title: How to signal "not implemented yet"?
body: <p>In the initial drafting of a new gem I need to leave some method implementations empty ( to be implemented in the next )</p>
  
  <p>Therefore, I would like to signal a "not implemented yet" exception</p>
  
  <p>I'm wondering if there is a <em>best practice</em> or <em>standard conventions</em> specific to the Ruby language to code this kind of placeholder / exception. </p>
  
  <p>i.e: something like: </p>
  
  <ul>
  <li><a href="http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/UnsupportedOperationException.html" rel="noreferrer">UnsupportedOperationException</a> in Java</li>
  <li><a href="http://msdn.microsoft.com/en-us/library/system.notimplementedexception.aspx" rel="noreferrer">NotImplementedException</a> in .Net Framework (C#)</li>
  </ul>