go語言fallthrough的用法心得

fallthrough：Go里面switch默認相當於每個case最后帶有break，匹配成功后不會自動向下執行其他case，而是跳出整個switch, 但是可以使用fallthrough強制執行后面的case代碼。

示例程序1：

switch {
    case false:
        fmt.Println("The integer was <= 4")
        fallthrough
    case true:
        fmt.Println("The integer was <= 5")
        fallthrough
    case false:
        fmt.Println("The integer was <= 6")
        fallthrough
    case true:
        fmt.Println("The integer was <= 7")
        fallthrough
    case false:
        fmt.Println("The integer was <= 8")
    default:
        fmt.Println("default case")
    }

輸出結果：

The integer was <= 5
The integer was <= 6
The integer was <= 7
The integer was <= 8

問題：是否在switch最后一個分支使用fallthrough？？？

有錯誤提示，顯示：cannot fallthrough final case in switch

fallthrough不能用在switch的最后一個分支。

示例程序2：

上述示例是true、false常量進行分支判斷，看如下變量示例。

s := "abcd"
    switch s[1] {
    case 'a':
        fmt.Println("The integer was <= 4")
        fallthrough
    case 'b':
        fmt.Println("The integer was <= 5")
        fallthrough
    case 'c':
        fmt.Println("The integer was <= 6")
    default:
        fmt.Println("default case")
    }

輸出結果如下：

The integer was <= 5
The integer was <= 6

更改為：

s := "abcd"
    switch s[3] {
    case 'a':
        fmt.Println("The integer was <= 4")
        fallthrough
    case 'b':
        fmt.Println("The integer was <= 5")
        fallthrough
    case 'c':
        fmt.Println("The integer was <= 6")
    default:
        fmt.Println("default case")
    }

輸出：

default case

總結：switch分支中使用變量進行判斷的時，fallthrough正確的分支開始其作用。