slot-unbound (class t)
instance slot-name
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.
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.
The default method on slot-unbound
signals an error of type unbound-slot.
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.