class Uninitialized {
  int? x;
}

class PartiallyInitialized {
  int? x;
  PartiallyInitialized(this.x);
  PartiallyInitialized.noInitializer();
}

class Initialized {
  int? x;
  Initialized(this.x);
}

class Forwarding {
  int? x;
  Forwarding.initialize(this.x);
  Forwarding(int? arg) : this.initialize(arg);
}

int? uninitializedTopLevel;
int? initializedTopLevel = 4;
main() {}