dispatch
Maybe you can share the problematic code in Scastie?
Just a sec.
I scastie it works, maybe it's a local setup. but here is a minimal example:
https://github.com/stsatlantis/magnolia-test what produces the the compilation error:
/Users/barnabasolah/workplace/oss/magnolia-test/src/main/scala/test/Csv.scala:26:54: macro implementations cannot have implicit parameters other than WeakTypeTag evidences
[error] implicit def deriveCsv[A]: Csv[A] = macro Magnolia.gen[A]I'm using openjdk:11
About ignoring case classes - that sounds weird to me. Sealed traits eventually have to implemented by something (case classes or case objects)
My use case is: I have several Events and each event has to have a way to define partitionKey, I opted to provide it via type class HasPartitionKey[T]
// relevant imports
def createRequest[A:HasPartitionKey](event: A) : Request= ???
object HasPartitionKey{
//no need for combine
def dispatch[A](ctx: SealedTrait[HasPartitionKey, A]): HasPartitionKey[A] = new HasPartitionKey[A] {
def apply(a: A): String =
ctx.dispatch(a)(sub => sub.typeclass(sub.cast(a)))
}
}
sealed trait Event
object Event {
case class AppleHarvested(field: String) extends Event
case object HarvestOver extends Event
// HasPartitionKey instances ...
implicit def deriveCsv[A]: Csv[A] = macro Magnolia.gen[A]
}
def sendEvent(e: Event) = {
...
val request = createRequest(e)
...
}Actually when the combine is called I would like to throw and exception at compile time, as you mentioned @implicitNotFound or this would require rewriting of the macro which relies on the combine method. ?
combine it will ofc not compile
We can do both. Then when updating Mercator in Magnolia should remember to remove the exclusions
I don't think adding an exclusion in magnolia will do anything useful, because we still need to have mercator in the dependencies, and ivy is going to pull in transitive dependencies, including mercator's.
@mberndt123 Not true, both coursier and ivy obey exclusions in the pom. If you don’t depend on mercator directly, it’s transitives will not be pulled - otherwise exclusions would’ve been useless. You can check the resolution with coursier resolve command, and you can pull all the jars with coursier too:
[~] % coursier resolve com.propensive:magnolia_2.13:0.15.0
com.propensive:magnolia_2.13:0.15.0:default
com.propensive:mercator_2.13:0.2.1:default
jline:jline:2.14.6:default
org.scala-lang:scala-compiler:2.13.0:default
org.scala-lang:scala-library:2.13.1:default
[~] % coursier resolve com.propensive:magnolia_2.13:0.14.5
com.propensive:magnolia_2.13:0.14.5:default
com.propensive:mercator_2.13:0.2.1:default
jline:jline:2.14.6:default
org.scala-lang:scala-compiler:2.13.0:default
org.scala-lang:scala-library:2.13.1:default
org.scala-lang:scala-reflect:2.13.0:defaultNote how 0.15 lacks the scala-reflect jar. The only difference between them is exclusions
gen[MyTypeClass[Foo[Bar]]] // typeArguments are OK object Baz {
type Type = MyTypeClass[Foo[Bar]]
}
gen[Baz.Type] // typeArguments are empty
c.enclosingUnit.asInstanceOf[global.CompilationUnit].toCheck += (() => println(s"*** $text ***")) It seems very easy to abuse. https://gist.github.com/som-snytt/b0a447ccc4555a4947c0eab33948db39
Hello guys, can you tell me what am I doing wrong:
import cats.Show
import magnolia._
import scala.language.experimental.macros
object ShowDeriver {
type TypeClass[T] = Show[T]
def combine[T](caseClass: CaseClass[TypeClass, T]): Show[T] = (t: T) => {
val paramShows = caseClass.parameters.map { p =>
p.label + "=" + p.typeclass.show(p.dereference(t))
}
caseClass.typeName + paramShows.mkString("(", ",", ")")
}
def dispatch[T](sealedTrait: SealedTrait[Show, T]): Show[T] = (t: T) => sealedTrait.dispatch(t) { subtype =>
subtype.typeclass.show(subtype.cast(t))
}
implicit def gen[T]: Show[T] = macro Magnolia.gen[T]
}Here is app:
import cats.Show
import cats.implicits._
case class Student(name: String, age: Int)
object TheApp extends App {
implicit val show = ShowDeriver.gen[Student]
val s = Student("john", 23).show
println(s)
}But I'm getting this:
[error] /home/oybek/Garage/magnolia-exp/src/main/scala/TheApp.scala:7:38: magnolia: the derivation object ShowDeriver does not define the Typeclass type constructor
[error] implicit val show = ShowDeriver.gen[Student]
[error] ^
[error] /home/oybek/Garage/magnolia-exp/src/main/scala/TheApp.scala:9:31: value show is not a member of Student
[error] val s = Student("john", 23).show
[error] ^
[error] two errors found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 15 s, completed May 31, 2020 4:23:07 PM