CLOS is more than fast enough for games (see e.g. Kandria, there are comments on HN about it, though it's easy enough to do one's own benchmark and see how easy

CLOS is more than fast enough for games (see e.g. Kandria, there are comments on HN about it, though it's easy enough to do one's own benchmark and see how easy it is to get hundreds of frames per second even with thousands of objects updated and drawn through methods every frame), and if you do have some numerical generic functions in a tight loop you can optimize them further with libraries like https://github.com/alex-gutev/static-dispatch https://github.com/alex-gutev/static-dispatch The book Object-Oriented Programming: The CLOS Perspective (1993) even includes as its final chapter/paper "Efficient Method Dispatch in PCL" which is essentially a memoization technique, so it's been a concern (or because of such techniques, not the biggest concern) for a long time. The dev experience of using defstruct is bad enough when I want to change something about it that I just default to defclass. I can see some people not liking the somewhat more verbose syntax (I don't mind myself) but of course that's a barrier trivially removed...