mop.md

MOP — CLOS Metaobject Protocol

A subset of the CLOS Metaobject Protocol (AMOP), exported from the MOP package. The AmiLisp closer-mop shim re-exports these under CLOSER-MOP names, which is how MOP-using Quicklisp libraries (serapeum, trivia, …) reach them.

• Package: MOP (uses/used-by CL during bootstrap)
• Inherited by: COMMON-LISP-USER.
• These follow the AMOP semantics. This page is a categorized index; the authoritative reference for each operator is The Art of the Metaobject Protocol and the closer-mop documentation. AmiLisp implements a working subset — see lib/clos.lisp and the limitation note below for what is and isn't covered.

Class metaobjects

Signature	Kind	Description
(classp object)	function	True if object is a class metaobject.
(class-direct-superclasses class)	function	Direct superclasses as given in the class definition.
(class-direct-subclasses class)	function	Classes that name this class as a direct superclass.
(class-direct-slots class)	function	List of direct slot-definition metaobjects.
(class-direct-methods class)	function	Methods specialized directly on this class.
(class-direct-default-initargs class)	function	The class's own :default-initargs.
(class-default-initargs class)	function	Effective (inherited) default initargs.
(class-precedence-list class)	function	The class precedence list (class must be finalized).
(class-slots class)	function	List of effective slot-definition metaobjects.
(class-effective-slots class)	function	Effective-slot accessor that class-slots delegates to.
(class-slot-index-table class)	function	Slot-name → index table used for fast slot access.
(class-finalized-p class)	function	True if the class has been finalized.
(class-prototype class)	generic function	A (lazily allocated) prototype instance of the class.
(finalize-inheritance class)	generic function	Finalize the class: compute CPL, effective slots, layout.
(ensure-class name &rest keys)	function	Define or redefine a class; what defclass expands into. Redefinition updates the existing class metaobject in place (same find-class object, methods specialized on it keep applying) and re-finalizes its subclasses; with a user metaclass it runs reinitialize-instance on the class.
(ensure-class-using-class class name &rest keys)	generic function	ensure-class protocol hook; class is the existing class or nil.
(validate-superclass class superclass)	generic function	Whether superclass may serve as a superclass of class.
forward-referenced-class	class	Placeholder for a superclass not yet defined.
funcallable-standard-class	class	Metaclass of funcallable classes (e.g. generic functions).
funcallable-standard-object	class	Superclass of instances that can be called as functions.
metaobject	class	Root class of all metaobjects.

Slot-definition metaobjects

Signature	Kind	Description
slot-definition	class	Root class of slot-definition metaobjects.
direct-slot-definition	class	Slot definition as written in a defclass form.
effective-slot-definition	class	Slot definition after inheritance is merged.
standard-slot-definition	class	Standard base class for slot definitions.
standard-direct-slot-definition	class	Standard class of direct slot definitions.
standard-effective-slot-definition	class	Standard class of effective slot definitions.
(direct-slot-definition-class class &rest initargs)	generic function	Class of direct slot-definition metaobjects to create.
(effective-slot-definition-class class &rest initargs)	generic function	Class of effective slot-definition metaobjects to create.
(compute-effective-slot-definition class name direct-slots)	generic function	Merge the direct slot definitions for name into one effective slot.
(compute-slots class)	generic function	Compute the list of effective slot definitions.
(slot-definition-name sd)	function	The slot's name (a symbol).
(slot-definition-allocation sd)	function	Allocation kind, :instance or :class.
(slot-definition-initargs sd)	function	List of :initarg keywords.
(slot-definition-initform sd)	function	The :initform expression, if any.
(slot-definition-initfunction sd)	function	Function of no arguments that evaluates the initform.
(slot-definition-type sd)	function	Declared :type of the slot.
(slot-definition-location esd)	function	Storage location of an effective slot (instance index).
(slot-definition-readers dsd)	function	Reader generic-function names of a direct slot.
(slot-definition-writers dsd)	function	Writer generic-function names of a direct slot.
(slot-definition-documentation sd)	function	The slot's documentation string.

Slot access protocol

Signature	Kind	Description
(slot-value-using-class class instance slot)	generic function	Read a slot through the class metaobject (also setf-able).
(slot-boundp-using-class class instance slot)	generic function	Slot boundness test through the class metaobject.
(slot-makunbound-using-class class instance slot)	generic function	Make a slot unbound through the class metaobject.
(standard-instance-access instance location)	function	Direct indexed access to a standard instance's slot storage.
(funcallable-standard-instance-access instance location)	function	Direct indexed access for funcallable instances.
(set-funcallable-instance-function gf fn)	function	Install fn as the function called when gf is invoked.

