I've just come across this error. Is it a known issue? ```class A { override fun equals(other: A...

# intellij

[Klitos Kyriacou]

I've just come across this error. Is it a known issue?

class A {
    override fun equals(other: Any?): Boolean {
        return true
    }
}
fun main() {
    val a = A()
    val b: A? = null
    println(a == b)  // It's always true, but IntelliJ warns it's always false
}

[Chris Lee]

that condition will always be false - its comparing an instance of A to null

[Chris Lee]

at least from IntelliJ’s perspective, which is static code anlysis, not execution of the code.

[Klitos Kyriacou]

No, it's true because of the overridden equals.

[Chris Lee]

correct.

[Klitos Kyriacou]

Note that if you change it to a.equals(b), then it doesn't give that warning.
Also, a.equals(null) doesn't give a warning - which is correct, since a == null is not the same as a.equals(null) according to the language spec, but this only applies for the literal null. If it's a value that happens to be null, then a == b is always the same as a.equals(b) and therefore IntelliJ shouldn't give that warning.

[ephemient]

that equals does not satisfy the contract

[ephemient]

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-any/equals.html

Never equal to null: for any non-null value x, x.equals(null) should return false.

[ephemient]

note that Java has the same wording, so this is true for non-Kotlin classes as well https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#equals-java.lang.Object-

[Jacob]

what does println(b == a) print?

[Anton Mefodichev]

I have created a ticket to KTIJ project: https://youtrack.jetbrains.com/issue/KTIJ-26980

[Klitos Kyriacou]

Thanks, Anton. Given what ephemient has pointed out, I can see why IntelliJ thinks the condition is always false (it assumes equals would satisfy the contract). It would be more important to see an inspection about equals not satisfying the contract, if that's possible. I made a comment on the ticket.