future/example7.cpp

#include <iostream>
#include <future>
#include <thread>

int main()
{
  // using namespace std::chrono_literals;
   std::promise<int> p;
   std::future<int> f = p.get_future();
   std::thread([&p] {
         std::this_thread::sleep_for(std::chrono::seconds(1));
         p.set_value_at_thread_exit(9);
   }).detach();

   std::cout << "Waiting..." << std::flush;
   f.wait();
   std::cout << "Done!\nResult is: " << f.get() << '\n';
   return 0;
}