What does the arrow (“->”) operator do in Kotlin?

The -> is part of Kotlin’s syntax (similar to Java’s lambda expressions syntax) and can be used in 3 contexts:

when expressions where it separates “matching/condition” part from “result/execution” block

 val greet = when(args[0]) {
   "Apple", "Orange" -> "fruit"
   is Number -> "How many?"
   else    -> "hi!"
 }

lambda expressions where it separates parameters from function body

  val lambda = { a:String -> "hi!" }
  items.filter { element -> element == "search"  }

function types where it separates parameters types from result type e.g. comparator
```
  fun <T> sort(comparator:(T,T) -> Int){
  }
```

Details about Kotlin grammar are in the documentation in particular: