"Protocol type ' ' cannot be instantiated" error

Question

This is an extension of the question : creating-a-function-on-a-parent-class-that-can-be-accessible-to-all-its-children

It was suggested instead of using a class for a function a protocol would be better. After attempting the protocol approach the error "Protocol type 'JSONObject ' cannot be instantiated" happens. Any help in fixing this error is appreciated. Here is the protocol:

protocol JSONObject: class, NSObjectProtocol { init(resultsDictionary: [String:Any]) } extension JSONObject { static func updateResultsDictionary(urlExtension: String, completion: @escaping (JSONObject?) -> Void) { let nm = NetworkManager.sharedManager _ = nm.getJSONData(urlExtension: urlExtension) {data in guard let jsonDictionary = nm.parseJSONFromData(data), let resultDictionaries = jsonDictionary["result"] as? [[String : Any]] else { completion(nil) return } for resultsDictionary in resultDictionaries { let jsonInfo = JSONObject(resultsDictionary: resultsDictionary)// Error haapens here completion(jsonInfo) } } } }

beeth0ven · Accepted Answer · 2017-01-14 03:07:56Z

Use Self like this:

static func updateResultsDictionary(urlExtension: String, completion: @escaping (Self?) -> Void) { let jsonInfo = self.init(resultsDictionary: [:]) completion(jsonInfo) }

Because you can't init some protocol, But you can init Type which conform to the protocol.

Self means the Type not the protocol.

And here is a tutorial about Protocol-Oriented Programming in Networking which will help you design Networking Architecture.

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