Code Optimization with Scala

Question

What structures of Scala can be used more efficiently than in Java, to increase execution speed? I don't know if this is possible, but to clear my doubts :)

Thanks

Answer 1

The scala @specialized annotation can generate multiple versions of a class, fine-tuned with specific primitive types. You can write all of that out in Java, but you probably don't want to.

Answer 2

As of 2.9, the parallel collections library is slated to be part of the standard distribution. This will allow extremely simple distribution of so-called "embarrassingly parallel" problems over multiple cores. Doing so in Java takes considerably more effort.

As a general rule, Scala benchmarks range from moderately slower than Java to slightly faster, depending on the problem and coding techniques.

Answer 3

To expand on Ross's answer, you can use @specialized to generate specific versions of a collection. For instance, in Java you'd generally use fastutil or Apache Primitives for collections of primitives. Scala's @specialized will generate these variants for you and hide them automatically like so:

class MyLinkedList[@specialized T] (args: T*) {
  // whatever it does
}

Other than that, actors make it easier to write concurrent applications. Coming up in 2.9 are parallel collections, which can apply higher-order functions in parallel across collections, speeding up any place you'd have the Scala equivalent of a Java loop (fold, foreach, etc). See this ScalaDays talk for the nitty-gritty on this.

Answer 4

I'll refrain from speculation on how the resulting performance might differ from an equivalent Java construct, but Scala does closure elimination, which might make a measurable difference, modulo HotSpot tricks.

Also stay tuned for Iulian's thesis which should be out soon and will provide a lot more information on the subject of Scala optimization.