Kotlin encourages to declare practically immutable variables with a val keyword, ensuring that their value will never change.

Example:

  fun example() {
      var primeNumbers = listOf(1, 2, 3, 5, 7, 11, 13)
      var fibonacciNumbers = listOf(1, 1, 2, 3, 5, 8, 13)
      print("Same numbers: " + primeNumbers.intersect(fibonacciNumbers))
  }

A quick-fix is suggested to replace the var keyword with val:

  fun example() {
      val primeNumbers = listOf(1, 2, 3, 5, 7, 11, 13)
      val fibonacciNumbers = listOf(1, 1, 2, 3, 5, 8, 13)
      print("Same numbers: " + primeNumbers.intersect(fibonacciNumbers))
  }