How can I cancel initialization of an object during init()?

Question

class User {
    var id: Int!
    init(data: JSON){
        id = data["id"].int
        //if id doesn't exist, then cancel the init and return nil.
    }
}

I want to initialize a user by passing a JSON to its constructor. However, sometimes the JSON doesn't match. In this case, I want the initialization to be cancelled, and User to be nil.

Answer 1

something like this:

class User {
    var id: Int!
    init?(data: JSON) {
        guard let id = Int(data["id"]) else {
            return nil
        }

        self.id = id
    }
}

Answer 2

Create a "Failable Initializer" - that is one will either return self or nil.

class User {
  var id: Int!

  init?(data: JSON){
    if <id doesn't exist> {
      return nil
    }

    id = data["id"].int
  }
}