Swift is a powerful, intuitive, and modern programming language developed by Apple for iOS, macOS, watchOS, and tvOS app development.
If you’re aiming for an iOS developer role, being well-prepared with commonly asked Swift interview questions can give you a major advantage.
This blog will cover the most important Swift interview questions along with descriptive answers to help you excel in interviews.
People Also Ask:
Q1. What is Swift mainly used for?
➔ Swift is primarily used for developing applications for Apple’s platforms, including iOS, macOS, watchOS, and tvOS.
Q2. Is Swift hard to learn?
➔ Swift is designed to be simple and beginner-friendly, making it relatively easy to learn, especially for those familiar with basic programming concepts.
Q3. What is the difference between Swift and Objective-C?
➔ Swift offers a safer, more concise syntax compared to Objective-C, and it supports modern programming concepts like optionals and type inference.
Q4. Why choose Swift for iOS development?
➔ Swift is fast, safe, modern, and continually updated by Apple, making it the best choice for iOS and Apple ecosystem development.
30+ Most Common Swift Interview Questions and Answers
1. What is Swift?
Answer:
Swift is a general-purpose, compiled programming language developed by Apple. It’s designed to be fast, safe, and expressive, and it provides modern programming features like closures, generics, and type inference.
2. What are the main features of Swift?
Answer:
- Safe and easy-to-read syntax
- Fast execution
- Support for optionals
- Type inference
- Protocol-oriented programming
- Automatic memory management
- Interoperability with Objective-C
3. What are Optionals in Swift?
Answer:
Optionals are a type that can either hold a value or nil.
They are used to handle the absence of a value safely without crashing the program.
Example:
var name: String? = "John"
4. What is the difference between var and let in Swift?
Answer:
varis used to declare mutable variables.letis used to declare immutable constants (cannot be changed after assignment).
5. What is type inference in Swift?
Answer:
Type inference means Swift automatically deduces the type of a variable or constant without explicitly mentioning it.
Example:
let name = "John" // Swift infers it as String
6. Explain “Optional Binding” in Swift.
Answer:
Optional binding is a safe way to find out if an optional contains a value and to extract that value into a temporary variable or constant.
Example:
if let name = optionalName {
print("Name is \(name)")
}
7. What is a Tuple in Swift?
Answer:
A tuple is a group of multiple values combined into a single compound value.
Example:
let person = (name: "John", age: 30)
8. What is a guard statement?
Answer:
A guard statement is used for early exits in functions or methods if a condition isn’t met, making the code more readable.
Example:
func greet(_ name: String?) {
guard let unwrappedName = name else { return }
print("Hello \(unwrappedName)")
}
9. What are closures in Swift?
Answer:
Closures are self-contained blocks of functionality that can be passed around and used in your code. They are similar to lambdas in other languages.
Example:
let greet = { print("Hello World") }
10. What is the difference between Struct and Class in Swift?
Answer:
- Struct: Value type (copied when assigned).
- Class: Reference type (shared reference when assigned).
11. What is ARC (Automatic Reference Counting)?
Answer:
ARC automatically manages memory usage by keeping track of strong references to instances and deallocating them when no longer needed.
12. What is a protocol in Swift?
Answer:
A protocol defines a blueprint of methods, properties, and other requirements suited for a particular task.
Example:
protocol Greetable {
func greet()
}
13. What is Protocol-Oriented Programming?
Answer:
In Swift, protocols are used extensively to design flexible, reusable, and scalable code. Protocol-oriented programming is preferred over inheritance-based designs.
14. What is Error Handling in Swift?
Answer:
Swift provides error handling using do-catch blocks where you can throw, catch, and handle errors gracefully.
Example:
do {
try someFunction()
} catch {
print("Error occurred")
}
15. What is an enum in Swift?
Answer:
Enums define a common type for a group of related values and enable you to work with those values in a type-safe way.
Example:
enum Direction {
case north, south, east, west
}
16. How do you define a lazy property?
Answer:
A lazy property is not initialized until it’s first accessed, using the lazy keyword.
Example:
lazy var greeting = "Hello"
17. What is a deinitializer?
Answer:
A deinitializer is called immediately before a class instance is deallocated.
Example:
deinit {
print("Deallocated")
}
18. How do you make a class singleton?
Answer:
You can use a static constant inside a class.
Example:
class Manager {
static let shared = Manager()
}
19. What is map, filter, and reduce in Swift?
Answer:
They are high-order functions used for collection transformations:
- map: Applies a function to all elements.
- filter: Selects elements matching a condition.
- reduce: Combines all elements into a single value.
20. What are extensions in Swift?
Answer:
Extensions add new functionality to existing classes, structs, enums, or protocols without modifying their original source code.
Example:
extension String {
func reversed() -> String {
return String(self.reversed())
}
}
21. Explain Access Control in Swift.
Answer:
Swift provides five access levels:
- open
- public
- internal
- fileprivate
- private
These control the visibility of classes, methods, and properties.
22. What is a computed property?
Answer:
A computed property calculates a value rather than storing it.
Example:
var area: Double {
return width * height
}
23. What is typealias?
Answer:typealias is used to provide a new name to an existing type.
Example:
typealias Name = String
24. What are generics in Swift?
Answer:
Generics allow you to write flexible and reusable functions and types that can work with any type.
Example:
swiftCopyEditfunc swapValues<T>(_ a: inout T, _ b: inout T)
25. What is the difference between synchronous and asynchronous tasks?
Answer:
- Synchronous tasks block the current thread.
- Asynchronous tasks allow the program to continue running without waiting.
26. How do you handle JSON parsing in Swift?
Answer:
Using Codable protocol to decode or encode JSON objects.
Example:
struct User: Codable {
let name: String
}
27. What is DispatchQueue in Swift?
Answer:
DispatchQueue manages the execution of tasks serially or concurrently on your app’s main or background threads.
28. What is @escaping closure?
Answer:
An @escaping closure is one that can outlive the function it’s passed into, typically used for asynchronous operations.
29. What is difference between strong, weak, and unowned references?
Answer:
- strong: Retains ownership.
- weak: Does not retain ownership (optional).
- unowned: Does not retain ownership (non-optional).
30. What are property observers?
Answer:
Property observers monitor changes to a property’s value using willSet and didSet blocks.
Conclusion
Preparing with these Swift interview questions equips you to confidently tackle technical interviews for iOS or macOS development roles. Understanding Swift deeply will not just help you crack interviews but also make you a better Apple ecosystem developer!