ViewModelType protocol and associatedtype limitations

[IvanKalaica]

Should't PostsViewModel be an protocol and not class? I think keeping protocol oriented view models is better than enforcing generic structure with associatedtype. Input/output transform can always be enforced per viewModel protocol. Thoughts?

[sergdort]

Hi, @IvanKalaica, thanks for the question :)

What benefits do you think we would get from using protocol? The only thing that comes to mind is snapshot and UITests.

Input/output transform can always be enforced per viewModel protocol.

Curious to see an example :)

[IvanKalaica]

I think interface based programming is always a good habit. :)

struct ExampleViewModelInput {
    
}

struct ExampleViewModelOutput {
    let speedInKmh: Observable<Int>
}

protocol ExampleViewModel {
    func transform(input: ExampleViewModelInput) -> ExampleViewModelOutput
}

final class DefaultExampleViewModel: ExampleViewModel {
    private let exampleService: ExampleService
    
    init(exampleService: VehicleService) {
        self.exampleService = exampleService
    }
}

extension DefaultExampleViewModel {
    func transform(input: ExampleViewModelInput) -> ExampleViewModelOutput {    
        return ExampleViewModelOutput(
            speedInKmh: self.exampleService.map { $0.speedInKmh }.distinctUntilChanged()
        )
    }
}

[ttkien]

@IvanKalaica Could you explain more why the below code is good habit?

[hr147]

@sergdort as per Dependency Inversion Principle (DIP) when 2 classes or modules are communicating with each other than both should link to abstraction rather than knowing about concrete module/class, which makes the system loosely coupled.