在Go语言中无法通过引用修改对象。

huangapple
go评论115阅读模式
英文:

Cannot modify object by reference in golang

问题

为什么我无法在golang中通过引用传递对象？我99%确定我是将对象通过引用传递给函数，而不是复制对象。我刚开始学习go语言，我总是喜欢在创建真正的代码之前做这样的练习。

无论如何，我的问题是为什么最后一行打印出"Doggy"？我期望最后一行打印出name of dog after: changed name!

代码

  1. package main
  3. import "fmt"
  5. // 基本类型
  6. type Animal struct {
  7. 	Name string
  8. 	Age  int
  9. }
  11. type Dog struct {
  12. 	Animal
  13. 	PropertyFoo1 int // 一些特定于狗的字段
  14. }
  16. func modifyAnimalName(animal *Animal) {
  17. 	(*animal).Name = "changed name!"
  18. }
  20. func main() {
  22. 	// 创建一个新的狗
  23. 	dog := Dog{
  24. 		Animal: Animal{
  25. 			Name: "Doggy",
  26. 			Age:  5,
  27. 		},
  28. 	}
  30. 	var animal Animal = dog.Animal
  32. 	// 调用 modifyAnimalName(&animal) 前后的值
  33. 	fmt.Printf("name of dog before: %s \n", dog.Name)
  34. 	modifyAnimalName(&animal) // 修改动物的名字
  35. 	// 为什么这里打印的是 Doggy?!
  36. 	fmt.Printf("name of dog after: %s \n", dog.Name)
  37. }

控制台输出:

  1. name of dog before: Doggy 
  2. name of dog after: Doggy

编辑

对不起，我问了这个愚蠢的问题，我刚开始学习go语言

@tkausl 谢谢。我刚注意到，由于你的评论，这一行是在复制一个实体对象。

  1. var animal Animal = dog.Animal

因此，我修改了代码如下：

  1. var animal *Animal = &dog.Animal
  3. fmt.Printf("name of dog before: %s \n", dog.Name)
  4. modifyAnimalName(animal)
  5. // 现在它打印出了不同的名字 :)
  6. fmt.Printf("name of dog after: %s \n", dog.Name)
英文:

Why is it that I am not able to pass an object by reference in golang? I am 99% sure I am passing the object by reference to the function instead of copying the object. I am new to go and I always like making exercises like this before creating real code

Anyways my question is why does the last line printing Doggy? I was epecting for the last line to print name of dog after: changed name!

Code

  1. package main
  3. import "fmt"
  5. // base type
  6. type Animal struct {
  7. 	Name string
  8. 	Age  int
  9. }
  11. type Dog struct {
  12. 	Animal
  13. 	PropertyFoo1 int // some field specific to a dog
  14. }
  16. func modifyAnimalName(animal *Animal) {
  17. 	(*animal).Name = "changed name!"
  18. }
  20. func main() {
  22. 	// create a new dog
  23. 	dog := Dog{
  24. 		Animal: Animal{
  25. 			Name: "Doggy",
  26. 			Age:  5,
  27. 		},
  28. 	}
  30. 	var animal Animal = dog.Animal
  32. 	// before and after values when calling modifyAnimalName(&animal)
  33. 	fmt.Printf("name of dog before: %s \n", dog.Name)
  34. 	modifyAnimalName(&animal) // modify animal name
  35. 	// why does this prints Doggy?!
  36. 	fmt.Printf("name of dog after: %s \n", dog.Name)
  37. }

console output:

  1. name of dog before: Doggy 
  2. name of dog after: Doggy

Edit

Sorry for asking this dumb question I just started learning go

@tkausl thanks. I just noticed thanks to your comment that this line was copying an entity object.

