// First register your cell
tableView.register(cellClass: PersonCell.self)

// Then dequeue with a type-safe function
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let person = people[indexPath.item]

    if person.role == "Engineer" {
        let cell = tableView.dequeueReusableCell(ofType: PersonCell.self, for: indexPath)
        cell.textLabel?.text = person.name
        cell.detailTextLabel?.text = person.role
        return cell
    } else {
        let cell = tableView.dequeueReusableCell(with: "SubtitleCell", for: indexPath) as UITableViewCell
        cell.textLabel?.text = person.name
        cell.detailTextLabel?.text = person.role
        return cell
    }
}