Improving the JVM for Scala [closed]

Question

What changes to the JVM would most benefit the Scala compiler and runtime?

The dynamic languages will benefit greatly in performance from the introduction of the InvokeDynamic byte code scheduled to arrive in JVM 7 and Scala will probably benefit from tail recursion (not sure if it will appear in JVM 8 or later).

What other changes could Scala, with its present feature set, benefit from in the JVM? Are these changes on the horizon?

Specifically, are there changes to the JVM that would improve performance with closures and functions-as-objects?

Answer 1

Basically, everything that John Rose has been campaigning for :)

• Fixnums - To eliminate the cost of boxing/unboxing primitives.

• Method Handles - Would speed up higher-order functions and allow the JVM to optimise them more effectively. SAM types can sometimes require an awkward flip/flopping between monomorphic and megamorphic call sites that prevents inlining.

• Continuations - To support asynchronous/concurrent design, as per node.js

• Interface Injection - Simplify mixin composition and the implementation of roles, as well as eliminating the need for generating some intermediate classes and making structural types possible without reflection in many cases.

• Tail-call optimisation - Should be a no-brainer :)

Reification is often quoted as something that would benefit Scala's pattern matching, but this would come at a high cost in terms of interop, given the different variance schemes that the two languages use. At this point, I believe that reification may actually cause more harm than it would do good.

I also think it unreasonable to expect anything that would break backwards compatibility in Java. That just ain't gonna happen.