fetchData function for medium blog post about DispatchGroup and DispatchSemaphore, https://link.medium.com/zJMQPUHaeZ

main.swift

func combineAsyncCallsWithDispatchGroup(completionHandler: @escaping (String)->()) {
    let group = DispatchGroup()
    var text = ""
    group.enter()
    fetchData(0, delay: 0.4) {
        text += $0
        group.leave()
    }
    group.enter()
    fetchData(1, delay: 0.2) {
        text += $0
        group.leave()
    }
    group.notify(queue: .main) {
        completionHandler(text)
    }
}

combineAsyncCallsWithDispatchGroup() {
    print($0)
    exit(0)
}

RunLoop.current.run()