Swift interview questions

Optional unwrapping

Which of these unwrap an optional safely? Pick all that apply.

#optional #unwrap

Value semantics

What does this code print? …

#struct #class #value-semantics #let

Type casting

Given let view: UIView = UILabel(), which of these casts can crash at runtime?

#type-casting #as #downcast #optional

Why optionals exist

Why does Swift have optionals?

#optional #enum #nil #safety

Collection types

You have tens of thousands of user IDs and need to check repeatedly whether a given ID is among them. Which collection fits best?

#array #set #dictionary #hashable

SwiftMultiple choiceIntroMeesho

Optionals and IUOs

Which of these three lines compile? Pick all that apply. …

#optional #iuo #implicitly-unwrapped #nil

SwiftShort answerIntroCapital One

Combining higher-order functions

Take ["a", "b", "c"] as input and produce ["c-0", "b-1", "a-2"]. You can't use a for loop, only higher-order functions. Which functions would you combine, and …

#higher-order #map #enumerated #reversed

SwiftShort answerIntroAdobe

Tuples: uses and limits

When is it appropriate to use a tuple in Swift?

#tuple #struct #multiple-return #destructuring

SwiftMultiple choiceIntroOura

Choosing a struct

In which of these cases is a struct the right choice over a class in Swift? Pick all that apply.

#struct #class #value-type #reference-type

SwiftMultiple choiceIntroInfosysinterview report

guard statement rules

Which statements about Swift's guard statement are correct? Pick all that apply.

#guard #early-exit #optional-binding #control-flow

SwiftShort answerIntro브랜디interview report

Force unwrap rule

Your team's code review rules include "no force unwrapping (!)." Why have a rule like that?

#optional #force-unwrap #iuo #code-review

SwiftShort answerBasicsAppleinterview report

Value vs reference types

In Swift, what's the fundamental difference between a struct and a class?

#struct #class #value-type #cow

Escaping closures

This code doesn't compile. What is the compiler asking for? …

#closure #escaping #non-escaping #capture

Access control

In a framework module, what's the difference between declaring open class and public class? Pick all correct statements.

#access-control #open #public #module

Protocol-oriented design

A teammate wants to create a BaseViewModel class and have every screen inherit from it. If you proposed a protocol-oriented alternative, how would you design i…

#protocol #pop #oop #protocol-extension

mutating and value types

Which line in this code fails to compile, and why? …

#mutating #struct #value-semantics #inout

defer ordering

What's the output order when you call this function? …

#defer #scope #cleanup

Any, AnyObject, NSObject

What can Any, AnyObject, and NSObject each hold?

#any #anyobject #nsobject #existential

Enum rules

Which statements about Swift enum are correct? Pick all that apply.

#enum #associated-value #raw-value #pattern-matching

Higher-order functions

What does this code print? …

#map #compactmap #flatmap #higher-order-function

lazy properties

Which statements about a lazy var stored property are correct? Pick all that apply.

#lazy #stored-property #initialization #thread-safety

KeyPath values

In Swift, what exactly does a KeyPath like \.name represent as a value?

#keypath #writablekeypath #referencewritablekeypath #kvo

SwiftShort answerBasics라인

Serialization model types

When you build model types to serialize and deserialize a server's JSON response, should you use a class or a struct? Give your reasons.

#struct #class #codable #serialization

SwiftMultiple choiceBasicsMeesho

Recursive value types

What happens when you compile this code? And if you change the same definition to class Person? …

#struct #class #recursive #memory-layout

SwiftMultiple choiceBasicsZomato

Swift type rules

Which of these statements about Swift language rules are correct? Pick all that apply.

#initializer #deinit #access-control #closure

SwiftShort answerBasicsGojek

private vs fileprivate

In one file you have class A { fileprivate func secret() {} } and class B. Can B call A().secret(), and what changes if you switch it to private?

#access-control #private #fileprivate #extension

SwiftShort answerBasicsWalmart

Implementing compactMap

Extend Array with a myCompactMap that behaves like the standard library's compactMap. How would you write the generic signature?

#generics #rethrows #extension #compactmap

SwiftShort answerBasicsSwiggy

Extending Optional

Extend Optional so that any optional can be asked for its nil status, like someOptional.isNil. How would you implement it?

#optional #extension #enum #pattern-matching

SwiftMultiple choiceBasicsDiDi

Init and observer rules

Which of these statements about class initialization, deinitialization, and property observers in Swift are correct? Pick all that apply.

#deinit #required #property-observer #set

SwiftShort answerBasicsIBMinterview report

Generics vs Any

During code review you find the same logic overloaded per type: func larger(_ a: Int, _ b: Int) -> Int, larger(_ a: Double, _ b: Double) -> Double, larger(_ a:…

#generics #any #specialization #type-safety

SwiftMultiple choiceBasicsTinderinterview report

inout parameters

Which statements about Swift's inout parameters (func bump(_ x: inout Int)) are correct? Pick all that apply.

