C++ pass argument to singleton

class Questionnary
{
  std::string _str;

  static Questionnary& getInstanceImpl(std::string* const s = nullptr)
  {
    static Questionnary instance{ s };
    return instance;
  }

  Questionnary(std::string* const s)
    : _str{ s ? move(*s) : std::string{} } // employ move ctor
  {
    if (nullptr == s)
      throw std::runtime_error{ "Questionnary not initialized" };
  }

public:
  static Questionnary& getInstance()
  {
    return getInstanceImpl();
  }
  static void init(std::string s) // enable moving in
  {
    getInstanceImpl(&s);
  }

  Questionnary(Questionnary const&) = delete;
  void operator=(Questionnary const&) = delete;
};

Source: stackoverflow.com

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