slot-boundp (ANSI and GNU Common Lisp Document)

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#### 7.7.9 slot-boundp [Function]

`slot-boundp` instance slot-name ⇒ generalized-boolean

#### Arguments and Values::

instance—an object.

slot-name—a symbol naming a slot of instance.

generalized-boolean—a generalized boolean.

#### Description::

Returns true if the slot named slot-name in instance is bound; otherwise, returns false.

#### Exceptional Situations::

If no slot of the name slot-name exists in the instance, slot-missing is called as follows:

     (slot-missing (class-of instance)
                   instance
                   slot-name
                   'slot-boundp)

(If slot-missing is invoked and returns a value, a boolean equivalent to its primary value is returned by slot-boundp.)

The specific behavior depends on instance’s metaclass. An error is never signaled if instance has metaclass standard-class. An error is always signaled if instance has metaclass built-in-class. The consequences are undefined if instance has any other metaclass–an error might or might not be signaled in this situation. Note in particular that the behavior for conditions and structures is not specified.

#### See Also::

slot-makunbound , slot-missing

#### Notes::

The function slot-boundp allows for writing after methods on initialize-instance in order to initialize only those slots that have not already been bound.

Although no implementation is required to do so, implementors are strongly encouraged to implement the function slot-boundp using the function `slot-boundp-using-class` described in the Metaobject Protocol.