Millions of Customers. Billions of Dollars: iOS Architecture at Scale

MILLIONS OF CUSTOMERS. BILLIONS OF DOLLARS. IOS ARCHITECTURE AT SCALE
1 — Parveen Kaler • @kaler • [email protected]

HOW LARGE? LARGE FORTUNE 500 COMPANY 2 — Parveen Kaler
• @kaler • [email protected]

HOW LARGE? I AM ONLY GOING TO TALK ABOUT THE
PRODUCT VIEW 3 — Parveen Kaler • @kaler • [email protected]

HOW LARGE? Total Lines of Code LANGUAGE FILES CODE Swift
2845 246570 Objective-C 1289 164414 C/C++ Header 1948 37311 Objective-C++ 47 16602 C 16 11861 JavaScript 78 7494 ... ... ... Total 6314 493367 4 — Parveen Kaler • @kaler • [email protected]

HOW LARGE? Product Module Lines of Code LANGUAGE FILES CODE
Swift 327 25670 Objective-C 84 16274 GraphQL 9 3004 C/C++ Header 86 1405 JavaScript 1 24 Total 507 46377 5 — Parveen Kaler • @kaler • [email protected]

HOW LEGACY? •Original code written in 2011 for iOS 5

•Before self-sizing UITableViewCells 7 — Parveen Kaler • @kaler • [email protected]

•Before self-sizing UITableViewCells •Before UICollectionView (iOS 6) 8 — Parveen Kaler • @kaler • [email protected]

•Before self-sizing UITableViewCells •Before UICollectionView (iOS 6) •Before Auto Layout (iOS 6) 9 — Parveen Kaler • @kaler • [email protected]

WHAT IS GOOD ARCHITECTURE? 10 — Parveen Kaler • @kaler
• [email protected]

WHAT IS GOOD Architecture? A SET OF DECISIONS 11 —
Parveen Kaler • @kaler • [email protected]

WHAT IS GOOD ARCHITECTURE? SMALL AND SIMPLE 12 — Parveen
Kaler • @kaler • [email protected]

! SIMPLE STATE MUTATION var heroImages: [URL] { didSet {
preProcessImages() } } 13 — Parveen Kaler • @kaler • [email protected]

SIMPLE DELEGATION weak var delegate: Tappable? @IBAction func somethingTapped(sender: UIButton)
{ delegate?.somethingTapped() } 14 — Parveen Kaler • @kaler • [email protected]

SIMPLE CALLBACKS cell.somethingHappened = { [weak self] } 15 —

SIMPLE OBSERVATION let observation = child.observe(\.productID) { (productID, change) in
} 16 — Parveen Kaler • @kaler • [email protected]

COMPLEX DATA FLOW REACTIVE PROGRAMMING self.selectedIndex = Signal.combineLatest( .merge( self.didSelectIndexProperty.signal,
self.switchToActivitiesProperty.signal.mapConst(1), self.switchToDiscoveryProperty.signal.mapConst(0), self.switchToSearchProperty.signal.mapConst(2), switchToLogin, switchToProfile, self.switchToDashboardProperty.signal.mapConst(3) ), self.setViewControllers, self.viewDidLoadProperty.signal) .map { idx, vcs, _ in clamp(0, vcs.count - 1)(idx) } 17 — Parveen Kaler • @kaler • [email protected]

! LESS FILES 18 — Parveen Kaler • @kaler •
[email protected]

! MORE FILES VIPER 19 — Parveen Kaler • @kaler

! LOCAL STATE let, protocol, DEPENDENCY INJECTION 20 — Parveen
Kaler • @kaler • [email protected]

! GLOBAL STATE static, sharedInstance, SINGLETONS 21 — Parveen Kaler

! DEBUGABILITY1 AND SMALL CALL STACKS 1 What does that
even mean? No one knows what it means, but it's provocative. 22 — Parveen Kaler • @kaler • [email protected]

TRANSITIONING TO SMALL AND SIMPLE •Objective-C ➡ Swift 23 —

TRANSITIONING TO SMALL AND SIMPLE •Objective-C ➡ Swift •Monolithic ➡
Modular 24 — Parveen Kaler • @kaler • [email protected]

Modular •REST ➡ GraphQL 25 — Parveen Kaler • @kaler • [email protected]

Modular •REST ➡ GraphQL •UITableView ➡ UICollectionView 26 — Parveen Kaler • @kaler • [email protected]

Modular •REST ➡ GraphQL •UITableView ➡ UICollectionView •Oh BTW, there was a redesign along the way, too 27 — Parveen Kaler • @kaler • [email protected]

OBJECTIVE-C SWIFT •way less code •less language-level bugs (mostly) 28
— Parveen Kaler • @kaler • [email protected]

OBJECTIVE-C BUGS •nil Unexpected data from web service resulting in
silent failure •@optional protocols and respondsToSelector Products may have complex optional functionality •Just a whole bunch of complexity from having a whole lot of code 29 — Parveen Kaler • @kaler • [email protected]

SWIFT BUGS •implicitly unwrapped optionals •force unwrapping3 We were learning
Swift on the fly. We made mistakes. 3 guard and defer were added in Swift 2.0 30 — Parveen Kaler • @kaler • [email protected]

OBJECTIVE-C SWIFT 31 — Parveen Kaler • @kaler • [email protected]

OBJECTIVE-C SWIFT SMALLER AND SIMPLER 32 — Parveen Kaler •
@kaler • [email protected]

MONOLITHIC MODULAR •Plugins •Router 33 — Parveen Kaler • @kaler

A modular architecture makes each module smaller and simpler. 34
— Parveen Kaler • @kaler • [email protected]

