Please give an example. I think there’s some confusion over what you mean by “runtime”, as nothing mentioned so far really has anything to do with the actual Obj-C runtime.
Sorry! I am using Obj-C runtime as umbrella term for : When we pass objects between Swift and Cocoa API through bridge/overlay etc. mechanism, hidden magic and annoyance with NS classes behavior, The memory management of these bridged objects without appropriate hints via the annotations that can be understood by Obj-C ( via compile time optimizations etc.), AnyObject generalizations etc.
Please see the post by @gwendal.roue in the above in this thread for some examples. #selector mechanism and the resulting delegation, KVC and am finding more and more as I am going through this exercise.
The post by @rljames above seems to say some of what I have discovered too.