HackerNewsAPI.sharedApi.newStories()            .observeOn(ConcurrentDispatchQueueScheduler.init(globalConcurrentQueueQOS: .Background))            .map { $0.dropLast($0.count - 15).map { HackerNewsAPI.sharedApi.item($0) } }            .map { $0.zip({ $0 }) }            .switchLatest()            .map { $0.map { ItemViewModel(item: $0) } }            .observeOn(MainScheduler.instance)            .doOnNext { [unowned self] _ in                self.endUpdateTableView()            }            .doOnError { [unowned self] _ in                self.endUpdateTableView()            }            .bindTo(tableView.rx_itemsWithCellIdentifier("ItemTableViewCell", cellType: ItemTableViewCell.self)) { (row, item, cell) in                cell.viewModel = item            }.addDisposableTo(disposeBag)