That's yet an other topic, as monkey patching can definitely be explicit in ruby. The dynamically generated things at runtime are generally through the catch all method missing facility that can be overwritten. This can also be done in, say, PHP. It just that the community is less fond of it. Not sure about what most popular ahead of time oriented languages expose as facility in this area, obviously one can always even decide to generate automodifying executable. There is nothing special about ruby when it comes to go into forbidden realms, except maybe it doesn't come to much in your way when you try to express something, even if that is not the most maintenance friendly path.