This talk will learn you how to develop clean, maintainable and stable applications in Swift. It will also look at some examples of how I applied these methods in my work.

1. Writing idealistic apps
by Joannis Orlandos

2. This presentation
» My background
» Definition of idealistic
» My recent journey
» Problems encountered
» The results
» Clean programming tips

3. My background
»
!
MongoKitten
»
"
Server Side Swift library developer
»
#
Vapor 3 core developers
»
$
iOS developer at FlexAppeal

4. MongoKitten
» MongoDB driver fully written in
Swift
» NOT a wrapper, no (Obj-)C
» Extremely performant

5. Vapor 3
!
» Extremely performant (async) web framework
» Huge focus on API design
» Large ecosystem
» Templating
» SQL drivers
» Protocol based dependency injection

6. iOS at FlexAppeal
» Employee engagement platform
» Retail, hotels and restaurants
» Striving for high quality

7. Idealistic

8. “A conception of
something in its
absolute
perfection”

9. “One that is
regarded as a
standard or model
of perfection or
excellence”

10. “An ultimate object
of endeavor; a goal”

11. How do I define perfection?
» Low maintenance
» Doesn't fight productivity
» Crash/bug free
» Quick startup time

12. The journey at Flex-Appeal

13. » A huge amount of experience in Swift on the Server
» Very familiar with front-end web development
» Fast learner
But...
» Overwhelming backlog
» Extremely troublesome code
» First time writing a real iOS app
» A severe lack of time and deadlines from the start

14. Almost unachievable

15. At least I can do my best
..to get close to perfection

16. Set up rules for my code
» Only allow interactions from parent to child
» Keep your children isolated from parents
» Responsibility must fit in a single sentence
» Keep state in one place only
» Forbid copying code at all times
» When there's code smell, always identify why
» Don't be afraid to remove code

17. The development process
1. Identify and layout visual hierarchy (from design)
2. Layout the view in objectively correct classes
3. Lay relations between times from parent to child
4. Identify and solve problems by abiding to the rules

18. I rewrote the our timeline
» Reduced code from 8066 to 3197 lines of code
» Added 3 new features
» Resolved ~10 bugs
» 1 week development time
» All newly introduced bugs were fixed in 5 minutes

19. Problems encountered
Due to my architecture

20. Problem: Relaying actions back up
class Timeline {
let cards: [TimelineCard]
}
class TimelineCard {
let header: TimelineCardHeader
...
}
class TimelineCardHeader {
// Only visible to the post's owner
let button: RemoveCardButton
}

21. Solution: Share a common child
class TimelineCard {
let removed: Future<Void>
let header: TimelineCardHeader
init() {
let removePromise = Promise<Void>()
header = TimelineCardHeader(onRemoval: removePromise.complete)
removed = removePromise.futureResult
}
}

22. Problem: Removing two cards
[
card-0 (index 0),
card-1 (index 1), // Remove this card first
card-2 (index 2),
card-3 (index 3), // Remove this card next
card-4 (index 4),
]
Result:
[
card-0 (index 0),
card-2 (index 1), // Card 2 got index 1 now, being pushed up
card-3 (index 2), // Card 3 still exists, because index 3 is removed
] // Card 4 was removed because it has index 3 now

23. // class Timeline
for card in cards {
card.removed.then {
// Unique (pointer) number for the instance
let cardIdentifier = ObjectIdentifier(card)
for i in 0..<cards.count {
if ObjectIdentifier(cards[i]) == cardIdentifier {
cards.remove(at: i)
return
}
}
}
}

24. The results
Of the journey

25. The obvious benefits
» Increased app stability and maintainability
» Reduced startup time by 90%
» Reduced code by 40%
» Reduced memory usage by 60%
» Closed 80% of the bugs
» Reduced development time for new features
» Created 1 big and 5 small features

26. The important benefits
» A lot of experience gained in iOS development
» Less stress during deployments
» Confidence and pride in your job

27. Programming tips

28. Separate code in modules
» Improved compile times
» Compile-time enforced anti-
!
» Consistent folder structure

29. Try to reduce state
» Switch to computed properties or reactivity
class User {
let birthDate: Date
var age: Int {
return Date().years(from: birthDate)
}
}

30. Less code is better
» Lower maintainance
» Less
!!!!!

31. Use KeyPaths
class Settings {
var shareEmail: Bool
}
class ToggleSettings {
let label: UITextView
let button: UISwitch
let settings: Settings
let keyPath: ReferenceWritableKeyPath<Settings, Bool>
init(...) { ... }
}
let button = ToggleSettings(
settings,
label: "Share email address",
atKeyPath: .shareEmail
)

32. Evaluate opensource projects
And learn the new concepts