void lobby_info::sort_users(bool by_name, bool by_relation)
{
    users_sorted_.clear();
    for(auto& u : users_) {
        users_sorted_.push_back(&u);
    }

    std::sort(users_sorted_.begin(), users_sorted_.end(), [&](const user_info* u1, const user_info* u2) {
        if(by_name && by_relation) {
            return u1->relation < u2->relation || (u1->relation == u2->relation && u1->name < u2->name);
        }

        return (by_name ? u1->name < u2->name : true) && (by_relation ? u1->relation < u2->relation : true);
    });
}
======================================================

struct user_sorter_name
{
    bool operator()(const user_info& u1, const user_info& u2)
    {
        return u1.name < u2.name;
    }
    bool operator()(const user_info* u1, const user_info* u2)
    {
        return operator()(*u1, *u2);
    }
};

struct user_sorter_relation
{
    bool operator()(const user_info& u1, const user_info& u2)
    {
        return static_cast<int>(u1.relation) < static_cast<int>(u2.relation);
    }
    bool operator()(const user_info* u1, const user_info* u2)
    {
        return operator()(*u1, *u2);
    }
};

struct user_sorter_relation_name
{
    bool operator()(const user_info& u1, const user_info& u2)
    {
        return static_cast<int>(u1.relation) < static_cast<int>(u2.relation)
               || (u1.relation == u2.relation && u1.name < u2.name);
    }
    bool operator()(const user_info* u1, const user_info* u2)
    {
        return operator()(*u1, *u2);
    }
};

void lobby_info::sort_users(bool by_name, bool by_relation)
{
    users_sorted_.clear();
    for(auto & u : users_)
    {
        users_sorted_.push_back(&u);
    }
    if(by_name) {
        if(by_relation) {
            std::sort(users_sorted_.begin(),
                      users_sorted_.end(),
                      user_sorter_relation_name());
        } else {
            std::sort(users_sorted_.begin(),
                      users_sorted_.end(),
                      user_sorter_name());
        }
    } else if(by_relation) {
        std::sort(users_sorted_.begin(),
                  users_sorted_.end(),
                  user_sorter_relation());
    }
}