Re: I think I figured out how Apple did their toll-free bridging.

[Luboš Doležel]

On Sat, 18 May 2013 05:35:50 +0800, Chan Maxthon wrote:
> I discovered this from stack traces of toll-free bridged calls.
>
> All CoreFoundation objects have an Objective-C isa pointer. For
> toll-free bridged objects, this pointer points to an Objective-C 
> class
> which is a subclass of the corresponding class cluster public class,
> like for CFArray the subclass is called __NSCFArray. This Objective-C
> class maps calls from Objective-C public API to corresponding
> CoreFoundation calls.
>
> All CoreFoundation functions that take toll-free-bridge-able objects
> detects if the argument passed in is CoreFoundation object. If Cocoa
> objects are used, base on the situation, either the object will be
> copied into its CoreFoundation counterpart, or the call will be 
> mapped
> back to Cocoa.
>
> This entangled nature guaranteed that at least all toll-free bridging
> private Cocoa classes, their public base classes and NSObject are
> inside CoreFoundation binary, or the linker will be seriously
> confused.

Well, CoreBase is written around the same idea. In my fork on GitHub, 
toll-free bridging already works for most common types/classes - but the 
infrastructure was supplied by Stefan Bidi who modelled it after Apple.

--
Luboš Doležel