How to map RxSwift Observable and Result

Question

I have a quick question:

• I have a network request that returns Observable<Result<String, RequestError>>, let’s call it requestToken
• if this request succeeds, I want to use the String (token) to do another request that returns Observable<Result<NSDictionary, RequestError>>, let’s call it requestData
• when that second request comes back, I wanna merge the token into its dictionary
• in the end I wanna map from Observable<Result<String, RequestError>> to Observable<Result<NSDictionary, RequestError>>

How can I achieve that without multiple nested levels in my code?

This is what I have today:

requestToken()
    .flatMap({ result -> Observable<Result<NSDictionary, RequestError>> in
        switch result {
        case .success(let token):
            return requestData(token: token).map({ $0.map({ $0 + ["token": token] }) })
        case .failure(let error):
            return Observable.of(.failure(error))
        }
    })

Answer 1

Updated:

It's a detailed example, hope this may help:

enum RequestError: Error {
    case unknown
}

func requestToken() -> Observable<String> {

    return Observable.create { observer in

        let success = true

        if success {
            observer.onNext("MyTokenValue")
            observer.onCompleted()
        } else {
            observer.onError(RequestError.unknown)
        }

        return Disposables.create()
    }
}

func requestData(token: String) -> Observable<[String: Any]> {

    return Observable<[String: Any]>.create { observer in

        let success = false

        if success {
            observer.onNext(["uid": 007])
            observer.onCompleted()
        } else {
            observer.onError(RequestError.unknown)
        }

        return Disposables.create()
    }
    .map { (data: [String: Any]) in
        var newData = data
        newData["token"] = token
        return newData
    }
}


requestToken()                      // () -> Observable<String>
    .flatMapLatest(requestData)     // Observable<String> -> Observable<[String: Any]>
    .materialize()                  // Observable<[String: Any]> -> Observable<Event<[String: Any]>>
    .subscribe(onNext: { event in
        switch event {
        case .next(let dictionary):
            print("onNext:", dictionary)
        case .error(let error as RequestError):
            print("onRequestError:", error)
        case .error(let error):
            print("onOtherError:", error)
        case .completed:
            print("onCompleted")
        }
    })
    .disposed(by: disposeBag)

Original:

I think it's much easier to achieve it using materialize() with less extra work:

func requestToken() -> Observable<String> { return .empty() }
func requestData(token: String) -> Observable<NSDictionary> { return .empty() }
enum RequestError: Error {}

requestToken()
    .flatMapLatest(requestData)
    .materialize()
    .subscribe(onNext: { event in
        switch event {
        case .next(let dictionary):
            print("onNext:", dictionary)
        case .error(let error as RequestError):
            print("onRequestError:", error)
        case .error(let error):
            print("onOtherError:", error)
        case .completed:
            print("onCompleted")
        }
    })
    .disposed(by: disposeBag)

Hope this may help.