instance.rb

class Customer

	attr_reader :name 

	def initialize(name) 
		@name = name   # @name instance variable, cause it's created when instance initialized 
	end

  @@class_variable = 'hello'

  def self.class_variable
    @@class_variable
  end

end

peter = Customer.new("Peter")
john = Customer.new("John")


puts peter.name 
puts john.name

puts peter.class.class_variable
puts john.class.class_variable

john.class.class_variable = 'bye' # this will give you an error