gistfile1.rb

module Blah
   refine String do
      def split(*)
         ['foo', 'bar']
      end
   end
end

module Baz
   refine Integer do; end
end

class Foo
   using Blah
   p 'hello'.split('l')
end

class Foo
   using Baz
   p 'hello'.split('l')
end