byme8 / ZeroIoC

The main goal of the ZeroIoC is to provide IoC for AOT platforms such as Xamarin, Unity, and Native AOT. It is powered by Roslyn Source Generator as a result executed on build and doesn't require Reflection.Emit to function.

Get Started

1. Install nuget package ZeroIoC to your project.

dotnet add package ZeroIoC

2. Declare your container that is inherited from ZeroIoCContainer as a partial class

    public interface IUserService
    {
    }

    public class UserService : IUserService
    {
        public Guid Id { get; } = Guid.NewGuid();

        public UserService(Helper helper)
        {
        }
    }

    public class Helper
    {
        public Guid Id { get; } = Guid.NewGuid();
    }

    public partial class Container : ZeroIoCContainer
    {
        protected override void Bootstrap(IZeroIoCContainerBootstrapper bootstrapper)
        {
            bootstrapper.AddSingleton<Helper>();
            bootstrapper.AddTransient<IUserService, UserService>();
        }
    }

3. Use your container:

  var container = new Container();
  var userService = container.Resolve<IUserService>();

4. You can override a constructor argument or some dependency:

  var container = new Container();
  var userService = container.Resolve<IUserService>(
    Overrides.Create()
        .Constructor(("helper", new Helper())));
  // ...
  var userService = container.Resolve<IUserService>(
    Overrides.Create()
        .Dependency<Helper>(() => new Helper()));

Features

I would say it is in the MVP stage. Under MVP, I mean that the set of features is big enough to be helpful in real projects. This set contains:

• Multiple IoC containers can be active at the same time.
• Support for the singleton, scoped, and transient lifetimes => basic things that cover 99% of all needs.
• Support for overrides, you can override a constructor argument or some dependency for one call => usefull in some advanced scenarios and during testing.
• Powered by source generation to avoid reflection and Reflection.Emit => you can use it inside the AOT Xamarin/Unity app.
• Fast enough, with minimal overhead => the end-user of the Xamarin app will not notice a difference.

How it works

The NuGet is deployed with the source generator and analyzer. Then it looks for class declarations that are inherited from the ZeroIoCContainer. Inside the generator looks for the ZeroIoCContainer.Bootstrap method. Based on its content, the source generator will generate another part of a partial class. For the case described above, it will look like that(skipping the performance magic):

public partial class Container
{

    public Container()
    {
        Resolvers = Resolvers.AddOrUpdate(typeof(global::Helper), new SingletonResolver(static resolver => new global::Helper()));
        Resolvers = Resolvers.AddOrUpdate(typeof(global::IUserService), new TransientResolver(static resolver => new global::UserService(resolver.Resolve<global::Helper>())));
    }

    protected Container(ImTools.ImHashMap<Type, InstanceResolver> resolvers, ImTools.ImHashMap<Type, InstanceResolver> scopedResolvers, bool scope = false)
        : base(resolvers, scopedResolvers, scope)
    {
    }

    public override IZeroIoCResolver CreateScope()
    {
        var newScope = ScopedResolvers
            .Enumerate()
            .Aggregate(ImHashMap<Type, InstanceResolver>.Empty, (acc, o) => acc.AddOrUpdate(o.Key, o.Value.Duplicate()));
        
        return new Container(Resolvers, newScope, true);
    }
}

It is pretty simple stuff. The logic is based on a dictionary with Type as a key and instance resolver as a value. Such a class is generated for each separate class declaration, and because there is no static logic, you can safely define as many containers as you like.

Limitations

Let's talk about the ZeroIoCContainer.Bootstrap method. It is not an ordinary method. It is a magic one. It allows you to define the relations between interface and implementation, but the .net will never execute it at the runtime. The ZeroIoCContainer.Bootstrap is just a declaration that will be parsed by source generation, and based on it, the mapping will be generated. It means that there is no point to use statements like that:

 public partial class Container : ZeroIoCContainer
    {
        protected override void Bootstrap(IZeroIoCContainerBootstrapper bootstrapper)
        {
            if(Config.Release)
            {
              bootstrapper.AddSingleton<IHelper, ReleaseHelper>();
            }
            else 
            {
              bootstrapper.AddSingleton<IHelper, DebugHelper>();
            }
            
            bootstrapper.AddTransient<IUserService, UserService>();
        }
    }

All of them will be just ignored. To prevent the bunch of WTF situations(and introduce a new one), I added a special analyzer that will warn you about it if you forget.

But If you want to do something at runtime, you can do it like that:

var container = new Container();
if(Config.Release)
{
    container.AddInstance<IHelper>(new ReleaseHelper());
}
else 
{
    container.AddInstance<IHelper>(new DebugHelper());
}

var userService = container.Resolve<IUserService>();

Such an approach doesn't use any reflection underhood and can be safely used inside the AOT environment.

Plans

• Performance improvements(it is already fast but can be better)
• Improve extensibility
• Create separate easy-to-use bootstrap nugets for common runtimes like Asp.Net Core, Xamarin, Unity3D.