root-binding.md

Root binding

In general, it is recommended to define one composition root for the entire application. But sometimes it is necessary to have multiple roots. To simplify the definition of composition roots, a "hybrid" API method RootBind<T>(string rootName) was added. It allows you to define a binding and at the same time the root of the composition. You can it in order to reduce repetitions. The registration composition.RootBind<IDependency>().To<Dependency>() is an equivalent to composition.Bind<IDependency>().To<Dependency>().Root<IDependency>().

interface IDependency;

class Dependency : IDependency;

interface IService;

class Service(IDependency dependency) : IService;

DI.Setup(nameof(Composition))
    .Bind().As(Lifetime.Singleton).To<Dependency>()
    .RootBind<IService>("MyRoot").To<Service>();
// It's the same as:
//  .Bind<IService>().To<Service>()
//  .Root<IService>("MyRoot")

var composition = new Composition();
composition.MyRoot.ShouldBeOfType<Service>();

The following partial class will be generated:

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

  private Dependency? _singletonDependency43;

  [OrdinalAttribute(256)]
  public Composition()
  {
    _root = this;
    _lock = new Lock();
  }

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

  public IService MyRoot
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      if (_root._singletonDependency43 is null)
      {
        using (_lock.EnterScope())
        {
          if (_root._singletonDependency43 is null)
          {
            _root._singletonDependency43 = new Dependency();
          }
        }
      }

      return new Service(_root._singletonDependency43!);
    }
  }
}

Class diagram:

---
 config:
  class:
   hideEmptyMembersBox: true
---
classDiagram
	Service --|> IService
	Dependency --|> IDependency
	Composition ..> Service : IService MyRoot
	Service o-- "Singleton" Dependency : IDependency
	namespace Pure.DI.UsageTests.Basics.RootBindScenario {
		class Composition {
		<<partial>>
		+IService MyRoot
		}
		class Dependency {
			+Dependency()
		}
		class IDependency {
			<<interface>>
		}
		class IService {
			<<interface>>
		}
		class Service {
			+Service(IDependency dependency)
		}
	}

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