Dependency Injection

DevFest Baltics 2018 in Jurmala, 16 November, 2018
https://devfest2018.gdg.lv

Transcript

1. !ZPJDIJUHZ Dependency Injection Yoichi Tagaya DevFest Baltics, 16 November, 2018
2. !ZPJDIJUHZ Yoichi Tagaya, from Tokyo, Japan About me
3. !ZPJDIJUHZ Tokyo evening view 1IPUP
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4. !ZPJDIJUHZ About me as Swinject author • Swinject: dependency injection framework for Swift • Maintained by 5 members • Recently by Jakub Vano especially! • 2,7k+ GitHub stars now and 1k clones everyday • 4 extensions provided
5. !ZPJDIJUHZ Agenda • Software architecture • Dependency injection (DI) • Swinject (DI container)
6. !ZPJDIJUHZ What is software architecture
7. !ZPJDIJUHZ What is software architecture
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8. !ZPJDIJUHZ Peter Eeles says An architecture • Defines structure and behavior • Focuses on significant elements • May conform to an architectural style • Influences team structure (inverse Conway maneuver) • Balances stakeholder needs • Is influenced by its environment • Embodies decisions based on rationale
9. !ZPJDIJUHZ Architecture is not static but dynamic "SDIJUFDUVSF :FBST
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10. !ZPJDIJUHZ Architecture is not static but dynamic .7$ "SDIJUFDUVSF :FBST
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11. !ZPJDIJUHZ Architecture is not static but dynamic $ # " /PX $ /FX
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12. !ZPJDIJUHZ Production / unit test $ # " 1SPEVDUJPO 6OJU
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13. !ZPJDIJUHZ We need flexibility in architecture
14. !ZPJDIJUHZ How to make architecture flexible? Dependency injection!
15. !ZPJDIJUHZ Because dependency injection is glue but sticky-like glue 5JHIU
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16. !ZPJDIJUHZ How to make the sticky-like glue?
17. !ZPJDIJUHZ SOLID principles • S - Single responsibility principle • O - Open/closed principle • L - Liskov substitution principle • I - Interface segregation principle • D - Dependency inversion principle • Should not depend on concretions but abstractions
18. !ZPJDIJUHZ Depending on concretions / abstractions Depending on concretions (tight coupling) *NQMFNFOUBUJPO $PODSFUF
    5ZQF Depending on abstractions (loose coupling) 3FGFSFODF *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF $PODSFUF
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19. !ZPJDIJUHZ Dependency injection: a way to realize dependency inversion principle *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF
20. !ZPJDIJUHZ Dependency injection: a way to realize dependency inversion principle *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF *OTUBODF
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21. !ZPJDIJUHZ Dependency injection: a way to realize dependency inversion principle *NQMFNFOUBUJPO Protocol (Interface) 3FGFSFODF $PODSFUF
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22. !ZPJDIJUHZ Code example of dependency injection protocol APIClientProtocol { ... } class APIClient: APIClientProtocol { ... } let vm = MyViewModel(apiClient: APIClient()) class MyViewModel { let apiClient: APIClientProtocol init(apiClient: APIClientProtocol) { self.apiClient = apiClient } } APIClientProtocol "CTUSBDU
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23. !ZPJDIJUHZ Try dependency injection with Swinject Register/resolve-style DI container like dictionary
24. !ZPJDIJUHZ How to use Swinject container $POUBJOFS Register Resolve
25. !ZPJDIJUHZ Code example of registration $POUBJOFS Register import Swinject let container = Container() container.register(MyViewModel.self) { resolver in let apiClient = resolver.resolve(APIClientProtocol.self)! return MyViewModel(apiClient: apiClient) } container.register(APIClientProtocol.self) { _ in APIClient() }
26. !ZPJDIJUHZ Code example of resolution $POUBJOFS Resolve import Swinject let vm = container.resolve(MyViewModel.self)!
27. !ZPJDIJUHZ In a production app class MyViewModel { init(dep1: D1, dep2: D2, dep3: D3, id: String, name: String) { ... } } .BOZ
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28. !ZPJDIJUHZ In a production app class MyViewModel { init(dep1: D1, dep2: D2, dep3: D3, id: String, name: String) { ... } } .BOZ
