Monitor is meant to be polymorphic, but its only virtual function is the destructor (see also https://github.com/italiangrid/storm-frontend/commit/728561c7a95106fd249135608fe44c29f080af02). However its only derived class is InstrumentedMonitor and C-style casts are used instead of virtual functions (see e.g. https://github.com/italiangrid/storm-frontend/blob/e4d5d975672d14ba883297949bded68aea73fadc/src/frontend/MonitorHelper.hpp#L39)