typealias CallBack = (result: [Int]) -> Void
func longCalculations (completion: CallBack) {

let backgroundQ = DispatchQueue.global(attributes: .qosBackground)

    let group = DispatchGroup()
    var fill:[Int] = []
    for item in 0...200 {
        group.enter()
        if item > 50 {
            fill.append(item)
        }
        group.leave()
    }

group.notify(queue: DispatchQueue.main, execute: {
    completion(result: fill)
    })
 }


longCalculations() { print($0) }