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import scala.reflect.macros.blackbox.Context
import scala.language.experimental.macros
trait Foo[T]
class C1(val x: Int)
class C2(val x: String)
trait LowPriority {
implicit def lessSpecific[T]: Foo[T] = null
}
object Foo extends LowPriority {
implicit def moreSpecific[T]: Foo[T] = macro Macros.impl[T]
}
object Macros {
def impl[T: c.WeakTypeTag](c: Context) = {
import c.universe._
val tpe = weakTypeOf[T]
if (tpe.members.exists(_.info =:= typeOf[Int]))
c.abort(c.enclosingPosition, "I don't like classes that contain integers")
q"new Foo[$tpe]{ override def toString = ${tpe.toString} }"
}
}
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