4.3.2 Defining Classes

The macro defclass is used to define a new named class.

The definition of a class includes:

• The name of the new class. For newly-defined classes this name is a proper name.
• The list of the direct superclasses of the new class.
• A set of slot specifiers. Each slot specifier includes the name of the slot and zero or more slot options. A slot option pertains only to a single slot. If a class definition contains two slot specifiers with the same name, an error is signaled.
• A set of class options. Each class option pertains to the class as a whole.

The slot options and class options of the defclass form provide mechanisms for the following:

• Supplying a default initial value form for a given slot.
• Requesting that methods for generic functions be automatically generated for reading or writing slots.
• Controlling whether a given slot is shared by all instances of the class or whether each instance of the class has its own slot.
• Supplying a set of initialization arguments and initialization argument defaults to be used in instance creation.
• Indicating that the metaclass is to be other than the default. The :metaclass option is reserved for future use; an implementation can be extended to make use of the :metaclass option.
• Indicating the expected type for the value stored in the slot.
• Indicating the documentation string for the slot.