object Main extends App { val t1 = "test1" val t2 = "test2" trait F[T] { type R; def value: R } implicit val t1F = new F[t1.type] { override type R = Int; override def value = 1 } implicit val t2F = new F[t2.type] { override type R = Unit; override def value = () } def a[T](x: T)(implicit i: F[T]): i.R = i.value println(a[t1.type](t1)) println(a[t2.type](t2)) }