DetachedCoroutine 似乎没有必要？ #147

struct FinalAwaiter {
    bool await_ready() const noexcept { return false; }
    template <typename PromiseType>
    auto await_suspend(std::coroutine_handle<PromiseType> h) noexcept {
        return h.promise()._continuation;
    }
    void await_resume() noexcept {}
};

// Lazy:
template <typename F>
void start(F&& callback) {
    // callback should take a single Try<T> as parameter, return value will
    // be ignored. a detached coroutine will not suspend at initial/final
    // suspend point.
    auto launchCoro = [](Lazy lazy,
                         std::decay_t<F> cb) -> detail::DetachedCoroutine {
        cb(std::move(co_await lazy.coAwaitTry()));
    };
    [[maybe_unused]] auto detached =
        launchCoro(std::move(*this), std::forward<F>(callback));
}

struct FinalAwaiter {
    bool await_ready() const noexcept { return false; }
    template <typename PromiseType>
    void await_suspend(std::coroutine_handle<PromiseType> h) noexcept {
        if (h.promise()._continuation) { // 如果调用者是协程，激活它；否则无需挂起并由编译器释放内存）。
            h.promise()._continuation.resume();
        }
    }
    void await_resume() noexcept {}
};

// Lazy:
template <typename F>
void start(F&& callback) {
    if (!isReady()) {
        _coro.resume(); // 激活当前挂起的协程
    }
    callback(coAwaitTry().await_resume()); // 获取协程运行结果
}