Defer execution order in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the defer keyword do in Go?

The defer keyword schedules a function call to run after the surrounding function finishes, just before it returns.

beginner

In what order are multiple deferred functions executed in Go?

Deferred functions are executed in last-in, first-out (LIFO) order. The last deferred function runs first.

beginner

Consider this code snippet:<br>

func example() {
  defer fmt.Println("first")
  defer fmt.Println("second")
  fmt.Println("middle")
}

<br>What is the output?

The output will be:<br>middle<br>second<br>first

Because deferred calls run after the function ends, in reverse order.

intermediate

Why is defer useful for resource management in Go?

Defer helps ensure resources like files or locks are released properly, even if the function returns early or an error occurs.

intermediate

Can deferred functions modify named return values in Go?

Yes, deferred functions can modify named return values because they run just before the function returns.

What happens when multiple defer statements are used in a Go function?

A They execute in the order they appear.

B Only the first defer executes.

C They execute in reverse order (last deferred runs first).

D They execute simultaneously.

Deferred functions run in last-in, first-out order, so the last deferred function runs first.

When exactly do deferred functions run in Go?

A Immediately when deferred.

B After the surrounding function returns, before it actually returns to the caller.

C At the start of the function.

D Only if the function panics.

Deferred functions run after the surrounding function finishes but before it returns to the caller.

Which of these is a common use case for defer in Go?

A Closing files or releasing locks.

B Opening network connections.

C Starting goroutines.

D Declaring variables.

Defer is often used to close files or release locks to ensure cleanup happens.

If a deferred function modifies a named return variable, when does that modification take effect?

A Before the function starts.

B After the function returns to the caller.

C It never takes effect.

D Just before the function returns to the caller.

Deferred functions run just before returning, so they can change named return values.

What will this Go code print?<br>

func f() {
  defer fmt.Println(1)
  defer fmt.Println(2)
  defer fmt.Println(3)
}

f()

A 3 2 1

B 1 2 3

C 1 3 2

D 2 3 1

Deferred calls run in reverse order, so it prints 3, then 2, then 1.

Explain how the defer keyword controls the execution order of deferred functions in Go.

Think about a stack of plates where the last plate placed is the first one taken.

Describe a practical example where using defer improves code safety or clarity.

Imagine you open a file and want to make sure it always closes.