@Override
    public Iterator<V> iterator() {
        return new Iterator<V>()
        {
            int cur = availabilityMap.nextSetBit(0);
            @Override
            public boolean hasNext()
            {
                return cur >= 0;
            }

            @Override
            public V next()
            {
                V ret = ids.get(cur);
                cur = availabilityMap.nextSetBit(cur + 1);
                return ret;
            }
            //TODO add remove support?
        };
    }