Swift 3 Playground on XCode 8“对成员的引用不明确 'joined()' 错误

Question

我有词典：

let alphabet: [Character: Int] = ["a": 0, "b": 1, "c": 2, "d": 3]

let validSet = CharacterSet.init(charactersIn: alphabet.keys.joined())

那是我收到错误的时候。我该如何解决这个问题，为什么会这样？ 有什么想法吗？

Answer 1

你唯一应该改变的是键的类型，从 Character 到 String:

let alphabet: [String: Int] = ["a": 0, "b": 1, "c": 2, "d": 3]
let validSet = CharacterSet.init(charactersIn: alphabet.keys.joined())

Answer 2

如果您不想按照已经建议的那样将密钥类型更改为字符串，则 map 将字符更改为字符串：

let alphabet: [Character: Int] = ["a": 0, "b": 1, "c": 2, "d": 3]
let validSet = CharacterSet(charactersIn: alphabet.keys.map{String([=10=])}.joined())