I'm wondering if there is a C++ to ObjC library interface that would be cleaner.
Never encountered any. I doubt it is possible since Obj-C is dynamically typed (binded) language, which means you can pass any kind of msg to any kind of obj and it will compile/run. Either you will receive an "method not found" exception or "nil" as return. It is very close to what Ruby is. Actually both Ruby & ObjC as based on Smalltalk idea.
Of course there's wxWidgets for example which wraps Cocoa as one of its backends, but the wrapper is C++ & ObjC mixture.
I really don't understand why Obj-C is treated as evil, even it would be part only of Mac platform of Wine and even it is supported by GDB and GCC on any possible platform :/ Once I thought when moving to Mac that its doggy idea to force some Obj-C on Mac, while other part of the World speak C/C++, but now I know that Obj-C is what defined OSX actually and way the whole system works. So wondering who of Obj-C dislikers at Wine HQ really uses Mac and really did any of native apps on Mac.
Regards,