From: Christopher Dicely <cmdicely@...>
Date: 2009-03-09T03:01:33+09:00
Subject: Re: Can I access or find a object from it's instance variable?

On Sun, Mar 8, 2009 at 8:32 AM, Aki Wakabayashi <zzyzx2001@gmail.com> wrote:
> 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

Note that because Ruby objects are passed as references, you generally
don't need to keep relationships using an identifier, you can just
keep a list of the "related" objects in an instance variable (the code
becomes less clear when you store an identifier instead of the object
itself, you probably aren't saving space, and you are probably hurting
performance by necessitating a method call to lookup the actual object
from the identifier.)