Update element of immutable vector - vector-set

Question

I'm using vectors to build a table for implement a dynamic program, it involves updating each element of the vector sequentially. But why is there no vector-set for immutable vectors? There is only vector-set! for mutable vectors, but we can see that there is dict-set and dict-set! for immutable and mutable dictionaries, also there is hash-set and hash-set! for immutable and mutable hash tables.

Answer 1

The reason why vector-set is missing, is to prevent people inadvertently using it without realizing the operation is O(n) and not O(1). Since vector-set! is O(1) it is not unlikely for someone to make this mistake.

Furthermore it is simple to write a vector-set when it is really needed:

#lang racket

(define (vector-set v i o)
  (vector->immutable-vector
   (for/vector ([j (in-range (vector-length v))])
     (if (= i j)
         o
         (vector-ref v j)))))

(vector-set (vector-immutable 10 11 12 13) 2 'a)

Output:

'#(10 11 a 13)