Go - Defer Statement

The defer statement defers the execution of a function until the surrounding function returns.

The deferred call’s arguments are evaluated immediately.

1package main
2
3import "fmt"
4
5func main() {
6  defer fmt.Println("world")
7
8  fmt.Println("hello")
9}

$go run main.go
hello
world

Staking defer Statements

The deferred function calls are pushed onto a stack.

When the function returns the deferred calls are executed in LIFO order (last in first out).

1package main
2
3import "fmt"
4
5func main() {
6  fmt.Println("counting")
7
8  for i := 0; i < 5; i++ {
9    defer fmt.Println(i)
10  }
11
12  fmt.Println("done")
13}

$go run main.go
counting
done
4
3
2
1
0