(setf (find-class symbol &optional errorp environment) new-class)
symbol—a symbol.
errorp—a generalized boolean. The default is true.
environment—same as the &environment argument to
macro expansion functions and is used to distinguish between
compile-time and run-time environments.
The &environment argument has
dynamic extent; the consequences are undefined if
the &environment argument is
referred to outside the dynamic extent
of the macro expansion function.
class—a class object, or nil.
Returns the class object named by the symbol
in the environment. If there is no such class,
nil is returned if errorp is false; otherwise,
if errorp is true, an error is signaled.
The class associated with a particular symbol can be changed by using
setf with find-class;
or, if the new class given to setf is nil,
the class association is removed
(but the class object itself is not affected).
The results are undefined if the user attempts to change
or remove
the class associated with a
symbol that is defined as a type specifier in this standard.
See Section 4.3.7 (Integrating Types and Classes).
When using setf of find-class, any errorp argument is evaluated
for effect, but any values it returns are ignored; the errorp
parameter is permitted primarily so that the environment parameter
can be used.
The environment might be used to distinguish between a compile-time and a run-time environment.
If there is no such class and errorp is true,
find-class signals an error of type error.