Setter方法未设置Golang的结构属性。

huangapple
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英文:

Setter method not setting struct property Golang

问题

我需要帮助理解为什么会出现这个错误：

我正在使用指针，因为我希望它更新字段。

> prog.go:56: 无法将MammalImpl字面量（类型为MammalImpl）用作Mammal数组元素的类型：MammalImpl未实现Mammal（SetName方法具有指针接收器）prog.go:57: 无法将MammalImpl字面量（类型为MammalImpl）用作Mammal数组元素的类型：MammalImpl未实现Mammal（SetName方法具有指针接收器）

我不确定为什么无法按照以下方式设置/覆盖名称属性。

  1.  package main
  3. import (
  4. 	"fmt"
  5. )
  7. type Mammal interface {
  8. 	GetID() int
  9. 	GetName() string
  10. 	SetName(s string)
  11. }
  13. type Human interface {
  14. 	Mammal
  16. 	GetHairColor() string
  17. }
  19. type MammalImpl struct {
  20. 	ID   int
  21. 	Name string
  22. }
  24. func (m MammalImpl) GetID() int {
  25. 	return m.ID
  26. }
  28. func (m MammalImpl) GetName() string {
  29. 	return m.Name
  30. }
  32. func (m *MammalImpl) SetName(s string) {
  33.     m.Name = s
  34. }
  36. type HumanImpl struct {
  37. 	MammalImpl
  38. 	HairColor string
  39. }
  41. func (h HumanImpl) GetHairColor() string {
  42. 	return h.HairColor
  43. }
  44. 	
  45. func Names(ms []Mammal) *[]string {
  46. 	names := make([]string, len(ms))
  47. 	for i, m := range ms {
  48. 		m.SetName("Herbivorous") // 这个修改没有任何效果，并且会抛出错误
  49. 		names[i] = m.GetName()
  50. 	}
  51. 	return &names
  52. }
  54. func main() {
  55. 	mammals := []Mammal{
  56. 		MammalImpl{1, "Carnivorious"},
  57. 		MammalImpl{2, "Ominivorious"},
  58. 	}
  60. 	numberOfMammalNames := Names(mammals)
  61. 	fmt.Println(numberOfMammalNames)
  62. }

Go Playground代码在这里：http://play.golang.org/p/EyJBY3rH23

英文:

I need help with understanding why this error is being thrown:

I am using a pointer because I want it to update the field.

> prog.go:56: cannot use MammalImpl literal (type MammalImpl) as type
> Mammal in array element: MammalImpl does not implement Mammal
> (SetName method has pointer receiver) prog.go:57: cannot use
> MammalImpl literal (type MammalImpl) as type Mammal in array element:
> MammalImpl does not implement Mammal (SetName method has pointer
> receiver)

I am not sure why this is unable to set/override the name property as follows.

  1.  package main
  3. import (
  4. 	"fmt"
  5. )
  7. type Mammal interface {
  8. 	GetID() int
  9. 	GetName() string
  10. 	SetName(s string)
  11. }
  13. type Human interface {
  14. 	Mammal
  16. 	GetHairColor() string
  17. }
  19. type MammalImpl struct {
  20. 	ID   int
  21. 	Name string
  22. }
  24. func (m MammalImpl) GetID() int {
  25. 	return m.ID
  26. }
  28. func (m MammalImpl) GetName() string {
  29. 	return m.Name
  30. }
  32. func (m *MammalImpl) SetName(s string) {
  33.     m.Name = s
  34. }
  36. type HumanImpl struct {
  37. 	MammalImpl
  38. 	HairColor string
  39. }
  41. func (h HumanImpl) GetHairColor() string {
  42. 	return h.HairColor
  43. }
  44. 	
  45. func Names(ms []Mammal) *[]string {
  46. 	names := make([]string, len(ms))
  47. 	for i, m := range ms {
  48. 		m.SetName("Herbivorous") // This modification is not having any effect and throws and error
  49. 		names[i] = m.GetName()
  50. 	}
  51. 	return &names
  52. }
  54. func main() {
  55. 	mammals := []Mammal{
  56. 		MammalImpl{1, "Carnivorious"},
  57. 		MammalImpl{2, "Ominivorious"},
  58. 	}
  60. 	numberOfMammalNames := Names(mammals)
  61. 	fmt.Println(numberOfMammalNames)
  62. }

Go Playground code is here http://play.golang.org/p/EyJBY3rH23

答案1

得分: 3

问题在于你有一个带有指针接收器的方法SetName()：

  1. func (m *MammalImpl) SetName(s string)

因此，如果你有一个类型为MammalImpl的值，该值的方法集不包含SetName()方法，因此它不实现Mammal接口。

但是，指向MammalImpl的指针（*MammalImpl）的方法集将包含SetName()方法，因此它将实现Mammal接口。

因此，当你填充mammals切片时，你必须使用*MammalImpl值进行填充，因为它实现了切片的元素类型（即Mammal）。如果你已经有一个MammalImpl值，你可以很容易地获得一个指向MammalImpl的指针：使用地址&运算符生成指向该值的指针：

  1. mammals := []Mammal{
  2.     &MammalImpl{1, "Carnivorious"},
  3.     &MammalImpl{2, "Ominivorious"},
  4. }

在Go Playground上尝试你修改后的程序。

英文:

The problem is that you have a method SetName() which has a pointer receiver:

  1. func (m *MammalImpl) SetName(s string)

So if you have a value of type MammalImpl, the method set of that value does not contain the SetName() method therefore it does not implement the Mammal interface.

But the method set of a pointer to MammalImpl (*MammalImpl) will contain the SetName() method therefore it will implement the Mammal interface.

So when you populate the mammals slice, you have to populate it with *MammalImpl values, because that is the one that implements the element type of the slice (which is Mammal). You can easily obtain a pointer to a MammalImpl if you already have a MammalImpl value: use the address & operator to generate a pointer to the value:

  1. mammals := []Mammal{
  2. 	&MammalImpl{1, "Carnivorious"},
  3. 	&MammalImpl{2, "Ominivorious"},
  4. }

Try your modified program on the Go Playground.

huangapple
  • 本文由 发表于 2015年2月9日 01:49:59
  • 转载请务必保留本文链接：https://go.coder-hub.com/28397240.html
  • go
  • methods
  • pointers
  • struct
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