Method operator==

12.19-constevalParmCheck1/main.cpp:70–73

  }

  constexpr bool operator==(const string& s) const noexcept
  {
    return std::equal(_data, _data + _length, s._data);
  }

  constexpr char*       data() { return _data; }
  constexpr char*       data() const { return _data; }