repository
    .observe()
    .observeOn(ConcurrentDispatchQueueScheduler(qos: .background))
    .subscribeOn(MainScheduler.instance)
    .subscribe(onNext: { (dataState: DataState<[Repo]>) in
        switch dataState.state() {
        case .noCache(let fetching, let errorDuringFetch):
            // Repos have never been fetched before for the GitHub user.
            break
        case .cache(let cache, let lastFetched, let firstCache, let fetching, let successfulFetch, let errorDuringFetch):
            // Repos have been fetched before for the GitHub user.
            // If `cache` is nil, the cache is empty.
            break
        }
                
        switch dataState.fetchingState() {
        case .fetching(let fetching, let noCache, let errorDuringFetch, let successfulFetch):
            // A new cache could be fetching, just completed fetching, or is not fetching at all.
            break
        }
    })