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make-instances-obsolete

make-instances-obsolete Standard Generic Function

Syntax:

make-instances-obsolete class → class

Method Signatures:

make-instances-obsolete (class standard-class)

make-instances-obsolete (class symbol)

Arguments and Values:

class—a class designator .

Description:

The function make-instances-obsolete has the effect of initiating the process of updating the instances of the class. During updating, the generic function update-instance-for-redefined-class will be invoked.

The generic function make-instances-obsolete is invoked automatically by the system when defclass has been used to redefine an existing standard class and the set of local slots accessible in an instance is changed or the order of slots in storage is changed. It can also be explicitly invoked by the user.

If the second of the above methods is selected, that method invokes make-instances-obsolete on (find-class class).

Examples:

See Also:

update-instance-for-redefined-class, Section 4.3.6 (Redefining Classes)

Expanded Reference: make-instances-obsolete​

Triggering Instance Updates​

make-instances-obsolete marks all existing instances of a class as needing updating. The next time a slot of such an instance is accessed, update-instance-for-redefined-class is called. Normally this happens automatically when a class is redefined via defclass, but it can be triggered manually.

(defclass versioned ()
  ((data :initarg :data :accessor versioned-data)))

(let ((obj (make-instance 'versioned :data "v1")))
  ;; Manually mark instances as obsolete
  (make-instances-obsolete 'versioned)
  ;; Next access triggers the update protocol
  (versioned-data obj))
=> "v1"

Automatic Invocation on Class Redefinition​

When you redefine a class with defclass, make-instances-obsolete is called automatically by the system if the slot layout changes.

(defclass point ()
  ((x :initarg :x :accessor point-x)
   (y :initarg :y :accessor point-y)))

(let ((p (make-instance 'point :x 1 :y 2)))
  ;; Redefine the class with an additional slot
  ;; (In practice this would be a separate defclass form)
  ;; The system calls make-instances-obsolete automatically
  ;; and instances are updated on next access.
  (point-x p))
=> 1

Using with a Class Object​

make-instances-obsolete accepts either a symbol (class name) or a class object.

(defclass demo () ((val :initarg :val :accessor demo-val)))

(make-instances-obsolete (find-class 'demo))
==> #<STANDARD-CLASS DEMO>