Skeleton Maybe in C#

Maybe.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Ploeh.Samples.ChainOfResponsibility
{
    public class Maybe<T>
    {
        internal bool HasItem { get; }
        internal T Item { get; }

        public Maybe()
        {
            this.HasItem = false;
        }

        public Maybe(T item)
        {
            if (item == null)
                throw new ArgumentNullException(nameof(item));

            this.HasItem = true;
            this.Item = item;
        }

        public TAccumulate Aggregate<TAccumulate>(
            TAccumulate seed,
            Func<TAccumulate, T, TAccumulate> func)
        {
            if (seed == null)
                throw new ArgumentNullException(nameof(seed));
            if (func == null)
                throw new ArgumentNullException(nameof(func));

            if (this.HasItem)
                return func(seed, this.Item);
            else
                return seed;
        }
    }
}

Usage example:

> var m = new Maybe<string>("foo").Aggregate("", (_, s) => s);
> m
"foo"

You can only get the value out of the container unless you somehow deal with the case where it might be empty. It's possible to build all sorts of convenience functionality (e.g. DefaultIfEmpty) on top of Aggregate.