kotlinjava-timetype-mismatchdatetime-comparison

Java8 time comparison in Kotlin

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:

enter image description here

Any ideas?

Solution

  • 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.