* elements in {@code a}, followed by the elements in {@code b}, followed by the elements in
   * {@code c}. The source iterators are not polled until necessary.
   *
   * <p>The returned iterator supports {@code remove()} when the corresponding input iterator
   * supports it.
   */
  public static <T extends @Nullable Object> Iterator<T> concat(

		f(m.root)
		sender.Close()
	}()
	return &Iterator[K, V]{receiver}
}

// Iterator is used to iterate over the map.
type Iterator[K, V any] struct {
	r *Receiver[keyValue[K, V]]
}

// Next returns the next key and value pair, and a boolean that reports
// whether they are valid. If not valid, we have reached the end of the map.
func (it *Iterator[K, V]) Next() (K, V, bool) {

    }
  }

  /**
   * Verifies that an Iterator is unmodifiable.
   *
   * <p>This test only works with iterators that iterate over a finite set.
   */
  public static void assertIteratorIsUnmodifiable(Iterator<?> iterator) {
    while (iterator.hasNext()) {
      iterator.next();
      try {
        iterator.remove();
        fail("Remove on unmodifiable iterator succeeded");

      @Override
      SortedMultiset<E> forwardMultiset() {
        return AbstractSortedMultiset.this;
      }

      @Override
      Iterator<Entry<E>> entryIterator() {
        return descendingEntryIterator();
      }

      @Override
      public Iterator<E> iterator() {
        return descendingIterator();
      }
    }
    return new DescendingMultisetImpl();
  }

      @Override
      SortedMultiset<E> forwardMultiset() {
        return AbstractSortedMultiset.this;
      }

      @Override
      Iterator<Entry<E>> entryIterator() {
        return descendingEntryIterator();
      }

      @Override
      public Iterator<E> iterator() {
        return descendingIterator();
      }
    };
  }

    SmallVector<Type, 2> dataset_types;
    for (int i = 0; i < dataset_input_size; ++i) {
      dataset_types.push_back(func_inputs[state_size + i]);
    }

    // Create dataset iterator and iterate dataset in while loop which calls
    // reduce_fn.
    AnonymousIteratorV3Op anonymous_iterator =
        CreateIterator(builder, dataset_types, reduce_dataset);

    }

    @Override
    Iterator<Entry<K, V>> entryIterator() {
      return Iterators.filter(unfiltered.entrySet().iterator(), entryPredicate);
    }

    @Override
    Iterator<Entry<K, V>> descendingEntryIterator() {
      return Iterators.filter(unfiltered.descendingMap().entrySet().iterator(), entryPredicate);
    }

    @Override
    public int size() {

    }

    @Override
    Iterator<Entry<K, V>> entryIterator() {
      return Iterators.filter(unfiltered.entrySet().iterator(), entryPredicate);
    }

    @Override
    Iterator<Entry<K, V>> descendingEntryIterator() {
      return Iterators.filter(unfiltered.descendingMap().entrySet().iterator(), entryPredicate);
    }

    @Override
    public int size() {

      @Override
      SortedMultiset<E> forwardMultiset() {
        return AbstractSortedMultiset.this;
      }

      @Override
      Iterator<Entry<E>> entryIterator() {
        return descendingEntryIterator();
      }

      @Override
      public Iterator<E> iterator() {
        return descendingIterator();
      }
    }
    return new DescendingMultisetImpl();
  }

		panic(fmt.Sprintf("unexpectedly found %q", []byte("d")))
	}

	gather := func(it *a.Iterator[[]byte, int]) []int {
		var r []int
		for {
			_, v, ok := it.Next()
			if !ok {
				return r
			}
			r = append(r, v)
		}
	}
	got := gather(m.Iterate())
	want := []int{'a', 'b', 'x'}
	if !a.SliceEqual(got, want) {
		panic(fmt.Sprintf("Iterate returned %v, want %v", got, want))
	}

}

func main() {
	TestMap()