assignResult.swift

public extension Publisher {
    /// Assigns each element from a Publisher to a property on an object.
    ///
    /// - Parameters:
    ///   - keyPath: The key path of the property to assign.
    ///   - object: The object on which to assign the value.
    /// - Returns: A cancellable instance; used when you end assignment of the received value. Deallocation of the result will tear down the subscription stream.
    func assignResult<Root>(to keyPath: ReferenceWritableKeyPath<Root, Result<Self.Output, Self.Failure>>,
                            on object: Root) -> AnyCancellable {
        sink(receiveCompletion: { completion in
            switch completion {
            case .finished:
                break
            case .failure(let error):
                object[keyPath: keyPath] = .failure(error)
            }
        }, receiveValue: { value in
            object[keyPath: keyPath] = .success(value)
        })
    }
    func unpackResult<ResultSuccess, ResultFailure: Error>() -> AnyPublisher<ResultSuccess, ResultFailure>
        where Output == Result<ResultSuccess, ResultFailure>, Failure == Never {
        tryMap {
            switch $0 {
            case .success(let value):
                return value
            case .failure(let error):
                throw error
            }
        }
            .mapError { error in
                return error as! ResultFailure
            }
            .eraseToAnyPublisher()
    }
}