class UniqueIndex extends AbstractAttributeIndex<A,O> implements OnHeapTypeIndex {

    public static <A, O> UniqueIndex<A, O> onAttribute(Attribute<O, A> attribute) {
        return onAttribute(new DefaultIndexMapFactory<A, O>(), attribute);
    }

    protected  UniqueIndex(Factory<ConcurrentMap<A,O>> indexMapFactory, Attribute<O, A> attribute);

}