Topic
Core language concepts, ownership, protocols, generics, concurrency, and the details interviewers use to separate memorization from real understanding.
Focus areas: Ownership, protocols, generics, concurrency, and language fundamentals
Explain UserDefaults as a small plist-backed prefs store covering size limits, async disk writes, suiteName vs standard, and why main-thread access is allowed but not free
Walk through Swift Dictionary as a CoW hash table — hashing invariants, collisions, complexity traps, nil removal, ordering, concurrency, and key design for senior interviews
Explain Swift's three method-dispatch mechanisms—static, table (vtable and protocol witness tables), and Objective-C message send—and show when final, value types, and @objc dynamic change which one the compiler uses
Compare Dictionary and NSCache on one concrete example, an image cache for a photo feed, and show where the two diverge on thread safety, automatic eviction, and key and value rules
Demonstrate Copy-on-Write with a value-typed linked list that shares storage on assignment and copies it only when a mutation occurs using isKnownUniquelyReferenced.
Under ARC, strong keeps an object alive, unowned tracks a direct non-owning pointer that must outlive use, and weak goes through a side table so access can become nil after deinit
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
Group design patterns into creational, structural, and behavioral, then explain real iOS examples from SDKs and your own implementation experience with the tradeoffs that matter in production
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
Explain MemoryLayout, padding, alignment, and stride; show why stored-property order changes a struct's footprint; and connect it to arrays, performance, and low-level interop
