Getting Started with ReactiveCocoa v4.1.0 2016/04/13 Reactive Swift Meetup Yasuhiro Inami / @inamiy 

Reactive Programming 

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Streams of Events over time 

ReactiveCocoa (ObjC/Swift) 

Signal (Hot Observable) SignalProducer (Cold Observable) 

‗ and ❄ 

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Hot & Cold Observables • Hot Observable ‗ • always active (may lose data if not subscribed) • uses same underlying source (broadcasting) • Cold Observable ❄ • paused until subscription • clones underlying source (not broadcasting) 

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In short... 

SignalProducer ↯ Signal ↯ Event 

SignalProducer ↯ Signal ↓ Observer 

SignalProducer ↯ Signal ↓ɹɹˣ ObserverɹObserver 

SignalProducer ↯　　　　↯ SignalɹSignal ↓ɹɹɹɹˣ ObserverɹObserver 

Function Composition 

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Signal -> Signal SignalProducer -> SignalProducer 

Signal Operations • Transforming: map, mapError, scan, reduce, ... • Filtering: filter, take, takeUntil, skip, sampleOn, ... • Combining: flatten (Merge/Concat/Latest), combineLatest, zip, flatMap, flatMapError, ... • Timing: delay, throttle, timeoutWithError, ... • Utility: observeOn, materialize, dematerialize, ... 

SignalProducer Operations • Transforming: map, mapError, scan, reduce, ... • Filtering: filter, take, takeUntil, skip, sampleOn, ... • Combining: flatten (Merge/Concat/Latest), combineLatest, zip, flatMap, flatMapError, ... • Timing: delay, throttle, timeoutWithError, ... • Utility: observeOn, materialize, dematerialize, ... • Producer-Only: startOn, concat, retry, etc... 

Why do we need 2 different types? 

Because ‗ and ❄ behaviors differ! 

Define types based on its behavior (as simple as possible) 

Signal / SignalProducer • Signal • Container for observers (for broadcasting) • .pipe = pair of (Signal, Observer) = Subject • SignalProducer • Container for startHandler (for cloning) • .buffer = pair of (SignalProducer, Observer) = ReplaySubject 

Other data types • Observer: Wrapper of Event -> () • Event: .Next, .Failed, .Completed, .Interrupted • Scheduler: GCD / NSThread wrapper • Disposable: Stateful container of () -> () • Property: Latest value + Signal(Producer) • Action: Stateful container of Input -> SignalProducer 

Compared to other FRPs... • Protocol-oriented, no abstract classes & subclassing • Functional, much less types to learn • Separation of Signal & SignalProducer • No shareReplay, refCount (ConnectableObservable) • Typed errors • combineLatest(o1, o2, ...) ... no mixed error types • property <~ signal ... only NoError is allowed 

Demo inamiy/ReactiveCocoaCatalog 

Recap • ReactiveCocoa has separated hot & cold observables • Signal • SignalProducer • Type safe, including generic Error type • Use RAC if you like Result more than Result • RAC is beautiful !✨ 

Thanks!