Re: CoreBase toll-free bridging

[Luboš Doležel]

On 03/11/2013 06:07 PM, David Chisnall wrote:
> As I recall, on OS X the isa pointer for bridged types contains the
> typeid.  The Objective-C runtime has some extra logic that checks if
> the isa pointer is <= 0xffff and, if so, looks up the class from a
> table.  The open source CFLite stuff doesn't have this.
>
> David

They actually use this:

#pragma pack(1)
struct apple_cfstring
{
        void* isa;
        uint8_t flags;
        uint8_t typeID;
        uint8_t unused[2];
#ifdef __x86_64__
        uint32_t extraFlags;
#endif
        void* data;
        unsigned long length;
};
#pragma pack()

So isa is kept separately from typeID.

--
Luboš Doležel