interface Bounds {
  readonly w: number, // width
  readonly h: number, // height
  area(): number,
}

function square (w: number, h: number) {
  const area = () => w * h;
  return { h, w, area };
}

function perimeter (b: Bounds) {
  return 2 * (b.w + b.h);
}

console.log(perimeter(square(2, 4)));