Comment by pregnenolone

I've always liked Scala as a language, but it's challenging to write high-performing and memory-efficient code on the JVM in general. Whenever you raise this issue, you'll encounter a horde of JVM fanboys who insist that it’s not true, giving you all kinds of nonsense excuses and accusing you of not measuring performance or memory consumption properly. If you genuinely want to produce well-performing JVM code, you're essentially writing C-style Java. As soon as you introduce abstraction, performance issues inevitably arise – largely due to the fact that features and modernizations from Project Valhalla haven’t yet been implemented/shipped. Scala proponents will suggest using macros and opaque types, but at scale this approach becomes incredibly cumbersome and even then you won't be able to completely prevent boxing that would actually be unnecessary; you could just as well be writing Rust.