How to Pass a Swift Interview: Top Questions and Answers

Introduction

An interview for an iOS/macOS developer position is not just about testing knowledge of UIKit or SwiftUI frameworks. First and foremost, the employer evaluates your understanding of the Swift language: its syntax, memory management features, multithreading, and type system. Even if you write applications confidently, without a theoretical foundation it's easy to fail a technical interview.

In this article, we have compiled the top questions most frequently asked at Swift interviews in 2025. Each question is accompanied by a detailed explanation and a code example. The material will be useful for both juniors and experienced developers looking to refresh their knowledge.

1. Optional Types (Optionals) and Safety

Why does Swift use Optionals?

Swift is a strongly typed language, and optional types are its key feature for safe nil handling. Unlike Objective-C, where nil is just a null pointer, in Swift Optional is an enum with two cases: none (nil) and some(Wrapped). This forces the developer to explicitly handle the absence of a value, preventing crashes.

How to extract a value from an Optional?

There are several ways:

• Force unwrapping — the ! operator. Used only when you are absolutely sure the value is not nil.
• Optional binding — the if let or guard let construct.
• Nil-coalescing operator — ?? for providing a default value.

var name: String? = "Alice"

// Force unwrapping (dangerous!)print(name!)

// Optional bindingif let unwrappedName = name {    print("Hello, \\(unwrappedName)")}

// Nil-coalescinglet displayName = name ?? "Guest"print(displayName)

What are Implicitly Unwrapped Optionals (IUO)?

This is an optional type that is automatically unwrapped upon access. It is declared using ! after the type. It is mainly used for properties that are initialized after init (e.g., IBOutlet in UIKit). However, in modern Swift (5.x), IUOs behave like regular Optionals, and the compiler warns about the risks.

2. Memory Management: ARC and Strong Reference Cycles

How does ARC work in Swift?

Automatic Reference Counting (ARC) is a reference counting mechanism. Each class instance has a reference count. When the count drops to zero, the object is deallocated from memory. ARC only works with reference types (classes, closures). Value types (structs, enums) are stored on the stack and managed by copying.

What is a strong reference cycle (retain cycle)?

A cycle occurs when two objects refer to each other through strong references, and ARC cannot deallocate them. This leads to a memory leak. The solution is to use weak (weak) or unowned (unowned) 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 — prevents the cycle    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 = john

john = nilunit4A = nil// Both objects will be deallocated

When to use weak, and when unowned?

• weak — always optional, automatically becomes nil when the object is deallocated. Used when the lifetime of the reference may be shorter than that of the owner.
• unowned — non-optional, assumes the object will live as long or longer. Dangerous: if the object is deallocated, accessing