Fix performance regression in bufferSliding

[Avasil]

I also updated to Scala 2.13.3 - sorry for the noise

2.12:

Benchmark                                         (chunkCount)  (chunkSize)   Mode  Cnt   Score   Error  Units
ChunkedEvalFilterMapSumBenchmark.monixObservable          1000         1000  thrpt   20  66.211 ± 2.483  ops/s

2.13, before the change:

Benchmark                                         (chunkCount)  (chunkSize)   Mode  Cnt   Score   Error  Units
ChunkedEvalFilterMapSumBenchmark.monixObservable          1000         1000  thrpt   20  35.212 ± 3.410  ops/s (2.13 before)

2.13, after the change:

Benchmark                                         (chunkCount)  (chunkSize)   Mode  Cnt   Score   Error  Units
ChunkedEvalFilterMapSumBenchmark.monixObservable          1000         1000  thrpt   20  72.209 ± 3.425  ops/s (2.13 after)

[Avasil]

This is the change

[alexandru]

It will be hard to keep track of these internal helpers.

[Avasil]

Any ideas? Alternatively, it could be placed in reactive (it has only one usage) but it would be even more scattered then.
I have put it in private [monix] in case we can delete it one day.

Initially I wanted to point to the same ArraySeq but mutable one doesn't perform well in my benchmarks. It seems like toSeq is quite expensive there.

[alexandru]

That's fine.

[alexandru]

We'll have to remember we have it I guess.

[Avasil]

I'm running benchmarks again and the results are all over the place, I'll rerun it over the night with Slack/Chrome/etc. closed

[Avasil]

I've run it more times and it seems to be OK:

2.13 this PR:
[info] Benchmark                                         (chunkCount)  (chunkSize)   Mode  Cnt   Score   Error  Units
[info] ChunkedEvalFilterMapSumBenchmark.monixObservable          1000         1000  thrpt   30  77.968 ± 3.677  ops/s


2.13 master:
[info] Benchmark                                         (chunkCount)  (chunkSize)   Mode  Cnt   Score   Error  Units
[info] ChunkedEvalFilterMapSumBenchmark.monixObservable          1000         1000  thrpt   30  53.559 ± 0.364  ops/s

2.12:
[info] Benchmark                                         (chunkCount)  (chunkSize)   Mode  Cnt   Score   Error  Units
[info] ChunkedEvalFilterMapSumBenchmark.monixObservable          1000         1000  thrpt   30  65.132 ± 1.613  ops/s

Still a lot of variance in some results between runs but there's consistent trend that it might be even slightly faster on Scala 2.13 now

[alexandru]

I think that's fine. You would help me if you merged this, given your 2.13 upgrade 🙂