lazy.md

Lazy

Demonstrates lazy injection using Lazy, delaying instance creation until the Value property is accessed.

using Shouldly;
using Pure.DI;

DI.Setup(nameof(Composition))
    .Bind<IGraphicsEngine>().To<GraphicsEngine>()
    .Bind<IWindow>().To<Window>()

    // Composition root
    .Root<IWindow>("Window");

var composition = new Composition();
var window = composition.Window;

// The graphics engine is created only when it is first accessed
window.Engine.ShouldBe(window.Engine);

interface IGraphicsEngine;

class GraphicsEngine : IGraphicsEngine;

interface IWindow
{
    IGraphicsEngine Engine { get; }
}

class Window(Lazy<IGraphicsEngine> engine) : IWindow
{
    public IGraphicsEngine Engine => engine.Value;
}

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

Lazy is useful for expensive-to-create objects or when the instance may never be needed, improving application startup performance.

The following partial class will be generated:

partial class Composition
{
  public IWindow Window
  {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get
    {
      Lazy<IGraphicsEngine> transientLazy418;
      // Injects an instance factory
      Func<IGraphicsEngine> perBlockFunc419 = new Func<IGraphicsEngine>(
      [MethodImpl(MethodImplOptions.AggressiveInlining)]
      () =>
      {
        return new GraphicsEngine();
      });
      Func<IGraphicsEngine> localFactory3 = perBlockFunc419;
      // Creates an instance that supports lazy initialization
      transientLazy418 = new Lazy<IGraphicsEngine>(localFactory3, true);
      return new Window(transientLazy418);
    }
  }
}

Class diagram:

---
 config:
  maxTextSize: 2147483647
  maxEdges: 2147483647
  class:
   hideEmptyMembersBox: true
---
classDiagram
	GraphicsEngine --|> IGraphicsEngine
	Window --|> IWindow
	Composition ..> Window : IWindow Window
	Window *--  LazyᐸIGraphicsEngineᐳ : LazyᐸIGraphicsEngineᐳ
	LazyᐸIGraphicsEngineᐳ o-- "PerBlock" FuncᐸIGraphicsEngineᐳ : FuncᐸIGraphicsEngineᐳ
	FuncᐸIGraphicsEngineᐳ *--  GraphicsEngine : IGraphicsEngine
	namespace Pure.DI.UsageTests.BCL.LazyScenario {
		class Composition {
		<<partial>>
		+IWindow Window
		}
		class GraphicsEngine {
				<<class>>
			+GraphicsEngine()
		}
		class IGraphicsEngine {
			<<interface>>
		}
		class IWindow {
			<<interface>>
		}
		class Window {
				<<class>>
			+Window(LazyᐸIGraphicsEngineᐳ engine)
		}
	}
	namespace System {
		class FuncᐸIGraphicsEngineᐳ {
				<<delegate>>
		}
		class LazyᐸIGraphicsEngineᐳ {
				<<class>>
		}
	}

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