Description

This generic function adds dependent to the dependents of metaobject. If dependent is already in the set of dependents it is not added again (no error is signaled).

The generic function map-dependents can be called to access the set of dependents of a class or generic function. The generic function remove-dependent can be called to remove an object from the set of dependents of a class or generic function. The effect of calling add-dependent or remove-dependent while a call to map-dependents on the same class or generic function is in progress is unspecified.

The situations in which add-dependent is called are not specified.

Description

This generic function is called to maintain a set of backpointers from a specializer to the set of methods specialized to it. If method is already in the set, it is not added again (no error is signaled).

This set can be accessed as a list by calling the generic function specializer-direct-methods. Methods are removed from the set by remove-direct-method.

The generic function add-direct-method is called by add-method whenever a method is added to a generic function. It is called once for each of the specializers of the method. Note that in cases where a specializer appears more than once in the specializers of a method, this generic function will be called more than once with the same specializer as argument.

The results are undefined if the specializer argument is not one of the specializers of the method argument.

Description

This generic function is called to maintain a set of backpointers from a class to its direct subclasses. This generic function adds subclass to the set of direct subclasses of superclass.

When a class is initialized, this generic function is called once for each direct superclass of the class.

When a class is reinitialized, this generic function is called once for each added direct superclass of the class. The generic function remove-direct-subclass is called once for each deleted direct superclass of the class.

Description

This generic function associates an unattached method with a generic function.

An error is signaled if the lambda list of the method is not congruent with the lambda list of the generic function. An error is also signaled if the method is already associated with some other generic function.

If the given method agrees with an existing method of the generic function on parameter specializers and qualifiers, the existing method is removed by calling remove-method before the new method is added. See the section of the CLOS Specification called Agreement on Parameter Specializers and Qualifiers for a definition of agreement in this context.

Associating the method with the generic function then proceeds in four steps:

1. add method to the set returned by generic-function-methods and arrange for method-generic-function to return generic-function;
2. call add-direct-method for each of the method's specializers;
3. call compute-discriminating-function and install its result with set-funcallable-instance-function; and
4. update the dependents of the generic function.

The generic function add-method can be called by the user or the implementation.

Description

This generic function is called to create a new, uninitialized instance of a class. The interpretation of the concept of an uninitialized instance depends on the class metaobject class.

Before allocating the new instance, class-finalized-p is called to see if class has been finalized. If it has not been finalized, finalize-inheritance is called before the new instance is allocated.

Description

This generic function determines the method applicability of a generic function given a list of required arguments. The returned list of method metaobjects is sorted by precedence order with the most specific method appearing first. If no methods are applicable to the supplied arguments the empty list is returned.

When a generic function is invoked, the discriminating function must determine the ordered list of methods applicable to the arguments. Depending on the generic function and the arguments, this is done in one of three ways: using a memoized value; calling compute-applicable-methods-using-classes; or calling compute-applicable-methods. (Refer to the description of compute-discriminating-function for the details of this process.)

The arguments argument is permitted to contain more elements than the generic function accepts required arguments; in these cases the extra arguments will be ignored. An error is signaled if arguments contains fewer elements than the generic function accepts required arguments.

The list returned by this generic function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this generic function.

Description

This generic function is called to attempt to determine the method applicability of a generic function given only the classes of the required arguments.

If it is possible to completely determine the ordered list of applicable methods based only on the supplied classes, this generic function returns that list as its first value and true as its second value. The returned list of method metaobjects is sorted by precedence order, the most specific method coming first. If no methods are applicable to arguments with the specified classes, the empty list and true are returned.

If it is not possible to completely determine the ordered list of applicable methods based only on the supplied classes, this generic function returns an unspecified first value and false as its second value.

When a generic function is invoked, the discriminating function must determine the ordered list of methods applicable to the arguments. Depending on the generic function and the arguments, this is done in one of three ways: using a memoized value; calling compute-applicable-methods-using-classes or calling compute-applicable-methods. (Refer to the description of compute-discriminating-function for the details of this process.)

