ARC overview for memory management in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Swift

var person: Person? = [1] Person()

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

Aunowned

Bweak

Cstrong

Dlazy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'weak' or 'unowned' when declaring a variable without initialization.

By default, variables hold strong references to instances in Swift.

2fill in blank

medium

Complete the code to declare a weak reference to avoid retain cycles.

Swift

class Person {
    weak var friend: [1]?
}

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

APerson

BString

CInt

DBool

Attempts:

3 left

💡 Hint

Common Mistakes

Using value types like String or Int with 'weak'.

Weak references must be optional and refer to class types to avoid retain cycles.

3fill in blank

hard

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

Swift

class Customer {
    var card: [1]?
}

class CreditCard {
    var owner: Customer?
}

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

ACreditCard

Bunowned CreditCard

Cweak CreditCard

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using strong references causing retain cycles.

Using 'weak' when the reference should not be optional.

Using 'unowned' breaks the strong reference cycle when the referenced instance is expected to always exist.

4fill in blank

hard

Fill both blanks to create a dictionary with keys as names and values as their lengths, filtering names longer than 3 characters.

Swift

let names = ["Anna", "Bob", "Catherine", "Dave"]
let nameLengths = [[1]: [2] for name in names if name.count > 3]

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

Aname

Bname.count

Cname.length

Dlen(name)

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name.length' which is not valid in Swift.

Using 'len(name)' which is Python syntax.

Use 'name' as key and 'name.count' as value to create the dictionary comprehension.

5fill in blank

hard

Fill all three blanks to create a closure that captures self weakly and prints a message.

Swift

class Printer {
    func printMessage() {
        let closure = { [[1] self] in
            print("Message from [2]")
        }
        closure()
    }
}

let printer = Printer()
printer.printMessage()

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

Aweak

Bstrong

Cself

DPrinter

Attempts:

3 left

💡 Hint

Common Mistakes

Not capturing self weakly causing retain cycles.

Using 'strong' which is not a capture keyword.

Use '[weak self]' to avoid retain cycles, refer to 'self' inside closure, and print class name 'Printer'.