#inout #copy-in-copy-out #exclusivity #value-type

SwiftShort answerBasicsSAP

Protecting the original

You passed a class instance to a function, changed a property inside it, and the caller's original changed too. How do you protect the original?

#reference-type #deep-copy #shallow-copy #nscopying

SwiftShort answerBasicsJD.com

How Swift enums differ

A colleague who mostly writes Java or C asks whether a Swift enum is just a list of constants in the end. What's fundamentally different about a Swift enum com…

#enum #associated-values #sum-type #exhaustive-switch

SwiftShort answerBasicsCapgeminiinterview report

How optional chaining behaves

When you chain several optional accesses like this and hit nil partway through, what happens? …

#optional-chaining #optional #short-circuit #flatten

SwiftShort answerBasicsCognizantinterview report

Type inference cost

Swift has type inference, so you rarely have to write types, yet your team convention says "annotate types on complex expressions and public APIs." How does ty…

#type-inference #compile-time #let #var

Opaque vs existential types

From the caller's side, what's the difference between func make() -> some Shape and func make() -> any Shape?

#some #any #existential #opaque

SwiftShort answerAdvancedUber

Generics and type erasure

You have an Iterator protocol with getNext() and hasNext(), and you want to change it from Int-only to generic with associatedtype Element. After the change, b…

#generic #associatedtype #type-erasure #any

Error handling

When designing a network layer, which would you make the default: throws functions, returning Result<T, E>, or Swift 6 typed throws (throws(NetworkError))?

#error #throws #result #typed-throws

Codable decoding strategies

The server's JSON uses snake_case keys, and dates come as strings like "2026-09-11T10:00:00Z". What would you set up on the decoder to decode this response wit…

#codable #decodable #codingkeys #json

String internals

Why can't you index a String with an integer like text[3], and why is text.count O(n)?

#string #unicode #grapheme #index

SwiftShort answerAdvancedTikTok

Method dispatch

In Swift, which method calls use static, table, and message dispatch?

#dispatch #static-dispatch #dynamic-dispatch #vtable

Property wrappers

What does this code print? …

#property-wrapper #projectedvalue #wrappedvalue

Initialization rules

Why doesn't this code compile? Can you explain it using the two-phase initialization rules? …

#initializer #designated #convenience #two-phase

SwiftShort answerAdvanced네이버웹툰

ContiguousArray vs Array

Say your resume claims "ContiguousArray is faster than Array." In a pre-interview the interviewer asks, "Then why don't developers use ContiguousArray much in …

#array #contiguousarray #performance #bridging

SwiftShort answerAdvancedAirbnb

An iterator of iterators

Given a 'collection of collections' like [[1, 2], [], [3], [4, 5, 6]], how would you design an iterator that hands out elements one at a time in flat order (1,…

#iteratorprotocol #sequence #flatten #generics

SwiftShort answerAdvancedXiaohongshu

Extensions and stored properties

You want to add a property to an existing type with an extension. Computed properties work, so why not stored properties?

#extension #stored-property #memory-layout #associated-object

SwiftShort answerAdvancedVerizoninterview report

Large collections in structs

You need to put a very large Dictionary, hundreds of thousands of entries, into a struct property and pass that struct around by value. What's the 'fastest' wa…

#cow #dictionary #value-type #performance

SwiftShort answerAdvancedGrabinterview report

Designing a custom Optional

Suppose there were no question-mark optional syntax and no standard Optional. If you had to design a type in Swift that expresses 'a value or nothing,' how wou…

#optional #enum #generics #map

SwiftShort answerAdvanced야놀자interview report

Using a C++ library

You need to use a C++ video-processing library from a Swift app. Would you go with the old approach (an Objective-C++ wrapper) or Swift 5.9's C++ interop?

#cpp-interop #objective-c++ #bridging #ownership

Protocol extension dispatch

What does this code print? …

#protocol #extension #dispatch #witness-table

Implementing copy-on-write

You need a struct ImageBuffer that wraps a large pixel buffer, keeps value semantics, and avoids needless copies. If you implemented copy-on-write yourself, wh…

#cow #copy-on-write #isknownuniquelyreferenced #value-semantics

Objective-C interop

A Swift module has to call into legacy Objective-C code and be called from it. How do you set up bridging in both directions?

#objc #bridging #interop #dynamic

ABI and library evolution

You're about to ship an internal shared module as an XCFramework binary. What do Swift ABI stability and Library Evolution (BUILD_LIBRARY_FOR_DISTRIBUTION) eac…

#abi #library-evolution #frozen #inlinable