Zio-Kafka: Producing messages to topic - scala

Question

I'm trying to produce some messages to a Kafka topic using the library zio-kafka, version 0.15.0.
Clearly, my comprehension of the ZIO ecosystem is suboptimal cause I cannot produce a simple message. My program is the following:
object KafkaProducerExample extends zio.App {
val producerSettings: ProducerSettings = ProducerSettings(List("localhost:9092"))
val producer: ZLayer[Blocking, Throwable, Producer[Nothing, String, String]] =
ZLayer.fromManaged(Producer.make(producerSettings, Serde.string, Serde.string))
val effect: RIO[Nothing with Producer[Nothing, String, String], RecordMetadata] =
Producer.produce("topic", "key", "value")
override def run(args: List[String]): URIO[zio.ZEnv, ExitCode] = {
effect.provideSomeLayer(producer).exitCode
}
}
The compiler gives me the following error:
[error] KafkaProducerExample.scala:19:28: Cannot prove that zio.blocking.Blocking with zio.Has[zio.kafka.producer.Producer.Service[Nothing,String,String]] <:< Nothing with zio.kafka.producer.Producer[Nothing,String,String].
[error] effect.provideSomeLayer(producer).exitCode
[error] ^
[error] one error found
Can anyone help me in understanding what's going on?

Answer 1

Ok, it was ZIO that requires some hints about types during the creation of the producer layer:
val producer: ZLayer[Blocking, Throwable, Producer[Any, String, String]] =
ZLayer.fromManaged(Producer.make[Any, String, String](producerSettings, Serde.string, Serde.string))
When calling the make smart constructor, we have to give him the types we want to use. The first represents the environment needed to build key and value serializer, while the last two are the types of the messages' keys and values.
In this case, we need no environment at all to build the two serializers, so we pass Any.
Finally, also the Producer.produce function requires some type hints:
val effect: RIO[Producer[Any, String, String], RecordMetadata] =
Producer.produce[Any, String, String]("topic", "key", "value")
After doing the above changes, the types perfectly align, and the compiler is happy again.