using System;

using System.Collections.Generic;

using System.Collections.ObjectModel;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        // An order is generated

        var order = new List<Item>

        {

            new Item { Name = "Apple", Price = 0.50m },

            new Item { Name = "Banana", Price = 0.75m },

            new Item { Name = "Vitamins", Price = 5.50m }

        };

​

        // The current sub total is $6.75

        Console.WriteLine("Subtotal: " + order.Sum(item => item.Price));

​

​

        Console.WriteLine("");

        Console.WriteLine("========================================");

        Console.WriteLine("");

​

​

        Console.WriteLine("Let the customer preview their order");

        var customerPreview = new ReadOnlyCollection<Item>(order);

​

        // The customer can't add or remove items, but they can change 

        //   the price of an item, even though it is a ReadOnlyCollection

        Console.WriteLine("Customer changes the price of the last item");

        customerPreview.Last().Price = 0.25m;

​

​

        Console.WriteLine("");

        Console.WriteLine("========================================");

        Console.WriteLine("");

​

​

        // The sub total is now only $1.50!

        Console.WriteLine("Subtotal: " + order.Sum(item => item.Price));

    }

}

​

public class Item

{

    public string Name { get; set; }

    public decimal Price { get; set; }

}