From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2013-04-22T22:52:04+09:00
Subject: Re: BEGINNER -CLASS QUERY

On Mon, Apr 22, 2013 at 3:45 PM, shaik farooq <lists@ruby-forum.com> wrote:
> HEY as we know that the object conatins the instance variables that are
> defined in the class

In statically typed languages, you have to declare the types of
variables. Instance variables are one example, and are defined in the
class typically.

> but in ruby we are not defining any data member in the class but object
> of that class contains the instance variables

Ruby is dynamically typed, you don't declare variables or their types
before hand. Assigning to a variable makes it exist.
So for instance variables, they come to existence when a method is
invoked that assigns to an instance variable.
Example:

class A
  def test
    @value = 3
  end
end

a = A.new

Now a, which is a local variable, exists, and it references an object
that is an instance of class A. Inside this object, no instance
variable exists yet. Now:

a.test

At this point, the instance variable @value has been created inside
the object referenced by a.

Hope this clears up your confusion a bit,

Jesus.