sclass WeakCompactHashSet<A> extends AbstractSet<A> {

  new CompactHashSet<MyWeakReference<A>> set;

  new ReferenceQueue<A> queue;

  sclass MyWeakReference<A> extends WeakReference<A> {

    int hash;

    *(A o) {

      super(o);

      hash = o.hashCode();

    }

    *(A o, ReferenceQueue<A> queue) {

      super(o, queue);

      hash = o.hashCode();

    }

    public int hashCode() { ret hash; }

    public bool equals(O o) {

      ret o instanceof MyWeakReference

        && eq(get(), ((MyWeakReference) o).get());

    }

  }

  // Make sure we get reaped once a minute (or whatever the policy is)

  *() {

    _registerWeakCollection(this);

  }

  void reap() {

    MyWeakReference ref;

    while ((ref = (MyWeakReference) queue.poll()) != null)

      set.removeIfSame(ref);

  }

  public int size() { reap(); ret set.size(); }

  public Iterator<A> iterator() {

    final Iterator<MyWeakReference<A>> it = set.iterator();

    ret iteratorFromFunction(() -> {

      while (it.hasNext()) {

        MyWeakReference<A> ref = it.next();

        A a = ref.get();

        if (a != null) ret a;

        // todo: clean up entry

      }

      null;

    });

  }

  public bool contains(O o) {

    reap();

    ret set.contains(new MyWeakReference(o));

  }

  public bool add(A a) {

    reap();

    ret set.add(new MyWeakReference(a, queue));

  }

  public bool remove(O o) {

    reap();

    ret set.remove(new MyWeakReference(o));

  }

  A find(O o) {

    reap();

    MyWeakReference<A> ref = set.find(new MyWeakReference(o));

    ret ref == null ? null : ref.get();

  }

}