Difference between Value and Pointer variable in Defer in Go

bebound@gmail.com (KK) — Thu, 19 Dec 2019 22:33:00 +0800

defer is a useful function to do cleanup, as it will execute in LIFO order before the surrounding function returns. If you don’t know how it works, sometimes the execution result may confuse you.

How it Works and Why Value or Pointer Receiver Matters

I found an interesting code on Stack Overflow:

type X struct {
 S string
}

func (x X) Close() {
 fmt.Println("Value-Closing", x.S)
}

func (x *X) CloseP() {
 fmt.Println("Pointer-Closing", x.S)
}

func main() {
 x := X{"Value-X First"}
 defer x.Close()
 x = X{"Value-X Second"}
 defer x.Close()

 x2 := X{"Value-X2 First"}
 defer x2.CloseP()
 x2 = X{"Value-X2 Second"}
 defer x2.CloseP()

 xp := &X{"Pointer-X First"}
 defer xp.Close()
 xp = &X{"Pointer-X Second"}
 defer xp.Close()

 xp2 := &X{"Pointer-X2 First"}
 defer xp2.CloseP()
 xp2 = &X{"Pointer-X2 Second"}
 defer xp2.CloseP()
}

The output is:

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Difference between Value and Pointer variable in Defer in Go

How it Works and Why Value or Pointer Receiver Matters