fallthrough：Go里面switch默认相当于每个case最后带有break，匹配成功后不会自动向下执行其他case，而是跳出整个switch, 但是可以使用fallthrough强制执行后面的case代码。

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")
    }

输出结果：

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

问题：是否在switch最后一个分支使用fallthrough？？？

有错误提示，显示：cannot fallthrough final case in switch

fallthrough不能用在switch的最后一个分支。

示例程序2：

上述示例是true、false常量进行分支判断，看如下变量示例。

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")
    }

输出结果如下：

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

更改为：

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")
    }

输出：

default case

总结：switch分支中使用变量进行判断的时，fallthrough正确的分支开始其作用。