Subtyping, inheritance and delegation

delegation.ts

class Quadrangle {
  name: string;
  width: number;
  height: number;
  constructor(name: string, width: number, height: number) {
    this.name = name;
    this.width = width;
    this.height = height;
  }
  getArea(): number {
    return this.width * this.height;
  }
}

// delegation
class Rectangle {
  quad: Quadrangle;
  constructor(name: string, width: number, height: number) {
    this.quad = new Quadrangle(name, width, height);
  }
  get name(): string {
    return this.quad.name;
  }
  getArea(): number {
    return this.quad.getArea();
  }
}

const rectangles = [new Rectangle("A", 100, 100), new Rectangle("B", 10, 10)];
console.log(
  rectangles.map((rectangle) => ({ [rectangle.name]: rectangle.getArea() }))
);

inheritance.ts

class Quadrangle {
  name: string;
  width: number;
  height: number;
  constructor(name: string, width: number, height: number) {
    this.name = name;
    this.width = width;
    this.height = height;
  }
  getArea(): number {
    return this.width * this.height;
  }
}

// implementation inheritance
class Rectangle extends Quadrangle {
  constructor(name: string, width: number, height: number) {
    super(name, width, height);
  }
}

const rectangles = [new Rectangle("A", 100, 100), new Rectangle("B", 10, 10)];
console.log(
  rectangles.map((rectangle) => ({ [rectangle.name]: rectangle.getArea() }))
);

subtyping.ts

interface Shape {
  name: string;
  getArea(): number;
}

// subtyping (interface inheritance)
class Rectangle implements Shape {
  name: string;
  width: number;
  height: number;
  constructor(name: string, width: number, height: number) {
    this.name = name;
    this.width = width;
    this.height = height;
  }
  getArea(): number {
    return this.width * this.height;
  }
}

class Cricle implements Shape {
  name: string;
  radius: number;
  constructor(name: string, radius: number) {
    this.name = name;
    this.radius = radius;
  }
  getArea(): number {
    return this.radius * this.radius * 3.14;
  }
}

const shapes: Shape[] = [
  new Rectangle("A", 100, 100),
  new Rectangle("B", 10, 10),
  new Cricle("C", 30),
];
console.log(shapes.map((shape) => ({ [shape.name]: shape.getArea() })));