Function f0

example/when_all.cpp:6–11

using namespace co_context;

task<int> f0() {
    printf("f0 start.\n");
    co_await timeout(std::chrono::seconds{1});
    printf("f0 done.\n");
    co_return 1;
}

shared_task<std::string> f1() {
    printf("f1 start.\n");