(in-package :collection-class)
 
 (defmethod sb-sequence:length ((sequence collection))
   (length (items sequence)))
 
 (defmethod sb-sequence:elt ((sequence collection) index)
   (elt (items sequence) index))
 
 (defmethod (setf sb-sequence:elt) (new-value (sequence collection) index)
   (setf (elt (items sequence) index) new-value))
 
 (defmethod sb-sequence:adjust-sequence ((sequence collection) length &key initial-element initial-contents)
   (let ((result (duplicate-collection sequence)))
     (when (or initial-element initial-contents)
       (setf (items result)
             (sb-sequence:adjust-sequence (items result) length
                                          :initial-element initial-element
                                          :initial-contents initial-contents)))
     result))
 
 (defmethod sb-sequence:make-sequence-like ((sequence collection) length &key initial-element initial-contents)
   (let ((result (duplicate-collection sequence)))
     (setf (items result)
           (sb-sequence:make-sequence-like (items result) length
                                           :initial-element initial-element
                                           :initial-contents initial-contents))
     result))