How to copy iterator in Scala?

Question

About duplicate

This is NOT a duplicate of How to clone an iterator?

Please do not blindly close this question, all the answers given in so-called

Answer 1

It's pretty easy to create a List iterator that you can duplicate without destroying it: this is basically the definition of the iterator method copied from the List source with a fork method added:

class ForkableIterator[A] (list: List[A]) extends Iterator[A] {
    var these = list
    def hasNext: Boolean = !these.isEmpty
    def next: A = 
      if (hasNext) {
        val result = these.head; these = these.tail; result
      } else Iterator.empty.next
    def fork = new ForkableIterator(these)
}

Use:

scala> val it = new ForkableIterator(List(1,2,3,4,5,6))
it: ForkableIterator[Int] = non-empty iterator

scala> it.next
res72: Int = 1

scala> val it2 = it.fork
it2: ForkableIterator[Int] = non-empty iterator

scala> it2.next
res73: Int = 2

scala> it2.next
res74: Int = 3

scala> it.next
res75: Int = 2

I had a look at doing this for HashMap but it seems more complicated (partly because there are different map implementations depending on collection size). So probably best to use the above implementation on yourMap.toList.