How can I convert "SignalProducer<Bool, NoError>" to "SignalProducer<Bool, NSError>" of ReactiveCocoa 3?

Question

I tried creating an instance of Action<AnyObject?, Bool, NSError> of ReactiveCocoa 3.

let action: Action<AnyObject?, Bool, NSError> = Action { _ in
    if self.flag {
        return self.fooSignalProducer  // SignalProducer<Bool, NoError>
    } else {
        return self.barSignalProducer  // SignalProducer<Bool, NSError>
    }
}

This code isn't able to compile with error 'SignalProducer<Bool, NoError>' is not convertible to 'SignalProducer<Bool, NSError>'.

How can I convert SignalProducer<Bool, NoError> to SignalProducer<Bool, NSError>?

Answer 1

You can use the mapError operator. Something along the lines of:

self.fooSignalProducer |> mapError { _ in NSError() }

Edit:

As Justin points out below, promoteErrors is specifically designed for this case:

self.fooSignalProducer |> promoteErrors(NSError)