From: Aki Wakabayashi <zzyzx2001@...>
Date: 2009-03-09T01:32:28+09:00
Subject: Re: Can I access or find a object from it's instance variable?

Thank you everyone. I would like thank every one one by one, but I think 
that will make this place look like a blog and I'm not sure if that's 
proper to this forum. But I really appreciate everyone's support.

Creating a class variable, or using weak references (though still 
complicated to me) made very much sense. The code at 
http://pastie.org/410782 was clear to the point where a @name instance 
variable is added to the class.

After cramming all this code into by head, I started to wonder if I was 
able to do what I wanted to by using the #object_id? I'm not sure at 
this point. Below is an example of what I wanted to achieve.

> What exactly do you mean by "actual identifier"?  If you mean #object_id
> then there is method ObjectSpace._id2ref.

I meant the variable that I used to point to the object, when they are 
created like:

var = Foo.new(77)

I wanted to get access to 'var' by using it's @some_id which is 77.

> The question is: what are you trying to achieve?

Thank you for asking. I was wondering how to update relations(imagine a 
social networking site) between objects of a single Class. I hope this 
will clarify why I want to access the variable of the object with its 
instance variable. This how far I got last night:

class Foo

  attr_accessor :name, :some_id, :relations

  def self.update_relationship(foo1, foo2)
    # code that adds @relations for foo1, and foo2 and updates it with
    # it's own MINUS its own :some_id, and updates other @some_id's 
included
    # in foo1.relations + foo2.relations.
  end

  def self.find_by_some_id(some_id)
    found = nil
    ObjectSpace.each_object(Foo) { |o| found = o if o.oid == oid}
    found
  end

  def to_s
    @name
  end

end


(create two objects):

John = Foo.new('John', 1,[])
Dave = Foo.new('Dave', 2,[])

(create a relationship between the two):

Foo.update_relationship(John, Dave)

John.relations -> [2]
Dave.relations -> [1]


Let's assume that along the line more objects are created and a new 
relationship is created with John.(I'm just going to create a new object 
and populate it's @relations instance variable, so the variables are 
visible)

Steve = Foo.new('Steve', 104, [55, 77])

Foo.update_relationship(Steve, John)

John.relations -> [2, 55, 77, 104]
Steve.relations -> [1,2,55,77]

...well, that's good, but all the other objects (with @some_id 2, 55 and 
77) would have to be updated right? For starters, Dave, the second 
object (with @some_id = 2) is currently still:

Dave.relations -> [1]

Where it has to be updated to [1, 55, 77, 104]

So in order to access the Dave object, I only had 2, it's @some_id 
instance variable to access it. Now, since I included the variable name 
in the instance variable I can access the Dave object with the 
find_by_some_id class method, and
get the @name instance variable which is the same as the variable (THIS 
IS WHERE I THOUGHT IT WAS NOT A RUBYIST SOLUTION)

I'm going to read a little more and see if I can use the object's 
#object_id to do all of this.

Thank you.

Aki


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