Immutability does not even have to be bound to functional programming. One can use persistent (= immutable from the user's perspective) data structures, like im

Immutability does not even have to be bound to functional programming. One can use persistent (= immutable from the user's perspective) data structures, like immutable.js and get most of the benefits. Moreover, persistent data structures can be optimized well (see Clojure), so that the performance issues may be relegated to the inner loops, as usual, and the rest of the program may use safe-for-sharing data structures.