    bool operator>(const const_iterator &rhs) const {
      if (charPtr_) {
        return charPtr_ > rhs.charPtr_;
      }
      return char16Ptr_ > rhs.char16Ptr_;
    }
    bool operator>(const const_iterator &rhs) const {
      if (charPtr_) {
        return charPtr_ > rhs.charPtr_;
      }
      return char16Ptr_ > rhs.char16Ptr_;
    }