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  ANSI Common Lisp   7 Objects   7.7 Dictionary of Objects

7.7.13 slot-unbound Standard Generic Function

Syntax:
slot-unbound class instance slot-name    {result}*

Method Signatures:
slot-unbound (class t) instance slot-name

Arguments and Values:
class - the class of the instance.

instance - the instance in which an attempt was made to read the unbound slot.

slot-name - the name of the unbound slot.

result - an object.

Description:
The generic function slot-unbound is called when an unbound slot is read in an instance whose metaclass is standard-class. The default method signals an error of type unbound-slot. The name slot of the unbound-slot condition is initialized to the name of the offending variable, and the instance slot of the unbound-slot condition is initialized to the offending instance.

The generic function slot-unbound is not intended to be called by programmers. Programmers may write methods for it. The function slot-unbound is called only indirectly by slot-value.

If slot-unbound returns, only the primary value will be used by the caller, and all other values will be ignored.

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

See Also:
slot-makunbound

Notes:
An unbound slot may occur if no :initform form was specified for the slot and the slot value has not been set, or if slot-makunbound has been called on the slot.

Allegro CL Implementation Details:
None.

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