Re: CoreBase toll-free bridging

[Fred Kiefer]

On 13.03.2013 09:12, Luboš Doležel wrote:
> So guys, what do we do? :-)
>
> I'd be unhappy if this topic just faded away...

Same here :-)

We need a solution where Corebase works without base being present. And 
when base is there it should fit in as well.
I read through the documentation at
http://developer.apple.com/library/mac/#documentation/CoreFoundation/Conceptual/CFDesignConcepts/Articles/tollFreeBridgedTypes.html

We have different options:

- Implementing CoreBase on top of base wont work as Stef Bidi pointed 
out, or rather it only would if we put the full CoreBase into base.

- Replacing the base classes with CoreBase ones, as implemented in your 
changes that started this thread, wont work either. As soon as somebody 
uses a self implemented NSString subclass that wont be bridgable to 
CoreBase.

- We could make all the CoreBase functions tiny wrappers around 
Objective-C classes that are independent of base. I think this was the 
idea I originally proposed when we started out on CoreBase. That way we 
would be able to pass in base objects into CoreBase functions and things 
still would work. This would not allow for the special deallocation 
functions that are possible for many CoreBase data types and would 
thereby limit the way CoreBase could be used.

- The only way that could work all the time is to add a test in each 
CoreBase function, whether the passed in reference is a CF reference or 
a real object and dispatch based on that. This is a lot of overhead, but 
only then we will have toll free bridging.

Having decided that I googled once more and found this article:
http://www.mikeash.com/pyblog/friday-qa-2010-01-22-toll-free-bridging-internals.html

Which just means, I could have saved myself a lot of reasoning, by doing 
this first :-) And this article even points to one with more details. I 
think this is the way to go. One downside here is that this means we 
will need each CoreBase function twice an internal version that contains 
the current implementation and an external, that checks the passed in 
reference before calling the internal one. And we will need to figure 
out a way to do the message send without objc_msgSend() for the old 
libobjc runtime.

Fred