to the object they are contained by.
> 
> for example:
> 
> 	a = "1"
> 	ar = [a]
> 	a.contained_by  # --> reference to ar
> 
> another:
> 
> 	class T
> 		attr_reader :a
> 	end
> 	t = T.new
> 	t.a.contained_by  # --> reference to t
> 
> and so on.
> 
> is this possible?

For starters, you need to clarify what you mean by an object 
"containing" another object.

For your first example, you're talking about one object that is a member 
of an Array. For your second example, you're talking about an object 
that is an instance variable of another object. Those are two different 
concepts.

If you just wanted to focus on the first case -- a method that returns a 
list of all the arrays that include the object as an array member -- you 
could use this:

     class Object
       # Return an array of the arrays that contain me
       def contained_by
         containers = []
         ObjectSpace.each_object(Array) { |anArray|
           containers << anArray if anArray.include? self
         }
         containers
       end
     end

Hope this helps,

Lyle