Yeah. A more nuanced approach is that you should copy things that don't consist of lots and lots of references to other things, and you should mutate things tha

Yeah. A more nuanced approach is that you should copy things that don't consist of lots and lots of references to other things, and you should mutate things that are mostly references to other structures. Which means, eventually, designing your data structures so you generally have two types of structures: one which isn't full of pointers, and one which mostly is.