add extension for result Type to access value and error

Result Extention

extension Result {
    
    var value: Success? {
        guard case .success(let value) = self else { return nil }
        return value
    }
    
    /// Returns the associated error value if the result is a failure, `nil` otherwise.
    var error: Failure? {
        guard case .failure(let error) = self else { return nil }
        return error
    }
    
    ///     let possibleData: Result<Data> = .success(Data(...))
    ///     let possibleObject = possibleData.flatMap {
    ///         try JSONSerialization.jsonObject(with: $0)
    ///     }
    ///
    /// - parameter transform: A closure that takes the success value of the instance.
    ///
    /// - returns: An `AFResult` containing the result of the given closure. If this instance is a failure, returns the
    ///            same failure.
    func flatMap<T>(_ transform: (Success) throws -> T) -> Result<T,Error> {
        switch self {
        case .success(let value):
            do {
                return try .success(transform(value))
            } catch {
                return .failure(error)
            }
        case .failure(let error):
            return .failure(error)
        }
    }
}