class Prawn::Table

def with_position
  x = case defined?(@position) && @position || :left
      when :left   then return yield
      when :center then (@pdf.bounds.width - width) / 2.0
      when :right  then  @pdf.bounds.width - width
      when Numeric then  @position
      else raise ArgumentError, "unknown position #{@position.inspect}"
      end
  dy = @pdf.bounds.absolute_top - @pdf.y
  final_y = nil
  @pdf.bounding_box([x, @pdf.bounds.top], :width => width) do
    @pdf.move_down dy
    yield
    final_y = @pdf.y
  end
  @pdf.y = final_y
end