{

// future from a packaged_task

std::packaged_task<int()> task([]{ return 7; }); // wrap the function

std::future<int> f1 = task.get_future(); // get a future

std::thread t(std::move(task)); // launch on a thread

// future from an async()

std::future<int> f2 = std::async(std::launch::async, []{ return 8; });

// future from a promise

std::promise<int> p;

std::future<int> f3 = p.get_future();

std::thread( [&p]{ p.set_value_at_thread_exit(9); }).detach();

std::cout << "Waiting..." << std::flush;

f1.wait();

f2.wait();

f3.wait();

std::cout << "Done!\nResults are: "

<< f1.get() << ' ' << f2.get() << ' ' << f3.get() << '\n';

t.join();