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Ray Ryan Timothy Donnelly Reactive Workflows Update

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Immutability is assumed Be reactive: push, don’t pull Natural separation of UI and business concerns Composition or go home Cardinal Architecture Virtues

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Workflow Business Objects Container

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Workflow Container Business Objects CRUD

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Workflow Navigation, View Model NewGame PlayGame QuitGame GameOver Business Objects CRUD Container

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Container Rendering, Event Handling Business Objects CRUD Workflow Navigation, View Model NewGame PlayGame QuitGame GameOver

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Business Objects CRUD State View Model Event Update Workflow Navigation, View Model NewGame PlayGame QuitGame GameOver Container Rendering, Event Handling

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val bar: BarValue fun setFoo(f: FooValue) fun setBar(b: BarValue) fun setBaz(b: Bazvalue) val bang: Observable val buzz: Observable

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fun perform(op: Operation) sealed class Operation { class Update(vararg stuff: Stuff) : Operation() class Delete(vararg ids: Int) : Operation() } val stuffs: Observable>

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fun perform(op: Operation) val stuffs: Observable> RxPreferences, Rooms SqlDelight Retrofit

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Container Rendering, Event Handling Business Objects CRUD Workflow Navigation, View Model NewGame PlayGame QuitGame GameOver State View Model Event Update

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NewGame PlayGame QuitGame GameOver

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New Game Screen Play Game Screen Quit Game Screen Game Over Screen

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New Game Play Game Quit Game Game Over

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Play Game X’s Turn Draw X Wins Quit O Wins O’s Turn

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Play Game Playing( X or O ) Completed( X, O, draw or quit )

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Play Game Playing( Symbol ) Completed( Ending ) Symbol { X, O, None } Ending { Victor(Symbol) Draw Quitter(Symbol) }

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Play Game Playing( Symbol ) Completed( Ending ) Event { TakeSquare(row, col) Quit } Symbol { X, O, None } Ending { Victor(Symbol) Draw Quitter(Symbol) }

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Play Game Playing( Turn ) Completed( Ending, Turn ) typealias Board = List> data class Turn( val players: Map, val playing: Symbol = X, val board: Board = EMPTY_BOARD )

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interface Workflow { val state: Observable val result: Single fun abandon() }

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class PlayGameWorkflow(initial: State) : Workflow { sealed class Event { class TakeSquare( val row: Int, val col: Int ) : Event() object Quit : Event() } private val events = PublishRelay.create() fun sendEvent(e: Event) = events.call(e)

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class PlayGameWorkflow(initial: State) : Workflow { sealed class Event { class TakeSquare( val row: Int, val col: Int ) : Event() object Quit : Event() } private val events = PublishRelay.create() fun sendEvent(e: Event) = events.call(e)

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class PlayGameWorkflow(initial: State) : Workflow { sealed class State { abstract val turn: Turn data class Playing( override val turn: Turn ) : State() data class Completed( val ending: Ending, override val turn: Turn ) : State() } data class Turn( val players: Map, val playing: Symbol = X, val board: Board = EMPTY_BOARD )

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class PlayGameWorkflow(initial: State) : Workflow { sealed class State { abstract val turn: Turn data class Playing( override val turn: Turn ) : State() data class Completed( val ending: Ending, override val turn: Turn ) : State() }

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class PlayGameWorkflow(initial: State) : Workflow { sealed class State { abstract val turn: Turn data class Playing( override val turn: Turn ) : State() data class Completed( val ending: Ending, override val turn: Turn ) : State() } sealed class Ending { object Victor : Ending() object Draw : Ending() object Quitter : Ending() }

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameWorkflow(initial: State) : Workflow { private val states = BehaviorRelay.create(Single.just(initial)) private val _state: ConnectableObservable = states .switchMap { it.toObservable() } .doOnNext { currentState -> states.call(nextState(currentState)) } .replay(1) override val state: Observable = _state.takeWhile { it !is Completed } .map { it.turn } override val result: Single = _state.ofType() .first() .toSingle() .cache()

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class PlayGameWorkflow(initial: State) : Workflow { private fun nextState(fromState: State): Single = when (fromState) { is Completed -> Observable.never() is Playing -> events.first().map { event -> when (event) { is TakeSquare -> takeSquareAndNextState(fromState.turn, event.row, event.col) Quit -> Completed(Quitter, fromState.turn) } } }.toSingle()

