Hi all, I see another solution for the cross-dll problem, but it has two disavantages: 1) it is not possible in a header-only library. 2) initialization type_id< T >::value is much slower. ( but any_cast() will be as fast ) If this is unacceptable, then it doesn't worth to continue reading this. Otherwise, the solution is to combine the numerical id approach ( to gain performance in any_cast() ) with RTTI Instead of using function next_id(), we do: template< class T > unsigned int type_id< T >::value = get_int_type_id<T>(); Function get_int_type_id<T> aways returns the same value for the same type T regardless of the library it is called from. To achieve this, a std::map is used ( although std::set maybe is more approprieate. I used std::map to make the sample code simpler ). This map takes typeid(T).name() as the key, and returns a unique integer value. This map would be instantiated in the compiled library any.a ( or any.so or any.dll ) Regards, Roberto Hinz