option_no_compile.cs

using System;

namespace Option
{
    public abstract class Option 
    {
        public static Option Wrap<T>(T value)
            where T : class
        {
            if(ReferenceEquals(value, null))
            {
                return new None();
            }
            
            return new Some<T>(value);
        }
    }

    public record class None : Option {}
    
    public record class Some<T>(T value) : Option 
    {
        public override string ToString() 
        {
            return string.Format("Some({0})", value);
        }
    }
    
    public class Program
    {
        public static void Main()
        {
            var x = "Hello, world!";
            var y = Option.Wrap(x);
            
            //The following line yields the error: option.cs(37,12): error CS0117: 'Option.None' does not contain a definition for 'is operator'
            if(y is None())
            {
                Console.WriteLine("None");
            }
            else
            {
                Console.WriteLine(y);
            }
        }
    }
}