Someone did several comparisons with `Float NaN` which led t

Question

Someone did several comparisons with `Float NaN` which led to this odd result `Float NaN === Float NaN` is `false` with JVM and JS targets and `true` with Kotlin Native I see that identity equality for `Float` has been deprecated but still figured I should check if this is a bug and should be reported or if it s just undefined behavior

karelpeeters · Answer

It has been deprecated Where How

Nicole · Answer

It shows up as deprecated in Intellij

Nicole · Answer

And this isn t covered by a test case <https github com JetBrains kotlin blob master compiler testData codegen box ieee754 equalsNaN kt L154 L226>

karelpeeters · Answer

Ah I didn t see it was `===` which indeed doesn t really make sense for primitives in the first place

Nicole · Answer

It seems like at least for the JVM and I suspect the same for JS is that the values are being boxed and since there isn t a cache of boxed values for floating point values the `===` operator returns false

Nicole · Answer

In native code I suspect it just doesn t or cannot box so it compares the values and they re the same

karelpeeters · Answer

Err no them not being boxed would return `false` since `Nan = Nan` according to IEEE

Nicole · Answer

On the JVM ` Float valueOf 10 = Float valueOf 10 `

Nicole · Answer

I figured that explained it but now I m just very confused why `Float NaN === Float NaN` in native =

karelpeeters · Answer

Wrong again `java lang Float equals` checks for actual bit equality not IEEE equality which it has to because of reflexivity

karelpeeters · Answer

so `Float valueOf 10 == Float valueOf 10 ` on the JVM

karelpeeters · Answer

So it s probably the other way around not boxed on the JVM so unequal but bowed for native so equal

Nicole · Answer

I actually ran ` Float valueOf 10 = Float valueOf 10 ` on a JVM and it prints true

Nicole · Answer

```System out println Floats + Float valueOf 10 = Float valueOf 10 Output Floats true```

damian · Answer

If this is java ` =` is comparing reference equality of boxes so that makes perfect sense

karelpeeters · Answer

Ah but that s Java s `==` so Kotlins `===` I was talking about Koltin s `==` You should have said `Float valueOf 10 == Float valueOf 10 ` stuck out tongue

Nicole · Answer

Basically I m just trying to understand how `Float NaN === Float NaN` is false on a JVM target but true in a native context

Nicole · Answer

This led me to looking at the JVM bytecode generated which seemd to be Float NaN == Float NaN after resolving the `FloatCompanionObject INSTANCE getNaN ` references

Nicole · Answer

Just for completeness I filed a bug about this

karelpeeters · Answer

Can I ask why you care about what `===` does It s deprecated because it was useless and confusing