The following consistency relationship between compute-applicable-methods-using-classes and compute-applicable-methods must be maintained: for any given generic function and set of arguments, if compute-applicable-methods-using-classes returns a second value of true, the first value must be equal to the value that would be returned by a corresponding call to compute-applicable-methods. The results are undefined if a portable method on either of these generic functions causes this consistency to be violated.

The list returned by this generic function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this generic function.

Description

This generic-function is called to determine the class precedence list of a class.

The result is a list which contains each of class and its superclasses once and only once. The first element of the list is class and the last element is the class named T.

All methods on this generic function must compute the class precedence list as a function of the ordered direct superclasses of the superclasses of class. The results are undefined if the rules used to compute the class precedence list depend on any other factors.

When a class is finalized, finalize-inheritance calls this generic function and associates the returned value with the class metaobject. The value can then be accessed by calling class-precedence-list.

The list returned by this generic function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this generic function.

Description

This generic function is called to determine the default initialization arguments for a class.

The result is a list of canonicalized default initialization arguments, with no duplication among initialization argument names.

All methods on this generic function must compute the default initialization arguments as a function of only: (i) the class precedence list of class, and (ii) the direct default initialization arguments of each class in that list. The results are undefined if the rules used to compute the default initialization arguments depend on any other factors.

When a class is finalized, finalize-inheritance calls this generic function and associates the returned value with the class metaobject. The value can then be accessed by calling class-default-initargs.

The list returned by this generic function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this generic function.

Description

This generic function is called to determine the discriminating function for a generic function. When a generic function is called, the installed discriminating function is called with the full set of arguments received by the generic function, and must implement the behavior of calling the generic function: determining the ordered set of applicable methods, determining the effective method, and running the effective method.

To determine the ordered set of applicable methods, the discriminating function first calls compute-applicable-methods-using-classes. If compute-applicable-methods-using-classes returns a second value of false, the discriminating function then calls compute-applicable-methods.

When compute-applicable-methods-using-classes returns a second value of true, the discriminating function is permitted to memoize the first returned value as follows. The discriminating function may reuse the list of applicable methods without calling compute-applicable-methods-using-classes again provided that:

1. the generic function is being called again with required arguments which are instances of the same classes,
2. the generic function has not been reinitialized,
3. no method has been added to or removed from the generic function,
4. for all the specializers of all the generic function's methods which are classes, their class precedence lists have not changed and
5. for any such memoized value, the class precedence list of the class of each of the required arguments has not changed.

Determination of the effective method is done by calling compute-effective-method. When the effective method is run, each method's function is called, and receives as arguments: (i) a list of the arguments to the generic function, and (ii) whatever other arguments are specified in the call-method form indicating that the method should be called. (See make-method-lambda for more information about how method functions are called.)

The generic function compute-discriminating-function is called, and its result installed, by add-method, remove-method, initialize-instance, and reinitialize-instance.

Description

This generic function is called to determine the effective method from a sorted list of method metaobjects.

An effective method is a form that describes how the applicable methods are to be combined. Inside of effective method forms are call-method forms which indicate that a particular method is to be called. The arguments to the call-method form indicate exactly how the method function of the method should be called. (See make-method-lambda for more details about method functions.)

An effective method option has the same interpretation and syntax as either the :arguments or the :generic-function option in the long form of define-method-combination.

More information about the form and interpretation of effective methods and effective method options can be found under the description of the define-method-combination macro in the CLOS specification.

This generic function can be called by the user or the implementation. It is called by discriminating functions whenever a sorted list of applicable methods must be converted to an effective method.

Description

This generic function determines the effective slot definition for a slot in a class. It is called by compute-slots once for each slot accessible in instances of class.

This generic function uses the supplied list of direct slot definition metaobjects to compute the inheritance of slot properties for a single slot. The returned effective slot definition represents the result of computing the inheritance. The name of the new effective slot definition is the same as the name of the direct slot definitions supplied.

