[Swift] Struct vs Class

Every interview I go… I see this question…

What is Struct and Class

• They are essential building blocks of program’s code
• In Swift, no need to create separate interface and implementation files for them

Common features of Struct and Class

• Container that can store multiple variables
• Using properties and methods to have structured data
• Initializers to set up initial state
• Can be extended to expand functionality
• Conform to protocols to provide standard functionality
• Access to property using subscript

Difference between Struct vs Class

Struct

• Value type
• Allocated in stack memory
• No inheritance
• Using Codable protocol, JSON ← → Struct conversion is easy
• Always copied to new variable, every thread gets its own copy, therefore in multi-thread environment, lesser problem

Class

• Reference type
• Allocated in heap memory (require reference counting to dealloc)
• Inheritance
• Type Casting in runtime
• deinitializer

Which to use?

• Struct if no need for inheritance and model size is not too big
• 1:1 mapping to JSON, Struct
• Transfer model or save to file with serialization, Class
• Model is also used in Obj-C, Class

Reference

• https://stackoverflow.com/questions/41350772/if-arrays-are-value-types-and-therefore-get-copied-then-how-are-they-not-thread