Thread reusage c++11

#include <thread>
#include <iostream>

void foo() {
        for(int i = 0; i < 7; ++i) {
                std::cout << i << std::endl;
        }
}

int main() {
        std::thread t;
        t.join();
        std::cout << "=======" << std::endl;

        std::thread(foo).swap(t);
        t.join();
        std::cout << "=======" << std::endl;

        std::thread(foo).swap(t);
        t.join();
        std::cout << "=======" << std::endl;
}