/// Specifies the superclass of an instance.
struct objc_super {
/// 指定类的实例
__unsafe_unretained _Nonnull id receiver;
/// Specifies the particular superclass of the instance to message.
#if !defined(__cplusplus) && !__OBJC2__
/* For compatibility with old objc-runtime.h header */
__unsafe_unretained _Nonnull Class class;
#else
__unsafe_unretained _Nonnull Class super_class;
#endif
/* super_class is the first class to search */
};
通过super调用方法，编译器会自动转成objc_msgSendSuper
objc_msgSendSuper(struct objc_super * _Nonnull super, SEL _Nonnull op, ...)
