Panic behavior in Go - Step-by-Step Execution

Concept Flow - Panic behavior

Start program

↓

Call function

↓

Panic occurs?

No→Continue normal execution

Yes↓

Run deferred functions

↓

Program crashes with panic message

The program runs normally until a panic happens, then it runs deferred functions before crashing.

Execution Sample

Go

package main
import "fmt"
func main() {
  defer fmt.Println("Deferred runs")
  panic("Something went wrong")
}

This code shows a panic happening and a deferred function running before the program crashes.

Execution Table

Step	Action	Output	State
1	Start main function		main started
2	Set defer to print 'Deferred runs'		defer set
3	Call panic with message 'Something went wrong'		panic triggered
4	Run deferred function: print 'Deferred runs'	Deferred runs	deferred function executed
5	Program crashes with panic message	panic: Something went wrong	program stops

💡 Program stops after panic and deferred functions run

Variable Tracker

Variable	Start	After panic	After defer	Final
panic state	false	true	true	program stopped

Key Moments - 2 Insights

Why does the deferred function run even after panic?

Because Go always runs deferred functions before the program crashes due to panic, as shown in step 4 of the execution table.

Does the program continue normal execution after panic?

No, after panic and running deferred functions, the program stops immediately, as shown in step 5.

Visual Quiz - 3 Questions

Look at the execution table, what is printed by the deferred function?

A Deferred runs

B Something went wrong

C panic: Something went wrong

D No output

💡 Hint

Check step 4 in the execution table where the deferred function output is shown.

At which step does the panic get triggered?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Action' column in the execution table for when panic is called.

If the defer statement was removed, what would change in the output?

A The panic message would not print

B The program would not panic

C The deferred message 'Deferred runs' would not print

D The program would continue running after panic

💡 Hint

Refer to the output in step 4 where the deferred function prints its message.

Concept Snapshot

panic("message") stops normal execution immediately
Deferred functions run before program crashes
Program prints panic message and exits
Use defer to clean up before panic ends program
Panic is like a run-time error causing crash

Full Transcript

This example shows how panic works in Go. The program starts main, sets a deferred function to print a message, then calls panic with a message. When panic happens, normal execution stops, but deferred functions still run. After running deferred functions, the program crashes and prints the panic message. This behavior ensures cleanup code runs even on errors. The execution table traces each step: starting main, setting defer, triggering panic, running defer, and stopping program. Variables track panic state changing from false to true. Key moments clarify why defer runs after panic and that the program does not continue after panic. The quiz tests understanding of output, panic timing, and effect of removing defer. The snapshot summarizes panic behavior simply and clearly.