"cheap" implementation of an immutable IndexedSeq backed by an array. `b` looks like an Array according to the types, but can't be modified nor cast back to a mutable Array.

gistfile1.scala

import scala.reflect.ClassTag
import scala.collection.mutable.WrappedArray
import scala.collection.mutable.ArrayLike

def ASeq[T](elt: T*)(implicit ct: ClassTag[T]): IndexedSeq[T] = {
   val a = elt.toArray.clone
   a.deep.asInstanceOf[IndexedSeq[T]]
}                                                 

val a = Array(1,2,3)                              //> a  : Array[Int] = Array(1, 2, 3)
val b = ASeq(a:_*)                                //> b  : IndexedSeq[Int] = Array(1, 2, 3)

a(2) = 4

println(b)                                        //> Array(1, 2, 3)