swift-playground - 元素序列，但 "join is unavailable: call the ' joinWithSeparator( )'"错误

Question

当我尝试在操场上运行它时，为什么会在第 16 行(下面的最后一行)收到错误“加入不可用:调用 joinWithSeparator()”？而且，我该如何解决？

class Person {
    var firstName: String?
    var lastName: String?
    let gender = "female"

    func fullName() -> String {
        var parts: [String] = []

        if let firstName = self.firstName {
            parts += [firstName]
        }

        if let lastName = self.lastName {
            parts += [lastName]
        }
        return " ".join(parts)
    }
} 

Answer 1

错误消息告诉您问题是什么，并告诉您如何修复它。阅读错误信息!执行错误消息所说的操作!

return parts.joinWithSeparator(" ")