What's Different in 3.x (tracking issue)

[akarnokd]

Many code changes in 3.x can be done independently, but updating the new What's Different in 3.x.md would conflict. This issue tracks which changes should be eventually described in the file:

• Introduction of the Supplier interface -> 3.x: Widen functional interface throws, replace Callable with Supplier #6511
• Callable use changed to Supplier in the API -> 3.x: Widen functional interface throws, replace Callable with Supplier #6511
• Removal of getValues() from various subjects and processors -> 3.x: remove getValues() from some subjects/processors #6516
• Maybe.defaultIfEmpty() returns Single -> 3.x: Various small API changes and removals #6517
• Removal of Maybe.toSingle(T) -> 3.x: Various small API changes and removals #6517
• Removal of Flowable.subscribe(4 args) -> 3.x: Various small API changes and removals #6517
• Removal of Observable.subscribe(4 args) -> 3.x: Various small API changes and removals #6517
• Removal of Single.toCompletable() -> 3.x: Various small API changes and removals #6517
• Removal of Completable.blockingGet() -> 3.x: Various small API changes and removals #6517
• ConnectableX redesign. -> 3.x: ConnectableFlowable/ConnetableObservabe redesign #6519
• Test consumer API changes. -> 3.x: Remove methods from test consumers, make internal versions #6526
• The rename of startWith+1 to startWithItem & startWithIterable -> 3.x: disambiguate startWith+1 to startWithItem & startWithIterable #6530
• Bounded replay() with eagerTruncate option -> 3.x: Add eager truncation to bounded replay() to avoid item retention #6532
• Removal replay(Scheduler) and its variants. -> 3.x: remove no-arg dematerialize(); remove replay(Scheduler) variants #6539
• Changes to using() order of upstream dispose and resource dispose -> 3.x: Make using() resource disposal order consistent with eager-mode #6534
• API promotions to standard -> 3.x: Promote Beta/Experimental to Standard #6537
• concatMap with Scheduler -> 3.x: Add concatMap with Scheduler guaranteeing where the mapper runs #6538
• Removal of the no-arg deserialize() -> 3.x: remove no-arg dematerialize(); remove replay(Scheduler) variants #6539
• Removal of onExceptionResumeNext()
• Removal of buffer(Supplier) and window(Supplier) variants.
• Rename of onErrorResumeNext(source) to onErrorResumeWith. -> Disambiguous some method call sites when calling from Kotlin  #6551
• More undeliverable errors reported due to cancellation.
• Widening of XOnSubscribe interfaces. -> 3.x: widen throws on the XOnSubscribe interfaces #6579
• Removal of combineLatest(vararg) & combineLatestDelayError(vararg) -> 3.x: Remove vararg overloads for combineLatest in Observable + Flowable #6635
• Removal of zip(O(O)) overload -> 3.x: Rename zipIterable, remove zip(O(O)), adjust concatMapX arg order #6638
• Rename of zipIterable to zip -> 3.x: Rename zipIterable, remove zip(O(O)), adjust concatMapX arg order #6638
• Change parameter order of concatMapDelayError and concatMapEagerDelayError -> 3.x: Rename zipIterable, remove zip(O(O)), adjust concatMapX arg order #6638
• Rename to combineLatestArray -> 3.x: Rename combineLatest methods that take an array to combineLatestArray #6640
• groupBy abandoned group behavior change -> 3.x: Fix groupBy not canceling upstream due to group abandonment #6642
• Flowable.groupBy signaling MissingBackpressureException instead of possibly hanging -> 3.x: Change Flowable.groupBy to signal MBE instead of possibly hanging #6740
• Add fair mode overload to Schedulers.from(Executor) -> 3.x: Add fair mode overload to Schedulers.from(Executor) #6744
• Make DisposableContainer public API -> 3.x: Make DisposableContainer public API #6745
• Change CompositeException::getCause() output and message -> 3.x: Change how the cause of CompositeException is generated #6748
• window handling abandoned inner windows -> 3.x: Fix Flowable.window (size, time) cancellation and abandonment #6758, 3.x: Fix Observable.window (size & time) cancellation and abandonment #6761, 3.x: Fix window (boundary, start/end) cancel and abandonment #6762
