John Carmack on mutable variables

> I wish it was the default, and mutable was a keyword.

I wish the IDE would simply provide a small clue, visible but graphically unobtrusive, that it was mutated.

In fact, I end up wishing this about almost every language feature that passes my mind. For example, I don't need to choose whether I can or can't append to a list; just make it unappendable if you can prove I don't append. I don't care if it's a map, list, set, listOf, array, vector, arrayOf, Array.of(), etc unless it's going to get in my way because I have ten CPU cores and I'll optimize the loop when I need to.

I use Swift for work. The compiler tell you this. If a mutable variable is never mutated it suggests making it non-mutable. And vice versa.

As will Typescript, at least using Biome to lint it does.