Updating

Previous sections show how to add and remove a binding from a given map. The function Map.update can do both depending whether some value is given for the new binding or not: in the former case, a new binding is added (and replaces any previous binding with the same key); in the latter case, any binding with the same key is removed and a new map is returned.

const my_map: map<int,string> = Map.literal(list([[1,"one"],[2,"two"]]));

const map_with_3 = Map.update (3, Some("three"), my_map);

const contains_3 = Map.mem(3, map_with_3); // == true

const map_without_2 = Map.update(2, None(), my_map);

const contains_2 = Map.mem (2, map_without_2); // == false

When we want to update a map, but also obtain the value of the updated binding, we can use Map.get_and_update.

// three == Some("three")

const [three, map_without_3] = Map.get_and_update(3, None(), map_with_3);

Note: See the predefined namespace Map