generic-composition-roots.md

Generic composition roots

Sometimes you want to be able to create composition roots with type parameters. In this case, the composition root can only be represented by a method.

Important

`Resolve()' methods cannot be used to resolve generic composition roots.

interface IDependency<T>;

class Dependency<T> : IDependency<T>;

interface IService<T>;

class Service<T>(IDependency<T> dependency) : IService<T>;

class OtherService<T>(IDependency<T> dependency) : IService<T>;

DI.Setup(nameof(Composition))
    // This hint indicates to not generate methods such as Resolve
    .Hint(Hint.Resolve, "Off")
    .Bind().To<Dependency<TT>>()
    .Bind().To<Service<TT>>()
    // Creates OtherService manually,
    // just for the sake of example
    .Bind("Other").To(ctx =>
    {
        ctx.Inject(out IDependency<TT> dependency);
        return new OtherService<TT>(dependency);
    })

    // Specifies to create a regular public method
    // to get a composition root of type Service<T>
    // with the name "GetMyRoot"
    .Root<IService<TT>>("GetMyRoot")

    // Specifies to create a regular public method
    // to get a composition root of type OtherService<T>
    // with the name "GetOtherService"
    // using the "Other" tag
    .Root<IService<TT>>("GetOtherService", "Other");

var composition = new Composition();

// service = new Service<int>(new Dependency<int>());
var service = composition.GetMyRoot<int>();

// someOtherService = new OtherService<int>(new Dependency<int>());
var someOtherService = composition.GetOtherService<string>();

Important

The method Inject()cannot be used outside of the binding setup.

The following partial class will be generated:

partial class Composition
{
  private readonly Composition _root;

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

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

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public IService<T2> GetOtherService<T2>()
  {
    OtherService<T2> transientOtherService0;
    IDependency<T2> localDependency62 = new Dependency<T2>();
    transientOtherService0 = new OtherService<T2>(localDependency62);
    return transientOtherService0;
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public IService<T2> GetMyRoot<T2>()
  {
    return new Service<T2>(new Dependency<T2>());
  }
}

Class diagram:

classDiagram
	class Composition {
		<<partial>>
		+IServiceᐸT2ᐳ GetMyRootᐸT2ᐳ()
		+IServiceᐸT2ᐳ GetOtherServiceᐸT2ᐳ()
	}
	OtherServiceᐸT2ᐳ --|> IServiceᐸT2ᐳ : "Other" 
	class OtherServiceᐸT2ᐳ
	ServiceᐸT2ᐳ --|> IServiceᐸT2ᐳ
	class ServiceᐸT2ᐳ {
		+Service(IDependencyᐸT2ᐳ dependency)
	}
	DependencyᐸT2ᐳ --|> IDependencyᐸT2ᐳ
	class DependencyᐸT2ᐳ {
		+Dependency()
	}
	class IServiceᐸT2ᐳ {
		<<interface>>
	}
	class IDependencyᐸT2ᐳ {
		<<interface>>
	}
	Composition ..> OtherServiceᐸT2ᐳ : IServiceᐸT2ᐳ GetOtherServiceᐸT2ᐳ()
	Composition ..> ServiceᐸT2ᐳ : IServiceᐸT2ᐳ GetMyRootᐸT2ᐳ()
	OtherServiceᐸT2ᐳ *--  DependencyᐸT2ᐳ : IDependencyᐸT2ᐳ
	ServiceᐸT2ᐳ *--  DependencyᐸT2ᐳ : IDependencyᐸT2ᐳ

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