Recover usage in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go program using recover?

Consider the following Go code that uses recover() inside a deferred function. What will it print?

Go

package main

import "fmt"

func main() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered from panic:", r)
        }
    }()
    fmt.Println("Start")
    panic("something went wrong")
    fmt.Println("End")
}

A Start\nEnd

B Start\nEnd\nRecovered from panic: something went wrong

C Start\nRecovered from panic: something went wrong

D Start\npanic: something went wrong

💡 Hint

Remember that defer runs after the panic, and recover() stops the panic.

The program prints "Start" first. Then it panics. The deferred function runs and calls recover(), which catches the panic and prints the message. The line after panic is never reached.

❓ Predict Output

intermediate

What happens if recover is called outside deferred function?

What will this Go program print?

Go

package main

import "fmt"

func main() {
    r := recover()
    fmt.Println("Recover returned:", r)
    panic("panic here")
}

A Recover returned: <nil>\npanic: panic here

B Recover returned: panic here

C Recover returned: <nil>

D Compile error: recover used outside deferred function

💡 Hint

recover() only works inside deferred functions during a panic.

Since recover() is called outside a deferred function and no panic is active, it returns nil. Then the program panics and prints the panic message.

🔧 Debug

advanced

Why does this recover not catch the panic?

Look at this Go code. It tries to recover from a panic but fails. Why?

Go

package main

import "fmt"

func main() {
    defer recoverPanic()
    panic("fail")
}

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

A The recover call is in a separate function, so it cannot catch the panic from main.

B The deferred function is called after main returns, so recover can't catch the panic.

C The recover call must be inside an anonymous deferred function to work.

D The panic is not active when recover is called because defer runs too late.

💡 Hint

Think about where the panic happens and where recover is called.

Recover only catches panics if called directly in the deferred function where the panic happened. Here, recover is called in a separate function deferred by main, so it cannot catch the panic from main.

📝 Syntax

advanced

Which option correctly uses recover to handle panic?

Which of the following Go code snippets correctly uses recover() to handle a panic?

A defer recover()

B defer func() { if r := recover(); r != nil { fmt.Println(r) } }()

C func handle() { r := recover(); if r != nil { fmt.Println(r) } } defer handle()

D defer func() { recover() }()

💡 Hint

Recover must be called inside a deferred function to catch panics.

Option B correctly defines an anonymous deferred function that calls recover and checks if a panic occurred. Option B calls recover directly in defer, which does nothing. Option B calls recover in a normal function deferred, but recover only works if called directly in the deferred function. Option B calls recover but ignores the result, so it does not handle the panic.

🚀 Application

expert

How many times will deferred recover run in nested panics?

Consider this Go program with nested panics and deferred recover calls. How many times will the recover print a message?

Go

package main

import "fmt"

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

    func() {
        defer func() {
            if r := recover(); r != nil {
                fmt.Println("Recovered in inner func:", r)
                panic("new panic")
            }
        }()
        panic("original panic")
    }()
}

A 1 time: only in inner func

B 0 times: recover does not catch panics here

C 1 time: only in main

D 2 times: once in inner func and once in main

💡 Hint

Think about how recover stops a panic and how a new panic inside a deferred function affects outer deferred functions.

The inner deferred function recovers from the original panic and prints a message. Then it panics again with a new panic. The outer deferred function in main recovers from this new panic and prints its message. So recover prints twice.