Indeed we could, and as a reply mentions some implementations do take liberties with various Ruby features like $~ and $_ (in MacRuby they are thread-local, whi

Indeed we could, and as a reply mentions some implementations do take liberties with various Ruby features like $~ and $_ (in MacRuby they are thread-local, which sorta works but is often broken behavior). Part of my challenge as a Ruby implementer is to figure out which features really must be implemented to the letter of the law and which ones can be fudged without impacting anyone. ObjectSpace was an example that could be fudged; it turned out nobody ever used it for anything other than iterating over all classes in the system. I also often make my case to the MRI/ruby-core folks and Matz himself as to features that are an unreasonable performance hit for not enough benefit. Sometimes I win those arguments, sometimes I lose them.