MemberNotNullWhen along with a parameter name-CodePudding

If heartbeat is true, the nullability warning over heartbeatTarget should go away. I remember there was the MemberNotNullWhen attribute. How do I use it in this case in order to disable the nullability warning over heartbeatTarget?

However, it won't compile due to typeof(heartbeat) it should be something else but not sure what.

internal static IGraph<SourceShape<IFeedMessage>,NotUsed> CreateGraph<TMat>(
    Source<string,TMat> publisher,
    bool                heartbeat       = false,
    [property: MemberNotNullWhen(true, typeof(heartbeat))]
    IActorRef?          heartbeatTarget = null,
    ILoggingAdapter?    log             = null
)
{
    var graph = GraphDsl.Create(builder =>
    {
        var origSource = builder.Add(publisher);
        var filter = builder.Add(Flow.Create<string, string>().WhereNot(x => string.IsNullOrEmpty(x)));
        var serializer = builder.Add(GdaxFeedFlows.JsonDeserializeFlow(log));
        builder.From(origSource.Outlet).To(filter.Inlet);
        builder.From(filter.Outlet).To(serializer.Inlet);
        var emptyFilter = builder.Add(GdaxFeedFlows.FilterEmpty());

        // add heartbeat detection capabilities if requested
        if (heartbeat)
        {
            var heartbeatFilter = builder.Add(GdaxFeedFlows.FilterHeartbeats(heartbeatTarget));
            builder.From(serializer.Outlet).To(heartbeatFilter.Inlet);
            builder.From(heartbeatFilter.Outlet).To(emptyFilter.Inlet);
        }
        else
        {
            builder.From(serializer.Outlet).To(emptyFilter.Inlet);
        }

        return new SourceShape<IFeedMessage>(emptyFilter.Outlet);
    });

    return graph;
}

CodePudding user response：

MemberNotNullWhen doesn't work like that. You are only allowed to attribute Methods and Properties with it which is why you put a [property:] as a compiler workaround.

Null annotations is supposed to help with compile time null-ref exceptions, but I don't think any of the current annotations would help here. Even if heartbeat is true, the heartBeatTarget could still be null since it's the callers responsibility to pass it in. You can't just assume it'll be true because you'll get a null ref.

I think you would be better off checking if it's not null at runtime.

Null check

        // add heartbeat detection capabilities if requested
        if (heartbeat && heartBeatTarget is not null)
        {
            var heartbeatFilter = builder.Add(GdaxFeedFlows.FilterHeartbeats(heartbeatTarget));
            builder.From(serializer.Outlet).To(heartbeatFilter.Inlet);
            builder.From(heartbeatFilter.Outlet).To(emptyFilter.Inlet);
        }