A ruby CSV class that extends build-in CSV and add ability that keeping original line

my_csv.rb

require 'csv'

class MyCsv < CSV
  # The line of the last row read from this file.
  attr_reader :line
  def shift
    if @_before_lineno != @lineno
      @_before_pos = pos
      @_before_lineno = @lineno
    end
    row = super
    after_pos = pos
    @io.pos = @_before_pos
    @line = @io.read(after_pos - @_before_pos)
    row
  end
end