在其他文件中使用功能更改结构

Question

I'm a super beginner with Go and trying to teach myself through playing, so I apologies if I'm not being fantastically coherent. I'm trying to use two files. On file 1, I want to create an instance of Person (aged 30, named Peter). In this file, I want to be able to call Change, and have his name changed to Alex.

This works if I just call user.NameChange - but not change(user). How do I go about getting this to work as intended?

Greatly appreciated.

FILE 1:

package main

import (
    "fmt"
    "greetings/person"
)

func Change(user person.User) {
    user.NameChange()
}

func main() {
    user := person.User{"Peter", 30}
    fmt.Println(user) // returns "Peter"
    Change(user)
    fmt.Println(user) // returns "Peter" - Expected "Alex"
}

FILE 2:

package person

type User struct {
    Name string
    Age  int
}

func (u *User) NameChange() {
    u.Name = "Alex"
}

Answer 1

Function parameters are passed by value, therefore, when you enter Change function, you get a copy of User struct in your user variable. And you call NameChange on a copy, not the original. To change the original struct, you have to pass the struct as a pointer.

File1:

package main

import (
    "fmt"
    "greetings/person"
)

// pass User as a pointer instead of value
func Change(user *person.User) {
    user.NameChange()
}

func main() {
    user := person.User{"Peter", 30}
    fmt.Println(user) // returns "Peter"
    Change(&user)
    fmt.Println(user) // returns "Peter" - Expected "Alex"
}

More about this here. Pointers are described here.