Returns a list of the specializers of method. This value is a list of specializer metaobjects. This is the value of the :SPECIALIZERS initialization argument that was associated with the method during initialization.

Returns a (possibly empty) list of the qualifiers of method. This value is a list of non-NIL atoms. This is the defaulted value of the :QUALIFIERS initialization argument that was associated with the method during initialization.

Returns the (unspecialized) lambda list of method. This value is a Common Lisp lambda list. This is the value of the :LAMBDA-LIST initialization argument that was associated with the method during initialization.

Returns the generic function that method is currently connected to, or NIL if it is not currently connected to any generic function. This value is either a generic function metaobject or NIL. When a method is first created it is not connected to any generic function. This connection is maintained by the generic functions ADD-METHOD and REMOVE-METHOD.

Returns the method function of method. This is the value of the :FUNCTION initialization argument that was associated with the method during initialization.

The evaluation or execution of a DEFMETHOD form requires first that the body of the method be converted to a method function. This process is described below. The result of this process is a method function and a set of additional initialization arguments to be used when creating the new method. Given these two values, the evaluation or execution of a DEFMETHOD form proceeds in three steps.

The first step ensures the existence of a generic function with the specified name. This is done by calling the function ENSURE-GENERIC-FUNCTION. The first argument in this call is the generic function name specified in the DEFMETHOD form.

The second step is the creation of the new method metaobject by calling MAKE-INSTANCE. The class of the new method metaobject is determined by calling CLOS:GENERIC-FUNCTION-METHOD-CLASS on the result of the call to ENSURE-GENERIC-FUNCTION from the first step.

The initialization arguments received by the call to MAKE-INSTANCE are as follows:

In the third step, ADD-METHOD is called to add the newly created method to the set of methods associated with the generic function metaobject.

The result of the call to ADD-METHOD is returned as the result of evaluating or executing the DEFMETHOD form.

An example showing a typical DEFMETHOD form and a sample expansion is shown in the following example:

(defmethod move :before ((p position) (l (eql 0))
                         &OPTIONAL (visiblyp t)
                         &KEY color)
  (set-to-origin p)
  (when visiblyp (show-move p 0 color)))

(let ((#:g001 (ensure-generic-function 'move)))
  (add-method #:g001
    (make-instance (generic-function-method-class #:g001)
                   :qualifiers '(:before)
                   :specializers (list (find-class 'position)
                                       (intern-eql-specializer 0))
                   :lambda-list '(p l &OPTIONAL (visiblyp t)
                                      &KEY color)
                   :function (function method-lambda)
                   'additional-initarg-1 't
                   'additional-initarg-2 '39)))

The processing of the method body for this method is shown below.

(let ((gf (ensure-generic-function 'move)))
  (make-method-lambda
    gf
    (class-prototype (generic-function-method-class gf))
    '(lambda (p l &OPTIONAL (visiblyp t) &KEY color)
       (set-to-origin p)
       (when visiblyp (show-move p 0 color)))
    environment))

(let* ((gf (make-instance 'standard-generic-function
                          :lambda-list '(p l &OPTIONAL visiblyp &KEY)))
       (method-class (generic-function-method-class gf)))
  (multiple-value-bind (lambda initargs)
       (make-method-lambda
         gf
         (class-prototype method-class)
         '(lambda (p l &OPTIONAL (visiblyp t) &KEY color)
            (set-to-origin p)
            (when visiblyp (show-move p 0 color)))
         nil)
    (add-method gf
                (apply #'make-instance method-class
                       :function (compile nil lambda)
                       :specializers (list (find-class 'position)
                                           (intern-eql-specializer 0))
                       :qualifiers ()
                       :lambda-list '(p l &OPTIONAL (visiblyp t)
                                          &KEY color)
                       initargs))))

A method metaobject can be created by calling MAKE-INSTANCE. The initialization arguments establish the definition of the method. A method metaobject cannot be redefined; calling REINITIALIZE-INSTANCE SIGNALs an ERROR.

Initialization of a method metaobject must be done by calling MAKE-INSTANCE and allowing it to call INITIALIZE-INSTANCE. Portable programs must not

Since metaobject classes may not be redefined, no behavior is specified for the result of calls to UPDATE-INSTANCE-FOR-REDEFINED-CLASS on method metaobjects. Since the class of a method metaobject cannot be changed, no behavior is specified for the result of calls to UPDATE-INSTANCE-FOR-DIFFERENT-CLASS on method metaobjects.

During initialization, each initialization argument is checked for errors and then associated with the method metaobject. The value can then be accessed by calling the appropriate accessor as shown in Table 29.5, “Initialization arguments and accessors for method metaobjects”.

This section begins with a description of the error checking and processing of each initialization argument. This is followed by a table showing the generic functions that can be used to access the stored initialization arguments. The section ends with a set of restrictions on portable methods affecting method metaobject initialization.

In these descriptions, the phrase “this argument defaults to value” means that when that initialization argument is not supplied, initialization is performed as if value had been supplied. For some initialization arguments this could be done by the use of default initialization arguments, but whether it is done this way is not specified. Implementations are free to define default initialization arguments for specified method metaobject classes. Portable programs are free to define default initialization arguments for portable subclasses of the class METHOD.

After the processing and defaulting of initialization arguments described above, the value of each initialization argument is associated with the method metaobject. These values can then be accessed by calling the corresponding generic function. The correspondences are as follows: