为什么在golang中，YAML.v3不根据String()方法来序列化结构体？

huangapple
go评论116阅读模式
英文:

Why doesn't YAML.v3 marshal a struct based on the String() in golang?

问题

我有一个包含基于枚举的类型的结构体。我想将其渲染为用户友好的字符串。以下是最小可行代码：

  1. package main
  3. import (
  4. 	"fmt"
  6. 	"gopkg.in/yaml.v3"
  7. )
  9. type Job struct {
  10. 	Engine Engine `json:"Engine" yaml:"Engine"`
  11. }
  13. //go:generate stringer -type=Engine --trimprefix=Engine
  14. type Engine int
  16. const (
  17. 	engineUnknown Engine = iota // 必须是第一个
  18. 	EngineDocker
  19. 	engineDone // 必须是最后一个
  20. )
  22. func main() {
  23. 	j := Job{Engine: EngineDocker}
  25. 	fmt.Printf("%+v\n\n", j)
  26. 	out, _ := yaml.Marshal(j)
  27. 	fmt.Println(string(out))
  28. }

这是生成的代码：

  1. // Code generated by "stringer -type=Engine --trimprefix=Engine"; DO NOT EDIT.
  3. package main
  5. import "strconv"
  7. func _() {
  8. 	// "invalid array index" 编译错误表示常量值已更改。
  9. 	// 重新运行 stringer 命令以再次生成它们。
  10. 	var x [1]struct{}
  11. 	_ = x[engineUnknown-0]
  12. 	_ = x[EngineDocker-1]
  13. 	_ = x[engineDone-2]
  14. }
  16. const _Engine_name = "engineUnknownDockerengineDone"
  18. var _Engine_index = [...]uint8{0, 13, 19, 29}
  20. func (i Engine) String() string {
  21. 	if i < 0 || i >= Engine(len(_Engine_index)-1) {
  22. 		return "Engine(" + strconv.FormatInt(int64(i), 10) + ")"
  23. 	}
  24. 	return _Engine_name[_Engine_index[i]:_Engine_index[i+1]]
  25. }

这是输出：

  1. {Engine:1}
  3. Engine: 1

这是我希望输出的内容：

  1. {Engine:Docker}
  3. Engine: Docker

我以为生成的文件中的String()方法可以实现这个。有没有办法做到这一点？谢谢！

英文:

I have a struct which contains a type based on an enum. I am trying to render it to a user friendly string. Here's minimum viable code:

  1. package main
  3. import (
  4. 	&quot;fmt&quot;
  6. 	&quot;gopkg.in/yaml.v3&quot;
  7. )
  9. type Job struct {
  10. 	Engine Engine `json:&quot;Engine&quot; yaml:&quot;Engine&quot;`
  11. }
  13. //go:generate stringer -type=Engine --trimprefix=Engine
  14. type Engine int
  16. const (
  17. 	engineUnknown Engine = iota // must be first
  18. 	EngineDocker
  19. 	engineDone // must be last
  20. )
  22. func main() {
  23. 	j := Job{Engine: EngineDocker}
  25. 	fmt.Printf(&quot;%+v\n\n&quot;, j)
  26. 	out, _ := yaml.Marshal(j)
  27. 	fmt.Println(string(out))
  28. }

Here's the generated code:

  1. // Code generated by &quot;stringer -type=Engine --trimprefix=Engine&quot;; DO NOT EDIT.
  3. package main
  5. import &quot;strconv&quot;
  7. func _() {
  8. 	// An &quot;invalid array index&quot; compiler error signifies that the constant values have changed.
  9. 	// Re-run the stringer command to generate them again.
  10. 	var x [1]struct{}
  11. 	_ = x[engineUnknown-0]
  12. 	_ = x[EngineDocker-1]
  13. 	_ = x[engineDone-2]
  14. }
  16. const _Engine_name = &quot;engineUnknownDockerengineDone&quot;
  18. var _Engine_index = [...]uint8{0, 13, 19, 29}
  20. func (i Engine) String() string {
  21. 	if i &lt; 0 || i &gt;= Engine(len(_Engine_index)-1) {
  22. 		return &quot;Engine(&quot; + strconv.FormatInt(int64(i), 10) + &quot;)&quot;
  23. 	}
  24. 	return _Engine_name[_Engine_index[i]:_Engine_index[i+1]]
  25. }

Here's the output:

  1. {Engine:1}
  3. Engine: 1

Here's what I'd like the output to be:

  1. {Engine:Docker}
  3. Engine: Docker

I thought the String() in the generated file would accomplish this. Is there any way to do this? Thanks!

答案1

得分: 1

yaml编组器不使用String方法。相反，YAML使用encoding.TextMarshaler和encoding.TextUnmarshaler接口。实际上，所有其他编解码方案 - JSON、XML、TOML等 - 都使用这些接口来读取/写入值。因此，如果您为自己的类型实现这些方法，您将免费获得所有其他编解码器。

这是一个示例，演示如何为枚举类型创建可读性强的编码：https://go.dev/play/p/pEcBmAM-oZJ

  1. type Engine int
  3. const (
  4. 	engineUnknown Engine = iota // 必须是第一个
  5. 	EngineDocker
  6. 	engineDone // 必须是最后一个
  7. )
  9. var engineNames []string
  10. var engineNameToValue map[string]Engine
  12. func init() {
  13. 	engineNames = []string{"Unknown", "Docker"}
  14. 	engineNameToValue = make(map[string]Engine)
  15. 	for i, name := range engineNames {
  16. 		engineNameToValue[strings.ToLower(name)] = Engine(i)
  17. 	}
  18. }
  20. func (e Engine) String() string {
  21. 	if e < 0 || int(e) >= len(engineNames) {
  22. 		panic(fmt.Errorf("Invalid engine code: %d", e))
  23. 	}
  24. 	return engineNames[e]
  25. }
  27. func ParseEngine(text string) (Engine, error) {
  28. 	i, ok := engineNameToValue[strings.ToLower(text)]
  29. 	if !ok {
  30. 		return engineUnknown, fmt.Errorf("Invalid engine name: %s", text)
  31. 	}
  32. 	return i, nil
  33. }
  35. func (e Engine) MarshalText() ([]byte, error) {
  36. 	return []byte(e.String()), nil
  37. }
  39. func (e *Engine) UnmarshalText(text []byte) (err error) {
  40. 	name := string(text)
  41. 	*e, err = ParseEngine(name)
  42. 	return
  43. }

