Conditional methods of Scala generic classes with restrictions for type parameters

Question

I believe that a generic class may make one of its methods available only assuming that its type parameters conform to some additional restrictions, something like (syntax i

Answer 1

there is another option involving implicit classes conversions

trait Col[T] extends Traversable[T] 

implicit class ColInt[T <: Int](val v : Col[T]) extends AnyVal {
    def sum : T = (0 /: v)(_ + _)
}

in this context you don't need the empty trait Col anymore, so you could further comprimize it to this:

implicit class ColInt[T <: Int](val v : Traversable[T]) extends AnyVal {
    def sum : T = (0 /: v)(_ + _)
}

The advantage of this method is, that it tells the compiler, that type T is really a subtype of Int, so List[T] <: List[Int] is still valid in this context, and no explicit conversion needs to be added. The implicit parameter adds implicit conversions that wouldn't work on List[T], because it only introduces an implicit conversion from T to Int, not from List[T] to List[Int]