WeakValueReferenceImpl(ReferenceQueue<V> queue, V referent, E entry) {
      super(referent, queue);
      this.entry = entry;
    }

    @Override
    public E getEntry() {
      return entry;
    }

    @Override
    public WeakValueReference<K, V, E> copyFor(ReferenceQueue<V> queue, E entry) {
      return new WeakValueReferenceImpl<>(queue, get(), entry);
    }
  }

  /**

      queue = new PriorityQueue<>(2, heapComparator);

      for (Iterator<? extends T> iterator : iterators) {
        if (iterator.hasNext()) {
          queue.add(Iterators.peekingIterator(iterator));
        }
      }
    }

    @Override
    public boolean hasNext() {
      return !queue.isEmpty();
    }

    @Override