#include <iostream>
#include <boost/fiber/all.hpp>

int main()
{
    auto say = []<typename T>(const T& t)
    {
        std::cout << "[" << boost::this_fiber::get_id() << "]: " << t << std::endl; 
    };

    boost::fibers::fiber f1([&]
    {
        say("f1");
        boost::fibers::fiber f2(say, "f2");
        f2.join();
        say("f1");
    });
    f1.join();
}