1. What is generics?
AdvancedAnswer: Write flexible, reusable functions and types
Generics enable type-safe reusable code: func swap<T>(_ a: inout T, _ b: inout T). Array<T>, Dictionary<K, V>. Constraints with where. Core Swift feature.
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Swift Interview Questions and Answers
24 questions that come up in Swift technical interviews, each with the answer and an explanation of why it is right.
Test yourself — 90 question bank2. What is Swift?
BeginnerAnswer: Modern, safe, fast programming language for Apple platforms
Swift is Apple's modern programming language for iOS, macOS, watchOS, and tvOS. Type-safe, fast, expressive. Introduced in 2014. Replaces Objective-C.
3. What is a protocol?
IntermediateAnswer: All of the above
Protocol defines requirements: protocol Drawable { func draw() }. Types conform: class Circle: Drawable. Multiple protocols. Protocol-oriented programming. Core Swift paradigm.
4. What is ARC?
AdvancedAnswer: Automatic Reference Counting for memory management
ARC automatically manages memory. Tracks references. Deallocates at zero. Classes only. Strong/weak/unowned references. No garbage collection. Deterministic cleanup.
5. What is protocol-oriented programming?
IntermediateAnswer: Design paradigm using protocols over inheritance
POP uses protocols and extensions. Composition over inheritance. Protocol extensions provide default implementations. Value types with protocol conformance. Swift philosophy.
6. What is the difference between var and let?
BeginnerAnswer: var is mutable, let is immutable
var creates mutable variable. let creates immutable constant. Prefer let for safety. Use var only when value needs to change. Immutability is encouraged.
7. What is strong reference?
AdvancedAnswer: Default reference, keeps object alive
Strong reference increases retain count. Default. Keeps object alive. let obj = MyClass(). Most common. Potential retain cycles. Be aware of ownership.
8. What is extension?
IntermediateAnswer: Adds functionality to existing types
Extensions add functionality: extension String { func reversed() -> String }. No subclassing needed. Retroactive modeling. Protocol conformance. Very powerful feature.
9. How do you declare a variable?
BeginnerAnswer: Both a and b
var age: Int = 25 for mutable. let name = "John" for immutable. Type inference: let count = 5. Explicit type: var price: Double = 9.99. Both are valid.
10. What is error handling?
IntermediateAnswer: do-catch-throw for managing errors
Error handling: throw errors, catch in do-catch. func throws. try, try?, try!. Error protocol. Typed errors. Different from exceptions. Swift approach.
11. What are Swift's basic types?
BeginnerAnswer: Int, Double, Bool, String, Character
Basic types: Int (integers), Double/Float (decimals), Bool (true/false), String (text), Character (single char). Type-safe. No implicit conversions.
12. What is weak reference?
AdvancedAnswer: Optional reference, doesn't prevent deallocation
weak reference doesn't increase count. weak var delegate: Protocol? Always optional. Becomes nil when deallocated. Break retain cycles. Common for delegates.
13. What is unowned reference?
AdvancedAnswer: Non-optional reference, assumes always valid
unowned assumes always valid. unowned let parent: Parent. Not optional. Crashes if accessed after deallocation. Use when guaranteed lifetime. Careful usage.
14. What is throw?
IntermediateAnswer: Propagates error from function
throw raises error: throw MyError.invalid. Function must be marked throws. Propagates up call stack. Caller must handle. Type-safe error propagation.
15. What is type inference?
BeginnerAnswer: Compiler automatically determines type
Type inference: compiler determines type from initial value. let count = 5 infers Int. Still type-safe. Can specify explicitly: let count: Int = 5. Cleaner code.
16. How do you create a function?
BeginnerAnswer: func name(param: Type) -> ReturnType { }
func greet(name: String) -> String { return "Hello, \\(name)" }. Parameters have labels. Return type with ->. Omit -> for Void. Clear syntax.
17. What is retain cycle?
AdvancedAnswer: Two objects hold strong references to each other
Retain cycle: mutual strong references. Objects never deallocated. Memory leak. Break with weak/unowned. Common with closures. Use capture lists.
18. What is do-catch?
IntermediateAnswer: Handles throwing function errors
do-catch: do { try throwingFunc() } catch Error.specific { } catch { }. Multiple catch blocks. Pattern matching. Generic catch. Handle or propagate.
19. What is string interpolation?
BeginnerAnswer: \(expression) embeds values in strings
String interpolation: "Hello, \\(name)". Any expression works: "Sum: \\(a + b)". More readable than concatenation. Type-safe conversion. Very Swift-like.
20. What is try??
IntermediateAnswer: try converts error to optional
try? converts result to optional. Returns nil on error. let result = try? throwingFunc(). Ignores error details. Use when error unimportant. Convenient shorthand.
21. What is capture list in closures?
AdvancedAnswer: Specifies how closure captures values
Capture list: { [weak self] in }. Control reference type. Avoid retain cycles. [weak self], [unowned self], [weak obj]. Essential for memory safety.
22. What is try!?
IntermediateAnswer: Force try, crashes if error
try! force tries. Crashes on error. Use only when certain no error. let result = try! throwingFunc(). Dangerous. Avoid in production. Debug/test use.
23. How do you create an array?
BeginnerAnswer: Both a and b
Arrays: var numbers: [Int] = [1, 2, 3] or var names = ["John", "Jane"]. Type inference. Shorthand [Int] or full Array<Int>. Both valid syntax.
24. What is async/await?
AdvancedAnswer: Modern concurrency with async functions
async/await: async func fetch() -> Data. Call with await. Structured concurrency. Task and Task Group. Swift 5.5+ feature. Replaces completion handlers.
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