Used in Variable doc in medium

instance_var.rb

class Inst_var
  # will initialize instance variable when class is initiated
  def initialize
    @count = 0
  end

  # add up
  def add_count
    @count += 1
  end

  def output
   @count
  end
end

# initiate class
object = Inst_var.new
# original instance variable value
object.output  # => 0
# updates original variable value
object.add_count
# new output
object.output  # => 1

# initiate new object
new_object = Inst_var.new
# back to original instance variable value
new_object.output  # => 0