Does it mean that I can read `Any?` from the array...

# random

[Marc Knaup]

Does it mean that I can read Any? from the array but write only X? and subtypes into it?
That .. confuses me because it looks like a range 🤔
Oh and the out thingy can be null. The in one not.

[dsavvinov]

Well, that’s… complicated 😉

- Platform types are indeed represented as a range of types internally. Indeed, platform String can be viewed as “Some type which can take values from String to String?, which is essentially `String..String?`“. If you’re curious, you can find more in this talk by Andrey Breslav:

https://www.youtube.com/watch?v=2IhT8HACc2E▾

(caution: a lot of nitty-gritty details!)

- Platform arrays are a special case of platform types: T[] is represented as Array<T!>..Array<out T> to maintain compatibility with both Kotlin code and Java code

- Use-site variance adds even more complexity to this example. TL;DR: yes, you’re right, you can read Any? from array and write subtypes of X?.
If you’re into academic reading and type systems, I suggest you reading Ross Tate’s paper on mixed-site variance (http://www.cs.cornell.edu/~ross/publications/mixedsite/mixedsite-tate-fool13.pdf)

[Marc Knaup]

Thank you Dmitry, that's helpful!
I do love details indeed and will check it out 🙂