Closures are reference types in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a closure that adds two numbers.

Swift

let add: (Int, Int) -> Int = [1] { $0 + $1 }

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

A{

Bfunc

Cclosure

Dlambda

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'func' keyword instead of closure syntax

Trying to use 'lambda' which is not a Swift keyword

The correct syntax to declare a closure in Swift uses curly braces { }. So { $0 + $1 } defines the closure body.

2fill in blank

medium

Complete the code to assign a closure to a variable and call it.

Swift

var multiply = [1] (Int, Int) -> Int = { $0 * $1 }
let result = multiply(3, 4)

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

Afunc

Blet

Cvar

Dclosure

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'func' keyword instead of closure type

Using 'var' incorrectly when 'let' is better here

Use let to declare a constant closure. Here, multiply is assigned a closure that multiplies two numbers.

3fill in blank

hard

Fix the error in the closure capturing a variable.

Swift

func makeIncrementer(forIncrement amount: Int) -> () -> Int {
    var total = 0
    let incrementer: () -> Int = {
        total [1]= amount
        return total
    }
    return incrementer
}

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

A/

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition

Forgetting to update total inside the closure

The closure should add amount to total each time it is called, so += is the correct operator.

4fill in blank

hard

Fill both blanks to create a closure that captures and modifies a variable.

Swift

func makeCounter() -> () -> Int {
    var count = 0
    return {
        count [1]= 1
        return count [2] 0
    }
}

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

A+

B-

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of addition

Using wrong comparison operators

The closure increments count by 1 using += and returns whether count is greater than 0 using >.

5fill in blank

hard

Fill all three blanks to create a closure that captures a string and returns its length if longer than 3.

Swift

func makeStringChecker(_ text: String) -> () -> Int? {
    return {
        let length = text.[1]
        if length [2] 3 {
            return length
        } else {
            return [3]
        }
    }
}

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

Acount

B>

Cnil

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong property name instead of count

Returning wrong value instead of nil

The closure gets the string length using count, checks if it is greater than 3, and returns nil if not.