比如， case int, float64 编译会报错，有没有什么方法能实现这种用法呢？
```
package main
import "fmt"
func do(i interface{}) {
switch v := i.(type) {
case int, float64: // Illegal! Then how?
fmt.Printf("Twice %v is %v\n", v, v*2)
case string:
fmt.Printf("%q is %v bytes long\n", v, len(v))
default:
fmt.Printf("I don't know about type %T!\n", v)
}
}
func main() {
do(21)
do(3.13)
do("hello")
do(true)
}
```
- case 匹配单个类型：case下面的语句可以将a当做此类型操作
- case 匹配多个类型：只能以i声明的类型进行操作，譬如如果声明的是interface{} 那就不能使用 len()
## 搬运：
- https://stackoverflow.com/questions/40575033/golang-multiple-case-in-type-switch
- https://golang.org/ref/spec#Type_switches
```
The TypeSwitchGuard may include a short variable declaration. When that form is used, the variable is declared at the beginning of the implicit block in each clause. In clauses with a case listing exactly one type, the variable has that type; otherwise, the variable has the type of the expression in the TypeSwitchGuard.
```
只能说，主动适应golang强类型语言的思维方式……（或者等泛型）
#6
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如果你这里把int和float64分到同一组是出于有相同的算数操作，那么可以考虑把这些操作归类到一个interface，然后将int和float64再自定义类型，`type MyInt int`，`type MyFloat64 float64`, 然后将MyInt和MyFloat64实现这个interface的接口，这样上面就可以统一为 ：
case MyInterface:
fmt.Printf("Twice %v is %v\n", v, v.Multiply(2))
#2
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