Integers Roman notation

gistfile1.rb

class Fixnum

  # Returns the corresponding roman notation for numbers < 1000. Nice message otherwise.
  def to_roman
    return "Who knows, my friend!!" unless (1...1000) === self
    [].tap do |result|
      reverse_figures.each_with_index do |figure, weight|
        result << figure.send(:to_roman_by_weight, weight)
      end
    end.reverse.join
  end


  private

    # Constant to map decimal units, tens and cents to roman notation.
    ROMAN_CONVERTER = [['', 'I', 'II', 'III', 'IV', 'V', 'VI', 'VII', 'VIII', 'IX'], # units,
                       ['', 'X', 'XX', 'XXX', 'XL', 'L', 'LX', 'LXX', 'LXXX', 'XC'], # tens,
                       ['', 'C', 'CC', 'CCC', 'CD', 'D', 'DC', 'DCC', 'DCCC', 'CM']  # cents
                      ]

    # Returns the roman notation of self based in weight (units = 0, tens = 1, cents = 2)
    def to_roman_by_weight(weight)
      ROMAN_CONVERTER[weight][self] if (0..9) === self
    end

    # Returns a list of the figures of self in reverse order (units first)
    def reverse_figures
      to_s.split('').reverse.map(&:to_i)
    end

end

(-1..1000).each {|d| puts "#{d} - #{d.to_roman}"} and true