gcd5.swift

import UIKit
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true

let pairOfNumbers  = [(2, 3), (5, 10), (4, 5)]
let operationQueue = OperationQueue()

//if set 1, it will be serial if commented it will be concurrent
operationQueue.maxConcurrentOperationCount = 1

for pair in pairOfNumbers{
    operationQueue.addOperation {
        let result = pair.0 * pair.1
        print("Result: \(result)")
        sleep(1)
    }
}