“无法将 'String' 类型的值分配给类型 'AnyObject?'"，Swift 3，Xcode 8 beta 6 [英] "Cannot assign value of type 'String' to type 'AnyObject?'", Swift 3, Xcode 8 beta 6

问题描述

一段相当简单的代码

var dict: [String: AnyObject] = [:]
dict["key"] = "value"

产生以下编译时错误

Cannot assign value of type 'String' to type 'AnyObject?'

简单的类型检查告诉我 String 是 AnyObject

Simple type checks tell me that String is AnyObject

"value" is AnyObject // returns true

我可以将 AnyObject 更改为 Any 并且一切正常

I could change AnyObject to Any and everything would work

var dict: [String: Any] = [:]
dict["key"] = "value"

但我想了解为什么会出现错误?String 不再是 AnyObject 了吗?或者这是一个错误?

but I want to understand why do I get the error? Is String no longer AnyObject? Or is this a bug?

推荐答案

在 b6 中，String 不再神奇地连接到 NSString.字符串不是一个类；这是一个结构.您需要手动进行桥接:

In b6, String no longer magically bridges to NSString. String is not a class; it's a struct. You need to do the bridging by hand:

dict["key"] = "value" as AnyObject

is 似乎仍在桥接的事实很可能是一个错误，应该报告.

The fact that is still seems to be bridging is likely a bug and should be reported.

不用说，[String: AnyObject] 和 [String: Any] 应该在您的代码中尽可能少地使用.

It goes without saying that [String: AnyObject] and [String: Any] should be used as little as possible in your code.

(请务必点击 Hamish 在下面评论中提供的链接.)

(Make sure to follow the link Hamish provides in the comments below.)

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