Writing a custom unmarshal function for YAML in Go

main.go

package main

import (
	"fmt"
	"log"

	"gopkg.in/yaml.v3"
)

type Blocktype uint8

const (
	Unknown Blocktype = iota
	Stone
	Copper
	Iron
	Gold
	Dirt
)

type Block struct {
	Blocktype Blocktype `yaml:"blocktype"`

	// How long should it take to "punch" the block
	Health uint16 `yaml:"health"`
}

func (b Blocktype) String() string {
	switch b {
	case Stone:
		return "Stone"
	case Copper:
		return "Copper"
	case Iron:
		return "Iron"
	case Gold:
		return "Gold"
	case Dirt:
		return "Dirt"
	default:
		return "Unknown Block Type"
	}
}

func (b *Blocktype) UnmarshalYAML(unmarshal func(interface{}) error) error {
	var blocktypes string
	if err := unmarshal(&blocktypes); err != nil {
		return err
	}
	switch blocktypes {
	case "Stone":
		*b = Stone
	case "Copper":
		*b = Copper
	case "Iron":
		*b = Iron
	case "Gold":
		*b = Gold
	case "Dirt":
		*b = Dirt
	default:
		*b = Unknown
	}
	return nil
}

func main() {
	var data = `
blocktype: Stone
health: 32
`
	var b Block

	err := yaml.Unmarshal([]byte(data), &b)
	if err != nil {
		log.Fatalf("cannot unmarshal data: %v", err)
	}
	fmt.Println(b.Blocktype)
	fmt.Println(b.Health)
}