type-attribute.md

Type attribute

Use the Type attribute to force a specific injected type, overriding the inferred type from the parameter or member.

using Shouldly;
using Pure.DI;

DI.Setup(nameof(Composition))
    .Bind().To<NotificationService>()

    // Composition root
    .Root<INotificationService>("NotificationService");

var composition = new Composition();
var notificationService = composition.NotificationService;
notificationService.UserNotifier.ShouldBeOfType<EmailSender>();
notificationService.AdminNotifier.ShouldBeOfType<SmsSender>();

interface IMessageSender;

class EmailSender : IMessageSender;

class SmsSender : IMessageSender;

interface INotificationService
{
    IMessageSender UserNotifier { get; }

    IMessageSender AdminNotifier { get; }
}

class NotificationService(
    // The [Type] attribute forces the injection of a specific type,
    // overriding the default resolution behavior.
    [Type(typeof(EmailSender))] IMessageSender userNotifier,
    [Type(typeof(SmsSender))] IMessageSender adminNotifier)
    : INotificationService
{
    public IMessageSender UserNotifier { get; } = userNotifier;

    public IMessageSender AdminNotifier { get; } = adminNotifier;
}

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

The Type attribute is part of the API, but you can define your own in any assembly or namespace.

The following partial class will be generated:

partial class Composition
{
  public INotificationService NotificationService
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      return new NotificationService(new EmailSender(), new SmsSender());
    }
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	NotificationService --|> INotificationService
	Composition ..> NotificationService : INotificationService NotificationService
	NotificationService *--  EmailSender : EmailSender
	NotificationService *--  SmsSender : SmsSender
	namespace Pure.DI.UsageTests.Attributes.TypeAttributeScenario {
		class Composition {
		<<partial>>
		+INotificationService NotificationService
		}
		class EmailSender {
				<<class>>
			+EmailSender()
		}
		class INotificationService {
			<<interface>>
		}
		class NotificationService {
				<<class>>
			+NotificationService(IMessageSender userNotifier, IMessageSender adminNotifier)
		}
		class SmsSender {
				<<class>>
			+SmsSender()
		}
	}

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