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

main.swift

func combineAsyncCalls(completionHandler: @escaping (String)->()) {
    var text = ""
    fetchData(0, delay: 0.4) { text += $0 }
    fetchData(1, delay: 0.2) { text += $0 }

    completionHandler(text)
}

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

RunLoop.current.run()