(defclass counter ()
  ((value :initform 0 :accessor counter-value)))

(defgeneric m-inc (counter)
  (:method ((counter counter))
    (incf (counter-value counter))))

(defun f-inc (counter)
  (incf (counter-value counter)))


(time (loop :with c := (make-instance 'counter)
            :repeat 1000000
            :do (m-inc c)
            :finally (return (counter-value c))))

(time (loop :with c := (make-instance 'counter)
            :repeat 1000000
            :do (f-inc c)
            :finally (return (counter-value c))))