Just a tiny note reqarding this equivalence question. One question that comes up again and again is that of const class members. struct X { const int m_i; int m_j; X(i) : m_i(i){} }; Some users want to use: template<class Archive> void serialize(Archive & ar, X & x, const unsigned int version){ ar & const_cast<int &>(m_i); ar & m_j; } while others believe the above is incorrect and use: template<class Archive> void serialize(Archive & ar, X & x, const unsigned int version){ ar & m_j; } while still others use save/load_construct_data(...) Is the loaded version going to be "==" to the saved version? Depends upon how "==" is implemented for X. Is the loaded version "equivalent" ? Regardless of the answer to these questions, I know that the serialization library is used to user's satisfaction by users who have differing answers to these questions. At first I thought I was going to have to impose a answers to these questions in order to finish the implementation. But since that turned out to be unnecessary, I just left it at the discretion of the user. This has left somethings ambiguous, but it has permited me to actually finish the package to the satisfaction of a varied group of users. Robert Ramey