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I need some opinions on Rx and MVVM. Its being done in iOS, but I think its fairly general programming question.

The small team I joined is using Rx (I've never used it before) and I'm trying to learn and catch up to them. Looking at the code, I think there are thousands of lines of over-engineered code that could be done so much simpler. From a non Rx point of view, I think we are following some bad practises, from an Rx point of view the guys are saying this is what Rx needs to be. I'm trying to discuss this with them, but they are shooting me down saying I just don't know enough about Rx. Maybe thats true, maybe I just don't get it, but they aren't exactly explaining it, just telling me i'm wrong and they are right. I need another set of eyes on this to see if it is just me.

One of the main points is that there are many places where network errors shouldn't complete the observable (i.e. can't call onError), I understand this concept. I read a response from the RxSwift maintainers that said the way to handle this was to wrap your response type in a class with a generic type (e.g. Result<T>) that contained a property to denote a success or error and maybe an error message. This way errors (such as incorrect password) won't cause it to complete, everything goes through onNext and users can retry / go again, makes sense.

The guys are saying that this breaks Rx principals and MVVM. Instead we need separate observables for every type of response. So we have viewModels that contain:

- isSuccessObservable
- isErrorObservable
- isLoadingObservable
- isRefreshingObservable
- etc. (some have close to 10 different observables)

To me this is overkill to have so many streams all frequently only ever delivering 1 or none messages. I would have aimed for 1 observable, that returns an object holding properties for each of these things, and sending several messages. Is that not what streams are suppose to do? Then the local code can use filters as part of the subscriptions. The major benefit of having 1 is that it becomes easier to make it generic and abstract away, which brings us to point 2.

Currently, due to each viewModel having different numbers of observables and methods of different names (but effectively doing the same thing) the guys create a new custom protocol (equivalent of a java interface) for each viewModel with its N observables. The viewModel creates local variables of PublishSubject, BehavorSubject, Driver etc. Then it implements the procotol / interface and casts all the local's back as observables. e.g.

protocol CarViewModelType {
isSuccessObservable: Observable<Car>
isErrorObservable: Observable<String>
isLoadingObservable: Observable<Void>
}

class CarViewModel {
isSuccessSubject: PublishSubject<Car>
isErrorSubject: PublishSubject<String>
isLoadingSubject: PublishSubject<Void>

// other stuff
}

extension CarViewModel: CarViewModelType {
isSuccessObservable {
return isSuccessSubject.asObservable()
}
isErrorObservable {
return isSuccessSubject.asObservable()
}
isLoadingObservable {
return isSuccessSubject.asObservable()
}
}

This has to be created by hand, for every viewModel, of which there is one for every screen and there is 40+ screens. This same structure is copy / pasted into every viewModel. As mentioned above I would like to make this all generic. Have a generic protocol for all viewModels to define 1 Observable, 1 local variable of generic type and handle the cast back automatically. The method to trigger all the business logic could also have its name standardised ("load", "fetch", "processData" etc.). Maybe we could also figure out a few other bits too. This would remove a lot of code, as well as making the code more readable (less messy), and make unit testing much easier. While it could never do everything automatically we could test the basic responses of each viewModel and have at least some testing done by default and not have everything be very boilerplate-y and copy / paste nature.

The guys think that subscribing to isSuccess and / or isError is perfect Rx + MVVM. But for some reason subscribing to status.filter(success) or status.filter(!success) is a sin of unimaginable proportions. Also the idea of multiple buttons and events all "reacting" to the same method named e.g. "load", is bad Rx (why if they all need to do the same thing?)

My thoughts on this are:

- To me its indentical in meaning and architecture, one way is just significantly less code.
- Lets say I agree its not textbook, is it not worth bending the rules to reduce code.
- We are already breaking the rules of MVVM to introduce coordinators (which I hate, as they are adding even more unnecessary code), so why is breaking it to reduce code such a no no.

Any thoughts on the above? Am I way off the mark or is this classic Rx?