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.