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
package main
import "fmt"
// 基本类型
type Animal struct {
Name string
Age int
}
type Dog struct {
Animal
PropertyFoo1 int // 一些特定于狗的字段
}
func modifyAnimalName(animal *Animal) {
(*animal).Name = "changed name!"
}
func main() {
// 创建一个新的狗
dog := Dog{
Animal: Animal{
Name: "Doggy",
Age: 5,
},
}
var animal Animal = dog.Animal
// 调用 modifyAnimalName(&animal) 前后的值
fmt.Printf("name of dog before: %s \n", dog.Name)
modifyAnimalName(&animal) // 修改动物的名字
// 为什么这里打印的是 Doggy?!
fmt.Printf("name of dog after: %s \n", dog.Name)
}
控制台输出:
name of dog before: Doggy
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。
var animal Animal = dog.Animal
因此，我修改了代码如下：
var animal *Animal = &dog.Animal
fmt.Printf("name of dog before: %s \n", dog.Name)
modifyAnimalName(animal)
// 现在它打印出了不同的名字 :)
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
package main
import "fmt"
// base type
type Animal struct {
Name string
Age int
}
type Dog struct {
Animal
PropertyFoo1 int // some field specific to a dog
}
func modifyAnimalName(animal *Animal) {
(*animal).Name = "changed name!"
}
func main() {
// create a new dog
dog := Dog{
Animal: Animal{
Name: "Doggy",
Age: 5,
},
}
var animal Animal = dog.Animal
// before and after values when calling modifyAnimalName(&animal)
fmt.Printf("name of dog before: %s \n", dog.Name)
modifyAnimalName(&animal) // modify animal name
// why does this prints Doggy?!
fmt.Printf("name of dog after: %s \n", dog.Name)
}
console output:
name of dog before: Doggy
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.
var animal Animal = dog.Animal
As a result I modified the code to:
var animal *Animal = &dog.Animal
fmt.Printf("name of dog before: %s \n", dog.Name)
modifyAnimalName(animal)
// now it prints a different name :)
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
package main
import "fmt"
// 基本类型
type Animal struct {
Name string
Age int
}
type Dog struct {
Animal
PropertyFoo1 int // 一些特定于狗的字段
}
func modifyAnimalName(animal *Animal) {
animal.Name = "修改后的名字！"
}
func main() {
// 创建一个新的狗
dog := Dog{
Animal: Animal{
Name: "狗狗",
Age: 5,
},
}
var animal *Animal = &dog.Animal
fmt.Printf("修改前的狗的名字：%s \n", dog.Name)
modifyAnimalName(animal) // 修改动物的名字
fmt.Printf("修改后的狗的名字：%s \n", dog.Name)
}
解决方案2：使用方法
package main
import "fmt"
type Animal struct {
Name string
Age int
}
type Dog struct {
Animal
PropertyFoo1 int // 一些特定于狗的字段
}
func (a *Animal) modifyAnimalName() {
a.Name = "修改后的名字！"
}
func main() {
// 创建一个新的狗
dog := Dog{
Animal: Animal{
Name: "狗狗",
Age: 5,
},
}
var animal *Animal = &dog.Animal
fmt.Printf("修改前的狗的名字：%s \n", dog.Name)
animal.modifyAnimalName()
fmt.Printf("修改后的狗的名字：%s \n", dog.Name)
}
英文:
You are not passing by reference. Here's two solution to the problem.
Solution 1: Using regular function
package main
import "fmt"
// base type
type Animal struct {
Name string
Age int
}
type Dog struct {
Animal
PropertyFoo1 int // some field specific to a dog
}
func modifyAnimalName(animal *Animal) {
animal.Name = "changed name!"
}
func main() {
// create a new dog
dog := Dog{
Animal: Animal{
Name: "Doggy",
Age: 5,
},
}
var animal *Animal = &dog.Animal
fmt.Printf("name of dog before: %s \n", dog.Name)
modifyAnimalName(animal) // modify animal name
fmt.Printf("name of dog after: %s \n", dog.Name)
}
Solution 2: Using method
package main
import "fmt"
type Animal struct {
Name string
Age int
}
type Dog struct {
Animal
PropertyFoo1 int // some field specific to a dog
}
func (a *Animal) modifyAnimalName() {
a.Name = "changed name!"
}
func main() {
// create a new dog
dog := Dog{
Animal: Animal{
Name: "Doggy",
Age: 5,
},
}
var animal *Animal = &dog.Animal
fmt.Printf("name of dog before: %s \n", dog.Name)
animal.modifyAnimalName()
fmt.Printf("name of dog after: %s \n", dog.Name)
}
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