The document discusses the adoption of Swift generics in iOS development, emphasizing their ability to create flexible and reusable code while addressing issues like dynamic type-casting and runtime errors. It presents a demonstration of using generics with UIKit, particularly in table views, to eliminate boilerplate code and improve type safety. The author also introduces an open-source project, TableKit, aimed at streamlining the development process with generics.

1. Adopting Swift Generics
Перейдем на <T>
Max Sokolov - iOS dev @ Avito
masokolov@avito.ru
max_sokolov

2. 2

3. 3
World’s 3rd
Biggest
Classifieds Site
35m
users
per month
500k
items
per day
100k
deals

4. Agenda
• Dynamic type-casting problem
• Generics in Swift
• Protocols with associated types
• Declarative type-safe UIKit
• Livecoding!
4

5. 🤔
class Matrix<T: Choiceable where T.T == T, T: Learnable, T: Fateable>

6. Generic code enables you to write flexible, reusable functions
and types that can work with any type, subject to requirements
that you define. You can write code that avoids duplication and
expresses its intent in a clear, abstracted manner.
Apple docs
What for?
6

7. 😎

8. Segmentation fault: 11

10. Why?
• One team of 5 people
• 3 different apps with shared components (mostly Swift)
• 20 private CocoaPods
• Large code base (~100k)
10

11. [go back];

12. Typical api request
API Resource
/users
Raw Data
NSData?
Parsed Object
[String: String]?
Model
User?
Request Parsing
ObjectMapper
12

13. Implementation
@implementation DataProvider
- (void)fetch:(NSString *)resources
mappingClass:(Class)mappingClass
completion:(void(^)(NSArray<id<Mappable>> *results))completion {
// Load data...
// Parse data...
if ([mappingClass conformsToProtocol:@protocol(Mappable)]) {
id result = [mappingClass initWithDictionary:response];
completion(@[result]);
}
}
@end
13

14. The problem?
@implementation DataProvider
- (void)fetch:(NSString *)resources
mappingClass:(Class)mappingClass
completion:(void(^)(NSArray<id<Mappable>> *results))completion {
// Load data...
// Parse data...
if ([mappingClass conformsToProtocol:@protocol(Mappable)]) {
id result = [mappingClass initWithDictionary:response];
completion(@[result]);
}
}
@end
14

15. RUN TIME!

16. What run time means?
DataProvider *provider = [DataProvider new];
[provider fetch:@"/users"
mappingClass:[NSString class] // compiler doesn’t warn you here...
completion:^(NSArray<User *> *results) {
}];
16

17. You are doing it wrong with Swift
let dataProvider = DataProvider()
dataProvider.fetch("/resource", mappingClass: User.self) { result in
// code smell...
guard let users = result.values as? [User] else {
return
}
}
17

18. <T>

19. Demo

20. UIKit<T>?

21. UITableView powered by generics

22. 90% of our screens are table views

23. 23

24. Problems with UITableView
• Boilerplate
• Painful when data sources are complex and dynamic
• Not type safe (dequeueReusableCellWithIdentifier etc.)
24

25. What table view actually needs?
Model ViewModel
UITableViewCell
Deadline ;)
25

26. <ItemType, CellType>

27. What if…

28. Line of code
let row = TableRow<String, MyTableViewCell>(item: "string")
28

29. Demo

30. TableKit
Open Source
https://github.com/maxsokolov/TableKit
🚀

31. TableKit
import TableKit
let clickAction = TableRowAction<String, MyTableViewCell>(.click) { (data) in
}
let row = TableRow<String, MyTableViewCell>(item: "string", actions: [clickAction])
tableDirector += TableSection(rows: [row])
31

32. Functional programming

33. The power of declarative approach
let rows: [Row] = strings.map { TableRow<String, MyTableViewCell>(item: $0) }

34. The view layer is simply
a mapping of our data layer
let rows: [Row] = users
.filter({ $0.active })
.map({ UserViewModel(user: $0) })
.map({ TableRow<UserViewModel, UserTableViewCell>(item: $0) })

35. Resume
• Currently, SDK/API’s are not generic
• Compiler is not perfect
• Can’t be used with Objective-C
• Compile-time type-safety help to know about potential
issues earlier
• We could build great, flexible, easy to use API’s
35

36. Links
36
Covariance and Contravariance
https://www.mikeash.com/pyblog/friday-qa-2015-11-20-covariance-and-contravariance.html
Protocols with Associated Types, and How They Got That Way
http://www.slideshare.net/alexis_gallagher/protocols-with-associated-types-and-how-they-got-that-way
Why Associated Types?
http://www.russbishop.net/swift-why-associated-types
TableKit
https://github.com/maxsokolov/TableKit

37. AvitoTech
https://twitter.com/avitotech

38. THANK YOU!

39. QUESTIONS?
Max Sokolov - iOS dev @ Avito
max_sokolov
https://github.com/maxsokolov