Overriding default values with operation class in Swift 3

Question

I am attempting to override some values with the Operation class in Swift 3 as part of a conversion process from 2.2, but am encountering an issue with overriding class properties. This is a simplified version of the code that works properly in Swift 2.2: ``` class ViewController: UIViewController { lazy var operationQueue: NSOperationQueue = { let queue = NSOperationQueue() queue.maxConcurrentOperationCount = 1 return queue }() override func viewDidLoad() { super.viewDidLoad() callOperation() } func callOperation() { var error: NSError? let words = ["A", "B"] words.forEach { word in let operation = TestOperation(text: word) operation.completionBlock = { error = operation.error } operationQueue.addOperation(operation) } operationQueue.addOperationWithBlock { if error == nil { print("No errors") } else { print(error?.localizedDescription) } } } } class TestOperation: NSOperation { private(set) var error: NSError? private var text: String? private var isExecuting: Bool = false private v…

Accepted Answer

So it turns out that I needed to prepend the private variables with an _ for the compiler to accept them.

The items of note have been highlighted with comments.

Below is the working code for Swift 3:

```
import UIKit

class ViewController: UIViewController {
    lazy var operationQueue: OperationQueue = {
        let queue = OperationQueue()
        queue.maxConcurrentOperationCount = 1

return queue
    }()

override func viewDidLoad() {
        super.viewDidLoad()

callOperation()
    }

func callOperation() {
        var error: NSError?

let words = ["A", "B"]

words.forEach { word in
            let operation = TestOperation(text: word)
            operation.completionBlock = {
                error = operation.error
            }
            operationQueue.addOperation(operation)
        }

operationQueue.addOperation {
            if error == nil {
                print("No errors")
            } else {
                print(error?.localizedDescription)
            }
        }
    }
}

class TestOperation: Operation {
    private(set) var error: NSError?

private var text: String?

private var _executing: Bool = false // Notice the _ before the name
    private var _finished: Bool = false // Notice the _ before the name

override var isAsynchronous: Bool {
        return true
    }

override var isExecuting: Bool {
        get {
            return _executing
        }
        set {
            willChangeValue(forKey: "isExecuting") // This must match the overriden variable
            _executing = newValue
            didChangeValue(forKey: "isExecuting") // This must match the overriden variable
        }
    }

override var isFinished: Bool {
        get {
            return _finished
        }
        set {
            willChangeValue(forKey: "isFinished") // This must match the overriden variable
            _finished = newValue
            didChangeValue(forKey: "isFinished") // This must match the overriden variable
        }
    }

init(text: String) {
        self.text = text

super.init()
    }

override func start() {
        if isCancelled {
            isFinished = true

return
        }

isExecuting = true

func completeOperation() {
            isFinished = true
            isExecuting = false
        }

DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
            print(self.text)
            completeOperation()
        }
    }
}
```

This now produces the following when run:

```
A
B
No errors
```

Overriding default values with operation class in Swift 3

Solution

Problem