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| ANSI Common Lisp 7 Objects 7.1 Object Creation and Initialization ### 7.1.6 Initialize-Instance The generic function initialize-instance is called by make-instance to initialize a newly created instance. It uses standard method combination. Methods for initialize-instance can be defined in order to perform any initialization that cannot be achieved simply by supplying initial values for slots. During initialization, initialize-instance is invoked after the following actions have been taken: The defaulted initialization argument list has been computed by combining the supplied initialization argument list with any default initialization arguments for the class. The validity of the defaulted initialization argument list has been checked. If any of the initialization arguments has not been declared as valid, an error is signaled. A new instance whose slots are unbound has been created. The generic function initialize-instance is called with the new instance and the defaulted initialization arguments. There is a system-supplied primary method for initialize-instance whose parameter specializer is the class standard-object. This method calls the generic function shared-initialize to fill in the slots according to the initialization arguments and the `:initform` forms for the slots; the generic function shared-initialize is called with the following arguments: the instance, t, and the defaulted initialization arguments. Note that initialize-instance provides the defaulted initialization argument list in its call to shared-initialize, so the first step performed by the system-supplied primary method for shared-initialize takes into account both the initialization arguments provided in the call to make-instance and the defaulted initialization argument list. Methods for initialize-instance can be defined to specify actions to be taken when an instance is initialized. If only after methods for initialize-instance are defined, they will be run after the system-supplied primary method for initialization and therefore will not interfere with the default behavior of initialize-instance. The object system provides two functions that are useful in the bodies of initialize-instance methods. The function slot-boundp returns a generic boolean value that indicates whether a specified slot has a value; this provides a mechanism for writing after methods for initialize-instance that initialize slots only if they have not already been initialized. The function slot-makunbound causes the slot to have no value.

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