Memory and ARC interview questions

Memory and ARCShort answerIntro카카오

ARC basics

What is ARC, and why do we need it?

#arc #reference-counting #retain #release

strong / weak / unowned

Which of the following statements about weak references are correct? Select all that apply.

#weak #unowned #strong #optional

Stack and heap

Which statement about the stack and the heap is correct?

#stack #heap #allocation #struct

Impact of memory leaks

What is a memory leak?

#leak #memory-warning #jetsam #user-impact

When deinit runs

What does this code print? …

#deinit #reference-count #lifetime

Memory and ARCShort answerIntro지마켓글로벌

weak vs strong

Can you explain the difference between weak and strong?

#weak #strong #arc #reference-counting

Memory and ARCShort answerIntroTeladoc Healthinterview report

ARC ownership and deallocation timing

In an iOS app written in Swift, how does ARC manage the lifetime of a class instance?

#arc #ownership #deinit #strong-reference

Memory and ARCShort answerIntroDeloitteinterview report

unowned access risk

A coworker wants to declare every delegate unowned instead of weak because unwrapping optionals is a hassle. Why isn't an unowned reference optional?

#unowned #weak #runtime-trap #arc

Diagnosing reference cycles

A view controller doesn't seem to leave memory after you close its screen. How would you confirm there's actually a reference cycle?

#retain-cycle #leak #memory-graph #deinit

Closure capture and leaks

Which of these two snippets creates a reference cycle? …

#closure #capture #weak-self #retain-cycle

Choosing weak vs unowned

When would you use unowned instead of weak?

#weak #unowned #lifetime #crash

Delegates and weak references

You try to declare weak var delegate: MyDelegate? and the compiler rejects it. Why, and how do you fix it?

#delegate #weak #anyobject #protocol

When cycles happen

Which of the following (with no extra measures) create a reference cycle or a permanent leak? Select all that apply.

#retain-cycle #timer #notification #closure

Retain cycle vs memory leak

Are "reference cycle" and "memory leak" the same thing?

#retain-cycle #leak #abandoned-memory

Capture lists

What does this code print? …

#closure #capture-list #value-capture

MRC and autorelease

Before ARC, Objective-C code called retain, release, and autorelease directly. What did each one do, and what did ARC change?

#mrc #retain #release #autorelease

Using autoreleasepool

This code spikes memory and gets the app killed. What's the most appropriate fix? …

#autoreleasepool #peak-memory #loop #uiimage

Shallow vs deep copy

In struct Order { var items: [Item]; let customer: Customer }, Item is a struct and Customer is a class. After var copy = order, what happens to the original i…

#shallow-copy #deep-copy #nscopying #struct

Objective-C property attributes

In Objective-C, why do you use copy instead of strong for an NSString property, as in @property (nonatomic, copy) NSString *name;? Pick the best reason.

#objective-c #copy #strong #nsstring

Memory and ARCMultiple choiceBasics하이퍼커넥트

Spotting leak patterns

Which of the following snippets keep a ViewController from being deallocated after it leaves the screen (that is, cause a leak)? Select all that apply. Each sn…

#leak #timer #notificationcenter #closure

Memory and ARCMultiple choiceBasicsZomato

Rules of ARC and weak

Which of the following statements about ARC and weak are correct? Select all that apply.

#arc #weak #compile-time #enum

Memory and ARCShort answerBasicsCRED

Proving a leak fix

Think of a memory leak you actually ran into. How did you find it, how did you pin down the cause, and how did you prove it was fixed?

#leak #memory-graph #instruments #regression-test

Memory and ARCShort answerBasicsDoorDashinterview report

Retain cycle example

Give me a concrete code example that creates a retain cycle, and fix it.

#retain-cycle #closure #singleton #weak-self

Memory and ARCShort answerBasicsSalesforceinterview report

Closure capture cycles

A messaging app's ViewModel keeps a completion closure in a property for a long time, and inside it updates self.messages. What reference graph creates the ret…

#closures #retain-cycle #weak-self #arc

Memory and ARCShort answerBasicsXiaomi

Deep copy, shallow copy, and COW

In Swift you assign a large array to another variable with var b = a and then modify only b. Is what happens a shallow copy or a deep copy? Explain it together…

#copy #cow #value-semantics #memory

Memory and ARCShort answerBasicsZillowinterview report

Finding who holds a view controller

You closed a UIKit screen but its ViewController stays in memory. Without just trusting the deinit log, how would you find who's holding it?

