每次发生突变时都会出现新对象吗？
问题描述：
I have this go code
package main
import (
"fmt"
)
type User struct {
Name string
Sex string
}
func main() {
u := &User{Name: "Leto", Sex: "Male"}
fmt.Printf("main() address: %p %p
", &u, &u.Name)
Modify(u)
Modify(u)
Modify2(u)
Modify2(u)
}
func Modify(u *User) {
u.Name = "Paul11"
fmt.Printf("Modify() address: %p %p
", &u, &u.Name)
}
func Modify2(u *User) {
u.Name = "Leto"
fmt.Printf("Modify() address: %p %p
", &u, &u.Name)
}
The output is
main() address: 0x1040a120 0x10434120
Modify() address: 0x1040a130 0x10434120
Modify() address: 0x1040a138 0x10434120
Modify() address: 0x1040a140 0x10434120
Modify() address: 0x1040a148 0x10434120
I wonder 1. why the address of the object after mutation is different. 2. why the first takes 16 bytes, and afterwards it is only 8 bytes. 3. why the mutated field is still using the same memory address.
Thanks!
答
The methods are printing the address of the receiver argument u, a **User.
Print u instead of &u and you will observe that the address remains the same. A new User value is not created on every mutation.
func Modify(u *User) {
u.Name = "Paul11"
fmt.Printf("Modify() address: %p %p
", u, &u.Name)
}
func Modify2(u *User) {
u.Name = "Leto"
fmt.Printf("Modify() address: %p %p
", u, &u.Name)
}