In which case should models be declared as classes and in which as structs in MVVM?

In iOS, when using the MVVM architecture, the choice between classes and structures for models depends on the requirements for behavior and memory management.

• Structures (struct) are value types, copied when passed. They are suitable for simple, immutable data models where avoiding side effects and ensuring thread safety are important. For example, models representing static data or DTOs.

• Classes (class) are reference types, passed by reference. They are used when the model needs to have mutable state, support inheritance, or when multiple parts of the application need to work with the same instance of the model.

In MVVM, models are usually declared as structures if they are simple and do not require complex state-changing logic. If the model contains business logic, observable properties, or needs to be shared state, it is better to use classes.

Example:

struct UserModel {
    let id: Int
    let name: String
}

class UserViewModel: ObservableObject {
    @Published var user: UserModel
    // business logic and data updates
}