1.4.4 How inheritance works

Defining an Objective-C class introduced the define-objc-class macro with the :objc-class-name class option for naming the Objective-C class. Since this macro is like defclass , it can specify any number of superclasses from which the Lisp class will inherit and also provides a way for superclass of the Objective-C class to be chosen:

• If some of the Lisp classes in the class precedence list were defined with define-objc-class and given an associated Objective-C class name, then the first such class name is used. It is an error for several such classes to be in the class precedence list unless their associated Objective-C classes are also superclasses of each other in the same order as the precedence list.
• If no superclasses have an associated Objective-C class, then the :objc-superclass-name class option can be used to specify the superclass explicitly.
• Otherwise NSObject is used as the superclass.

For example, both of these definitions define an Objective-C class that inherits from MyObject , via my-object in the case of my-special-object and explicitly for my-other-object :

(define-objc-class my-special-object (my-object)

  ()

  (:objc-class-name "MySpecialObject"))

(define-objc-class my-other-object ()

  ()

  (:objc-class-name "MyOtherObject")

  (:objc-superclass-name "MyObject"))

The set of methods available for a given Objective-C class consists of those defined on the class itself as well as those inherited from its superclasses.