How should I wrap this code correctly to use with Cats Effect 3? Should I use a resource?

Question

Is the below code correct to work with cats effect and IO?

Should this be using a resource, if so, can someone help me as I haven't used resource before.

object AWS {
  val client = AWSClientBuilder.defaultClient()

  def blah(...): IO[Unit] = IO {
     client.submitJob(new AwsRequest(....))
  }
}

Answer 1

Technically not, since client (and thus AWS) are shared mutable state.
However, the refactoring is not only using Resource, but also not using a global object and passing down the dependency explicitly.

Like this:

// Make AWS an interface that defines the operations it provides.
trait AWS {
  def foo(...): IO[Unit]
}

// In the companion object put a factory method that instantiates the resources.
object AWS {
  def instance(...): Resource[IO, AWS] =
    Resource
      .make(IO(AWSClientBuilder.defaultClient))(client => IO(client.close()))
      .map(client => new AWSImpl(client))
}

// Have a private implementation of the interface.
private[pckg] final class AWSImpl (client: AWSClient) extends AWS {
  def blah(...): IO[Unit] = IO {
    client.submitJob(new AwsRequest(...))
  }
}

// Whatever was using AWS globally before now must require its dependency.
final class Domain(aws: Aws) {
  def bar(...): IO[Unit] =
    aws.foo(...)
}

// Assembly the dependency graph on the main.
final class Main extends IOApp.Simple {
  override final val run: IO[Unit] =
    Aws.instance(...).use { aws =>
      val domain = new Domain(aws)
      domain.bar(...)
    }
}

This is a very general idea, don't follow blindly.