returning no effect in an effect mapping

[yspreen]

we have this pattern where we frequently create a Effect<Result<Response, Error>, Never> inside our reducers, which is then getting mapped to a new action. but some of those results don't result in new actions. this leads to the following code:

case .someAction:
        return environment.dataClient.apiCall().map { result in
            if result.someCondition {
              return .newAction
            }
            return .none
        }

we can't just return nil because that's an invalid mapping. this means we have to add a none case to all of our action enums. is there a better way for that? like a conditional fire and forget or something?

[importRyan]

Undoubtedly there are other practices, but our pattern is to have an apiCallFinished action that accepts the Result<Response, Error> to limit the scope of responsibilities. The reaction to someCondition is handled in that action.

    return environment.dataClient
      .apiCall()
      .receive(on: environment.mainQueue)
      .catchToEffect(Action.apiCallFinished)
      .cancellable(id: APICallId(), cancelInFlight: true)

  case let .apiCallFinished(.success(response)):
    // if some condition
    return .none

  case let . apiCallFinished(.failure(error)):
    // handle error
    return .none

[stephencelis]

we can't just return nil because that's an invalid mapping.

Instead of map, you can use Combine's compactMap, which lets you filter out nil outputs in the closure. Just make sure you call .eraseToEffect() on the publisher it returns to get things back in an Effect.

[yspreen]

genius!

[lukeredpath]

I’d recommend the approach in the post of above and handle this logic in your reducer, but you can also use flatMap and conditionally return an Effect(value:) or Effect.none.