AsyncOperation wrapper for OperationQueue

AsyncOperation.swift

class AsyncOperation: Operation {
    enum State: String {
        case ready = "Ready"
        case executing = "Executing"
        case finished = "Finished"
        
        fileprivate var keyPath: String {
            return "is" + rawValue
        }
    }
    
    var state: State = .ready {
        willSet {
            willChangeValue(forKey: newValue.keyPath)
            willChangeValue(forKey: state.keyPath)
        }
        
        didSet {
            didChangeValue(forKey: oldValue.keyPath)
            didChangeValue(forKey: state.keyPath)
        }
    }
    
}

extension AsyncOperation {
    override var isReady: Bool {
        return super.isReady && state == .ready
    }
    
    override var isExecuting: Bool {
        return state == .executing
    }
    
    override var isFinished: Bool {
        return state == .finished
    }
    
    override var isAsynchronous: Bool {
        return true
    }
    
    override func start() {
        if isCancelled {
            state = .finished
            return
        }
        main()
        state = .executing
    }
    
    override func cancel() {
        state = .finished
    }
}

Extend it, overwrite main() and don't forget to call self.state = .finished when you've completed your operation.