Apple added a lot of sugar to different parts of Objective-C and a few side features – dot syntax, synthesised properties, blocks, etc. They're still adding twe

Apple added a lot of sugar to different parts of Objective-C and a few side features – dot syntax, synthesised properties, blocks, etc. They're still adding tweaks like nullability, generics and other Swift-compatibility features. And they were continually changing things like NSString and NSNumber internal representations and allocation patterns to avoid actually allocating. They really only changed the runtime once – Objective-C 2.0 – which they mostly hid behind the transition to 64-bit. This introduced layout resilience (so they could add fields to objects without breaking compatibility) and tagged pointers (so the reference count could be stored inside the pointer).