Why ARC matters for Swift developers - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a strong reference to an instance.

Swift

class Person {
    var name: String
    init(name: String) {
        self.name = name
    }
}

var person1: Person? = Person(name: "Alice")
var person2 = [1]

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

Aperson1

Bnil

Cself

DPerson()

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning nil instead of the existing instance.

Creating a new instance instead of referencing the existing one.

Assigning person1 to person2 creates a strong reference to the same instance.

2fill in blank

medium

Complete the code to declare a weak reference to avoid a strong reference cycle.

Swift

class Person {
    var name: String
    weak var friend: Person? // Avoid strong reference cycle
    init(name: String) {
        self.name = name
    }
}

var alice: Person? = Person(name: "Alice")
var bob: Person? = Person(name: "Bob")
alice?.friend = [1]

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

Abob

Balice

Cnil

DPerson(name: "Bob")

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning nil instead of the other instance.

Assigning a new instance instead of the existing one.

Assigning bob to alice?.friend as a weak reference prevents a strong reference cycle.

3fill in blank

hard

Fix the error in the code to prevent a strong reference cycle using unowned reference.

Swift

class Customer {
    let name: String
    var card: CreditCard?
    init(name: String) {
        self.name = name
    }
}

class CreditCard {
    let number: UInt64
    unowned let customer: [1]
    init(number: UInt64, customer: Customer) {
        self.number = number
        self.customer = customer
    }
}

var john: Customer? = Customer(name: "John Appleseed")
john?.card = CreditCard(number: 1234_5678_9012_3456, customer: john!)

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

AString

BCreditCard

CCustomer

DAnyObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong class type for the unowned reference.

Using a value type like String instead of a class.

The unowned reference must be of the class type Customer to avoid a strong reference cycle.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that stores word lengths only for words longer than 3 characters.

Swift

let words = ["apple", "bat", "car", "dolphin"]
let lengths = words.reduce(into: [:]) { dict, word in
    if word.count [1] 3 {
        dict[word] = [2]
    }
}

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

A>

Bword.count

C<

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Assigning the word itself instead of its length.

The condition word.count > 3 filters words longer than 3 characters, and word.count stores their lengths.

5fill in blank

hard

Fill all three blanks to create a dictionary of uppercase keys and values for words longer than 4 characters.

Swift

let words = ["swift", "code", "apple", "bug"]
let result = words.reduce(into: [:]) { dict, word in
    if word.count [1] 4 {
        dict[[2]] = [3]
    }
}

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

A>

Bword.uppercased()

Cword

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Swapping keys and values.

The condition word.count > 4 filters words longer than 4 characters. The dictionary keys are uppercase words, and values are the original words.