ManuallyFinishingOperation.swift

class ManuallyFinishingOperation: BlockOperation {
    override var isFinished: Bool {
        return _isFinished && super.isFinished
    }

    var _isFinished: Bool = false {
        willSet { willChangeValue(forKey: "isFinished") }
        didSet { didChangeValue(forKey: "isFinished") }
    }

    init(_ block: @escaping (ManuallyFinishingOperation) -> Void) {
        super.init()
        addExecutionBlock { block(self) }
    }
}