Golang：界面函数来打印内存地址

Question

I am curious as to why just printing the memory address on a var directly works but trying to do the same action through an interface doesn't print out the memory address?

package main

import "fmt"

type address struct {
    a int
}

type this interface {
    memory()
}

func (ad address) memory() {
    fmt.Println("a - ", ad)
    fmt.Println("a's memory address --> ", &ad)
}

func main() {
    ad := 43
    fmt.Println("a - ", ad)
    fmt.Println("a's memory address --> ", &ad)

    //code init in here
    thisAddress := address{
        a: 42,
    }
    // not sure why this doesnt return memory address as well?
    var i this
    i = thisAddress
    i.memory()
}

https://play.golang.org/p/Ko8sEVfehv

Just wanted to add this after fixing errors, it now functions as expected. Testing shifting memory pointers

package main

import "fmt"

type address struct {
  a int
}

type this interface {
  memory() *int
}

func (ad address) memory() *int {

  /*reflect.ValueOf(&ad).Pointer() research laws of reflection */
  var b = &ad.a

  return b
}

func main() {



  thisAddress := address{
      a: 42,
  }
  thatAddress := address{
      a: 43,
  }

  var i this
  i = thisAddress
  a := i.memory()

  fmt.Println("I am retruned", a)
  fmt.Println("I am retruned", *a)
  i = thatAddress
  c := i.memory()
  fmt.Println("I am retruned", c)
  fmt.Println("I am retruned", *c)
}

https://play.golang.org/p/BnB14-yX8B

Answer 1

Because in your second case inside the memory() method:

func (ad address) memory() {
    fmt.Println("a - ", ad)
    fmt.Println("a's memory address --> ", &ad)
}

ad is not an int but a struct, ad is of type address. And you're not printing the address of an int but an address of a struct. And the default formatting for pointer to a struct is: &{}.

Quoting from package doc of fmt regarding default formats:

struct:             {field0 field1 ...}
array, slice:       [elem0 elem1 ...]
maps:               map[key1:value1 key2:value2]
pointer to above:   &{}, &[], &map[]

If you modify the line to print the address of the address.a field which is of type int:

fmt.Println("a's memory address --> ", &ad.a)

You will see the same pointer format printed in hexadecimal format, e.g.:

a's memory address -->  0x1040e13c