using System;

using System.Collections;

using System.Collections.Generic;

using System.IO;

using System.Linq;

​

namespace MaybeProp

{

    public class Program

    {

        public static void Main(string[] args)

        {

            int[] ids = new[] { 1, 2, 3, 4, 5 };

​

            var storage = new Storage();

​

            foreach (var id in ids)

            {

                Console.WriteLine("{0}: {1}", storage.GetStorageName(id), storage.GetContent(id));

            }

            Console.WriteLine();

​

            var someStorage = new NotSoReliableStorage();

​

            foreach (var id in ids)

            {

                try

                {

                    Console.WriteLine("{0}: {1}", someStorage.GetStorageName(id), someStorage.GetContent(id));

                }

                catch

                {

                    Console.WriteLine("{0}: NO CONTENT", someStorage.GetStorageName(id));

                }

            }

            Console.WriteLine();

​

            var betterStorage = new BetterNotSoReliableStorage();

​

            foreach (var id in ids)

            {

                string message = "";

​

                if (betterStorage.TryGetContent(id, out message))

                    Console.WriteLine("{0}: {1}", betterStorage.GetStorageName(id), message);

                else

                    Console.WriteLine("{0}: NO CONTENT", betterStorage.GetStorageName(id));

            }

            Console.WriteLine();

​

            var maybeStorage = new MaybeStorage();

​

            foreach (var id in ids)

            {

                Console.WriteLine("{0}: {1}",

                                    maybeStorage.GetStorageName(id),

                                    maybeStorage.GetContent(id)

                                        .DefaultIfEmpty(string.Format("NO CONTENT"))

                                    .Single());

            }

​

        }

    }

​

    public class Storage

    {

        public string GetStorageName(int id)

        {

            return Path.Combine(@"C:\", id + ".txt");

        }

        public string GetContent(int id)

        {

            return string.Concat(Enumerable.Repeat("hello ", id));

        }

    }

​

    public class NotSoReliableStorage

    {

        public string GetStorageName(int id)

        {

            return Path.Combine(@"C:\", id + ".txt");

        }

        public string GetContent(int id)

        {

            if (id % 2 == 0)

                throw new ArgumentException("Cannot find it");

​

            return string.Concat(Enumerable.Repeat("hello ", id));

        }

    }

​

    public class BetterNotSoReliableStorage

    {

        public string GetStorageName(int id)

        {

            return Path.Combine(@"C:\", id + ".txt");

        }

        public bool TryGetContent(int id, out string content)

        {

            if (id % 2 == 0)

            {

                content = null;

                return false;

            }

​

            content = string.Concat(Enumerable.Repeat("hello ", id));

            return true;

        }

    }

​

    public class MaybeStorage

    {

        public string GetStorageName(int id)

        {

            return Path.Combine(@"C:\", id + ".txt");

        }

        public Maybe<string> GetContent(int id)

        {

            if (id % 2 == 0)

                return new Maybe<string>();

​

            return new Maybe<string>(string.Concat(Enumerable.Repeat("hello ", id)));

        }

    }

​

    public class Maybe<T> : IEnumerable<T>

    {

        private readonly IEnumerable<T> values;

​

        public Maybe()

        {

            this.values = new T[0];

        }

​

        public Maybe(T value)

        {

            this.values = new[] { value };

        }

        public IEnumerator<T> GetEnumerator()

        {

            return this.values.GetEnumerator();

        }

​

        IEnumerator IEnumerable.GetEnumerator()

        {

            return this.GetEnumerator();

        }

    }

}

​