¿Cómo serializar objeto a std :: string usando rapidjson? He implementado

class Person{
public:
    std::string name;
    uint64 id; // uint64 is typedef

    template <typename Writer>
    void Serialize(Writer& writer) const {
        writer.StartObject();
        writer.String("name");
        writer.String(name);
        writer.String(("id"));
        writer.Uint64(id);
        writer.EndObject();
    }
     std::string serialize(){
        FileStream s(stdout);
        PrettyWriter<FileStream> writer(s);   
        Serialize(writer);
        return  ? /// There is a problem

    }
}

¿El problema está en la función de serializar qué devolver?