允许在方法中使用指针或值作为参数。

huangapple
go评论110阅读模式
英文:

Allow pointer or value as argument in method

问题

我想要能够限制与Auth相关联的类型，同时允许将指针或值作为参数传递给Marshal方法中的val。Unmarshal需要一个指针，但是Marshal可以是指针或值，而不影响功能（所有不必要的代码已被删除）。这种情况是否可行？

原因是我希望能够调用Marshal并传递一个基本类型，例如字符串，而不必获取其指针。

我希望能够这样做：

  1. a := &Auth{}
  2. a.Marshal("val")

当前的实现方式：

  1. a := &Auth{}
  2. s := "val"
  3. a.Marshal(&s)

注释：
使用Marshal(val A)将无法正常工作。
例如：

  1. a := Auth[string]
  2. a.Marshal("val") // 只有在Unmarshal使用*A时才有效
  4. type temp struct {}
  5. b := Auth[*temp]
  6. b.Marshal(&temp{})
  7. out := new(temp)
  8. b.Unmarshal(data, &out) // 这是我最初提出的问题，但现在出现在unmarshal中
英文:

I would like to be able to restrict the type tied to Auth while allowing for either a pointer or value to be passed as an argument, namely val, for the Marshal method. The Unmarshal requires a pointer, but the Marshal can be either a pointer or value without affecting functionality (all unnecessary code was removed). Is this possible?

  1. type Auth[A any] struct {
  2.     // ...
  3. }
  5. func (a *Auth[A]) Unmarshal(b []byte, val *A) error {
  6. 	// ...
  7. 	if err := json.Unmarshal(b, val); err != nil {
  8. 		return err
  9. 	}
  11. 	return nil
  12. }
  14. func (a *Auth[A]) Marshal(val *A) ([]byte, error) {
  15. 	b, err := json.Marshal(src)
  16. 	if err != nil {
  17. 		return nil, err
  18. 	}
  20. 	// ...
  21. 	return b, nil
  22. }

Reasoning why I would like to be able to do this: I would like to be able to call Marshal with a basic type, eg. a string, without having to get a pointer to it.

What I would like to be able to do:

  1. a := &Auth{}
  2. a.Marshal("val")

Current implementation:

  1. a := &Auth{}
  2. s := "val"
  3. a.Marshal(&s)

Comments:
Using Marshal(val A) will not work.
Eg.

  1. a := Auth[string]
  2. a.Marshal("val") // works, but only if Unmarshal uses *A
  4. type temp struct {}
  5. b := Auth[*temp]
  6. b.Marshal(&temp{})
  7. out := new(temp)
  8. b.Unmarshal(data, &out) // this is the issue that I first presented, but now in the unmarshal

答案1

得分: 1

如果我理解你想要实现的内容，你需要进行两个小的更改：

  1. 对一个A值进行操作，而不是*A。
  2. 从Unmarshal()返回一个新的A，而不是接受一个*A参数。

即：

  1. type Auth[A any] struct{}
  3. func (a *Auth[A]) Unmarshal(b []byte) (A, error) {
  4. 	result := new(A)
  5. 	err := json.Unmarshal(b, result)
  6. 	return *result, err
  7. }
  9. func (a *Auth[A]) Marshal(val A) ([]byte, error) {
  10. 	return json.Marshal(val)
  11. }

在使用时，使用一个string类型的参数和一个*Foo类型的参数（为了清晰起见，省略了错误处理）：

  1. type Foo struct {
  2. 	S string
  3. }
  5. func main() {
  6. 	va := Auth[string]{}
  7. 	pa := Auth[*Foo]{}
  9.     // Marshal a value type and a pointer to a Foo
  10. 	mv, _ := va.Marshal("string")
  11. 	mp, _ := pa.Marshal(&Foo{"bar"})
  13.     // Emit the marshalled []bytes
  14. 	fmt.Printf("%s\n", mv)
  15. 	fmt.Printf("%s\n", mp)
  17.     // Unmarshal from the marshalled []byte for
  18.     // both the value and the pointer
  19. 	v, _ := va.Unmarshal(mv)
  20. 	p, _ := pa.Unmarshal(mp)
  22.     // Emit the unmarshalled results and their type
  23. 	fmt.Printf("%s %[1]T\n", v)
  24. 	fmt.Printf("%s %[1]T\n", p)
  25. }
英文:

If I understand what you are trying to achieve you need to make 2 small changes:

  1. operate on an A value, not *A
  2. return a new A from Unmarshal() rather than accepting a *A arg

i.e.:

  1. type Auth[A any] struct{}
  3. func (a *Auth[A]) Unmarshal(b []byte) (A, error) {
  4. 	result := new(A)
  5. 	err := json.Unmarshal(b, result)
  6. 	return *result, err
  7. }
  9. func (a *Auth[A]) Marshal(val A) ([]byte, error) {
  10. 	return json.Marshal(val)
  11. }

In use, using a string type argument and a *Foo type argument (where Foo is a struct type) (error handling omitted for clarity):

  1. type Foo struct {
  2. 	S string
  3. }
  5. func main() {
  6. 	va := Auth[string]{}
  7. 	pa := Auth[*Foo]{}
  9.     // Marshal a value type and a pointer to a Foo
  10. 	mv, _ := va.Marshal("string")
  11. 	mp, _ := pa.Marshal(&Foo{"bar"})
  13.     // Emit the marshalled []bytes
  14. 	fmt.Printf("%s\n", mv)
  15. 	fmt.Printf("%s\n", mp)
  17.     // Unmarshal from the marshalled []byte for
  18.     // both the value and the pointer
  19. 	v, _ := va.Unmarshal(mv)
  20. 	p, _ := pa.Unmarshal(mp)
  22.     // Emit the unmarshalled results and their type
  23. 	fmt.Printf("%s %[1]T\n", v)
  24. 	fmt.Printf("%s %[1]T\n", p)
  25. }

huangapple
  • 本文由 发表于 2023年4月11日 00:39:04
  • 转载请务必保留本文链接：https://go.coder-hub.com/75978909.html
  • generics
  • go
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