Can I deconstruct variables while assigning them? Works:

var (a ,b) = somethingReturningAPair()

But what does not work:

var a: Int
var b: Int
(a, b) = somethingReturningAPair()

Or does it only work when initalizing variables?

You have to initialize variables as they are not nullable

Yeah, kotlin supports destructuring only in declarations (including for loops and lambdas) so you can't destructure into pre-existing variables. However it is convenient to use it with

let

, so you can

var a: Int = ... // some number
var b: Int = ... // some number

somethingReturningAPair().let { (a, b) -> 
    // a,b shadowed here 
}

Please for it at https://youtrack.jetbrains.com/issue/KT-11362