return (object == null) ? -1 : Lists.indexOfImpl(this, object);
  }

  @Override
  public int lastIndexOf(@Nullable Object object) {
    return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object);
  }

  public final boolean addAll(int index, Collection<? extends E> newElements) {
    throw new UnsupportedOperationException();
  }

  public final E set(int index, E element) {

    return (object == null) ? -1 : Lists.indexOfImpl(this, object);
  }

  @Override
  public int lastIndexOf(@CheckForNull Object object) {
    return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object);
  }

  @Override
  public boolean contains(@CheckForNull Object object) {
    return indexOf(object) >= 0;
  }

  // constrain the return type to ImmutableList<E>

  /**

        if (element.equals(list.get(i))) {
          return i;
        }
      }
    }
    return -1;
  }

  /** An implementation of {@link List#lastIndexOf(Object)}. */
  static int lastIndexOfImpl(List<?> list, @CheckForNull Object element) {
    if (list instanceof RandomAccess) {
      return lastIndexOfRandomAccess(list, element);
    } else {

    return (object == null) ? -1 : Lists.indexOfImpl(this, object);
  }

  @Override
  public int lastIndexOf(@CheckForNull Object object) {
    return (object == null) ? -1 : Lists.lastIndexOfImpl(this, object);
  }

  @Override
  public boolean contains(@CheckForNull Object object) {
    return indexOf(object) >= 0;
  }

  // constrain the return type to ImmutableList<E>

  /**