injections-on-demand-with-arguments.md

Injections on demand with arguments

This example illustrates dependency injection with parameterized factory functions using Pure.DI, where dependencies are created with runtime-provided arguments. The scenario features a service that generates dependencies with specific IDs passed during instantiation.

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

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

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

var composition = new Composition();
var service = composition.Root;
var dependencies = service.Dependencies;
dependencies.Count.ShouldBe(2);
dependencies[0].Id.ShouldBe(33);
dependencies[1].Id.ShouldBe(99);

interface IDependency
{
    int Id { get; }
}

class Dependency(int id) : IDependency
{
    public int Id { get; } = id;
}

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

class Service(Func<int, IDependency> dependencyFactoryWithArgs): IService
{
    public IReadOnlyList<IDependency> Dependencies { get; } =
    [
        dependencyFactoryWithArgs(33),
        dependencyFactoryWithArgs(99)
    ];
}

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

Key components:

• Dependency class accepts an int id constructor argument, stored in its Id property.
• Service receives Func<int, IDependency> delegate, enabling creation of dependencies with dynamic values.
• Service creates two dependencies using the factory – one with ID 33, another with ID 99.

Delayed dependency instantiation:

• Injection of dependencies requiring runtime parameters
• Creation of distinct instances with different configurations
• Type-safe resolution of dependencies with constructor arguments

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
    {
      int overInt320;
      Func<int, IDependency> perBlockFunc1;
      var localLockObject97 = new Object();
      Func<int, IDependency> localFactory98 = new Func<int, IDependency>((int localArg13) =>
      {
        lock (localLockObject97)
        {
          overInt320 = localArg13;
          IDependency localValue99 = new Dependency(overInt320);
          return localValue99;
        }
      });
      perBlockFunc1 = localFactory98;
      return new Service(perBlockFunc1);
    }
  }
}

Class diagram:

---
 config:
  class:
   hideEmptyMembersBox: true
---
classDiagram
	Dependency --|> IDependency
	Service --|> IService
	Composition ..> Service : IService Root
	Dependency *--  Int32 : Int32
	Service o-- "PerBlock" FuncᐸInt32ˏIDependencyᐳ : FuncᐸInt32ˏIDependencyᐳ
	FuncᐸInt32ˏIDependencyᐳ *--  Dependency : IDependency
	namespace Pure.DI.UsageTests.Basics.InjectionOnDemandWithArgumentsScenario {
		class Composition {
		<<partial>>
		+IService Root
		}
		class Dependency {
			+Dependency(Int32 id)
		}
		class IDependency {
			<<interface>>
		}
		class IService {
			<<interface>>
		}
		class Service {
			+Service(FuncᐸInt32ˏIDependencyᐳ dependencyFactoryWithArgs)
		}
	}
	namespace System {
		class FuncᐸInt32ˏIDependencyᐳ {
				<<delegate>>
		}
		class Int32 {
			<<struct>>
		}
	}

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