ExperimentalAttribute

Report warnings for references to types and members marked with Windows.Foundation.Metadata.ExperimentalAttribute.

namespace Windows.Foundation.Metadata
{
    [AttributeUsage(
        AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum |
        AttributeTargets.Interface | AttributeTargets.Delegate,
        AllowMultiple = false)]
    public sealed class ExperimentalAttribute : Attribute
    {
    }
}

Warnings

The warning 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.

The warning is reported for any reference to a type or member marked with the attribute. (The AttributeUsage is for types only so the attribute cannot be applied to non-type members from C# or VB, but the attribute could be applied to non-type members outside of C# or VB.)

[Experimental]
class A
{
    internal object F;
    internal static object G;
    internal class B { }
}
class C
{
    static void Main()
    {
        F(default(A));   // warning CS08305: 'A' is for evaluation purposes only ...
        F(typeof(A));    // warning CS08305: 'A' is for evaluation purposes only ...
        F(nameof(A));    // warning CS08305: 'A' is for evaluation purposes only ...
        var a = new A(); // warning CS08305: 'A' is for evaluation purposes only ...
        F(a.F);
        F(A.G);          // warning CS08305: 'A' is for evaluation purposes only ...
        F<A.B>(null);    // warning CS08305: 'A' is for evaluation purposes only ...
    }
    static void F<T>(T t)
    {
    }
}

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

[Experimental]
class A<T>
{
    [Experimental]
    internal virtual void F()
    {
    }
}
class B : A<int> // warning CS08305: 'A<int>' is for evaluation purposes only ...
{
    internal override void F()
    {
        base.F(); // warning CS08305: 'A<int>.F' is for evaluation purposes only ...
    }
}
class C
{
    static void F(A<object> a, B b) // warning CS08305: 'A<object>' is for evaluation purposes only ...
    {
        a.F(); // warning CS08305: 'A<object>.F' is for evaluation purposes only ...
        b.F();
    }
}

There is no automatic suppression of warnings: warnings are generated for all references, even within [Experimental] members. Suppressing the warning requires an explicit compiler option or #pragma.

[Experimental] enum E { }
[Experimental]
class C
{
    private C(E e) // warning CS08305: 'E' is for evaluation purposes only ...
    {
    }
    internal static C Create() // warning CS08305: 'C' is for evaluation purposes only ...
    {
        return Create(0);
    }
#pragma warning disable 8305
    internal static C Create(E e)
    {
        return new C(e);
    }
}

ObsoleteAttribute and DeprecatedAttribute

ExperimentalAttribute is independent of System.ObsoleteAttribute or Windows.Framework.Metadata.DeprecatedAttribute.

Warnings for [Experimental] are reported within [Obsolete] or [Deprecated] members. Warnings and errors for [Obsolete] and [Deprecated] are reported inside [Experimental] members.

[Obsolete]
class A
{
    static object F() => new C(); // warning CS08305: 'C' is for evaluation purposes only ...
}
[Deprecated(null, DeprecationType.Deprecate, 0)]
class B
{
    static object F() => new C(); // warning CS08305: 'C' is for evaluation purposes only ...
}
[Experimental]
class C
{
    static object F() => new B(); // warning CS0612: 'B' is obsolete
}

Warnings and errors for [Obsolete] and [Deprecated] are reported instead of [Experimental] if there are multiple attributes.

[Obsolete]
[Experimental]
class A
{
}
[Experimental]
[Deprecated(null, DeprecationType.Deprecate, 0)]
class B
{
}
class C
{
    static A F() => null; // warning CS0612: 'A' is obsolete
    static B G() => null; // warning CS0612: 'B' is obsolete
}