GO中的赋值问题

Question

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?

Answer 1

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.

Example