exposed-roots-with-tags.md

Exposed roots with tags

Composition roots from other assemblies or projects can be used as a source of bindings. When you add a binding to a composition from another assembly or project, the roots of the composition with the RootKind.Exposed type will be used in the bindings automatically. For example, in some assembly a composition is defined as:

public partial class CompositionWithTagsInOtherProject
{
    private static void Setup() =>
        DI.Setup()
            .Bind().As(Lifetime.Singleton).To<MyDependency>()
            .Bind("Some tag").To<MyService>()
            .Root<IMyService>("MyService", "Some tag", RootKinds.Exposed);
}

class Program([Tag("Some tag")] IMyService myService)
{
    public void DoSomething() => myService.DoSomething();
}

DI.Setup(nameof(Composition))
    // Binds to exposed composition roots from other project
    .Bind().As(Lifetime.Singleton).To<CompositionWithTagsInOtherProject>()
    .Root<Program>("Program");

var composition = new Composition();
var program = composition.Program;
program.DoSomething();

The following partial class will be generated:

partial class Composition
{
  private readonly Composition _root;
  private readonly object _lock;

  private Integration.CompositionWithTagsInOtherProject? _singletonCompositionWithTagsInOtherProject39;

  [OrdinalAttribute(20)]
  public Composition()
  {
    _root = this;
    _lock = new object();
  }

  internal Composition(Composition parentScope)
  {
    _root = (parentScope ?? throw new ArgumentNullException(nameof(parentScope)))._root;
    _lock = _root._lock;
  }

  public Program Program
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      if (_root._singletonCompositionWithTagsInOtherProject39 == null)
      {
        lock (_lock)
        {
          if (_root._singletonCompositionWithTagsInOtherProject39 == null)
          {
            _root._singletonCompositionWithTagsInOtherProject39 = new Integration.CompositionWithTagsInOtherProject();
          }
        }
      }

      Integration.IMyService transientIMyService1;
      Integration.CompositionWithTagsInOtherProject localInstance_1182D1276 = _root._singletonCompositionWithTagsInOtherProject39!;
      transientIMyService1 = localInstance_1182D1276.MyService;
      return new Program(transientIMyService1);
    }
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public T Resolve<T>()
  {
    return Resolver<T>.Value.Resolve(this);
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public T Resolve<T>(object? tag)
  {
    return Resolver<T>.Value.ResolveByTag(this, tag);
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public object Resolve(Type type)
  {
    var index = (int)(_bucketSize * ((uint)RuntimeHelpers.GetHashCode(type) % 1));
    ref var pair = ref _buckets[index];
    return pair.Key == type ? pair.Value.Resolve(this) : Resolve(type, index);
  }

  [MethodImpl(MethodImplOptions.NoInlining)]
  private object Resolve(Type type, int index)
  {
    var finish = index + _bucketSize;
    while (++index < finish)
    {
      ref var pair = ref _buckets[index];
      if (pair.Key == type)
      {
        return pair.Value.Resolve(this);
      }
    }

    throw new InvalidOperationException($"{CannotResolveMessage} {OfTypeMessage} {type}.");
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public object Resolve(Type type, object? tag)
  {
    var index = (int)(_bucketSize * ((uint)RuntimeHelpers.GetHashCode(type) % 1));
    ref var pair = ref _buckets[index];
    return pair.Key == type ? pair.Value.ResolveByTag(this, tag) : Resolve(type, tag, index);
  }

  [MethodImpl(MethodImplOptions.NoInlining)]
  private object Resolve(Type type, object? tag, int index)
  {
    var finish = index + _bucketSize;
    while (++index < finish)
    {
      ref var pair = ref _buckets[index];
      if (pair.Key == type)
      {
        return pair.Value.ResolveByTag(this, tag);
      }
    }

    throw new InvalidOperationException($"{CannotResolveMessage} \"{tag}\" {OfTypeMessage} {type}.");
  }

  private readonly static int _bucketSize;
  private readonly static Pair<Type, IResolver<Composition, object>>[] _buckets;

  static Composition()
  {
    var valResolver_0000 = new Resolver_0000();
    Resolver<Program>.Value = valResolver_0000;
    _buckets = Buckets<Type, IResolver<Composition, object>>.Create(
      1,
      out _bucketSize,
      new Pair<Type, IResolver<Composition, object>>[1]
      {
         new Pair<Type, IResolver<Composition, object>>(typeof(Program), valResolver_0000)
      });
  }

  private const string CannotResolveMessage = "Cannot resolve composition root ";
  private const string OfTypeMessage = "of type ";

  private class Resolver<T>: IResolver<Composition, T>
  {
    public static IResolver<Composition, T> Value = new Resolver<T>();

    public virtual T Resolve(Composition composite)
    {
      throw new InvalidOperationException($"{CannotResolveMessage}{OfTypeMessage}{typeof(T)}.");
    }

    public virtual T ResolveByTag(Composition composite, object tag)
    {
      throw new InvalidOperationException($"{CannotResolveMessage}\"{tag}\" {OfTypeMessage}{typeof(T)}.");
    }
  }

  private sealed class Resolver_0000: Resolver<Program>
  {
    public override Program Resolve(Composition composition)
    {
      return composition.Program;
    }

    public override Program ResolveByTag(Composition composition, object tag)
    {
      switch (tag)
      {
        case null:
          return composition.Program;

        default:
          return base.ResolveByTag(composition, tag);
      }
    }
  }
}