ruby-1.9.2-p0 :069 > f = Foo.new
 => #<Foo:0x0000010a87c8b8>

ruby-1.9.2-p0 :075 > module Dupa
ruby-1.9.2-p0 :076?>   def cycki
ruby-1.9.2-p0 :077?>     "fajne sa"
ruby-1.9.2-p0 :078?>     end
ruby-1.9.2-p0 :079?>   end
 => nil

ruby-1.9.2-p0 :080 > f.extend(Dupa)
 => #<Foo:0x0000010a87c8b8>

ruby-1.9.2-p0 :081 > f.cycki
 => "fajne sa"