class Task {
    var cancelled = false

    func cancel() {
        cancelled = true
    }

    static func dispatch_after(deadline: DispatchTime, on targetQueue: DispatchQueue, execute work: @escaping () -> ()) -> Task {
        let task = Task()
        targetQueue.asyncAfter(deadline: deadline) {
            if !task.cancelled {
                work()
            }
        }
        return task
    }
}

let task = Task.dispatch_after(deadline: DispatchTime.now()+2, on: DispatchQueue.main) {
    print("yoyo")
}
task.cancel()