The first argument is weak, arrays are THE mutable structure and no functional language uses it as it is. For the exact reasons of GC overhead, FP languages use

The first argument is weak, arrays are THE mutable structure and no functional language uses it as it is. For the exact reasons of GC overhead, FP languages use persistent data structures meaning when you modify the data, what you get is (roughly) old data + delta , no need to deep copy anything