// future from a packaged_task

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

std::future<int> fut1 = task.get_future(); // get a future

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

// future from an async()

std::future<int> fut2 = std::async(std::launch::async, []{ return 8; });

// future from a promise

std::promise<int> prom;

std::future<int> fut3 = prom.get_future();

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

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

fut1.wait();

fut2.wait();

fut3.wait();

th.join();

std::cout << "Done!" << std::endl;

std::cout << "Results are: "

<< fut1.get() << ' ' << fut2.get() << ' ' << fut3.get() << std::endl;

return 0;