Why closures are fundamental in Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a simple closure that adds two numbers.

Swift

let add = { (a: Int, b: Int) -> Int in return a [1] b }

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' will subtract instead of add.

The closure adds two integers using the + operator.

2fill in blank

medium

Complete the code to call the closure with arguments 3 and 5.

Swift

let result = add([1])

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A(3, 5)

B3, 5

C3 5

D[3, 5]

Attempts:

3 left

💡 Hint

Common Mistakes

Passing arguments without parentheses or commas causes syntax errors.

Closures with multiple parameters are called with parentheses and comma-separated values.

3fill in blank

hard

Fix the error in the closure that captures a variable and increments it.

Swift

var count = 0
let increment = { count [1] 1 }

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A-=

B++

C+=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '++' causes a syntax error in Swift 3 and later.

The '+=' operator increments the variable by 1 inside the closure.

4fill in blank

hard

Fill both blanks to create a closure that filters even numbers from an array.

Swift

let numbers = [1, 2, 3, 4, 5]
let evens = numbers.filter { $0 [1] [2] 2 == 0 }

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

A%

B==

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' will select odd numbers instead.

The modulo operator '%' checks the remainder, and '==' compares it to zero to find even numbers.

5fill in blank

hard

Fill all three blanks to create a closure that maps strings to their lengths if length is greater than 3.

Swift

let words = ["apple", "cat", "banana"]
let filteredLengths = words.reduce(into: [:]) { dict, word in
    if word.count [1] [2] {
        dict[[3]] = word.count
    }
}

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

A>

B3

Cword

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' will filter the wrong words.

The closure checks if the word length is greater than 3 and adds it to the dictionary with the word as the key.