Enable access to stacked return value in AT EXIT rules by binding $! to reference it

I have an AT EXIT rule and needed to BIND to the returned value. Nothing in the docs told me this was possible. I was going to go into the code and see if I can implement it, but I came across this:

} else if (name.equals("$$"))

{ // $$ references the helper implicitly associated with a builtin call index = HELPER; }

else if (name.equals("$!")) {
// $! refers to the current return value for the triggger method and is only valid when
// the rule is triggered AT EXIT
index = RETURN;

So it looks like this is already supported! Yea for me.

This JIRA is to ensure that $! gets documented in the Byteman user guide. I also see that $$ is an undocumented feature too - should mention that one as well in the docs.