Cold and hot streams? What is the difference and why Kotlin coroutines need both: <https://medium.co...

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[elizarov]

Cold and hot streams? What is the difference and why Kotlin coroutines need both: https://medium.com/@elizarov/cold-flows-hot-channels-d74769805f9

[streetsofboston]

@elizarov Can `Flow`s be shared/published/ref-counted, to have multiple collections receive the values from the same flow-lambda?

[elizarov]

Not now, but nothing prevents you (or us) from adding the corresponding feature.

[elizarov]

You can publish a channel which is analogue of "sharing" it.

[streetsofboston]

I can't find a function called publish... On which class/interface is this defined?

[gildor]

As I understand, broadcastIn is similar to publish, it converts flow to BroadcastChannel

[sdeleuze]

See my question about hot Flow https://kotlinlang.slack.com/archives/C1CFAFJSK/p1554801575237600 in #coroutines

[streetsofboston]

@gildor broadcastIn will start collecting and return a BroadcastChannel.

Is there a way to publish/share/ref-count a Flow without collecting and that returns another Flow?

[elizarov]

You can do .asFlow() on a broadcast channel

[streetsofboston]

But a BroadcastChannel is hot.... Is there a way to share a cold Flow and use some sort of subscription/collect counting (much like Rx ref-count) or something like the need to call 'connect', to 'start' the cold Flow?

[elizarov]

By calling connect you’ve turned a cold stream into a hot one.

[streetsofboston]

Yes, but I can subscribe multiple times (like 'collect' in Flow) without making it hot, until it's time to finally call connect. Only then it becomes hot.

[elizarov]

We don’t have that yet. What is the use-case? Can you please explain in an issue at http://github.com/kotlin/kotlinx.coroutines/issues

[streetsofboston]

@elizarov I wrote a Flow<T>.publish(): ConnectableFlow<T> extension-function and its initial implementation seems to work quite well (no thread-safety though).

Its use-case is the same as the RxJava’s Flowable.publish() method.

https://gist.github.com/streetsofboston/39c3f8c882c9891b35e0ebc3cd812381

For thing like this, should we also use http://github.com/kotlin/kotlinx.coroutines/issues?

[elizarov]

Yes. “They have it in RxJava” is not a use-case, though.

[streetsofboston]

True 😀
I was a bit lazy and just assumed the use-cases of why RxJava has 'publish' were self-evident

[elizarov]

It is not evident that publish use-cases need to be solved with publish operator and don’t have other solutions that should be considered as well

[streetsofboston]

Absolutely.
I’ll open a feature request on the github’s issues list.

[streetsofboston]

I opened this issue: https://github.com/Kotlin/kotlinx.coroutines/issues/1086

Please be gentle 🙂