return new RegularImmutableList<>(elementsWithoutTrailingNulls);
    }
  }

  ImmutableList() {}

  // This declaration is needed to make List.iterator() and
  // ImmutableCollection.iterator() consistent.
  @Override
  public UnmodifiableIterator<E> iterator() {
    return listIterator();
  }

  @Override
  public UnmodifiableListIterator<E> listIterator() {
    return listIterator(0);
  }

    checkNotNull(elements); // for GWT
    return (elements instanceof Collection)
        ? copyOf((Collection<? extends E>) elements)
        : copyOf(elements.iterator());
  }

  public static <E> ImmutableList<E> copyOf(Iterator<? extends E> elements) {
    return copyFromCollection(Lists.newArrayList(elements));
  }

  public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) {

    }
    return new RegularImmutableList<E>(elements, length);
  }

  ImmutableList() {}

  // This declaration is needed to make List.iterator() and
  // ImmutableCollection.iterator() consistent.
  @Override
  public UnmodifiableIterator<E> iterator() {
    return listIterator();
  }

  @Override
  public UnmodifiableListIterator<E> listIterator() {
    return listIterator(0);
  }