anchor.diff:          index++;
         }
       }
  +
       _truncate(record);
       _iterable = collection;
       return isDirty;
  
positive.code:     _object = obj;
      if (obj == null) {
        _mode = _MODE_IDENTITY_;
      } else if (field == null) {
        _instanceMirror = null;
        if (obj is Map) {
          if (_mode != _MODE_MAP_) {
  
negative.code:     identical(_iterable, collection)) {
        // Short circuit and assume that the list has not been modified.
        return false;
      }
  
      if (collection is List) {
        List list = collection;
        for(int index = 0; index < list.length; index++) {
          var item = list[index];
  