Config via override

conf_via_methods.rb

class Conf
  class << self
    class << self
      def if_undef method, &block
        define_method method, &block unless Conf.respond_to? method
      end
    end
    if_undef :foo do
      "foo"
    end
    def bar
      "original"
    end
    if_undef :bar do
      "new"
    end
  end
end
puts Conf.foo
puts Conf.bar