ExperimentalAttribute

Note

This article is a feature specification. The specification serves as the design document for the feature. It includes proposed specification changes, along with information needed during the design and development of the feature. These articles are published until the proposed spec changes are finalized and incorporated in the current ECMA specification.

There may be some discrepancies between the feature specification and the completed implementation. Those differences are captured in the pertinent language design meeting (LDM) notes.

You can learn more about the process for adopting feature speclets into the C# language standard in the article on the specifications.

Report warnings for references to types and members marked with System.Diagnostics.CodeAnalysis.ExperimentalAttribute.

namespace System.Diagnostics.CodeAnalysis
{
    [AttributeUsage(AttributeTargets.Assembly |
                    AttributeTargets.Module |
                    AttributeTargets.Class |
                    AttributeTargets.Struct |
                    AttributeTargets.Enum |
                    AttributeTargets.Constructor |
                    AttributeTargets.Method |
                    AttributeTargets.Property |
                    AttributeTargets.Field |
                    AttributeTargets.Event |
                    AttributeTargets.Interface |
                    AttributeTargets.Delegate, Inherited = false)]
    public sealed class ExperimentalAttribute : Attribute
    {
        public ExperimentalAttribute(string diagnosticId)
        {
            DiagnosticId = diagnosticId;
        }

        public string DiagnosticId { get; }
        public string? UrlFormat { get; set; }
        public string? Message { get; set; }
    }
}

Reported diagnostic

Although the diagnostic is technically a warning, so that the compiler allows suppressing it, it is treated as an error for purpose of reporting. This causes the build to fail if the diagnostic is not suppressed.

The diagnostic is reported for any reference to a type or member that is either:

• marked with the attribute,
• in an assembly or module marked with the attribute,

except when the reference occurs within [Experimental] members, when it is automatically suppressed.

It is also possible to suppress the diagnostic by usual means, such as an explicit compiler option or #pragma.
For example, if the API is marked with [Experimental("DiagID")] or [Experimental("DiagID", UrlFormat = "https://example.org/{0}")], the diagnostic can be suppressed with #pragma warning disable DiagID.

An error is produced if the diagnostic ID given to the experimental attribute is not a valid C# identifier.

If a value for Message property is not provided, the diagnostic message is a specific message, where '{0}' is the fully-qualified type or member name.

'{0}' is for evaluation purposes only and is subject to change or removal in future updates.

If a value for Message property is provided, the diagnostic message is a specific message, where '{0}' is the fully-qualified type or member name and '{1}' is the Message.

'{0}' is for evaluation purposes only and is subject to change or removal in future updates: '{1}'.

The attribute is not inherited from base types or overridden members.

ObsoleteAttribute and DeprecatedAttribute

Warnings for [Experimental] are reported within [Obsolete] or [Deprecated] members.
Warnings and errors for [Obsolete] and [Deprecated] are reported inside [Experimental] members.
But warnings and errors for [Obsolete] and [Deprecated] are reported instead of [Experimental] if there are multiple attributes.