gistfile1.builder

#uses transient baz
class Foo
  def new(baz = Baz.new)
    @baz = baz
  end

  # do stuff with baz here
end

#uses singleton baz
class Bar
  def new(baz = Baz.singleton)
    @baz = baz
  end

  # do stuff with baz here
end

class Baz
  extend CanBeSingleton  
end