Dealing with isa

Historically isa was part of the object structure and it was an easy way to get at the class of an object. This doesn't work in mulle-objc, because isa is outside the structure for regular objects or doesn't even exist for tagged pointers.

For backwards compatibility isa can be defined as a shortcut for calling _mulle_objc_object_get_isa( self). This doesn't enable changing isa on the fly of course. To enable isa compile with -DMULLE_OBJC_ISA_HACK.

#ifdef MULLE_OBJC_ISA_HACK
# define isa       ((Class) _mulle_objc_object_get_isa( self))
#endif

This will lead to problem when isa is used a normal identifier as in:

struct my_struct
{
    int   isa;
}

or

void   *isa( void *p)

This belongs to MulleObjC really.