Class-name—a non-nil symbol.
Superclass-name—a non-nil symbol.
Slot-name—a symbol. The slot-name argument is a symbol that is syntactically valid for use as a variable name.
Reader-function-name—a non-nil symbol. :reader can be supplied more than once for a given slot.
Writer-function-name—a generic function name. :writer can be supplied more than once for a given slot.
Reader-function-name—a non-nil symbol. :accessor can be supplied more than once for a given slot.
Allocation-type—(member :instance :class). :allocation can be supplied once at most for a given slot.
Initarg-name—a symbol. :initarg can be supplied more than once for a given slot.
Form—a form. :init-form can be supplied once at most for a given slot.
Type-specifier—a type specifier. :type can be supplied once at most for a given slot.
Class-option— refers to the class as a whole or to all class slots.
Initarg-list—a list of alternating initialization argument names and default initial value forms. :default-initargs can be supplied at most once.
Class-name—a non-nil symbol. :metaclass can be supplied once at most.
new-class—the new class object.
The macro defclass
defines a new named class. It returns
the new class object as its result.
The syntax of defclass
provides options for specifying
initialization arguments for slots, for specifying default
initialization values for slots, and for requesting that
methods on specified generic functions be automatically
generated for reading and writing the values of slots.
No reader or writer functions are defined by default;
their generation must be explicitly requested. However,
slots can always be accessed using slot-value
.
Defining a new class also causes a type of the same name to be
defined. The predicate (typep
object class-name)
returns
true if the class of the given object is
the class named by class-name itself or
a subclass of the class class-name. A class object
can be used as a type specifier.
Thus (typep
object class)
returns true
if the class of the object is
class itself or a subclass of class.
The class-name argument specifies the proper name
of the new class.
If a class with the same proper name already exists
and that class is an instance of standard-class
,
and if the defclass
form for the definition of the new class
specifies a class of class standard-class
,
the existing class is redefined,
and instances of it (and its subclasses) are updated
to the new definition at the time that they are next accessed.
For details, see Section 4.3.6 (Redefining Classes).
Each superclass-name argument
specifies a direct superclass of the new class.
If the superclass list is empty, then the superclass
defaults depending on the metaclass,
with standard-object
being the
default for standard-class
.
The new class will inherit slots and methods from each of its direct superclasses, from their direct superclasses, and so on. For a discussion of how slots and methods are inherited, see Section 4.3.4 (Inheritance).
The following slot options are available:
(setf
reader-function-name)
to be
used with setf
to modify the value of the slot.
:allocation :instance
.
defclass
form. The value of the slot is shared by all
instances of the class.
If a class C1 defines such a shared slot, any
subclass C2 of
C1 will share this single slot unless the defclass
form
for C2 specifies a slot of the same name or there is a
superclass of C2 that precedes C1 in the class precedence
list of C2 and that defines a slot of the same name.
defclass
form was evaluated.
Note that the lexical environment refers both to variables and to
functions. For local slots, the dynamic environment is the dynamic
environment in which make-instance
is called; for shared
slots, the dynamic environment is the dynamic environment in which the
defclass
form was evaluated.
See Section 7.1 (Object Creation and Initialization).
No implementation is permitted to extend the syntax of defclass
to allow (
slot-name form)
as an abbreviation for
(
slot-name :initform
form)
.
initialize-instance
, the value will be stored into the given slot,
and the slot's :initform slot option, if any, is not
evaluated. If none of the initialization arguments specified for a
given slot has a value, the slot is initialized according to the
:initform slot option, if specified.
Each class option is an option that refers to the class as a whole. The following class options are available:
make-instance
, the
corresponding default initial value form is evaluated, and the
initialization argument name and the form's value are added to the end
of the initialization argument list before the instance is created;
see Section 7.1 (Object Creation and Initialization).
The default initial value form is evaluated each time it is used. The lexical
environment in which this form is evaluated is the lexical environment
in which the defclass
form was evaluated. The dynamic
environment is the dynamic environment in which make-instance
was called. If an initialization argument name appears more than once
in a :default-initargs class option, an error is signaled.
standard-class
).
Note the following rules of defclass
for standard classes:
defclass
form for that class is evaluated.
defmethod
form.
The object system can be extended to cover situations where these rules are not obeyed.
Some slot options are inherited by a class from its superclasses, and some can be shadowed or altered by providing a local slot description. No class options except :default-initargs are inherited. For a detailed description of how slots and slot options are inherited, see Section 7.5.3 (Inheritance of Slots and Slot Options).
The options to defclass
can be extended. It is required that
all implementations signal an error if they observe a class option or
a slot option that is not implemented locally.
It is valid to specify more than one reader, writer, accessor, or initialization argument for a slot. No other slot option can appear more than once in a single slot description, or an error is signaled.
If no reader, writer, or accessor is specified for a slot,
the slot can only be accessed by the function slot-value
.
If a defclass
form appears as a top level form,
the compiler must make the class name be recognized as a
valid type name in subsequent declarations (as for deftype
)
and be recognized as a valid class name for defmethod
parameter specializers and for use as the :metaclass option of a
subsequent defclass
. The compiler must make
the class definition
available to be returned by find-class
when its environment
argument is a value received as the environment parameter of a macro.
If there are any duplicate slot names,
an error of type program-error
is signaled.
If an initialization argument name appears more than once in
:default-initargs class option,
an error of type program-error
is signaled.
If any of the following slot options appears more than once in a
single slot description, an error of type program-error
is signaled: :allocation,
:initform, :type, :documentation.
It is required that all implementations signal
an error of type program-error
if they observe a class option
or a slot option that is not implemented locally.
documentation, initialize-instance (Standard Generic Function), make-instance, slot-value, Section 4.3 (Classes), Section 4.3.4 (Inheritance), Section 4.3.6 (Redefining Classes), Section 4.3.5 (Determining the Class Precedence List), Section 7.1 (Object Creation and Initialization)