Common Lisp the Language, 2nd Edition

28.1.8.2. Standard Metaclasses

The Common Lisp Object System provides a number of predefined metaclasses. These include the classes standard-class, built-in-class, and structure-class:

• The class standard-class is the default class of classes defined by defclass.

• The class built-in-class is the class whose instances are classes that have special implementations with restricted capabilities. Any class that corresponds to a standard Common Lisp type might be an instance of built-in-class. The predefined Common Lisp type specifiers that are required to have corresponding classes are listed in table 28-1. It is implementation-dependent whether each of these classes is implemented as a built-in class.

• All classes defined by means of defstruct are instances of structure-class.