generic json serialize/deserialize in swift 4

Credentials.swift

//
//  Credentials.swift
//
//  Created by Yunus Oksuz on 30.12.2017.
//  Copyright © 2017 Yunus Oksuz. All rights reserved.
//

import Foundation

class Credentials {
    
    let defaults = UserDefaults.standard;
    static let instance = Credentials()
    
    var accessToken: AccessToken? {
        set {
            self.set(key: KEY_ACCESS_TOKEN, data: newValue)
        } get {
            return self.get(key: KEY_ACCESS_TOKEN, type: AccessToken.self)
        }
    }
    
    var user: User? {
        set {
            self.set(key: KEY_USER, data: newValue)
        }
        get {
            return self.get(key: KEY_USER, type: User.self)
        }
    }
    
    func updateToken(with data: Data) {
        self.set(key: KEY_ACCESS_TOKEN, type: AccessToken.self, data: data)
    }
    
    func updateUser(with data: Data) {
        self.set(key: KEY_USER, type: User.self, data: data)
    }
    
    private func set<T : Encodable & Decodable>(key: String, type: T.Type, data: Data) {
        do {
            let object = try JSONDecoder().decode(type, from: data)
            self.set(key: key, data: object)
        } catch let err {
            debugPrint(err)
        }
    }
    
    private func set<T: Encodable>(key: String, data: T) {
        do {
            let payload = try JSONEncoder().encode(data);
            self.defaults.set(payload, forKey: key);
        } catch let err {
            debugPrint(err)
        }
    }
    
    private func get<T : Decodable>(key: String, type: T.Type) -> T? {
        if let payload = self.defaults.value(forKey: key) as? Data {
            do {
                return try JSONDecoder().decode(type, from: payload);
            } catch let err {
                debugPrint(err)
            }
        }
        return nil
    }
}