generic-builders.md

Generic builders

Demonstrates how to create generic builders for all types derived from a generic base type known at compile time.

using Shouldly;
using Pure.DI;

DI.Setup(nameof(Composition))
    .Bind(Tag.Id).To(() => (TT)(object)Guid.NewGuid())
    .Bind().To<MessageTracker<TT>>()
    // Generic builder to inject dependencies into existing messages
    .Builders<IMessage<TT, TT2>>("BuildUp");

var composition = new Composition();

// A Query is created (e.g. by API controller), ID is missing
var query = new QueryMessage<Guid, string>();

// Composition injects dependencies and generates an ID
var queryWithDeps = composition.BuildUp(query);

queryWithDeps.Id.ShouldNotBe(Guid.Empty);
queryWithDeps.Tracker.ShouldBeOfType<MessageTracker<string>>();

// A Command is created, usually with a specific ID
var command = new CommandMessage<Guid, int>();

// Composition injects dependencies only
var commandWithDeps = composition.BuildUp(command);

commandWithDeps.Id.ShouldBe(Guid.Empty);
commandWithDeps.Tracker.ShouldBeOfType<MessageTracker<int>>();

// Works with abstract types/interfaces too
var queryMessage = new QueryMessage<Guid, double>();
queryMessage = composition.BuildUp(queryMessage);

queryMessage.ShouldBeOfType<QueryMessage<Guid, double>>();
queryMessage.Id.ShouldNotBe(Guid.Empty);
queryMessage.Tracker.ShouldBeOfType<MessageTracker<double>>();

interface IMessageTracker<T>;

class MessageTracker<T> : IMessageTracker<T>;

interface IMessage<out TId, TContent>
{
    TId Id { get; }

    IMessageTracker<TContent>? Tracker { get; }
}

record QueryMessage<TId, TContent> : IMessage<TId, TContent>
    where TId : struct
{
    public TId Id { get; private set; }

    [Dependency]
    public IMessageTracker<TContent>? Tracker { get; set; }

    // Injects a new ID
    [Dependency]
    public void SetId([Tag(Tag.Id)] TId id) => Id = id;
}

record CommandMessage<TId, TContent> : IMessage<TId, TContent>
    where TId : struct
{
    public TId Id { get; }

    [Dependency]
    public IMessageTracker<TContent>? Tracker { get; set; }
}

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 provide compile-time type safety while allowing flexible object graph construction.

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

  #pragma warning disable CS0162
  [MethodImpl(MethodImplOptions.NoInlining)]
  public IMessage<T1, T4> BuildUp<T1, T4>(IMessage<T1, T4> buildingInstance)
    where T1: struct
  {
    if (buildingInstance is null) throw new ArgumentNullException(nameof(buildingInstance));
    switch (buildingInstance)
    {
      case QueryMessage<T1, T4> QueryMessage_TT_TT2:
        return BuildUp(QueryMessage_TT_TT2);
      case CommandMessage<T1, T4> CommandMessage_TT_TT2:
        return BuildUp(CommandMessage_TT_TT2);
      default:
        throw new ArgumentException($"Unable to build an instance of typeof type {buildingInstance.GetType()}.", "buildingInstance");
    }
    return buildingInstance;
  }
  #pragma warning restore CS0162

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public CommandMessage<T1, T4> BuildUp<T1, T4>(CommandMessage<T1, T4> buildingInstance)
    where T1: struct
  {
    if (buildingInstance is null) throw new ArgumentNullException(nameof(buildingInstance));
    CommandMessage<T1, T4> transientCommandMessage501;
    CommandMessage<T1, T4> localBuildingInstance10 = buildingInstance;
    localBuildingInstance10.Tracker = new MessageTracker<T4>();
    transientCommandMessage501 = localBuildingInstance10;
    return transientCommandMessage501;
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public QueryMessage<T1, T4> BuildUp<T1, T4>(QueryMessage<T1, T4> buildingInstance)
    where T1: struct
  {
    if (buildingInstance is null) throw new ArgumentNullException(nameof(buildingInstance));
    QueryMessage<T1, T4> transientQueryMessage504;
    QueryMessage<T1, T4> localBuildingInstance11 = buildingInstance;
    T1 transientTT507 = (T1)(object)Guid.NewGuid();
    localBuildingInstance11.Tracker = new MessageTracker<T4>();
    localBuildingInstance11.SetId(transientTT507);
    transientQueryMessage504 = localBuildingInstance11;
    return transientQueryMessage504;
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	MessageTrackerᐸT4ᐳ --|> IMessageTrackerᐸT4ᐳ
	Composition ..> IMessageᐸT1ˏT4ᐳ : IMessageᐸT1ˏT4ᐳ BuildUpᐸT1ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuildersScenario.IMessage<T1, T4> buildingInstance)
	Composition ..> CommandMessageᐸT1ˏT4ᐳ : CommandMessageᐸT1ˏT4ᐳ BuildUpᐸT1ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuildersScenario.CommandMessage<T1, T4> buildingInstance)
	Composition ..> QueryMessageᐸT1ˏT4ᐳ : QueryMessageᐸT1ˏT4ᐳ BuildUpᐸT1ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuildersScenario.QueryMessage<T1, T4> buildingInstance)
	CommandMessageᐸT1ˏT4ᐳ *--  MessageTrackerᐸT4ᐳ : IMessageTrackerᐸT4ᐳ
	QueryMessageᐸT1ˏT4ᐳ *--  MessageTrackerᐸT4ᐳ : IMessageTrackerᐸT4ᐳ
	QueryMessageᐸT1ˏT4ᐳ *--  T1 : "Id"  T1
	namespace Pure.DI.UsageTests.Generics.GenericBuildersScenario {
		class CommandMessageᐸT1ˏT4ᐳ {
				<<record>>
			+IMessageTrackerᐸT4ᐳ Tracker
		}
		class Composition {
		<<partial>>
		+IMessageᐸT1ˏT4ᐳ BuildUpᐸT1ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuildersScenario.IMessage<T1, T4> buildingInstance)
		+CommandMessageᐸT1ˏT4ᐳ BuildUpᐸT1ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuildersScenario.CommandMessage<T1, T4> buildingInstance)
		+QueryMessageᐸT1ˏT4ᐳ BuildUpᐸT1ˏT4ᐳ(Pure.DI.UsageTests.Generics.GenericBuildersScenario.QueryMessage<T1, T4> buildingInstance)
		}
		class IMessageTrackerᐸT4ᐳ {
			<<interface>>
		}
		class IMessageᐸT1ˏT4ᐳ {
				<<interface>>
		}
		class MessageTrackerᐸT4ᐳ {
				<<class>>
			+MessageTracker()
		}
		class QueryMessageᐸT1ˏT4ᐳ {
				<<record>>
			+IMessageTrackerᐸT4ᐳ Tracker
			+SetId(T1 id) : Void
		}
	}

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