1. Why the Dark Side
should use Swift and
a SOLID Architecture
Jorge D. Ortiz-Fuentes
@jdortiz
#SwiftDarkSide

2. A Canonical
Examples
production
#SwiftDarkSide

3. #SwiftDarkSide
Agenda
The Weaknesses of the Dark Side
SOLID Architecture
Design patterns

4. Weaknesses
of the Dark
Side

5. Conspiracy Theory

6. Agility and the MVP

7. Moving a Planet

8. SPoF

9. Whose blame is
that?

10. Framework
dependency

11. Teams can hardly
work together

12. Do you see
any
problems?

13. #SwiftDarkSide
Needs to Address
Fast growth
Robustness
• testable
• decoupled
• debuggable
(blame)
Team collaboration
Reusable
Defer decisions
Replaceable
frameworks

14. There is a way:
SOLID Principles

15. AKA
Clean
Architecture

16. I find your lack of
faith disturbing

17. SOLID
Architecture

18. Clean Architecture
AppDelegate
View (VC) Presenter Interactor Entity Gateway
Connector

19. #SwiftDarkSide
Single Responsibility
MVC is not enough
More classes, but more cohesive: only one
reason to change

20. #SwiftDarkSide
Business Logic
import Foundation
class ShowAllSpeakersInteractor {
// MARK: - Properties
let entityGateway: EntityGatewayFetchSpeakersProtocol
weak var presenter: SpeakersListPresenterProtocol?
// MARK: - Initializers
init(entityGateway: EntityGatewayFetchSpeakersProtocol) {
self.entityGateway = entityGateway
}
}
extension ShowAllSpeakersInteractor: InteractorCommandProtocol {
func execute() {
let entities = entityGateway.fetchAllSpeakers()
let displayData = entities.map({entity in
return SpeakerDisplayData(speaker: entity)})
presenter?.presentAllSpeakers(displayData)
}
}

21. #SwiftDarkSide
Open Close
Open to Extension, Closed to Modification

22. #SwiftDarkSide
class SpeakersTableViewController:
UITableViewController, SegueHandlerTypeProtocol {
static let speakerCellIdentifier = "SpeakerCell"
var eventHandler:
SpeakersListEventHandlerProtocol?
var numberOfRows = 0
override func viewDidLoad() {
super.viewDidLoad()
eventHandler?.viewDidLoad()
}
override func tableView(tableView: UITableView,
numberOfRowsInSection section: Int) -> Int {
return numberOfRows
}
override func tableView(tableView: UITableView,
cellForRowAtIndexPath indexPath: NSIndexPath) ->
UITableViewCell {
let cell =
tableView.dequeueReusableCellWithIdentifier(SpeakersTa
bleViewController.speakerCellIdentifier, forIndexPath:
indexPath) as! SpeakerTableViewCell
eventHandler?.presentCell(cell, indexPath:
indexPath)
return cell
}
}
extension SpeakersTableViewController:
SpeakersListViewProtocol {
func
configureListWithNumberOfRows(numberOfRows
: Int) {
self.numberOfRows = numberOfRows
}
func addRowsAtIndexPaths(indexPaths:
[NSIndexPath]) {
self.tableView.insertRowsAtIndexPaths(inde
xPaths, withRowAnimation:
UITableViewRowAnimation.Automatic)
}
}
Passive View

23. #SwiftDarkSide
Liskov Substitution
It should be possible to use derived classes
without special care

24. #SwiftDarkSide
extension SpeakersListsPresenter:
SpeakersListEventHandlerProtocol {
func viewDidLoad() {
interactor.execute()
}
func presentCell(cell:
SpeakerCellProtocol, indexPath:
NSIndexPath) {
let index = indexPath.row
guard index < speakers.count else {
return }
let speaker = speakers[index]
cell.displayName(speaker.name)
cell.displayTitle(speaker.title)
cell.displayDateSubmitted(relativeDateStrin
gFromDate(speaker.dateSubmitted))
}
}
Presentation
class SpeakersListsPresenter {
weak var view: SpeakersListViewProtocol?
let interactor: ShowAllSpeakersInteractor
private var speakers: [SpeakerDisplayData]=[]
// MARK: - Initializer
init(interactor: ShowAllSpeakersInteractor,
deleteInteractor: DeleteSpeakerInteractorProtocol) {
self.interactor = interactor
}
}
extension SpeakersListsPresenter:
SpeakersListPresenterProtocol {
func presentAllSpeakers(speakers:
[SpeakerDisplayData]) {
view?.configureListWithNumberOfRows(speakers.count)
self.speakers = speakers
let addedIndexPaths = speakers.enumerate()
.map({(index, _) in return
NSIndexPath(forRow: index, inSection: 0)})
view?.addRowsAtIndexPaths(addedIndexPaths)
}
}

25. #SwiftDarkSide
Interface Segregation
Don’t force a class to depend on methods
that it won’t use
One interactor will not likely use every
functionality of the entity gateway

