som-snytt commented on code in PR #1026:
URL: https://github.com/apache/incubator-pekko/pull/1026#discussion_r1468539619
##########
stream/src/main/scala/org/apache/pekko/stream/impl/fusing/CollectWhile.scala:
##########
@@ -43,18 +44,17 @@ private[pekko] final class CollectWhile[In, Out](pf:
PartialFunction[In, Out]) e
private lazy val decider =
inheritedAttributes.mandatoryAttribute[SupervisionStrategy].decider
import Collect.NotApplied
+ @nowarn("msg=Any")
override final def onPush(): Unit =
try {
// 1. `applyOrElse` is faster than (`pf.isDefinedAt` and then
`pf.apply`)
// 2. using reference comparing here instead of pattern matching can
generate less and quicker bytecode,
// eg: just a simple `IF_ACMPNE`, and you can find the same trick
in `Collect` operator.
// If you interest, you can check the associated PR for this
change and the
// current implementation of
`scala.collection.IterableOnceOps.collectFirst`.
- val result = pf.applyOrElse(grab(in), NotApplied)
- if (result.asInstanceOf[AnyRef] eq NotApplied) {
- completeStage()
- } else {
- push(out, result.asInstanceOf[Out])
+ pf.applyOrElse(grab(in), NotApplied) match {
+ case _: NotApplied.type => completeStage()
Review Comment:
The clunky pattern is just to avoid a clunky `eq`.
You might use a local val to avoid "cost of obtaining the value".
This is like pattern match on List with Nil case, where match on `::` first,
then just `case nil`. It's nice if you have a type to check.
An example where just "obtaining the value" is expensive is `NoSymbol` in
the compiler, because of the "cake". There are edits trying to choose between
`eq` and `==` but that is swamped by the fetch. It is outweighed by style
concerns.
If you can measure a difference reliably, then of course you are equipped to
choose.
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