Value Types vs. Reference Types
The primary difference lies in how they are stored in memory. A Struct is a Value Type: when you assign it to a new variable, the entire data is copied. A Class is a Reference Type: when you assign it, you are just creating a new pointer to the same instance in memory. As an Engineering Manager, you should enforce 'Structs by default' to avoid the 'hidden state' bugs common in shared-reference architectures.
- Structs: The Lightweight Choice
Structs are stored on the Stack, making them incredibly fast. They are ideal for data models, UI state, and small pieces of information. One major benefit is the Memberwise Initializer—Swift automatically creates a constructor for all properties, saving you from writing boilerplate code.
- Classes: The Shared Source of Truth
Classes are stored on the Heap. Use them when you need Identity (referring to the same single object from multiple places) or Inheritance. In your iOS Runner, Classes are typical for Service layers, Database managers, or ViewControllers.
- Comparison Table for Architects
| Feature | Struct (Value Type) | Class (Reference Type) |
|---|---|---|
| Storage | Stack (Fast) | Heap (Slower) |
| Assignment | Deep Copy | Shared Reference |
| Inheritance | No | Yes |
| Mutability | Controlled by 'let' or 'var' | Can modify even if constant |
| Deinitializers | No | Yes (deinit method) |
| Use Case | Data models, UI State | Services, Managers, UI Controllers |
- Identity vs. Equality
With Structs, we care about Equality (is the data the same?). With Classes, we care about Identity (is this the exact same object?). In Swift, you use == to check if values are equal and === to check if two references point to the same class instance.