kotlinrange

Test if a float is in open or semi-open range in Kotlin

In Kotlin, is there an idiomatic way to test if a float is in a range where either (or both) the start or the end of the range is exclusive?

E.g. something like

val inRange = 10.f in (0.0f until 20f)

I can't seem to find anything on this in the docs.

How would one deal with semi-open ranges as well?

Solution

  • The until function creates the semi-closed integer (not float) range, where the left part is included and the right part is excluded. https://kotlinlang.org/docs/reference/ranges.html

    There is closed float ranges support in Koltin https://kotlinlang.org/docs/reference/ranges.html#utility-functions

    You may implement double-open floating point range yourself:

    data class OpenFloatingPointRange(
    val startExclusive: Double,
    val endExclusive: Double,
)

infix fun Double.untilOpen(endExclusive: Double) = OpenFloatingPointRange(
    startExclusive = this,
    endExclusive = endExclusive,
)

operator fun OpenFloatingPointRange.contains(
    value: Double,
) = startExclusive < value && value < endExclusive

val ClosedFloatingPointRange<Double>.open: OpenFloatingPointRange
    get() = OpenFloatingPointRange(
        startExclusive = this.start,
        endExclusive = this.endInclusive,
    )


val inRange = 10.0 in (0.0 untilOpen 20.0)

    Here I use several tricks from Kotlin: https://kotlinlang.org/docs/reference/functions.html#infix-notation https://kotlinlang.org/docs/reference/operator-overloading.html#in