Apart from the obvious syntactic difference, are t...

# getting-started

[CLOVIS]

Apart from the obvious syntactic difference, are there any other differences between these two snippets, performance-wise, etc?

// #1

class Outer {
    fun inner(): Any = Inner()

    private inner class Inner
}

// #2

class Outer {
    fun inner(): Any = Inner(this)

    private class Inner(val outer: Outer)
}

From my understanding, these are both absolutely identical, but maybe some platforms have magic ways of handling the first one better?

[Huib Donkers]

You're not allowed to nest a non-inner class in an inner class. I don't know the reason, but maybe it's related to some kind of fundamental difference between the two snippets. Or maybe this kind of nesting is just a bad idea, and no effort was made to allow it.

class Outer {
    fun inner(): Any = Inner()

    private inner class Inner {
        class A // compile error: must be inner class
    }
}

class Outer {
    fun inner(): Any = Inner(this)

    private class Inner(val outer: Outer) {
        class A // allowed
    }
}

[CLOVIS]

Uh, that's an interesting difference. Thanks for the info

[ephemient]

it seems more explicable with object,

class Outer {
    inner class Inner {
        companion object

(or any other nested object type) is rejected, while

class Outer {
    class Inner {
        companion object

is OK. which sort of makes sense to me as Outer.Inner can't exist without an Outer, so an Outer.Inner.Companion which can exist without Outer is strange

[ephemient]

I don't see anything in https://kotlinlang.org/spec/ that looks like it mentions this though