Clever use of typeclasses to enrich existing type while preserving existing type in type system

gistfile1.scala

// Type information got lost because of implicit conversion - instead of type 
// Array[T], we have the runtime type WrappedArray[T]

scala> def first[T](x: Traversable[T]) = (x.head, x)
first: [T](x: Traversable[T])(T, Traversable[T])

scala> first(Array(1,2,3))
res0: (Int, Traversable[Int]) = (1,WrappedArray(1, 2, 3))

// Use implicit type constraints when we want to enrich an existing type while
// preserving that type in the type system

scala> :paste
// Entering paste mode (ctrl-D to finish)

trait ExtendedOps[F[_]] {
  def first[A](c: F[A]): (A, F[A])
}

object ExtendedOps {
  implicit object ArrayOps extends ExtendedOps[Array] {
    def first[A](c: Array[A]) = (c.head, c.tail) 
  }

  // functional extension method
  def first[A, F[_]](c: F[A])(implicit ev: ExtendedOps[F]) = ev.first(c)
}

import ExtendedOps._

// Exiting paste mode, now interpreting.

warning: there were 2 feature warning(s); re-run with -feature for details
defined trait ExtendedOps
defined module ExtendedOps
import ExtendedOps._

scala> first(Array(1,2,3))
res2: (Int, Array[Int]) = (1,Array(2, 3))

scala> :paste
// Entering paste mode (ctrl-D to finish)

// object-oriented extension method - pimp an existing type Array[A]
implicit class ArrayAugs[A](val x: Array[A]) extends AnyVal { 
  def first(implicit ev: ExtendedOps[Array]) = ev.first(x) 
} 

// Exiting paste mode, now interpreting.

defined class ArrayAugs

scala> Array(1,2,3).first
res0: (Int, Array[Int]) = (1,Array(2, 3))