Deeply copying arbitrarily-deep nested arrays via type classes! (thanks for the typeclass idea from Erik Osheim)

gistfile1.scala

trait Nested[A] {
  def length(a: A): Int
  def clone(a: A): A
}

object Nested {
  implicit def nested[A] = new Nested[A] {
    def length(a: A): Int = 1
    def clone(a: A): A = a
  }

  implicit def nestedArray[A](implicit ev: Nested[A], mf: Manifest[A]) = new Nested[Array[A]] {
    def length(as: Array[A]): Int = as.map { a => ev.length(a) }.sum
    def clone(as: Array[A]): Array[A] = as.map { a => ev.clone(a) }  
  }
}

def deepCopy[A](array: Array[A])(implicit ev: Nested[Array[A]]): Array[A] = {
  ev.clone(array)
}
  
// with above definitions imported into the REPL:  
scala> val a = Array(Array(1,2,3), Array(4,5,6), Array(7,8,9))
a: Array[Array[Int]] = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))

scala> val c = deepCopy(a)
c: Array[Array[Int]] = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))

scala> a(0)(0) = 9999

scala> a
res1: Array[Array[Int]] = Array(Array(9999, 2, 3), Array(4, 5, 6), Array(7, 8, 9))

scala> c
res2: Array[Array[Int]] = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))

just to make it more object like with postfix notation:

implicit class NestedArray[A](array: Array[A])(implicit ev: Nested[Array[A]]) {
    def deepCopy: Array[A] = ev.clone(array)
    def length: Int = ev.length(array)
}

val c = a.deepCopy

Nice, Pierre!