zalando/grafter

Daniel Karch

@danielkarch

My problem is that in the companion object of the trait I need explicitly define the instance to use. But I cannot specify, say, FutureFooService.reader because it has the wrong (non-generic) type.

Eric Torreborre

@etorreborre

I'm thinking that In the companion object we can put implicit val reader: Reader[ApplicationConfig, FooService[Task]] = genericReader and then when we finally instantiate the whole application with F = Task this instance should be found. If we need anything else than F = Task we need to provide other instances

Daniel Karch

@danielkarch

I think this is what I want: https://gist.github.com/danielkarch/a78458b659f22dd1a861062731c883be

You have some components where even the implementation is generic, because they just call their (generic) dependencies, and some components where you only have a specific implementation.

Matthew de Detrich

@mdedetrich

Is there a way to retrieve a singleton class instance from your graph?

Eric Torreborre

@etorreborre

You can collect all the elements of a given type and check if the list has size 1 if you want to check that a singleton exists

Matthew de Detrich

@mdedetrich

Cheers

@etorreborre How exactly do you retrieve the graph from an existing application?

Actually found it, nvm

Eric Torreborre

@etorreborre

cool, I was about to direct you to the QuickStart section

Philipp Martini

@maphi

Hi guys, is it true that nesting configs is not possible? This always fails as scalac is not able to resolve implicits (using lightbend scala 2.12.5):

import cats.Eval
import cats.data.Reader
import cats.implicits._
import org.zalando.grafter.{Start, StartResult}
import org.zalando.grafter.macros.{reader, readers}
import org.zalando.grafter.syntax.rewriter._

@readers
case class ApplicationConfig(httpConfig: HttpConfig)

@readers
case class HttpConfig(cfg1: HttpSubConfig1, cfg2: HttpSubConfig2)

case class HttpSubConfig1(port: Int)
case class HttpSubConfig2(host: String)

@reader
case class HttpClient(config: HttpSubConfig2) extends Start {
  override def start: Eval[StartResult] = StartResult.eval("HttpClient")(println("Start HttpClient"))
}


@reader
case class SomeService(client: HttpClient) extends Start {
  override def start: Eval[StartResult] = StartResult.eval("SomeService")(println("Start SomeService"))
}

@reader
case class Application(someService: SomeService)


object MyApp extends App {
  val config = ApplicationConfig(HttpConfig(HttpSubConfig1(80), HttpSubConfig2("bla")))

  val app = Application.reader[ApplicationConfig].apply(config).singletons

  val started = app.startAll.value

  if (started.forall(_.success))
    println("application started successfully")
  else
    println(started.mkString("\n"))
}

Error is: could not find implicit value for parameter someServiceReader: cats.data.Reader[...ApplicationConfig,....SomeService]

Bjørn Madsen

@aeons

can you try removing the @readers macro on HttpConfig?

i think it might generate an ambiguous implicit value

Philipp Martini

@maphi

Doesn't help. I think its missing an Reader[ApplicationConfig, HttpSubConfig2]

Bjørn Madsen

@aeons

does ApplicationConfig.cfg2Reader exist?

Philipp Martini

@maphi

scalac says no

Bjørn Madsen

@aeons

just for completeness does ApplicationConfig.cfg1Reader exist?

Philipp Martini

@maphi

Nope. Just for completeness: Using grafter 2.6.0

Bjørn Madsen

@aeons

can you try with 2.5.0

i think I might have broken this :|

Philipp Martini

@maphi

ok. just FYI (with 2.6.0): HttpConfig. cfg1Reader/cfg2Reader exists when using @readers on HttpConfig

Bjørn Madsen

@aeons

yeah, that makes sense

I think I’ve misunderstood something with how it should owkr :)

Philipp Martini

@maphi

same problem with 2.5.0

Bjørn Madsen

@aeons

ok, not my fault then :D

Philipp Martini

@maphi

^^ But it should be possible to nest configs?

Bjørn Madsen

@aeons

i thought so

but I can’t see where it can go down a level in the macros

Philipp Martini

@maphi

y that could be the problem as it got a Reader[ApplicationConfig, HttpConfig] and a Reader[HttpConfig, HttpSubConfig2] in scope and if i create Reader[ApplicationConfig, HttpConfig] manually from the two above it works

Bjørn Madsen

@aeons

in the documentation it does mention to annotate the configuration with @readers

which sounds like there’s only supposed to be one :)

Philipp Martini

@maphi

Y, looks like ^^, thanks 4 help. Macro expansion on ApplicationConfig shows only httpConfigReader, applicationConfigReader, thus scalac has no clue how to resolve it. I'll stick with flat config then.

Bjørn Madsen

@aeons

Eric Torreborre

@etorreborre

@maphi I don’t have time to test this idea right now but I think putting a @reader annotation on top of HttpConfig might work, or something… I’ll come back to you

Philipp Martini

@maphi

I tried putting both(@reader and @readers) on top of HttpConfig but that didn't worked.

Eric Torreborre

@etorreborre

Fair enough, I'll check what I can do if can get enough battery time during my flight 😄

Philipp Martini

@maphi

cool thx, nice flight then

Bjørn Madsen

@aeons

Have you tried both at the same time?

Philipp Martini

@maphi

yes

Eric Torreborre

@etorreborre

@maphi I found a solution for this issue which unfortunately is breaking something else. In the meantime things should work if you annotate HttpConfig with @readers and then import HttpConfig._ where you want to create the application. I’ll try to find a fix that’s working in all cases.

Philipp Martini

@maphi

thx @etorreborre i'll try that

Eric Torreborre

@etorreborre

I’m unfortunately not sure that my solution can be implemented with the current Scala macros, we might have to resort to 2 different annotations, one for the “flat” case, one for the “nested” one

Eric Torreborre

@etorreborre

@maphi can you please try grafter-2.6.1 (and annotate your “nested” configs with @readers)?

Philipp Martini

@maphi

works now :), thanks a lot

Eric Torreborre

@etorreborre

Great it wasn’t obvious to get there :-)

Jakub Kozłowski

@kubukoz

hey, has anyone tried using grafter with Play?

Eric Torreborre

@etorreborre

I haven't but that's something I wanted to investigate

Jakub Kozłowski

@kubukoz

my team regularly has problems with components that don't have a bound implementation in production, so I'm trying to convince them to move to compile-time injection

so I'm investigating options :P

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