@itemize
@item
-the abstract @code{metaobject} class is not present in the class
-hierarchy;
-
-@item
-the @code{standard-object} and @code{funcallable-standard-object}
-classes are disjoint;
+@findex compute-effective-method
+@findex sb-mop:compute-effective-method
+@code{compute-effective-method} only returns one value, not two.
+
+There is no record of what the second return value was meant to
+indicate, and apparently no clients for it.
@item
-@code{compute-effective-method} only returns one value, not two;
-
+@findex ensure-generic-function
+@findex generic-function-declarations
+@findex sb-mop:generic-function-declarations
+the arguments @code{:declare} and @code{:declarations} to
+@code{ensure-generic-function} are both accepted, with the leftmost
+argument defining the declarations to be stored and returned by
+@code{generic-function-declarations}.
+
+Where AMOP specifies @code{:declarations} as the keyword argument to
+@code{ensure-generic-function}, the Common Lisp standard specifies
+@code{:declare}. Portable code should use @code{:declare}.
+
@item
-the system-supplied @code{:around} method for @code{compute-slots}
-specialized on @code{funcallable-standard-class} does not respect the
-requested order from a user-supplied primary method.
+@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.
@end itemize
@section Efficiency Hacks
The @code{sb-ext:purify} function causes SBCL first to collect all
-garbage, then to mark all uncollected objects as permanent, never
-again attempting to collect them as garbage. This can cause a large
-increase in efficiency when using a primitive garbage collector, or a
-more moderate increase in efficiency when using a more sophisticated
-garbage collector which is well suited to the program's memory usage
-pattern. It also allows permanent code to be frozen at fixed
-addresses, a precondition for using copy-on-write to share code
-between multiple Lisp processes. it is less important with modern
-generational garbage collectors.
+garbage, then to mark all uncollected objects as permanent, never again
+attempting to collect them as garbage. This can cause a large increase
+in efficiency when using a primitive garbage collector, or a more
+moderate increase in efficiency when using a more sophisticated garbage
+collector which is well suited to the program's memory usage pattern. It
+also allows permanent code to be frozen at fixed addresses, a
+precondition for using copy-on-write to share code between multiple Lisp
+processes. This is less important with modern generational garbage
+collectors, but not all SBCL platforms use such a garbage collector.
@include fun-sb-ext-purify.texinfo
projects / sbcl.git / blobdiff