ForwardingImmutableList() {}

  abstract List<E> delegateList();

  public int indexOf(@Nullable Object object) {
    return delegateList().indexOf(object);
  }

  public int lastIndexOf(@Nullable Object object) {
    return delegateList().lastIndexOf(object);
  }

  public E get(int index) {
    return delegateList().get(index);
  }

  private final ImmutableCollection<E> delegate;
  private final ImmutableList<? extends E> delegateList;

  RegularImmutableAsList(ImmutableCollection<E> delegate, ImmutableList<? extends E> delegateList) {
    this.delegate = delegate;
    this.delegateList = delegateList;
  }

  RegularImmutableAsList(ImmutableCollection<E> delegate, Object[] array) {

  // serialized.
  E element;

  SingletonImmutableList(E element) {
    this.delegate = singletonList(checkNotNull(element));
    this.element = element;
  }

  @Override
  List<E> delegateList() {
    return delegate;
  }

  RegularImmutableList(List<E> delegate) {
    // TODO(cpovirk): avoid redundant unmodifiableList wrapping
    this.delegate = unmodifiableList(delegate);
  }

  @Override
  List<E> delegateList() {
    return delegate;
  }

  }

  @Override
  public Spliterator<E> spliterator() {
    return CollectSpliterators.indexed(
        size(),
        ImmutableList.SPLITERATOR_CHARACTERISTICS | Spliterator.SORTED | Spliterator.DISTINCT,
        delegateList()::get,
        comparator());
  }

  // redeclare to help optimizers with b/310253115
  @SuppressWarnings("RedundantOverride")
  @Override
  @J2ktIncompatible // serialization