14. Map and Set

Map[K, V] and Set[T] are built-in persistent containers: every "modification" returns a new container and leaves the original alone. There is no literal syntax; the operations live in the std/map and std/set modules. Iteration order = insertion order, on the JVM and on native alike.

use std/map
use std/set

pub fn main() -> Unit !io = {
  let m = map.insert(map.insert(map.empty(), "a", 1), "b", 2)
  println(to_string(map.get(m, "a")))
  println(to_string(map.get(m, "z")))
  println(to_string(map.keys(m)))

  let s = set.from([3, 1, 2, 1, 3])
  println(to_string(set.len(s)))
  println(to_string(set.has(s, 2)))
}

Open in playground

Some(1)
None
["a", "b"]
3
true

A key may be of any type with structural equality (Int/String/tuples/ADTs/records). map.get returns an Option[V] — a miss is None, not an exception. Equality ignores order: two Maps with the same keys and values are equal.