Defer Panic and Recover in Go

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February 15, 2025
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4 min read

In Go, error handling is managed using defer, panic, and recover. These mechanisms help in handling unexpected errors and ensuring proper resource cleanup.

1. defer Statement

🔹 defer is used to delay the execution of a function until the surrounding function returns. It is mainly used for cleanup operations like closing files, releasing locks, etc.

🔹 Syntax of defer

Go
defer functionName()
  • The deferred function executes after the surrounding function completes.
  • Multiple defer statements are executed in LIFO (Last In, First Out) order.

🔹 Example of defer

Go
package main

import "fmt"

func main() {
    fmt.Println("Start")
    
    defer fmt.Println("Deferred: This executes last")
    
    fmt.Println("Middle")
}

🔹 Output:

Bash
Start
Middle
Deferred: This executes last

👉 Explanation:

  • "Deferred: This executes last" runs at the end because it is deferred.

🔹 Multiple defer Example (LIFO Order)

Go
package main

import "fmt"

func main() {
    defer fmt.Println("First")
    defer fmt.Println("Second")
    defer fmt.Println("Third")
    
    fmt.Println("Main function executed")
}

🔹 Output:

Bash
Main function executed
Third
Second
First

👉 Explanation:

  • The last defer statement is executed first.

2. panic in Go

🔹 panic is used to stop program execution immediately.
🔹 It is usually used when the program cannot recover from an error.
🔹 When panic occurs, it executes deferred statements before stopping the program.

🔹 Syntax of panic

Go
panic("Error message")

🔹 Example of panic

Go
package main

import "fmt"

func main() {
    fmt.Println("Start")
    
    panic("Something went wrong!")  // Program stops here
    
    fmt.Println("End") // This line will not execute
}

🔹 Output:

Bash
Start
panic: Something went wrong!

👉 Explanation:

  • "Start" prints.
  • panic("Something went wrong!") stops execution.
  • "End" does not execute.

🔹 panic with defer (Deferred function still runs)

Go
package main

import "fmt"

func main() {
    defer fmt.Println("This will execute before panic stops the program")

    fmt.Println("Before panic")
    panic("Something went wrong!")
}

🔹 Output:

Bash
Before panic
This will execute before panic stops the program
panic: Something went wrong!

👉 Explanation:

  • Deferred function still runs before panic stops execution.

3. recover in Go

🔹 recover is used to catch a panic and prevent the program from crashing.
🔹 It is used inside a defer function to handle errors gracefully.

🔹 Syntax of recover

Go
recover()
  • recover() returns nil if there is no panic.
  • It stops the panic and resumes execution.

🔹 Example of recover Handling Panic

Go
package main

import "fmt"

func main() {
    defer handlePanic()

    fmt.Println("Start")
    panic("Something went wrong!")
    fmt.Println("End")  // This line will NOT execute
}

func handlePanic() {
    if r := recover(); r != nil {
        fmt.Println("Recovered from panic:", r)
    }
}

🔹 Output:

Bash
Start
Recovered from panic: Something went wrong!

👉 Explanation:

  • panic("Something went wrong!") occurs.
  • handlePanic() runs because of defer.
  • recover() catches the panic and prevents a crash.

🔹 Example: panic, defer, and recover Together

Go
package main

import "fmt"

func main() {
    fmt.Println("Main started")
    
    safeFunction()

    fmt.Println("Main function continues")
}

func safeFunction() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered from:", r)
        }
    }()

    fmt.Println("Inside safeFunction")
    panic("Critical error!")  // Triggers panic
    fmt.Println("This line will not execute")
}

🔹 Output:

Bash
Main started
Inside safeFunction
Recovered from: Critical error!
Main function continues

👉 Explanation:

  • panic("Critical error!") is triggered.
  • recover() inside defer catches the panic.
  • The program continues execution instead of crashing.

Key Takeaways

FeatureDescription
deferDelays execution of a function until the surrounding function completes. Useful for cleanup tasks.
panicStops program execution immediately. Used for critical errors.
recoverCaptures panic and prevents program crash. Used inside defer.

āĻŦāĻžāĻ‚āĻ˛āĻž āĻŦā§āĻ¯āĻžāĻ–ā§āĻ¯āĻž

1. defer āĻ•ā§€?

🔹 defer āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻž āĻšāĻ¯āĻŧ āĻ•ā§‹āĻ¨ā§‹ āĻĢāĻžāĻ‚āĻļāĻ¨ā§‡āĻ° āĻāĻ•ā§āĻ¸āĻŋāĻ•āĻŋāĻ‰āĻļāĻ¨ āĻŦāĻŋāĻ˛āĻŽā§āĻŦāĻŋāĻ¤ āĻ•āĻ°āĻ¤ā§‡āĨ¤
🔹 āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ āĻĢāĻžāĻ‡āĻ˛ āĻ•ā§āĻ˛ā§‹āĻœ, āĻ°āĻŋāĻ¸ā§‹āĻ°ā§āĻ¸ āĻ°āĻŋāĻ˛āĻŋāĻœ āĻ•āĻ°āĻžāĻ° āĻœāĻ¨ā§āĻ¯ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻž āĻšāĻ¯āĻŧāĨ¤

✅ defer āĻāĻ° āĻ‰āĻĻāĻžāĻšāĻ°āĻŖ

Go
package main

import "fmt"

func main() {
    fmt.Println("Start")
    
    defer fmt.Println("āĻāĻŸāĻŋ āĻ¸āĻŦāĻļā§‡āĻˇā§‡ āĻšāĻ˛āĻŦā§‡")
    
    fmt.Println("Middle")
}

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Bash
Start
Middle
āĻāĻŸāĻŋ āĻ¸āĻŦāĻļā§‡āĻˇā§‡ āĻšāĻ˛āĻŦā§‡

2. panic āĻ•ā§€?

