The GNU Objective-C runtime used to provide a different API, which we call the “traditional” GNU Objective-C runtime API. Functions belonging to this API are easy to recognize because they use a different naming convention, such as
class_get_super_class() (traditional API) instead of
class_getSuperclass() (modern API). Software using this API includes the file objc/objc-api.h where it is declared.
Starting with GCC 4.7.0, the traditional GNU runtime API is no longer available.