def test[T <: Comparable[T]](a1: T, a2: T): Int = a1.compareTo(a2)

test(LocalDate.of(2017,1,2), LocalDate.of(2017, 2, 2))

type arguments [java.time.LocalDate] do not conform to method test's type parameter bounds [T <: Comparable[T]] test[LocalDate](a1, a2)