Parsing enums into fields returns default value

[GalLalouche]

Hi all,

Complete go newbie here. I'm trying to write the following code:

package main

import (
	"errors"
	"fmt"
	"strings"
	"github.com/alecthomas/kong"
)

type MediaType int

const (
	Tv MediaType = iota
	Movie
)

func (t *MediaType) UnmarshalText(text []byte) error {
	res, err := mediaTypeFromString(string(text))
	if err == nil {
		t = &res
	}

	return err
}
func mediaTypeFromString(s string) (MediaType, error) {
	switch strings.ToLower(s) {
	case "tv":
		return Tv, nil
	case "movie":
		return Movie, nil
	default:
		return 0, errors.New(fmt.Sprintf("Invalid media type: '%s'", s))
	}
}
func (t MediaType) String() string {
	switch t {
	case Tv:
		return "tv"
	case Movie:
		return "movie"
	default:
		panic("Unreachable")
	}
}

var Example struct {
  Mode MediaType
}

func main() {
  kong.Parse(&Example)
  fmt.Println(Example)
}

But when I try to run program using go run . --mode movie, I get Tv printed. What am I doing wrong?
Note: when I do print debugging, I see that UnmarshalText is being called, and that the correct value is being parsed. If I replace type from MediaType to String and do the parsing myself (i.e., I don't rely on Kong to do the parsing), I see that the string value is movie.

[alecthomas]

What's going wrong is that this:

		t = &res

Needs to be this:

		*t = res

The latter sets the value pointed to by t, while the former sets the pointer to to the location of res.

[GalLalouche]

Thank you! Haven't used pointers since undergrad 😅, so I'm definitely a bit rusty.