final class HelloWorldViewModel: ViewModelType {
  let input: Input
  let output: Output

  struct Input {
    let name: Anyobserver<String>
  }

  struct Output {
    let greeting: Driver<String>
  }

  private let nameSubject = ReplaySubject<String>.create(bufferSize: 1)

  init() {
    let greeting = nameSubject
    	.map { name in
              return "Hello \(name)"
        }
    	.asDriver(onErrorJustReturn: "Hello Doe")

    self.output = Output(greeting: greeting)
    self.input = Input(nameSubject.asObserver())
  }
}