ios - Swift 4.2 解包问题 (??)

Question

使用 swift 4.2 时遇到奇怪的问题并使用 ?? 解包

简单代码:

var someVar:String?

override func viewDidLoad() {
   someOp = "print some string"

    subTitleLabel.text = "text one" + someVar ?? "unwrapped"
}

编译器抛出错误:

Value of optional type 'String?' must be unwrapped to a value of type 'String'

Swift 4.2 有什么变化？

Answer 1

这是因为 operator precedence .

+的优先级高于??所以要加括号

subTitleLabel.text = "text one" + (someVar ?? "unwrapped")