class ImageModel {

    func saveImageToDisk(from url: URL, completion: @escaping (UIImage?) -> Void) {
        DispatchQueue.global().async {
            let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
                guard let imageData = data else { return }
                let image = UIImage(data: imageData)
                DispatchQueue.main.async {
                    completion(image)
                }
            }
            task.resume()
        }
    }
}


//========

class ViewController: UIViewController {

        let imageModel = ImageModel()
        let imageView = UIImageView()

        let url = URL(string: "httpspspsfdspfjdspofjsdpfj")

        imageModel.saveImageToDisk(from: url) { [weak self] (image, name) in
            self?.imageView.image = image
        }
}