Recover usage in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to recover from a panic and print a message.

Go

func safeDivide(a, b int) {
    defer func() {
        if r := [1](); r != nil {
            println("Recovered from panic:", r)
        }
    }()
    println(a / b)
}

Drag options to blanks, or click blank then click option'

Arecover

Bpanic

Cdefer

Dclose

Attempts:

3 left

💡 Hint

Common Mistakes

Using panic() instead of recover() inside the deferred function.

Calling recover() outside a deferred function.

The recover() function is used inside a deferred function to catch a panic and prevent the program from crashing.

2fill in blank

medium

Complete the code to safely handle a panic and print a custom message.

Go

func handlePanic() {
    defer func() {
        if err := [1](); err != nil {
            println("Error caught:", err)
        }
    }()
    panic("something went wrong")
}

Drag options to blanks, or click blank then click option'

Arecover

Bpanic

Cclose

Dexit

Attempts:

3 left

💡 Hint

Common Mistakes

Using panic() instead of recover() to catch errors.

Not using defer with recover().

recover() captures the panic value inside the deferred function, allowing graceful error handling.

3fill in blank

hard

Fix the error in the code to properly recover from a panic.

Go

func faulty() {
    defer func() {
        if r := [1](); r != nil {
            println("Recovered:", r)
        }
    }()
    panic("fail")
}

Drag options to blanks, or click blank then click option'

Apanic()

Brecover

Crecover()

Ddefer

Attempts:

3 left

💡 Hint

Common Mistakes

Using recover without parentheses.

Calling panic instead of recover.

The recover() function must be called with parentheses to execute it and get the panic value.

4fill in blank

hard

Fill both blanks to create a function that recovers from panic and prints the panic message.

Go

func safeRun() {
    defer func() {
        if err := [1](); err != nil {
            println("Caught panic:", [2])
        }
    }()
    panic("unexpected error")
}

Drag options to blanks, or click blank then click option'

Arecover

Berr

Cpanic

Drecover()

Attempts:

3 left

💡 Hint

Common Mistakes

Using panic instead of recover.

Printing recover() instead of the variable.

Use recover() to get the panic value and print the variable holding it.

5fill in blank

hard

Fill all three blanks to recover from panic and print a detailed message.

Go

func execute() {
    defer func() {
        if panicVal := [1](); panicVal != nil {
            println("Recovered panic:", [2], "with value", [3])
        }
    }()
    panic("critical failure")
}

Drag options to blanks, or click blank then click option'

Arecover

BpanicVal

Dpanic

Attempts:

3 left

💡 Hint

Common Mistakes

Using panic instead of recover.

Using different variable names inconsistently.

Call recover() to get the panic value, then print the variable holding it twice for clarity.

Practice

1. What is the main purpose of the recover function in Go?

easy

A. To handle errors returned by functions

B. To start a new goroutine

C. To pause the execution of a function

D. To catch a panic and prevent the program from crashing

Solution

1. Step 1: Understand panic and recover

   Panic causes a program to stop immediately unless recovered.

2. Step 2: Role of recover

   Recover catches the panic inside a deferred function to keep the program running.

3. Final Answer:

   To catch a panic and prevent the program from crashing -> Option D

4. Quick Check:

   recover catches panic = A [OK]

Hint: Recover catches panics only inside deferred functions [OK]

Common Mistakes:

• Thinking recover handles normal errors
• Using recover outside deferred functions
• Confusing recover with panic

2. Which of the following is the correct way to use recover in Go?

easy

A. Call recover directly inside the main function

B. Call recover inside a deferred function

C. Call recover inside a goroutine

D. Call recover after a panic has finished

Solution

1. Step 1: Identify recover usage rules

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

2. Step 2: Analyze options

   Only Call recover inside a deferred function calls recover inside a deferred function.

3. Final Answer:

   Call recover inside a deferred function -> Option B

4. Quick Check:

   recover inside defer = B [OK]

Hint: Always use recover inside defer to catch panics safely [OK]

Common Mistakes:

• Calling recover directly without defer
• Calling recover after panic ends
• Using recover in goroutines without defer

3. What will be the output of this Go program?

package main
import "fmt"
func main() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("Recovered from panic:", r)
        }
    }()
    panic("something went wrong")
    fmt.Println("This will not print")
}

medium

A. Recovered from panic: something went wrong

B. something went wrong

C. This will not print

D. Program crashes with panic message

Solution

1. Step 1: Understand defer and recover behavior

   The deferred function runs after panic starts, calling recover to catch it.

2. Step 2: Output analysis

   Recover prints the panic message, so output is "Recovered from panic: something went wrong".

3. Final Answer:

   Recovered from panic: something went wrong -> Option A

4. Quick Check:

   defer + recover prints panic message = C [OK]

Hint: Recover prints panic message inside deferred function [OK]

Common Mistakes:

• Expecting code after panic to run
• Thinking panic message prints directly
• Ignoring deferred recover function

4. What is wrong with this Go code snippet?

func main() {
    recover()
    panic("error")
}

medium

A. panic() cannot be called without defer

B. panic() must be called before recover()

C. recover() is called outside a deferred function and will not catch panic

D. recover() cannot be called in main function

Solution

1. Step 1: Check recover usage

   Recover only works inside deferred functions to catch panics.

2. Step 2: Analyze code

   Recover is called directly, so it won't catch the panic, causing program to crash.

3. Final Answer:

   recover() is called outside a deferred function and will not catch panic -> Option C

4. Quick Check:

   recover outside defer = no panic catch = D [OK]

Hint: Recover must be inside defer to catch panic [OK]

Common Mistakes:

• Calling recover directly without defer
• Assuming recover catches panic anytime
• Misunderstanding panic and recover order

5. You want to safely handle panics in a function that divides two numbers and returns the result. Which code snippet correctly uses recover to avoid crashing when dividing by zero?

hard

A. func safeDivide(a, b int) int {
defer func() {
if r := recover(); r != nil {
fmt.Println("Recovered from panic")
}
}()
return a / b
}

B. func safeDivide(a, b int) int {
if b == 0 {
recover()
}
return a / b
}

C. func safeDivide(a, b int) int {
return a / b
defer recover()
}

D. func safeDivide(a, b int) int {
defer recover()
return a / b
}

Solution

1. Step 1: Identify correct recover usage

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

2. Step 2: Analyze options

   Only func safeDivide(a, b int) int { defer func() { if r := recover(); r != nil { fmt.Println("Recovered from panic") } }() return a / b } uses defer with an anonymous function calling recover properly.

3. Final Answer:

   func safeDivide(a, b int) int { defer func() { if r := recover(); r != nil { fmt.Println("Recovered from panic") } }() return a / b } -> Option A

4. Quick Check:

   defer func with recover = safe panic handling = A [OK]

Hint: Use defer with anonymous func calling recover to catch panics [OK]

Common Mistakes:

• Calling recover without defer
• Calling recover outside anonymous function
• Placing defer after return statement