Named return values in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function with named return values.

Go

func greet() (message string) {
    message = "Hello, Go!"
    return [1]
}

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

Amessage

Bgreet

Cstring

Dmsg

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a variable not declared as a named return value.

Returning the function name instead of the variable.

The function uses a named return value message. Returning message returns the named value.

2fill in blank

medium

Complete the code to use named return values and omit the return expression.

Go

func add(a, b int) (sum int) {
    sum = a + b
    [1]
}

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

Areturn sum

Breturn a + b

Creturn

Dreturn sum + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the variable explicitly when a bare return is enough.

Returning an incorrect expression.

When using named return values, a bare return returns the current values of those variables.

3fill in blank

hard

Fix the error in the function by completing the return statement correctly.

Go

func divide(a, b float64) (result float64, err error) {
    if b == 0 {
        err = fmt.Errorf("division by zero")
        [1]
    }
    result = a / b
    return
}

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

Areturn 0, err

Breturn result, nil

Creturn err, 0

Dreturn nil, err

Attempts:

3 left

💡 Hint

Common Mistakes

Returning error and result in wrong order.

Returning nil instead of zero for result.

When division by zero occurs, result should be zero and err should hold the error. So return 0, err.

4fill in blank

hard

Fill both blanks to complete the function with named return values and a bare return.

Go

func multiply(a, b int) (product int, err error) {
    if a < 0 || b < 0 {
        err = fmt.Errorf("negative input")
        [1]
    }
    product = a * b
    [2]
}

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

Areturn

Breturn product, err

Creturn 0, err

Dreturn err

Attempts:

3 left

💡 Hint

Common Mistakes

Using bare return in the error case without setting product to zero.

Returning only error without product.

If inputs are negative, return zero product and the error. Otherwise, assign product and use a bare return to return named values.

5fill in blank

hard

Fill all three blanks to complete the function using named return values and proper error handling.

Go

func subtract(a, b int) (result int, err error) {
    if a < b {
        err = fmt.Errorf("a is less than b")
        [1]
    }
    result = a - b
    [2]
    [3]
}

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

Areturn 0, err

Breturn

Creturn result, err

Dreturn err

Attempts:

3 left

💡 Hint

Common Mistakes

Returning error only without result.

Not using bare return after assigning result.

When a < b, return zero and error. Otherwise, assign result and use bare return twice (the second bare return is redundant but included for the exercise).

Practice

1. What is the main benefit of using named return values in Go functions?

easy

A. They prevent the function from returning any value.

B. They allow returning multiple values without specifying types.

C. They automatically convert return types to strings.

D. They make the function's return values easier to understand and use.

Solution

1. Step 1: Understand named return values

   Named return values give explicit names to the outputs of a function, making it clear what each returned value represents.

2. Step 2: Identify the benefit

   Because the return values are named, the code becomes easier to read and understand, especially when returning multiple values.

3. Final Answer:

   They make the function's return values easier to understand and use. -> Option D

4. Quick Check:

   Named return values improve readability = D [OK]

Hint: Named returns clarify output meaning quickly [OK]

Common Mistakes:

• Thinking named returns change return types
• Believing named returns prevent returning values
• Confusing named returns with automatic type conversion

2. Which of the following Go function signatures correctly uses named return values?

easy

A. func add(a, b int) (int sum) { return a + b }

B. func add(a, b int) int sum { return a + b }

C. func add(a, b int) (sum int) { return a + b }

D. func add(a, b int) sum int { return a + b }

Solution

1. Step 1: Check syntax for named return values

   Named return values are declared inside parentheses with the type after the name, like (sum int).

2. Step 2: Identify correct syntax

   func add(a, b int) (sum int) { return a + b } uses (sum int) correctly. Options B, C, and D have incorrect syntax for named returns.

3. Final Answer:

   func add(a, b int) (sum int) { return a + b } -> Option C

4. Quick Check:

   Named returns syntax = (name type) [OK]

Hint: Named returns use (name type) inside parentheses [OK]

Common Mistakes:

• Placing type before name in return signature
• Omitting parentheses around return values
• Using invalid order like 'int sum'

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

package main
import "fmt"
func divide(a, b int) (result int, err string) {
    if b == 0 {
        err = "division by zero"
        return
    }
    result = a / b
    return
}
func main() {
    r, e := divide(10, 0)
    fmt.Println(r, e)
}

medium

A. 10 division by zero

B. 0 division by zero

C. 0

D. Runtime error

Solution

1. Step 1: Analyze divide function behavior

   If b is zero, err is set to "division by zero" and function returns immediately. result is not set, so defaults to zero.

2. Step 2: Check main function output

   Calling divide(10, 0) returns result=0 and err="division by zero". fmt.Println prints both separated by space.

3. Final Answer:

   0 division by zero -> Option B

4. Quick Check:

   Named returns default zero + error string = A [OK]

Hint: Named returns default zero values if not set [OK]

Common Mistakes:

• Expecting result to be 10 when dividing by zero
• Assuming runtime error instead of handled error string
• Forgetting named returns default zero values

4. Which of the following best improves this Go function using named return values:

func multiply(a, b int) (product int) {
    product = a * b
    return product
}

medium

A. The return statement should be just 'return' without specifying 'product'.

B. The function must return two values, not one.

C. Named return values cannot be assigned inside the function.

D. The function should not have a return statement.

Solution

1. Step 1: Understand named return values usage

   When using named return values, you can simply use 'return' without arguments to return the named variables.

2. Step 2: Identify the improvement in return statement

   Here, 'return product' is allowed but redundant. The idiomatic way is just 'return' to return named values.

3. Final Answer:

   The return statement should be just 'return' without specifying 'product'. -> Option A

4. Quick Check:

   Named returns allow bare 'return' [OK]

Hint: Use bare 'return' with named return values [OK]

Common Mistakes:

• Returning named variable explicitly instead of bare return
• Thinking named returns require multiple return values
• Believing assignment to named returns is disallowed

5. Given this Go function with named return values, what will be the output?

package main
import "fmt"
func stats(nums []int) (sum, count int) {
    for _, n := range nums {
        if n > 0 {
            sum += n
            count++
        }
    }
    return
}
func main() {
    s, c := stats([]int{3, -1, 0, 4, 5})
    fmt.Printf("Sum: %d, Count: %d\n", s, c)
}

hard

A. Sum: 12, Count: 3

B. Sum: 12, Count: 5

C. Sum: 0, Count: 0

D. Sum: 3, Count: 1

Solution

1. Step 1: Analyze the loop filtering positive numbers

   The function loops over nums and adds only positive numbers to sum and increments count.

2. Step 2: Calculate sum and count for given slice

   Positive numbers are 3, 4, 5. Sum = 3+4+5=12, Count = 3.

3. Final Answer:

   Sum: 12, Count: 3 -> Option A

4. Quick Check:

   Sum positive nums = 12, Count positive nums = 3 [OK]

Hint: Named returns can be returned bare after assignment [OK]

Common Mistakes:

• Including zero or negative numbers in sum and count
• Forgetting to return named values
• Miscounting positive numbers in slice