FRP in Swift 3101

© Andy Jacobs, ixor.be 2016 1

Andy Jacobs7 years iOS development2 years FRP experience

1.5 year FRP enthusiast

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Topics• What?

• Why?

• Basic concepts

• Real world example

• Tip

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What?streams of values over time

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What?streams of values over time

+ operations and bindings

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Streams

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OperationsMost operators operate on a given stream and will return a stream. This allows you to apply these operators one after the other, in a chain.

Each operator in the chain modifies the stream that results from the operation of the previous operator.

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Common Operators

// Creatingcreate, just, from, ..// Transformingmap, flatMap, scan, ..// Filteringfilter, skip, take, ..// CombiningcombineLatest, merge, zip, ..// Utilitysubscribe, delay, observeOn, ..// ConditionaltakeUntil, skipWhile, ..// Mathematical & Aggregateconcat, reduce, ..// Connectablepublish, replay, connect, ..

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Bindingsbind the stream of values to an endpoint.

• Subjects • Variables• UI

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Why?You might already be doing some reactive programming

var title: String { didSet { // react to changes in variables view.titleLabel.text = title }}

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Heavy lifting

Libraries asRxSwift, ReactiveCocoa, ReactKit, Bond, ..bring so much more to the table.

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RxSwift, ReactiveX

In short, using Rx will make your code:Composable ⇠ Because Rx is composition's nicknameReusable ⇠ Because it's composableDeclarative ⇠ Because definitions are immutable and only data changesUnderstandable and concise ⇠ Raising the level of abstraction and removing transient statesStable ⇠ Because Rx code is thoroughly unit testedLess stateful ⇠ Because you are modeling applications as unidirectional data flowsWithout leaks ⇠ Because resource management is easy

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Basic concepts• Observable

• Event

• Disposing

• Subjects

• Hot vs Cold

• Schedulers

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Observable

Every Observable sequence is just a sequence. The key advantage for an Observable vs Swift's Sequence is that it can also receive elements asynchronously.

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Event

Each value in the stream is defined as an event.• Next

• Error

• Completed

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Interface

enum Event<Element> { case next(Element) // next element of a sequence case error(Swift.Error) // sequence failed with error case completed // sequence terminated successfully}

class Observable<Element> { func subscribe(_ observer: Observer<Element>) -> Disposable}

Sequences can have 0 or more elements.Once an error or completed event is received, the sequence cannot produce any other element.© Andy Jacobs, ixor.be 2016 16

Disposing

A Disposable is used to disconnect the observable wrapper from its source, causing subscribed observer to stop receiving values from the underlying observable sequence.

error, completed, dispose(), takeUntil

all internal resources that compute sequence elements will be freed

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SubjectsA Subject is a sort of bridge or proxy that is available in some implementations of Rx that acts as both an observer and Observable. Because it is an observer, it can subscribe to one or more Observables, and because it is an Observable, it can pass through the items it observes by reemitting them, and it can also emit new items.

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Subjects

• PublishSubject

Broadcasts new events to all observers as of their time of the subscription.

• ReplaySubject

Broadcasts new events to all subscribers, and the specified bufferSize number of previous events to new subscribers.

• BehaviorSubject

Broadcasts new events to all subscribers, and the most recent (or initial) value to new subscribers.

• Variable

Wraps a BehaviorSubject, so it will emit the most recent (or initial) value to new subscribers. And Variable also maintains current value state. Variable will never emit an Error event. However, it will automatically emit a Completed event and terminate on deinit.

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Hot ! vs Cold ❄

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! vs ❄(demo)

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SchedulersSchedulers abstract away the mechanism for performing work.

Different mechanisms for performing work include the current thread, dispatch queues, operation queues, new threads, thread pools, and run loops.

• CurrentThreadScheduler (default, serial)

• MainScheduler (serial)

• SerialDispatchQueueScheduler (serial)

• ConcurrentDispatchQueueScheduler (concurrent)

• OperationQueueScheduler (concurrent)

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Real world examplelive coding

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Tips

When you are using Rx, first try to compose built-in operators.

rxmarbles.com, rxmarbles.appstor.io

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Tips

When you are using Rx, first try to compose built-in operators.

rxmarbles.com, rxmarbles.appstor.io

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Tips

If using some (combination of) operators often, create your convenience operators.

extension ObservableType where E: MaybeCool {

@warn_unused_result(message="http://git.io/rxs.uo") public func coolElements() -> Observable<E> { return filter { e -> Bool in return e.isCool } }}

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Tips

Avoid nesting subscribe calls at all cost

textField.rx_text.subscribe(onNext: { text in performURLRequest(text).subscribe(onNext: { result in ... }) .addDisposableTo(disposeBag)}).addDisposableTo(disposeBag)

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Tips

Preferred way of chaining disposables by using operators.

textField.rx_text .flatMapLatest { text in // Assuming this doesn't fail and returns result on main scheduler, // otherwise `catchError` and `observeOn(MainScheduler.instance)` can be used to // correct this. return performURLRequest(text) } ... .addDisposableTo(disposeBag) // only one top most disposable

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Credits..

• RxSwift documentation

• https://www.youtube.com/watch?v=7AqXBuJOJkY

• https://realm.io/news/nacho-soto-functional-reactive-programming/

• https://realm.io/news/altconf-ash-furrow-functional-reactive-swift/

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rxdevcon.com

Saturday, October 7, 2017

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Questions?

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Thank you— @avalanched

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