Dictionaries

{K: V} maps keys to values. Keys may be integers, strings, booleans, payload-free enums, or tuples made from those types. {:} is the empty dictionary.

A bare loop binding receives keys. A top-level tuple pattern receives (key, value) entries. Dictionaries preserve first-insertion order, including when a value is replaced.

fn main() {
  let mut ages = {"Ada": 36, "Grace": 36}
  ages["Ada"] += 1
  for (name, age) in ages {
    println("$name:$age")
  }
}