void test(int a, Exchanger<int>& e, std::promise<int> p) {
    a = e.exchange(a);
    p.set_value_at_thread_exit(a);
}


int main()
{
    Exchanger<int> e;
    std::promise<int> p1, p2;
    std::future<int> f1, f2;

    f1 = p1.get_future();
    f2 = p2.get_future();

    std::thread t1([&e, &p1]() { int a = 3;
    a = e.exchange(a);
    p1.set_value_at_thread_exit(a);
     });

    std::thread t2(test, 10, std::ref(e), std::move(p2));

    t1.detach();
    t2.detach();



    std::cout << "threads created\n";


    std::cout << "thread 1: " << f1.get() << "\n";
    std::cout << "thread 2: " << f2.get() << "\n";

    std::cout << "finished\n";

    return 0;
}