Swift Interview Questions

Swift is an indispensable part of application development in the Apple ecosystem. Especially for iOS developers, Swift knowledge is one of the most critical technical evaluation criteria during hiring processes. In this article, we will deeply explore topics such as Swift interview questions, Swift developer interview questions, iOS interview questions, Swift async/await interview questions, Swift performance optimization interview questions, and Swift Core Data interview questions, complete with code examples.

1. Differences Between Struct and Class in Swift

• Structs are value types, so they are copied in memory.
• Classes are reference types, so they reference the same memory address.
• Structs can be updated with mutating functions.
• Classes support inheritance; structs do not.

Code Example:

struct UserStruct {
  var name: String
}

class UserClass {
  var name: String
  init(name: String) {
      self.name = name
  }
}

Struct Example:

var a = UserStruct(name: "Ayşe")
var b = a
b.name = "Zeynep" print(a.name) // Ayşe

Class Example:

var x = UserClass(name: "Ali")
var y = x
y.name = "Veli" print(x.name) // Veli

2. What is Optional in Swift and How to Use It?

Optional is a data type used to safely handle null values in Swift. It enforces nil checks.

Usage Methods:

• Optional binding with if let
• Early exit with guard let
• Default value with nil coalescing operator ??

Code Example:

var name: String? = "Techcareer"

if let unwrappedName = name {
  print("Hello, \(unwrappedName)")
} else {
  print("Name not found.")
}

let result = name ?? "Name is undefined" print(result)

3. Async/Await Structure in Swift

This structure makes asynchronous operations more readable and is often asked in Swift async/await interview questions.

Code Example:

func fetchData() async -> String {
  return "Data received"
}

Task {
  let result = await fetchData()
  print(result)
}

Tip:
You must be inside a Task block when using await. You can start parallel tasks with async let.

4. What is the iOS Lifecycle?

iOS developers must know the app lifecycle. Important AppDelegate methods include:

• didFinishLaunchingWithOptions
• applicationDidBecomeActive
• applicationDidEnterBackground

func applicationDidEnterBackground(_ application: UIApplication) {
  print("App entered background")
}

5. ARC and Memory Management in Swift

Memory management is a common topic in Swift performance optimization interviews.

Reference Types:

• Strong: Default
• Weak: Not counted by ARC, can be nil
• Unowned: Not counted by ARC, cannot be nil

Code Example:

class A {
  var b: B?
}

class B {
  weak var a: A?
}

6. What is Core Data?

Core Data is Apple’s framework for persistent data storage, frequently asked in Swift Core Data interview questions.

Code Example:

let newData = NSEntityDescription.insertNewObject(forEntityName: "Note", into: context)
newData.setValue("Interview practice", forKey: "content")

do {
  try context.save()
} catch {
  print("Error: \(error)")
}

7. Swift Collection Types

Basic collections:

• Array<T>
• Set<T>
• Dictionary<K, V>

let numbers = [1, 2, 3, 4]
let cities: Set = ["Istanbul", "Ankara", "Izmir"]
let ages = ["Ali": 25, "Ayşe": 30]

8. Performance Optimization Tips

• Use lazy var for deferred loading
• Run tasks on background threads with GCD
• Monitor ARC and retain cycles

Code Example:

DispatchQueue.global(qos: .background).async {
  let data = heavyTask()
  DispatchQueue.main.async {
      self.label.text = data
  }
}

9. Protocol and Protocol-Oriented Programming

Swift promotes POP (Protocol-Oriented Programming) over classical OOP.

protocol Animal {
  func makeSound()
}

struct Cat: Animal {
  func makeSound() {
      print("Meow")
  }
}

10. Possible iOS Interview Scenario

Scenario: Your app crashes on the App Store. How do you fix it?

Answer:

• Download crash logs (Organizer)
• Symbolicate crash reports
• Perform regression testing
• Release a hotfix
• Resubmit to the App Store

11. Error Handling in Swift

Throwing and catching errors:

enum ErrorType: Error {
  case dataNotFound
}

func fetchData() throws {
  throw ErrorType.dataNotFound
}

do {
  try fetchData()
} catch {
  print("Error received: \(error)")
}

12. ViewController Lifecycle

Lifecycle methods:

• viewDidLoad()
• viewWillAppear()
• viewDidAppear()
• viewWillDisappear()
• viewDidDisappear()

13. Using Alamofire for API Calls

Alamofire is a popular 3rd-party library for iOS networking.

import Alamofire

AF.request("https://api.techcareer.net")
.responseJSON { response in
    debugPrint(response)
}

14. Unit Test Example

func add(_ a: Int, _ b: Int) -> Int {
  return a + b
}

func testAdd() {
  assert(add(2, 3) == 5)
}

15. SwiftUI vs UIKit

• SwiftUI: Declarative approach, iOS 13+
• UIKit: Imperative, broader support

Swift interviews are won not just with basic knowledge but with code reading/writing skills, optimization, and Apple ecosystem mastery. This guide, including Swift interview questions, Swift async/await questions, Swift Core Data questions, and performance optimization questions, provides a strong resource for comprehensive preparation.

If you want to further improve yourself and connect with other professionals in the industry while preparing for Swift interviews, Techcareer.net offers carefully prepared interview question guides and extensive resources to keep you one step ahead!

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