perblock.md

PerBlock

The PreBlock lifetime does not guarantee that there will be a single dependency instance for each instance of the composition root (as for the PreResolve lifetime), but is useful for reducing the number of instances of a type.

interface IDependency;

class Dependency : IDependency;

class Service(
    IDependency dep1,
    IDependency dep2,
    (IDependency dep3, IDependency dep4) deps)
{
    public IDependency Dep1 { get; } = dep1;

    public IDependency Dep2 { get; } = dep2;

    public IDependency Dep3 { get; } = deps.dep3;

    public IDependency Dep4 { get; } = deps.dep4;
}

DI.Setup(nameof(Composition))
    // This hint indicates to not generate methods such as Resolve
    .Hint(Hint.Resolve, "Off")
    .Bind().As(Lifetime.PerBlock).To<Dependency>()
    .Bind().As(Lifetime.Singleton).To<(IDependency dep3, IDependency dep4)>()

    // Composition root
    .Root<Service>("Root");

var composition = new Composition();

var service1 = composition.Root;
service1.Dep1.ShouldBe(service1.Dep2);
service1.Dep3.ShouldBe(service1.Dep4);
service1.Dep1.ShouldNotBe(service1.Dep3);

var service2 = composition.Root;
service2.Dep1.ShouldNotBe(service1.Dep1);

The following partial class will be generated:

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

  private (IDependency dep3, IDependency dep4) _singletonValueTuple42;
  private bool _singletonValueTuple42Created;

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

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

  public Service Root
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      if (!_root._singletonValueTuple42Created)
      {
        using (_lock.EnterScope())
        {
          if (!_root._singletonValueTuple42Created)
          {
            Dependency perBlockDependency2 = new Dependency();
            _root._singletonValueTuple42 = (perBlockDependency2, perBlockDependency2);
            Thread.MemoryBarrier();
            _root._singletonValueTuple42Created = true;
          }
        }
      }

      Dependency perBlockDependency1 = new Dependency();
      return new Service(perBlockDependency1, perBlockDependency1, _root._singletonValueTuple42);
    }
  }
}

Class diagram:

classDiagram
	class Composition {
		<<partial>>
		+Service Root
	}
	Dependency --|> IDependency
	class Dependency {
		+Dependency()
	}
	class ValueTupleᐸIDependencyˏIDependencyᐳ {
		+ValueTuple(IDependency item1, IDependency item2)
	}
	class IDependency {
		<<interface>>
	}
	Composition ..> Service : Service Root
	Service o-- "2 PerBlock" Dependency : IDependency
	Service o-- "Singleton" ValueTupleᐸIDependencyˏIDependencyᐳ : ValueTupleᐸIDependencyˏIDependencyᐳ
	ValueTupleᐸIDependencyˏIDependencyᐳ o-- "2 PerBlock" Dependency : IDependency

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