Why is for (x <- range) not optimised yet?

Language Design
1

So following up on this, and double-checking with :javap, I wonder if there is a deeper reason why

for (x <- (range: Range)) ...

is not compiled to while loops yet by scalac (tested in 2.12)? Wouldn’t that be a rather trivial optimisation, and one that would apply in many many cases?

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2

Because no one knows how to use the optimizer flags.

Even if it were optimized, it would sit behind a flag that’s never enabled. It wouldn’t be the deprecated flag you’ve been using, it would be that other flag you haven’t heard of if you weren’t reading the PR comments.

3 Likes
3

That’s -opt:l:magick, right?

Or, if EPFL are supportive, -opt-in-dotty.

4

spire has cfor which does exactly that.

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5

I thought scala.js already does it.

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6

Scala.js does it, yes. It comes down to @som-snytt’s comment: in Scala.js the optimizer is enabled by default, but not in Scala/JVM. And that it can do because it can always work in a close world.

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