Simple Swift AsyncOperation

AsyncOperation.swift

class AsyncOperation : Operation {

    private var _isExecuting = false
    private var _isFinished = false

    override func start() {
        guard !isCancelled else {
            finish()
            return
        }

        willChangeValue(forKey: "isExecuting")
        _isExecuting = true
        main()
        didChangeValue(forKey: "isExecuting")
    }

    override func main() {
        // NOTE: should be overriden
        finish()
    }

    func finish() {
        willChangeValue(forKey: "isFinished")
        _isFinished = true
        didChangeValue(forKey: "isFinished")
    }

    override var isAsynchronous: Bool {
        return true
    }

    override var isExecuting: Bool {
        return _isExecuting
    }

    override var isFinished: Bool {
        return _isFinished
    }
}

class MyAsyncOperation: AsyncOperation {
    override func main() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 3) { [weak self] in
            guard let self = self else { return }
            // do the work
            print("Hello3")
            self.finish()
        }
    }
}