ใช้การประกอบแทนการสืบทอด

using System;
using System.Collections.Generic;
using System.Linq;

record LineItem(string Name, decimal Price);
class Order
{
    public List<LineItem> Items { get; } = new();
    public decimal Total => Items.Sum(item => item.Price);
}

class Program
{
    static void Main()
    {
        var order = new Order();
        order.Items.Add(new("Book", 30m));
        order.Items.Add(new("Pen", 5m));
        Console.WriteLine(order.Total);
    }
}