OperationQueueDependency.swift

import Foundation

//OperationQueue

class RawMaterialImporter: Operation {
    override func main() {
        guard !self.isCancelled else { return }
        print("raw material importing started...")
        sleep(4)
    }
}

class CarMaker: Operation {
    override func main() {
        guard !self.isCancelled else { return }
        print("car making started...")
    }
}

let operationQueue = OperationQueue()
operationQueue.maxConcurrentOperationCount = 1

let importOperation = RawMaterialImporter()
let carMakingOperation = CarMaker()

carMakingOperation.completionBlock = {
    print("car making completed...")
}

importOperation.completionBlock = {
    print("importing completed...")
}

operationQueue.addOperation(importOperation)
operationQueue.addOperation(carMakingOperation)