You can have a look at the code in libs-corebase for an example on how to call method from C code. All the bridge code is in Source/GSObjCRuntime.h.
I am very interested in building a bridge between Swift and GNUStep's Objective-C Runtime.
Given that the Objective-C implementation provided by GNUStep doesn't interact directly with Swift as Swift can with Apple's Objective-C runtime, I was wondering if there was a way to call into GNUStep from C. If someone could show me an example of a way to call into GNUStep using either C as a bride though a Swift project or directly from Swift, I would be more than willing to start building a bridge. I just don't currently understand how to do it.
I malignly want to do this so I could more rapidly build software for OnFlapp's GNUStep Desktop, but I think this would ultimately benefit everyone.