1class Fixnum
 2  def lbs
 3    to_f.lbs
 4  end
 5
 6  def kg
 7    to_f.kg
 8  end
 9end
10
11class Float
12  def lbs
13    Quantity.new(self, :lbs)
14  end
15
16  def kg
17    Quantity.new(self, :kg)
18  end
19end
20
21class NilClass
22  def to(units)
23    0.0.lbs.to(units)
24  end
25end