struct Item {
	owner_id ?string
}

fn get_opt() ?int {
	return 1
}

fn main() {
	item := Item{
		owner_id: 'key'
	}
	arr := [1, 2, 3]
	m := {
		'key': 1
	}

	// Optional struct field with map
	_ = item.owner_id in m

	// Optional function return with array
	_ = get_opt() in arr
}