[go-nuts] Is this a compiler bug?

[Ignazio Di Napoli]

I'm very curious about the answer to this unanswered StackOverflow 
question: 
http://stackoverflow.com/questions/41357948/what-golang-compiler-will-do-when-fmt-println


import (
    "fmt")

type shout interface {
    echo()}

type a struct {}
func (*a) echo () {
    fmt.Println("a")}

type b struct {}
func (*b) echo () {
    fmt.Println("b")}

func compare(a, b shout) {
    //fmt.Println(&a, &b)
    if a == b {
        fmt.Println("same")
    } else {
        fmt.Println("not same")
    }}

func main() {
    a1 := &a{}
    b1 := &b{}
    a2 := &a{}
    a1.echo()
    b1.echo()
    compare(a1, b1)
    compare(a1, a2)
    compare(a1, a1) }


The output is different if a fmt.Println is commented or not. 

Commented:

not samenot same
same


Not commented:

0x1040a120 0x1040a128not same0x1040a140 0x1040a148
same0x1040a158 0x1040a160
same



To me, it seems a compiler bug, or some undefined behaviour.
Can someone help me understand?


Thank you.



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