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class PlayGameReactor : Reactor() { override fun onReact(fromState: Playing): Single> = selectEvent { onEvent { EnterState(takeSquareAndNextState(fromState.turn, it.row, it.col)) } onEvent { FinishWith(Completed(Quitter, fromState.turn)) } }

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class PlayGameReactor : Reactor() { override fun onReact(fromState: Playing): Single> = selectEvent { onEvent { EnterState(takeSquareAndNextState(fromState.turn, it.row, it.col)) } onEvent { FinishWith(Completed(Quitter, fromState.turn)) } }

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class PlayGameReactor : Reactor() { override fun onReact(fromState: Playing): Single> = selectEvent { onEvent { EnterState(takeSquareAndNextState(fromState.turn, it.row, it.col)) } onEvent { FinishWith(Completed(Quitter, fromState.turn)) } }

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class PlayGameReactor : Reactor() { override fun onReact(fromState: Playing): Single> = selectEvent { onEvent { EnterState(takeSquareAndNextState(fromState.turn, it.row, it.col)) } onEvent { FinishWith(Completed(Quitter, fromState.turn)) } }

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class PlayGameReactor : Reactor() { typealias PlayGameWorkflow = ReactorWorkflow companion object { fun startWorkflow( x: String, o: String ): PlayGameWorkflow = PlayGameReactor().asWorkflow(Playing(Turn(x, o))) }

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class PlayGameReactor : Reactor() { typealias PlayGameWorkflow = ReactorWorkflow companion object { fun startWorkflow( x: String, o: String ): PlayGameWorkflow = PlayGameReactor().asWorkflow(Playing(Turn(x, o))) fun resumeWorkflow(turn: Turn): PlayGameWorkflow = PlayGameReactor().asWorkflow(Playing(turn)) }

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New Game Quit Game Game Over Play Game

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New Game PlayGameWorkflow Quit Game Game Over

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class GameAppReactor : Reactor() { sealed class State { class NewGame( val defaultXName: String = "X", val defaultOName: String = "O" ) : State() class Playing(val workflow: PlayGameWorkflow) : State() class MaybeQuitting(val completedGame: Completed) : State() class GameOver(val completedGame: Completed) : State() }

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class GameAppReactor : Reactor() { sealed class Event { class StartGame( val x: String, val o: String ) : Event() object ConfirmQuit : Event() object ContinuePlaying : Event() object StartNewGame : Event() object QuitApp : Event() }

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class GameAppReactor : Reactor() { override fun onReact(state: State): Single> = when (state) {

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class GameAppReactor : Reactor() { override fun onReact(state: State): Single> = when (state) { is NewGame -> selectEvent { onEvent { FinishWith(Unit) } onEvent { EnterState(Playing(PlayGameReactor.startWorkflow(it.x, it.o))) } }

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class GameAppReactor : Reactor() { override fun onReact(state: State): Single> = when (state) { is NewGame -> selectEvent { onEvent { FinishWith(Unit) } onEvent { EnterState(Playing(PlayGameReactor.startWorkflow(it.x, it.o))) } }

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class GameAppReactor : Reactor() { override fun onReact(state: State): Single> = when (state) { is NewGame -> selectEvent { onEvent { FinishWith(Unit) } onEvent { EnterState(Playing(PlayGameReactor.startWorkflow(it.x, it.o))) } } is Playing -> state.workflow.result.map { result -> when (result.ending) { Quitter -> EnterState(MaybeQuitting(result)) else -> EnterState(GameOver(result)) } }

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class GameAppReactor : Reactor() { override fun onReact(state: State): Single> = when (state) { is Playing -> state.workflow.result.map { result -> when (result.ending) { Quitter -> EnterState(MaybeQuitting(result)) else -> EnterState(GameOver(result)) } } is MaybeQuitting -> selectEvent { onEvent { EnterState(GameOver(state.completedGame)) } onEvent { EnterState(Playing(PlayGameReactor.resumeWorkflow(state.completedGame.turn))) } }

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class GameAppReactor : Reactor() { override fun onReact(state: State): Single> = when (state) { is Playing -> state.workflow.result.map { result -> when (result.ending) { Quitter -> EnterState(MaybeQuitting(result)) else -> EnterState(GameOver(result)) } } is MaybeQuitting -> selectEvent { onEvent { EnterState(GameOver(state.completedGame)) } onEvent { EnterState(Playing(PlayGameReactor.resumeWorkflow(state.completedGame.turn))) } }

