a.dart

class Event {}
class CoolEvent extends Event {}

class EventHandler<T extends Event> {}

extension<T extends Event> on EventHandler<T> {
  Type get eventType => T;
}


void func<T extends Event>(EventHandler<T> e) {
  print(e.eventType);
  print(e.runtimeType);
  print(e.eventType == CoolEvent);
}

void main() {
  final EventHandler<Event> a = EventHandler<CoolEvent>();
  
  func(a);
}