Generic Function

Summary

Describes how a defclass slot option is parsed.

Package

clos

Signature

process-a-slot-option metaclass option value already-processed-other-options slot => processed-options

Arguments

metaclass

The metaclass of the class being parsed.

option

The slot option name.

value

The value of the slot option.

already-processed-other-options

A plist of initargs for non-standard options that have been processed already.

slot

The whole slot description.

Values

processed-options

A plist of initargs.

Description

The generic function process-a-slot-option describes how the value of a slot option is parsed. It is called at defclass macroexpansion time. By default LispWorks parses slot options as defined in AMOP, but you need to supply a method if you need slot options with different behaviour.

processed-options should be a plist of slot initargs and values containing those from already-processed-other-options together with initargs for option as required. These are added to any other initargs for the slot.

Example

(defclass extended-class (standard-class)())

(defmethod clos:process-a-slot-option 

           ((class extended-class) option value 

            already-processed-options slot)

  (if (eq option :extended-slot)

      (list* :extended-slot 

             value 

             already-processed-options)

    (call-next-method)))

(defclass extended-direct-slot-definition 

          (clos:standard-direct-slot-definition)

  ((extended-slot :initarg :extended-slot :initform nil)))

(defmethod clos:direct-slot-definition-class 

           ((x extended-class) &rest initargs)

  'extended-direct-slot-definition)

(defclass test ()

  ((regular :initform 3)

   (extended :extended-slot t :initform 4))

  (:metaclass extended-class))

To add a slot option :special-reader whose value is a non-evaluated symbol naming a reader:

(defmethod clos:process-a-slot-option 

           ((class my-metaclass) option value

            already-processed-options slot)

  (if (and (eq option :special-reader) 

           (symbolp value))

      (list* :special-reader 

             `',value already-processed-options)

    (call-next-method)))

To allow repeated :special-reader options which are combined into a list:

(defmethod clos:process-a-slot-option 

           ((class my-metaclass) option value

            already-processed-options slot)

  (if (and (eq option :special-reader) (symbolp value))

      (let ((existing (getf 

                       already-processed-options

                       :special-reader)))

        (if existing ; this is a quoted list of symbols

            (progn

              (setf (cdr (last (cadr existing))) (list value))

              already-processed-options)

          (list* :special-reader

                 `'(,value) 

                 already-processed-options)))

    (call-next-method)))

See also

defclass
process-a-class-option