Tuesday, September 11, 2012

Using MethodHandle's in jSuneido

This is a continuation to my last post, Moving jSuneido to Java 7.

Previously, the implementation of a built-in method looked like:

The new version, using method handles (behind the scenes) looks like:

At first, I wasn't sure how to handle the parameter information since I no longer had a class to put it in. Then I thought of using annotations, which I think works very nicely.

To use an annotation, it was easiest to specify the parameter information as a single string description rather than separate arguments. This means a little more work to parse it and split it up, but it makes the description cleaner. Of course, I could have done this before as well.

As before, during startup the methods are picked up by reflection. The difference is that now an instance of a generic class is created, containing a MethodHandle pointing to the static method. I still need the methods and instances to handle adjusting call arguments i.e. filling in default argument values, handling named arguments, and collecting or spreading arguments. (Suneido has a more flexible argument / parameter scheme than Java.)

Once I start using invokedynamic the argument adjustment will probably be done by composing method handles. I could do some of that now if I wanted, but it fits better with invokedynamic.

One advantage of this approach is that the methods can now be static and don't need to take an implicit "this" argument (which I didn't use) in addition to my own explicit "self" argument. Before, they had to be instance methods so I could call them virtually.

Meanwhile, I've been playing with invokedynamic and figuring our how best to use it. I'll post more on this as I progress.

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