Metamethods

Update: as of 2008/10/15, metamethod support has been removed from Helma. It had too much of a performance impact, and most things can be achieved by other means, often reducing complexity.

Since I have gotten a more frustrated with JSAdapter lately, I have started working on a new metaprogramming extension to Rhino which I call Metamethods. It is based on JOMP, but looks for methods in the target object itself rather than a separate meta object. It is also thread-safe and adds a method to control behavior of the equals operator (==).

In detail, Metamethods looks for the following methods in a JavaScript object:

• __has__(property): this method is called when checking for a property
• __get__(property): this method is called when getting a property
• __set__(property, value): this method is called when setting a property
• __delete__(property): this method is called when deleting a property
• __getIds__(): this method is called when iterating over property ids
• __hasInstance__(object): this method is called when the instanceof operator is used
• __equals__(object): this method is called when the == operator is used

Currently you have to manually patch and build Rhino to use Metamethods using the patch attached to this page.

Update 1: The patch is in the current svn/git snapshots, but of course you can still use the patch to build it by yourself.

Update 2: Due to a very silly bug, __set__ methods were called without the second argument in the initial version. This is fixed in the new patch as well as git/svn repositories.

This patch is against the current Rhino CVS snapshot. Let me know if it fails to apply to earlier versions of Rhino.