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

In this case you can only use an implicit parameter, as the type gets determined before the method call.

trait Col[T] extends Traversable[T] {
  def sum(implicit num: Numeric[T]) :T = ???
}

If the method you are calling would be parameterized, you could use context bounds, which are just syntactic sugar for the implicit parameter bound to the type parameter:

def foo[A](implicit ev: Something[A]) = ???

is equivalent to

def foo[A : Something] = ???