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| ANSI Common Lisp 7 Objects 7.7 Dictionary of Objects
7.7.12 slot-missing | Standard Generic Function
Syntax: slot-missing class object slot-name operation `&optional` new-value {result}* Method Signatures: slot-missing (class t) object slot-name operation `&optional` new-value Arguments and Values: class - the class of object. object - an object. slot-name - a symbol (the name of a would-be slot). operation - one of the symbols setf, slot-boundp, slot-makunbound, or slot-value. new-value - an object. result - an object. Description: The generic function slot-missing is invoked when an attempt is made to access a slot in an object whose metaclass is standard-class and the slot of the name slot-name is not a name of a slot in that class. The default method signals an error. The generic function slot-missing is not intended to be called by programmers. Programmers may write methods for it. The generic function slot-missing may be called during evaluation of slot-value, `(setf slot-value)`, slot-boundp, and slot-makunbound. For each of these operations the corresponding symbol for the operation argument is slot-value, setf, slot-boundp, and slot-makunbound respectively. The optional new-value argument to slot-missing is used when the operation is attempting to set the value of the slot. If slot-missing returns, its values will be treated as follows: If the operation is setf or slot-makunbound, any values will be ignored by the caller. If the operation is slot-value, only the primary value will be used by the caller, and all other values will be ignored. If the operation is slot-boundp, any boolean equivalent of the primary value of the method might be is used, and all other values will be ignored. Exceptional Situations: The default method on slot-missing signals an error of type error. See Also: defclass, slot-exists-p, slot-value Notes: The set of arguments (including the class of the instance) facilitates defining methods on the metaclass for slot-missing. Allegro CL Implementation Details: None.

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