Generic-function & method metaobjects

Signature	Kind	Description
(generic-function-name gf)	function	Name of the generic function.
(generic-function-lambda-list gf)	function	The generic function's lambda list.
(generic-function-methods gf)	function	List of the generic function's method metaobjects.
(generic-function-method-class gf)	function	Default class of the generic function's methods.
(generic-function-method-combination gf)	function	The generic function's method-combination metaobject.
(generic-function-declarations gf)	function	Declarations from the defgeneric form.
(generic-function-argument-precedence-order gf)	function	Argument order used to sort applicable methods.
(ensure-generic-function-using-class gf name &rest args)	generic function	ensure-generic-function protocol hook; gf is the existing GF or nil.
(compute-discriminating-function gf)	generic function	Function that dispatches calls to the generic function.
(compute-applicable-methods-using-classes gf classes)	generic function	Applicable methods from argument classes alone.
(compute-effective-method gf combination methods)	generic function	Effective-method form combining the sorted applicable methods.
(compute-default-initargs class)	generic function	Compute a class's effective default initargs.
(compute-class-precedence-list class)	generic function	Compute a class's precedence list.
(make-method-lambda generic-function method lambda-expression environment)	generic function	Transform a method body into the function to compile.
(ensure-method gf-or-name lambda-expression &key qualifiers lambda-list specializers method-class)	function	Create a method object and add it to the generic function.
(method-function m)	function	The function implementing the method body.
(method-generic-function m)	function	The generic function the method belongs to.
(method-lambda-list m)	function	The method's (unspecialized) lambda list.
(method-specializers m)	function	The method's specializer metaobjects.
(extract-lambda-list specialized-lambda-list)	function	Ordinary lambda list from a specialized one.
(extract-specializer-names specialized-lambda-list)	function	Specializer names from a specialized lambda list.
standard-method-combination	class	Class of the standard method combination.
(find-method-combination generic-function name options)	generic function	Method-combination metaobject for name with options.

Specializers

Signature	Kind	Description
specializer	class	Root class of method specializers.
(specializer-direct-methods specializer)	generic function	Methods that specialize on this specializer.
(specializer-direct-generic-functions specializer)	generic function	Generic functions with a method specialized on it.
eql-specializer	class	Specializer matching one object under eql.
(eql-specializer-p object)	function	True if object is an eql-specializer.
(eql-specializer-object spec)	function	The object an eql-specializer matches.
(intern-eql-specializer object)	function	The canonical eql-specializer for object.

Accessor / reader / writer methods

Signature	Kind	Description
standard-accessor-method	class	Superclass of slot reader/writer methods.
standard-reader-method	class	Class of automatically generated slot reader methods.
standard-writer-method	class	Class of automatically generated slot writer methods.
(accessor-method-slot-definition method)	generic function	The direct slot definition an accessor method accesses.
(reader-method-class class direct-slot &rest initargs)	generic function	Class of reader methods to generate for a slot.
(writer-method-class class direct-slot &rest initargs)	generic function	Class of writer methods to generate for a slot.

Dependent maintenance & class structure mutation

Signature	Kind	Description
(add-dependent metaobject dependent)	generic function	Register dependent for update notifications.
(remove-dependent metaobject dependent)	generic function	Remove a registered dependent.
(map-dependents metaobject function)	generic function	Call function on each registered dependent.
(update-dependent metaobject dependent &rest initargs)	generic function	Notification hook called when metaobject changes.
(add-direct-method specializer method)	generic function	Record that method specializes on specializer.
(remove-direct-method specializer method)	generic function	Remove that record.
(add-direct-subclass class subclass)	generic function	Record subclass as a direct subclass of class.
(remove-direct-subclass class subclass)	generic function	Remove that record.

User-defined metaclasses

A subclass of standard-class may be defined and used as a class's metaclass via the defclass (:metaclass …) option. The class it creates is an instance of that metaclass, so methods specialized on the metaclass — allocate-instance, initialize-instance (including :around), validate-superclass — dispatch on it, and metaclass slots (with :initarg/:reader) and :default-initargs work. A metaclass initialize-instance :around may rewrite :direct-superclasses while the class is being built. This covers the two common ecosystem patterns (serapeum's abstract-standard-class and topmost-object-class); see tests/test_mop_metaclass.c for runnable examples.

The class metaobject keeps a fixed internal layout for speed on the 68020: metaclasses add their own slots after the standard ones, but a metaclass whose own layout diverges from standard-class (full meta-recursion) is not supported.

Limitation: the MOP implementation is a working subset, not the complete AMOP — see Known Limitations ("full CLOS MOP").

Source of truth

tests/test_clos.c and the CLOS/MOP blocks in tests/amiga/run-tests.lisp; implementation in lib/clos.lisp. The closer-mop re-export mapping lives in the AmiLisp closer-mop fork (#+amilisp branch of closer-mop-packages.lisp plus closer-amilisp.lisp), installed into quicklisp's local-projects.