Swift：switch语句中未解析的标识符

Question

我在Xcode6-Beta4的操场上尝试以下操作，跟随苹果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switch语句中定义的变量vegetableComment，我得到Use of unresolved identifier 'vegetableComment'错误

是否与swift中switch语句的范围/闭包有关？

Answer 1

  

是否与swift中switch语句的范围/闭包有关？

是的，它与变量的范围有关。你有四个常量叫vegetableComment。每个范围都限定在case语句的switch。

要访问您在switch内分配的变量，您需要在进入交换机之前将其声明为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."
}