One of the more dynamic features of Ruby is method_missing, a way of intercepting method calls that would cause a NoMethodError if method_missing isn’t there. This feature is by no means unique to Ruby. It exists in Smalltalk, Python, Groovy, some JavaScripts, and even most CLOS extensions have it. But Ruby being what it is, for some reason this feature seem to have more heavily used in Ruby than anywhere else. It’s also a feature most Ruby developers seem to know about. Is this because Ruby people are power hungy, crazy monkey patchers? Maybe, but method_missing is also potentially very useful, if used correctly. But of course, it’s exceedingly easy to misuse. In almost all cases you think you need method_missing, you actually don’t.

The purposes of this post is to take a look at a few ways people are using method_missing in the wild, what the consequences are and what you can do to mitigate them. I’m bound to have missed a few use cases here, so please feel free to add more in the comments.