How do you return a Publisher error?

Question

Gargoyle OP

Created Jul ’19

Replies 2

Boosts 1

Views 5.9k

Participants 3

I'm trying to wrap my head around Combine still, and so in my class that handles web requests I've written this method:

static func downloadNumbersPublisher(datesByType: [LottoType: (start: Date, end: Date)]) -> URLSession.DataTaskPublisher {
    guard let url = downloadUrl(using: datesByType) else { return }

    var request = URLRequest(url: url)
    request.addValue("gzip", forHTTPHeaderField: "Accept-Encoding")

    let session = URLSession(configuration: .ephemeral)
    return session.dataTaskPublisher(for: request)
}

What I'm not clear on though is what I actually return on line 2, the guard statement.

Boost

Answer 1

Claude31 OP

Jul ’19

what you return on line 2 is in case you fail.

I would try either:

- make the func failable, so it would return nil

- or create an instance of the correct type

Note: I do not find in reference the DataTaskPublisher for URLSession (URLSession.DataTaskPublisher)

I just find

func dataTask(with url: URL) -> URLSessionDataTask

0

Answer 2

sofapps OP

Oct ’21

Something like that, should work for your specific need.

func fetchFeeds() -> AnyPublisher<Any, Error> {
    guard let feedsURL = feedsURL else {
        return Fail(error: NSError(domain: "Missing Feed URL", code: -10001, userInfo: nil)).eraseToAnyPublisher()
    }

    ...
}

3