future/example11.cpp

// packaged_task::get_future
#include <iostream>     // std::cout
#include <utility>      // std::move
#include <future>       // std::packaged_task, std::future
#include <thread>       // std::thread

// function that launches an int(int) packaged_task in a new thread:
std::future<int> launcher (std::packaged_task<int(int)>& tsk, int arg) {
   if (tsk.valid()) {
     std::future<int> ret = tsk.get_future();
     std::thread (std::move(tsk),arg).detach();
     return ret;
   }
   else return std::future<int>();
}

int main ()
{
 std::packaged_task<int(int)> tsk ([](int x){return x*2;});
 std::future<int> fut = launcher (tsk,25);
 std::cout << "The double of 25 is " << fut.get() << ".\n";
 return 0;
}