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class GameAppReactor : Reactor() { override fun onReact(state: State): Single> = when (state) { is Playing -> state.workflow.result.map { result -> when (result.ending) { Quitter -> EnterState(MaybeQuitting(result)) else -> EnterState(GameOver(result)) } } is MaybeQuitting -> selectEvent { onEvent { EnterState(GameOver(state.completedGame)) } onEvent { EnterState(Playing(PlayGameReactor.resumeWorkflow(state.completedGame.turn))) } }

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New Game PlayGameWorkflow Quit Game Game Over

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Playing(PlayGameWorkflow) NewGame GameOver(Completed) MaybeQuitting(Completed)

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Game Service Playing(PlayGameWorkflow) NewGame MaybeQuitting(Completed) ConfirmQuit Continue Playing Quitter !Quitter StartNewGame GameOver(Completed) StartNewGame

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Game Service Playing(PlayGameWorkflow) NewGame GameOver( Completed, SyncState ) MaybeQuitting(Completed) ConfirmQuit Continue Playing Quitter !Quitter StartNewGame StartNewGame

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override fun onReact(state: State): Single> = when (state) { // Left as an exercise for the reader. // // Hint: Retrofit requests are rx.Single<*>

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Container Rendering, Event Handling Business Objects CRUD Workflow Navigation, View Model NewGame PlayGame QuitGame GameOver State View Model Event Update

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Workflow Navigation, View Model Container Rendering, Event Handling Business Objects CRUD ?

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/** * @param data A complete rendering of this screen. * @param eventHandler The object that accepts events for this screen. */ class Screen( val data: D, val eventHandler: E )

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/** * @param data A complete rendering of this screen. * @param eventHandler The object that accepts events for this screen. */ class Screen( val data: D, val eventHandler: E ) typealias AnyScreen = Screen<*, *>

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/** * @param data A complete rendering of this screen. * @param eventHandler The object that accepts events for this screen. */ class Screen( val data: D, val eventHandler: E ) typealias AnyScreen = Screen<*, *> /** * A [Workflow] that exposes its state as a stream * of [screen models][Screen]. */ typealias ScreenWorkflow = Workflow

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class GameAppScreens(private val wrapped: GameAppWorkflow) : ScreenWorkflow { override val state: Observable = wrapped.state.switchMap { when (it) { is Playing -> it.workflow.state.map { playing -> Screen(playing.turn, it.workflow) } else -> just(Screen(it, wrapped)) } } override val result: Single = wrapped.result override fun abandon() = wrapped.abandon() }

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class GameAppScreens(private val wrapped: GameAppWorkflow) : ScreenWorkflow { override val state: Observable = wrapped.state.switchMap { when (it) { is Playing -> it.workflow.state.map { playing -> Screen(playing.turn, it.workflow) } else -> just(Screen(it, wrapped)) } } override val result: Single = wrapped.result override fun abandon() = wrapped.abandon() }

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class GameAppScreens(private val wrapped: GameAppWorkflow) : ScreenWorkflow { override val state: Observable = wrapped.state.switchMap { when (it) { is Playing -> it.workflow.state else -> just(Screen(it, wrapped)) } } override val result: Single = wrapped.result override fun abandon() = wrapped.abandon() }

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Tim Time

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Workflows + Swift

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public struct ViewRegistry { // ... public func provideView(for screen: T) -> View // ... } The View Registry turns screen models into live views.

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public struct ViewRegistry { // ... public func provideView(for screen: T) -> View // Registers a factory block for the screen type `T`. public mutating func register( screenType: T.Type, factory: @escaping (Observable, ViewRegistry) -> View // ... } The View Registry requires screens to be registered. 73

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public struct ViewRegistry { // ... public func provideView(for screen: T) -> View // Registers a factory block for the screen type `T`. public mutating func register( screenType: T.Type, factory: @escaping (Observable, ViewRegistry) -> View // ... } The View Registry is recursive. 74

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78 Adapting UIKit to a reactive world

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79 Back Stack

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public struct BackStackScreen: Screen { public var currentItem: Item public struct Item { public var screen: Screen public var key: String public var barContent: NavigationBarContent } }

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88 Modal Container

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public struct ModalContainerScreen: Screen { public var main: Screen public var modal: Screen? } 89

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93 Demo

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95 What else can we do with a fully decoupled UI layer?

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97 ...and what about debugging tools?

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square.com Ray Ryan / octodon.social/@rjrjr Timothy Donnelly / twitter.com/tdonnelly github.com/JakeWharton/RxRelay github.com/square/coordinators