I've actually used metaclasses today! Ensuring a #Python class is never instantiated twice with the same arguments:
miniblog.
Related Posts
https://stevelosh.com/blog/2018/07/fun-with-macros-if-let/ is an excellent post on implementing if-let and when-let macros.
It discusses the different ways you could expand the code, and ensuring the macro composes with other (Common) Lisp features.
Really useful macro too, I'm a big fan of the elisp equivalent.
Ansible is great for ensuring a whole group of servers is shipshape. $ ansible all -m apt -a "update_cache=yes" --sudo