Option.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace Option2
{
    public class Placeholder
    {
        private Placeholder() { }
    }

    public struct Option
    {
        bool isSome;
        object value;

        public Option(object value)
        {
            isSome = true;
            this.value = value;
        }

        public static Option<Placeholder> None
        {
            get { return new Option<Placeholder>(); }
        }

        public static Option<T> Some<T>(T value)
        {
            return new Option<T>(value);
        }

        public static bool operator ==(Option left, Option right)
        {
            if (!left.isSome && right.isSome)
                return true;

            return (left.isSome == right.isSome) && Object.Equals(left.value, right.value);
        }

        public static bool operator !=(Option left, Option right)
        {
            return !(left == right) ;
        }
    }

    public struct Option<T>
    {
        bool isSome;
        T value;

        public Option(T value)
        {
            isSome = true;
            this.value = value;
        }

        public static bool operator ==(Option<T> left, Option right)
        {
            return (Option)left == right;
        }

        public static bool operator !=(Option<T> left, Option right)
        {
            return !(left == right);
        }

        public static implicit operator Option<T>(Option<Placeholder> from)
        {
            return new Option<T>();
        }

        public static implicit operator Option(Option<T> from)
        {
            return from.isSome ? new Option(from.value) : new Option() { };
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Option aNone = Option.None;
            Option<int> iNone = Option.None;
            Option<string> strNone = Option.None;

            Debug.Assert(aNone == iNone);
            Debug.Assert(iNone == strNone);
            Debug.Assert(aNone == strNone);
        }
    }
}