List<int> normalList = new List<int> { 1, 2, 3 }; ReadOnlyCollection<int> readonlyList = normalList.AsReadOnly(); FrozenSet<int> frozenSet = normalList.ToFrozenSet(); ImmutableList<int> immutableList = normalList.ToImmutableList(); normalList.Add(4); Console.WriteLine($"List count: {normalList.Count}"); Console.WriteLine($"ReadOnlyList count: {readonlyList.Count}"); Console.WriteLine($"FrozenSet count: {frozenSet.Count}"); Console.WriteLine($"ImmutableList count: {immutableList.Count}");