Generic Func: Key path value type '[T]' cannot be converted-CodePudding

I'm playing with Combine to learn it and improve my reactive programming skills, and I'm trying to create some generic class that convert data to my T type

I have this error, and I don't understand why

Key path value type '[T]' cannot be converted to contextual type 'T'

class Fetcher<T: Codable>: ObservableObject {
    private var task: AnyCancellable?
    @Published var result = [T]()

    init<T: Codable> (type: T.Type) {
    guard let url = URL(string: "https://api.example.com") else { return }
    task = URLSession.shared.dataTaskPublisher(for: url)
        .map{$0.data}
        .decode(type: T.self, decoder: JSONDecoder())
        .receive(on: DispatchQueue.global(qos: .background))
        .replaceError(with: T.self as! T)
        .assign(to: \.result, on: self)
    }
}

CodePudding user response：

Since the URL gives you an array of Ts, you should decode an array, rather than a single T in the decode call. This line

.decode(type: T.self, decoder: JSONDecoder())

should be:

.decode(type: [T].self, decoder: JSONDecoder())

That replaceError call is going to crash your app, as T.self is not a T (it's a T.Type), and you are force-casting. Since you are receiving an array, a logical choice for a value to replace errors with, is the empty array []:

.replaceError(with: [])

Also, remove your generic parameter on init:

init() {