The class of the effective slot definition metaobject is determined by calling effective-slot-definition-class. The effective slot definition is then created by calling make-instance. The initialization arguments passed in this call to make-instance are used to initialize the new effective slot definition metaobject. See Initialization of Slot Definition Metaobjects for details.

Description

This generic function computes a set of effective slot definition metaobjects for the class class. The result is a list of effective slot definition metaobjects: one for each slot that will be accessible in instances of class.

This generic function proceeds in 3 steps:

1. The first step collects the full set of direct slot definitions from the superclasses of class.

2. The direct slot definitions are then collected into individual lists, one list for each slot name associated with any of the direct slot definitions. The slot names are compared with eql. Each such list is then sorted into class precedence list order. Direct slot definitions coming from classes earlier in the class precedence list of class appear before those coming from classes later in the class precedence list. For each slot name, the generic function compute-effective-slot-definition is called to compute an effective slot definition. The result of compute-slots is a list of these effective slot definitions, in unspecified order.

3. In the final step, the location for each effective slot definition is set. This is done by specified around-methods; portable methods cannot take over this behavior. For more information on the slot definition locations, see the section Instance Structure Protocol.

The list returned by this generic function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this generic function.

Description

When a class is initialized, each of the canonicalized slot specifications must be converted to a direct slot definition metaobject. This generic function is called to determine the class of that direct slot definition metaobject.

The initargs argument is simply the canonicalized slot specification for the slot.

Description

This generic function is called by compute-effective-slot-definition to determine the class of the resulting effective slot definition metaobject. The initargs argument is the list of initialization arguments and values that will be passed to make-instance when the effective slot definition metaobject is created.

Description

Some of the keyword arguments accepted by this function are actually processed by ensure-class-using-class, others are processed during initialization of the class metaobject (as described in the section called Initialization of Class Metaobjects).

This function is called to define or redefine a class with the specified name, and can be called by the user or the implementation. It is the functional equivalent of defclass, and is called by the expansion of the defclass macro.

The behavior of this function is actually implemented by the generic function ensure-class-using-class. When ensure-class is called, it immediately calls ensure-class-using-class and returns that result as its own.

The first argument to ensure-class-using-class is computed as follows:

• If name names a class (find-class returns a class when called with name) use that class.

• Otherwise use nil.

The second argument is name. The remaining arguments are the complete set of keyword arguments received by the ensure-class function.

Description

This generic function is called to define or modify the definition of a named class. It is called by the ensure-class function. It can also be called directly.

The first step performed by this generic function is to compute the set of initialization arguments which will be used to create or reinitialize the named class. The initialization arguments are computed from the full set of keyword arguments received by this generic function as follows:

• The :metaclass argument is not included in the initialization arguments.

• If the :direct-superclasses argument was received by this generic function, it is converted into a list of class metaobjects. This conversion does not affect the structure of the supplied :direct-superclasses argument. For each element in the :direct-superclasses argument:

  • If the element is a class metaobject, that class metaobject is used.

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    If the element names a class, that class metaobject is used.

  • Otherwise an instance of the class forward-referenced-class is created and used. The proper name of the newly created forward referenced class metaobject is set to name.

• All other keyword arguments are included directly in the initialization arguments.

If the class argument is nil, a new class metaobject is created by calling the make-instance generic function with the value of the :metaclass argument as its first argument, and the previously computed initialization arguments. The proper name of the newly created class metaobject is set to name. The newly created class metaobject is returned.

If the class argument is a forward referenced class, change-class is called to change its class to the value specified by the :metaclass argument. The class metaobject is then reinitialized with the previously computed initialization arguments. (This is a documented violation of the general constraint that change-class not be used with class metaobjects.)

If the class of the class argument is not the same as the class specified by the :metaclass argument, an error is signaled.

Otherwise, the class metaobject class is redefined by calling the reinitialize-instance generic function with class and the initialization arguments. The class argument is then returned.

