Avoid double evaluation of pattern matchers in Chunk.collect #3364
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flipp5b
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flipp5b
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Dec 20, 2023
| @@ -87,7 +87,8 @@ abstract class Chunk[+O] extends Serializable with ChunkPlatform[O] with ChunkRu | |||
| def collect[O2](pf: PartialFunction[O, O2]): Chunk[O2] = { | |||
| val b = makeArrayBuilder[Any] | |||
| b.sizeHint(size) | |||
| foreach(o => if (pf.isDefinedAt(o)) b += pf(o)) | |||
| val f = pf.runWith(b += _) | |||
| foreach { o => f(o); () } | |||
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Well, this looks rather ugly. pf.runWith returns O => Boolean so we have to transform it to O => Unit to avoid warnings. This could be rewritten as follows (at the cost of extra lambda call per Chunk item):
foreach(pf.runWith(b += _).andThen(_ => ()))@armanbilge, which one would you prefer?
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Ugly but performant is the right choice 😅
|
Here is some benchmark results. 1. Masterforeach(o => if (pf.isDefinedAt(o)) b += pf(o))2. This PR val f = pf.runWith(b += _)
foreach { o => f(o); () }3. This PR (prettified)foreach(pf.runWith(b += _).andThen(_ => ()))Option 2 (this PR) shows slightly better score than the other two options. |
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armanbilge
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@armanbilge Thank you for the prompt and kind feedback :) |
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fs2.Chunk#collectevaluates pattern matchers and guards of a passed partial function twice because it callspf.isDefinedAtand thenpf.apply:Scala collections use
pf.applyOrElse/pf.runWith(depending on scala version) instead to avoid double evaluation. This PR implements the same approach in aChunk.It should be noted that this may change observable behavior for those who use a partial function with side-effecting matchers/guards. But hey, side-effecting matchers/guards is considered a bad practice anyway, and I doubt that there's an fs2 user relying on that double evaluation "feature."