Kotlin: Condition that double-value is a "normal" number

Question

How can I test if a value of type Double in Kotlin is not Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, Double.NaN or some other special value?

I'd like to have something like require(Double.isNormal(x))

al3c · Accepted Answer · 2020-06-22T13:29:41.090

9

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/is-finite.html

require(x.isFinite()) is what you need.

edited Jun 22 '20 at 13:29

answered Jun 22 '20 at 13:24

al3c

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score 1 · Answer 2 · answered Jun 22 '20 at 13:26

1

Sounds like you've answered your own question.... write a function that checks the 3 cases, and takes a lambda to run if the precondition is met:

fun ifNormal(double: Double, toDo: () -> Unit) {
    if (double != Double.POSITIVE_INFINITY 
        && double != Double.NEGATIVE_INFINITY 
        && double != Double.NaN) {
        toDo()
    }
}

Then use it like so:

ifNormal(1.0) {
  // Do stuff
}

answered Jun 22 '20 at 13:26

Thomas Cook

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I think I'm gonna go with the solution of @al3c, but seeing how you could use functional arguments is nice too see too. Wouldn't have thought of that. – Moritz Groß Jun 22 '20 at 13:29
No worries, their answer addresses your question more directly to be fair. – Thomas Cook Jun 22 '20 at 13:30
2

I think `double != Double.NaN` will always return true, as NaN should compare not equal to any Double, NaN included. – al3c Jun 22 '20 at 14:09
Fair enough, I was just answering OP question, didn't do the graft to check all 3 conditions actually made sense – Thomas Cook Jun 22 '20 at 14:12
Although, according to: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/is-finite.html, it would appear that a double could be NaN? – Thomas Cook Jun 22 '20 at 14:12
Yup, you're wrong mate, from Primitives.kt, you can see: `public val NaN: Double` – Thomas Cook Jun 22 '20 at 14:14
This compiles fine; ` val d: Double = Double.NaN` – Thomas Cook Jun 22 '20 at 14:16
1

The problem is that then `d == Double.NaN` is false (and `!=` is true). This is how `NaN` works in basically every language. That's why there is a separate `d.isNaN()`. – Alexey Romanov Jun 22 '20 at 16:29
Alexey Romanov - is that true? val d = Double.NaN; d == Double.NaN == false? – Thomas Cook Jun 22 '20 at 18:20

Kotlin: Condition that double-value is a "normal" number

2 Answers2