json.Unmarshal无法正确解码为内部接口{}

Question

I'm developing a Telegram Bot API wrapper for Golang (I know there are already some but I'm doing this for learning). I have a Response struct:

type Response struct {
  Ok bool `json:"ok"`
  ErrorCode int64 `json:"error_code"`
  Description string `json:"description"`
  Result interface{} `json:"result"`
}

I can't know the actual type of Result: a lot can be returned by Telegram servers; I made a struct for each one, but I don't know which one will be in Result. When Unmarshaling a JSON from an HTTP response into the Response struct, everything is loaded correctly, except Result.

In a function where I am sure Result will be an User (for example), I'm doing user := resp.Result.(*User), but I get the following error at runtime: panic: interface conversion: interface {} is map[string]interface {}, not *tgbot.User. So, Result is a map[string]interface{}. How can I transform it into a *User?

Thanks for any answers.

Answer 1

Make it a json.RawMessage and unmarshal it in a second step, when you're sure what type it is.

Take a look at the examples at https://golang.org/pkg/encoding/json/#RawMessage.