generic-builder.md

Generic builder

Demonstrates how to create generic builders for build-up patterns with type parameters.

using Shouldly;
using Pure.DI;

DI.Setup(nameof(Composition))
    .Bind(Tag.Id).To(() => (TT)(object)Guid.NewGuid())
    .Bind().To<Repository<TT>>()
    // Generic service builder
    // Defines a generic builder "BuildUp".
    // This is useful when instances are created by an external framework
    // (like a UI library or serialization) but require dependencies to be injected.
    .Builder<ViewModel<TTS, TT2>>("BuildUp");

var composition = new Composition();

// A view model instance created manually (or by a UI framework)
var viewModel = new ViewModel<Guid, Customer>();

// Inject dependencies (Id and Repository) into the existing instance
var builtViewModel = composition.BuildUp(viewModel);

builtViewModel.Id.ShouldNotBe(Guid.Empty);
builtViewModel.Repository.ShouldBeOfType<Repository<Customer>>();

// Domain model
record Customer;

interface IRepository<T>;

class Repository<T> : IRepository<T>;

interface IViewModel<out TId, TModel>
{
    TId Id { get; }

    IRepository<TModel>? Repository { get; }
}

// The view model is generic, allowing it to be used for various entities
record ViewModel<TId, TModel> : IViewModel<TId, TModel>
    where TId : struct
{
    public TId Id { get; private set; }

    // The dependency to be injected
    [Dependency]
    public IRepository<TModel>? Repository { get; set; }

    // Method injection for the ID
    [Dependency]
    public void SetId([Tag(Tag.Id)] TId id) => Id = id;
}

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 builders enable flexible object initialization while maintaining type safety across different generic types.

The following partial class will be generated:

partial class Composition
{
#if NET9_0_OR_GREATER
  private readonly Lock _lock = new Lock();
#else
  private readonly Object _lock = new Object();
#endif

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public ViewModel<T3, T4> BuildUp<T3, T4>(ViewModel<T3, T4> buildingInstance)
    where T3: struct
  {
    if (buildingInstance is null) throw new ArgumentNullException(nameof(buildingInstance));
    ViewModel<T3, T4> transientViewModel495;
    ViewModel<T3, T4> localBuildingInstance8 = buildingInstance;
    T3 transientTTS498 = (T3)(object)Guid.NewGuid();
    localBuildingInstance8.Repository = new Repository<T4>();
    localBuildingInstance8.SetId(transientTTS498);
    transientViewModel495 = localBuildingInstance8;
    return transientViewModel495;
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	RepositoryᐸT4ᐳ --|> IRepositoryᐸT4ᐳ
	Composition ..> ViewModelᐸT3ˏT4ᐳ : ViewModelᐸT3ˏT4ᐳ BuildUpᐸT3ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuilderScenario.ViewModel<T3, T4> buildingInstance)
	ViewModelᐸT3ˏT4ᐳ *--  RepositoryᐸT4ᐳ : IRepositoryᐸT4ᐳ
	ViewModelᐸT3ˏT4ᐳ *--  T3 : "Id"  T3
	namespace Pure.DI.UsageTests.Generics.GenericBuilderScenario {
		class Composition {
		<<partial>>
		+ViewModelᐸT3ˏT4ᐳ BuildUpᐸT3ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuilderScenario.ViewModel<T3, T4> buildingInstance)
		}
		class IRepositoryᐸT4ᐳ {
			<<interface>>
		}
		class RepositoryᐸT4ᐳ {
				<<class>>
			+Repository()
		}
		class ViewModelᐸT3ˏT4ᐳ {
				<<record>>
			+IRepositoryᐸT4ᐳ Repository
			+SetId(T3 id) : Void
		}
	}

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