Rick DeNatale wrote:
> I don't know what JRuby does.

In JRuby 1.2 and prior, it was slot-based for up to 5 varables and then 
a simple hashtable for anything larger.

In 1.3 and up, instance variables are all slot-based and should use less 
memory as well. The implementation is similar to 1.9, except that the 
instance variable slot locations are call-site cached (so subsequent 
lookups to the same ivar against the same type are only a few memory 
dereferences).

The new impl still passes all the same RubySpecs.

- Charlie