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A Tour of Combine
- 2. VY-SHANE XIE I build software things at WiseTime https://vyshane.com I'm @vyshane on
- 3. The Combine framework provides a declarative Swift API for processing values over time.
- 4. The Combine framework provides a declarative Swift API for processing values over time.
- 5. STREAMS Publisher SubscriberOperator Subscriber Functional Reactive Programming FRP is a programming paradigm for asynchronous stream processing using the building blocks of functional programming (e.g. map, reduce, filter).
- 6. FRP RxSwift ReactiveSwift Is not new in the Swift ecosystem Combine
- 7. HOW IS COMBINE DIFFERENT?
- 8. COMBINE IS A foundational framework Deeply integrated with SwiftUI Closed source Not available on Linux
- 9. https://forums.swift.org/t/will-swiftnio-adapt-to-the-new-combine-framework/25166/11 ONE MORE THING
- 10. REACTIVE STREAMS SPEC? Enables JVM streaming libraries to interoperate Provides a design for implementing back pressure
- 11. BACK PRESSURE?
- 12. userIDs getProfile save Slow IO
- 13. PRODUCER CONSUMERPROCESSOR CONSUMERuserIDs getProfile save Slow IO 😰 Incoming rate higher than we can process
- 14. PRODUCER CONSUMERuserIDs save Slow IO getProfile 💥We're out of memory
- 15. PRODUCER CONSUMERuserIDs save Slow IO getProfile On overflow drop elements Not Great! 😒
- 16. PRODUCER CONSUMERPROCESSOR CONSUMERgetProfile save Slow IO 🚦 😎 Signal demand upstream THIS IS BACK PRESSURE userIDs
- 17. COMBINE IS A low level framework Deeply integrated with SwiftUI Closed source Not available on Linux The first Swift FRP library that has back pressure built in
- 19. SUBSCRIBEROperator 3 MAIN CONCEPTS Publisher Subscriber
- 20. PUBLISHER Knows how to deliver a stream of values over time Publisher
- 21. PUBLISHER The stream may complete successfully Publisher
- 22. PUBLISHER Or fail with an error Publisher
- 23. PUBLISHER An infinite stream that never ends is legal Publisher
- 24. PUBLISHER A stream that completes without emitting anything is OK Publisher
- 25. THE PUBLISHER PROTOCOL A publisher declares an Output type as well as a Failure type
- 26. SOME BUILT-IN WAYS TO PUBLISH VALUES
- 27. SUBSCRIBER ‣ Requests values from a publisher ‣ Acts on values as it receives them ‣ Declares an Input type and a Failure type
- 28. SUBSCRIBING TO A PUBLISHER A subscriber can subscribe to a publisher if: ‣ Its input type matches the output type of the publisher ‣ Its failure type matches that of the publisher Publisher Subscriber O F I F
- 29. SUBSCRIBING TO A PUBLISHER A subscriber can subscribe to a publisher if: ‣ Its input type matches the output type of the publisher ‣ Its failure type matches that of the publisher
- 31. Assign Subscriber Assigns elements it receives to an object property at a keypath The assign(to:on:) operator creates an Assign subscriber and subscribes it to the upstream publisher
- 32. Sink Subscriber Accepts closures that receive values and completion events Useful when writing tests
- 33. OPERATORS Operate on streams and allow you to: ‣ Transform values ‣ Filter values ‣ Combine publishers together ‣ Manipulate timing ‣ Perform sequence and aggregation operations
- 34. Operators are instance methods on the Publisher protocol
- 35. Many operators subscribe to the upstream publisher and return a publisher of their own This allows you to compose them into pipelines EXAMPLE: CALLING A WEB SERVICE
- 36. EXAMPLE: CALLING A WEB SERVICE
- 37. EXAMPLE: CALLING A WEB SERVICE assign(to:on:) is a subscription operator, returns an AnyCancellable on which you can call .cancel()
- 38. RETURN TYPES OF CHAINED OPERATIONS
- 40. DEBUG OPERATORS Combine ships with some handy operators that you can insert into your pipelines to debug them: ‣ print(_:to:) ‣ breakpoint(receiveSubscription:receiveOutput: receiveCompletion:) ‣ breakpointOnError() ‣ handleEvents(receiveSubscription:receiveOutput: receiveCompletion:receiveCancel:receiveRequest:)
- 41. ... all yuor operators
- 43. PUBLISHER SUBSCRIPTION SUBSCRIBER Subscribes Creates Sends Requests values Emits value Returns demand Updates demand Emits value Demand fulfilled, pauses Returns demand Requests values Emits value Updates demand Returns demand No more values Emits completion Receives demand Stream ends Publishers are lazy (cold)
- 44. PUBLISHER SUBSCRIPTION SUBSCRIBER Subscribes Creates Sends Requests values Emits value Returns demand Receives demand Stream cancelled Deallocated
- 45. EXAMPLE - DEALLOCATED SUBSCRIPTION Times out, test fails
- 46. EXAMPLE - DEALLOCATED SUBSCRIPTION
- 47. CANCELLABLE ‣ Can be cancelled ‣ Can be stored/retained
- 48. SUPPORTED PLATFORMS Same as SwiftUI
- 49. SUPPORTED PLATFORMS Swift 5.1+ iOS 13.0+ macOS 10.15+ tvOS 13.0+ watchOS 6.0+ Mac Catalyst 13.0+
- 50. RESOURCES ‣ Using Combine web book (free): https://heckj.github.io/swiftui-notes/ ‣ Combine: Asynchronous Programming with Swift (ebook): https://store.raywenderlich.com/products/combine- asynchronous-programming-with-swift ‣ WWDC: Introducing Combine (video) https://developer.apple.com/videos/play/wwdc2019/722/ ‣ WWDC: Combine in Practice (video) https://developer.apple.com/videos/play/wwdc2019/721/
- 51. ANY QUESTIONS? THANKS FOR LISTENING