Logs for a service

Service logging

One downside of a simple logging is that in every service class you have to write this line:

private implicit val logging: Logging[F] = Logging.Make[F].forService[MyService[F]]

It is quite boilerplate-ish, so tofu.logging has the workaround:

class MyService[F[_] : Monad : MyService.Log](someDependency: DependencyService) {

  def makeThis: F[Unit] = someDependency.foo(30) >> info"Something"

  def makeThat: F[Unit] = someDependency.foo(30).flatTap(result => warn"Some another thing $result")
}

object MyService extends LoggingCompanion[MyService]

The line object MyService extends LoggingCompanion[MyService] mixes in type Log to the companion, which is just alias for ServiceLogging[F, MyService].

This type carries information about which class it is supposed to be used for, so Scala compiler is able to implicitly create from Logs and pass desired ServiceLogging instance.

And in the wiring of the app, just as in simple logging:

import cats.effect.ExitCode

def run: IO[ExitCode] = {
  implicit val logs: Logging.Make[IO] = Logging.Make.plain[IO] // or Make.contextual[IO, C]

  val service = new MyService[IO](???)
}

The MyService.Log instance is created implicitly just for this service from the implicit value of Logging.Make.