Generics.md

Generics

Example

This example shows how to define a generic that takes any Codable as a type and then decode it's when parsing JSON decoder.decode(T.self).

struct Service {

    static let sharedInstance = Service()

    func fetchUser(completion: @escaping (User?, Error?) -> () ) {

        Alamofire.request("https://yyy", method: .get, encoding: JSONEncoding.default, headers: headers).responseData { response in

            self.handle(response: response, completion: completion)
        }
    }

    func fetchCreditCardToken(completion: @escaping (CreditCardToken?, Error?) -> () ) {

        Alamofire.request("https://xxx", method: .post, parameters: parameters, encoding: JSONEncoding.default, headers: headers).responseData { response in

            self.handle(response: response, completion: completion)
        }
    }
    
    func handle<T: Codable>(response: DataResponse<Data>, completion: @escaping (T?, Error?) -> ()) {
        switch response.result {
            case .success:
                guard let jsonData = response.result.value else {
                    completion(nil, ServiceError.noData)
                    return
                }

                let decoder = JSONDecoder()
                do {
                    let tweets = try decoder.decode(T.self, from: jsonData)
                    completion(tweets, nil)
                } catch {
                    completion(nil, ServiceError.parsingJSON)
                }

            case .failure(let error):
                completion(nil, error)
        }
    }    
}