Ayende's modern version of the AbstractFactory

Program.cs

/*
 * thanks to Ayende for idea, http://tekpub.com/shows/mct/1
 */
using System;

namespace AbstactFactory;

class Program
{
    public static void Main()
    {
        Setup();

        var factory = new Factory();
        string greeting = factory.Create();

        Console.WriteLine($"AbstractFactory say's {greeting}");

        Console.Write("Press any key to continue . . . ");
        Console.ReadKey(true);
    }

    static void Setup()
    {
        Console.Write("Choose 1 or 2? ");
        var input = Console.ReadLine();
        if (input.Contains("1"))
            Factory.FactoryCreated += factory => factory.Create = () => "Hello World!";
        else if (input.Contains("2"))
            Factory.FactoryCreated += factory => factory.Create = () => "Hejsan";
        else
            Factory.FactoryCreated += factory => factory.Create = () => "you wrote: " + input;
    }
}

/// <summary>
/// A factory class that provides a greeting string.
/// </summary>
public sealed class Factory
{
    /// <summary>
    /// An event that is raised when a new factory is created.
    /// </summary>
    public static event Action<Factory> FactoryCreated;

    /// <summary>
    /// Initializes a new instance of the <see cref="Factory"/> class.
    /// </summary>
    /// <exception cref="ArgumentException">Thrown when no configuration exists for creation.</exception>
    public Factory()
    {
        if (FactoryCreated == null)
            throw new ArgumentException("No configuration exist for creation.");
        FactoryCreated(this);
    }

    /// <summary>
    /// Gets or sets a function that creates a greeting string.
    /// </summary>
    public Func<string> Create { get; set; }
}