Learn to Program, 2nd Edition

Chapter 13Creating New Classes, Changing Existing Ones

Back here, we wrote a method to give the English phrase for a given integer. It wasn’t an integer method, though; it was just a generic “program” method. Wouldn’t it be nice if you could write something like 22.to_eng instead of english_number 22? Here’s how:

class Integer
  def to_eng
    if self == 5
      english = 'five'
    else
      english = 'forty-two'
    end
    english
  end
end
#  I'd better test on a couple of numbers...
puts 5.to_eng
puts 42.to_eng

five
forty-two

Well, I tested it; it seems to work. ☺

We defined an integer method by jumping into the Integer class, defining the method there, and jumping back out. Now all integers have this (somewhat incomplete) method. In fact, you can do ...