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