[drob518]

The only benefit to mutability is efficiency. If you make immutability cheap, you almost never need mutability. When you do, it’s easy enough to expose mechanisms that bypass immutability. For instance in Clojure, all values are immutable by default. Sometimes, you really want more efficiency and Clojure provides its concept of “transients”[1] which allow for limited modification of structures where that’s helpful. But even then, Clojure enforces some discipline on the programmer and the expectation is that transient structures will be converted back to immutable (persistent) structures once the modifications are complete. In practice, there’s rarely a reason to use transients. I’ve written a lot of Clojure code for 15 years and only reached for it a couple of times.

[1] https://clojure.org/reference/transients