The function objc-object-var-value
returns the value of the instance variable var-name in the Objective-C foreign object associated with object. The type of value depends on the declared type of the instance variable. If this type is a foreign structure type, then the result-pointer argument should be passed giving a pointer to a foreign object of the correct type that is filled with the value.
The corresponding setf function can be used to set the value.
Note that it is only possible to access instance variables that are defined in Lisp by define-objc-class, not those inherited from superclasses implemented in Objective-C.
LispWorks Objective-C and Cocoa Interface User Guide and Reference Manual - 15 Feb 2015