In the initial drafting of a new gem I need to leave some method implementations empty ( to be implemented in the next )

Therefore, I would like to signal a "not implemented yet" exception

I'm wondering if there is a *best practice* or *standard conventions* specific to the Ruby language to code this kind of placeholder / exception. 

i.e: something like: 

* [UnsupportedOperationException](http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/UnsupportedOperationException.html) in Java
* [NotImplementedException](http://msdn.microsoft.com/en-us/library/system.notimplementedexception.aspx) in .Net Framework (C#)