.ts

export interface Product {    getPrice(): number;  }
  
  export class ProductA implements Product {
    private _price: number;
  
    constructor(price: number) {
      this._price = price;
    }
    getPrice(): number {
      return this._price;
    }
  }
  
  export class Packaging implements Product {
    private _product: Product;
    constructor(product: Product) {
      this._product = product;
    }
    getPrice(): number {
      return this._product.getPrice() + 0.5;
    }
  }