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:
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.