Jochen Theodorou wrote:

I doubt it would add much overhead to the compiler; you'd just be checking if all cases are a literal type and whether there's enough of them for it to be a valid optimization. If not, you don't do it. Unless there are hundreds of switches being used in the system, you'd probably never see any impact. Don't most people precompile Groovy anyway? It would be much more of a concern in JRuby, where nobody precompiles anything and we compile at runtime on-demand for all applications. And even there I'm not worried about it at all.

For what it's worth, compilation time in JRuby pales in comparison to class loading and verification time.

The best way to get performance to improve is going to be mapping things as often as possible directly to their Java equivalents. The more magic you have to use the slower things will run, and optimizing a switch to actually be a switch is a simple optimization to add for cases where it's valid.

Of course it shouldn't take priority over other things that are more generally useful; I never said that, and we've always tried to address general performance issues before specific ones. But this thread is about switches :)

You're thinking about this like a language implementer; there are many cases where you'd want to be able to do a fast switch on literal values beyond writing a lexer. Hell, just for general flow control in an application I've moved a series of ifs into a single switch in Java code many times, because it was worth doing so. I'm just saying you could easily make the compiler do this for cases where it's valid. And again, this doesn't have to take priority over other optimizations...but it's a perfectly valid optimization. Don't discount it out of hand.

The fact that most switches are around 11 in the lexer is meaningless if the one you need to perform well runs slowly. I know I've seen some large switches in both Ruby and Java codebases, and I know many of those could or would benefit from a jump table.

There's no point in doing any optimizations if nobody's complaining about performance. But if you're going to start adding optimizations, this would be a valid optimization to add. Again, just because you don't think it would be useful doesn't mean it's not useful. And I honestly don't think it's that hard to do.

- Charlie