#memory-graph #viewcontroller #timer #observer

Core Foundation and ARC

When you handle a Core Foundation object returned by a C API like SecItemCopyMatching or CGImageSource in Swift, when do you use Unmanaged, takeRetainedValue()…

#core-foundation #unmanaged #toll-free-bridging #takeretainedvalue

How closure capture works

What actually happens in memory when a closure captures an outside variable? Using the output of the code below, explain the difference between using a capture…

#closure #capture #capture-list #box

iOS memory and Jetsam

Sometimes an app you sent to the background comes back and starts from scratch. Explain this using how iOS manages memory: virtual memory, compression, and Jet…

#virtual-memory #jetsam #memory-warning #background

Class performance and ARC traffic

Which of these actually improve the performance of class-based code (dispatch and ARC cost)? Select all that apply.

#final #private #dispatch #arc-traffic

unowned crash scenario

This code, which loads an image asynchronously in a UITableView cell, crashes now and then. Under what condition does it crash, and why? …

#unowned #crash #lifetime #closure

Memory cost of value types

How far is it true that "using a struct means no ARC cost"?

#value-type #cow #arc-traffic #struct

Judging unowned

In which of the following is a [unowned self] capture safe? Select all that apply.

#unowned #weak #closure #lifetime

Task and self capture

After moving to Swift Concurrency, your team is arguing about whether you always need [weak self] inside Task { }. When is it unnecessary, and in which Tasks i…

#task #swift-concurrency #weak-self #capture

Memory and ARCShort answerAdvanced쿠팡

Subscription lifetime

In a live coding session you're handed the following Combine ViewModel. Add a feature that subscribes to the price stream and reflects it in priceText, and exp…

#combine #cancellable #closure #weak-self

Memory and ARCShort answerAdvanced네이버웹툰

ARC follow-up drill

Starting from "explain ARC," the follow-ups keep coming. First: who inserts retain and release, and when?

#arc #retain-release #value-type #ownership

Memory and ARCShort answerAdvancedPayPal

ARC deallocation steps

From the moment an object's last strong reference goes away until the memory is actually returned, what does ARC do? Walk me through it step by step.

#arc #deinit #weak #unowned

Memory and ARCShort answerAdvancedFlipkart

Struct copies and COW buffers

… After s2.a = 9, are the addresses where s1.a and s2.a are stored the same or different, and what about the buffer address of the tags array?

#struct #cow #array #memory-address

Memory and ARCShort answerAdvancedMicrosoft

autorelease buildup in loops

A for loop that runs fine on up to 5,000 records crashes after a memory warning above that. Inside the loop you slice and concatenate strings and repeatedly co…

#autoreleasepool #runloop #foundation #bridging

atomic properties and increments

In Objective-C you declare @property (atomic) int a; and run self.a = self.a + 1 a combined 10,000 times from several threads. Is a 10,000 at the end? And how …

#objective-c #atomic #thread-safety #race-condition

Memory and ARCShort answerAdvancedXiaohongshu

Dangling pointers and Zombie Objects

In what situations does a dangling (wild) pointer, one that touches a deallocated object, arise under ARC?

#dangling-pointer #zombie #exc-bad-access #asan

Memory and ARCShort answerAdvancedShopee

ARC vs garbage collection

iOS manages memory with reference counting (ARC). If you had to implement automatic memory management without reference counts, what approach could you take?

#arc #garbage-collection #deterministic #design-rationale

Memory and ARCShort answerAdvancedJD.com

Stored closures and self lifetime

A UIKit ViewController keeps an upload completion block in a property, and the block changes one of the ViewController's labels. After the upload finishes the …

#closure #retain-cycle #completion #lifetime

Memory and ARCShort answerAdvanced네이버웹툰

Shared references inside value types

A webtoon app's Episode struct has an ImageCache property of class type. If you copy the struct and change the cache on one side, what state is shared with the…

#struct #class #value-semantics #reference

How weak works at runtime

Why is it true that "weak is slower than strong"? Explain it with the Swift runtime's reference count layout: the inline refcount and the side table.

#weak #side-table #refcount #runtime

Memory layout

What are MemoryLayout<T>.size, stride, and alignment, and why can the three differ? Use the struct below as your example. …

#memorylayout #size #stride #alignment

Advanced leak hunting

Both the Leaks instrument and Memory Graph are clean, yet every time you go back and forth to a certain screen, memory on a real device grows by 30MB. What cou…

#leak #instruments #malloc-stack #vm-tracker

Ownership modifiers and ~Copyable

Which statement about Swift 5.9's ownership features (borrowing/consuming parameters, ~Copyable types) is correct?

#ownership #borrowing #consuming #noncopyable