Why DOESN’T Kotlin smart cast work here? ```fun SLLNode?.sumListWith(node: SLLNode?, carry: Int = 0)...

# announcements

[Gopal S Akshintala]

Why DOESN’T Kotlin smart cast work here?

fun SLLNode?.sumListWith(node: SLLNode?, carry: Int = 0): SLLNode? =
    when {
        this == null && node == null -> if (carry == 0) null else SLLNode(carry)
        this == null -> node.also { it!!.value += carry } // Smart cast doesn't work here.
        node == null -> this.also { value += carry } // Works here.
        else -> {
            ...
        }
    }

[vinayagasundar]

It's because your not adding any null check to the also method. Change like this node?.also

[Animesh Sahu]

@vinayagasundar he meant if (this==null&&node==null) is false and (this==null) is true then node must be not-null. So he asked why would he need to use null checks 😃

[vinayagasundar]

Hmm, for that we need to understand how the && operator works. if the first condition fails ie. this == null . It won't evaluated the seconds condition node==null. because we already know the final result will be false anyway.

[vinayagasundar]

This is called short-circuit evaluation

[Animesh Sahu]

+1

[Gopal S Akshintala]

I see thanks @vinayagasundar, seems the compiler cannot connect two lines while smart casting