docs: @SuppressWarnings("unchecked")
    private static <V extends FeatureVector<F>, F> ArrayAdapter<F, ? super V> getAdapter(Factory<V, F> factory) {
      if(factory instanceof NumberVector.Factory) {
        return (ArrayAdapter<F, ? super V>) NumberVectorAdapter.STATIC;
      }
      return (ArrayAdapter<F, ? super V>) FeatureVectorAdapter.STATIC;
    }