> JRuby could support such a feature, but I can tell you right now it would 
> negatively impact performance, and we'd probably make it an optional flag 
> so folks not interested in using the feature could run without it.
That would be the equivalent of the -O0 flag on gcc-compiled languages.
Namely: if you want to debug your code, remove optimizations. It seems
quite normal to me.
-- 
Sylvain