在闭包中突变模型结构

Question

我有一个用户模型，该模型还处理有关该用户的信息保存到我的数据库（Firestore）中。当用户更新其信息时，我需要将其保存到Firestore，但我也需要更新模型。我不确定如何处理此问题，目前正在获取“关闭无法隐式捕获变异的自身参数”。

我应该创建一个单独的处理程序类，还是该怎么做？

型号：

struct User {
    var displayName: String?
    var lastLoggedInAt: Int?
    var createdAt: Int?
    private(set) var questionsLeft: Int?
    var currency: Int?

    var dictionary: [String: Any]

    init(dictionary: [String: Any]) {
        self.displayName = dictionary["displayName"] as? String
        self.lastLoggedInAt = dictionary["lastLoggedInAt"] as? Int
        self.createdAt = dictionary["createdAt"] as? Int
        self.questionsLeft = dictionary["questionsLeft"] as? Int
        self.currency = dictionary["currency"] as? Int

        self.dictionary = dictionary
    }

    mutating func setQuestionsLeft(to num: Int) {
        questionsLeft = num
        dictionary["questionsLeft"] = num
    }
}

// MARK: Set Firestore User Data
extension User {
    mutating func set(data: Data, then handler: Handler = nil) {
        guard let uid = Auth.auth().currentUser?.uid else { return }

        let firestore = Firestore.firestore()
        let ref = firestore.collection("users").document(uid)

        ref.setData(data, merge: true) { (error) in
            if let error = error {
                handler?(.failure(error))
            }
            // update current user struct
            // get an error
            let keys = data.keys
            for key in keys {
                self.dictionary[key] = data[key]
            }
            self = User(dictionary: self.dictionary)
            handler?(.success("Successfully Set User Data"))
        }
    }
}