using System;

using System.Collections.Generic;

using System.Collections.ObjectModel;

​

public class Program

{

    public static void Main()

    {

        var groceryList = new List<string> { "Apple", "Banana" };

​

        var readOnlyGroceryList = new ReadOnlyCollection<string>(groceryList);

        Console.WriteLine(nameof(readOnlyGroceryList) + ":");

        Console.WriteLine("--------");

        Console.WriteLine(string.Join("\r\n", readOnlyGroceryList));

​

​

        Console.WriteLine("");

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

        Console.WriteLine("");

​

​

        Console.WriteLine("Add an item to the source list: Vitamins");

​

        //readOnlyGroceryList.Add("Candy");         // Compiler Error - Items cannot be added to a ReadOnlyCollection object

        groceryList.Add("Vitamins"); // ..but they can be added to the original collection

​

​

        Console.WriteLine("");

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

        Console.WriteLine("");

​

​

        // The last item on the read only list is now "Vitamins"

        Console.WriteLine(nameof(readOnlyGroceryList) + ":");

        Console.WriteLine("--------");

        Console.WriteLine(string.Join("\r\n", readOnlyGroceryList));

    }

}