Insertion-ordered map.

OrderedMap(K, V) preserves the order in which keys were first inserted, similar to JavaScript's Map or Python's dict (≥ 3.7). Backed by a HashMap for O(1) average-time lookup and an ArrayList of keys for deterministic iteration order.

Complexity

• set (new key): O(1) amortized
• set (existing key): O(1) — value updated in place, order unchanged
• get / contains_key: O(1) average
• remove: O(n) — must rebuild the key order list to skip the removed key
• iter / keys / values: O(n), in insertion order

Example

{ OrderedMap } :: import "std/collections/ordered_map";

m := OrderedMap(String, i32).new();
m.set(`alpha`, i32(1));
m.set(`beta`,  i32(2));
m.set(`gamma`, i32(3));

// Iteration yields keys in insertion order.
it := m.keys();
while true, {
  match(it.next(),
    .Some(k) => println(k),
    .None => break
  );
};