func.md

Func

Func helps when the logic must enter instances of some type on demand or more than once. This is a very handy mechanism for instance replication. For example it is used when implementing the Lazy<T> injection.

using Shouldly;
using Pure.DI;
using System.Collections.Immutable;

DI.Setup(nameof(Composition))
    .Bind().To<Dependency>()
    .Bind().To<Service>()

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

var composition = new Composition();
var service = composition.Root;
service.Dependencies.Length.ShouldBe(3);

interface IDependency;

class Dependency : IDependency;

interface IService
{
    ImmutableArray<IDependency> Dependencies { get; }
}

class Service(Func<IDependency> dependencyFactory): IService
{
    public ImmutableArray<IDependency> Dependencies =>
    [
        dependencyFactory(),
        dependencyFactory(),
        dependencyFactory()
    ];
}

Running this code sample locally

• Make sure you have the .NET SDK 9.0 or later is installed

dotnet --list-sdk

• Create a net9.0 (or later) console application

dotnet new console -n Sample

• Add references to NuGet packages
  • Pure.DI
  • Shouldly

dotnet add package Pure.DI
dotnet add package Shouldly

• Copy the example code into the Program.cs file

You are ready to run the example 🚀

dotnet run

Be careful, replication takes into account the lifetime of the object.

The following partial class will be generated:

partial class Composition
{
  private readonly Composition _root;

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

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

  public IService Root
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      Func<IDependency> perBlockFunc1 = new Func<IDependency>(
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      () =>
      {
        IDependency localValue103 = new Dependency();
        return localValue103;
      });
      return new Service(perBlockFunc1);
    }
  }
}

Class diagram:

---
 config:
  class:
   hideEmptyMembersBox: true
---
classDiagram
	Dependency --|> IDependency
	Service --|> IService
	Composition ..> Service : IService Root
	Service o-- "PerBlock" FuncᐸIDependencyᐳ : FuncᐸIDependencyᐳ
	FuncᐸIDependencyᐳ *--  Dependency : IDependency
	namespace Pure.DI.UsageTests.BCL.FuncScenario {
		class Composition {
		<<partial>>
		+IService Root
		}
		class Dependency {
			+Dependency()
		}
		class IDependency {
			<<interface>>
		}
		class IService {
			<<interface>>
		}
		class Service {
			+Service(FuncᐸIDependencyᐳ dependencyFactory)
		}
	}
	namespace System {
		class FuncᐸIDependencyᐳ {
				<<delegate>>
		}
	}

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