Result.md

Result

How to fire success or failure

completion(Swift.Result.success(()))
completion(Swift.Result.failure(error))

How they work

An enum representing success or failure in an operation. If success return the success. If failure return the failure.

/// A value that represents either a success or a failure, including an
/// associated value in each case.
public enum Result<Success, Failure> where Failure : Error {

    /// A success, storing a `Success` value.
    case success(Success)

    /// A failure, storing a `Failure` value.
    case failure(Failure)

Example

class GameService {
    func fetchGames(completion: @escaping ((Result<[Game], Error>) -> Void)) {

        // Success
        let games = [Game(name: "Space Invaders")]
        completion(Result.success(games))

       // Error
       completion(Result.failure(ActivationError.coreData))
    }
}

And then when you call you pull the payload or error from the result like this by defining lets

GameService().fetchGames { [weak self] result in
    switch result {
    case .success(let games):
        self?.games = games
        self?.tableView.reloadData()
    case .failure(let error):
        print(error.localizedDescription)
    }
}

How to return a Void Success Result

    public func activate(completion: @escaping (Result<Void, Error>) -> Void) {
        completion(Swift.Result.success(()))
    }

"Void" doesn't mean "returns nothing." It's a type in Swift, a type that has exactly one value: the empty tuple (). That also happens to be the type:

public typealias Void = ()

As a matter of convention, we use Void to mean the type, and () to mean the value. The one thing that's a bit strange about using Void this way in a Result is the syntax. You wind up with something like:

return .success(())

How to inline an error

guard error == nil else {
    enum ForcedActivationError: Error { case failure }
    completion(Swift.Result.failure(ForcedActivationError.failure))
    return
}

Links that help

• Void Success Result
• Paul Hudson Result example