数据类型判断问题

for k, v := range gobook2 {
    switch v2 := v.(type) {
    case string:
        fmt.Println(k, "is string", v2)
    case int:
        fmt.Println(k, "is int", v2)
    case bool:
        fmt.Println(k, "is bool", v2)
    /*case []interface{}:
    fmt.Println(k, "is an arry: ")
    for i, iv := range v2 {
        fmt.Println(i, iv)
    }*/
    default:
        fmt.Println(k, "is another type not handle yet")
    }
}

这是结果:

IsPublished is bool true
Price is another type not handle yet
Title is string Golang programming
Authors is another type not handle yet
Publisher is string ituring.com.cn

我想问:v2到底是个什么东西?