instance and class variables in rails controller

Question

I\'m new to rails and ruby. I was studying the concept of class and instance variables. I understood the difference but when I tried it out using the controller in rails it got

Answer 1

When you declare @instworld you are inside BooksController class (i.e. self will return BooksController. Weird thing in ruby is that classes are also objects (the are instances of class Class) hence you in fact declares instance variable @instworld for this particular instance of class Classm not for instance of BooksController.

You can check it really easily by declaring class method:

class A
  # self here returns class A
  @variable = 'class instance variable'
  @@variable = 'class variable'

  def initalize
    # self here returns the instance
    @variable = 'instance variable'
  end

  def self.test_me
    # self here returns class A
    @variable
  end

  def test_me
    # self returns the instance
    @variable
  end

  #class variable is accessible by both class and instance 
  def test_me2
    @@variable
  end

  def self.test_me2
    @@variable
  end
end

A.test_me       #=> 'class instance variable'
A.new.test_me   #=> 'instance variable'
A.test_me2      #=> 'class variable'
A.new.test_me2  #=> 'class variable'