Explain the primary differences between a struct and a class in Swift

Tests whether you understand value versus reference semantics and how that shapes memory layout, mutation behavior, and architectural choices. A strong answer covers four things in order: first, structs copy on assignment while classes share a single heap instance; second, structs lack inheritance and deinit; third, classes incur ARC overhead and retain cycles; fourth, copy-on-write enables efficient large struct mutation. Red flag: claiming structs are always on the stack, that classes are faster, or that value types cannot leak.