泛型：处理具有相同数据成员类型的不同结构类型

huangapple
go评论114阅读模式
英文:

go generics: processing different struct types with same data member types

问题

有两种结构类型，Foo和Bar，都有一个int类型的数据成员val。我正在尝试编写一个通用函数，可以处理这两种类型。我尝试了以下代码，但不起作用。

  1. package main
  3. import "fmt"
  5. type Foo struct {
  6. 	val int
  7. }
  9. type Bar struct {
  10. 	val int
  11. }
  13. func Add[T any](slice []T) int {
  14. 	var sum int
  15. 	for _, elem := range slice {
  16. 		sum += elem.val
  17. 	}
  18. 	return sum
  19. }
  21. func Test() {
  22. 	f1 := Foo{val: 2}
  23. 	f2 := Foo{val: 2}
  24. 	fslice := []Foo{f1, f2}
  25. 	fsum := Add(fslice)
  26. 	fmt.Printf("fsum = %d\n", fsum)
  28. 	b1 := Bar{val: 3}
  29. 	b2 := Bar{val: 3}
  30. 	bslice := []Bar{b1, b2}
  31. 	bsum := Add(bslice)
  32. 	fmt.Printf("bsum = %d\n", bsum)
  33. }
  35. func main() {
  36. 	Test()
  37. }

编译器报错如下。

  1. $ go run generics1.go
  2. # command-line-arguments
  3. ./generics1.go:16:15: elem.val undefined (type T has no field or method val)

Go Playground链接：https://go.dev/play/p/mdOMH3xuwu7

有什么可能的方法来解决这个问题？

英文:

There are two struct types, Foo and Bar, with an int data member val. I am trying to write a generic function that can handle both types. I tried the following and this did not work.

  1. package main
  3. import "fmt"
  5. type Foo struct {
  6. 	val int
  7. }
  9. type Bar struct {
  10. 	val int
  11. }
  13. func Add[T any](slice []T) int {
  14. 	var sum int
  15. 	for _, elem := range slice {
  16. 		sum += elem.val
  17. 	}
  18. 	return sum
  19. }
  21. func Test() {
  22. 	f1 := Foo{val: 2}
  23. 	f2 := Foo{val: 2}
  24. 	fslice := []Foo{f1, f2}
  25. 	fsum := Add(fslice)
  26. 	fmt.Printf("fsum = %d\n", fsum)
  28. 	b1 := Bar{val: 3}
  29. 	b2 := Bar{val: 3}
  30. 	bslice := []Bar{b1, b2}
  31. 	bsum := Add(bslice)
  32. 	fmt.Printf("bsum = %d\n", bsum)
  33. }
  35. func main() {
  36. 	Test()
  37. }

The compiler throws the following error.

  1. $ go run generics1.go
  2. # command-line-arguments
  3. ./generics1.go:16:15: elem.val undefined (type T has no field or method val)

Go playground link: https://go.dev/play/p/mdOMH3xuwu7

What could be a possible way to approach this?

答案1

得分: 2

根据golang 1.18发布说明：

Go编译器不支持访问类型参数类型的结构字段x.f，即使类型参数的类型集中的所有类型都有字段f。我们可能会在将来的版本中删除此限制。

你可以定义一个GetVal()接口方法来获取val，并将此方法作为泛型的类型约束的一部分。

示例代码：

  1. type Foo struct {
  2. 	val int
  3. }
  5. func (f Foo) GetVal() int {
  6. 	return f.val
  7. }
  9. type Bar struct {
  10. 	val int
  11. }
  13. func (b Bar) GetVal() int {
  14. 	return b.val
  15. }
  17. type MyType interface {
  18. 	Foo | Bar
  19. 	GetVal() int
  20. }
  22. func Add[T MyType](slice []T) int {
  23. 	var sum int
  24. 	for _, elem := range slice {
  25. 		sum += elem.GetVal()
  26. 	}
  27. 	return sum
  28. }

https://go.dev/play/p/0eJZpqy7q8f

英文:

Per golang 1.18 release note

> The Go compiler does not support accessing a struct field x.f where x is of type parameter type even if all types in the type parameter's type set have a field f. We may remove this restriction in a future release.

You could define one GetVal() interface method to retrieve the val, and use this method as part of type constraint of generic.

Sample codes

  1. type Foo struct {
  2. 	val int
  3. }
  5. func (f Foo) GetVal() int {
  6. 	return f.val
  7. }
  9. type Bar struct {
  10. 	val int
  11. }
  13. func (b Bar) GetVal() int {
  14. 	return b.val
  15. }
  17. type MyType interface {
  18. 	Foo | Bar
  19. 	GetVal() int
  20. }
  22. func Add[T MyType](slice []T) int {
  23. 	var sum int
  24. 	for _, elem := range slice {
  25. 		sum += elem.GetVal()
  26. 	}
  27. 	return sum
  28. }

https://go.dev/play/p/0eJZpqy7q8f

huangapple
  • 本文由 发表于 2022年11月8日 09:19:45
  • 转载请务必保留本文链接：https://go.coder-hub.com/74354709.html
  • generics
  • go
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