Rust is adding a new type for pointers to data that can't move! https://github.com/withoutboats/rfcs/blob/pin-and-move/text/0000-pin.md
This is useful in lots of situations: dealing with FFI/GC in other language runtimes, self references, amongst others.
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Linux historically used magic numbers to recognise structs being used incorrectly with void pointers. These have been increasingly replaced with type-safe macros: https://lwn.net/SubscriberLink/915163/ba83480903b82cb8/
Some of the original files were unchanged from the 90s!
This article discusses how you often need #'foo rather than foo in Clojure code so you can redefine foo whilst testing your app interactively: https://srasu.srht.site/var-evaluation.html
Perhaps function pointers should evaluate to themselves? I wonder if there's a language solution here.
Smalltalk has a remarkable method named #become: that allows you to modify all pointers to a given object to point to a different object!
https://gbracha.blogspot.com/2009/07/miracle-of-become.html
This goes even further than updating instances when a class changes, it's changing instance references.