I am writing this post as a result of a discussion in the ALT.Net mailing list and DI containers in Ruby. Since I promised that I would build such a thing, it made it interesting to see how far I can minimize an IoC container.

The result is, as I said, 15 lines of significant code (ignoring blank lines or line with just curly braces).

You can see the sample model on the right. It is fairly typical model, I believe. I want to get the login controller instance without having to worry about the dependencies, and I want to do it in a non invasive way.

How can we handle that?

Well, it is pretty simple, as a matter of fact, here is the full source code for the container:

public class DemoContainer
{
	public delegate object Creator(DemoContainer container);

	private readonly Dictionary<string, object> configuration 
                   = new Dictionary<string, object>();
	private readonly Dictionary<Type, Creator> typeToCreator 
                   = new Dictionary<Type, Creator>();

	public Dictionary<string, object> Configuration
	{
		get { return configuration; }
	}

	public void Register<T>(Creator creator)
	{
		typeToCreator.Add(typeof(T),creator);
	}

	public T Create<T>()
	{
		return (T) typeToCreator[typeof (T)](this);
	}

	public T GetConfiguration<T>(string name)
	{
		return (T) configuration[name];
	}
}

 Not really hard to figure out, right? And the client code is as simple:

DemoContainer container = new DemoContainer();
//registering dependecies
container.Register<IRepository>(delegate
{
	return new NHibernateRepository();
});
container.Configuration["email.sender.port"] = 1234;
container.Register<IEmailSender>(delegate
{
	return new SmtpEmailSender(container.GetConfiguration<int>("email.sender.port"));
});
container.Register<LoginController>(delegate
{
	return new LoginController(
		container.Create<IRepository>(),
		container.Create<IEmailSender>());
});

//using the container
Console.WriteLine(
	container.Create<LoginController>().EmailSender.Port
	);

I should probably mention that While this handles dependency injection quite nicely, it is absolutely not what I would consider an appropriate container to use. More on that in the next post.