is there a trick to implementing preincrement for ...

# announcements

[bbaldino]

is there a trick to implementing preincrement for an inline class wrapping an int? post-increment is working fine for me but preincrement isn't

[bbaldino]

yeah that's what i thought, but i get different behaviors for each. let me see if i can slim down an example

[bbaldino]

inline class WrappingInt(val value: Int) {
    operator fun inc(): WrappingInt = plus(1)
    operator fun plus(num: Int): WrappingInt = WrappingInt((value + num) and 0xFFFF)
}

fun main() {
    var x = WrappingInt(65535)
    x++
    println(x) // prints 0 (correct)

    var y = WrappingInt(65535)
    ++y
    println(y) // prints 65536
}

[bbaldino]

cool, will file something

[bbaldino]

https://youtrack.jetbrains.com/issue/KT-33119?project=kt

[bbaldino]

ah yeah, see that now

[bbaldino]

something like this does seem to work:

var z = WrappingInt(65535)
    val zz = { ->
        ++z
        println(z)
    }

[bbaldino]

i guess it's triggering some boxing maybe?

[bbaldino]

i had unit tests for pre-increment and they actually work inside a kotlintest should block for this reason, i think, so this was a sneaky one 😕