Swift 元組作為字典值

Question

我有一個以下類，它使用下標作為其本質上圍繞 Swift 字典的包裝器。

class STCTruthDict: NSObject, SequenceType {

  typealias IpRelationshipTuple = (String, String?)

  private var truthDict: [String : IpRelationshipTuple] = [ : ]

  subscript(key: String) -> IpRelationshipTuple? {
    get {
        return self.truthDict[key]
    }
    set {
        truthDict[key] = newValue
    }
  }

  // MARK: - Initializers

  override init() {
      super.init()
  }

func generate() -> DictionaryGenerator <String, IpRelationshipTuple> {
    return self.truthDict.generate()
}

}

我正在嘗試使用以下代碼使用這個類及其來自另一個類的下標：

private var truthDict: STCTruthDict?
.....
.....
.....

 // Get ip and userId
 let ipToBeAdded = responseData["ip"] as! String
 let userIdForIP = responseData["user_id"] as! String
 // update truth table
 let relationshipTuple = (ipToBeAdded, nil) as STCTruthDict.IpRelationshipTuple?
 self.truthDict[userIdForIP] = relationshipTuple

但我收到一條錯誤消息：

“Cannot assign to immutable value of type ‘IpRelationshipTuple?’ “

誰能告訴我在這里做錯了什么？

這是操場快照：

Answer 1

因為您的truthDict被定義為可選的，所以您需要解開它。 我沒有得到與您相同的錯誤，但您應該嘗試truthDict!["you"]或完全從定義中刪除可選項。

var truthDict = STCTruthDict()

或者

truthDict!["you"] = relationshipTuple
//       ^