[boost] share_ptr serialization

In the course if making a new shared_ptr seriailzation implementation, I've come upon a question. If a shared pointer has been created with a custome deleter, how is one to determine what kind of deleter is attached without opening the implementation of shared_ptr? That is, I see no way to correctly serialize/deserialize a shared_ptr with a custom deleter from the published interface of shared_ptr. Can anyone explain how to do this? Robert Ramey