I just stumbled upon this post on r kotlin

Question

I just stumbled upon this post on r kotlin <https www reddit com r Kotlin comments axnr0o negative zero 00 is equal to zero sometimes > Why does this happen Is it a bug ``` println 0 0 == 0 0 true println $ 0 0 == 0 0 false ```

marstran · Answer

Also this ``` println 0 0 lt 0 0 false println $ 0 0 lt 0 0 true ```

serebit · Answer

thinking face

serebit · Answer

I m trying to figure out why this could be the case but I can t think of any reasonable explanation

serebit · Answer

Interestingly the following ``` println buildString append 0 0 lt +0 0 ``` produces `false`

serebit · Answer

And if you run the following ``` val n = 0 0 val p = +0 0 println $ n lt p ```

serebit · Answer

that also produces `false`

Czar · Answer

apparently ``` println 0 0 == 0 0 true println $ 0 0 == 0 0 false ``` gets translated by kotlin compiler into ``` boolean var0 = 0 0D == 0 0D System out println var0 String var1 = false System out println var1 ``` So the problem if it is a problem lies in the code of kotlin compiler responsible for String interpolation Its equality algorithm is probably different from what JVM uses

serebit · Answer

Looks like compiler optimization gone wrong

cbruegg · Answer

Yeah this looks like a bug

marstran · Answer

I tried with different versions of Kotlin on <http play kotlinlang org|play kotlinlang org> It works as expected in v1 0 7 but not in v1 1 60 and up

Czar · Answer

albeit an innocent one if at least one of the parts in the interpolated expression is a val var the comparison works correctly only happens if literals are used

serebit · Answer

Interestingly even when calling an inline function from string interpolation that compares the two it still returns false Hell of an edge case

Czar · Answer

that s logical inline function gets inlined so you re back at `0 0 == 0 0` and that gets evaluated

serebit · Answer

No I mean the following ``` inline fun foo = 0 0 lt 0 0 fun main println $ foo ``` prints false

marstran · Answer

But that is expected 0 0 is not less than 0 0

serebit · Answer

Correct but I would expect that it would erroneously return true as inlining `foo` into the string interpolation would be the same as `print $ 0 0 lt 0 0 `

Nikky · Answer

do inline function actually count there i recall being unable to call inline funtions in string interpolation when passing them in annotations the compiler complained

Nikky · Answer

so but it inline into string interpolation and do that calculation during compilation or will it just inline this and do a bunch of String building and the comparison in between

Nikky · Answer

it compiles to ``` public static final void main int $i$f$foo = false String var1 = String valueOf 0 0D lt 0 0D System out println var1 ``` that explains it i think

Nikky · Answer