I have the following exported factory function in a DLL I'm building on Windows: extern "C" void BOOST_EXTENSION_EXPORT_DECL export_aspects( boost::extensions::factory_map& fm ) { using namespace vfx::aspects; using namespace vfx::messenger; fm.get<Aspect, MessageReader&, unsigned int>()[0].set<Appearance>(); fm.get<Aspect, MessageReader&, unsigned int>()[1].set<Health>(); } As you can see, I am specifying that each class accepts a single construction parameter- a reference to a MessageReader object. However, this isn't compiling because I don't think that it likes reference types. How can I specify that the constructor takes a reference? boost::ref? I would post the compiler warnings & errors I'm getting, however they're exceedingly large. Most of the warnings and errors are coming from std::map, basically complaining that it's trying to create a map of reference types, which can't possibly work. Help is appreciated. As an unrelated note, I would really like to see the template parameters cleaned up. There's at least 5 places I've had to redundantly specify the same 3 template parameters (like in the example above). I already brought this up in another thread, but I can't tell you how important it is. If I ever change the number of construction parameters my Appearance or Health classes take (mapped above), I will have to shift through 5 or more files simply to adjust all of the template parameters to make everything compile.