Ruby method missing

Method_missing is one of those special sauces that make Ruby such a wonderful programming language. It acts like a catch-all method in a class - if you call a method that the class doesn’t know how to respond to, Ruby will first look for a method_missing method to handle this unexpected method call. If method_missing doesn’t exist, then the typical NoMethodError will be raised. With method_missing, you can truly create dynamic classes that respond to a wide variety of methods, based on things like database fields - Active Record uses method_missing extensively to define getter and setter methods for each of the fields in the model’s database table. For an contrived example of method_missing in the flesh, you could define a class like the following:

class StringLength
   def method_missing(arg)
       "'#{arg}' has #{arg.length} letters!"
     end
end

And then interact with your class like so:

> StringLength.new.a_word
=> "'a_word' has 6 letters!"
> StringLength.new.something_long
=> "'something_long' has 14 letters!"
> StringLength.new.does_it_respond_to_anything?
=> "'does_it_respond_to_anything?' has 28 letters!"

You probably won’t use method_missing extensively in your Rails apps, but it’s good to know it exists, and the kinds of dynamic interfaces it can create.