Swift Interview: Complete Preparation Guide with Code Examples

Swift at the Interview: How Not to Lose Face

Imagine: you're sitting across from a team lead or HR manager, and suddenly the question comes up: "Tell me, what is the difference between a class and a struct in Swift?". It seems basic. But it's precisely on such "simple" questions that many candidates get lost. And if you add the pitfalls of ARC, closures, and optional types — a Swift interview can turn into a real ordeal.

In this article, we'll break down how to prepare for a Swift interview so you feel confident. You'll get not just theory, but real code examples, life hacks, and a checklist of topics to review before meeting with an employer.

Why Are Swift Interviews So Specific?

Swift is a young but very powerful language. It combines low-level memory management (ARC) with high-level abstractions (protocols, generics, functional programming). In an interview, you will be tested on several fronts at once:

• Basic syntax — optionals, enums, tuples, guard/if-let.
• Memory management — ARC, retain cycles, weak and unowned references.
• OOP and protocol-oriented programming — classes vs structs, extensions, protocols.
• Functional capabilities — closures, map/filter/reduce, async/await.
• iOS specifics — UIKit, ViewController lifecycle, Auto Layout.

The good news: all of this can be learned and practiced. Let's go!

Top 5 Topics You Need to Know Inside Out

1. Structs vs Classes: Battle of the Titans

This is perhaps the most common question in a Swift interview. Let's break it down with an example.

// Class — reference typeclass Car {    var model: String    init(model: String) { self.model = model }}

// Struct — value typestruct Bike {    var model: String}

var myCar = Car(model: "Tesla")var sameCar = myCarsameCar.model = "BMW"print(myCar.model) // BMW — reference!

var myBike = Bike(model: "Stels")var sameBike = myBikesameBike.model = "Author"print(myBike.model) // Stels — copy!

What's important to emphasize in the interview:

• Classes support inheritance, structs do not (but protocols do).
• Structs are value types, classes are reference types.
• Structs automatically have a memberwise initializer.
• For multithreading, structs are safer — no shared state.

2. ARC and Memory Management — The Main Pain Point for iOS Developers

Without understanding ARC (Automatic Reference Counting), there's nothing to do in a Swift interview. The most common problem is a retain cycle (circular reference).

class ProfileViewController {    var onLogout: (() -> Void)?        func setup() {        // Attention! Strong reference to self inside the closure        onLogout = {            self.dismiss(animated: true)        }    }}

How to fix it? Use [weak self]:

onLogout = { [weak self] in    self?.dismiss(animated: true)}

Typical ARC questions:

• What is the difference between weak and unowned?
• When does a retain cycle occur?
• How does ARC work with closures?

3. Closures — From Simple to Complex

Closures in Swift are anonymous functions that capture context. No callback or completion handler can do without them.

// Simple closurelet greeting = { (name: String) in    print("Hello, \\(name)!")}greeting("Swift") // Hello, Swift!

// Sorting an arraylet numbers = [3, 1, 7, 2]let sorted = numbers.sorted { $0 < $1 }print(sorted) // [1, 2, 3, 7]

Tricky question: "What t