Can't find SttpBackends + "Error occurred in an application involving default arguments." - scala

Question

I'm trying to create a extremely simple Telegram bot in Scala using bot4s. I'm pretty much following the example there. Here's the code:
package info.jjmerelo.BoBot
import cats.instances.future._
import cats.syntax.functor._
import com.bot4s.telegram.api.RequestHandler
import com.bot4s.telegram.api.declarative.Commands
import com.bot4s.telegram.clients.{FutureSttpClient, ScalajHttpClient}
import com.bot4s.telegram.future.{Polling, TelegramBot}
import scala.util.Try
import scala.concurrent.Future
import com.typesafe.scalalogging.Logger
object BoBot extends TelegramBot
with Polling
with Commands[Future] {
implicit val backend = SttpBackends.default
def token = sys.env("BOBOT_TOKEN")
override val client: RequestHandler[Future] = new FutureSttpClient(token)
val log = Logger("BoBot")
// val lines = scala.io.Source.fromFile("hitos.json").mkString
// val hitos = JSON.parseFull( lines )
// val solo_hitos = hitos.getOrElse( hitos )
onCommand("hey") { implicit msg =>
log.info("Hello")
reply("Conseguí que funcionara").void
}
}
And here's the build.sbt
name := "bobot"
version := "0.0.1"
organization := "info.jjmerelo"
libraryDependencies += "com.bot4s" %% "telegram-core" % "4.4.0-RC2"
val circeVersion = "0.12.3"
libraryDependencies ++= Seq(
"io.circe" %% "circe-core",
"io.circe" %% "circe-generic",
"io.circe" %% "circe-parser"
).map(_ % circeVersion)
libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.9.2"
retrieveManaged := true
Circe is for later
Anyway, I managed to compile most of it, but I still get these two errors:
[info] compiling 2 Scala sources to /home/jmerelo/Asignaturas/cloud-computing/BoBot/target/scala-2.12/classes ...
[error] /home/jmerelo/Asignaturas/cloud-computing/BoBot/src/main/scala/info/jjmerelo/BoBot.scala:21:26: not found: value SttpBackends
[error] implicit val backend = SttpBackends.default
[error] ^
[error] /home/jmerelo/Asignaturas/cloud-computing/BoBot/src/main/scala/info/jjmerelo/BoBot.scala:23:49: could not find implicit value for parameter backend: com.softwaremill.sttp.SttpBackend[scala.concurrent.Future,Nothing]
[error] Error occurred in an application involving default arguments.
[error] override val client: RequestHandler[Future] = new FutureSttpClient(token)
[error] ^
[error] two errors found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 5 s, completed 11 nov. 2020 8:19:38
I can't figure out either of the two. SttpBackends is missing, that's clear, but there's nothing in the example that indicates it's needed, or, for that matter, what library should be included. The second one about the default arguments I simply can't figure it out, even if I define token as String or if I change def to val. Any idea?

Answer 1

Your error messages is associated with each other.
First error tells us that compiler couldn't find object SttpBackends which has field of SttpBackend.
The second one tells us that compiler couldn't find implicit backend: SttpBackend for constructing FutureSttpClient. It requires two implicits: SttpBackend and ExecutionContext.
class FutureSttpClient(token : _root_.scala.Predef.String,
telegramHost : _root_.scala.Predef.String = { /* compiled code */ })
(implicit backend : com.softwaremill.sttp.SttpBackend[scala.concurrent.Future, scala.Nothing],
ec : scala.concurrent.ExecutionContext)
extends com.bot4s.telegram.clients.SttpClient[scala.concurrent.Future] {...}
You can create it by yourself as in bot4s examples.
If you will try to find SttpBackends object in bot4s library you would found this code in bot4s examples:
import com.softwaremill.sttp.okhttp._
object SttpBackends {
val default: SttpBackend[Future, Nothing] = OkHttpFutureBackend()
}
add this object to your project to make it compilable.