Hash Tables

Hash Tables are arbitrary value-indexed collections of references to values. The only value you cannot use as a key is #n.

simple-hash-tables.idio
;; use the default equivalence and hashing functions
h1 := make-hash #n #n 2
printf "h1 has %d keys: %s\n" (hash-size h1) h1

hash-set! h1 'a "apple"

;; access it again
printf "%s is for %s\n" 'a (hash-ref h1 'a)

;; the dot operator is more convenient but slightly slower
printf "%s is for %s\n" 'a h1.'a

;; similarly for setting entries
h1.'b = "banana"

;; the key is evaluated so key becomes the symbol c
key := 'c
h1.key = "carrot"

printf "h1 has %d keys: %s\n" (hash-size h1) (hash-keys h1)

;; hash-keys returns a list so it is easy to iterate with
for k in (hash-keys h1) {
  printf "%s is for %s\n" k h1.k
}

;; hash-walk is another form of iterator
define (walker k v) {
  printf "%s maps to %s\n" k v
}

hash-walk h1 walker

;; static construction (using key/value pairs) does not allow
;; evaluation of elements so just "self-evaluating" constants,
;; numbers and strings.
h2 := #{ ('c & (hash-ref h1 'c)) }
printf "h2 is %d elements: %s\n" (hash-size h2) h2
$ idio simple-hash-tables
h1 has 0 keys: #{ }
a is for apple
a is for apple
h1 has 3 keys: (a c b)
a is for apple
c is for carrot
b is for banana
a maps to apple
c maps to carrot
b maps to banana
h2 is 1 elements: #{ ('c & (hash-ref h1 'c))}

Note

The order in which keys are accessed is not well-defined.

Last built at 2024-05-19T06:11:39Z+0000 from 77077af (dev) for Idio 0.3