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RxSwift to Combine Cheatsheet

This is a Cheatsheet for RxSwift developers interested in Apple's new Combine framework.

It's based on the following blog post: https://medium.com/gett-engineering/rxswift-to-apples-combine-cheat-sheet-e9ce32b14c5b

Basics

RxSwift Combine
Deployment Target iOS 8.0+ iOS 13.0+
Platforms supported iOS, macOS, tvOS, watchOS, Linux iOS, macOS, tvOS, watchOS, UIKit for Mac ¹
Spec Reactive Extensions (ReactiveX) Reactive Streams (+ adjustments)
Framework Consumption Third-party First-party (built-in)
Maintained by Open-Source / Community Apple
UI Bindings RxCocoa SwiftUI ²

Core Components

RxSwift Combine Notes
AnyObserver AnySubscriber
BehaviorRelay Simple wrapper around BehaviorSubject, could be easily recreated in Combine
BehaviorSubject CurrentValueSubject This seems to be the type that holds @State under the hood
Completable
CompositeDisposable
ConnectableObservableType ConnectablePublisher
Disposable Cancellable
DisposeBag A collection of AnyCancellables Call anyCancellable.store(in: &collection), where collection can be an array, a set, or any other RangeReplaceableCollection
Driver ObservableObject Both guarantee no failure, but Driver guarantees delivery on Main Thread. In Combine, SwiftUI recreates the entire view hierarachy on the Main Thread, instead.
Maybe Optional.Publisher
Observable Publisher
Observer Subscriber
PublishRelay Simple wrapper around PublishSubject, could be easily recreated in Combine
PublishSubject PassthroughSubject
ReplaySubject
ScheduledDisposable
SchedulerType Scheduler
SerialDisposable
Signal
Single Deferred + Future Future has to be wrapped in a Deferred, or its greedy as opposed to Single's laziness
SubjectType Subject
TestScheduler There doesn't seem to be an existing testing scheduler for Combine code

Operators

RxSwift Combine Notes
amb()
asObservable() eraseToAnyPublisher()
asObserver()
bind(to:) assign(to:on:) Assign uses a KeyPath which is really nice and useful. RxSwift needs a Binder / ObserverType to bind to.
buffer buffer
catchError catch
catchErrorJustReturn replaceError(with:)
combineLatest combineLatest, tryCombineLatest
compactMap compactMap, tryCompactMap
concat append, prepend
concatMap
create Apple removed AnyPublisher with a closure in Xcode 11 beta 3 :-(
debounce debounce
debug print
deferred Deferred
delay delay
delaySubscription
dematerialize
distinctUntilChanged removeDuplicates, tryRemoveDuplicates
do handleEvents
elementAt output(at:)
empty Empty(completeImmediately: true)
enumerated
error Fail
filter filter, tryFilter
first first, tryFirst
flatMap flatMap
flatMapFirst
flatMapLatest switchToLatest
from(optional:) Optional.Publisher(_ output:)
groupBy
ifEmpty(default:) replaceEmpty(with:)
ifEmpty(switchTo:) Could be achieved with composition - replaceEmpty(with: publisher).switchToLatest()
ignoreElements ignoreOutput
interval
just Just
map map, tryMap
materialize
merge merge, tryMerge
merge(maxConcurrent:) flatMap(maxPublishers:)
multicast multicast
never Empty(completeImmediately: false)
observeOn receive(on:)
of Sequence.publisher publisher property on any Sequence or you can use Publishers.Sequence(sequence:) directly
publish makeConnectable
range
reduce reduce, tryReduce
refCount autoconnect
repeatElement
retry, retry(3) retry, retry(3)
retryWhen
sample
scan scan, tryScan
share share There’s no replay or scope in Combine. Could be “faked” with multicast.
skip(3) dropFirst(3)
skipUntil drop(untilOutputFrom:)
skipWhile drop(while:), tryDrop(while:)
startWith prepend
subscribe sink
subscribeOn subscribe(on:) RxSwift uses Schedulers. Combine uses RunLoop, DispatchQueue, and OperationQueue.
take(1) prefix(1)
takeLast last
takeUntil prefix(untilOutputFrom:)
throttle throttle
timeout timeout
timer Timer.publish
toArray() collect()
window collect(Publishers.TimeGroupingStrategy) Combine has a TimeGroupingStrategy.byTimeOrCount that could be used as a window.
withLatestFrom
zip zip

Contributing

Add any data/operators to the appropriate CSV files in the Data folder, run bundle install and generate.rb.

Finally, commit the changes and submit a Pull Request.