Named return values in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are named return values in Go?

Named return values are variables defined in a function's signature that hold the return values. They allow you to return values without explicitly specifying them in the return statement.

beginner

How do you declare named return values in a Go function?

You declare named return values by specifying variable names and types inside the parentheses after the function parameters, like: func example() (result int, err error).

intermediate

What happens if you use a bare return statement in a function with named return values?

A bare return returns the current values of the named return variables. This means you don't have to specify the variables explicitly in the return statement.

intermediate

Can named return values improve code readability? Why or why not?

Yes, named return values can improve readability by giving meaningful names to return values, making it clear what each returned value represents without needing extra comments.

beginner

Show a simple Go function using named return values to return the sum and difference of two integers.

Example:

func calc(a, b int) (sum int, diff int) {
    sum = a + b
    diff = a - b
    return
}

This function returns sum and diff without explicitly listing them in the return statement.

In Go, how do you define named return values in a function?

A By naming variables in the return type parentheses

B By declaring variables inside the function body

C By using global variables

D By using pointers only

Named return values are declared by naming variables in the return type parentheses of the function signature.

What does a bare return statement do in a function with named return values?

A Returns the current values of named return variables

B Returns zero values

C Causes a compile error

D Returns nothing

A bare return returns the current values of the named return variables without needing to specify them.

Which of the following is a benefit of using named return values?

A They allow multiple return types

B They improve code readability by naming return values

C They prevent runtime errors

D They make functions run faster

Named return values improve readability by giving meaningful names to the returned data.

What is the output of this Go function? func example() (x int) { x = 5 return } A call to example() returns:

A 0

B An error

C 5

D Undefined

The function sets x to 5 and returns it using a bare return, so the output is 5.

Can you mix named and unnamed return values in a Go function signature?

A Only if the function has one return value

B No, all must be named or unnamed

C Only in Go versions before 1.10

D Yes, but it's discouraged

You can mix named and unnamed return values, but it is generally discouraged for clarity.

Explain what named return values are in Go and how they affect the return statement.

Think about how naming return variables changes how you write return statements.

Write a simple Go function using named return values to return the quotient and remainder of two integers.

Use division and modulus operators and name the return values clearly.

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