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.NET 8–Using reflection in a AOT enabled application

With the upcoming .NET 8 release, Microsoft is spending a lot of effort in further improving AOT(Ahead-of-Time) compilation. Using Native AOT compared to the JIT(Just-in-Time) compiler offers the following benefits:

  • Minimized disk footprint: When publishing using native AOT, a single executable is produced containing just the code from external dependencies that is needed to support the program. Reduced executable size can lead to:    
    • Smaller container images, for example in containerized deployment scenarios.
    • Reduced deployment time from smaller images
  • Reduced startup time: Native AOT applications can show reduced start-up times, which means    
    • The app is ready to service requests quicker.
    • Improved deployment where container orchestrators need to manage transition from one version of the app to another.
  • Reduced memory demand: Native AOT apps can have reduced memory demands, depending on the work done by the app. Reduced memory consumption can lead to greater deployment density and improved scalability.

Although the list above should make it obvious that using AOT has a lot of benefits, it also comes with some limitations.

One of these limitations is the lack of support for reflection. For example, setting a private field using reflection is no longer possible. So the following code will not work using native AOT:

The code above is using reflection which is slow. .NET 8 provides a new zero-overhead way to access private members. This is done using the [UnsafeAccessorAttribute] attribute.

Let us rewrite our example using this attribute:

This not only works for private fields but can also be used for:

  • Constructors: [UnsafeAccessor(UnsafeAccessorKind.Constructor)]
  • Methods: [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "MethodName")]
  • Properties: [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "set_PropertyName")]

More information

ASP.NET Core support for native AOT | Microsoft Learnt

Native AOT deployment overview - .NET | Microsoft Learn

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