Below is the implementation of the object_cxxDestructFromClass method. the line below the for loop if (!cls->hasCxxDtor()) return; Some questions: If a subclass inherits a parent class, and one of the middle classes does not have a CxxDtor, but the parent class does, will there be any problems with the release of the instance? static void object_cxxDestructFromClass(id obj, Class cls) { void (*dtor)(id); // Call cls's dtor first, then superclasses's dtors. for ( ; cls; cls = cls->getSuperclass()) { if (!cls->hasCxxDtor()) return; dtor = (void(*)(id)) lookupMethodInClassAndLoadCache(cls, SEL_cxx_destruct); if (dtor != (void(*)(id))_objc_msgForward_impcache) { if (PrintCxxCtors) { _objc_inform("CXX: calling C++ destructors for class %s", cls->nameForLogging()); } (*dtor)(obj); } } }