This sounds like a warm-up but it sprawls fast.
Start by defining the core semantic difference: classes are reference types and structs are value types, then systematically cover memory, mutability, inheritance, and deinitialization. Conclude by explaining when to choose each, tying your answer to performance, safety, and real-world scenarios like Snapchat's high-scale systems.
Pro tip: Emphasize that Swift's standard library uses structs for most types (Array, String, Dictionary) to leverage copy-on-write and value semantics, which reduces bugs and improves thread safety—showing you understand Apple's design philosophy and can apply it to scalable systems.
State that classes are reference types (instances share a single memory location) while structs are value types (each instance gets its own copy). This distinction drives all other differences.
Explain that classes are allocated on the heap and managed via ARC, while structs are typically stack-allocated (or inlined) and copied on assignment. For mutability, struct methods that modify properties must be marked 'mutating', whereas class methods can modify properties freely.
Highlight that classes support inheritance (single inheritance) and deinitializers, allowing hierarchical modeling and resource cleanup. Structs cannot inherit or have deinitializers, promoting composition over inheritance.
Use structs by default for simple data models, thread safety, and value semantics; use classes when you need identity, shared mutable state, inheritance, or Objective-C interoperability. Mention SwiftUI's preference for structs and performance considerations.
Connect the choice to system design: structs reduce bugs from unintended sharing and improve performance via stack allocation and copy-on-write; classes enable shared state and polymorphism but require careful memory management.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.