Magnet.scala

class A[T]
class C[T]
object Apply {
  trait ApplyMagnet {
    type R
    def apply(): R
  }
  
  object ApplyMagnet {
    implicit def aMagnet[T](a: A[T]): ApplyMagnet {type R = String} = new ApplyMagnet {
      override type R = String

      override def apply(): R = {
        "A is applied"
      }
    }

    implicit def cMagnet[T](a: C[T]): ApplyMagnet {type R = String} = new ApplyMagnet {
      override type R = String

      override def apply(): R = {
        "C is applied"
      }
    }
  }
  
  def apply(magnet: ApplyMagnet): magnet.R = magnet.apply()
}

Apply(new A[String])

Apply(new C[String])