[boost] [serialization] using non-intrusive load and save

Hi, What's the recommended way to spit non-intrusive serialization into two functions? It looks like I could use tag dispatch with the nested metafunction is_saving or is_loading, but I want to give a very simple example of non-intrusive serialization. Also, is there any reason that instances of these metafunctions aren't convertible to bool, like the boolean metafunctions from type_traits and mpl? Jonathan