🔹 panic āĻšāĻ˛ā§‹ āĻ­ā§āĻ˛ āĻšāĻ˛ā§‡ āĻĒā§āĻ°ā§‹āĻ—ā§āĻ°āĻžāĻŽ āĻĨāĻžāĻŽāĻžāĻ¨ā§‹āĻ° āĻœāĻ¨ā§āĻ¯āĨ¤
🔹 āĻāĻŸāĻŋ āĻāĻ•ā§āĻ¸āĻŋāĻ•āĻŋāĻ‰āĻļāĻ¨ āĻ¤āĻžā§ŽāĻ•ā§āĻˇāĻŖāĻŋāĻ•āĻ­āĻžāĻŦā§‡ āĻŦāĻ¨ā§āĻ§ āĻ•āĻ°ā§‡āĨ¤

✅ panic āĻāĻ° āĻ‰āĻĻāĻžāĻšāĻ°āĻŖ

Go
package main

import "fmt"

func main() {
    fmt.Println("Start")
    
    panic("āĻ¸āĻŽāĻ¸ā§āĻ¯āĻž āĻĻā§‡āĻ–āĻž āĻĻāĻŋāĻ¯āĻŧā§‡āĻ›ā§‡!")  // āĻĒā§āĻ°ā§‹āĻ—ā§āĻ°āĻžāĻŽ āĻāĻ–āĻžāĻ¨ā§‡ āĻĨā§‡āĻŽā§‡ āĻ¯āĻžāĻŦā§‡
    
    fmt.Println("End") // āĻāĻŸāĻŋ āĻāĻ•ā§āĻ¸āĻŋāĻ•āĻŋāĻ‰āĻŸ āĻšāĻŦā§‡ āĻ¨āĻž
}

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Bash
Start
panic: āĻ¸āĻŽāĻ¸ā§āĻ¯āĻž āĻĻā§‡āĻ–āĻž āĻĻāĻŋāĻ¯āĻŧā§‡āĻ›ā§‡!

3. recover āĻ•ā§€?

🔹 recover āĻšāĻ˛ā§‹ panic āĻ•ā§āĻ¯āĻžāĻĒāĻšāĻžāĻ° āĻ•āĻ°āĻžāĻ° āĻ‰āĻĒāĻžāĻ¯āĻŧāĨ¤
🔹 āĻāĻŸāĻŋ defer āĻāĻ° āĻ­āĻŋāĻ¤āĻ°ā§‡ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°āĻž āĻšāĻ¯āĻŧ panic āĻĨā§‡āĻ•ā§‡ āĻ°āĻ•ā§āĻˇāĻž āĻĒā§‡āĻ¤ā§‡āĨ¤

✅ recover āĻāĻ° āĻ‰āĻĻāĻžāĻšāĻ°āĻŖ

Go
package main

import "fmt"

func main() {
    defer handlePanic()

    fmt.Println("Start")
    panic("āĻ•āĻŋāĻ›ā§ āĻāĻ•āĻŸāĻž āĻ¸āĻŽāĻ¸ā§āĻ¯āĻž āĻšāĻ¯āĻŧā§‡āĻ›ā§‡!")
}

func handlePanic() {
    if r := recover(); r != nil {
        fmt.Println("āĻĒā§āĻ¯āĻžāĻ¨āĻŋāĻ• āĻĨā§‡āĻ•ā§‡ āĻ‰āĻĻā§āĻ§āĻžāĻ°:", r)
    }
}

🔹 āĻ†āĻ‰āĻŸāĻĒā§āĻŸ:

Bash
Start
āĻĒā§āĻ¯āĻžāĻ¨āĻŋāĻ• āĻĨā§‡āĻ•ā§‡ āĻ‰āĻĻā§āĻ§āĻžāĻ°: āĻ•āĻŋāĻ›ā§ āĻāĻ•āĻŸāĻž āĻ¸āĻŽāĻ¸ā§āĻ¯āĻž āĻšāĻ¯āĻŧā§‡āĻ›ā§‡!

āĻ‰āĻĒāĻ¸āĻ‚āĻšāĻžāĻ°

✅ defer → āĻĻā§‡āĻ°āĻŋāĻ¤ā§‡ āĻšāĻžāĻ˛āĻžāĻ¯āĻŧ
✅ panic → āĻ¤āĻžā§ŽāĻ•ā§āĻˇāĻŖāĻŋāĻ•āĻ­āĻžāĻŦā§‡ āĻĨāĻžāĻŽāĻžāĻ¯āĻŧ
✅ recover → panic āĻ āĻŋāĻ• āĻ•āĻ°ā§‡

🚀 Go-āĻ¤ā§‡ defer, panic, āĻ“ recover āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻ•āĻ°ā§‡ āĻāĻĢāĻŋāĻļāĻŋāĻ¯āĻŧā§‡āĻ¨ā§āĻŸ āĻāĻ°āĻ° āĻšā§āĻ¯āĻžāĻ¨ā§āĻĄāĻ˛āĻŋāĻ‚ āĻ•āĻ°āĻž āĻ¯āĻžāĻ¯āĻŧāĨ¤

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