title: Automatic type hints resolving in json4s
body: <p>Suppose I have a class hierarchy like:</p>
  
  <pre><code>trait Event
  case class ThisEvent extends Event
  case class ThatEvent extends Event
  case class AnotherEvent extends Event
  </code></pre>
  
  <p>Currently in my serialization code I have to use this:</p>
  
  <pre><code>implicit val formats = new DefaultFormats {
    override val typeHintFieldName = "_t"
    override val typeHints = ShortTypeHints(List(classOf[ThisEvent], classOf[ThatEvent], classOf[AnotherEvent]))
  }
  </code></pre>
  
  <p>But I would very much prefer something like this:</p>
  
  <pre><code>implicit val formats = new DefaultFormats {
    override val typeHintFieldName = "_t"
    override val typeHints = ShortTypeHints(List(classOf[Event]))
  }
  </code></pre>
  
  <p>How would you solve this?</p>