It's My Turn To Build An IoC Container In 15 Minutes and 33 Lines

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Last night I’ve built a nice new tool called StaticMapGenerator which is used to generate a typed static resources site-map for ASP.NET sites (works for MonoRail, ASP.NET MVC and even WebForms).

I’ll blog about it on a separate post in details.

Since I didn’t want any dependency (but .NET 2.0 runtime) for the generator and the generated code, I couldn’t use Windsor to IoC. That calls for a hand rolled simple IoC implementation

Ayende has already done it in 15 lines, but I wanted also to automagically set dependencies and have a simpler registration model.

so I’ve quickly hacked together a configurable DI resolver (a.k.a. IoC container) in 15 Minutes and 22 Lines Of Code. Call me a sloppy-coder, call me whadever-ya-like. It just works.

static class IoC {
  static readonly IDictionary<Type, Type> types = new Dictionary<Type, Type>();

  public static void Register<TContract, TImplementation>()  { 
    types[typeof(TContract)] = typeof(TImplementation);
  }

  public static T Resolve<T>()  {
    return (T)Resolve(typeof(T));
  }

  public static object Resolve(Type contract) {
    Type implementation = types[contract];
    ConstructorInfo constructor = implementation.GetConstructors()[0];
    ParameterInfo[] constructorParameters = constructor.GetParameters();
    if (constructorParameters.Length == 0) { 
      return Activator.CreateInstance(implementation);  
    }
    
    List<object> parameters = new List<object>(constructorParameters.Length);
    foreach (ParameterInfo parameterInfo in constructorParameters) {  
      parameters.Add(Resolve(parameterInfo.ParameterType));
    }

    return constructor.Invoke(parameters.ToArray()); 
  }
}

Ok, I’ve cheated. You’d need using statements too, but you can see that I was generous enough with newlines …

Usage:

Given those:

public interface IFileSystemAdapter { }

public class FileSystemAdapter : IFileSystemAdapter { }

public interface IBuildDirectoryStructureService { }

public class BuildDirectoryStructureService : IBuildDirectoryStructureService{ 
  IFileSystemAdapter fileSystemAdapter; 

  public BuildDirectoryStructureService(IFileSystemAdapter fileSystemAdapter) { 
    this.fileSystemAdapter = fileSystemAdapter; 
  }
}

You can do that:

IoC.Register<IFileSystemAdapter, FileSystemAdapter>();
IoC.Register<IBuildDirectoryStructureService, BuildDirectoryStructureService>(); 
IBuildDirectoryStructureService service = IoC.Resolve<IBuildDirectoryStructureService>();

You need not worry about supplying the BuildDirectoryStructureService with an implementation for the service it depends on, but only to register an implementation for that service.

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