;;;; units/unit.lisp

(in-package #:wheelwork)

(defclass/std unit ()
  ((cached-application  :a)
   (container :with :a)))

(defmethod (setf closer-mop:slot-value-using-class) :after
    (newval class (unit unit) slot)
  (case (closer-mop:slot-definition-name slot)
    (container
     (setf (cached-application unit) nil))))


(defun app-of-unit (unit)
  "Returns the APPLICATION instance, if any, of which this UNIT is a
part. NIL indicates that the unit has not been added to any container
in this application."
  (or (cached-application unit) 
      (setf (cached-application unit) 
            (labels ((rec (u)
                       (when-let (c (unit-container u))
                         (etypecase c
                           (application c)
                           (unit (rec c))
                           (null nil)))))
              (rec unit)))))