typescript
1// Component interface
2interface ShippingUnit {
3  getWeight(): number;
4  getDimensions(): Dimensions;
5  getItemCount(): number;
6  accept(visitor: ShippingVisitor): void;
7}
8
9// Leaf
10class Item implements ShippingUnit {
11  constructor(
12    public readonly sku: string,
13    private weight: number,
14    private dimensions: Dimensions
15  ) {}
16
17  getWeight(): number {
18    return this.weight;
19  }
20
21  getDimensions(): Dimensions {
22    return this.dimensions;
23  }
24
25  getItemCount(): number {
26    return 1;
27  }
28
29  accept(visitor: ShippingVisitor): void {
30    visitor.visitItem(this);
31  }
32}