字符串不可转换为DictionaryIndex< String，Any> [英] String is not Convertible to DictionaryIndex<String, Any>

问题描述

我正在使用Swift中的字典，它需要持有不同类型的值，虽然键几乎都是字符串。这是Objective-C很容易，但Swift的一般非常有用的类型安全性似乎使这更加困难。

我一直在使用[String：AnyObject]字典直到我遇到无法将生成的AnyObject下转到Swift字符串，这在技术上不是一个对象，而是一个值类型。我可以和平，因为它似乎是有道理的，虽然如果有办法（除了恢复NSString对象，我不想做），我想知道。

上面的逻辑解决方案似乎是切换到使用 [String：Any] 字典，但是在这样做时，我找到了一个即使使用基本代码：

  func abc（）{
 var dict：[String：Any] = [String：Any]（）
如果dict [success]！= nil {
 ... 
} 
} 
  

上面的第三行代码出现错误：

'String'不能转换为'DictionaryIndex< String，Any>'。

现在我似乎有一个包含类型的字典我怀疑我可以根据需要进行倒塌，但是这个钥匙不再可以看到，据我所知，这些键是完全正确的（确实，尽管它是亵渎，甚至错误表明我正在传递一个String）。我所缺少的是，所有我实际想要实现的是具有易于访问的多种类型的值的字典，我可以在正确的Swift类型的v​​ar / let中实际检索到

解决方案

这里的问题似乎是您使用任何。 字典有两个下标方法：

  subscript（i：DictionaryIndex< Key ，Value>） - > （Key，Value）{get} 
下标（key：Key） - >值？ 
  

编译器错误地假设你想要第一个，然后抱怨说您传入的字符串不能转换为 DictionaryIndex< Key，Value> 。

为了避免这个问题，您可以：

• 强制使用特定的下标访问器：




• 将您的字典声明为 [String：AnyObject] 而不是 - 因为元组不是对象。从指南，

  
  

  
  

  • AnyObject 可以表示任何类型的实例。

  
  

  • 任何可以表示一个实例除了功能类型之外，任何类型的文件都是任何类型的。

  
  

  





如果您认为这是错误，您可能希望提交错误。

I'm working with dictionaries in Swift which need to hold differing types of value, although the keys are pretty much all strings. This was painfully easy with Objective-C, but Swift's generally very useful type safety seems to make this more difficult.

I had been working with [String: AnyObject] dictionaries until I ran into being unable to downcast a resulting AnyObject to a Swift string, which technically isn't an object but a value type. I can make peace with this as it seems to make sense, although if there's a way around it (besides reverting to NSString objects which I don't want to do), i'd like to know it.

The logical solution to the above seems to be switching to use [String: Any] dictionaries, but in doing so I'm finding a problem even with a basic piece of code:

func abc() {
    var dict : [String: Any] = [String: Any]()
    if dict["success"] != nil {
       ...
    }
}

The 3rd line of code above gives the error:

'String' is not convertible to 'DictionaryIndex<String, Any>'.

Now I seem to have a dictionary that contains types that I suspect I can downcast as I need to, but that no longer seems accessible by its keys, which as far as I can see are of exactly the right type (indeed, although it's a literal, even the error suggests I am passing a String). What am I missing, given all I'm actually trying to achieve is dictionaries with easily accessible values of multiple types which I can actually retrieve in a var/let of the correct Swift type?

解决方案

The issue here seems to be your use of Any. Dictionary has two subscript methods:

subscript (i: DictionaryIndex<Key, Value>) -> (Key, Value) { get }
subscript (key: Key) -> Value?

The compiler incorrectly assumes you want the first one, and then complains that the String you passed in can't be converted to DictionaryIndex<Key, Value>.

To avoid this problem, you can either:

• Force it to use a specific subscript accessor: if dict["success"] as Any? != nil ...

• Declare your dictionary as [String:AnyObject] instead — since tuples aren't objects. From the guide,

  • AnyObject can represent an instance of any class type.

  • Any can represent an instance of any type at all, apart from function types.

If you believe this is an error, you may wish to file a bug.

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