Description

The generic function ensure-generic-function-using-class is called to define or modify the definition of a globally named generic function. It is called by the ensure-generic-function function. It can also be called directly.

The first step performed by this generic function is to compute the set of initialization arguments which will be used to create or reinitialize the globally named generic function. These initialization arguments are computed from the full set of keyword arguments received by this generic function as follows:

• The :generic-function-class argument is not included in the initialization arguments.

• If the :method-class argument was received by this generic function, it is converted into a class metaobject. This is done by looking up the class name with find-class. If there is no such class, an error is signaled.

• All other keyword arguments are included directly in the initialization arguments.

If the generic-function argument is nil, an instance of the class specified by the :generic-function-class argument is created by calling make-instance with the previously computed initialization arguments. The function name function-name is set to name the generic function. The newly created generic function metaobject is returned.

If the class of the generic-function argument is not the same as the class specified by the :generic-function-class argument, an error is signaled.

Otherwise the generic function generic-function is redefined by calling the reinitialize-instance generic function with generic-function and the initialization arguments. The generic-function argument is then returned.

Description

This generic function is called to finalize a class metaobject. This is described in the Section named Class Finalization Protocol.

After finalize-inheritance returns, the class metaobject is finalized and the result of calling class-finalized-p on the class metaobject will be true.

Description

This generic function is called to determine the method combination object used by a generic function.

Description

The generic function make-instance creates and returns a new instance of the given class. Its behavior and use is described in the CLOS specification.

Description

This generic function is called to produce a lambda expression which can itself be used to produce a method function for a method and generic function with the specified classes. The generic function and method the method function will be used with are not required to be the given ones. Moreover, the method metaobject may be uninitialized.

Either the function compile, the special form function or the function coerce must be used to convert the lambda expression to a method function. The method function itself can be applied to arguments with apply or funcall.

When a method is actually called by an effective method, its first argument will be a list of the arguments to the generic function. Its remaining arguments will be all but the first argument passed to call-method. By default, all method functions must accept two arguments: the list of arguments to the generic function and the list of next methods.

For a given generic function and method class, the applicable methods on make-method-lambda and compute-effective-method must be consistent in the following way: each use of call-method returned by the method on compute-effective-method must have the same number of arguments, and the method lambda returned by the method on make-method-lambda must accept a corresponding number of arguments.

Note that the system-supplied implementation of call-next-method is not required to handle extra arguments to the method function. Users who define additional arguments to the method function must either redefine or forego call-next-method. (See the example below.)

When the method metaobject is created with make-instance, the method function must be the value of the :function initialization argument. The additional initialization arguments, returned as the second value of this generic function, must also be passed in this call to make-instance.

Description

This generic function applies function to each of the dependents of metaobject. The order in which the dependents are processed is not specified, but function is applied to each dependent once and only once. If, during the mapping, add-dependent or remove-dependent is called to alter the dependents of metaobject, it is not specified whether the newly added or removed dependent will have function applied to it.

Description

This generic function is called to determine the class of reader methods created during class initialization and reinitialization. The result must be a subclass of standard-reader-method.

The initargs argument must be the same as will be passed to make-instance to create the reader method. The initargs must include :slot-definition with slot-definition as its value.

Description

This generic function removes dependent from the dependents of metaobject. If dependent is not one of the dependents of metaobject, no error is signaled.

The generic function map-dependents can be called to access the set of dependents of a class or generic function. The generic function add-dependent can be called to add an object to the set of dependents of a class or generic function. The effect of calling add-dependent or remove-dependent while a call to map-dependents on the same class or generic function is in progress is unspecified.

The situations in which remove-dependent is called are not specified.

Description

This generic function is called to maintain a set of backpointers from a specializer to the set of methods specialized to it. If method is in the set it is removed. If it is not, no error is signaled.

This set can be accessed as a list by calling the generic function specializer-direct-methods. Methods are added to the set by add-direct-method.

