List.sum on custom class

Question

I have the following code that represents GF2 field:

trait GF2 {
  def unary_- = this
  def + (that: GF2): GF2
  def * (that: GF2): GF2

  def / (that: GF2)          


        

Answer 1

Look at the signature of sum:

def sum[B >: A](implicit num: Numeric[B]): B

I was about to suggest that you make GF2 a member of Numeric typeclass by providing and implicit value of type Numeric[GF2], but then I looked at the definition of Numeric and realized that it contains a ton of operations completely irrelevant to summation that you would have to implement.

I don't like this, I think sum method should require some more abstract typeclass (a monoid, perhaps?).

So, I think your best option (unless you want to implement entire Numeric instance) is to use either reduce (will work only with non-empty lists) or fold:

yourList.reduce(_ + _)
yourList.fold(Zero)(_ + _)