Convert async operation into sync getter

syncGetter.swift

func syncGetter<T>(block: (@escaping (T?) -> Void) -> Void) -> T? {
    let dispatchGroup = DispatchGroup()
    var returnValue: T?
    dispatchGroup.enter()
    block() { value in
        returnValue = value
        dispatchGroup.leave()
    }
    dispatchGroup.wait()
    return returnValue
}

///EXAMPLE
let downloadImage = { (completion: @escaping (UIImage?) -> Void) in
    DispatchQueue.global().async {
        let data = try! Data(contentsOf: URL.init(string: "https://upload.wikimedia.org/wikipedia/commons/6/69/NASA-HS201427a-HubbleUltraDeepField2014-20140603.jpg")!)
        completion(UIImage(data: data))
    }
}
        
let image: UIImage? = syncGetter(block: downloadImage)