/**
   * If this collection is backed by an array of its elements in insertion order, returns the offset
   * where this collection's elements start.
   */
  int internalArrayStart() {
    throw new UnsupportedOperationException();
  }

  /**
   * If this collection is backed by an array of its elements in insertion order, returns the offset
   * where this collection's elements end.
   */
  int internalArrayEnd() {

  /**
   * Copies the contents of this immutable collection into the specified array at the specified
   * offset. Returns {@code offset + size()}.
   */
  @CanIgnoreReturnValue
  int copyIntoArray(@Nullable Object[] dst, int offset) {
    for (E e : this) {
      dst[offset++] = e;
    }
    return offset;
  }

  @J2ktIncompatible // serialization
  @GwtIncompatible // serialization
  Object writeReplace() {

  /**
   * Copies the contents of this immutable collection into the specified array at the specified
   * offset. Returns {@code offset + size()}.
   */
  @CanIgnoreReturnValue
  int copyIntoArray(@Nullable Object[] dst, int offset) {
    for (E e : this) {
      dst[offset++] = e;
    }
    return offset;
  }

  @J2ktIncompatible // serialization
  @GwtIncompatible // serialization
  Object writeReplace() {