class KeyTypeManager {

  public KeyFactory<?, KeyProtoT> keyFactory() {
    throw new UnsupportedOperationException("Creating keys is not supported.");
  }

  @SafeVarargs // Safe because we do not reference the array (see Effective Java ed. 3, Item 32). protected  KeyTypeManager(Class<KeyProtoT> clazz, PrimitiveFactory<?, KeyProtoT>... factories);

}