  1. var animal Animal = dog.Animal

As a result I modified the code to:

  1. 	var animal *Animal = &dog.Animal
  3. 	fmt.Printf("name of dog before: %s \n", dog.Name)
  4. 	modifyAnimalName(animal)
  5. 	// now it prints a different name :)
  6. 	fmt.Printf("name of dog after: %s \n", dog.Name)

答案1

得分: 1

你没有通过引用传递。以下是问题的两个解决方案。

解决方案1：使用普通函数

  1. package main
  3. import "fmt"
  5. // 基本类型
  6. type Animal struct {
  7.     Name string
  8.     Age  int
  9. }
  11. type Dog struct {
  12.     Animal
  13.     PropertyFoo1 int // 一些特定于狗的字段
  14. }
  16. func modifyAnimalName(animal *Animal) {
  17.     animal.Name = "修改后的名字！"
  18. }
  20. func main() {
  21.     // 创建一个新的狗
  22.     dog := Dog{
  23.         Animal: Animal{
  24.             Name: "狗狗",
  25.             Age:  5,
  26.         },
  27.     }
  29.     var animal *Animal = &dog.Animal
  30.     fmt.Printf("修改前的狗的名字：%s \n", dog.Name)
  31.     modifyAnimalName(animal) // 修改动物的名字
  32.     fmt.Printf("修改后的狗的名字：%s \n", dog.Name)
  33. }

解决方案2：使用方法

  1. package main
  3. import "fmt"
  5. type Animal struct {
  6.     Name string
  7.     Age  int
  8. }
  10. type Dog struct {
  11.     Animal
  12.     PropertyFoo1 int // 一些特定于狗的字段
  13. }
  15. func (a *Animal) modifyAnimalName() {
  16.     a.Name = "修改后的名字！"
  17. }
  19. func main() {
  20.     // 创建一个新的狗
  21.     dog := Dog{
  22.         Animal: Animal{
  23.             Name: "狗狗",
  24.             Age:  5,
  25.         },
  26.     }
  27.     var animal *Animal = &dog.Animal
  28.     fmt.Printf("修改前的狗的名字：%s \n", dog.Name)
  29.     animal.modifyAnimalName()
  30.     fmt.Printf("修改后的狗的名字：%s \n", dog.Name)
  31. }
英文:

You are not passing by reference. Here's two solution to the problem.

Solution 1: Using regular function

  1. package main
  3. import "fmt"
  5. // base type
  6. type Animal struct {
  7. 	Name string
  8. 	Age  int
  9. }
  11. type Dog struct {
  12. 	Animal
  13. 	PropertyFoo1 int // some field specific to a dog
  14. }
  16. func modifyAnimalName(animal *Animal) {
  17. 	animal.Name = "changed name!"
  18. }
  20. func main() {
  21. 	// create a new dog
  22. 	dog := Dog{
  23. 		Animal: Animal{
  24. 			Name: "Doggy",
  25. 			Age:  5,
  26. 		},
  27. 	}
  29. 	var animal *Animal = &dog.Animal
  30. 	fmt.Printf("name of dog before: %s \n", dog.Name)
  31. 	modifyAnimalName(animal) // modify animal name
  32. 	fmt.Printf("name of dog after: %s \n", dog.Name)
  33. }

Solution 2: Using method

  1. package main
  3. import "fmt"
  5. type Animal struct {
  6. 	Name string
  7. 	Age  int
  8. }
  10. type Dog struct {
  11. 	Animal
  12. 	PropertyFoo1 int // some field specific to a dog
  13. }
  15. func (a *Animal) modifyAnimalName() {
  16. 	a.Name = "changed name!"
  17. }
  19. func main() {
  20. 	// create a new dog
  21. 	dog := Dog{
  22. 		Animal: Animal{
  23. 			Name: "Doggy",
  24. 			Age:  5,
  25. 		},
  26. 	}
  27. 	var animal *Animal = &dog.Animal
  28. 	fmt.Printf("name of dog before: %s \n", dog.Name)
  29. 	animal.modifyAnimalName()
  30. 	fmt.Printf("name of dog after: %s \n", dog.Name)
  31. }

huangapple
  • 本文由 发表于 2022年4月14日 08:30:57
  • 转载请务必保留本文链接：https://go.coder-hub.com/71865152.html
  • go
  • pass-by-reference
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