CODEWITHSUNDEEP
go
NghiaTran
NghiaTran

Reputation: 65

Golang defer doesn't work if put after panic?

I have the code as below and defer wasn't executed.

Doesn't defer work if we put it after panic?

package main

import (
  "fmt"
)

func main() {
  fmt.Println("begining of main")
  panic("stop here")
  defer fmt.Println("end of main")
}

nghiatran@nghiatran-VB:~/go/src/defer$ go run main.go
begining of main
panic: stop here

goroutine 1 [running]:
main.main()
        /home/nghiatran/go/src/defer/main.go:9 +0x96
exit status 2
nghiatran@nghiatran-VB:~/go/src/defer$

Upvotes: 2

Views: 10770

Answers (2)

Grzegorz Żur
Grzegorz Żur

Reputation: 49171

The order of statements is wrong. Defer pushes function call to the stack. At the end of the function execution stacked calls are taken in reverse order and are executed. It does not matter whether function panics or not.

You need to push the function call first and then panic.

package main

import (
  "fmt"
)

func main() {
   defer fmt.Println("end of main") // push the call to the stack
   fmt.Println("begining of main")
   panic("stop here")
   // the deffered functions are called as if they where here
}

The defer statement works differently than catch and finally blocks but it offer the same functionality.

See Use of defer in Go

Upvotes: 14

Himanshu Patel
Himanshu Patel

Reputation: 99

defer won't work after panic because the control never reached the statement, hence it was never registered. This is like printing something after a return statement in a function, it's basically an unreachable code.

Upvotes: 2

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