generic-injections-on-demand.md

Generic injections on demand

Demonstrates how to create generic dependencies on demand using factory delegates with generic type parameters.

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

DI.Setup(nameof(Composition))
    .Bind().To<Worker<TT>>()
    .Bind().To<Distributor<TT>>()

    // Composition root
    .Root<IDistributor<int>>("Root");

var composition = new Composition();
var distributor = composition.Root;

// Check that the distributor has created 2 workers
distributor.Workers.Count.ShouldBe(2);

interface IWorker<T>;

class Worker<T> : IWorker<T>;

interface IDistributor<T>
{
    IReadOnlyList<IWorker<T>> Workers { get; }
}

class Distributor<T>(Func<IWorker<T>> workerFactory) : IDistributor<T>
{
    public IReadOnlyList<IWorker<T>> Workers { get; } =
    [
        // Creates the first instance of the worker
        workerFactory(),
        // Creates the second instance of the worker
        workerFactory()
    ];
}

Running this code sample locally

• Make sure you have the .NET SDK 10.0 or later installed

dotnet --list-sdk

• Create a net10.0 (or later) console application

dotnet new console -n Sample

• Add references to the 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

Note

Generic on-demand injection provides flexibility for creating instances with different type parameters as needed.

The following partial class will be generated:

partial class Composition
{
  public IDistributor<int> Root
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      Func<IWorker<int>> perBlockFunc517 = new Func<IWorker<int>>(
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      () =>
      {
        return new Worker<int>();
      });
      return new Distributor<int>(perBlockFunc517);
    }
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	DistributorᐸInt32ᐳ --|> IDistributorᐸInt32ᐳ
	WorkerᐸInt32ᐳ --|> IWorkerᐸInt32ᐳ
	Composition ..> DistributorᐸInt32ᐳ : IDistributorᐸInt32ᐳ Root
	DistributorᐸInt32ᐳ o-- "PerBlock" FuncᐸIWorkerᐸInt32ᐳᐳ : FuncᐸIWorkerᐸInt32ᐳᐳ
	FuncᐸIWorkerᐸInt32ᐳᐳ *--  WorkerᐸInt32ᐳ : IWorkerᐸInt32ᐳ
	namespace Pure.DI.UsageTests.Generics.GenericInjectionsOnDemandScenario {
		class Composition {
		<<partial>>
		+IDistributorᐸInt32ᐳ Root
		}
		class DistributorᐸInt32ᐳ {
				<<class>>
			+Distributor(FuncᐸIWorkerᐸInt32ᐳᐳ workerFactory)
		}
		class IDistributorᐸInt32ᐳ {
			<<interface>>
		}
		class IWorkerᐸInt32ᐳ {
			<<interface>>
		}
		class WorkerᐸInt32ᐳ {
				<<class>>
			+Worker()
		}
	}
	namespace System {
		class FuncᐸIWorkerᐸInt32ᐳᐳ {
				<<delegate>>
		}
	}

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