PLUGIN PROTOCOL protocol Pluggable { var identifier: String var dependencies:
[String] func startup(_ supervisor: Supervisor) } Also forwards all UIApplicationDelegate messages to each plugin 35 — Parveen Kaler • @kaler • [email protected]

PLUGIN PROTOCOL A Supervisor manages access to other plugins. Supervisor.pluginAPI(forIdentifier:
ProductDetailsID) as? ProductDetailsAPI 36 — Parveen Kaler • @kaler • [email protected]

PLUGIN PROTOCOL Pass data or call a function. protocol ProductDetailsAPI
{ func productData(with productID: String) -> ProductData } 37 — Parveen Kaler • @kaler • [email protected]

ROUTER Responsible for navigation and presenting views class Router {
func register(route: Route) func routeTo(urlString: String) } 38 — Parveen Kaler • @kaler • [email protected]

BACK TO THE PRODUCT MODULE 39 — Parveen Kaler •

LEGACY: CLIENT SIDE NETWORKING •written before NSURLSession •rethink: Objective-C blocks
and GCD queue use 40 — Parveen Kaler • @kaler • [email protected]

LEGACY: SERVER SIDE NETWORKING •web service originally targeted desktop web
•some responses were very sloooooow •some responses were very faaaaaaat 41 — Parveen Kaler • @kaler • [email protected]

NOW: GRAPHQL •ability to query for just the JSON that
you need •fields are kinda typed 42 — Parveen Kaler • @kaler • [email protected]

REST VS GRAPHQL •versioning is hard 43 — Parveen Kaler

REST VS GRAPHQL •versioning is hard •POST breaks HTTP semantics

•caching is hard 45 — Parveen Kaler • @kaler • [email protected]

•caching is hard •there are really only 5 queries 46 — Parveen Kaler • @kaler • [email protected]

FUTURE: NETWORKING •exploit GraphQL schema to optimize payload size •who
owns networking? 47 — Parveen Kaler • @kaler • [email protected]

WHO OWNS NETWORKING? •Right now the view model layer owns
it •I think this is terrible 48 — Parveen Kaler • @kaler • [email protected]

SERIALIZATION OBJECTIVE-C ➡ OBJECTMAPPER CODABLE 49 — Parveen Kaler •

OBJECTIVE-C @interface ProductModel: ModelObject { } @implementation ProductModel - (NSDictionary*)mappingDictionaryForData:(id)data
{ return @{ @"productID": mo_key(self.productID) }; } - (BOOL)isValidModel { } @end 50 — Parveen Kaler • @kaler • [email protected]

OBJECTMAPPER class Product: Mappable { init?(map: Map) { } func
mapping(map: Map) { } } 51 — Parveen Kaler • @kaler • [email protected]

CODABLE class Product: Codable { var productID: Int enum CodingKeys:
String, CodingKey { case productID } init(from decoder: Decoder) throws { let container = try decoder.container(keyedBy: CodingKeys.self) self.productID = try container.decode(Int.self, forKey: .productID) } } 52 — Parveen Kaler • @kaler • [email protected]

CODABLE THE TOOLCHAIN MAY GENERATE CODE FOR YOU: •Type conforms
to Codable •Each property conforms to Codable class Product: Codable { var productID: Int } 53 — Parveen Kaler • @kaler • [email protected]

LEGACY CONTROLLER • ! Fat UITableViewController 54 — Parveen Kaler

LEGACY CONTROLLER • ! Fat UITableViewController • ! Conformed to
too many protocols 55 — Parveen Kaler • @kaler • [email protected]

too many protocols • ! Picked the wrong abstraction: SectionControllers 56 — Parveen Kaler • @kaler • [email protected]

too many protocols • ! Picked the wrong abstraction: SectionControllers • ! UITableView scrolling performance issues 57 — Parveen Kaler • @kaler • [email protected]

CURRENT CONTROLLER INITIATIVE OBJECTIVE-C SWIFT class ProductViewController: UIViewController { }
extension ProductViewController: MFMessageComposeViewControllerDelegate { } • ! Strategic use of extension to break out protocol conformance 58 — Parveen Kaler • @kaler • [email protected]

CURRENT CONTROLLER INITIATIVE UITABLEVIEWCONTROLLER UICOLLECTIONVIEW 59 — Parveen Kaler •

CURRENT CONTROLLER INITIATIVE UITABLEVIEWCONTROLLER UICOLLECTIONVIEW • ! Modern API improves
scroll performance • ! Less code 60 — Parveen Kaler • @kaler • [email protected]

CURRENT CONTROLLER INITIATIVE UITABLEVIEWCONTROLLER UICOLLECTIONVIEW 61 — Parveen Kaler •

CURRENT CONTROLLER INITIATIVE UITABLEVIEWCONTROLLER UICOLLECTIONVIEW • ! Extract controller code
into plain Swift objects 62 — Parveen Kaler • @kaler • [email protected]

into plain Swift objects • ! Extract UICollectionViewLayout, UICollectionViewLayoutAttributes 63 — Parveen Kaler • @kaler • [email protected]

into plain Swift objects • ! Extract UICollectionViewLayout, UICollectionViewLayoutAttributes • ! Extract UICollectionViewDataSource, UICollectionViewDelegate 64 — Parveen Kaler • @kaler • [email protected]

SMALL AND SIMPLE •Objective-C ➡ Swift •Monolithic ➡ Modular •REST
➡ GraphQL •UITableView ➡ UICollectionView 65 — Parveen Kaler • @kaler • [email protected]

SMALL AND SIMPLE THANK YOU ! 66 — Parveen Kaler

Millions of Customers. Billions of Dollars: iOS Architecture at Scale

Millions of Customers. Billions of Dollars: iOS Architecture at Scale

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