slot-unbound (ANSI and GNU Common Lisp Document)

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#### 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.