MemberNotNullWhen on interface members?

[weitzhandler]

Hi,

I'm trying to apply MemberNotNullWhen attribute on an interface member but it seems to be ignored by the compiler.

public interface IPathSegment
{
    public int? DescriptorId { get; }

    [MemberNotNullWhen(true, nameof(DescriptorId))]
    public bool IsFinal => ...
}

But when I do the following I still get an error when accessing DescriptorId:

var segment = GetPathSegment();
if (segment.IsFinal)
{
    int descriptorId = segment.DescriptorId; // error - cannot implicitly convert int? to int
}

Is there a way to use these diagnostic attributes with interfaces?

[HaloFour]

Those attributes apply to nullable reference types, not value types. You still have to cast from int? to int as they are two separate types.

[weitzhandler]

Is there a way around it?
Why wouldn't we instruct the compiler to use it as int if the value is guaranteed not to be null? Of what help is the variable if we still need to cast it to nullable?

[TahirAhmadov]

@weitzhandler the nullable value types existed before nullable reference types and the nullability state analysis. If C# was made from scratch, they could (potentially) make this scenario smoother, but at this point, it's impossible.

Minor correction to what @HaloFour wrote: the attributes apply to nullable value types, too, just differently: when you access the .Value property, if it thinks that it's not null, the .Value will not warn, whereas otherwise it would.
Try changing it to int descriptorId = segment.DescriptorId.Value; and let us know if it still warns.