remove-method

remove-method Standard Generic Function

Syntax:

remove-method generic-function method → generic-function

Method Signatures:

remove-method (generic-function standard-generic-function)

method

Arguments and Values:

generic-function—a generic function.

method—a method.

Description:

The generic function remove-method removes a method from generic-function by modifying the generic-function (if necessary).

remove-method must not signal an error if the method is not one of the methods on the generic-function.

See Also:

find-method

Expanded Reference: remove-method

Removing a Method from a Generic Function

remove-method removes a method object from a generic function. It returns the generic function. If the method is not on the generic function, no error is signaled.

(defgeneric transform (x))

(defmethod transform ((x integer)) (* x 2))
(defmethod transform ((x string)) (string-upcase x))

(transform 5)
=> 10
(transform "hello")
=> "HELLO"

;; Remove the integer method
(let ((m (find-method #'transform '() (list (find-class 'integer)))))
  (remove-method #'transform m))

(transform "hello")
=> "HELLO"

;; Integer method is gone
(find-method #'transform '() (list (find-class 'integer)) nil)
=> NIL

Removing Qualified Methods

You can also remove :before, :after, and :around methods.

(defgeneric process (x))

(defmethod process ((x number)) x)
(defmethod process :before ((x number)) (format t "before~%"))

(process 42)
.. before
..
=> 42

;; Remove the :before method
(let ((m (find-method #'process '(:before) (list (find-class 'number)))))
  (remove-method #'process m))

(process 42)
=> 42

Safe Removal (No Error on Missing Method)

remove-method silently does nothing if the method is not present on the generic function.

(defgeneric noop-gf (x))
(defmethod noop-gf ((x t)) x)

;; Removing the same method twice does not signal an error
(let ((m (find-method #'noop-gf '() (list (find-class 't)))))
  (remove-method #'noop-gf m)
  (remove-method #'noop-gf m))  ;; No error