using System.Collections.Generic;
using System.Collections.Immutable;
public static void Main()
var list = ImmutableList<int>.Empty.Add(1);
Console.WriteLine("list count: {0}", list.Count);
Console.WriteLine("list count: {0}", list.Count);
((ICollection<int>)list).Add(2);
Console.WriteLine("list count: {0}", list.Count);