BOOST_SERIALIZATION_SPLIT_FREE
// In header: <boost/date_time/posix_time/time_serialize.hpp> BOOST_SERIALIZATION_SPLIT_FREE(boost::posix_time::ptime);
time_duration objects are broken down into 4 parts for serialization: types are hour_type, min_type, sec_type, and fractional_seconds_type as defined in the time_duration class
