Eoops (Emacs OOP System) implements a Smalltalk-80-like language in GNU Emacs-Lisp
(Lewis 90). Eoops is a simple but efficient compiler for a class-based, single inheritance,
object-oriented language that uses explicit message passing for both method ...
Probably should mention this is from 1992 and doesn’t use CLOS. Is Eoops used in Emacs at all these days? Looks defunct: https://www.emacswiki.org/emacs/EmacsObjectOrientedProgrammingSystem
I should have embedded the date, it was more for historical value :)
It is. You can still use it. There is an implementation that byte compiles with just some minor warnings but EIEIO (a simplified CLOS version) is what is available in Emacs as built-in and there is much more available resources to learn from if you want to use an object-oriented system in Emacs.