let x where x.hasSuffix(“pepper”) 如何工作

Question

在下面的代码块中，我无法理解 let x where x.hasSuffix("pepper").

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 sandwhich"
    case let x where x.hasSuffix("pepper"):
        let vegetableComment = "Is it a spicy \(x)"
    default:
        let vegetableComment = "Everything tastes good in soup."
}

控制台输出

蔬菜评论： 是辣红辣椒吗

似乎正在发生以下逻辑。

x = vegetable
if (x's suffix == 'pepper') 
    run case

有人能为我更好地解释一下吗？

Answer 1

vegetable 是一个隐含的 String. 。这和你写的一样：

var vegetable: String = "red pepper"

hasSuffix 被声明为 func hasSuffix(suffix: String) -> Bool 因此返回 a Bool. 。这 where 关键字指定附加要求，并且只能用于 switch 声明。
因为这一切都充满了， vegetable 变量被分配给 x (let x).

您可以阅读更多有关 where 和 switch 这里.