memoize.ts

type ReturnType<F> = F extends (...args: any[]) => infer R ? R : any;

type MemoizeResolver<F extends (...args: any[]) => any> = (
  ...args: Parameters<F>
) => string;

type MemoizedFuntion<F extends (...args: any[]) => any> = ((
  ...args: Parameters<F>
) => ReturnType<F>) & {
  clear: () => void;
};

function memoize<F extends (...args: any[]) => any>(
  fn: F,
  resolver: MemoizeResolver<F>,
): MemoizedFuntion<F> {
  let cache: { [key: string]: ReturnType<F> } = {};

  const memoizedFn = function(...args: Parameters<F>) {
    const key = resolver(...args);
    return cache[key] === undefined ? (cache[key] = fn(...args)) : cache[key];
  };

  memoizedFn.clear = () => (cache = {});
  return memoizedFn;
}

const add = (a: number, b: number) => a + b;
const memoizedAdd = memoize(add, (a, b) => `${a}.${b}`);