26. #SwiftDarkSide
class InMemorySpeakersRepo {
// MARK: - Properties
var speakers: [Speaker] = []
init() {
}
}
extension InMemorySpeakersRepo: EntityGatewayFetchSpeakersProtocol {
func fetchAllSpeakers() -> [Speaker] {
return speakers
}
}
extension InMemorySpeakersRepo: EntityGatewayCreateSpeakerProtocol {
func createSpeaker(name name: String, title: String, synopsis: String, dateSubmitted: NSDate) {
let id = IdentityGenerator.newUUID()
speakers.append(Speaker(id: id, name: name, title: title, synopsis: synopsis, dateSubmitted:
dateSubmitted))
}
}
extension InMemorySpeakersRepo: EntityGatewayDeleteSpeakerProtocol {
func deleteSpeaker(id: String) {
speakers = speakers.filter { speaker in speaker.id != id }
}
}
Different Functions of the
Entity Gateway

27. #SwiftDarkSide
Dependency Inversion
The business case SHOULDN’T depend on
the frameworks

28. #SwiftDarkSide
Deletion Use Case
class DeleteSpeakerInteractor {
let entityGateway: EntityGatewayDeleteSpeakerProtocol
var id: String?
init(entityGateway: EntityGatewayDeleteSpeakerProtocol) {
self.entityGateway = entityGateway
}
}
extension DeleteSpeakerInteractor : InteractorCommandProtocol {
func execute() {
guard let id = self.id else { return }
entityGateway.deleteSpeaker(id)
}
}

29. Design
Patterns

30. Take me Outta Here
func presentCell(cell: SpeakerCellProtocol, indexPath:
NSIndexPath) {
let index = indexPath.row
guard index < speakers.count else { return }
let speaker = speakers[index]
cell.displayName(speaker.name)
cell.displayTitle(speaker.title)
cell.displayDateSubmitted(relativeDateStringFromDate(s
peaker.dateSubmitted))
}
Know
That!

31. var control = Houston(fuel: 1.0,
astronaut: nil, spaceshipOK: true)
do {
try control.launchSpaceship()
} catch Houston.LaunchError.NoFuel {
// Add Fuel
print("Adding fuel")
} catch
Houston.LaunchError.NoAstronaut {
print("Next in line")
} catch
Houston.LaunchError.BrokenShip(let
problem) {
print(problem)
} catch let unknowError {
//
}
Ready for Life
class Houston {
let fuel: Double
let astronaut: String
let spaceshipOK: Bool
init (fuel: Double, astronaut: String?,
spaceshipOK: Bool) {
self.fuel = fuel
self.astronaut = astronaut ?? ""
self.spaceshipOK = spaceshipOK
}
enum LaunchError: ErrorType {
case NoFuel, NoAstronaut, BrokenShip(String)
}
func launchSpaceship() throws {
guard fuel >= 1.0 else { throw
LaunchError.NoFuel }
guard astronaut != "" else { throw
LaunchError.NoAstronaut }
guard spaceshipOK else { throw
LaunchError.BrokenShip("Engine") }
print("Launching spaceship")
}
}
Know
That!

32. class Text {
func displayContents() {
print("Hola")
}
}
class NullText: Text {
override func displayContents() {
print(“Not much here")
}
}
func fetchText() -> Text {
return NullText()
}
let text = fetchText()
text.displayContents()
Null Object
class Text {
func displayContents() {
print("Hola")
}
}
func fetchText() -> Text? {
return nil
}
if let text = fetchText() {
text.displayContents()
}

33. Poor Template
class PoorTrooper {
func getIntoSpaceShip() { print("Commencing countdown engines on") }
func conquer(target: String) {
fatalError()
}
func comeBack() { print("Planet earth is blue") }
func attack(target: String) {
getIntoSpaceShip()
conquer(target)
comeBack()
}
}
let cloneTrooper = PoorTrooper()
cloneTrooper.attack("Alderaan")

34. Swifty Template
protocol Trooper {
func getIntoSpaceShip()
func conquer(target: String)
func comeBack()
func attack(target: String)
}
extension Trooper {
func getIntoSpaceShip() { print("Commencing countdown engines on") }
func comeBack() { print("Planet earth is blue") }
func attack(target: String) {
getIntoSpaceShip()
conquer(target)
comeBack()
}
}
class StormTrooper: Trooper {
func conquer(target: String) { print("Become part of the Empire, (target)") }
}
let finn = StormTrooper()
finn.attack("Tatooine")

35. Next Steps

36. #SwiftDarkSide
Recommendations
Pay attention to your architecture; It
always pays off
Use Principles to take decisions
Take advantage of the language and adapt
the patterns to it
In case of doubt, ask for an architecture
loan and ship it

37. canonicalexamples.com
coupon:
APPSTERDAMERS16

38. Thank
you!

39. @jdortiz
#SwiftDarkSide