anchor.diff:    }
   
     void handleUndo(LeaveBehindItem item) {
  -    int insertionIndex = lowerBound(leaveBehindItems, item,
  -      compare: (LeaveBehindItem a, LeaveBehindItem b) => a.index.compareTo(b.index)
  -    );
  +    int insertionIndex = lowerBound(leaveBehindItems, item);
       setState(() {
         leaveBehindItems.insert(insertionIndex, item);
       });
  
positive.code:   final String name;
    final String subject;
    final String body;
  }
  
  class LeaveBehindDemo extends StatefulWidget {
  
negative.code:   rightSwipe
  }
  
  class LeaveBehindItem implements Comparable<LeaveBehindItem> {
    LeaveBehindItem({ this.index, this.name, this.subject, this.body });
  
    LeaveBehindItem.from(LeaveBehindItem item)
  