custom-generic-argument-attribute.md

Custom generic argument attribute

Demonstrates how to create and use custom attributes for generic type arguments, enabling advanced generic binding scenarios.

using Shouldly;
using Pure.DI;

DI.Setup(nameof(Composition))
    // Registers custom generic argument
    .GenericTypeArgumentAttribute<GenericArgAttribute>()
    .Bind<IRepository<TMy>>().To<Repository<TMy>>()
    .Bind<IContentService>().To<ContentService>()

    // Composition root
    .Root<IContentService>("ContentService");

var composition = new Composition();
var service = composition.ContentService;
service.Posts.ShouldBeOfType<Repository<Post>>();
service.Comments.ShouldBeOfType<Repository<Comment>>();

[AttributeUsage(AttributeTargets.Interface | AttributeTargets.Class | AttributeTargets.Struct)]
class GenericArgAttribute : Attribute;

[GenericArg]
interface TMy;

interface IRepository<T>;

class Repository<T> : IRepository<T>;

class Post;

class Comment;

interface IContentService
{
    IRepository<Post> Posts { get; }

    IRepository<Comment> Comments { get; }
}

class ContentService(
    IRepository<Post> posts,
    IRepository<Comment> comments)
    : IContentService
{
    public IRepository<Post> Posts { get; } = posts;

    public IRepository<Comment> Comments { get; } = comments;
}

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

Custom generic argument attributes are useful when you need to pass metadata specific to generic type parameters during binding resolution.

The following partial class will be generated:

partial class Composition
{
  public IContentService ContentService
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      return new ContentService(new Repository<Post>(), new Repository<Comment>());
    }
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	ContentService --|> IContentService
	RepositoryᐸPostᐳ --|> IRepositoryᐸPostᐳ
	RepositoryᐸCommentᐳ --|> IRepositoryᐸCommentᐳ
	Composition ..> ContentService : IContentService ContentService
	ContentService *--  RepositoryᐸPostᐳ : IRepositoryᐸPostᐳ
	ContentService *--  RepositoryᐸCommentᐳ : IRepositoryᐸCommentᐳ
	namespace Pure.DI.UsageTests.Attributes.CustomGenericArgumentAttributeScenario {
		class Composition {
		<<partial>>
		+IContentService ContentService
		}
		class ContentService {
				<<class>>
			+ContentService(IRepositoryᐸPostᐳ posts, IRepositoryᐸCommentᐳ comments)
		}
		class IContentService {
			<<interface>>
		}
		class IRepositoryᐸCommentᐳ {
			<<interface>>
		}
		class IRepositoryᐸPostᐳ {
			<<interface>>
		}
		class RepositoryᐸCommentᐳ {
				<<class>>
			+Repository()
		}
		class RepositoryᐸPostᐳ {
				<<class>>
			+Repository()
		}
	}

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