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  ANSI Common Lisp   7 Objects   7.7 Dictionary of Objects

7.7.12 slot-missing Standard Generic Function

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.

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:

Exceptional Situations:
The default method on slot-missing signals an error of type error.

See Also:
defclass, slot-exists-p, slot-value

The set of arguments (including the class of the instance) facilitates defining methods on the metaclass for slot-missing.

Allegro CL Implementation Details:

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