does kotlin support anon union types (e.g. String ...

# announcements

[Bernhard]

does kotlin support anon union types (e.g. String | Int)

[Birneee]

No currently not
But I think it would be a great addition to the type system

[igor.wojda]

I am not so sure. In general I have seen only one useful example for union types and Kotlin. Can you provide few examples where union types would provide value?

[Bernhard]

mostly when compiling down to javascript

[Bernhard]

you have to deal with functions that can return different types

[Bernhard]

example: return object on success or false on failure, which certainly is bad practice but nonetheless cases like this exist in js

[Bernhard]

e.g. https://www.npmjs.com/package/@types/screenfull

[Bernhard]

https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/screenfull/index.d.ts#L9

[Bernhard]

in Kotlin you probably would have to wrap these two types in a sealed class

[Bernhard]

sealed class ScreenfullType { class Actual(val obj: ScreenFull); class DoesNotExist}

[Bernhard]

I suppose

[igor.wojda]

Honestly I don’t see a point of pouting the core language only because one of the targets had bad architecture. These ScreenFull classes seems to be doing correct thing by abstracting bad code 🤔

BTW For JS as a target you could also use dynamic type (I know it’s far from perfect) https://kotlinlang.org/docs/reference/dynamic-type.html

[Bernhard]

right, that's the first use case that comes to my mind

[thanksforallthefish]

have fun reading (rabbit hole): https://youtrack.jetbrains.com/issue/KT-13108

but it does not seem unions will land anytime soon

[Hamza]

Just have Any refference and a variable for keeping info of what type the object is