• Java 8 support -> 3.x: [Java 8] Upgrade to Java 8, add Flowable.fromX operators #6765
• Disposables utility class inlined into Disposable -> 3.x: Migrate Disposables static factories to Disposable interface #6781
• BehaviorProcessor, PublishProcessor and MulticastProcessor offer null-check change. -> 3.x: XProcessor.offer to throw NPE immediately #6799
• MulticastProcessor.offer now throws IllegalStateException when called in fusion mode. -> 3.x: XProcessor.offer to throw NPE immediately #6799
• Add blockingForEach(Consumer, int) overloads -> 3.x: Add blockingForEach(Consumer, int) overload #6800
• Removal of fromFuture(..., Scheduler) overloads -> 3.x: Remove fromFuture(..., Scheduler) overloads #6814
• Operators used to throw IndexOutOfBoundsException (skipLast, takeLast, takeLastTimed) now throw IllegalArgumentException for param validation.
• skip(count) now throws IAE if count < 0
• Remove Observable.concatMapIterable(Function, int) overload -> 3.x: Remove a pointless Observable.concatMapIterable overload #6837
• Rename combineLatestDelayError(array) to combineLatestArrayDelayError(array) -> 3.x: Rename to combineLatestArrayDelayError #6838
• Rename Single.equals to Single.sequenceEqual
• Change input type in Flowable.buffer(openingIndicator) overloads -> 3.x: Verify the use of base interfaces in operator inputs & lambdas #6858
• Add blockingSubscribe across -> 3.x: Add Maybe/Single/Completable blockingSubscribe #6862
• Add Maybe.delayError(..., delayError) overload -> Adding delayError to Maybe.delay #6864
• Add onErrorComplete across -> 3.x: Add onErrorComplete to Flowable, Observable and Single #6867
• Add onErrorResumeWith across -> 3.x: Add Completable.onErrorResumeWith #6868
• Add retryUntil -> 3.x: Add Single/Completable retryUntil + marbles #6869
• Add switchOnNext[DelayError] to M/S/C -> 3.x: Add Maybe/Single/Completable switchOnNext & switchOnNextDelayError #6870
• Add Maybe.dematerialize -> 3.x: Add Maybe.dematerialize #6871
• Add fromAction, fromRunnable, fromMaybe, fromSingle, fromPublisher, fromObservable -> 3.x: Add many fromX operators + marbles #6873
• Changed fromAction and fromRunnable to not execute if cancelled upfront. -> 3.x: Add many fromX operators + marbles #6873
• Add timeInterval and timestamp to M/S -> 3.x: Add timeInterval & timestamp to M/S #6874
• Add toFuture to M/C ->3.x: Add Maybe/Completable toFuture #6875
• Add ofType to M/S -> 3.x: Add Single.ofType #6876
• Add doOnLifecycle to M/S/C -> 3.x: Add doOnLifecycle to Maybe, Single & Completable #6877
• Add concatMapX missing across -> 3.x: Add concatMapX operators (aliases) #6879
• Add concatMapXDelayError missing across -> 3.x: Add various concatXDelayError operators #6881
• Add Single.mergeArrayX -> 3.x: Add Single.mergeArray & mergeArrayDelayError #6882
• Add Completable.sequenceEqual -> 3.x: Add Completable.sequenceEqual #6884
• Add startWith missing across -> 3.x: Add missing startWith overloads #6885
• Add Completable.onErrorReturn[Item] -> 3.x: Add Completable.onErrorReturn[Item] #6886
• Add safeSubscribe to M/S/C -> 3.x: Add safeSubscribe to Maybe, Single & Completable #6887
• Swap Maybe.flatMapSingle and Maybe.flatMapSingleElement -> 3.x: Swap Maybe.flatMapSingle and Maybe.flatMapSingleElement #6891
• Add Single.flatMap(F, F) and Single.flatMap(F, Bi) operators -> 3.x: Reenable XFlatMapTest.maybeSingle, add missing Single operators #6893
• Add concatEager(Iterator, int) and concatEagerDelayError across -> 3.x: Add concatEagerDelayError across #6899
• Merge as() into to() -> 3.x: Merge as() into to() #6514

[ZacSweers]

Why was TestObserver#assertNotTerminated removed? That's a useful API IMO

[akarnokd]

The poll indicated only a few people were using it. Replace it with assertNoErrors().assertNotComplete().

[akarnokd]

I've written most of the wiki page about the changes.

https://github.com/ReactiveX/RxJava/wiki/What's-different-in-3.0

Still a few dozen new operators are not yet written from this list and from #6776.

Let me know if I've forgotten something else.

[akarnokd]

Done.