Using boost::variant with boost::serialization gives me a warning about unused type in the boost::serialization namespace: D:/Boost/boost/serialization/variant.hpp:69:75: warning: typedef 'types' locally defined but not used [-Wunused-local-typedefs] typedef typename boost::variant::types types; I looked up boost::ignore_unused, which says it's for unused types also, but everything I've tried for using in my code (following the definition of my variant) results in a syntax error or other bug claim. How should I use ignore_unused in this case?