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Go 语言中的 switch 语句 — blog.huangz.me

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source link: https://blog.huangz.me/2020/switch-in-go.html
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Go 语言中的 switch 语句

本文摘录自《Go语言趣学指南》第 3 章， 请访问 gpwgcn.com 以获取更多相关信息。

../_images/gpwgcn1.jpg

正如代码清单 3-6 所示，Go 提供了 switch 语句，它可以将一个值和多个值进行比较。

代码清单 3-6 switch 语句： concise-switch.go

fmt.Println("There is a cavern entrance here and a path to the east.")
var command = "go inside"

switch command {    // 将命令和给定的多个分支进行比较
case "go east":
    fmt.Println("You head further up the mountain.")
case "enter cave", "go inside":     // 使用逗号分隔可选值
    fmt.Println("You find yourself in a dimly lit cavern.")
case "read sign":
    fmt.Println("The sign reads 'No Minors'.")
default:
    fmt.Println("Didn't quite get that.")
}

执行这个程序将产生以下输出：

There is a cavern entrance here and a path to the east.
You find yourself in a dimly lit cavern.

除了文字以外， switch 语句还可以接受数字作为条件。

switch 的另一种用法是像 if...else 那样，在每个分支中单独设置比较条件。 正如代码清单 3-7 所示，switch 还拥有独特的 fallthrough 关键字，它可以用于执行下一分支的代码。

代码清单 3-7 switch 语句： switch.go

var room = "lake"

switch {    // 比较表达式将被放置到单独的分支里面。
case room == "cave":
    fmt.Println("You find yourself in a dimly lit cavern.")
case room == "lake":
    fmt.Println("The ice seems solid enough.")
    fallthrough    // 下降（fall through）至下一分支。
case room == "underwater":
    fmt.Println("The water is freezing cold.")
}

执行这段代码将产生以下输出：

The ice seems solid enough.
The water is freezing cold.

在 C、Java、JavaScript 等语言中， 下降是 switch 语句各个分支的默认行为。 Go 对此采取了更为谨慎的做法， 用户需要显式地使用 fallthrough 关键字才会引发下降。


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