如何拆分和重用Typescript类型？

type Person = {
  name: string;
  age: number;
};

type Employee = {
  id: number;
  department: string;
};

type Developer = Person & Employee;

const dev: Developer = {
  name: "John",
  age: 25,
  id: 123,
  department: "IT"
};

type Shape = Square | Circle;

interface Square {
  kind: "square";
  size: number;
}

interface Circle {
  kind: "circle";
  radius: number;
}

function calculateArea(shape: Shape): number {
  if (shape.kind === "square") {
    return shape.size * shape.size;
  } else {
    return Math.PI * shape.radius * shape.radius;
  }
}

function toArray<T>(value: T): T[] {
  return [value];
}

const arr1: number[] = toArray(1);
const arr2: string[] = toArray("hello");

type Point = {
  x: number;
  y: number;
};

type Rectangle = {
  topLeft: Point;
  bottomRight: Point;
};

const rect: Rectangle = {
  topLeft: { x: 0, y: 0 },
  bottomRight: { x: 10, y: 10 }
};