so yeah, walrus operator?

var next = stack.last
    get() {
        field = stack.pop()
        field
    }

var next = stack.last
    get() = field := stack.pop()

They special cased

when

just to be able to avoid adding this operator 🙂

Yeah, I'd like to know why they wanted to avoid it so badly yet added it to when

What the special case?

when(val x = foo())

is allowed

Meanwhile you can't do

if (val x = foo())

like you can in Java.

But may I ask “why”? The example code you’ve given is a horrible anti-pattern — a property with a side effect 😱 Of course, there are some legitimate use-cases for “get and assign” operator. They are too infrequent to warrant a special operator, though. In cases where it is really needed you can do this (let’s name it properly in this example to highlight its side effect):

fun moveNext() = stack.pop().also { next = it }

don't iterators have side effects to

next

also? and, yeah, i used

also

in similar code i wrote. I wasn't really writing up this code as a good example of why it'd be nice to have, but instead just showcasing how it works. i think the better example of where they'd be applicable are in while and if statements:

if ((val n = password.length) < 6) error("pw length of $n is too short. must be >= 6")

Iterator.next()

is a function.