@CanIgnoreReturnValue
  public static <K, V> ImmutableMap<K, V> uniqueIndex(
      Iterable<V> values, Function<? super V, K> keyFunction) {
    if (values instanceof Collection) {
      return uniqueIndex(
          values.iterator(),
          keyFunction,
          ImmutableMap.builderWithExpectedSize(((Collection<?>) values).size()));
    }
    return uniqueIndex(values.iterator(), keyFunction);
  }

  /**