export const memoize = <A extends string | number, R>(
  fn: (arg: A) => R,
) => {
  const cache = new Map<A, R>();
  return (arg: A): R => {
    if (cache.has(arg)) return cache.get(arg)!;
    const res = fn(arg);
    cache.set(arg, res);
    return res;
  };
};

// Usage
const expensiveCalc = memoize((n: number) => {
  console.log('Computing...');
  return n * n;
});

expensiveCalc(5); // Computing... 25
expensiveCalc(5); // 25 (cached)