Covariant/contravariant message handler/subscriptions?

[Meigs2]

Hello!

Is there any sort of mechanism within the Messengers to allow for covariant/contravariant subscriptions?

In one of my projects I have been looking into using an EventAggregator, and so far my current solution is using Reactive Extension's Subject<object> to allow for contravariant subscriptions by using the OfType<T>() extension method to filter the Subject. Lets say we have a few events defined like so:

public record Event;
public record SpecificEvent : Event;

If I wanted to subscribe to all Events, I can use RX as such:

public Subject<Event> Subject { get; } = new();

// Subscribe
Subject.OfType<Event>.Subscribe(e => {/* handle event */});

Subject.OnNext(new SpecificEvent()); // Invokes handler above, SpecificEvent is covariant to Event

However, it appears that the messengers in MVVM toolkit do not have this behaviour:

WeakReferenceMessenger.Default.Register<Event>(this, e => {/* handle event */});

WeakReferenceMessenger.Default.Send(new SpecificEvent()); // DOES NOT raise above handler

The IRecipient<T> interface does not appear to work either for this situation.

Is there currently any way in the toolkit to allow covariant/contravariant subscriptions to messages?

Thanks!