call-this-impl.ts

export type Point = {
  t: 'point',
  readonly x: number;
  readonly y: number;
}
function get_distance(this: Point, other: Point) {
  return Math.sqrt(Math.pow(this.x - other.x, 2) + Math.pow(this.y - other.y, 2));
}

type Display<T> = {
  display(t: T): string;
}

function display<T>(this: T, impl: Display<T>) {
  return impl.display(this);
}

// usage

const display_for_point: Display<Point> = {
  display(self: Point) {
    return `(${self.x}, ${self.y})`;
  }
}

const p1: Point = { t: 'point', x: 0, y: 0 } as const;
const p2: Point = { t: 'point', x: 3, y: 4 } as const;

const ret = get_distance.call(p1, p2);
console.log(ret);

console.log(display.call(p2, display_for_point));