+(defbinding type-default-interface-peek (type) pointer
+ ((find-type-number type t) type-number))
+
+(defbinding %object-interface-list-properties () pointer
+ (iface pointer)
+ (n-properties unsigned-int :out))
+
+(defun query-object-interface-properties (type &optional inherited-p)
+ (let* ((type-number (find-type-number type))
+ (iface (type-default-interface-ref type-number)))
+ (unwind-protect
+ (multiple-value-bind (array length)
+ (%object-interface-list-properties iface)
+ (unless (null-pointer-p array)
+ (unwind-protect
+ (%map-params array length type-number inherited-p)
+ (deallocate-memory array))))
+ (type-default-interface-unref iface))))
+
+
+(defun expand-interface-type (type forward-p options &rest args)
+ (declare (ignore args))
+ (let ((class (type-from-number type))
+ (slots (getf options :slots)))
+ `(defclass ,class (,(supertype type))
+ ,(unless forward-p
+ (slot-definitions class (query-object-interface-properties type) slots))
+ (:metaclass interface-class)
+ (:gtype ,(register-type-as type)))))
+
+(defun interface-dependencies (type options)
+ (delete-duplicates
+ (cons
+ (supertype type)
+ (append
+ (mapcar #'param-value-type (query-object-interface-properties type))
+ (loop
+ for slot in (getf options :slots)
+ as type = (getf (rest slot) :type)
+ when (and type (symbolp type) (find-type-number type))
+ collect (find-type-number type))))))
+
+
+(register-derivable-type 'interface "GInterface" 'expand-interface-type 'interface-dependencies)