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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 | ||
| 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.