interface{} to []string

Question

I'm trying to parse some YAML file into go struct, but the file itself can not be treated as ordinary go structure: some of values may be either string or map[string][]string.

What I have tried is to do custom unmarshal func:

func (domain *Domain) UnmarshalYAML(unmarshal func(interface{}) error) error {
    fmt.Println("Parsing domain")

    var hostUrl interface{}
    unmarshal(&hostUrl)
    fmt.Println(reflect.TypeOf(hostUrl))

    switch hostUrl.(type) {
    case string:
        domain.Host = hostUrl.(string)
    case map[interface {}]interface {}:
        fmt.Println("got map")
        v := reflect.ValueOf(hostUrl)
        fmt.Println(v.MapKeys()[0])
        for _, host := range v.MapKeys() {
            domain.Host = host.Interface().(string)

            fmt.Println(v.MapIndex(host)) 
            //HERE I NEED TO DO SMTH LIKE THIS:
            //domain.Urls = v.MapIndex(host).([]string)

        }
    default:
        return errors.New("invalid config file, cant parse domains")
    }

    return nil
}

My domain structure looks like this:

type Domain struct {
    Host        string
    Urls        []string
}

But this code causes an error:

invalid type assertion: v.MapIndex(host).([]string) (non-interface type reflect.Value on left) 

So my question may sound like "how to convert {}interface to []string?" or it may become more complex: "How to parse YAML file into go struct if some key can be either simple string or map[string][]string?"

UPDATE: Responding to @mkopriva:

fmt.Println(v.MapIndex(host))
for url := range v.MapIndex(host).Interface().([] interface{}) {
        fmt.Println(url)
}

Didnt help me, as now it just prints some integers (0), but there should be a string. Converting it to an array of strings throws another error:

panic: interface conversion: interface {} is []interface {}, not []string

Answer 1

Thanks to @mkopriva and the snippet from the sandbox. The reason of integer appearing during iterating over v.MapIndex(host).Interface().([] interface{}) is that range returns two values: index and corresponding to that index value. I was only catching the first one. It is why I wasn't able to cast it to string.

Working loop:

for _, url := range v.MapIndex(host).Interface().([] interface{}) {
    fmt.Println(url.(string))
    domain.Urls = append(domain.Urls,url.(string) )
}