function-keywords

function-keywords Standard Generic Function

Syntax:

function-keywords method → keys, allow-other-keys-p

Method Signatures:

function-keywords (method standard-method)

Arguments and Values:

method—a method.

keys—a list.

allow-other-keys-p—a generalized boolean.

Description:

Returns the keyword parameter specifiers for a method.

Two values are returned: a list of the explicitly named keywords and a generalized boolean that states whether &allow-other-keys had been specified in the method definition.

Examples:

(defmethod gf1 ((a integer) &optional (b 2) 
		&key (c 3) ((:dee d) 4) e ((eff f))) 
  (list a b c d e f)) 
→ #<STANDARD-METHOD GF1 (INTEGER) 36324653> 
(find-method #’gf1 ’() (list (find-class ’integer))) 
→ #<STANDARD-METHOD GF1 (INTEGER) 36324653> 
(function-keywords \*) 
→ (:C :DEE :E EFF), *false* 
(defmethod gf2 ((a integer)) 
  (list a b c d e f)) 
→ #<STANDARD-METHOD GF2 (INTEGER) 42701775> 
(function-keywords (find-method #’gf1 ’() (list (find-class ’integer)))) 
→ (), *false* 
(defmethod gf3 ((a integer) &key b c d &allow-other-keys) 
  (list a b c d e f)) 
(function-keywords \*) 
→ (:B :C :D), *true* 

Affected By:

defmethod

See Also:

defmethod

Expanded Reference: function-keywords

Inspecting Keyword Parameters of a Method

function-keywords returns two values: a list of keyword parameter names accepted by a method, and a boolean indicating whether &allow-other-keys was specified.

(defgeneric make-thing (type &key))

(defmethod make-thing ((type (eql :box)) &key width height depth)
  (list :box width height depth))

(let ((m (find-method #'make-thing '() (list (intern-eql-specializer :box)))))
  ;; Note: intern-eql-specializer is not standard; use find-method differently
  )

;; A more portable approach using compute-applicable-methods:
(defgeneric create-item (kind &key))

(defmethod create-item ((kind (eql :circle)) &key radius color)
  (list kind radius color))

;; Inspect keywords via a method found through the generic function
(let* ((methods (compute-applicable-methods #'create-item '(:circle)))
       (m (first methods)))
  (multiple-value-list (function-keywords m)))
=> ((:RADIUS :COLOR) NIL)

Detecting &allow-other-keys

The second return value indicates whether the method accepts arbitrary keyword arguments.

(defgeneric flexible-op (x &key))

(defmethod flexible-op ((x integer) &key start end &allow-other-keys)
  (list x start end))

(let* ((methods (compute-applicable-methods #'flexible-op '(42)))
       (m (first methods)))
  (multiple-value-list (function-keywords m)))
=> ((:START :END) T)

Methods with No Keywords

A method without &key returns empty keyword information.

(defgeneric simple-op (x))

(defmethod simple-op ((x number)) x)

(let* ((methods (compute-applicable-methods #'simple-op '(42)))
       (m (first methods)))
  (multiple-value-list (function-keywords m)))
=> (NIL NIL)