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class-of

class-of Function

Syntax:

class-of object ! class

Arguments and Values:

object—an object.

class—a class object.

Description:

Returns the class of which the object is a direct instance.

Examples:

(class-of ’fred) *!* #<BUILT-IN-CLASS SYMBOL 610327300> 
(class-of 2/3) *!* #<BUILT-IN-CLASS RATIO 610326642> 
(defclass book () ()) *!* #<STANDARD-CLASS BOOK 33424745> 
(class-of (make-instance ’book)) *!* #<STANDARD-CLASS BOOK 33424745> 
(defclass novel (book) ()) *!* #<STANDARD-CLASS NOVEL 33424764> 
(class-of (make-instance ’novel)) *!* #<STANDARD-CLASS NOVEL 33424764> 

(defstruct kons kar kdr) *!* KONS 
(class-of (make-kons :kar 3 :kdr 4)) *!* #<STRUCTURE-CLASS KONS 250020317>

See Also:

make-instance, type-of

Expanded Reference: class-of​

Querying the Class of Built-In Objects​

class-of returns the class of which the given object is a direct instance.

(class-of 42)
==> #<BUILT-IN-CLASS FIXNUM>
(class-of "hello")
==> #<BUILT-IN-CLASS SIMPLE-BASE-STRING>
(class-of 'foo)
==> #<BUILT-IN-CLASS SYMBOL>
(class-of #\a)
==> #<BUILT-IN-CLASS CHARACTER>
(class-of '(1 2 3))
==> #<BUILT-IN-CLASS CONS>

Querying the Class of CLOS Instances​

For user-defined classes, class-of returns the class created by defclass.

(defclass animal ()
  ((name :initarg :name)))

(defclass dog (animal) ())

(let ((d (make-instance 'dog :name "Rex")))
  (class-name (class-of d)))
=> DOG

Comparing class-of with typep​

class-of returns the most specific (direct) class, while typep checks membership in a class and all its superclasses.

(defclass shape () ())
(defclass circle (shape) ())

(let ((c (make-instance 'circle)))
  (list (class-name (class-of c))  ;; Direct class
        (typep c 'circle)           ;; Is a circle
        (typep c 'shape)            ;; Is also a shape
        (typep c 'standard-object)));; Is also a standard-object
=> (CIRCLE T T T)

Using class-of with Structures​

Structure types defined with defstruct also have classes.

(defstruct point x y)

(let ((p (make-point :x 1 :y 2)))
  (class-name (class-of p)))
=> POINT