why it required me to add `!!` in my `while` loop, while I already check node.right will never be nu...

# announcements

[Chi]

why it required me to add !! in my while loop, while I already check node.right will never be null

-.kt

[Shawn]

val is needed for smart-casting to work

[streetsofboston]

Because the compiler cannot guarantee that another thread never changes the value of node.right right
after the null check

[Shawn]

`var`s are at risk of TOCTOU errors https://en.wikipedia.org/wiki/Time_of_check_to_time_of_use

[Chi]

is there another way to write a better code here?

[streetsofboston]

while (node?.right != null) {
        node = node?.right
    }

[streetsofboston]

^^^ only if you are sure that there are no race conditions, ie no other threads can suddenly and unexpectedly change the .right of the node(s).

[Dico]

while (true) {
    node = node.right ?: break
}

[Shawn]

you probably could make this a tailrec fun

[Dico]

But I dont think it would be beneficial

[Shawn]

I mean, it would make the node argument immutable, slightly more elegant than caching in a val or anything like that

[Stephan Schroeder]

you could put the value into a local variable so that’s insured that no other thread can change it

private fun predecessor(): Int {
        var node = this.left!!
        var rightNode = node.right
        while (rightNode != null) {
            rightNode = rightNode.right
        }
        return rightNode?.data ?: node.data
    }

[Stephan Schroeder]

a tailrec solution

private fun predecessor(): Int {
    tailrec fun getRightMostData(node: Node): Int {
        val rightNode = node.right
        return if(rightNode==null) node.data
               else getRightMostData(rightNode) 
	}
    return getRightMostData(this.left!!)
}