The Road To Damascus, or FRP and Me

Presentation I gave at NSSpain 2017 about my thoughts on Functional Reactive Program and whether I should use it.

Transcript

1. The Road to Damascus
   or, FRP and me
   Abizer Nasir | @abizern | abizern.org
   

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2. I like to keep things simple
   • MVC
   • Dependency Injection, protocols, value types
   • Storyboards
   • Core Data
   

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3. Functional Reactive Programming
   • Reactive: Treats data as a flow over time rather than individual
   events. A sequence.
   • Functional: map and filter and reduce can be applied to these
   sequences - the things we like about Swift
   

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4. Choices
   • RxSwift
   • ReactiveCocoa
   • PromiseKit
   • ReSwift
   

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5. Functional Reactive Programming
   (FRP) is not a solution for Massive
   View Controllers.
   

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6. Not a good starting point
   “The RepositoryListViewController is also a delegate and a data
   source for the table view. It handles the navigation, formats model
   data to display and performs network requests. Wow, a lot of
   responsibilities for just one View Controller!”
   

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7. FRP is not just a wrapper around
   KVO
   

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8. FRP “flattens” asynchronous code
   — Me.
   

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9. An Observable is a sequence of
   events.
   

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10. Events only have three states
    public enum Event {
    case next(Element)
    case error(Swift.Error)
    case completed
    }
    

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11. Events are emitted when an Observable is
    subscribed to
    Think of subscribing as repeatedly calling next() an an Iterator.
    

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13. RxMarbles.com
    

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14. RxMarbles.com
    

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15. RxMarbles.com
    

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16. RxMarbles.com
    

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17. RxMarbles.com
    

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18. “Flattens Asynchronous Code”
    By that I mean they are treated as the same thing.
    • A single value injected into a View Controller
    • The text in a Text View
    • The response from a network request.
    

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19. Validate UserName & Password, Classic
    final class ViewController: UIViewController {
    @IBOutlet private var name: UITextField! {
    didSet { name.addTarget(self, action: #selector(validate(_:)), for: .editingChanged) }
    }
    @IBOutlet private var password: UITextField!{
    didSet { password.addTarget(self, action: #selector(validate(_:)), for: .editingChanged)}
    }
    @IBOutlet private var confirm: UIButton!
    @objc private func validate(_ sender: UITextField) {
    let name = self.name.text ?? ""
    let password = self.password.text ?? ""
    confirm.isEnabled = !name.isEmpty && !password.isEmpty
    }
    }
    

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20. Validate UserName & Password, RxSwift
    class LoginViewController: UIViewController {
    @IBOutlet private var name: UITextField!
    @IBOutlet private var password: UITextField!
    @IBOutlet private var confirm: UIButton!
    let disposeBag = DisposeBag()
    override func viewDidLoad() {
    super.viewDidLoad()
    let username = name.rx.text.orEmpty.asObservable()
    let password = password.rx.text.orEmpty.asObservable()
    confirmButtonValid(username: username, password: password)
    .bind(to: confirmButton.rx.isEnabled)
    .disposed(by: disposeBag)
    }
    func confirmButtonValid(username: Observable, password: Observable) -> Observable {
    return Observable.combineLatest(username, password { (username, password) in
    return !username.isEmpty && !password.isEmpty
    }
    }
    }
    

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21. func confirmButtonValid(username: Observable, password: Observable) -> Observable {
    return Observable.combineLatest(username, password { (username, password) in
    return !username.isEmpty && !password.isEmpty
    }
    }
    

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22. Observable can be
    - .next(Bool)
    - .error(Error)
    - .completed
    Looks a lot like Result
    - .success(Bool)
    - .failure(Error)
    

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23. Composition
    searchBar.rx.text
    .orEmpty
    .filter { $0.characters.count > 3 }
    .debounce { 0.5, scheduler: MainScheduler.instance }
    .map { query in
    let url = URLBuilder.urlFor(query)
    return URLRequest(url: url)
    .flatMapLatest{ request in
    return URLSession.shared.rx.json(request: request)
    .catchErrorJustReturn([])
    }
    .map { json -> [Model] in
    guard let items = json as? [[String: Any]] else { return [] }
    return items.flatMap { Model.init }
    }
    .bindTo(tableView.rx.items) { tableView, row, model in
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell")
    cell.configureWith(model)
    return cell
    }
    .disposed(by: disposeBag)
    h/t Marin Todorov @icanzilb
    

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24. The code is in one place. It is
    readable, the order is determined
    and easy to reason about.
    

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25. Magic?
    • Not really. The code is still there.
    • Boilerplate is hidden away
    

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26. It’s a Big DSL
    • RxSwift for FRP
    • RxBindings for working with UI elements
    • RxTest
    

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27. It’s a Large Dependency
    • Active project with many contributors and users.
    • Easily installed with CocoaPods or Carthage, but these are the
    days of Xcode transitions.
    • You don’t have to use it everywhere, but if you’ve added it...
    

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28. Where Am I on the road?
    Well, I’m still on it.
    

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29. RxSwift
    https://store.raywenderlich.com/
    products/rxswift
    

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30. Thank You
    !
    Abizer Nasir | @abizern | abizern.org
    

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