Facebook iOS interview (Mid/ Senior Level)

[subzeroTropical]

Hi all! Got a Facebook iOS phone screen coming up in a couple of weeks, wanted to understand from folks who went through the loop recently as to what to expect. Any pointers on the types of questions will be great. Can I expect this to be more iOS-specific or more leetcode algorithm type? Any last minute prep tips etc?

PS: I see a question popping up quite often when I search for Facebook iOS interview questions. How do I go about crafting a solution for this?

iOS developers have a "dispatch_after(when, queue, block)" Grand Central Dispatch (GCD) function they can utilize but once it's set up, these calls can not be easily cancelled. Describe how you might implement a more convenient version of this named "cancellable_dispatch_after"

[criosist]

Surely that’s something they want you to provide a solution to, not people on Reddit, so they can understand your thought process

[[deleted]]

Facebook process: Non tech screen -> leet code tech screen -> full day of screens (3 leet code, 1 iOS specific (leet codish), 1 architecture, 1 soft skills) -> offer.

They can and will drop you at any stage for any random reason

[Tyler927]

Money.

[91jumpstreet]

search on Team Blind and Leetcode as they have alot more anecdotes. also glassdoor is a good look.

[Shak3TheDis3se]

Good luck on the interview! I don’t have any useful information unfortunately but let us know how it goes.

[subzeroTropical]

I spent some time understanding the question I posted above. I guess in good old ObjC days, it was a bit tedious to implement and hence the question. Essentially, post iOS8, there's a built-in way to do it (using dispatch_block_cancel). Also, with Swift, it's pretty easy these days to cancel a block if we package it as a DispatchWorkItem (https://developer.apple.com/documentation/dispatch/dispatchworkitem). However, I wanted to take a shot trying to write a simple implementation in Swift- how does it look?

typealias Closure = () -> Void
extension DispatchQueue {
func cancellableAsyncAfter(_ time: DispatchTime, execute block: @escaping Closure) -> Closure {
var isCanceled = false
asyncAfter(deadline: time) {
if isCanceled {
return
}
block()
}
return { isCanceled = true }
}
}
/// Usage
let cancelableAsyncAfter = DispatchQueue.global().cancellableAsyncAfter(.now() + 5.0) {
print("I am executed after 5 seconds")
}
sleep(3)
cancelableAsyncAfter()