用新值覆盖现有值

Question

Look at the following code snippet.

package main

import (
    "fmt"
)

type class struct {
    prop1 string
    prop2 string
}

func main() {

    va1 := &class{"Hello", "Foo"}
    fmt.Println(&va1)
    va1 = &class{"TOO", "Boo"}
    fmt.Println(&va1)

}

As a result I've got the same pointed address.

0x1215a0c0
0x1215a0c0

With &T{} it will allocate new zeroed value address. But why here I've got the same address? Do I just override on second assignment the value?

Answer 1

The statement

fmt.Println(&va1)

prints the address of the variable va1, not what va1 is pointing to. The address of the variable does not change.

Try this program:

va1 := &class{"Hello", "Foo"}
fmt.Printf("&va1: %v, pointer: %p, value: %v
", &va1, va1, va1)

va2 := va1
va1 = &class{"TOO", "Boo"}

fmt.Printf("&va1: %v, pointer: %p, value: %v
", &va1, va1, va1)
fmt.Printf("&va2: %v, pointer: %p, value: %v
", &va2, va2, va2)

This program prints:

&va1: 0x1030e0c0, pointer: 0x10328000, value: &{Hello Foo}
&va1: 0x1030e0c0, pointer: 0x10328050, value: &{TOO Boo}
&va2: 0x1030e0d0, pointer: 0x10328000, value: &{Hello Foo}

Note that the address of the variable va1 does not change, but what va1 points to does change. Also, the assignment of a pointer to va1 does not modify the value va1 pointed to.