ref-dependencies.md

Ref dependencies

Demonstrates how to use ref and out parameters in dependency injection for scenarios where you need to pass values by reference.

using Shouldly;
using Pure.DI;

DI.Setup("Composition")
    // Represents a large data set or buffer
    .Bind().To<int[]>(() => [10, 20, 30])
    .Root<Service>("MyService");

var composition = new Composition();
var service = composition.MyService;
service.Sum.ShouldBe(60);

class Service
{
    public int Sum { get; private set; }

    // Ref structs cannot be fields, so they are injected via a method
    // with the [Ordinal] attribute. This allows working with
    // high-performance types like Span<T> or other ref structs.
    [Ordinal]
    public void Initialize(ref Data data) =>
        Sum = data.Sum();
}

// A ref struct that holds a reference to the data
// to process it without additional memory allocations
readonly ref struct Data(ref int[] data)
{
    private readonly ref int[] _dep = ref data;

    public int Sum() => _dep.Sum();
}

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

ref dependencies are useful for scenarios where you need to return multiple values or modify parameters during injection.

The following partial class will be generated:

partial class Composition
{
  public Service MyService
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      int[] transient320 = [10, 20, 30];
      int[] transient320_ref = transient320;
      var transientService318 = new Service();
      Data transientData319_ref = new Data(ref transient320_ref);
      transientService318.Initialize(ref transientData319_ref);
      return transientService318;
    }
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public T Resolve<T>()
  {
    return Resolver<T>.Value.Resolve(this);
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public T Resolve<T>(object? tag)
  {
    return Resolver<T>.Value.ResolveByTag(this, tag);
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public object Resolve(Type type)
  {
    #if NETCOREAPP3_0_OR_GREATER
    var index = (int)(_bucketSize * (((uint)type.TypeHandle.GetHashCode()) % 1));
    #else
    var index = (int)(_bucketSize * (((uint)RuntimeHelpers.GetHashCode(type)) % 1));
    #endif
    ref var pair = ref _buckets[index];
    return Object.ReferenceEquals(pair.Key, type) ? pair.Value.Resolve(this) : Resolve(type, index);
  }

  [MethodImpl(MethodImplOptions.NoInlining)]
  private object Resolve(Type type, int index)
  {
    var finish = index + _bucketSize;
    while (++index < finish)
    {
      ref var pair = ref _buckets[index];
      if (Object.ReferenceEquals(pair.Key, type))
      {
        return pair.Value.Resolve(this);
      }
    }

    throw new CannotResolveException($"{CannotResolveMessage} {OfTypeMessage} {type}.", type, null);
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public object Resolve(Type type, object? tag)
  {
    #if NETCOREAPP3_0_OR_GREATER
    var index = (int)(_bucketSize * (((uint)type.TypeHandle.GetHashCode()) % 1));
    #else
    var index = (int)(_bucketSize * (((uint)RuntimeHelpers.GetHashCode(type)) % 1));
    #endif
    ref var pair = ref _buckets[index];
    return Object.ReferenceEquals(pair.Key, type) ? pair.Value.ResolveByTag(this, tag) : Resolve(type, tag, index);
  }

  [MethodImpl(MethodImplOptions.NoInlining)]
  private object Resolve(Type type, object? tag, int index)
  {
    var finish = index + _bucketSize;
    while (++index < finish)
    {
      ref var pair = ref _buckets[index];
      if (Object.ReferenceEquals(pair.Key, type))
      {
        return pair.Value.ResolveByTag(this, tag);
      }
    }

    throw new CannotResolveException($"{CannotResolveMessage} \"{tag}\" {OfTypeMessage} {type}.", type, tag);
  }

  private readonly static uint _bucketSize;
  private readonly static Pair<IResolver<Composition, object>>[] _buckets;

  static Composition()
  {
    var valResolver_0000 = new Resolver_0000();
    Resolver<Service>.Value = valResolver_0000;
    _buckets = Buckets<IResolver<Composition, object>>.Create(
      1,
      out _bucketSize,
      new Pair<IResolver<Composition, object>>[1]
      {
         new Pair<IResolver<Composition, object>>(typeof(Service), valResolver_0000)
      });
  }

  private const string CannotResolveMessage = "Cannot resolve composition root ";
  private const string OfTypeMessage = "of type ";

  private class Resolver<T>: IResolver<Composition, T>
  {
    public static IResolver<Composition, T> Value = new Resolver<T>();

    public virtual T Resolve(Composition composite)
    {
      throw new CannotResolveException($"{CannotResolveMessage}{OfTypeMessage}{typeof(T)}.", typeof(T), null);
    }

    public virtual T ResolveByTag(Composition composite, object tag)
    {
      throw new CannotResolveException($"{CannotResolveMessage}\"{tag}\" {OfTypeMessage}{typeof(T)}.", typeof(T), tag);
    }
  }

  private sealed class Resolver_0000: Resolver<Service>
  {
    public override Service Resolve(Composition composition)
    {
      return composition.MyService;
    }

    public override Service ResolveByTag(Composition composition, object tag)
    {
      switch (tag)
      {
        case null:
          return composition.MyService;

        default:
          return base.ResolveByTag(composition, tag);
      }
    }
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	Composition ..> Service : Service MyService
	Service *--  Data : Data
	Data *--  ArrayᐸInt32ᐳ : ArrayᐸInt32ᐳ
	class ArrayᐸInt32ᐳ {
			<<array>>
	}
	namespace Pure.DI.UsageTests.Basics.RefDependenciesScenario {
		class Composition {
		<<partial>>
		+Service MyService
		+ T ResolveᐸTᐳ()
		+ T ResolveᐸTᐳ(object? tag)
		+ object Resolve(Type type)
		+ object Resolve(Type type, object? tag)
		}
		class Data {
				<<struct>>
			+Data(ArrayᐸInt32ᐳ data)
		}
		class Service {
				<<class>>
			+Service()
			+Initialize(Data data) : Void
		}
	}

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