#include <coroutine>
#include <cstdio>

struct coro
{
    struct promise_type
    {
        coro get_return_object() { return handle_type::from_promise(*this); }
        std::suspend_always initial_suspend() noexcept { return {}; }
        std::suspend_always final_suspend() noexcept { return {}; }
        void unhandled_exception() {}
    };

    using handle_type = std::coroutine_handle<promise_type>;
    handle_type handle;
    coro(handle_type h) : handle(h) {}
    ~coro() { if (handle) handle.destroy(); }
};

coro f()
{
    std::printf("cogito");
    co_await std::suspend_always{};
    std::printf("ergo");
    co_await std::suspend_always{};
    std::printf("sum!\n");
}

int main()
{
    coro c = f();
    while (!c.handle.done())
    {
        std::printf(" -> ");
        c.handle.resume();
    }
}