def move_by(x_delta, y_delta)
            the_point_array = @args.compact
            the_point_array = the_point_array.first if the_point_array.first.is_a?(Array)
            self.point_array = the_point_array.each_with_index.map {|coordinate, i| i.even? ? coordinate + x_delta : coordinate + y_delta}