RxSwift subject to provide public triggering but private subscription

Driver+Create.swift

extension Driver {
    /// Create separate input/output access to the same underlying subject
    ///
    /// This allows the subject to be hidden and enforce singular access to input/output
    /// as well as only exposing input _or_ output if needed.
    ///
    /// - Parameters:
    ///   - default: The default value to emit in the case of any errors
    ///   - value: The value to start with
    public static func create(withDefault default: E? = nil, startingWith value: E) -> (input: AnyObserver<E>, output: Driver<E>) {
        let (input, output) = create(withDefault: `default`)
        return (input, output.startWith(value))
    }
    
    /// Create separate input/output access to the same underlying subject
    ///
    /// This allows the subject to be hidden and enforce singular access to input/output
    /// as well as only exposing input _or_ output if needed.
    ///
    /// - Parameter default: The default value to emit in the case of any errors
    public static func create(withDefault default: E? = nil) -> (input: AnyObserver<E>, output: Driver<E>) {
        let instance = PublishSubject<E>()
        return (
            AnyObserver(instance),
            instance.asDriver(onErrorDriveWith: `default`.map(Driver.just) ?? .never())
        )
    }
}

Example.swift

class API {
    func obtainIds() -> Observable<[Int]> {
        return .just([1,2,3,4])
    }
}

class ViewModel {
    let update: AnyObserver<Void>
    let dataUpdated: Driver<[String]>

    init(api: API) {
        //
        // here is where we create the input/output
        let update = Driver<Void>.create()
        //
        //

        self.update = update.input
        self.dataUpdated = update.output
            .flatMap {
                return api
                    .obtainIds()
                    .asDriver(onErrorJustReturn: [])
            }
            .map { $0.flatMap(String.init) }
    }
}

// in your view controllers data binding..
let viewModel = ViewModel(api: API())
// perhaps bind to a tableview
viewModel.dataUpdated.drive { e in
    print(e)
}
// button triggers the input
someButton.rx.tap.bind(to: viewModel.update)