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Swift fundamentals
Value vs reference types, optionals, generics, error handling, property wrappers, concurrency basics, capture lists.
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UIKit & views
Auto Layout, view lifecycle, tables/collections, navigation, gestures, accessibility.
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SwiftUI
State, bindings, navigation, lifecycle, performance, interoperability with UIKit.
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Architecture
MVVM, coordinators, dependency injection, feature modules, testing seams.
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Networking
URLSession, Codable, auth, caching, WebSockets, error handling at the edge.
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Concurrency
async/await, actors, tasks, GCD vs structured concurrency, thread safety.
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Memory & performance
ARC, Instruments, image pipelines, launch and scroll performance.
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Data persistence
UserDefaults, Keychain, Core Data, files, sync strategies.
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Testing
XCTest, doubles, UI tests, flaky-test hygiene, CI.
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System design
Feeds, offline mode, modular apps, APIs at scale — interview-scale designs.
Full question lists and explanations: The iOS Interview Handbook.