使用方法返回作为字段的JSON Marshal结构体

huangapple
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英文:

JSON Marshal struct with method return as field

问题

可以将具有方法返回值作为字段的结构进行编组吗？例如，我想要以下JSON：

  1. {
  2.   "cards": [1,2,3],
  3.   "value": 6,
  4.   "size": 3
  5. }

使用以下类型的结构：

  1. type Deck struct {
  2.    Cards []int    `json:"cards"`
  3.    Value func() int `json:"value"`
  4.    Size  func() int `json:"size"`
  5. }

有人知道吗？

英文:

Is it possible to marshal a struct with method return as field? For example, I want this JSON

  1. {
  2.   "cards": [1,2,3],
  3.   "value": 6,
  4.   "size": 3
  5. }

With this kind of struct

  1. type Deck struct {
  2.    Cards []int    `json:"cards"`
  3.    Value func() int `json:"value"`
  4.    Size  func() int `json:"size"`
  5. }

Anyone?

答案1

得分: 15

你可以实现一个类似这样的Marshaler，代码示例可以在这里找到：http://play.golang.org/p/ySUFcUOHCZ（或者这里：http://play.golang.org/p/ndwKu-7Y5m）。

  1. package main
  3. import "fmt"
  4. import "encoding/json"
  6. type Deck struct {
  7.     Cards []int
  8. }
  10. func (d Deck) Value() int {
  11.     value := 0
  12.     for _, v := range d.Cards {
  13.         value = value + v
  14.     }
  15.     return value
  16. }
  18. func (d Deck) Size() int {
  19.     return len(d.Cards)
  20. }
  22. func (d Deck) MarshalJSON() ([]byte, error) {
  23.     return json.Marshal(struct {
  24.         Cards []int `json:"cards"`
  25.         Value int   `json:"value"`
  26.         Size  int   `json:"size"`
  27.     }{
  28.         Cards: d.Cards,
  29.         Value: d.Value(),
  30.         Size:  d.Size(),
  31.     })
  32. }
  34. func main() {
  35.     deck := Deck{
  36.         Cards: []int{1, 2, 3},
  37.     }
  39.     b, r := json.Marshal(deck)
  40.     fmt.Println(string(b))
  41.     fmt.Println(r)
  42. }
英文:

You can implement a Marshaler like this http://play.golang.org/p/ySUFcUOHCZ (or this http://play.golang.org/p/ndwKu-7Y5m )

<!-- language: lang-go -->

  1. package main
  3. import &quot;fmt&quot;
  4. import &quot;encoding/json&quot;
  6. type Deck struct {
  7. 	Cards []int
  8. }
  10. func (d Deck) Value() int {
  11. 	value := 0
  12. 	for _, v := range d.Cards {
  13. 		value = value + v
  14. 	}
  15. 	return value
  16. }
  17. func (d Deck) Size() int {
  18. 	return len(d.Cards)
  19. }
  21. func (d Deck) MarshalJSON() ([]byte, error) {
  22. 	return json.Marshal(struct {
  23. 		Cards []int `json:&quot;cards&quot;`
  24. 		Value int   `json:&quot;value&quot;`
  25. 		Size  int   `json:&quot;size&quot;`
  26. 	}{
  27. 		Cards: d.Cards,
  28. 		Value: d.Value(),
  29. 		Size:  d.Size(),
  30. 	})
  31. }
  33. func main() {
  34. 	deck := Deck{
  35. 		Cards: []int{1, 2, 3},
  36. 	}
  38. 	b, r := json.Marshal(deck)
  39. 	fmt.Println(string(b))
  40. 	fmt.Println(r)
  41. }

