如何读取具有结构地址的接口值

type UserData struct {
    UserID string `json:"user_id"`
    UserName string `json:"user_name"`
}

type Result struct {
    Status string `json:"status"`
    Data interface{} `json:"data"`
}

var res Result
res.Data = &UserData
json.Unmarshal([]byte(`{"status": "success", "data": {"user_id":15,"user_name":"abc"}}`), &res)
fmt.Println(res.Data) //working fine
fmt.Println(res.Data.UserName) //getting error: type interface{} has no field or method UserName

package main

import (
    "encoding/json"
    "fmt"
)

type userdata struct {
    userid   string `json:"user_id"`
    username string `json:"user_name"`
}

type result struct {
    status string      `json:"status"`
    data   interface{} `json:"data"`
}

func main() {
    var res result
    res.data = &userdata{}
    json.unmarshal([]byte(`{"status": "success", "data": {"user_id":15,"user_name":"abc"}}`), &res)
    fmt.println(res.data)
    fmt.println(res.data.(*userdata).username)
}

package main

import (
    "encoding/json"
    "fmt"
    "log"
)

type dbbatch struct {
    fieldtokeep  string `json:"field_to_keep"`
    fieldtokeep2 string `json:"field_to_keep2"`
}

func main() {
    jsonbatch := `{"field_to_keep":"xxxxx","field_to_keep2":"26400527","field_to_delete":"whynotdeleted"}`
    var i interface{} = dbbatch{}
    fmt.printf("%t\n", i) // type is dbbatch
    if err := json.unmarshal([]byte(jsonbatch), &i); err != nil {
        log.println(err)
    }
    fmt.printf("%t\n", i) // type is not dbbatch anymore, instead it's map[string]any

    i = &dbbatch{}
    fmt.printf("%t\n", i) // type is *dbbatch
    if err := json.unmarshal([]byte(jsonbatch), &i); err != nil {
        log.println(err)
    }
    fmt.printf("%t\n", i) // type is *dbbatch
}

main.DBBatch
map[string]interface {}
*main.DBBatch
*main.DBBatch