Would it make sense to add `typealias Null = Nothi...

# stdlib

[Ruckus]

Would it make sense to add typealias Null = Nothing? to the stdlib (and preamble)? Common use case:

class Info<T>(val description: String, val payload: T, ...)

interface Base<T> {
    fun getInfo(): List<Info<T>>
}

class Derived: Base<Null> {
    override fun getInfo() = listOf(Info("...", null, ...), ...)
}

IMO it reads easier than class Derived: Base<Nothing?>.
(Yes, I understand I could use Unit in this case to achieve basically the same thing in this contrived example. That's beside the point.)

[ilya.gorbunov]

An interesting idea. Do you think there are many cases where Nothing? is used and where Null would be more expressive?

[ilya.gorbunov]

It's interesting to consider what is primary and what is derivative. E.g. Null can be a typealias to Nothing?, and Nothing? can be considered as a union of Nothing | Null

[ilya.gorbunov]

Though at this point, introducing Null identifier in a package imported by default would be rather disturbing. There can be objects named Null (https://github.com/pact-foundation/pact-jvm/blob/7cd4ff4d3be7f8e4a3534ae67c3ef18d0b998dc8/core/support/src/main/kotlin/au/com/dius/pact/core/support/json/JsonValue.kt#L41) and they can lead to a conflict or confusion when being in scope with the Null typealias.

[Ruckus]

That's a good point. I imagine Null is probably a common class name for a number of serialization / data interchange libraries.

As far as how many cases there are (where Nothing? is used and where Null would be more expressive), I'm not sure how to gauge that. While I use it in a number of my projects, the use case is admittedly pretty niche. I'd guess that most cases where Nothing? is used, Null would be more expressive (at least I can't think of a good counter example right now).

[Ruckus]

When it comes to primary vs derivative, that's an interesting chicken / egg scenario. I guess it would make more sense to forgo Null altogether, and have null be both a value and a type, though then it feels like we're stepping on `Unit`'s toes a bit.