我不明白为什么我会收到这个错误。SomeController是一个类，而不是一个结构，它不是不可变的。有解决办法吗？
class SomeController: APIFetchable {
let baseUrl = "https://jsonplaceholder.typicode.com"
let defaultSession = URLSession(configuration: .default)
var dataTask: URLSessionTask?
func fetchDataFromAPI(atPath path: String, _ callback: ()-> Void){
fetchDataAtPath(path) { data, error in /*Error on this line -> "Cannot use mutating member on immutable value: 'self' is immutable"*/
}
}
}
protocol APIFetchable {
var baseUrl: String {get}
var defaultSession: URLSession {get}
var dataTask: URLSessionTask? {get set}
mutating func fetchDataAtPath(_ path: String, _ callback: @escaping (Data?, Error?)-> Void)
}
extension APIFetchable {
mutating func fetchDataAtPath(_ path: String, _ callback: @escaping (Data?, Error?)-> Void){
dataTask?.cancel()
if var urlComponents = URLComponents(string: baseUrl) {
urlComponents.path = path
guard let url = urlComponents.url else {return}
dataTask = defaultSession.dataTask(with: url) { data, response, error in
defer {self.dataTask = nil}
if let error = error {
print("data task error \(error.localizedDescription)")
callback(nil, error)
} else if let data = data, let response = response as? HTTPURLResponse, response.statusCode == 200 {
callback(data, nil)
}
}
dataTask?.resume()
}
}
}