}

    /**
     * Create a key using the given class and id.
     */
    static <T> Key<T> key(Class<T> clazz, Object id) {
        return new Key<>(clazz, id);
    }

    /**
     * Key used to query the session data
     * @param <T> the type of the object associated to this key
     */
    final class Key<T> {

        private final Class<T> type;
        private final Object id;