类型reflect.Value不支持索引

Question

I have an array of generic type interface{} and I would to check if that array contains a certain value in one of its JSON object.

 history := reflect.ValueOf(historyInterface)
        for i := 0; i < history.Len(); i++ {
            // here I can get a map object
            test := history.Index(i) 
            // then I tried to access the id property of the object 
            // but here it fails
            fmt.Println("test", test["id"].(string)) 
        }

Below is what test will look like for each iteration:

first iteration
map[id:5afbff19bf07c79c19ed9af9 date:Saturday, January 21, 2017 9:21 PM certitude:33]
second iteration
map[id:afbff198658487a3e3e376b date:Thursday, March 3, 2016 2:24 PM certitude:30]

invalid operation: test["id"] (type reflect.Valuedoes not support indexing)

Answer 1

If historyInterface is created by unmarshaling JSON to an interface{}, then the map has type map[string]interface{}. Use a type assertion to get the map as that type:

 history := reflect.ValueOf(historyInterface)
 for i := 0; i < history.Len(); i++ {
    test := history.Index(i).Interface().(map[string]interface{})
    fmt.Println("test", test["id"].(string)) 
 }

Also based on the assumption on the source of data, the application can use type assertions instead of reflect.

 history := historyInterface.([]interface{})
 for _, m := range history {
     test := m.(map[string]interface{})
     fmt.Println("test", test["id"].(string)) 
 }