    const_iterator operator--(int) {
      const_iterator tmp(charPtr_, char16Ptr_);
      if (charPtr_) {
        --charPtr_;
      } else {
        --char16Ptr_;
      }
      return tmp;
    }
    const_iterator operator--(int) {
      const_iterator tmp(charPtr_, char16Ptr_);
      if (charPtr_) {
        --charPtr_;
      } else {
        --char16Ptr_;
      }
      return tmp;
    }