anchor.diff:      }
       return false;
     }
  -                                                
  +
     Iterator<E> get iterator =>
         new _CompactIterator<E>(this, _data, _usedData, -1, 1);
   
  
positive.code:     }
      return firstDeleted >= 0 ? -firstDeleted : -i;
    }
    
    void operator[]=(K key, V value) {
      final int size = _index.length;
      final int sizeMask = size - 1;
  
negative.code:   // TODO(koda): Ask gbracha why I cannot have fields _equals/_hashCode.
    int _hashCode(e) => _hasher(e);
    bool _equals(e1, e2) => _equality(e1, e2);
  
    bool containsKey(Object o) => _validKey(o) ? super.containsKey(o) : false;
    V operator[](Object o) => _validKey(o) ? super[o] : null;
    V remove(Object o) => _validKey(o) ? super.remove(o) : null;
  