Scala performance question

Question

In the article written by Daniel Korzekwa, he said that the performance of following code:

list.map(e => e*2).filter(e => e>10)

is muc

Answer 1

Scala approach is much more abstract and generic. Therefore it is hard to optimize every single case.

I could imagine that HotSpot JIT compiler might apply stream- and loop-fusion to the code in the future if it sees that the immediate results are not used.

Additionally the Java code just does much more.

If you really just want to mutate over a datastructure, consider transform. It looks a bit like map but doesn't create a new collection, e. g.:

val array = Array(1,2,3,4,5,6,7,8,9,10).transform(_ * 2)
// array is now WrappedArray(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)

I really hope some additional in-place operations will be added ion the future...