I am curious about the inner workings of the Apple SDK overlays. For example, when we import Foundation what does the Swift compiler? The output executable seems to be linked against both to libswiftFoundation.dylib and the Foundation.framework.
Also, all the overlays mark the original Objective-C frameworks as
@_exported so if we import the Swift equivalent we would have the Objective-C module imported as well.
How this works under-the-hood?