internal Enumerator(UniqueHashSet<T> coll)
 {
     if (coll == null) throw new System.ArgumentNullException("coll");
     _coll = coll;
     _stamp = coll._generation;
     _next = 0;
     _current = default(T);
 }
 public void Dispose()
 {
     _coll = null;
 }