答案2

得分: 1

你还可以创建一个实现了JSONMarshaler和JSONUnmarshaler接口的函数类型。但是它有一些缺点。

  2. import "fmt"
  3. import "encoding/json"
  5. type IntFunc func() int
  7. func (f IntFunc) MarshalJSON() ([]byte, error) {
  8. 	return json.Marshal(f())
  9. }
  11. // 注意：在这里你将失去原始函数
  12. func (f *IntFunc) UnmarshalJSON(b []byte) error {
  13. 	var i int
  14. 	err := json.Unmarshal(b, &i)
  16. 	// 你可以添加一个虚拟函数，或者通过不给*f赋值来将其保持为nil
  17. 	*f = func() int { return i }
  18. 	return err
  19. }
  21. type Deck struct {
  22. 	Cards []int   `json:"cards"`
  23. 	Value IntFunc `json:"value"`
  24. 	Size  IntFunc `json:"size"`
  25. }
  27. func main() {
  28. 	deck := Deck{
  29. 		Cards: []int{1, 2, 3},
  30. 	}
  31. 	deck.Value = ValueOf(&deck)
  32. 	deck.Size = SizeOf(&deck)
  34. 	fmt.Printf("Size: %v, Cards: %v, Value: %v\n", deck.Size(), deck.Cards, deck.Value())
  35. 	deck.Cards = append(deck.Cards, 8)
  36. 	fmt.Printf("Size: %v, Cards: %v, Value: %v\n", deck.Size(), deck.Cards, deck.Value())
  37. 	fmt.Println()
  39. 	b, err := json.Marshal(deck)
  40. 	fmt.Println("Marshal Error:", err)
  41. 	fmt.Println("Marshal result:", string(b))
  42. 	fmt.Println()
  44. 	var d2 Deck
  45. 	err = json.Unmarshal([]byte(`{"cards":[1,2,3,8],"value":14,"size":4}`), &d2)
  46. 	fmt.Println("Unmarshal Error =>", err)
  47. 	fmt.Printf("Unmarshal Result => Size: %v, Cards: %v, Value: %v\n", d2.Size(), d2.Cards, d2.Value()) // 如果Size()和Value()为nil，可能会抛出错误
  48. }
  50. func SizeOf(d *Deck) IntFunc {
  51. 	return func() int {
  52. 		return len(d.Cards)
  53. 	}
  54. }
  56. func ValueOf(d *Deck) IntFunc {
  57. 	return func() int {
  58. 		i := 0
  59. 		for _, v := range d.Cards {
  60. 			i += v
  61. 		}
  62. 		return i
  64. 	}
  65. }
英文:

You could also create a function type that implement JSONMarshaler and JSONUnmarshaler. But it has some drawbacks.

  2. import &quot;fmt&quot;
  3. import &quot;encoding/json&quot;
  5. type IntFunc func() int
  7. func (f IntFunc) MarshalJSON() ([]byte, error) {
  8. 	return json.Marshal(f())
  9. }
  11. // NOTES you&#39;ll lose the original function here
  12. func (f *IntFunc) UnmarshalJSON(b []byte) error {
  13. 	var i int
  14. 	err := json.Unmarshal(b, &amp;i)
  16. 	// you could either add dummy function or leave it nil by not assigning *f
  17. 	*f = func() int { return i }
  18. 	return err
  19. }
  21. type Deck struct {
  22. 	Cards []int   `json:&quot;cards&quot;`
  23. 	Value IntFunc `json:&quot;value&quot;`
  24. 	Size  IntFunc `json:&quot;size&quot;`
  25. }
  27. func main() {
  28. 	deck := Deck{
  29. 		Cards: []int{1, 2, 3},
  30. 	}
  31. 	deck.Value = ValueOf(&amp;deck)
  32. 	deck.Size = SizeOf(&amp;deck)
  34. 	fmt.Printf(&quot;Size: %v, Cards: %v, Value: %v\n&quot;, deck.Size(), deck.Cards, deck.Value())
  35. 	deck.Cards = append(deck.Cards, 8)
  36. 	fmt.Printf(&quot;Size: %v, Cards: %v, Value: %v\n&quot;, deck.Size(), deck.Cards, deck.Value())
  37. 	fmt.Println()
  39. 	b, err := json.Marshal(deck)
  40. 	fmt.Println(&quot;Marshal Error:&quot;, err)
  41. 	fmt.Println(&quot;Marshal result:&quot;, string(b))
  42. 	fmt.Println()
  44. 	var d2 Deck
  45. 	err = json.Unmarshal([]byte(`{&quot;cards&quot;:[1,2,3,8],&quot;value&quot;:14,&quot;size&quot;:4}`), &amp;d2)
  46. 	fmt.Println(&quot;Unmarshal Error =&gt;&quot;, err)
  47. 	fmt.Printf(&quot;Unmarshal Result =&gt; Size: %v, Cards: %v, Value: %v\n&quot;, d2.Size(), d2.Cards, d2.Value()) // could throw error if Size() and Value() is nil
  48. }
  50. func SizeOf(d *Deck) IntFunc {
  51. 	return func() int {
  52. 		return len(d.Cards)
  53. 	}
  54. }
  56. func ValueOf(d *Deck) IntFunc {
  57. 	return func() int {
  58. 		i := 0
  59. 		for _, v := range d.Cards {
  60. 			i += v
  61. 		}
  62. 		return i
  64. 	}
  65. }

答案3

得分: 0

通常情况下是可以的。你需要使用reflect包，并且基本上编写自己的编组器。

但是使用Go的encoding/json包就不需要了。

英文:

In general, yes. You'd have to use the the reflect package and essentially write your own marshaller.

With Go's encoding/json package, no.

huangapple
  • 本文由 发表于 2015年8月6日 14:59:11
  • 转载请务必保留本文链接：https://go.coder-hub.com/31848836.html
  • go
  • json
  • marshalling
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