Question

If I have a stack using the mutable scala stack collection, is there a way I can copy the stack so that I can analyze its elements by popping it without altering the original stack? For instance, suppose I have a stack and code as follows:

import scala.collection.mutable.Stack
var stack1 = new Stack[Int]
/** Code that pushes integers on stack1*/
var stackCopy = stack1
while (!stackCopy.isEmpty) {
    println(stackCopy.pop)
}

I want to use a while loop to print all elements in stack1. But when I make a copy and pop off that copy, the original stack (i.e. stack1) is also altered. I want to preserve the original stack, so how can I just get the contents, not the address?

Answer 1

You could use for comprehension:

for( i <- stack1 ) { println(i) }

or simply call the foreach method:

stack1 foreach println

If you insist using a while loop, you can convert it to a list first:

var is = stack1.toList
while( is.nonEmpty ) {
  println( is.head )
  is = is.tail
}

With all these methods, the original stack will be preserved.