The Art of the Metaobject Protocol- P6: The work described here is synthetic in nature, bringing together techniques and insights from several branches of computer. | Concepts 149 slot specification. If one of these slot options appears more than once the value of the property will be a list of the specified values. An implementation is free to add additional properties to the canonicalized slot specification provided these are not symbols accessible in the common-lisp-user package or exported by any package defined in the ANSI Common Lisp standard. Returning to the correspondence between arguments to the defclass macro and the arguments received by the ensure-class function y The default initargs class option if it is present in the defclass form becomes the value of the direct-default-initargs keyword argument to ensure-class. Special processing of this value is done to properly capture the lexical scope of the default value forms. This is done by converting each default initarg in the class option into a canonicalized default initarg. The resulting list of canonicalized default initargs is the value of the direct-default-initargs keyword argument to ensure-class. A canonicalized default initarg is a list of three elements. The first element is the name the second is the actual form itself and the third is a function of zero arguments which when called returns the result of evaluating the default value form in its proper lexical environment. The metaclass class option if it is present in the defclass form becomes the value of the metaclass keyword argument to ensure-class. The documentation class option if it is present in the defclass form becomes the value of the .documentation keyword argument to ensure-class. Any other class options become the value of keyword arguments with the same name. The value of the keyword argument is the tail of the class option. An error is signaled if any class option appears more than once in the defclass form. In the call to ensure-class every element of its arguments appears in the same left-to-right order as the corresponding element of the defclass form except that the order of the .
