The Experimental Attribute in .NET 8 and C# 12

Introduction

The ExperimentalAttribute p;is a new feature in C# .NET 8 that indicates an API is experimental and may change in the future. It can be applied to various elements like assemblies, classes, methods, etc. This attribute allows call sites to be flagged with a diagnostic that an experimental feature is used. It requires a diagnosticId parameter, used by the compiler when reporting a use of the API the attribute applies to. The diagnostic is technically a warning but is treated as an error for reporting purposes. This causes the build to fail if the diagnostic is not suppressed.

ExperimentalAttribute and its usage

The ExperimentalAttribute is defined in the System.Diagnostics.CodeAnalysis namespace and is part of the System.Runtime.dll assembly. It can be applied to various elements such as assemblies, classes, constructors, delegates, enums, events, fields, interfaces, methods, modules, properties, and structs. This attribute allows call sites to be flagged with a diagnostic that indicates that an experimental feature is used1. Authors can use this attribute to ship preview features in their assemblies.

Constructors and Properties

The ExperimentalAttribute requires a diagnosticId parameter to be passed in the constructor. This diagnosticId is used by the compiler when reporting a use of the API the attribute applies to. It also accepts a format string instead of an actual URL for corresponding documentation, creating a generic URL that includes the diagnostic ID1.

Diagnostic Reporting

Although the diagnostic is technically a warning, it is treated as an error for the purpose of reporting. This causes the build to fail if the diagnostic is not suppressed. The diagnostic can be suppressed with #pragma warning disable DiagID.

Let’s look at how the ExperimentalAttribute can be used :

The ExperimentalAttribute is particularly useful when you’re developing a library or an API and you want to introduce new features that are still in the experimental phase. By marking these features with the ExperimentalAttribute, you can communicate to the users of your library or API that these features are not finalized and may change in the future.

Here’s an example of how you might use it in a real-world scenario:

using System.Diagnostics.CodeAnalysis;

namespace DotNet8Examples
{
    [Experimental(diagnosticId: "Test001")]
    public class ExperimentalAttributeDemo
    {
        public void Print()
        {
            Console.WriteLine("Hello Experimental Attribute");
        }
    }
}

In this example, the MyExperimentalMethod method is marked with the ExperimentalAttribute. The "Test001" argument is the diagnostic ID that will be used by the compiler to report the usage of this method.

When another developer uses this method in their code, they will receive a warning indicating that the method is experimental as below.

They can choose to suppress this warning if they still want to use the method, understanding the risks associated with using experimental features as below.

 public class Program
 {
     static void Main(string[] args)
     {
         #pragma warning disable Test001
         ExperimentalAttributeDemo experimentalAttributeDemo = new ExperimentalAttributeDemo();
         #pragma warning restore Test001
         System.Console.WriteLine("Hello World!");
     }
 }

In this way, the ExperimentalAttribute provides a mechanism for library and API authors to introduce new features in a safe and controlled manner, while clearly communicating the experimental nature of these features to their users

Conclusion

The ExperimentalAttribute in C# .NET 8 is a powerful tool for developers, particularly for those who are developing libraries or APIs. It allows developers to introduce new features in a controlled manner, while clearly communicating to the users that these features are experimental and may change in the future.

By using the ExperimentalAttribute, developers can ensure that they are providing a safe and stable experience for their users, while also having the freedom to innovate and experiment with new features. This attribute is a testament to the flexibility and forward-thinking design of the C# language and the .NET platform.

I hope you will find this article helpful. If you have any suggestions, then please feel free to ask in the comment section.

Thank you.