Is it a bug or a feature? ```fun main() { var numbers = emptySequence<Int>() numbers ...

# stdlib

[Igor Kolomiets]

Is it a bug or a feature?

fun main() {
    var numbers = emptySequence<Int>()

    numbers = sequence {
        yieldAll(numbers)
        yield(1)
    }

    println(numbers.iterator().next()) // throws StackOverflowError
}

I do realize that such an approach to build up a sequence may seem unnatural, but for my case (I have to implement Kotlin Serialization’s Encoder interface which methods adds/yields next value for the sequence) I haven’t figured out an alternative.

[ephemient]

the emptySequence<Int>() part is irrelevant, you have written something (mostly) equivalent to

lateinit var numbers: Sequence<Int>
numbers = sequence {
    yieldAll(numbers)
    yield(1)
}

[Igor Kolomiets]

wow… but still it doesn’t work - an attempt to

println(numbers.iterator().next())

still throws StackOverflowError… 😞

[ephemient]

I expected that it would be obvious from my replacement code why it (and your original) don't work

[Igor Kolomiets]

oh, so basically, this is expected. I did have feeling that it won’t work due to obviously lazy evaluation of numbers when it won’t be an empty sequence by the time iterator is created and likely leads to an infinite recursion…

[Chris Lee]

it’s a sequence that contains itself

[nkiesel]

So just to be crystal clear: your problem is the re-use of the name "number". The following would work w/o problems:

fun main() {
    val numbers = emptySequence<Int>()

    val myNumbers = sequence {
        yieldAll(numbers)
        yield(1)
    }

    println(myNumbers.iterator().next())
}