Strong reference cycles between classes in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a class named Person.

Swift

class [1] {
    var name: String
    init(name: String) {
        self.name = name
    }
}

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

AHuman

BPerson

CAnimal

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different class name like Human or Animal.

The class is named Person, so the blank should be filled with 'Person'.

2fill in blank

medium

Complete the code to declare a strong reference property 'apartment' in Person class.

Swift

class Person {
    var name: String
    var [1]: Apartment?
    init(name: String) {
        self.name = name
    }
}

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Aroom

Bbuilding

Capartment

Dhouse

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different property name like house or room.

The property name is 'apartment' to represent the relationship.

3fill in blank

hard

Fix the error in the Apartment class to avoid a strong reference cycle by making the tenant reference weak.

Swift

class Apartment {
    let unit: String
    [1] var tenant: Person?
    init(unit: String) {
        self.unit = unit
    }
}

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Astrong

Blazy

Cunowned

Dweak

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'strong' or 'unowned' which do not break the cycle.

Using 'lazy' which is unrelated here.

The 'tenant' property should be declared weak to avoid a strong reference cycle.

4fill in blank

hard

Fill both blanks to complete the code that creates a strong reference cycle between Person and Apartment.

Swift

let john = Person(name: "John")
let unit4A = Apartment(unit: "4A")
john.[1] = unit4A
unit4A.[2] = john

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Aapartment

Btenant

Cowner

Dresident

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like owner or resident.

The Person's apartment property is set to unit4A, and Apartment's tenant property is set to john, creating a strong reference cycle.

5fill in blank

hard

Fill all three blanks to complete the code that breaks the strong reference cycle using weak reference and optional chaining.

Swift

class Apartment {
    let unit: String
    [1] var tenant: Person?
    init(unit: String) {
        self.unit = unit
    }
}

let john = Person(name: "John")
let unit4A = Apartment(unit: "4A")
john.[2] = unit4A
unit4A.tenant = john
unit4A.tenant?.[3] = nil

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

Aweak

Bapartment

Cname

Dstrong

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'strong' instead of 'weak' for tenant.

Using wrong property names for john's apartment or tenant's property.

The tenant property is weak, john's apartment is set, and the tenant's apartment is accessed with optional chaining to set it to nil, breaking the cycle.