Always wrap up your third parties

2008-01-10

Today I was working through some code refactoring when I came across my implementation of the Castle Windsor container exposed off of the Global.asax file. I had put it there because I needed to get it initialized during Application_Start and I wanted to put it somewhere that was easy to get at from the rest of the code. When I exposed it off of Application_Start, I did it as a property of type IWindsorContainer.

In the end I needed to be able use a different implementation of a container. Since I’m not in control of the IWindsorContainer interface, I didn’t feel comfortable creating a new implementation based on that. Instead I created my own interface and implementation. The implementation for the main production container is just an adapter wrapping the IWindsorContainer. It looked something like this:

public class WindsorDependencContainer : IDependencyContainer
{
    private readonly IWindsorContainer _windsorContainer;

    public WindsorDependencContainer(IWindsorContainer windsorContainer)
    {
      _windsorContainer = windsorContainer;
    }

    public Interface ResolveFor<Interface>()
    {
      return _windsorContainer.Resolve<Interface>();
    }
}

Because I’m using my own interface I could go ahead and implement another simple container and make use of it. Maybe something like this:

public class SimpleDependencyContainer : IDependencyContainer
{
  private IDictionary<Type, object> _dependencies;

  public SimpleDependencyContainer() : this(new Dictionary<Type, object>())
  {
  }

  public SimpleDependencyContainer(IDictionary<Type, object> dependencies)
  {
    _dependencies = dependencies;
  }

  public Interface ResolveFor<Interface>()
  {
    return (Interface) _dependencies[typeof(Interface)];
  }
}

I went from having my code being tied to the Windsor implementation of an IoC container to having my application be able to implement any container that I desire. I’ve preached and preached that you should wrap everything that you’re implementing from a third party. For some reason I forgot this time and it damn near bit me in the ass.

Why this was important to me is the subject of a future blog post.

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