How to instantiate struct that is defined in different package from struct name and provide fields

huangapple
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英文:

How to instantiate struct that is defined in different package from struct name and provide fields

问题

假设我在pkg包中定义了一些struct：

  1. package pkg
  3. type Foo struct {
  4.     FieldA string
  5.     FieldB string
  6. }
  8. type Bar struct {
  9.     FieldA string
  10.     FieldB string
  11. }
  13. func (Foo) Show() {
  14.     fmt.Println("Foo")
  15. }
  17. func (Bar) Show() {
  18.     fmt.Println("Bar")
  19. }
  21. type Showable interface {
  22.     Show()
  23. }
  25. Registry := map[string]Showable{
  26.     "Foo": Foo,
  27.     "Bar": Bar,
  28. }

我想要动态实例化这些struct，类似于这样：

  1. package main
  3. import "url/user/pkg"
  5. func main() {
  6.     foo := pkg.Registry["Foo"]{
  7.         FieldA: "A",
  8.         FieldB: "B",
  9.     }
  10.     
  11.     bar := pkg.Registry["Bar"]{
  12.         FieldA: "X",
  13.         FieldB: "Y",
  14.     }
  15.     foo.Show()
  16.     bar.Show()
  17. }

上述代码显然无法工作。

是否有可能实现这个目标？我对Go语言还不熟悉。我已经看过reflect，尝试使用指针、空实例的指针来构建Registry，但是无法找到解决方法。

最终，我想要编写一个命令行实用程序来更改某些程序的主题。我已经编写了特定于程序的方法（类似上面示例中的Show方法），并尝试从config.json文件中读取程序特定的参数，并动态创建实例。

英文:

Suppose I have some structs defined in package pkg:

  1. package pkg
  3. type Foo struct {
  4.     FieldA string
  5.     FieldB string
  6. }
  8. type Bar struct {
  9.     FieldA string
  10.     FieldB string
  11. }
  13. func (Foo) Show() {
  14.     fmt.Println("Foo")
  15. }
  17. func (Bar) Show() {
  18.     fmt.Println("Bar")
  19. }
  21. type Showable interface {
  22.     Show()
  23. }
  25. Registry := map[string]Showable{
  26. //not sure about value type^
  27.     "Foo": Foo,     // staticcheck shows: not a type
  28.     "Bar": Bar,     //
  29. }
  30.

And I want to instantiate the structs dynamically; something like this:

  1. package main
  3. import "url/user/pkg"
  5. func main() {
  6.     foo := pkg.Registry["Foo"]{
  7.         FieldA: "A",
  8.         FieldB: "B",
  9.     }
  10.     
  11.     bar := pkg.Registry["Bar"]{
  12.         FieldA: "X",
  13.         FieldB: "Y",
  14.     }
  15.     foo.Show()
  16.     bar.Show()
  17. }

The above clearly doesn't work.

Is it possible to achieve this? I am new to [tag:go]. I have looked at reflect, I have tried to build the Registry with pointers, pointers of empty instance, but couldn't figure out a way to do this.

Ultimately, I am trying to write a command line utility to change themes of certain programs. I have written program specific methods (like Show in above example), and I am trying to read the program specific params from a config.json file, and create the instances dynamically.

答案1

得分: 2

如果我正确理解你想要实现的内容，以下是实现的方法：

registry.go:

  1. package pkg
  3. import (
  4. 	"fmt"
  5. 	"io"
  6. )
  8. type NewShowable func(r io.Reader) Showable
  10. type Showable interface {
  11. 	Show()
  12. }
  14. type Foo struct {
  15. 	FieldA string
  16. 	FieldB string
  17. }
  19. func newFoo(r io.Reader) Showable {
  20. 	// 从 r 中读取配置并构造 Foo
  21. 	return Foo{}
  22. }
  24. func (Foo) Show() {
  25. 	fmt.Println("Foo")
  26. }
  28. type Bar struct {
  29. 	FieldA string
  30. 	FieldB string
  31. }
  33. func newBar(r io.Reader) Showable {
  34. 	// 从 r 中读取配置并构造 Bar
  35. 	return Bar{}
  36. }
  38. func (Bar) Show() {
  39. 	fmt.Println("Bar")
  40. }
  42. var Registry = map[string]NewShowable{
  43. 	"Foo": newFoo,
  44. 	"Bar": newBar,
  45. }

main.go:

  1. package main
  3. import (
  4. 	"log"
  5. 	"os"
  7. 	"url/user/pkg"
  8. )
  10. func main() {
  11. 	f, err := os.Open("config.json")
  12. 	if err != nil {
  13. 		log.Fatalln(err)
  14. 	}
  15. 	defer f.Close()
  16. 	foo := pkg.Registry["Foo"](f)
  18. 	f2, err := os.Open("config2.json")
  19. 	if err != nil {
  20. 		log.Fatalln(err)
  21. 	}
  22. 	defer f2.Close()
  23. 	bar := pkg.Registry["Bar"](f2)
  24. 	foo.Show()
  25. 	bar.Show()
  26. }
英文:

If I correctly understand what you are trying to achieve, here is
the way to do that:

registry.go:

  1. package pkg
  3. import (
  4. 	"fmt"
  5. 	"io"
  6. )
  8. type NewShowable func(r io.Reader) Showable
  10. type Showable interface {
  11. 	Show()
  12. }
  14. type Foo struct {
  15. 	FieldA string
  16. 	FieldB string
  17. }
  19. func newFoo(r io.Reader) Showable {
  20. 	// Read config from r and construct Foo
  21. 	return Foo{}
  22. }
  24. func (Foo) Show() {
  25. 	fmt.Println("Foo")
  26. }
  28. type Bar struct {
  29. 	FieldA string
  30. 	FieldB string
  31. }
  33. func newBar(r io.Reader) Showable {
  34. 	// Read config from r and construct Bar
  35. 	return Bar{}
  36. }
  38. func (Bar) Show() {
  39. 	fmt.Println("Bar")
  40. }
  42. var Registry = map[string]NewShowable{
  43. 	"Foo": newFoo,
  44. 	"Bar": newBar,
  45. }

main.go:

  1. package main
  3. import (
  4. 	"log"
  5. 	"os"
  7. 	"url/user/pkg"
  8. )
  10. func main() {
  11. 	f, err := os.Open("config.json")
  12. 	if err != nil {
  13. 		log.Fatalln(err)
  14. 	}
  15.     defer f.Close()
  16. 	foo := pkg.Registry["Foo"](f)
  18. 	f2, err := os.Open("config2.json")
  19. 	if err != nil {
  20. 		log.Fatalln(err)
  21. 	}
  22.     defer f2.Close()
  23. 	bar := pkg.Registry["Bar"](f2)
  24. 	foo.Show()
  25. 	bar.Show()
  26. }

huangapple
  • 本文由 发表于 2021年12月31日 14:21:00
  • 转载请务必保留本文链接：https://go.coder-hub.com/70539550.html
  • go
  • reflection
  • struct
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