The generic function remove-direct-method is called by remove-method whenever a method is removed from a generic function. It is called once for each of the specializers of the method. Note that in cases where a specializer appears more than once in the specializers of a method, this generic function will be called more than once with the same specializer as argument.

The results are undefined if the specializer argument is not one of the specializers of the method argument.

Description

This generic function is called to maintain a set of backpointers from a class to its direct subclasses. It removes subclass from the set of direct subclasses of superclass. No error is signaled if subclass is not in this set.

Whenever a class is reinitialized, this generic function is called once with each deleted direct superclass of the class.

Description

This generic function breaks the association between a generic function and one of its methods.

No error is signaled if the method is not among the methods of the generic function.

Breaking the association between the method and the generic function proceeds in four steps:

1. remove method from the set returned by generic-function-methods and arrange for method-generic-function to return nil;

2. call remove-direct-method for each of the method's specializers;

3. call compute-discriminating-function and install its result with set-funcallable-instance-function; and

4. update the dependents of the generic function.

The generic function remove-method can be called by the user or the implementation.

Description

The generic function (setf slot-value-using-class) implements the behavior of the (setf slot-value) function. It is called by (setf slot-value) with the class of object as its second argument and the pertinent effective slot definition metaobject as its fourth argument.

The generic function (setf slot-value-using-class) sets the value contained in the given slot of the given object to the given new value; any previous value is lost.

The results are undefined if the class argument is not the class of the object argument, or if the slot argument does not appear among the set of effective slots associated with the class argument.

Description

This generic function implements the behavior of the slot-boundp function. It is called by slot-boundp with the class of object as its first argument and the pertinent effective slot definition metaobject as its third argument.

The generic function slot-boundp-using-class tests whether a specific slot in an instance is bound.

The results are undefined if the class argument is not the class of the object argument, or if the slot argument does not appear among the set of effective slots associated with the class argument.

Description

This generic function implements the behavior of the slot-makunbound function. It is called by slot-makunbound with the class of object as its first argument and the pertinent effective slot definition metaobject as its third argument.

The generic function slot-makunbound-using-class restores a slot in an object to its unbound state. The interpretation of restoring a slot to its unbound state depends on the class metaobject class.

The results are undefined if the class argument is not the class of the object argument, or if the slot argument does not appear among the set of effective slots associated with the class argument.

Description

This generic function implements the behavior of the slot-value function. It is called by slot-value with the class of object as its first argument and the pertinent effective slot definition metaobject as its third argument.

The generic function slot-value-using-class returns the value contained in the given slot of the given object. If the slot is unbound slot-unbound is called.

The results are undefined if the class argument is not the class of the object argument, or if the slot argument does not appear among the set of effective slots associated with the class argument.

Description

This generic function returns the possibly empty set of those generic functions which have a method with specializer as a specializer. The elements of this set are generic function metaobjects. This value is maintained by the generic functions add-direct-method and remove-direct-method.

Description

This generic function returns the possibly empty set of those methods, connected to generic functions, which have specializer as a specializer. The elements of this set are method metaobjects. This value is maintained by the generic functions add-direct-method and remove-direct-method.

Description

This generic function is called to update a dependent of metaobject.

When a class or a generic function is reinitialized, each of its dependents is updated. The initargs argument to update-dependent is the set of initialization arguments received by reinitialize-instance.

When a method is added to a generic function, each of the generic function's dependents is updated. The initargs argument is a list of two elements: the symbol add-method, and the method that was added.

When a method is removed from a generic function, each of the generic function's dependents is updated. The initargs argument is a list of two elements: the symbol remove-method, and the method that was removed.

In each case, map-dependents is used to call update-dependent on each of the dependents. So, for example, the update of a generic function's dependents when a method is added could be performed by the following code:

(map-dependents generic-function
                #'(lambda (dep)
                    (update-dependent generic-function
                                      dep
                                      'add-method
                                      new-method)))