RxCheatsheet.md

RxSwift to ReactiveSwift Cheatsheet

This is a Cheatsheet for RxSwift developers migrating to projects using ReactiveSwift.

Inspired by the RxSwift to Combine cheatsheet

Basics

	RxSwift	ReactiveSwift
Deployment Target	iOS 9.0+	iOS 11.0+
Platforms supported	iOS, macOS, tvOS, watchOS, Linux	iOS, macOS, tvOS, watchOS, Linux
Spec	Reactive Extensions (ReactiveX)	Originally ReactiveX, with significant divergence
Framework Consumption	Third-party	Third-party
Maintained by	Open-Source / Community	Open-Source / Community
UI Bindings	RxCocoa	ReactiveCocoa

Core Components

RxSwift	ReactiveSwift	Notes
AnyObserver	Signal.Observer	In practice, since there are no different Observer types, the AnyObserver concept is redundant in ReactiveSwift
BehaviorRelay	Property / MutableProperty	Since MutableProperty can never have errors, we don't need a Relay specific version.
BehaviorSubject	Property / MutableProperty
Completable	Signal / SignalProducer	A Signal or SignalProducer where Value == Never can only complete or emit an error event
CompositeDisposable	CompositeDisposable
ConnectableObservableType	❌
Disposable	Disposable	In ReactiveSwift you rarely have to keep hold of Disposables or manage their lifetime manually, it's mostly automatic.
DisposeBag	CompositeDisposable	The concepte of a DisposeBag is not really needed in ReactiveSwift, see above.
Driver	❌
Maybe	❌	Trivial to create using take(first: 1)
Observable	Signal / SignalProducer	Signal is a "hot" observable, and SignalProducer is a "cold" observable that will only emit values once a subscription is started
Observer	Signal.Observer
PublishRelay	❌	Could be recreated easily in ReactiveSwift using the flatMapError operator on a Signal.pipe()
PublishSubject	Signal.pipe()	There is no Subject type, but Signal.pipe() returns a tuple of (output: Signal, input: Signal.Observer) which you use to both observe and send values
ReplaySubject	❌	Can be created using the replayLazily(upTo:) operator
ScheduledDisposable	❌
SchedulerType	Scheduler
SerialDisposable	SerialDisposable
Signal	❌	Not to be confused with ReactiveSwift Signal which is completely different
Single	❌	Could easily be created as an initializer for SignalProducer
SubjectType	Signal.pipe()	There is no Subject type, but Signal.pipe() returns a tuple of (output: Signal, input: Signal.Observer) which you use to both observe and send values
TestScheduler	TestScheduler

Operators

RxSwift	ReactiveSwift	Notes
amb()	flatten(.race)
asObservable()	❌	Not required in ReactiveSwift, although Property.producer and Property.signal are similar
asObserver()	❌
bind(to:)	<~ operator (BindingTargets)
buffer	❌	(it used to exist, but was removed)
catchError	flatMapError
catchErrorJustReturn	❌	Easy to create as flatMapError { _ in SignalProducer<Value, Never> (value: value) }
combineLatest	combineLatest
compactMap	compactMap
concat	concat / prefix
concatMap	❌
create	SignalProducer.init { }
debounce	debounce
debug	logEvents
deferred	❌	Trivial to create
delay	delay
delaySubscription	❌
dematerialize	dematerialize
distinctUntilChanged	skipRepeats
do	on
elementAt	❌
empty	SignalProducer.empty
enumerated	❌
error	SignalProducer.init(error:)
filter	filter
first	take(first:)	See also take(last:)
flatMap	flatMap(.merge)
flatMapFirst	flatMap(.throttle)
flatMapLatest	flatMap(.latest)
from(optional:)	❌	Easy to create using .init(.value: Value?).skipNil()
groupBy	❌
ifEmpty(default:)	❌
ifEmpty(switchTo:)	❌
ignoreElements	❌	Easy to create
interval	❌
just	SignalProducer.init(value:)
map	map
materialize	materialize
merge	merge
merge(maxConcurrent:)	❌
multicast	replayLazily(upTo:)
never	SignalProducer.never
observeOn	observe(on:)
of	SignalProducer.init(_ values:)
publish	❌
range	❌
reduce	reduce
refCount	❌	Not meaningful in ReactiveSwift
repeatElement	repeat
retry, retry(3)	retry(upTo:)
retryWhen	❌
sample	sample(on:), sample(with:)
scan	scan
share	replayLazily(upTo:)
skip	skip(first:)
skipUntil	skip(until:)
skipWhile	skip(while:)
startWith	prefix
subscribe	startWithValues / observeValues
subscribeOn	start(on:) / observe(on:)
takeLast	take(last:)
takeUntil	take(until:)
throttle	throttle
timeout	timeout
timer	SignalProducer.timer
toArray	collect
window	❌
withLatestFrom	combineLatest
zip	zip