为什么struct上的＆运算符不返回数字地址？

Question

I just started to learn the golang.

I found the & operator behaves differently for simple type and struct.

• For simple type, & returns an address.

• For struct, it returns something else.

Code:

package main

import "fmt"

type person struct {
    name string
    age  int
}

func main() {
    s1 := "abc"
    fmt.Println("s1 address =", &s1)

    s2 := person{"Sam", 55}
    fmt.Println("s2 address = ", &s2)

}

Output:

[ `hello` | done: 79.0079ms ]
    s1 address = 0xc04203c1e0
    s2 address =  &{Sam 55}   <======== What's this? And why not some address like above?

Again, is this design a have-to or a happen-to?

Answer 1

The unitary operator & behaves the same for builtin types and structs, it's used to get the memory address of a var. In this case we'll see &{Sam 55} because Go always checks by default if the parameter in fmt.Println() is a struct or a pointer to struct and in that case will try to print each field of the struct for debugging purposes, but if you want to see a pointer you can use fmt.Printf() with %p, like this:

func main() {
    s1 := "abc"
    fmt.Println("s1 address =", &s1)

    s2 := person{"Sam", 55}

    fmt.Println("s2 as pointer =", &s2)

    fmt.Printf("s2 address = %p value with fields %+v", &s2, s2)
}

Bonus: you can use %+v to print field names and values

https://play.golang.org/p/p7OVRu8YWB