enum_example_marshalling.go

// https://go.dev/play/p/HTKZzENHPcG
package main

import (
	"encoding/json"
	"fmt"
)

type Color struct{ c uint }

var (
	Undefined = Color{}
	Red       = Color{1}
	Green     = Color{2}
	Blue      = Color{3}
)

var colors = map[Color]string{
	Red:   "red",
	Green: "green",
	Blue:  "blue",
}

var colors_inv = map[string]Color{
	"red":   Red,
	"green": Green,
	"blue":  Blue,
}

func (s *Color) UnmarshalText(text []byte) error {
	s.c = colors_inv[string(text)].c
	return nil
}

func (c Color) MarshalText() ([]byte, error) { return []byte(c.String()), nil }

func (c Color) String() string { return colors[c] }

type V struct {
	Color Color `json:"color"`
}

func main() {
	var v V
	s := `{"color": "red"}`
	json.Unmarshal([]byte(s), &v)
	fmt.Println(v)
}