title: Codable inheritence
body: <p>I have three classes:</p>
  
  <pre><code>class User : NSObject, Codable{
  
      var id: Int! = 0
      var userName: String!
  
     enum CodingKeys:String,CodingKey{
        case id
        case userName = "user_name"
     }
  
  }
  
  class SpecialUser : User{
      var isAdmin: Bool!    
  }
  
  class BlockedUser : User{
      var isBlocked: Bool!
  }
  </code></pre>
  
  <p>When I try to decode Special user or BlockedUser their extra properties always come up null
  How do I decode SpecialUser and BlockedUser correctly?</p>