Lazy VariantServiceProvider #564

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1. Junbo Wang (juniwang)

   assigned

   Zhiyuan Liang (zhiyuanliang-ms)

   on Nov 4, 2025
2. Zhiyuan Liang (zhiyuanliang-ms)

   assigned

   Copilot

   on Nov 6, 2025
3. zhiyuanliang-ms commented on Nov 24, 2025

   

   Zhiyuan Liang (zhiyuanliang-ms)

   on Nov 24, 2025

   Member

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   Hi, Olavo Castro (@olavopeixoto)
   Sorry for the late response. Unfortunately, the current design of variant service provider cannot achieve the lazy instantiation. There is no proper API from ActivatorUtilities to get instance from DI container when the service is registered through factory method.

   If you take a look at PR #567, the implementation is actually fighting against the .NET DI system. See this comment for more information.

   .NET 8 introduced "Keyed Service". This feature is a perfect match for the concept of variant service.

   For example, user can register keyed service:

   builder.Services.AddKeyedSingleton<ICache, BigCache>("big");
   builder.Services.AddKeyedSingleton<ICache, SmallCache>("small");
   
   builder.Services.AddFeatureManagement()
          .WithVariantService<ICache>("CacheVariantFeature");

   And the variant service provider only need to call ServiceProvider.GetKeyedService("variant-name"). It can achieve the lazy instantiation goal.

   However, the feature management library is targeted on netstandard. There is not a clean solution for us to adapt the variant service provider to the implementation that uses keyed service registration, which is very unfortunate.

   The solution we are considering now is to offer a new interface

   public interface INamedServiceProvider<TService>
   {
       TService GetService(string name);
   }

   The VariantServiceProvider will use INamedServiceProvider to retrieve variant service if it could be found in the DI container. Otherwise, it will still get IEnumerable<TService> from DI and pick the correct intance based on the allocated variant.

   Any thought or feedback is welcome. Thank you for your understanding!
4. Stepami commented on May 13, 2026

   

   Степан (Stepami)

   on May 13, 2026

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   Zhiyuan Liang (@zhiyuanliang-ms) why don't you use package-provided keyed di?

   <Project Sdk="Microsoft.NET.Sdk">
   
       <PropertyGroup>
           <TargetFramework>netstandard2.0</TargetFramework>
       </PropertyGroup>
   
       <ItemGroup>
         <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="8.0.1" />
       </ItemGroup>
   
   </Project>
   

   👀React with 👀1Reacted by Zhiyuan Liang
5. zhiyuanliang-ms commented on May 14, 2026

   

   Zhiyuan Liang (zhiyuanliang-ms)

   on May 14, 2026

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   Hey, Степан (@Stepami) Thanks for reaching out.

   Do you mean we offer different functions fro netstand2.0 and .net 8+?
6. Stepami commented on May 14, 2026

   

   Степан (Stepami)

   on May 14, 2026

   Last edited by Stepami

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   Zhiyuan Liang (@zhiyuanliang-ms) Despite the feature management library is targeted on netstandard Keyed DI can still be used through package.

   Moreover there are already 8.0.x packages referenced in the feature management library

   👍React with 👍1Reacted by Zhiyuan Liang
7. Stepami commented on May 14, 2026

   

   Степан (Stepami)

   on May 14, 2026

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   Zhiyuan Liang (@zhiyuanliang-ms) Opened PR to prove my point

   • feat(VariantBasedInjection): Keyed DI support #605