+@findex validate-superclass
+@findex finalize-inheritance
+@findex sb-mop:validate-superclass
+@findex sb-mop:finalize-inheritance
+@tindex standard-class
+@tindex funcallable-standard-class
+@tindex sb-mop:funcallable-standard-class
+@tindex function
+@findex sb-mop:class-prototype
+@findex class-prototype
+although SBCL obeys the requirement in AMOP for
+@code{validate-superclass} for @code{standard-class} and
+@code{funcallable-standard-class} to be compatible metaclasses, we
+impose an additional requirement at class finalization time: a class
+of metaclass @code{funcallable-standard-class} must have
+@code{function} in its superclasses, and a class of metaclass
+@code{standard-class} must not.
+
+@findex typep
+@findex class-of
+@findex subtypep
+At class finalization, a class prototype which is accessible by a
+standard mop function @code{sb-mop:class-prototype}. The user can
+then ask whether this object is a @code{function} or not in several
+different ways: whether it is a function according to @code{typep};
+whether its @code{class-of} is @code{subtypep} @code{function}, or
+whether @code{function} appears in the superclasses of the class. The
+additional consistency requirement comes from the desire to make all
+of these answers the same.
+
+The following class definitions are bad, and will lead to errors
+either immediately or if an instance is created:
+@lisp
+(defclass bad-object (funcallable-standard-object)
+ ()
+ (:metaclass standard-class))
+@end lisp
+@lisp
+(defclass bad-funcallable-object (standard-object)
+ ()
+ (:metaclass funcallable-standard-class))
+@end lisp
+The following definition is acceptable:
+@lisp
+(defclass mixin ()
+ ((slot :initarg slot)))
+(defclass funcallable-object (funcallable-standard-object mixin)
+ ()
+ (:metaclass funcallable-standard-class))
+@end lisp
+and leads to a class whose instances are funcallable and have one slot.
projects / sbcl.git / blobdiff