Quick syntax/compatibility question with libobjc2 and clang 3.4+

[Tom Bruno]

I'm currently using libobjc2 and clang 3.4.  I was researching how NSObject is implemented just learning the ins and outs (I'm very interested in the memory management and such).

One of the things I've noticed is that placing variables in @implementation does not work on linux but seems to work fine on osx like this (Sources at end of email):

#import <objc/runtime.h>

@implementation MAObject {
    Class isa;
    volatile int32_t retainCount;
}

The compiler complains isa and retainCount do not exist.  I've kindof put together that only OSX 64bit mode will work with this code.  Is this a limitation in libobjc2 or clang on linux itself?  Is there something we can do to support this new syntax?

  Tom

Sources: 

https://www.mikeash.com/pyblog/friday-qa-2013-01-25-lets-build-nsobject.html

https://github.com/mikeash/MAObject/blob/master/MAObject.h

https://github.com/mikeash/MAObject/blob/master/MAObject.m