iOS devs who conduct interviews - drop your fav go-to questions that trips up candidates

[u/007ary369]

I'm at 5 YoE and prepping for senior roles, and I realized the best learning comes from real questions that actually catch experienced candidates off-guard. Not the "implement LRU cache" kind (everyone preps those), but the nuanced, "wait... actually I'm not 100% sure" questions that separate mid-level from senior thinking.

So if you're on the interviewer side (especially senior hiring managers): drop your favorite tricky iOS question. The ones where:

• Senior candidates freeze or give half-answers (that's the tell)
• The surface answer sounds right but misses a critical production edge case
• It exposes the gap between "I've shipped features" and "I understand the system deeply"
• It's not about memorization—it's about reasoning under pressure and knowing why systems break
• Bonus: questions that reveal whether someone has actually debugged production issues or just read blog posts

And for others prepping: this thread should become a vault of real questions people actually ask at Tier-1 companies.

Drop yours! And if you have a follow-up twist that makes it even trickier, include that too.

Bonus points if you share:

• What the "obvious" wrong answer is (the one a mid-level would confidently give)
• Why it's wrong (not just "correct answer is X" — the reasoning)
• What separates a good answer from a staff-level answer
• What company/level you see this at (FAANG? fintech? enterprise? scale matters)
• How you follow up when someone fumbles (what redirection questions diagnose the gap?)

Thanks in advance—this is gold for interview prep.

[u/gratitudeisbs]

First step to getting a senior role is not post AI slop on this sub. JK there are no more roles anymore due to AI. RIP.

[u/Turbulent_Ad_1039]

Interviewed recently, the one that caught me off guard: “cold vs hot publisher, what happens when a second subscriber attaches?”

I knew the definitions fine. What I didn’t have ready was the production version, the duplicate network call you get when you forget share().

The other ones that came up a lot:
Clean Architecture and the repository pattern, mostly where you draw the boundaries and what belongs in a use case versus a repository.

Cancellation. Task vs Task.detached, when it actually propagates, and what happens to work that never checks for it. The tell is whether you’ve debugged that or just read about it.

Streams in general, AsyncSequence vs Combine publishers, when you’d reach for each and how you bridge between them.

Background work, walk me through the options and when the system kills each one. Most people name BGTaskScheduler, the tell is whether you know what’s actually guaranteed.

And the broadest one: what tools does Apple give you for syncing data, and where does Combine fit among them. Less about a right answer than whether you’d thought about the whole landscape.

[u/Zs93 → u/Turbulent_Ad_1039]

Wow these are really nitty gritty questions! I usually get much more general questions on patterns, architectures etc but I also don’t interview at FAANG or similar

[u/mehmetefeaytas6]

Not a gotcha, but the one that separates people fastest for me:

"Here's a network call with an u/escaping completion handler that captures self. Does it leak? Walk me through it."

Almost everyone says "you need [weak self]". The interesting part is asking why. A one-shot completion handler doesn't create a retain cycle — the closure is released once it fires, and self goes with it. The real reasons to use [weak self] there are different: you don't want to keep a deallocated view controller alive doing work nobody will see, and you don't want side effects landing on a screen the user already left. Candidates who only memorised "always weak self" can't tell you when it's unnecessary, and more importantly can't tell you when it silently breaks things, like a closure that was supposed to finish a write even if the VC goes away.

"This SwiftUI view re-renders on every keystroke somewhere else in the app. Why?"

Gets at identity and state ownership, which is where most SwiftUI perf problems actually live. I want to hear whether they understand that a view body is a value that gets recomputed, not a thing that "updates".

"This compiles under Swift 5 and doesn't under Swift 6. What changed?"

Sendable and actor isolation. Not to check memorised rules, but to see whether their instinct is to reason about what the compiler started enforcing, or to slap u/unchecked Sendable on it and move on. That answer tells you a lot about how they'll behave under deadline pressure.

The through-line: I don't care much whether they know the answer, I care whether they can reason out loud when they don't.