将Swift集转换为NSMutableSet

Question

我可以从NSMutableSet转换为Set no problem，但在执行相反的操作时会遇到问题。

例如，这是有效的：

let nsSet = NSMutableSet(array: ["a", "b"])
let swiftSet = nsSet as! Set<String>

但当我尝试时：

let nsSet2 = swiftSet as? NSMutableSet

nsSet2最终变成了nil。

Answer 1

看起来swift Set需要先转换成NSSet：

let nsSet2 = NSMutableSet(set: set as NSSet)

或者速记：

let nsSet2 = NSMutableSet(set: set)

或者从NSSet到Swift Set再回到NSSet：

let nsSet = NSMutableSet(array: ["a", "b"])
let set = nsSet as! Set<String>
let nsSet2 = set as NSSet
let nsSet3 = NSMutableSet(set: nsSet2)