Today I was coding up a tricky bit of logic where I was using BasicObject to delegate all methods to another object it was encapsulating and I learned that raise is not a keyword in ruby.

To give a bit of detail here is generically what I had coded up…

class GateKeeper < BasicObject
  def initialize(obj)
    @obj = obj
  end
 
  def method_missing(method, *args, &block)
    @obj.send(method, *args, &block)
  rescue ::StandardError => error
    raise error unless method.to_s == 'pesky_method'
    # ... log things about failure and try known fallbacks
  end
end

Everything looks okay with this little patching class right? Little did I know I had created an infinte loop that was very difficult to debug. I’ll quickly walk through the stack and explain what happened.

1. GateKeeper receives method normal_method
2. method_missing catches the call and sends the method to @obj
3. normal_method raises an exception that is rescued
4. normal_method does not equal pesky_method so the error is re-raised…
5. raise is not a method so it is sent to method missing
6. raise is called on @obj and an exception is raised, which is caught
7. raise is not equal to pesky_method so the error is re-raised…
8. ….

Now you understand the infinite loop. This little bugger evaded me for awhile and I learned a very powerful lesson, raise is just a method, not a keyword in the ruby language. If you find yourself havinging the same problem you can use Kernel.raise to throw an exception. Rule of thumb, when using BasicObject don’t expect any methods to work, including raise !