Add switch/switchMap

[nadavwr]

the switch and switchMap operators, as described in Rx (and also implemented in Monix), are very useful.

For anyone not familiar with it, switch operates over a stream of streams, always emitting from the latest stream, discarding older streams left behind.

See here for a quick standalone implementation and example.

[johanandren]

Sounds interesting, I like the name latest better than switch, with Akka Streams terminology it should maybe even be flatMapLatest (flatMapConcatLatest is maybe a bit much of a mouthful).

I think it may even be useful enough that it should be a part of Akka Streams core, and implemented as a custom stage rather than composed. WDYT?

[nadavwr]

@johanandren Sorry for the late response—Google Inbox has been playing tricks on me again.

I agree this would be sufficiently useful to justify including in the core library—I chose to implement it partly because it is a "core" Rx combinator (and partly to see if I can get anywhere using non-trivial composition over the flow DSL, where Monix and FS2 have a small advantage due to abundance of combinators).

If you think this issue should be migrated to the core library, I'd be happy to reimplement and contribute it as a custom stage. Should I open an issue there?

Naming: latest is a very reasonable alternative name for switch—Rxrb uses latest, and both RxPY and RxSwift use switch_latest and switchLatest respectively. Regarding switchMap, I agree thatflatMapLatest is sufficiently clear—the word "latest" already precludes merging in any meaningful sense, so specifying the concat suffix would be redundant.

[johanandren]

Yeah, please open a ticket in core Akka and give it a try, thanks!