Comment by pcwalton

Objective-C uses a hash table cache for all method calls. It's a bit different in that Objective-C deals with collisions by just not handling them: since it's only a cache, collisions will result in going through the slow name lookup path.

Mike Ash has a nice series that goes through the disassembly of objc_msgSend: https://www.mikeash.com/pyblog/friday-qa-2017-06-30-dissecti...