What problems does diffable data source solve, and what does it not solve?
Show where UIKit snapshot-based updates help and where state modeling still matters
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Difficulty: Intermediate
What collection types are available in Swift, and when would you use each one?
Explain Swift's protocol-driven collection model, then compare Array, Set, Dictionary, and Range by behavior, complexity, hashing, ordering, copy-on-write, and thread-safety tradeoffs
What concurrency problems should you know in Swift?
Distinguish race conditions, data races, priority inversion, deadlock, and actor reentrancy anomalies with short Swift examples and practical fixes
On which thread does Swift call deinit?
Explain that deinit runs where the last strong reference is released, then connect that rule to UI safety, MainActor isolation, and isolated deinit
What is a retain cycle and how do you avoid it?
Define retain cycles in ARC terms, show the most common ways teams create them, and explain how to prevent and debug them in production code
How do you make shared mutable state thread-safe in Swift?
Start with the race condition, then compare locks, semaphores, queues, barriers, and actors for protecting shared mutable state in real Swift code
What is the difference between ObservableObject and @Observable in SwiftUI?
Compare Combine-era observation with the iOS 17 Observation system, focusing on invalidation granularity, boilerplate, and how ownership changes in SwiftUI
How do you decide between @State, @StateObject, @ObservedObject, and @EnvironmentObject?
Map SwiftUI property wrappers to ownership boundaries rather than memorizing them in isolation
How do task groups differ from async let in practical iOS code?
Explain when fixed child tasks make `async let` the better tool, and when dynamic fan-out or incremental result handling pushes you to task groups
What's the difference between frame and bounds in iOS?
Explain how `frame` and `bounds` describe the same view from two different coordinate systems, then connect that model to layout, transforms, and scrolling