Kafka.Id is private

[chenharryhua]

I failed to annotate the return type because Kafka.Id is private.

val k: ProducerMessage[kafka.Id, K, V, Unit] //compiler error: Symbol Id is inaccessible from this place
would it be better to use cats.Id instead?

[vlovgr]

Thanks for raising this @chenharryhua!

We cannot use cats.Id because the type parameter is invariant, while we need it to be covariant (type Id[+A] = A). I've raised #87 to make fs2.kafka.Id public, but in the meantime you can define it yourself if you want to.

[chenharryhua]

Thanks. I am waiting for next release. Let intellij complain for a while. :)