validated-class

The validated-class metaclass provides a :validators slot parameter. :validators takes a list of one or more predicates which are run on object creation and slot updates. Failed valiadtors singnal the validation-error condition.

Usage

(defun less-than-5? (value)
  (< (length value) 5))

(defclass test-class ()
  ((foo :initarg :foo
        :accessor foo
        :validators (stringp less-than-5?)))
  (:metaclass validated-class))

;; CL-USER> (make-instance 'test-class :foo 123)
;; STRINGP failed when setting FOO to 123
;;    [Condition of type VALIDATION-ERROR]
;;
;; CL-USER> (make-instance 'test-class :foo "12345")
;; LESS-THAN-5? failed when setting FOO to 12345
;;    [Condition of type VALIDATION-ERROR]
;;
;; CL-USER> (make-instance 'test-class :foo "1234")
;; #<TEST-CLASS {7007E09133}>

Other implementations worth exploring

• canonicalized-initargs