英文:
Trouble assigning value in GO
问题
我正在尝试理解为什么会出现错误：invalid memory address or nil pointer dereference。
假设我有以下代码（这不是真实的代码，但类似）：
type (
Cat struct {
Name string
}
Dog struct {
Name string
}
Pets struct {
c *Cat
d *Dog
}
)
func (c *Cat) Rename(d Dog) string {
err := SomeErrorChecks()
name := strings.TrimSpace(d.Name)
c.Name = name // 在这一行出现错误
return err
}
func (p *Pets) SomeFunction() string {
p.d = &Dog{}
p.c = &Cat{}
p.d.Name = "Foo"
err := p.c.Rename(*p.d)
return err
}
func main() {
// 一些代码
err := SomeFunction()
// 一些与错误处理无关的代码
}
我已经检查过strings.TrimSpace(d.Name)返回了期望的字符串。我也确认了c.Name的类型是字符串。那么，为什么我不能将name赋值给c.Name，如果它们都是相同的类型呢？
英文:
I'm trying to understand why I'm getting the error: invalid memory address or nil pointer dereference
Let's say I have this code (this is not the real one but similar):
type (
Cat struct {
Name string
}
Dog struct {
Name string
}
Pets struct{
c *Cat
d *Dog
}
)
func (c *Cat) Rename(d Dog) string {
err := SomeErrorChecks()
name := strings.TrimSpace(d.Name)
c.Name = name // In this line is where I get the error
return err
}
func (p *Pets) SomeFunction() string{
p.d = &Dog{}
p.c = &Cat{}
p.d.Name = " Foo "
err := p.c.Rename(*p.d)
return err
}
func main(){
//some code
err := SomeFunction()
//some error handling not relevant
}
I've checked that strings.TrimSpace(d.Name) returns de desired string. And I've checked that the type of c.Name is string. So, why I can't assing name to c.Name if both are the same type?
答案1
得分: 1
我看不出代码有什么问题。也许只是代码风格和方法名的问题。为了使其工作，我添加了一些返回值，你需要进行调整，并删除了C++风格的注释。
请注意，由于p := &Pets{}的赋值，nil接收器的问题不是一个问题。
package main
import (
"fmt"
"strings"
)
type (
Cat struct {
Name string
}
Dog struct {
Name string
}
Pets struct{
c *Cat
d *Dog
}
)
func (c *Cat) Rename(d Dog) (string, error) {
name := strings.TrimSpace(d.Name)
c.Name = name
return "", nil
}
func (p *Pets) SomeFunction() (err error){
p.d = &Dog{}
p.c = &Cat{}
p.d.Name = " Foo "
p.c.Rename(*p.d)
return nil
}
func main(){
p := &Pets{}
p.SomeFunction()
fmt.Printf("%s\n", p.c.Name)
}
你可以在这里查看代码：https://play.golang.org/p/bavuUn9IpT
英文:
I see no problem with the code. Maybe just the code style and the method name. To make it work I added some return values that you should adjust and removed the C++ style comments.
Note that the problem with a nil receiver is not an issue because of the p := &Pets{} assignment.
https://play.golang.org/p/bavuUn9IpT
package main
import (
"fmt"
"strings"
)
type (
Cat struct {
Name string
}
Dog struct {
Name string
}
Pets struct{
c *Cat
d *Dog
}
)
func (c *Cat) Rename(d Dog) (string, error) {
name := strings.TrimSpace(d.Name)
c.Name = name
return "", nil
}
func (p *Pets) SomeFunction() (err error){
p.d = &Dog{}
p.c = &Cat{}
p.d.Name = " Foo "
p.c.Rename(*p.d)
return nil
}
func main(){
p := &Pets{}
p.SomeFunction()
fmt.Printf("%s\n", p.c.Name)
}
答案2
得分: 1
正如@JimB在他的评论中指出的那样：
> 你正在使用一个空接收器调用Rename
这意味着，由于你在c.Name = name处遇到错误，Rename方法内部的c接收器是空的。在调用Rename之前，你需要确保初始化c。
英文:
As @JimB already pointed out in his comment
> You are calling Rename with a nil receiver
which means that, since you're getting the error at c.Name = name, the c receiver inside the Rename method is nil. You need to make sure to initialize c before calling Rename.
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