shareReplay fix does not support lift

[cartant]

The fix made to shareReplay in #2910 sees a non-lifted observable returned. The previous implementation returned an observable lifted from the source.

RxJS version: 5.5.0-beta.5

[kwonoj]

what's exact issue? is there regression occurred?

[cartant]

Yes, the previous implementation used multicast which calls lift on the source observable, allowing a source-determined instance to be returned. However, the fix uses Observable.create and the source's lift is no longer called and a source-determined instance won't be returned.

I can give you example code if you really want it, but I thought the issue was clear. That is, the source's implementation of lift will no longer be called.

[kwonoj]

I recall there were few non lifted around multicasting behavior, but can't recall exactly. /cc @benlesh

[kwonoj]

@cartant

implementation of lift will no longer be called.

yes, that's part I need to confirm that I recall there was few non-lifted around multicast already but I can't recall exactly (I mostly didn't write those)

[cartant]

I just noticed this when looking more closely at the fixed shareReplay in an attempt to determine what its expected behaviour ought to be - as I'd thought the previous, unfixed implementation was the expected behaviour.

Whether or not it should be lifted, I doubt is especially important. And it's not a regression that affects me. But it is a change.

[cartant]

Regarding multicast calling lift: it does. I checked the behaviours of the pre and post fix shareReplay implementations before creating this issue.

[benlesh]

FWIW: shareReplay has waffled between supporting lift and not, I think I can fix this before we close the beta.

[lock]

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