split Signal/SignalProducer

Signal+split.swift

import ReactiveCocoa
import ReactiveSwift

extension SignalProducer {

    func result() -> SignalProducer<Result<Value, Error>, Never> {
        return map(Swift.Result<Value, Error>.success)
            .flatMapError { SignalProducer<Result<Value, Error>, Never>(value: .failure($0)) }
    }
}

extension Signal {

    func result() -> Signal<Result<Value, Error>, Never> {
        return map(Swift.Result<Value, Error>.success)
            .flatMapError { SignalProducer<Result<Value, Error>, Never>(value: .failure($0)) }
    }

    func split() -> (value: Signal<Value, Never>, error: Signal<Error, Never>) {
        let result = self.result()
        return (
            value: result
                .filter(ResultUtil.isSuccess)
                .map(ResultUtil.valueOrNil)
                .skipNil(),
            error: result
                .filter(ResultUtil.isFailure)
                .map(ResultUtil.errorOrNil)
                .skipNil())
    }
}

private enum ResultUtil {

    static func isSuccess<Value, Error>(_ result: Result<Value, Error>) -> Bool {
        switch result {
        case .success:
            return true
        default:
            return false
        }
    }

    static func isFailure<Value, Error>(_ result: Result<Value, Error>) -> Bool {
        return !isSuccess(result)
    }

    static func valueOrNil<Value, Error>(_ result: Result<Value, Error>)  -> Value? {
        switch result {
        case let .success(value):
            return value
        default:
            return nil
        }
    }

    static func errorOrNil<Value, Error>(_ result: Result<Value, Error>) -> Error? {
        switch result {
        case let .failure(value):
            return value
        default:
            return nil
        }
    }
}