How to Pass a Swift Interview: Top Questions from A to Z

Introduction: Why Swift is the Key to a Successful Interview

A Swift interview is not just a syntax check. The Apple ecosystem requires an understanding of the language's fundamental principles, memory management, and modern frameworks. In this article, we will break down the top questions you will definitely be asked at any level — from Junior to Senior. You will learn not only the correct answers but also the typical pitfalls candidates fall into.

The article is written for the educational portal PythonLib but is adapted for Swift. We have structured the material so you can quickly review key topics before your interview.

1. Swift Basics: Optional, Value vs Reference Types

What is an Optional and why is it needed?

An Optional is an enum that can be either .none (nil) or .some(Wrapped). It is Swift's way of safely handling the absence of a value.

var name: String? = "Alice"var age: Int? = nil

// Safe unwrappingif let unwrappedName = name {    print("Hello, \\(unwrappedName)")} else {    print("Name is nil")}

Common mistake: Using force unwrap (!) without checking. Always prefer guard let or if let.

Value Types vs Reference Types

Swift strictly separates types:

• Value Types (structs, enums, basic types) — copied on assignment.
• Reference Types (classes) — passed by reference.

struct Point {    var x: Int    var y: Int}

class Car {    var model: String    init(model: String) { self.model = model }}

var point1 = Point(x: 1, y: 2)var point2 = point1point2.x = 5 // point1.x remains 1

var car1 = Car(model: "Tesla")var car2 = car1car2.model = "BMW" // car1.model also becomes "BMW"

Interview question: "Why does Apple recommend using structs instead of classes?" Answer: thread safety, predictability, no ARC overhead.

2. Memory Management and ARC: How to Avoid Leaks

How does Automatic Reference Counting (ARC) work?

ARC automatically counts references to class objects. When the count reaches zero, memory is freed. Problems arise with cyclic references.

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

class Apartment {    let unit: String    weak var tenant: Person?  // weak — weak reference    init(unit: String) { self.unit = unit }    deinit { print("Apartment \\(unit) deallocated") }}

var john: Person? = Person(name: "John")var unit4A: Apartment? = Apartment(unit: "4A")john?.apartment = unit4Aunit4A?.tenant = johnjohn = nilunit4A = nil// Both objects will be deallocated

Key modifiers:

• weak — always optional, automatically becomes nil upon deallocation.
• unowned — non-optional, assumes the object is alive (risk of crash).

Typical question: "What is the difference between weak and unowned?" Answer: weak is safer, unowned is more convenient for mandatory dependencies (e.g., delegate).

3. Frameworks: UIKit vs SwiftUI, GCD and Protocols

UIKit: ViewController Lifecycle and Delegate Pattern

Understanding viewDidLoad, viewWillAppear, viewDidDisappear is basic. But in interviews, they often ask about the Delegate pattern:

protocol MyDelegate: AnyObject {    func didTapButton()}

class MyView: UIView {    weak var delegate: MyDelegate?        @objc func buttonTapped() {        delegate?.didTapButton()    }}

class MyViewControlle