How to make a compile time constant NaN or POSITIVE_INFINITY in Kotlin?

Question

I tried:

import kotlin.Double.Companion.POSITIVE_INFINITY
import kotlin.Double.Companion.NaN

const val inf = POSITIVE_INFINITY
const val nan = NaN

But I get:

Const 'val' initializer should be a constant value

EDIT:

The reason I need to do this is because of Junit5's parametrized tests:

 @ParameterizedTest
 @ValueSource(doubles = doubleArrayOf(nan, inf, -2* epsilon,  1.5, -0.5, 1.0 + 2* epsilon))
 fun ensureNotAProbability(number: Double)
 {
     ...
 }

Due to some limitations of Java annotations (described in this SO answer) the things 'passed to an annotation' can only be compile-time constants. Therefore I would need a compile time NaN, positive, and negative infinities.

hotkey · Accepted Answer · 2017-10-04T16:11:05.100

7

As a workaround, you can use the fact that the IEEE 754 standard guarantees 0.0 / 0.0 to be NaN and 1.0 / 0.0 to be +∞:

@Suppress("DIVISION_BY_ZERO")
const val NAN: Double = 0.0 / 0.0

@Suppress("DIVISION_BY_ZERO")
const val INFINITY: Double = 1.0 / 0.0

fun main(args: Array<String>) {
    println(NAN) // NaN
    println(INFINITY) // Infinity
}

edited Oct 04 '17 at 16:11

answered Oct 04 '17 at 14:17

hotkey

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score 2 · Answer 2 · answered Oct 04 '17 at 13:14

2

You don't need to redefine anything. Just import with an alias:

import kotlin.Double.Companion.POSITIVE_INFINITY as inf
import kotlin.Double.Companion.NaN as nan

answered Oct 04 '17 at 13:14

Michael

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Thank you for your answer, but this does not solve my problem. I need these values to be compile-time constants so that I can use them in a Java annotation. – Martin Drozdik Oct 04 '17 at 13:35
@MartinDrozdik it's interesting, could you share your use case in the question? – Ilya Oct 04 '17 at 22:17
@Ilya Certainly :) I expaned my question to include a real-world use case. – Martin Drozdik Oct 04 '17 at 22:44

How to make a compile time constant NaN or POSITIVE_INFINITY in Kotlin?

2 Answers2