Go switch語句範例

switch語句表示式條件可跨多個分支條件語句。

所有的範例程式碼，都放在 F:\worksp\golang 目錄下。安裝Go程式設計環境請參考：/2/23/798.html

這裡有一個基本的switch語句用法。可以在同一個case語句中使用逗號分隔多個表示式。 在這個例子中也使用可選的 default 情況。

無表示式的switch語句是表達if/else邏輯的替代方式。這裡還顯示了case表示式可以為非常數資料。

型別switch比較的是型別而不是值。可以使用它來發現介面值的型別。在這個例子中，變數t將具有對應於其子句的型別。

switch.go的完整程式碼如下所示 -

package main

import "fmt"
import "time"

func main() {

    // Here's a basic `switch`.
    i := 2
    fmt.Print("Write ", i, " as ")
    switch i {
    case 1:
        fmt.Println("one")
    case 2:
        fmt.Println("two")
    case 3:
        fmt.Println("three")
    }

    // You can use commas to separate multiple expressions
    // in the same `case` statement. We use the optional
    // `default` case in this example as well.
    switch time.Now().Weekday() {
    case time.Saturday, time.Sunday:
        fmt.Println("It's the weekend")
    default:
        fmt.Println("It's a weekday")
    }

    // `switch` without an expression is an alternate way
    // to express if/else logic. Here we also show how the
    // `case` expressions can be non-constants.
    t := time.Now()
    switch {
    case t.Hour() < 12:
        fmt.Println("It's before noon")
    default:
        fmt.Println("It's after noon")
    }

    // A type `switch` compares types instead of values.  You
    // can use this to discover the the type of an interface
    // value.  In this example, the variable `t` will have the
    // type corresponding to its clause.
    whatAmI := func(i interface{}) {
        switch t := i.(type) {
        case bool:
            fmt.Println("I'm a bool")
        case int:
            fmt.Println("I'm an int")
        default:
            fmt.Printf("Don't know type %T\n", t)
        }
    }
    whatAmI(true)
    whatAmI(1)
    whatAmI("hey")
}

執行上面程式碼，將得到以下輸出結果 -

F:\worksp\golang>go run switch.go
Write 2 as two
It's the weekend
It's after noon
I'm a bool
I'm an int
Don't know type string