export namespace MapUtil {
  export const take =
    <Key, T>(dict: Map<Key, T>) =>
    (key: Key, generator: () => T): T => {
      const oldbie: T | undefined = dict.get(key);
      if (oldbie) return oldbie;

      const value: T = generator();
      dict.set(key, value);
      return value;
    };
}