How to convert string from interface to []string in golang?

Question

I'm parsing a JSON object which contains an array of strings :

var ii interface{}
json := "{\"aString\": [\"aaa_111\", \"bbb_222\"], \"whatever\":\"ccc\"}"

err := json.Unmarshal([]byte(json), &ii)
if err != nil {
    log.Fatal(err)
}
data := ii.(map[string]interface{})
fmt.Println(data["aString"]) // outputs: ["aaa_111" "bbb_222"]

I tried to convert data["aString"] to []string to be able to loop over it, but it fails :

 test := []string(data["aString"]).([]string)
 fmt.Println(test) // panic -> interface conversion: 
                   //          interface is string, not []string

How can I convert data["aString"] ?

---

edit:

I didn't express myself properly. If I print data, I have such map :

map[aString:["BBB-222","AAA-111"] whatever:ccc]

I want to loop over aString (to manipule each array entry). But I can't find how, because aString is type interface {} :

for i, v := range aString { // <-- fails
     // ...
     fmt.Println(i, v)
}

That's why I want to convert aString. I don't want to convert a string which looks like an array to an array.

Answer 1

I recommend you move away from this implementation in general. Your json may vary but you can easily use objects and avoid all this type unsafe nonsense.

Anyway, that conversion doesn't work because the types inside the slice are not string, they're also interface{}. You have to iterate the collection then do a type assertion on each item like so:

aInterface := data["aString"].([]interface{})
aString := make([]string, len(aInterface))
for i, v := range aInterface {
    aString[i] = v.(string)
}