I had to swap 2 numbers in one line expression using no other variable except x and y. So I wrote the following .c program to swapp two numbers with the given conditions and it works like charm.

int main() {
    
    int x =5, y =2;
    x = y-x (y=x);
    printf("X=%d, y=%d", x, y);

    return 0;
}

But when i try to do the same in kotlin it gives me an error that

Assignments are not expressions, and only expressions are allowed in this context,

I can resolve this issue by introducing a third variable just like this. But I'm not allowed to have any other variable except x and y which are already given. So is there any other way I can do this in one line using any kotlin property?

Below is the kotlin program

fun main() {
    
    var x = 5
    var y = 10
    x = y-x (y=x)   
    println("X = $x, Y = $y")

}

CodePudding user response：

While I have two suggestions below, I want to start with a recommendation against either of them, at least in this simple example.

It's usually a lot more clear to optimise code for developers to read in the following ways:

• create an extra variable with a descriptive name
• prefer val over var to avoid accidental mutations
• and try to make the code 'linear', so the operations can be read from top-to-bottom without jumping between functions
• avoid code that needs an IDE to see what the type-hints are

And I'll trust that the compiler will make make the code performant.

fun main() {
  val x = 5
  val y = 10

  val newX = y
  val newY = x

  println("X = $newX, Y = $newY")
}

Local function

You could use a local function to perform the swap, as the function will still be able to access the original values.

fun main() {
  var x = 5
  var y = 10

  fun swap(originalX: Int, originalY: Int) {
    y = originalX
    x = originalY
  }

  swap(x, y)

  println("X = $x, Y = $y")
}

Scope function

This could be code-golfed into one line

• useto to create a Pair<Int, Int>,
• and a scope function to use the result.

fun main() {
  var x = 5
  var y = 10

  (x to y).apply  { x = second; y = first }

  println("X = $x, Y = $y")
}

One line? Yes. More difficult to read? I think so.