switch v := v.(type) 求解

package golang

import (
    "fmt"
    "testing"
)

func valType(v interface{}) {
    switch v := v.(type) {
    case *int:
        fmt.Println("*int", v == nil)
    case int:
        fmt.Println("int", v)
    }
}

func valType2(v interface{}) {
    switch v := v.(type) {
    case *int, *string:
        fmt.Println("*int or *string", v == nil) // 为什么不为nil
    case int:
        fmt.Println("int", v)
    }
}

func TestValType(t *testing.T) {
    var v *int
    valType(v)
    valType2(v)
    var s *string
    valType2(s)
}