How can I refactor this to instead use `kotlin.time.Duration`? I thought this would be simple (it pr...

# stdlib

[Zoltan Demant]

How can I refactor this to instead use kotlin.time.Duration? I thought this would be simple (it probably still is) but my first attempt didnt result in the behavior I was expecting, and Im not 100% clear on why that is (code for that in 🧵).

fun round(
    duration: Long,
    period: Long = 1000,
): Long {
    val half = period / 2
    return (duration + half) / period * period
}

[Zoltan Demant]

This does not produce the same results:

fun round(
    duration: Duration,
    period: Duration = 1.seconds,
): Duration {
    val half = period / 2
    return (duration + half) / period * period
}

[Szymon Jeziorski]

in your original function with duration as Long, (duration + half) / period uses Long division meaning that entire decimal section is cut out, so that for example (9800 + 500) / 1000 gives 10, whereas Duration / Duration uses double division meaning above example would give 10.3.

If you want version with Duration to give same results as the one with Long you may for example use floor to ignore decimal part of division: floor((duration + half) / period) * period

[Klitos Kyriacou]

It uses Long (not double) division, but represents the durations in nanoseconds. So, one way to do it is this:

val periodNanos = period.inWholeNanoseconds
    return ((duration + period / 2).inWholeNanoseconds / periodNanos * periodNanos).nanoseconds

[Szymon Jeziorski]

@Klitos Kyriacou I'm pretty sure it uses double division unless I'm missing something https://github.com/JetBrains/kotlin/blob/30788566012c571aa1d3590912468d1ebe59983d/libraries/stdlib/src/kotlin/time/Duration.kt#L626

[Klitos Kyriacou]

@Szymon Jeziorski you're right. I was looking at Duration.div(Int) instead. So it uses Long division for val half = period / 2 but indeed it uses Double division for dividing by period.

[Zoltan Demant]

Thank you both, that makes perfect sense! 🙏🏽