Limitations and best practices in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Understanding value type limitations in Swift structs

What is the output of this Swift code snippet?

Swift

struct Counter {
    var count = 0
    mutating func increment() {
        count += 1
    }
}

var c1 = Counter()
let c2 = c1
c1.increment()
print(c1.count, c2.count)

A 1 0

B 1 1

C 0 0

D 0 1

💡 Hint

Remember that structs are value types and copying creates independent instances.

In Swift, structs are value types. When you assign c1 to c2, it copies the value. Incrementing c1 does not affect c2. So c1.count is 1, but c2.count remains 0.

❓ Predict Output

intermediate

Best practice for optional unwrapping

What will be printed by this Swift code?

Swift

var name: String? = "Alice"
if let unwrappedName = name {
    print("Hello, \(unwrappedName)!")
} else {
    print("No name provided.")
}

A nil

B No name provided.

C Optional("Alice")

D Hello, Alice!

💡 Hint

Check how optional binding works with if let.

The if let syntax unwraps the optional name safely. Since name contains "Alice", it prints "Hello, Alice!".

🔧 Debug

advanced

Identify the cause of a retain cycle

Which line in the following Swift code causes a retain cycle leading to a memory leak?

Swift

class Person {
    var name: String
    var apartment: Apartment?
    init(name: String) { self.name = name }
    deinit { print("Person \(name) is being deinitialized") }
}

class Apartment {
    var unit: String
    var tenant: Person?
    init(unit: String) { self.unit = unit }
    deinit { print("Apartment \(unit) is being deinitialized") }
}

var john: Person? = Person(name: "John")
var unit4A: Apartment? = Apartment(unit: "4A")
john!.apartment = unit4A
unit4A!.tenant = john

A john!.apartment = unit4A

B unit4A!.tenant = john

C var tenant: Person? in Apartment class

D var apartment: Apartment? in Person class

💡 Hint

Think about strong references between classes causing retain cycles.

The line unit4A!.tenant = john creates a strong reference from Apartment to Person. Since Person also strongly references Apartment, this creates a retain cycle. To fix, tenant should be a weak reference.

📝 Syntax

advanced

Which option correctly declares a protocol with an associated type?

Choose the correct Swift syntax for declaring a protocol with an associated type named Item.

A

protocol Container {
    associatedtype Item
    func append(_ item: Item)
}

B

protocol Container {
    typealias Item
    func append(_ item: Item)
}

C

protocol Container {
    var Item: Type
    func append(_ item: Item)
}

D

protocol Container {
    associatedtype Item = Any
    func append(_ item: Item)
}

💡 Hint

Recall the keyword for declaring associated types in protocols.

The correct keyword is associatedtype. Option A uses it properly. Option A uses typealias which is invalid here. Option A tries to declare a variable instead of an associated type. Option A tries to assign a default type which is invalid syntax.

🧠 Conceptual

expert

Best practice to avoid force unwrapping optionals

Which approach is considered the best practice to safely handle optionals in Swift and avoid runtime crashes?

A Use <code>as!</code> to cast optionals to non-optionals directly.

B Use force unwrapping <code>!</code> whenever you are sure the optional contains a value.

C Use optional binding with <code>if let</code> or <code>guard let</code> to unwrap optionals safely.

D Convert optionals to implicitly unwrapped optionals to avoid unwrapping syntax.

💡 Hint

Think about safety and avoiding crashes.

Using if let or guard let safely unwraps optionals and prevents runtime crashes. Force unwrapping (!) can cause crashes if the optional is nil. Implicitly unwrapped optionals and forced casts are risky and should be avoided unless absolutely sure.