Ruby class extensions for Chilean RUTs

rut.rb

class Fixnum
  def to_rut
    digits = self.to_s.to_rut
  end
end

class String
  def to_rut
    count = -1
    sum = self.each_char.to_a.map(&:to_i).reverse.
      inject(0){|s, i| s + i * (((count += 1) % 6) + 2)}
    verifier = ((11 - (sum % 11)) % 11)
    verifier = "K" if verifier == 10
    self.to_s + "-" + verifier.to_s
  end
end