gistfile1.rb

class MyClass

  def i_understand_how_this_works(local_var)
    @the_string ||= "omg"
    @the_string << local_var
  end

  def how_is_that_possible
    @the_string ||= "omg"
  end

  def put
    puts "> #{@the_string}"
  end

end



vasya = MyClass.new

vasya.put # >

vasya.i_understand_how_this_works " wtf"

vasya.put  # > omg wtf

vasya.how_is_that_possible << " igo"
                                     # It modifies an instance var without
                                     # either exposing it via attr_writer
                                     # or doing an assignment withing the method!

vasya.put  # > omg wtf igo