adopting swift generics

Adopting Swift GenericsПерейдем на <T>

Max Sokolov - iOS dev @ Avitomasokolov@avito.ru max_sokolov

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Agenda

• Dynamic type-casting problem

• Generics in Swift

• Protocols with associated types

• Declarative type-safe UIKit

• Livecoding!

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🤔

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

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?

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😎

Segmentation fault: 11

Why?

• One team of 5 people

• 3 different apps with shared components (mostly Swift)

• 20 private CocoaPods

• Large code base (~100k)

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[go back];

Typical api request

API Resource /users

Raw DataNSData?

Parsed Object[String: String]?

ModelUser?

Request Parsing

ObjectMapper

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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

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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

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RUN TIME!

What run time means?

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

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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 } }

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<T>

Demo

UIKit<T>?

UITableView powered by generics

90% of our screens are table views

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Problems with UITableView

• Boilerplate

• Painful when data sources are complex and dynamic

• Not type safe (dequeueReusableCellWithIdentifier etc.)

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What table view actually needs?

Model ViewModel

UITableViewCell

Deadline ;)

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<ItemType, CellType>

What if…

Line of code

let row = TableRow<String, MyTableViewCell>(item: "string")

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Demo

TableKitOpen Source

https://github.com/maxsokolov/TableKit

🚀

TableKit

import TableKit

let clickAction = TableRowAction<String, MyTableViewCell>(.click) { (data) in }

let row = TableRow<String, MyTableViewCell>(item: "string", actions: [clickAction])

tableDirector += TableSection(rows: [row])

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Functional programming

The power of declarative approach

let rows: [Row] = strings.map { TableRow<String, MyTableViewCell>(item: $0) }

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) })

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

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Links

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Covariance and Contravariancehttps://www.mikeash.com/pyblog/friday-qa-2015-11-20-covariance-and-contravariance.html

Protocols with Associated Types, and How They Got That Wayhttp://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

TableKithttps://github.com/maxsokolov/TableKit

AvitoTechhttps://twitter.com/avitotech

THANK YOU!

QUESTIONS?

Max Sokolov - iOS dev @ Avito

max_sokolovhttps://github.com/maxsokolov