> But if you just have an internal helper function for that, then think about if you really want to lock its existence and behavior into place, or if that would just hinder future architectural changes.

I agree with everything you’ve said up until this point. The add function should be locked down, whether or not it’s internal code. I’ve written some physics libraries for games I’ve coded in the past, and you can bet that I wanted to lock in the functionality of that complex physics code by working some examples by hand and then codifying them into unit tests!

I think you’re right at the end, everything is nuanced. Using the right tool for the right job is easier said then done :)