anchor.diff:      }
     }
   
  -  Future<void> _startScroll(
  -      {@required int index,
  -      double alignment,
  -      @required Duration duration,
  -      Curve curve = Curves.linear,
  -      @required List<double> opacityAnimationWeights}) async {
  -    final lastTarget = _showFrontList ? frontTarget : backTarget;
  +  Future<void> _startScroll({
  +    @required int index,
  +    double alignment,
  +    @required Duration duration,
  +    Curve curve = Curves.linear,
  +    @required List<double> opacityAnimationWeights,
  +  }) async {
  +    final lastTarget = _showFrontList ? front.target : back.target;
       final direction = index > lastTarget ? 1 : -1;
       final startingListDisplay = listDisplay;
       final startingScrollController = scrollController;
  
positive.code:   }
  
    void _cancelScroll(_ListDisplay startingListDisplay) {
      frontScrollController.jumpTo(frontScrollController.offset);
      backScrollController.jumpTo(backScrollController.offset);
      if (startingListDisplay == _ListDisplay.front && opacity.value >= 0.5 ||
          startingListDisplay == _ListDisplay.back && opacity.value > 0.5) {
        setState(() {
  
negative.code:                         itemBuilder: widget.itemBuilder,
                          separatorBuilder: widget.separatorBuilder,
                          itemCount: widget.itemCount,
                          itemPositionsNotifier: front.itemPositionsNotifier,
                          positionedIndex: front.target,
                          controller: front.scrollController,
                          scrollDirection: widget.scrollDirection,
                          reverse: widget.reverse,
                          cacheExtent: cacheExtent,
                          alignment: front.alignment,
                          physics: widget.physics,
                          addSemanticIndexes: widget.addSemanticIndexes,
                          semanticChildCount: widget.semanticChildCount,
  