title: Mixins with C# 4.0
body: <p>I've seen various questions regarding if mixins can be created in C# and they are often directed to the re-mix project on codeplex.  However, I don't know if I like the "complete interface" concept.  Ideally, I would extend a class like so:</p>
  
  <pre><code>    [Taggable]
      public class MyClass
      {
         ....
      }
  </code></pre>
  
  <p>By simply adding the Taggable interface, I can create objects of type MyClass via some kind of object factory.  The returned instance would have all the members defined in MyClass as well as all members provided by adding the tagging attribute (like a collection of tags).  It seems like this would be easily doable using C# 4.0 (the dynamic keyword).  The re-mix project uses C# 3.5.  Does anyone have any good ways to extend objects via C# 4.0 without altering the classes themselves? Thanks.</p>