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The ANSI Common Lisp standard specifies slot-value, (setf
slot-value), slot-boundp and slot-makunbound for
standard-objects, and furthermore suggests that these be implemented in
terms of Metaobject generic functions slot-value-using-class,
(setf slot-value-using-class), slot-boundp-using-class and
slot-makunbound-using-class. To make performance of these
operators tolerable, a number of optimizations are performed, at both
compile-time and run-time1.
[1] Note that ,at present,
slot-makunbound and slot-makunbound-using-class are not
optimized in any of the ways mentioned below.