anchor.diff:    ((owned :initform t)))
   
   (defclass entity (owned-thing visible-thing)
  -   ((grid-pos 
  +   ((grid-pos
        :initform (list -1 -1)
        :accessor grid-pos)
       (invalid ;if t, entity is scheduled for removal and won't be drawn or anything else
  
positive.code:    (selectable
      :initform t)))
  
  (sb-mop:finalize-inheritance (find-class 'unit))
  
  (defmethod initialize-instance :after ((unit unit) &key (weapons ()) (group ()) (dont-add nil))
    (unless dont-add
  
negative.code: (defmethod initialize-instance :after ((entity entity) &key (dont-add nil))
    (unless dont-add
      (push entity *entities*)))
  
  (defclass independent-entity (entity)
    ())
  
  