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kotlinlang

in an if check, `in` is the same as `contains`. What is the operator function for `in` when we use it in a loop?

It's a regular function called `iterator`.

ok I thought operators always need an operator fun

It's `operator fun iterator()` and the return type needs to conform to
```
operator fun hasNext(): Boolean
operator fun next(): T
```
Where T can be anything, including primitives and inline classes, which won't be subject to auto boxing. That would happen if you use the `Iterator` type though because of generics.

All these functions can also be extension functions. I wouldn't particularly recommend that in this case.

just to make that clear, the same operator is used for 2 completely different things

because the word "in" fits in both situations

Why do the functions in many files have no body but the classes are not abstract

I think they get generated later or something?

maybe because they depend on the compilation target

I have to say I am not the most experienced dev, also not in Java

Can you give some examples so we can give a specific answer?

yea if you go into Array.kt or Primitives.kt where Int, Long etc. are declared

for example, I try to see the iterator() implementation for Arrays but I just end up at `public operator fun iterator(): Iterator&lt;T&gt;`

when I step into an Array's iterator() function with the debugger, I get into ArrayIterator.kt

but yea ArrayIterator.kt actually contains the code