如何在golang中将字符串从接口转换为[]字符串？

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)
}

Answer 2

Is it what you need?

package main

import (
    "fmt"
    "encoding/json"
)

func main() {
    js := "{\"aString\": [\"aaa_111\", \"bbb_222\"], \"whatever\":\"ccc\"}"
    a := make(map[string]interface{})
    json.Unmarshal([]byte(js), &a)
    for _, v := range a["aString"].([]interface{}) {
        str := v.(string)
        fmt.Println(str)
    }
}

Check on Go Playground

Answer 3

For another approach, you can use a struct instead:

package main

import (
   "encoding/json"
   "fmt"
)

func main() {
   s := []byte(`{"aString": ["aaa_111", "bbb_222"], "whatever":"ccc"}`)
   var t struct {
      Astring []string
      Whatever string
   }
   json.Unmarshal(s, &t)
   fmt.Printf("%+v\n", t) // {Astring:[aaa_111 bbb_222] Whatever:ccc}
}