Trait for creating the line path type class instances for LinePathDbl2 final classes. Instances for the LinePathDbl2Builder type class, for classes / traits you control, should go in the companion object of type B, which will extend Dbl2Elem. The first type parameter is called B, because it corresponds to the B in map[B](f: A => B)(implicit build: ArrTBuilder[B, ArrB]): ArrB function.
BuffT can be inbuilt Jvm type like ArrayBuffer[Int] for B = Int and BB = Ints, or it can be a compile time wrapped Arraybuffer inheriting from BuffProdHomo.
BuffT can be inbuilt Jvm type like ArrayBuffer[Int] for B = Int and BB = Ints, or it can be a compile time wrapped Arraybuffer inheriting from BuffProdHomo.