title: Multiple-Inheritance type class inheritance in ruby
body: <p>I got a <code>Base</code> superclass and a bunch of derived classes, like <code>Base::Number</code>, <code>Base::Color</code>. I'd like to be able to use those child classes as if I they inherited from say <code>Fixnum</code> in the case of <code>Number</code>.</p>
  
  <p>What's the best way to do this, while still having them respond appropriately to <code>is_a? Base</code> ?</p>
  
  <p>So, I should be able to do </p>
  
  <pre><code>Number.new(5) + Number.new(6) # =&gt; 11
  Number.new.is_a? Base         # =&gt; true
  </code></pre>
  
  <p>I'm thinking I could mix-in Base, and overwrite the is_a?, kind_of? and instance_of? methods, but hopefully there's a cleaner way.</p>