defer

The defer statement defers the execution of a function until the surrounding function returns. Let’s try to explain this a bit better. Inside a function, you have a defer statement in front of a function that you are calling. Essentially, that function will execute right before the function you are currently inside completes. Still confused? Perhaps an example will make this concept a little clearer:

package main
import "fmt"
func main() {
  defer done()
  fmt.Println("Main: Start")
  fmt.Println("Main: End")
}
func done() {
  fmt.Println("Now I am done")
}

The output for the defer example is as follows:

Main: Start
Main: End
Now I am done

Inside the main() function, we have a deferred function, defer done(). Notice that the done() function has no new or special syntax. It just does a simple print to the console.

Next, we have two print statements. The results are interesting....