title: class needs to be abstract since its members are not instantiated
body: <p>I am trying to create a class rat having parameters "value" and "dimensions". Rat has a member "fitness". I want this member to be initialized by constructor, but declaring this member enforces it to be explicitly instantiated. </p>
  
  <p>This  is a class rat having a member fitness. I have declared but not defined the member as I want to get it through constructor.</p>
  
  <pre><code>class rat(value:Int,dimensions:Int){
     var fitness:Int
     def rat(){
        fitness=sol_fit()
     }
     def sol_fit():Int={
        var f=value*dimensions
        f 
     }
  }
  </code></pre>