addListener method
Implementation
void addListener(Type t, NopListener listener) {
if (_subNopListeners.containsKey(t)) return;
_subNopListeners[t] = listener;
final sync = _syncTypePointers;
if (sync == null) {
_updateDependence();
return;
}
if (sync.findCurrentTypeArg(t) != null) return;
sync.addListener(t, listener);
if (sync is! NopDependencies) listener.onDependenceAdd(sync);
}