Why is `MyId(1) === MyId(1)` not `true`? Why does it still see two object references? There can't be...

# getting-started

[Stefan Oltmann]

Why is MyId(1) === MyId(1) not true?
Why does it still see two object references?
There can't be two "instances" of a primitive long on the JVM.
(Also 1L === 1L is true.)

@JvmInline
value class MyId(
    val value: Long
)

[Michael Krussel]

Because inline classes may be represented both as the underlying value and as a wrapper, referential equality is pointless for them and is therefore prohibited.

https://kotlinlang.org/docs/inline-classes.html

[ephemient]

Also 1L === 1L is true.

only somewhat accidentally, on most JVMs "128".toLongOrNull() !== "128".toLongOrNull() and there's ways to bypass the small number cache even for smaller constants

[CLOVIS]

Which version of Kotlin are you using? Referential equality on value classes has been forbidden for a few versions (playground).

Also, 1L === 1L is deprecated (CTRL ALT H to see warnings) and will be forbidden in the future (for the reasons explained by @ephemient).

[Stefan Oltmann]

1.9.23

[Stefan Oltmann]

In playground I get this error message too, but in IDEA I just receive "false"

[CLOVIS]

Maybe you have an old IDEA version?

[Stefan Oltmann]

2024.1

[Stefan Oltmann]

But doesn't matter. Eventually it will show the same error message and my question is answered. 🙂