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import scala.reflect.macros.blackbox.Context
import language.experimental.macros
trait Complex[T]
class Foo(val bar: Bar)
class Bar(val s: String)
object Complex {
def impl[T: c.WeakTypeTag](c: Context): c.Expr[Complex[T]] = {
import c.universe._
val tpe = weakTypeOf[T]
for (f <- tpe.declarations.collect{case f: TermSymbol if f.isParamAccessor && !f.isMethod => f}) {
val trecur = appliedType(typeOf[Complex[_]], List(f.typeSignature))
val recur = c.inferImplicitValue(trecur, silent = true)
if (recur == EmptyTree) c.abort(c.enclosingPosition, s"couldn't synthesize $trecur")
}
c.Expr[Null](Literal(Constant(null)))
}
implicit object ComplexString extends Complex[String]
implicit def genComplex[T]: Complex[T] = macro impl[T]
}
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