Swift India Conf 2019: Combine! All the things

Speaker: Ritesh Gupta, iOS Engineer, Over Inc

Twitter: https://twitter.com/_riteshhh/

Bio: Ritesh Gupta is an iOS Engineer at Over. He believes in protocol-oriented & reactive programming and also enjoys writing about them on medium. He also had the honor of writing an issue of iOS dev weekly & has given multiple talks on various meetups/conferences. When he is not coding, you can find him exploring Indian fusion cuisines.

Abstract: Recently in WWDC'19, Apple has announced their reactive framework called Combine and I couldn't be more excited as I have been tinkering with reactive programming for the last 4 years now. In this talk, we will go through the basics of reactive programming and gradually dive into how we can use Combine through a demo app. In this journey, we will explore various concepts like Publisher, Subscriber, Subject along with some of the operators like map, flatmap, filter, merge, zip, etc through real-life examples.

Transcript

1. Combine! All the things Ritesh Gupta @_riteshhh
2. Ritesh Gupta @_riteshhh riteshhh.com github.com/riteshhgupta
4. Beta 1, 2, 3, 4…!
5. Combine • It provides a declarative Swift API for processing values over time • These values can represent many kinds of asynchronous events • Customise handling of asynchronous events by combining event-processing operators
6. • It’s a reactive framework by Apple Combine
7. Reactive (Rx) Programming
8. Rx Programming • Observer Pattern (publish >> observe) • Operations (dependent tasks) • Simple (yet powerful) Operators like merge, zip, debounce… • Open Source: ReactiveSwift, RxSwift
9. Why we need Rx?
10. Why Rx? • multiple async tasks • better state management • loose coupling of components • declarative & cleaner api
11. source: https://twitter.com/diegopetrucci/status/1135655480825655297 Current state of Combine
12. Foundation of Combine!
13. Foundation of Combine! • Publisher • Subscriber • Operators (map, flatMap, filter, merge, zip…)
14. Publisher
15. Publisher • emit sequence of values over time • delivers values to one or more Subscriber instances • protocol with two generic types (Output, Error) • completion via .finished or .failure
16. Publisher
17. • Notification Publisher • URLSession Publisher • Just, Future • CurrentValueSubject, PassthroughSubject Free Publishers
18. Subscriber
19. Subscriber • receive emitted values from a Publisher • represents end of the chain of a stream • protocol with two generic types (Input, Error) • can cancel a subscription • Sink, Assign, AnySubscriber
20. Subscriber
21. Publisher Subscriber
22. Subscription
23. Assign
24. Assign
25. Sink
26. Sink
27. subscribe(on:) vs receive(on:)
28. Threading
29. • `receive(on:)` affects downstream events • `subscribe(on:)` affects upstream events • In the example, requests to `$queryPublisher` are performed on `backgroundQueue`, but elements received from it are performed on `Dispatch.main` Threading
30. Lifecycle of Publisher & Subscriber
31. Lifecycle
32. Operators
33. • pre-defined functions (publishers) • used b/w a publisher & a subscriber • transform the stream • map, flatMap, filter, merge, zip, debounce… Operators
34. Operators
35. Map
36. Filter
37. Debounce
38. FlatMap
39. Merge
40. Zip
41. Demo
42. Next?
43. • Subject • Memory Management • Error Handling • Debugging Next?
44. • ConnectablePublisher • Back Pressure (`Demand`) • Multicasts Next?
45. Further Reading
46. Thank you!