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29. !ZPJDIJUHZ Using typealias of dependency tuple init(dependency: Dependency, id: String, name: String) 5ZQFBMJBT
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30. !ZPJDIJUHZ Example of class definition with typealias of tuple protocol APIClientProtocol { ... } class APIClient: APIClientProtocol { ... } protocol LoggerProtocol { ... } class Logger: LoggerProtocol { ... } 5ZQFBMJBT
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31. !ZPJDIJUHZ DI Registration let container = Container() container.register(APIClientProtocol.self) { _ in APIClient() } container.register(LoggerProtocol.self) { _ in Logger() } $POUBJOFS Register container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) }
32. !ZPJDIJUHZ DI Resolution let myViewModel = container.resolve( MyViewModel.self, argument: "abc")! $POUBJOFS Resolve
33. !ZPJDIJUHZ Easier to see the dependencies and parameters!
34. !ZPJDIJUHZ But, still too many “!”s. Is it OK? "
35. !ZPJDIJUHZ Let’s try adding another dependency to implement a new feature
36. !ZPJDIJUHZ Add another dependency let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol )
37. !ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol )
38. !ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } }
39. !ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } 8SPOH
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40. !ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger, database): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger) = dependency self.id = id } } 8SPOH
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41. !ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger, database): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger, database) = dependency self.id = id } } 8SPOH
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42. !ZPJDIJUHZ Add another dependency protocol DatabaseProtocol { ... } class Database: DatabaseProtocol { ... } class MyViewModel { typealias Dependency = ( APIClientProtocol, LoggerProtocol, DatabaseProtocol ) let (apiClient, logger, database): Dependency let id: String init(dependency: Dependency, id: String) { (apiClient, logger, database) = dependency self.id = id } }
43. !ZPJDIJUHZ Add another dependency container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")!
44. !ZPJDIJUHZ Add another dependency container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")! $BOOPU
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45. !ZPJDIJUHZ Add another dependency container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")! container.register(DatabaseProtocol.self) { _ in Database() } $BOOPU
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46. !ZPJDIJUHZ Add another dependency container.register(DatabaseProtocol.self) { _ in Database() } $BOOPU
    DPOWFSU ❕ container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)!, resolver.resolve(DatabaseProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")!
47. !ZPJDIJUHZ Add another dependency container.register(DatabaseProtocol.self) { _ in Database() } container.register(MyViewModel.self) { (resolver, id: String) in let dependency = ( resolver.resolve(APIClientProtocol.self)!, resolver.resolve(LoggerProtocol.self)!, resolver.resolve(DatabaseProtocol.self)! ) return MyViewModel( dependency: dependency, id: id ) } let myViewModel = container.resolve( MyViewModel.self, argument: "abc")!
48. !ZPJDIJUHZ Just follow what Swift compiler says to add new dependencies!
49. !ZPJDIJUHZ Summary • Architecture is not static but dynamic to evolve. • Dependency injection is sticky-like glue. • Use a typealias to group dependencies. • Just follow Swift compiler to add new dependencies.
50. !ZPJDIJUHZ More info, thanks! • Swinject Tutorial for iOS: Getting Started by Gemma Barlow at raywenderlich.com • iOS App Development: Design Patterns for Mobile Architecture by Jon Bott at lynda.com • Dependency injection in Swift by Manuel Munoz at blog.quadiontech.com • Adventures in Dependency Swinjection by Ben Dietzkis at medium.com/@topLayoutGuide • Swinject - Dependency Injection in iOS by Iron Ben Zvi at speakerdeck.com/oronbz