嵌套泛型类型：重用函数的类型参数

huangapple
go评论104阅读模式
英文:

Nested generic types: Reuse function's Type parameter

问题

给定以下定义：

  1. type Collector[T, C any] interface {
  2. 	Collect(T, C) C
  3. }
  5. type mapCollector[K comparable, V any] struct {
  6. 	GetKey func(result V) K
  7. }
  9. func (m *mapCollector[K, V]) Collect(value V, c *sync.Map) *sync.Map {
  10. 	c.Store(m.GetKey(value), value)
  11. 	return c
  12. }

我正在尝试为mapCollector编写一个模板化的make函数。
这个不起作用：

  1. func MakeUserMapCollector[K UserId, V User]() *mapCollector[K, V] {
  2.     c := mapCollector[K, V]{
  3.         GetKey: func(user V) K {
  4.             return user.getId()
  5.         }
  6.     }
  7.     return &c
  8. }

相反，我必须重复一遍：

  1. func MakeUserMapCollector() *mapCollector[UserId, User] {
  2.     c := mapCollector[UserId, User]{
  3.         GetKey: func(user User) UserId {
  4.             return user.getId()
  5.         }
  6.     }
  7. }

有没有办法重用MakeUserMapCollector的类型参数来在函数中声明类型？

英文:

Given the following definitions:

  1. type Collector[T, C any] interface {
  2. 	Collect(T, C) C
  3. }
  5. type mapCollector[K comparable, V any] struct {
  6. 	GetKey func(result V) K
  7. }
  9. func (m *mapCollector[K, V]) Collect(value V, c *sync.Map) *sync.Map {
  10. 	c.Store(m.GetKey(value), value)
  11. 	return c
  12. }

I am trying to write a templated make function for mapCollector.
This does not work

  1. func MakeUserMapCollector[K UserId, V User]() *mapCollector[K, V] {
  2.     c := mapCollector[K, V]{
  3.         GetKey: func(user V) K {
  4.             return user.getId()
  5.         }
  6.     }
  7.     return &c
  8. }

Instead I have to be repetitive

  1. func MakeUserMapCollector() *mapCollector[UserId, User] {
  2.     c := mapCollector[UserId, User]{
  3.         GetKey: func(user User) UserId {
  4.             return user.getId()
  5.         }
  6.     }
  7. }

Is there a way to reuse the MakeUserMapCollector type parameters to declare types in the function?

答案1

得分: 2

你可以创建一个通用的构造函数，该函数接受一个用于"collection"的函数，并将其传递给你的mapCollector结构体。

代码如下所示：

  1. func MakeUserMapCollector[K comparable, V any](collect func(result V) K) *mapCollector[K, V] {
  2. 	return &mapCollector[K, V]{
  3. 		GetKey: collect,
  4. 	}
  5. }

然后，你可以使用你的类型作为类型参数以及你的"collection"函数调用构造函数：

  1. mc := MakeUserMapCollector[UserId, User](func(result User) UserId { return result.GetId() })

完整示例（Go Playground）：

  1. package main
  3. import (
  4. 	"fmt"
  5. )
  7. type mapCollector[K comparable, V any] struct {
  8. 	GetKey func(result V) K
  9. }
  11. func (m mapCollector[K, V]) Collect(result V) K {
  12. 	return m.GetKey(result)
  13. }
  15. type UserId string
  17. type User struct {
  18. 	Id UserId
  19. }
  21. func (u User) GetId() UserId {
  22. 	return u.Id
  23. }
  25. func MakeUserMapCollector[K comparable, V any](collect func(result V) K) *mapCollector[K, V] {
  26. 	return &mapCollector[K, V]{
  27. 		GetKey: collect,
  28. 	}
  29. }
  31. func main() {
  32. 	u := User{
  33. 		Id: "12",
  34. 	}
  36. 	mc := MakeUserMapCollector[UserId, User](func(result User) UserId { return result.GetId() })
  37. 	fmt.Println(mc.Collect(u))
  38. }
英文:

You can create a generic constructor function that accepts a function for "collection" and then passes it to your mapCollector struct.

That would look something like this:

  1. func MakeUserMapCollector[K comparable, V any](collect func(result V) K) *mapCollector[K, V] {
  2. 	return &mapCollector[K, V]{
  3. 		GetKey: collect,
  4. 	}
  5. }

Then you can call the constructor function with your types as type parameters and your "collection" function:

  1. mc := MakeUserMapCollector[UserId, User](func(result User) UserId { return result.GetId() })

Full example (Go Playground):

  1. package main
  3. import (
  4. 	"fmt"
  5. )
  7. type mapCollector[K comparable, V any] struct {
  8. 	GetKey func(result V) K
  9. }
  11. func (m mapCollector[K, V]) Collect(result V) K {
  12. 	return m.GetKey(result)
  13. }
  15. type UserId string
  17. type User struct {
  18. 	Id UserId
  19. }
  21. func (u User) GetId() UserId {
  22. 	return u.Id
  23. }
  25. func MakeUserMapCollector[K comparable, V any](collect func(result V) K) *mapCollector[K, V] {
  26. 	return &mapCollector[K, V]{
  27. 		GetKey: collect,
  28. 	}
  29. }
  31. func main() {
  32. 	u := User{
  33. 		Id: "12",
  34. 	}
  36. 	mc := MakeUserMapCollector[UserId, User](func(result User) UserId { return result.GetId() })
  37. 	fmt.Println(mc.Collect(u))
  38. }

huangapple
  • 本文由 发表于 2022年9月27日 02:02:06
  • 转载请务必保留本文链接：https://go.coder-hub.com/73858175.html
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