title: Kotlin traits and retrofit
body: <p>I'm trying to implement the example from <a href="http://howrobotswork.wordpress.com/2013/10/28/using-rxjava-in-android/" rel="noreferrer">here</a> in Kotlin. I get this error at runtime "Caused by: java.lang.IllegalArgumentException: Interface definitions must not extend other interfaces". Is there any way to treat Kotlin traits as java interfaces when they don't have any methods implemented, or do I have to use java interfaces? Here's the code:</p>
  
  <pre><code>public trait RestAPI {
  
      [GET("/weather")]
      fun getList([Query("q")] place: String,
                  [Query("units")] units: String)
              : Observable&lt;WeatherData&gt;
  }            
  </code></pre>
  
  <p>And the call that causes the error:</p>
  
  <pre><code>val service = restAdapter?.create(javaClass&lt;RestAPI&gt;())
  </code></pre>