title: How to keep dry in the property method
body: <p>If I want to watch rounds and savingHoursPerRound,</p>
  
  <p>I should put them into property,</p>
  
  <p>is there anyway to auto-watch all variable in the function ?</p>
  
  <pre><code>  savingHoursPerYear:function(){
      return this.get("rounds")*this.get("savingHoursPerRound");
    }.property("rounds","savingHoursPerRound"), 
  </code></pre>