using System;

using System.Collections.Generic;

using System.Linq;

using System.Reflection;

using System.Collections.Immutable;

public class Program

{

    public static void Main()

    {

        IReadOnlyDictionary<long, long?> d = ImmutableDictionary<long, long>.Empty;

        d.TryGetValue(1, out var z);

        Console.WriteLine($"Hello World; {d.GetValueOrDefault(1)} {z}");

    }

    public enum MyEnum

    {

        NotDefault = 1

    }

}

​

​