Java8 time comparison in Kotlin

Question

I stumbled across some strange behaviour when comparing Java8 time objects. The below does not appear to be valid code.

val t1 = LocalTime.now()
val t2 = LocalTime.now()
val foo: Int = t1 > t2

Yet hovering over the undersquiggled code shows that the overridden function return type is correct:

Any ideas?

Answer 1

According to the documentation, when using the natively overloaded operators (comparison operators specifically) - Kotlin doesn't just call compareTo but rather performs a compareTo against 0 (thus ending up as a bool).

https://kotlinlang.org/docs/operator-overloading.html#comparison-operators

Comparison operators

Expression	Translated to
a > b	a.compareTo(b) > 0
a < b	a.compareTo(b) < 0
a >= b	a.compareTo(b) >= 0
a <= b	a.compareTo(b) <= 0

All comparisons are translated into calls to compareTo, that is required to return Int.

The documentation snippet you attached is admittedly a bit confusing.