How to return a string via interface{}-CodePudding

I have the following function. I want to return the *string via the object interface{} parameter. If json.Unmarshal succeeds then it manages to return valid data, but I can't seem to.

I tried a bunch of variations but still it's coming out blank from the calling function. Although the type showing on the outside for the object is "string*", although it's empty. How can I do this?

My actual code below. But, for simplicity here an even simpler version.
https://go.dev/play/p/nnsKZxvU42M

// UnmarshalObject decodes an object from binary data
func UnmarshalObject(data []byte, object interface{}) error {
    err := json.Unmarshal(data, object)
    if err != nil {
        s := string(data)
        object = &s
    }

    return nil
}

It's being called like this

func (connection *DbConnection) GetObject(bucketName string, key []byte, object interface{}) error {
// ...

    err = UnmarshalObject(data, object)

    return err

}

From this function

// DBVersion retrieves the stored database version.
func (service *Service) DBVersion() (int, error) {
    var version string
    err := service.connection.GetObject(BucketName, []byte(versionKey), &version)
    if err != nil {
        return 0, err
    }
    return strconv.Atoi(version)
}

In this case, Atoi fails because version is ""

CodePudding user response：

Generally, use a type-switch to check if the interface is any of your expected types.

func UnmarshalObject(data []byte, object interface{}) error {
    err := json.Unmarshal(data, object)
    if err {
        return error;
    }

    switch object.(type) {
        case string:
            // object is a string
        case int:
            // object is an integer
        default:
            // object is something you did not expect.
            return fmt.Errorf("Unknown type %T", v)
    }

    return nil;
}

CodePudding user response：

I figured it out and learned something along the way. This form works.

   // UnmarshalObject decodes an object from binary data
func UnmarshalObject(data []byte, object interface{}) error {
    err := json.Unmarshal(data, object)
    if err != nil {
       if s, ok := object.(*string); !ok {
            return err
       }

       *s = string(data)
    }

    return nil
}