examples/src/main/scala/cats.scala


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package magnolia.examples.cats

import scala.collection.immutable.ListMap
import scala.language.experimental.macros
import scala.language.higherKinds

import cats.Show
import magnolia.ContravariantDerivation
import magnolia.Macros

object instances extends instances1 {

  implicit val showDerivation = new ContravariantDerivation[Show] {
    type Return = String
    def call[T](show: Show[T], value: T): String = show.show(value)
    def construct[T](body: T => String): Show[T] = body(_)
    def join(xs: ListMap[String, String]): String = xs.map { case (k, v) => s"$k=$v" }.mkString("{", ", ", "}")
  }
}

trait instances1 {
  implicit def genericShow[T]: Show[T] = macro Macros.magnolia[T, Show[_]]
}