它的工作原理：

  1. func main() {
  2. 	j := Job{Engine: EngineDocker}
  4. 	fmt.Printf("%#v\n\n", j)
  5. 	out, err := yaml.Marshal(j)
  6. 	if err != nil {
  7. 		panic(err)
  8. 	}
  9. 	fmt.Printf("YAML: %s\n", string(out))
  11. 	var jj Job
  12. 	err = yaml.Unmarshal(out, &jj)
  13. 	if err != nil {
  14. 		panic(err)
  15. 	}
  16. 	fmt.Printf("%#v\n\n", jj)
  18. 	// == JSON ==
  19. 	out, err = json.Marshal(j)
  20. 	if err != nil {
  21. 		panic(err)
  22. 	}
  23. 	fmt.Printf("JSON: %s\n", string(out))
  25. 	var jjs Job
  26. 	err = json.Unmarshal(out, &jjs)
  27. 	if err != nil {
  28. 		panic(err)
  29. 	}
  30. 	fmt.Printf("%#v\n\n", jjs)
  32. }

输出结果：

  1. main.Job{Engine:1}
  3. YAML: Engine: Docker
  5. main.Job{Engine:1}
  7. JSON: {"Engine":"Docker"}
  8. main.Job{Engine:1}

看到了吗？它在YAML和JSON中都以字符串形式写入和读取，而无需任何额外的努力。

英文:

yaml marshaler doesn't use String method. Instead YAML uses encoding.TextMarshaler and encoding.TextUnmarshaler interfaces. Actually, all other codec schemes - JSON, XML, TOML, etc. - use those interfaces to read/write the values. So, if you implement those methods for your type, you will receive all other codecs for free.

Here is an example how to make a human-readable encoding for your enum: https://go.dev/play/p/pEcBmAM-oZJ

  1. type Engine int
  3. const (
  4. 	engineUnknown Engine = iota // must be first
  5. 	EngineDocker
  6. 	engineDone // must be last
  7. )
  9. var engineNames []string
  10. var engineNameToValue map[string]Engine
  12. func init() {
  13. 	engineNames = []string{&quot;Unknown&quot;, &quot;Docker&quot;}
  14. 	engineNameToValue = make(map[string]Engine)
  15. 	for i, name := range engineNames {
  16. 		engineNameToValue[strings.ToLower(name)] = Engine(i)
  17. 	}
  18. }
  20. func (e Engine) String() string {
  21. 	if e &lt; 0 || int(e) &gt;= len(engineNames) {
  22. 		panic(fmt.Errorf(&quot;Invalid engine code: %d&quot;, e))
  23. 	}
  24. 	return engineNames[e]
  25. }
  27. func ParseEngine(text string) (Engine, error) {
  28. 	i, ok := engineNameToValue[strings.ToLower(text)]
  29. 	if !ok {
  30. 		return engineUnknown, fmt.Errorf(&quot;Invalid engine name: %s&quot;, text)
  31. 	}
  32. 	return i, nil
  33. }
  35. func (e Engine) MarshalText() ([]byte, error) {
  36. 	return []byte(e.String()), nil
  37. }
  39. func (e *Engine) UnmarshalText(text []byte) (err error) {
  40. 	name := string(text)
  41. 	*e, err = ParseEngine(name)
  42. 	return
  43. }

How it works:

  1. func main() {
  2. 	j := Job{Engine: EngineDocker}
  4. 	fmt.Printf(&quot;%#v\n\n&quot;, j)
  5. 	out, err := yaml.Marshal(j)
  6. 	if err != nil {
  7. 		panic(err)
  8. 	}
  9. 	fmt.Printf(&quot;YAML: %s\n&quot;, string(out))
  11. 	var jj Job
  12. 	err = yaml.Unmarshal(out, &amp;jj)
  13. 	if err != nil {
  14. 		panic(err)
  15. 	}
  16. 	fmt.Printf(&quot;%#v\n\n&quot;, jj)
  18. 	// == JSON ==
  19. 	out, err = json.Marshal(j)
  20. 	if err != nil {
  21. 		panic(err)
  22. 	}
  23. 	fmt.Printf(&quot;JSON: %s\n&quot;, string(out))
  25. 	var jjs Job
  26. 	err = json.Unmarshal(out, &amp;jjs)
  27. 	if err != nil {
  28. 		panic(err)
  29. 	}
  30. 	fmt.Printf(&quot;%#v\n\n&quot;, jjs)
  32. }

the output

  1. main.Job{Engine:1}
  3. YAML: Engine: Docker
  5. main.Job{Engine:1}
  7. JSON: {&quot;Engine&quot;:&quot;Docker&quot;}
  8. main.Job{Engine:1}

See? It writes and reads strings to both YAML and JSON without any extra effort.

huangapple
  • 本文由 发表于 2022年9月28日 08:31:46
  • 转载请务必保留本文链接：https://go.coder-hub.com/73875048.html
  • go
  • yaml
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