xcode - Swift:来自 switch 语句的未解析标识符

Question

我正在 Xcode6-Beta4 的 Playground 上尝试以下操作，跟随苹果的 swift tour :

let vegetable = "red pepper"
switch vegetable{
case "celery":
    let vegetableComment = "Add some raisins and make ants on a log."
case "cucumber", "watercress":
    let vegetableComment = "That would make a good tea sandwich."
case let x where x.hasSuffix("pepper"):
    let vegetableComment = "Is it a spicy \(x)"
default:
    let vegetableComment = "Everything tastes good in soup."
}

然后我尝试调用在 switch 语句中定义的变量 vegetableComment，我得到了一个错误 Use of unresolved identifier 'vegetableComment'

它是否与 swift 中 switch 语句的作用域/闭包有关？

Answer 1

Is it something relating the the scope / closure of switch statement in swift?

是的，跟变量的作用域有关。您有四个名为 vegetableComment 的常量。每一个都限定在 switch 语句的 case 范围内。

为了访问您在 switch 中分配的变量，您需要在进入 switch 之前将其声明为 var:

var vegetableComment = String()
let vegetable = "red pepper"
switch vegetable{
case "celery":
    vegetableComment = "Add some raisins and make ants on a log."
case "cucumber", "watercress":
    vegetableComment = "That would make a good tea sandwich."
case let x where x.hasSuffix("pepper"):
    vegetableComment = "Is it a spicy \(x)"
default:
    vegetableComment = "Everything tastes good in soup."
}