Swift5-SampleResultType.swift

enum ServerError: Error {
    case urlFailed
    case networkFailed
    case serverFailed
    case dataFailed
}

func fetchDataFromServer(_ urlString: String, completion: @escaping (Result<Data, ServerError>) -> ()) {
    // Check if URL valid
    guard let url = URL(string: urlString) else {
        completion(.failure(.urlFailed))
        return
    }

    let defaultSession = URLSession(configuration: URLSessionConfiguration.default)
    let dataTask : URLSessionTask = defaultSession.dataTask(with: url) { data, response, error in
        guard error == nil else {
            completion(.failure(.serverFailed))
            return
        }

        guard let data = data else {
            completion(.failure(.dataFailed))
            return
        }

        completion(.success(data))
    }

    dataTask.resume()
}


fetchDataFromServer("https://samples.openweathermap.org/data/2.5/weather?q=London,uk&appid=b6907d289e10d714a6e88b30761fae22") { result in
    switch result {
    case .success(let data):
        print("Data from server = \(String(data: data, encoding: .utf8) ?? "Convert data to string failed")")
    case .failure(let error):
        print("Error: \(error)")
    }
    
    // Use get() method of Result type to get value sample
//    if let data = try? result.get() {
//        print("Data from server = \(String(data: data, encoding: .utf8) ?? "Convert data to string failed")")
//    }
}