If I'm not mistaken, those extra bits are pulled from the "isa" pointer, present in all objects and similar to a C++ vtable pointer. That is, they're in the obj

If I'm not mistaken, those extra bits are pulled from the "isa" pointer, present in all objects and similar to a C++ vtable pointer. That is, they're in the object itself, not the pointers to it. Mike Ash wrote an excellent summary: http://www.mikeash.com/pyblog/friday-qa-2013-09-27-arm64-and-you.html http://www.mikeash.com/pyblog/friday-qa-2013-09-27-arm64-and...