LG

#include <iostream>
#include <experimental/generator>
 
std::experimental::generator<int> loop(int iterations)
{
  for (int i = 0; i < iterations; i++)
  {
    co_yield i;
  }
}
 
int main()
{
  for (int i : loop(100))
  {
    std::cout << i << std::endl;
  }
}

#include <future>
#include <iostream>
 
std::future<int> t()
{
   return std::async([]() { std::cout << "I" << std::endl; return 1; });
}
 
std::future<void> foobar()
{
   std::cout << " First call !\n";
   std::cout << " Ret " << co_await t() << std::endl;
   std::cout << " Still first call !\n";
   std::cout << " Ret2 " << co_await t() << std::endl;
   std::cout << " Only after resumed !\n";
}
 
void tt()
{
   auto ttt = foobar();
   for (int i = 0; i < 10; i ++)
      std::cout << i << std::endl;
   for (int i = 0; i < 100; i++)
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
   ttt.wait();
}
 
int main()
{
   tt();
}

Retour possible :

 First call !
 Ret I
0
1
2
1
 Still first call !
 Ret2 3
4
5
6
7
8
9
I
1
 Only after resumed !